Development of IMPACTS-BRC, Version 2.1

IMPACTS-BRC is a computer program developed to conduct scoping analyses for use in supporting rulemaking on petitions for exemption of waste streams from multiple producers. It was not initially intended for use on individual license applications for specific sites. However, the Federal Register, Volume 51, Number 168, specifies that IMPACTS-BRC be used to evaluate incoming license applications. This creates a problem since IMPACTS-BRC is not being used for its intended purpose. It is a generic code that is now being used for site specific applications. This is only a valid procedure if it can be shown that generic results from IMPACTS-BRC are conservative when compared to results from site specific models. Otherwise, IMPACTS-BRC should not be used. The purpose of this work was to verify that IMPACTS-BRC works as specified in its user's guides (1,2,3). In other words, Sandia National Laboratories (SNL) has determined that the mathematical models given in the user's guide are correctly implemented into the computer code. No direct work has been done to verify that the mathematical models used in the code are appropriate for the purpose that they are being used. In fact, scrutiny of the groundwater transport models in IMPACTS-BRC has led us to recommend that alternate geosphere models should be used. Other work carried out for this project included verifying that the input data for IMPACTS-BRC is correct and traceable. This was carried out, and a new version of the data with these qualities was produced. The new version of the data was used with the verified IMPACTS-BRC, Version 2.0 to produce IMPACTS-BRC, Version 2,1. Note that no code changes were made in the evolution to Version 2.1: performance differences between Version 2.0 and 2.1 are caused by the updated data. (author)