ARCHIVED REPORTS_XR0011645 - Laserfiche WebLink

Home Browse Search

Monitoring Well Installation Report Tosco(Former BP)SS#11195,Lathrop California r. >3 July 24,2002 diameter temporary groundwater extraction conductor casing was installed in the former UST pit prior to backfilling. The locations of pertinent site facilities are shown of Figure 2. 2.2 Geology and Hydrogeology The site is situated on generally flat topography at an elevation of approximately 10 feet above mean sea level (MSL). The San Joaquin River is located approximately 1.1 miles southwest of the site and Weatherbee Lake is located approximately 2.7 miles south of the site. The static depth to groundwater in the eleven existing monitoring wells at the site was measured at 7.69 to 11.94 feet below ground surface(bgs) on June 18, 2002. The groundwater flow direction on June 18, 2002, was toward the southwest at a gradient range of 0.006 to 0.0.1. The historical groundwater flow direction is generally southward at an average gradient of 0.001 (GR 1st Quarter, 2002). 2.3 Previous Environmental Work A retail gasoline outlet has been located at the subject site since at least 1983. BP Oil Company(BP) acquired the site from Mobil Oil Corporation in 1989, then sold the site to Tosco in .1994.(Alisto, Additional Site Investigation Report, dated January 25, 1999). Five on-site groundwater monitoring wells (MW-1 through MW-5)were installed in December 1992. Soil samples collected from the borings were reported to contain petroleum hydrocarbons at concentrations of up to 120 parts per million (ppm) of Total Petroleum Hydrocarbons as gasoline (TPHg), and 16 ppm of benzene. The initial groundwater samples collected from wells MW-3 and MW-4 contained concentrations of up to 10,000 parts per billion (ppb) of TPHg(Alisto, 1999). Two additional wells (MW-6 on-site and MW-7 off-si(e) were installed in September 1993. Soil samples collected at a depth of 6 feet bgs were non-detect for petroleum hydrocarbons (Alisto, 1999). One 550-gallon fiberglass waste oil UST and associated remote fill line were removed in 1997. One soil sample was collected from the bottom of the waste oil UST excavation at 10 feet bgs. A second soil sample was collected from beneath the remote fill line at 3 feet bgs. Both samples were non-detect for petroleum hydrocarbons (GeoStrategies, Waste Oil UST and Remote Fill Line Soil Sampling Report, dated August 6, 1997). In July 1998,an abandoned water well,located north of the former UST pit adjacent to Louise Avenue, was properly destroyed. The well was destroyed by perforating the steel casing and grouting the well with neat cement placed by the use of a grout pump and tremie_pipe. The well destruction was permitted and observed by the SJCPHS-EHD. Five off-site wells (MW-8 through MW-12) were installed and one off-site well MW-7 was destroyed 140193.12-2 2 I