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18 November 1996 <br /> AGE-NC-Project No 95-0134 <br /> Page 3 of 8 <br /> 23 REMEDIATION OF HYDROCARBON-IMPACTED SOIL <br /> On 11 June 1991, one two-inch vapor well (EW-1) was installed by Geological Audit Services, Inc <br /> (GeoAudrt) near the center of the contaminant plume for remediation Designed for soil vapor <br />' extraction, the well has a slotted interval from 5 to 77 feet bsg Organic vapor was measured at <br /> concentrations as high as 2,679 ppmv in soil samples from this boring No soil samples were <br />' analyzed from above a depth of 55 feet Only low concentrations of benzene, toluene and xylenes <br /> were detected in soil samples collected from 55 to 70 feet bsg Procedures and findings were <br /> summarized in a report, titled Installation of Extraction Well at Genova Bakei y, prepared by <br />' GeoAudrt dated 08 July 1991 <br /> A vapor extraction system (VES) was installed on 15 August 1991 and was operated under permit <br />' number 91-61 of the San Joaquin Air Pollution Control District The extraction unit operated for the <br /> first ninety-six hours on the recovered vapors only Between August 1991 and July 1993, the VES <br /> was in operation for approximately 13,500 hours During that period, hydrocarbon vapors were <br />' extiacted from the main extraction well, EW-1 Between 07 December and 11 December 1992, <br /> MW-1 was also used as an additional vapor extraction well for approximately fifty hours <br /> Hydrocarbon vapor concentrations were monitored at the inlet to the VES on a weekly basis using <br /> a photo-ionization detector(PID) The vapor concentrations are summarized on Table 5 and plotted <br />' against time on Figure 4, as recorded <br /> Vapor samples weie collected on 22 February and 28 April 1993 by GcoAudit and analyzed for <br />' TPH-g and BTE&X The sample results were then correlated with the field readings This <br /> information was used to determine the volume and efficiency of hydrocarbon removal Analytical <br /> results of soil vapor samples are summarized on Table 6 Procedures and findings of the vapor <br />' extraction system monitoring were summarized in numerous quarterly i eports prepared by <br /> GeoAudrt <br />' <br /> 24 REGULATORY MEETING <br />' As a result of a 20 August 1993 meeting with the PHS/EHD, the vapor extraction unit was re-started <br /> and operated from 20 September to 26 September and again from 08 November to 07 December <br /> t1993 The unit was shut-off on 07 December 1993 and has not been put in operation since then <br /> The concentration of vapors removed from the soil at the site during the "rebound" period from <br />' September to November 1993 was not significant It appeared that the continued operation of the <br /> vapor extraction unit would not result in additional removal of a considerable volume of <br /> hydrocarbons GeoAudrt recommended that the unit be permanently disconnected and vapor <br /> 1 <br /> 1 <br />