ARCHIVED REPORTS XR0008058 - Laserfiche WebLink

Home Browse Search

June 13, 1997 Page 5 • tank excavation No information was found on the size or contents of the two USTs These additional USTs were removed on February 9, 1990 Following the removal of the newly encountered USTs, a total of four samples were collected on February 9, 1990 within the UST pit TPH-g and BTEX were reported non-detect at the newly encountered UST pit(GTI, April 1990) In August 1990, GTI observed the aeration and backfilling of the previously removed soil generated from the excavation of the gasoline and waste oil USTs, and the two additional USTs The excavations were backfilled with clean imported soil, clean overburden soil, and aerated soil Initial TPH concentrations encountered in the stockpile soil were reported at an average of 70 ppm After 3 months of aeration of the soil, San Joaquin County Health Services Department permitted the reuse of aerated soil for backfilling (GTI, August 1990) In August 1990, GTI drilled three soil borings onsite, all of which were completed as groundwater monitoring wells (Attachment D) All three borings were drilled to a depth of approximately 60 feet bgs A total of 5 soil samples between the three bonngs were analyzed for TPH-g and BTEX TPH-g was reported non-detect in all three borings Benzene was reported in Bonng/Well MW-3 at 18 5 feet and 34 feet bgs with concentrations of 0 08 ppm and 0 05 ppm, respectively Groundwater analytical results for TPH-g and benzene were reported non-detect in Well MW-2 Wells MW-1 and MW-3 reported TPH-g at 810 parts per billion (ppb) and 1,500 ppb, and benzene at 0 5 ppb and 890 ppb, respectively Depth to water was reported at approximately 40 feet In August 1990, groundwater was reported to flow northwest at a gradient of 0 02 (GTI, August 1990) On July 20, 1991, GTI installed offsite monitoring Well MW-4 approximately 90 feet downgradient of the subject site Well MW-4 was installed to provide information on groundwater conditions downgradient of the site A soil sample was collected at 50 feet bgs and reported non-detect for TPH-g and BTEX Analyses of groundwater samples indicated non-detectable concentrations of TPH-g and BTEX in groundwater In addition, groundwater was analyzed for fecal coliform because the monitoring well is located within 50 feet of the City of Stockton sewer line Fecal Coliform was reported at 220 ppb (GTI, September 1991) On September 16, 1991, GTI discovered a 550-gallon waste oil tank onsite approximately 50 feet north of the former gasoline USTs (GTI, November 1991) On December 30, 1991, GeoStrategies, Inc (GSI) observed the removal of the waste oil tank Approximately 15 cubic yards of soil (10 foot long by 13 foot wide by 4 foot deep) was generated from the excavation Confirmation soil sample CW-I was collected at a depth of 6 feet bgs and analyzed for TPH-g, total petroleum hydrocarbons calculated as diesel (TPH-d), total petroleum hydrocarbons calculated as oil (TPH-o), benzene, toluene, ethylbenzene, xylenes (BTEX) and Oil and Grease No detectable 9201036A/CL OSLIRF DOC