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/ / C February 12, 2020 / Page 4 of 6 of the dissolved phase hydrocarbon plume. Since no detectable hydrocarbons were found in groundwater samples collected from MW-11, ATC suggested the vertical extent of the groundwater contamination was defined and recommended adding MW11 to the semi-annual groundwater monitoring and sampling schedule. In correspondence dated January 26, 2010, the SJCEHD concurred with the recommendations regarding the SVE system and directed the sampling of MW11 be reduced to a biennial frequency during the fourth quarter of every odd year. ATC initiated the process of exploring ozone injection technology to remediate residual hydrocarbons below the groundwater surface. ATC submitted soil and groundwater samples collected from the site for bench scale testing and received the Report of Findings Bench Scale Testing to Evaluate Oxidation of Hydrocarbons by Ozone Former Greer Property Escalon, California, dated August 31, 2009, from PRIMA Environmental, Inc. as part of this effort. ATC evaluated ozone sparging as a remedial alternative in a Feasibility Study dated June 11, 2010, and an addendum dated May 20, 2011. The current property owner was opposed to this method of treatment and relocation of the on- site domestic well was recommended. In September 2015, Cardno ATC submitted a Site Conceptual Model and No Further Action Request. In correspondence dated October 20, 2015, the CRWQCB denied the request for closure and directed additional assessment and an addendum to the site conceptual model. On November 5, 2015, ATC obtained access from the owner of the adjacent property immediately north of the site and sampled domestic well PDW. Laboratory analyses of the groundwater sample collected from this well identified the presence of MTBE and 1,2-dichloroethane (1,2-DCA). PDW was resampled on January 5, 2016, and a low concentration of MTBE was reported in the sample. Consequently, in a letter dated January 11, 2016, the CRWQCB ordered monthly groundwater sampling of PDW for a period of three months to evaluate the impact to the well. Subsequent samples collected in February and March 2016 did not contain detectable concentrations of petroleum hydrocarbons. On January 14, 2016, a letter addendum to the Site Conceptual Model and No Further Action Request was submitted to the CRWQCB. The request for No Further Action was not accepted and the CRWQCB requested additional assessment. On April 25, 2016, soil borings B-3, B-4, and B-5 were advanced near the locations of the former USTs and former dispensers. Soil samples were continuously collected from the soil borings between depths of approximately ground surface and 10 feet bgs. The soil samples did not contain detectable concentrations of benzene, ethylbenzene, or naphthalene. Based on the findings of the assessment, ATC concluded that shallow soil at the site does not pose a threat from direct contact or outdoor air exposure. In correspondence dated May 11, 2016, the CRWQCB requested quarterly sampling from MW11 and PDW for one year. On July 18 and 22, 2016, ATC repaired the well casing of monitoring well MW-8 and a new well monument was installed. ATC performed the work under permit from the SJCEHD. On October 11, 2016, ATC returned to the site to install bollards around the well monument to prevent damage in the future. In April 2018, off-site Sawyer Domestic Well (SDW) was installed to replace PDW. The well was completed to a depth of 310 feet deep with a bentonite seal to 107 feet bgs. The screened interval was from 290 to 310 feet bgs.