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1.0 INTRODUCTION ENV America Incorporated (ENV America) has prepared this work plan on behalf of Pacific Gas and Electric Company (PG&E) for the former manufactured gas plant (MGP) (Site) in Stockton, California (Figure 1). PG&E has completed various phases of investigations and remedial actions at the Site since 1987, including the excavation of affected soil for offsite disposal, injection of Oxygen Release Compound (ORC) into the subsurface, installation of a cap, annual cap inspection, and regular groundwater monitoring. Regulatory oversight of the Site has been provided by the Department of Toxic Substances Control (DTSC). The Remedial Action Plan (RAP) and the Operation and Maintenance (O&M) Plan for the Site (CH2M HILL, 1998 and 2000) were approved by the DTSC. The approved remedial action includes excavation, capping, and a program to monitor the progress of natural attenuation of the constituents of concern (COCs) in groundwater at the Site. In a 2004 letter to PG&E (DTSC, 2004), the DTSC approved a revised annual groundwater monitoring program for the Site and also requested the following: 1. The DTSC indicated the acenaphthene concentrations in well MW-26R have increased, and the goals and objectives for groundwater protection are not achieved in the vicinity of MW-26R. The DTSC requested that PG&E submit a plan to evaluate the groundwater conditions in the vicinity of MW26R, identify and define the problem, and propose a solution to address the issue. 2. The DTSC approved the decommissioning of eight existing groundwater monitoring wells at the Site and requested that PG&E submit a well decommissioning work plan for approval prior to field activities. 3. The DTSC requested a revised cost estimate for the long-term O&M activities at the Site based on the revised annual groundwater monitoring program. 1 ENV,' A M E R I C A P:\PGM PGE-05-01 Stockton MW26R Inves6gation\MW26 Work Plan\PGE Stockton MW26R W P doc