Aerated Floors for Green and Sustainable Mitigation of Vapor Intrusion to Indoor Air

| October 14, 2015 | 0 Comments

by Chuck Raymond and Susan Welt

Cupolex schematic

Cupolex schematic

In many parts of the Northeast, greenfield sites are becoming increasingly hard to find due to a number of factors, including a strong economy, vibrant real estate market, and population density. One of the advantages of greenfield sites is that they are less likely than previously developed sites to be impacted by remnants of past industrial use such as subsurface soil and groundwater contamination. As greenfield sites become more scarce, particularly in popular urban areas that have seen the most infill recently, developers have increasingly turned towards brownfield sites that have varying levels of subsurface contamination issues.

One of the risk factors that brownfield developers need to weigh when deciding what parcels to purchase and develop is the risk of vapor intrusion, a process where vapors from subsurface contamination emanate upwards into occupied space in the building above. According to the U.S. EPA, the main concern associated with vapor intrusion is whether the concentration of chemicals in the indoor air, even at low levels, poses an unacceptable risk to human health, including cancer, due to long- and even short-term exposure.

There are both active and passive methods to mitigate or control vapor intrusion. Active methods include sub-slab depressurization, which involves connecting an electric fan to a suction pit dug into the foundation slab that is connected to a series of pipes under the building to actively remove vapors and emit them outside the building. Another method is over-pressurization of the building, where the air pressure indoors is increased relative to the air pressure beneath the slab, keeping the vapors out. Both of these methods can work very well, but due to their electricity needs over a long period of time, they can be expensive to operate and maintain.

Cupolex layout

Cupolex layout

A greener and more sustainable option that is also less costly and equally effective is a passive venting system. As the name implies, these systems operate passively, requiring little or no energy to run. They involve installing a void space of some type beneath the basement or under the at-grade slab of a building. The void space is used to accumulate the vapors, which are then vented outdoors using solar fans or wind turbines, or even by simply taking advantage of atmospheric and building pressure differentials. Since the vapors are vented outside, the potential for vapors to accumulate in living or working space within the building is greatly reduced, lessening potential health risks for building occupants.

One example of a passive system is an aerated floor, such as the Cupolex system. With Cupolex, concrete is poured over modular dome forms, made from 100% recycled plastic that come in a variety of sizes, to create floating or structural slabs with an under-slab void.

Some of the benefits of aerated floors include:

  1. They are a green product, made from 100% recycled plastic.
  2. They offer up to five LEED points towards USGBC green building certification.
  3. Their use reduces steel and aggregate volume and costs.
  4. There is no need for long-term and expensive operation, maintenance, and monitoring.
  5. Using no fans, or solar-powered fans, they incur no electricity costs after installation.
  6. They are easy to install, especially in new buildings, and no certified contractors are required.
  7. They are stronger than traditional slabs because of the arch effect of the Cupolex forms.
  8. Cupolex forms create a continuous void space that eliminates the need for a crushed stone layer and sub-slab vapor mitigation piping.
  9. They protect against not just vapor intrusion from groundwater or soil contamination, but also mold and radon.
  10. The void space can be used to run utility conduits.

In summary, aerated floors offer many advantages over conventional active venting systems when an owner is faced with the potential for vapor intrusion issues in new construction. In a densely populated area like New England where subsurface contamination issues are common, passive aerated floors are a cost-effective and green alternative to other methods of mitigating vapor intrusion risks.


Welt S_2015

Susan Welt

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Chuck Raymond

Chuck Raymond, CPSM, is the marketing manager at Geosyntec Consultants in Acton, Massachusetts.

Susan Welt, M.P.H., P.E., is a senior environmental engineer at Geosyntec Consultants in Latham, New York.


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