SITE INFORMATION AND CORRESPONDENCE 1995-2004

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0 0 James L. Tjosvold, P.E. August 19, 1996 Page 9 soils. They also state that arsenic, copper, and lead had maximum background concentrations of 15.2 mg/kg, 76 mg/kg, and 185.6 mg/kg, respectively. Section 4.2.2 states that subsurface soil samples were not collected from Area II because of electrical hazards. Furthermore, based on the absence of facilities which could have been the source for metals or PCBs and relative immobility of the compounds, the FS assumes that the compounds detected in the surface do not extend five feet below ground surface (bgs). PG&E should assess the threat to ground water quality posed by the presence of arsenic, copper, and lead at concentrations which exceed background concentrations. The presence of utility lines should not prevent PG&E from taking additional samples beyond five bgs. Sampling techniques, such as using hand auger to clear utility lines and a Geoprobe to take depth samples, have been used successfidly at other sites where typical drilling methods are not appropriate. Conclusions should be based on data, which are obtainable, and not on assumptions. Response: 6. As discussed in the response to comment#5, the background soil and groundwater concentrations were discussed in detail in the Remedial InvestigationI report and will be included in the FS. PNAs were detected in all background surface soil samples (as described in the Remedial Investigation and Risk Assessment Report),which was expected since PNAs are ubiquitous in the environment. PNAs are commonly found in soil resulting from the incomplete combustion of organic materials, whether natural (forest fires or volcanoes) or man-made (combustion of fuel). Based on a national literature review, background surface soil total PNA concentrations ranged from nondetect to 113 ppm (44 ppm total carcinogenic). The presence of PNAs in the background samples indicates that they are commonly present at elevated levels in the vicinity of the site and PNAs onsite may not be entirely related to site operations. Regarding the metals concentrations found in Area II surface soil samples; these samples were collected in and around the highly dangerous electrical grid in Area H. These are not locations where deep drilling would be safe to conduct. The data indicate that the extent of soils containing lead, copper, arsenic, and PCBs is limited within Area H. There is no current groundwater exposure pathway in this area. The conclusions based on these results and the results of the risk assessment were approved by the agencies at the conclusion of the Remedial Investigation and Risk Assessment Report. In addition, wells (and well borings) were installed in Area H during the Phase IV investigation in the only locations available for subsurface drilling.