6.2 Tier I Leachate Evaluation

Tier III provides site-specific laboratory testing and mathematical modeling

approaches to evaluate leachate quality. Both batch and column leaching tests are

available. Leachate testing considers concentrations of COC released from the

dredged material and, after allowance for attenuation and diffusion in the existing

materials in the CDF, dikes, foundation soils and aquifer, the predicted leachate

quality (Myers, Brannon, and Tardy 1996; Brannon, Myers, and Tardy 1994). The

predictive technique can be applied to evaluate the performance of existing sites and

to design new sites. For existing sites, the technique can be used to characterize the

leaching and adsorption of contaminants for the existing materials in the CDF.

6.2 Tier I Leachate Evaluation

The Tier I evaluation for a proposed project (Chapter 3) will result in

determination of the need for contaminant evaluations, identification of pathways

of concern, identification of contaminants of concern, and decisions based on

existing information.

It is important to consider prior evaluations of the leachate pathway in Tier I

to determine if additional evaluations are needed. For example, if prior tests or

evaluations are available, and project conditions and dredged material

characteristics are unchanged, new evaluations would not be required.

After consideration of the Tier I leachate quality information, one of the

following conclusions is reached for leachate:

1. Information is sufficient to reach a decision without further evaluation.

2. Information is not sufficient to reach a decision regarding leachate

quality. Conduct Tier II evaluations.

6.3 Tier II Leachate Quality Evaluations

If the Tier I evaluation indicates insufficient information for a leachate

decision, the Tier II leachate quality screening evaluation is appropriate. The

screening evaluation considers the bulk concentration of contaminants in the

dredged material and mixing, diffusion, and attenuation in groundwater at the

disposal site.

The Tier II leachate screen evaluates leachate quality based on bulk sediment

data for the proposed dredged material. If adequate bulk sediment data are not

available, samples should be collected and the bulk sediment chemistry should be

determined. It is possible to skip the screens and go directly to the Tier III

leachate test. However, this is not an efficient use of resources in most cases,

since bulk sediment data are also needed for screening evaluations for the other

pathways.

6-8

Chapter 6

Leachate to Groundwater