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' 18 February 1997 AGE-NC Project No 95-0104 ' Page 5 of 22 ' at MW-3 and MW-4 may be attributed to screen intervals submerged beneath water A vacuum was not measured in well MW-2 during the pilot test, located approximately 30 feet from ' VW-1 However, a strong vacuum was measured at MW-1 Therefore, based upon the vacuums measured from VW-1 and MW-1, it is likely that the effective radius of influence for soils at the site is approximately twenty feet 3 5 ANALYTICAL RESULTS OF VAPOR SAMPLES ' Hydrocarbon concentrations in the effluent stream from VW-1 were monitored at regular intervals utilizing a PID The PID field measurements ranged from 275 ppm to 423 ppm Laboratory analysis ' of the four vapor samples collected detected TPH-g concentrations ranging from 11,000 micrograms per liter (ug/1) to 23,000 pg/1 (see Table 3) Converting these values to parts per million volume (ppmv), concentrations ranged from 3,080 ppmv to 6,440 ppmv The laboratory report and chain-of- custody are included in Appendix B Equations for conversion of ugll to ppmv are included in Appendix C 40 ASSESSMENT OF HYDROCARBON-IMPACTED SOIL,AND GROUNDWATER IBetween 1988 and 1996, one soil boring (B-1), six ground water monitoring wells (MW-1 through MW-6) and one soil vapor extraction well (VW-1) were installed at the cite to investigate the extent I of hydrocarbon-impacted soil and ground water in the vicinity of the former UST The greatest concentrations of hydrocarbon-impacted soil and ground water has been encountered at SVT-well VW-1 A general decline of concentrations of dissolved petroleum hydrocai bons has been reported in wells MW-1 and MW-2 However, since April 1994, ground water surface has been above the slotted screen interval in MW-2 and, therefore, data from MW-2 may not accurately represent surficial ground water composition Analytical results of soil and ground water samples are summarized in Table Nos 1 and 2 Figures 4 and 5 depict general hthology and selected soil sample results beneath the site in cross sectional view When the data collected at the site is plotted in both plan view and cross sectional view, the apparent volume of petroleum impacted soil beneath the site is approximately 220 cubic yards (Appendix D) A mass-volume calculation usingthe data collected during investigation of the former g g UST area, yields approximately 308 gallons of gasoline in the remaining impacted soil at the site (Appendix Dl Assuming that VW-1 is within the source area, an effective radius of fifteen-feet was used to estimate the volume of impacted soil An average concentration of 14,000 ppm was used to calculate the total volume of remaining hydrocarbons from 15 to 30 feet bsg, while 1 1 ppm was used to calculate the