Development and application of an integrated model for ecological risk assessment employing the spatial habitat equivalency metho

Ecological risk assessment has traditionally been associated with risk-based remediation under the Comprehensive Environmental Response, Compensation and Liability Act. Recent movement to risk-based closure under the Resource Conservation and Recovery Act, adoption of risk-based environmental compliance regulations, and heightened public awareness requires development of holistic risk-based tools and procedures. Current risk assessment models and procedures typically address only the toxicological stresses of spill-site contaminants under the "no action" or "as is" condition. A statement or prediction of unacceptable risk is useful in determining potential contaminants of concern but does not provide the data needed to evaluate other options. A holistic risk assessment model is needed that provides decision-makers with sufficient information to evaluate not only risk under existing conditions but also the overall environmental health and ecological gains and losses of varying alternatives and combinations of alternatives.;In this research project, I developed a habitat equivalency model by integrating habitat equivalency methods traditionally used in resource management into the field of ecological risk assessment of contaminated sites. The project focused on the development of a holistic approach by translating ecological effects into gain or loss of habitat value, or "weighted usable habitat." Habitat value is based on a simple scale from 0.0 to 1.0 (1.0 being the ideal habitat). The habitat value is supported by numerous measurable variables that are translated into one habitat or resource value, The approach integrates the traditional contaminant fate and transport modeling typically used in remediation investigations with resource valuation methodologies and models typically used in natural resource assessment. This spatial approach provides (1) a measure of weighted usable habitat under the current and future no action alternative, (2) a method to determine net ecological benefit and impact of the potential remediation alternatives, and (3) a method to evaluate replacement of lost habitat through mitigation. This approach expands the scope of the traditional ecological risk assessment by providing a habitat equivalency approach and an "Integrated Risk Assessment Tool" to support the decision-making process to address multiple stakeholder concerns.