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1117 Lone Palm Ave., Suite B <br /> Modesto, California 95351. <br /> www.atc-enviro.c&n . <br /> .t 1II-C^'s r ,, 209.579:2221 <br /> rrr!,A1 711 Fax 209579.2225 <br /> 1.� A S 5'0 C 1 A T E S I N C <br /> !•'� r= <br /> P I <br /> Septembet 9, 2402 <br /> 54.22493.0001 <br /> 11%Is. Margaret Lagorio <br /> San Joaquin County Environmental Health Department <br /> 304 East Weber Street, Third Floor <br /> Stockton, California 95202-2708 <br /> Subject: Monitoring Report Third Quarter 2002, Eggiman Property, 1112 East Harding <br /> Way, Stockton, California <br /> Dear Ms. Lagorio: <br /> This report presents the results of quarterly groundwater monitoring and sampling performed on <br /> July 23, 2002 by ATC Associates Inc. at the site located at 1112 East Harding Way, Stockton, <br /> California (Figure 1). Monitoring was performed to determine groundwater flow direction and <br /> the hydraulic gradient in the uppermost aquifer. Sampling was performed to monitor the <br /> petroleum hydrocarbons in the groundwater at the site. <br /> BACKGROUND <br /> In April 1987, SEMCO removed and disposed of two 1,000-gallon regular gasoline underground <br /> storage tanks (USTs), associated piping, and fuel dispenser from the locations shown on Figure <br /> 2• A soil sample was collected from the end of each tank at approximately 17 feet below ground <br /> surface. Analytical testing indicated the collected samples contained detectable concentrations <br /> of petroleum hydrocarbon constituents. The excavation was subsequently backfilled to the <br /> ground surface. <br /> • I <br /> On July 24, 1997, to investigate the extent of residual soil contamination at the site, a total of six <br /> soil borings were advanced to depths ranging from approximately 16 to 31 feet below ground <br /> surface (bgs). Detectable concentrations of total petroleum hydrocarbons as gasoline (TPHg), <br /> total petroleum hydrocarbons as diesel (TPHd), and benzene, toluene, ethylbenzene, and xylenes <br /> (BTEX) were observed in soil samples collected from the site. The distribution of petroleum <br /> constituents beneath the site has been essentially defined and appears to be limited laterally to <br /> the immediate vicinity of the former tank pit. The highest concentrations were reported between <br /> 10 and 20 feet bgs and generally attenuate rapidly with depth. Only low concentrations of <br /> toluene (0"064 mg/kg) and xylenes (0.012 mglkg) were detected at approximately 30 feet bgs in <br /> one boring, the maximum depth explored. Attempts were made to further advance the Geoprobe <br /> unit in several of the borings, however probe refusal was encountered at depths ranging from <br /> approximately 16 to 30 feet bgs due to the hardness of the formation. The results of the <br /> subsurface investigation were summarized in Smith Technology's Summary Report, Subsurface <br /> �• Investigation, dated December 22, 1997. <br /> w:wordpro12249311Z09"iENTAL, GEOTECHNICAL LAND MATERIALS PROFESSIONALS <br />