SITE INFORMATION AND CORRESPONDENCE 1993-1995

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James L. Tjosvold, P.E. February 23, 1995 Page 2 • Of the wells installed prior to Phase III, groundwater monitoring would be performed annually in the wells located at or near the perimeter of the site. Wells which are located in the center of the site would not be included in the groundwater monitoring program. These include MW-4 and MW-8 in Zone A, and MW-5 in Zone B. • Samples from the wells in the monitoring program would be analyzed for PNAs and BTEX compounds. Samples would also be analyzed for barium and antimony one time only(in March, 1995). In addition, samples from wells MW-9 and MW- 19 would be analyzed for cyanide one time only (in March, 1995). • Quarterly water level measurements would be collected from all wells. Table 1 presents a summary of the proposed monitoring program described above. The details and rationale of the proposed program and how it varies from the program presented in the Workplan are described for each Zone below. Zone A: The Workplan specifies that samples from Zone A wells will be analyzed quarterly for PNAs, VOCs and sulfides. The rationale was to evaluate concentrations of chemical previously detected on-site and evaluate concentration for treatment and POTW disposal options. PG&E recommends the following revisions to this sampling program: • Delete MW-1, MW-4 and MW-8 from the sampling program. MW-1 has been abandoned and replaced by MW-1R. MW-4 and MW-8 are located in the center of the site and are surrounded by a sufficient number of wells to characterize the nature and extent of constituents in the groundwater. • Reduce the frequency of sampling quarterly to annually for the remaining wells installed prior to the Phase III investigation(MW-2, MW-3, MW-7, MW-9, MW- 10, MW-I 1 and MW-12). These wells have been sampled between five and eight times. Annual monitoring will be sufficient to monitor temporal changes in groundwater quality. • Delete analysis for sulfides because sulfides were not detected in any wells during the previous three sampling events.