Performance Evaluation of Injection Wells for Groundwater Recharge

The study was conducted to determine the performance of injection wells for groundwater recharge using surface runoff with respect to its groundwater recharging potential and impact on groundwater quality. The mean recharge rates of21.2 m3day' and 8.0 m3d-1were observed for injection wells installed below water table (saturated zone) and above water table (vadose zone), respectively. The results indicated that recharge rates increased with increase in recharge head and the incremental increase (increase in injection rate per meter increase in recharge head) was 20 m3d-'m-1 and 8.66 m3d-1m-1 for the well installed in the saturated and the vadose zone, respectively. It was also found that injection rate was more for the well constructed in the saturated zone than the injection well installed in the vadose zone since soil formation of the former had higher proportion of coarse sand mixed with gravel. The laboratory analysis of pre and post recharge groundwater samples has shown considerable change in chemical and biological qualities. The EC and pH values decreased for both the cases. The Na and K concentrations in groundwater increased after recharge at vadose zone recharge site. Similarly, Most Probable Number (MPN /1 00 m!) and Chemical  Oxygen Demand (COD) for saturated and vadose zone recharge sites were found to be 26,65 and 110 and 175 ppm respectively whereas for pre recharge water samples corresponding values were 0 and 10.