9.4.3 Tier III - Plant Bioaccumulation Decision

9.4.3 Tier III - Plant Bioaccumulation Decision

After consideration of the Tier III plant bioaccumulation information in the

context of the conceptual site model and the complete exposure routes to ROC

populations outside the CDF, one of the following conclusions is reached.

1. Bioaccumulation from the dredged material is not statistically greater than

bioaccumulation from the reference material. No further evaluation of

plant bioaccumulation is necessary.

2. Bioaccumulation from the dredged material is statistically greater than

bioaccumulation from the reference material. Therefore the magnitude of

potential effects on ROC populations outside the CDF must be

considered, leading to a conclusion that either:

a. There is little potential for effects on ROC populations outside the

CDF. No further evaluation of plant bioaccumulation is necessary.

b. Effects on ROC populations outside the CDF are likely, and

management actions should be considered. A decision to implement

management actions for plant 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 plant

bioaccumulation is necessary.

c. Information is not sufficient to reach a decision regarding plant

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 plant

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 plant bioaccumulation is necessary.

9.5 Tier IV Plant Bioaccumulation Risk

Assessment

9.5.1 Evaluation

The elimination of incomplete exposure pathways in Tier I and the

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

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

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).

9-11

Chapter 9

Plant Bioaccumulation