RAC is well-versed in reviewing and estimating releases of chemical and radioactive materials to the environment (source terms). Source term estimates are an essential part of the risk assessment process to determine health impacts to the surrounding population. Our source term analysis capabilities can address historical, present day, or future releases. We have conducted a number of historical dose reconstructions of nuclear facilities, and as part of those studies, we have estimated historical releases from facilities that began operation many decades ago. We use these release estimates, coupled with transport modeling and contemporary environmental measurements, to understand the effects of the operations on environmental concentrations and to evaluate whether other nearby sources or natural processes may also contribute to those concentrations. RAC also assists facilities in assessing future emissions, whether from new facilities or as a result of process or effluent treatment modifications to existing plants. Careful analyses of releases and their movement in the environment can provide a sound basis for determining historic, current, and future public exposures.

Cerro Grande fire – Predicted hourly-average X/Q values (s m-3) for 2 January, 1994 at 03:00 h using CALPUFF, a Lagrangian Puff model. The meteorological conditions during the hour were a wind speed of 1.5 m/s, wind direction of 270 degrees, and stable atmospheric conditions.

Contaminant transport modeling provides a quantitative estimate of concentrations in environmental media (soil, air, surface water, groundwater, and biota) in the past, present, or future. These contaminant concentrations can then be used to estimate impacts on human health and the environment. RAC uses off-the-shelf models when appropriate, but also has developed custom numerical models that fit the specific needs, circumstances, and objectives of the project. RAC team members have extensive programming skills including fluency in FORTRAN, C++, Perl, Visual Basic, .Net/C#, php, and Javascript. As a matter of course, RAC applies quality management principles to the design, development, verification, benchmarking, and testing of the computer models it develops. Our team understands the limitations of numerical models and has developed empirical models when appropriate field data are available. Moreover, RAC has extensive experience in uncertainty analysis so the limitations of model-estimated contaminant concentrations in the environment are more fully understood and appreciated. From a credibility perspective, RAC recognizes the importance of testing any models applied in a study to the maximum extent possible and searches for opportunities to do this within a project.

Relevant projects: Fernald Dosimetry Reconstruction Project, Rocky Flats Historical Public Exposures Project, Risk-based Screening for Releases to the Columbia River at Hanford, Assessment of the Cerro Grande Fire, Uravan Historical Dose Reconstruction, Apollo Historical Dose Reconstruction, Analysis of Release from Single-Shell Tank at Hanford

Selected Publications