8.2.2 Development of Conceptual Site Model

The conceptual model serves two purposes in evaluation of animal

bioaccumulation, based on the Tier I compilation of existing information

(Chapter 3):

a. Site characterization. Site characterization is a general description of

the environmental setting that is an integral part of an ecological or

human health evaluation of animal bioaccumulation. It should:

Provide a brief overview of the CDF in terms of its current and past

uses.

ii.

Characterize the CDF relative to receptors.

iii.

Describe the presence of contaminants in the dredged material.

b. Defining complete exposure routes. Complete exposure routes are the

links between sources of COC and humans or ecological ROC. A

complete exposure route is a combination of physical, chemical, and

biological processes that may transport a COC from a source, such as

dredged material in a CDF, into direct physiological contact with a

specified human or ecological ROC. The presence of a complete

exposure route does not necessarily translate to risk. The conceptual

model attempts only to describe the potential for migration of COC based

on the site-specific physical conditions, chemistry, and biology. It

provides neither a quantitative estimate of the amount of COC moving

along a specific route nor an estimate of resulting exposure

concentrations. Subsequent components of the risk assessment will

incorporate information on the amount of each COC moving along each

complete exposure route and evaluate whether that amount poses a

potential risk to a human or ecological ROC.

The following are the seven steps in developing a conceptual site model using

the existing information compiled in Chapter 3. The discussion here focuses on

identification of COC and ROC, determination of complete exposure routes

involving animal bioaccumulation, and elimination of those potential routes that

are not complete from further evaluation. Detailed guidance on all steps is

available in Cura, Wickwire, and McArlde (in preparation).

1. Describe the dredged material management activity. This description

should include the dredging, transportation and disposal processes, the

amount and source of dredged material, and physical, chemical and

biological characteristics of the CDF and its surroundings. The product

of this step is a written description of the proposed dredged material

management activity.

2. Identify the kinds and spatial extent of habitats and land uses that are

present in and around the CDF and those that may reasonably exist in the

future. It is important to identify habitats in and near the CDF, because

these will largely determine human uses and ecological receptors for the

conceptual model. The identifications should be specific and conform to

8-7

Chapter 8

Animal Bioaccumulation