Use of the Multimedia Environmental Pollutant Assessment System (MEPAS) in a baseline risk assessment

A risk assessment has been performed for two waste sites that are part of the Depatment of Energy (DOE) complex. The Multimedia Environmental Pollutant Assessment System (MEPAS) has been used for the risk assessment to be performed. Population and Maximum Individual Risks have been estimated as well as risks from noncarcinogenic contaminants. MEPAS is a set of computer analysis tools that calculates exposure and human health risk estimates for waste sites, based on the initial problem as was specified by the user. MEPAS is not intended for detailed analysis of an individual site, but rather to compare risks among groups of sites. The first site that has been analyzed here used to be a burial ground for a wide variety of radioactive, organics, and inorganic wastes. There is a nearby well that is used almost daily. In 1973 it was determined that significant amounts of radioactivity were escaping from the burial ground to soil and to groundwater. The risks to the receptors using the well have been assessed, and a comparison was made between predicted and measured concentrations. MEPAS overpredicted the concentrations by at least an order of magnitude. The second site was a waste pit and it is believed that it is the source of a groundwater uranium plume that is located 7000 ft away. A risk assessment has been performed for this site, and the model predicted and measured concentrations have been compared. The model overpredicted the concentrations by at least an order of magnitude.