Evaluation of Management Actions and Controls for Open-water Disposal

Framework for Dredged Material Management

May 2004

Control measures to minimize contaminant impacts may include operational

modification, submerged discharge, lateral confinement, treatment, and capping. These

control measures are described in paragraph 4.4. If the control measures are determined

to be effective, then the alternative is environmentally acceptable from the standpoint of

contaminants. If not, then the open-water disposal alternative at the site under

consideration should be eliminated.

4.4 Evaluation of Management Actions and Controls for Open-water

Disposal

In cases where evaluations of direct physical impacts, site capacity, or

contaminant pathways indicate the Criteria or Guidelines will not be met when

conventional open-water disposal techniques are used, a variety of management actions

and contaminant control measures may be considered. Such techniques include

operational modifications, use of subaqueous discharge points, use of diffusers,

subaqueous lateral confinement of material, thin-layer placement, or capping of

contaminated material with clean material.

Descriptions of the commonly used management actions and contaminant

controls are given in the following paragraphs. Additional guidance on selection of

contaminant controls for open-water disposal is found in Francingues et al. (1985),

Cullinane et al. (1986), and Truitt (1987a and 1987b).

The primary consideration in selecting management or control options is to

identify the impacts to be addressed by the management or control options and choose an

option that best addresses the issue(s) of concern. The management and contaminant

controls discussed in this section are to be considered and implemented on both a site-

specific and case-specific basis. General considerations for each option are presented

within each section below. It is important to note that not all options work under all

situations or in all cases. Before any option is selected for implementation, a complete

review of the material-specific and site-specific conditions and circumstances should be

completed.

4.4.1 Modification of Dredging and Disposal Operations

Modifications of dredging and disposal operations can be an effective control for

both physical effects and water-column or benthic contaminant pathways. The purpose of

operational modification as a control is to reduce water-column dispersion and/or spread

of material on the bottom. The most obvious control measure for open-water disposal is a

modification in the technique or equipment used for placement. For example, if water-

column concentrations of dredged material exceed water-quality criteria or toxicity

criteria for a proposed hopper dredge discharge, an operational modification to clamshell

dredging with discharge from barges would reduce the water-column release. Discharge

of mechanically dredged material from barges also results in less spread of material as

compared with hopper discharge. Other operational modifications include constraints on

location of disposal, rate of disposal, and timing of disposal.