SITE INFORMATION AND CORRESPONDENCE

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i 1117� Lone Palm Avenue,Suite 201 Modesto,California 95351 . ATC 209-579-2221 Shaping the Future; Fax:209-579-2225 800 feet west). The first screen interval in this well is located from 79 to 83 feet bgs. Because this well is located upgradient from the site, it was ATC's judgment that itas unlikely that the well has been impacted by petroleum hydrocarbons from the site. The only well located downgradient from the site was a groundwater monitoring well located on the corner of North Wilson Way and East Harding•Way, however this well was destroyed in 1992. The remaining twelve wells discovered during the well survey are located either upgradient or crossgradient from the site and are more than 1,000 feet -from the site or have been destroyed. Based on this information, it was ATC's judgment that it is unlikely that these wells have been impacted by petroleum hydrocarbons from the site: 7.0 LOW RISK CLOSURE CRITERIA NFAR for Cases above Background Groundwater Conditions JCriterion 1: The source of the UST release has been identified and removed. The UST system which was removed in April 1987 appears to.have-been the source of the release.Data collected from the site do not suggest a release from other sources. V/ Criterion 2: Free-phase product in groundwater:has been removed to the full extent practicable, in accordance with UST regulations(Title 23,CCR,Section 2655). The site has not had reported occurrences of free product. Criterion 3: Contaminants remaining in the vadose zone cannot.migrate in soil vapor or leach at concentrations that would cause groundwater to exceed water quality supply:objectives. According to ATCS Site Conceptual Model dated March 2008, the mass of remaining petroleum hydrocarbons at the site are reported to be contained in silts and clay materials. The concentrations of petroleum hydrocarbons in the groundwater appear to be decreasing over time, showing that.the residual petroleum hydrocarbons are either not migrating from the silt and clay material into groundwater or. concentrations of petroleum hydrocarbons in.the silt and clay / materials have declined over time. /Criterion 4: There are no existing water supply wells, surface waters, or other_ receptors threatened by the remaining contaminants in soil or groundwater. A sensitive receptor survey was performed in 1999 by ATC. According to ATC's report Well Survey for Eggiman, Andrew and Edith Trust, for the Property at 1112 East Harding Way, Stockton, California,dated April 1999,a well located at the northeast corner of the State Hospital (Well No. 11, Attachment 1) is the closest to the site (within approximately 800 feet west). The first screen interval in this well is located from 79 to 83 feet bgs. Because this well is located upgradient from the site,it was ATC's judgment that it is unlikely that the well has been impacted by petroleum hydrocarbons from the site.- S: ite:S:Enviromenta1\22493\Reports\Eggiman Closure Report.doc 9