Overview of Environmental Transport Models Contained in the Risk Analysis, Communication, Evaluation, and Reduction (RACER) Software Tools at Los Alamos National Laboratory - 9070

The objective of the Risk Analysis, Communication, Evaluation, and Reduction (RACER) project is to provide more relevant and timely access to information related to chemicals and radionuclides in the environment around Los Alamos National Laboratory (LANL), and to develop tools to support an effective and logical evaluation and reduction of human health risks and ecological impacts associated with exposures to these materials. The guiding principle of RACER is an open and transparent process that considers community input as an integral part of making decisions about how to most effectively reduce risks related to LANL operations. Tools and resources include a database of geo-referenced environmental data, mapping software to display spatial data, environmental transport models, a risk assessment module, and various options to assist with interpreting the results. Human health risk assessment is performed for a user-defined exposure scenario using current environmental measurements, environmental transfer functions to estimate contaminant concentrations in environmental media that do not have measurements, and environmental transport models to estimate contaminant concentrations in the future. Environmental transport and transfer models address transport in air, vadose zone, groundwater, and the food chain. Recognizing that environmental transport models are generally developed on a site-specific basis, the RACER software tools incorporate methodology to distill complex site-specific model behavior into simple functional forms that are stored within the RACER database tables and are executed either by external dynamic-linked libraries or within Visual Basic code. Groundwater model computer run times can be excessively long and construction and operation of the model require specialized expertise. Instead of incorporating a complex groundwater model directly into the tool, a response surface model was developed that abstracts the behavior of an external groundwater model into simple response functions that can be stored within the RACER database. The convolution of the contaminant flux to the aquifer with the response function yields contaminant concentrations in the aquifer. Likewise, atmospheric transport models can involve detailed analysis and specialized expertise. RACER incorporates site-specific and radionuclide-specific dispersion factors for each potential emission point that are calculated with an external atmospheric transport model. The product of the contaminant emission rate and the site-specific dispersion factor yields the concentration of the contaminant in ambient air. Generic models are also incorporated to address situations where detailed modeling is not warranted or site-specific data necessary for complex models are lacking. RACER is currently being instituted at Los Alamos National Laboratory. The three-dimensional MODFLOW/MT3D groundwater flow and transport model was used to develop response functions for over 800 potential release points and over