BMC to survey 227 SWD outfalls for preventing ingress of sewage into sea

Mumbai: In order to assess and prevent the flow of sewage into creeks, rivers and the Arabian Sea, the Brihanmumbai Municipal Corporation (BMC) will survey 227 storm water drain (SWDs) outfalls across the city

Mumbai: In order to assess and prevent the flow of sewage into creeks, rivers and the Arabian Sea, the Brihanmumbai Municipal Corporation (BMC) will survey 227 storm water drain (SWDs) outfalls across the city.

BMC to survey 227 SWD outfalls for preventing ingress of sewage into sea

The move is part of the BMC’s larger efforts at remediating the city’s drainage network, including sewers and SWDs, after the various orders of the National Green Tribunal (NGT) and the Supreme Court instructed it to do so, in response to public interest litigation (PIL) by city-based environment group Vanashakti.

As per the BMC’s SWD department’s records, there are at least 185 outfalls into the Arabian Sea, and 42 which open out into the Mithi, Dahisar, Poisar and Oshiwara rivers. As per the BMC’s terms of reference for prospective consultants, “The proposed consultancy services are aimed at a comprehensive study of the stormwater drains outfalls and suggestion of short-term measures of in-situ treatment... using bioremediation/phytoremediation and any other suitable method to treat the stormwater at all the outlets before discharging into the water bodies.”

An official with the BMC’s Mumbai Sewage Disposal Project (MSDP), said, “Our long-term goal is to divert all liquid municipal waste to STPs, but the establishment of sewers, particularly in slum areas, is still a long way off. So, this survey is meant to suggest short-term pollution abatement measures. We are also in process of commissioning a survey to identify specific points across the city where sewage is entering storm-water drains. This survey deals with outfall points, so both ends of the drainage channels will be covered.”

The official added that the BMC will be carrying out water sample analyses and flow measurements at all SWDs more than 3-metres in width, to ascertain the nature and extent of pollutants which are currently escaping into natural water bodies. The entire exercise, along with the preparation of a detailed project report (DPR), is expected to take six months from the date of the tender being awarded.

The BMC has already begun work to measure dry weather flow and carry out in-situ treatment of 78 storm water drains in wards H, K, P and R, based on a study by IIT-Bombay. Dry weather flow refers to wastewater flowing in a sewer system during dry weather conditions, i.e. outside of the monsoon season. Excess quantity of such material in SWDs -- instead of sewers leading to treatment plants -- tends to clog up the drains and render them ineffective during periods of heavy rainfall.

Similar work on another 53 drains in wards F, M, L and S is expected to begin by early next year, based on feasibility studies by VJTI and NEERI which are currently in progress.

“The outfall survey will also have to identify where these drains are leading to, and if there is any improvement in the water quality at the point of discharge into the sea due to in-situ treatment upstream,” the BMC official said.

To entirely prevent the dry weather flow of untreated sewage in the city’s creeks and rivers, Mumbai needs a well-connected system of sewer lines. The existing 2,025-km-long network services only 84% of Mumbai’s developed area and 68% of the city’s population, as per BMC’s submissions before the SC.