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Chevron Station #9-5775 - 2 - 15 April 2005 301 W. Kettleman Lane, Lodi GWP&T system to conduct a rebound test, as a prelude to possible site closure. A City of Lodi Municipal Supply Well (Well #12), a potential sensitive receptor, is located approximately 375 feet from the groundwater plume. Fate and Transport modeling in the GMMReport predicts no impact to City of Lodi Municipal Well #12 after the GWP&T system is shut off. Well #12 is screened greater than 200 feet below ground surface, and has not been impacted by petroleum hydrocarbon contamination to date. Discussion: I reviewed the case file, including the following documents submitted by SECOR International Incorporated (SECOR) on behalf of Chevron Products Company and Messrs. Ivern and Roger Baffoni (Responsible Parties): Groundwater Modeling Report (GWM Report), received 31 January 2005; Fourth Quarter 2004, Quarterly Progress Report (4Q2004 Report), which was received as an Adobe Acrobat attachment in an email on 16 February 2005, and Recommendations Clarification (Letter), received 23 March 2005. The GWM Report provides the results of groundwater modeling and fate & transport modeling, and includes a recommendation to halt this remediation system to conduct a rebound test. The 4Q2004 Report recommends continued operation of the GWP&T system to maintain hydraulic control. The Letter clarifies the intent of the two conflicting reports recommendations by saying that the recommendation for a rebound test (GWM Report) "... supercede... " the continued operation of the GWP&T system (4Q2004 Report). Comments: GWM Report The groundwater and fate & transport modeling (Modeling) was done in accordance with standard groundwater modeling practices, which include the following: • Site specific datum was used for input parameters, • Sensitivity Testing was described in detail in text, • Narrative description and graphic representation of results are adequately presented, and • Multiple modeling layers and realistic boundary conditions were used to represent site- specific geology. The GWM Report provides sufficient documentation to verify the accuracy of the modeling results. Modeling appears to adequately address regulatory concerns that residual petroleum hydrocarbon contamination, when released from the hydraulic control now provided by the GWP&T system, will not reach Well #12. Therefore I agree with the GWMReport recommendation to perform a rebound test of the GWP&T system, provided the rebound test is at least a two -months duration. During the test I recommend performing monthly groundwater sampling of a sufficient number of wells to show whether the plume remains stable without California Environmental Protection Agency 0 Recycled Paper