Changes in the recoverable fractions during successive cycles of aquifer storage and recovery system in North-West India.

Aquifer storage and recovery (ASR) is an effective method of recharging reclaimed or surplus surface water into confined or semi-confined permeable formations for later extraction. A key factor in the long-term viability of ASR is the extent of mineral interaction between two dissimilar water types, their recoverable fractions and consequent impact on water quality and aquifer stability. An ASR well study was undertaken in the semi-arid region of northern India to assess the technical viability, environmental sustainability and commercial/economic feasibility of the ASR system in a generic sense. 300 m 3 of canal water was injected in each recharge cycle of brackish water and 100% of the mixture was extracted during each recovery cycle of the experiment. The study revealed that groundwater quality of the recovered water was better than that of the native water and recovery percentage of the recharged water (EC > 2 dS m -1 ) increased from 27% to 42% in the successive recovery cycles. The potassium concentration in the recovered water was greater than that of the injected water as a result of potassium release from clay minerals in the aquifer. Borate was also released from the aquifer due to tourmaline dissolution and desorption from clay minerals under lower pH conditions caused by surface water injection.