[CPEO-BIF] My preliminary comments on California VI guidance

[Lenny Siegel <lsiegel@cpeo.org>]

I have reviewed California's December 15, 2004 California's Interim
Final "Guidance for the Evaluation for the Evaluation and Mitigation of
Subsurface Vapor Intrusion to Indoor Air." The document is strong on
process but potentially weak on outcome. My comments here are
preliminary and intentionally incomplete. I have not addressed those
technical and practical elements where my expertise is particularly
weak. For an overview of the document, download it from 
http://www.dtsc.ca.gov/ScienceTechnology/HERD_POL_Eval_Subsurface_Vapor_Intrusion_interim_final.pdf
and read the executive summary.
While I've tried to make my comments stand alone, they are best read in
conjunction with the original document.

On the whole, the Guidance is a comprehensive approach to vapor
intrusion. It includes some important new ideas, including how to do
site development. On the other hand, there is room for improvement. I
address my three major concerns before proceeding through the document,
page by page.

*1. First and foremost, it defines vapor intrusion as simply an indoor
air problem. But vapor intrusion responses should be based upon
conceptual site models that consider all sources, all pathways, and all
receptors. Low level toxic air contamination in the outdoor air
shouldn't be treated as acceptable background, but as the result of
contamination subject to full characterization and possible remedial
response. Venting indoor contamination outdoors may be necessary, but it
is not a complete solution.

*2. The Guidance is biased against indoor air sampling because, it says,
it is costly, time-consuming, and requires the cooperation of residents.
It fails to recognize that many residents, with good scientific
evidence, don't accept conclusions based upon models. They want to know
what they're breathing. Under the right conditions, the process should
allow project managers to proceed directly to indoor air measurements.
This wouldn't eliminate the need for soil gas sampling, but it would
accept the notion that actual measurements, not models, are the final word.

*3. The table on page 29 is the primary place in the Guidance that comes
close to suggesting a generic action level. On the positive side, it
distinguishes the concentrations that would trigger monitoring from the
levels that would prompt actual engineering controls. On the other hand,
if these guidelines are used, mitigation will never occur. That is,
unless I'm reading the guidance improperly, for engineering controls to
be applied at a state-led site, indoor vapor levels would have to exceed
the concentrations corresponding to the one-in-ten-thousand additional
lifetime cancer risks using state toxicity standards. For TCE, which has
a state standard of about 1 microgram per cubic meter in residential
air, corresponding to a one excess cancer among a million people, it
would take readings of 100 micrograms per cubic meter, and I've never
heard of such readings inside homes. The document does make it clear
that actual cleanup levels must be determined through standard
regulatory processes, such as the National Contingency Plan, but even as
a suggestion the weak threshold is disturbingly unprotective.

4. The language on page 5 that soil gas characterization should
continue, laterally and vertically, until there are no detections is
important. Since there is no magic concentration level that determines
the likelihood of vapor intrusion, it's best to map the entire plume

5. The call for high sampling densities on page 6 seems good, but the
concept should be expanded to intensify groundwater sampling. Reliance
on interpolation may be inadequate, because the density of sampling
required to characterize groundwater plumes isn't sufficient to support
vapor intrusion investigations. For example, just west of the MEW
Superfund Study Area in Mountain View, there's a home somewhere near the
5 ppb TCE-in-groundwater contour, and it has significant vapor
intrusion. When we looked at the basis for that contour line, we found
monitoring wells, at some distance, with concentrations of 50 ppb and 1
ppb. This example suggests that the 100-foot -from-contamination
boundary for air testing should be moved out, because of the uncertainty
over where the edge of the plume lies, or more sampling locations should
be used,

6. The requirement that analytic detection limits for soil gas not
exceed 500 times the indoor air goal seems obvious, but I've seen less
careful approaches. So I'm glad that it is expressed here.

7. The assumptions for using default attenuation factors, on page 14,
include "Preferential pathways do not exist." However, it appears that
preferential pathways are common, unless buildings have been
specifically designed and constructed to resist vapor intrusion.   There
should be a requirement to disprove the presence of such pathways before
default factors are used. In the absence of such proof, investigations
should include indoor air sampling as well as soil gas sampling. (See #2 above.)

8. The restriction of screening based upon groundwater sampling to
downgradient areas (page 15) also makes sense, though it must be
recognized that source areas are often unrecognized.

9. It is good that the guidance reinforces the requirement to report all
releases, not just those exceeding SB 32 screening numbers (p. 17).

10. The document (bottom of page 19) recommends a default attenuation
factor  of .01, compared to U.S. EPA's .1. The default attenuation
factor should be based upon the maximum likely exposure, not the
average, because it's more important to test homes or other structures
that might have vapor intrusion than to avoid sampling units which might
not be impacted.

11. This guidance document's discussion of future buildings (p. 22 and
pp. 37-39) is a breakthrough. I have seen nothing comparable elsewhere.
Still, there is room for improvement. Reasonable steps to eliminate the
sources of vapor intrusion should be taken before construction, because
engineering controls, while likely to be effective in the short run,
require monitoring, possible operation and maintenance, and contingency
planning should they fail. In California, periodic earthquakes or other
geologic forces are likely to create cracks in otherwise impermeable
foundations. That is, engineering controls should not be viewed as a
substitute for maximum practical cleanup before construction.

12. The statement (page 24) that ambient data shouldn't be used to
reduce the indoor air impacts is appropriate. Furthermore, it would help
to have a clear distinction between "ambient" air, which may be affected
by subsurface contamination in the neighborhood (through subslab
venting, treatment system offgassing, and direct vapor releases), and
"background" measurements, which should be taken some distance from
known sources.

13. The discussion on utility corridors (also on p. 24) is very helpful.

14. The placement of sampling locations within residences (page 26)
should consider potential internal pathways. There is a home in Hopewell
Junction, New York, where the upstairs registers greater TCE
concentrations than the downstairs. Apparently the contamination is
rising through the walls.

15. Furthermore, in buildings with multiple attached units, indoor air
sampling should occur in each ground-floor unit, and depending upon the
structure, units on other levels. If a single unit among several
attached units has a preferential pathway, it can collect vapors from
the entire structure and thus magnify a  modeled concentration that is
based upon single unit calculations. Unless preferential pathways are
transparent, sampling a single unit (or a small percentage of units) in
such structures is akin to Russian Roulette. A non-detect or low-detect
result in one, or even several units may miss high concentrations in
other units.

16. The concern for privacy (page 30) is good, but that should not be
used to hide problems from the public at large. There should be a
requirement for public disclosure of all air sampling results. Specific
addresses should be disclosed only if a resident agrees, except that
prospective buyers and tenants should be notified in any case. Public
disclosure should be built into the broader program of public involvement.

17. The section on identifying preferential pathways (page 31) is
strong, but it could be strengthened more by expanding the discussion of
real-time field sampling that may be used to home in on such pathways.
Real-time and near-real-time sampling devices, such as EPA's Trace
Atmospheric Gas Analyzer (TAGA) have proven effective for this purpose.
The TAGA can only sample for two analytes at a time, so it is best used
once the contaminants of concern have been identified. The TAGA - and
presumably similar equipment - can be used to identify preferential
pathways and confounding sources such as household products. It can also
correlate concentrations with meteorological conditions such as wind,
temperature, and atmospheric pressure.

18. The statement that indoor air sampling should be done in an
environment representative of normal use (page 32) is also good. On the
one hand, the sampling of vacant, unheated units (as the Navy has done
at Moffett Field's Orion Park Housing Area) may miss climate
control-induced vapor flows. On the other hand, the sampling of
commercial buildings with no active air conditioning may intensify the
concentration of vapors, as at the MEW site in Mountain View. (As a
sampling technique, that may be effective, because it magnifies the
problem, but there may need to be an adjustment when risk is assessed,
if the building is designed only to be used with ventilation systems on.)

19. The section on Vent Riser design (p. 37) is good, but it could be
improved with a brief discussion of ways to ensure that vented vapors
not be aimed at neighbors' homes - assertedly the case in some homes in
Endicott, NY - or the air conditioning intakes on commercial buildings.

20. I don't have the expertise to know whether the discussion of surface
paving (page 40) is sufficient, but I'm glad that it has been included
in the document.

21. The language on institutional controls  (p. 40) is original and
good. I suggest, though, that language be added to promote cooperation
between environmental regulators and local officials. Local officials,
in the approval of zoning, issuance of building permits, and review of
CEQA documents, are the first line of defense in preventing
inappropriate use or activities on contaminated property. Mountain View
has pioneered this approach, including vapor intrusion mitigation in its
CEQA approval, but it was only able to do so after U.S. EPA experts
reviewed technical documents. Such cooperation should be the standard -
that is, it should not rely upon individual initiative. Among Mountain
View's commendable initiatives, it is requiring point-of-marketing
disclosure at a VI development sites as part of CEQA approval. State
disclosure laws notify buyers only at closing. That's too late.

22. Perhaps my clearest expertise is in the area of public involvement
(p. 44). Where there is public interest, I strongly suggest the
formation of community advisory groups. This allows representative
members of the local community to develop gradually the expertise to
understand the vapor intrusion project. This helps the community provide
constructive advice. For example, the home west of MEW was tested
because the homeowner, a CAG member, requested it. It also creates a
group of people capable, when it is merited, of re-assuring their
neighbors when/where those neighbors are skeptical of the statements of
government officials.

However, it is important to distinguish the open process of general
public involvement from the sometimes private process of dealing with
residents about their own homes. In Mountain View, many such residents
take part in the community advisory group, but they usually address
house-specific issues privately.

23. The explanation  (p. C-4 and Appendix F) why OSHA Permissible
Exposure Levels don't generally apply in vapor intrusion investigations
is very helpful.

Lenny
-- 


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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