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�> Gold Camp Drive <br /> Delta 00 JU,aJ !/CE Suite 200 <br /> c y Rancho Cordova,CA 95670-6021 <br /> 1/. Environmental u Pm <br /> �� ,�.,U S.A. <br /> Consultants,Inc. `?. 916/638-2085 <br /> FAX:916/638-8385 <br /> June 5, 2000 <br /> Margaret Lagorio <br /> San Joaquin County, Public Health Services <br /> Environmental Health Division <br /> 304 East Weber Ave., Third Floor <br /> Stockton, CA 95202 <br /> Subject: Work Plan for Groundwater Assessment <br /> ARCO Station 6100 <br /> 25775 Patterson Pass <br /> Tracy, California <br /> Dear Ms. Lagorio: <br /> On behalf of ARCO Products Company, Delta Environmental Consultants, Inc. (Delta) is submitting <br /> this work plan to conduct a groundwater investigation beneath the ARCO facility located at 25775 <br /> Patterson Pass, Tracy, California (see Figure 1). This work plan addresses those issues outlined by <br /> the California Regional Water Quality Control Board (CRWQCB), in their letter dated March 14, <br /> 2000 "Nonoccurrence with San Joaquin County's No Further Action Required Determination". <br /> The purpose of this work is to investigate the possible impact of petroleum hydrocarbons, including <br /> fuel oxygenates, to groundwater beneath the site. The proposed scope of work recommends drilling <br /> one soil boring in the area of the deepest known impact to assess the vertical extent. If groundwater is <br /> encountered, the boring will be completed as a monitoring well and will be developed and sampled. <br /> Site Background <br /> The project site is on the northwestern corner of Patterson Pass Road and Interstate 580 in Tracy, <br /> California. The site is approximately 300 feet above sea level and slopes slightly toward the southeast. <br /> The area surrounding the property is undeveloped land. The site is currently an operating retail <br /> service station. <br /> Originally, one 550-gallon waste oil underground storage tank (UST), one 10,000- gallon gasoline <br /> UST, and four 6,000-gallon gasoline USTs were present at the site. The waste oil tank was removed in <br /> 1987. From November 1990 to February 1991, the five gasoline USTs and associated product <br /> delivery lines were replaced with four 10,000-gallon USTs. <br /> Soil investigations were conducted between 1991 and 1995. Concentrations of TPHG and BTEX <br /> constituents were identified in soil from 6 to 115 feet bgs; with the highest concentration identified at <br /> approximately 26 to 45 feet bgs. A total of 31 soil borings, ranging in depth from 26 to 116 feet bgs, <br /> Providing a Competitive Edge <br />