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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 /> Between May 24 and June 8, 2007, an ATC geologist supervised the installation of monitoring wells MW8 through
<br /> MW11. MW8 and MW11 were installed off site to the northeast and north adjacent to 1139 and 1107 East Harding
<br /> Way, respectively, to evaluate the lateral extent of petroleum impacted groundwater downgradient of the subject
<br /> site. Details of these activities are summarized in ATC's Subsurface Investigation Report, dated November 19,
<br /> 2007.
<br /> Ozone injection was recommended as the preferred remediation option in ATC's Feasibility Study Addendum for
<br /> the Eggiman Property, dated January 9, 2009. To expedite the testing and installation process, the EHD requested
<br /> comparison of the site with other nearby remediation sites already using or approved to use ozone injection, on the
<br /> basis that similar soil stratigraphy and water chemistry could be expected to give similar results. This comparison
<br /> was presented in ATC's Site Geology Comparison, dated September 24, 2009.
<br /> Between May 24 and May 26, 2010, seven injection wells (OS1s, OS1d, OS2s, OS2d, OS3, OS4, and OS5)were
<br /> installed in five borings on site. On July 27 and 28, 2010, narrow trenches were excavated to a depth of
<br /> approximately six inches and 1/2" stainless steel piping was installed to connect the injection wells to the compound
<br /> location on the south face of the garage building on site. Details of these activities are summarized in ATC's
<br /> Remediation Well Installation Report, dated October 25, 2010.
<br /> On March 24, 2011, a cabinet-mounted ozone generator was delivered to the site and installed adjacent to the on-
<br /> site building. Ozone injection into OW1s, OW1d, OW2s, OW2d, and OW3 was initiated on April 1, 2011.
<br /> Connections to OW4 and OW5 were completed on April 4, 2011 and the injection cycle was expanded to cover all
<br /> seven points. Reduced petroleum hydrocarbon concentrations were reported in the groundwater samples collected
<br /> from the injection wells and most of the monitoring wells at the end of the pilot test on June 14, 2011, while
<br /> increased petroleum hydrocarbon concentrations were reported in the groundwater samples collected from MW1.
<br /> The reduced petroleum hydrocarbon concentrations associated with the groundwater sample collected from the
<br /> injection wells at the end of the pilot test suggest ozone injection was effective in reducing petroleum hydrocarbon
<br /> concentrations at these locations. No significant rebound effects were observed during the post remediation
<br /> monitoring performed on November 15, 2011. Details of these activities are summarized in ATC's Ozone
<br /> Treatability Pilot Testing Report, dated June 8, 2012.
<br /> In letters dated September 12, 2012 and February 22, 2013 respectively, the EHD stated the site was a candidate
<br /> for closure under the new Low Threat Closure Policy (LTCP) that had been recently adopted and implemented by
<br /> the State Water Resources Board and the CVRWQCB, and requested completion of a Case Closure Report for the
<br /> site.
<br /> Cardno ATC prepared a Case Closure Report that compared the characteristics of the release that had occurred at
<br /> the site with the parameters included with the LTCP. Cardno ATC concluded that the theoretical human health
<br /> risks imposed on the building's occupants could exceed acceptable levels as determined by the Johnson Ettinger
<br /> Model for Subsurface Vapor Intrusion into Buildings. Cardno ATC recommended collecting soil vapor samples to
<br /> evaluate actual contaminant concentrations present in the soil to better define this risk. The report stated that if the
<br /> results indicate the incremental risk from vapor intrusion to indoor air and the hazard index quotient from vapor
<br /> intrusion to indoor air were below acceptable levels, Cardno ATC would recommend no further action. The context
<br /> for this recommendation and additional details are included in Cardno ATC's Case Closure Report, dated March
<br /> 26, 2013.
<br /> In a letter dated May 22, 2013, the EHD determined that the site investigation and remedial action of contamination
<br /> resulting from an unauthorized release from the LISTS formerly and/or currently located at the site had been
<br /> completed. Furthermore, the EHD concluded that the completed corrective actions were adequate to protect
<br /> public health for current land use and forwarded a Case Closure Summary to the CVRWQCB for concurrence. In a
<br /> letter dated June 5, 2013, the CVRWQCB staff stated that they concurred with the EHD's recommendation for
<br /> closure. In a letter dated June 13, 2013, the EHD stated it had received concurrence from the CVRWQCB with
<br /> www.cardnoatc.com
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