Abstract
A significant component of domestic demand for water of urban areas located in the Gangetic plains is met by heavy pumping of groundwater. The present study is focused on the Patna municipal area, inhabited by 17 million people and spanning over 134 km2, where entire urban water demand is catered from pumping by wells of various capacities and designs. The present study examines the nature of the aquifer system within the urban area, the temporal changes in the water/piezometric level and the recharge mechanism of the deeper aquifers. The aquifer system is made up of medium-to-coarse unconsolidated sand, lying under a ~40-m-thick predominantly argillaceous unit holding 8- to 13-m-thick localised sand layers and continues up to 220 m below ground. Groundwater occurs under semi-confined condition, with transmissivity of aquifers in 5,500–9,200 m2 day−1 range. Hydraulic head of the deeper aquifer remains in 9–19 m range below ground, in contrast to 1–9 m range of that of the upper aquitard zone. The estimated annual groundwater extraction from the deeper aquifer is ~212.0 million m3, which has created a decline of 3.9 m in the piezometric level of the deeper aquifer during the past 30 years. Unregulated construction of deep tube wells with mushrooming of apartment culture may further exacerbate the problem. The sand layers within the aquitard zone are experiencing an annual extraction of 14.5 million m3 and have exhibited stable water level trend for past one and half decades. This unit is recharged from monsoon rainfall, besides contribution from water supply pipe line leakage and seepage from unlined storm water drains.
Published Version
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