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Mr Daniel K Barber, P E September 9,2003 Page 13 of 17 ' area is in use for drinking water use (based on the well survey results), application of the drinking water standard does not appear to be appropriate However, for consideration of the ' potential impacts, the regulators generally rule by the assumption that site groundwater is a known or potential source of drinking water, unless a site-specific variance is granted The likelihood of groundwater impacts to beneficial use in this area appears to be negligible CONCLUSIONS AND RECOMMENDATIONS ' Based on our review of the site investigation and regulatory communication data provided by D K Barber & Associates for the Western Oil & Spreading, Inc Acampo Plant Site in Acampo, California, the following conclusions were reached ■ In October 1987, five USTs were removed in two separate UST excavations at the property, along with an undisclosed amount of hydrocarbon-contaminated soil The UST excavations were located approximately 250 feet apart, the excavation in the southwestern part of the site (500-gallon gasoline UST, 1,000-gallon gasoline UST, and 2,000-gallon diesel UST) showed no contamination of regulatory concern The shallow subsurface • contamination is due mainly to the former 20,000-gallon liquid asphalt UST located in the northeastern portion of the property near monitoring well MW-1 Another area of soil contamination is also apparent near MW-4, however, there are no known sources in ' that area The soil contamination, mainly at a depth of 30 feet bgs, may reflect lateral migration into the perched aquifer zone and subsequent sorption onto the clays in the 30- to 40-foot zone ■ In a "notice of responsibility" letter dated April 25, 1997, the SJCEHD notified Western Oil & Spreading, Inc that the site could not be considered for closure until further site investigation or remedial action was completed ■ The first investigation to further define the extent of contamination occurred in 1999, with six exploratory bores from which soil and grab-groundwater samples were collected Soil contamination was noted near the current locations of wells MW-1, MW-2, and MW-4, in the general area of the 20,000-gallon asphalt USTs, but was not found in the area of the ' southwestern excavation where the former gasoline and diesel USTs were located ■ A source area monitoring well (MW-1) was first installed and monitored in December 2000 By June 2002, six groundwater monitoring wells were installed to monitor the groundwater and evaluate groundwater hydrologic and hydrochemical trends ■ Site lithologic and hydrologic data show an unconfined sand-dominated sediment profile to 60 feet bgs, with groundwater generally found at the 50-foot bgs elevation What 1 Stellar Environmental Solutions ' F PRNECIS3 W3 Acve Roya100]40-OA9uMn1.oM[ImvlAywl ob FpwsiREPORT—&gsmhr RI003 doc