This study compares the HI-RUN (Highway Runoff Dilution and Loading) and SELDM (Stochastic Empirical Loading and Dilution) models for use in WSDOT biological assessments for western Washington highway projects. Current WSDOT policy and an interagency agreed-upon analytical approach require the use of HI-RUN in these assessments, which are completed in order to comply with Section 7 of the Endangered Species Act. SELDM is a model developed by the USGS and FHWA which could possibly be used in biological assessment analysis. This study was completed to determine the feasibility and cost benefits of use of either model for biological assessments in western Washington projects. The study consists of three primary components: comparison of model results, comparison of model usability, and comparison of costs and benefits of each model.
The comparison demonstrates that SELDM provides similar assessment results to HI-RUN and that with preliminary steps as detailed in the study, both models were found to be similarly usable. Ongoing maintenance costs were also found to be similar, but implementation costs related to use of SELDM within current policy requirements was found to be prohibitive. The recommendation of these findings is for continued use of the HI-RUN model, with the condition that further analysis be completed if policy conditions were to change. Additionally, it is recommended that WSDOT investigate other possible needs and situations where the SELDM model would be beneficial.