5.1.7 Overview of Evaluations for Runoff Discharges

5.1.7 Overview of Evaluations for Runoff Discharges

A flowchart illustrating the tiered evaluation for runoff is shown in Figure 5-2.

It should be noted that two types of evaluations of runoff may by required:

1. An evaluation of water quality to determine if applicable water quality

standards will be met.

2. An evaluation of water column toxicity.

Each of these aspects involves separate evaluation and testing as appropriate.

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

existing information in Tier I, Tier II provides methods for screening based on

conservative assumptions. Tier III provides tests for evaluating potential runoff

quality and methods for conducting water column bioassays for evaluating water

column toxicity for the runoff discharge. The toxicity evaluations are used if there

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

are of concern. The Tier II and Tier III evaluations will be sufficient for evaluation

of runoff discharges in the vast majority of cases. As with all pathways, Tier IV

evaluations would involve consideration of runoff within the framework of a risk

assessment.

The procedures in the various tiers are designed to evaluate runoff for both

new and existing sites. For new sites, the runoff evaluation can provide

information necessary to design the CDF to manage runoff water effectively to

meet water quality standards. For existing sites, additional controls, not part of

the existing design and management, may need to be added to control runoff. The

techniques described in this chapter are designed to evaluate worst-case

conditions, and specific conditions such as vegetative cover, low precipitation

intensities and other factors that restrict runoff should be evaluated on a case-by-

case basis. Management of runoff should be considered as part of an overall long-

term management strategy.

5.2 Tier I - Initial Evaluation of Runoff

The Tier I evaluation for a proposed project (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 runoff 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 runoff quality information, one of the

following conclusions is reached for runoff (Figure 5-2).

5-5

Chapter 5

Surface Runoff After Disposal Operations