ARCHIVED REPORTS XR0003037 - Laserfiche WebLink

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• • The data were not from Geoprobe samples The reason for the first criterion is that, since only onsite exposures are examined in the PEA, only onsite data should be used For the second point, because the remedial system designed for the site began operation on July 3, 2000, using older data would not be representative of current (and future) site conditions; as for most risk assessments, the PEA does not address previous, "retrospective" exposures Finally, Geoprobe data was collected to aid in site characterization, but is generally not used for risk assessment purposes when actual monitoring well data is available, as in the present case Table P-1 shows the onsite groundwater dataset used for the PEA, as well as the statistical analysis performed on this data Soil Data SECOR used all available onsite soil data for the PEA, including data collected prior to the system startup The rationale for this choice is based on the fact that soil data, unlike groundwater, is less tune-vanable Table P-2 shows the onsite soil dataset used for the PEA, as well as the statistical analysis TIER 1 EVALUATION In a tier 1 evaluation, detected site chemical concentrations in the various impacted media are compared with appropriate nsk based concentrations (RB Cs), as described by ASTM (1995) For the present analysis, SECOR used the nsk-based screening levels (RBSLs) recently developed by the RWQCB — San Francisco Bay Region These RBSLs are desirable for the present analysis because, unlike the USEPA Region 9 Preliminary Remediation Goals (DRGs), they are pathwaLspecific In fact, RBSLs have been developed for the soil and groundwater volatilization to indoor air pathways, which are the focus of this PEA On April 26, 2001, SECOR received verbal authorization from Marty Hartzell of the RWQCB to use these RBSU under the provision that this analysis be performed with the sole objective of identifying, or eliminating, potential exposure pathways, and not as part of a request for closure Groundwater Table P-3 shows the Tier 1 evaluation for groundwater As the table shows, all detected chemicals for which RBSLs are listed could be eliminated from further evaluation, that is, their detected concentrations were found to be below the listed RBSLs However, for four chemicals, methanol, ethanol, TBA, and EDB, listed RBSLs were not available These four chemicals were therefore evaluated further in the Tier 2 assessment Soil As Table P-4 shows, all chemicals detected in site soil could be eliminated from further evaluation in the Tier 1 assessment 49