10.3 Engineered Control Measures

volatilization of contaminants. Whether to cultivate or inhibit plant and animal

propagation is also an issue. Management of the site both during filling and after

disposal requires a comprehensive understanding of the migration pathways and

the effects various management actions have on the overall mass balance and rate

of contaminant releases. The decision to apply certain management actions

requires trade-offs for the site and contaminant- specific conditions for the project.

Selective placement is another management action especially useful for

control of the leachate pathway. Options include:

Sequencing or sandwiching with alternating layers of clean and

contaminated material to provide for attenuation (sorption, ion exchange,

filtration, biodegradation, etc.) or containment of contaminants.

Self-sealing/self-lining taking advantage of the fine-grained nature of

dredged material which yields low permeability when subjected to

Placing dredged material with suitable chemical and physical properties

as the final layer in a CDF, forming a de facto cover.

Placement of sand layers to enhance dewatering and consolidation.

Control of ponded water to reduce hydrostatic head or maintain a

negative hydraulic gradient, causing seepage flow into the CDF as

opposed to flow from the CDF.

10.2 Treatment of Effluent, Runoff, and Leachate

Discharges

For CDF liquid streams, the solids remaining will be clay or colloidal size

material that may require flocculants to promote further settling in clarifiers or

sedimentation ponds. Chemical clarification using organic polyelectrolytes is a

proven technology for CDF effluents (Schroeder 1983; Schroeder and Shields

1983, HQUSACE 1987). Filtration, permeable dikes, sand-filled weirs, and

wetlands have also been used on occasion for CDF demonstrations or pilot

evaluations.

10.3 Engineered Control Measures

Site controls (e.g., surface covers and liners) can be effective management

actions applied at a CDF to prevent migration of contaminants from the dredged

material (Cullinane et al. 1986; Averett, Perry, and Torrey 1990). There are few

CDFs where operational or physical management actions have been implemented.

Most of these sites are associated with sediment remediation projects, which

involve more highly contaminated sediments than normally associated with

navigation projects (Palermo and Averett 2000). The implementability and

effectiveness of these management actions is highly specific to the CDF location

10-3

Chapter 10

CDF Contaminant Management Actions