SITE INFORMATION AND CORRESPONDENCE

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I' i Donald Sinclair' Shirley Thompson 3780 Linne Road,Tracy Page 2 of 4 In the Addendum, GTI has provided cost comparisons, but changed their final remediation proposal from excavation of contaminated soil to "we recommend that the APT in situ advanced oxidation remediation process be used..." GTI did not explain what `APT' refers to, or state specifically which in situ oxidation process they are proposing. GTI states that this change in choice of remediation alternative is based on their cost study, that excavation of the contaminated soil would be more expensive, and that they consider it possible "to reach the desired goal of 90% destruction of the contaminants with the in situ procedure". SJC/EHD appreciates that reevaluation of site conditions and remedial alternatives is natural and potentially beneficial for effective, cost-efficient remediation of a site. However, the switch of preferred method from excavation per the June 2003 CAP to AOP per the Addendum raises several questions and concerns. 1. In November 2003, GTI oversaw.a site investigation conducted utilizing Geoprobe direct push technology. A total of ten soil borings were advanced; soil samples were collected from each boring and submitted for analysis. The purpose of this investigation was to-define the extent of the petroleum hydrocarbon impacted soil that would need to be excavated, and to allow GTI to prepare a more accurate cost estimate of the proposed excavation. This work was reported to SJCIEHD in "Report: Additional Site Characterization & 4th Quarter Groundwater Monitoring" (Report) dated February 20, 2004. In the Report, GTl.estimated there is approximately 700 cubic yards of contaminated soil remaining at your site (4.0 Conclusions and Recommendations), and that generally the upper 7.5 feet of soil is clean and could be used as backfill. In the Addendum GTI estimates there is 3 feet of clean overburden, though 7 of the 10 borings had non-detect results reported in samples collected at 7.5 feet below surface grade (bsg), and states "An estimated 1,500 cubic yards would be excavated from this area, which.would equate to approximately 2,000 yards would have to be disposed of(assuming a 30% fluff factor)." GTI offered no explanation for this more than 100% increase in their estimate of the quantity of contaminated soil remaining at your site. 2. The June 2003 CAP cited tight soil conditions and underground utilities as making the site an unlikely candidate for an AOP remediation alternative (section r 2.4). In the Addendum, tight soil conditions are not a concern as "the issue with fine grained soils and shallow groundwater could be easily dealt with" (section t 2.2.1). This begs the question'What changed so that the tight soil issue that s was a stopper in June 2003 could be easily dealt with in April 2004? How will the tight soil issue be dealt with? 3. In the Addendum GTI states, "The goal of in situ injection is a 90-95% destruction rate leaving 5-10% bound to soil and/or dissolved in groundwater''. While this E may be an achievable goal of in situ remediation, it is not an acceptable cleanup goal in San Joaquin County. The Regional Water Quality Control Board, Central Valley Region 5, which covers San Joaquin County, applies the goals set forth in the Basin Plan, which are to cleanup to background concentrations, or non- detect. The minimum cleanup goals for groundwater accepted in San Joaquin County, if background levels prove to be unattainable, are the primary and secondary drinking water standards, known as the maximum contaminant levels (MCL's) set by the State of California Department of.Health Services. The i