SITE INFORMATION AND CORRESPONDENCE

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Mr. David a. Rosso California State University Stanislaus 1252 N. Stanislaus Street, Stockton Page 2 of 3 the California Code of Regulations Section 2725 (g)(1). While health risk-based modeling results are one element considered when evaluating closure requests, they are not accepted or agreed to as clean up goals. The W PSGW R proposes to: • Install ground water extraction wells on the site and initiate ground water extraction (GWE) to reduce the ground water elevation, • Excavate impacted soil to a depth of approximately 45 feet bsg, removing approximately 8,000 cubic yards of soil, an estimated 2,500 cubic yards of which has been impacted by the unauthorized release of fuel hydrocarbons; and • Install and operate an ozone injection system to address impacted ground water. You should note and acknowledge that the PAWP compared excavation to soil vapor extraction (SVE) with ground water extraction (GWE) and found that excavation was significantly greater in cost than SVE with GWE. The WPSGWR does not demonstrate that excavation and disposal will be the most cost effective remedial option. There was discussion during the March 2003 meeting that soil excavation and disposal may be the best option to satisfy requirements" of the Department of Toxic Substances Control. EHD will approve the proposed excavation and disposal of soil as an interim remedial action if California State University Stanislaus decides to proceed with this scope of work. However, the final remediation plan for this site cannot be prepared and approved until the impacted ground water has been fully delineated, the hydrologeological framework fully characterized and the feasibility of remedial alternatives evaluated. EHD notes that the proposed extraction wells will be set between 50 and 70 feet bsg; these depths may include the significant sand at an approximate depth of 55 feet bsg, which may contribute a large volume of water to the extraction process and reduce the expected total drawdown. It may be beneficial to avoid completing the extraction wells in that sand body or complete a pumping test to be sure the desire effects will be achieved. EHD approves the ozone sparging to remediate impacted ground water as an interim remediation measure, but recommends delaying this scope of work pending final characterization of the extent and distribution of impacted ground water. At that time it may be more beneficial to prepare a corrective action plan that compares potentially feasible remedial alternatives, including ozone sparging, from which a final remediation approach can be selected.