[CPEO-MEF] El Toro and the potential for vapor intrusion

[Lenny Siegel <lsiegel@cpeo.org>]

EL TORO AND THE POTENTIAL FOR VAPOR INTRUSION
Lenny Siegel
December 27, 2004

In January, 2005,  large portions of the former El Toro Marine Corps Air
Station go up for sale. Because El Toro is a "Superfund" National
Priorities List site, with significant trichloroethylene contamination,
I have been asked whether I consider vapor intrusion a risk either to
the redevelopment plans or to the people who will live on or otherwise
use the property after transfer from federal ownership or control.

After reviewing a series of documents and visiting the base, I have
concluded that indoor air contamination is unlikely to be a problem at
El Toro because the land known to be contaminated with TCE is planned
for open space. Furthermore, the potential for vapor intrusion should
not impact the property auction because the TCE-contaminated sites have
been carved out of the sale parcels - they are being offered for lease.
Still, the Navy and regulatory agencies could take steps, such as air
sampling and the imposition of vapor-intrusion-specific institutional
controls, to enhance the level of protection for future residents and
users of the property.

El Toro consists of nearly 5,000 acres of land in Orange County,
California. It was the Marines' principal  jet fighter base on the west
coast. When El Toro was approved for closure in 1993, Orange County
initially planned to convert it into a commercial airport. However,
residents of adjacent communities objected, and they eventually won the
political battle. El Toro will be split among a federal enclave, a
"Great Park," and residential and commercial development.

For the Navy, El Toro represents an innovative, though not unprecedented
approach to base closure property disposition. Instead of transferring
lands to a reuse authority and completing a series of public benefit
conveyances, it has divided the non-federal portion of the base into
four sale parcels. In cooperation with the General  Services
Administration, it will auction those parcels on the open market. It
will be the responsibility of the buyers to make land available for
public benefit uses, as prescribed in the city of Irvine's planning
documents. See http://www.heritagefields.com/ for details.

The sale plan has national significance, not only as a precedent for
future sales - though it follows a smaller sale at nearby Tustin Marine
Corps Air Station - but because it could generate more than $1 billion
in revenues. The Navy plans to use that money to fund its Base
Realignment and Closure activities, including environmental cleanup.
However, El Toro does not follow the Navy's model for privatization of
cleanup. Because the base is relatively far along in the cleanup
process, the Navy will retain management of the cleanup even after
property transfer.

El Toro has two major volatile organic compound (VOC), primarily TCE,
source areas: Site 16 and Site 24. Both have contamination of soil, soil
gas, and "shallow" groundwater, but in this case "shallow" is more than
150 feet deep. Site 24 is the source of a three-mile-long off-post
plume, but fortunately the plume dives under a shallower water-bearing
zone as it leaves the property, thus posing no threat of vapor intrusion
to neighboring residents. The Navy has removed significant quantities of
VOCs from both sites using soil vapor extraction. It is treating the
off-post plume (from Site 24) in cooperation with local water districts.
The selected remedy for Site 16 is monitored natural attenuation with
institutional controls.

In June 2004, the Navy's contractor, Bechtel Environmental, completed a
technical memorandum evaluating indoor air risk above Sites 16 and 24.
Using soil gas measurements and standard modeling calculations, Bechtel
and the Navy concluded: "Total cancer risks at Sites 16 and 24 using
both U.S. EPA and Cal/EPA toxicity criteria for residential and
industrial scenarios are acceptable, or fall with the 10^-6 to 10^-4
risk range that may be acceptable depending on site-specific and other
factors considered appropriate for risk management decisions." 

Among the detailed findings, they found, "The estimated cancer risk for
a hypothetical resident adult exposed to indoor-air COPCs [chemicals of
potential concern] at Site 16 for 350 days a year over 30 years was
quantified at 3.2 x 10^-6 (using U.S. EPA criteria) and 5.7 x 10^-8
(using Cal/EPA criteria)." It also concluded, "The estimated cancer risk
for a hypothetical resident adult exposed to indoor-air COPCs at Site 24
for 350 days a year over 30 years was quantified at 7.8 x 10^-6 (using
U.S. EPA criteria) and 1.3 x 10 ^-8 (using Cal/EPA criteria)." The
provisional U.S. Region 9 EPA criterion  for TCE is significantly more
stringent that the promulgated California level.

In my view, those numbers - placing cancer risk above one in a million
using U.S. EPA's 2001 draft toxicity assessment - are neither cause for
panic nor reassuring enough to simply dismiss the potential for vapor
intrusion. That is, the modeled levels of TCE in air are high enough
that more sampling, including indoor and outdoor air, should be
conducted. Evidence elsewhere shows that the model often both
underpredicts and overpredicts air concentrations, so levels that even
approach the health standard should trigger sampling.

I do not, however, consider the potential for vapor intrusion at El Toro
to be a showstopper. The Navy has carved out, from the sale parcels, the
most contaminated areas, including Sites 16 and 24 as well as buffer
zones or at least 300 and 500 feet, respectively. Those properties will
be leased and conveyed only after remedies are in place.

Of course, the lease properties are slated for reuse and will be open to
the public. Still, the risk of indoor air exposures is minimal because
no residences will be built in those areas. The site 24 carve-out will
include an "Open Space - Exposition Center," and "Open Space - Sports
Park," and an Orange County "Institutional" use. I don't know exactly
what types of structures those entail, but I assume the people won't be
in those areas around the clock or even for long-term full-time work.
That is, the marginal risk that might be present will be mitigated by
the absence of structures.

To reinforce that assumption, I believe that the current land use plan
should be reinforced with enforceable institutional controls. Structures
in VOC-contaminated areas should be prohibited or restricted.
Restrictions could include the type and duration of use, or a
requirement to install inexpensive passive mitigation elements - such as
impermeable slab liners - during construction. There should be
continuing monitoring to ensure that the restrictions remain in place as
long as the contamination is present

Furthermore, in the absence of sampling, I am concerned that emissions
from these plumes might generate, as I believe has happened in my own
community, an outdoor toxic cloud that could be a source of continuing
low-level exposures in nearby areas slated for housing or, since it's
already in place, the California State University-Fullerton campus annex
near Site 16. Based on the limited data that is available, I doubt that
there is a serious problem, but in the absence of actual air sampling
I'm not prepared to tell students or prospective residents that
everything is OK. As I've argued elsewhere, outdoor air contamination
from subsurface sources can't be resolved through mitigation , but it
may be a reason to modify remedial strategies to accelerate removal or
degradation of soil or groundwater contamination.

Finally, some members of the local community, as well as consultants for
the city of Irvine, have argued that the Navy and the regulatory
agencies may have missed other important sources of contamination on the
5,000-acre base. I have seen no evidence that this is true, but given
the experience at other closing bases being switched from industrial to
residential use, I think it's likely that more problems will be found
when demolition, excavation, and construction occur. At that point, it
will be necessary to evaluate whether any of those new sources pose a
risk of vapor intrusion. Given the Navy's long history of professional
investigation at El Toro, I don't expect any new source to be as large
as Site 24 or even Site 16.

In summary, I am not satisfied with the Navy's outright dismissal of
vapor intrusion - to indoor or outdoor air - as a risk at El Toro. I
think it's unlikely to be a serious problem, but I believe air sampling
is necessary before ruling it out. The entire situation seems to be
saved by the reuse plan and the division of the property between sale
and lease parcels. The sections most likely to be sources of VOC vapors
are not being sold, and they are not planned for continuous human
presence. Measures, such as institutional controls, should be
implemented to keep it that way.


-- 


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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