Criteria Used to Evaluate Importance of Uncertainty Sources

Table 1 indicates whether the source of uncertainty results from a lack of

knowledge (uncertainty), population heterogeneity (variability), or both. Table 1

also identifies the general type of uncertainty: parameter, model, or scenario.

Criteria Used to Evaluate Importance of

Uncertainty Sources

The importance of each uncertainty source in Table 1 to estimates of impact

from dredged material management activities was evaluated using three criteria:

a. The uncertainty results from a failure to consider a potential adverse

impact.

b. The magnitude of the uncertainty.

c. The ease with which the uncertainty can be reduced with available or

readily obtained data and information.

Relevant scientific literature is reviewed in Chapters 3 through 5, and details

of the USACE/USEPA tiered evaluation are compared against these criteria to

evaluate uncertainty sources. The criteria are listed in order of importance, and

uncertainty sources are scored accordingly as described in the following

subsections. The data and information used to assign all scores are provided in

the discussion of uncertainty sources in Chapters 4 and 5.

Failure to consider potential adverse effect

If a source of uncertainty exists because a potential adverse effect is not

considered in the tiered evaluation (although it might be considered in a complete

risk assessment conducted in Tier IV), the source was given a score of 3.

Otherwise, no score was assigned to the source.

Magnitude of uncertainty

This criterion is used to indicate the degree of uncertainty associated with a

particular source using quantitative data from the scientific literature. If no data

were available to quantify uncertainty, the source was not ranked (NR) under this

criterion. Some sources of uncertainty were classified as project-specific (PS) or

model-specific (MS). None of these rankings received a score, but this does not

necessarily mean the source of uncertainty is unimportant.

A ranking of "low" indicates uncertainty of up to one order of magnitude. A

ranking of "moderate" indicates uncertainty of approximately one to two orders

of magnitude, and a "high" ranking indicates uncertainty greater than two orders

of magnitude. A low ranking received a score of 1, "moderate" received a score

of 2, and "high" received a score of 3. NR, PS, and MS rankings did not receive a

score.

Chapter 2 Preliminary Ranking Approach