4.1.6 CDF Design for Dredged Material Retention

Table 4-1

Summary of Data Requirements for Prediction of the Quality of

Effluent from Confined Dredged Material Disposal Areas

Data Required

Symbol

Source of Data

Dredge inflow rate

Project information; site design

Dredge inflow solids concentration

Project information; site design

Ponded area in disposal site

Project information; site design

Average ponding depth in disposal site and at the

Dp, Dpw

Project information; site design

weir

Dye tracer or theoretical

Hydraulic efficiency factor

HEF

determination

Effluent total suspended solids concentration

SSeff

Laboratory column settling tests

Dissolved concentration of contaminant in effluent Cdiss

Effluent elutriate tests

Fraction of contaminant in the total suspended

FSS

Effluent elutriate tests

solids in effluent

* This summary includes only those data required for effluent quality prediction. It is assumed that

the disposal area under consideration is designed for effective sedimentation and storage capacity.

Data requirements for such design or evaluation are found in EM 1110-2-5027 (Headquarters,

USACE 1987).

4.1.6 CDF Design for Dredged Material Retention

When the quality of the effluent from a CDF is of concern, the design,

operation, and management of the site should be carefully managed to ensure

retention of TSS within the CDF. This includes aspects relating to both the

volume required for effective sedimentation and the storage capacity of the site.

Procedures for such evaluations are presented in Engineer Manual 1110-2-2-5027

(Headquarters (HQ), USACE 1987) a copy of which is included in Appendix K),

and should be considered prior to the evaluations of potential effluent contaminant

impacts for the project. These design procedures will determine the surface area

and ponding depth required to achieve effective sedimentation, the required

containment volume for storage (including required freeboard), and the proper

sizing of weir structures. The prediction of the quality of the effluent is an exten-

sion and refinement of these design procedures. A list of data items required from

the design evaluation is shown in Table 4-1.

4.1.7 Summary of Tiered Evaluations for Effluent

A flowchart illustrating the tiered evaluation for effluent is shown in Figure

4-2. It should be noted that two types of evaluations of effluent may by required:

1) an evaluation of water quality to determine if applicable water quality standards

will be met, and 2) an evaluation of water column toxicity. Each of these aspects

involves separate evaluation and testing as appropriate.

If a decision regarding effluent cannot be reached based on the evaluation of

existing information in Tier I, Tier II provides methods for effluent screening

based on conservative assumptions. Tier III provides methods for column settling

tests for evaluation effluents TSS, effluent elutriate tests (EET) for evaluating

potential effluent water quality, and methods for conducting effluent water

column toxicity tests. The toxicity evaluations are appropriate if there are COC

for which WQS have not been established, or interactive effects of COC are of

concern.

4-5

Chapter 4

Effluent During Disposal Operations