The Minnesota Pollution Control Agency’s (MPCA) policies regarding vapor intrusion are changing. If pre-construction soil gas samples exhibit volatile organic compound (VOC) concentrations exceeding ten times the Intrusion Screening Values (ISVs), the MPCA Voluntary Investigation and Cleanup (VIC) program may require follow-up sampling in addition to installing sub-slab vapor mitigation systems and/or vapor barriers in newly constructed buildings. New requirements may also include sub-slab sampling at discrete locations through the newly constructed slabs. Further response actions such as indoor air sampling and upgrading to active venting may also be required if follow-up post-construction sub-slab VOC concentrations are elevated, such as exceeding ten times the ISVs.

An underground parking garage is a common example of a site where post-construction sub-slab sampling may now be necessary. In the past, parking garages generally weren’t required to have sub-slab vapor mitigation response actions due to the presence of vehicle exhaust venting systems. Now, it appears that the MPCA VIC program may require sub-slab vapor samples for all structures to verify post-construction soil vapor concentrations.

There are multiple options for sub-slab sampling in newly constructed buildings. Sample ports can be installed during, or after slab installation. There are pros and cons associated with both of these approaches. Because of the complexity in performing post-construction sub-slab soil vapor sampling and the rapidly changing regulatory environment, Braun Intertec develops recommended approaches for this work on a case-by-case basis. If you have a project where the MPCA is requiring sub-slab soil vapor sampling, please contact Chris McElligott or one of our vapor mitigation staff members for more information.