Site Operations

Framework for Dredged Material Management

May 2004

Some of these treatment processes have been applied in pilot-scale

demonstrations, and some have been applied full scale (Myers and Bowman 1999;

Myers, Bowman, and Myers 2003; Olin-Estes et al. 2002a; USACE Los Angeles District

2002; USEPA 1999; Tetra Tech and Averett 1994). Recent work on phytoremediation of

lead contaminated sediments can be found in Lee and Price (2003). Potential for

biotreatement or phytoremediation of contaminated sediments is discussed in the

following references (Price and Lee 1999; Fredrickson et al.1999; Price, Lee and

Simmers 1999; Myers and Williford 2000).

The cost of treatment alternatives relative to the cost of conventional disposal is a

major constraint on their potential use. The potential for implementation of

immobilization processes is better than other treatment processes, because they are not as

sensitive to process-control conditions, and they are relatively cost effective techniques

for reducing contaminant mobility. The opportunity for applying these processes in situ

in a CDF is also an advantage.

The environmental pathway most affected by immobilization processes is

transport of contaminants as leachate to the groundwater or surface water. Most of the

immobilization processes fall into the category of solidification/stabilization (S/S).

Objectives of S/S are generally to improve the handling and physical characteristics of

the material, decrease the surface area of the sediment mass across which transfer or loss

of contaminants can occur, and/or limit the solubility of contaminants by pH adjustment

or sorption phenomena. Effectiveness of S/S processes is usually evaluated in terms of

reduction of leaching potential. Reductions are process and contaminant specific, with

immobilization of some contaminants accompanied by increased mobility of other

contaminants.

5.4.5 Site Operations

Site operations can be used as a control measure for CDFs to reduce the exposure

of material through the surface water, volatilization, and groundwater pathways.

Operational controls may include management of the site pond during and after disposal

operations. Mobilization of contaminants from dredged material depends on the oxidation

state of the solids. Most metals are much less mobile when maintained in an anaerobic

reduced condition. On the other hand, aerobic sediments generally improve conditions for

biodegradation of organic contaminants. Maintaining ponded water on the site may

decrease the rate at which volatilization occurs (though not necessarily the overall mass

flux) but produces a hydraulic gradient that increases the potential for movement of

leachate through the site. 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

contaminant controls have on the overall mass balance and rate of contaminant releases.

The decision to apply certain management options requires trade-offs for the site and

contaminant-specific conditions for the project.