Vapor intrusion (VI) of radon gas has been recognized as a potential cancer risk for more than 30 years. Radium, a breakdown product of uranium, produces the short-lived daughter product Radon, which presents itself as a gas that can migrate into living space of overlying buildings. More recently, volatile organic compounds (VOC’s), such as trichloroethylene (TCE), Tetrachloroethylene (PCE), and constituents associated with gasoline, such as benzene has been identified as compounds likely to migrate into indoor air as well.
It’s generally thought that vapor intrusion occurs from the subsurface to the basements, crawl spaces and first floor slabs on grade, but also through adjoined attics and walls in commercial\retail spaces. Some buildings are better insulated and sealed than others and heating, ventilation & air conditioning (HVAC) systems vary in vacuum and flow. Hence, the HVAC system running in ‘building A’ can draw odors in from adjoined ‘building B’. I have personally experienced cigarette smoke and bathroom odors (something which isn’t so funny if you are on the receiving end) being drawn into my commercial space from the industrial condo next door.
So What’s Being Done about Vapor Intrusion?
The ASTM vapor encroachment screening standard (E 2600-10) was published in 2010 to provide guidance to environmental professionals performing Phase 1 assessments on determining when a vapor encroachment condition (VEC) exists. Two VI guidance documents were issue for external review by EPA in April, 2013. Closer to home, the NCDENR-DWM released a VI guidance document in April 2014 on the DWM home page which was intended to emphasize the potential impact of VI on due diligence in property transactions and allocation of responsibility among the parties for VI issues.
Since early 2013, a number of State agencies and professional associations have developed guidance documents and short courses to educate professionals and the public on issues associated with vapor intrusion.
In the past six months we have had a huge increase in orders for custom sub-slab depressurization systems with control panels for vapor mitigation. These systems typically are designed to capture and remove migrating vapors before they enter indoor air. Most of these systems have been designed to remedy problems with existing commercial and residential structures. Recently, we have noticed more designs for systems being installed with new structures, which is typically much easier than retrofitting an existing structure. The amount of controls and sensors associated with the system is typically a reflection of the danger associated with the migrating vapors. Some larger systems incorporate remote telemetry to monitor the operation of the vapor mitigation system and to make sure any malfunctions are repaired quickly.
I look forward to building more of these custom systems in the near future!
Brian E Chew Sr. P.G.
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