1 General Overview Vapor Intrusion
[Cheryl Prowell, DTSC]
Welcome to the overview presentation for the
Draft Supplemental Guidance: Screening and
Evaluating Vapor Intrusion targeted to communities
and the general public.
My name is Cheryl Prowell. I work for the
Department of Toxic Substances Control and I am a member of the CalEPA Vapor Intrusion
In response to the COVID-19 crisis, the CalEPA
Workgroup is providing these presentations
as modules for public viewing at your leisure
during the public comment period for the draft
The supplemental guidance is developed by
a California Environmental Protection Agency
workgroup including members from:
Department of Toxic Substance Control or DTSC,
the State Water Resources Control Board,
San Francisco Bay Regional Water Quality Control
the Santa Ana Regional Water Quality Control Board,
the Office of Environmental Health Hazard Assessment
In addition to the key agencies listed, this
has been a statewide effort with input from
all DTSC offices, the nine regional water
boards, many local agencies, and even from
U.S. EPA Region 9.
Specific Team Members for the development
of the supplemental guidance include:
Karen Baker, Barbara Renzi, Dan Gallagher,
Claudio Sorrentino, and myself with DTSC,
Carmen Milanes and Amanda Palumbo with OEHHA,
Ross Steenson, Nicole Fry, Jessica Law, Tina
Ures, Marina Perez, Abe Waggoner, and Steve
McMasters for the Water Boards.
If you have questions on this presentation,
please send them to our
email with the subject line of 'Overview Presentation
This presentation is a standalone presentation
for general audiences that summarizes vapor
intrusion science and the draft supplemental
In addition, CalEPA’s vapor intrusion workgroup
has provided four technical presentations
available to support the Draft Supplemental
Guidance. This series of talks provide more
technical detail and background for many of
the topics discussed in the general overview.
In the first of these presentations, Steve
McMasters provides an introduction and describes
the process for submitting formal comments.
Next, Cheryl Prowell and Dan Gallagher
present an in-depth summary of
the Draft Supplemental Guidance.
Tina Ures gives an overview of new features GeoTracker, the Water Board’s online
records system, to help build a vapor intrusion
Lastly, Nicole Fry provides a case study to
demonstrate the four-step and decision process
described in the Draft Supplemental Guidance.
To answer questions regarding the guidance,
the CalEPA Workgroup will also be hosting
live question and answer sessions
May 14, 2020 and May 19, 2020 from 1:30 pm
to 3:30 pm Pacific Standard Time. We will focus
on questions related to the technical aspects
of the guidance.
From 6 pm to 8 pm Pacific Standard Time on
the same days, we will have sessions to answer
general questions about the guidance or about
Information regarding the call-in and BlueJeans
Event is posted on both the DTSC and Water
Board’s Vapor Intrusion websites shown here.
Here is a short outline of what is presented
in this general overview.
Discussion of vapor intrusion basics.
Then an overview of the draft supplemental
Focus on how the guidance may impact you
How and when we anticipate starting to use
Public Comment Information and process.
And finally, a short summary of the CalEPA
VI Workgroup’s next steps.
So why is CalEPA updating existing vapor intrusion
What’s out there now is DTSC’s 2011 Vapor
Intrusion Guidance and the San Francisco Bay
Region’s 2014 trichloroethylene framework
Both of these documents are over 5 years old
and science is rapidly evolving
In order to maintain protection of human health
and promote statewide consistency, a joint
vapor intrusion guidance is appropriate.
Now let’s get into the overview.
Vapor intrusion is complex, but I’ll explain
each part of the process.
Vapor forming chemicals are chemicals that
easily volatilize or form vapors and move
from a liquid into air.
Dry cleaner fluids such as tetrachloroethylene
solvents used for degreasing such as trichloroethylene
gasoline and diesel fuels,
paints and thinners,
and elemental mercury.
What is the process for vapors to enter into
When there has been a spill to soil or groundwater,
such as the spilled barrel shown to the left,
there is potential that contaminants will
form vapors, also called soil gas, that can
move through the soil or sewer lines into
These vapors move through dry pockets within
soil towards the surface.
Building’s foundations act as a barrier
to migrating vapors; however, vapors can enter
the building through cracks and faulty sewer
Once the vapors migrate into the building,
they will mix and dilute with air inside of
the building and may be vented to outside
There can also be vapors inside the home from
commonly used household products such as furniture
and carpets, dry-cleaned clothing, and cleaning
How do we identify if there is a vapor intrusion
Environmental professionals use various sampling
tools to identify if contamination and vapors
Monitoring wells are used to observe and measure
contamination in groundwater.
Soil gas wells or probes are used to observe
vapor concentrations above the groundwater.
Sub-Slab samples are collected below a building’s
foundation to observe the vapors immediately
below a building.
Lastly, indoor air samples are used to observe
any vapors within a building.
Can those vapors cause health problems? – Yes,
they can in some cases.
It depends on the type of chemical, what concentration
you are exposed to, and how long you’ve
Some possible short term effects include:
Headache, nausea, and shortness of breath.
There also could be complications with fetal
Some possible long term effects include:
Cancer, Damage to organs such as liver, kidneys,
One chemical of concern is trichloroethylene
TCE is a common industrial solvent that is
also found in many household products such
as gun cleaners or repellants.
Although takes a very long time, TCE can also
form as tetrachloroethylene or PCE breaks
down in the environment.
So why is it a concern?
It is a chemical known to cause cancer, in
In 2011, EPA identified that TCE at very low
concentrations and short exposures, can possibly
cause birth defects during the first trimester
So uniquely for this chemical, we need to
have an accelerated response if TCE vapors
Building characteristics can strongly control
Buildings with intact foundations (such as
the one on the left) prevent or minimize vapor
Whereas buildings with heavy cracking of the
foundation or a lot utilities penetrating
the foundation (such as that on the right)
have increased risk for vapor intrusion.
Also, buildings with basements are more at
risk from vapor intrusion and indoor air concentrations
in the basement may be higher if there is
low mixing of outside air.
Lastly, as buildings age, normal settling
of the buildings occur and unfortunately building
foundations will develop increased cracks.
Weather and climate can also strongly control
Changes in weather cause pressure differences
between the atmosphere, below the building,
and within the building.
When it gets cold outside, we turn on our
heater. The hot air rises in the building
thus pulling vapors below the building into
In contrast, when it is hot outside, we turn
on our air conditioning, usually, this over
pressurizes the building this pushing vapors
out of the building.
Rain can saturate the soil outside of the
building’s footprint, which concentrates
vapors in the dry areas below the building.
Strong winds can cause internal building pressure
to reduce thus causing more vapor to enter
into a building.
The simple way to think of it is that our
heating and air conditioning systems and wind
can act as a pump. Pushing vapors out and
pulling vapors into the building.
It can be a challenge when interpreting sampling
results to determine if chemicals present
in indoor air are coming from vapor intrusion
from the subsurface.
Are the vapors coming from outside or ambient
air? – To check for this, we sample the
outdoor air at the same time as sampling indoor
Are the vapors coming from common household
products? – To check for this, we should
remove household products that may be interfering
with our sampling.
Now let’s discuss the supplemental guidance.
The supplemental guidance improves vapor intrusion
Outlining and describing good processes that
environmental professionals should use to
conduct vapor intrusion sampling.
And collect representative samples.
Recommends that vapor intrusion sampling be
done early in a site investigation rather
than waiting for a full site investigation
to be complete to protect public health.
Promotes a statewide consistent approach.
The supplemental guidance covers:
Focusing first on occupied buildings close
The recommended samples to be collected and
results used to screen buildings for vapor
Proper sample locations.
Based on sample results, which steps to take
Incorporation of sewer samples to identify
if vapors are entering into the buildings
through sewer laterals.
When we need to make changes to our approach
based on sample results.
The supplemental guidance is similar to existing
vapor intrusion guidance documents including
U.S. EPAs 2015 guidance in that:
Buildings should be screened with soil gas
Multiple rounds of sampling should be collected
to account for variations due to weather and
Still focusing on protection of human health.
Vapor behavior will always be complicated
and somewhat unpredictable if data is lacking.
The key differences of the supplemental guidance
It promotes conducting vapor intrusion sampling
early during a site investigation to identify
if there is a problem for building occupants
to protect people faster.
It encourages making decisions based on sampling
results rather than models.
It recommends use of U.S. EPA’s screening
numbers to decide when to move into indoor
Collection of vapor samples within sewer laterals
to identify if indoor air results are from
Provides a prescriptive 4-step screening process
to conduct an indoor air assessment.
Introduces the concept that both current and
future conditions should be evaluated.
Let’s spend a little time walking you through
the four-step process for screening buildings.
This process and efforts to identify vapor
intrusion issues should be done early during
a overall site investigation to protect human
(Step 1) Once a spill or contamination is
known, the first step is to identify which
buildings are located within 100 feet of the
spill and are occupied.
(Step 2) After we identify buildings of interest,
the next step or Step 2 is to install soil
gas probes in proximity to those buildings
then collect samples.
We recommend multiple rounds of sampling and
at different seasons .
If any of the soil gas sample results indicate
there is a potential vapor intrusion problem,
we recommend proceeding with a vapor intrusion
assessment for that building.
(Step 3) As part of this third step, indoor
air sampling and air sampling just below a
buildings foundation should be done at multiple
locations for an individual building and repeated
multiple times at different seasons.
Also, there may be situations where we need
to go strait to indoor air sampling, especially
if the building overlies shallow contamination.
All sampling results should be compared to
screening levels to identify if there is any
vapor intrusion issue currently or may be
one in the future.
If a vapor intrusion issue identified, then
Step 4 provides direction how to manage the
vapor intrusion problem likely through a combination
of mitigation measures and cleanup of contamination.
As a supplemental guidance, we want to make
clear that this guidance is not a holistic
document for vapor sampling.
It does not provide direction how to collect
How to use mathematical models to evaluate
It does not set cleanup goals.
And does not tell the reader how to cleanup
We recommend that you use DTSC 2011 Vapor
Intrusion Guidance, DTSC’s 2011 Vapor. Intrusion
Mitigation Advisory or VIMA, and USEPA’s
2015 OSWER guidance for direction on sample
collection, mitigation measures, and cleanup
Cleanup goals should be worked out with the
lead agency for a specific project.
We want to make sure you are all aware of
the potential impacts that this guidance may
have to properties undergoing environmental
investigation and neighboring properties.
First, indoor air sampling may happen earlier
in the process.
We anticipate that more buildings will need
This may include more neighboring properties
and will mean more coordination with the owners
and occupants of those nearby properties to
gain access to the property to sample and
to communicate the results.
if potential problems are identified, then
we want to conduct indoor air and air sampling
beneath a building’s foundation.
Because of the multiple rounds of sampling,
this may the overall project take longer.
If we find vapor intrusion issues, we will
want to control those vapor through a combination
of mitigation measures and cleanup efforts
If concentrations are high enough, there will
be a component of long term monitoring to
insure mitigation measures and cleanup efforts
are having the desired results.
With the increased monitoring and screening
process it may delay redevelopment projects
thus may drive cost up.
Lastly, if neighboring properties are impacted
from vapor intrusion, those impacts should
be disclosed as part of property transfer.
This might impact property values until the
situation is fully resolved.
You all may be asking when this guidance will
We would like to start implementing it after
we have received all public comments, revised
the guidance based on that feedback, then
finalized the guidance.
After finalization we will be training regulatory
So how will we view cases?
New cases – recommend using the guidance
Existing cases – we need to evaluate what
sampling has already been done and what is
For closed cases – with any new science
some closed cases may need to be re-evaluated.
Each agency will evaluate their closed cased.
Many will do this case by case, based on changing
land use or referrals, some may systematically
re-evaluate a portion of their caseload.
With USEPA’s information regarding TCE,
we need to look at our TCE sites more closely.
Now let’s discuss the process for providing
We want to share some upcoming activities
associated with the Draft Supplemental Guidance
and vapor intrusion.
As mentioned previously, we are hosting live
question and answer sessions on May 14 and
19, 2020 for both the technical presentations
from 1:30 to 3:30 pm and the general overview
presentation from 6 to 8 pm.
The public comment period started February
14 and will end on June 1, 2020. This deadline
was extended from the original April 30, 2020
deadline, due to the complexities with the
The CalEPA vapor intrusion workgroup will
review public comments and incorporate input,
as appropriate, into a finalized guidance
We anticipate that this may take up to 3 months
and the final version may be ready by late
fall/winter of this year but may take longer
with the volume of comments received.
Additionally, CalEPA is exploring proceeding
with vapor intrusion regulation or policy
that may develop in the near future.
The draft supplemental guidance document can
be found online at both DTSC’s and the State
Water Boards’ vapor intrusion websites.
Unfortunately, hard copies are currently not
available due to the COVID-19 crisis and directives
from the Governor to Shelter in Place. If
lifted, hard copies will be available for
viewing at each of our Water Board and DTSC
If you are having difficulty obtaining an
electronic copy of the Draft Supplemental
Guidance or would like to receive a hard copy,
please contact Abe Waggoner. His information
is provided on the next slide and on the public
Again, the public comment period started February
14, 2020 and will end on June 1, 2020.
Please send comments either by mail to the
State Water Board address provided or by email
to [email protected]
Email is preferred as I will explain in a
To assist you with your comment submittal,
we have provided Public Comment Instructions.
These instructions can be found on both DTSC
and State Water Board’s vapor intrusion
websites in both English and in Spanish.
Again, if you have any questions on the submittal
instructions, please contact Abe Waggoner.
You have options to submit your comments.
A comment letter can be sent to us either
by mail or email.
However, if you would like to help the workgroup,
we have provided a couple of pre-prepared
comment forms for your use that will help
us categorize your comments.
These pre-prepared comment forms are available
as PDF and Microsoft Word documents. The PDF
version has added capability by providing
dropdown boxes to help target specific sections
or attachments to the supplemental guidance.
If either of these forms are used, we would
prefer that you submit them by email so we
can copy and paste your comments into a database.
Of course, you can send these forms to us
through mail as well.
If you’d like any help with the forms or
how to submit comments, please contact Mr.
Abe’s contact information is found on the
public notice and the comment instructions
discussed in the previous slide.
The CalEPA vapor intrusion workgroup anticipates
that your comments will available to the public
and posted on the State Water Board’s and
DTSC’s vapor intrusion websites.
It is unlikely that the actual comment letters
will be available to the public due to the
new Americans with Disabilities Act requirements.
It is likely that comments will be provided
as a tabular format.
Following the comment period ending on June
1, 2020, the CalEPA vapor intrusion workgroup
will review all comments.
The workgroup will respond to comments on
a categorical basis.
Comments and response to comments will likely
be provided when the Supplemental Guidance
is finalized likely in the fall/winter 2020
The Workgroup’s next steps are to:
Complete the question and answer sessions.
The last is scheduled for May 19th
Receive all public comments by June 1st
Workgroup will then compile all comments for
review and develop responses.
Concurrently, the workgroup will revise the
guidance for recommendations that strengthen
We anticipate we will release the final guidance
by late fall/winter 2020.
Lastly, we may be moving forward with development
of vapor intrusion regulation or policy.
More information is available from DTSC and
the Water Boards online, or you can request
more information via email using the email
addresses shown here.
This concludes the general overview presentation.
If you have any questions regarding this presentation,
or general questions about the guidance, please
send your questions to [email protected]
with the Subject Line: General Presentation
The workgroup will review your question and
respond to as many as possible during the
live Q&A sessions to be held in May 2020.
Thank you for your time.