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ATC Associates Inc. <br /> 1117 Lone Palm Avenue,Suite 201 <br /> Modesto, California 95351 <br /> 209-579-2221 <br /> Fax:209-579-2222 <br /> ASSOCIATES I NC . <br /> May 24, 2011 RECEIVED <br /> 54.22493.0001 <br /> Ms. Lori Duncan JUN 0 7 2011 <br /> San Joaquin County <br /> Environmental Health Department ENVIRONMENTAL HEALTH <br /> 600 East Main Street PERMIT/SERVICES <br /> Stockton, CA 95202 <br /> Subject: Monitoring Report First Semi-Annual 2011, Eggiman Property, 1112 East Harding <br /> Way, Stockton, California <br /> Vr <br /> Dear Ms. Duncan: <br /> This report presents the results of the first 2011 semi-annual groundwater monitoring and <br /> sampling event performed on March 24 and 25, 2011, by ATC Associates Inc. (ATC) at the site <br /> located at 1112 East Harding Way, Stockton, California (Figure 1). Monitoring was performed <br /> to evaluate groundwater flow direction and the hydraulic gradient in the uppermost aquifer. <br /> Sampling was performed to monitor petroleum hydrocarbons in groundwater at the site. <br /> BACKGROUND <br /> 1�1 <br /> In April 1987, SEMCO removed and disposed of two 1,000-gallon underground storage tanks <br /> (USTs) used to store regular gasoline, associated piping, and a fuel dispenser from the <br /> .. locations shown on Figure 2. A soil sample was collected from beneath the end of each tank at <br /> approximately 17 feet below ground surface (bgs). Analytical testing indicated the collected <br /> samples contained detectable concentrations of petroleum hydrocarbon constituents. The <br /> excavation was subsequently backfilled to the ground surface. <br /> On July 24, 1997, six soil borings were advanced to depths ranging from approximately 16 to 31 <br /> feet bgs to investigate the extent of residual soil contamination at the site. Detectable <br /> concentrations of total petroleum hydrocarbons as gasoline (TPHg), total petroleum <br /> hydrocarbons as diesel (TPHd), and benzene, toluene, ethylbenzene, and total xylenes (BTEX) <br /> were present in soil samples collected from the site. The distribution of petroleum constituents <br /> beneath the site was evaluated and appeared to be limited laterally to the immediate vicinity of <br /> the former tank pit. The highest concentrations were reported between 10 and 20 feet bgs and <br /> generally attenuate rapidly with depth. 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 /> In April 1999, ATC conducted a sensitive receptor survey for the subject property. ATC reviewed <br /> groundwater well construction logs and conducted a site walk in the vicinity of the site to identify <br /> groundwater wells located within a 2,000-foot radius of the site. This survey identified 14 wells <br /> -• located within approximately 2,000 feet of the site. The closest of these wells is located <br /> approximately 800 feet upgradient of the project site. The receptor survey findings are <br /> s:\environmental\22493\Reports\QMR 2011 SA1.doc 1 <br />