Integrated use of geophysical, hydrological and geographic information system (GIS) methods in enhancing the groundwater quality in a fluoride-endemic terrain (Andhra Pradesh, India)Utilisation intégrée des méthodes géophysiques et hydrologiques et d’un système d’information géographique en vue de l’amélioration de la qualité de l’eau de nappe dans une région à fluor endémique (Andhra Pradesh, Inde)Uso integrado de los métodos geofísicos, hidrológicos y de sistemas de información geográfica (SIG) para mejorar la calidad del agua subterránea en un terreno endémico de fluoruro (Andhra Pradesh, India) 应用地球物理、水文和地理信息系统(GIS)综合方法改善印度Andhra Pradesh氟异常区地下水质Uso integrado de métodos geofísicos, hidrológicos e de sistemas de informação geográfica (SIG) para melhoramento da qualidade da água subterrânea num terreno com fluoreto endémico (Andhra Pradesh, Índia)

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.