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Former Beacon Station No. 12474 March 18,2002 Stockton, California Problem Assessment Report/Corrective Action Plan 7.0 FEASIBILITY STUDIES Horizon has conducted soil and groundwater feasibility studies to evaluate the effectiveness of remediation alternatives. Feasibility studies included an aquifer pumping test (Horizon Environmental, 1997a) and vapor extraction and air sparge tests (Horizon Environmental, 2000a). 7.1 Aquifer Pumping Test In May and June 1997, Horizon conducted aquifer pumping tests to evaluate aquifer characteristics of the shallow water-bearing zone beneath the site. Drawdown in pumping monitoring well MW-2 was approximately 10 feet as shown on the groundwater pumping contour map (Appendix D, Figure 3). On the basis of time-drawdown data from the observation wells MW-I and MW-3, the calculated aquifer hydraulic conductivity ranged was 28 and 30 feet per day, respectively. An average hydraulic conductivity of 29 feet per day was used to characterize a theoretical capture zone resulting from extracting 2.0 gallons per minute from monitoring well MW-2 (Appendix D, Figure 4). The down-gradient stagnation point was calculated to be approximately 20 feet from monitoring well MW-2 and the maximum width of the capture zone was calculated to be approximately 126 feet. Groundwater level data collected during the test suggests that sustained, continuous pumping would likely result in a larger capture zone. The results of aquifer pumping tests and capture zone calculations reflect the relatively flat groundwater gradient and fine-grained aquifer materials beneath the site. The high values of hydraulic conductivity may indicate the presence of sandy stringers interbedded with the predominantly fine-grained sediments. 474PARCAP3-02.doc l 1 Project No. 1474.23 HORIZON ENVIRONMENTAL INC.