[CPEO-BIF] New York's new TCE standard/matrix

[Lenny Siegel]

Buried in Appendix A of the final New York State Department of Health 
(DOH) Vapor Intrusion Guidance is a memo effectively tightening the 
state's indoor air standard for TCE. In the appendix there is an October 
12, 2006 memo, from Nancy Kim, Director of the DOH Division of 
Environmental Health Assessment. To download the appendix, go to 
http://www.health.state.ny.us/nysdoh/gas/svi_guidance/ and click on 
"Appendix A - Revisions Summary."

New York still uses a matrix, rather than a single number, to guide 
vapor intrusion mitigation decisions. That makes a lot of sense, because 
the matrix allows the mitigation of POTENTIAL vapor intrusion (at sites 
where there are high soil gas concentrations of volatile organic 
compounds but low measured indoor air concentrations thus far) and 
discourages vapor-intrusion mitigation at sites where sources OTHER than 
subsurface contamination are the likely cause of indoor air pollution.

Unfortunately, the matrix is difficult to understand and even harder to 
explain. But I'll try.

The right-hand column for the TCE matrix still uses 5.0 micrograms per 
cubic meter to require mitigation, except that mitigation is an option 
where the subslab soil gas concentrations is under 5.0 micrograms per 
cubic meter. That is, 5.0 applies, with some wiggle room, to all levels 
of soil gas concentrations.

Remember, because of diffusion and other forms of vertical attenuation, 
in most cases indoor air concentrations are much lower than measured 
subslab concentrations. This is what the Johnson-Ettinger model 
calculates. It predicts indoor air concentrations as a small fraction 
(usually one one-hundredth or less) of soil gas sampling results.

FORMERLY, the second column from the right, in the DOH TCE matrix, used 
2.5 micrograms per cubic meter as the action threshold. At locations 
where subslab measurements of TCE were above 50 micrograms per cubic 
meter AND indoor air measured more than 2.5, mitigation was required. In 
most cases, subslab levels below 50 do not cause indoor air readings of 
2.5, or even 1.0 microgram per cubic meter, if vapor intrusion is truly 
occurring. (Exceptions will be where the subslab readings are 
unrepresentative or where the indoor air contamination comes from other 
sources.)

THE BIG NEWS is that DOH is lowering the number in the second column to 
1.0 microgram per cubic meter. This means that the state will require 
mitigation at most sites where indoor air readings of TCE, resulting 
from vapor intrusion, are above 1.0.

Moreover, Kim also recommends that box 10 of the matrix include 
"Mitigate" as an option, in addition to the current requirement, 
"Monitor." This means that mitigation MAY be required at sites where the 
indoor air concentration of TCE is between .25 and 1.0 micrograms per 
cubic meter (and subslab levels still exceed 50). That is, mitigation 
may be required for TCE vapor intrusion wherever indoor air levels 
exceed a typical background (outdoor air) concentration.

Finally, Kim re-states a general protective principle: "Reasonable and 
practical action should be taken to reduce TCE exposure when indoor air 
levels are above background, even when they are below the guideline of 5 
[micrograms per cubic meter]."

Lenny Siegel






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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 at cpeo.org>
http://www.cpeo.org