Draft Vapor Intrusion Guidance
Graphic adapted from figure by Thomas McHugh, GSI Environmental.
Used by permission.
December 8, 2010
Ecology has suspended for one year work on updating the MTCA cleanup regulation.
We will continue work on finalizing the VI guidance.
April 30, 2010
The Washington Department of Ecology is in the process of
revising and updating the Models Toxics Control Act (MTCA)
cleanup regulation. As part of this effort, Ecology is updating
clarifying provisions on addressing threats posed by subsurface
vapor phase contaminants.
Ecology has formed an advisory group to provide input on vapor
intrusion issues. In forming this Vapor Workgroup, Ecology
has two main goals:
Workgroup members were chosen to provide a balanced set of
knowledge and experience. The group will meet three to four
times between May and July, 2010. The first meeting is scheduled
for May 13 at the Ecology Headquarters Building in Lacey.
- Develop a
final VI guidance document. Ecology believes the
document provides a solid foundation for evaluating this
pathway. However, several issues were identified during
the public comment period that Ecology would like to discuss
with workgroup members before finalizing the guidance document.
- Develop draft
MTCA rule language. This rule language will support
implementation of the phased decision-making process specified
in the Washington draft VI guidance document and in recent
federal guidance materials.
The first meeting will review the purpose and objectives of the
workgroup, discuss the guidance (including public comments
received) screening levels, rule revisions, and a strategy for
working through remaining issues.
Here is a link to information about the MTCA Cleanup Regulation
The Washington State Department of Ecology’s Toxics Cleanup
Program asked for comments on a
Guidance for Evaluating Soil Vapor Intrusion in Washington
State: Investigation and Remedial Action.
All comments on the document provided to Ecology by November
30, 2009, will be considered when the guidance is finalized.
This technical guidance is intended to help responsible
parties, environmental professionals, and Ecology site managers
assess vapor intrusion at cleanup sites in Washington.
Vapor intrusion (VI) refers to the vapor phase migration of
volatile organic and/or inorganic compounds into occupied
buildings from underlying contaminated ground water or soil.
These substances may contaminate indoor air and impact human
health. This technical guidance document provides
techniques for evaluating whether vapor intrusion has the
potential to contaminate indoor air. It also recommends ways to
protect building occupants.
This draft guidance includes the following:
Chapter 2: How to do a
preliminary assessment to determine which areas and buildings
that vapor intrusion could potentially affect.
Chapter 3: How to further
assess those site areas and buildings identified by the
Chapter 4: Interacting with
the affected public.
Chapter 5: Vapor intrusion
Chapter 6: Deriving
protective subsurface concentrations and evaluating the need for
Chapter 7: References
Appendix A: Terminology.
Appendix B: Shallow groundwater and soil gas screening levels that protect indoor air.
Appendix C: Soil gas sampling.
Appendix D: Using the Johnson and Ettinger Model during vapor intrusion assessments.
Appendix E: Estimating the contribution of vapor intrusion to indoor air using soil gas and indoor air measurement data.
The draft guidance addresses a wide range of vapor intrusion
issues. With a number of these issues, Ecology recognizes
that a national consensus has yet to emerge. Ecology asked
for feedback on:
- The tiered
approach. For example, is using soil gas or groundwater data to
make screening decisions reasonably conservative? We have tried
to be consistent with the general approaches used by other state
and federal agencies. Do you believe this is a reasonable
approach for implementing the current MTCA rule provisions? If
not, what do you suggest?
- The list of VI
contaminants of potential concern. The draft list of screening
levels is designed to provide a reasonably conservative approach
for identifying potential VI problems that would be implemented
within a tiered decision-making framework. Should additional
chemicals be included on the list? Do you believe the benefits
of a longer chemical list outweigh the potential costs? If
not, what suggestions do you have for modifying the list?
- Use of the
Johnson and Ettinger model. Do the draft recommendations seem
reasonable? If not, what do you suggest?
of background concentrations resulting from indoor and outdoor
sources of volatile hazardous substances. Do the draft
recommendations seem reasonable? If not, what do you
- Our recommendations concerning petroleum hydrocarbons. Are the draft
recommendations reasonable? If not, what do you suggest?
- Level of detail and terminology. Ecology received a wide range of
comments on earlier drafts related to the use of qualitative
terms (like “slightly above”). Some commenters also felt
we should be more consistent, or exact, in how we characterized
our recommendations (when, for example, should “expect” be used
versus “recommend”). Does the current document provide a
reasonable balance between general guidance and specific
This draft guidance supports implementation of the Model Toxics Cleanup Act (MTCA) cleanup regulation. Ecology is currently in the process of reviewing and updating this regulation. As part of this process, Ecology is examining the investigation and cleanup requirements applicable to vapor intrusion to determine if changes should be made.
Feedback on this guidance document is helping Ecology determine what rule changes (if any) might be needed to effectively deal with vapor intrusion problems at cleanup sites.
Ecology plans to complete work on the vapor intrusion guidance document in 2010. The rulemaking process is currently scheduled to be completed in 2011. If necessary, Ecology will update the vapor intrusion document to reflect regulatory changes following rule adoption.
All comments received by 5 p.m. on November 30, 2009, are
being considered. Although we are unable to respond to each comment
individually, Ecology will issue a general responsiveness
summary that describes the issues identified by reviewers and
explains the changes we made to the draft document in response.
If you have questions, please contact Martha Hankins at
firstname.lastname@example.org or (360) 407-6864.