Effects Assessment Workgroup Summary

Effects Assessment

Workgroup Summary

Estimating the environmental effects associated with dredging is an important

component of the dredging regulatory program. The Effects Workgroup focused

its discussion on how risk assessment can be used within the framework of the

dredged material management program to estimate environmental effects.

Determination of Toxicity

and Unacceptable Risk

The Effects Workgroup discussed whether the occurrence of toxicity

(significant and substantial mortality in sediment toxicity tests in comparison to

reference), as defined under the Ocean Testing Manual (USACE/USEPA 1991)

and the Inland Testing Manual (USACE/USEPA 1998), always equates to an

unacceptable risk for placement of material at the disposal site. The consensus

was that significant mortality in toxicity tests does not always equate to an

unacceptable risk, because determination of risk must depend upon the size of the

project, the nature of the contaminants, and the spatial and temporal aspects of the

ecosystem features that we are trying to protect.

The workgroup noted that predictions of the effects of dredging and disposal

are often based solely on the concentration and toxicity of contaminants in the

material to be dredged, without consideration of the specific conditions at the

disposal site. For example, the kinds and numbers of ecological receptors present

at the disposal site and the actual potential for exposure of the receptors to

contaminants from dredged material may be considered in the initial designation of

a disposal site, but not when decisions are made about individual dredging

projects. Also, the potential for photochemical and microbial degradation of

contaminants, which can result in a decrease in the concentration of contaminants

when dredged material is removed from the source of contamination, is not

considered. The particular characteristics of the disposal site (e.g., types of

receptors present at the site, types of potential exposure pathways) are not

Chapter 3 Effects Assessment Workgroup Summary