WORK PLANS_FILE 1 - Laserfiche WebLink

Home Browse Search

Work ei For Additional Assessment and Feast, tY Y Stud , Quik Stop Market No. 132 3555 West Hammer Lane Stockton, California APPENDIX A BACKGROUND In 1987, Exceltech installed a vadose monitoring system around the three existing gasoline underground storage tanks (USTs). In July 1990, hydrocarbon vapor was detected in the vicinity of the gasoline USTs. Subsequent excavation around the product lines indicated the presence of hydrocarbon impacted soil. Between August 23 and September 13, 1990, Exceltech completed an initial site assessment consisting of the completion of five soil borings (B-1, B-2, B-3, B-4 and B-5)and the installation of four groundwater monitoring wells (MW-1, MW-2, MW-3 and MW-4). The soil and groundwater samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg) and benzene, toluene, ethylbenzene and xylenes (BTEX) in accordance with EPA test methods 8015 and 8020, respectively. TPHg was present in at least one soil sample obtained from B-3 and B-5. BTEX (at least one constituent) was present in at least one soil sample obtained from B-1, B-2, B-3, B-5 and MW-1. The maximum TPHg concentration was 460 milligrams per kilograms (mg/kg) in the soil sample obtained fromB-3at a depth of 15 feet below ground surface (bgs). The maximum benzene concentration was 3.9 mg/kg in the soil sample obtained from B-3 at a depth of 15 feet bgs. TPHg was present in the groundwater sample obtained from MW-1 [320 micrograms per liter (pg/L)]. BTEX (at least one constituent) was present in the groundwater samples obtained from MW-1 and MW-2. The maximum benzene concentration was 34 gg/L in the groundwater sample obtained from groundwater monitoring well MW-1. The locations of soil borings and groundwater monitoring wells are shown on Figure 2. Review of the site geology indicates that two separate groundwater bearing zones may exist beneath the site. The upper groundwater bearing zone appears to be present from approximately 14 to 19 feet bgs, and the lower groundwater bearing zone appears to be present from approximately 20 to 30 feet bgs. Consequently, on October 3, 1990, Exceltech abandoned groundwater monitoring well MW-1 due to the concern that this groundwater monitoring well could possibly connect the two groundwater bearing zones. On April 2, 1991, Exceltech completed an additional site assessment consisting of the installation of two additional groundwater monitoring wells (MW-IA and MW-5). The soil and groundwater samples (from new and existing groundwater monitoring wells) were analyzed for TPHg and BTEX in accordance with EPA test methods 8015 and 8020, respectively: TPHg and BTEX were not present in any of the soil borings. TPHg was present in the groundwater sample obtained from MW-5 (210 pg/L). Benzene (3.4 pg/L) and xylenes (2.1 µg/1.,) were present in the groundwater sample obtained from groundwater monitoring well MW-5. The locations of groundwater monitoring wells are shown on Figure 2.