IDEM STRENGTHENS ITS EMPHASIS ON CONCEPTUAL SITE MODELS

FOR ENVIRONMENTAL PROJECTS                

  James M. King, PhD, LPG-Technical Director jking@astburyenviro.com  

If you haven’t already, you’ll soon be hearing a lot about Conceptual Site Models, or CSMs, for environmental projects in Indiana. CSMs have been used for decades in some quarters, particularly in federal programs, to guide environmental investigation and remediation.  General discussions for developing and using CSMs appeared in U.S. EPA Superfund-related guidance documents in the late 1980s, and CSMs are an important part of EPA’s influential Soil Screening Guidance published in April 1996.  ASTM published its first CSM standard guidance (ASTM1689) in 1995 (reapproved in 2008).

In spite of their longevity, CSMs historically have not been a staple of environmental site closures in Indiana.  CSMs were only sparingly mentioned in the Indiana Department of Environmental Management’s (IDEM’s) Risk Integrated System of Closure (RISC) Technical Resource Guidance Document first issued in 2001.  However, with IDEM’s newly refocused attention on risk-based closures, the May 2011 draft of the Remediation Closure Guide (RCG), which will replace the Tech Guide in early 2012, devotes five of its 13 sections specifically to CSM development under the topics of presampling and sampling activities, characterizing contaminant plume behavior, vapor migration, and background and off-site sources.  These categories are subject to change when the final RCG is issued, but IDEM’s emphasis on CSMs is clear.

CSMs are basically formats (systems, frameworks, patterns) for (1) organizing and summarizing information already known or suspected about a contaminated site and (2) identifying information that must still be collected (data gaps) to more fully understand a site and to make sound decisions for the ongoing investigation and remediation.  They focus not just on what contaminants are present, but how they move, what paths they follow, and how exposures occur – the whole picture.  

CSMs