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V 1117 Lone Palm Avenue Suite B <br /> Modesto California 95351 <br /> www atc-enviro corn <br /> 209 579 2221 <br /> l*r Fax 209 579 2225 <br /> A S S D C I A T E S I N C <br /> ren <br /> September 20, 2000 <br /> Mr Harlin Knoll <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 E Weber Ave , Fourth Floor <br /> Stockton, CA 95201-0388 <br /> Subject Second Quarter 2000 Groundwater Monitoring Report for 26056126080 Thornton <br /> Road, Thornton, CA, Site Code 1864 <br /> Mr Knoll <br /> This letter report summarizes field activities conducted during the Second Quarter 2000 by ATC <br /> Associates Inc at the subject site (Figure 1) <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 pat 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 (MWI 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 which was present <br /> S! beneath the station building The demolition of the station building was requested in PHS/EHD <br /> correspondence dated July 7, 1994 A required demolition asbestos survey conducted previously <br /> to 1625821quanlyl2gr-2000 doc 1 <br />