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ENVIRONMENTAL COSI MANAOSMENT,INC. :. :. August 16, 2010 AUG 1 8 4W James Brownell, P.G. ENVIRONMENT HEALTH Central Valley Regional Water Quality Control Board PERMIT/SERVICES 11020 Sun Center Drive, #200 Rancho Cordova, CA 95670 Ref.: On-Site (TRAP) Groundwater Extraction System — System Performance Assessment and Proposed Operational Changes, Former Nestle USA, Inc. 230 Industrial Avenue Ripon, CA 95366 Dear Mr. Brownell: On behalf of Nestle USA, Inc. (Nestle) Environmental Cost Management, Inc. (ECM) has prepared this IRAP System Modification Request letter for the following purposes: To present an updated assessment of the hydraulic capture zone induced by the two extraction wells EU-3 and EU-4 operated as the Interim Remedial Action Plan (IRAP) • To document and compare the field-measured capture zone to the capture zone predicted by the numeric flow model • To propose a 60-day test modifying the current operating condition of extraction wells EU-3 and EU-4 to assess the possibility of extracting additional mass within the stagnation zone Background In a June 11, 2009 letter, ECM proposed a system modification responding to the 85% to 95% reduction in mass removal rates from the two extraction wells since well operations started in February 2008. ECM proposed the modification to determine whether the rapid reduction COC concentration was due to mass removal, or whether a stagnation zone exists between the extraction wells that hinder mass removal. The proposed modification included shutting down well EU-3, while continuing to pump from well EU-4. Groundwater model simulations showed that the proposed modification will not affect the capture zone significantly. Though Regional Water Control Board (RWQCB) did not object to the proposed modification, additional validation of the projected capture zone was requested via the installation of additional monitoring wells at the Industrial Avenue site.