ARCHIVED REPORTS_XR0012638 - Laserfiche WebLink

Home Browse Search

;SII PRELIMINARY REPORT AND TANK CLOSURE REPORT Tracy Boulevard Shell - — 3725 Tracy Boulevard,Tracy,Calirwnia Delta Project No.40-89-012 Page 16 A topographic map was used to infer the regional direction of ground water flow. Due to the orientation and elevations of the valley and drainage network, the regional direction of ground water flow is expected i to be to the northwest and north. Slug test and grain size analyses indicate the hydraulic conductivity values for the sandy silt to silty sand beneath the site range between 0.25 and 34 feet per day with an average value of 15 feet per day(Table 3 and 4). The values obtained from the slug and grain size analysis correlate with expected hydraulic conductivity values for similar soils. 5.3 Petroleum Hydrocarbons in Sall Results of chemical analyse:,for BTEX,TPH,and organic lead on soil samples collec,ed Pr,!t the former tank excavation,the new tank excavation,the formar product line locations,and the overexcav-ation work (figure 9) indican: that soil containing hydrocarbons to a depth of approximately 9 feet (near the water table)have been removed from the site. However,petroleum constituents have been identified in soil at the water table,approximately 10 feet below the ground surface. Figure 10 presents the soil sampling locations where petroleum constituents have been identified at the water table. 5.4 Petroleum f4drocarbons In Ground Water Chemical analyses of the ground water samples collected on September 26,1989,from the on-site monitoring wells(abandoned on duly 5, 1990) indicated that concentrations of BTEX and TPH were below detection limits. Chemical analyses of the grt unil. water samples collected on August 28, 1990, f•om the on-site 1 replacement monitoring wells (installed on August 16, T990) indicated that concentrations of BTEX and TPH were below election limits(Table 6,Appendix r). Aground water sample collected from the former (((` tank excavation indicates that the TPH concentration was 500 ppb and the BTEX concentrations ranged from 5.4 to 58 ppb (Table 7, Apperdix G). The EDB and organ c Ir-.zd concentrations were below the analytica, inethod detection limits. 6.0 WORK PLAN ; Delta proposes to continue gt:arterly ground water monitoring of wells MW-IA,MW-2A,and MW-3A for four additional quarters. Each well will be purged and ground water samples collected in November 1990, and February,May,and August 1991. Ground water samples wili be shipped to a state-certified laboratory ' . and a.^.a!;��for BTEX and TPH.