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(VYATC <br />A S S O C I A T E S I N C. <br />1117 Lone Palm Avenue, Suite B <br />Modesto, California 95351 <br />www.atc-enviro.com <br />209.579.2221 <br />Fax 209.579.2225 <br />ENVIRONMENTAL HEALTH DIVISION <br />304 E. Weber Ave. Third Floor <br />March 1, 2001 P. O. Box 388, St9.9kton CA 95201-0388 <br />Approved <br />Denied <br />Mr. Harlin Knoll Conditio s <br />San Joaquin County Public Health Se ice ate 171m by <br />Environmental Health Division 11.. <br />6tt304 E. Weber Ave., Fourth Floor n ` coSfS �fyyp C(_ cvt7�- <br />Stockton, CA 95201-0388 ' <br />Subject: Fourth Quarter 2000 Groundwater Monitoring Report and Workplan for <br />Groundwater Extraction Pilot Test for 26056/26080 Thornton Road, Thornton, <br />CA, Site Code 1864 <br />Dear Mr. Knoll: <br />This report summarizes field activities conducted during the Fourth Quarter 2000 by ATC <br />Associates Inc. at the subject site (Figure 1). Additionally, this letter presents ATC's workplan <br />for a groundwater extraction pilot test at the subject site, per your request. <br />BACKGROUND <br />On September 6, 1989, Western Meter Service of Stockton, California removed three <br />underground gasoline storage tanks at the project site. Soil samples were collected beneath each <br />tank and the associated piping. Soil samples collected from beneath two of the tanks contained <br />moderate to high levels of ethylbenzene and xylenes (1.2 to 70 parts per million [ppm]) as well <br />as total petroleum hydrocarbons as gasoline (TPHg) at 470 to 830 ppm. <br />Due to the presence of elevated concentrations of petroleum hydrocarbons in the tank pit soil <br />samples, further investigation was required by San Joaquin County Public Health Services, <br />Environmental Health Division (PHS/EHD). <br />In a two -phased approach beginning on November 1, 1990, RESNA Industries Inc. personnel <br />advanced six soil borings (MW1 through MW6) to depths ranging from 27 to 30 feet below <br />grade at the project site to accomplish the following: 1) define the lateral and vertical extent of <br />hydrocarbon impacted soils; 2) determine soil stratigraphy; and 3) install groundwater <br />monitoring wells within the uppermost aquifer in order to assess groundwater quality. The <br />boring/well locations are plotted on Figure 2. Field methodology and analytical results are <br />discussed in detail in RESNA's Interim Problem Assessment Report, dated January 13, 1992. <br />The site's station building and garage were demolished in December 1994 to facilitate corrective <br />action activities including the removal of hydrocarbon contaminated soil that was present <br />w: \625 82\q u and y\4 q r-2000. d o c <br />