Main Content


Michigan EGLE Provides Clarification on Sample Density of VI Studies

By: Craig A. Cox, CPG

As a consultant and advisor on vapor intrusion (VI) projects implemented throughout North America, South America, and Europe, one of the most frequently asked questions is “How many samples should we take to assess this building?” The answer, as one would suspect, depends on a lot of factors, including the goals of assessment, the size and use of the building, the COCs, etc. If you happen to practice in the State of Michigan, you may be interested to know that EGLE has updated their 2013 VI Guidance document to eliminate some confusion concerning sample density for sub-slab soil gas sample points in commercial buildings.

According to EGLE’s January 10, 2020 notification, they have modified Table 5-2: Sampling Density in Commercial Buildings to clarify the expected sample density.

“There has been consistent reliance on the minimum number of samples without consideration of the building size. Language has been added to the table to clarify the minimum number of samples is only appropriate for a building that meets the minimum of the square footage listed within the table. A sample density less than what is expected from the table may be proposed but must have justification for how it will represent the building conditions.”

Questions regarding the use of the department’s 2013 VI Guidance should be directed to Matthew Williams, Volatilization to Indoor Air Specialist, or 517-284-5171 or any of the VI TAPS POCs.

Craig Cox is a principal and co-founder of Cox-Colvin & Associates, Inc., and holds degrees in geology and mineralogy from the Ohio State University and hydrogeology from the Colorado School of Mines. Mr. Cox has over 30 years of experience managing large environmental project implemented under CERCLA and state voluntary action programs. Mr. Cox is the inventor of the Vapor Pin® and has developed a variety of software products including Data Inspector, an internet-enabled environmental database application. Mr. Cox is a Certified Professional Geologist (CPG) with AIPG and is a Certified Professional (CP) under Ohio EPA’s Voluntary Action Program.