Each implant is installed by drilling a 1-inch diameter hole through the concrete slab
foundation to a depth of 12-inches below the slab using a hand-held electric hammer drill.
The borings are reamed out to create an open hole for the placement an implant; which
consisted of a new, porous plastic diffusing stone attached to ¼” diameter Nylaflow® nylon
Sand is then placed around the implant to approximately 1 inch above the top of the
diffusing stone to create a porous zone for vapor migration.
Two to three inches of granular bentonite is then placed above the sand and hydrated with
distilled water to create an airtight seal between the indoor air above the concrete slab and
the implant below the slab; the seal prevents dilution of the sample from the ambient air.
Prior to sample collection, each implant is leak-tested to confirm the integrity of the seal.
The leak test consisted of placing a PVC cup or shroud over the implants and threading the
sample tubing through the top. Helium was then added to the cup through a side port,
followed by a low flow purging of the implant (using a syringe). Air collected from the implant
was then transferred to a Tedlar® bag and analyzed with a hand held Helium meter. If
Helium was detected in the Teldar® bag, the seal would have to be replaced.
Following the leak test, the ambient air within the tubing is purged a second time before the
sample is collected.
One (1) sub slab vapor sample is collected from each implant in a laboratory-supplied 400-
milliliter summa canister. The collected samples are hand delivered under chain of custody
to a NELAP Certified Laboratory for TO-15 analysis.
Sub-slab Vapor Assessment