Low-flow hydraulic conductivity tests at wells that cross the water table

Wells with screens and sand packs that cross the water table represent a challenging problem for determining hydraulic conductivity by slug testing due to sand pack drainage and resaturation. Sand pack drainage results in a multisegmented recovery curve. One must then subjectively pick a portion of the curve to analyze. Sand pack drainage also results in a change in the effective radius of the well which requires a guess at the porosity or specific yield in analyzing the test. In the study of Robbins et al. (2009), a method was introduced to obtain hydraulic conductivity in monitoring wells using the steady-state drawdown and flow rate obtained during low-flow sampling. The method was tested in this study in wells whose screens cross the water table and shown to avoid sand pack drainage problems that complicate analyzing slug tests. In applying the method to low-flow sampling, only a single pair of steady-state flow rate and drawdown are needed; hence, to derive meaningful results, an accurate determination of these parameters is required.