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Environmental Modeling Community of Practice

3MRA Methodology

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

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As a result of their regulatory reform efforts, the Office of Solid Waste (OS) in November 1999 introduced a new open-architecture, multimedia, multi-pathway, and multi-receptor exposure and risk assessment methodology designed to support their Hazardous Waste Identification Rule (HWIR). The new modeling system, referred to as the 3MRA technology, is envisioned as the foundation for eventually integrating other regulatory support decision tools in the future. Toward that end, and with the goal of integrating predictive modeling needs across the Office of Solid Waste and Emergency Response (OSWER) rule-makings and a variety of other agency Program Office regulatory thrusts, there is a need to build upon the 3MRA technology system in several directions. Among these are 1) a collection of science support research activities focused on improving, and making more realistic, some of the existing physical, chemical, and biological processes algorithms found in the current system; 2) adapting the methodology for use at larger spatial scales, or for use in concert with larger spatial scale modeling systems; 3) adding provisions to make the methodology applicable to a variety of related regulatory support problems such as the surface impoundment study and other emerging needs (e.g., mining waste, RCRA Corrective Action, waste management/leaching/modeling, etc.); 4) adding the front-end capability for the user to input data for a specific site; 5) enhancing the technology with more comprehensive uncertainty assessment capabilities; 6) implementing a comprehensive independent testing and validation program; and 7) establishing an easily accessible, Internet-based distribution and support network for the user community.


The primary objective of the research program is to develop, test, and apply a multimedia, multi-pathway, multi-receptor exposure and risk assessment modeling system (3MRA) in support of regulatory-based applications.


This research program has been selected and designed to be explicitly integrated with other EPA Ecosystems Research programs with the overall goal of establishing an integrated approach to multimedia-based exposure and risk assessment. The following discussion provides a brief description of the genesis of this EPA vision in order to provide context for this particular research and development program.

In 1997 EPA's Ecosystems Research program embarked on a four step process to understand and satisfy Agency needs for science-based tools to support increasingly complex assessments of human and ecological exposure and risk.

Step 1 involved the development of a comprehensive view of the integrated system of activities within the Agency that results in the bi-directional flow of knowledge and information between science, on one end of the continuum, and regulation on the opposite end. This effort provided a framework for understanding Agency needs for science-based products and, perhaps more importantly, provided a clear picture of the relationship between and among the myriad of science products developed to ultimately support the Agency's mission. Understanding this relationship has become extremely important due to the increasingly complex questions posed by regulators and the related need to integrate research results across virtually all disciplines in order to provide answers.

Step 2 focused on a formal "needs assessment", the necessary step before pursuing a formal research program. After years of supporting various Program Offices in the conduct of regulatory assessments it became increasingly clear that there was significant common scientific and technological ground emerging among the assessments. Program Offices previously focused on exposures and risks occurring within a single medium of concern were being pushed more and more to consider secondary impacts of contamination originating within their medium of interest. For example, the Office of Air, in the development of their regulations were increasingly criticized for not addressing the transfer to watersheds and waterbodies of pollutants emitted to the atmosphere and the exposures that occur via these additional pathways. The Office of Solid Waste was criticized for assessing only groundwater pathway impacts of land-based disposal units. The reality of an integrated environment was now being expressed through the regulatory process. In an attempt to document this move to holistic or multimedia-based regulatory assessment ERD undertook a study to formally survey the EPA Program and Regional Offices (as well as other Federal Agencies and State Agencies) to determine the exact extent of this emerging common ground. This effort provided a clear picture of the common need for science-based tools to address issues involving the integrated multimedia fate and transport of chemicals in the context of human and ecological exposure and risk assessment.

The next step was to respond to this need. Heretofore, no research and development program was specifically designed to directly link science and regulation with multimedia-based tools. While it was clear that new technologies involving national environmental databases, multimedia models, GIS, uncertainty assessment, etc. were needed it was not so clear exactly what form the technologies would take and to what extent the technologies could be configured for application to multiple clients (EPA Program/Regional Offices, ORD scientists/engineers).

ERD's response was to develop a research program focused on designing, building, testing, and applying modeling-based technologies. These technologies will serve to 1) integrate the results of research efforts throughout the environmental community, and 2) form the bridge that directly links science and regulation. These technologies must : 1) be scientifically current, 2) allow for consistent application of the science across program office assessments, 3) allow user's representing decision makers (i.e., model/database developers) to use the technology as a platform for further development, and 4) be designed to allow for a smooth transition from existing technology (i.e., legacy models) to a much more powerful application of emerging computer-based technologies.

To implement this program ERD has designed an approach that serves both the relatively short-term needs of specific clients (i.e., 2-5 years) and prepares the ground for development of assessment technologies that will serve the same client community, and more, in the future (i.e., 5-15 years out).

The essence of the implementation plan is for ERD to participate intimately in the conduct of three representative assessments and to focus on providing the science and modeling technology. ERD believes that the best way to design a technology is to first work intimately with the eventual user's of the technology in solving real problems. Thus, ERD will be an active participant in these assessments and be accountable for delivering the needed science and technology in a timely manner (i.e., within a timeframe dictated by the client office and it's responsibilities to meet real deadlines). ERD will use these assessments to design and implement prototypes of key technological components (models, databases, software integration tools) that will be needed in the future. From this experience will come the necessary information concerning what common technologies are needed and how best to design and build them in/for the future.

The assessments selected for this program include 1) a site-based national assessment of human and ecological risks posed by the disposal of industrial wastes in land-based units (Multi-media, Multi-receptor, Multi-stressor Risk Assessment - 3MRA), 2) a watershed-based assessment of the assimilative capacity of aquatic systems (Total Maximum Daily Loads - TMDLs), and 3) the assessment of ecosystem sustainability/vulnerability to both chemical and non-chemical stressors (.... - BASE). Interacting with all of the assessment teams will be a computer-based technology team charged with facilitating the design and implementation of software systems that contain the models and databases needed in the assessments and more importantly to extract from these assessments the detailed design requirements for future integrated technologies (this effort is referred to as the Multimedia Integrated Modeling System - MIMS).

Given this background it is the purpose of this research plan to detail activities associated with the future of the 3MRA component of the overall ERD modeling-based research and development program. The 3MRA modeling system is designed to underpin decisions establishing constituent specific exit levels for low risk hazardous wastes that would amend existing regulations under the Resource Conservation and Recovery Act (RCRA). These amendments are being considered under the general heading of the Hazardous Waste Identification Rule (HWIR) originally proposed by OS in December 1995, with a different, underlying model support methodology. Wastes applicable under HWIR were those designated as hazardous because they were listed, or had been mixed with, derived from, or contained the listed wastes. Under the HWIR proposal, waste generators of listed wastes that could meet the new exit level criteria defined by the HWIR methodology, would no longer be subject to the hazardous waste management system specified under Title C of RCRA for those wastes. Basically, this established a risk based "floor" for low risk hazardous wastes that would encourage pollution prevention, waste minimization, and the development of innovative waste treatment technologies. The purpose of the rule-making was to reduce possible over-regulation arising from the older "mixture" and "derived-from" rules promulgated earlier. In a number of cases, wastes were listed on the basis of containing both toxic hazardous constituents and exhibiting one or more of the hazardous waste characteristics that do not relate to chemical toxicity (e.g., ignitability, corrosivity, reactivity). If such a waste still exhibits any characteristic after complying with the exemption criteria proposed in the HWIR, it must continue to be managed as a characteristically hazardous waste. The "mixture" rule and the "derived-from" rule were promulgated as part of the first comprehensive regulatory program for the management of hazardous wastes under RCRA in May of 1980. The mixture rule defined as a hazardous waste any solid waste that is mixed with one or more listed wastes, and the derived-from rule labeled as hazardous waste any solid waste generated from the treatment, storage or disposal of a listed hazardous waste. Both were/are considered important definitions in regulating the disposal of hazardous wastes consistent with reducing risk to human health and the environment; however, since they apply regardless of the concentrations or mobilities of hazardous constituents associated with the solid wastes, the potential for over-regulation is a possibility.

Conceptual Approach:

The conceptual foundation of the technical approach to achieving the HWIR goals is the risk paradigm and the associated relationship between a source of contaminant, its release to and transport through the environment, subsequent contact (i.e., exposure) with human and ecological receptors, and the resulting risk of health effects. The following general statement reflects the most essential features of the technical approach taken to achieve the HWIR objectives.

The HWIR assessment is a 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 human and ecological health risks is site-based and include, 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 that result. The assessment includes an estimation of the potential exposures, per exposure pathway/receptor, and an estimation of the resulting carcinogenic and non-carcinogenic health effects. The end point of the assessment is the establishment of chemical-specific exit levels representing 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 are applicable to all waste streams and all locations, i.e., nationally.

Specific Approach:

There are five principal activities involved in this task: Model development (science-based), Model development (technology-based), Development of uncertainty assessment methods, Model applications, and Model distribution and user support. The goal of the model development (science-based) activity is to enhance existing and develop new science modules to be contained in the modeling system. Input to this activity will include insights from the conduct of the Model application activity as well as feedback from the user's community (i.e., Program and Regional Office clients and the public). This activity is critical in the context of providing users with a technology that grows in response to the evolving needs of it's users and availability of new science. The goal of the model development (technology-based) activity is to enhance and update the modeling system from a software engineering perspective. To keep the modeling system efficient, user friendly, and Internet aware will require the application of computer science principles on an ongoing basis. Capabilities related to database management, cross-platform simulation, GIS interfaces, etc. will require 3MRA technology developers to remain current with the state-of-the-art related to computer science. The direction for the technology-based model development is coordinated, and eventually integrated, with the larger NEAL-based technology development under the MIMS research area. The goal of the uncertainty assessment activity is to research and develop innovative methods for quantifying uncertainty in the context of performing complex exposure and risk assessments. The uncertainty assessment activity will address issues related to sensitivity analysis, uncertainty analysis, and model validation. The methods developed within this activity area will be presented to the Model developers (science-based) for incorporation into the 3MRA modeling system. The goal of the model application activity is to establish a modeling team consisting of multimedia modelers and database experts and charge the team with selecting and executing key Agency assessments related to multimedia-based exposure and risk. The primary criteria for selecting assessments will be based on the uniqueness and complexity. These assessments may be site-specific, regional, or national in scale. The purpose of this activity is to apply the 3MRA technology to new and important assessments in order to determine what new modeling capabilities should be added in the future. The goal for the model distribution and user support activity is to establish a computer-based and science-based support system that will provide users with technical support needed to acquire and install the modeling technology and access experts to answer detailed questions related to the science contained in the modeling system. In providing user support it may become necessary to establish a model application support team to go beyond answering individual questions from users and actually engage users in the conduct of their assessments. Finally, it is anticipated that user support will include conducting training courses for users.

Collaboration-based Approach:

Finally, the 3MRA model development will be conducted in conjunction with the Department of Energy (DOE), the Department of Defense/Corps of Engineers (DOD/COME), and the Nuclear Regulatory Commission (NRC). These three agencies have joined EPA in an effort to develop site-scale multimedia modeling technologies that are scientifically defensible and, as important, consistent among the Agencies. This collaborative effort has been ongoing for three years and is anticipated to expand to other agencies in the future. By cooperating, each Agency will be assured that their assessments are facilitated with commonly accepted modeling technologies and also each Agency will directly benefit by each other's model development activities, thus increasing each Agency's modeling capability and reducing, if not eliminating, unnecessary duplication in the context of model development.

Staff involved in 3MRA:

Lead: Gerry Laniak

Others: Justin Babendreier

Further information: