Vapor Intrusion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 447

In finished or partially finished basements, it may be difficult to locate and seal
cracks, as these may be obscured behind floor and wall coverings. In the short-term
after application, some sealants will emit VOC vapors, which should be considered
prior to subsequent indoor air sampling and analysis.
10.6.1.5 Air Filtration
Indoor air quality can be improved using filtration units, for example a drum of
activated carbon fitted with a blower or fan that circulates indoor air through the
carbon, trapping VOCs and SVOCs. These filters typically use activated carbon to
trap VOC vapors, and come with an integral fan unit that circulates air through them.
They are readily available, can be set up and running in very short order, and provide
tangible results almost immediately. The activated carbon requires replacement on
a regular basis, which makes this technology generally less attractive for long-term
applications.
10.6.2 Methods/Technologies for Future Buildings
Brownfield re-development is a growing opportunity, but vapor intrusion concerns
must be considered and in some cases, may pose a potential risk to a planned or
hypothetical future building. The technologies described in Section 10.6.1 can be
used after building construction, but there are also several methods of mitigation
that can be incorporated in the building design or construction, as described below.
10.6.2.1 Intrinsically Safe Building Design
Podium style construction is increasingly common in low-lying areas that are prone
to floods, but this design may also be worth considering for redevelopment of land
with potential vapor intrusion concerns. Ground-level or underground levels may
be used for vehicle parking, and as such, would have adequate ventilation to man-
age vehicle exhaust, which also would minimize the potential for subsurface vapor
intrusion concerns.
10.6.2.2 Vapor Barriers and Ventilation Layers
Subsurface vapor control can be achieved by a vapor barrier and ventilation layer
beneath a building. Incorporating these features is relatively inexpensive if place-
ment occurs before the building slab is constructed and the utilities are placed.
The most common design consists of a highly permeable layer of granular fill with
vent pipes overlain by welded plastic sheets (geomembrane). The vent pipes are
connected to a common header that is connected to a blower that can either run
continuously, or be automated to run when sensors beneath the building indicate