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V 1117 Lone Palm Avenue, Suite B Modesto, CA 95351 kTc http l/www atcassociates corn 209 579 2221 Fax 209 579 2225 Assoc 1 A T � s � w c _ ceee- U� �LL--3 MAY � 2015 July 27, 2004 54 22493 0001 B UI PERMIT/SERVICES I HEALTH Mr Jeff Wong San Joaquin County Environmental Health Department 304 East Weber Street, Third Floor Stockton, California 95202-2708 Subject Monitoring Report Third Quarter 2004, Eggiman Property, 1112 East Harding Way, Stockton, California Dear Mr Wong This report presents the results of the third quarter 2004 groundwater monitoring and sampling performed on July 7, 2004, by ATC Associates Inc (ATC) 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 storage tanks (USTs), associated piping, and fuel dispenser from the locations shown on Figure 2 A soil sample was collected from beneath the end of each tank at approximately 17 feet below ground surface (bgs) 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 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 Geoprobeg 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 • In April 1999, at the request of PHSIEHD, ATC completed a receptor survey for the subject property ATC reviewed PHS/EHD groundwater well construction logs, Department of Water Resources s�environmenL111224931R ONIWNML, GEOTECHNICAL AND MATERIALS PROFESSIONALS