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INTERIM PROBLEM ASSESSMENT REPORT[U4M IM REMEDIAL ACTION PLAN -12- Former Beacon Station No. 494, 2185 East Fremont Street Stockton, CA--AMV Project No. 19005.07 ' wear on theum used - p p ed in the 48-hour continuous test. Because of the increased pumping capacity (greater than the well's recharge rate), AMV installed level controls to turn off the Pump when water level reached a low point in the well, and to turn the pump back on when the well recharged to a high point. After installing the new pump and level controls, the second phase of pumping began on July 7, 1993, and ran through July 19, 1993. At the conclusion of the test, AMV collected water samples for laboratory analysis of VOCs by EPA Methods 624 and 625. The result for benzene was nondetectable, at a detection limit of 10 gg/l. No nonpetroleum compounds were detected. ' Appendix M contains a copy of the certified analytical report for all samples collected during the pumping test. ' 6.2 Vapor Extraction Test On March 17 and 18, 1993, Remediation Testing and Design (RTD) conducted vapor extraction feasibility testing by applying a vacuum to vapor extractions wells VW-la, VW-lb, VW-2a, VW-2b, VW-3a, VW-3b, VW-4a, VW-4b, monitoring well MW-3, and nine 3/4-inch-diameter ' probes (Figure 4). Testing on VW-2a and VW-2b lasted 65 minutes for each well. Testing on the other wells lasted only long enough to determine a relationship between vacuum applied and extraction flow rate (step test). An applied vacuum of 5 inches mercury (Hg) induced airflow ' in all of the vapor extraction wells, but not in monitoring well MW-3. The flows at a vacuum of 5 inches Hg ranged from 10 standard cubic feet per minute (scfm) for vapor extraction well VW-3a to 27 scfm for VW-4a, with an average for all vapor extraction wells of about 19 scfm. In the 65-minute tests on VW-2a and VW-2b both conducted with an applied vacuum of 10 inches Hg, vacuum influence was observed as far away as extraction wells VW-3a and ' VW-3b during both tests. Wells VW-3a and VW-3b are approximately 50 feet from wells VW-2a and VW-2b. Observed flow rates at these conditions were 29 scfm for VW-2a and 35 scfm for VW-2b. ' Air samples collected from extraction wells VW-2a and VW-2b at the conclusion of the respective 65-minute tests contained a TPHg concentration of 10,000 ppmv- for VW-2a and ' 15,000 ppmv for VW-2b, the calculated rates of hydrocarbon removal are 95 pounds per day for VW-2a and 168 pounds per day for VW-2b. Appendix N contains the calculations used by AMV to determine the hydrocarbon removal rates. ' rr mi