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SECOR vmv-secor.com <br /> INTERNATIONAL 3017 Kilgore Road , Suite 100 <br /> S E C O R INCORPORATED Rancho Cordova , CA 95670 <br /> 916-861-0400 TEL <br /> 916-861-0430 FAX <br /> February 12, 2007 <br /> Mr. Mike Infurna m <br /> San Joaquin County <br /> Environmental Health Department <br /> 304 East Weber Avenue, Third Floor <br /> Stockton , CA 95202 <br /> RE: Work Plan for Additional Assessment , <br /> ARCO Service Station 2130 <br /> 7906 North EI Dorado Street <br /> Stockton, California <br /> SECOR Project No. : 771313.02130.01 . 0136 <br /> Dear Mr, Infurna: <br /> This document , prepared by SECOR International Incorporated (SECOR) on behalf of <br /> Atlantic Richfield Company, a BP Affiliated Company, was prepared in response to the San <br /> Joaquin County Environmental Health Department (SJCEHD) letter dated January 12, 2007 <br /> (Attachment A) . As requested, this document presents an evaluation of the residual soil <br /> contamination , a work plan for the installation of groundwater monitoring wells, and a work <br /> plan for bench scale testing prior to oxygen injection at ARCO Service Station #2130 (the <br /> "Site") . <br /> SITE DESCRIPTION <br /> The site is located at the northeast corner of the intersection of Hammer Lane and EI <br /> Dorado Street in Stockton , California (Figure 1 ) . The site is an operating ARCO service <br /> station and AM/PM mini- mart. Currently, site facilities include double-walled fiberglass <br /> gasoline underground storage tanks (LISTS) , two dispenser islands, and associated product <br /> lines. <br /> PREVIOUS ASSESSMENTS <br /> An initial subsurface investigation was performed in June 1991 . During this investigation <br /> one boring (131 ), located just north of the UST complex, was drilled and sampled between <br /> 15 and 68 feet below ground surface (bgs) . Soil samples contained a maximum <br /> concentration of 2,400 milligrams per kilogram (mg/kg) total petroleum hydrocarbons as <br /> gasoline (TPHg) , 13 mg/kg benzene, 75 mg/kg toluene, 31 mg/kg ethylbenzene, and 170 <br /> mg/kg total xylenes. <br /> Another investigation was conducted in December 1991 . During this investigation , seven <br /> borings were drilled (B-2 through B-8) and sampled for TPHg and benzene, toluene, <br /> ethylbenzene , and total xylenes (BTEX) . Soil sample results generally increased with <br /> depth . The highest concentrations were detected north , south , and west of the UST <br /> complex. Three of these borings (13-2, B-6, and B-8) were converted to monitoring wells <br /> (MW- 1 through MW-3) and four of the borings (13-3 through B-5 and B-7) were converted to <br /> vapor extraction wells (VW- 1 through VW-4) . <br /> Following the installation of the vapor wells, a soil vapor extraction (SVE) test was <br /> conducted in December 1991 . Using a wellhead flow rate of 110 cubic feet per minute <br />