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SECOR <br /> • International Incorporated <br /> September 13, 2002 <br /> Project 77BP 50595 02 0136 <br /> Ms Lor! Duncan <br /> San Joaquin County Environmental Health Division N ;a n <br /> 304 East Weber Avenue, Third Floor y� <br /> Stockton, California 95202 — = TM <br /> Re Site Assessment Report <br /> w� <br /> ARCO Service Station No 595 <br /> 6100 North Highway 99 co <br /> Stockton, California ` <br /> Dear Ms Duncan <br /> SECOR International Incorporated (SECOR) has prepared this letter on behalf of <br /> Atlantic Richfield Company to document the installation of two deep on-site <br /> groundwater monitoring wells, one deep off-site groundwater monitoring well, and three <br /> shallow off-site groundwater monitoring wells at the site referenced above (Figures 1 <br /> and 2) The purpose of this work was to evaluate the lateral and vertical extent of <br /> petroleum hydrocarbons in soil and groundwater beneath the site This work was <br /> performed as described in SECOR's Work Plan for Additional Site Assessment dated <br /> February 15, 2002, and in accordance with the San Joaquin County Environmental <br /> Health Division (SJCEHD) work plan approval letter dated February 25, 2002 <br /> (Attachment A) <br /> SITE BACKGROUND <br /> The site is located at 6100 North Highway 99 in Stockton, California, and is an operating <br /> AMIPM mini-mart and ARCO service station The site is bordered by orchards to the <br /> north, east, and south, and Highway 99 to the west The site currently contains three <br /> 12,000-gallon gasoline underground storage tanks (USTs), associated product lines, and <br /> product dispensers Additionally, a domestic water supply well (WSW) is currently in <br /> operation at the service station, and is located in the southwest corner of the property <br /> (Figure 2) <br /> In September 1999, product lines and dispensers were upgraded and replaced in the same <br /> trench locations Twenty-one soil samples were collected from beneath the product <br /> lines, vapor lines, dispensers, and other product lines previously abandoned-in-place <br /> Total petroleum hydrocarbons as gasoline (TPHg) was detected at concentrations ranging <br /> from 194 mg/kg (milligrams per kilogram) to 11,300 mg/kg Benzene was reported at <br /> concentrations ranging from 0 0316 mg/kg to 4$ 3 mg/kg Methyl tertiary butyl ether <br /> (MtBE) was reported at concentrations ranging from 0 110 mg/kg to 6 47 mg/kg <br /> Tertiary butyl alcohol (TBA), di-isopropyl ether(RIPE), ethyl tertiary butyl ether(EtBE), <br /> 3017 Kilgore Road, Suite 100, Rancho Cordova, CA 95670 916 861 0400 916 861 0430 Fax www secor com <br />