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Report on Additional Excavatioln and Confirmation Soil,Sampling Ca Bulk Transportation Facility, Stockton, California Hygieketics Environmental Services,Inc. Slough flows into the San Joaquin River, which flows northward approximately 7,000 feet west of the site. E � `f 1.2.2 Geology I The site is within the Great Valley Geomorphic Province in central California. Primary geomorphic units with the province include dissected uplands; low alluvial plains and fans, river flood plains and channels, and overflow lands and lake bottoms. Stockton and the site lie within the river flood plains and channels geomorphic units. Near sinface sediments underlying the site include Holocene-age flood basin deposits. These deposits, which occur from the ground surface to as much as 100 feet below grade, consist of unconsolidated units of clay, silt, and some sand (Page, 1986), Shallow sediments observed duringremoval of the UST and d dispenser facilities in October 2002 and during additional excavation beneath the fuel pipeline in July 2003 include dark brown, high plasticity, silty clay between 1 foot and approximately 4 feet below grade and yellow-brown silt between 4 and 16 feet below grade. Brown,silty fine-grained sand was observed at the 16-foot depth in the western portion of the UST excavation. 1.2.3 Ground Water !{ I No ground water was observed in the UST excavation in October 2002. Depth to first ground water, therefore, is inferred to be greater than 16 feet below the ground surface. Information from San Joaquin County Environmental Health Department and Bulk Transportation (Mr.t Andrew 4 Woods, verbal communication, July 30, 2003) indicates ground water in the area may be at a depth of approximately 30 feet below the ground surface11. i 1.3 Removal of Underground Storage Tank and Dispenser Facilities Foss excavated and removed the dispensers and associated 'fuel piping during the ;week of j October 14 through 18, 2002 and removed the UST on October 21, 2002. A total length of approximately 55 feet of trench line was excavated between the eastern edge of the UST pit and the dispenser facilities. These trenches were approximately 3 feet wide and extended to a depth L of 3 feet below the ground surface. The UST excavation was'43 feet long by 17 feet wide and extended to a depth of 16 feet below grade. The extent of excavation in October 2002 is shown on Plate 2. �# Hygienctics collected a total of seven soil samples at locations beneath the tank, pipelines, and dispensers shortly after tank removal. These samples were submitted to a state certified laboratory for analysis for total petroleum hydrocarbons as jdiesel,(TPHd) and the aromatic hydrocarbons benzene, toluene, ethylbenzene, and total xylenes (BTEX). The results of the laboratory analyses showed no detectable concentrations of TPHd or BTEX were found in the three soil samples collected from the UST pit and the soil sample collected beneath the former location of the northern satellite dispenser. A concentration of 42 parts per million (ppm) TPHd , was detected in soil beneath the former location of the southern satellite dispenser; 1,700 ppm TPHd was detected in soil beneath the former location of the central Control dispenser; and 2,400 ppm TPHd was detected in soil beneath the location of the fuel supply,line. No BTEX was found in these latter three samples. The laboratory report noted that.foil-range petroleum hydrocarbons comprised a significant fraction of the hydrocarbons detected in!,the three samples, which 2 ''