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Former Beacon Station No 12419 March 18,2002 Stockton California Problem Assessment Report/Corrective Action Plan 9.0 FEASIBILITY STUDIES Horizon has conducted groundwater and soil vapor extraction feasibility studies to evaluate the effectiveness of remediation alternatives Feasibility studies included aquifer pumping tests (Horizon Environmental, 1997), and soil vapor extraction and air sparge tests (Horizon Environmental, 1999b) 9.1 Aquifer Pumping Test In May 1997, Horizon conducted aquifer pumping tests to evaluate aquifer characteristics of the shallow water-bearing zone beneath the site, and to evaluate the potential of groundwater pumping as a remedial option Groundwater was pumped from monitoring well MW-3 at a rate of approximately 4 0 gallons per minute (gpm) for approximately 47 3 hours • Drawdown was measured in monitoring wells MW-1, MW-2 and MW-6 Approximately 12,200 gallons of groundwater were extracted during the aquifer pumping test To evaluate long-term effects of aquifer pumping from monitoring well MW-3, groundwater extraction was continued at 2 to 4 gpm until 16 June 1997 resulting in extraction of approximately 54,400 additional gallons Evaluation of aquifer pumping test data indicated a range of hydraulic conductivity (K) values from 5 7 to 46 feet per day (fpd) which are reasonable for the type of aquifer material known to exist at the site Average K values of 19 5 and 28 fpd and pumping rates of 2 5 and 3 0 gpm were used to derive monitoring well MW-3 theoretical steady state capture zones and down-gradient stagnation points Estimated capture zone widths ranged from 430 to 700 feet and estimated down-gradient stagnation points ranged from 68 to 110 feet Results of the aquifer pumping test and the shallow groundwater gradient indicate that groundwater extraction and treatment is a feasible remedial option for the site On the basis of extracted groundwater analyses, it was calculated that approximately 1 3 pounds of TPHg 419PARCAP3-02 doc 17 Project No 1419 23 HORIZON ENVIRONMENTAL INC.