9.2.1 Compilation and Evaluation of Existing Information

If a decision about the need for management actions based on plant

bioaccumulation cannot be reached based on existing information in Tier I, the

evaluation may be carried to Tier II. Tier II consists of evaluation of the potential

for bioaccumulation of metals by plants growing in freshwater dredged material in

terrestrial or upland habitats based on dredged material extraction with

diethylenetriamine pentaacetic acid (DTPA), as well as a prescreen applicable in

specific circumstances described in Section 9.3. Those metals for which the

DTPA results indicate little potential for bioaccumulation may be eliminated with

regard to plant bioaccumulation, and those metals and other COC for which

further information is necessary to reach a decision may be carried to Tier III.

Tier III consists of laboratory bioaccumulation tests for the remaining COC by

plants growing in freshwater or saltwater dredged material under terrestrial or

wetland conditions. Those COC for which the results indicate little potential for

bioaccumulation may be eliminated with regard to plant bioaccumulation, and

those for which further information is necessary to reach a decision may be carried

to Tier IV. The evaluations of Tiers I through III will be sufficient to reach a

decision about most COC in most cases. In those situations where this is not the

case, a full risk assessment of the remaining COC may be conducted in Tier IV.

The procedures in the various tiers can be applied to evaluate the performance

of existing CDFs and to design new sites. For existing sites, the techniques can be

used to predict the potential for bioaccumulation for a given set of anticipated opera-

tional conditions (e.g., CDF size). In a similar manner, the required operational

conditions for a new site (e.g., frequency of new lifts) to avoid bioaccumulation can

be determined by comparing the predicted bioaccumulation for a variety of assumed

operational conditions. In either case, evaluation of bioaccumulation must be

considered in conjunction with a sound design of the CDF for retention of

suspended solids and initial storage of the sediments to be dredged.

9.2 Tier I Initial Evaluation of Plant

Bioaccumulation

Plant bioaccumulation is evaluated only if the Tier I evaluation of the

proposed project (Chapter 3) demonstrates that contaminant evaluations are

needed and that plant bioaccumulation is a contaminant mobility pathway of

concern for the project. It is important to consider prior evaluations of the plant

bioaccumulation pathway to determine if additional evaluations are needed. For

example, if prior tests or evaluations are available, and project conditions and

dredged material characteristics are unchanged, new evaluations may not be

necessary.

9.2.1 Compilation and Evaluation of Existing Information

The Tier I information generated in Chapter 3 is the technical basis for the

Tier I evaluation of plant bioaccumulation. Because the Tier I plant (and animal)

bioaccumulation evaluation relies more heavily on a risk assessment approach

than the evaluation of the other pathways, the Tier I information from Chapter 3 is

9-4

Chapter 9

Plant Bioaccumulation