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1 G� Cardno® January 17,2014 ATC Eggiman Well Destruction Report Shaping the Future SITE LOCATION The Eggiman Property (Site) is located on the south side of East Harding Way and east of Union Street, in Stockton, California, as shown on Figures 1 and 2. The Site is currently developed as a hydraulic repair shop and located within in a mixed residential, commercial, and light industrial area. SITE HISTORY 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 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, in an effort 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 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. In April 1999, at the request of the EHD, ATC completed a receptor survey for the subject property. ATC reviewed EHD groundwater well construction logs, Department of Water Resources (DWR)groundwater well construction logs, and conducted a site walk in the vicinity of the site to identify any groundwater wells located within a 2,000- foot radius of the site. This survey revealed 14 wells located within approximately 2,000 feet of the site. The closest of these wells is located approximately 800 feet upgradient of the project site. The receptor survey findings are summarized in ATC's Well Survey for Andrew and Edith Trust, for the Property at 1112 East Harding Way, Stockton, California, dated April 9, 1999. On April 11, 2000, a single soil boring (SB7)was advanced to approximately 65 feet bgs to evaluate whether groundwater had been impacted at the subject site. Groundwater was initially encountered at approximately 45 feet bgs and a sample was subsequently collected from the soil boring using a Hydropunch groundwater-sampling tool. In order to determine the vertical extent of contamination in the most cost-effective manner, the soil boring was further advanced to a total completion depth of 66.5 feet bgs where field observations suggested the vertical extent of the petroleum hydrocarbons had been realized. Analytical results and field observations indicated that soil and groundwater beneath the location of the former USTs were impacted by residual petroleum hydrocarbon constituents. The vertical extent of impacted soil and groundwater appeared to be defined. However, the lateral extent of petroleum hydrocarbon constituents at or near the groundwater interface was undefined. Additional work to further characterize the extent of contamination was requested by the EHD in correspondence dated September 20, 2000. On November 15 and 16, 2001, an ATC geologist supervised the advancement of three soil borings to approximately 54 to 55 feet bgs. Soil borings were then completed as groundwater monitoring wells MW1, MW2, and MW3. The soil sample collected from boring MW2 at a depth of 35.5 feet bgs contained the highest concentrations of TPHg, ethyl benzene, and xylenes. The soil samples collected from boring MW2 at depths of 30 www.cardnoatc.com