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1117 Cone Palm Avenue Suite B <br /> Modesto California 95351 <br /> a l www atc-enviro com <br /> ' a 209 579 2221 <br /> Fax 209 579 2225 <br /> • A S S O C I A T E S I N C <br /> June 4, 2001 <br /> 54 62582 0001 <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 First Quarter 2001 Groundwater Monitoring Report for 26056/26080 Thornton <br /> Road, Thornton, CA, Site Code 1864 <br /> i <br /> i <br /> Dear Mr Knoll <br /> I <br /> This report presents the results of quarterly groundwater monitoring and sampling performed on <br /> March 29, 2001 by ATC Associates Inc at the site located at 26080 Thornton Rd Thornton, <br /> California (Figure 1) Monitoring was performed to determine the groundwater flow direction <br /> and the hydraulic gradient in the aquifer Sampling was performed to monitor the distribution of <br /> petroleum hydrocarbons in groundwater at the site <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 bonngs (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 /> W 1Wordpro1625821Quardy\1QR-2001 doc 1 <br />