SITE INFORMATION AND CORRESPONDENCE_FILE 1

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1%ftwl N"0011 xx GEOMATRIX Ms. Wendy Cohen Regional Water Quality Control Board - Central Valley 7 November 1994 Page 2 very high concentrations are present in soil. A simple equilibrium calculation (from Feenstra, et al, 1991 and Sitar, et al 1990) shows that soil containing 330 µg/kg anthracene (detection limit for soil), if present in the saturated zone, would be in equilibrium with a theoretical maximum concentration of 2 1Ag/1 (barely measurable) in the groundwater in the pore spaces of the soil. The same calculation for benzo(a)pyrene shows that a 330 µg/kg soil concentration would be in chemical equilibrium with a theoretical maximum of 0.006 µg/1 (not measurable) in the pore water. These calculations assume a log K, of 4.15 and'6.74 for anthracene and benzo(a)pyrene, respectively, and a fraction of organic carbon (fes) of 0.01. In summary, we believe that the analytical method for the data provided for the stockpiled soil and the soil in the drums is sufficient for characterization purposes and to allow the reuse of the soil as backfill on the site. As you are aware, we will be collecting undisturbed soil samples at the site and analyzing for PNAs by EPA Method 8310 in support of the Screening Health Risk Assessment (SHRA). We propose to resample the stockpiles and drums and analyze the soil samples for PNAs by EPA Method 8310 to provide analytical data consistent with that collected for the SHRA. We will collect one sample from each of the four stockpiles and collect a drum composite sample, for a total of five soil samples. Pursuant to Mr. Moody's letter and our telephone conversation, we will use the stockpiled and drummed soil as backfill if detected PNA concentrations will not pose a threat to water quality. The analytical results from the stockpile and drum samples will not be used in the SHRA due to the disturbed nature of the samples; disturbed samples are not considered representative for SHRA purposes. Mr. Moody's letter also requested that a sample be collected from the open trench bottom. As he and I discussed on 31 October, the purpose of this sample is unclear, especially relative to the goal of using stockpiled and drummed soil as backfill. The trenches excavated by Toxic Technology almost certainly did not remove all of the petroleum-affected soil, because they stopped remedial activities early in the process. If the RWQCB requested the trench bottom sample to evaluate the presence of PNAs remaining at depth, we suggest that the data gathered during the Screening Health Risk Assessment (SHRA) fieldwork will be sufficient and appropriate for that purpose. EXTENT OF AFFECTED SOIL Mr. Moody's letter suggested that the borings for the SHRA may not adequately define the full lateral or vertical extent of affected soil. On 31 October, he and I discussed the fact that definition of extent is not the purpose of the SHRA borings. Further, I suggested that the