Leachate

Framework for Dredged Material Management

May 2004

As for effluent, partitioning analysis may be used to provide an initial estimate of

runoff concentrations, and this can be done for both oxidized and unoxidized conditions

(Price, Schroeder, and Estes in preparation). There also is now available a simplified test

procedure for prediction of runoff quality (SLRP) (Price, Skogerboe and Lee 1998 and

USACE 2003). A soil lysimeter testing protocol (Lee and Skogerboe 1983 and USACE

2003) has also been used to predict surface runoff quality with good results. The

lysimeter is equipped with a rainfall simulator and can be used in the laboratory or

transported to the field site. The soil lysimeter is a more expensive and elaborate testing

protocol, requiring large volumes of sediment and approximately 8 months for test

completion.

Computerized programs are available to compare predicted runoff concentrations

with water quality criteria (Schroeder, Gibson, and Dardeau 1995). If runoff

concentrations exceed water quality standards, appropriate controls may include

placement of a surface cover or cap on the site, maintenance of ponded water conditions

(although this may conflict with other management goals), vegetation to stabilize the

surface, treatments such as liming to raise pH, or treatment of the runoff as for effluent

(Lee and Skogerboe 1987). Risk assessment may be used to evaluate the environmental

effects associated with runoff and determine the need for controls where standards are

predicted to be exceeded, or standards are not available (Cura, Wickwire and McArlde in

preparation). Procedures for evaluation of runoff toxicity bioassay tests can also be

found in Brandon, Schroeder, and Lee (1997b).

5.3.6 Leachate

Subsurface drainage from upland CDFs may reach adjacent aquifers or may enter

surface waters. Fine-grained dredged material tends to form its own disposal-area liner as

particles settle with percolation of water, but some time may be required for sufficient

consolidation to occur. Particulate transport in leachate is also minimal. Constituents

present in leachate are primarily found in the dissolved fraction.

Evaluation of the leachate quality from a CDF must include a prediction of which

contaminants may be released in leachate and the relative degree of release or mass of

contaminants (Schroeder 2000). Pore water analysis may provide a good preliminary

estimate of leachate quality. Partitioning analysis may also be used to estimate

concentrations of constituents in leachate, based on measured sediment concentrations

(Myers, Schroeder and Estes in preparation (a)). Experimental procedures have been

developed for prediction of leachate quality from dredged material (Myers and Brannon

1991; Brannon, Myers and Tardy 1994; Myers, Brannon and Tardy 1996, USACE 2003).

These procedures are based on theoretical analysis and laboratory batch testing and

column testing, but have not been routinely applied due to the time required to perform

these tests and the associated cost.

The experimental testing procedures only give data on leachate quality. Estimates

of leachate quantity must be made by considering site-specific characteristics and

groundwater hydrology. Computerized procedures such as the USEPA Hydrologic