Analysis of Pathways for CDFs

Framework for Dredged Material Management

May 2004

the material desiccates through evapotranspiration, it becomes aerobic and oxidized,

mobilizing some contaminants as described previously. At this point, the surface layer

has characteristics similar to that of material in an upland CDF.

The bottom of an in-water CDF below the low-tide or groundwater elevation

remains saturated and anaerobic, favoring insolubility and contaminant attraction to

particulate matter. After dewatering of the dredged material above the flooded zone

ceases and consolidation of the material in the flooded zone reaches its final state, water

movement through the flooded material is minimal and the potential for migration of

contaminants is low.

The intermediate layer between the saturated and unsaturated layers will be a

transition zone and may alternately be saturated and unsaturated as the water surface

fluctuates. The depth of this zone and the volume of dredged material affected depend on

the difference in tide elevations and on the permeability of the dike and of the dredged

material. With low-permeability material, the volume of CDF material impacted by this

pumping is very small compared with the in-water CDF's total volume.

5.3.3 Analysis of Pathways for CDFs

Guidance for analysis of contaminant pathways for CDFs is provided in the

Upland Testing Manual or UTM (USACE 2003). This manual is a resource document

providing detailed testing procedures and approaches for evaluation of potential

contaminant migration pathways from diked confined disposal facilities (CDFs).

Consideration of pathways for migration of contaminants from the site and potential

contaminant impacts is required to determine the need for operational or engineered

measures to control contaminant releases. During the 1980s and 1990s, a number of

evaluation procedures and laboratory tests were developed for CDF pathway evaluations

and serve as the technical basis for procedures in the UTM (Environmental Laboratory

1987, Francingues and Averett 1988, Palermo et al. 1989, Brannon et al. 1990, and Myers

1990).

The UTM uses a tiered approach similar to that long used for evaluation of open

water placement of dredged material (USEPA/USACE 1991 and 1998). The pathways of

concern for CDFs include effluent discharges to surface water during filling operations,

rainfall surface runoff, leachate into groundwater, volatilization to the atmosphere, and

direct uptake by plants and animals on site and subsequent cycling through food webs.

Additional discussion of the respective CDF pathways including appropriate testing

protocols and evaluation procedures are given in the following paragraphs.

5.3.4 Effluent Discharge

The effluent from a CDF may contain both dissolved and particulate-associated

contaminants. A large portion of the total contaminant concentration is tightly bound to

the particulates. Effluent from a CDF is considered a dredged material discharge under