PROBLEM

ERDC TN-DOER-R2

December 2001

an exposure assessment model should be used. The exposure assessment can use screening level

models that employ simplifying, conservative assumptions to reduce the complexity, data require-

ments, modeling effort, time requirements, and costs. Screening level risk assessment is appropriate

for comparative risk assessment or when a lower level of precision, resolution, and accuracy is

needed. Comprehensive models are more physically based, both spatially and temporally, than the

screening level models and typically require increased data and computing resources.

Comparative risk assessment is a methodology that uses sound science, policy, economic analysis,

and stakeholder participation to identify and address the areas of greatest environmental risks and

provide a framework for prioritizing environmental problems. Comparative risk assessment can be

used to determine the relative risks of environmental hazards by a systematic, documented process

that provides technical information to decision-makers. The comparative risk process should be

viewed as a whole, from collecting data, analyzing data, and ranking risk to developing an action

plan and implementing new strategies for reducing risk. The results of a comparative risk analysis

can be used to provide a technical basis for targeting activities, management priorities, and resources

when there are not enough resources available to address all the environmental needs of a

community.

The baseline condition in a comparative risk assessment for dredging operations is the no-action

scenario, which represents the present and future risk posed by a contaminated sediment and water

body without performing dredging. Dredging operations alter the short-term and long-term risks.

When the risks of dredging operations are compared with the risks of the no-action scenario, the

relative risk of dredging operations and changes in short- and long-term risk can be determined.

Comparison of the no-action scenario with dredging in the absence of disposal of dredged material

and discharge of dredging effluents to the water body provides comparative risk assessment for the

aquatic environment.

PROBLEM: Environmental risk assessment can be a complex process requiring multidisciplinary

expertise. To facilitate initial screening level assessments, PC-based risk assessment decision

support tools have been and are being developed and applied to numerous land sites for estimating

both human and ecological risks from exposures to hazardous and radioactive wastes. While these

decision support tools have proven successful in providing site-specific risk estimates for human

health and potential ecological impacts at Superfund sites, they have not been adapted for use in

evaluating the potential impacts of navigation dredging operations. Numerous tools and protocols

as presented in the Automated Dredging and Disposal Alternatives Modeling System (ADDAMS)

(Schroeder and Palermo 1995) and the U.S. Army Corps of Engineers (USACE)/USEPA technical

framework document (1992) have been developed to evaluate contaminant pathways at dredging

operations. These dredging-related tools must be incorporated into a comprehensive risk assess-

ment modeling system that provides linkages among fate models and toxicity databases to facilitate

risk assessment in a manner consistent with the USACE/USEPA Technical Framework for Evalu-

ating Environmental Effects of Dredged Material Management Alternatives.

OBJECTIVE: The objective of this research was to develop a PC-based, risk assessment decision

support tool for evaluating the effects of dredging and disposal operations on human and ecological

resources through modification of existing technology. Risk assessment scenarios (conceptual

models and templates of model selection and integration with databases and assessment tools) were