ARCHIVED REPORTS XR0003077 - Laserfiche WebLink

Home Browse Search

Monitoring Well Installation Report Former Chevron Service station #9-5775 June 2 1999 from the north) and the San Joaquin River (flowing from the south) which join in the delta area east of Suisun Bay The site is a relatively flat, unpaved, vacant lot at an elevation of approximately 42 feet above mean sea level Soil in the site vicinity consists of Pliocene to Holocene continental rocks and deposits consisting of heterogeneous mix of generally poorly sorted clay, silt, sand, and gravel, some beds of claystone, sdtstone, sandstone, and conglomerate (R W Page, 1986) The nearest surface water is South Main Canal located approximately 3/4 miles west of the site Pixley Slough is located approximately 21/2 miles south of the subject site and Mokelumne River is located approximately 23/4 miles north of the subject site Based on the site topography, groundwater in the vicinity of the site flows toward the southwest Based on information supplied by Mr Harlin Knoll of the SJCPHS prior to beginning work, groundwater in the vicinity of the subject site was believed to be at a depth of approximately 40 feet below ground surface (bgs) Data from monitoring wells in the site vicinity indicate the historic groundwater low to be approximately 65 feet bgs 2.3 Previous Enviromnental Work The five former USTs, former hydraulic hoist, former dispenser islands and associated product piping were . removed on August 24, 1998 Soil samples were collected from beneath the USTs and product piping Very low to non-detectable concentrations of petroleum hydrocarbons were detected in all the soil samples from beneath the waste oil USTs, the products lines, the hydraulic hoist, and five of the six samples from the gasoline UST pit The sample from 14 5 feet bgs beneath the eastern end of the middle gasoline UST contained 14,000 parts per million (ppm) of Total Petroleum Hydrocarbons as gasoline (TPHg), 84 ppm of benzene and 56 ppm of methyl tertiary butyl ether (MtBE) Based on field screening data, the area beneath the eastern end of the middle gasoline UST was excavated from 14 5 to 16 feet bgs, and a second sample was collected This sample contained 880 ppm of TPHg and 11 ppm of MtBE Benzene was not detected in this sample 0 The area beneath the eastern end of the middle gasoline UST was overexcavated from 16 to 22 5 feet bgs on August 31, 1998 Soil samples were collected from the base and the eastern wall of this excavated area The base sample contained 2,300 ppm of TPHg, 4 1 ppm of benzene and 330 ppm of MtBE The wall sample, collected at 18 5 feet bgs, contained 290 ppm of TPHg, 0 35 ppm of benzene and 22 ppm of MtBE 3.0 WELL SURVEY GR conducted a survey to locate municipal and domestic wells within a t/2 -mile radius of the subject site Information from the SJCPHS indicated that a City of Lodi municipal well is located in the southwestern vicinity of the subject site On March 15,1999, GR personnel reviewed files of the California Department of Water Resources (CDWR) The CDWR file review indicated that two groundwater monitoring wells are located within the 1/2 -mile radius of the subject site and two municipal wells and one domestic well are 346408 04-2