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r 1117 Lone Palm Ave., Suite B o Modesto, California 95351 tai WWW.atC7envieo.com 209.579.2221 Fax 209.579.2225 A S 8 0 C I A T E s I N C til 41 July 22, 2002' 54.92054.0001 no Ms. Margaret Lagorio ,AUL 2 2442 San Joaquin County Environmental Health Department 304 East Weber Street, Third Floor ENVIROAIVIE-N� HEAt�H Stockton, California 95202-2708 P7=RMI�ISERVICES Subject: Monitoring Report Second Quarter 2002, Eggiman Property, 1112 East Harding Way, Stockton, California Dear Ms. Lagorio: This report presents the results of quarterly groundwater monitoring and sampling performed on April 22, 2002 by ATC Associates Inc. at the site located at 1112 East Harding Way, Stockton, California (Figure 1). Monitoring was performed to determine groundwater flow direction and the hydraulic gradient in the uppermost aquifer. Sampling was performed to monitor the petroleum hydrocarbons in the groundwater at the site. • BACKGROUND In April 1987, SEMCO removed and disposed of two 1,000-gallon regular gasoline underground I storage tanks (USTs), associated piping, and fuel dispenser from the locations shown on Figure 2. A soil sample was collected from the end of each tank at approximately 17 feet below ground surface. Analytical testing indicated the collected samples contained detectable concentrations of petroleum hydrocarbon constituents. The excavation was subsequently backfilled to the ground surface. On July 24, 1997, to investigate the extent of residual soil contamination at the site, a total of six soil borings were advanced to depths ranging from approximately 16 to 31 feet below ground surface (bgs). Detectable concentrations of total petroleum hydrocarbons as gasoline (TPHg), total petroleum hydrocarbons as diesel (TPHd), and benzene, toluene, ethylbenzene, and xylenes (BTEX) were observed in soil samples collected from the site. The distribution of petroleum constituents beneath the site has been essentially defined and appears to be limited laterally to the immediate vicinity of the former tank pit. The highest concentrations were reported between 10 and 20 feet bgs and generally attenuate rapidly with depth. Only low concentrations of toluene (0.064 mg/kg) and xylenes (0.012 mg/kg) were detected at approximately 30 feet bgs in one boring, the maximum depth explored. Attempts were made to further advance the Geoprobe unit in several of the borings, however probe refusal was encountered at depths ranging from approximately 16 to 30 feet bgs due to the hardness of the formation. The results of the subsurface investigation were summarized in Smith Technology's Summary Report, Subsurface Investigation, dated December 22, 1997. w:Iwurdpro192054192054ff #UMMMWiM, GEOTECHNICAL AND MATERIALS PROFESSIONALS :k