USE OF EPA'S INDUSTRIAL WASTE MANAGEMENT EVALUATION MODEL TO SUPPORT BENEFICIAL-USE DETERMINATIONS

As of now, the beneficial-use (recycling) of secondary materials (e.g. coal-fly ash) in highway construction is limited. In 1998 and 1999, the Association of State and Territorial Solid Waste Management Officials (ASTSWMO) conducted a Beneficial-Use Survey to determine the issues that states face when evaluating potential beneficial-use applications for recycled/secondary materials. The report identified the largest obstacle as the lack of good information for use in evaluating potential risks to human health and the environment (i.e. soil and groundwater contamination) from beneficial-use applications. The absence of such data has resulted in reluctance in the beneficial-use of such materials causing them to be stockpiled indefinitely or disposed of in landfills. It is believed that the USEPA's Industrial Waste Management Evaluation Model (IWEM) may aid in the evaluation of whether secondary materials are safe enough for beneficial use applications in the highway environment. IWEM uses the EPA's Composite Model for Leachate Migration with Transformation Products (EPACMTP) to model the fate and transport of constituents through the subsurface. Specifically designed for simulating constituents leaching from waste management units (e.g. landfills and waste piles), IWEM is able to solve the advection-dispersion equation in both the unsaturated and saturated zones while accounting for transport processes that include linear/nonlinear equilibrium sorption isotherms and first-order decay and zero-order production reactions. Currently, validation of the model is being addressed using data from field studies in Wisconsin. Use of these types of predictive tools should improve acceptance of the appropriate recycling of secondary industrial materials, which can help to conserve natural aggregate and reduce unnecessary disposal. The ultimate goal is to promote IWEM as a valuable tool so that State EPAs, DOTs, and construction companies will be more apt to use secondary materials for highway structural support with a greater understanding of potential risks posed to groundwater.