When, Where, and How to Use Risk Assessment

considered in enough detail so that risk managers can make decisions about the

potential for adverse ecological effects at the site.

The USACE is currently developing national guidance for incorporating

environmental risk assessment into the dredged material management program.

Participants of the Effects Workgroup expect that environmental risk assessment

will be used when the results of standard biological tests are not definitive. For

example, the suitability of a sediment for open ocean disposal depends upon

whether results of toxicity and bioaccumulation tests are "significantly different"

in dredged sediments in comparison to reference sediments. However, the amount

of contaminant accumulated from a dredged material may be significantly greater

than from reference sediments but too small to produce an adverse effect in

exposed organisms. In an environmental risk assessment, the concentration of

contaminant in tissue can be compared to concentrations previously shown to

produce adverse effects. Thus, risk assessment allows managers to make better

predictions about the potential for adverse effects associated with exposure to

contaminated dredged material.

When, Where, and How to Use Risk Assessment

Considerable discussion revolved around when risk assessment should be used

in the tiered evaluation process, and several views were expressed. Some

members thought that risk assessment should replace the tiered framework. Other

members thought that environmental risk assessment should not be used as a

replacement for the present tiered evaluation of dredged materials

(USACE/USEPA 1991) or as a replacement for biological testing. Rather, it

should be used as an evaluation framework for interpreting data that are presently

collected in standard toxicity and bioaccumulation tests. Some members felt that

it should be used as the ultimate tier in difficult situations when lower levels have

not provided a clear answer. Others thought that the tiered framework should be

maintained, but that over time, the current tiered evaluation paradigm should

gradually be replaced with risk assessment.

Members suggested that an ecological risk assessment framework could be

developed as part of the disposal site designation process. The effects of

individual dredging projects could be evaluated consistently by using a model risk

assessment for the site. The workgroup discussed whether, for each contaminant

of concern, a single risk-based criterion could be developed for the designated

disposal site. Some members felt any risk-based criteria would have to account

for the bioavailability of the contaminant in sediment. Bioavailability could be

estimated by normalization of sediment concentrations to total organic carbon

(TOC) or acid volatile sulfides (AVS) or measured with assays of

bioaccumulation.

The implementation of a standard risk assessment model would address

concerns expressed by members of the regulated community in the workgroup

about the lack of consistency and predictability in the regulatory process from one

Chapter 3 Effects Assessment Workgroup Summary