SITE INFORMATION AND CORRESPONDENCE_FILE 2

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W. Carl W. Knowles, Successor Trustee Page 3 of 5 Knowles Family Trust 23 December 2009 Former Roek Construction 102 S. Wilson Way migrate laterally until encountering another interval of permeability that allowed continued vertical migration. The differing depth intervals of impacted soil may also be due in part to the soil vapor extraction remediation 'cleaning up' some soil between sample acquisition periods. The EHD believes the data demonstrates that soil on your site was impacted to depths as great as 95 feet bsg by the unauthorized release(s) from your former UST system. The soil so impacted was impacted primarily by TPHG and variously by BTEX, as is the groundwater in the former UST system area and in the down-gradient direction. The correlation of soil contaminant species with those in groundwater provides a strong argument that the TPHg and BTEX in groundwater underlying your former UST system area and down-gradient of it are related to the unauthorized release from your former UST system. Soil samples collected from soil borings prior to 2001 were generally not analyzed for 1,2-DCA, and the compound has not been detected in soil samples collected since 2001; but the contaminant concentration distribution in groundwater on your site is consistent with an on-site source. On Figure 11 of Third Quarter 2006 Groundwater Sampling Report & Site Conceptual Model (SCM), your consultant, Ground Zero Analysis (GZA) shows a high concentration 1,2-DCA plume centered on monitoring well MW-13B on your site, a moderate concentration 1,2-DCA plume centered on the former Top Filling Station site (101 S. Wilson Way), and an isolated, small, low concentration 1,2-DCA plume on the Arco site (130 S. Wilson Way). The EHD considers this to show that 1,2-DCA in groundwater on your site is derived from an unauthorized release on your site. Your consultant, GZA, states on page 6 of the SCM, that the Knowles plume, centered about the former USTs, is characterized by the occurrences of TPHg, BTEX and 1,2-DCA, but without MTBE. In the RCC, you characterize the water impacted by the unauthorized releases on the former Top Filling site, the Arco site and your site as a 'single groundwater plume". The EHD believes that most qualified environmental professionals would interpret Figures 8 through 11 of the SCM to show that three distinct plumes, one centered on each of the three sites, with some commingling between sites. The EHD considers GZA to have adequately shown that the TPHg/BTEX/1,2-DCA dissolved plume is genetically related to impacted soil on your site - soil that was impacted by the unauthorized release from the UST system formerly on your site. In the RCC, you state that"The Knowles Family Trust sold the property located at 102 S. Wilson Way (the site) on August 5, 1977 to the Pepsi-Cola Bottling Company, after which the underground storage tanks were no longer in use."This statement indicates to the EHD that use of the USTs, and the unauthorized release from the UST system, occurred prior to August 5, 1977 and that you are the proper responsible party to take corrective actions to address the impact of the unauthorized release on groundwater. Although there has been some commingling between plumes and a significant plume migrated most likely from the former Top Filling site across the southern portion of your site, the EHD does not regard the plumes from each release to be commingled to an extent that they can be characterized as a single plume. The EHD believes that individually addressing each plume is an effective way to restore groundwater to background conditions as most remediation efforts are usually focused in the source area where contaminant concentrations are highest and remediation efforts are commonly most cost-effective. Effective reduction of contaminant mass in the source area may enable natural attenuation to remediate the more distant portions of the plume. Site Closure Request Response 1209