Tier I Evaluation

Tier I Evaluation

The purpose of Tier I is to establish whether a determination of potential

environmental impact can be made on the basis of existing information. All

existing and readily available information on the proposed project, including

previously collected chemical and biological monitoring and testing data, is

evaluated. This information can be used to make a preliminary determination

concerning the need for dredged material testing, under a principle commonly

known as "reason to believe." The reason to believe that contaminants are not

present and no testing is required is based on the type of material to be dredged

(e.g., sand, silt, etc.) and its potential to be contaminated (e.g., due to proximity

to sources of contamination). Contaminants of potential concern include those

that might reasonably be expected to cause an unacceptable adverse impact if the

dredged material is discharged.

Identification of contaminants of concern

The contaminants of concern (COCs) in the dredged material are selected

based on the following criteria:

a. Presence in the dredged material.

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

reference sediment.

c. Toxicological importance.

d. Persistence in the environment.

e. Propensity to bioaccumulate from sediments.

Misapplication of selection criteria may result in the inappropriate inclusion

or exclusion of chemicals as COCs. The following uncertainties are associated

with the selection criteria:

a. Background comparison. Chemicals may be inappropriately retained or

removed as COCs if background measures are not truly representative of

background conditions.

b. Frequency of detection. Use of a high detection frequency (> 5 percent)

as a selection criterion may result in the inappropriate exclusion of

chemicals as COCs.

c. Essential nutrients/trace elements. Inclusion of essential nutrients or

trace elements that are present naturally at beneficial concentrations or

exclusion when present at toxic levels may result in inappropriate

selection of COCs (U.S. Army Engineer Division, Huntsville, 1995).

The uncertainty associated with the selection criteria for identifying COCs is

typically low and can be addressed by appropriate application of the criteria.

Section 9 of the ITM (USEPA/USACE 1998) provides an extensive list of

Chapter 4 Uncertainty in Tiered Evaluation of Dredged Material