Arsenic concentrations and bacterial contamination in a pilot shallow dugwell program in West Bengal, India

• Published in: Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering Toxic/hazardous substances & environmental engineering, 2007-01, Vol.42 (1), p.89-95
• Main Authors: Hira-Smith, Meera M., Yuan, Yan, Savarimuthu, Xavier, Liaw, Jane, Hira, Alpana, Green, Cynthia, Hore, Timir, Chakraborty, Protap, von Ehrenstein, Ondine S., Smith, Allan H.
• Format: Article
• Language: English
• Subjects: Arsenic; Arsenic - analysis; Arsenic mitigation; Arsenic Poisoning - prevention & control; Assessments; Bacteria; Bacteria - isolation & purification; Chlorination; Contamination; Cylinders; Drinking water; Dugwells; Fresh Water - chemistry; Fresh Water - microbiology; India; Pilots; Sand; Summer; Surface water; Water Pollutants, Chemical - analysis; Water Supply; Wells
• ISSN: 1093-4529; 1532-4117
• DOI: 10.1080/10934520601015834

Project Well has developed a pilot self-supporting community-based mitigation program to provide arsenic-safe water to the villagers of North 24 Parganas, West Bengal, India. Shallow concrete dugwells, less than 25 feet deep, that tap into an unconfined aquifer are constructed following stipulated guidelines. The design differs from the traditional dugwell in two major ways: (i) there is a layer of coarse sand in the annular space enveloping the outer wall of the concrete cylinder; and (ii) handpumps are used for water extraction to reduce the potential for bacterial contamination. Monitoring programs for arsenic and coliform bacteria in selected dugwells have been completed. In summer, when the water levels were low, the arsenic concentrations were measured. In 11 wells, measured over three years, the average water arsenic concentration was 29 μ gL −1 . Two dugwells had high concentrations of arsenic (average 152 μ gL −1 and 61 μ gL −1 ), but the remaining nine dugwells had an overall average of 11 μ gL −1 . Seasonal variation was assessed in five wells with monthly measurements and there was a direct relationship between increases in arsenic concentrations and decreases in the volume of water in the dugwells in the dry summer season. To control bacterial contamination, sodium hypochlorite solution containing 5% chlorine was applied once a month. In 2005, fecal coliform was undetected in 65% (n = 13) of the dugwells but detected at high levels in 35% (n = 7) of the dugwells. The program clearly reduced exposure to arsenic, but we conclude that further study of increases in arsenic concentrations in the dry season are warranted, as well as assessment of ways to more effectively control bacterial contamination such as more frequent chlorination, perhaps with lower doses on each occasion.