Radiation risk assessment models are important tools for decision makers. They are used to assess risk and dose for the public and workers due to radioactivity resulting from radioactively contaminated sites. These models can be used for a variety of purposes including risk assessment, risk communication, remediation, decommissioning, and decontamination. DOE, EPA, states, and different countries have developed a variety of models with varying default input parameters, and Neptune has used many of these models over the last 25 years for a variety of federal, state, and international agencies.

Model selection is a critical first step and depends on the site conditions, radiological source material, the regulatory agency (decision makers), and the types of exposure scenarios being evaluated. A second step is the selection and characterization of model input parameters. While models are often initially run with single input parameters that provide a single answer, Neptune has specialized in understanding the uncertainty associated with each input parameter and providing decision makers and the public with a deeper understanding of potential radiological risk. From radiological data evaluation to dose and risk calculations, Neptune provides decision makers and the public with a transparent and detailed understanding of the strengths and uncertainties that contribute to the site decision-making process, including sites where both radiological and chemical risks need to be integrated.

Neptune has developed radiological and mixed chemical-radiological risk assessments and has performed radiological modeling work in a wide variety of contexts. Neptune provides risk assessment and modeling support to the Nuclear Waste Program of the Washington Department of Ecology, and provided technical support to the U.S. Army Corps of Engineers for developing a conceptual site model related to environmental contamination from abandoned uranium mines located within the Cove Wash watershed of the Navajo Nation in AZ. Neptune also supports the Tennessee Department of Environmental Conservation in its evaluation of a proposed Environmental Management Disposal Facility that was developed in the RESRAD-OFFSITE modeling platform, with additional modeling performed using HELP (Hydrologic Evaluation of Landfill Performance), STOMP (Subsurface Transport Over Multiple Phases), and the USGS groundwater flow and transport computer codes MODFLOW and MT3D. 

Neptune also has a large body of relevant radiological exposure modeling and risk assessment work conducted under CERCLA risk assessment guidance and applied in the RCRA Corrective Action Process. For example, since 1996 Neptune has supported Los Alamos National Laboratory (LANL) in the evaluation of mixed chemical and radiological contamination in the canyons of the Pajarito Plateau. LANL operations are primarily conducted on finger-like mesas that comprise the Plateau, on which the Laboratory is situated. The canyons that cut Pajarito Plateau into mesas have a combined length of approximately 110 miles and have received direct and indirect contaminant releases from operations on the mesas. Neptune staff are members of an interdisciplinary technical team responsible for developing and implementing the approach to this complex investigation.