Evaluation of well yield and groundwater quality changes before and after air surging for well rehabilitation

In this study, air surging, the most commonly used physical method among well rehabilitation techniques, was performed to evaluate the improved effects of the method in bedrock aquifers. At two wells in bedrock aquifer for agricultural uses, step drawdown tests were conducted and water qualities and substances deposited inside the wells were analyzed. To analyze the step drawdown test data, the method of Birsoy and Summers was applied. The changes in drawdowns, specific discharges and transmissivities on each step based on a reference time, 1 day by the adjusted time were compared with each other. Drawdowns were reduced in both test wells, and accordingly, the average specific discharges and the average transmissivities were increased. Well efficiency could not be evaluated due to factors such as the uncertainty of the aquifer model, aquifer inhomogeneity and hydrogeologic boundary. The improvement of groundwater quality was investigated by analyzing the groundwater quality during the pumping tests before and after surging. The increase in EC and decrease in pH during the pumping test after surging seem to be related to the inflow of groundwater containing contaminants in the shallow strata close to the surface. Most of the dissolved components were high in the surging process, and FDOM observed in groundwater collected during well surging mainly consists of humic-like and protein-like substances, and anthropogenic pollutants from agricultural activities were also observed. The fluorescence index (FI) for the groundwater mostly showed a value of 1.7 or higher, which indicating the humic-like substances of the terrestrial origin. The materials collected during surging and the substances deposited inside the well pipe were analyzed using XRD, XRF, and SEM-EDS. The materials are mostly amorphous, and there are few minerals with a definite crystalline structure. According to SEM-EDS analysis, Fe-related substances mainly constitute the deposit materials such as Fe-Oxides. Fe accounts for most of the weight percent with 45.4~47.3% from the materials deposited inside the pipes of the D-8 well. The other elements, arsenic and zinc, exist together with iron or could be be eluted from the well casing. Acknowledgement: This research was funded by the Korea Environment Industry and Technology Institute (KEITI) through the Demand Responsive Water Supply Service Program (or Project), funded by the Korean Ministry of Environment (MOE).