I would like to re-iterate Bruce Snead's request for technical performance data for soil gas mats. They appear to be an innovative and cost-effective solution to the installation of expensive aggregate materials.
If any researcher or manufacturer has conducted tests of soil gas mats with various soil types and applied vacuum, I would like to see it.
Bruce Schaepe, Braun Intertec, Minneapolis, MN bschaepeatbraunintertecdotcom

Thomas E. Thies
I am a retired radon mitigator in New Mexico. I have been using soil gas mat without gravel in NM for 15+ years. This SGM system is installed without gravel on well compacted soils. I have never had a post installation test fail. This system has been used on single family houses and multi family 3 story residential structures up to 20,000 SF foundation footprints. Gravel is not used in 90+% of our foundations because of the high structural quality of our soils. The few contractors that have tried the gravel base are not converts and believers in a properly designed/installed SGM system

Bruce,
I would check with the folks on the vapor intrusion side. They tend to have more research dollars and might have some data. Obviously Tom Hatton - but other folks only doing VI as well.

I support folks (both manufacturers and professional installers) bringing whatever quantified evidence they can to Mr. Snead.
While perhaps Mr. Thies's experience may not be dispositive for all scenarios nationwide, it might strike me as very close to it if he could also quantify the volume of installations he's done over the years, with data for installations with such mats compared with data for non-installation situations (the control group) in the same region. Add other practitioners from elsewhere in the country with similar datasets and affidavits, and that should be convincing for most.
This also leads me to ask:
- What level of proof do the Denver code officials say they need from those who are proponents of installing soil gas mat systems?
- What level of proof are they now satisfied with that demonstrates to them that gravel is effective and necessary?
It seems to me that the volume and quality of evidence for soil gas mat systems today might well match what was in place decades ago when the use of gravel originally became recognized as an effective solution.