[CPEO-BIF] The Implications of the NRC Report on TCE

[Lenny Siegel <lsiegel@cpeo.org>]

[Please excuse the multiple postings. - LS]

THE IMPLICATIONS OF THE NRC REPORT ON TCE
Lenny Siegel
August 3, 2006

Last week (on July 27, 2006) the National Research Council (NRC), an arm 
of the National Academies of Sciences, issued its report, "Assessing the 
Human Health Risks of Trichloroethylene: Key Scientific Issues." The 
report is likely to have enormous implications for federal, state, and 
private cleanup programs, because TCE is found in groundwater at 
thousands of contamination sites throughout the United States.

The NRC concluded that the evidence that TCE causes cancer is becoming 
stronger. Furthermore, it recommended that EPA extrapolate the cancer 
risk using a linear model, which among other things means there is no 
concentration so low that it doesn't pose a cancer risk - the risk just 
goes down in proportion to the concentration.

The NRC Committee recommended "that federal agencies finalize their risk 
assessment with currently available data so that risk management 
decisions can be made expeditiously." Significantly, this seems to 
suggest that EPA update and complete its 2001 Human Health Risk 
Assessment, rather than start anew. I assume that this lead 
recommendation was made to "federal agencies" because the study was 
sponsored by the Defense Department, Energy Department, and NASA, as 
well as EPA. However, of those agencies, only EPA has the statutory 
authority to issue this type of risk assessment.

The Committee made this recommendation even though it documented 
scientific uncertainty in a number of key areas. It defined several 
important areas for future research, as well as methodological 
suggestions. In particular, it laid out guidelines for a new 
meta-analysis, a study that combines data from multiple studies.

Most observers seem to think that the completed risk assessment will 
lead to a new federal drinking water standard - a maximum contaminant 
level, or MCL. Some suggest that the MCL will be lowered from its 
current 5 parts per billion (ppb) to 1 ppb. In 2003, the Air Force 
evaluated the impact of such a change on groundwater remediation alone. 
It estimated that the Defense Department's cost for addressing TCE would 
double from $5 billion to $10 billion, primarily because of the ongoing 
costs of operation and maintenance.

I believe those numbers are exaggerated. There is substantial evidence 
that conventional remediation - "pump and treat" - declines in 
effectiveness over time. Systems are likely to be turned off when the 
concentration vs. time graph reaches an asymptote, and in a majority of 
cases this will be above 1 ppb or even 5 ppb - of TCE in groundwater.

Also, in 2003, when it appeared that EPA was going to promulgate more 
protective TCE standards, EPA toxicologists calculated a TCE indoor air 
screening level of under .02 micrograms per cubic meter to correspond to 
one excess cancer for every million people exposed to this concentration 
over thirty years. This number was included in EPA's 2002 draft Vapor 
Intrusion Guidance, and or a short time, it served as a default 
screening level at many sites where vapor intrusion investigations were 
underway.

However, since background - ambient air in many metropolitan areas - is 
at least an order of magnitude above the .02 level, outdoor readings 
were the de facto screening levels, since there is no practical way to 
keep indoor air cleaner than the outdoor air that inevitably drifts in.

When EPA management decided not to continuing using the 2001 Draft Risk 
Assessment, EPA field personnel shifted to indoor air screening levels 
averaging about 1 microgram per cubic meter.

Vapor intrusion projects are more sensitive to health standards than 
drinking water response. It seems that a large number of people are 
exposed at levels near the screening levels, so any change in the 
screening levels affects how many homes or other structures are tested 
as well as how many structures are mitigated. To responsible parties, 
the cost differential can indeed be enormous.

But the area where more stringent TCE standards are likely to have the 
greatest impact is the intersection between air exposure and groundwater 
contamination. It is not addressed often, because air and water are 
dealt with by different regulatory organizations under different 
statutes. As I wrote above, TCE is persistent in outdoor air in many 
metropolitan areas, despite its half life of three to eight days. As I 
documented in my recent report on TCE in the Los Angeles area, (see 
http://www.cpeo.org/pubs/TCE-LA.doc) monitoring stations in Azusa, 
Burbank, and Los Angeles most recently detected an average concentration 
of .3 micrograms of TCE in each cubic meter of air. This is startling 
because manufacturers in the region report almost no current use of TCE, 
and because consumer products contain relatively small quantities of the 
compound. (In other states, such as Kansas and Georgia, TCE is still 
being used in significant quantities.)

Since TCE does not occur in nature, it has to be coming from somewhere. 
The best explanation, at least in California, is that is it making its 
way to the surface from landfills and groundwater plumes. The pathways 
include vapor intrusion, outdoor vapor migration, and releases from 
treatment systems.

The key point is not that one can't clean indoor air because outdoor air 
is contaminated, but that millions of people are breathing unsafe levels 
of TCE around the clock. The levels are low, but using a linear cancer 
model, the likely health impacts add up.

To minimize releases into the air, therefore, there is a need to 
accelerate the cleanup of subsurface TCE. Conventional responses may be 
adequate to limit the spread of groundwater contamination, but they are 
painfully slow and in a majority of cases may never even meet the 
current MCL.

Fortunately, new technologies - active bioremediation, advanced 
oxidation, permeable iron barriers, etc. - in many scenarios not only 
destroy the contamination, but they reduce concentrations much more 
rapidly. It might seem unrealistic to get responsible parties to switch 
over to alternative technologies, but it turns out that in many cases 
the new, more protective technologies are less expensive, because the 
costs - such as electricity - don't keep rising and don't continue 
indefinitely. Many polluters, including the Air Force and Navy, now 
routinely evaluate and sometimes replace old pump-and-treat systems with 
innovative technologies. This could be done on a much larger scale.

It is likely that the findings of the NRC committee will lead EPA to 
calculate a more protective action level of TCE in indoor air than the 
current average 1 microgram per cubic meter level. If so, that level 
should be applied to outdoor air that is at or above that level. I don't 
expect Clean Air Act regulators to take the lead on this issue, because 
1) they're more concerned about diesel exhaust and 2) they don't 
regulate the subsurface sources. So it's up to the those responsible for 
investigating and remediating subsurface TCE pollution to systematically 
review the treatment systems in place and find ways to use newer 
technologies to accelerate the reduction of risk.

Furthermore, there needs to be a comprehensive approach. Government 
agencies should compile a complete list of TCE sites throughout the 
country, including what is known about continuing releases, even at low 
concentrations. Right now that information is fragmented among agencies, 
and few agencies know to what degree the sites they regulate are 
emitting TCE vapors.

TCE doesn't have to remain a permanent blight on public health - if we 
admit the risk and decide to eliminate it cheaper, faster, and better.



--


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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