Implementation of Dredging Risk Assessment Modeling Applications for Evaluation of the No-Action Scenario and Dredging Impacts

ERDC TN-DOER-R2

December 2001

Implementation of Dredging Risk Assessment

Modeling Applications for Evaluation of the

No-Action Scenario and Dredging Impacts

PURPOSE: This technical note describes the development of Dredging Risk Assessment Mod-

eling Applications (DRAMA) for evaluation of the no-action scenario and the impacts of dredging

operations without consideration of disposal. Implementation templates for these scenarios use

existing dredging models to characterize exposure for the evaluation of potential human health and

ecological risk. The models selected have been incorporated into the Framework for Risk Analysis

in Multimedia Environmental Systems (FRAMES), a part of the Army Risk Assessment Modeling

System (ARAMS).

BACKGROUND: The risk assessment paradigm (Figure 1) is typically a problem formulation

leading to both exposure and effects assessments, which are integrated to perform a risk charac-

terization (Moore et al. 1998). The

basic premise is to calculate risk as

a function of both exposure, human

or ecological, and effects resulting

from exposure. The effects of con-

cern may result from short- or long-

term exposures.

The risk

assessment techniques for the

evaluation of dredging activities re-

quire exposure effects data and/or

predictions generated by models.

Exposure models are required to

predict exposures resulting from

proposed alternatives where expo-

sure data do not exist. The combi- Figure 1. U.S. Environmental Protection Agency risk

nation of the exposure and effect

assessment paradigm

components results in a calculated

risk characterization. Risk assessments are useful planning tools for the evaluation and determina-

tion of the impact of dredging and disposal alternatives on both human and ecological resources

(Moore et al. 1998).

Historically, there have been several options for conducting risk assessments. Perhaps the simplest

of these involves direct field measurements to estimate exposure concentrations for a given exposure

scenario. These direct exposure estimates are then compared to effects data to estimate a risk, e.g.,

a hazard quotient (U.S. Environmental Protection Agency (USEPA) 1992). One problem with this

method is the assumption that the exposure concentrations collected at the sample sites are

temporally constant. In addition, the spatial distribution of the exposure concentrations is generally

limited due to the expense of field measurements. To gain an understanding of the influence of time

and spatial variances upon the estimated exposure concentration (for a given exposure scenario),