Example 6: Description of Complete Exposure Pathways

The risk assessor used the following questions to guide the determination of complete exposure pathways

between the proposed dredged material and the potential receptors:

a. Could contaminants reach receptors via direct contact?

b. Are one or more receptors inhabiting or using an area where contamination exists or will exist?

c. Is the location of contamination such that one or more receptors could contact it currently or in the

future?

d. Are there advective or dispersive processes which may deliver the contaminant to a receptor or

habitat?

e. Could contaminants reach receptors via indirect contact?

f. Is contamination bioaccumulative or bioconcentratable?

g. Are there higher order predators which may accumulate the contaminant?

h. Could contaminants reach receptors or habitats via groundwater?

i. Can contaminants leach into groundwater?

j. Does groundwater discharge to aquatic habitats?

k. Are contaminants present at surface sediments?

l. Can contaminants be leached or eroded from surface sediments or soil?

The answers to these questions indicate that there is a benthic community with potential for direct contact

and ingestion of sediments by invertebrate organisms at the management area. There is then potential for

bioaccumulation to higher-order predators through ingestion of the benthic organisms. There is some

potential for bioconcentration of COCs from suspended sediments in the water column to forage fish and

zooplankton, given the moderate vertical mixing which may occur at the site in winter. The management

option does not have an effluent discharge, so there is minimal likelihood of dissolved contamination in

the water column (there is a potential for exposure in the water column during disposal, but it is of short

duration). There is a commercial fishery, winter flounder, which results in a complete pathway to humans

through ingestion of flounder. The management area is too far offshore (5 km (3 miles)) to consider

groundwater discharge as a likely exposure pathway. Also, the management option does not result in

sediment exposures at the water surface as might be the case for an offshore containment island.

Sources of information for developing conceptual model

Each risk assessment will require site-specific information. The following

sources provide data on various estuaries, coastal areas, and long-term monitoring

programs for biological, chemical, and physical characteristics of an area:

a. Environmental impact statements for disposal site designations.

b. Previous assessments of dredged material disposed at the site.

c. NOAA Programs:

Chapter 2 Problem Formulation