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i <br />- 6) Hydrocarbon - recovery— data - from -the - VES --(daily -influent <br /> �• concentration, days of operation) are summarized on attached <br /> Thermal Oxidizer Destruction Efficiency Data - Table 1A, and <br /> Hydrocarbon Recovery lbs/day and cumulative - Figures B and C, and <br /> Table B) . The consultants on the project (EA, and Geraghty and <br /> Miller) have stated that the air flow rate had been maintained at <br /> a relatively steady rate of approximately 100 cfm. Influent <br /> hydrocarbon concentrations were measured with an FID/GC. The <br /> hydrocarbon recovery calculation for the final system monitoring <br /> event (September 1992) , is based on an approximate influent <br /> concentration of 100 ppm-v (verbal communication - David Thomas, <br /> Geraghty and Miller) . <br /> 7) Monitor well MW-9 is the only groundwater sampling point, <br /> located within the area of hydrocarbon impacted soil, which has <br /> contained sufficient water for sampling from July 1991 to the <br /> present. The position of the well provides a reference point to <br /> measure the impact to groundwater caused by the presence of <br /> residual hydrocarbons present in the local unsaturated zone. The <br /> presence of dissolved hydrocarbons in MW-9 have declined since July <br /> 1991, with the most recent two sampling events showing the <br /> following analytical values: <br /> B T E X TPH-G (ppb) <br /> 4/6/94 ND ND ND ND ND <br /> 7/8/94 ND 3 . 2 ND ND 80 <br /> It should be noted that the concentrations of dissolved <br /> hydrocarbons in MW-9 have continued to decline, in spite of the <br /> changes in groundwater elevation since July 1991. <br /> 8) Confirmation soil borings (SB-1 to -9) were installed at the <br /> site in December 1993 and May 1994. Soil borings SB-1, -2 and -3 <br /> were the only VES post-operation borings containing measurable <br /> concentrations of hydrocarbon compounds (see attached Soil <br /> Analytical Data Tables) . <br /> A comparison of soil analytical data collected from borings <br /> installed prior to, and during VES operation, to soil data sampled <br /> after the system was turned off, provides a means of evaluating the <br /> degree of hydrocarbon removal. As shown on the attached Site Map <br /> (Figure 2) , matching sets of pre- and post-VES soil data are found <br /> in V-5/MW-4/SB-1 and V-3/MW-9/SB-2/SB-3 (see attached Soil <br /> Analytical Data - Figure D) . The matching soil data sets are <br /> derived from pre-existing borings located adjacent to a <br /> confirmation boring. <br /> Conclusions <br /> 3 <br />