Figure 1-2. Schematic of contaminant migration pathways for upland CDFs

1. Effluent discharges to surface water during filling operations and

subsequent settling and dewatering.

2. Precipitation surface runoff.

3. Leachate into groundwater.

4. Volatilization to the atmosphere.

5. Direct uptake by plants and animals living on the dredged material and

subsequent cycling through food webs. For evaluation in the UTM, the

direct uptake pathway is subdivided into animal bioaccumulation and

plant bioaccumulation.

Volatilization

Surface

Plant / Animal

Runoff

Uptake

Weir

Unsaturated

Dike

Saturated

Infiltration

Seepage

Effluent

Leachate

Figure 1-2. Schematic of contaminant migration pathways for upland CDFs

Effects on surface water quality, groundwater quality, air quality, plants, and

animals depend on the characteristics of the dredged material, management, and

operation of the site during and after filling, and the proximity of the CDF to

potential receptors of the contaminants.

Pathways for a nearshore CDF are illustrated in Figure 1-3 and include a

number of the pathways that are considered for upland CDFs. However, the

relative importance of pathways for a nearshore CDF differs from an upland CDF.

A primary advantage of the nearshore CDF is that contaminated dredged material

may remain within the saturated zone so that anaerobic conditions prevail and

contaminant mobility is minimized. A disadvantage is water level fluctuation via

water level changes or other mechanisms, which cause a pumping action through

the exterior dikes, which are generally constructed of permeable material. The

pumping action may result in soluble convection through the dike in the partially

saturated zone and soluble diffusion from the saturated zone through the dike.

Pathways for island CDFs would be similar to nearshore sites. That portion

of a nearshore or island CDF raised to above the mean high water elevation will

essentially function as an upland CDF.

1-4

Chapter 1

Introduction