[CPEO-MEF] Comment on EPA's Draft Vapor Intrusion Guidance

[Lenny Siegel <lsiegel@cpeo.org>]

[I am submitted these comments to U.S. EPA today. - LS]

I appreciate the opportunity to comment on EPA's "Draft Guidance For
Evaluating The Vapor Intrusion to Indoor Air Pathway From Groundwater
And Soils" (Docket ID No. RCRA-2002-0033). I am pleased that EPA
recognizes this pathway as an important potential human health risk, and
I believe the Draft Guidance's tiered approach is reasonable. However,
there is significant room for improvement.

1. The vapor intrusion pathway does not exist in isolation. The Guidance
should require, at least at the third tier, the development of a
conceptual site model that considers all contaminants, including
breakdown products, all pathways, and all receptors. If EPA believes
that other guidance documents adequate address other pathways, then this
guidance should explain how to integrate vapor intrusion with other
exposure routes.

2. I am particularly concerned that the guidance fragments risk by
excluding as "background" outdoor air contamination and indoor sources.
While I don't believe that responsible parties should be responsible for
addressing indoor air contamination caused by residents' or businesses
current or recent use of chemicals, I believe that risk should still be
assessed. 

3. Moreover, I do not believe that outdoor air contamination should be
excluded from risk evaluation or the remedial response. Unlike metals in
soil, such as arsenic and manganese, volatile organic compounds are not
naturally occurring substances. Contamination from outdoor air may be
caused by the same sources as the vapor intrusion pathway, and the risk
from such contamination is additive.

There are at least six potential sources for outdoor air contamination,
all of which may increase both indoor and outdoor air exposures. They
should therefore considered in the creation of the conceptual site model.

A. Contamination that follows the indoor air pathway may migrate outside
- and possibly increase contamination in other structures. 

B. Systems which protect indoor air through venting may increase
concentrations in outdoor air.

C. Volatile compounds may rise directly through the soil into the air.

D. Groundwater treatment systems may release contamination into the air.

E. Continuing use of volatile organic compounds, while diminishing, may
directly release contaminants into the air.

F. Similar sources around the region may lead to widespread, but low
levels of ambient contamination.

To protect public health, all such sources must be evaluated in
conjunction with the indoor air pathway. 

This is not just a hypothetical concern. At the military housing area at
Moffett Field, California the responsible party, the U.S. Navy, is
arguing that the residents are NOT at risk because it believes that
outdoor air or undefined indoor sources are the cause of unsafe indoor
air toxic levels, identified as a result of sampling by the Navy.
Nearby, the responsible parties at the MEW Superfund Study Area are
proposing, in their air monitoring workplan, to consider their work
complete if outdoor contaminant concentrations exceed indoor levels.

4. The draft guidance barely mentions the potential for degradation. Yet
in many environments, volatile organic compounds react as they rise to
the surface. In fact, certain degradation products, such as vinyl
chloride, are more likely to pollute the air. Furthermore, the
atmospheric breakdown products may be quite different, yet just as
toxic. The guidance should identify potential breakdown products to
analyzed in all media, and it should underscore the importance of
including potential chemical change in the conceptual site model

Again, this is not a hypothetical problem. At Ohio's former Marion
Engineering Depot, sampling for vinyl chloride has been insufficient,
despite indications that it is being released from an underground TCE source.

5. There may be a need to better explain the requirements for soil gas
sampling below or near suspected indoor air pathways. At the Moffett
housing site, the Navy is using soil gas tests to rule out the pathway,
but it's my understanding that EPA intends to challenge that assertion,
arguing that the Navy's sampling protocol is inadequate.

6. On page 9 on the draft guidance, EPA states, "For the purposes of
making Current Human Exposures Under Control EI determinations with
respect to vapor intrusion under RCRA and CERCLA, EPA generally
recommends the use of 10^-5 values." However, there is no justification.
I believe the more stringent 10^-6 level of projected increased cancer
risk should be used unless otherwise justified on a site-specific basis."

7. Finally, it's important to stress that the forced migration or
dilution of indoor air contamination is not a sufficient permanent
solution. Remedies should be developed that reduce the likelihood that
contamination will rise through the soil, and if remedies are already in
place they should be reconsidered. Otherwise, contamination simply moves
to the nearby outdoor air, other buildings, and the regional air basin. 

That is, indoor air contamination should be treated as a sign that a
site's cleanup should be reviewed and probably improved. It should not
be evaluated or "treated" in isolation.

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

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