Arsenic contamination of ground water from Yamuna floodplains in Delhi is several times the permissible limit and the prime culprit for this poisoning is fly ash and other residue from Delhis thermal power plants,a study by the Department of Geology at Delhi University (DU) has found. Samples were collected from the Yamuna floodplains,one of the most important ground water recharging sources in the city,to study the level of arsenic content in it. While permissible concentration of arsenic in ground water is 10 parts per billion (ppb),concentrations of up to 180 ppb were found in the 120 water samples collected, said Dr Chandra S Dubey,lead author of the study and head of DUs geology department. Though arsenic contamination in Delhi has been reported earlier,the study has established for the first time that the source of the contamination is fly ash and slurry from coal-based thermal power plants. Surface water samples across the Yamuna floodplains show high values of arsenic contamination. It is estimated that the Rajghat power plant releases 5.5 tonnes of arsenic into the Yamuna every year while the Indraprastha power plant pumps in 1.96 tonnes a year. There is a need to take immediate steps to stop this, said Dr Dubey. The study,titled Anthropogenic arsenic menace in Delhi Yamuna floodplains,concentrated on the floodplains of the river surrounding the Rajghat and Indraprastha power plants and to a smaller extent on the regions around the Badarpur plant. However,the highest arsenic content found (180 ppb) was present in post-monsoon ground water samples collected near the Badarpur plant. Coal used in the Badarpur and Rajghat power plants was found to contain over 200 ppb of arsenic,while the arsenic content in fly ash from Rajghat was found to be as high as 3,200 ppb. There must be some check on leaching from the fly ash ponds. The drain water from thermal plants cannot be allowed to flow into the Yamuna, said Dr Dubey. Near Akshardam temple in Mayur Vihar Phase 1,where land is used for vegetable cultivation,arsenic contamination of more than 135 ppb was found. Surveys show stomach,gastric and gastrointestinal problems reported by the people who drank hand pump water in highly arsenic contaminated areas,the study reports. Compared to ground water,surface water reported less concentration of the toxic element due to constant flow,the study says. The samples for the study,published in January this year were collected in two phases between May and June (pre-monsoon) and at the end of August (post-monsoon) in 2007. Of the ground water samples collected,more than 75 per cent was contaminated with arsenic while 55 per cent contained the toxic element at a level higher than WHO standards.
