What is the role of risk assessment in the dredged material risk management process?

Technical Note DOER-R1

September 1998

survival or reproduction of these receptors?" The Tier I characterization of the sediments relies on

available results of prior chemical testing, measurements of physical characteristics, organic carbon

content, grain size, and review of regulatory records and published literature regarding the material

to be dredged (published studies, permit reviews, Federal databases, etc.). This information is

generally sufficient for a risk assessor to develop the Hazard Identification and a list of contaminants

of concern (COCs). Note that specifying COCs is an integral part of risk assessment that will have

already been accomplished as a Tier I activity based on explicit criteria in the Dredged Material

Testing Manuals.

The identification of COCs during Tier I depends in part on the toxicological importance of each

contaminant. This Tier I task therefore provides a start on the risk assessment's Toxicity or Effects

Assessment, which answers the question, "Is there a known quantity of the chemical or physical

hazard that results in an adverse effect to the likely receptors?" The risk assessment may require

that this information be reformulated to conform to the parameters used in human health or

ecological exposure models. This is generally accomplished by reference to on-line USEPA and

USACE databases or an expanded literature review.

The exposure assessment addresses the question, "Are there any conservative but realistic activities

or physical and biological pathways by which the receptors may encounter the chemical or physical

hazards?" This is a considerable expansion of Tier I sediment characterizations or Tier II modeling

activities and also incorporates the bioaccumulation testing conducted in Tier III. This is the risk

assessment component that will require the most expansion upon prior data gathering activities

because this is the point that integrates the site selection information with the dredged material

evaluation. Although it generally will not require new data collection, it will require a reformulation

of the information into a site-specific conceptual model. The conceptual model attempts to link

management technology, site characteristics, and dredged material evaluations (Figure 1).

In summary, the activities of site selection and dredged material evaluation provide most of the

information needed to conduct a risk assessment. There will be some necessary renewed literature

reviews and a reformulation of the data, but expensive, time-consuming field data collections are

unlikely.

What is the role of risk assessment in the dredged material risk management

process? Risk assessment alone cannot compel a decision at a dredged material management

site. In those cases where the dredged material manager chooses to apply risk assessment, he or she

should consider it as part of a larger risk analysis process that includes risk management. In prior

considerations of risk management, USACE (1995) views this process as a function of several

factors: risk and uncertainty, cost, schedule, value of resources protected, regulatory requirements,

political factors, economic factors, technical feasibility, environmental justice/equity. The role of

the risk assessment in this general process is to provide realistic assessments, not hypothetical or

highly conservative assessments that do not provide meaningful risk information to decision makers.

Within the risk management process, the risk assessment contributes most readily to the evaluation

of alternatives.

The Framework Document (USEPA/USACE 1992) provides comprehensive guidance on

identifying, screening, and selecting "reasonable" dredged material disposal alternatives. The