Treatment of Dredged Material Solids

Framework for Dredged Material Management

May 2004

these controls is highly specific to the CDF location and the dredged material

characteristics.

Use of site controls such as liners, slurry walls, groundwater pumping, and

subsurface drainage are limited in most nearshore, in-water CDFs. Graded stone dikes

with sand or steel sheet pile cutoffs have been used or proposed at upland CDFs and a

few in-water CDFs to control leachate migration. The low permeability of fine-grained

sediments following compaction can reduce the need for liners in many cases, but it can

also limit the effectiveness and implementability of groundwater pumping and subsurface

drainage controls.

A cover can be highly effective in reducing leachate generation by avoiding

rainfall infiltration, isolation from bioturbation and uptake by plants and animals,

minimizing volatilization of contaminants from the surface, and eliminating detachment

and transport of contaminants by rainfall and runoff. A layer of clean material can

achieve the last three benefits mentioned. However, prevention of infiltration requires a

barrier of very low permeability, such as a flexible membrane or a compacted clay layer,

both of which are not easily or reliably implemented for CDFs. Other leachate control

measures include groundwater pumping, liners, subsurface drainage, sheet pile walls,

slurry walls, and surface drainage. Liners have not been used extensively for

contaminated dredged material sites because of the inherent low permeability of fine-

grained dredged material, the retention of contaminants on solids, and the difficulty and

expense of construction of a reliable liner system for wet dredged material, particularly

for in-water or nearshore sites. Leachate collection techniques, such as groundwater

pumping and subsurface drainage, have been evaluated in a limited number of situations,

but these techniques appear to have limited feasibility for in-water sites. Sheet pile walls

and slurry walls can be used to provide barriers to leachate and seepage movement from a

CDF. To be effective, the barrier should tie to a geologic formation with very low

permeability. Sheet pile walls are not leakproof and deteriorate over time; therefore, they

should not be considered as a primary containment measure. More detailed guidance on

site controls for CDFs is available (Cullinane et al. 1986; Averett et al. 1990; USACE

1983 and USACE in preparation).

5.4.4 Treatment of Dredged Material Solids

Treatment of the dredged material might be considered if this would facilitate

beneficial use of the material, or provide a cost effective alternative to treatment of the

various discharges from a CDF. A variety of treatment processes have been proposed for

dredged material solids (i.e., the mass of dredged material following placement within a

CDF) or dredged material slurries. These processes fall under one of the following

categories: bioremediation (use of bacteria, fungi, or enzymes to break down organic

contaminants), chemical treatment (e.g., oxidation, reduction, chelation, hydrolysis,

detoxification, nucleophilic substitution, and thionation processes), extraction (removal

of contaminants by dissolution in fluid), thermal (e.g., incineration), immobilization

(processes which limit the mobility of contaminants) and volume reduction (physical

separation of contaminated fractions).