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Alms*,
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<br /> Workplan for Destruction of Groundwater Monitoring Wells
<br /> Eggiman Hydaulic Garage
<br /> Stockton,California 95205
<br /> July 29,2013
<br /> observed in soil samples collected from the site. The highest concentrations were reported between 10 and 20 feet
<br /> bgs and generally attenuate rapidly with depth. Only low concentrations of toluene (0.064 mg/kg) and xylenes
<br /> (0.012 mg/kg)were detected at approximately 30 feet bgs in one boring, the maximum depth explored. Attempts
<br /> were made to further advance the Geoprobe unit in several of the borings; however probe refusal was encountered
<br /> at depths ranging from 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 Investigation,
<br /> dated December 22, 1997.
<br /> In April 1999, at the request of the EHD, ATC completed a receptor survey for the subject property. ATC reviewed
<br /> EHD groundwater well construction logs, Department of Water Resources (DWR) groundwater well construction
<br /> logs, and conducted a site walk in the vicinity of the site to identify any groundwater wells located within a 2,000-
<br /> foot radius of the site. This survey revealed 14 wells located within approximately 2,000 feet of the site. The
<br /> closest of these wells is located approximately 800 feet upgradient of the project site. The receptor survey findings
<br /> are summarized in ATC's Well Survey for Andrew and Edith Trust, for the Property at 1112 East Harding Way,
<br /> Stockton, California, dated April 9, 1999.
<br /> On April 11, 2000, a single soil boring (S67)was advanced to approximately 65 feet bgs to evaluate whether
<br /> groundwater had been impacted at the subject site. Groundwater was initially encountered at approximately 45
<br /> feet bgs and a sample was subsequently collected from the soil boring using a Hydropunch groundwater-sampling
<br /> tool. In order to determine the vertical extent of contamination in the most cost-effective manner, the soil boring
<br /> was further advanced to a total completion depth of 66.5 feet bgs where field observations suggested the vertical
<br /> extent of the petroleum hydrocarbons had been realized. Analytical results and field observations indicated that
<br /> soil and groundwater beneath the location of the former USTs were impacted by residual petroleum hydrocarbon
<br /> constituents. The vertical extent of impacted soil and groundwater appeared to be defined. However, the lateral
<br /> extent of petroleum hydrocarbon constituents at or near the groundwater interface was undefined. Additional work
<br /> to further characterize the extent of contamination was requested by the EHD in correspondence dated September
<br /> 20, 2000.
<br /> On November 15 and 16, 2001, an ATC geologist supervised the advancement of three soil borings to
<br /> approximately 54 to 55 feet bgs. Soil borings were then completed as groundwater monitoring wells MW1, MW2,
<br /> and MW3. The soil sample collected from boring MW2 at a depth of 35.5 feet bgs contained the highest
<br /> concentrations of TPHg, ethyl benzene, and xylenes. The soil samples collected from boring MW2 at depths of 30
<br /> feet bgs and 55 feet bgs contained only trace concentrations of TPHg, ethyl benzene, and/or xylenes. The soil
<br /> samples collected from borings MW1 and MW3 at depths of 35 feet bgs contained trace concentrations of xylenes
<br /> and TPHg, respectively. The samples collected from borings MW1 and MW3 at depths of 40 feet bgs did not
<br /> contain detectable concentrations of TPHg or BTEX. MTBE, t-amyl methyl ether(TAME), t-butanol (TBA), ethyl t-
<br /> butyl ether(ETBE), di-isopropyl ether(DIPE), 1,2-dichloroethane (1,2-DCA), or 1,2-dibromoethane (EDB)were not
<br /> detected in any soil samples collected from borings MW1, MW2, and MW3, though the detection limits were
<br /> elevated in the MW2 sample from 35.5 feet bgs due to the high concentrations of TPHg noted previously.
<br /> In July and December 2003, ATC conducted additional subsurface investigation activities at the site that included
<br /> cone penetration testing, advancing a soil boring (SB8), and installation of monitoring wells MW4 through MW7.
<br /> Petroleum hydrocarbons were detected in soil samples collected from the boreholes of MW5 and MW6, and in the
<br /> groundwater samples collected from MW4 through MW-7.
<br /> On November 17 and 18, and December 5 and 28, 2005, an ATC geologist supervised the advancement of five soil
<br /> borings, S69 through SB 13. The borings were advanced for the purposes of evaluating the horizontal extent of
<br /> petroleum hydrocarbon impacted soil and groundwater in the vicinity of the site. Details of these activities are
<br /> summarized in ATC's Summary Report of Additional Subsurface Investigation, dated July 12, 2006.
<br /> www.cardnoatc.com
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