Introduction - trdoer20010

Introduction

Evaluating the potential environmental consequences associated with dredging

and dredged material disposal is a difficult task. Scientific advancements have

made possible the collection of large amounts of complex technical information.

The dredged material manager must often rely on "best professional judgement" to

weigh and balance among multiple and sometimes conflicting lines of evidence to

reach a decision, and each decision involves a finite level of uncertainty.

In the current dredged material regulatory program, a tiered approach is used

to reach a determination regarding the suitability of the material for aquatic

disposal. This tiered approach provides for the efficient utilization of resources

while ensuring that sufficient information is collected to make technically sound

decisions. In each of the tiers, data are collected to assess the potential for

exposure and effects. In the earlier tiers (Tiers I and II) existing information and

simple screening tools are used, while in the later tiers more sophisticated effects-

based laboratory bioassays are employed. In many cases, the interpretation of

this information is fairly straightforward (e.g., toxicity was observed in an acute

sediment toxicity test, therefore the material is unsuitable for aquatic disposal).

However, in a smaller percentage of cases interpreting the significance of the

information is more difficult (e.g., slightly elevated tissue concentrations of a

chlorinated organic in a bioaccumulation test). In addition, concerns may arise

that are not explicitly addressed within the existing tiered assessment framework

(e.g., what is the risk to human health as a result of the potential trophic transfer

of sediment associated contaminants to fish/shellfish species consumed by

humans?). Questions such as these require a more thorough treatment of the

information utilizing approaches and methods standard to environmental risk

assessment. Environmental risk assessment provides a stepwise framework for the

integration of complex information to yield quantifiable estimates of risk,

including uncertainty. In addition, risk assessment allows the dredged material

manager to make explicit the types of information considered and how a decision

is reached regarding the suitability of a dredged material for a particular

management option. It is important to note that much of the information necessary

to conduct a risk assessment is already being collected within the existing

regulatory program. How best to use this information and what tools are available

for developing risk-based estimates and evaluating uncertainty for the dredging

program were the focus of the workshop discussions reported herein.

Chapter 1 Introduction