ARCHIVED REPORTS_XR0002998 - Laserfiche WebLink

Home Browse Search

Ms. Lori Duncan Page 2 of 5 San Joaquin County Environmental Health Department November 23, 2005 from northeast to southeast, with hydraulic gradients ranging from 0.002 feet/foot (ft/ft) to 0.03 ft/ft(see Table 1 and Figure 9). Site History ' Consult the SCM for site history prior to December 2004. In December 2004, two groundwater monitoring wells (MW-7 and MW-8) were installed to monitor the lateral and vertical extent of groundwater impacts at the site.MW-7 is located off site and down gradient of the former USTs and MW-8 was installed in the vicinity of the former USTs to monitor deep groundwater. ' Well locations are shown in Figure 2. f Selected soil samples were collected and analyzed from each monitoring well boring and submitted for analysis by gasoline-range organics(GRO)by EPA Method 8015B(preparation by EPA Method 5030),and r; for benzene,ethylbenzene,toluene,and xylenes,(BTEX),methyl-tert butyl ether(MtBE),tert butyl alcohol (TBA), di-isopropyl ether (DIPE), ethyl tert-butyl ether (ELBE), tert-amyl methyl ether (TAME), 1,2- dichloroethane(1,2-DCA),and 1,2-dibromomethane(EDB),by EPA Method 8260B (preparation by EPA Method 5030). GRO, benzene, toluene, ethylbenzene, and xylenes were reported in soil samples from MW-8. All fuel oxygenates analyzed were reported as below laboratory detection limits. The soil sample collected from MW-7 was reported below laboratory detection limits for all analytes.Soil analytical data for the December 2004 sampling event are summarized in Appendix C. HYDROCARBON DISTRIBUTION Hydrocarbons in the Unsaturated Zone Soil samples collected during drilling activities conducted between 1990 and 1993 indicated that hydrocarbon-impacted soils were confined primarily to the vicinity of the UST complex. Soil samples collected at 15.5 feet bgs during UST removal activities in February 1998 contained up to 8,200 milligrams �+ per kilogram (mg/kg) TPHg and up to 4.6 mg/kg benzene. Soil samples collected beneath the piping in February 1998 contained maximum concentrations of 12 mg/kg of TPHg and 0.03 mg/kg of benzene. Soil samples collected from MW-8 identified GRO and BTEX from 45 to 98 feet bgs.Because the water table has risen to approximately 25 feet bgs, the historical soil impacts are now below the water table. Hydrocarbons in Groundwater 1, Groundwater at the site has been monitored regularly since site investigations began.Results of monitoring since 1995 are summarized in Appendix D. Table 2 summarizes construction details for all site wells. Groundwater analytical data from the September 2005 monitoring event are presented in Figures 3 through 8 and 10 through 15. Groundwater impacted by GRO is generally confined to the southeastern portion of the site,extending from the area of the UST complex downgradient to MW-5(Figures 3 and 4).The maximum concentration of GRO KAWprocessU5 BP ARCd10054812005 SCM Update\SCM Update Text.doc