Development of a Conceptual Model

Development of a Conceptual Model

The term conceptual model is a "term of art" in risk assessment and has specific

meaning. The conceptual model is an integration of existing information which

attempts to identify the contaminants and their sources, describe the pathways by

which they may reach humans or other organisms, and specify which humans or

organisms might be linked to the contaminants by these pathways. These humans

and organisms are called receptors. The assessment presents the conceptual model

as a narrative or diagram which describes the links between contaminant sources

and receptors along explicit fate and transport pathways. As demonstrated in the

various summaries of state, Federal, and industry guidance in Appendix A, nearly

all guidance documents for risk assessments require the development of a

conceptual model.

The development of the conceptual model may resolve questions. For example,

any incomplete exposure pathways defined in the conceptual model are eliminated

from further consideration. This is the opportunity to focus the questions upon those

issues of real concern. In the development of the conceptual model, it is important,

to obtain meaningful information through the Public Coordination Process from

Federal and state regulatory agencies, special interest groups, and the general public.

Goals of conceptual model

The conceptual model has two goals:

a. Site characterization which is a general description of the environmental

setting.

b. Defining complete exposure pathways which are the links between sources

of contamination and humans or organisms.

Site characterization is an integral part of the ecological and the human health

risk assessment. It should:

a. Provide a brief overview of the management area in terms of its current and

past uses.

b. Characterize the management area relative to receptors.

c. Describe the presence of contaminants in potential exposure media

(sediments, biota, suspended sediments, water).

A complete exposure pathway is a physical, chemical, or biological mechanism

or some combination which may transport a contaminant from a source, such as

sediment, to a specified human or other organism such as a commercial fish species

or an endangered aquatic bird. A complete exposure pathway does not necessarily

translate to risk. The conceptual model attempts only to describe the potential for

Chapter 2 Problem Formulation