In order to assess the necessity for remedial actions at sites on CSSA, site-specific concentrations will be compared to background concentrations. Should the decision be made to evaluate the site using TRRP, the potential impacts of exposure to COPCs in soils, groundwater, surface water, and sediment, will be evaluated through a comparison of the site-specific concentrations to PCLs as outlined in the TRRP. This section presents a general overview of the approach for performing this comparison. Following sections of this document (Sections 3 through 6) provide additional detail on the technical approach and assumptions for performing this comparison which are applicable to all of the sites.

The first major step of the process involves an evaluation of available data. Analytical data will be evaluated to determine the chemicals that were detected in the various media. Site data will be validated following Air Force Center for Environmental Excellence (AFCEE) Quality Assurance Project Plan (QAPP) Version 3.0.

COPCs are chemicals detected in environmental media at the facility. They include all contaminants identified in media that represent potentially complete exposure pathways for the facility. The selection of COPCs will follow United States Environmental Protection Agency (USEPA) and TNRCC recommended data evaluation and screening criteria as outlined in Section 4.3.

The next step is the human health and ecological exposure assessments. The exposure assessments for each site will identify and evaluate the nature of the chemical releases, the potential exposure pathways, potential receptors, and exposure scenarios. An initial component of the exposure assessment involves preparation of conceptual site models (CSMs) for each site identifying potential human health and ecological pathways. The findings presented in the CSMs will be used to determine if the default exposure pathways and assumptions provided in the TRRP are appropriate for use at CSSA.

As described in Section 7, development of the initial list of COPCs for the ecological Risk Assessments (RAs) will be in a manner similar to that described for the human health assessments, but will be subject to further refinement based on toxicity screening against ecological benchmarks. Appropriate species representing the various potential trophic levels and pathways identified in the CSMs will be utilized to determine screening levels.

The statistical computations to derive representative contaminant concentration values (i.e., C-term) are discussed further in Section 4 of this document. The statistical evaluation will include calculation of the 95 percent upper confidence limit (UCL). If further evaluation is necessary, a determination of the data distribution, arithmetic mean, 95 percent UCL, and C-term for each detected analyte will be conducted. Outliers and other anomalies associated with the data sets will be identified during these procedures.

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