4.1.8 Sampling Requirements

The chemical and biological evaluations in Tier II and Tier III will be

sufficient for evaluation of effluent discharges in the vast majority of cases. As

with all pathways, Tier IV evaluations would involve consideration of effluent

within the framework of a risk assessment.

The procedures in the various tiers can be applied to evaluate the performance

of existing CDFs and to design new CDFs. For existing CDFs, the techniques can

be used to predict the effluent quality for a given set of anticipated operational

conditions (known flow and containment area size). In a similar manner, the

required operational conditions for a new CDF (size, geometry, maximum

allowable dredge size, etc.) can be determined to meet a given effluent quality

requirement by comparing the predicted effluent quality for a variety of assumed

operational conditions. In either case, evaluation of effluent quality can only be

considered in conjunction with a sound design of the CDF for retention of

suspended solids and initial storage of the sediments to be dredged.

4.1.8 Sampling Requirements

Note that water from the dredging site is used in the Tier III EET for

evaluation of effluent discharges. Dredging site water is used since the effluent

discharge only involves a small fraction of dredged material solids and the

fractionation of contaminants to the dissolved phase will be influenced primarily

by characteristics of the dredging site water. Note that disposal site receiving

water samples should also be taken and analysed to evaluate mixing.

4.2 Tier I - Initial Evaluation of Effluent

The Tier I evaluation for a proposed project (see Chapter 3) will result in

determination of the need for contaminant evaluations, identification of pathways

of concern, identification of contaminants of concern, and decisions based on

existing information.

It is important to consider prior evaluations of the effluent pathway in Tier I to

determine if additional evaluations are needed. For example, if prior tests or

evaluations are available, and project conditions and dredged material

characteristics are unchanged, new evaluations would not be required.

After consideration of the Tier I effluent quality information, one of the

following conclusions is reached for effluent (Figure 4-2).

1. Information is sufficient to reach a decision without further evaluation.

2. Information is not sufficient to reach a decision regarding effluent quality.

Conduct Tier II and/or Tier III evaluations.

4-7

Chapter 4

Effluent During Disposal Operations