2.1.5 Progressing through the Tiers

A quarter-century of experience clearly demonstrates that these conditions

seldom exist at dredged material aquatic and nonaquatic disposal sites. In the great

majority of cases, the environmental consequences of disposal were sufficiently

known after Tier III or earlier to make a technical decision; Tier IV might have

further refined the prediction of consequences but would not have fundamentally

changed it. In such cases, socio-economic and political considerations are more

important than technical information, and no amount of further testing will

provide additional socio-economic or political insight. Under these circumstances,

it is an inappropriate use of time and money to carry the evaluation to Tier IV in

hopes that the additional technical detail will resolve nontechnical controversies.

At any tier except Tier IV, failure to make a decision regarding the need for

management actions results in additional testing at a subsequent, more complex

tier unless a decision is made to seek other disposal alternatives. The final tier

(Tier IV) consists of detailed site-specific evaluations intended to provide

whatever technical information is necessary for a decision, within the limits of the

present scientific state-of-the-practice.

2.1.5 Progressing through the Tiers

It is necessary to proceed through the tiers only until information sufficient to

make a decision about the pathway being evaluated has been obtained. For

example, if the available information is sufficient to make a decision in Tier I

about surface runoff, no further evaluation of surface runoff is required. The

evaluation would then shift to the next pathway, which might have to be carried

through Tier III to generate sufficient information to make a decision. The

approach is to enter Tier I and proceed as far through the sequence of tiers as

necessary to make a decision. Although the goal is to make a decision about each

pathway in the earliest possible tier, enough information should be available to

make technically defensible decisions about every pathway. It is acceptable and

often desirable to carry evaluations of different pathways through different tiers to

generate the information necessary and sufficient to make technically defensible

decisions regarding the need for management actions. It is important to recognize

that management actions implemented for one pathway may influence other

pathways.

As the investigation progresses through the tiers within a pathway, as many

questions as possible should be answered at each tier. Only specific questions that

cannot be answered satisfactorily after one tier should be evaluated further in the

next tier. It is neither necessary nor appropriate, and is counter-productive, to shift

all questions to the subsequent tier and repeat the investigation of questions that

have already been answered sufficiently.

The system is structured so that Tier I should be conducted for every pathway

that is evaluated, sufficient information for a decision will almost always be

available after Tier II or Tier III, and Tier IV will seldom be necessary. Prior to

initiating testing, it is essential that the informational requirements of each tier be

thoroughly understood and that the information necessary for interpreting results

at the advanced tiers be assembled. For example, it is always appropriate to gather

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Chapter 2 Structure and Approach of the UTM