Guidance for Conducting Risk Assessments and Related Risk ...

• ensure that data collection activities support the project data quality objectives.
The site-specific data set is evaluated to ensure that the quality of the data is appropriate based on the
project-specific data quality objectives. If the data evaluation has not been completed in earlier phases of
the investigation, it may be completed as part of the risk assessment. Appendix B contains detailed
guidance for conducting the data evaluation and determining the chemicals of potential concern (COPCs)
for quantitative risk assessments. In general, the data evaluation performed for risk assessment purposes
consists of the following steps.
• Evaluate analytical methods, quantitation limits, qualifiers and codes, and blanks. The risk
assessor performs the following actions, regardless of whether the data have or have not been
validated by an independent party or if the action items have already been performed.
— Evaluate the data set to ensure that the analytical methods were appropriate for the chemical
analyzed and the sample matrix.
— Evaluate the quantitation limits to ensure that the detection limits were not unusually high.
— Evaluate the qualifiers and codes to ensure that the data are valid.
— Evaluate and perform a comparison of blank concentrations to actual sample concentrations to
ensure that the concentrations were not biased by either the laboratory preparation methods or the
analytical methods.
• Determine if tentatively identified compounds are significant. Tentatively identified compounds
are retained as chemicals of potential concern only if they are detected frequently and have been
associated with site operations.
• Compare data set to background and reference samples. A comparison of sample concentrations
with available background concentrations is useful for identifying non-site-related chemicals and
radionuclides. The background values represent naturally-occurring levels of chemicals that are
present under ambient conditions (i.e., not influenced by anthropogenic sources). In general, this
comparison is applicable only to inorganic chemicals and a select number of radionuclides.
Information specific to the ORR background concentrations is listed below.
— Soil background concentrations for the ORR were obtained from a comprehensive effort. The
soils data obtained from this effort are presented in the Final Report on the Background Soil
Characterization Project at the Oak Ridge Reservation, Oak Ridge, Tennessee, Volumes 1–3
(DOE 1993). These data are used to screen environmental data sets and eliminate contaminants
determined to not exceed background concentrations.
— Chemicals eliminated as a result of background or reference sample comparisons are discussed in
the text of the baseline risk assessment report. Appendix C presents detailed guidelines on
statistical approaches that can be used to compare site-specific data and background.
— Groundwater background concentrations do not exist for all of the ORR; however, background
concentrations for inorganic chemicals in groundwater at the Y-12 Plant were developed using
groundwater data collected under the Y-12 Groundwater Monitoring Program. The methodology
used to develop these background concentrations and the values themselves are contained in
Determination of Reference Concentrations for the inorganic Analytes in Groundwater at the U.
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