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• Following statistical evaluation of Phase I data, determine if additional Phase II sampling is required to determine the extent of metals and pesticides. 23. Pages 5-193 and 197, PCE in Areas 2 and 3 soil In the Phase II recommendation for both Areas 2 and 3, VOCs are not proposed for further investigation. EPA believes the number of soil borings drilled in the Phase I RI may be inadequate to delineate the lateral extent of VOCs. PCE was detected in the soil of Areas 2 and 3. In Area 2, the highest concentration was detected in a shallow soil sample at a depth of about 2 feet (SB-114). Of the samples collected from soil boring SB-117 in Area 3, the highest PCE concentration was detected in a shallow soil sample at a depth of 2 feet. Since deeper samples detected PCE at lower concentrations, it is less likely that the PCE originates from volatilization of the contaminated saturated zone and more likely it is from a shallow source in the vadose zone or a surface spill. • During the Phase II RI, the use of soil gas surveys should be performed to delineate the lateral extent of contamination around the spots where the highest PCE concentrations were detected. Also, vertical profile surveys of soil VOC vapor concentrations may locate potential vadose zone sources. 24. Section 6, 'Preliminary Risk Evaluation" Section 6 generally describes the approach to be used for the baseline risk assessment. However there are a number of areas/issues which require further clarification or elaboration. Further, it is not clear how 'conclusions" presented in this preliminary Risk Evaluation will relate to the draft BRA Work Plan (due to the regulatory agencies on February 12, 1994). a. Current and future land use conditions have not been clearly distinguished. In a baseline risk assessment, it is necessary to provide estimates for both current and expected future land uses. If existing and future land use conditions are anticipated to be the same, this needs to be discussed. This is important because the potential exposure pathways shown in the site conceptual model (Figure 6-1) may differ for current and future land use scenarios. • Please distinguish between current and future land uses. b. Potential receptors, not included in the site conceptual model (Figure 6-1) are trespassers, visitors, and attendees at the on-site day-care center. • These receptors should be considered. C If groundwater at the site is considered potable or potentially potable, other EPA 14FEB94 a/10