ARCHIVED REPORTS_XR0002565 - Laserfiche WebLink

Home Browse Search

1 r A S S O C I A T E S I N C immediate vicinity of the former tank pit_ The highest concentrations were reported between 10 and 20 feet bgs and generally attenuates rapidly with depth. Only low concentrations of toluene (0.064 mg/kg) and xylenes (0.012 mg/kg) were detected at approximately 30 feet bgs, the ' maximum depth explored. Attempts were made to further advance the Geoprobe unit in several of the borings, however probe refusal was encountered at depths ranging from approximately 16 to 31 feet bgs due to the hardness of the formation. The results of the subsurface investigation were summarized in ATC's Summary Report, Subsurface Investigation, dated December 22, 1997. ' Based on previous communications with PHS/EHD personnel and San Joaquin County, Flood Control and Water Conservation District data (Spring 1997 Report) groundwater is estimated to be present at approximately 55 feet bgs. Regional groundwater flow direction has been reported to be easterly (Spring 1997 Report). This groundwater flow direction is consistent with a former ATC project site located approximately 2,000 feet east-southeast of the subject property which ' exhibited a consistent easterly gradient during the duration of the project (1994 to 1996). WELL SURVEY ' ATC reviewed PHS/EHD groundwater well construction logs, Department of Water Resources (DWR) groundwater well construction logs, and conducted a site walk in the vicinity of the site to identify any groundwater wells located within 2,000-foot radius of the site. The search revealed fourteen wells located within approximately 2,000 feet of the site. None of the fourteen wells are located within 500 feet of the site. The well locations are shown on Figure 2. ' The wells were located on the map according to "well location" description information provided on the well construction logs. Available well construction logs are contained in Attachment 1. ' Based on ATC's current work at a project located approximately one mile southwest of the site, the inferred regional groundwater gradient is to the northeast. ' The well located at the northeast corner of the State Hospital (Well No. 11, Attachment 1) is the closest to the site (within approximately 800 feet west). According to the well log, the well is ' approximately 250 feet deep and supplies irrigation water to the State Hospital. The first screen interval in this well is located from 79 to 83 feet below ground surface (bgs). The well is also screened from 188 to 191 feet bgs, 194 to 220 feet bgs, and 240 to 250 feet bgs. Because this ' well is located upgradient from the site, it is ATC's judgment that it is unlikely that the well has been impacted or is threatened by petroleum hydrocarbons from the site. ' The only well located downgradient from the site was a groundwater monitoring well located on the corner of North Wilson Way and East Harding Way (Well No. 6, Attachment 1), but this well was destroyed in 1992. The remaining twelve wells discovered during the well survey are located ' either upgradient or crossgradient from the site and are more than 1,000 feet from the site or have been destroyed (Well No. 4, Attachment 1). Based on this information, it is ATC's judgment that it is unlikely that these wells have been impacted or are threatened by petroleum hydrocarbons ' from the site. w:\97736VeP01U\we15urv.d0C 2