SITE INFORMATION AND CORRESPONDENCE 1995-2004

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James L. Tjosvold,P.E. August 7, 1996 Page 5 varies and the ratio of lighter weight or heavier weight PNAs varies. It is clear from the research that has been performed on diesel fuels,that PNAs are part of diesel and that those PNAs detected at the site as well as offsite are known to be found in diesel fuels. Wells MW- 14, MW-15, and MW-16 located upgradient and cross-gradient of Area I have had acenaphthene and naphthalene detected,both of which have been found to be part of diesel fuels. These references also site that BTEX compounds are a part of diesel and gasoline fuels. It should be noted that BTEX compounds have been detected in all three groundwater zones at upgradient and cross-gradient locations in addition to onsite wells. This enclosed table does not prove that PNAs found in cross-gradient or upgradient wells are not related to PG&E MGP activities or that other upgradient sources have contributed to the groundwater near the site. However, the table indicates that there may not be a clear distinction between other petroleum releases,that have not been studied in as much detail as the PG&E site, and the sources related to PG&E MGP activities. PG&E does not propose to drill on other properties at this time however with this information the agencies are being made aware that PG&E may not be the only source of low levels of petroleum-related compounds detected in the groundwater. Comment: 2. Page ES-2, Executive Summary The report states that PNAs were detected in hydropunch samples from Zone A in MW-14 and from Zones A and B in MW-15 during the drilling of these Zone C wells. The report also states that since these wells are upgradient of the site, there could be upgradient sources of the PNAs in ground water. However, the presence of PNAs in ground water in Zone A at MW-14 and PNAs in Zones A and B at MW-15 has not been confirmed because of the absence of monitoring wells (Ws) at these locations. Furthermore, all the MWs which show PNA contamination around PG&E could have been contaminated by PG&E due to ground water elevation fluctuations and flow reversals. Some evidence offlow reversal is shown in Table 3-4. In addition, the MWs at the Fire Department (northwest of PG&E) show a Zone A ground flow direction to the northeast which differs from PG&E Zone A ground water flow direction which is predominantly to the east. This could be an artifact offlow reversal or some hydrogeologic condition which results in different ground water flow directions in Zone A. Also, onsite and offsite ground water elevations have only been measured since 1992. The plant started operations in the 1800s. It is likely that ground water flow reversals and fluctuations occurred over the years and could have resulted in the formation ofpockets of contamination which are now contributing sources to the overall contamination coming from locations of former MGP structures. For example, MW-14 is only approximately 70 feet west of MW-IR and MW-ID, both of which have PNA contamination. The proximity of MW- 14 to onsite MWs showing contamination, the very flat gradient, and the potential for flow reversal suggest that MW-14 has been impacted by onsite contamination.