Step 4: Specify contaminants of concern (Cont.)

they are so bioaccumulative that they present a potential problem to higher trophic

levels. In Tier I, the testing manuals specify four properties which control the

propensity to bioaccumulate:

a. Hydrophobicity.

b. Aqueous solubility.

c. Stability.

d. Stereochemistry.

Application of Tier I criteria for selecting COCs. All compounds identified as

potential COCs in Tier I will be carried in the risk assessment unless evaluations in

subsequent tiers are available to eliminate a compound from the COC list.

Summary of Tier II evaluations. Tier II of the sediment evaluation procedure

provides a method to screen sediments for potential impact and thereby eliminate

the need for further testing. Tier II evaluates the COCs identified in Tier I for

compliance with water-quality criteria (WQC), and calculates Theoretical

Bioaccumulation Potential (TBP) to address potential benthic impact.

To evaluate water-column impact, the Tier II evaluation predicts a water-column

concentration for all of the contaminants of concern identified in Tier I. This

prediction makes the conservative assumption that all of the contaminants in the

dredged material are released into the water column. If the predicted concentrations

of all potential COCs are below the WQC concentrations, and no synergistic effects

are suspected, then the dredged material complies with Tier II WQC requirements.

If the predicted concentrations of any of the potential COCs exceed WQC, if there

are no criteria available, or if synergistic effects are suspected, further testing is

required in Tier III.

To evaluate benthic impact, the TBP calculated for the nonpolar organic COCs

in the dredged material are compared to the TBP calculated for the same

contaminants in the reference sediment. If the TBP of nonpolar organic compounds

for the dredged material exceeds that of the reference sediment, further evaluation of

bioaccumulation in Tier III is appropriate. Tier III evaluation is also necessary if the

COCs include compounds other than nonpolar organics which may bioaccumulate.

Application of Tier II results for selecting COCs. If the sediment evaluation

procedure progressed to Tier II, then compounds which do not have WQC or whose

predicted water-column concentration exceeds its WQC should be retained as

COCs. Note that the comparison should be made to all available WQC including:

a. Acute criteria for the protection of aquatic life.

b. Chronic criteria for the protection of aquatic life.

c. Criteria for the protection of humans from consumption of organisms only.

Chapter 2 Problem Formulation