Vapor Intrusion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 435

Table 10.2 Summery of main benefits and limitations of the various sample collection options

Compartment General description/comment Benefits Limitations

Groundwater Groundwater monitoring wells are installed

outside the building footprint. Screened
interval must cross the water table, and
preferably be short.

Is not intrusive into residence.
Simpler access agreements
Sampling protocols are more mature than
soil gas equivalents

May not be representative of conditions
immediately beneath building
Existing wells may not have shallow and
short screens
Requires extrapolation or modeling to
estimate indoor air concentrations

Sub-slab soil gas Probes are drilled through building
foundation to collect soil gas sample.

More representative of composition of
subsurface vapors that may migrate to
indoor air.
Impacts of background sources of
contaminants are less significant

Intrusive. Requires access to living area,
and may cause minor damage to flooring
Multiple samples (in time and position) are
necessary to estimate representative
concentrations beneath entire floor slab
Requires extrapolation or modeling to
estimate indoor air concentrations

Soil gas Probes are installed outside of building

footprint. Typical depths range from 5 to
30 ft/10 m (but can be deeper).

Is not intrusive into residence. Simpler
access agreements
Impacts of background sources of
contaminants are typically not
significant, although equipment
contamination may be significant
Soil gas program may be used to quantify
the significance of biodegradation.

May not be representative of conditions
immediately beneath building because of
rain-shadow beneath building, and
possible impedance to O 2 recharge under
floor slab.
Requires extrapolation or modeling to
estimate indoor air concentrations

Indoor air Typically, 8 or 24 h sample collected from

basement or living area of building

Evaluates the concentration of
contaminants of concern at the point of
exposure.

Intrusive. Requires access to living area
Difficult to distinguish background impacts
on analytical results. The measured
concentration may not be due to vapor
intrusion pathway.
Multiple samples (in time and position) are
necessary to estimate representative
concentration for a 30 year exposure
scenario (or longer-duration samples)