Laserfiche WebLink
Site Conceptual Model October 3, 2002 <br /> ARCO Facility No 6100 <br /> 7 SUMMARY <br /> • The site is currently developed as a retail gasoline facility in the vicinity of Tracy, <br /> California The area surrounding the service station is undeveloped <br /> • Existing gasoline USTs, product piping, and dispensers have been upgraded to current <br /> standards A waste oil UST was removed in 1987, the gasoline UST's were replaced in <br /> 1990, and the product piping was replaced in 2002 <br /> • Petroleum hydrocarbons appear to have been initially released to the subsurface from the <br /> former product dispensers and product piping <br /> • An unknown quantity of petroleum hydrocarbon impacted soil was removed from the site <br /> in October 1990 and February 1991 Approximately 315 tons of petroleum hydrocarbon <br /> impacted soil were removed from the site in January 2002 <br /> • The lithology beneath the site consists of an upper silty unit containing discontinuous <br /> sand lenses, underlain by a predominantly sandy unit with two laterally continuous sandy <br /> . strata, overlying a lower silty unit <br /> • The strata beneath the site appear to dip toward the southeast, 5° from horizontal, at a <br /> strike of approximately N1 70E <br /> • The bulk of the contaminant mass in soil occurs between 10 and 45 feet bgs in the <br /> vicinity of the dispensers and product piping Localized high concentrations are <br /> encountered at depths ranging from 45 to 80 feet bgs The on-site extent of hydrocarbon <br /> impact to soil appears has been adequately assessed <br /> • The highest concentrations of petroleum hydrocarbons detected in soil samples collected <br /> from offsite boring B-32/MW-1 were present between approximately 105 to 125 feet bgs <br /> Vertical characterization of off-site soil impact has been adequately assessed <br /> • Permeability rates on soil from approximately 120 feet to 200 feet bgs in boring <br /> B-32/MW-1 are relatively low <br /> • The extent of subsurface fuel oxygenate impact in soil appears to be adequately <br /> characterized Impact appears limited to the near surface in the vicinity of the dispensers <br /> and former product piping <br /> • Groundwater in Sand 1 and Sand 2 appears to migrate along the lithologic contact <br /> between the sand stratum and an underlying silt The groundwater appears to be meteoric <br /> in origin There appears to be vertical pathways allowing the groundwater from Sand 1 to <br /> P 1Bp-Arco for URS161001Reports16100 SCM doe Page 14 Stratus <br />