THE CONCEPTUAL SITE MODEL A Visual Journey Though Data and Time October 29, 2013.

THE CONCEPTUAL SITE MODELA Visual Journey Though Data and Time

October 29, 2013

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WHAT IS A CONCEPTUAL SITE MODEL ?

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A Conceptual Site Model (CSM) describes site features and surface/subsurface conditions to understand contaminants

and the risk(s) they pose to receptors.

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A CSM is included in the Part 213 definition of RBCA which directly references the ASTM:

Standard guide for development of conceptual site models and remediation strategies for light nonaqueous-phase liquids released to the subsurface, designation E 2531-06 E1, which references the

Standard guide for development of conceptual site models for Contaminated Sites, designation E 1689-95 (Reapproved 2008), which states (paraphrased):

A CSM is a written or pictorial representation of an environmental system and the processes that determine transport of contaminants from sources to receptors.

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A CSM describes site conditions by:

- Identifying sources, pathways and receptors for contamination.

- Identifying critical biological, chemical or physical processes.

- Identifying the presence (and absence) of contamination.

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The CSM is an EVOLVING document.

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DEVELOPMENT OF A CONCEPTUAL SITE MODEL

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1. Scope

2. Summary

3. Sources

4. Pathways and Receptors

5. Narrative and Visual Description

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1. Scope of the Conceptual Site Model

- What Needs to be Characterized

- Extent of Area to be Investigated

- Human and/or Ecological Receptors

- Contaminants of Concern (COCs)

- Applicable Remedial Criteria

- Immediate/Long Term Environmental Concerns

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2. Summarize Available Information

- Property Description

- Historical Information

- Off-site and Regional Information

- Geologic and Hydrogeological Information

- Other

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3. Identify and Characterize Sources

- Operational and Ownership History

- Current and Historic Releases

- Location and Content of Releases

- Extent/Volume/Mass

- Prior Remedial Actions

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4. Identify Pathways and Receptors

- Exposure Pathways• Current • Potential Future Use

- Human and/or Ecological Receptors

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4. Identify Pathways and Receptors

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5. A Narrative and Visual Description

- Puts all the pieces together in a summary fashion for the site as it is understood at that time.

- The CSM should describe the site, contaminants, pathways, and receptors. More complex sites should include a discussion of data gaps or uncertainties.

Note: this is probably the most critical part of a CSM. You need to be able to provide a clear description of your model and graphics with an explanation are a great way to do this.

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LET THE FUN BEGIN…

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The Narrative:

A release of NAPL occurred from a dispenser. That NAPL migrated into the subsurface and migrated along a clay layer at 10 feet and then entered an aquifer 30 feet west of the source. The NAPL then pancaked in a classical fashion and created a groundwater plume that is migrating to the NE. That plume included BTEX at levels representative of a NAPL source and has migrated 260 feet down-gradient.

The source area presents a VI risk but soil vapor data indicate that the risk is contained and has not reached any structures. Down-gradient drinking wells are in the path of migration of the dissolved phase…

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Contact InformationJoseph DeGrazia, C.P.G.

Senior GeologistMichigan Department on Environmental Quality

Remediation and Redevelopment DivisionSoutheast Michigan District Office

(586) 753-3812degraziaj@michigan.gov