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Technical Memorandum April 7, 2017 Page 4 Following completion of the work, the boreholes were backfilled with neat cement via tremie grouting under oversight of the San Joaquin County Environmental Health Department. The surface of the boreholes were patched with concrete to match existing surface conditions. DISCUSSION OF RESULTS The results of the CPT activities indicate that the higher PCE concentrations in the LCP, as represented by the 500 }tg/1 contour on Figure 1, does not extend south of Tokay Street. However, PCE concentration at monitoring well G-25A, an upper intermediate zone well screened from 89 to 99 ft-bgs, was observed to be 1,100 Itg/L in November 2017. These data suggest that the leading edge of the 500 gAg/L contour in the intermediate zone is located between G-25A and CPT-38. Langan performed a step-drawdown test at G-25A on October 17, 2016 to estimate the production capacity of the upper intermediate zone and whether an extraction well installed near G-25A would produce the required pumping rate to attain capture of the LCP in that area. The results of the step-drawdown test indicated that groundwater levels decreased a total of 3.6 feet and stabilized within 15 minutes from the start of each step test. With a 2-inch diameter well casing, the maximum pumping rate from G-25A was 8 gpm. These data suggest that an extraction well screened in the upper intermediate zone near G-25A could pump at a stable rate of 8 gpm. The step-drawdown data was evaluated using AQTESOLV, a curve fitting software that incorporates various commonly used aquifer-testing models, to estimate the hydraulic conductivity of the upper intermediate zone. Using the Jvandel and Tsang formula for estimating capture zones (Jvandel and Tsang, 1986, Capture-Zone Type Curves: A Tool for Aquifer Cleanup, in Groundwater, Vol. 24 Issue 5, September 1986), the maximum step-drawdown test pumping rate of 8 gpm, a hydraulic gradient of 0.0035 feet per foot for the upper intermediate zone (see Figure 3, Fourth Quarter and Annual 2016 Groundwater Monitoring Report — Central, Western, Southern, and Northern Plumes, Lodi, California, Stantec, January 31, 2017), and the estimated average hydraulic conductivity value of 10 feet per day, the width of the capture zone at G-25A was estimated to be approximately 870 feet. This indicates the higher PCE concentrations in the LCP in the upper intermediate zone can be captured and contained by an extraction well located near G-25A and screened from 89 to 99 ft-bgs. RECOMMENDED EXTRACTION WELL LOCATION Based on the analysis of currently-available data, results of the step-drawdovvn test at G-25A, results of the CPT investigation, and capture zone analysis, we recommend that a 6-inch diameter replacement extraction well EW-7R be located approximately 20 feet north of monitoring well -25A (see Figure 1). The recommended extraction rate is 8 gpm and the recommended screen interval is from 75 to 100 ft-bgs. Final depth and screen interval will be based on location-specific data collected during drilling. Final extraction rate for EW-7R will be determined during the GWET system startup activities, which will include performing a step-drawdown test at EW-7R. WEST YOST ASSOCIATES cAA21 3 \ 17-17-37 \wp \LPEDW-7RLocation \ 040517_2M