Vapor Intrusion occurs when chemical vapors migrate from contaminated soil and groundwater into the basements or foundations of buildings. The regulatory atmosphere for vapor intrusion issues has changed dramatically over recent years, resulting in an increased focus on this issue for commercial/industrial property owners and developers.
Our site assessment team helps our clients minimize risks due to vapor intrusion issues throughout the project life cycle. Pinnacle personnel are experienced in the identification of vapor encroachment conditions in accordance with ASTM standards so that the identification of potential liabilities can be made. Our field personnel are experienced in performing vapor sampling from temporary soil vapor borings exterior to the building slab, and if required, interior sub-slab vapor sampling and/or indoor air sampling.
- Mitigation System Design
- Mitigation System Installation
- Mitigation System O&M Plans
- Site Characterization
- Exterior Sub-Slab Soil Vapor Sampling
- Indoor Air Sampling
- Passive Soil Vapor Sampling
- Vapor Intrusion Building Reviews
Pinnacle’s senior engineering staff has been addressing soil vapor intrusion issues for clients for over 15 years under a variety of regulatory environments, including several U.S. states and European countries. Pinnacle can evaluate soil vapor results and provide a risk management strategy in line with the client’s best interests. There are often many complexities in understanding the vapor migration pathways at sites with existing (and sometimes very old) buildings with complicated building envelope issues. Pinnacle can perform the design and installation of vapor intrusion mitigation systems, conduct and evaluate post-mitigation performance testing, and write operation and maintenance plans.
Pinnacle has provided valuable consulting services recently to several clients who have been impacted by the changing regulatory environment surrounding vapor intrusion issues. This includes the use of both traditional and cutting edge investigation techniques to differentiate vapor intrusion sources which have made a major impact on vapor intrusion liability management issues. Our approach is to provide the knowledge and experience to properly assess and address vapor intrusion impacts in a cost-effective manner.
WHAT IS REQUIRED?
The Minnesota Pollution Control Agency (MPCA) has developed Guidance including the Best Management Practices for Vapor Investigation and Building Mitigation Decisions and Intrusion Screening Values (ISVs) for evaluating potential risks from vapor intrusion (Feb. 2017).
Two rounds of seasonal sub-slab soil vapor samples are required to demonstrate that a building is not a risk for vapor intrusion (and to get a letter of assurance from the MPCA):
- One sampling event in the heating season (Nov. 1 through Mar. 31)
- One sampling event in the non-heating season (Apr. 1 through Oct. 31)
If sub-slab sampling is conducted, a building walkover performed by an experienced vapor intrusion professional is critical to document that the use of the new 33X ISV soil vaporscreening levels is appropriate given the building conditions.
*Seasonal sampling must occur at least 30 days apart.
UPDATED ATTENUATION FACTOR, UPDATED ISVs
The ISVs represent a concentration in indoor air which does not present an unacceptable risk to building occupants. The "attenuation factor" takes into account the barrier provided by a concrete slab and separation distance between the soil vapor and the indoor areas. The MPCA guidance increases the acceptable soil vapor concentration from 10X ISV to 33X ISV. Additionally, the ISVs for specific chemicals have been updated multiple times, primarily based on toxicological profile updates.
THE PROPERTY TRANSFER PERSPECTIVE
Phase I Environmental Site Assessments are commonly conducted as part of property transactions or at the request of financing institutions. Attention to potential soil vapor issues in now required for Phase I's. As a rule of thumb, sites with soil and/or groundwater that are potentially impacted with chlorinated volatile organic compounds like tetrachloroethene (PCE) or trichloroethene (TCE), which can be associated with dry cleaner operations or industrial solvent use, typically result in more rigorous soil vapor investigations.
*New MPCA Best Management Practices for Commercial and Industrial Property Mitigation Guidance is currently under development, with an expected publication timeline of 2017-2018.
This video, which was made by the Minnesota Pollution Control Agency, demonstrates the steps and methods for collecting a representative sub-slab vapor sample from beneath a building's concrete floor slab.
*Credit: Minnesota Pollution Control Agency
If you're in need of assistance with a project, or would like to learn more about our Vapor Intrusion services, contact:
Keith Rapp, PG
Office: 763.277.8422 Cell: 612.382.3763
Lyndsey Howard, PE