Site Capacity

Framework for Dredged Material Management

May 2004

present, the organisms which recolonize the site may be different from those present prior

to disposal.

Suspended solids may also affect water column organisms, although these effects

are uncommon because of the large dilution factor. Potential physical effects are

addressed during the site designation/specification process. If at all possible, a site should

not be located where significant undesirable effects will occur on or off the site. Prior to

disposal, the physical characteristics of the material should be evaluated to determine if it

is compatible with the use of a particular site. Models are frequently used to predict the

behavior of the material during and after disposal, and, in some instances, monitoring

may be needed to verify the model predictions. Both USACE and USEPA have generated

a large database on potential physical effects through the large number of site-designation

surveys performed nationwide.

If site conditions and uses are unchanged, collection of additional data to evaluate

direct physical impacts would generally be unnecessary for evaluation of a proposed

discharge of material under MPRSA because such impacts were evaluated as a part of the

site-designation process as well as during the site monitoring and management activities.

However, for Section 404 open-water disposal, direct physical impacts must be

considered as a part of the site-specification process for the specific discharge. Under

both MPRSA and CWA, appropriate site management and monitoring concerns must be

addressed.

4.2.2 Site Capacity

The physical capacity of predominantly nondispersive sites to hold the dredged

material without (1) resuspension and transport of disposed material by surface waves or

(2) interference with navigation traffic or other operational conflicts, must also be

evaluated. This may involve (1) setting a maximum height for mounds of disposed

dredged material or (2) estimating mounding rates over the long term, taking into account

erosion and consolidation of the mound (Dortch et al. 1990; Scheffner 1991; Poindexter-

Rollings 1990). Site capacity of predominantly dispersive sites is not normally a concern.

4.2.3 Need for Management Actions

If the evaluation of direct physical impacts and evaluation of site capacity indicate

that the site is adequate, the evaluation of contaminant pathways can be initiated. If the

evaluations of direct physical impacts and site capacity indicate unacceptable impacts

will result, or that site capacity is inadequate, management actions are required to reduce

physical impacts. Management actions to reduce physical impacts to acceptable levels

may include operational modification, submerged discharge, lateral confinement, or thin-

layer placement. These same management approaches can be considered to extend the

physical capacity of the site. Management actions are described in paragraph 4.4. If the

management actions are determined to be effective, the evaluation of contaminant

pathways can be initiated. If not, then the open-water disposal alternative at the site under

consideration should be eliminated.