The Importance of a Conceptual Site Model (CSM)


The Challenge – Understanding Contamination and Sources

My goal today is to discuss the importance of developing a conceptual site model in the early stages of a Site investigation, before major decisions are made in advancing remediation and how high-resolution site characterization methods, such as passive soil vapor surveys, can provide depth and confidence in your CSMs.


At its heart, a CSM answers the key questions that help us determine how a spill occurred, the media affected, the path of contaminant migration, the human and ecological risk, and helps us determine whether remediation is warranted.  When it is developed completely and in a detailed way, it provides the regulatory agency with sufficient confidence to approve the actions proposed by the consultant.


The corollary, of course, is that it is difficult to know what actions are appropriate to take when critical data gaps exist and a CSM has not been adequately developed.


The Setting – “It’s Dark Down There!”

At the end of a good murder mystery, the detective presents their explanation of how it happened.  When it happened, who done it, how it was carried out, and why (aka the “motive”).  A CSM is very similar.  If we are to make sound recommendations about remediation, we need to know the operation or tank that caused the release.  We need to understand whether it was a sudden and accidental release, or whether it was the result of chronic poor housekeeping.  We need to know the lateral and vertical extent of impact, and we need to know what are the properties of the soil through which the material is migrating.  Lastly, we need to understand whether the current state of contaminant distribution presents a hazard to humans or the environment.


But practitioners are often piecing this explanation together decades after it happened and describing contaminants they can’t see in a setting that is underground.  So how can they accomplish such a detailed model?  The answer is in the use of high-resolution site characterization (HRSC) methodologies!


Best Practices in Environmental Remediation

Development of a CSM is an iterative process that feeds detail into itself as additional data is gathered; in other words, development of a CSM is the replacement of assumptions with facts provided through data.


The emergence of HRSC methodologies over the last 20 years has allowed the creation of more targeted, more effective remedy designs.  For example, Murex no longer prepares in-situ remediation designs without conducting some form of high-resolution characterization first.  The level of detail provided allows us to 1) develop more successful deployment designs, and 2) it allows us to be more cost-competitive in the estimating and implementation phases.  In addition, it provides the case managers at DTSC and RWQCB confidence that our approaches will be successful.




The image displayed is an example of an MiHPT, or membrane interphase probe and hydraulic profiling tool survey output.  The combination of volatile chemical detection, electrical conduction, and hydraulic property measurement is invaluable in the selection of injection intervals, estimating injection flow rates, and prevents loss of substrate across heterogeneous zones.


Murex’s principals treat every client and every site as a unique opportunity to strategically solve site challenges.  Contact us today for a free, no-obligation consultation on the approach, progress, and plan for closure of your client’s site.

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