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20 May 1999 <br /> -AGE-NC Project No. 98-0466 <br /> Page 2'of 7 <br /> UST'sarnple at concentrations of 5.5 milligrams per kilogram (mg/kg) and 63 mg/kg,-and.in the <br /> south product line piping sample at-conceritrations of 99 mg/kg and 9.10 mg/kg,respectively. A <br /> piping stockpile soil sample contained 450 mg/kg PH-g and 5,800, mg/kg TPH-d: Minor <br /> concentrations of toluene, ethylberizene and xylenes were detected in some samples; benzene was <br /> not detected in any samples. The analytical-results of the soil samples are included in Table 1. <br /> A Tetter work plan for excavation of°impacted soil ' as' prepared by Stockton Service. Station <br /> Equipment Co., Inc. (SSSEC),on 27 January 1994-and amended by an addendum dated 02 March. <br /> 1994. The area of excavation was not'specifically note in-either'document, although soil sample <br /> localities'were shown near the `Pump& Island' south(f the UST and adjacent building. <br /> Excavation of impacted soil south of the former UST anc adjoining building was conducted between <br /> 10 March 1994 and 28 March 1994. PHS-EHD field n tes for 11 March 1994 note that the lateral <br /> F extent of contamination.appeared to.be defined,.bui od r:was present at 13 feet bsg. The,24' x 30' . <br /> x 13'.deep excavation of 11 March 1994 was expanded t a 20' x 30'x 45' deep excavationand ramp <br /> .by 28 March 1994. Excavation and stockpile soil sampl s were collected on 22 March'1994 and 28 <br /> March 1994: The' :22 March 1994 excavation soil sample (N1-22) collected on the 'north wall of the <br /> excavation at a depth of 22-feet bsg; did not contain detectable concentrations of TPH-g, TPH-d or <br /> BTEX compounds. <br /> Three soil samples were collected from'the.excavation bottom,-at 45 feet bsg, on 28 March 1994. <br /> Soil stockpiles composed of soil removed to construct ramp into the main excavation were also <br /> sampled for laboratory analysis. TP.H-d and BTEX compounds were not detected-in-the excavation <br /> bottom soil.sample.s. TPH-d was detected in,four-out of five corriposited stockpile soil samples at <br /> concentrations as high as 210 mg/kg. Only 0.013-mg/kg xylenes were detected in:one composite <br /> stockpile soil sample; BTEX compounds were not detected in the other-four composite samples. <br /> Table 2 shows the data obtained from the 28 March 1994 soil samples. <br /> Between 28, March and 20 April 1994, the excavation as backfilled:On 20 April 1994, the soil <br /> stockpiles composed of excavated hydrocarbon-impactedsoil'were sampled for laboratory analysis <br /> for characterization. TPH-d was detected in..five of nine stockpile soil samples at concentrations as <br /> high as 7,300 mg/kg. Low concentrations:of toluene,et hylbenzene and/or xylenes were detected in <br /> seven samples at concentrations as high as 47 mg/kg (xylenes). Benzene was not detected in any of <br /> the samples analyzed: Analytical results for the samples are.presented in.Table 3. <br /> PHS-EHD-field diagrams indicafe that the area of excavation was the former dispenser and/orpiping <br /> location;and suggest that the former UST did:not contri ute significantly to the soil contamination. <br /> The data and field riotes available strongly suggests that most of the hydrocarbon-:impacted soil had <br /> been excavated and that the vertical extent of impacted soil had been exceeded at 45 feet bsg in the <br /> excavation. <br /> Advanced GeoEnvironmental,Inc. <br />