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a <br /> 1117 Lone Palm Avenue, Suite 8 <br /> Modesto, CA 95351 <br /> http//www atcassociates com <br /> 209 579 2221 <br /> C, <br /> A S S O G I A T 8 8 I N c Fax 209 579 2225 <br /> 2flas UP 29 <br /> September 26, 2005 S A IN 10� G_,l i l C 0�i 1.1 i y <br /> 54 25912 0003 Eldlll,to dl';ll-JTAL <br /> HEAL 1HGE1'AR T�IENT <br /> Mr Harlin Knoll <br /> San Joaquin County Environmental Health Department <br /> 304 E Weber Street, Third Floor <br /> Stockton, California 95202 <br /> Subject Monitoring Report - Second Quarter 2005, 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 May <br /> 11, 2005 by ATC Associates Inc (ATC) at USA Gasoline Station #110 This work was performed <br /> on behalf of USA Petroleum Corporation The site is located at 2132 East Mariposa Road, Stockton, <br /> California (Figure 1) Sampling was performed to monitor the distribution of petroleum <br /> hydrocarbons in groundwater at the site and to evaluate the hydraulic gradient direction and <br /> magnitude in the uppermost aquifer <br /> . SITE HISTORY <br /> The following historical information was obtained from GHH Engineering reports dated December <br /> 1997 and February 2000 In March 1987, Pacific Environmental Group (PEG) advanced four soil <br /> borings at the site, one of which was completed as a groundwater-monitoring well Total petroleum <br /> hydrocarbons as gasoline (TPHg) and benzene, toluene, ethylbenzene, and total xylenes (BTEX) <br /> were detected in the soil samples collected from the borings BTEX constituents were detected in the <br /> water sample collected from the monitoring well <br /> In October 1987, Applied Geo Systems installed two groundwater-monitoring wells at the site and <br /> 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 vapor <br /> extraction well A vapor extraction treatability study was performed and the groundwater quality <br /> was monitored In October 1995, Park Corporation installed three additional wells at the site Park <br /> Corporation performed quarterly monitoring and sampling until May 1997 <br /> In 1997 GHH Engineering removed three 12,000-gallon gasoline underground storage tanks (USTs), <br /> one 3,000-gallon diesel UST, and fuel pipelines The highest concentration of total petroleum <br /> hydrocarbons as diesel (TPHd) detected was 5,000 milligrams per kilogram (mg/kg) in the soil <br /> sample collected beneath the diesel fuel dispenser The highest TPHg concentration detected was <br /> 4,800 mg/kg in the soil sample collected beneath the gasoline USTs Benzene was detected at <br /> • concentrations up to 4 2 and 6 4 mg/kg in the soil samples collected beneath the USTs and <br /> ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS <br />