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VAPOR INTRUSION

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Published on Jun 12, 2017

Vapor/vapour Intrusion (VI) is an emerging environmental issue that is increasingly important in the overall environmental assessment process. In this brief video, Dragun's environmental experts help you understand VI.
Vapor intrusion is the process by which chemicals that have gotten into either the soil or groundwater, so anywhere in the subsurface migrate up into a building to where people might be able to breathe it.
Vapor intrusion is caused by a group of chemicals called volatile chemicals. They are chemicals that can vaporize – they prefer to be in vapor rather than in water or attached to soil.
Vapor intrusion is potentially dangerous, there are certain chemicals that readily vaporize from the groundwater or the soil and those are easily transported into a building and some of those are carcinogenic.
The volatile chemicals that are driving a lot of sites these days are chemicals that are related to dry cleaning and vapor degreasing those would be call trichloroethylene or TCE perchloroethylene or PERC. Gasoline stations also have volatile chemicals, the toxicity of those chemicals can vary. They can be carcinogenic.
It is something that has come to light more lately. Vapor intrusion is one of the things in our business that is actually changing fairly quickly. I think that is evidenced by the fact that the US Government and a number of states have released brand new guidance and how to assess and deal with vapor intrusion over the last year or two. These days it’s really driving a lot of our projects as we’ve become more aware of how often it is occurring and the potential consequences that can arise from it.
From a business perspective, vapor intrusion really entered into a lot of our client’s lives. We work with clients that are buying or selling properties – it is absolutely driving a number of issues relative to transactions.
Vapor intrusion is not hard to detect but you have to use specific techniques to be able to assess it and those techniques vary by state or by region depending on what that regulatory body wants you to be doing. You can either take vapor samples from below the building and find out what could be potentially coming into a building or you can take vapor samples from inside the building to find out what the people would actually be breathing.
Previously, when we would look at potential vapor intrusion issues, we worked off an algorithm and model that had been developed, the Johnson and Ettinger model. So a lot of different factors that could play into, if you had a chemical, say trichloroethylene, in soil, they would back calculate what number could be in that soil, how high concentration that could be before it would cause a vapor intrusion into the home. So if we looked at data from soil or groundwater, and it was below that threshold criterion, we would say vapor intrusion is not an issue at this site.
More recently, they found problems with Johnson Ettinger model that didn’t accurately predict what was happening. Now were more focused more because of there the regulations gone, where the science has gone, to collect vapor samples, sub-slab samples, and sometimes indoor air samples, to better characterize what is actually happening with this phenomenon of vapor intrusion.
We’re working on a project that’s a large former air force base in Salina, Kansas. They used a lot of the solvent, trichloroethylene. We tested about 40 industrial buildings, and a number of residential buildings, for the air beneath the slab, we call that sub-slab vapor and the air within the buildings, to determine what the people are actually breathing.
So it’s a fairly wide-spread investigation of how this could be affecting the people that live and work that live and work above water plumes.
We like to be sure about our findings before we take the step of spending a lot of money on a mitigation system and we like make sure that detection is real, make sure we know that is coming from vapor intrusion and not potentially something from the building that people might be using. We like to take a little more sure approach before have someone committing a lot of money to a mitigation system.
We have a really strong grasp on the science behind the mechanisms and the phenomenon that vapor intrusion is based on. Using that we able to take a solid position on whether or not you need to be assessing vapor intrusion, potentially stay out of the process altogether. We like to say, don’t get on the on ramp rather than looking for an off ramp. And when we do take a position, we are able to justify that based on the science and most often come to a solution quickly.

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