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r • . yc v 1' - - n; TABLE 2 SOIL VAPOR EXTRACTION PILOT TEST RESULTS EXTRACTED VAPOR CONCENTRATIONS (in µgli) MANTECA BEAN FACILITY, MANTECA, CALIFORNIA MAY 8-14, 1990 - SAMPLE FLOW RATE ELAPSED TIME BENZENE TPH-G POINT (CFM) (HOURS) (µI 11) (µ91I) MW-2A 130 0.33 5,800 170,000 MWI 130 22.75 1,200 82,000 MW-2C 130 45.25 1,200 83,000 MW-2D 130 64.75 750 56,000 MW-2E 130 -,135.25 220 20.000.,,..- MW-3A 0.0001MW-3A 130 0.95 3,100 110,000 MW-5A 130 0.88 510 26,000 MW-6A 130 1.00 59 3,400 The highest soil vapor concentrations were measured in wells near the former underground tank (MW-2 and MW-3), as expected from the results of the soil gas survey. li and MW-6 exhibited one and two orders of magnitude lower benzene concentrations, respectively. Soil vapor was extracted from MW-2 at a rate of 130 cfm for 135 hours to determine the rate at 9 which hydrocarbon concentrations decrease with time. A graph of benzene and TPH-G concentration versus gime is included in Appendix I. At the start of the test,0.04 feet of separate phase petroleum was measured in MW-2. No separate phase petroleum was detected on the second day. The water table had mounded up approximately 0.79 feet due to the negative pressure exerted by the vacuum blower. The blower was off due to an electrical failure between hours 40 and 44,hence samples MI and MW-2C have similar concentrations of TPH-G and benzene. The p&oleum�hydrocarbon mass extraction rate: fldm MW-2 at the'end of the test was 233 lbs(day The pilot test was successful in providing data with which to design an extraction and treatment system. The radius of influence was evaluated for different tiuw ,aces to allow selection of the proper vacuum blower. Hydrocarbon concentrations.were evaluated from several candidate extraction wells to allow extraction well selection. Finally, a hydrocarbon dissipation curve was calculated for predicting concentrations to be treated after prolonged operation of the system. 3.3.3 Soil Vapor Extraction and Emission Control System Design - remove rale from W 2 after 135 hours or•. of vapextractlan-was,233jbs/day�. ----- The San Joaquin County Air Pollution Control District uses risk based criteria to evaluate allowable L .GROUNIAVATEIZ Twisol.oc)`,INC.