Framework for Dredged Material Management
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).
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.
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.