Vapor intrusion is relatively new to the facility regulatory scene, but
its effects which can be harmful to human health due to exposure to
volatile organic compounds (VOCs), have become a concern when
acquiring or changing the use of property.
What is vapor intrusion?
Vapor intrusion is the transfer of a volatile contaminant(s) in its
gaseous form through the subsurface soil into a structure via cracks in
walls and floors as well as other penetrations such as sewer lines and
floor drains. Vapor intrusion assessments aim to identify suspected
risks and help lead to the development of mitigation plans to address
assessments at sites
impacts by collecting
soil gas samples outside the footprint of
or beneath a building
slab primarily via
two methods, hydraulic push-probes into
site soil or through a
Vapor Pin® installed
through a floor slab.
Samples are commonly collected into
which are under
vacuum and opened
once connected to the
probe or Vapor Pin®.
Samples are analyzed
for VOCs and the
results are compared
to the state or federal
criteria. These criteria have been established to assess risk based on the
use of a site (i.e. industrial or residential).
Recognized Environmental Conditions (RECs) originating from past
or threatened releases of petroleum products, solvents and/or other
hazardous substances can be identified during a Phase I Environmental Site Assessment (ESA) performed at a Site. A Phase II or Limited
Site Investigation might be conducted to assess potential impacts to
surface or subsurface media (soil, groundwater, and soil gas). Impacts
identified during a Phase II or LSI can create potential exposure issues
through vapor intrusion.
When elevated concentrations of VOCs are detected beneath a building
at concentrations that warrant some form of mitigation, there are sev-
eral methods used to address the vapor risk for both new construction
and existing buildings. Mitigation systems can include passive barriers
consisting of a rolled or spray-applied membrane, barriers with passive
venting, or active sub-slab depressurization. The active systems are
much like radon mitigation systems using a blower to exhaust vapors
from beneath the slab to the atmosphere. These methods vary in cost
and are largely dependent on building use, design, and size.
• Passive Barriers: Relatively
low cost and
are common in
new builds where
is a low-risk
consist of a 10-
to 20-mil thick
beneath the floor
are taped and/or
• Passive Ventilation: Barriers with passive ventilation include perforated PVC pipe beneath the barrier and is vented above the building roofline. This is generally installed at a site where risk from vapor intrusion
is elevated but does not warrant active venting.
•Active Ventilation: Active ventilation includes a fan or blower
connected to the perforated piping system to assist with movement of
air beneath the slab and exhaust impacted air above the roofline. The
system is often installed with a series of sumps to depressurize the sub-slab.
Case Study: Design and oversight during installation of a sub-slab
A client was in the process of selling a portfolio of multi-family
Photo showing collection of soil gas sample
outside of building footprint via push-probe
using Post-run Tubing methods and 1-liter
Passive barrier using spray-applied barrier. A grid work of venting is
located beneath the barrier.
Photo showing collection of soil gas sample outside
of building footprint via push-probe using Post-run
Tubing methods and 1-liter Summa Canister.
– Risks and Solutions
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