Regulatory Evaluations of Dredged Material

The U.S. Army Corps of Engineers is required to evaluate and limit the potential for dredging operations to cause adverse environmental effects. This requirement includes considering the potential for adverse effects resulting from the bioaccumulation of contaminants which may be present in dredged material. For example, regulations implementing §103 of the Marine Protection, Research and Sanctuaries Act (MPRSA) of 1972 state that "Materials shall be deemed environmentally acceptable for ocean dumping only when...no significant undesirable effects will occur due either to chronic toxicity or to bioaccumulation" (40 CFR § 227.6).

The Ocean Testing Manual (USEPA/USACE 1991) describes the testing procedures to be used during regulatory evaluations of dredged material covered under the regulations implementing MPRSA. The Draft Inland Testing Manual (USEPA/USACE 1994) describes the testing procedures for dredged materials covered under the Clean Water Act of 1972. Both of these testing manuals describe a tiered approach for evaluating the potential for dredged material to produce adverse effects through direct toxicity and bioaccumulation.

Tier I

The purpose of Tier I is to determine whether a compliance decision can be reached regarding dredged material disposal on the basis of existing information, including all previously collected physical, chemical, and biological data. A primary task in Tier I is to identify the environmental contaminants of importance in the dredged material under consideration. Such an identification is necessary in order to select appropriate analyses in Tiers II, III, and IV.

Tier II

The tasks in Tier II are designed to provide a rapid screen for determining the potential for contaminant bioaccumulation from dredged material and for evaluating potential water column effects. Calculation of the theoretical bioaccumulation potential (TBP) provides an estimate of the potential for contaminants in dredged material to be bioaccumulated. Marine water quality criteria or state water quality standards are used in combination with a numerical mixing model (the STFATE model of ADDAMS) to evaluate the potential for acute toxicity in the water column.

Tier III

Tier III testing is designed to evaluate the toxicity and bioavailability of contaminants in dredged material. Short-term toxicity tests are performed using sensitive organisms to evaluate the potential for contaminants in dredged material to produce significant lethality. Longer term bioaccumulation tests are performed to evaluate the bioavailability of contaminants in dredged material.

Tier IV

When sufficient information has not been acquired during previous tiers to reach a decision regarding dredged material disposal, Tier IV evaluations may be used. Tier IV evaluations consist of case-specific tests for evaluating the potential for significant toxicity or bioaccumulation resulting from long-term exposures to dredged material.