Arsenic aquifer sealing technology in wells: A sustainable mitigation option

Abstract

The act of constructing unprotected/unsealed wells to extract water from deep aquifers is a worrisome ongoing practice in most parts of developing countries of the globe. The paper is first of its kind in exploring sealing technology as a potential mitigation measure to prevent arsenic contamination of deep aquifers. The technology has been assessed not only as a safeguard to potential microbiological or mineralogical contamination of aquifers but also as an adaptive option in case of climate-induced disasters like drought or flood where it can serve as emergency safe drinking water source. This paper puts forward comparative findings of mini-arsenic blanket testing of 358 wells (unsealed) performed at an interval of 8 years in Nawalparasi, district of Nepal, along with the performance monitoring of eight different sealed wells ranging from 20 to 80 m deep for over a period of 7 years. The paper focuses on the construction methodology and performance evaluation of four sealed shallow wells constructed in the same district. Mini-arsenic blanket test results show 38, 37, and 25 % of bore wells with respective increasing, decreasing, and constant level of arsenic concentrations whereas the sealed wells exhibit steadiness in arsenic concentration range of particular tapped aquifers within Nepal drinking water quality standard for arsenic of 50 μg/l over a long period, even though the tapped aquifers lie intercepted in between adjacent arsenic elevated aquifers. Sealed shallow wells exhibit good aquifer seal characteristics beyond potential resultant existing positive difference to cause downward aquifer cross-contamination. The presented technology can be used and replicated in deep/multi-aquifer hydrogeology of Nepal and South Asia for extraction of water from deep and safer aquifers in rural and urban water supply systems by escaping overlying arsenic-contaminated aquifers.