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When water extraction ceases in a well, the water level will rebound or recover. The measure of water elevation rebound versus time (as a function of the ratio of the time since discharge started divided by the time since extraction stopped) is known as residual drawdown. The residual drawdown plotted on a graph with time plotted on a ' logarithmic axis ideally will result in a straight line. In this instance the well discharge rate used was calculated as the total volume of water extracted divided by the time over which water was extracted from the well. Analyses were completed by downloading data from the pressure transducers and uploading the data to the Aquifer Test Pro version 3.5 computer software. The software uses the residual drawdown plot with the well discharge rate to calculate hydraulic conductivity for the well. This analysis assumes the following: • The well is screened across the entire aquifer. • The aquifer is confined. • The piezometric surface is flat. • The aquifer is homogeneous, isotropic, and of uniform thickness. • Pumping occurs at a uniform rate. • Water removed from storage is discharged instantaneously with a decline in head. • The well diameter is small and casing storage effects are negligible. The results of the calculations are shown on charts presented in Appendix E2. As shown, the residual recovery data for wells MW-9A and MW-11A plot as a straight line over the entire data set. The data from well MW-10A exhibit a slight deviation from the straight line plot. The deflection in the curve occurs over a time period of only about 1.5 ' minutes and may not be an accurate reflection of the aquifer system. The calculated hydraulic conductivity for each well is presented on Table 8. As summarized on the table, the fastest hydraulic conductivity value was measured in well MW-9A at 0.0383 feet/day and the slowest was measure in well MW-10A using the late time data at 0.0059 feet/day. Table 8 ' Calculated Hydraulic Conductivity Values for the Phase II EMP Wells Well Hydraulic Conductivity(feet/day) MW-9A 0.0383 feet/day MW-10A early 0.0065 feet/day MW-10A late 0.0059 feet/day MW-11 0.0136 feet/day Geometric Mean 0.0119 feet/day ' The groundwater flow velocity around the site is a function of the hydraulic conductivity, the gradient, and the effective porosity. A range of groundwater flow EMP Report—Phase IIGeo-foga Page ■ 16 Corral Hollow Sanitary Landfill ASSOCIATES August 21,2012