5.5 Tier IV Runoff Risk Assessment

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

further runoff evaluation is necessary.

5.5 Tier IV Runoff Risk Assessment

5.5.1 Tier IV Runoff 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 in Cura, Wickshire, 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.

5.5.2 Tier IV Runoff Decision

After consideration of the Tier IV 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 runoff, such as placement of surface covers or

treatment, may require more detailed information for design of such

actions.

5.6 Runoff Management Actions

If the evaluation indicates that runoff may be a concern after consideration of

mixing, appropriate management actions may be considered. The runoff pathway

may require management as long as the dredged material is exposed to precipitation.

Management should take into consideration the short- and long-term physical and

chemical changes to dredged material that occur as a result of drying and oxidation.

Runoff management may include actions such as providing increased ponded area

and depth to minimize runoff discharge, treatment or filtration of runoff to reduce

the concentration of suspended solids and associated contaminants in the runoff,

5-14

Chapter 5

Surface Runoff After Disposal Operations