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Page Title: When, Where, and How to Use Risk Assessment
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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
15
Chapter 3 Effects Assessment Workgroup Summary

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