ARCHIVED REPORTS_XR0003251 - Laserfiche WebLink

Home Browse Search

1 ' 31 July 2000 AGE-NC Project No. 98-0468 Page 3 of 11 Soil Excavation and Sampling In April 1995, petroleum hydrocarbon-impacted soil was excavated and removed from the area of the former diesel UST. During the excavation activities, soil samples were;not collected due to encountering the ground water'table above the base'of the former tank excavation. Therefore, a ground water sample was collected from the excavation. Laboratory analysis of the ground water sample detected elevated levels of benzene '(1;000 ppb), toluene (2,000 ppb), ethylbenzene (800 ppb), total xylenes (6,400 ppb), and TPH-g (17,000 ppb). In August 1995, additional petroleum hydrocarbon impacted soil was excavated.and removed from the former diesel UST location and soil samples collected for analysis. Laboratory analysis of the soil samples collected from the four sidewalls of the excavation detected benzene (5.9 ppm),toluene (46 ppm),ethylbenzene(23 ppm),total xylene(150 ppm),TPH-g(3,800 ppm),and TPH-d(45 ppm). The majority of the reported detections of petroleum hydrocarbon compounds were from the east and west sidewalls of the excavation. Subsequently, the City of Stockton backfilled and compacted the excavation. Site Characterization In 1996, The Twining Laboratories, Inca conducted a site investigation to assess the lateral extent of petroleum hydrocarbon impacts •to soil and ground water at the site. The site characterization activities consisted of the advancement of seven soil probes(SB-1 through SB-7) and the collection of soil and in-situ ground water samples for laboratory analysis (Figure 2). Laboratory analysis of soil samples detected BTEX, TPH-d, TPH-g and methyl tertiary-butyl ether (MTBE) for samples collected from soil probe boring SB-5. In addition, relatively low concentrations of petroleum hydrocarbon compounds were detected for soil samples collected from SB-4 and SB-7. The analytical results of ground water samples collected from the soil probe borings suggested that ground water has been extensively impacted by BTEX, TPH-d, TPH-g and MTBE. The greatest petroleum hydrocarbon impacts to groundwater were reported.for soil probe boring locations SB-5 and SB-7 located north of the former diesel UST location. Laboratory analysis of ground water samples collected from- soil probe SB-5 detected benzene (6,500 ppb), toluene ; (35,000 ppb), ethylbenzene (4,500 ppb), total xylenes (25,000 ppb), TPH-d (320,000 ppb), TPH-g (93,000 ppb), and MTBE (560 ppb). Additional Soil and Ground Water Assessment -In April 1999, additional soil and ground water assessment activities were conducted at the.site. A total,of five soil borings were completed, soil samples were collected for analysis, and two Advanced GeoEnvironmental,Inc.