The groundwater table near the Najafgarh drain has been contaminated with metals such as the cancer-inducing lead, and cadmium apart from other health hazards such as arsenic, nitrate, manganese and iron.
The Najafgarh drain traverses through southwest, west, northwest districts of Delhi. While barely two-three drains join it before Kakraula in southwest Delhi, as many as 38 big and small drains join it after.
The presence of metals in the groundwater in the vicinity of the drain has been established in a study by two scholars from the Department of Geology, Delhi University. The research establishes that an unlined open drain carrying sewage can contaminate ground water. As per the study, shallow groundwater along the drain is contaminated and is not suitable for large-scale groundwater development for drinking water purposes.
Groundwater samples were lifted from evenly distributed locations all along the drain and the sampling was done in pre-monsoon days last year from the hand pumps. These samples were analysed at the Central Ground Water Board's chemical laboratory and variations in chemical components were studied in perspective of permissible limits of drinking water following Bureau of Indian Standards (BIS 1991) and World Health Organisation (WHO 2011).
"It (the sample analysis) also suggested that the sewage treatment level can be estimated so that the drain bank filtrated water into aquifer attains potable drinking water standards. This can be enforced on the authorities concerned undertaking sewage treatment projects along the drain," the authors - Shashank Shekhar and Aditya Sarkar - said. The study was published in the February 2013 issue of the Journal of Earth System Sciences.
"It is possible that traces of heavy metals in groundwater were introduced due to industrial waste in the catchments of the drain system," they said.
Explaining the health hazard to thousands of residents living in the vicinity, Diwan Singh of Natural Heritage First, said: "Heavy metals even in small quantities dissolved in water are highly toxic for a human body and can cause irreparable damage." The 51-km-long drain contributes 60% of the total sewage falling into the Yamuna.