Towards Using Comparative Risk Assessment to Manage Contaminated Sediments

Comparative risk assessment (CRA) has been used as an environmental decision making tool at a range of regulatory levels in the past two decades. Contaminated and uncontaminated sediments are currently managed using a range of approaches and technologies; however, a method for conducting a comprehensive, multidimensional assessment of the risks, costs and benefits associated with each option has yet to be developed. The development and application of CRA to sediment management problems will provide for a more comprehensive characterization and analysis of the risks posed by potential management alternatives. The need for a formal CRA framework and the potential benefits and key elements of such a framework are discussed. 1. CRA – Background and Applications Comparative risk analysis has been most commonly applied within the realm of policy analysis, in that it supports tradeoff decisions with broad implications. Andrews et al. (2004) distinguish CRA uses at macro and micro scales. Levner, E., Linkov, I., Proth, J.M., eds. “Strategic Management of Marine Ecosystems,” Kluwer, Amsterdam 2004 (in press). At the macro scale, programmatic CRA has helped to characterize environmental priorities on regional and national levels by comparing the multi-dimensional risks associated with policy alternatives. U.S. government agencies at various levels have logged significant experience with policy-oriented, macro-level CRA. Gutenson (1997) suggests that the starting point was a series of Integrated Environmental Management Projects performed during the 1980s. These took place in Santa Clara, CA, Philadelphia, PA, Baltimore, MD, Denver, CO, and the Kanwha Valley, WV. Their common goal was to improve local environmental decision-making by supporting it with quantitative risk analysis. However, it was the national-level “Unfinished Business” report (US EPA, 1987) that created sustained momentum for the use of CRA. During this time period the USEPA offered grants to encourage U.S. regions, states, and localities to undertake similar projects. From 1988 to 1998, some twenty-four states and more than a dozen localities undertook comparative risk projects. See Andrews et al., 2004, Andrews, 2002, and Jones, 1997 for detailed descriptions of the nature of these projects. International CRA applications are reviewed in Tal and Linkov, 2004 and in Linkov and Ramadan, 2004. At smaller scales, so-called micro studies in CRA have been used to compare interrelated risks involved in a specific policy choice (e.g. drinking water safety: chemical versus microbial disease risks). In these micro applications, the CRAs often had more focused objectives within the general goal of evaluating and comparing possible alternatives and their risks in solving problems. The number and varied nature of CRA applications suggest that there is a measurable degree of acceptance for CRA as a decision-making tool even though no clear or specific guidance exists on how to conduct a CRA or use the information the analysis produces. This paper expands the discussion on the micro applications of CRA by identifying the benefits and key elements of an effective CRA framework that can be used for managing contaminated sediments. 2. CRA and Management of Sediments Several different management alternatives and technologies exist for contaminated and uncontaminated sediments. While the number of management options is constrained, the relevant exposure pathways, receptors at potential risk, and implementation costs and benefits vary broadly. Example sediment management alternatives include unrestricted open-water placement, confined aquatic disposal (i.e., capping), use in constructed wetlands projects, disposal in lined landfills, chemical or physical stabilization technologies, cement manufacture, lightweight aggregate production, topsoil production, and in situ treatment (Seager and Gardner; 2005). Selection of the “best” option is complicated by the varied nature of the risks, costs and benefits associated with the options. A “mind-opening” approach for analyzing the risks, costs and benefits for each potential management alternative will provide for more informed and credible decision making. Levner, E., Linkov, I., Proth, J.M., eds. “Strategic Management of Marine Ecosystems,” Kluwer, Amsterdam 2004 (in press). Cura et al. (2004) reviewed CRA in an attempt to rectify or at least demonstrate the differences among the varied definitions offered in the literature, explain the use of CRA at various regulatory levels, and search for an application of CRA at operational, as opposed to policy, levels. They reviewed the status of CRA within the context of environmental decision-making, evaluated its potential application as a decisionmaking framework for selecting alternative technologies for managing dredged material and made recommendations for implementing such a framework. Cura et al. (2004) emphasize in their review that CRA, however conducted, is an inherently subjective, value-laden process. They found that while there was some objection to this lack of total scientific objectivity (“hard version” of CRA), that the “hard versions” provided little help in suggesting a method that surmounted the psychology of choice in decisionmaking schemes. The application of CRA in the decision making process at dredged material management facilities will involve the use of value-based professional judgments. The literature suggested that the best way to incorporate this subjectivity and still maintain a defensible comparative framework was to develop a method that was logically consistent and addressed this issue of uncertainty by comparing risks on the basis of more than one set of criteria, more than one set of categories, and more than one set of experts. 3. CRA Outcomes and Framework There is no single, precise definition for CRA. In the context of sediment management problems, it can be viewed as a part of a decision making process that relies on estimated relative risks or impacts associated with each management alternative under consideration. These risks can be expressed in terms of their relationship to the natural environment, human health, the legal or regulatory context, and socioeconomics. Estimation and interpretation (possibly weighing or ranking) of relative risks is also an integral part of the CRA process. From this broad definition, it is clear that application of CRA to sediment management problems inherently avoids an overly narrow and isolated consideration of alternatives as CRA begins with the notion that various options are available and need to be evaluated with respect to the differences that exist among them. An effective CRA of sediment management alternatives can provide a range of benefits to the decision-making process. A CRA can be used to promote a structured, fair, and open exchange of ideas among scientists, citizens, and government officials on a broad range of issues related to characterizing the risks, costs and benefits of management options. The comprehensive and comparative nature of a CRA will lead to assumptions being more transparent and reduce the hidden influence of undeclared biases. For these reasons CRA should result in more consistent and reproducible decision making. While the benefits of CRA as a decision tool are well recognized, a formal, accepted procedure for conducting a CRA does not exist. We propose that CRA can provide the necessary data inputs concerning risks, costs and benefits that pertain to identifying the “best” sediment management alternative; however, a guidance framework for applying Levner, E., Linkov, I., Proth, J.M., eds. “Strategic Management of Marine Ecosystems,” Kluwer, Amsterdam 2004 (in press). CRA to sediment problems must be developed in order to realize the benefits of the approach. A process that provides for incorporating specific stakeholder concerns and perspectives about the attributes of the problem at hand will make for a transparent and comprehensive analysis of risks, costs and benefits. To be effective, a CRA framework must guide the analysis and comparison of disparate endpoints (e.g., human health hazard indices and cancer risks, ecological toxicity quotients, management costs, habitat loss/creation etc.) that are expressed in different units and scales. To address the needs of decision makers a CRA should identify the management alternative, or set of alternatives, that maximize risk reduction and minimize the risk of not achieving the risk reduction objective per unit cost (e.g., dollars per m of sediment managed or remediated). A comprehensive CRA framework should lead to providing the answers to such questions as: • How will the analysis address the decision drivers • How will the sufficiency of the analysis be determined? • What are the bases of comparison among the alternatives? • What are the analytical components/causal pathways in the analysis? • Which alternative maximizes the risk reduction per unit cost? • Where is the best place to put this material? • Which alternative minimizes risk? • Which alternative minimizes cost? • Which alternative minimizes uncertainty? • What are the sources of uncertainty and variability in the assessment? • Which alternative reflects stakeholder preferences? • Does the analysis address the decision drivers? Implementing a CRA framework to achieve specific programmatic or regulatory objectives raises several additional questions including: • What, if any, programmatic or regulatory constraints exist for using CRA to inform decision making? • How will the CRA incorporate stakeholder concerns and preferences? • How will uncertainties in the analysis be accounted for in the decision making process? • How will the results of the analysis be communicated to stakeholders and decision-makers ?