SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Valley Motors - 2 - 1 May 2012 } 800 E. Main St., Stockton San Joaquin County Second continues with a question whether the pilot study needed to be concluded by 27 April 2012. There is no mention of a pilot study report or associated field action due date in my letter, which clearly stated the bi-weekly update on submittals to the Fund was to start 27 April 2012. UEC understands what is meant by this date when they provided the bi-weekly Fund update in the last paragraph in the Letter. Third, the Letter questions whether additional investigation is necessary to prove the existence of the chlorinated solvent plume, the plume's location and source, prior to submitting the FS. The Letter answers the question of chlorinated solvent plume existence in the VM-2 chlorinated solvent results from the 2009 groundwater extraction pilot study; the plume location and source are addressed below. Third states chlorinated solvent groundwater monitoring samples were last collected over ten years ago, and due to the length of time, concentrations of chlorinated solvents have declined significantly ( to 14% of 1997 concentrations). The Letter recommends sampling VM-9, the extraction well, for chlorinated solvents to determine the vertical extent (known to be approximately 5' in the remaining monitoring wells), since the site conceptual model has been complicated by the presence of chlorinated solvents. Fourth answers the question whether additional investigation of the location and source of the chlorinated plume is necessary, by stating the Fund will not pay for chlorinated solvents investigations. However, the chlorinated solvents will be referred to the Regional Board Site Cleanup Section, which oversees non-USTs related pollution. Fourth also asks if the Regional Board is directing cleanup of both chlorinated solvents and petroleum hydrocarbons, or simply cleanup petroleum hydrocarbons; asks for cleanup limits (maximum concentrations); and also asks for case closure since SJCEHD has closed cases with similar concentrations. My letter required the FS propose a cleanup that would not draw chlorinated solvents onsite and increase remediation costs, as would groundwater extraction; hence, there is no request to clean up both commingled plumes. That said, all technologies would clean up all pollution within the USTs source area, regardless of the source. Based on your estimates of 14% of the initial chlorinated solvent concentrations from 1997, it appears that the additional remediation cost for the chlorinated solvents already onsite will not be significant, if the additional mass from the chlorinated solvent plume is not actively drawn onsite by groundwater extraction. The Regional Board establishes cleanup limits for petroleum hydrocarbons on a case-by-case basis, as that we do allow closure when a case qualifies for a low risk closure. To date, your case has not shown evidence that a low risk closure is appropriate, as stated in my letter dated 25 January 2012. However, the path to closure is outlined in Appendix A — Reports, Tri-Regional Board Staff Recommendation for Preliminary Investigations and Evaluation of Underground Storage Tank Sites, April 2004, which may be downloaded at.` http://www.waterboards.ca.gov/centraIvaIIey/water issues/underground storage tanks/tri- regionals appendix a.pdf.