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SECOR 0U'oNeWo m <br /> INTERNATIONAL gore oad,Suite 100 <br /> S E C O R Rancho Cordova,TEL 95670 <br /> INCORPORATED 916.861-0400 reg <br /> 916-861-0430 FAx <br /> May 27, 2005 2005 JUN -6 PM 2: 38 <br /> Ms. Lori Duncan SAN J074 3U'ITY <br /> ENYf`Z %HETAL <br /> San Joaquin County Environmental Health Division HEALTH DEPARTMENT <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, CA 95202 S <br /> Re: Work Plan for Soil and Groundwater Delineation and <br /> Addendum to Work Plan for Well Destruction and UST Removal <br /> Chevron Service Station # 9-4275 <br /> 2905 West Benjamin Holt Drive <br /> Stockton, California <br /> Arco Service Station # 2133 <br /> 2908 West Benjamin Holt Drive <br /> Stockton, California <br /> SECOR Project No.: 77BP.52133.05.0003 <br /> Dear Ms. Duncan: <br /> SECOR International Incorporated (SECOR) has prepared this letter on behalf of Chevron <br /> Environmental Management Company (EMC) and ARCO to present a work plan to <br /> delineate the lateral and vertical extent of petroleum hydrocarbons in soil and groundwater <br /> at the above-referenced sites (Figures 1 and 2). This work is being proposed as requested <br /> in a San Joaquin County Environmental Health Department (SJCEHD) letter dated March _ <br /> 7, 2005 (Attachment 1). This letter also presents an addendum to SECOR's Work Plan for— "Oc' <br /> Well Destruction and UST Removal, dated February 18, 2005. The proposed construction <br /> of replacement monitoring wells at the Chevron site, as discussed in the original work plan, <br /> has been modified. <br /> A discussion of the site background, previous investigations, proposed scope of work, and <br /> schedule are presented in the following sections. <br /> SITE BACKGROUND <br /> Chevron <br /> Four single walled, fiberglass underground storage tanks (USTs) were installed at this <br /> service station in 1973. A gasoline release from a product line was discovered in 1985. In <br /> January 1989, these four USTs (three gasoline and one waste oil) were removed, a new <br /> UST pit was excavated, and five double-walled, fiberglass USTs were installed (4 gasoline <br /> and 1 methanol). <br /> An air sparge (AS) system was activated in April 1997, and a soil vapor extraction (SVE) <br /> system was activated in September 1997 at the site. The AS system consisted of a 1.5-hp <br /> rotary vane compressor, alternately injecting air into nine wells (GM-1 through GM-9). The <br /> SVE system was comprised of ten SVE wells (VW-1 and GM-1 through GM-9), a 5- <br /> horsepower (hp) positive-displacement blower, and 100-cubic feet per minute (cfm) <br />