4.5 Tier IV - Effluent Risk Assessment

b. The effluent toxicity poses a risk after consideration of mixing, and

management actions should be considered. If management actions

are selected, no further effluent evaluation is necessary.

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

toxicity. The case-specific risk from effluent should be determined in

Tier IV, or management actions as an alternative to further evaluation

should be considered. If management actions are selected, no further

effluent evaluation is necessary.

4.5 Tier IV - Effluent Risk Assessment

4.5.1 Evaluation

Tier IV is intended to answer whatever specific, well-defined technical

questions may remain unanswered after thorough evaluation in earlier tiers. If

earlier tiers are used properly, Tier IV should rarely be necessary.

By the nature of the tiered evaluation approach, any technical questions that

remain unresolved after Tier III can best be answered by a detailed, case-specific

evaluation. By their very nature, detailed case-specific evaluations are not

amenable to the kind of generic guidance that can be presented in a national

manual. They require individual design to address unique technical questions

under site-specific conditions.

The best approach for Tier IV is usually a case-specific risk assessment.

Detailed guidance for conducting risk assessments for CDFs in Tier IV can be

found by Cura, Wickwire, and McArlde (in preparation). The information

generated in Tiers I through III should be used to the maximum extent technically

justified throughout the Tier IV risk assessment.

4.5.2 Tier IV Effluent Decision

After consideration of the Tier IV effluent evaluation results, all relevant

information is available and no further evaluation is possible. One of the

following conclusions is reached.

1. No management actions are required.

2. Management actions should be considered. A decision to implement

management actions for effluent, such as operational modification or

effluent treatment, may require more detailed information prior to design

of such actions.

4.6 Effluent Management Actions

If the testing and associated analysis of the effluent pathway indicates applicable

WQS or toxicity concerns will not be satisfied after consideration of mixing,

appropriate management actions may be considered to reduce effects. These may

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Chapter 4

Effluent During Disposal Operations