Sub-Slab Depressurization and Building Renovation

NYSDEC commissioned Aztech to remediate a chlorinated solvent spill underneath an active business and two adjacent homes.

Beneath an active dry cleaning business a chlorinated solvent spill was affecting the building and two adjacent residences with vapor intrusion. Previous unsuccessful efforts of air quality remediation included a soil vapor extraction system. The New York State Department of Environmental Conservation then commissioned Aztech as the remedial contractor to design and install a sub-slab depressurization system (SSDS).

Aztech was asked to sample and remediate the indoor air at the three buildings. All buildings required structural repairs to their basements, so that vapors couldn’t intrude and sub-slab depressurization systems could be successfully installed.

Repairs included pointing and parging of the walls, sealing all existing cracks and old drains in the slab, installing new pads for mechanicals and installing new, reinforced concrete slab. Parging of the fieldstone foundation walls was completed by applying Throroseal water proofing compound and installing a six-mil poly membrane across the earthen crawl space. The sub-base for the concrete slab consisted of two-inches of number-one stone and a layer of Delta MS underlayment to provide a preferential pathway for the soil vapors. Once the installation was complete a communication test was conducted under the concrete slab. This yielded an acceptable minimum vacuum of 0.004 inches of water column.

At each location, a shallow well was built into each slab, with a perforated pipe surrounded by stone, allowing communication between the soil and the well. As the volatilized vapors in the soil seek upward release, they are collected beneath the slab and vented through the well. Using passive and active vacuum pump systems, the vapors are withdrawn and vented up and outside the structure above the roof line. 

Aztech installed instrumentation to record weather data, sub-slab differential pressure, temperature, flow and humidity trends inside the SSDS riser pipe. Aztech also installed a Davis Vantage Pro 2 weather station at this location to record temperature, precipitation, wind speed, wind direction and humidity trends over the course of the sampling events.

Upon installation, Aztech conducted air sampling, weather monitoring, differential pressure  monitoring and SSDS monitoring for several months. Today these structures are fully habitable, and the SSDS systems have effectively remediated the vapor intrusion.

    Download Project PDF