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IDI1117 Lone Palm Avenue, Suite B� Modesto, CA 95359 www atc-enviro com CVYATCFEB 2 6 2004 209 579 2221 A s s o C ! A r E s i N c Fax2095792225 lI PEPMIT/SEE VIOES February 23, 2004 54 62577 0001 Ms Lori Duncan San Joaquin County Environmental Health Department 304 E Weber Street, Third Floor Stockton, California 95202 Subject Groundwater Monitoring Report Fourth Quarter 2003, Diesel Performance, 2804 East Fremont Street, Stockton, California Dear Ms Duncan This report presents the results of quarterly groundwater monitoring and sampling performed during fourth quarter 2003 by ATC Associates Inc (ATC) at the site located at 2804 East Fremont Street in Stockton, California (Figure 1) Sampling was performed to monitor concentrations of petroleum hydrocarbons in groundwater at the site Monitoring was performed to evaluate groundwater quality and to determine the hydraulic gradient and direction in the uppermost aquifer BACKGROUND INFORMATION In February 1987, SEMCO removed and disposed of one 3,000-gallon unleaded gasoline underground storage tank (UST), associated piping, and fuel dispenser from the location shown on Figure 2 A soil sample collected from 13 feet below ground surface (bgs) contained elevated concentrations of petroleum hydrocarbon contaminants The excavation was subsequently backfilled and resurfaced On July 23, 1997, an ATC geologist supervised the advancement of five soil borings ranging in depth from 6 to 46 feet bgs The soil borings were advanced using a truck mounted Geoprobe® narrow diameter rig employing direct push technology Petroleum hydrocarbons were detected in soil samples submitted for laboratory analyses Site activities are summarized in ATC's Summary Report for Subsurface Investigation, dated October 20, 1997 On September 25, 1998, ATC personnel supervised the advancement of soil boring MW1 at the site to a depth of approximately 65 feet bgs to evaluate groundwater for the presence of petroleum hydrocarbons The soil boring was completed as a groundwater monitoring well and on September 28, 1998 the well was developed and sampled Analytical data indicated that soil and groundwater _ samples contained detectable concentrations of petroleum hydrocarbons Field activtties and l analytical results are detailed in ATC's Summary Report of Additional Subsurface Investigation, dated January 8, 1999 In December 1999, ATC personnel supervised the advancement of soil borings MW2, MW3, and MW4 at the site to depths of approximately 65 feet bgs to evaluate groundwater for the presence of w 16257714QR-2003 doc ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS