Daily Environment Report  [Printer-friendly version]
September 20, 2004


[Rachel's introduction: People involved with the cleanup or
redevelopment of sites contaminated with volatile organic compounds
are facing a new environmental challenge, vapor intrusion, which
occurs when volatile compounds move up through cracks, gaps, or pores
in soil and foundations into homes, other buildings, and even the
outdoor air.]

By Lenny Siegel**

The characterization and cleanup of vapor intrusion at sites
contaminated with volatile organic compounds (VOCs) is the new
frontier of environmental response. Most vapor intrusion responses
have focused on the direct vertical transport of contamination into
overlying homes, but increasingly it is being recognized as a
neighborhood phenomenon, both indoor and outdoor. The most common VOC,
trichloroethylene (TCE), has been identified in at least 852 of the
nearly 1,500 sites on the superfund National Priorities List and is
found at thousands of other sites across the country. No one yet knows
how many of the sites that have TCE intrusion pose a risk to public

The vapor intrusion problem also exists at sites where soil has been
excavated and groundwater treatment remedies are in place. At these
sites, regulatory agencies and responsible parties are re-opening
their programs to consider this previously ignored exposure pathway.
Furthermore, the presence of VOCs in groundwater or soil also presents
a challenge for development or redevelopment. There are no clear rules
of thumb for determining when or how sensitive uses, such as day-care
centers, homes, and schools, should be located above sites
contaminated by carbon tetrachloride, perchloroethylene, TCE, and
related compounds.

One of the communities in which vapor intrusion is rising to the
surface is Mountain View, Calif., my community--the community where I
started learning about hazardous substances nearly 30 years ago. The
response to detected vapor intrusion at four distinct but neighboring
Mountain View sites is breaking new ground. All stakeholders are
learning a great deal about the nature and extent of vapor intrusion,
as well as what can be done about it.

I. Background

In the early 1980s, following the discovery of TCE pollution from
underground storage and waste tanks at a Fairchild Semiconductor
facility in south San Jose, Calif., environmental regulators asked
other Bay Area electronics plants to look for contamination, too.
Throughout Silicon Valley they found it. One of the largest chemical
plumes was found in the Mountain View industrial area that was the
birthplace of the commercial semiconductor industry, where Fairchild
Semiconductor, Intel, and Raytheon Semiconductor got their start, all
of whom are among the responsible parties at the site.

Today the area is known by the three streets that, along with the
Bayshore Freeway (Highway 101), bind most of the offending
facilities--"The Middlefield-Ellis-Whisman (MEW) Study Area." Covering
300 acres, the MEW study area now hosts offices for firms such as
Netscape, Nokia, Verisign, and Veritas.

Led by the Silicon Valley Toxics Coalition, the local community
successfully campaigned to get the Environmental Protection Agency to
add the MEW area to the National Priorities List in 1986. In 1987, EPA
also added the 2,200-acre Moffett Naval Air Station to the National
Priorities List not only because it contributed to the MEW plume but
because it also had created a couple dozen other contaminated sites.
The Navy turned over most of the naval air station to NASA in 1994,
but it retained responsibility for addressing most of the
contamination released during its tenure.

In the early 1990s, EPA's Resource Conservation and Recovery Act
program began working with GTE Sylvania, which found three smaller TCE
plumes on its 75-acre property. GTE lies just south of the MEW area,
and the company worked hard to keep its contamination and legal
situation separate from the larger, multi-source superfund problem

In the late 1990s, the Navy found a previously undocumented plume
under the 72-acre Orion Park military housing area, now owned by the
U.S. Army. The source of that plume still is subject to debate among
the local responsible parties.

The regulatory agencies and responsible parties gradually embarked on
a comprehensive cleanup of the MEW area that included soil removal,
underground "slurry wall" barriers, and the installation of "pump-and-
treat" systems. The goal was to protect the deep aquifers that supply
a fraction of the Mountain View water supply. Still, because of the
difficulty inherent in removing TCE from groundwater, EPA's cleanup
standards will not be met for decades.

To further ensure the public would not be exposed to TCE and other
contaminants, the city of Mountain View relocated a drinking water
supply well and undertook routine water testing. Long-term exposure to
low levels of TCE is believed to cause cancer, liver disease, and
neurological problems, plus a host of other ailments.

A. Community Gets Involved

Beginning in 1990, the Navy invited community activists to meetings to
learn about and oversee its superfund cleanup. The Moffett Field
Technical Review Committee, now the Restoration Advisory Board, has
become the model for about 300 such advisory groups at military bases
across the United States, as well as dozens of similar bodies at
civilian contamination sites. At meetings that occur every other
month, community volunteers, local officials, state and federal
regulators, representatives of the Navy, and other responsible parties
meet to discuss contamination and cleanup plans. Several times since
the Restoration Advisory Board's inception, local activists have used
this cordial body to influence the Navy's cleanup activities at

B. Reusing the Middlefield-Ellis-Whisman Site

As Silicon Valley moved from chip manufacturing to software
development, the MEW area was rebuilt. New buildings in the area
relied on "impermeable" slab foundations and positive air pressure to
protect occupants from the poisons below. The redevelopment was
praised, and in October 2000, EPA featured Netscape's MEW campus on
the cover of its brochure, "Reusing Superfund Sites."

Meanwhile, at the GTE site, the city of Mountain View approved an
award-winning planned community of more than 500 townhouses and
single-family residences centered around a new Valley Transportation
Authority light rail station. The homes quickly sold in 1997 during
the "dot-com" boom. In fact, people camped out to form a line at the
sales office when properties first went on the market. Townhomes
initially fetched about $350,000 in 1997, and by early 2003, when the
vapor intrusion scare struck, units were selling for $200,000 to
$300,000 more.

In Mountain View, compared to many other polluted communities, the
system seemed to be working. Still, residents and MEW-area employees
wondered about the effects of the toxic releases being emitted by the
air strippers that were part of the groundwater extraction systems in
the area. Small concentrations of volatile compounds escaped from
these devices via contaminated groundwater pumped from below and
wafted into the local atmosphere. Three such air strippers, looking
like Disney's Rocket-to-the-Moon ride, stood out like sore thumbs.

At a May 2001 meeting, EPA officials told community members not to
worry. Though the air strippers released untreated TCE directly into
the atmosphere, the concentrations were too low to cause any health
concern, according to those officials.

Not all community members were convinced. In 2002, when residents
adjacent to MEW counted five cases of Parkinson's disease on one
residential block, they suspected TCE was responsible.

II. Vapor Intrusion Rises to the Surface

In 1999, NASA announced plans to create a research park on the former
Navy property, centered on the regional TCE plume. It conducted
environmental studies in support of that plan and detected TCE vapors
inside some of the Navy's old buildings. That information was not
widely circulated. After the Navy in October 2000 discovered TCE
contamination just 10 feet below the Orion Park military family
housing complex, however, members of the Moffett Restoration Advisory
Board expressed concern the contamination might be entering the homes.
They called for indoor air sampling.

Then two developments on the national level changed the game.

First, in January 2002, the Denver Post published a lengthy series
showing how indoor air sampling ordered by the state of Colorado had
found significant levels of TCE in homes where the computer model
recommended by U.S. EPA had predicted little or no contamination
inside. As a result, EPA began a national effort to understand and
respond to what became known as "vapor intrusion."

Volatile compounds in shallow groundwater vaporize and rise. Vapor
intrusion occurs when these volatile compounds move up through cracks,
gaps, or pores in soil and foundations into homes, other buildings,
and even the outdoor air. The original cleanup programs at GTE, MEW,
Moffett, and thousands of other potential vapor intrusion sites did
not fully consider this potentially hazardous pathway.

A. EPA's Draft Toxicity Assessment

The second development that changed the game occurred in August 2001
when EPA released its draft toxicity assessment for TCE. It found
children were more susceptible to TCE exposure than adults, and TCE
was five to 65 times more toxic than previously believed.

EPA's Science Advisory Board peer review praised the "groundbreaking"
assessment, saying, "We believe the draft assessment is a good
starting point for completing the risk assessment of TCE. The Panel
commends the Agency for its effort and advises it to proceed to revise
and finalize the draft assessment as quickly as it can address the
advice provided in this report." 2

EPA Region IX took the draft toxicity assessment seriously. In 2002,
it adopted new, more stringent screening levels for TCE in both water
and air. The new air screening level in residential or "unrestricted
use" scenarios, corresponding to one excess lifetime (30-year) cancer
among a million people, is 0.017 micrograms per cubic meter. The old
screening level in Mountain View, based upon California's standard, is
0.96 micrograms per cubic meter. When EPA calculated the new levels,
it did not have the technology to measure such low concentrations
accurately. However, consultants for most of the responsible parties
in Mountain View gradually have developed techniques to match the new

Most other EPA regions also adopted more stringent screening levels
for TCE, though not all are aggressively investigating vapor intrusion
sites. However, because the assessment has not been finalized, the
regions face limits in imposing those numbers on responsible parties.

If the new numbers officially are promulgated as a drinking water
standard--the maximum contaminant level or MCL--it will force cleanup
projects to pump-and-treat longer or adopt innovative remedies to
address the contamination. At locations where traces of TCE are found
in water supplies, the new standard will require more treatment or the
utilization of alternate water sources. The most immediate impact of
these more stringent standards, however, will be at sites where
shallow contamination is intruding to the surface as vapor because the
vapors already have a direct pathway to human receptors.

In spring 2002, the Navy agreed to conduct air sampling at Orion Park.
It found low concentrations of TCE both indoors and outdoors. Though
the Navy still doubts underlying groundwater pollution is the source,
public concern has grown. Local residents are worried about TCE
exposure, whether caused by vapor intrusion from cleanup sites or
landfills, releases from treatment systems, or continuing industrial

Sampling Simplified

Historical data on groundwater contamination in the most shallow
aquifer, taken from monitoring wells or direct punch measurements, are
plotted on a contour map. For TCE, concentrations over or within about
100 feet of the 5 parts-per-billion level (the promulgated drinking
water standard) usually are used to predict those areas that might
have significant vapor intrusion. However, there is some evidence,
particularly when preferential pathways are present, a lower
concentration should serve as the guide. In Mountain View, some have
questioned whether groundwater samples have been taken at enough
locations to draw accurate contours in the plume "border" area.

Probes are inserted into the soil underneath and near the perimeter of
structures to measure soil gas concentrations. In the absence of
preferential pathways, soil gas concentrations are a good predictor of
indoor air contamination. Most regulatory agencies use the Johnson-
Ettinger model to predict indoor air concentrations from soil gas
readings. In the absence of structures, soil gas measurements may be
the only way to estimate potential vapor intrusion into new

Using "Summa" vacuum canisters, which look like stainless steel
softballs or bowling balls, indoor or outdoor air is collected over
multiple eight- or 24-hour periods and sent to labs for analysis,
along with meteorological data. Before sampling, units are cleared of
people and potential chemical interferents, and they are sealed from
outside air. Great care must be taken to avoid contamination of the
canisters and the sample.

B. The Test Case: Mountain View

With the Mountain View community expressing increasing alarm about TCE
in the air, EPA Region IX decided to make Mountain View a test case
for its new approach to vapor intrusion and TCE toxicity. It convened
a public meeting in January 2003, and more than 400 people showed up.
EPA and the responsible parties--GTE, the Navy, and the group of MEW
companies--began new sampling programs to detect TCE and similar
compounds in indoor air with a few outdoor samples taken for

The parties also shut down all the unfiltered air stripping systems in
the area, eliminating the releases they had found acceptable two years
earlier. They replaced most of the air strippers with water filtration
systems, but a number of Mountain View residents expressed concern
that the filters from Mountain View would be shipped out of state for
incineration, affecting the health of other, poorer communities.
Unfortunately, no one conducted outdoor air sampling before the air
strippers were shut down.

With support from EPA and the responsible parties, residents formed
the Northeast Mountain View Advisory Council to review plans and
oversee responses. Each month EPA project managers brief the advisory
council on site progress, and community participants offer suggestions
for strengthening the program. Notably, the Northeast Mountain View
Advisory Council members have urged EPA and the responsible parties to
go beyond the conventional, limited notion of vapor intrusion and
consider all sources, receptors, and pathways, and adapt their
investigative and remedial strategies as new information becomes
available. The advisory council members take what they learn back to
City Hall, homeowners' associations, and parent-teachers associations,
and the local weekly paper, the Mountain View Voice, covers its

Because TCE in air dissipates due to degradation (with a reported
half-life of four days), advection (wind), and dispersion, there must
be persistent sources in the northeast Mountain View area. While
investigators still may find additional active sources, it is more
likely the sources are the historical groundwater and soil
contamination. There is a large volume of TCE underground in Mountain
View, and it "wants" to come to the surface. The local indoor air
investigations suggest preferential pathways, such as cracks and
utility lines, predominate over homogeneous vertical migration, and
such pathways exist outdoors as well as indoors.

The results of the various sampling efforts have trickled in over the
past several months. Relatively high levels of TCE vapors have been
found in a number of buildings, including at least one home at the GTE
site and an older house just across Whisman Road from the MEW area.
TCE at levels causing concern has been found in some incomplete
commercial buildings, and a utility vault appears to have opened a
"preferential pathway" at one of the newer, supposedly vapor-resistant

Lower levels of TCE have been found outdoors, inconsistently,
throughout the area, including at Slater Elementary School. Some of
the results at the school were about 0.2 micrograms per cubic meter,
and other reference locations showed even higher readings. Occasional
higher "spikes" of TCE--roughly 3 to 6 micrograms per cubic meter--
have been found in some spots, such as the open space Bay View area of
Moffett Field.

The local community appreciates the extent to which the responsible
parties, property owners, and regulatory agencies are studying this
problem. Some of the work--in lowering detection limits and conducting
repeated sampling--is cutting edge. But there is room for improvement.

Outdoor sampling should not be done simply for reference purposes. If
contaminants are detected above health-based screening levels,
sampling should be designed to map the extent and concentration of the
outdoor plume. Because that map will vary over time due to wind and
other conditions, there should be multiple "snapshots" taken.

Investigators should use methodologies and technologies to map outdoor
contamination plumes over time, and all the parties should work with
EPA to create an umbrella database of local sampling results. This
would better quantify public exposures. For example, in Mountain View,
it would make a difference to learn whether schoolchildren are exposed
to TCE above the screening level once a month or most of the time.
Also, by correlating measurements to wind direction, frequent or near-
continuous measurements would help identify sources.

Air contamination above shallow groundwater plumes seems high enough
and consistent enough to merit an additional response. If continuing
studies bear this out, more cleanup--not just mitigation techniques
such as land-use controls or venting--may be necessary. Engineering
controls may be necessary, but if they simply divert contamination
without destroying it, they will be insufficient.

The existing remedies being used at the sites are conventional slurry
walls and pump-and-treat systems. To protect the public, the
regulators and responsible parties should consider newer cleanup
technologies that are designed to treat or remove contamination near
the surface, such as accelerated bioremediation, advanced oxidation,
permeable reactive barriers, etc. These technologies have been
demonstrated locally, and some already are being introduced piecemeal
at the various properties and operable units.

III. The Health Standard Debate

Although EPA's program in Mountain View is moving in this new
direction, it could grind to a halt. The Air Force, on behalf of the
entire Defense Department, has challenged EPA's TCE toxicity
assessment. The Air Force is challenging the science, but the cost of
additional TCE investigation and cleanup is considered by some in the
current administration to be prohibitive. EPA has delayed promulgation
of new health standards, and it may instruct its regional offices not
to use the more protective levels.4 If so, public health in Mountain
View and probably hundreds of other sites with serious, shallow TCE
contamination will be sacrificed to the economic concerns of the
Defense Department and other polluters.

This is not just an abstract problem. After months of requests by one
member of the Northeast Mountain View Advisory Council, EPA and the
MEW companies sampled the air inside her home. They announced the
results in May 2004. In her 11-year-old son's bedroom, where he has
apparently lived above the TCE plume his entire life, TCE was found at
0.8 micrograms per cubic meter, well above the new health screening
level. If that screening standard is raised back to its old levels,
then he would supposedly be "safe," even though EPA's Science Advisory
Board commended EPA for coming up with health-based exposure levels
designed to be protective for children.

Residents of Mountain View and other local communities are better
educated, wealthier on average, and more empowered than most. For the
past quarter century they have been able to get the government and
private parties to address TCE and other pollution in their community
in an effective, open fashion. However, if national standards are
rolled back, they will become guinea pigs again and will continue to
be exposed to contaminants until national policymakers decide the key
purpose of environmental protection is to safeguard public health.

IV. To Build or Not to Build

Most vapor intrusion projects are being conducted at sites where
people already are living or working directly above contamination.
Figuring out when, where, and how best to protect those people is a
challenge enough in itself. But in the long run, it may be the tip of
the iceberg. Many more new developments, including sensitive uses such
as housing, will be proposed for sites contaminated with VOCs.

This is the emerging challenge for brownfields development across the
country, as well as any other approach that emphasizes the reuse of
polluted properties. At shallow TCE sites, it often is not enough to
dig and haul polluted soil and stop pumping contaminated water.
Residents and other potential occupants must be assured the air they
breathe, indoors and out, will be safe if such developments are to
remain viable.

This is not just an environmental problem. The vapor intrusion issue
has enormous implications for toxic tort litigation. One of the first
physical signs of exposure to TCE in one's own airspace is a
propensity to litigate.

Very little thought has gone into how to evaluate development
proposals based upon their potential impact on public health.
Stakeholders must embark on a better system that permits or even
encourages development while delineating, warning of, and addressing
vapor intrusion.

Admittedly, many community activists are from the start suspicious of
development projects. The developer, after all, is there to make
money. Yet Silicon Valley also suffers from a severe, chronic housing
shortage. As such, there is a consensus among economic development
proponents, environmental advocates, and social justice activists that
new housing, even new neighborhoods, should be built on former,
sometimes polluted industrial land in Mountain View and nearby cities.

Elsewhere, communities have a greater need for offices, stores, and
other uses that might open new contamination pathways. It is
imperative to determine how to meet those needs without exposing
employees, residents, shoppers, etc. to unacceptable contamination.

In Mountain View, the city just approved 46 new townhomes for the GTE
site, each expected to sell for $600,000, and another project is being
proposed on the edge of the MEW study area. At Moffett Field, the Army
has big plans for new, privatized housing, but the developer has
delayed action in the Orion Park area because of the contamination.
Other communities across the country are facing similar proposals, but
there is as yet no standard protocol for considering vapor intrusion
in development.

It is not enough to simply slap sub-slab venting systems onto new
housing or commercial units in suspect areas. Projects require
careful, up-front review. Fortunately, in approving the 46 new units,
Mountain View used the review required under the California
Environmental Quality Act to consider and mitigate potential vapor
intrusion hazards.

Based on the experience in Mountain View, plus ideas heard elsewhere,
the following is a summary of the questions that typically must be
resolved if a property has volatile compounds in the soil or

A. Is the Property Ready for Development?

Obviously, it is much easier to drill wells, test soil gas, and
conduct other characterization and remediation activities before
building, though some activities, such as soil removal, can be
coordinated with construction. As much investigation and cleanup as
practical should be completed before development occurs, and
development agreements should guarantee continuing access to the
property for the operation of remediation systems, long-term
monitoring, and the enforcement of any land-use controls.

Procedurally, this is trickier than it sounds. The agencies
responsible for overseeing environmental responses usually are not the
bodies that approve and oversee development. At the new 46-unit
development in Mountain View, EPA risk assessors reviewed the
developer's studies, but it was the city that imposed conditions--
mitigation measures under the California Environmental Quality Act--
after consulting with EPA. For example, it declared, "Construction
Activities shall not interfere with ongoing and proposed soil and
groundwater remediation and monitoring activities." 5

The precise form of cooperation will vary from state to state, but at
a minimum, local planning jurisdictions, such as cities, should
coordinate with environmental regulators and determine which site
restrictions should be incorporated either into cleanup or development

Some localities are not satisfied with existing regulatory
requirements. Ventura County, Calif., where major housing projects are
proposed near Boeing's contaminated Santa Susana Field Laboratory, now
requires groundwater and soil testing for TCE and perchlorate (a
rocket fuel component that does not pose a vapor intrusion hazard) at
proposed property developments within two miles of the lab.

There is at least one instance where a community group believes a site
is not ready for development for forensic reasons. In Beaverton, Ore.,
Victims of TCE Exposure (VOTE) are asking for a halt to redevelopment
of the former Viewmaster production plant until all data pertaining to
past worker exposures to TCE is collected.6

B. What Vapor Exposures Are Likely?

At existing structures, indoor air sampling can be used to guide
decisionmaking, but before buildings are erected, it is important to
model potential vapor intrusion. In fact, each site requires a
conceptual site model that considers all potential impacts on both
indoor and outdoor air. Will digging basements or the preparation of
foundations reduce attenuation? Will parking lots or other covers
reduce degradation? Will utility lines and vaults create preferential
pathways? Do ambient levels of TCE pose a long-term risk?

C. How Can Exposures Be Mitigated?

Unfortunately, today's modeling science, while useful, does not have
all the answers, so caution is in order. The city of Mountain View,
after taking flak for approving earlier projects at the GTE site, is
requiring protective measures even on the 46-unit parcel, where
studies show the risk from vapor intrusion is low. The new development
will have parking and storage on the ground floor, minimizing vapor
releases into living areas. In addition, the city is insisting upon
"commercial-grade vapor barriers under each unit."

Above the most contaminated portions of the MEW area, commercial
building designs usually have worked. Impermeable slabs and positive
air pressure keep indoor contamination levels down to the levels found
in outside air. There have been exceptions, however. Where direct
measurement has found contamination in indoor air, EPA quickly has
required corrective measures.

If a development relies on built-in engineering controls, the
longevity of such controls must be considered. In California and other
areas subject to land movement, foundations crack. Any development
that depends on impermeable foundations over the life of contamination
should have a monitoring scheme, as well as a contingency plan should
monitoring find new pathways have been opened. Where climate control
systems are used to minimize contamination, institutional controls
should mandate their proper operation and inspection.

Thus, even apparently effective engineering controls must be
integrated into long-term stewardship plans that (1) legally require
the controls as part of the remedy and/or development permits, (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 beyond the CEQA
mitigation requirements. If construction and ventilation are regarded
as ways to limit human exposure, then they should be legally
incorporated into the cleanup.

Of course, if ambient air in the neighborhood of the contamination
exceeds health-based screening levels, mitigation that just blows the
contaminants outside is no solution. Accelerated cleanup, designed to
destroy shallow contamination, should be a requirement if development
is to occur.

D. What Should Potential Buyers or Renters Be Told?

In many communities, the market can reinforce regulatory actions to
force the protection of public health--if the buying public knows
about the potential risk. In California, property buyers are notified
about hazardous waste sites in their neighborhood at closing time.
Unfortunately, that does not give people time to consider the
potential impact of the contamination on their health or their
property values. Consequently, many residents of the GTE site are
suing project developers.

Mountain View's solution is to require notification as part of normal
marketing. That is, potential buyers will be able to weigh the impact
of underlying or nearby contamination before they make their decision.
This should motivate the developer, and in turn, the responsible
parties, to take extra steps to clean up or control contamination.

But even this creative approach has its shortcomings. When individual
homeowners put property up for resale, there is no requirement that
they notify in advance potential buyers of potential vapor intrusion
issues. Some Mountain View homeowners, already unhappy that the
publicity about TCE may have limited the appreciation of their
property values, may wish to hide the news. To protect subsequent
buyers, there should be institutional controls that require
notification each time a property is put up for sale. Similarly,
potential rental occupants should be given the same warning.

Warning, while valuable, may have unintended consequences. It may, for
example, lead to de facto housing discrimination. If all buyers are
informed that the more stringent health standards are designed to
protect young children, childless families may buy while those with
kids look elsewhere. Finally, while knowledge that cleanup is on the
way may be enough for buyers in tight housing markets such as Silicon
Valley to purchase new units, in other areas buyers may avoid such


It is too late to undo the drinking water TCE exposures of the
Viewmaster workers in Beaverton and others across the country who have
been exposed to TCE. One can only hope the Northeast Mountain View
Advisory Council member's son does not contract a serious disease from
growing up in a bedroom with TCE vapors. But it is possible to
carefully consider and plan development so many fewer people are
exposed to volatile organic compounds in the future.

1 The Navy maintains a Web site for the Restoration Advisory Board
(RAB) at http://www.navybracpmo.org/bracbases/california/moffett/.
Among other documents, it includes RAB minutes.

2 The Science Advisory Board's review of EPA's draft TCE Health Risk
Assessment is available at http://www.epa.gov/sab/pdf/ehc03002.pdf
on the World Wide Web. The cover letter also states, "The Board
advises the Agency to move ahead to revise and complete this important
assessment. The assessment addresses a chemical, trichloroethylene
(TCE), significant for being a nearly ubiquitous environmental
contaminant in both air and water, being a common contaminant at
Superfund sites, and because it is 'listed' in many Federal statutes
and regulations. The draft assessment is also important because it
sets new precedents for risk assessment at EPA."

3 For more information, see http://www.whisman.net/nmac/ on the
World Wide Web.

4 EPA explained the status of the health standard in its June 2004
Draft First Five-Year Review Report for the Middlefield-Ellis-Whisman
(MEW) Superfund Study Area, Mountain View, California(pp. 6-8): EPA's
Office of Research and Development and Office of Solid Waste and
Emergency Response have requested additional external peer review of
the draft TCE Health Risk Assessment by the National Academy of
Sciences. Consequently, review of the toxicity value for TCE may
continue for a number of years. In the interim, because of the
uncertainties associated with the draft TCE Health Risk Assessment,
EPA Region IX is considering both the draft TCE Health Risk Assessment
toxicity values and the California TCE toxicity value (similar to
EPA's previously listed TCE toxicity value from 1987) in evaluating
potential health risks from exposure and making protectiveness
determinations. The draft report is available from the NMAC at ht
tp://www.whisman.net/nmac on the Web.

5 "City of Mountain View Findings Report/Zoning Permit" No. 211-02-
PCZA, April 13, 2004, p. 6.

6 VOTE wrote the city, "It is critical that an independent risk
assessment be completed to determine the rate and duration of
exposures of the former employees. The integrity of the structure,
plant operations, land contours and historic wetland dumping processes
of the site must be maintained for such an evaluation."

** Lenny Siegel is executive director of the Center for Public
Environmental Oversight and director of the Pacific Studies Center in
Mountain View, Calif. He is an expert on military facility
contamination and has served on numerous advisory committees,
including the ASTM/ISR Steering Committee on Brownfields Restoration,
California's CLEAN Loan Committee, EPA's Negotiated Rulemaking
Committee on All Appropriate Inquiry, the Moffett Field Restoration
Advisory Board, and the Northeast Mountain View Advisory Council. More
information on CPEO is available at http://www.cpeo.org on the World
Wide Web. Siegel can be contacted at lsiegel@cpeo.org.

Copyright 2006 The Bureau of National Affairs, Inc.