Capping and Contained Aquatic Disposal

Framework for Dredged Material Management

May 2004

modification of the discharge terminus for mobility) and is potentially suitable for large

quantities of dredged material. There are few references in the literature on this topic. A

brief discussion can be found in Nester and Rees (1988).

4.4.5 Capping and Contained Aquatic Disposal

Capping is the controlled placement of contaminated material at an open-water

site followed by a covering or cap of clean isolating material. Capping is a control

measure for the benthic contaminant pathway. Level bottom capping is a term used for

capping without means of lateral containment. If some form of lateral containment is

used in conjunction with the cap, the term contained aquatic disposal is used.

Considerations in evaluating the feasibility of capping include site bathymetry, water

depth, currents, wave climate, physical characteristics of contaminated sediment and

capping sediment, and placement equipment and techniques. Because long-term stability

of the cap is of concern, capping is generally considered to be more technically feasible

in low-energy environments. Precise placement of material is necessary for effective

capping, and use of other control measures such as submerged discharge and lateral

containment increase the effectiveness of capping. Guidelines and recommendations are

available for planning and design of capping projects (Palermo et al. 1998a and 1998b;

Fredette et al. 2000).

4.4.6 Treatment

Treatment of discharges into open water may be considered to reduce certain

water-column or benthic impacts. For example, the Japanese have used an effective in-

line dredged material treatment scheme for highly contaminated harbor sediments

(Barnard and Hand 1978). However, this strategy has not been widely applied, and its

effectiveness has not been demonstrated for solution of the problem of contaminant

release during open-water disposal.

4.4.7 Monitoring

Monitoring is a management action which may be used to establish the

effectiveness of other specific management actions and the need for modification of such

actions, the necessity of which is a case-by-case decision. Technical guidance for

monitoring open-water disposal sites (physical and biological) is available (Marine Board

1990; Fredette et al. 1990a, 1990b).

4.5 Retention of Environmentally Acceptable Open-water Alternatives

Once appropriate open-water assessments are complete, a determination of

environmental acceptability is made. This determination must ensure that all applicable

standards or criteria are met. If control measures were considered, a determination of the

effectiveness of the control measure in meeting the standards or criteria must be made. If

all standards or criteria are met, the open-water alternative can be considered

environmentally acceptable. At this point in the framework, other factors can be

considered in the selection of an alternative as described in paragraph 3.6 and Chapter 7.