SITE INFORMATION AND CORRESPONDENCE

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Mr. James Taylor • - 3 - • 4 October 2007 Groundwater Model The parameters for the groundwater model were derived from an aquifer test conducted from MW-3B in 2001 (as documented in the 16 November 2001 Interim Remedial Action Plan, prepared by Haley & Aldrich, Inc.), and from supplemental hydraulic conductivity tests performed on soil samples obtained from the subsurface in November 2006. The observed changes in water surface elevation near the extraction and injection well as a result of recirculation will provide a means to verify or update the model. It is likely that the hydraulic conductivity of the iron will be different than the hydraulic conductivity of the surrounding formation, and these differences will need to be incorporated into the model. Groundwater Monitoring ContiGroup has been conducting groundwater monitoring as described in Monitoring and Reporting Program No. (MRP) 5-00-858, in addition to those prescribed by Waste Discharge Requirements MRP No. R5-2004-0160. Since monitoring conducted pursuant to the Waste Discharge Requirements is specific to injection of iron, a draft Monitoring and Reporting Program has been prepared to update and replace MRP No. 5-00-858, and to incorporate monitoring specific for the proposed pilot study. The draft MRP includes a section for groundwater plume monitoring, and a section for groundwater recirculation system monitoring. When Regional Water Board staff concur that the recirculation pilot study is completed, this portion of the monitoring program can be removed. Please review the attached draft MRP and provide comments to Regional Water Board staff. Conditional Concurrence with Recirculation Pilot Study Regional Water Board staff conditionally concur with the Groundwater Recirculation Pilot Study, subject to the following conditions: • A work plan for extraction wells, injection wells, and monitoring well installation and a schedule for implementation shall be provided to Regional Board staff with a copy to San Joaquin County Environmental Health Department for approval before installation. The work plan may be submitted electronically. • Proposed monitoring well MW-13B shall be relocated between EW-11B and IW-BH2A, as shown in the Remedial Action Plan. • Within one month prior to starting the extraction/injection well pair, groundwater samples shall be obtained from MW-3B, MW-4B, MW-5B, MW-96, MW-10B, and MW-13B, and shall be analyzed for volatile organic constituents, dissolved iron, and chloride. • Install water level transducers in MW-313, MW-4B and MW-9B in addition to MW-106, MW-13B, and EW-12B, if available. • Recirculation may begin when the wells are installed and when the Monitoring and Reporting Program has been finalized and issued by the Executive Officer. • If injection into IW-BH2A causes an increase in water surface elevation in MW-3B, Regional Water Board shall be notified and the injection rate shall be decreased. Reporting During the first three months of operation, monthly constituent data and groundwater elevation data shall be transmitted to Regional Water Board staff, and may be transmitted electronically, The data should be tabulated and should be accompanied by a figure. Quarterly reports need to include narrative descriptions, data, figures and should be submitted in hardcopy format.