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21 August 2000 • AGE-NC Protect No 97-0343 Page 2 of 9 2 2 UNDERGROUND STORAGE TANK REMOVAL Two 550-gallon USTs were removed from the site on 03 October 1986 by Stockton Service Station Equipment Company According to correspondence from the PHS-EHD,both USTs were reportedly used to store gasoline Upon removal of the USTs, one soil sample was collected from the floor of the excavation The sample was analyzed by California Water Labs, hic , a state-certified analytical laboratory, for total petroleum hydrocarbons quantified as diesel (TPH-d), benzene, toluene and xylene TPH-d and xylene were detected in the soil sample at concentrations of 3,000 parts per million(ppm) and 0 188 ppm, respectively Benzene and toluene were not detected above the analytical method reporting limit of 010 ppm Based upon results of the soil sample analysis,the PHS-EHD required assessment of the lateral and vertical extent of hydrocarbon-imp acted soil and/or ground water in the area of the former UST 23 PREVIOUS SUBSURFACE INVESTIGATION On 18 September 1997,five soil probe borings(B-1 through B-5)were advanced at the site to assess • the lateral and vertical extent of petroleum-impacted soil TPH-g was detected in samples from B 1, B3 and B5 at concentrations as high as 14,000 ppm(reported as milligrams per kilogram) Benzene was detected in only one sample(B1-40),which contained a concentration of 0 042 ppm Toluene, ethylbenzene and xylenes were detected in samples from B1, B3 and B5 at concentrations as high as 1,600 ppm (xylenes in B5-25) TPH-d was detected in samples from B-1, B-3 and B-5 at concentrations as high as 12,000 ppm (B3-10, B3-15) None of the samples analyzed from borings B-2 or B-4 contained detectable concentrations of TPH- g, TPH-d, BTE&X or MTBE The analytical results by EPA analytical methods 8015-m and 8020 as shown in Table 1 Results of the September 1997 investigation were reported in Preliminary Site Investigation Report dated 30 December 1997, prepared by AGE From 22 to 24 February 2000, four soil borings (MW-1 through MW-3 and B-6)were advanced at the site TPH-g was detected in 9 of the 16 soil samples analyzed at concentrations as high as 6,700 parts per million(ppm,reported as milligrams per kilogram),TPH-d was detected in 7 of the 16 soil samples analyzed at concentrations as high as 5,800 ppm Benzene was detected in 4 of the 16 samples at concentrations as high as 0 027 ppm Toluene, ethylbenzene and xylenes were detected in 11 of 16 samples at concentrations as high as 370 ppm MTBE was not detected in any samples analyzed Petroleum hydrocarbons were not detected in 5 of the 16 soil samples analyzed Analytical results of soil samples are summarized on Table I Advanced Geo Environmental,Inc