Evaluation of Well Improvement and Water Quality Change before and after Air Surging in Bedrock Aquifers

Abstract

When a drought occurs, drought response is mainly focused on the development of new wells. However, it is inefficient to respond to droughts by developing additional new wells in areas where many existing groundwater wells have been developed. Rather, it is necessary to find a way to use the existing wells efficiently and, if possible, increase the amount of groundwater that can be pumped. In this study, a pumping test and analysis method were used to evaluate the effect of air surging on improving existing wells. Drawdowns were reduced in the test wells, and, accordingly, the average specific discharges and transmissivities were increased. Since many factors in bedrock aquifers must be considered in order to calculate the well efficiency for the evaluation of the well performance, it seems better to compare the pumping rate and drawdown based on a reference time calculated by an adjusted time. Such factors could be the uncertainty of the aquifer model, aquifer inhomogeneity, and a hydrogeologic boundary. Additionally, in this process, the changes in groundwater quality were investigated, as well as the substances that caused the degradation of the well performance in bedrock aquifers. According to the results of the groundwater quality analysis conducted during the surging process and the step drawdown tests, there was no significant groundwater quality change before and after surging, but it appeared that there was an inflow of contaminants from the upper shallow strata close to the surface. According to the results of the XRD, XRF, and SEM-EDS analyses for the substances collected during surging and the substances deposited inside the well pipe, most of the substances were Fe-related amorphous components. Additionally, Fe coexisted with components such as As, V, and Zn, which formed the well casing together with Fe and were eluted in the surging process and step drawdown tests.