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Mumbai: Three weeks after locals first drew attention to an effluent leak in Thane Creek Flamingo Sanctuary, near an offshore MIDC pipeline, carrying treated wastewater into the open sea, officials are yet to plug the leak. Meanwhile, laboratory tests undertaken by non-government organisation Vanashakti on two water samples collected at the site show that the quantity of pollutants in the area are exceeding permissible limits for environmental discharge by a significant degree.

The leak was first flagged by environmentalist and director of Vanashakti Stalin D and Harish Sutar, a local fisherman, on Friday, May 20. The pipeline in question has been operational since 2021 and was built to replace a 25-year-old channel to carry effluents from a treatment plant in Mahape into the deep sea, beyond the limit of Thane Creek, where it is discharged at an appropriate location depending on the capacity of the area to dilute the effluents. The effluent comes from the Maharashtra Industrial Development Corporation’s (MIDC) Trans-Thane Creek facility in Pawne, Navi Mumbai.

On May 30, Stalin collected two one-litre water samples close to the pipeline, where the effluent was most visible. The samples were tested for broad environmental parameters, including biological oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids, and acidity. While the pH values were within the permissible range, the other parameters indicated high levels of pollution.

Sample 1’s BOD level stood at 900mg/litre, which is higher than the permissible limit of 100mg/litre (for discharge in marine coastal areas), as per Schedule VI of the Environment Protection Rules (1986). The permissible BOD for public sewers is 350mg/litre. The COD level stood at 2880mg/litre, up from the permissible limit of 250. And the TDS level stood at 27,366mg/litre, up from the permissible limit of 100mg/litre. Similarly, Sample 2’s BOD level was 450mg/litre, COD was 1,440mg/litre and TDS at 4,655mg/litre.

RT Meshram, a deputy engineer working at MIDC-TTC, initially refuted claims of a leak, or that of effluents polluting the sanctuary, saying that the discharge is treated and compliant with environmental standards. On May 30, Meshram confirmed that there is an effluent leak at the site, and said they would act swiftly to plug the leak at the source. He said, “We have not yet identified the exact source of the leak. We are conducting a site visit today. As for the laboratory reports, I will check them up with the central effluent treatment plant.”

The pipeline in question has been operational since 2021 and was built to replace a 25-year-old channel to carry effluents from a common treatment plant in Mahape into the deep sea, beyond the limit of Thane Creek, where it is discharged at an appropriate location depending on the capacity of the area to dilute the effluents. It passes through the Thane Creek Flamingo Sanctuary, a protected wetland under the Wildlife Protection Act (1972).

Officials in the Maharashtra Pollution Control Board (MPCB), including joint director Yashwant Sontakke and regional officer (Navi Mumbai) DB Patil, did not respond to requests for comment on Thursday.

Stalin D, who first raised the complaint last month, said, “It is a serious lapse of duty on the part of both the MIDC and the MPCB that the leak has not yet been plugged. That they have not been able to even identify the exact source of the leak three weeks after it was brought to their attention demonstrates their sheer laxity towards environmental pollution.”

BOD and COD in brief

Biological oxygen demand (BOD) is the amount of dissolved oxygen required by microorganisms to break down organic materials in a given sample of water. It is a metric commonly used as an indicator of environmental pollution. Higher the level of organic pollutants in the water, such as in sewers, the higher the BOD.

Similarly, chemical oxygen demand (COD) refers to the amount of dissolved oxygen in a given sample of water which can be oxidised through chemical reactions. A higher COD indicates the greater presence of inorganic or chemical pollutants, such as in industrial effluents.

Total suspended solids, meanwhile, refers to the combined quantity of inorganic and organic materials (minerals, heavy metals, salts and molecular ions) present in a sample of water in suspended form. A high TDS level indicates the presence of pollutants.

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