soil vapor intrusion
DESCRIPTION
Soil Vapor Intrusion. A Decade of Regulatory Requirements & Experiences. Paul W. Locke MA DEP Bureau of Waste Site Cleanup One Winter Street Boston, MA 02108 617-556-1160 [email protected]. Late 1980s…. Hillside School, Needham Mass…. Wow…that can happen?. - PowerPoint PPT PresentationTRANSCRIPT
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ENVIRONMENTAL PROTECTION
Soil Vapor Intrusion...
A Decade of Regulatory Requirements & Experiences
Paul W. Locke
MA DEP Bureau of Waste Site CleanupOne Winter StreetBoston, MA 02108
of Massachusetts Department
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Late 1980s…
Hillside School,
Needham Mass…
Wow…that can happen?
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ENVIRONMENTAL PROTECTION
MADEP Regulatory Response:
1. Place concern on radar screen
2. Incorporate into cleanup standards
3. Obtain “real world” data to gauge scope/parameters of problem
4. Provide tools/toolbox to regulated community
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#1: On the Radar Screen…
Training/awareness: agency staff and regulated community
Regulatory requirement to notify MADEP if pathway likely or confirmed
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#2: Incorporate into Cleanup Standards
Transport Model
Calc Source Conc in GW
Ceiling Conc
50% Solubility
Lowest of 3 orGW background
or PQL,whatever higher
GWStandard
Air
Groundwater
Lowest of 3or
IAQ Background,whatever is higher
Non-Cancer RiskBased Indoor Air Conc
Cancer Risk BasedIndoor Air Conc
50% Odor Threshold
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1993 Standards Transport ModelJohnson & Ettinger
Assumed 10% Henry’s Law Equilibrium Condition
GW to Soil Gas:
Soil Gas to Indoor Air: = 5 x 10-4
“crude and limited application of J&E”
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Calculated GW Standards (1993)
Compound Standard (g/L)
TCE 300
1,1,1-TCA 4000
PCE 3000
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1996 Evaluation
Are these Standards Really Protective?
Let’s take a Look at our Files…
GW Conc
Soil Gas Conc
Indoor Air Conc
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MADEP Records Review
Database Search
DEP Files6000
Potential SitesEvaluated
177
Adequate Data 59 sites
Chlorinated 36 (61%)
BTEX23 (39%)
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Petroleum Sites?
Chlorinated Solvent Sites?
Findings: Were the 1993 Standards Generally Conservative & Protective?
☺
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Proposed Revisions(2004)
Chemical-Specific Evaluations
Conservative Pathway Scenario
Conservative Site/Soil Properties
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Key J&E Inputs (MADEP 2004)
Groundwater• 7 feet below grade;• 1 foot below basement floor
Sand, total porosity • n = 0.43
Building Depressurization • P= 4 Pa (40 g/cm-s2); • 0.45 air exchanges/hour
Vadose Zone Moisture Content • [w] = ????
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Moisture Level Below Buildings
Dry Soils?
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Vadose Zone Soil Moisture
What is a realistic, conservative value….. beneath buildings?
Little study data available, but….
Fair amount of chemical analytical data from soil samples beneath buildings!
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Soil Moisture (v/v) Distribution
0
5
10
15
20
25
30
35
0-5 6-10 11-15 16-20 21-25 >25
Soil Moisture Value (% by volume)
Nu
mb
er
of
Sa
mp
les
*Moisture (w/w) to Soil Moisture(v/v)
0.06
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Proposed Revisions to Current MADEP Groundwater Standards
(Soil Vapor Pathway)
Up to an order of magnitude lower for some chlorinated solvents
Public Comment Period Ended December 10, 2004
Stay Tuned…..
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#4: Provide Tools & Toolboxes Site-Specific Evaluations
Guidance Documents
Rules of Thumb
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Site-Specific Pathway Evaluation
(Mandatory when > Generic GW Standard)
Key Tools:
Soil Gas Assessment
Indoor Air Analysis
Vertical Profiling
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F i g u r e 4 - 1 : E v a l u a t i n g I n d o o r A i r P a t h w a y v i a M e t h o d 2
C o n t a m i n a n t s > G W - 2 s t a n d a r d , c o n t a m i n a t e d s o i l s n e a r b u i l d i n g ,
a n d / o r o t h e r e v i d e n c e o f p o t e n t i a l i n d o o r a i r i m p a c t s
I n s t a l l s o i l g a s p r o b e s b e n e a t h
p o t e n t i a l l y i m p a c t e d s t r u c t u r e ( s )
P I D / F I D c o n c o f t o t a l o r g a n i c v a p o r s
< a c t i o n l e v e l s i n T a b l e 4 - 9 ?
G C s c r e e n i n g c o n c o f s o i l - g a s < a c t i o n
l e v e l s l i s t e d i n T a b l e 4 - 1 0 ?
I n d o o r a i r l e v e l s < p u b l i s h e d b a c k g r o u n d
c o n c e n t r a t i o n s i n T a b l e 4 - 1 1 ?
E v a l u a t e c h e m i s t r y o f
i n d o o r a i r d a t a
S a m p l e i n d o o r a i r v i a T O - 1 4 o r A P H m e t h o d
d u r i n g “ w o r s t c a s e ” s e a s o n a l c o n d i t i o n s
C o l l e c t s i t e - s p e c i f i c i n f o r m a t i o n o n
s o i l / b u i l d i n g
C o n d u c t s i t e - s p e c i f i c m o d e l o f i n d o o r a i r
p a t h w a y ( e . g . , J o h n s o n a n d E t t i n g e r )
E v a l u a t e a l l l i n e s o f e v i d e n c e t o d e c i d e i f
i n d o o r a i r i m p a c t i s m o r e l i k e l y t h a n n o t
I n d o o r a i r i m p a c t s a r e n o t l i k e l y ( a b s e n t a n y o t h e r i n f o r m a t i o n o r d a t a t o
t h e c o n t r a r y )
I n d o o r a i r i m p a c t s c o n f i r m e d , l i k e l y , o r c a n n o t b e r u l e d o u t – p r o c e e d w i t h
n o t i f i c a t i o n / I R A / r i s k a s s e s s m e n t / C E P m i t i g a t i o n a s n e e d e d
O p t i o n a l p a t h w a y / s e c o n d a r y i t e r a t i o n s R e c o m m e n d e d f i r s t i t e r a t i o n
N o
N o
Y E S
Y E S N o
Y E S
MA
DE
P R
ecom
men
ded
Ap
pro
ach
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MADEP Guidelines for Soil Gas Evaluation:
Compound
Screen out levels ppmV
PID (eV)
FID<10 10-11.4 >11.4
Toluene 11 12 12 10
Ethylbenzene 4 4 4 3
Xylenes 25 26 24 22
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MADEP Guidelines for Obtaining Soil Gas Samples
depth togroundwater
buildingfoundation
foundation cracks
enclosed space
vadose zonediffusing vapors
capillary zone
dissolved chemical ingroundwater
Infiltration displaces/ solubilizes soil gases
Negative bias
grass
pavement
place probe below bldg/pavement for
representative samples
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Real World Example of Negative Bias: TCE Soil Gas Data from 2 Homes
Date Interior Exterior
9/96 397 / 281 24 / <1 12/96 16 / 80 <1 / <1 3/97 6 / 64 <1 / <1
6/97 19 / 226 <1 / <1 8/97 157 / 594 4 / <1
All data ppb v/v TCE
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Obtaining Indoor Air Samples
Winter months usually “worst case” - Other
times may not rule out pathway
frost layer
Furnace combustion
Stack Effects
Vapors
windows closed
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Groundwater/Vertical Profiling
Infiltration
VOC plume
fresh water lens
well
groundwater flow
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For More Information…..• [email protected] or [email protected]
• Characterizing Risks Posed by Petroleum Contaminated Sites: Implementation of the MADEP VPH/EPH Approachwww.mass.gov/dep/bwsc/files/02-411.pdf
• Indoor Air Sampling and Evaluation Guidewww.mass.gov/dep/ors/files/indair.pdf
• MCP Numerical Standards: GW-2 www.mass.gov/dep/bwsc/files/standard /gw2/gw2.htm