SITE INFORMATION AND CORRESPONDENCE

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Mary Misemer November 9, 1999 Page 2 risk-based clean closure of the site under the Voluntary Cleanup Program. Sampling details, analytical methodology, and technical approach were evaluated. General Comments A total of 16 soil samples and 7 grab groundwater samples were taken to define the ver- ticatand horizontal extent of petroleum hydrocarbon affected soil and groundwater. Soil sample depth began at 5 feet bgs and advanced downward to 10-to 16.5 feet bgs. Surface soils were not affected and, presumably, the former pipeline was located approximately 5 feet below grade. The extent of petroleum hydrocarbon contamination in the soils and groundwater adja- cent to the former pipeline right-of-way is limited vertically and horizontally. Levels of petro- leum-related hydrocarbons ranged from ND to 21,000 mg/kg for TPHcrude in soils and up to 700 µg/L for TPHdiesel in water. BTEX in soils ranged from 0.007 mg/kg for benzene to 2.5 mg/kg for ethylbenzene. Low levels of PAHs (commonly associated with crude oils, fuel oils, and diesel) were detected up to 2.5 mg/kg for naphthalene. Chrysene was the only PAH de- tected at the site that is a potential carcinogen (0.35 mg/kg). None of the constituents identified above were from surface soil samples. The reported maximum levels of petroleum-related constituents were compared to the USEPA Region IX Preliminary Remediation Goals for residential soils. These goals are calcu- lated based on a risk level of 1 x 10-6and assume no additivity for other constituents. As re- ported, the concentrations of constituents identified at the site are well below the respective PRGs for soil and tap water. However, as a general policy, HERD does not use the USEPA Region IX PRGs to screen sites for risk levels and provide the basis for risk-based site closure. HERD recommends that the basis for closure should be risk levels as calculated using the equations provided in the Preliminary Endangerment Assessment guidance (DTSC, 1994). Specific Comments 1. In the text, it was stated that BTEX compounds were analyzed using USEPA Method 8021 B Tables 1 and 2 report BTEX analyzed as 8020A. The correct method should be 8021 B. The text should be revised appropriately. 2. Text states petroleum-affected soils were observed from 4 to 14 feet bgs. However, the ta- bles reflect the depths as 5 to 16.5 feet bgs. The text should be revised appropriately. 3. Section 5, Human Health Risk Assessment should be entitled Risk Screening as the current title implies that there was a formalized risk assessment conducted for the site. The authors should revise the text appropriately. 4. Section 5 should clearly state that the risk screening was based on analytical results from soils at depth, not surface soil where human exposure is most likely to occur. 5. The conclusions should be revised to reflect that risk levels were less than 1 x 10$for can- cer and that the hazard index for the site is less than 1.0 as evidenced by screening level calculations based on the PEA guidance. The authors may want to include a statement that the 1 x 10"6 risk level is considered a point of departure for risk significance.