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amec GROUNDWATER INTERIM REMEDIAL ACTION PLAN UniFirst Facility Stockton, California 1.0 INTRODUCTION Groundwater beneath the UniFirst Corporation (UniFirst) facility at 819 North Hunter Street in Stockton, California (the site), and in the vicinity contains chlorinated volatile organic compounds (CVOCs) and petroleum hydrocarbon constituents. The sources of these chemicals in groundwater include past operations at the site. Other sites nearby also are sources of these chemicals in groundwater in this part of Stockton. With oversight by the California Regional Water Quality Control Board--Central Valley Region (RWQCB), UniFirst has completed the characterization of the nature and extent of the chemicals in groundwater from their site. The results of the characterization and a selected remedial alternative, monitored natural attenuation (MNA), are described in the Groundwater Corrective Action Plan (CAP) submitted to the RWQCB in April 2010 (AMEC, 2010a). The RWQCB commented on the CAP in an August 2, 2010, letter to UniFirst(RWQCB, 2010). In the August 2010 letter to UniFirst, the RWQCB concurred that MNA is an appropriate groundwater remediation strategy for the site. The RWQCB also agreed that the CVOCs in groundwater beneath the site and vicinity are being degraded by natural processes, primarily through reductive dechlorination of the CVOCs. However, the RWQCB requested that UniFirst propose a remediation plan to reduce the mass of CVOCs in groundwater more rapidly than by natural attenuation alone prior to adopting MNA as the final groundwater remediation strategy. This document describes UniFirst's proposed remediation plan as requested by the RWQCB. The proposed plan is to stimulate the naturally-occurring degradation of the CVOCs in groundwater via reductive dechlorination through the injection into the saturated zone of a commercially available material that serves as an electron donor. UniFirst proposes first to evaluate the effectiveness of this method in the area where CVOCs concentrations in groundwater are the highest(in the vicinity of monitoring well cluster MW-5) and to obtain performance data that could be used for subsequent application to other locations, if necessary. Therefore, this document is considered an interim remedial action plan (RAP) and on behalf of UniFirst, AMEC Geomatrix, Inc. (AMEC), is submitting this groundwater Interim RAP for RWQCB approval. _ AMEC Ge_o_matrix, Inc. IM 3000s\13290\Archive113290-49-DOC 1