[CPEO-MEF] VOCs: Past vapor intrusion at El Toro Marine Corps Air Station (CA)?

[Lenny Siegel <lennysiegel@gmail.com>]

Marine veterans recently asked me to look into the possibility that 
workers/Marines at the former El Toro Marine Corps Air Station might 
have been exposed to unacceptable levels of trichloroethylene (TCE) in 
the indoor air at buildings (hangars) 296 and 297, part of Site 24 at 
that base.

My knowledge of the situation is incomplete. I last reviewed El Toro 
data in late 2004, when I considered potential future vapor intrusion. See
http://www.cpeo.org/lists/military/2004/msg01100.html

But I think I know enough to recommend further, detailed evaluation.

 From my earlier research, I have in my files a few pages from the June 
2002 "Draft Final Site Closure Report for Vadose Zone Remediation, IRP 
Site 24, Volatile Organic Compounds Source Area." Table 3-4 shows 
Closure Sampling Analytical Results. This table compares the 
post-closure (of the treatment system) TCE sampling results of soil gas 
from vapor extraction wells under and near the buildings with "baseline 
TCE concentrations," the sampling results before soil vapor extraction 
took place. If I recall correctly from my earlier tour of El Toro, the 
SVE system removed a large quantity of TCE from the vadose zone (soil 
above the groundwater table) at El Toro.

Here's a typical baseline result. In well 24SVE49, screened at a depth 
of 83 to 103 feet, the TCE soil gas concentration was 120 
micrograms/liter on August 12, 1999. That equals 120,000 
micrograms/cubic meter.

With a common but low-end attenuation factor of 1/1000, that could cause 
indoor air contamination of 120 micrograms/cubic meter. In reality, 
attenuation depends upon the building. Sumps, drains, cracks in the 
floor, and other holes could increase indoor concentrations. Active 
ventilation, open hangar doors, and a high ceiling could reduce indoor 
contamination levels. Also, the depth to groundwater (and thus depth of 
the samples) might have also caused less concentrated TCE exposures.

Dividing by 12 to get from 25-year exposure to the 2 years a typical 
marine might have worked in the building, that's still the equivalent of 
10 micrograms/cubic meter over "lifetime" exposure, enough to correspond 
to a 1 in 400,000 excess lifetime cancer risk for an occupational 
exposure. Any Marine/worker exposed to the same or similar chemicals 
before or after - in water or air - would have an increased risk of 
cancer. People who worked there longer would also have a greater risk of 
cancer.

Of course, if workers were still using TCE in the hangar, the air 
concentrations were likely much higher.

In summary, I don't know enough to say how likely it was that someone 
working in these buildings would contract cancer as a result of 
workplace exposure. But if I read the numbers correctly, there is enough 
information to merit a full retrospective evaluation of the risks.

Lenny

-- 


Lenny Siegel
Executive Director, Center for Public Environmental Oversight
a project of the Pacific Studies Center
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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