On larger buildings, a design is pilot tested in a small space and the results are projected across the entire building. However, variations in results caused by inconsistent sub-slab conditions can pop up during building-wide implementation and design adjustments may be needed during construction. For this reason, it can be helpful to work with a contractor who can do the design and construction; a design-build model will minimize any delays if quick field decisions and design adjustments are needed mid-project.
When vapor intrusion is discovered in spaces that are already finished, there are some other techniques, such as directional boring from the exterior or less trenching and more isolated vacuum points, which can help to minimize disturbance in finished spaces. We often use combinations of these techniques, depending on the unique configuration and pilot test results obtained.
In the case of our Minneapolis charter school, we were able to identify the scope of the problem and complete the mitigation process in time for the opening day of school. Just two weeks after startup of the system, the indoor air was below state standards and the sub-slab concentrations reduced from 70,000 parts per billion (ppb) to below 4,000 ppb. These concentrations in the sub-slab are nearly eliminated with continued operation of the mitigation system.
Necessary Diligence
A Phase I Environmental Site Assessment (ESA) is the standard by which property due diligence is completed. In 2013, the EPA changed that standard to require all environmental practitioners to make a determination of whether a project is free of potential vapor risk, based on past building use and what is known about the site through official property records. A Phase I ESA does not typically require sampling. If the ESA determines the property has a risk of vapor problems, the buyers are required to do some sort of intrusion testing, potentially leading to mitigation.
Because of this requirement, real-estate transactions drive the majority of vapor investigations and cleanups. It is simple economics—there is a buyer, a seller and a pot of money available to deal with the problem. However, we see some interest from people who are looking to position their land to sell or who intend to repurpose it someday and want to make sure it’s safe. For these types of vapor-mitigation projects, the place to start still is with the Phase I ESA.
Although costs vary greatly by building size and type, building owners should expect a Phase I ESA to cost between $2,000 and $4,000. If collection and laboratory testing of vapor samples is needed, it can likely cost between $10,000 to $40,000, depending upon the size of the property. Mitigation can vary widely based on the building size, use and specific situation. It’s worth noting that in some states, such as Minnesota, there are often grants or remediation funds available that allow for reimbursement of mitigation costs. Your state’s pollution control agency will provide more information.
There are ongoing costs associated with vapor mitigation, as well. There can be a substantial electrical cost associated with running a blower motor to maintain permanent and consistent vacuum under a building. Often there is a deed restriction placed on the title of the property that requires current and future owners of the property to maintain operation of the system.
Looking Ahead
Some states only require mitigation of vapors once they make their way into the breathing space of a building while others, such as Minnesota, require you to mitigate if there is a presence of subsurface vapors that have the potential of risk to building occupants. However, the trend is moving toward more proactive diagnosis and mitigation, especially as properties change ownership or intended use. A property that may have had a successful real-estate closing five or 10 years ago may not close today because vapors weren’t considered as much of a risk at that time. The best way to determine if your building is at risk is to proactively work with a trusted environmental practitioner to conduct a Phase I ESA and learn what your options are for your building.
As the problem of vapor intrusion continues to rise to prominence, the technologies and best practices of the industry will continue to evolve, as well. Often, mitigation systems must operate for the life of the building, but we, as an industry, will continue to find more efficient and cost effective methods of mitigating vapors in indoor spaces.
Photo: Wenck