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1117 tone Palm Avenue, Suite B <br /> V Modesto, CA 95351 <br /> http llwww atcassociates com <br /> 209 579 2221 <br /> Fax 209 579 2225 <br /> A S S O C I A T E S I N C <br /> January 31, 2005 � <br /> 54 25912 0003 R E C E� Vn�7 E(U <br /> FEB 0 A 2005 <br /> Mr Harlin Knoll ENVIRONMENT HEALTH <br /> San Joaquin County Environmental Health Department HEYMIT Q.ERVIOES <br /> 304 E Weber Street, Third Floor <br /> Stockton, California 95202 <br /> Subject Monitoring Report - Fourth Quarter 2004, USA Gasoline Station #110, 2132 East <br /> Mariposa Road, Stockton, California <br /> Dear Mr Knoll <br /> This report presents the results of quarterly groundwater monitoring and sampling performed on <br /> November 10, 2004 by ATC Associates Inc (ATC) at USA Gasoline Station #110 This work <br /> was performed on behalf of USA Petroleum Corporation The site is located at 2132 East <br /> Mariposa Road, Stockton, California (Figure 1) Sampling was performed to monitor the <br /> distribution of petroleum hydrocarbons in groundwater at the site and to evaluate the hydraulic <br /> gradient direction and magnitude in the uppermost aquifer <br /> SITE HISTORY <br /> The following historical information was obtained from GI-11-1 Engineering reports dated <br /> December 1997 and February 2000 In March 1987, Pacific Environmental Group (PEG) <br /> advanced four soil borings at the site, one of which was completed as a groundwater-monitoring <br /> well Total petroleum hydrocarbons as gasoline (TPHg) and benzene, toluene, ethylbenzene, and <br /> total xylenes (BTEX) were detected in the soil samples collected from the borings BTEX <br /> constituents were detected in the water sample collected from the monitoring well <br /> In October 1987, Applied Geo Systems installed two groundwater-monitoring wells at the site <br /> and collected groundwater samples Petroleum hydrocarbons were detected in the water samples <br /> collected from the wells and the hydraulic gradient was reported to be towards the northwest <br /> In September 1992, Park Corporation installed three groundwater-monitoring wells and one <br /> vapor extraction well A vapor extraction treatability study was performed and the groundwater <br /> quality was monitored In October 1995, Park Corporation installed three additional wells at the <br /> site Park Corporation performed quarterly monitoring and sampling until May 1997 <br /> In 1997 GHH Engineering removed three 12,000-gallon gasoline underground storage tanks <br /> (USTs), one 3,000-gallon diesel UST, and fuel pipelines The highest concentration of total <br /> petroleum hydrocarbons as diesel (TPHd) detected was 5,000 milligrams per kilogram (mg/kg) in <br /> s lenvironmentaIU591210003-StocktonlQuartly�3QR-2004 doc 1 <br /> ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS <br />