Vapor Intrusion and Sub-Slab Depressurization Systems

by Brian Chew on October 29, 2014

vapor intrusion & migration diagramVapor 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.
Principal Hydrogeologist

For more information please email: remediation@enviroequipment.com.

{ 0 comments }

Planting the Seeds of Environmental Stewardship

by Brian Chew on September 30, 2014

loblolly-pine-tree-farmBack in the late 1970’s, when I was still a student at Indiana University in Bloomington, I was notified that my Great Aunt Lillian Graves had passed away. This was a sad time for me as I was very fond of her. She had lived in New York City during the summer and in Greenwood SC during the winter. She had a very young soul for an elderly person, and was great fun to be around and talk to. I remember when my father told me about her death, and I was very surprised when he also informed me that she had left me something in her will. That something was a loblolly pine tree farm in Georgia that had been in our family for generations. Aunt Lil had leased the land to Georgia Kraft, a timber company, and the land had a healthy tract of trees growing at the time the land became mine. What I didn’t know was that Georgia Kraft was going to clear cut the property and leave 118.75 acres of stumps and brush piles, but that was exactly what happened.

About a year after graduating from IU with a geology degree I married my college sweetheart. It was 1980, the country was in a deep economic recession, and interest rates were in double digits. We began our marriage with one old car, some used furniture donated by my family, and little else. We had no money in the bank, few job offers that paid more than minimum wage, but we did have our 118.75 acres of stumps and brush piles (wind rows).

It wasn’t long before a forester called and inquired on whether we were going to sell the property or plant trees. Selling it did cross our minds. Most 23 year olds would have sold the property and bought a nice car. We considered everything and decided to carry on the family tradition of being tree farmers and investing for the future. We called the forester back and he told us of several programs through the US Department of Agriculture that would provide some monetary assistance for planting. The rest of the cost of planting would be up to us. Somehow over the next 5 years, with loans and the assistance of the USDA, we managed to become tree farmers by planting parcels of the land in stages.

Thirty plus years later we still have the farm and the trees have grown tall. They are now saw timber size. We managed to dodge forest fires, droughts, and pine beetles attacks, but not poor economies and lousy governments. In the last several decades Canada has allowed timber companies to cut timber on their federal lands basically for free and dump the timber on the US market. This has resulted in many timber companies and mills closing their doors in the south. It is still not a good time to sell timber. While we wait, we do take some comfort in knowing that we are doing our share to help clean the air in Georgia. No one knew anything about carbon footprints back in the early 1980’s when we planted our tree farm, but it is a real concern now.

If the housing industry recovers, and US saw timber prices rise, we may finally realize a return on our investment. In the meantime, we love being tree farmers, helping the environment, and carrying on our family tradition. I know Aunt Lil would be proud.

 

 

{ 0 comments }