18 Jul Vapor intrusion mitigation: Bringing contaminated properties back to life – safely
As North Carolina continues to grow and thrive, property development plays a major role. Sometimes a property’s previous use can create stumbling blocks to development, particularly if a site has been contaminated. At many sites, this contamination could reside near or beneath an existing or proposed structure and may lead to vapor intrusion concerns.
For challenging properties, vapor intrusion may be a substantial concern, and can require remediation or mitigation to aid in development. Ben Whitley, PE, is an environmental engineer at WithersRavenel who provides clients with vapor intrusion services.
“Contamination that resides in the soil or groundwater can travel vertically upwards in the vapor or gas phase,” Whitley said. “In addition, horizontal migration of contamination from on-site and offsite releases can potentially be an issue. If the contaminant source is significant, and if building conditions are right, those vapors can travel into the interiors of building spaces.”
Situations where services make sense
Vapor intrusion services often come into play on industrial or commercial properties that previously used or stored chlorinated solvents or petroleum products.
“Chlorinated solvents are a major source of contamination that usually requires vapor intrusion mitigation almost by default,” Whitley said. “Chlorinated solvents are pretty nasty actors. Some of the compounds that they can break down to in the environment are even worse than the chemicals that the contamination started with.”
“Industrial facilities can have a wide range of contaminants depending on what the processes and the activities were. Dry cleaner products are also a very common source of contamination. Historically, they used several different types of solvents.” And although properties where petroleum was used and/or stored, such as gas stations or bulk terminals pose less of a contamination risk, vapor intrusion mitigation can be required for those sites as well. Even sites adjacent to these types of properties can become contaminated and should be investigated.
These contaminated properties can often be enrolled into the North Carolina Department of Environmental Quality (NCDEQ) Brownfields program. NCDEQ defines a Brownfields site as “an abandoned, idled or underused property where the threat of environmental contamination has hindered its redevelopment.” And this is where WithersRavenel’s vapor intrusion services come into the picture.
“We can provide assessment, whether that is sampling and investigating soil and groundwater or subslab soil/gas sampling to evaluate whether or not a vapor intrusion concern is present on a property,” Whitley said. “If it is potentially a concern, then we can offer design and consultation services in terms of mitigating that risk.
“The path forward and the options are site specific, whether it is an existing structure or new construction over a potential contaminant plume. We can tailor the solution as necessary.”
State provides vapor intrusion guidance
Whitley said that NCDEQ is developing a more robust guidance document for the procedures necessary to rehabilitate a Brownfields site. The program is driving a greater focus on vapor intrusion, assessment, and mitigation as a safeguard for not only the people who ultimately use a redeveloped Brownfields site, but also the site owners and companies like WithersRavenel who work on the property’s vapor intrusion project.
When designing a system and implementing it, some challenges are obvious. You can’t see vapor and you don’t always smell it. Some of the concerns are very long-term in nature; an occupant could be in a building for years and not see the effects of vapor intrusion. Additionally, while the Environmental Protection Agency (EPA) has been around since 1979 and mostly focused on surface water contamination and groundwater contamination, vapor intrusion services have really only been formalized in North Carolina for a little more than 10 years, and NCDEQ is continuing to update guidance and those regulations.
For WithersRavenel, the process at a contaminated site begins with research.
“There’s usually a way to figure out the source of contamination, such as researching site usage history, records and investigating,” Whitley said. “Occasionally, there may be a site that was abandoned for 50 years, there may not be anyone around who knows anything about it and spotty written records of what happened there or where certain tanks may be or underground systems.” That is where WithersRavenel’s Subsurface Utility Engineering (SUE) professionals can help. Using Ground Penetration Radar (GPR), they can find what lies beneath to better inform the environmental team.
After the investigation, Whitley said removing the contamination source so it doesn’t continue to get worse should be the next step, if possible. The investigation then may need to continue to determine how widespread the contamination is.
“How deep is the contamination? Laterally how far has it spread? Who is it affecting at present? Once you’ve characterized the contamination and understand the risk, the next step is designing a system so people are not exposed.”
“It’s good that we have the Brownfields program to allow beneficial reuse of some of these areas,” Whitley said. “Some of these places become unusable because of the liabilities and the contamination present. The Brownfields program steps in to require the vapor mitigation systems that make these properties safely reusable.”
When doing nothing makes sense
But sometimes the best decision, and NCDEQ agrees, is not to remediate a contaminated site at all.
“The general approach from NCDEQ is not necessarily to remediate contamination,” Whitley said. “They are becoming more of a risk-based program. After assessment and investigation to better characterize and understand the contamination, sometimes it is more economical and just as safe to leave the contamination in place, and rather install a vapor mitigation system as a barrier to protect occupants of buildings.
“Cleanup of contamination is very expensive in a lot of cases. Sometimes it is more economical and reasonable from a health and safety standpoint to put a barrier in place so people can’t come into contact with contaminants or breathe it. Or, for example, putting a restriction in place so the groundwater isn’t being exposed to somebody. NCDEQ is taking more of a common-sense approach than a wholesale ‘let’s clean it all up’ approach.”
Regardless of the amount of vapor intrusion services a client needs, Whitley is confident that the environmental team at WithersRavenel can create a site-specific solution. “We have a good group of people with a lot of experience, technical knowledge and know-how,” he said.
Do you have a need for WithersRavenel’s vapor intrusion mitigation services? Contact Ben Whitley at (919) 535- 5141 or firstname.lastname@example.org.