Integrated use of geophysical, hydrological and geographic information system (GIS) methods in enhancing the groundwater quality in a fluoride-endemic terrain (Andhra Pradesh, India)

Abstract

The concept of groundwater recharge and quality improvement is often implemented in arid and semi-arid areas with depleted aquifers. Nalgonda district in Andhra Pradesh, India, has endemic fluoride, with concentrations in drinking water varying between 3 and 8 mg/l. Numerous techniques adopted in the recent past for defluoridizing groundwater proved to have limitations. The integrated approach of a geographic information system (GIS) and an analytic hierarchy process (AHP), to identify suitable sites for recharge structures over an area of ∼115 km2, is highlighted. Further, to validate the delineated sites, a micro-watershed basin (2 km2) was selected for detailed recharge assessment and site feasibility studies through geophysical and tracer tests. Groundwater velocity (7 m/day) and flow direction through fractures in the shallow horizon were established through tracer experiments. The efficacy of the recommended recharge structures and their impact on groundwater quality were assessed over a period of 5 years, from 2002 to 2007, and the mean groundwater fluoride concentration of > 3.5 mg/l over the study area was brought down to < 1.5 mg/l.