Characterization of stormwater runoff in the powai region of Mumbai.

Urban stormwater runoff could be a significant non-point source of surface water pollution during India's monsoon season (June - September). This study aims to characterize the stormwater runoff in the Powai region of Mumbai and investigate interlinkages between precipitation characteristics and runoff quality. The levels of conventional water quality parameters (physical, chemical, microbiological) and emerging contaminants in the runoff were determined. Runoff samples were collected from various outfall locations (SL1, SL2, SL3, SL4 and SL5) which drain into the Powai Lake. Runoff sampling was conducted for ten storm events spread over the 2022 and 2023 monsoon seasons. Two outfall locations (SL4, SL5) convey runoff originating primarily from an institutional township, and have reported the lowest organic loads and fecal contamination. However, runoff within the township contains elevated levels of metals such as iron, lead and Aluminum. In addition, emerging contaminants such as phthalates, pesticides, pharmaceuticals and personal care products were detected in the runoff. The runoff outside the township (SL1, SL2, SL3) had low DO levels and highest mean concentrations of TSS, BOD, and oil and grease. The potential mixture of untreated sewage with runoff was identified as the probable cause for low DO, which was further substantiated by the high fecal coliform loads (1600 MPN/100 mL). The findings from this study identify runoff as one of the dominant causes of degrading water quality and will serve as a reference to further scientific efforts in quantifying the pollutant loads, and development of export coefficients for the Powai Lake watershed.