BMC seeks consultant to identify, fix ingress of sewage into storm drains

The exercise will involve conducting a drone study of nullahs, and a ground-truthing exercise to identify DWF entry points, dumping grounds, and silt deposition.

Mumbai: In addition to four proposed river rejuvenation projects in the city, the Brihanmumbai Municipal Corporation (BMC) has begun taking steps to arrest the entry of dry weather flows (DWF), or sewage, into at least 39 minor drains and tributaries across the city and suburbs. The BMC, earlier this month, floated a tender seeking a consultant to prepare a detailed project report (DPR) for the same.

A total of 12 nullahs emptying into Thane and Mahul Creeks will be studied in the eastern suburbs (Pratik Chorge/HT Photo)

According to BMC’s tender document, the objective of the assignment “is to examine the feasibility of interception and diversion of dry weather flows into stormwater drains and any other natural surface water body and prepare a DPR for solutions for the same.”

The exercise will involve conducting a drone study of nullahs, and a ground-truthing exercise to identify DWF entry points, dumping grounds, and silt deposition.

The consultant will also do a “further study of current sewage collection and WWTF and conveyance system,” to treat the DWF either in situ (original place) or transport it to the nearest sewer line or sewage treatment plant (STP), of which there are eight in the city.

A total of 12 nullahs emptying into Thane and Mahul Creeks will be studied in the eastern suburbs, in addition to 27 nullahs in the eastern suburbs which are emptying into the Malad, Oshiwara, Gorai and Versova Creeks, the Arabian Sea, and the Dahisar mangroves. Another nine outfall points, seven in Mahul and two in south Mumbai, will also be studied as part of the works.

“This study is distinct from the BMC’s river rejuvenation project,” said an official with the BMC’s sewerage department.

“While Mithi, Poisar, Oshiwara and Dahisar rivers are being tackled under different packages, this DPR is meant for minor nullahs and their tributaries. The main priority is to intercept sewage before it reaches the nullah. The draft DPR should be ready in four months, and then within a year from award of tender we will float a fresh tender for executing the physical works, “ the official added.

A total of 747 megaliters of untreated sewage are released into four rivers in Mumbai each day, finding their way through minor nullahs and tributaries, according to a civil appeal petition filed by the Municipal Corporation of Greater Mumbai (MCGM) in the Supreme Court last year.

BMC officials said that tenders for infra works, which will divert sewage away from these water bodies and into the municipal treatment and disposal system, are close to being awarded.

Broadly, the work involves laying down new sewer lines, building retaining walls, constructing small capacity sewage treatment plants and installing drainage interceptors at strategic locations. However, the commissioning of these works is still some time away.

“As per the instructions of the National Green Tribunal (NGT), nearly all tenders have been floated and some financial packages have also been opened. We are in the final process of awarding the work to appropriate contractors. But the work, being undertaken as part of the Municipal Sewerage Improvement Program, is expected to be finished in about three to four years,” said P Velarasu, additional municipal commissioner, Mumbai.