Water-Column Impacts

Framework for Dredged Material Management

May 2004

4.3.1 Water-Column Impacts

Potential water-column contaminant effects are evaluated by comparing

contaminant release in an elutriate of the material to be disposed with applicable water-

quality criteria or standards as appropriate. In addition, acute water-column toxicity

bioassays considering initial mixing may be needed. The procedures to be used in

elutriate or water-column bioassays are provided in the MPRSA and CWA testing

manuals (USEPA/USACE 1991; USEPA/USACE 1998; USACE 2003). For disposal

operations under the MPRSA, specific criteria for water quality and water-column

toxicity must be met, and specific allowances are specified for initial mixing

(USEPA/USACE 1991). For disposal operations under CWA, water quality and water-

column toxicity standards and allowances for initial mixing are specified by the States as

a part of the Section 401 water-quality certification requirements. Models are available

for mixing calculations (USEPA/USACE 1991; USEPA/USACE 1998; USACE 2003).

4.3.2 Benthic Impacts

In assessing potential benthic effects of contaminants under MPRSA, if the

exclusion criteria of 40 CFR 227.13 (b) are met, biological testing of the dredged material

is not necessary. If the exclusion criteria are not met, toxicity and bioaccumulation

information is required to evaluate the suitability of the material for disposal. If disposal

is under the authority of the CWA, a chemical comparison of the material to be disposed

and a reference sediment may be conducted. If contaminant concentrations in the dredged

material and an adjacent disposal site are substantially similar and contaminants will not

leave the adjacent disposal site or if controls are available to reduce contamination to

acceptable levels within the disposal site, no further evaluation may be required [40 CFR

230.60(c) and (d)]. If this is not the case, bioassays and bioaccumulation tests are

required to complete the evaluation.

Contaminants may affect benthic organisms through acute toxicity or by the

uptake of the contaminants (bioaccumulation). The evaluations compare acute toxicity

and/or bioaccumulation in benthic organisms exposed to the material to be disposed with

organisms exposed to a reference sediment. Procedures for conducting and interpreting

the acute toxicity and bioaccumulation evaluations are described in detail in the MPRSA

Ocean Testing Manual (USEPA/USACE 1991) and CWA Inland Testing Manual

(USEPA/USACE 1998). The Upland Testing Manual (USACE 2003) provides detailed

procedures for evaluation of dredged material proposed for disposal at CDFs.

4.3.3 Need for Contaminant Controls

If the contaminant pathway testing indicates that the impact Criteria or Guidelines

are met, the open-water disposal alternative is environmentally acceptable from the

standpoint of contaminant effects. If the impact Criteria or Guidelines are not met,

contaminant control measures must be considered to reduce impacts to acceptable levels

if the open-water alternative is to be further considered.