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25 February 1997 <br /> AGE-NC Project No 95-0134 <br /> Page 2 of 3 <br /> 2.0. SOIL DISPOSITION <br /> On 15 May 1991, soil samples were collected from drums stored on-site and composited for <br /> analysis The drums contained auger returns from the installation of momtonng wells MW-1 through <br /> MW-7 Total volatile hydrocarbons(total petroleum hydrocarbons as gasoline,TPH-g)were detected <br /> at a concentration. of 5 3 mg/kg (milligrams per kilogram, equivalent to parts per million, ppm) <br /> Volatile aromatics (benzene, toluene, ethylbenzene and xylenes, BTE&X) were not detected at the <br /> reporting limit of 0 0024 ppm <br /> On 10 June 1991, a permit was requested from the San Joaquin County Air Pollution Control District <br /> for the aeration of approximately 3 cubic yards of soil Due to the low volume of soil, the site was <br /> found to be exempt from air pollution control regulation A letter from the Air Pollution Control <br /> District is attached The drummed soil was subsequently spread northwest of the former vapor <br /> extraction unit location A sample was collected from the soil stockpile on 10 July 1991 TPH-g was <br /> detected at a concentration of 4 6 ppm, BTE&X were not detected at the reporting limit of 0 005 <br /> ppm The laboratory reports and chain-of-custody forms are attached <br /> In June 1994, borings C13-1, C13-2, MW-8 and MW-9 were installed at or near the site Soil from <br /> these borings was stockpiled north of the former extraction unit location Petroleum hydrocarbons <br /> were not detected in soil samples collected during the installation of borings MW-8 or MW-9 <br /> Approximately 1 3 cubic yards of soil originating from borings CBI and C132 was spread on plastic <br /> sheeting for aeration The soil ,vas subsequently covered with asphalt during paving of a parking <br /> area on the site in May 1996 <br /> 3.0 EXTRACTED HYDROCARBONS <br /> Calculations of extracted hydrocarbons were based upon engine operational time and PID reading <br /> PTD readings were correlated with analytical results of two air samples collected during the <br /> extraction unit operation Calculations are summarized on Table 7 The method of calculations is <br /> also included, using the first operational time period as an example Approximately 720 gallons of <br /> gasoline were calculated to have been removed between August 1991 and December 1993 <br /> The volume of gasoline removed was calculated using a ratio of 1 51 between PID readings and <br /> analytical results This ratio has varied greatly at other vapor extraction sites, and has commonly <br /> been several times higher than those observed from vapor samples collected at the subject site A <br /> higher ratio would yield a greater calculated volume of removed hydrocarbons Therefore,the actual <br /> volume of hydrocarbons removed by vapor extraction may be much greater <br />