Steps in developing a conceptual model

migration of contaminants based on the site-specific physical conditions, chemistry,

and geology. It provides neither a quantitative estimate of the amount of

contaminant moving along a specific pathway nor an estimate of resulting

concentrations. Subsequent components of the risk assessment will incorporate

information on the amount of a contaminant moving along this pathway and

evaluate whether that amount poses a potential risk to a human or other organism.

The dredged material manager will recognize that much of the information

necessary to meet these goals is available through the Tiered Evaluation Process.

Figure 2 shows where information obtained during that process relates to these

overall goals. In most cases, attaining these goals does not require new data but is

an integration of the comprehensive analysis conducted in Tier I, supplemented with

the information collected in Tier II of the testing manuals. The risk assessor should

review National Environmental Policy Act (NEPA) documentation and associated

information during the development of the conceptual model. Clearly, the various

Tier I tasks such as summaries of physical, chemical, and biological information,

field monitoring studies, descriptions of the various sources of contaminants to the

dredged material, and the review of regulatory permits in the area contribute to the

development of the characterization. The conceptual model is a framework for

organizing previously acquired information.

Steps in developing a conceptual model

There are seven steps in developing a conceptual model (Figure 3).

1. Describe the dredged material management activity.

2. Identify the kinds and spatial extent of habitats that are present in and

around the management area.

3. Identify the species and humans that may use these habitats and that may be

potential receptors.

4. Specify the contaminants of concern.

5. Describe mechanisms which may bring a contaminant into contact with a

human or other organism.

6. Describe the potential routes of contact between the contaminant and the

receptor.

7. Describe the complete exposure pathway.

Step 1: Describe dredged material management activity

The first step in developing the conceptual model is to provide a narrative

description of the proposed dredged material management activity. This description

should include the manner of sediment dredging and disposal, the amount of

material under consideration, and the source of dredged material. The

Chapter 2 Problem Formulation