Surface Runoff

Framework for Dredged Material Management

May 2004

Section 404 of the CWA and is also subject to water quality certification under Section

401 State/Tribal water quality standards.

Prediction of effluent quality may be made using partitioning analysis (Estes,

Schroeder, and Bailey in preparation), or the effluent elutriate test procedure (Palermo

1985; Palermo and Thackston 1988, USEPA/USACE 1998, USACE 2003). Partitioning

analysis provides an estimate of effluent concentrations that will result for measured

sediment and carrier water concentrations. This can be helpful in narrowing the

constituents of concern to those that appear to be present at concentrations that may be

environmentally problematic. The modified elutriate test simulates the geochemical and

physical processes occurring during confined disposal. This test provides additional

information on dissolved and particulate contaminant concentrations. The column settling

test (USACE 1987) and expert system SETTLE (Hayes and Schroeder 1992) used for

CDF design provide an estimate of the effluent solids concentrations. Results of both

elutriate and settling tests can be used to predict a total concentration of contaminants in

the effluent. The predicted effluent quality, with allowance for any mixing zone, can be

compared directly with water quality standards. Computerized programs are also

available to compare predicted effluent concentrations with water quality criteria

(Palermo and Schroeder 1991).

Where water quality standards are unavailable or are predicted to be exceeded,

risk assessment may be necessary to further evaluate the environmental impacts

associated with the effluent discharge. Guidance regarding effluent toxicity bioassays

and ecological and human health risk assessment in aquatic environments can be found in

Brandon, Schroeder, and Lee (1997a) and Cura et al. (2001), respectively. The modified

elutriate test can be used to develop the water medium for bioassays if a biological

approach to evaluation of effluent quality is needed. These bioassays are conducted in a

manner similar to those for open-water disposal. The quality of a reference water (usually

the receiving water) should be considered in test interpretation.

If impacts of effluent contaminant concentrations are unacceptable, appropriate

controls should be considered. Control measures available for effluent discharge include

improved settling design or reduced flow to the containment area, chemical clarification

or filtration to remove particulate contaminants, and removal of dissolved contaminants

by more sophisticated treatment processes.

5.3.5 Surface Runoff

Immediately after material placement in a CDF and after ponding water is

decanted, the settled material may experience surface runoff. Rainfall during this initial

period will likely be erosive, and runoff will contain elevated solids concentrations.

Geochemically speaking, the contaminant release is controlled by anaerobic conditions.

Once the surface is allowed to dry, the runoff will contain a lesser concentration of solids,

but the release is now controlled by aerobic conditions, and release of some dissolved

contaminants may be elevated. Runoff water quality requirements may be a condition of

the water quality certification or considered as part of the NEPA process.