[CPEO-BIF] Vapor Intrusion Policies Fall Short

[Lenny Siegel <lsiegel@cpeo.org>]

Vapor Intrusion Policies Fall Short
Lenny Siegel, CPEO
October, 2003

There is a fundamental shortcoming in existing vapor intrusion policies.
Most significant, those policies focus solely on the indoor air pathway,
instead of addressing the full range of sources, pathways, and receptors
at vapor intrusion sites. The data at such sites, the concerns of the
residents and employees of such areas, and analysis by technical experts
all suggest the broader approach.

According to a presentation by Robert Ettinger at a recent Groundwater
Resources Association of California technical conference, background
levels of indoor air contaminants often exceed air contamination from
underlying groundwater plumes and even may be above health-based
standards. He described this as a policy question, and neither Ettinger
nor any of the other experts presenting at the conference were willing
to tackle this issue.

In my community of Mountain View, California - a test case for U.S.
EPA's Vapor Intrusion Guidance - we can't escape the question, however.
Ambient - I prefer this term to "background" - levels of TCE and PCE,
above EPA screening levels, have been found at local school and
playground sites. Responsible parties suggest that if outdoor air
concentrations exceed indoor air contamination, then no further action
is necessary, even though my neighbors continue to breathe unsafe air.
Furthermore, test results at one dwelling unit with significant indoor
air contamination show that the common "remedy" of venting actually
increases outdoor air contamination.

Since ambient  concentrations of TCE and PCE do not arise naturally, it
is necessary to determine the sources, analyze the risks, and if
concentrations exceed health-based goals, take steps to eliminate or
reduce exposures. Based upon preliminary data in Mountain View, I
identify three POTENTIAL descriptions of our vapor intrusion problem.

Three Scenarios

1) Elevated health risks may exist ONLY in buildings directly above or
within 100 feet of shallow groundwater plumes of volatile organic
compounds. We have some buildings where concentrations have been
measured well above the old cleanup goal, so we know that there are
indoor risks that should be addressed promptly, but that's not enough.

2) Ambient levels throughout Silicon Valley might be elevated. This has
been suggested by some regulators and some responsible parties, and it's
a scary possibility. Imagine a million or more people, including the
most susceptible populations, exposed to unhealthy concentrations of TCE
and/or PCE around the clock, for decades. However, I don't think the
sampling supports this conclusion.

3) Most likely, TCE and maybe PCE at levels above EPA screening levels
are present in the neighborhood of shallow groundwater plumes. This
would mean that tens of thousands of people are probably being exposed a
good percentage of the time. Contamination is rising inside buildings
and outside buildings, as well as coming from other unknown sources, at
a fairly steady rate, because these compounds break down and diffuse
rather rapidly. That is, the presence of ambient concentrations suggests
that there is are continuing sources, and those sources should be addressed.

If I'm right, then current strategies for both sampling and remediation
are either wrong or incomplete. As currently practiced, outdoor air
sampling is conducted purely for reference purposes. It is not designed
to determine the extent or timing of outdoor concentrations of volatile
organic compounds, nor to identify potential sources. If the outdoor
contamination is treated as a potential risk factor, then sampling
should attempt to bound the atmospheric plume, and samples should be
timed to evaluate the impact of weather and industrial activity on
readings. Sampling should help evaluate whether groundwater treatment
systems or continuing industrial activity are among the likely sources
of contamination. While this may mean that cleanup program need to go
"out of bounds," measuring emissions from industry not under its
jurisdiction, I believe it can be justified as part of the effort to
rule out non-waste sources.

If indeed, as I believe, outdoor air must be addressed, then it may NOT
make sense to solve indoor air problems by venting indoor or subslab
contamination. Moving contamination around is not a solution. Instead,
the cleanup team should consider removing contaminated soil or using
techniques, perhaps air sparging or bioremediation, designed to remove
or break down near-surface contamination. Much of the effort to improve
the cleanup to TCE and PCE has focused on their tendency to sink within
aquifers. That's still an important problem, but near-surface cleanup
may require earlier responses.

Preferential Pathways and Land Use Controls

Moreover, evidence from the field suggests that preferential pathways
are often the primary pathway. For example, at a new building (with
engineering controls) here in Mountain View, recent sampling discovered
unexpectedly high levels of indoor TCE. The likely culprit: a connection
to an unprotected utility vault. The models for predicting indoor air
contamination break down where there are preferential pathways, and
there may be such pathways at virtually every site. Furthermore, such
pathways exist outdoors as well as indoors. Even if the soil above
plumes tends to trap or degrade volatile organic compounds, preferential
pathways may be large enough to drive a Hummer through. That is, a small
hole or crack may defeat the mechanisms that might prevent vertical transport.

Other than at the building with the unprotected utility vault, the new
commercial/office buildings in Mountain View, built directly above high
concentrations of volatile organic compounds, report levels of indoor
contamination comparable to outdoor readings. That is, the engineering
controls of impermeable slabs and positive air pressure appear to be
effective. I don't believe the studies have shown which of those is most
responsible. Still, in earthquake country there is no guarantee that the
slabs will remains impermeable, and over the life of the buildings there
is no guarantee that the ventilation systems will not be changed.

Thus, even effective engineering controls must be integrated into
long-term stewardship plans that 1) legally require the controls as part
of the remedy, 2) provide for the long-term monitoring of their
protectiveness, and 3) provide for additional remedial action if they
prove unprotective. Yet to my knowledge none of the Mountain View sites
have any registered institutional controls related to vapor intrusion.
If construction and ventilation are regarded as ways to limit human
exposure, then they should be legally incorporated into the cleanup.

Detection Limits and Other Compounds

In addition, it is difficult to project risk and design remedies when it
is difficult if not impossible to measure air contamination down to
preliminary remediation goals. Yet in Mountain View, EPA reports a
detection limit roughly an order of magnitude above that goal. One of
the responsible parties uses a lab that claims a lower detection limit,
but it is still above the health-based goal. This suggests a technical
priority: A new detection method or technology should be developed to
bring the detection limit in line with the levels necessary to
characterize and remediate these sites. It may be beyond the reach of
foreseeable technologies, but community members seek - for their own
assurance - real-time or near-real time monitoring systems that detect
low concentrations of such contaminants, as well.

The focus of the Mountain View investigations is TCE, even though PCE is
found in the outdoor air in similar concentrations. One of the reasons
is that EPA has completed a draft toxicity assessment for TCE, but not
for PCE. It would be a mistake to focus resources on one contaminant
while ignoring other, similar compounds if there is a chance that
further toxicity assessments would lower the health-based goals for the
other compounds. At least, those responding to vapor intrusion should
consider approaches that deal with a wide range of compounds, to avoid
the chance that they may have to come back to a site later to deal with
those ignored the first time around.


-- 


Lenny Siegel
Director, Center for Public Environmental Oversight
c/o PSC, 278-A Hope St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/961-8918
<lsiegel@cpeo.org>
http://www.cpeo.org

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