Surface Runoff After Disposal Operations

Surface Runoff After

Disposal Operations

5.1 General Considerations

Runoff is the water and associated suspended and dissolved materials released

from island, nearshore, or upland CDFs resulting from precipitation events on

exposed dredged material. The tiered structure of evaluation procedures for

surface runoff is similar to that for effluent. Like effluent, runoff typically enters

nearby surface water but may be released onto the surface of the adjacent soil.

Unlike effluent, which is generated only during the disposal and initial dewatering

of dredged material, runoff is a long-term pathway that exists as long as the dredged

material surface is exposed to precipitation and there is a discharge of runoff from

the CDF.

The runoff evaluation procedures generally consider worst-case scenarios in

the evaluation of runoff release:

1. Newly placed dredged material that is easily eroded during precipitation

events.

2. Oxidized, older material subject to increased solubility of metals.

3. No vegetative cover.

4. Direct discharge of generated runoff water.

5. Intense precipitation event equivalent to rainfall of 5.08 cm (2 in.) per

hour.

Considerations of runoff retention through ponding, effects of vegetation, and

low precipitation rates are currently not incorporated into the evaluation process.

These and other considerations will be included in the evaluation process as the

runoff pathway evaluation procedures are further developed.

5-1

Chapter 5

Surface Runoff After Disposal Operations