Methodology for Determination of Exposure Point Concentration Using both Systematic and Biased Samples for Radiological Risk and Dose Assessments - 11488

Residual radiological dose and risk assessments are performed as a part of Baseline Risk Assessment and/or as a part of the Final Status Survey to assess the dose and risk due to the presence of residual contaminants at the Site. Determination of source term or exposure point concentrations (EPCs) for each of the radiological contaminants present at the Site is one of the major steps during the determination of residual radiological dose and risk. Both systematic and biased sampling results are utilized during the determination of EPC for each of the radiological contaminants present at the Site. When the sampling results collected from the site are either random or systematic, the methods for computing the mean and confidence limits around the mean are relatively straightforward. However, in most cases, the sample results available are not strictly random or systematic; instead they include biased sample results as well. Biased samples are collected from areas with presumed higher concentrations. Inclusion of sampling results for both biased and systematic samples can result in erroneous statistics. Giving an equal weight to both systematic and biased samples will generally lead to an over estimation of EPCs and therefore increased dose and risk for the site, which can lead to unnecessary additional cleanup costs. However, ignoring the biased samples from the sampling results can lead to an under estimation of the EPCs which can lead to ineffective cleanup resulting in added risk to current and future receptors. By incorporating both systematic and biased sample results with their corresponding impacted area information, the problems related to both over and under estimation can be minimized and a more accurate estimation of dose and risk can be obtained.