Re: [CPEO-BIF] TCE Found Inside Mountain View Offices

[Lenny Siegel <lsiegel@cpeo.org>]

To me, the discovery of significant concentrations of trichloroethylene
(TCE) in the indoor air of commercial buildings in Mountain View came as
somewhat of a surprise. For many years, I've believed that the only
pathway of concern has been our local drinking water supply. I've even
commented, "People all over Silicon Valley live or work above TCE
plumes." Vapor intrusion, I believed, was an unusual threat.

The studies described in the August 29, 2003 Mountain View Voice show
otherwise. The data that I've had a chance to review suggests two major
conclusions. First, TCE is wafting up through the soil over a large
area. Second, mitigation techniques, such as solid slabs and venting,
help. TCE levels high enough to trigger immediate action have been found
primarily - perhaps exclusively - inside buildings with foundation
cracks or utility tunnels. But lower levels, some above EPA Region 9's
provision preliminary remediation goal (PRG), have been detected both
outdoors and within buildings constructed with the most modern
mitigation techniques built in. That goal sets .048 micrograms per cubic
meter as the risk threshold for one-in-a-million additional cancers in
an occupational scenario, based upon EPA's draft TCE toxicity assessment.

I support EPA's immediate emphasis on mitigating exposure through
construction and additional venting, but that's not enough. If occupants
of newer buildings - where vapor concentrations are low, but often
measurable - are to be "safe" in the long run, the performance of
built-in mitigation must be guaranteed for the life of the plume. That
is, as long as underground contamination continues to migrate upwards,
the responsible parties or owners/managers of buildings with either
protective designs or new mitigation should regularly monitor air
concentrations and ensure that new cracks or other openings do not
trigger new releases. These long-term land use controls should not be
voluntary. They should be mandatory, recorded in amended decision documents.

Furthermore, the best way to reduce the long-term risk is to attack the
source, because mitigation is uncertain, there are many pathways, and
continuing or at least repeated exposures occur over a broad area. While
it is difficult to totally remove TCE from contaminated aquifers because
in liquid form it tends to sink, it may be technically feasible to
reduce concentrations in upper shallow aquifers, as well as the soil, to
dramatically reduce vapor migration.

Across the country, people may be living and working above hundreds of
shallow aquifers containing TCE and other volatile organic compounds. To
protect them, it's essential to act quickly to develop detection methods
that can measure contamination quickly at the low concentrations
highlighted by the new toxicity assessment, and to develop and
demonstrate treatment and removal technologies that reduce the potential
for vapor migration.

The good news is that TCE vapor is rarely found at levels that pose an
immediate health risk. That gives us time to solve the problem, but it
must not lull us into complacency.


-- 


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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