3.1.2 Conceptual Site Models
DU sizes and locations are key outcomes of the conceptual site model (CSM).CSMs are essential elements of the systematic planning process. A CSM serves to conceptualize the relationship between contaminant sources and receptors through consideration of potential or actual migration and exposure pathways. It presents the current understanding of the site, helps to identify data gaps, and helps to focus the data collection efforts. The CSM should be maintained and updated as new information is collected throughout the life cycle of the project. Various styles of CSM are useful, from text explanations to a series of figures depicting current and assumed future site conditions in three dimensions. Some form of visualization aid (e.g., figures, graphs, charts, tables) that relates site conditions to receptors in a manner that lends itself to the explanation and use of ISM is suggested (Figure 3-1 provides an example). The sampling strategy should reflect the assumptions about the transport phenomena and exposure scenarios reflected in the CSM.
Information on the development of CSMs is readily available in a number of guidance documents, including the following:
- Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA (USEPA 1988)
- Data Quality Objectives Process for Hazardous Waste Site Investigations: Final Guidance. (USEPA 2000a)
- Conceptual Site Models for Ordnance and Explosives (OE) and Hazardous, Toxic, and Radioactive Waste (HTRW) Projects (USACE 2003)
- Standard Guide for Developing Conceptual Site Models for Contaminated Sites (ASTM 2008)
The reader is directed to these and other relevant guidance documents for development of CSMs.