E.4.2 Data requirements

Figure E-1. Schematic of typical single-source effluent discharging into a receiving water

body with unidirectional flow

E.4.2 Data requirements

The following data are required for evaluating mixing-zone sizes for

confined disposal area effluents:

a. Effluent concentrations at the point of discharge and receiving water

background concentrations for all contaminants of concern.

b. WQS applicable at the limit of the allowable mixing zone for all

contaminants of concern.

c. Depth, cross-sectional area, and current velocity of the receiving water

body during expected low flow conditions during the period of dredging.

d. Effluent volumetric flow rate.

E.4.3 Calculation procedure

a. Step 1. Verify that the assumptions on which the equations depend are

reasonable for conditions at the proposed discharge site.

b. Step 2. Use effluent, receiving water, and WQS concentrations of all

contaminants of concern to identify the critical contaminant. The critical

contaminant is the one that requires the greatest dilution, which will

define the boundary of the mixing zone. If mixing evaluations are

conducted for toxicity test results, the background concentration of

dredged material is assumed to be zero and the percentages of dredged

material are used to calculate the required dilution.

c. Step 3. Use receiving-water depth and velocity data to calculate a lateral

mixing coefficient. This coefficient is a measure of how rapidly the

effluent is dispersed through the receiving water.

Appendix E Evaluation of Mixing in Surface Waters