Figure 5-1. Contaminant Pathways for Upland CDFs

Framework for Dredged Material Management

May 2004

Figure 5-1. Contaminant Pathways for Upland CDFs

association with the dredged material. 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.

Migration pathways affected by nearshore CDFs are illustrated in Figure 5-2 and

include all of the pathways previously discussed. Additional considerations for nearshore

sites (with one or more sides within the influence of water level fluctuations) are soluble

convection through the dike in the partially saturated zone and soluble diffusion from the

saturated zone through the dike. Groundwater seepage into or through the site can also be

a factor affecting contaminant migration. These additional potential fluxes primarily

affect the surface water pathway.

5.3.2 Geochemical Environments for CDFs

When dredged material is placed in an upland environment, physical and/or

chemical changes may occur (Francingues et al. 1985). The dredged material initially is

dark in color and reduced, with little oxygen. If the material is hydraulically placed in the

CDF, the ponded water will usually become oxygenated. This may affect the release of

contaminants in effluent discharged during hydraulic filling.

Once disposal operations are completed, and any ponded water has been removed

from the surface of the CDF, the exposed dredged material will become oxidized and

lighter in color. The dredged material may begin to crack as it dries out. Accumulation of

salts will develop on the surface of the dredged material and especially on the edge of the

cracks. Rainfall events will tend to dissolve and remove these salt accumulations in

surface runoff. Certain metal contaminants may become dissolved in surface runoff.