The MMSOILS Model Review Subcommittee (MMRS) of the Environmental Engineering Committee (EEC) of the EPA Science Advisory Board (SAB) has prepared a report on the Agency's Office of Solid Waste (OSW) MMSOILS Multimedia Contaminant Fate, Transport, and Exposure Model. This model and guidance document was developed as a technical resource for estimating potential health risks at sites contaminated by toxic wastes or spills of toxic chemicals. The review by the SABs MMRS dealt with the adequacy of methods for using a screening level model where there is substantial subsurface heterogeneity or where non-aqueous phase contaminants are present, the appropriateness of the Agencys approach for aggregating releases from solid waste management units (SWMUs) to estimate concentration at exposure points over time, and the adequacy of the Agencys approach for developing long-term effectiveness and failure scenarios for site remedies. The general consensus of the MMRS was that the use of a multimedia pathway model for screening purposes could be an appropriate approach for developing risk and cost estimates for a national-level Regulatory Impact Analysis (RIA), as long as the input parameters are accurate and the model is not applied outside its range of validity. Furthermore, the Agencys use of a single model, to the extent defensible for each facility considered, was viewed by the MMRS as necessary in order to ensure consistency among model results. The major overriding concerns of the MMRS were: (a) application of MMSOILS outside its range of validity; (b) large uncertainties in input parameters; (c) consequent large uncertainties in MMSOILS results; (d) clear communication of this uncertainty to decision-makers; and (e) presentation of the results in the draft RIA document in a scientifically defensible manner that communicates the uncertainties of the calculations and their implications for the cost/benefit analysis.

"November 1993." "EPA-SAB-EEC-94-002." Includes bibliographical references (p. B1-B3).