Step 4: Specify contaminants of concern

Step 4: Specify contaminants of concern

This step in the development of the conceptual model is closely tied to the tiered

sediment evaluation. Those procedures have explicit methods for identifying COCs

and for deciding whether they may present a potential environmental problem. The

risk assessment rests heavily upon this prior work and should not introduce COCs

previously screened from consideration by the prior evaluation procedures.

The risk assessment should address risk from the COCs identified during the

tiered sediment evaluation process. The ocean dumping regulations (40 CFR Ch. 1

[7-1-88 edition] 227.6) and dredged material testing manuals (USEPA/USACE

1991, 1998) provide guidance regarding the selection of contaminants of concern

for dredged material.

Figure 4 shows the process for making the selection. It is a step-wise process

that uses information from the sediment evaluation procedure to select COCs. This

subsection summarizes the Tier I, II, and III sediment evaluation procedures and

describes how they apply to the selection of COCs for risk assessment.

Summary of Tier I evaluations. The Tier I procedures identify potential COCs as

those constituents which the regulations consider prohibited as other than trace

constituents. These include:

a. Organohalogen compounds.

b. Mercury and mercury compounds.

c. Cadmium and cadmium compounds.

d. Oil.

e. Known carcinogens, mutagens, or teratogens.

In addition, the testing manuals describe several bases upon which to identify

contaminants of concern. These include:

a. Presence in the dredged material.

b. Presence in the dredged material relative to the concentration in the

reference material.

c. Toxicological importance.

d. Persistence in the environment.

e. Propensity to bioaccumulate from sediments.

Simple presence is not sufficient to include a contaminant as a potential

contaminant of concern. However, a persistent and toxic chemical would be

included. Some contaminants may occur in sediments below their toxic levels, yet

Chapter 2 Problem Formulation