Vapor Mitigation Testing, Design, and Installation

Aztech Environmental Technologies was asked by the NYSDEC to install a vapor mitigation system in a town’s Village Hall, where an adjacent dry cleaning business, had created a large underground plume of chlorinated solvents.

These solvents included trichloroethylene and perchloroethylene, which were slowly volatilizing and venting upward through the soil media, releasing vapors into the structures above.

The scope of work included designing and installing both a Sub-Slab Depressurization System (SSDS) and a Sub-Membrane Depressurization System (SMDS) to prevent vapor intrusion in the structure.

Checking Communication

In October, 2009, work began with a communication test to identify the effects of negative pressure applied to material beneath the sub-slab and the subsequent radius of influence of each extraction point. Aztech determined that nominal communication could be established between the temporarily installed extraction points and the monitoring test points. Subsequent investigation indicated several locations in the floor were in poor condition, requiring repair to increase the communication potential across the slab.

Improving Communication

After approval was secured from the Village Administrator to repair and seal holes and cracks in the slab, a more thorough investigation revealed several floor drains and piping routes beneath the basement floor. Aztech sealed the floor drains and piping runs to prevent interference with the proposed SSDS. Aztech then performed additional tests to determine whether more communication could be established between extraction points and vapor monitoring points.

With results in hand, Aztech designed and built a combination SSDS for the basement, and a SMDS for the crawlspace.

Installation of the SSDS

Construction of the SSDS system began in April 2010. The system was located on the western side of the structure and used three (3) sub-slab depressurization extraction points vented through a GP-501 Radon Away fan. A second fan was used for two (2) additional sub slab extraction points and the SMDS that was installed in the crawlspace located along the eastern side of the structure.

The earthen floor crawlspace required an airtight membrane covering and vacuum-assisted venting from below. The sub membrane system used three (3) legs of slotted poly-vinyl chloride (PVC) pipe connecting to a 2” PVC ball valve. The slotted PVC pipe was extended from the front to back of the crawlspace to mitigate soil vapors from beneath the installed vapor barrier made of Radon Away Rufco 450 WB. The vapor barrier was attached to the foundation walls in the crawlspace using furring strips and then sealed to the side of the foundation using foam spray. Next, caulking was spread across the face of the strips and another furring strip sandwiched the vapor barrier between the two, to create a seal.

The Radon Away GP-501 system fans typically operate between a cost-saving 70 and 140 watts. The fans were attached to the mitigation piping via 3” x 3” furnco fittings in order to reduce the vibration caused by the operating fan. Schedule 40 piping and fittings were installed to convey soil vapor from the extraction points to the system fans located on the exterior of the Village Hall. Plastic pipe hangers were used to support the piping at several locations around the system.

Radon Away model Dynameter Monometers were installed at each extraction point to monitor vacuum at each wellhead. A condensate collection system was installed to protect the system fans by collecting and transferring water back to the extraction points throughout the system. It is installed around the system fan and protects the fan from potential water damage.

Passing the Final Test

A final communication test was conducted in May 2010. Results from the test indicated the system was working well within its specifications, and the building is now vapor free and habitable again.

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