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i ! <br /> 3.0 WORK PLAN TO ADDRESS GROUNDWATER <br /> CONDITIONS IN THE VICINITY OF MW-26R <br /> DTSC (2004) indicated that acenaphthene concentrations in the groundwater samples <br /> collected from MW-26R have increased from 9.6 to 19 micrograms per liter (Ng/L) in <br /> 1997 and 1998 to 100 pg/L in 2004. DTSC requested that PG&E evaluate the <br /> groundwater conditions, identify and define the problem, and propose a solution to meet <br /> the remedial goals for groundwater protection according to the RAP for the Site (CH2M <br /> HILL, 1998). <br /> The following stepped approach will be used to assess and subsequently address the <br /> acenaphthene concentrations in groundwater in the vicinity of well MW-26R: <br /> 1. Review existing groundwater monitoring data (Section 3.1). <br /> 2. Identify data gap(s) (Section 3.1). <br /> 3. Propose assessment to obtain additional data (Section 3.2). <br /> 4. Evaluate existing and new data (Section 5.0). <br /> 5. Propose additional assessment and/or remedial action, if necessary, to mitigate <br /> acenaphthene concentrations in groundwater downgradient of Site (Section 5.0). <br /> The review of existing groundwater monitoring data at the Site and the proposed <br /> assessment are described in the following sections. <br /> 3.1 Acenaphthene Concentrations in Groundwater at the Site <br /> Acenaphthene concentrations are typically higher compared to those of the other PAHs <br /> in the groundwater samples collected from the monitoring wells at the Site (refer to <br /> Exhibit C of the 2004 Third Quarter Groundwater monitoring Report, ENV America, <br /> 2005b). Historically, the highest acenaphthene concentrations at the Site have been <br /> reported in the groundwater samples collected from the B-zone wells MW-23R and <br /> MW-26R (100 pg/L to 140 pg/L). <br /> 7 ENVA <br /> A M E R / C A <br /> PAPG&MPGE-05-0t Stockton MW26R InvestigaticMMW26 Work Pan\PGE Stockton MW26R WP.doc <br />