File: ABSTRACT.TXT


                  Multimedia, Multi-pathway, Multi-receptor 
                     Exposure and Risk Assessment (3MRA)

                                Version 1.0
                                July, 2003

               Center for Exposure Assessment Modeling (CEAM)
    National Exposure Research Laboratory - Ecosystems Research Division
                  Office of Research and Development (ORD)
               U.S. Environmental Protection Agency (U.S. EPA)
                          960 College Station Road
                         Athens, Georgia 30605-2700

                                706/355-8400


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SUMMARY

The 3MRA technology provides the ability to conduct screening-level
risk-based assessment of potential human and ecological health risks
resulting from long-term (chronic) exposure to HWIR chemicals released from
land-based waste management units (WMUs) containing currently listed waste
streams.

The assessment of potential health risks is possible for both human and
ecological receptors.  The assessment is national in scale and site-based,
that is, risks are assessed at individual sites across the U.S. where HWIR
WMUs may be located.  The resulting national distribution of site-based risks
forms the basis for establishing exit criteria.  For each site, statistically
sampled from a national database of WMUs, the simultaneous release of
chemicals from the WMU to each environmental medium, the fate and transport
of the chemical through a multimedia environment, and the receptor-specific
exposures and risks is simulated.  Human receptors include child and adult;
residents, home gardeners, beef and dairy farmers, and recreational fishers.

Exposure pathways include inhalation of outdoor air and shower air and
ingestion of contaminated drinking water, garden and farm products and fish.
Ecological exposure and risk focuses on population effects related to key
species within habitats found in the proximity of sites.  The assessment
includes an estimation of the potential exposures per exposure
pathway/receptor and aggregated across pathways followed by an estimate of
the resulting carcinogenic and noncarcinogenic health effects.  The end point
of the technical assessment is a rolling-up of the site-based risks to form a
national scale joint distribution reflecting the relationship between
chemical concentration in waste streams and human and ecological health risk.

Specific exit levels are selected from these distributions on the basis of
Agency policy concerning appropriate degrees of protectiveness.  The
resulting chemical-specific exit levels represent threshold waste
concentrations below which the associated waste stream is not considered
hazardous and therefore does not require Subtitle C type disposal.  The exit
levels will be applicable to all waste streams and all locations, i.e.,
nationally.

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