file under: Environment, Federal Government, Sustainability

Conceptual Site Models: A Key Tool for Remediation Insight and Communication

Remediation Perspectives

Ernest AshleyErnest Ashley

Our success as environmental professionals often requires making sense of complex scientific data sets at our sites to a diverse audience that may include risk assessors, earth scientists, remediation engineers, regulators and the public. Conceptual site models (CSMs) are a valuable tool for understanding and communicating large data sets, and for making good decisions throughout the site remediation process. The CSM provides a “picture” of the physical, chemical and biological processes that influence the transport, migration and potential impacts of contamination from its sources through environmental media to receptors within the environmental system. Conceptual site models help stakeholders visualize these complex interactions and create a common understanding for decisions and actions.

Dynamic Models Evolve with Remediation Progress
CSMs are not static, and should never be considered totally accurate or “complete”; instead, they should be viewed as dynamic and evolving as the remediation process progresses and new data are collected. They have a different role in each phase of a remediation project from preliminary investigation through remedial action (often overlooked) and post-cleanup monitoring:

  • Preliminary – Initiate an investigation. 
  • Baseline – Guide the investigation based on systematic planning. 
  • Characterization – Dictate any needed modifications to address important data gaps by incorporating new information through iterative updates as the investigation proceeds. 
  • Remedy selection and design – Form the basis of the feasibility study and remedial design. 
  • Remediation and post-remedial action monitoring – Provide a means to optimize (or modify) the remedy through iterative updates as performance monitoring data are collected.

Because we cannot “see” into the ground or characterize every aspect of a site, CSMs will always be based on assumptions and interpretations. We must balance the degree of uncertainty with current decision needs. A key decision point in the life of a remediation project is deciding when the investigation phase is done and the CSM is sufficiently complete to identify and select appropriate remedies. From a risk assessment standpoint, this usually means potential migration pathways are evaluated and exposure point concentrations adequately quantified. From a contaminant distribution standpoint, this usually means delineation of the nature (contaminants and concentrations) and extent. However, often overlooked until too late in the characterization stage are many of the hydrogeological and biogeochemical attributes of a site that influence the selection of potential remedial technologies, cost estimating and the remedial design. Accordingly, a critical stage in the development of a robust CSM is the identification of data needs of all parties involved in the selection and design of the remedial solutions.

GIS and Visualization Tools Enhance CSMs
As sites and conceptual site models become more complex, CDM Smith has found that geographic information systems (GIS), effective data management and visualization tools greatly facilitate the functionality of the CSM. GIS-based CSMs are especially well suited for environmental site characterization and remediation because they are a means to compile, visualize, compare and analyze lots of spatially related data, bringing the many pieces of the puzzle together. This also facilitates nearly automated CSM updates through addition of newly collected data to the database. In addition, they enable remedy evaluations by allowing the environmental professional to quickly calculate numerical and area-weighted average concentrations, graphically select data sets to assess remediation volumes, evaluate residual concentrations, and target specific regions and geologic strata for potential remedies. Regulatory interactions regarding the adequacy of site characterization and realistic remedy selection are enhanced because all the data are visually integrated and at your fingertips for real-time manipulation. Finally, GIS-based CSMs greatly facilitate report preparation and enhance communications with stakeholders and the public.

Ernest Ashley, C.P.G., LEP, LSP, CHMM, is a geologist with more than 30 years of experience specializing in hydrogeological and hazardous waste site investigations. He is active with the Interstate Technology & Regulatory Council, participating in the DNAPL Site Characterization, Long-term Contaminant Management Using Institutional Controls, and Groundwater Statistics and Monitoring Compliance teams. He has developed and maintained CSMs for a variety of complex sites, including former chlor-alkali and manufactured gas plants, aluminum and aircraft manufacturing facilities, and VOC DNAPL impacted sites.