8.5 Tier IV Animal Bioaccumulation Risk

complete exposure routes to ROC populations outside the CDF may

require more detailed information prior to design of such actions. If

management actions are selected, no further evaluation of animal

bioaccumulation is necessary.

3. Information is not sufficient to reach a decision regarding animal

bioaccumulation. Further evaluation in Tier IV, or management actions

as an alternative to further evaluation, should be considered. A decision

to implement management actions for animal bioaccumulation by

interrupting complete exposure routes to ROC populations outside the

CDF may require more detailed information prior to design of such

actions. If management actions are selected, no further evaluation of

animal bioaccumulation is necessary.

8.5 Tier IV Animal Bioaccumulation Risk

Assessment

8.5.1 Evaluation

The elimination of incomplete exposure pathways in Tier I and the

elimination of COC that do not bioaccumulate to levels causing effects in ROC

populations outside the CDF in Tiers II and III should have resolved most animal

bioaccumulation issues for most dredged materials. Tier IV is intended to answer

whatever specific, well-defined technical questions may remain unanswered after

thorough evaluation in earlier tiers. If earlier tiers are used properly, Tier IV

should rarely be necessary for navigation projects (Sections 2.1.4 and 2.1.5).

By the nature of the tiered evaluation approach, any technical questions that

remain unresolved after Tier III can best be answered by a detailed, case-specific

evaluation. By their very nature, detailed case-specific evaluations are not

amenable to the kind of generic guidance that can be presented in a national

manual. They require individual design to address unique technical questions

under site-specific conditions.

The best approach for Tier IV is usually a case-specific risk assessment.

Detailed guidance for conducting risk assessments for CDFs in Tier IV can be

found in Cura, Wickwire, and McArlde (in preparation). The information

generated in Tiers I through III should be used to the maximum extent technically

justified throughout the Tier IV risk assessment.

8.5.2 Tier IV - Animal Bioaccumulation Decision

After consideration of the Tier IV evaluation results, all relevant information

is available and no further evaluation is possible. One of the following

conclusions is reached.

1. No management actions are required.

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Chapter 8

Animal Bioaccumulation