SITE INFORMATION AND CORRESPONDENCE 1995-2004

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James L. Tjosvold, P.E. August 7, 1996 Page 8 first sampling event after well installation. Subsequent sampling events have shown nondetectable levels of benzene and TPHd. It is possible that during well installation, contamination was pushed down from a contaminated zone by the drilling equipment or the drilling equipment itself was contaminated. Laboratory error also could have caused the one-time detection of benzene and TPHd. In June 1995, TPHg was detected with an estimated concentration of 0.014 pg/l which is lower than the detection limit of 0.015 ug/1 making this result highly questionable. Based on the monitoring data, it seems that benzene and TPH were not really present at MW-14 in Zone C. There does not seem to be sufficient evidence to support that the potential upgradient source, which is the Fire Department, is a contributing source. However, we need to resolve with PG&E the issue of potential upgradient sources and their contribution, if any, to the contamination at PG&E, because it always comes up in reports and meetings. Response: 6. The responses to these comments were included in the responses to RWQCB-specific comments 1 and 2. In the RWQCB's comment 2, there is mention of possible groundwater gradient reversals. If the RWQCB has evidence of such reversals,we would like to see this evidence. To date,the groundwater gradients in all three groundwater zones indicate that the Fire Department is upgradient of the site. There appears to be an inconsistency in the expectations of lateral and vertical characterization in the investigation being conducted at the Fire Department site as compared to PG&E's site (the Fire Department has not been required to investigate the groundwater in Zones B and C and the Fire Department has not been required to investigate the fire training area immediately across the street from PG&E's site). Comment: 7. Page 16, Modifications to the Work Plan The report states that MW-22R, which is the alternative to the original MW-22 location, indicated a diesel odor in the soil. Based on this information and the knowledge that there were former service stations on the far side of Church Street, PG&E decided to install MW- 22 in the original location which had PNAs and VOCs. The boring log for MW-22R shows specks of lampblack at 3-7 feet, black staining at 20-26 feet, slight diesel odor at 45 feet, and indication of contamination all the way to the water table. In spite of the visual evidence of contamination, PG&E did not take soil samples for laboratory analysis. PG&E should explain why soil samples were not taken. Also, PG&E should explain further why it attributes the contamination to the former service stations when there is clear evidence of contamination by MGP residues. More importantly, PG&E should explain how it will determine the lateral and vertical extent of soil contamination and its potential to contaminate ground water. The report states that the final location of MW-23R may be downgradient of former sources such as the service stations on Church and El Dorado Streets. This statement is true, but