Framework for Dredged Material Management
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
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
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.