AssesImnt/Ansis oReport E0071 India - Bombay Sewage DispOg Prpjpst Category A 4 of 4 Environmental Assessment January 1995 This report has been prepared by the Borrower or its Consultant FINAL REPORT BOMBAY SEWAGE DISPOSAL PROJECT BHANDUP AND GHATKOPAR SPONSOR MUNICIPAL CORPORATION OF GREATER BOMBAY - National Environmental Engineering Research Institute January 1995 FOREWORD Municipal Corporation of Greater Bombay (MCGB) is in the process of implementing wastewater treatment and disposal schemes with the World Bank assistance. These schemes are planned under the Bombay Sewage Disposal Project and envisage disposal of preliminary treated sewage from Colaba, Bandra and. Worli drainage zones through marine outfalls into the Arabian Sea, treated wastewaters from aerated lagoons at Versova and Malad into Malad Creek, and from aerated lagoons at Bhandup and Ghatkopar into Thane Creek. Implementation of the proposed facilities is expected to significantly improve beaches and coastal water quality in and around Bombay. The large scale construction activities, however, have potential adverse environmental impacts. MCGB retained the National Environmental Engineering Research Institute (NEERI), in September 1991, for assessing the potential impacts of the construction and operation of the proposed facilities. The first report on the study Bombay Sewage Disposal Project Marine Outfalls, submitted in October 1993, provided exhaustive baseline water quality data for west coast of Bombay and presented water quality scenarios for different lengths of outfalls, developed through mathematical models. The second report, submitted in October, 1994, dealt with environmental issues related to construction and operation of aerated lagoons at Versova and Malad and presented plan for assimilative capacity based i gwater quality management of Malad Creek. The findings of these studies led to major modifications in proposed disposal and treatment schemes. This report, the last of three reports envisaged on the project, deals with environmental issues related to construction and operation of aerated lagoons at Bhandup and Ghatkopar. The report presents the existing environmental status of Thane Creek; and details the methodology and results of mathematical. modelling which formed the basis for assimilative capacity based water quality management of the creek. The cooperation and assistance rendered by Er. I.C.Gandhi, Deputy Municipal Commissioner; Er. M.K.Gokhale, Deputy Municipal Commissioner (Retd.); and other staff of MCGB in the preparation of this report is gratefully acknowledged. The contributions of Binnie & Partners and the World Bank towards review of the draft report are sincerely appreciated. Thanks are also due to officials of a number of agencies who readily furnished information for the study. January, 1995 ( Khanna) - CREDITS Project Coordinator Dr. P. Khanna OPERATION PHASE STUDIES Project Leaders Dr. Vijay Joshi Mr. Rakesh Kumar Project Scientists NEIER, BZL NEERI, HQ Ms. Chandorkar A.A. Mr. Apte V. Mr. Deshpande S.V. Mr. Bhide A.D Ms. Dhage S.S. Dr4Mrs) Gadkari AS Mr. Kulkarni A.L Dr. Chash T.K. Dr4Mrs.) Lala K. Mr. Pentu Saheb S. DrMrs.) Padiyar V Dr. Shekadr AM. Ms. Patil M.M. Ms. Patkie S.A. Mr. Ro4rio K.E. Ms. Subramaniam J. Mr. hakur S.C. Mr. Tipnis SS. Scientific Assistance NEERI BZL Ms. Divekar N. Ms. Jalta S. Ms. Joshi P. Ms. Kale V. Secretarial Assistance NEERI BZI. Mr. Chaudhari V. Mr. Chinchulkar ILD. Mr. Joshi A.K. Mr Sawant 5. Mr. Shidhaye 5.V. Ms. Siddhu J. . . CONSTRUCION PHASE STUDIES Project Leaden Dr. Badrinath S.D. Dr. Chalapati Rau) C.V. Project Sciendst NEER HQ Mr. Apte V.R. Dr. Kale C.K. Mr. Chakradhar B. Mr. Khadakkar S.N. Dr4Mrs) Chakravarti C. Dr. Kondawar V.K. Dr. Charkarvarti T. Mr. Mahaian A.U. Dr. Deshpande V.P. Dr. OIaniya MS. Dr. Gadkari S. Mr. Pawan Kumar Scientific Assistance Ms. Aluwala V. br.(Ms) Pradhan S. Ms. 13hanja A. Mr. Raman N.S. Mr. Dabir P. Dr. Ramesh Kumar G. Dr. Dhaneshwar RS. Mr. Sen M.K. Ms. Huddar P. Ms. Shah V. Dr. Iyer V.N. Ms. Sharma A. Mr. Joshi M.W. Mr. Sharma N. Ms. Joshi T. Dr. (Mrs) Sharma S. Ms. Khan S. Mr. Shukla S.S. Mr. Kundalia A. Mr. Siracoumer R. Mr. Manglurkar A.D. Mr. Sunil Kumar C.S. Mt Manuel A.C. Mt Talkhande AN. Ms. Mudaliar S.L Ms. Uma TS. Mr. Murthy V.R. Ms. Vadini V. Mr. Narayanan Rao N. Ms. Verma B. EXTERNAL STUDIES Pm. S.K.Guha Secretarial Assistance NEER[ HQ Ms. Awale M. Mr. Khan A. Mr. Anturkar PS. Mr. Kunte P10. Mr. Deshpande D.C. Mr. Labhe S.T. Mr. Dhawale A.H. Mr. Negi 55. Mr. Dighekar D.. Mr. Ojha S.N. Mr. lyer V.V. Mr. Panchpatkar SI. Ms. Kalyankar D. Mr. Raman M.V Mr. Kasture PA. Ms. Sarkar K. Contents Page No. List of Figures. iv List of Tables. vi Executive Summary. viii CHAPTER 1 INTRODUCTION 1.1 Preamble 1.1 1.2 Objectives. 1.3 1.3 Organisation of the report. 1.4 CHAPTER 2 PROJECT SETTING 2.1 Preamble. 2.1 2.2 Bombay : the city, its genesis and growth. 2.1 2.3 Geography. 2.2 2.4 Regional geology and structure. 2.2 2.5 Climatology. * 2.4 2.6 Demography. 2.4 2.7 Environmental setting. 2.4 2.8 Major environmental concerns. 2.5 CHAPTER 3 BOMBAY SEWAGE DISPOSAL PROJECT 3.1 History of the project 3.1 32 Development Plan 1 3.2 3.3 Development Plan II 32 3.4 Review of Development Plan II 32 3.5 Development Plan III 3.4 3.6 First phase facilities 3.7 3.7 Present status 3.10 CHAPTER 4 AERATED LAGOONS 4.1 Preamble 4.1 42 Salient features of aerated lagoons 4.2 4.2.1 Types and Design Features 42 4.2.2 Construction features 4A AEAHMDUlAONS 4.3 Lagoon effluent characteristics 4.7 4.4 Environmental repercussions 4.8 45 Environmental safeguards 4.8 4.6 Prooosed aerated lagoons at Bombay 4.9 4.6.1 Design specifications 4.12 4.7 Inference 4.15 CHAPTER 5 METHODOLOGY AND DATA GENERATION FOR ENVIRONMENTAL MANAGEMENT PLAN 5.1 Preamble 5.1 52 Scope of field studies .52 . 53 Methodology and findings 53 53.1 Air quality 53 532 Noise studies 5.5 5.32.1 Sound level measurement at Bhandup lagoon site 5.5 53.2.2 Sound level measurement at Ghatkopar lagoon site 5.5 5.3.3 Land environment 5.9 53.3.1 Land use 5.9 533.2 Soil characteristics 5.12 5.33.3. Terrestrial Ecosystem 5.15 53.4 Water quality 5.17 53.4.1 Reconnaissance survey 5.17 53.4.2 Summer water quality survey 5.23 53.4.3 Winter water quality survey 535 5.3.5 Biological parameters 5.43 5.3.6 Trace metal levels 5.45 5.3.7 Nutrients in sediments 5.52 53.8 Detergents 5.55 53.9 Wastewater characterization 5.58 53.10 Solid waste characterization 5.63 5.4 Conclusions 5.64 CHAPTER 6 NUMERICAL MODEL FOR THANE CREEK 6.1 Preamble 6.1 62 Model selection 6.1 63 Thane creek model 6.4 6.4 Model calibration for water quality parameters 6.9 6.5 Conclusions 6.14 AVWED UGOONS CHAPTER 7 PREDICTION OF IMPACTS 7.1 Preamble 7.1 7.2 Construction phase impacts 7.1. 7.2.1 Impacts of mangroves reclamation 7.1 7.2.2 Noise impacts 7.2 7.2.2.1 Noise impacts on construction workers 7.6 7.2.3 Air quality impacts 7.6 7.24 Water quality impacts 7.6 73 Operation phase impacts 7.7 73.1 Air quality impacts 7.7 73.2 Water quality impacts 7.9 7.321 Proposed treatment 7.9 7.3.2.2 Analysis of alternatives 7.11 7.3.2.3 No action scenario 7.11 73.2.4 Augmentation of wastewater management effort 7.12 7.4 Socio economic impacts 7.24 75 Conclusions 7.24 CHAPTER 8 RECOMMENDATIONS FOR MANAGEMENT PLAN 8.1 Preamble 8.1 8.2 Management options for Thane creek 8.2 83 Mitigation plan . 8.5 8.3.1 Construction phase 8.5 8.3.2 Operation phase 8.10 8.3.3 Environmental monitoring 8.10 8.3A Public participation 8.11 8.3.5 Institutional needs 8.11 ABUSEDIQO0NS List of Figures 1.1 Proposed wastewater disposal/treatment schemes under Bombay Sewage Disposal Project 1.2 2.1 Geographical setting of Bombay city and its suburbs 23 3.1 Physical boundaries of service areas 3.3 4.1 Layout of facultative aerated lagoon 4.3 4.2 Layout of aerobic flow through lagoon 4.5 4.3 Typical layout of aerobic lagoon with solids recycle 4.6 4.4 Schematic layout of treatment units Bhandup 4.16 4.5 Schematic layout of treatment units Ghatkopar 4.17 5.1 Observed noise levels at Bhandup lagoon site 5.6 5.2 Observed noise levels at Ghatkopar lagoon site 5.8 53 Sampling transects for reconnaissance survey of 20.03.93 5.19 5.4 Sampling locations during reconnaissance survey of 13.04.93 5.21 5.5a Intertidal water quality at Transect 2 of Thane creek 5.36 (Summer spring tide) 5.5b Intertidal water quality at Transect 2 of Thane creek 536 (Summer neap tide) 5.6a Intertidal water quality at Transect 3 of Thane creek 5.37 (Summer spring tide) 5.6b Intertidal water quality at Transect 3 of Thane creek 537 (Summer neap tide) 5.7a Intertidal water quality at Transect 4 of Thane creek 5.38 (Summer spring tide) 5.7b Intertidal water quality at Transect 4 of Thane creek 538 (Summer neap tide) 6.1 Bathymetric features and wastewater discharge location in Thane creek 6.3 6.2 North and south boundaries for Thane creek model 6.5 63 Tidal elevations arid open boundaries of Thane creek model 6.7 6.4 Locations of current and water quality observations 6.8 6.5 Hydrodynamic calibration of Thane creek model (inner region) 6.10 6.6 Hydrodynamic calibration of Thane Creek model (outer region) 6.11 6.7a Predicted DO distribution 09.00 hrs. on 06.02.93 6.15 6.7b Predicted DO distribution 11.00 hrs. on 06.02.93 6.15 6.7c Predicted DO distribution 1230 hrs. on 06.02.93 6.16 6.7d Predicted DO distribution 14.00 hrs. on 06.02.93 6.16 6.8a Predicted BOD distribution 09.00 hrs. on 06.02.93 6.17 6.8b Predicted BOD distribution 11.00 hrs. on 06.02.93 6.17 6.8c Predicted BOD distribution 12.30 hrs. on 06.02.93 6.18 6.8d Predicted BOD distribution 14.00 hrs. on 06.02.93 6.18 ABUGED MGOONS 7.1 Predicted noise levels at Bhandup lagoon site 7.4 7.2 Predicted noise levels at Ghatkopar lagoons site 7.5 7.3 Predicted DO in Thane creek during high tide for management scenario 1 (Single cell aerated lagoon with 2005 flows) 7.16 7.4 Predicted DO in Thane creek during low tide for management scenario 1 (Single cell aerated lagoon with 2005 flows) 7.16 7.5 Predicted DO in Thane creek during high tide for management scenario 2 (Single cell aerated lagoon with 2005 flows after diverting 50 mid for industrial use at Ghatkopar) 7.18 7.6 Predicted DO in Thane creek during low tide for management scenario 2 (Single cell aerated lagoon with 2005 flows after diverting 50 mid for industrial use at Ghatkopar) 7.18 7.7 Predicted DO in Thane creek during high tide for management scenario 3 (Three cell aerated lagoons with 2005 flows after diverting 50 mid for industrial use at Ghatkopar) 7.19 7.8 Predicted DO in Thane creek during low tide for management scenario 3 (Three cell aerated lagoons with 2005 flows after diverting 50 mid for industrial use at Ghatkopar) 7.19 AeMEDLAGOONS List of Tables 3.1 Wastewater treatment and disposal facilities proposed under Development Plan I - 3.5 3.2 On-Line pumping stations planned under first phase of Development Plan III 3.8 33 Projected and revised estimates of average dry weather flow (mid) 1 3.11 4.1 Tolerance limit for water quality after receiving discharges (IS :7967 1976) 4.10 42 General standards for discharge of effluents 4.11 4.3 Design specifications of proposed aerated lagoons 4.13 5.1 Sound levels at Bhandup aerated lagoon site 5.7 5.2 Sound levels at Ghatkopar aerated lagoon site 5.7 53 Land use pattern around the aerated lagoon site at Bhandup 5.10 5.4 Land use pattern around the aerated lagoon site at Ghatkopar 5.11 5.5 Proposed quarry site 5.13 5.6 Physical properties of soils at the aerated Lagoon sites 5.13 5.7 Chemical properties of soils at the aerated lagoon sites 5.14 5.8 Cation exchange properties of soils at the aerated lagoons sites 5.14 5.9 Reconnaissance survey of Thane Creek on 28.03.93; physico- chemical parameters 5.20 5.10 DO values in Thane creek on 13.04.93 5.22 5.11 Schedule for sampling in Thane creek during summer 5.24 5.12 Observations on water quality indicators in Thane Creek during summer 5.25 5.13 Phytoplankton observations in Thane creek (summer) 5.28 5.14 Intertidal variations in water quality of Thane creek (summer): Transect 2 5.29 5.15 Intertidal variations in water quality of Thane creek (summer): Transect 3 5.31 5.16 Intertidal variations in water quality of Thane creek (summer): Transect 4 533 5.17 Schedule for sampling in Thane creek during winter 5.39 5.18 Observations on water quality indicators in Thane creek during winter 5.40 5.19 Phytoplankton observations in Thane creek (winter) 5.44 5.20 Zooplankton observations in Thane creek (winter) 5.46 5.21 Total heavy metal concentration in Thane creek during summer 5.48 5.22 Total heavy metal concentration in Thane creek during winter 5.50 5.23 Heavy metals in Thane creek sediments during summer 5.53 5.24 Ratio of trace metal concentration in Thane creek sediments to Bombay urbal soil and World shale backgrounds 5.54 ARATED AOCONS VI EXECUTIVE SUMMARY Preamble 1. Bombay 'is the hub of commercial and industrial activities and has witnessed a rapid growth during past few decades. According to 1991 census, 9.93 million persons reside within the municipal limits of Greater * Bombay which has a land area of 603 square kilometers. 2. The infrastructural development, however, has not kept pace with the growth of population.'As a result, the city suffers from shortage of all basic amenities including housing, water supply, sanitation and transport. Amongst these, sanitation is perhaps the most neglected sector. Only a miniscule proportion, 22.5 mid out of approximately 2000 mid municipal wastewater generated in the city , receives treatment before disposal to adjoining coastal and creek regions. Discharge of such large quantity of untreated sewage into the marine environment has resulted in widespread impairment of coastal and creek water quality. Bombay Sewage Disposal Project (BSDP) 3. The first integrated wastewater management scheme for the city was planned in 1970. The scheme envisaged disposal of screened wastewater from entire Bombay municipal area through two marine outfalls at Worli and Bandra. 4. The plan, since then, has undergone many revisions. The most recent Development Plan III, divides the Bombay municipal region into seven service areas. The plan provides for disposal of wastewater after preliminary treatment through marine outfalls at Colaba, Worli and Bandra into coastal sea and after treatment in aerated lagoons at Bhandup and Ghatkopar in Thane creek and at Malad and Versova in Malad creek respectively (Figure 3.1). The proposed facilities Aerated lagoons 5. The proposed lagoons, are combination of aerobic and facultative lagoons. Each lagoon comprises of four identical streams of three cells of average residence time of 1.4, 1.8 and 1.1 days respectively. Out of three cells, the first cell is designed to operate as a flow-through aerated lagoon and the following two cells as facultative aerated lagoons. The over-all removal efficiency of the treatment system is expected to be 80 percent for Biochemical Oxygen Demand (BOD) and 70 percent for Suspended Solids A-l MZOONS VM (SS). The salient design details of the aerated lagoons are presented in Table 4.3., 6. Due to financial constraints the original plan of implementation has been modified and implementation has been divided into two phases. During the first phase activities, the first cells of four streams are being constructed and will be operated as facultative aerated lagoons with expected BOD removal efficiency of 50 per cent. Figures 4.4 and 4.5 describe the layouts of the aerated lagoons at Bhandup and Ghatkopar, respectively, The shaded portion in these figures indicate the facilities proposed to be built during the first phase. Need for present study 7. The present study has been undertaken in keeping with the World Bank. policy and procedure for the environmental assessment of bank lending operations with respect to Bombay Sewage Disposal Project, Development Plan IIL Procedures as listed under Operational Directive 4.01 have been followed during the assessment. The study also meets the requirements of the State of Maharashtra and the Government of India for environmental clearance of development projects. Objectives of environmental assessment 8. The objective of this environmental assessment study has been to evaluate the impact of proposed first phase facilities at Bhandup and Ghatkopar on the water quality in Thane creek. The study also envisaged to ascertain whether the facilities when augmented to three cell lagoons would be adequate to provide the desired water quality benefits and o not. what modifications in the form of higher degree of treatment and mode of disposal would be necessary. The design perod iur the primary recommendations has been kept upto the year 2005 9. In view of the need to define water quality management tramework beyond the year 2005, the study was also expected tv evaluate wastewater treatment options for the year 2015 and after. The objective for such extension was to provide broad guidelines for future wastewater management in the creek. As the project involves large scale construction activities, the study, also aimed at assessing the potential negative impacts during the construction phase of the project and delineation of necessary mitigatory measures. AERAGED LAeOONS 10. With the above objectives, the study was planned to cover the following environmental aspects: * Assessment of environmental impacts of proposed aerated lagoons on water quality in Thane creek with special emphasis on improvement of Dissolved Oxygen (DO) levels. * Evaluate the existing water quality in Thane creek and the adequacy of proposed single and three cell aerated lagoons at Bhandup and Ghatkopar to achieve the acceptable -DO levels of the creek water. SField investigations and data collection to set up appropriate hydrodynamic and solute transport model for Thane creek to enable water quality predictions. * Based on the modeling studies, broadly delineate possible augmentations of proposed scheme with respect to additional wastewater treatment/ transport/disposal measures for planning beyond the year 2005. Assessment of impacts on air, noise, land, water and socio-economic environment due to construction of aerated lagoons and delineation of mitigatory measures. Environmental Standards 11. Environment (Protection) Act, 1986 vests in Central Government, the powers to lay down standards for environment protection. Central and State Pollution Control Boards are responsible for compliance of these standards. The Boards, based on local conditions, have power to stipulate more stringent location specific standards. 12. For protection of coastal water quality, two standards apply in India. The first of these standards is in the form of receiving water quality and is based on best designated use of the water body such as for bathing, fishing or navigation. The creek and coastal waters used for recreational purposes or fishing, accordingly, should always have BOD less than 5.0 mg/L, total coliforms not more than 1000/100 ml and DO more than 3.0 mg/L 13. The second is in the form of effluent standards for discharges into marine coastal area. According to this standard, effluents with BOD and SS up to 100 mg/L each and ammoniacal nitrogen up to 50 mg/L can be discharged into the creeks. AMMUIED AGOONS 14. The standards for receiving water and effluent discharges do not complement each other as the latter does not take into account the assimilative capacity of the receiving waters. If the effluent volume is large, i 'discharges in compliance with the effluent standard may still lead to severe deterioration of receiving water quality. Also, for smaller water bodies, even a very high degree of treatment of municipal discharges may fail to comply with bacterial quality prescribed by the receiving water standard. A rational view, thus, would be to take decisions which ensure DO levels necessary to achieve minimal conditions to sustain a healthy creek ecosystem in the receiving waters. The water quality management objective for Thane creek was, therefore, aimed at achieving a minimum DO level of 2 mg/L. Methodology for environmental assessment 15. In order to assess adequacy of proposed treatment facilities at Bhandup and Ghatkopar, the existing water quality status of Thane creek was determined through elaborate field surveys. As inputs to water quality model, hydrodynamic and bathymetric data on Thane creek were also collected. 16. Water quality predictions were carried out mainly for DO and BOD, using mathematical models. These models were calibrated for local environmental conditions through in-situ and laboratory experiments. 17. For processes involving highly complex interactions such as nutrient. enrichment, bioaccumulation and ecological transformations, the approach of observations at and inference from the regions which have been receiving similar wastewater discharges over a long period was adopted. 18. For estimation of construction phase impacts. field nvestigations on ambient air quality, noise levels, creek and coastal water quality were conducted. Land-use pattern and soil characteristics near the construction sites were also studied. Area under mangrove cover in entire inner Thane creek was determined through satellite imageries. 19. The observations and model predictions were used to examine the efficacy of proposed single and three cell aerated lagoons in achieving the desired environmental benefits. Probable augmentations of the proposed treatment effort catering to increased flows by the year 2015 and after, in the form of higher treatment and options for wastewater disposal at new locations in the creek, were evaluated. The scope for additional field observations and modeling work to finalise such options was also highlighted. A"AE 1 oons Existing environmental status 20. The major impacts of present wastewater discharges are creek water quality impairment in terms of low DO, high BOD, SS and total coliforms. Thane creek, in its inner regions, receives approximately 400 mid untreated wastewater from Bhandup and Ghatkopar service areas. Due to shallow depths and narrow cross-section, the creek in this region does not have sufficient capacity to assimilate these discharges. As a result, about 10 kilometers long stretch along the west bank of the creek exhibits poor water quality characterised by low DO and high BOD levels. 21. Concentrations of BOD as high as 7 mg/L and total coliforms exceeding 10'/100 ml are frequently observed in the creek. Observations on biological indicators present a picture similar to those of physico-chemical parameters. The creek sediments also show high concentration of nitrogen, depicting accumulation of nutrients due to large wastewater discharges. 22. Ambient air quality analyses at Bhandup and Ghatkopar aerated lagoon sites indicate that present air quality in terms of NO and SO, at both sites fall within Indian standards for ambient air quality. 23. Observations on noise levels at the lagoon sites are within the limits prescribed for urban residential areas. Environmental impacts of proposed project Construction phase impacts 24. The major construction activities for the project are site :varanme. land filling, earth work and material transfer. The most important impaict t these activities is the loss of about 40 hectares of mangrove cwvr amountang to 5 per cent of total mangrove forests in inner Thanw c.rsi. Quantitative estimation of impact of such reclamation on Thane creek water qualin is not possible. However, considering the role of mangroves in sustenance of coastal ecosystem, it is essential to compensate for the lost mangrove cover. 25. The other prominent impacts during the construction are rise in ambient noise levels and marginal increase in air borne pollutants like SPM at the construction site. The higher SPM levels would be witnessed for short periods only during peak periods of construction activities. There will be insignificant increase in the gaseous pollutants such as SO and NOx. ARAED LAGOONS A15 26. Predictions of noise levels at the sensitive locations, located at more than 1 kilometer distance from the aerated lagoons, indicate an addition of 40 dBA to a similar background noise level at the time of construction activities. The noise due to constructions, thus, wilt be attenuated to the background levels at sensitive locations. 27. With the exception of the effects of mangrove loss (see para 24.), construction of aerated lagoons will not have any adverse impacts on creek water quality or fishing interests as all construction activities except for effluent channel will be restricted to land. The construction is not expected to have significant impacts on drainage characteristics of the region. However, it will be necessary not to block any natural drainage channel in the vicinity of lagoons. Operational phase impacts 28. The planned treatment level at Bhandup and Ghatkopar aerated lagoons along with the present and projected flows for the year 2005 are presented in Table 7.3. Thane creek water quality projections developed through rigorous hydrodynamic and water quality modeling, indicate that the proposed first phase treatment effort through single cell aerated lagoons would not provide significant improvement in creek water quality. Such implementation would, however, arrest rising trend of water quality impairment. 29. The present design capacity of Bhandup lagoons is only 180 mid against the estimated flows of 280 mid. If built to the design flows, Bhandup lagoons will be considerably over loaded. It will, therefore, be necessary to redesign the Bhandup lagoons for the new flows. 30. H5 emission in the event of malfunctioning of the aerators could lead to significant odour nuisance within 1 kilometer radius of the lagoon on a typical stable winter day. However, impacts would not be significant in areas which are beyond 1.5 to 2 kilometers distance from the lagoon. Analysis of alternatives No action scenario 31. The municipal wastewater discharges from Bhandup and Ghatkopar service areas are presently estimated at 400 mid and are expected to rise to 515 mld by the year 2005. A further steep rise in wastewater generation in these service areas is expected due to planned augmentation of water supply. By 2015, wastewater generation in these areas is expected to reach 1000 mid. If no wastewater treatment facilities are implemented, creek water quality ARAED AGOONS X9 which already exhibits widespread impairment during the low tides, would be considerably further degraded. * Augmentation of wastewater management effort 32. When augmented to three cell aerated lagoons designed to achieve 35 mg/L or lower BOD in the effluents, the proposed wastewater treatment would provide adequate level of pollution abatement in the affected creek region untill wastewater flows exceed the projected flows for the year 2005. 33. Water quality scenarios developed to examine the benefits of further raising the treatment level at Ghatkopar to activated sludge process indicate that such augmentation for 2005 flows would give rise to only a marginal improvement of 0.3 mg/L in creek dissolved oxygen over three cell aerated lagoons option. Shifting effluent discharge location to center of the creek also does not yield any significant improvement in creek DO. Long term water quality perspective 34. When extended to 2015 flows, the simulations indicated that it was not feasible to discharge effluents beyond projected flows for the year 2005 at Bhandup and Ghatkopar even after nitrification of effluents. For future flows, it will thus be necessary to build additional wastewater treatment facilities and discharge the effluents at new locations in the creek. The analysis indicates, that, if one were to discharge within the inner Thane creek, it would be possible to discharge upto 260 mid after secondary treatment near VikhroLi. To cater to entire excess flows of 520 mid between the year 2015 and the year 2005, however, such option would entail tertiary level treatment. The simulated creek DO levels for management scenanos described above are summarised in Table 7.4. 35. Considering the high cost of tertiary treatment and also the need to plan even beyond the year 2015, it is desirable that options for discharging the wastewaters in other regions of the creek be explored. Under such case, it may be adequate to treat the effluents only upto secondary level and cost of transporting the wastewater may be off-set by savings in the cost of its treatment. Socio-economic impacts 36. The project area for Bhandup and Ghatkopar lagoons is uninhabited and does not involve any displacement of people. The project, during the construction, is expected to generate some employment which would have AEMUED LAGOONS XV marginal positive impact The operation of aerated lagoons does not require a large workforce and therefore, no large scale residential development in the region, is expected, due to the implementation of the project. The implementation of the project, may result in beneficial impacts in terms of higher fish yield thereby increasing fishing activities in inner Thane creek. Mitigation plan Construction phase 37. Lass of about 5 per cent of the total mangrove cover in the inner Thane creek due to land reclamation for lagoons, is the most important construction phase impact of the project. To compensate for the unavoidable loss of mangrove area, MCGB should designate about 200 hectares of mangrove area along the creek as protected area and take measures against further reclamation or unauthorized cutting. Alternatively, MCGB should undertake fresh planting of mangrove forests of area equivalent to the reclaimed area in the inner Thane creek region. 38. Another potentially negative impact of aerated lagoon construction is a rise in the ambient noise and dust levels. This impact can be prevented by adherence to good construction and house keeping practices. Measures such as avoidance of unnecessary idling of construction machinery and spillage of fuel and oil and adequate maintenance of construction machinery to ensure efficient and trouble free operation should be provided for in the construction contracts. 39. Analysis of the noise levels at the site and surrounding areas indicate that the effect of construction activities during the day, is not felt outside the construction site due to the local noises. At night, however, the construction activities can raise the noise levels and the nearby residential locations beyond the night time standards for such areas. The noise generating construction activities thereforeshould be restricted only to day time hours. 40. Air quality analysis at the sites indicates the air quality in terms of SPM, NO and SO, are well within the Indian Standards for ambient air quality. However, the SPM levels may, on some occasions, surpass the standards at the time of site clearing and construction activities. Provision of water spraying on all haul roads at the construction site should be made to minimize the dust Also, green belts should be developed around the boundary of the lagoon sites on the sides facing habitation to safeguard against aesthetic impairment An inventory of requisite mitigatory* -measures is provided in Table &. AME LASOM a Operation phase 41. If the facilities are limited to single cell lagooms, water quality in the affected region of the creek will remain below the level necessary for a healthy ecosystem. An adequate mitigatory measure, therefore, would be to construct three cell aerated lagoons at this stage itself or to augment the single cell lagoons to three .cell configuration as soon as possible. With respect to the treatment facilities care should be taken to extend the effluent discharge point upto 20 meters beyond the low water line in the creeklets to avoid formation of sludge mats in the inter-tidal zone. 42. In order to achieve acceptable environmental conditions in the vicinity of the creek proper functioning of aerators is of prime importance. Adequate back up systems should be incorporated in the design stage itself to ensure their continuous and trouble free operation. Recommendations 43. Construction of properly designed single cell aerated lagoons at Bhandup and Ghatkopar is the minimum admissible treatment effort necessary to meet the current effluent discharge standards. Construction of such wastewater treatment facilities at Bhandup and Ghatkopar would be a positive step towards the objective of overall water quality improvement in .Thane creek and is strongly recommended. 44. For significant improvement in creek water quality, it would be essential to augment the aerated lagoons at Bhandup and Ghatkopar to a three cell configuration designed to produce effluents with BOD below 35 mg/L. Considering that such augmentation would remain effective only upto the year 2005, subject to funds being available, consider implementation of this configuration could be considered at the present stage. 45. The recommended long term water quality management option for the Thane creek is to build three cell aerated lagoons at Bhandup and Ghatkopar and to develop additional treatment units with facilities to discharge the effluent at new locations within the creek. One of the suitable discharge locations has been identified near Vikhroli and has potential to receive about 260 mid of effluents after secondary treatment. 46. Additional water quality modelling studies are recommended to assess assimilative capacity of the creek south of Trombay as possible new effluent discharge areas for expected wastewater flows in Bhandup and Ghatkopar service areas by the years 2015 and after. ABSAD POONS MM 47. The conclusions of this assessment are limited to the study of municipal wastewater loads from Bhandup and Ghatkopar service areas. For achieving the full water quality benefits of the investments in treatment that MCGB plans to make, it is imperative that a comprehensive management plan be developed for the creek, with comparable treatment levels applied to other discharges. Because this involves multiple jurisdictions, it may be best accomplished by Government of Maharashtra. Considering the probable environmental impairment due to delays, It is desirable that immediate priority be assigned to planning and implementation of such a management scheme. Environmental monitoring * 48. A systematic water quality monitoring effort within the creek should be initiated before and after commissioning the aerated lagoons at both the discharge locations. At the post-commissioning stage, the mondtoring should be aimed at an evaluation of water quality projections and validating the water quality model used in the present study. Such validation will be useful for future planning. 49. A regular effluent monitoring program to establish the performance parameters for the treatment system should, however, be undertaken immediately after commissioning the treatment systems and continued during the entire operation period of the treatment systems. Guidelines for such monitoring are provided in Table 8.1. 50. Creek water quality monitoring along with observations on hydrodynamic parameters should, however, be initiated by Government of .Maharashtra to develop a comprehensive water quality model for the entire Thane creek, a prerequisite for developing the overall wastewater mnaugenent plan for the region. The exercise should aim at developing location specific discharge standards for various industrial discharges into the creek to ensure that the overall pollution load to the creek are within its assimilative capacity. 51. A limited monitoring at the creek may also be undertaken to document the improvement in the creek ecosystem comparing the pre and post-project water quality conditions (Table 8.1). Public participation 52. The proposed wastewater management effort along Thane creek involves * significant investment of public funds. The findings of the study indicate that even more comprehensive treatment efforts will be necessary to AHUMED LAGOONS Xv. safeguard the creek water quality in the not-too-distant future. It is, therefore, desirable to create public awareness for the project activities to facilitate their involvement in the decision making. Tbwards this end, findings of this study should be placed for public discussions among representatives of fishing communities, general public and local NGOs. The report summary should alos be translated in local languages and distributed among the fishing communities. 53. A comprehensive awareness program on the need for the project, major technical and social issues and the environmental benefits should be undertaken through local media., The coverage should include discussions on TV and radio by panels comprising eminent citizens and officials connected with implementation and environmental assessment of the project. An outline for environmental awareness program has also been suggested. Institutional needs 54. There is a need for substantial institutional development within the MCGB for effective operation of aerated lagoons and the additional treatment and diversion options which will have to be developed later. Training programs for various levels of associated staff of MCGB should be conducted for efficient operation of the project On certain environmental aspects such*as use of water quality models for effective water quality monitoring in the creek, evaluation of long term post project environmental impacts and planning for wastewater management of future discharges it may be necessary for MCGB to take recourse to the expertise available with the research Institutes active in these areas. 55. For effective implementation of the recommended environmental monitoring, it will be necessary to develop adequate facilities fur sampling and analysis. It will be desirable to operate an environmental monitoring cel, with adequate training and instrumentation support for coastal water quality monitoring and analysis related to the aerated lagoon project. Government and private laboratories with adequate infrastructural facilities and expertise may also be identified to assist in these activities. AUED LAGOONS - Chapter 1 INTRODUCTION 1.1 Preamble Rapid growth of Bombay city over past few decades has given rise to innumerable problems of diverse nature and of significant dimensions. One of the major problems is the deterioration of water quality in creeks and coastal regions around the city, due to more or less unrestricted disposal of large volumes of domestic and industrial wastewaters. Loss of clean recreational beaches and sea fronts, and probable damage to coastal ecosystem are some of the manifestations of such pollution that has caused serious concern to planners and the residents alike. Regardless of the wastewater treatment method, Bombay, being an island city, warrants discharge of the effluents to Thane creek on the east coast and to the Arabian sea on the west coast. In the late seventies, M/s. Metcalf & Eddy carried out detailed hydrodynamic and water quality studies in Thane creek and in Arabian sea to examine the impact of such discharges on water quality. These studies indicated the feasibility of discharging the primary treated effluents into the sea through marine outfalls and secondary treated effluents directly into the creek. The findings and recommendations of these studies culminated in the formulation of Development Plan III of the Bombay Sewage Disposal Project. It comprised construction of primary treatment facilities followed by marine outfalls at Bandra, Colaba and Worli; and aerated lagoons to provide secondary treatment prior to disposal of wastewaters from Malad and Versova into Malad creek and Ghatkopar and Bhandup into Thane creek (Figure 1.1). The Municipal Corporntion of Greater Bombay (MCGB) was to undertake the implementation of these works througha series of large scale co-ordinated pollution abatement programmes. Before implementing the above works, MCGB desired to ascertain the environmental impacts of construction and operation of the proposed facilities in keeping with the World Bank policy and procedure for the environmental assessment of Bank lending operations. In September 1991, MCGB retained NEERI to undertake the environmental assessment studies for all wastewater disposal and treatment schemes envisaged under the Bombay Sewage Disposal Project. The study also meets the requirements of Government of Maharashtra and Government of India for environmental clearance of development projects. Disposal of untreated/partially treated municipal wastewater could have a variety of impacts on the receiving marine environment. The most prominent of these are water quality impairment due to depletion of dissolved oxygen and bacteriological contamination, probable build-up of nutrients in sea AEAD IAGoONs 1.1 Figure : 1.1 Proposed wastewater disposal 1 treatment schemes under Bombay Sewage Disposal Project K .IfK ... ..l..... LW .l ... l. ..I. l ......... ..'I.....J ..?l 's v sa'I.. Vagal crul egel pi. mångt; P BHANDUP MALAD SALSETTE VERSOVA,' 5 sv GHATKOPAR senscres9.1 Bandra BANDRA OUTFALL - TOMBAY, WORLIOUTFALL 0 r e i l- , aa a G_ICT_e Ni COLABA \ liljvipl T ,7 . LLg i' l 7 1lt i *0 N 0M 70' water giving rise to algal blooms under adverse meteorological conditions, and accumulation of metals and trace organics in sediments and benthos through the process of biomagnification. Constr.ction activities associated with the project implementation could also lead to negative impacts on environment in the vicinity of the construction sites. Although, marine outfalls and aerated lagoons are designed to achieve improvement of coastal water quality around Bombay, their operational mechanism is radically different. Marine outfalls are designed to carry the wastewater to open coastal regions of adequate assimilative capacity to render the discharges environmentally safe, whereas aerated lagoons aim at reducing the pollution load before disposal to match the limited available assimilative capacity in the receiving creeks. Due to differences in hydrodynamic characteristics, physical extent and ambient water quality of open coastal areas and creeks, different approaches were required to evaluate the impacts of wastewater discharges into the respective regions. The investigations and reporting on environmental impact assessment for marine outfalls and aerated lagoons were, therefore, segregated. The field studies related to marine outfalls were completed by the end of 1992 and a final report on the environmental impact assessment after the requisite review was submitted in October 1993. Studies on environmental impacts of discharges from proposed aerated lagoons into Malad and Thane creeks were subsequently undertaken. The preliminary investigations indicated that discharges into Malad creek were potentially more sensitive due to their widespread negative impacts in the region. The Malad creek studies, therefore, were undertaken ahead of Thane creek studies and the final report after reviewing the findings was submitted in October 1994. Finally, the environmental impact assessment of proposed municipal discharges into Thane creek has been completed and forms the subject matter of this report. 1.2 Objectives Thane creek extends northward from the Bombay harbour and segregates the island from the main land on the east. At its northern end, the creek receives an outlet from Ulhas river but with very little discharge as the river flows past the creek head. In its upper region, the creek is narrow and only a few meters deep. It, however, spreads to more than 5 kilometers as it opens into the harbour. The total length of the creek is about 25 kilometers with an average depth of about 5 meters. The creek is dominated by diurnal tides which range from approximately 1 to 4.8 meters during the neap and spring AERATED LAGOONS 1. tides, respectively. The creek provides natural drainage to the eastern suburbs comprising Bhandup and Ghatkopar service areas and receives about one third of the total municipaL wastewater generated in Bombay. Due to inadequate dilution, these discharges give 'rise to significant water quality impairment in the inner region of Thane creek. In order to ease the onus of pollution on the creek, construction of aerated lagoons having disign capacity of 176 mid at Bhandup and 386 mid at Ghatkopar, is planned. The aerated lagoons are expected to reduce the organic loading to the creek by approximately 60 percent. The proposed degree of treatment, was determined based on the studies conducted by Metcalf & Eddy on Thane creek in 1976. The revised wastewater estimates, however, indicated a significant variation in wastewater generation and entailed a fresh scientific study to assess the adequacy of the proposed treatment schemes. Considerable advances in creek water quality modelling have also taken place since 1976. The present study makes elaborate use of advance water quality models in conjunction with comprehensive field investigations to establish the impacts of proposed treatment schemes on creek water quality. The major areas of investigations under this study are: * Assessment of environmental impacts of proposed aerated lagoons on water quality in Thane creek with special emphasis on improvement in dissolved oxygen levels * Field investigations and data collection to set up an appropriate hydrodynamic and solute transport model for Thane creek to enable water quality predictions * Delineation of additional wastewater treatment /storage /transport measures, if required, to ensure a safe level of dissolved oxygen in Thane creek based on the modelling studies * Assessment of impacts due to construction of aerated lagoons on air, water, land and socioeconomic components of the environment. 13 Organisation of the report This report addresses all environmental issues, delineated under section 1.2, pertaining to the impacts of construction and operation of proposed aerated' lagoons at Ghatkopar and Bhandip. The report comprises of eight chapters, the subject matter of which is briefly described below. AHMED LAGOONS IA Chapter fl of the report provides the project setting with brief description on city of Bombay with respect to its growth, geography, climatology, demography and environment. The chapter also summarizes the major environmental problems, which need immediate attention, for betterment of quality of life of large sections of population in Bombay. Chapter III describes the history of Bombay Sewage Disposal Project and the present status of project implementation. Chapter IV highlights the salient features of aerated lagoons, repercussions on the coastal environment due to lagoon effluents and presents the design features of the proposed lagoons. Chapter V details the methodology and inferences of investigations on existing. environmental quality in Thane creek, construction sites and neighbouring areas. Chapter VI provides an overview of methodology of field surveys for hydrodynamic and water quality observations. It also details the depth-average hydrodynamic and solute transport model used for predicting the water quality impacts and use of hydrodynamic and water quality observations in model calibration. Chapter VI1 highlights the inferences drawn from the environmental impact predictions. It describes the overall environmental impacts of the proposed project and underscores the areas of deficiency. This chapter also provides the possible management alternatives to achieve desired water quality improvement after a comprehensive examination of feasible options. Chapter VIII is the concluding chapter of the repo)rt ..n i*ruents recommendations of the study. It delineates the environmientaia nuanl.unwn plan for construction and operation phases of the project and prouides %auent leatures for future monitoring programme in the project area. AERAID LAGOONS 1.5 Chapter 2. PROJECT SETTING 2.1 Preamble A small cluster of islands burgeoning into a megapolis sounds incredible. However, this is the story of the growth of Bombay, within a span of about ten decades. Bombay has witnessed unprecedented industrial and commercial growth in this period and has emerged as the industrial capital of India. The industrial growth of Bombay has been accompanied by an equally phenomenal rise in population. The infrastructural development, however, could not keep pace with the growing population. This has led to shortage of water supply, lack of proper sanitation facilities, proliferation of slums, inadequate transport facilities etc. in the city. Disposal of untreated wastewater into the coastal regions has led to deterioration of water quality in the adjoining areas and poor beach aesthetics. In order to curb the increasing environmental impairment, civic authorities have planned large scale waste management schemes in the city Construction of aerated lagoons to provide secondary treatinent, prior to disposal of wastewaters from Ghatkopar and Bhandup service areas into Thane creek, is one such scheme envisaged under the Bombay Sewage Disposal Project. An environmentally sound design for the proposed lagoons, however, entails considerations of local coastal environment, socio-economic and other infrastructural conditions. In the context, this chapter describes Bombay city, its geological and demographical characteristics and the relevant environmental setting. 2.2 Bombay : the city, its genesis and growth Bombay, situated at 18.55ON latitude and 72.54 E longitude was originally a cluster of seven islands of Colaba, Fort, Byculla, Parel, Worli, Matunga and Mahim. Now Greater Bombay is extended upto Mulund and Dahisar. It is no- more an island but a sort of peninsula. its early inhabitants were Kolis or fishermen. Bombay was a part of the Mauryan Empire (273 -232 BC). It was under the Silara Kings (810 AD 1260 AD). On Dec. 23, 1534, Bombay was ceded to D.Joans III, King of Portugal by Sultan Bahadurshah. In 1549, the islands of Bombay were handed over in perpetuity to Dr Pracia da Orfa. In 1625, an Anglo-Dutch fleet captured Bombay fort by a surprise attack They looted the island and left. On June 23, 1661 King Charles H of England married Princess Catherine Le Breganza of Portugal and the island of Bombay was given in dowry to King Charles II. Thus, Bombay went to the AMEDL AGOONS 2.1 British by an alliance of marriage. In 1668, Bombay was handed over to East India Company by a Royal Charter. Sir George Oxender was the first Governor of Bombay. Decades of development and reclamation resulted in the expansion of the city area to 70.2 square kilometers in 1950, to which the area of Bombay Suburban District was added in 1951, bringing a total area of 235 square kilometers under Greater Bombay. In 1957, more villages were added and the area increased to 4663 square kilometers. 2.3 Geography Greater Bombay comprises of the island of Bombay, Trombay and major parts of Salsette. In the north, the Salsette island is separated from the main land by Bassein creek on the west, and by Thane creek on the east Figure 2.1. The- Mahim creek, on the south of Salsette island separates it from the island of Bombay, while the western margin is further indented by Manori and Malad creeks. The island is bounded on west and south sides by Arabian Sea and has a natural deep water harbour protected by the island of Bombay on the west coast and the main land of Konkan on the east. Bombay is the largest port along the west coast of India. City of Bombay, on the southern side of Mahim creek is highly overcrowded with unplanned growth. The suburban development on the northern side, is relatively better planned and is aligned to the two railways, the western and the central, dividing this area into western and eastern suburbs. Suburbs on Central railway comprise the main industrial belt of Bombay. The important industries include paints and varnishes, miscellaneous chenical products manufacturing, machinery and electrical appliances etc. 2.4 Regional geology and structure The regional geological setting of western India and in particular of Bombay, may be termed Deccan Trap as described in both Geology of India chapter XVI pp 275-286 and in Geology of India and Burma chapter XV pp 405-421. The basaltic rocks extend over an area of some 500,000 square kilometers and the thickness of the Deccan Trap may be as much as 2,000 to 3,000 meters along the present western margins, where the rocks dip 5-15 degrees to the west; the only sea where the rocks are not effectively horizontal. The Traps are divided into 3 sub-units; Lower, Middle and Upper Traps. The Bombay area (Upper Traps), is noted for its inter-trappean sedinuutary beds, lava flows and ash deposits. MAW AGDONS 2 Geogr4phical setting of Bombay city and its suburbs 6m* ~~~a 411 10i20 Olm; e »lga 1LEGENDbl central RciewayPI A~ LAG~2.3 The basaltic rocks have been erupted from vents and along fissures. The individual flows vary between 10 and 30 meters thick, although composite flows of a number of smaller units, which are difficult to differentiate can give rise to apparently thicker flow sequences. The lavas can, and often do, show sedimentary 'coercing-downwards' like differentiation within the flows, giving rise occasionally to brecciated deposits. Two major flow formation mechanisms (each of which can be subdivided into two types) are seen although breccias, tuffs and other variations due to minor changes in the magma mineralogy are also noted. 2.5 Climatology The climate of Bombay is fairly equable with average annual maximum and Uuum temperature of 31.4*C and 22.9*C respectively and the average annual maximum and minimum Relative Humidity of 95.7 per cent and 34.0 per cent respectively. The average annual rainfall is around 2000 millimeters occurring mostly during July to September. Strong land and sea breeze effect is observed, particularly during monsoon. Predominant wind directions during monsoon are north-west and west. 2.6 Demography In a little over a century, the population of Bombay has almost increased by hundred folds to about 10 million. The rise in population has been caused by large scale migration from various parts of the country on account of better employment opportunities in Bombay. The most commonly spoken languages are Hindi and Marathi. The city of Bombay is divided into 23 wards and its population according to the 1991 census is 99.26 lakhs. Inadequate housing has forced a large number of people in Bombay to reside in slums. According to 1981 census, more than 30 per cent of Bombay's population lived in slum areas. The present estimates indicate that approximately 5 million people live in slums. Marine produce was the main source of income for inhabitants of Bombay before it developed into an industrial centre. Fishing in the coastal waters of Bombay however, is still an important economic activity. 2.7 Environmental setting Bombay is endowed with a natural harbour, beaches and hill ranges, lakes and river It was estimated in 1959, that the area of mangrove forests in Bombay and adjacent coastal districts was about 24,70 ha. The revised estimates indicate that the same was around 20,000 ha in 1975. AR Loo2 There are two major forest areas in Bombay. It has few good national parks and a small bird sanctuary that has been preserved. Vegetation cover in the city of Bombay is not very good. The suburban areas, however, are much greener than the main area of Bombay city. The mangrove swamps of Bombay are worst affected by human interferences. The principal cause for their degradation, is large scale reclamation of mangrove swamp areas for housing due to increasing population pressure. 2.8 Major environmental concerns The environmental problems in Bombay have been caused due to high population pressure and intensive industrial and commercial activities within a small physical area. Discharge of large quantum of untreated waste water into the surrounding coastal and creek regions, formation of pockets of acute air pollution due to industrial and vehicular emissions, inadequate disposal of solid wastes, congested roads and overcrowded trains, noise pollution, encroachment of forest area and open spaces and aesthetic impairment are some of the consequences of Bombay's phenomenal growth. The solution of these problems entails an integrated and well coordinated effort considering the problem as a whole. The wastewater management plan undertaken by Municipal Corporation in the form of Bombay Sewage Disposal Project is an important and positive step towards restoration of environmental quality in and around Bombay. AMMED LGOONS 2. Chapter 3 BOMBAY SEWAGE DISPOSAL PROTECT 3.1 History of the project Wastewater management facilities in Bombay, date back to the 1860's following the inauguration of the Vihar Lake scheme to provide Bombay with the first piped water supply. Following a Government Commission report in 1872, the Wodi outfall, discharging wastewater into the Arabian Sea, was completed in 1880. Lack of funds, however, prevented the construction of the outfall as initially proposed to discharge below the low water level. Wastewater collection facilities within the city continued to expand, and by 1900 all wastewater was directed to Love Grove from where it was pumped to sea through the Worli outfall. Problems of pollution in this area had started to become evident even at this early date. By 1905, the basis of the present wastewater collection, treatment and disposal system within the city, had been established. Subsequent demands were met by the duplication of sewers, provision of overflows to relieve surcharging in developed areas, addition of new sewers in developing areas, construction of additional facilities at Love Grove, and the construction of new treatment facilities at Banganga, Dharavi and Dadar. Following the second World War, the rapid increase in population of the city rendered many of the wastewater facilities completely inadequate. To correct this situation extensive relief works were sanctioned in 1948 under the Relief Sewerage Scheme. Unfortunately, because of the length of time taken to complete these works, and because population forecasts prepared in 1948 proved to be far too low, the relief works did little to alleviate the problems. In 1950, the Municipal Corporation boundary was extended to include what are now Wards H,CL,M,N, and part of P Ward. The boundary was further extended in 1957 to its present position. Wastewater facilities within these suburbs and extended suburbs were very limited during that period. A High Level Committee of Experts (appointed by the Municipal Corporation) to advise on water supplies and wastewater facilities for the Greater Bombay area, submitted its report in 1963. This report made recommendations for expansion and upgrading of the wastewater facilities within the city and the suburbs to meet the demands of wastewater flows expected from population prolected for 1981. AwnmAUooNs3. Although some minor improvements were carried out; the collection, treatment, and disposal facilities continued to be completely inadequate to deal with the increasing quantities of wastewater. 3.2 Development Plan I In May 1970, M/s. Binrie & Partners (India) Ltd. were retained to advise on water and wastewater problems in the Greater Bombay area. Their study of the wastewater problems culminated in the preparation of Development Plan L This plan set out a programme for expansion of existing facilities to meet the demands of the projected population in 1991. The plan recommended disposal of screened wastewater from the entire Greater Bombay area through two marine outfalls at Worli and Bandra. 3,3 Development Plan B On instructions of the Deputy Municipal Commissioner (Special Engineering), an alternate plan for the treatment and disposal of wastewater from the Greater Bombay area, as per the projection for 1991, was prepared. This plan was referred to as Development Plan II. Development Plan H recommended the disposal of screened wastewater from Malabar, Worl, and Mahim drainage zones through marine outfalls at Worli and Bandra (Figure 3.1). Wastewater flow from Chembur drainage zone was planned to be treated in plants at Bhandup and Chembur prior to discharge into Thane creek, and the flow from Marve zone at a treatment plant at Marve followed by discharge into Malad creek. In this plan, the Dadar treatment plant was to be retained and expanded to meet the needs of Dadar. Sludges from all treatment plants were planned to be disposed into the Arabian Sea through the marine outfalls. 3A Review of Development Plan II The Municipal Corporation proceeded with some of the sewerage proposals contained in Development Plan II, and the detailed design of eight pumping stations and feasibility studies of eleven more pumping stations. However, no work was carried out, on the treatment and disposal aspects of the plan. Before proceeding with design and construction of facilities to augment the treatment and disposal of wastewater, the Municipal Corporation, in consultation with the International Development Association, decided on a fresh review of the recommendations contained in Development Plan IL To this end, the services of M/s. Metcalf & Eddy Inc. of Boston, U.S.A. and M/s. AERAD UOBOONS 32 Figume : 3.1 Phical boundaries of service areas alaal jaasi *ANO~~& DUIMLL asa rsaaem an a * -AW rEo 2 I-- weg5 %, Il4 emu ~ 9-9 Ne - ILABA TA 11 4 Gh-ellprrl,i .... as. AEIM3EDAAOO0N Environmental Engineering Consultants of Bombay, were retained with the view to solve the immediate and mid-term wastewater problems of Bombay. The prime objectives of the review were : * - To produce a wastewater treatment and disposal plan for Bombay (Development Plan 111) for the period through 2005 that would achieve and maintain satisfactory levels of public health and environmental quality - Determination of the wastewater assimilation capacities of Thane creek and coastal waters around Bombay for their optimal utilization for disposal of municipal wastewater - To prepare feasibility studies, preliminary designs and cost estimates for a first-stage programme catering to the wastewater flows for 1981 - To outline further environmental or related studies required for the development of a long-range environmental quality improvement programme M/s. Metcalf & Eddy submitted an Interim Report in 1977, setting out their proposed solution to the problems of treatment and disposal of wastewater generated in the Greater Bombay Area. This proposed solution was subsequently revised in consultation with MCGB engineers and became the basis of Development Plan IIL 3.5 Development Plan III Under the Development Plan IIL the design period for the wastewater management facilities was extended to the year 2005. Under the scheme, it was envisaged that the sewage generated in the municipal boundaries of city of Bombay shall be treated and disposed into the coastal and creek regions through seven different works. The drainage zones envisaged in the earlier plan were reorganized to form seven service areas. Provision for the treatment/disposal of entire wastewater generated in an area, was made at the works within that area itself. The physical boundaries of the service areas and location of the treatment/disposal works designated for each of those are presented in Figure 3.L The salient features of these works are presented in Table 3.1 and are summarized below. PMWGD ONS 3 Table : 3.1 Wastewater treatment and disposal facilities proposed under Development Plan III Sr Service Area Facility Design Flow Present Status No. (mld) 1. Colaba Marine outfal 41 12 km. length facility inoperationsince 1988. 2. ove Grove Marine outfall 757 498 m outfal in operation since 1990. 3. Ghatkopar Aerated lagoon 386 in planning stage 4. Ihandup Aerated lagoon 178 in planning stage 5. Bandra Marine outfall 797 200 m outfall laid (not in operation) 6. Versova Aerated lagoon 131 under revision 7. Malad Aerated lagoon 280 under revision ARAED LAGOONS Colaba service area Disposal of 41.1 mid by the year 2005 into the harbour, after 1 hour sedimentation at an expanded and upgraded Colaba Treatment PlanL Love Grove service area The existing treatment plant at Dadar to be retained as a training and research establishment. Provision for expansion and upgradatIon of facilities to provide secondary treatment for a flow of 22.5 mid, in year 2005. Wastewater generated within the remainder of Malabar zone and all of Worli zone to be conveyed to the Love Gro-e site for treatment and disposaL Recommended facilities for the design flow of 757 mid in 2005 to comprise screening, grit removal, one-hour sedimentation and chlorination before disposal to the Arabian Sea through a marine outfall. Sludge processing by gravity thickening and vacuum filtration before disposal to landfill sites or application to agricultural land. Screenings and grit from preliminary treatment facilities to be disposed off through landfill. Bandra service area Disposal of wastewater from the Mahim zone to the Arabian Sea through an outfall. The design flow of 796 mid to be subjected to screening, grit removal, one-hour sedimentation and chlorination before disposal to the Arabian sea through a marine outfall. Processed sludge after gravity thickening and vacuum filtration for landfill or agricultural application. Disposal of screening and grit from preliminary facilities through landfill. Ghatkopar service area Disposal of wastewater from South Chembur zone, to the tune of 3S6 mid in 2005, to Thane creek after treatment in aerated lagoons at Ghatkopar. Pretreatment to consist of screening and degritting, with provision for disposal of screenings and grit to a landfill. Removal of stabilized sludge from the lagoons required at approximately ten-year intervals. The sludge to be used for land application or landfAlling. Bhandup service area Disposal of wastewater from North Chembur zone, to the tune of 176 mid in 2005, to mane creek after treatment in aerated lagoons at Bhandup. Pretreatment to consist of screening and degritting, with provision for AEMD LA.OONS 3A disposal of screenings and grit to a landfill. Removal of stabilized sludge from the lagoons required at approximately ten-year intervals. The sludge to be used for land application or landfilling. * Malad service area Disposal of wastewater from North Marve zone to the tune of 280 mid in 2005, to Malad creek after treatment in aerated lagoons situated at Malad.- Pretreatment to consist of screening and degritting, with provision for disposal of screenings and grit to a landfill. Removal of stabilized sludge from the lagoons required at approximately ten-year intervals. The sludge to be used for land application or landfilling. Versova service area Disposal of wastewater from South Marve zone to the tune of 131 mid in 2005, to Malad creek after biological treatment in aerated lagoon situated at Versova. Pretreatment to consist of screening and degritting, with provision for disposal of screenings and grit to a landfill. Removal of stabilized sludge from the lagoons required at approximately ten-year intervals. The sludge to be used for land application or for landfilling. Concurrently with the studies by M/s. Metcalf & Eddy, MCGB had also authorized Tata Consulting Engineers, to investigate the feasibility for upgrading eleven existing pumping stations and to undertake preliminary engineering on eight new stations, who submitted the reports on these proposed works in 1978. The service areawise description of these pumping stations is given in Table 32. 3.6 First phase facilities In order to reduce initial capital requirements, the Municipal Corporation decided to implement Development Plan M in two phases. Phase I programme which was targeted to be completed by 1984, included the following components in addition to upgrading and construction of pumping stations. Colaba treatment works Inuent pumping station, screens, aerated grit chambers and 1.1 km long outfall with a design flow of 41 mid, will be provided for disposal of wastewater in the Bombay harbour. AWWWED 1AGOONS 3.7 Table : 32 On-line pumping stations planned under- first phase of Development Plan III Sr. Collection Area Pumping Station Ultimate Capacity No. (Approx.) (mld) New Pumping Stations 1. Colaba Kitridge Road 22 N.F. Road 22 2. Lovegrove Dadar 220 Carrol Road 30 3. Bandra Kalina 32 Saki.Naka 160 Pumping Stations to be Uprated 1. Lovegrove Jacob Circle 250 Globe Mill Passage 145 Tulsi Pipe 170 Tank Bunder 16 2. Bandra Matunga 150 Wadala 125 Sion Koliwada 22 Mahim 120 ABULED AOONS . Love Grove treatment works Influent pumping station, screens, aerated grit chamber and a 3 km long outfall with a design flow of 757 mid will be provided for disposal of wastewater into the Arabian Sea. Bandra treatment works Influent pumping station, aerated grit chambers and a 3 km long outfall, with design flow of 796 mid will be provided for disposal of wastewater in to Arabian Sea. 9.0 kilometers of tunnel to collect sewage from within the Mahim zone and convey it to the Bandra influent pumping station. Versova treatment works Influent pumping station, screens, aerated grit chambers and aerated. lagoons, with a design flow of 131 mid, will be provided at Versova. 2.93 kilometers of force main to convey sewage from pumping station to aerated lagoon site. Malad treatment works Influent pumping station, screens, aerated grit chambers and aerated lagoons with a design flow 280 mid, will be provided at Malad. 2.23 kilometers of force main to convey sewage from punmpu -tation to aerated lagoon site Ghatkopar treatment Works Influent pumping station, screens, aerated grit chambers and aerated lagoons with a design flow 386 mid, will be provided at Ghatkopar. 2.4 kilometers of sewer tunnel to collect sewage from the south part of the Chembur zone and convey it to the Ghatkopar influent pumping station 0.95 kilometers of force main to convey sewage from pumping station to aerated lagoon site AUED LAGO0NSa Bhandup treatment works Influent pumping station, screens, aerated grit chambers and acrated lagoons with a design flow of 176 mid, will be provided at Bhandup. 1.15 kilometers of force main to convey sewage from pumping station to aerated lagoon site 3.7 Present status Due to techno-economic reasons and logistic constraints, the execution schedule of the first phase facilities has been considerably delayed. Further, recent observations on wastewater generation in the service areas have indicated deviations from the original estimates. For instance, the present wastewater flows in Worli, Bandra and Ghatkopar service areas have been found to be considerably less than the projected wastewater flows for the year 1992. Whereas the wastewater flows already reaching the pumping stations at Bhandup, Malad and Versova are considerably higher than the- estimates. In view of the above and the findings of ongoing environmental impact assessment studies, the design for Bandra and Worli outfalls, and aerated lagoons at Malad and Versova are under review. Importantly, the 3 kilometer long outfalls at Worli and Bandra will now be constructed with the option for augmenting their length in future. The option of constructing an outfall instead of aerated lagoons catering to Malad and Versova service areas is also being currently evaluated. The design period for these schemes has also been extended to year 2015 in view of considerable delays on the project. The revised estimates of wastewater flows for the years 1992, 2005 and 2015, along with the original estimates of M/s. Metcalf & Eddy and percent change with respect to those, have been presented in Table 33. All calculations in this report for assessment of environmental impacts of Bhandup and Ghatkopar aerated lagoons are based on the revised estimates for the year 2005. The report also highlights possible additional wastewater management options to cater to estimated wastewater flows for the year 2015. Regarding the prcigress of work on the pumping stations, at both I(itridge Road and N.F.Road, in Colaba service area, new pumping stations have been commissioned. In Love Grove service area also all pumping stations as envisaged in phase I, have been commissioned. AD LAGOONS 3.10 Table :3.3 Projected and revised estimates of average dry weather flow (mid) Drainage 199i 2005 Zones AsperMetaf As calculated Variation As per Metcalf As calculated Variation and Eddy from water and Eddy from water projections supply data projections supply data from HZs from I.E's DepL Dept Colaba 38 32 -15.50 41 37 -10.07 Love Grove 687 315 -54.20 757 511 -32.46 Bandra 619 492 -30.70- 797 552 -30.66 Versova 97 115 19.06 131 164 24.92 Malad 203 193 -5.00 280 364 29.75 Ghatkoper* 301 250 -21.77 386 321w -17.00 handup' 125 150 4.30 176 208w 100 Total 2070 1547 2568 2157 * - These flows are expected to be 674 mid and 345 mid for Ghatkopar and Bhandup bermice areas iespectively by the year 2015 (August, 1994 estimates) - These flows have been further revised to 285 mId for Ghatkopar and 280 mid for Bhandup service areas respectively, (November 1994, estimates) ALUMi LA00ONS 11 In Bandra service area, among the four pumping stations to be upgraded in this area, Mahim and Wadala pumping stations have been commissioned. For Sion Koliwada and Matunga pumping stations, the work is in different stages of progress and the stations are expected to be commissioned by the end of 1995 and 1996, respectively. AEAIED LAOON 312 Chapter 4 AERATED LAGOONS 4.1 Preamble Major cities, all over the world, have witnessed accelerated rise in population under the onslaught of urbanisation and industrialisation. As the cities struggled to develop the infrastructural facilities to keep pace with the growing needs, environmental priorities were invariably neglected. All major cities, thus, faced environmental crisis at one point or the other during the process of their development, the most common being widespread- pollution of the nearby water bodies. Very poor water quality in river Thames, downstream London, and in river Seine, downstream Paris, upto middle of 60's are examples of such neglect in the two major cities of Europe. As the true dimensions of ecological damage due to inadequate treatment and disposal of wastewater became apparent, town planners began to pay more attention to wastewater management The sustained effort towards better management of water resources, in the developed countries, has led to appreciable success in control of water pollution due to disposal of domestic wastewater. Developing countries, however, are still witnessing ising pollution of inland and coastal aquatic resources due to low key and sporadic efforts in the area of wastewater management. In the control of domestic wastewater pollution, wastewater treatment has been the key element. For such treatment, naturally occurring biological processes have been exploited the most, wherein microorganisms utilize the organic matter in the wastewater as substrate and thus reduce the pollution load in effluents. Biological degradation is carried out by microorgamisms under either aerobic or anaerobic environments. Aerobic biological processes have been more popular for treatment of domestic wastewater. These processes include a wide spectrum of treatment technology options, starting from simple oxidation ponds to technologically advanced options such as activated sludge systems running on pure oxygen. The processes, however, greatly differ in their land, power and maintenance requirements. For instance, power and maintenance need of stabilization ponds is virtually nil. These, however, entail very large land area. On the other hand, activated sludge process requires negligible land area in comparison to stabilization ponds but is highly energy intensive and demands skilled operation and maintenance. Aerated lagoons fall in the middle of the two extremes. The land requirement for aerated lagoons is much less than the stabilization ponds. The energy requirements although ALW=E LAAOONS AI are comparable to activated sludge process, the process is almost maintenance free. Availability of sufficient land in the four service areas and low skilled maintenance needs perhaps were the prime factors for selecting aerated lagoons as the sewage treatment technology for Bombay. 4.2 Salient features of aerated lagoons 4.2.1 Types and Design features Aerated lagoons are earthen basins generally 2.5 to 5.0 meters deep, provided with mechanical aerators installed on floats or fixed columns. Raw sewage is fed from one end into the lagoon after preliminary treatment and leaves from the other end after a desired period of aeration. Depending upon the power input per unit lagoon volume and the provision or otherwise of a recirculation arrangement, the solids in the system either settle, flow-through or build-up. Thus, based on the way solids are handled, the aerated lagoons could be classified as: 1. Facultative 2. Aerobic, flow-through, or 3. Aerobic, with solids recycle The different ways of handling the solids have a substantial effect on efficiency, power requirement, detention time, sludge disposal etc. and the. design methods have to take these differences into account although the basic principles of biological treatment apply equally well to all the three types. In facultative aerated lagoons the power input per unit %-olume i! only sufficient for diffusing the required amount of oxygen into the liquid to keep the dissolved oxygen in the lagoon at about 1-2 mg/L. The aeration, however, is not sufficient for maintaining all the solids an suspension. Consequently, some of the suspended solids entering the lagoon and some of the new solids produced in the lagoon as a result of substrate removal, tend to settle down and undergo anaerobic decomposition at the bottom. The activity in such a lagoon is, therefore, partly aerobic and partly anaerobic which gives it the name 'facultative'. These are also sometimes referred to simply as 'aerated lagoons'. Such lagoons generally provide 70-90 per cent BOD removal efficiency for domestic sewage. A typical layout of a facultative aerated lagoon is shown in Figure 4.1. Aerobic, flow-through lagoons are those where the power level is high enough not only to diffuse enough oxygen into the liquid but also to keep AMED MLAGOONS Figure : 4.1 A mechanically aerated facultative lagoon. FLOATINS OR P1EO TYPE VERTICAL AlIS AERATOR . DAPPLE INLET CNAMBER AERDBIC WERTIE ErLUENT WITH W MOTCH DOUTLEY ANAERDBIC SECTION rFT1- -EFFUENT IRXLET AEAATOR CHAMBER PLAN AfAM LAGOONS 4.3 all solids in suspension as in an activated sludge aeration tank. No settlement of solids, therefore, occurs within the basin. In these lagoons the wastewater leaves along with solids under aeration. Thus, efficiency of BOD removal attained in these lagoons is only in the range of about 50 to 60 percent. Additional treatment is necessary if better BOD and solids removal is desired. In fact, these lagoons are generally followed by facultative stabilization ponds or aerated lagoons or are designed with the intention of converting them eventually to aerobic lagoons with solids recycle. As the entire lagoon contents are aerobic, these lagoons are also sometimes referred to as 'aerobic lagoons' to distinguish them from 'aerated lagoons' a term used for facultative lagoons. A typical. layout of an aerobic flow-through lagoon is shown in Figure 4.2. Aerobic lagoons with solids recycle are just like activated sludge or extended aeration systems. The power input level is sufficient to meet the oxygen requirements and keep all solids in suspension. But the solids concentration in such a lagoon is quite high, since the system is designed to prevent the solids from escaping out with the effluent by the incorporation of some form of solids settlement and recycle. In such lagoons, BOD removal efficiencies can be as high as 95 to 98 per cent and nitrification can also be achieved. A typical layout of aerobic lagoons with solids recycle is shown in Figure 4.3. 4.2.2 Construction features Lagoons are generally built 2.5 to 5 meters in liquid depth in earth work with the slopes partly or fully pitched in stone and the inlet and outlet located on opposite banks. Where fixed aerators are used, it is essential that the liquid level in the lagoon is maintained constant so as to ensure the required degree of submergence of the aerator blades. This implies (a) watertight conditions in the lagoons, and (b) discharge of effluent over a weir located at the desired leveL To avoid percolation, the lagoon has to be located in relatively impervious soil or suitably lined or constructed in masonry or concrete. The latter is generally avoided owing to the volume involved. Control of percolation is also to be considered from the point of view of ground water pollution. Where floating aerators are used percolation does not affect aeration since the aerator submergence always remains the same. Hence, the lagoon can be constructed easily and inexpensively in earthwork and provided with pitching if necessary. This is the main advantage of using floating aerators. AUED MLAGOONS Figure : 4.2 A mechanically aerated flow-through lagoon. FLOATING OR FIED TYPE VERTICAL AXIS AERATOR INLET CHAMBER AERDBIC PIPE EFFLUENT WITH SCREEN QUTLET AND v NOTCH SECTION INLET CHAMBER PLUAD AIR~GO PJ 4U Fignr : 4.3 Aerobic aerated lagoon with solids recycle. FLOATING O FIXEtD- TYPE VERTICAL AXIS ACWATOR INLET CHAND AATOR PIPC Tr WITH SCREEN 01TLET AND V NDrN SLUDGE EXCESS SECTION atrunD5E-- stuest SL-O RETURN -~SLUDGE ORIN PUN P SLUDGE NETURN SLUDGE EXCESS SLUDGC ;ses swooM AEAE -AON The floats or pontoons should be fabricated from non-corrodable material to ensure durability. The steel ropes used to anchor the aerator to the side banks also serve to carry the cable connections. For repairs or maintenance the aerator can be pulled or dragged in water to a corner of the lagoon where a small loop or arm can be provided to 'wet-dock' the aerator or enable its lifting for inspection. Aerated lagoons are often rectangular in shape although they could be built in any shape to conform to natural typographical features. In case of uneven shape, the number and disposition of aerators are designed to ensure uniform oxygenation. It is preferable that the inlet pipe is submerged to avoid odours and short-circuiting, while the outlet weir is provided of sufficient length to avoid heading up at peak flows which would change the aerator submergence in the case of fixed aerators. The outlet weir should be provided with a stilling baffle to avoid the sewage splashing over the weir due to agitation in the lagoons. In the design and construction of these lagoons, the usual principles of good civil engineering practice apply as for waste stabilization ponds, particularly with regard to embankment slopes, compaction of earth work, pitching, flood irrigation etc. The water level in the lagoon may be so kept as to enable flow by gravity to adjoining fields for irrigation or to the receiving water body at the time of flood or high tide as applicable. 4.3 Lagoon effluent characteristics As is evident from description of various types of aerated lagoons. BOD removal efficiency in such systems (aerated lagoons) could varv over a wide range between 50 - 98 per cent. Also, effluent from lagoons with or without recycle could significantly differ in ammoniacal-N and nitrate concentrations. Wide range of coliform removal is also observed subject to the lagoon design. In view of above, the lagoon effluent characteristics can not be a priori precisely defined. For facultative aerated lagoons treating domestic sewage, however, 80 per cent BOD removal, 90 per cent coliform removal and no reduction in ammoniacal-N may be assumed as reasonable. Under these assumptions, a raw sewage of about 200 mg/L BOD, 1x107/100 ml total coliforms and 20 mg/L ammoniacal-N is expected to yield an effluent AEWAlE LAGXOMN& having 40 mg/L BOD, 1x106/100 ml total coliforms and 15-20 mg/L ammoniacal-N. 4.4 Environmental repercussions The impact of aerated lagoon effluents on the receiving water body is governed by the available dilution and assimilative capacity. For effluent characteristics described above, approximately 12 times dilution would be necessary to bring down the BOD and ammoniacal-N levels sufficiently to avoid an adverse depletion of dissolved oxygen. A few hours of travel time before the effluent reaches the sensitive locations, however, will be necessary for total coliforms to decay to a level of about 10000/ 100mi which may be considered safe for bathing. For discharge of effluents into creeks, available dilution at the low tide slack period could be of overriding importance as during the fiood tide, pollutants are pushed into inner regions of the creek and may cause significant dissolved oxygen depletion. In the absence of adequate dilution, bacterial contamination of water and sediments may also occur in the water body. The impact of lagoon effluents on the receiving waters, however, is closely linked with the performance of the aerated lagoons. Inadequate lagoon performance can also lead to odour problem due to formation and dispersion of hydrogen sulphide. Another aspect of lagoon operation is periodic desludging of facultative lagoons. Adequate measures are also necessary for proper disposal of sludge to safeguard against ground water contamination due to formation of leachates at the sludge disposal sites. Environmental repercussions may also arise due to the civil works activity during the donstruction of the lagoons. These impacts are primarily, air and noise pollution at the construction and quarrying sites, due to material hauling and operation of construction machinery 4.5 Environmental safeguards Environmental safeguards for regulating the beneficial uses of receiving waters against industrial/municipal discharges are achieved through compliance with the environmental standards. In India, Environment (Protection) Act, 1986 vests in Central Government, the powers to lay down standards for environment protection. Central and State Pollution Control Boards are responsible for ascertaining compliance of these standards. The Boards, based on local conditions, have power to stipulate more stringent location specific standards. AED iONS 4 For protection of coastal water quality, two standards apply in India. The first of these standards is in the form of receiving water quality and is based on best designated use of the water body such as for bathing, fishing or navigation. Details of these standards (IS:7967-1976 ) are provided in Table 4.1. The creek and coastal waters used for recreational purposes or fishing,. accordingly, should always have BOD less than 5.0 mg/L, total coliforms less than 1000/100 ml ( 95 per cent of observations) and dissolved oxygen more than 3.0 mg/L. Another set of standards in the form of effluent standards for discharges into tidal creeks, however, is also applicable to Thane creek (Table 4.2). According to this standard, effluent with BOD and suspended solids of 100 mg/L each and ammoniacal-N upto 50 mg/L can be discharged into the creek and form the basis for the discharge consent given by the Maharashtra Pollution Control Board (MPCB) to MCGB for discharging treated sewage effluent into Thane Creek from proposed Bhandup and Ghatkopar lagoons. On careful consideration of these standards, a possible incompatibility between the receiving water and effluent standards becomes apparent. For concurrent compliance of effluent and receiving water standards, a minimum dilution of about 20 times is necessary within the creek. Such dilution may be attainable for small discharges but is extremely difficult for effluents of the order of 12 m3/s, the combined estimated discharges from. Bhandup and Ghatkopar service areas in the year 2015. Further, the receiving water standards entail that if the creek waters are used for fishing, 95 percentile total coliform levels should be less than 1000/100 ml. The effluent standards, however, do not specify a bacteriological standard and total coliform levels in Thane creek as a result of expected discharge of 12 m/s with total coliforms levels of about 10"/100 ml shall certainly remain above 10,000/100 ml. A rational environmental objective with respect to effluent discharges in Thane creek, therefore, would be to safeguard the ecological role of the creek as the breeding area for a variety of coastal marine fauna. Such an objective may be achieved if the dissolved oxygen in the creek is maintained above 2 mg/L for the entire tidal cycle and accumulation of toxic substances in the sediments is avoided. 4.6 Proposed aerated lagoons at Bombay The important factors affecting choice of type of lagoons for a particular. application are their power and land requirement vis-a-vis their performance and operating characteristics. Generally, the choice lies Am= LAGKDONS AL Table : 4.1 Tolerance limits for water quality after receiving discharges (IS : 7967-1976)* Sr. Characteristics Tolerance limits for bathing, recreation, No. commercial fish culture and salt manufacture (1) (2) (3) 1. Color and odour No noticeable color or offensive odour 2. Floating material No visible floating matter of sewage or industrial waste origin 3. Suspended solids No visible suspended solids of sewage or industrial waste origin 4. pH value 65 to 85 5. Free ammonia (as N), mg/T., Max 1.2 6. Phenolic compounds (as CHsOH), 0.1 ag/L, Max 7. Dissolved oxygen, Min 40 percent saturation value or 3 mg/L whichever is higher & Biochemical oxygen demand (5 days at 20*Q 5.0 mg/L Max 9. Coliform Bacteria, MPN index per 1,000 100 ni, Max * Abridged AllAED IACoNS 4.10 Table : 4.2 General standards for discharge of effluents*+ Sr. Parameter Standards No. Marine coastal areas 1. Suspended solids, mg/L, Max 100 2. pH value 5.5 to 9.0 3. Temperature, aC, Max 45-at the point of discharge 4. Oil and grease mg/L, Max 20 5. Total residual chlorine, mg/L 10 6. Ammoniacal nitrogen (as N), mg/L, Max 50 7. Total Kjeldahl nitrogen (as N), mg/L, Max 100 & Free ammonia (as NH3), mg/L, Max 5.0 9. Biochemical oxygen demand (5 days at 20 *C), mg/L, Max 100 10. Chemical oxygen demand, mg/L, Max 250 * Abridged + Ref.: Environment Protection Act, 1986, Schedule II. Amended as per Notification dated 19th May 1993 as schedule VI. AEAWE LAON 4.11 between a facultative type aerated lagoon and an aerobic lagoon with solids recycle. A flow-through type lagoon is often considered in stagewise development leading eventually to recycle of solids or is followed by other treatment to obtain a better quality effluent. Lagoons with solids recycle are mostly of the extended aeration type as these avoid the need for sludge digestion units which would be necessary with conventional activated sludge systems. Extended aeration type lagoons, though relatively easy to operate, do require a greater degree of attention compared to the facultative lagoons, which are, in fact, the simplest to operate as their extent of mechanization is truly minimal. With regard to power and land requirement, the two types of lagoons have , opposite characteristics : the extended aeration lagoons require more power but much less land, the facultative lagoons require more land but less power. Facultative lagoons may be favoured for a large number of situations under which the oxidation pond may not be acceptable owing to its high land requirement, and the other methods like activated sludge may not be desirable either owing to their technological requirements or simply because a higher quality effluent is not essential. Both these factors have been responsible for favouring a treatment system based on facultative aerated lagoons at Bombay. 4.6.1 Design specifications The wastewater generated in Bhandup, Ghatkopar, Malad and Versova service areas is proposed to be treated in aerated lagoons before its discharge into the adjoining Thane and Malad creeks. Initially, all the proposed four lagoons were to comprise of four streams of three cells each. The wastewater after primary treatment was to be divided into four equal and identical streams comprising of three lagoons or cells with average residence times of 1.4,1.8 and 1.1 days respectively. Out of the three cells, the first cell was to operate as a flow through aerated lagoon and the following two cells as facultative aerated lagoons. The overall removal efficiency of the treatment system was expicted to be 80 per cent of BOD and 70 per cent of suspended solids respectively. The salient design details of the aerated lagoons are presented in Table 43. Due to paucity of funds and low effluent standards prescribed by MPCB entailing about 50 - 60 per cent BOD and suspended solids reduction, the original plan of implementation has been modified. The first phase activities at Biandup, Ghatkopar and Malad are proposed to be restricted to AEATED LAGOONS 4.12 Table 4.3 Design specifications of proposed aerated lagoons Lagoon type and Lagoons design parameter Versova Malad Ghatkopar Bhandup Aerobic Retention period (d) 1.40 1.40 1.40 1.40 Volume of pond liquor (tcn) 256.26 326.88 326.88 256.26 Soluble BOD loading (kg/tcm/d) 128.69 128.60 150.00 150.14 BOD loading (kg/d) 32,978.10 42,036.77 75,375.00 38,474.88 Soluble BODs reduction (% / 100) 0.65 0.65 0.72 0.72 BOD reduction (kg/d) 21,435.76 27,323.90 54,270.00 27,701.91 First faciltative aerated Retention period (d) 1.80 1.80 1.80 1.80 Volume of pond liquor (tcm) 32037 420.28 420.28 320.37. Soluble BOD loading (kg/tcm/d) 33.03 35.00 32.67 32.60 BOD loading (kg/d) 10,581.82 14,709.80 20,843.46 10,444.06 Soluble-BODs reduction (% / 100) 0.66 0.66 0.71 0.71 BOD reduction (kg/d) 7,015.75 9,708.47 14,798.86 7,415.28 Contd... AATDI AG06NS 4.13 Table 4.3 (Contd.) Lagoon type and Lagoons design parameter Versova Malad Ghatkopar Bhandup Second facultative aerated Retention period (d) 1.10 1.10 1.10 1.10 Volume of pond liquor (tcm) 199.68 256.84 256.84 199.68 Soluble BOD loading (kg/tcm/d) 18.94 19.47 15.50 15.15. BOD loading (kg/d) 3781.94 6234.00 6334.08 3025.15 General No. of lagoon sets (No.) 4.00 4.00 4.00 4.00 No. of lagoon per set (No.) 3.00 3.00 3.00 3.00 Overall BOD reduction (% / 100) 0.80 0.80 0.80 0.80 Detention period (d) 4.30 4.30 4.30 4.30 AMWED LAGOONS L14 construction of only first cell of the four streams. While at Versova, two streams of the originally proposed three cell lagoons are proposed to be constructed. Further, based on recent findings of environmental impact assessment of Malad and Versova lagoons (Malad and Versova Aerated. Lagoons- Final ReportNEERI, 1994), the proposed construction of aerated lagoons at these sites is being reviewed and marine outfalls are being considered as alternative option. During the first phase of implementation at Bhandup and Ghatkopar, the single cell lagoons are proposed to be operated as facultative aerated lagoons instead of flow through aerated lagoons allowing the settlement of suspended solids. These modifications will also considerably reduce the operating costs of the lagoons. Figures 4.4 and 4.5 describe the layout of the aerated lagoons at Bhandup and Ghatkopar respectively. The shaded portion in these figures indicates the facilities proposed to be built during the first phase of project implementation. 4.7 Inference Aerated lagoons provide a robust system for treatment of domestic wastewater. If the land availability is not a constraint, lagoons provide good option for wastewater treatment specially for the developing countries due. to their lower capital costs, favourable environmental conditions and ease of operation. Facultative aerated lagoons can achieve treatment efficiencies upto 90 percent removal of BOD and can, therefore, provide desirable levels of treatment for most conditions. The effluents from the proposed aerated lagoons at Bhandup and Ghatkopar will be discharged into Thane creek. Certain discrepancies between the effluent discharge standards and receiving water quality standards for the creek are apparent and the proposed treatment level may not be adequate during the later part of the design period to maintain desired water quality in the creek. The water quality response of creek regions to pollutants loading is primarily governed by their hydrodynamic behaviour under tidal forcing. Comprehensive hydrodynamic and associated waste assimilation considerations are, therefore, necessary to assess the impact of effluent discharges in Thane creek and to delineate water quality management plan for the region. AMAM oos 4.is Figure : 4.4 Schematic layout of treatinent units - Bhandup 3 ou cc 6'. : um 3 z 5, r r 5, 5, r t II, It r r v '1 0 0 fl fl c z fl fl 3 1 3 5, <II el, AWJID AGOONS 416 rat i FAL FAV 2-1 2 AtIF a - 2 FAL 2-2 , rpa AL 2 AL -3 FAL 2-3 APPROACH ''<0 0. r 0 A - ra UTAIv 0 PROPOSED UNDER PHASE g * q,4 Chapter 5 METHODOLOGY AND DATA GENERATION FOR ENVIRONMENTAL MANAGEMENT PLAN 5.1 Preamble The wastewater drainage scheme of Bombay comprises of seven service areas. About 60 percent of the total wastewater generated in the city reaches the west coast either through direct discharges into the coastal - regions or through other adjoining surface water bodies such as Malad creek and Mahim bay. The remaining 40 percent wastewater is discharged into on the east coast of Bombay through a marine outfall at Colaba and direct discharges of Bhandup and Ghatkopar in Thane creek. Disposal of such large quantities of wastewater into the coastal regions around Bombay, despite the significant assimilative capacity of receiving coastal waters, has led to serious impairment of aquatic environment of certain regions. Thane creek at the north-east coast is one such affected region. It is a triangular mass of brackish water which forms the eastern boundary of island of Bombay and widens out and opens to Arabian sea in the south. It receives an outlet from Ulhas river at its northern end but with very little discharges as the river flows past the creek head. Thus except during high tide, its connection to Ulhas river is rarely effective. The creek is dominated by diurnal tides. The maximum tidal range in the creek is about 5 meters. During an average spring tide the water level rises by about 4.7 meters above the low tide level. The tidal elevation for an average neap tide is about 1 meter. During an average spring tide the creek stores about 126x10' m' of water at the time of low water which increases to about 2'3x10" m3 at high waters. At an average neap low tide the volume of water in the creek is about 1.74 x10' m3 which rises to about 1.92 x10" r' at the time of high tide. During the spring tide the average water exchange in the creek, therefore, is about 5.4 times that of neap tide. Due to the natural ground slopes, the creek receives municipal and industrial wastewater discharges through a number of channels from the eastern suburbs. The sewage pumping stations at Ghatkopar and Muiund which discharge municipal wastewater from Ghatkopar and Bhandup service areas, however, form the principal pollution loads to inner Thane creek. Combined discharges from these two sources exceed 400 mid and ADUMM LAGOONS 51 are slated to increase to above 1000 mid by 2015. As the wastewater discharged into the creek remains entrapped in a confined volume and moves back and forth with the tidal action, their continued discharge has. given rise to considerable water quality impairment in inner Thane creek. In order to mitigate the adverse impacts of municipal wastewater discharges in Thane creek, construction of aerated lagoons of design capacities of 170 mid and 385 mid is planned at Bhandup and Ghatkopar, respectively. Though, the treatment of sewage through the aerated lagoons is expected to alleviate the pollution stress on the creek, a scientific study is necessary to establish its adequacy for desired water quality improvement in the region. Such an investigation can be carried out through a dual approach of predictive modelling and field investigations. The present chapter discusses the methodology adopted for delineating the existing environmental condition in these areas and summarizes the present status of the environment. 5.2 Scope of field studies The construction and operation of aerated lagoons are expected to have significant environmental impacts. During the project implementation, air. and noise pollution at the construction and material excavation sites are the major construction phase impacts. The change in hydrodynamic characteristics of the creek due to reclamation of part of the inter tidal zone for construction of the lagoons and consequent possibility of flooding of nearby areas during the monsoon is another concern needing investigation. Field investigations on ambient air quality, noise levels, tidal current pattern, meteorology and sources of noise and air pollutants during the construction work were undertaken to generate requisite data for assessment of these impacts. The major environmental impacts of the project, however, are those associated with the operation of aerated lagoons and are largely beneficial. Most prominent of these is expected to be the widespread improvement in the water quality in Thane creek due to reduction of pollution load on the creek. It is also necessary that extent of mixing of industrial discharges with the sewage in the drainage area is investigated, as such, disposal in marine. environment could have certain additional impacts due to the presence of potentially hazardous substances. These impacts are reflected in the form of direct toxicity to aquatic life or through biomagnification. The latter AERED LAGOONS 52 could also have health impacts on the human population through consumption of contaminated sea food. The magnitude of water quality impacts arising from aerated lagoon's operation, are governed by a variety of physico-chemical and biological interactions in the creek environment and are substantially influenced by the ambient tidal currents. Due to the variable hydrodynamic conditions in the creek and complex nature of water quality transformations, only those variations which primarily depend on physical processes or simpler bio-chemical processes are amenable to mathematical modelling. The relevant processes include advection and dispersion of pollutants with tidally driven currents, reaeration due to surface oxygen transfer and decay of organic matter due to microbial activity. For processes involving more complex interactions such as altered nutrient balance in sediments and ecological transformations in the creek, it is necessary to adopt the approach of observation and inference on the regions which have water quality similar to the expected quality in Thane creek after implementation of the schemes. In view of the above, the sampling and data generation on coastal environment had two distinct objectives. One set of activities were undertaken to define the existing water quality in Thane creek and observations on ecological status in areas which currently have conditions similar to those aimed to be achieved in Thane creek later. Other set of data was collected to obtain ambient environmental conditions and local estimates of model coefficients needed for quantitative predictions of the impacts using mathematical models. Sampling and characterization of raw wastewater in the Bhandup and Ghatkopar service areas were also undertaken during the course of the field studies. Methodology and findings of the field studies for defining the ambient environmental conditions are described in the following sections. The field monitoring programmes to establish model coefficients for predictive modelling are presented in chapter 7. 53 Methodology and findings 5.3.1 Air quality To establish the baseline status of air quality near the construction sites of aerated lagoons at Bhandup and Ghatkopar, air quality monitoring was carried out at two locations for each site. Samples for gaseous pollutants viz. NO. and SO, and suspended particulate matter(SPM) were collected AUAED AGOONS U as 8 hourly averages. As winter season is generally considered critical period for air quality, the observations were made during February, 1992. The monitoring was carried out continuously for one week at each site. Concurrent to air quality monitoring, site direction micrometeorological data viz. wind speed and direction were collected at 8 meters above the ground level through an automatic computerized weather station. The recorded data was used to draw wind roses for both the sites. The wind roses for Bhandup and Ghatkopar sites indicate that the predominant winds are from NW and NNW directions for Bhandup and from NW, NNW and NWW directions for Ghatkopar respectively. The observations have been found to be in conformity with the climatological normals of the region for the month of February. The wind speed was observed to be in the range of 1-5 kmph for 10 and 21 percent of the. duration at Bhandup and Ghatkopar respectively The wind speeds of 6-10, 11-15 and 16-20 kmph occurred for 29, 13 and 8 percent of the survey period respectively at Bhandup and 18, 15 and 9.7 percent at Ghatkopar. Calm conditions (below 1 kmph) prevailed for about 40 and 36 percent of the times at Bhandup and Ghatkopar, respectively. During the air quality monitoring survey, 8 hourly samples were collected at two locations for each lagoon site. Round the clock observations were carried out for a period of seven days resulting in 42 observations at each site. The samples were analyzed for SO2, NO, and SPM levels. The average SO2, NO, and SPM levels at Bhandup lagoon sites were observed to be 3.5, 12.2 and 246 pg/m3 respectively. The maximum and minimum observed concentration for these parameters were 9 and 3; 42 and 3. and 51S and 122 pg/m3, respectively. Observations at Ghatkopar indicated that the average lvls r SO.. NO. and SPM were 63, 15.6 and 339 gg/3n respectively The maxmum and minimum observed concentrations were 22 and 3 pg.. m for S,. 34 and 3 jig/&' for NOz and 677 and 86 4g/n for SPM, respectively. According to the Development Plan for Bombay, Bhandup and Ghatkopar are designated as residential areas. Comparison of the observed air quality levels at Bhandup and Ghatkopar aerated lagoons sites with the ambient air quality standards prescribed by Central Pollution Control Board for residential urban areas, indicates that the levels for all air pollutants at these sites are well within the prescribed limits for such areas. AERAD LAGOONS SA 5.3.2 Noise studies The objective of field observations on noise levels was to generate noise data for estimating the rise in ambient levels due to construction activities at those residential areas (sensitive zones) which are in close proximity of the proposed sites. The observations, therefore, included measurements on ambient sound levels at lagoon sites and nearby sensitive areas. In addition, inventory of construction machinery as sources of noise and their operation pattern during the construction was also determined. 5.3.2.1 Sound levels at Bhandup lagoon site Sound level measurements at Bhandup aerated lagoon site were carried out at various locations as depicted in Figure 5.1. No excavation or construction activity at the site is in progress as the proposed lagoons are scheduled to be constructed only in 1996. Sound level measurements were carried out around the periphery as well as at the centre of the site. The observed sound levels are presented in Table 5.1 . The observations indicate that the ambient noise levels at the lagoon site are in the range of 45 to 50 dBA which occasionally rise to 54 dBA due to the blowing of wind, chirping of birds etc. As no construction activity was in progress and the nearest human settlements are located beyond 1 kilometer from the lagoon site, sound levels at these locations are unlikely to be affected by construction activities. No sound level measurements were, therefore, conducted at these localities. 53.2.2 Sound levels at Ghatkopar lagoon site During the survey, the construction of aerated lagoons was not in progress. The wastewater treatment facility construction was nearly complete with some metalling activity being carried out at the time of . survey. Sound level measurements were carried out around the periphery and centre portions of the lagoon sites. The measured sound levels along with the description of prominent activity at the point of observations is presented in Table 5.2 . The observations indicate that the ambient noise levels at the lagoon site are in the.range of 41 to 45 dBA which occasionally rise to 60 dBA due to the vehicular traffic on the highway (Figure 5.2). AERMED LAGOONS U Figre : 5.1 Observed noise levels at Bandup lagoon site NO OEVLOPMENT ZONE . AERATEo LAGOON . 3 CREEK AERATEDLAGOONS 5.6 Table : 5.1 Sound levels at Bhandup aerated lagoon site Point No. Sound level Activity dBA 1 41.8-51.2 Nil 2 43.8 - 46.0 Nil 3 44.1 - 54.2 Nil 4 42.4 - 52.0 Nil 5 46.8 - 53.2 Nil 6 45.0 - 49.0 Nil 7 41.0 - 45.0 Nil 8 39.2-43.0 Nil Table : 5.2 Sound levels at Ghatkopar aerated lagoon site Point No. Sound level Activity dBA 1 45.0 - 603 Metalling of surtace in tront of wastewater treatment facility 2 41.0 - 57.4 Nil 3 37.0 - 41.6 Nil 4 40.1-44.4 Nil 5 393 - 43.4 Nil 6 38.8 - 429 Nil 7 38.8-43.0 Nil 8 392-44.1 Nil 9 40.2 - 45.6 Nil AERADLAGOONS 57 Figum : 5.2 Observed noise levels at Ghatkopar lagoon site ÅER ÅTE 0 L& GOON 166 5< Au~ LAG As the nearest human settlements are located beyond 1 kilometer from the lagoon site, sound levels at these locations are unlikely to be affected by construction activities. No sound level measurements were, therefore, conducted at these localities. 533 Land environment 533.1 Land use The baseline data on land environment pertains to present land use pattern in and around the aerated lagoon sites and properties of soils. The land-uses have been recorded around each lagoon site in eight directions, keeping the specific site in the centre with necessary discretion for area coverage in each direction. It may be noted that most of the residential and commercial areas are located in South-East, North-East, East, South, West and South-West directions in the same order. Some of the play grounds and gardens are also located in these directions with respect to lagoon site. The data on land use pattern around Bhandup lagoon site is presented in Table 53. The proposed site is being developed by reclaiming approximately an area of about 40 hectares partially covered by mangroves on the west bank of the creek. There is no municipal park, national highway or residential area in the immediate vicinity. The nearest residential and commercial areas are located on north-west, west, south-west and north of this lagoon. A BEST bus depot is located on the west and a MSEB sub-station in the north west direction of the lagoon site. Land use pattern around Ghatkopar lagoon site is presented in Table 5.4. The area of this lagoon site is considerably bigger than that of Bhandup. The proposed site is being developed by reclaiming approximately 90 hectares of land partially covered by mangroves on the west bank of Thane creek near Ghatkopar. Most of the residential and commercial areas are concentrated towards the.west, north west, south-west and north sides. In view of significant requirements of construction materials such as murum, boulders and bricks for the project and consequent environmental impacts of quarrying operations, two of the quarry sites were also studied for ambient environmental quality. Land use pattern around all the identified quarry sites, within 1 kilometer radial distance, is more or less similar. All the quarry sites are accessible by roads. They are either located on no development zones or beyond 500 AATED LAGOONS 5.9 Table: 5.3 Land use pattern around the aerated lagoon site at Bhandup (area in hectares) Sr. Type of land use Direction (w.it lagoon site) No. E S-E S S-W W N-W N N-E 1. Lagoon area - - - 58 - - - - (Approximate) 2. Creek 62.2 400 1583 16.6 21.0 Nil Nil 6 3. Municipal park Nil Nil Nil Nil Nil - 70 91 4. National highway Nil Nil Nil 13.0 10.3 3.3 9.2 Nil 5. Residential and Nil Nil Nil 72.6 140.0 397 40 Nil commercial areas including road network and salt pans 6. No development 92.8 Nil 21.7 302 89.4 Nil 9.5 32 zone 7. Recreational/play Nil Nil Nil 17 28 - 10 Nil grounds 8. Others - - - - 4+ 7- - + RS receiving station ++ B.E.S.T bus depot and MS.E.B. sub-station. AIRAEDLAOONS .ID - Table :5.4 Land use pattern around the aerated lagoon site at Ghatkopar (area in hectares) Sr. Type of land use Direction (wit. lagoon site) No. E S-E S S-W W N-W N N-E 1. Lagoon area - - - 108 - - - - (approximate) 2. Creek 55 8 Nil Nil Nil Nil Nil 40 3. Municipal park Nil Nil Nil Nil Nil Nil Nil Nil 4. National highway Nil Nil Nil 6 11 Nil 13 Nil 5. Residential and Nil. Nil 89 213 227 390 209 Nil commercial areas including road network and salt pas 6. No development 223 287 9 30 5 Nil 98 280 zone 7. Recreational/play Nil Nil 9 27 15 10 28 Nil -nds 8. Others Nil 62 100 *4* 13 Nil Nil Nil * Part of IVth railway terminal ARALED LAoN 5.11 meters from the nearest residential and commercial areas. Railway lines, water reservoirs and public gardens are located at safe distances from the new quarry sites. The proposed sites are as listed in Table 5.5. Since general principles of reclamation, rehabilitation and environmental management are basically similar for all quarrying operations, it is felt adequate to study two quarry sites which are in operation. These are Oshiware/ Ambivali quarry in Andheri Taluka and Damupada quarry in Borivili Tebsil. The first quarry is mainly surrounded by slum hutments. with stone crushers located at several places. The area is devoid of trees and vegetation. The surrounding areas mainly include residential and commercial developments along the S.V. Road, encroachments by slums and a few multistoreyed buildings. In the case of Damupada quarry site, 8 hectares are covered by the quarry, 30 by Sports Authority of India (SAI) and 242 hectares by slums. The SAI campus has a number of trees planted within their area. The remaining area has no vegetation. 5.3.3.2 Soil characteristics Considerable portions of the areas close to the construction sites have to be reclaimed from the creek. Irrespective of the refill material used, due to its exposure to marine water owing to capillary action the soils in the region tend to become saline which can retard the growth of many plant species. A number of soil samples were collected covering the regions surrounding the lagoon sites with the view to examine the nutrient levels and exchangeable properties. Such information is necessary for the design of the green belts around the sites to mitigate the negative aesthetic impacts due to the construction of wastewater treatment schemes in close proximity to residential areas. Surface soil samples were collected from the lagoon sites. The main objective of sampling was to assess the soil properties relevant to plant growth on the refilled lagoon sites, in their immediate vicinity and along the sides of major roads. In the case of lagoon sites at Bhandup and . Ghatkopar, the major road is Eastern Express Highway (EEH). Surface samples were collected from 4-6 different locations in each case and composited. Two composite samples were collected at each lagoon site and analysed for relevant soil properties. The data is presented through Tables 5.6, 5.7 and 5.8. The data on physical properties of the soils indicate high soil porosities along the EEH and at Ghatkopar lagoon site (Table 5.6). At Bhandup lagoon site the soil porosities are relatively less. The soil texture is loamy. AERMWE LAGOOMS 5.-12' Table:5.5. Proposed quarry sites Sr District Site No. I Bombay Borivali 2 Thane Vasai Thane Kalyan Ullasnaga Bhivandi 3 Raigarh Alibag Uran Karat Panvel Khalapur Pen Table :5.6 Physical properties of soils at the aerated lagoon sites Sr Sitel Sample Density, Porosity Particle size distribution Soil No. particulars (g cc) (per cent) (per cent) texture Particle Bulk Clay Silt Fine Coarse sand sand 1 Bhandup EEH-sides 1.128 2.487 54.6 14.5 12.0 8.0 65.5 Loam Lagoon site 1247 2.079 40.0 10.0 28.0 12.0 50.0 Silty 81oam 2. Ghatkopar EEH-side 1.113 2.578 56.8 14.0 8.5 9.7 67.8 Sandy loam Lagoon site 1.246 2.709 54.0 7.5 11.5 11.0 70.0 Loamy EEH - Eastern express highway.. AVAM LAGOONS 5.13 Table:5.7 Chemical properties of soils at the aerated lagoon sites Sr. Sitel Sample pH Conductivity Cations Anions No. particulars g mhos/ cm (Meql l) (Meql 1) Ca++ Mg++ Na+ K + C- HCOf- SO4 L Bhandup EEH-side 730 7.60 130 1.12 11.40 0.f 8.60 0.20 4.30 Lagoon site 7.60 8490 40.00 62.00 67.00 020 10.50 15.00 49.00 2 Ghatkopar EEN-side 8.20 1.50 130 0.80 0.45 0.08 128 0.15 LO Lagoon site 7.70 4720 38.00 2320 33.00 0.20 70.00 8.50 15.50 EEE - Eastern express highway Table : 5.8 Cation exchange properties of soils at the aerated lagoon sites Sr. Sitel Sample Exchangeable cations Exchangeable No. Particulars (meq/ 100g) Sodium per cent Ca++ Mg++ Na+ K+ (ESP) 1 Bhandup EEH-side 9.0 3.0 21.8 2.5 60.0 Lagoon site 32.0 24.0 11.6 2.1 16.6 2. Ghatkopar EEH-side 27.0 2.1 2.7 2.0 8.0 Lagoon site 8.0 5.2 7.1 2.0 31.8 EEH - Eastern express highway AERAME LAGOCM 5.14 Physical properties of these soils would not normally pose problems for plant growth unless chemical properties, such as dissolved salts, or exchangeable properties such as exchangeable sodium percent (ESP) of the soils impose their influence on plant growth. The 1:2 soil-water extract analysis presented in Table 5.7 indicates that the soils have a pH range usually encountered in the case of normal soils (pH 6.5-8.5). However, the dissolved solids as revealed by the electrical .conductivity (EC) values, are very high for the lagoon sites . In sites with high EC values the concentration of divalent cations and sodium are quite high and in comparable concentrations. Similarly, amongst the anions, concentrations of cfloride and sulphate ions are high and comparable. The cation exchange properties of the soils (Table 5.8), indicate that exchangeable sodium percentage is more than the maximum permissible limit in all soils except at EEH near Ghatkopar lagoon site. 5.33.3 Terrestrial ecosystem The terrestrial ecosystems at the lagoon sites constitute a habitat consisting of shrubs which mostly include mangroves and halophytes along estuarine shores and mud flats . Mangrove formation and zonation are influenced by several factors like tidal range, temperature, salinity, rainfall, landwash, substrate characteristics, nature of the shore etc. The different systems followed for making zonation patterns mainly depend either on the frequency of inundation, salinity of the soil or dominant tree species. The species that are found at the lower levels are inundated by sea water twice daily during semidiurnal tides, whereas those found at the higher levels get submerged in water only during high tides. The vegetation and fauna occupying the swamp get adapted to varying levels of salinity and show tolerance to the fluctuations in saline concentrations. It was estimated in 1959 that the area of mangrove forests in Bombay and adjacent coastal districts is about 24,870 ha. The revised estimates indicate that the same is around 20,000 ha in 1975 .The mangrove swamps of Bombay are worst affected by human interference. The main factors include increase in population pressure and consequent large scale reclamation of mangrove swamp areas for housing, indiscriminate cutting of plants. According to recent satellite imageries the total mangrove area available in inner Thane creek is approximately about 750 hectares. Significant mangrove areas have also been reclaimed for salt pan construction. Baseline studies on vegetation with reference to species composition, diversity, abundance and distribution have been carried out AERATED LAGOONS in the study areas at the two lagoon sites viz; Bhandup and Ghatkopar. Quadrat method was adopted for sampling in approachable areas. Most of the mangroves have adapted themselves to their environment through development of required parts for attachment to soft or loose substrata, formation of respiratory roots and aerating devices, evolution of vivipary, use of specialised means for seed dispersal and development of xerophytic structures. Usually they are shallow rooted and lack. well-developed tap roots due to high salt concentrations,water saturation and anaerobic substratum which is organically rich. A number of adaptations in root morphology are typical of most of the mangroves. The roots may be 'prop' (from lower part of the stem) or 'drop' (from upper part of the stem) type that terminate after growing for few centimeters in the ground (e.g. Rhizophora sp.). In other cases, 'surface' (1-5 centimeters deep) horizontal roots grow out from the stem base and produce negatively geotropic, erect, aerial roots called pneumatophores (eg. Avicennia sp.). All these roots act as ventilation systems by having specialised air space systems, and they further produce anchoring and feeding types of roots, which help in absorption. Bhandup The most dominant species at this site were found to be Avicennia marina, followed by Salvadora persica and Ceiriops sps. with an Importance Value Index of 81.90, 12.21 and 5.89 respectively. It was again observed here that Avicennia were dwarfed with an average height of 0.61 meter as compared to the other plants with an average height of 1.08 and 0.72 meter respectively . The total mangrove area being reclaimed for lagoon construction is 608 meters x 574 meters. The area is partially covered by marshy grass Acluropus villosus along with Sesuviuin portukcastrunt. Mud flats were also observed in patches at some places. Aviccnnia species was abundantly found at some places whereas the same were found to be absent in some areas. This may be due to human interference for fire wood/fuel wood and other purposes. Ghatkopar The most dominant species observed at this site was again Avicevmia exhibiting monoculture vegetation with an Importance Value Index of 100. The plants were taller as against the observations made at the other sites, with an average height of 1.34 meters. Other species observed here include Salvadora persica. Nearly 90 hectares of land partially covered by mangroves is expected to be needed for lagoon construction out of which about 50 percent has already been reclaimed. AERAED IAGOONS - 5.16 The fauna present in mangrove forests were also studied. A number of insects especially mosquitoes and midges were present. Water. accumulates in the rot holes of branches and these are the ideal habitats for the- mosquitoes and midges larvae. Mudskippers from the channels flip their way across the soil. Hermit crabs were also observed in these forest. Among the mammals fox, jackal, fishing cat, dog, rat and mongoose were f6tand within the sLUdy area of two lagoon sites. Differeit types of bird populations were also observed in marshy areas around these sites. It was reported that some common migratory birds visit the marshy areas in the December-January and stay till March-April of each year.. They feed on small fish, floating garbage and waste materials which adhere to the marshy land especially during low tide. These birds are often called as "scavengers'. 5.3.4 Water quality Water quality in creeks which receive significant wastewater discharges, is intricately linked with the tidal conditions. The water exchange with the coastal sea is far greater during the spring tide in comparison to the neap tide. The volume of water retained in the creek at the low tide is, however,. more during the neap tide than the spring tide. Identification of critical tidal conditions in a creek with respect to the creek water quality, therefore, is not straight forward and requires water quality investigations which cover both spring and neap tide conditions of differing tidal strength. Also, the regions of water quality impairment due to wastewater discharges shift with the tidal conditions. Delineation of such regions along with quantification of the extent of water quality impairment necessitates repeated observations for different tidal conditions extending preferably over one full tidal cycle. Water quality observations on Thane creek which receives wastewater from a number of domestic as well as industrial sources along both of its banks was initiated in the summer of 1993. As the first step towards selection of sampling stations to identify the impacts of major municipal discharges reaching the creek through Bhandup and Ghatkopar creeklet, a reconnaissance survey was conducted on March 28, 1993 during a spring tide. 5.3.4.1 Reconnaissance survey During this survey it was established that Bhandup and Ghatkopar municipal discharges were the only major sources of pollution along the west bank of Thane creek within about 20 kilometers stretch beginning AERAD LAGOONS 5.17 from Thane rail bridge - and extending upto about 6 kilometers downstream Vashi bridge. The creek was observed to receive significant industrial wastewater discharges along its eastern bank but due to the significant width of the creek these did not overlap with the domestic discharges coming from the western bank. To establish the spatial extent of region of impact of Ghatkopar and Bhandup discharges water quality samples were collected at six transects from 1 kilometer downstream Vashi bridge to 3 kilometers upstream Bhandup creeklet (Figure 53). The sampling times were adjusted so as to collect the samples at the time when the wastewater flow from the adjacent discharge point directed towards the respective transects. For instance, at transect 1 below the Ghatkopar creeklet, samples were collected at the fag end of ebb tide. The transects above Ghatkopar and Bhandup creeklet were sampled during the flood tide. At each transect two samples, one near the west bank and one at about 500 meters inside the creek from the west bank were collected. The samples were analyzed for physico chemical parameters and the results are presented in Table 5.9. The observations indicated that most portions of inner Thane creek were significantly polluted up to a minimum of 500 meters from the west bank. Observed dissolved oxygen levels in these regions were at many times about 2 mg/L or below with concurrent BOD levels of about 5 mg/L and nitrogen levels of up to 4 mg/L. Total coiform concentration also indicated polluted creek conditions. To confirm above observations and to compare the pollution levels during the spring tide with the neap tide conditions, another survey was conducted on April 13, 1993 and both these surveys constituted the reconnaissance survey. During this survey, effort was primarnly rocused at the west bank of Thane creek. The sampling was carried out at five fixed positions along the west bank, 100 meters inside the creck from the lowest low tide line (Figure 5.4). Sampling at the outer locatnons was conducted during the ebb tide and at the inner locations during the flood tide. The regions above the Bhandup discharge were sampled by allowing a boat to drift with the current during ebb as well as flood tide. The samples were collected at regular half hourly intervals. The observatioins on dissolved oxygen levels indicated that the neap tide conditions were more critical in comparison to the spring tide conditions. It was further established that in the outer creek region about 1/3 width of the creek on the west was heavily polluted due to discharges from the west bank. In the upper creek regions, however, the creek substantially narrows and entire cross section of the creek exhibits heavily polluted conditions in this region during neap tide (Table 5.10). AEMGO 5.1 Figire : 5.3 Sampling transects for reconnaissance survey of 20.03.93 IdG 2k Bhan dup Ikm G j.. km Gha tko halr 1 .5 k Table: 5.9 Reconnalsance survey of Thane creek on 28.03.93: physico-chemical parameters Sr. 'llm in Sample pH Thibldity DO BOD Chlorides Nitrates Total Ammonlacal Soluble No. location as Cl as N Kjehldal Nitrogen phosphate Nitrogen as N as P as N hous NTU mgI L mg/ L mg/ L mg/ L mg/ L mg L mgI L 1 8.00 Tr 1(A)' 7.6 15.0 2.6 3.1 22,500 1.84 2.4 1.90 0.10 2 8.00 Tr l(B)o 7.4 12.0 2.2 4.2 20,000 1.76 3.5 1.54 0.12 3 9.00 Tr 2(A) 7.4 15.0 2.2 3.6 19,300 1.84 28 130 0.09 4 10.00 Tr 3(A) 7.4 15.0 1.2 5.7 19,900 1.56 4.2 130 0.16* 5 11.30 Tr 4(A) 7.4 12.0 1.8 4.5 20,000 1.26 35 1.10 0.12 6 11.30 Tr 4(6) 7.2 14.0 1.8 6.5 20,000 1.34 4.2 1.60 0.13 7 1230 Tr 5(A) 7.5 14.0 23 4.9 21,500 1.94 35 232 0.10 8 12.30 Tr 5(B) 7.5 12.0 2.6 3.6 22,000 1.50 2.8 1.30 0.12 9 13.30 Tr 6(A) 7.8 10.0 3.6 2.8 21,700 1.68 2.1 0.50 0.10 A sample collected at 500 m fom the west bank 8 sample collected at 100 m from (he west bank 0 Transect Figure : 5.4 Sampling locations during reconnaissance survey of 13.04.93 Sampling Locatlons ouring bridgc o Ebb Tide J Flood Tide 'g" Bhandup B. Ihandu cr:tkiet Ir - -II ih 3-S5km B G Ghko par chIko a,SO I<' Ohatopar A~LG ASEMEED lAON 5.21 Table : 5.10 DO values in Thane creek on 13.04.93 (LT-10.18 hrs.; HT-17.34 hrs.) Sampling location Time in 4 km downstream 500 m downstream 1 km downstream hours Ghatkopar discharge Vashi Bridge Bhandup discharge West Centre East A. Ebb tide sampling 830 2.8 13 9.00 1.4 1.0 2.9 13 2.0 930 2.0 0.9 10.00 0.8 0. 1.6 1030 - 1.1 1.5 15 15 Sampling location Timein 500 m upstream 4 km upstream Boat allowed to drift north hours Ghatkopar discharge Chatkopar discharge of Bhandup discharge point B. Flood tide sampling 11.00 2.8 2.3 1130 1.4 1.6 - 12.00 1.8 03 19 1230 2.6 1.5 2.4 13.00 23 0.6 2.4 1330 3.0 2.6 2.6 14.00 2.5 2.8 2.6 14.30 3.0 2.2 25 15.00 2.9 23 2.9 15.30 3.2 23 2.7 16.00 3.2 2.5 3.3 1630 3.6 2.5 2.9 17.00 3.4 2.6 3.4 1730 3.6 2.6 - Values expressed as mg/L AERMED LAGOONS - 5.3.4.2 Summer water quality survey To establish summer water quality conditions in the creek two detailed surveys on April 25 and 29 representing spring and neap tide conditions followed the reconnaissance survey. During these surveys, samples were collected across the entire creek width. A description of the sampling details, highlighting time and locations of sampling is provided in Table 5.31. The samples were analyzed for physico-chemical, bacteriological and biological parameters and the analytical results are presented through Tables 5.12 and 5.13. It is observed from results on physico-chemical parameters that at low tide slack for spring as well as neap tides, water quality conditions at transect 4 do not indicate significant presence of pollutants. This indicates that the impact of wastewater discharges into the creek remains confined to a region less than 7 kilometers south of Vashi bridge. The main mechanism of assimilation of pollutants in the creek, therefore, is biodegradation rather than dilution due to water exchange with the coastal region. The observations on bacterial parameters, however, indicate that impact of. wastewater discharges reaches upto Transect 4 during the spring low tide (Table 5.12). It appears that bacterial contaminations travel considerable distance during spring ebb tide due to swift tidal currents and high initial contamination levels at the point of discharge. Observations in the inner portion of the creek (Transects 1 and 2) indicate that the regions along the west bank of the creek are heavily polluted specially during the low tide. The high pollutant levels are, infact, observed up to the middle of the creek at these transects which occasionally extend to the east side of the creek also. The typical dissolved oxygen and total coliform concentrations in this region of creek are 1.5-3.0 mg/L and 10s10s per 100 ml, respectively (Table 5.12). BOD values as high as 7 mg/L have been observed on the west bank of the creek. Similar water quality conditions have been observed for spring and neap tides during these surveys. The reason for the similarity in observations may be attributed to the fact that the difference in tidal elevation of 2.5 meters during the neap tide was not very significantly low in comparison to that of 4.0 meters during the spring tide. These differences were much less than. possible range of about 0.5 meter during the neap and 5 meters during the spring tides, respectively. The intertidal observations on creek water quality at transects 2, 3 and 4 for DO, BOD, NIf,-N, total coliforms and other relevant physico-chemical parameters are presented in Table 5.14 to 5.16, respectively. The ASGED UkGOONS 523 Table : 5.11 Schedule for sampling in Thane creek during summer Sampling locations Sampling 3 lan north of 4 ki north of 1km south of 7 lan south of Date Bhandup discharge Ghatkopar creek Vashi bridge Vashi bridge arm near Trombay (Transect 1) (Thausect 2) (Transect 3) (Transect 4) A. Spring tide (25.04.93) 1. Water samples Low tide Centre Centre, east and Centre east and Centre, east and west shore west shore west shore Intertidal period - Two samples at Near west shore Centre 1, 2 and after low tide centre 1, 2 1, 2 & 5 hrs after 45 hr after 45 hrs after low tide slack low tide slack low tide slack - High tide Centre, east and Centre, east and Centre Centre west shore west shore 2. Sediment Centre, east and Centre, east and Centre, east and Centre west shore west shore west shore B. Neap tide (29.04.93) 1. Water samples intertidal period - 2,1 hr before 2 hr before low 2 1 hr before before low tide low tide tide at west shore low tide Low tide Centre Centre, east and Centre. east and Centre, east and west shore west shore west shore Intertidal period - 1, 2 and 4. hrs Near west shore 1, 2 and 45 hrs after low tide after low tide at 2 4.5 and 6 hrs after low tide at centre after low tide centre High tide Centre, east and Centre, east and Centre Centre west shore west shore AERED LAGOONS 1e Table : 5.12 Observations on water quality indicators in Thane creek during summer Dissolved oxygen Biochemical oxygen demand Total colifonus (mg/ L) (mg/ L) (counts/ loomi x 1000) T HT LT HT LT HT Location W C E W C E W C E W C E W C E W C E Tidal condition: Spring tide (25.04.93), Range : 4 m, Time LT-07.25 hrs.; HT-14.25 hrs. Transect I - 2.7 - 2.4 2.7 3.1 - 32 - 5.3 3.9 2.7 - 238 - - 0.7 - Transect 2 15 24 25 - - 3.2 5.9 4.3 3.7 4.1 3.7 3.8 120 - - 1.8 - Transect 3 2.8 2.0 3.7 4.0 3.9 - 5.1 4,7 2.8 2.2 3.0 - 16.2 65 - 1.2 1.1 - Transect 4 4.7 5.0 5.3 - 4.9 - 1.6 17 1.2 - 2.8 - 114 124 - - 1.2 - Tidal condition: Neap tide (29.04.93), Range : 2.5 m, Time LT-10.30 hrs.; HT-17.45 his. Transect - 216 - 36 40 3.5 - 4.8 - 1.9 4.2 3.6 - - - - - Transect 2 29 - 2.8 46 45 47 7.5 25 3.3 29 3.6 3.9 - 1.9 - - 0.5 Transect 3 2.1 4.5 2.6 - 50 - 2.5 3.0 2.2 - 2.6 - 94 -- - 2.1 - - Transect 4 4.7 5.5 4.8 - 4.4 - 23 2.2 2.5 - 1.0 - - 45 - - 0.2 - Table : 5.12 (Contd..) Soluble Phosphale as P Ammonacal Nitrogen as N Total Klelddal Nitragen as N Nitrate Nitrogen as N (mglL)(mgl L) (mg/ Li (mgl L) LT HT LT HT LT HT LT HT Lacation W C E W C E W C E W C B W C E W C E W C E W C E Tidal candition : Spring tide (25-04-93), Range : 4 m, Time LT-07.25 hrs.; HT-14.25 hrs. Transect I - 0.40 - 0.27 0.27 0.30 - 3.5 - 1.70 1.30 2.10 - 5.1 - 21 2.1 2.3 - 050 - 0.55 0.59 0.58 Transect 2 0.27 0.28 0.32 0.17 0.18 0.16 2.2 1.4 4.0 048 0.77 0.80 2.8 3.1 11.2 2. 1.4 1.4 0.39 0.47 0.62 0.62 0.93 0.58 Transect 3 0.20 0.28 0.18 0.18 0.17 - 1.0 1.3 0.7 0.20 0.40 - 6.3 35 1.7 1.7 1.4 - 0,42 0.40 0.56 0.69 0.76 - Transect 4 0.18 0.05 0,06 - 0,10 - 0,6 0.4 0.6 - BDL - 1.7 3.8 1.4 - 7.0 - 0.74 0,59 0.59 - 0.55 - Tidal condition: Neap tide (29.04.93), Range : 2.5 m, Time LT-10.30 hrs.; EIT-17.45 hrs. Transect I - 0.44 - 0.28 027 038 - 4.14 - 3.5 2.40 1.80 - 5.6 - 380 3.5 3.2 - 0.30 - 0.29 0.29 03 Transect 2 0.34 052 0.40 0.24 0 25 0.24 37 3.00 4.6 BDL 1.32 1.06 4.2 3.5 4.8 1.05 2.1 2.1 0.59 0.29 0.29 0.42 0.35 0.3 Transect 3 0.07 0.12 0.11 - 005 - 06 0.56 1.4 - 0.71 - 1.4 1 2.8 - 1.4 - 0.31 0.39 0.30 - - 0.36 - Transec 4 0.05 0,05 0.09 - 012 - 0 2 BDL 0.2 - BDL - 1A 4.9 4.2 - 1.4 - 0.44 0.35 0,38 - 0.42 - Table : 5.12 (Contd..) Temperature pH Thbidity Chlorides as Cl (*C) (NTU) (mgl L x 100) LT HT LT HT LT HT LT HT Location W C E W C E W C E W C B W C E W C E W C E W C E a I Tidal condition: Spring tide (25.04.93), Range: 4 m, Time LT-07.25 hrs.; HT-14.25 hIs. Transect1 - 28 - 30 30 .31 - 7.3 - 7.3 7.1 7.3 - 31 - .55 45 45 - 183 - 198 200 200 Transect 2 28 28 27 31 30 31 76 7.5 7.5 7.7 7.6 7.7 38 32 50 42 48 45 188 190 196 200 204 198 Transect3 27 28 28 31 31 - 7.6 7.5 7.6 7.7 7.8 7.7 50 21 23 25 23 - 204 190 204 195 195 - Transect 4 27 27 28 - 30 - 7.8 7.8 7.8 - 7.8 - 38 73 100 - 72 - 202 205 206 - 202 - . Tidal condition : Neap tide (29.04.93), Range : 2.5 m, Time LT-10.30 hrm.; HT-17.45 hrs. Transect I - 32 - 32 31 32 - 73 - 76 7.6 7.6 - 12 - 18 18 12 - 226 - 180 196 187 Transect 2 32 33 32 32 32 33 7.6 7.7 7.7 7.1 7.7 7.7 18 15 16 32 28 27 173 189 188 200 204 198 Transect 3 31 33 32 - 32 - 8.3 7.5 8.1 - 8.1 - 13 12 15 - 36 - 200 212 204 - 207 - Transect 4 32 31 31 - 32 - 7.7 7.8 7.7 - 7.1 - 20 17 20 - 32 - 211 210 212 - 207 - Table : 5.13 Phytoplankton observations in Thane creek (summer) Tidal Sampling Total Per cent composition in groups condition station counts per Bacillario- Cmlor- Cyano- Chmjso- Dino- 100 ml phyceae phyccae phyceae phyceae phyceac A. Spring tide (25.04.93) High tide Transect 1 2457 87.13 - 7.69 5.12 - Transect 2 1800 91.62 5.55 2.77 - - Transect 3 1450 100.00 - - - - Transect 4 900 94.42 - - - 5.55 Low tide Transect 1 3750 91.98 - 8.00 - - Transect 2 3087 95.89 2.04 2.04 - - Transect 3 2079 93.93 - 6.06 - - Transect 4 1200 100.00 - - - - B. Neap tide (29.04.93) High tide Transect 1 2995 94.45 - 5.54 - - Transect 2 2709 90.67 - 9.30 - - Transect 3 1150 86.89 4.34 8.69 - - Transect 4 1008 95.81 - - - 4.17 Low tide Transect 1 4252 88.24 - 11.76 - - Transect 2 3541 94.11 - 5.87 - - Transect 3 2350 8932 - 6.38 4.25 - Transect 4 1350 96.20 - - 3.70 - AUMAED MGOONS 5 Table : 5.14 Intertidal variations in water quality of Thane creek (summer) Sampling Tume DO BOD Total Coliforms Location* hours (mgl L) (mg/ L) (counts/ 100 mi) Tidal condition: Spring tide (25.04.93), Range: 4 m, rune: LT-07.25 hrs.; IT-14.25 hrs. Transect 2 8.15 2.4 43 1. x 105 930 2.7 5.7 9.7 x 106 12.15 2.8 5.5 1.6 x 105 1430 3.7 3.2 1.8 x 103 Tidal Condition: Neap tide (29.04.93), Range:2.5 m, Time: LT-10-30 hrs.; HT-17.45 hrs. Transect 2 8.30 2.8 2.6 1.90 x 103 9.30 2.6 3.5 7.25 x 103 10.30 - 2.5 2.16 x 10' 11.30 3.2 3.7 3.62 x 10s 12.15 3.8 43 131 x 104 15.30 5.5 3.5 Z.09 x 104 17.00 4.5 3.6 1.0 x 103 At the centre of the creek AIRAe LAGOONS Table : 5.14 (Contd...) sampling Tume Temp. pH Turbidity Chlorides Total Ammoniacal Nitrate Soluble Location* as CI Kjeldahl nitrogen nitrogen phosphate nitrogen hous oC NTU (ml L) ( maL) 62gUIL) (mgi L) (mg/ L) (mg/ L) Tidal condition: Spring tide (25.04.93), Range : 4 m, Time: LT-07.25 hrs.; HT-14.25 hrs. Transect 2 8.15 28 7.5 32 19000 3.1 1A 0.47 028 9.30 29 7.4. 55 19200 3.1 2.4 0.65 031 12.15 30 7.5 33 19400 2.8 1.8 0.48 0.27 1430 30 7.6 48 20400 1.4 0.8 0.95 0.18 Tidal condition: Neap Tide (29.04.93), Range -2.5 m, Time LT-10.30 hrs4 HT-17.45 hrs. Transect 2 8.30 28 7.6 12 18800 3.5 3.4 0.25 033 9.30 30 7.8 13 19000 4.2 4.1 0.24 0.20 10.30 32 7.7 15 18900 3.5 3.0 0.29 0.52 11.30 32 7.5 14 18400 3.6 3.5 0.24 0.28 12.15 32 7.5 15 18500 3.6 3.5 0.34 034 15.30 32 7.7 35 20000 2.8 13 0.30 0.27 17.00 31 7.7 28 20000 2.1 1.3 0.35 0.25 At centre of the creek AHUED LAGOONS 5.30 Table : 5.15 Intertidal variations in water quality of Thane creek (summer) Sampling Time DO BOD Total Coliforms Location' hours (mgf L) (mg/ L) (counts/ 100 ml) Tidal condition: Spring Tide (25.04.93), Range:4 m, Time: LT-07.25 hrs.; HT-14.25 hrs. Transect 3 9.00 2.8 5.1 6.50 x 10 9.30 2.8 4.7 1.62 x 104 10.40 3.4 2.8 1.78 x 104 12.05 3.8 2.3 1.22 x 103 1430 4.0 2.2 1.22 x 103 Tidal condition: Neap Tide (29.04.93), Range: 2.5 m, Tme: LT-10.30 hrs, HT-17.45 hIs. Transect 3 8.30 3.8 2.3 9.40 x 104 11.10 2.1 2.5 3.70 x 103 12.30- 5.7 4.3 1.66 x 104 15.10 63 2.0 6.60 x 103 17.00 5.6 3.9 1.13 x 10 *Near the west shore of the creek A9MED lAGOONS 5.31 Table : 5.15 (Contd...) Sampling Time Temp. pH Tuibidity Chlorides Total Ammoniacal Nitrate Soluble Location* as Cl Kjeldaht nitrogen nitrogen phosphate nitrogen hours *C NTU (mgi L) (mg/ L (mg/ L) (mg L) (mgL U (mgi L) Tidal condition: Spring tide (25.04.93), Range: 4 m, rme: LT-07.25 hr.; HT-14.25 hrs. Transect 3 9.00 29 75 50 20400 63 1.0 0.42 0.21 9.30 29 7.6 28 20000 2.1 09 0.50 0.18 10.40 30 7.7 30 20200 1.7 05 0.53 0.16 12.05 30 73 60 20000 1.0 0.2 0.54 0.17 14.30 30 7.7 25 19500 1.7 02 0.70 0.18 Tidal condition: Neap tide (29.06.93), Range: 2.5 m, Time: LT-10.30 hrs.; HT-17.45 hrs. Transect 3 8.30 29 77 36 20700 2.1 0.9 036 0.10 11.10 30 83 13 20000 1.4 0.6 031 0.07 1230 31 82 26 20400 1.4 03 031 0.06 15.10 32 8.0 17 21900 1.0 0.1 0.42 0.15 17.00 31 72 30 20900 1.0 02 0.51 0.05 Near the west shore of the creek A=E EIAGOONS Table : 5.16 Intertidal variation in water quality of Thane creek (summer) Sampling Thie DO 8OD Total Coliforus Location* hours (mg/ L) (mg/ L) (counts/ 100 ml) T1dal condition: Spring tide (25.04.93), Range: 4 m, rume: LT-07.25 hrs.; HT4.25 hrs. Transect 4 8.30 5.0 1.7 1.24 x 105 9.30 4.9 1.0 1.61 x 105 12.30 4.9 - 5.50 x 104 14.00 4.9 2.8 1.16 x 103 Tidal Condition: Neap tide (29.04.93), Range:2.5 m, Tme: LT-1030 hrs.; HT-17.45 hrs. Transect 4 8.30 4.7 4.0 - 9.30 4.9 1.2 4.50 x 104 10.45 4.7 2.3 3.20 x 102 11.30 5.9 1.7 5.45 x 103 12.30 5.9 2.9 2.54 x 104 15.00 5.9 1.9 1.20 x 103 17.30 4.4 1.0. 2.10 x 102 At centre of the creek 5.33 AUGED LAONS Table : 5.16 (Contd...) Sampling Time Temp. pH Turbidity Chlorides Total Amnoniacal Nitrate Soluble Location as Cl Kjeldahl nitrogen nitrogen phosphate nitrogen hours *C NTU (mgi U (mUgL (mg/ IU (mg?L) (ugf L mgI L) Tidal condition: Spring tide (25.0.93), Range: 4 m, Time: LT-07.25 hrs.; HT-14.25 hrs. Transect 4 8.30 28 7.8 73 20500 3.8 0.4 0.60 0.06 9.30 28 7.8 35 20400 5.1 03 0.45 0.08 12.30 30 7.8 64 20200 1.7 03 0.60 0.09 14.00 30 7.7 72 20200 7.0 BDL 0.55 0.10 Tidal condition: Neap tide (29.04.93), Range: 2.5 n, rune : LT-10.30 hrs.; HT-17.45 hrs. Transect 4 830 28 8.0 22 20700 2.8 0.2 036 0.08 9.30 30 7.0 17 20400 2.8 0.1 038 0.05 10.45 31 7.8 17 21000 4.9 0.1 0.35 0.06 11.30 32 7.7 18 21000 1.7 0.1 035 0.09 1230 32 7.2 17 20700 1.0 BDL 0.58 0.12 15.00 32 7.6 23 20900 1.0 BDL 0.38 0.13 17.30 31 7.1 32 20700 1.4 BDL 0.42 0.12 At centre of the creek BDL - Below detectable limit AEM LUMOMS observations indicate that water quality conditions at the inner transect 2 remain poor for at least two hours before and after the low tide slack ( Figure 5.5). During the ebb tide pollutants from Bhandup discharges move and spread towards the transect 2 whereas during the flood tide* Ghatkopar discharges move up and pollute the inner middle regions of .the creek. It is observed that it may take upto 4 hours before relatively dean sea water from outer Thane creek reaches this portion. The regions near the west bank of creek at outer transect 3 also exhibit elevated concentration of total coliforms and low dissolved oxygen levels during the ebb tide (Figure 5.6). This transect is only about 2 kilometers away from the mouth of Ghatkopar creeklet and the pollutants emanating from the creeklet flow along the west bank of the creek in this region. With the flood tide, however, water quality conditions at this transect rapidly improve. Water quality conditions at the outer most transect (transect 4) remain unchanged during the low and high tides, indicating that the creek portion at this transect are away from the region of immediate impacts of wastewater discharges. The bacterial contamination levels at this transect, however, are high during the ebb tide and indicate that the pollutants from the discharges do reach this transect but are observed only in terms of microbial parameters due to their high initial concentration (Figure 5.7). 5.3.4.3 Winter water quality survey In order to have complete representation of water quality with respect to seasonal variation sampling was also planned during the winter. Surveys were conducted on January 28 and February 6, 1994 to study winter water quality variations under spring and neap tidal conditions. respectively. During these surveys, samples were collected across the entire creek width at low and high tide slacks at three transects. The sampling --chedule and locations for these surveys are described in Table 5.17. The samples were analyzed for physico-chemical, bacteriological and biological parameters and the analytical results are presented through Tables 5.18 to 5.20, respectively. The observations on physico-chemical parameters as presented in Table 5.18 indicate that at tidal slacks creek dissolved oxygen is generally higher during the spring tides in comparison to the neap tides. Under the neap tidal conditions water quality remains unaffected by the wastewater discharges in regions downstream Vashi bridge. This indicates that due to weak tidal currents during neap tides wastewater discharges remain confined within relatively short distances (about 5 kilometers) from the point of discharge. At low tides transects 2 and 3 show marked water AUED LAGOONS 5.35 Figure : 5.5 Intertidal water quality at transect 2 of Thane creek (Summer-Spring tide) 7 × 4- 8 1* 7 8 9 10 11 12 13 14. 15 Sampling Time in hrs. +- DO (mg/I) -- BOD (mg/I0 --×-Log of Tc ats/10 mI LT 14.25 hrs. HT ø 20.11 hri. Intertidal water quality at transect 2 of Thane creek (Summer-Neap tide) 6x 5X --------'---- 8. 2- 0i 0-- 1| 1 8 9 10 11 12 18 14 15 16 17 Sampling Time in hrs. -a- DO (mg/I -- BOD (mg/ - -x- Log of TC cts/100 mi 'T10.30 r. 14T 17.4 "r. AER~ED LAGOONS 5.36 Figure : 5.6 Intertidal water quality at transec 3 of Thane creek (Summer-Spring tide) 8911112 13 14 15 Sampling Time In hrs. - Da (mg/1) -- BOD (mg/I) -X- Log of TC ata/100 ml LT 14.25 hrs. HT v 20.11 hrM. Intertidal water quality at tiansect 3 of Thane creek (Summer-Neap tide) 7 6x S-------------- 2- B 9 10 11 12 1 14 1S 18 17 Sampling Time In hrs. -a- Do (mg/O -a- BOD (mg/) -- Log af TC ats/100 mi LT a 10.80 hr. MT * 17.46 hs. M GOON 5.37 Figure 5.7 Intertidal water quality at transect 4 of Thane creek (Summer-Spring tide) 4- 8 2- 1 5 9 10 11 12 13 14 15 Sampling Time In hrs. DO (mO/) -- BOD (mg/l -- Log of TC ats/100 mi LT ' 14.26 bro. HT , 0.11 sre. Intertidal water quality at transect 4 of Thane creek (Summer-Neap tide) 7 4- q *- 0- 8 9 10 11 12 13 14 1 18 17 18 Sampling Time in hra. DO (mgi -- BOD (mg/1) -- Log of TO otsl00 mI LT m 10.30 hre HT . 17.41 hre. AEMED LAGOONS 5. Table : 5.17 Schedule for sampling in Thane creek during winter Sampling location Sampling 4 km north of I km south of 7 lan south of Date Ghatkopar creek anm Vashi Bridge Vash Bridge near Trombay (Tansect 2) (Transect 3) (Transect 4) A. Spring tide (25.194). 1. Water samples Low tide Centre, East and West Centre, East and West Centre, East and West High tide Centre West Centre Centre 2. Sediment Centre Centre Centre B. Neap tide (06.2.94). . L Water samples Low tide Centre, East and West Centre, East and West Centre, East and West High tide Centre, East and Centre, and West Centre West L Sediment Centre - Centre AERAED LAGOONS Table : 5.18 Observations on water quality indicators for Thane creek during winter Dissolved oxygen Biochemical oxygen demand Total coliforms (mg L) (mgl L) (counts/ 100 ml x 100) LT HT LT IT LT HT Location W C E W C 8 W C E W C E W C E W C E Tidal condition : Spring tide (28.01.94), Range : 3.75 m, Time LT-18.32 hrs.; HT-12.28 hrs. Transect 2 3.0 3.0 5.0 5.8 6.8 6.1 4.0 4.0, 3.4 3.8 3.9 4.4 340 110 18 13 5 8.6 Transect 3 3.2 4.4 4.5 - 5.5 - 2.8 2.7 BDL - 2.0 105 340 - 10 10 - Transect 4 43 5.0 6.6 - 6.3 - 3.3 3.1 4.2 - 2.9 - 840 22 7 - 25 - Tidal condition : Neap tide (06.02.94), Range: 2.5 m, Time : LT-14.32 hrs.; HT-07.4S hrs. Transect 2 1.5 1.5 6.3 3.1 3.0 38 3.0 2.6 4.7 2.0 3.7 2.1 374 430 500 220 196 97 Transect 3 35 2.0 4.8 5.3 4.9 - 2.9 5,2 BDL 1.7 1.9 - 88 84 9 106 0.8 - Transect 4 3.2 4.4 4.7 - 4.2 - 1.5 2.9 6.3 - 1.9 - 49 . 48 21 - 1.4 - DDL - Below detectable limit Table : 5.18 (Contd...) idal condition : Sping tide (28.01.94), Range :3.75 m, Time HT-12,25 luo.; LT-18.32 hr. Soluble phosphate as P Ammoniacal nitrogen as N Total kjeldahl nittagen as N (mg LI (mg/ L) (mgI L) LT IT LT HT LT HT Location W C E W C E W C E W C E W C E W C E Transect2 0.27 0.28 0.26 0.26 0.14 0.15 2.3 2.3 15 0.9 1.2 0,6 4.2 4.2 2.8 . 4.2 2.8 2.8 Transect3 0.15 0.30 0.05 - 0.11 - 1.4 0.9 0.6 - 0.3 - 2.8 2.8 1.4 - 2.8 - Transect4 0.10 0.10 0,05 - 0.10 - 0.7 0.7 0.4 - 1.0 - 4.2 4.2 4.2 - 2.8 - Tidal condition: Neap tide (062-94), Range : 2.5 m, Time HT07.48 bis.; LT-1432 brs. Soluble phosphate as P Ammoniacal nitrogen as N Total kieldahl nitrogen as N (mgi LI (mgl L) (mg/ L) LT HT LT HT LT HT Location W C E W C E W C E W C E W C E W C E Transect2 0.33 0.29 0.19 0.18 0.20 0.14 1.5 2.4 1.20 0.2 1A0 1.2 4.2 3.9 3.4 2.8 4.20 3.40 Transect 3 0.23 0.25 0.07 0.08 0.08 - 1.9 2.1 0.35 0.7 0.40 2.6 3.6 4.3 8.2 1.7 0.23 0.25 Transect4 0.10 0.13 0.11 - 0.08 - 1.2 0.5 0.70 - 0.15. - 1.2 2.8 2.8 -- 1.10 - Table : 5.18 (Contd...). Temperature pH Turbidity Chlorides as C1 OC NTU (mg/L x 100) LT HT LT HT LT HT LT HT Location W C E W C E W C E W C E W C E W C E W C E W C E Tidal condition : Spring tide (28.01.94), Range : 3.75 m, Time HT-12.28 hrs.; LT-1832 hrs. Transect 2 26. 26 26 27 27 27 7.2 7.2 7.4 7.6 7.5 .7.7 45 55 63 20 15 12 180 178 182 -185 184 187 Transc t3 26 25 26 - 27 - 7.3 7.4 7.7 - 7.6 - 65 90 28 - 32 - 180 183 184 - 192 - Transect 4 26 25 25 - 27 - 7.4 7.4 7.6 - 7.7 - 80 13 7 - 26 - 180 188 193 - 200 - Tidal condition: Neap tide (06.02.94), Range: 2.5 m, Time HT-07.48 hrs.; LT-1432 hs. Transect 2 28 28 27 25 26 26 7.3 7.3 7.5 7.3 7.4 7.5 14 5 11 13 14 11 181 210 204 208 194 208 TransctO 26 25 26 - 27 - 73 7.4 7.7 - 7.6 - 65 90 28 - 32 - 180 183 184 - 192 - Transect 4 7 28 28 - 25 - 7.6 7.5 7.4 - 7.6 - 18 14 15 - 30 - 194 197 189 - 205 - quality impairment in considerable transverse section of the creek, presumably the regions which fall in the path of wastewater plumes flushing out of the creek with the ebb tide. Water quality at transect 3, however, significantly improves during the high tide with influx of relatively clean water from outer Thane creek. Bacterial counts in the creek also present a scenario similar to physico-chemical parameters. The nutrient parameters analyzed for water samples collected from the various transects included ammoniacal nitrogen, total nitrogen and soluble phosphates. The observations were taken with respect to seasonal and tidal variation and are presented in Tables 5.12 to 5.19. Higher nutrient concentrations are observed in the inner transects as compared to the outer transects thereby indicating higher pollution. The total nitrogen values ranged from 2.8 mg/L to 63 mg/L in the inner Thane creek. 5.3.5 Biological parameters Phytoplankton Phytoplankton levels and its compositions were estimated inside the Thane creek at four different transects stretching from Vashi bridge downstream to a distance of about 7 kilometers to 3 kilometers upstream Bhandup discharge and are presented in Tables 5.13 and 5.19. For all sampling conditions, phytoplankton counts show a decreasing trend from inner to outer transects. The observation indicates higher productivity in the creek compared to the outer coastal region. Low tide counts are also found to be higher than that of high tide. The observations further indicate higher counts in summer than in winter. Lower water exchange with coastal regions during the neap tide, as observed from the physico-chemical observations, is further confirmed by the higher phytoplankton counts observed during neap tides in comparison to spring tides. The over all phytoplankton counts in the creek, however, are fairly low and range below 5000 per 100 ml in all observations. Bacillariophyceae was the prominent group of phytoplankton at all transects. A noteworthy feature was the presence of Dinophyceae at transect 4 for all tidal conditions in winter and during high tide in summer thus indicating cleaner regions at locations further south. The above fact can be further reaffirmed by the absence of Cyanophyceae the indicator group of organic pollution at transect 4 for all tidal conditions both in summer and winter. AMUAED LAGOONS 53 Table : 5.19 Phytoplankton observations in Thane creek (winter) Tidal Sampling Total Per cent composition in groups condition station counts per Bacillaio- Chloro- Cyano- Chryso- Dino- 100 ml phyceae phycene phyceae phyceae phyceae A. Spring tide (2B.01.94) High tide Transect 2 1650 93.90 3.03 3.03 - - Transect 3 1310 94.17 - 359 2.17 Transect 4 850 92.08 - - 5.26 2.63 Low tide Transect 2 2196 85.32 6.14 5.16 3.33 Transect 3 1600 93.71 - 4.74 1.51 - Transect 4 1176 92.67 - - 3.64 3.64 S. Neap tide (06.0.94) High tide Transect 2 1820 89.8 3.64 6.50 - - Transect 3 1314 93.47 - 5.02 1.47 - Transect 4 1230 92.89 - - - 7.07 Low tide Transect 2 2275 90.08 3.92 4.73 1.25 - Transect 3 - - Sample not collected - - Transect 4 1590 94.14 - - - 5.83 ARMED LASOONs SM Zooplankton Zooplankton is a very important group in the aquatic ecosystem acting as a major source of link between the phytoplankton and the primary carnivores. Zooplankton levels and its compositions were estimated inside Thane creek at locations stretching from south of Vashi bridge to north of Bhandup discharge (Table 5.20). Samples were collected and preserved in buffered formalir solution. Copepods followed by Ciliates were the most predominant species observed which may be attributed to the presence of abundant phyt6plankton, decaying organic matter and bacteria in the creek. The number of groups observed during high tide are more as compared to low tide. The total zooplankton counts are observed to be higher during the spring ti ie in comparison to neap tides due to higher flooding and drying of mangroves which act as breeding areas for zooplankton. 5.3.6 Trace metal levels Thane creek receives significant inputs of heavy metals due to the influx from the surrounding basaltic terrain as well as through domestic and industrial wastewater discharges. The dissolved trace metals added through these influxes get immobilized into creek sediments due to alkaline pH of creek waters and related transformations. A partial resuspension of precipitated metals is possible due to strong tidal currents but a rise in dissolved metal levels in the creek water is not expected, due to resuspension. Due to established high cation exchange capacity of Thane creek sediments, the metal pollutants are most likely to be accumulated in creek sediments. In order to examine the status of trace metal contamination in Thane creek study area creek water and sediment samples from a number of locations were analysed for total and dissolved metals. The municipal wastewater samples were also analysed for total metals to assess the load of trace metals through such discharges into the creek. The water quality survey was conducted in summer and winter seasons and covered high and low water conditions during the spring and neap tides. Sampling locations for the creek surveys during the two seasons were identical. The results of creek water analysis for Zn, Cu, Ni, Mn, Cr, Cd and Pb for summer and winter surveys are presented in Tables 5.21 and 5.22. These results indicate that the total metal concentrations were higher during summer in comparison to winter. These levels, however, do not indicate significantly higher metal levels as the observed concentrations are only AMAED AGOONS AS Table: 520 Zooplankton observations in Thane creek Location Tobl- Percent composition In gaups - Shannon Zooplanklon Weaver per 100 M3 Divasy Index Witer, spring tide (28.01.94) Tr-2C/HT 1.683 076 152 229 038 - 251 076 - 62J - - JE 152 75&76 22 - 38 1.71 Tr- 2C/LT 1,4129 - - - 1627 55 19 -63 - - 3.41 - - - - 110 - 123 Tr- 4.CjH 45729 - -09 - 117 36 241 483 12 601 10 622 - - 35C - 9A7 240 Tr- 4C/LT 8,61.12 0.46 - - 0he 0.46 083 883 - 749 0.46 - 0.13 7A8 - - 0.93 0.62 418 1.40 a - C -Cae Table : 5.20 (Contd...) Location Total Percent composiOn In groups Shamnno Zooplanktan - Weaver per 100 m3 - - ovenky Index Winter, neap tide (06.02.94) Tr-2-C/HT 363 - 958 - - l la - 13 - - 1.3 03 Tr - 2IT 5,926 - 27.02 1591 54M5 - - - 1.4 Tr - 4C/HT 1,02A21 1815 28M 469 3M1 12 14.41 722 IB 397 - 2.7 Tr - KILT 14,693 1123 3320 - - 32I - - 1123 1123 - - 21 # Tawmt CCeTIw C-Cth Table 5.21 Total heavy metal concentration in Thane creek during summer (spring tide) Location Ni Mn Zn Cr Cu Cd Pb (mg/ L) Tr 1 LT C 0.05 1.19 0.26 0.11 0.06 BDL 0.08. Tr 2 LT W 0.06 1.65 0.22 030 0.17 BDL 0.11 Tr 2 LT C BDL . 0.80 0.12 0.25 0.30 0.01 0.08' Tr 2 LT E 0.05 0.62 0.11 0.15 0.26 BDL 0.20 Tr 3 LT W 0.02 0.72 0.19 0.20 0.17 BDL 0.09 Tr 3 LT C 0.06 0.43 0.28 0.17 0.24 BDL 0.99 Tr 3 LT E 030 0.40 0.14 0.20 0.06 BDL 0.02 Tr 4 LT W 0.08 0.57 0.53 0.10 1.48 BDL 0.06 Tr 4 LT C 0.06 0.87 0.35 0.18 0.75 BDL 0.09 Tr 4 LT E 0.08 0.54 0.38 0.22 1.12 BDL 0.10 Tr 1 HT W 0.04 1.73 0.18 0.14 039 BDL 0.05 Tr 1 NT C 0.04 . 0.47 0.29 0.06 035 BDL 0.03 Tr 1 HT E 0.01 2.15 1.04 0.25 0.53 BDL 0.13 Tr 2 HT W 0.02 1.30 0.26 0.04 0.06 BDL 0.11 Tr 2 HT C 0.06 0.71 0.11 0.20 BDL BDL 0.08 Tr 2 HT E 0.04 130 0.09 0.17 BDL BDL 0.03 Tr 3 HT C 0.05 0.39 0.17 0.06 0.03 BDL 0.06 Tr 4 HT C 0.03 0.62 0.43 0.19 0.13 BDL 0.08 * - Transect C - centre; W - west; E - east BDL - Below detectable limit AERATED LAGOONS 548 Table : 5.21 (Contd.) Total heavy metal concentration in Thane creek during summer (neap tide) Location Ni Mn Zn Cr Cu Cd Pb (mgI L) Tr '1 LT C 0.12 1.30 0.75 0.03 1.21 BDL 0.04, Tr 2 LT W 0.09 2.22 0.37 0.02 1.46 BDL 0.02 Mr 2 LT C 0.11 1.53 0.36 BDL 0.38 BDL BDL Tr 2 LT E 0.08 1.45 0.34 BDL 0.28 BDL 0.03 Tr 3 LT W 0.06 0.39 0.29 0.14 0.59 BDL 0.18. Tr 3 LT C 0.09 0.43 0.25 BDL 1.95 BDL BDL Tr 3 LT E 0.09 1.14 0.27 BDL 0.48 BDL BDU Tr 4 LT W 0.09 1.82 0.22 0.05 0.25 BDL 0.02 Tr 4 LT C 0.06 0.37 0.28 BDL 0.32 BDL BDL Tr 4 LT E 0.12 0.19 0.34 0.20 0.36 BDL BDL Tr 1 HT W 0.08 0.78 0.23 BDL 0.56 BDL BDL Tr I HT C 0.03 0.79 0.42 0.17 0.47 BDL 0.06 Tr 1 HT E 0.08 2.01 0.21 0.08 2.77 BDL 0.01 Tr 2 HT W 0.05 0.62 0.31 0.07 0.23 BDL BDL Tr 2 HT E 0.10 1.27 0.27 BDL 0.30 BDL BDL Tr 3 HT C 0.04 030 0.36 0.21 0.32 0.01 0.05 Tr 4 HT C 0.05 0.61 0.25 0.13 0.37 BDL 0.01 * - Transect W - west, C - centre, E - east BDL - Below detectable limit AERATED LGOONS 54 Table - 5.22 Total heavy metal concentration in Thane creek during winter (spring tide) Location Ni Mn Zn Cr Cu Cd Pb (mgf L) Tr*2 LT W 0.08 0.87 0.24 0.34 0.05 BDL BDL Tr 2 LT C BDL 0.49 0.14 0.19 0.02 BDL BDL Tr 2 LT E BDL 0.55 0.10 0.44 0.01 BDL BDL Tr 3 LT W BDL 0.34 0.10 0.45 0.02 BDL BDL Tr 3 LT C BDL 0.51 0.04 0.43 BDL BDL BDL Tr 3 LT E BDL 0.28 0.08 024 0.01 BDL BDL. Tr 4 LT W BDL 0.17 0.07 0.31 0.03 BDL BDL Tr 4 LT C 0.02 0.24 0.10 0.09 0.02 BDL BDL Tr 4 LT E BDL 0.54 0.07 0.30 0.02 BDL BDL Tr 2 HT W 0.02 0.10 034 0.21 0.03 BDL BDL Tr 2 HT C 0.13 0.03 0.05 0.26 BDL BDL BDL Tr 2 HT E BDL 0.04 0.01 0.22 0.02 BDL BDL Tr 3 HT C BDL 0.12 0.17 0.48 BDL BDL BDL Tr 4 HT C BDL 0.45 0.04 031 0.07 BDL BDL * - Transect W - west, C - centre, E - east BDL - Below detectable limit AAWD lAGOONS Table : 5.22 (Contd ...) Total heavy metal concentration in Thane creek during winter (neap tide) Location Ni Mn Zn Cr Cu Cd Pb (mg/ L) Tr*2 LT W BDL 0.57 0.06 035 BDL BDL BDL Tr 2 LT C 0.01 0.35 BDL 0.60 0.02 BDL BDL Tr 2 LT E 0.12 0.59 0.03 050 BDL BDL BDL Tr 3 LT W 0.04 0.17 0.08 0.36 BDL BDL BDL Tr 3 LT C BDL 0.16 BDL 050 BDL BDL BDL Tr 3 LT E BDL 0.55 0.04 0.37 BDL BDL BDL Tr 4 LT W BDIL 0.06 0.02 0.62 BDL BDL BDL Tr 4 LT C BDL 0.17 0.05 0.42 0.01 BDL BDL Tr 4 LT E 0.06 0.07 0.19 0.48 BDL BDL BDL Tr 2 HT W 0.03 0.26 0.17 0.25 0.02 BDL BDL Tr 2 HT C 0.03 0.08 0.04 0.59 BDL BDL BDL Tr 2 HT E 0.06 0.68 BDL 0.42 0.01 BDL BDL Tir 3 HT C 0.14 0.04 0.03 0.47 BDL BDL BDL Tr 4 HT C BDL 0.01 0.22 0.41 BDL BDL BDL * - Transect W - west, C - centre, E - east BDL - Below detectable limit - AED MLAGOONS L51 marginally higher than the drinking water standards for some of the trace metals. Further, their comparison with the tolerance level of sensitive marine biota indicates that the dissolved metal concentrations are lower than the tolerance values. The comparison, however, could not be made for Cr, as total soluble Cr was estimated during the survey whereas the tolerance values are in terms of hexavalent Cr. A comparison of metal levels in water column among the various transects do not indicate a appreciable difference. The levels for some metals are, however, higher than those observed in municipal discharges and thus indicate inputs from other sources. Due to the alkaline pH of creek waters, sediments are expected to be major sink for trace metals and their levels in sediments is a Ouperior indicator of status of metal pollution in the creek. Accordingly, the sediment samples in summer and winter were collected at all the four transects. The sampling region was confined to the creek center as the sediments from the sides are expected to move and accumulate in the central region of the creek under the influence of natural hydrodynamic processes. The results of the trace metal analysis in the sediments are presented in Tables 5.23. For their interpretation, these values were compared with the naturally occurring trace metal levels in Bombay soils and also with the World Shale. Table 524 presents the ratio of trace metals in Thane creek with respect to the World Shale and Bombay urban soils. The results indicate considerably higher values of Cr, Cu, Pb and Zn in comparison to natural Bombay soil and World Shale levels. The concentrations for Cr and Cu are upto 2 to 6 times higher in the major part of the creek and indicate significant industrial pollution. The trace metal levels in winter, however, are significantly lower in comparison to summer values. The possible reasons for these differences could be flushing of the enriched sediments to the open coastal regions during the monsoon and deposition of fresh natural soil through run-offs. When compared to the metal levels along the west coast of Bombay, it is- observed that Cr, Cu and Mn levels in Thane creek are upto 10 times higher In view of low metal concentration in domestic wastewater discharged into Thane creek, these high trace metal levels can not be attributed to municipal discharges and underscore the presence of significant industrial influx into the creek. 53.7. Nutrients in sediments For estimations of nutrients in sediments in Thane creek, samples from the AEMED LAGOON.S .5 Table : 5.23 Heavy metals in Thane creek sediments Sampling station* Ni Mn Zn Cr Cu Cd Pb (mg/ kg) Summer Mansect 1 142 1508 189 321 - BDL 45 Transect 2 136 1059 234 434 - BDL 55 Transect 3 141 1462 225 461 - BDL 59 Transect 4 153 1093 187 489 - BDL 47 Winter - - - - - - - Transect1 - - - - - - - Transect 2 80 1020 199 116 128 BDL 37 Transect 3 65 911 119 102 98 BDL 22 Transect 4 78 889 279 110 197 BDL 41 * - Samples were collected along the main channel of the creek BDL - Below detectable limit AERMED LAGOONS 553 Table : 5.24 Ratio of trace metal concentration in Thane creek sediments to Bombay urban soil and World Shale backgrounds Element Bombay Urban Soil World Shale Background Background Winter Summer Winter Summer max min max min max min max min Ni 0.44 0.58 0.93 105 0.95 1.25 2.00 2.25 Mn 0.79 1.02 1.04 1.48 0.94 1.22 124 1.77 Zn 0.91 331 1.43 1.80 1.25 4.53 1.96 2.46 Cr 1.24 1.51 3.91 5.96 1.13 137 3.56 5.43 Cu 0.66 1.91 - - 2.18 6.30 - - Pb 0.51 1.34 1.04 1.37 1.10 2.90 2.25 2.95 AOMM LAGOONS selected transects were collected during the winter and summer seasons. The sampling was restricted to the central portion of the creek as the sediments from the sides are expected to move and accumulate in the middle region of the creek due to tidal currents. These samples were analyzed for nutrient parameters comprising total nitrogen and phosphorus, results of which are presented in Tables 5.25. The total nitrogen concentrations in Thane creek sediments were observed to be significantly lower during the summer in comparison to the winter Total nitrogen levels in Thane creek ranged from 2400 to 3750 mg/kg in winter compared to 1032 to 1505 mg/kg in summer. Similar seasonal trends in total nitrogen levels were observed along the west coast of Bombay. The values observed during summer in the creek are comparable to the concentrations observed along the west coast. Creek sediment nitrogen levels during the winter were higher than the observed levels along the west coast and may be attributed to higher accumulation during winter due to lower rates of biological activity and relatively higher concentration of organic loading in the creek. The phosphorus levels exhibit more pronounced variation in the sediment samples at different transects in comparison to total nitrogen. Lowest value of 150 mg/kg of total phosphorus was observed at the inner most transect. At the remaining transects, the levels of total phosphorus varied from 750 to 1000 mg/kg during summer and 575 to 900 mg/kg during winter. These concentrations were comparable to those observed at 1 kilometer reference line along the west coast of Bombay. 53.8. Detergents Wastewater and water The procedure adopted for estimation of anionic detergents was the Methyl Green method (Moore and Kolbeson, 1956). Detergent analyses was carried out at the four transects as mentioned earlier for summer and winter during spring and neap tidal conditions respectively. The results are presented in Tables 5.26. The analysis conducted during summer indicate that the concentration of detergent is higher on the eastern banks of the inner transects (1 and 2) as compared to that of the outer transects (3 and 4). This difference in detergent concentration was more pronounced during the low tide than high tide. Besides, although, the sewage was being discharged on the western banks, the detergent concentration on the eastern bank was comparable or occassionally higher to that on western bank. One can infer from this observation that discharges carrying AOMLED AGOONS 5.55 Table : 5.25 Nutrients in Thane creek sediments Sampling station* Total kjeldah[ nitrogen as N Total phosphorus as P (mgf kg) (mg/ kg Summer Transect 1 1032 150 Transect 2 1050 950 Transect 3 1400 1000 Transect 4 1505 750 Winter Transect 1 - Transect 2 3750 575 Transect 3 2400 900 Transect 4 2800 650 * - Samples were collected along the main channel of the creek AED LAGOONS 5.56 Table : 5.26 Detergents in Thane creek water Neap tide Spring tide LT HT LT HT Sampling station W C E W C E W C E W C E Summer Tasect 1 - 034 - 05 0.27 0.73 - 031- 0.24 0.03 0.24 Transect 2 024 0.15 1.07 001 0.05 0.15 0.23 0.22 031 0.22 0.28 031 Transect 3 0.15 0.03 0.15 0.04 0.11 - 0.15 0.19 031 - 0.23 - Transect 4 0.15 0.04 0.04 - 0.01 - 0.23 0.15 032 - 0.03 - Winter Transect 1 - -- - - - - -- - - - Transect 2 - - BDL BDL BVL - 0.006 BDL BDL BDL BDL BDL Transect 3 - BDL - BDL BDL - - - - - BDL - Transect 4 BDL - BDL - BDL - - - - - BDL - Concentrations are in mg/L W-west, C-centre, E-east BDL - Below detectable limit AERMD IAGOONS 557 detergents are also reaching the creek from the industrial belt on the east. However, the observed concentration in the creek were within the prescribed water quality standard of 1 mg/L except on one occasion along the east bank. Sedimits The Methyl Green method reported by Moore and Kolbeson, (1956) is for the analysis of anionic detergent is sewage and wastewater samples. The method was suitably modified by incorporating a pretreatment procedure, to analyse for detergents in sediments. The results are presented in Table 5.27. The detergent concentrations observed in Thane creek sediment are significantly higher (upto 10 times in most of the samples) than values observed along the west coast of Bombay and indicate higher proportion. of industrial discharges into the creek. The winter concentrations are, however, significantly lower than summer and perhaps indicate that most of the polluted sediments are washed out to sea during the monsoon. 5.3.9 Wastewater characterization The wastewater drainage zones in Bombay are divided into seven service areas. The wastewater from Bhandup and Ghatkopar service areas directly discharge along the western bank of Thane creek These discharges constitute about 20 per cent of the total municipal wastewater generated in the city. Estimation of the impact of these discharges on the creek and adjoining coastal ecosystem, evidently, entails their characterization. Hourly wastewater samples were collected from terminal pumping stations and characterized for physico-chemical and nutrient parameters (Tables 5.22 and 530). Composite samples were also analysed for trace metal concentrations. Observations on general parameters indicate that the sewage generated in Ghatkopar and Bhandup service areas is medium to low strength. The total coliform counts in the sewage from Bhandup and Ghatkopar areas were observed to range between 1 t 3.x 105 counts per 100 ml. The results of trace metal analysis in municipal discharges from Ghatkopar and Bhandup pumping stations ( leading to Bhandup aerated lagoons) are presented in Table 5.30. The results, inspite of Ghatkopar being one of the major industrial area, do not show significantly elevated metal concentrations in sewage. The concentrations for Mn, Zn, Cu are only marginally higher in comparison to other drainage zones. The results further indicate that the municipal discharges do not pose significant AERATED AGOONS 5.58 Table : 5.27 Detergents in Thane creek sediments Sampling station Concentration (pg g wet wt) W C E Summer Transect 1 - 3.03 - Transect 2 1.78 1.89 1.41 Transect 3 1.23 0.00 3.53 Transect 4 - 1.18 - Winter Transect 1 - Transect 2 - 0.4 - Transect 3 0.1 - - Transect 4 0.3 - - W-west, C-centre, E-east ARAWD LAGOONS 5.59 Table : 5.28 Physico-chemical characteristics of sewage (Bhandup pumping station) Time pH Conductvity Chlorides Ammoniacal Soluble COD BOD nitrogen phosphate asN asP hours nhos/ cm mg( L mg L mg/ L mgI L mgI L 08.0 7.4 4030 1380 18.2 1.9 347 200 09.00 7.2 3700 1280 16.8 3.0 445 238 10.00 7.1 3540 1180 12.6 2.6 264 160 11.00 7.1 3670 1260 105 2.0 292 145 12.00 7.1 4000 1440 8.1 1.8 292 143- 13.00 7.1 4260 1500 7.7 1.6 320 128 14.00 7.1 4450 1600 6.7 1.6 236 153 15.00 7.1 4810 1700 63 1.4 236 113 16.00 7.1 3270 1900 63 1.1 222 120 17.00 72 5710 2026 7.0 1.4 320 145 AERAE AGDONS & Table : 5.29 Physico-chemical characteristics of sewage (Ghatkopar pumping station) 'Time pH Conductivity Chlorides Ammoniacal Soluble COD BOD nitrogen phosphate as N as P hours mhost cm mg/ L mgI L mg/ L mg/ L mg/ L 0730 7.1 683 240 21.0 3.1 768 283 060 7.4 707 140 21.7 3.1 912 290 0930 7.2 67C 140 168 3.1 528 270 1030 7.1 740 130 15A 3.1 704 245 1130 7.1 778 160 15.4 3.0 544 210 1230 7.0 1097 150 14.0 3.0 400 210 13.30 6.8 653 290 12.8 2.8 464 200 14.30 7.1 856 150 10.5 2.9 320 223 15.30 7.1 977 200 133 25 384 230 1630 7.0 934 230 14.0 3.1 304 210 1730 7.0 937 200 14.7 3.1 400 200 AlED LAGOONS S6 Table : 530 Heavy metal levels in sewage (Bhandup and Ghatkopar pumping station) Zn CU Ni Mn Cr Cd Pb (mgf L) Summer Shandup 0.14 0.03 BDL 0.44 0.01 BDL 0.05 0.12 0.03 BDL 0.37 0.06 BDL BDL Ghatkopar 0.26 0.09 BDL 0.66 0.05 BDL BDL 0.27 0.06 BDL 0.42 0.06 BDL 0.03 Winter Bhandup 0.11 0.04 0.01 0.40 0.01 0.01 0.13 0.42 0.89 0.08 1.46 0.03 BDL 0.05 Ghatkopar 0.16 0.06 0.03 0.41 0.01 0.01 0.03 0.46 1.14 0.07 1.15 0.07 BDL 0.03 BDL - Below detectable limits AERATED NS SM hazard of metal pollution of receiving waters as these concentrations are not only well below the permissible limits for industrial effluents and sewage discharges into marine and coastal areas (Environment (Protection) Act, 1986) but also are fairly close to the permissible limits for drinking water standards. Sewage samples from Bhandup and Ghatkopar pumping stations were analyzed for detergent content by the Methyl Green method. The detergent contents in sewage on an average were observed to be 1.0 mg/L, for both Bhandup and Ghatkopar. Comparison with the receiving water quality standards for fresh surface water for Alkyl Benzene Sulfonate content of 1.0 mg/L reveals that the detergent contents of the sewage samples just meets this permissible limit. 5.3.10 Solid wastes characterization The operation of preliminary treatment facilities at the aerated lagoons, shall result in the production of screenings and grit wastes. If improperly disposed, these wastes may give rise to foul odour, fly breeding and pollute the near by areas. In addition to attracting flies, poor solid waste disposal practices may also lead to other vermin such as scavenging birds (crows, mynahs), rats, mice and perhaps dogs. Selection of a proper methodology for disposal of screenings and grit is governed by the characteristics of these wastes. The solid wastes generated at the existing facilities were analyzed to obtain data on their organic and inorganic content, moisture, particle size and calorific value,. so as to enable the choice of a suitable management option Screenigs The detailed analysis of samples of screenings collected from Mulund (terminal pumping station for Bhandup drainage zone) and Worli pumping stations for their physico-chemical characteristics are given in Tables A 5.54 and 5.55 (Ref. Marine outfalls Report). Physical analysis indicates that the screenings are not biodegradable and only 15 to 25 per cent of the screenings are compostable. Average moisture content of the waste ranges from 67.8 to 73.7 per cent and C/N ratio varies between 193 to 20.1 per cent. The screenings are therefore not suitable for composting. The average calorific value is found to be 690.0 Kcal /kg. The low calorific values and high moisture contents of the screenings render them unsuitable for incineration. However, these wastes contain' some putrifiable fraction which may decompose and cause odour problems. AOMoon LAGON Screenings should, therefore, be transported as early as possible after collection to disposal site. Observations on heavy metals indicate low concentrations and, therefore, the screenings may be disposed off along with city refuse. Grit Grit consists of the solids which are removed from the grit chambers. At the initial stage grit samples were collected from Lovegrove pumping. station. These samples were analyzed for particle size and basic physico-chemical characteristics. The results are presented in Tables A 5.56 and A 5.57 (Ref. Marine outfalls Report). A few grit samples collected from Love Grove treatment plant were also analyzed for various particle sizes and heavy metal distribution. The detailed results are given in Tables A 5.58 and A 5.59 respectively (Ref. Marine outfalis Report). The data indicate that the organic fraction (loss on ignition) decreases with decrease in particle size. Phosphorous and Potassium were also distributed in a similar way. The C/N ratio, however, varied in reverse order. Heavy metal distribution among the variable size grit particulates was more or less uniform and does not show any variation for the metals ai alyzed. The overall concentrations of heavy metals in grit are well below the levels prescribed for their land application (WPCF, 1989). On observation the physical and physico- chemical properties of screenings from Lovegrove and Mulund pumping stations compare well. Though the characterization of Mulund grit has not been carried out, it is assumed that grit characteristics at Worli could be used for Mulund service area. Presently, most of the solid wastes generated in Bombay are being disposed at locations identified by the MCGB, which have been considered for disposal for screenings and grit. Present estimate from two pumping stations is not more than 1-2 trips of solid wastes generated per day. As this quantity is negligible in comparison to the 5000 tonnes of city refuse generated daily, screenings and grit can be disposed along with it and is not expected to cause any additional impacts. 5.4 Conclusions Continued wastewater discharges from Bhandup and Ghatkopar service area to the inner Thane creek have resulted in significant water quality impairment in this region. The observations on creek water quality indicate that the wastewater discharged into the creek moves back and AENED LAGooNS 5.64 forth with the tidal action and remains trapped within the creek. Due to negligible exchange with the coastal sea, the pollutant concentrations in the creek are entirely governed by the rate of their assimilation within the creek. In inner regions, the creek is shallow and narrow where combined discharges from Bhandup and Ghatkopar overwhelm the available assimilative capacity. As a result, about 10 kilometers long stretch along the west bank of the creek has very poor water quality with low dissolved. oxygen and high BOD levels. During the ebb tides, in these regions dissolved oxygen routinely falls below 2 mg/ L and BOD levels rise upto 7. mg/L. The observations on bacterial quality in the creek also indicate its poor status with frequent occurrences of total coliform concentrations exceeding 10 per 100 ml. The creek sediments also show high concentration of ammoniacal nitrogen depicting organic pollution due to large sewage discharges. Observations on biological indicators present inferences similar to those evidenced by the physico-chemical parameters. The analyses, of sediment samples indicate significant accumulation of heavy metals at the centre of the creek. The concentrations are considerably high especially for Cr and Cu thereby, indicating significant industrial pollution. The levels of trace metals are lower in winter as compared to summer. The sediments and water samples show high detergent concentrations during summer. Due to its remoteness and good vegetation cover, the region does not suffer from air and noise pollution. Air quality analyses at Bhandup and. Ghatkopar lagoon sites indicate that present air quality in term of SPM NO, falls within Indian standards for ambient air quality at both sites The observations on noise levels are also well within the limits prescribed for urban residential. AERAl G LeOONS 5.65 Chapter 6 NUMERICAL MODEL FOR THANE CREEK 6.1 Preamble For scientific assessment of a wastewater management scheme, it is desirable to quantify the impacts of effluent discharges on water quality of the receiving waters. Tidal currents which dilute, disperse and advect the effluent, play the most prominent role in governing the pollutant levels in the coastal environment. Simulation of ambient coastal currents in relation to the tidal variations, bathymetry and bed characteristics, therefore, is an integral part of water quality simulation. The fate of water quality constituents, however, also depends upon the natural biochemical and physical processes. Numerical models which provide necessary framework to simulate the hydrodynamic features along with the simpler assimilative processes in. coastal environment, therefore, have become a popular choice for analysis of water quality impacts of coastal water quality management schemes. As water quality impacts on Thane creek are the most important considerations for assessing the proposed project, the scope of this chapter - has been confined to detail the numerical model used for water quality simulation in the creek. The model description includes bathymetric features and tidal variations in the creek, and also details the results of calibration of the numerical model against the observed water quality and hydrodynamic features. 62 Model selection In a wide range of flow and pollutant transport model studies, the hydraulic basin can be assumed to be well mixed vertically and the hydrodynamic model can be reduced to a two-dimensional model of the depth integrated type. For studies where this assumption can be justified, including pollutant transport studies in non-stratified coastal waters, the depth integrated form- of three-dimensional equation of motion is used. With the time varying water elevation and velocity fields being obtained from the numerical solution of two dimensional depth integrated equations of motion, a range of water quality parameter distributions can be solved for by adding the general form of the advective-diffusion equation to the corresponding hydrodynamic model. In the present application, the effluents from Bhandup and Ghatkopar aerated lagoons are proposed to be discharged in Thane creek. With the tidal action, the discharges could advect to the harbour and coastal regions in the south and the adjacent 1assein creek in the north which are connected AEUMM LAOONS 6.1 through Thane creek (Figure 2.1). As the first step towards model selection, therefore, data on creek bathymetry, tidal elevations, tidal currents, and spatial extent of Thane creek and the adjacent coastal regions were collected. The data was then evaluated to decide the extent of modelling domain, model resolution and suitability of use of depth integrated form for the present application. A scaled map of the creek with the salient bathymetric features and locations of the proposed effluent discharge points is presented in Figure 6.1. The maximum tidal range in the creek is of the order of 5 meters and the associated maximum current speeds range between 12 -1.5 meters per second. It is further observed from Figure 6.1, that the discharge points from the proposed aerated lagoons are in the sidearms of the creek. The present wastewater discharges from Bhandup and Ghatkopar drainage zones also reach the creek through the respective sidearms. From the bathymetric information on the creek, it was observed that even for the maximum tidal height of 5 meters during the highest spring tides, water depth near Bhandup effluent discharge point did not exceed 7 meters. Whereas maximum depth near Ghatkopar effluent discharge point was approximately 7 meters near the westward region of main channel and about 9 meters in its center. These depths are negligible in comparison to the spring tide creek width of about 3 kilometers and creek length of approximately 30 kilometers between the harbour region towards south and Bassein creek towards north ( Figure 2.1). Based on these observations, it was considered appropriate to assume that soon after their discharge the effluents will achieve vertical homogeneity in the creek The hydrodynamic and water quality variations under tidal forcing in Thane creek, were therefore, simulated through a 2-dimensional numerical model. Acronymed DIVAST (Depth Integrated Velocity and Solute Transport), the model was originally developed by Falconer* and uses finite difference schemes to solve the governing equations for fluid flow and solute transport in2-dimensional form. The model operates by defining the bathymetry of the region of interest over a uniform rectangular grid which divides the water body into cells of uniform area. The tidal forcing at the open boundaries is specified by defining the water elevations and/or flows obtained through field observations at relevant locations. Using the principles of continuity of * FaIome, R.A. (1984) A mathematical model study of the nushing characteristics of a shallow tidal bay. Prac. Ist. CWH EnS., Part 2, Val. 77, 3H-3. Falconer, R.A. (1986) A water quality simulation study of natural harbour. 1. Watewy ort, Coast Ocean Engineering, ASCE, Vol. 11Z 234-259 ARAID LAGOONS 62 Figum: 6.1 Bathymetric features and wastewater discharge location in Thane creek Depth s: r. 3 m liiir BhandupB // IVI 4/ AEWWW LMBN mass and conservation of momentum, the water level, flow and solute concentration in each cell are computed as they vary throughout the tidal cycle. While simulating pollutant concentration in a tidally influenced water body, it is generally necessary to consider a large modeling domain so that the pollutants' concentrations near the open boundaries reduce to the background levels. Such considerations for Thane creek would have required that the model covered a large portion of the narrow channel on the north connecting the Thane and Bassein creeks. This would have increased the size of the model and necessitated coverage of regions with poorly defined bathymetry. Similarly, it would have been necessary to extend the southward model boundary to include portions of harbour region where restrictions due to vessel traffic regulations would have made it difficult to obtain the current observations. To circumvent the above difficulty, a modified version of the numerical model providing flexibility of defining solute concentration for tidal inflow at open boundaries as a function of outgoing solute concentration at the time of tide reversal and background concentration was used. For instance, the incoming solute concentration for the neap tide was considered equal to the outgoing concentration upto one hour after the tide reversal and was linearly allowed to achieve the background levels in next one and a half hour period. In view of stronger tidal currents and consequent higher dispersion and dilution of pollutants, the respective time intervals for spring tide were lowered to half an hour and one hour. These values were selected based on insitu observations on water quality variations with tide at the southward boundary of modelled region of Thane creek. 6.3 Thane creek model Bathymetry The domain for Thane creek model covered the entire creek including the main creek arms over a 20 kilometer stretch beginning from the Bombay- Thane rail bridge (Figure 6.2). The southward boundary of the model extended upto Trombay, about 7 kilometers south of Bombay-Vashi rail bridge. The south boundary, thus, was located just north of dredged channel maintained in the harbour region to facilitate movement of vessels. The bed topography of the modelled region was obtained from the hydrographic charts prepared by the concerned departments of Government of Maharashtra in 1990. The charts had a resolution of 25 meters by 10o meters. The depth at sides of 200 meters by 200 meters grid used for model AEUMED LAGOONS Figure : 6.2 North and south boundaries for Thane creek model boundaryMm lig. Bhandup E0 km Ghatkopar AgaG I ,de T I,3 computations were arrived at by averaging the depths provided in hydrographic charts. It was further observed from creek bathymetry that the creek bed sloped gradually towards the harbour and had a minor depression in the southward region near Vashi bridge (Figure 6.1). Tidal elevations The tidal variations in water elevation and currents in the creek were simulated by defining the tidal elevations at the south and north boundaries which were the only open boundaries of the model. The elevations were obtained by deploying recording type tide gauges at the respective boundaries for a period of 8 days and covered pre- and post-tidal variations for the neap tide of February 6, 1994. A set of limited tidal elevations was obtained at Vashi bridge for model calibration. The tidal conditions used to simulate about 66 hours long simulation at south and north boundaries of the model are presented in Figure 6.3. The south boundary was approximately 7 kilometers south of Ghatkopar discharge near Trombay, whereas the north boundary was about 6 kilometers north of Bhandup discharge at Kalva bridge. The two boundaries were 20 kilometers apart and the tidal elevations at these boundaries differ significantly in phase, the high and low waters at Trombay preceding those at Kalva bridge by about 60-90 minutes. Tidal curnts The Thane creek model was tuned to simulate the hydrodynamic conditions in the creek by comparing the observed and predicted tidal currents at two positions in the creek. The current observations were made on February 6 at about 4 kilometers north and 1 kilometer south of Vashi bridge in the main creek channeL These locations (position 1 and 2) represented the inner and outer creek regions, respectively ( Figure 6.4). These observations were carried out by placing the boats at the desired locations and lowering the current meters into the water over a complete tidal cycle. The observations commenced at the high tide slack and continued upto subsequent high tide. The water level on the day of current observation fell by 2.5 meters during the ebb tide and rose by 2.8 meters during the subsequent flood tide. While simulating the flood and ebb tides, only those cells where water depth exceeded 30 centimeters were used for computing water elevations and tidal currents. The simulation was carried out for a bed roughness height of 20 millimeters. ABOMD LACOONS Figure : 6.3 Tidal elevations at open boundaries of Thane creek model ELEVATION BOUNDARIES FOR THANE MODEL VARIATION IN WATER ELEVATION WITH NEAP TIDE 5.0 03. 1- 1.0 20 - 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 TIME IN HOURS FROM HIGHTIDE SLACK SOUTH BOUNDARY AT TROMBAY NORTH BOUNDARY AT KALVA BRIDGE AEAIEDLAGOONS 6.7 Figurm : 6.4 Locations for current and water quality observations i I I |ia .a %alfa bridge SObservation Locat ions 11 6G ko '4i* 49g 03oet The predicted and observed tidal currents in the inner and Outer region of modelling domain for neap tide variations of February 6, 1994, are presented in Figures 6.5 and 6.6, respectively. The observations indicated a fair agreement in observed and predicted speed of tidal currents at both the locations in the creek. The flood currents were observed to be slightly stronger than the ebb currents, perhaps due to higher variation in elevation during the flood tide on February 6. The maximum currents observed were in the range of 0.6 meters/second. A minor phase difference in observed and predicted currents was observed in the outer region. The variation, however, was not expected to significantly affect simulation of advection in the creek. 6A Model calibration of water quality parameters Depth integrated advection-diffusion model for water quality simulations used the results of hydrodynamic model for simulating creek water quality in terms of Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD) and ammoniacal-N. The model considered that carbonaceous organic matter and ammoriacal-N removal was governed by the first order kinetics. The difference between the oxygen transfer due to surface reaeration and oxygen uptake due to Sediment Oxygen Demand (SOD); oxidation of carbonaceous organic matter and ammoniacal-N governed the net dissolved oxygen levels in the creek. While simulating polluted creek conditions, the modelled dissolved oxygen levels were not allowed to drop below 1 mg/L. A flag was used to indicate the violation of aerobic kinetics of water quality transformation. For calibration of water quality component of the model, water quality observations were carried out at two locations in the creek on February 6, 1994. The sampling locations, designated as Location 1 and 2 are depicted in Figure 6.4 with respect to the model boundaries and discharge. locations. Water quality observations were commenced soon after the high tide slack and samples were collected every one anda half hour until the low tide slack. The model was tuned by varying the model coefficient for BOD removal rate. The coefficients for SOD and ammoniacal-N removal were selected based on the published values in literature for coastal waters receiving raw municipal wastewaters and were kept at 5 g/m:2/day and 0.4 per day, respectively. The reaeration coefficient was adjusted in the model internally for water depths and velocities based on Owen's relation. The results of modi calibration for DO and BOD are presented in Tables 6.1 and 62 for locations 1 and 2, respectively. For different times of observations, the tables provide the observed, simulated concentrations of dissolved oxygen and BOD, and also the distance of nearest position from the sampling locations where model results matched well with the observations. A8LED LAGOONS Figurm : 6.5 . Hydrodynamic calibration of Thane creek model (inner region) VARIATION IN TIDAL CURRENTS DURING NEAP TIDE INNER CREEK REGION 0.8 0.7 f 2 0.6 Iz 05 ~0.4 - *02 0.1- 0 - 11111 ...-- - 2.5 3.5 45 5,5 65 7.5 8.5 9.5 105 115 12.5 13.5 14.5 TIME IN HOURS AFTER LOW TIDE SLACK Simulated Profile at Location I * Observed profile at Location I AERATED LAOONS 6.10 Figre :6.6 Hydrodynamic calibration of Thane creek model (outer region) VARIATION IN TIDAL CURRENTS DURING NEAP TIDE OUTER CREEK REGION 0.8- OJ--7 - - --a 0.7 -- - - O*" 0.5 - 0.4, 0 2.5 3.S 45 5S5 635 7.5 &.5 9S10.5 11IS 1235 13.S 14.S 'liME IN HOURS AFTER LOW TIDE SLACK -Simulated Profile at Location 2 *observed profile, at Location 21 AEM LAGOONS 6.11 T hI to : 6.1 Calibration results for dissolved oxygen Time of Observed Simulated . Nearest location where simulated Matched observation DO DO value matches observed value simulated (hours) (mgI L (mg/ U- value Distance from Direction with (g U point of respect to point observation of observation (M) Inner Thane creek 9.00 3.0 1.5 800 East 3.0 11.00 2.3 2.0 200 East 2.5 12.30 2.5 1.6 200 East 2.6 14.00 1.5 2.7 400 West 2.0 Outer Thane creek 9.00 4.9 5.6 400 West 5.1 11.00 5.2 3.6 1000 South 5.2 12.30 4.5 2.7 800 East 4.5 14.00 2.0 2.0 Nil 2.0 AERAWE UW-OO 6.12 Table :62 Calibration results for biochemical oxygen demand Time of Observed Simulated Nearest location where simulated Matched observation DOD DOD value matches observed value simulated (hours) (mg/ L) (mgl L value Distance from Direction with (mgl L) point of respect to point observation of observation (a') Inner Thane creek 9.00 2.7 1.8 400 West 2.6 11.00 2.4 1.6 400 North 23 1230 1:9 4.7 400 South 2.2 14.00 2.6 4.0 200 East 2.8' Outer Thane creek 9.00 1.6 1.2 - 1.2 11.00 2.9 1.0 400 East 2.7 12.30 3.2 0.9 600 West 3.5 14.00 5.2 1.2 700 North-West 5.1 * None of the simulated values were above 1.2 mg/L in outer creek region. AERAED IAGOONS 6.13 When viewed with Figures 6.7 and 6.8, depicting simulated water quality distribution in the creek, these values dearly indicate the degree of precision achieved by the model in simulating creek water quality for existing wastewater discharges. A comparison of simulated and predicted water quality at the inner creek regions indicated that simulated results matched the observations within 400 meters of the sampling location, except for dissolved oxygen at 9 hours when match was obtained at 800 meters. For the outer region, the model results were in good agreement with all the observations within 1000 meters of the monitoring locations. On many occasions, however, a good match was obtained within 600 meters of the sampling location (Figures 6.7 and 6.8). Considering the extent of modelling domain and advection of pollutants with tidal currents, calibration results were considered satisfactory for model. application for developing water quality scenarios in the creek. 6.5 Conclusions In Thane creek, water depths are much smaller in comparison to horizontal dimensions of the creek. The hydrodynamic and water quality features of the creek were, therefore, simulated through numerical model using depth integrated form of equation of motions along with the advective-diffusion equation. The model was calibrated for hydrodynamic and water quality features for neap tide conditions which are found to be critical for creek water quality. Simulated tidal currents and DO and BOD levels at two critical locations in the creek were compared with those observed over a complete tidal C%cle and were found 'o be in reasonable agreement. AEM LAGOONS .4 Chapter 7 PREDICTION OF IMPACTS 7.1 Preamble The major activities associated with the construction of aerated lagoons at Bhandup and Ghatkopar are site clearance, earth work and material transfer. The site clearance involves removal of mangroves from parts of the sites, filling and leveling operations and transfer of unusable material for disposal. The prominent impacts of these activities are rise in ambient noise levels and impairment of air quality near the construction site. During the operation phase, being a pollution abatement project, the proposed aerated lagoons are expected to improve the water quality in Thane creek. Higher dissolved oxygen level in creek waters and cleansing of the bed sediments through natural biological processes are the primary impacts expected after the reduction of wastewater loads into the creek. Based on the extent of improvement in creek water quality, the most important secondary impacts would be increased yield of marine biota in the creek. The most significant associated air quality impact would be elimination of malodorous conditions common around the polluted creek during the low tides, at present Jointly, these improvements shall considerably enhance the aesthetic value of the region and may open up the possibility of developing Thane creek as recreational area for water sports at a later date. Some of the important processes which govern the primary enviromnental impacts of construction and operation of aerated lagoons can be mathematically modelled. The associated impacts can, therefore, be predicted with reasonable confidence. Mathematical models for simulation of these processes along with the method of their calibration and verification have been presented in the previous chapter. For estimating the efficacy of aerated lagoons in restoring the creek ecosystem, a qualitative approach was adopted. Accordiigly, observations on ecological parameters were carried out in the areas which had water quality similar to the futuie projections for Thane creek after implementation of wastewater treatment scheme. 7.2 Construction phase impacts 7.2.1 Impacts of mangroves reclamation Mangroves protect the coastal regions by moderating the strength of tidal currents and provide spawning grounds for a number of coastal species. Mangroves, thus play a vital role in maintaining ecological stability of AUMED LAGONS creeks and coastal regions. Recent satellite imageries indicate that about 750 hectares of inter tidal region in upper Thane creek support rich growth of mangrove forests comprising Avicennia, Salvadora and Ceriops sps., as the dominant species. It is estimated that approximately 40 hectares of this cover will be lost due to reclamation of land for construction of the proposed three cell aerated. lagoons. A quantitative estimate of the impacts of loss of about 5 per cent of the mangrove cover in the region on creek ecosystem is not possible. The mangroves in this region represent one of the best such surviving areas along Bombay's coast which once supported them extensively. Any further loss of these areas is evidently undesirable and should be compensated by replanting equivalent areas. Alternatively, the remaining mangrove areas should be protected against future encroachment and illegal felling so that their growth offsets the loss due to proposed- reclamation. 7.2.2 Noise impacts For predicting the increase in noise levels at sensitive locations near the aerated lagoon sites during construction, data on noise characteristics and operation pattern of construction machine units during different stages of construction were collected (Table 7.1). A site survey to measure ambient noise levels at the lagoon sites was conducted. It was observed that the nearest residential locations are about 1 to 1.5 kilometers away from the site. A direct impact of construction activities at lagoon site on the noise levels at these locations could not be ascertained as no significant construction activity has been in progress for about one year at these sites. The noise characteristics data of construction machinery and observations during their operation indicated that noise levels could be upto 96 dBA near the generator sets. For noise predictions it was assumed that all machine units were in simultaneous operation and were randomly located within a 50m by 50m area at the construction site. The predictions were made using the model for hemispherical sound wave propagation. The model results in terms of isopleths of sound pressure level in dBA (A-weighted decibels) are presented in Figures 7.1 and 7.2 for Bhandup and Ghatkopar, respectively. The nearest residential areas at Bhandup and Ghatkopar are more than 1 kilometer away from the aerated lagoon sites. The results of noise modelling indicate that the noise due to construction is expected to drop to approximately 40 dBA at the receptor location in these areas and thus AMMWPOMN 7.2 Table: 7.1 Noise levels generated by different machineries used in construction Machines No. in Noise level in Operation dBA 1. Cement concrete mixer 1 89 2. Crane with clamshell bucket 1 88 3. Generator sets 1 96 4. Trucks 2 85 AAn LAGOONS 7.3 Fignsm: 7.1 Predicted noise levels at Bhandup lagoon site NO DEVELOPMENT ZONE CREEK 7A Figum : 7.2 Predicted noise levels at Ghatkopar lagoon site AEn?ED LAGOO7.5 would be fully attenuated to the background levels. The construction activities associated with the aerated lagoons, therefore, are not expected to give rise to any adverse noise related impacts. 7.22.1 Noise impacts on construction workers Equivalent sound level averaged over 8 hours, Leq (8 hrs), is used to describe exposure of noise in work places. The damage risk criteria for hearing, as enforced by OSHA (Occupational Safety and Health Administration) and other organizations to reduce hearing loss, stipulates that noise levels upto 90 dBA are acceptable for eight hours exposure (Leq (8 hr)) per day. Whereas ACGIH (American Conference of Government Industrial Hygienists) proposed an Leq (8 hr) limit of 85 dBA. Exposure to impulses or impact noise should not exceed 140 dBA (Peak acoustic pressure). Exposure to 10,000 impulses of 120 dBA are permissible per day. The Director General of Mines Safety in his circular No.DG(Tech)/18 of 1975 has prescribed the noise level in mining occupations (TLV) for workers, in an 8 hour shift period with unprotected ear as 90 dBA or less. Although there are some noise sources which are likely to exceed the limit, they do not produce sound levels above 90 dBA for more than 2-5 hours per shift reducing Leq (8 hr) to be well within the limits. Heavy machinery drivers and personnel working very near to these machineries are likely to get exposed to higher levels than the prescribed limits if the exposure is continuous and should therefore be provided with protective gear. 7.2.3 Air quality impacts The concentration levels of air borne pollutants such as NO, SO. and SPM are well within the prescribed air quality standards. However, the values of SPM levels may go up on commencement of construction activities and' may require mitigatory measures for its control. 7.2.4 Water quality impacts The construction of aerated lagoons would not have any major impact on the creek water quality because the transient discharges, if any, during the construction phase will be insignificant in comparison to the existing pollution load on the creek Similarly as the area covered by the lagoons is less than even 2 per -cent of the intertidal zone region of the creek, construction of aerated lagoons would not have an adverse effect such as ARAED LAGOONS 7A flooding of regions adjoining the lagoons. Care should, however, be taken not to close any natural drainage channel while reclaiming the land for the lagoons with out providing adequate diversion for run-off. 7.3 Operation phase impacts 7.3.1 Air quality impacts Findings on creek water quality impacts do not indicate a significant improvement after the implementation of the proposed single cell aerated lagoons (section 7.3.2). Anaerobic conditions in the creek giving rise to. malodorous conditions in the surrounding areas, therefore, will persist. Also, there is a possibility of significant I-kS emissions from the lagoons in the event of their malfunctioning, especially that of aerators. The probable air quality impacts for such incidences have been quantified by modelling ground level concentrations of EiS around the lagoon sites. A multi-source Gaussian plume model for Point, Area and Tine sources (PAL) has been used for air quality simulation. This model is part of the family of air quality models available under the UNAMAP package released by US Environmental Protection Agency, U.S.A. The I-4S emissions from aerated lagoon sites have been considered as area sources in this model and the effective height of emissions at both Bhandup and Ghatkopar are considered to be at ground level. The hourly ground level concentrations as well as 8 hourly averages of I-LS concentrations have been predicted for a typical winter day. A total of 441 receptors separated by 0.5 ki distance, in a square grid of 10 Lu x 10 km, have been considered for this purpose. The simulations haive been carried out by assuming the lagoons as an area source of HS emissions at the center of the grid. Surface meteorological data recorded at Bombay during 1992 have been used for this purpose. The emissions at aerated lagoons have been evaluated through an empirical.formula reported in literature*. The source details of Bhandup and Ghatkopar lagoons are given in Table 7.2. Air quality simulation results show that H25 impact around the aerated lagoon will be maximum in the morning hours, in south through west directions from the lagoon sites during winter. Considerable impact could be observed upto 2 kilometers distance from the project sites under stable conditions. The predicted 8 hourly average concentrations of H.S varied between 193 gg/n at 0.5 kilometers to 33 tig/rO at 2.0 kilometers distance around Ghatkopar site and from 132 g/me at 0.5 kilometers to 24 itg/m at 2.0 kilometers distance at Bhandup site in the south from the lagoons. Wwmuwwr tratnnt for polltio control l y Soli. Arceivali (19M). Tata M4raw Hill Nbli&hing Compiny Limnid. AEATED LAGOONS 7.7 Table : 7.2 H2S Emissions at aerated lagoons of Bombay sewage disposal project Aerated Design Total Emission Areia Source SW corner coordinates lagoon capacity Emission Rate East North E-W N-S (1/ day) (gf day) (gI sed m2) (Km) (Km) (Km) (Km) Bhandup 164.0x106 4.990x105 4.637x10-5 4.880 4.741 0.240 0.519 Ghatkopar 363.x106 1.164x106 1.326x10-6 4.734 4.905 0.532 0.191 b8 The minimurm levels which a human being can detect according to some surveys are in the range of 60-90 pg/mnr. The predicted values thus indicate that malfunctioning of the aeration mechanism in lagoons could create serious odour nuisance near the Bhandup lagoons within about 1.0 kilometer radius. For Ghatkopar lagoons, due to their larger capacity, the impacts could be discernible upto as far as 1.5 kilometers from the lagoon sites. 7.3.2 Water quality impacts 73.2.1 Proposed treatment Direct municipal discharges into Thane creek have caused widespread degradation of water quality especially in the inner creek region. Approximately 400 mid of municipal w.. awater is discharged into inner Thane creek from Bhandup and Ghatkopar service areas. Poor creek water quality in this region indicates that the pollution load carried by these discharges exceeds the assimilative capacity of the inner creek especially during the neap tides. Wastewater treatment as will be initiated by the proposed project, therefore, is essential for upgrading the creek environment. The planned treatment level at Bhandup and Ghatkopar aerated lagoons along with the present and projected flows for the year 2005 are presented in Table 73. The present design capacities of Bhandup and Ghatkopar lagoons are 180 and 385 mid respectively. In view of significantly larger estimated flows (280 mid) in Bhandup service area for the year 2005, it will be necessary to redesign the Bhandup lagoons for the new flows. The projected wastewater flows at Ghatkopar by the year 2005 ( 235 mid after diversion of 50 mid for industrial use), however, are considerably less than the design flows. Ghatkopar lagoons, therefore, would be underloaded in the year 26005 by about 40 per cent and are expected to achieve effluent BOD of 90 mg/L and 35 mg/L for single and three cell configurations, respectively. These lagoons would not contribute to any significant reduction in ammoniacal nitrogen load in the wastewater. Table 7.3 also summarises the present and expected carbonaceous BOD load in the year 2005 on the creek with single cell as well as three cell lagoons. It is seen that single cell lagoons will achieve 45 per cent reduction in the present carbonaceous BOD load on the creek and three cell lagoons will reduce it by 80 per cent. The following sections of the chapter present a comprehensive analysis of water quality impacts of discharges from the proposed single and three AEAW AOONS 7.9 Table: 7.3 Present and projected BOD loads in Thane creek (Municipal discharges) Treatment Service Wastewated Wastewated Pollution load option area effluent flow effluent BOD (Kg BOD/ day) (mild) level (mg/ L) Present flows No treatment Bhandup 150 225 33,750 Ghatkopar 250 225 56,250 Total 90,000 Projected flows for the year 2005 Single cell Bhandup 280 100 28,000 lagoons (as Ghatkopar 235 90 21,150 proposed in first phase Total 49,150 Three cell Bhandup 280 35 9,800 lagoons Ghalkpiar 235' 35 8,225 Total 18,025 * The expected flow is 285 mid from which 50 mId will be used in neighbouring industries. cell lagoons for the projected wastewater flows in the year 2005. With a view to developed a long term wastewater management strategy, various options for wastewater treatment and disposal were also examined for the projected flows for the year 2015. The options considered, however, assume that wastewater discharge locations for future options remain within the Bhandup-Ghatkopar stretch of the creek. This analysis, thus, does not examine the possible advantages of transporting wastewater to regions outside the modelled area. 7.3.22 Analysis of alternatives The proposed level of wastewater treatment effort at Bhandup and Ghatkopar was selected with the objective to achieve effluent standards of 100 mg/L both for BOD and suspended solids. The effluent standards, as a condition for discharge of treated wastewater into Thane creek, were specified by Maharashtra Pollution Control Board. Unfortunately, constraints on creek assimilative capacity due to weak tidal flushing during the neap tides were not taken into account while specifying the effluent standards. It is apparent from the discussion in section 73.2.1 that due to considerable quantum of wastewater flows by the year 2005, only marginal improvement in creek water quality is expected by meeting the prescibed effluent standards. The management alternatives were, therefore, evaluated with respect to the objective of achieving minimal necessary improvement in Thane creek water quality to restore its ecological role in sustaining marine life. A management goal to ensure a minimum dissolved oxygen level of 2 mg/L in the creek was selected. Water quality scenarios for competing management options were developed using a depth integrated hydrodynamic and water quality model DIVAST, calibrated for Thane creek through field surveys. Following section describes the results of such analyses as also the probable impact on water quality if the present creek discharges are allowed to be continued. 73.2.3 No action scenario The municipal wastewater discharges from Bhandup and Ghatkopar service areas are presently estimated at 400 mid and are expected to rise to 520 mid by the year 2005. A further steep rise in wastewater generation in these service areas is expected due to planned augmentation of water AER Aoons 7.11 supply. By 2015, wastewater generation in these areas is expected to reach 1000 mid. Due to the natural slopes, the entire wastewater ultimately will drain into the inner Thane creek giving rise to approximately a two and a half fold increase in the pollution load. If no wastewater treatment facilities are implemented, creek water quality which already exhibits widespread impairment during the low tides, would further be considerably degraded. Under such scenario the entire inner Thane creek region is expected to be devoid of dissolved oxygen for considerable portions of the tidal cycles. 7.32.4 Augmentation of wastewater management effort For examining the impact of different wastewater management options on creek water quality, quantitative estimates were developed through computer simulation. The solute transport model DIVAST which was earlier calibrated for both neap and spring tide conditions, was used for . water quality predictions. While simulating water quality, the reaeration rate coefficient was internally calculated by Owen's relation. The BOD decay coefficient was allowed to vary from 0.5 to 03 /day and sediment oxygen demand (SOD) from 4 to 3 g/mOday, subject to the degree of wastewater treatment effort For instance, BOD decay coefficient of 0.5 per day along with SOD of 4 g/mV/day was used for single cell aerated lagoon effluents. The values were gradually decreased to 0.3 per day for BOD decay coefficient and 3 g/mF/day for SOD as the degree of treatment was raised to secondary level. Removal rate for ammoniacal-N was considered at 0.4/per day for all simulations. In a tidally influenced water body, water quality is intimately related with the tidal strength which undergoes a fortnightly cyclic change. Water quality simulations for a complete neap-spring-neap tidal cycle were impractical due to greater computer time requirement. The management alternatives were, therefore, developed by running the simulation for about 72 hours for five and a half tidal cycles centered about the neap tide of February 21, 1994. During this period, the minimum rise in water elevation from low to high tide recorded was 0.65 meters which was the sixth lowest for the entire year. The simulations were started at the high water slack period assuming clean water quality conditions in the creek. 'bese conditions were defined by DOD and DO levels of 3 mg/L and 4 mg/L, respectively. Further, as the creek considerably widens near the Vashi bridge, where the Ghatkopar discharges reach the creek, considerable lateral water quality differences occur in this region. For instance, a patch of low dissolved oxygen (less AERM IAGOONS 7.12 than 1 mg/L) can occur near the discharge points whereas dissolved oxygen near the opposite bank could be above 4 mg/L. The results of water quality simulations for different management options were, therefore, interpreted by considering the spatial extent of attainable dissolved oxygen levels for respective options. If a management option was found unsuitable due to occurrence of wide spread dissolved oxygen depletion, the management effort was raised by increasing degree of treatment or shifting the. discharge location near the creek center. Attainment of dissolved oxygen above 2 mg/L during the entire tidal cycle, was defined as the water quality management objective. Further, while evaluating the management options, the treatment efficiencies were so selected as to be compatible with the proposed facilities. The augmentations in treatment effort, to the extent possible, were considered as phased development to the first phase facilities (single cell lagoons). The options for treatment effort, however, were defined in .terms of treatment efficiencies rather than treatment flow sheets to allow wider choice of tre!itment options and their combinations. As the first management alternative, four streams of single cell aerated lagoons both at Bhandup and Ghatkopar were considered for flows for the year 2005. The effluent BOD and NH3-N levels under this option were taken to be 100 mg/L and 15 mg/L for Bhandup and 90 mg/L and 15 mg/L for Ghatkopar lagoons. The simulations were carried out for summer (water temperature 30C) which constitute the critical conditions for creek water quality due to higher BOD decay rates and lower dissolved oxygen saturation levels. The predicted creek dissolved oxygen for the treatment option are summarised in Table (7.4 [item 1]) and Figures. 73 and 7.4. The simulations were carried out for five and a half tidal cycles and the interpretations were based on the final tidal cycle which corresponded with minimum tidal variations between the high and low tides. The simulation results indicate widespread depletion of dissolved oxygen in inner creek regions. For instance, at the time of high tide, dissolved oxygen in approximately 50 per cent of the upper creek area north of Vashi bridge, is expected to fall below 2.5 mg/L. The area with dissolved oxygen below 2 mg/L at this stage is expected to be about 4.2 kilometers long and 1.3 kilometers wide near Ghatkopar creeklet Another low oxygen patch about one-fourth the size of that expected near Ghatkopar is likely to develop near Bhandup discharge location. ABAW GOONS 7.13 Table : 7.4 Water quality distribution in Thane creek for various management scenarios Management Management Effort Simulation Effluent characteristics Probable impacts on creek Scenarios conditions and disposal scheme water quality 1 Single cell aerated lagoons Summer BOD-100 mg/L, DO Nil, Widespread occurrences of water both at Bhandup Neap tide NH3 -N-15 mg/L, quality state with DO below 2 mg/L and Ghatkopar 2005 flows during the entire tidal cycle. 2 Single cell aerated lagoons Summer BOD-100 mg/L, DO Nil, Widespread occurrences of water both at Bhandup Neap tide NH3 -N-15 mg/L, quality state with DO below 2 mg/L and Ghatkopar 2005 flows, 50 mid exceeding I km length and 05 in diverted at Ghatkapar during the entire tidal cycle. for industrial use. 3 Three cell aerated lagoons Summer BOD-35 mg/L, DO Nil, Minor occurrences of DO marginally below both at Bhandup Neap tide NH3 -N-15 mg/L, 2 mg/L. The affected region not and Ghatkopar 2005 flows, 50 mid exceeding 2.2 kilometers in length and diverted at Ghatkopar 0.8 kilometers in width at any for Industrial use. time of the tidal cycle. Table : 7.4 (Contd..) Management Management Effort Simulation Effluent characteristics Probable impacts on creek Scenarios conditions and disposal scheme water quality 4 High efficiency secondary Summer Glatkopar Marginal improvement in DO treatment at Ghatkopar Neap tide 8OD-15 mg/L, (less than 0.5 mg/L) and three cell aerated DO-2 mg/L as compared to scenario 3. lagoons at Bhandup NH3-N-15 mg/L, Bhandup BOD-SO mg/L, DO-Nil, NH3-N 15 mg/L, 2005 flows, 50 mid diverted at Ghatkopar for industrial use. 5 Three cell aerated lagoons Summer Ghatkopar & Bhandsp Minor occurrences of DO marginally below both at 8handup Neap tide BOD-35 mg/I, DO Nil, 2 mg/L, near Bhandup and Ghatkopar. and Ghatkopar NH3 -N-IS mg/L, The affected region not exceeding 2005 flows, 50 mid 2.2 kilometers in length and Nitrification followed by diverted at Ghatkopar 0.8 kilometers in width at ay secondary treatment for for industrial use. time of the tidal cycle. discharges near Vikhroli Near Vi&iaroni DO always above 2.5 mg/i BOD-3 mg/L, near Vikh2m li. DO-2 mg/I, NH3-N-15 mg/L, Wastewater flow 520 mid During the low tide, the low dissolved oxygen region shifts southwards with the ebb currents and is expected to occupy about 60 per cent of the creek width, south of Ghatkopar creeklet. The dissolved oxygen levels in a region of 4 kilometers in length and 1.1 kilometers in width near Vashi bridge are expected to be below 2 mg/L. The concurrent BOD levels near the discharge point are expected to be 10-12 mg/L with occurrence of BOD above 4 mg/L in large portions of inner creek Another set of simulations, for single cell lagoons at Bhandup and Ghatkopar, were carried out by reducing the wastewater flow at Ghatkopar by 50 mid, the expected demand for raw sewage for the industrial use in Ghatkopar service area. The expected water quality scenario for this management alternative is presented in Figures 7.5 and 7.6 and the observations on creek DO are summarised in Table 7.4(item 2). A comparison of Figures 73 and 7.4 with Figures 7.5 and 7.6, respectively, reveals only a marginal improvement in creek water quality for the .reduced wastewater flow at Ghatkopar. None of these options achieves the minimal desired water quality for the year 2005 flows. It is evident from this analysis that implementation of proposed first phase facilities, although would arrest the growing impairment of creek water quality, would not result in its significant improvement, even up to the year 2005. As the next management option, treatment facilities comprising four streams of three cell aerated lagoons both at Bhandup and Ghatkopar were considered. The water quality scenarios were developed for projected wastewater flows for the year 2005 after accounting for sewage demand at Ghatkopar. The effluent BOD and ammoniacal-N levels for this option were assumed to be 35 mg/L and 15 mg/L. Simulation results for 2005 flows indicate considerable improvement in creek water quality with respect to single cell aerated lagoons (Table 7.4 (item 3)). The results indicate that for this option, during the high tide only small region of dissolved oxygen below 2 mg/L develops in the creek. The extent of the region with low oxygen remains below 1.5 kilometers in length and 500 meters in width (Figure 7.7 & 7.8). Further only approximately one-fourth of the creek region north of Vashi bridge exhibits DO below 2.5 mg/L. At low tide, the low dissolved oxygen region shifts to south and centers at about 2 kilometers south of Vashi bridge. The spatial extent of this region is about 2.2 kilometers in length and 800 meters in width. BOD levels under this management option are above 4 mg/L in stretches of 1 kilometer and 500 meters along the creek's west bank near Bhandup and Ghatkopar creeklets, respectively. ANOED lAGOONS 7.17 Further water quality scenarios for 2005 flows were also developed to evaluate the efficacy of enhanced secondary treatment options, such as the activated sludge process at Ghatkopar. For these simulations the effluent BOD of 15 mg/L and ammoniacal-N of 15 mg/L were assumed. Simulation results indicated a marginal improvement of 0.3 mg/L in creek dissolved oxygen over three cell aerated lagoons option (Table 7.4 (item 4)). Shifting the effluent discharge location to the center of the creek also does not yield any significant improvement in creek DO. It was further observed that for 2005 flows nitrification was necessary to raise creek DO above 2.5 mg/L at this location. When extended to 2015 flows, the simulations indicated that it was not feasible to discharge effluents beyond the flows projected for the year 2005 at Bhandup and Ghatkopar, even after nitrification of effluents. The need for an additional discharge location when the wastewater flows exceed 2005 projections, is thus apparent Simulations were, therefore, performed with different discharge locations for additional flows. The results revealed that the creek in its inner region near Vikhroli could assimilate discharge of 260 mid after secondary treatment (effluent BOD 15 mg/L) in addition to the 280 mId and 235 mid to be discharged at Bhandup and Ghatkopar, respectively. The projected combined wastewater flows in Bhandup and Ghatkopar service areas for 2015, however, exceed the 2005 projections by about 520 mid. It will be necessary to provide nitrification for these additional flows. Creek water quality conditions for such wastewater management option are described in Table 7.4 (item 5). The above analysis indicates that constructing three cell aerated lagoons for the proposed design flows is an adequate measure for creek water quality management upto the year 2005. These discharges will, however, fully exhaust the assimilative capacity of the creek in regions around the discharge locations presently identified. For future flows, it will thus be necessary to build additional wastewater treatment facilities and discharge the effluents at new locations in the creek. The analysis indicates, that if one were to discharge within the inner Thane creek, it would be possible to do so near Vikhroli. Such an option, however, would entail tertiary level treatment of the discharges of Vikhroli and would be adequate only upto the year 2015. Considering the need to plan even beyond the year 2015, it would be prudent to investigate options for discharging the wastewaters in other regions of the creek. Under such case, because of assimilative capacity.of these waters, it may be adequate to treat the effluents only upto secondary level and the cost of transporting the wastewater may be off-set by savings in the cost of its treatment. AER T o 7.o 7.4 Socio-economic impacts Rehabilitation of displaced populations is generally one of the major social concern associated with development projects. The project area for Bhandup and Ghatkopar lagoons, however, is uninhabited and does not involve any displacement of people. The project, during the construction, is expected to generate some employment which would have marginal positive impacL The operation of aerated lagoons does not require a large workforce and therefore any large scale residential development in the region, due to the implementation of the project, is not expected. The implementation of the project, would result in beneficial impacts in terms of higher fish yield thereby increasing fishing activities in inner Thane creek. However, the extent of these impacts will be difficult to quantify. 7.5 Conclusions The environmental impacts arising due to construction of aerated lagoons are the possible increase in noise and SPM levels during construction. The noise predictions indicate that the impact of noise at the nearest residential localities was negligible and the- high SPM levels could be controlled through mitigatory measures. The visual impairment, if any, due to construction of treatment systems amidst green regions can also be. effectively mitigated by developing green-belt around the lagoons. Another important impact of construction of proposed lagoons is the loss of about 40 hectares of mangroves due to land reclamation. It is necessary to compensate for this loss by replanting equivalent areas in the inner creek region itself and protecting existing mangrove: from future encroachment The major environmental impacts of the project will Lccur during its operation and if fully developed to three cell configuration and commissioned by the year 2005 will be highly beneficial. The water quality predictions through rigorous hydrodynamic and water quality modelling, indicate that the proposed first phase treatment effort through single cell aerated lagoons would not provide significant improvement in creek water quality. Such implementation would, however, arrest rising trend of water quality impairment. When augmented to three cells aerated lagoons, the proposed wastewater treatment would be adequate until wastewater flows exceed the projected flows for the year 2005. Importantly, the post-project ecological conditions in inner Thane creek are expected to be similar to those existing in Manori creek on the west coast of Bombay. Observations on Manori creek have AEU= VAMM 721 confirmed that the creek sustains a diverse ecosystem and plays an invaluable role in maintaining the bio-productivity of adjoining coastal ecosystem. An adequate water quality effort at Bhandup and Ghatkopar, therefore, also has potential of enriching the coastal ecology of Thane creek. In order to sustain water quality conditions favourable for supporting a healthy ecosystem in the creek after 2005, it would be necessary to build additional treatment facilities and discharge the effluents at new locations. Within the inner creek region, additional flows upto 260 mld.could be discharged near Vikhroli after secondary treatment. For effective future wastewater management, however, it appears necessary to explore the wastewater assimilative capacity of other regions of the creek. A combination of wastewater treatment and transport enabling effluent discharges in outer Thane creek, in areas south of Trombay, appears necessary for effective future water quality management in the creek. ARMED LAGONS 7.22 Chapter 8 RECOMMENDATIONS FOR MANAGEMENT PLAN 8.1 Preamble Bombay Sewage Disposal Project is one of the most ambitious pollution abatement schemes undertaken in India. Under the project, construction of two marine outfalls at Worli and Bandra; and four aerated lagoons at. Bhandup, Ghatkopar, Malad and Versova is envisaged. With the implementation of the project, considerable improvement in coastal water quality around Bombay is expected due to the large reduction in pollution loads in wastewaters presently reaching the near-shore coastal waters. As the project involves large expenditure for environmental improvement, the most important aspect of environmental impact assessment is to determine the effectiveness of the project in achieving desired environmental benefits and to suggest modifications, if required. The process should also identify the adverse impacts associated with the construction of the project and delineate the mitigatory measures. The environmental impact assessment study of the project, therefore, was aimed at fulfilling these objectives. The findings and recommendations on project components of (a) marine outfalls at Worli and Bandra and (b) aerated lagoons at Malad and Versova have already been documented in the two preceding reports. This report, the last in the series of the three reports envisaged on the project, deals with the environmental issues related with the proposed aerated lagoons in Bhandup and Ghatkopar. service areas. As the wastewater from the terminal pumping stations in Bhandup and Ghatkopar service areas drains into Thane creek, creek water quality scenarios for a number of wastewater treatment and discharge options were developed. The results of this effort clearly establish that the current effluent standards prescribed by the Maharashtra Pollution Control Board . (MPCB) for discharging treated wastewater into the creek are not related to the latter's assimilative capacity. It is observed that due to the large volume of expected wastewater discharges into the creek by the years 2005 through 2015, meeting the prescribed effluent standards will not be adequate to protect the ecological health of the creek. The recommendations of this study, therefore, are based cm an assessment of achievable creek water quality if different treatment strategies are implemented and are not constrained by assuming the adoption of a strategy which only complies with the stipulated effluent standards. In due ANED MAGOONS course MPCB may consider developing location specific discharge standards for all major discharges into Thane creek and promulgate the necessary regulations in a time bound manner to supplement the pollution abatement effort undertaken by the MCGB. This study and its recommendations attempt to provide a robust framework for evolving - such standards. 8.2 Management options for Thane creek The findings of the study indicate that notwithstanding the significant assimilative capacity of Thane creek, approximately 80 per cent reduction in the present carbonaceous BOD load generated in MCGB area will be- necessary to achieve the minimal conditions (DO more than 2 mg/L) required to sustain a healthy creek ecosystem. For the projected wastewater flows for the year 2005 and 2015, the requisite pollution abatement effort implies 84 and 92 per cent reduction in carbonaceous BOD load to the creek, respectively. If options of transporting the effluents to new creek regions are not considered, an additional reduction of approximately 80 per cent of projected nitrogenous BOD load will be necessary by the year 2015. MCGB has proposed the construction of single cell aerated lagoons at Bhandup and Ghatkopar. If designed to treat the projected flows, these are expected to provide 50 per cent reduction in the estimated pollution load in the year 2005 from Ghatkopar and Bhandup service areas. Whilst the single cell lagoon treatment would satisfy the discharge consent standards, the model simulations indicate that this treatment effort would not achieve the minimal conditions to sustain a healthy creek ecosysteni in umer Thane creek. The construction would certainly arrest the ongomg deterioration of creek water quality and after implementation, the overall water quality condition in the creek in the year 2005 is expected to be tetter than it is at present. However, the projected fows at Bhandup for the year 2005 exceed by about 50 per cent, the capacity for which those lagoons are at present designed. As a result, BOD levels in the effluent from single cell lagoons at Bhandup would be higher than 100 mg/L, the standard stipulated by MPCB and would thus fall short of the minimum statutory requirement for effluent discharge. It would, therefore, be necessary that the lagoons at Bhandup be designed for the flows which they will be expected to treat by 2005. If, instead of constructing single cell, three cells aerated lagoons to achieve ABU= LAGOONS 2 effluent BOD of 35 mg/L or below were constructed then the assessment indicates that when operating at their full capacity, the lagoons would be able to attain acceptable ecological conditions in Thane creek for wastewater flows upto 280 mid at Bhandup and 235 mid at Ghatkopar. If 50 mId sewage in Ghatkopar service area is diverted to nearby industries for reuse, these limiting design flows are not expected to be exceeded until the year 2005. With such treatment of sewage, the dissolved oxygen all along the creek would rarely fall below 2 mg/L and when it did it would only do so marginally. The effluent discharges near Ghatkopar and Bhandup, however, would fully exhaust the assimilative capacity of the creek at these locations. The results indicate that even activated sludge treatment instead of aerated lagoons at Ghatkopar and Bhandup would not provide a significant improvement in minimum DO levels in the affected regions of the creek. While the investigations firmly establish that three cells aerated lagoons would significantly improve the existing ecological status of the inner Thane creek and would provide a reasonable degree of pollution control upto 2005, advanced treatment facilities would be necessary to cater to the wastewater flows after 2005. To accommodate the future increases in wastewater flows, it will be necessary to build additional treatment facilities and transport the treated effluent for discharge at new locations in the creek. The studies indicate that in regions near Vikhroli, it will be possible to discharge additional wastewater flows of about 260 mid after secondary treatment and upto 520 mid after advanced biological treatment (nitrification after removal of. carbonaceous matter). Additional treatment capacity of 520 mid along with the proposed aerated lagoons at Bhandup and Ghatkopar would then accommodate the projected wastewater flows upto 2015. However, if an option to discharge the effluents in creek regions south of Trombay are considered, treatment upto secondary level may be adequate to achieve desired creek water quality. In order to put the management objective of achieving minimum di-;3lved oxygen of 2 mg/L in the creek in a correct perspective, simulations were conducted to determine highest achievable creek dissolved oxygen levels near Bhandup and Ghatkopar for the projected flows in the year 2005. It was observed that even a highly resource intensive treatment effort, comprsing of activated sludge process followed by nitrification facilities and targeted to provide effluent BOD of below 15 mg/L and ammoniacal AMED LAGOONS 8.3 nitrogen of below 1 mg/L, would not be adequate to raise creek dissolved oxygen significantly above 2.5 mg/L, at all times. Construction of properly designed single cell aerated lagoons at Bhandup and Ghatkopar is thus, the minimum admissible treatment effort necessary to meet the current effluent discharge standards. Construction of such wastewater treatment facilities at Bhandup and Ghatkopar would be a positive step towards the objective of overall water quality improvement in Thane creek and is strongly recommended. For significant improvement in creek water quality, however, it will be essential to augment the aerated lagoons at Bhandup and Ghatkopar to a three cells configuration designed to produce effluents with BOD below 35 mg/L Considering that such augmentation would remain effective only upto the year 2005, subject to funds being available, implementation of this configuration could be considered at the present stage. If the three cell lagoons are not to be considered immediately then single cell lagoons should be so designed that they can be extended to three cell lagoons yielding an effluent with 35 mg/L BOD. The recommended long term water quality management option for the Thane creek is, therefore, to build three cell aerated lagoons at Bhandup and Ghatkopar and to develop additional treatment units with facilities to discharge the effluent at new locations within the creek. One of the suitable discharge locations has been identified near Vikhroli and has potential to receive about 260 mid of effluents after secondary treatment It will be necessary to conduct additional water quality modelling studies to assess assimilative capacity of the creek south of Trombay, as a possible new effluent discharge area for expected wastewater flows in Bhandup and Ghatkopar service areas by the years 2015 and after. The conclusions of this assessment, however, are limited to the study of* municipal wastewater loads from Ghatkopar and Bhandup service areas. While evaluating the management options, it was assumed that the water quality in the inner Thane creek is not significantly affected by other discharges entering the creek, especially from its eastern catchment area. This assumption would be valid only if other wastewater discharges into the creek also are adequately treated. For achieving the full water quality benefits of the investments in treatment that MCGB plans to make, it is thus imperative that a comprehensive management plan be developed for the creek, with comparable treatment levels applied to other discharges. Because this involves multiple jurisdictions, it may be best accomplished by Government of Maharashtra. Considering the probable environmental impairment due to delays, it is desirable that immediate priority be AUAED LAGOONS BA nitrogen of below 1 mg/L, would not be adequate to raise creek dissolved oxygen significantly above 2.5 mg/L, at all times. Construction of properly designed single cell aerated lagoons at Bhandup and Ghatkopar is thus, the minimum admissible treatment effort necessary to meet the current effluent discharge standards. Construction of such wastewater treatment facilities at Bhandup and Ghatkopar would be a positive step towards the objective of overall water quality improvement in Thane creek and is strongly recommended. For significant improvement in creek water quality, however, it will be essential to augment the aerated lagoons at Bhandup and Ghatkopar to a three cells configuration designed to produce effluents with BOD below 35 mg/L. Considering that such augmentation would remain effective only upto the year 2005, subject to funds being available, implementation of this configuration could be considered at the present stage. If the three cell lagoons are not to be considered immediately then single cell lagoons should be so designed that they can be extended to three cell lagoons yielding an effluent with 35 mg/L BOD. The recommended long term water quality management option for the Thane creek is, therefore, to build three cell aerated lagoons at Bhandup and Ghatkopar and to develop additional treatment units with facilities to discharge the effluent at new locations within the creek. One of the suitable discharge locations has been identified near Vikhroli and has potential to receive about 260 mid of effluents after secondary treatment. It will be necessary to conduct additional water quality modelling studies to assess assimilative capacity of the creek south of Trombay, as a possible new effluent discharge area for expected wastewater flows in Bhandup and Ghatkopar service areas by the years 2015 and after. The conclusions of this assessment, however, are limited to the study of- municipal wastewater loads from Ghatkopar and Bhandup service areas. While evaluating the management options, it was assumed that the water quality in the inner Thane creek is not significantly affected by other discharges entering the creek, especially from its eastern catchment area. This assumption would be valid only if other wastewater discharges into the creek also are adequately treated. For achieving the full water quality benefits of the investments in treatment that MCGB plans to make, it is thus imperative that a comprehensive management plan be developed for the creek, with comparable treatment levels applied to other .discharges. Because this involves multiple jurisdictions, it may be best accomplished by Government of Maharashtra. Considering the probable environmental impairment due to delays, it is desirable that immediate priority be ABUm LAGOONS aA assigned to planning and implementation of such a management scheme. 8.3 Mitigation plan 8.3.1 Construction phase Loss of about 5 per cent of the total mangrove cover in the inner Thane creek due to land reclamation for lagoons is the most important construction phase impact of the project. To compensate for the unavoidable loss of mangrove area, MCGB should designate about 200 hectares of mangrove area along the creek as protected area and take measures against further reclamation or unauthorized cutting.. Alternatively, MCGB should undertake fresh planting of mangrove forests of area equivalent to the reclaimed area in the inner Thane creek region. Another potentially negative impact of aerated lagoon construction is a rise in the ambient noise and dust levels. This impact can be prevented by adherence to good construction and house keeping practices. Measures such as avoidance of unnecessary idling of construction machinery and spillage of fuel and oil and adequate maintenance of construction machinery to ensure efficient and trouble free operation should be provided for in the construction contracts. Analysis of the noise levels at the site and surrounding areas indicate that the effect of construction activities during the day, is not felt outside the construction site due to the local noises. At night, however, the construction activities can raise the noise levels and the nearby residential locations beyond the night time standards for such areas. It is, therefore, recommended that the noise generating construction activities should be restricted only to day time hours. Air quality analysis at the sites indicates that observed levels of SPM, NO, and SO, are well within the Indian Standards for ambient air quality. - However, the SPM levels may, on some occasions, surpass the standards at the time of site clearing and construction activities. Provision of water spraying on all haul roads at the construction site should be made to minimize the dust. Also, green belts should be developed around the boundary of the lagoon sites on the sides facing habitation to safeguard against aesthetic impairment. An inventory of requisite mitigatory measures is provided in Table 8.1. The recommended specifications for the green belts are presented in Table 8.2. AOM LAGOONS Table : 8.1 Mitigation plan for construction and operational impacts of areated lagoons No. Environmental Issues Actions to be taken Responsible entity A. Construction phase 1. Dust contamination at Construction sites and MCGB/Prospective site and on haul roads access roads will be Contractor (PC) watered twice each day 2. Noise pollution Operation of heavy cons- MCGB/PC truction machinery causing noise pollution to be restricted to daytime hours Well maintained vehicles to be used for muck and material transport. The vehicle speed should be limited to 40 kilometers per hour in the residential areas. 3. Air pollution Monitoring at site and on MCCB access roads for SPM, NOx and SO2 twice each week 4. Disposal of excavated In case of semi solid waste MCGB material and provision to be made for construction debris dewatering/drying prior to its use for reclamation Daily inspection at haul MCGB road and sites for construction debris, its collection and disposal to landfill sites AHMW MOO Table : 8.1 (Contd...) No. Environmental Issues Actions to be taken Responsible entity 5. Traffic and All hauling materials to be PC transportation covered while being transported Routine check of vehicle PC used for transportation and their proper maintenance to minimize vehicular pollution 6. Domestic sewage and Provision of waste disposal PC rubbish facilities like septic tanks at construction worker's colony Provision at site and in PC worker's colony for waste- bins for solid waste collection Transportation for PC dumping the solid waste from worker's colony to a nearby collection or landfill within the area 7. Public participation Public awareness MCGB programmes to be* conducted 8. Loss of about 40 Mangrove replantation of MCGB hectares of mangroves equivalent area in inner for site clearance Thane creek AED LSDONS Table : 8.1 (Contd..) W No. Environmental Issues Actions to be taken Responsible entity B. Operational phase 9. Effluent monitoring Weekly monitoring of MCGB/NEERI monitoring lagoon effluents quality for BOD, suspended solids, NH3-N, Org. -N and DO prior to discharge into Thane creek Monthly monitoring of MCGB/NEER[ metal concentrations in lagoon effluants 10. Environmental Seasonal monitoring in the MCGB/NEERI monitoring creek for BOD, DO and NH1-N levels and biological parameters during the neap tides. The observations should cover region of impacts during pre- and post-project period 11. Maintenance Routine maintenance of all mechanical and electrical equipments like aerators and pumps for efficient operation 12. Solid Waste Disposal Disposal of screenings and MCGB grit along with city refuse Environmentally suitable MCGB/NEERI disposal of sludge from desludging operations of lagoons taking into account concentration of heavy metals in the sludge AIL= LAGOONS a Table : &2 Recommended plantation in areas near the proposed aerated lagoon sites Site Total Name of the plant Plant to Total length species plant number approx. spacing of plants (M) (m) required Three rows of plants 2000 Pride of India 10 200 along the boundary of Cocos nucifera 10 200 Bhandup aerated lagoon Pride of India 10 200 site Three rows of plants 1800 Pride of India 10 180 along the boundary of Cocos nucifera 10 180 Ghatkopar aerated Pride of India 10 180 lagoon site AEUoLsoONS as 8.3.2 Operation phase If the facilities are limited to single cell lagoons, water quality in the region of discharge into the creek will remain below the level necessary for a healthy ecosystem. An adequate mitigatory measure, therefore, would be to construct three cell aerated lagoons at this stage itself or to augment the single cell lagoons to three cell configuration as soon as possible. With respect to the treatment facilities, care should be taken to extend the effluent discharge point upto 20 meters beyond the low water line in the. creeklets to avoid formation of sludge mats in the inter-tidal zone. In order to achieve acceptable environmental conditions in the vicinity of the creek proper functioning of aerators is of prime importance. Adequate back up systems should be incorporated in design stage itself to ensure their continuous and trouble free operation. 83.3 Environmental monitoring A systematic water quality monitoring effort within the creek should be initiated before and after commissioning the aerated lagoons at both the discharge locations. At the post-commissioning stage, the monitoring should be aimed at evaluation of water quality projections and validating the water quality model used in the present study. Such validation will be useful for future planning. A regular effluent monitoring programme to establish the performance parameters for the treatment system should, however, be undertaken immediately after commissioning the treatment systems and continued. during the entire operation period of the treatment systems. Guidelines for such monitoring are provided in Table 8.1. Creek water quality monitoring along with observations on hydrodynamic parameters should, be initiated by Government of Maharashtra to develop a comprehensive water quality model for the entire Thane creek, a prerequisite for developing the overall wastewater management plan for the region. The exercise should aim at developing location specific discharge standards for various industrial discharges into the creek to ensure that the overall pollution load to the creek are within its assimilative capacity. A limited monitoring at the creek may also be undertaken to document the improvement in the creek ecosystem comparing the pre and post-project water quality conditions. A summary of the recommendations for environmental monitoring are presented in Table 8.1. AELED LAGOONS 8.10 8.3.4 Public participation The proposed wastewater management effort along Thane creek involves significant investment of public funds. The findings of the study indicate that even more comprehensive treatment efforts will be necessary to safeguard the creek water quality in the not-too-distant future. It is, therefore, desirable to create public awareness for the project activities to facilitate their involvement in the decision making. Towards this end, findings of this study should be placed for public discussions among representatives of fishing communities, general public and local NGOs. The report summary should also be translated in local languages and distributed among the fishing communities. A comprehensive awareness program on the need for the project, major technical and social issues and the environmental benefits should be undertaken through local media. The coverage should include discussions on TV and radio by panels comprising concerned citizens and officials connected with implementation and environmental assessment of the project An outline for environmental awareness programme has already been suggested in the report on marine outfalls submitted earlier. 8.3.5 Institutional needs There is a need for substantial institutional development within the MCGB for effective operation of aerated lagoons and the additional treatment and effluent diversion options which will have to be developed later. Training programmes for various levels of associated staff of MCGB should be conducted for efficient operation of the project. On certain environmental aspects such as use of water quality models for effective water quality monitoring in the creek, evaluation of long term post-project environmental impacts and wastewater management planning for future discharges it may be necessary for MCGB to take recourse to the expertise available with the research Institutes active in these areas. For effective implementation of the recommended effluents and environmental monitoring, it will be necessary to develop adequate facilities for sampling and analysis. It will be desirable to operate an . environmental monitoring cell, with adequate training and instrumentation support for coastal water quality monitoring and analysis related to the aerated lagoon project. Government and private laboratories with adequate infrastructural facilities and expertise may also be identified to assist in these activities. ALED LAGOONS 1.11
Groupe de la Banque mondiale · Environmental Assessment
India - Bombay Sewage Disposal Project : environmental assessment (Vol. 4 of 4) : Final report : aerated lagoons : Bhandup & Ghatkopar
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