distinguishing vapor intrusion sources from background
TRANSCRIPT
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NEMC – AUGUST 6, 2019 1
Distinguishing Vapor Intrusion Sources from Background Sources of Volatile Organic
Chemicals in Indoor Air Using Building Pressure Control
Presented by:
Helen Dawson1, Ph.D.
William Wertz1, Todd McAlary1, Theresa Gabris1, Daniel Carr2
Geosyntec Consultants1, DBCarrconsulting2
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NEMC – AUGUST 6, 2019 2
Topics
• Conventional approach to vapor intrusion (VI) assessment
• Key factors influencing VI
• Cross‐slab pressure differentials
• Building Pressure Control (BPC)
• Technology applications
• Regulatory acceptance
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Conventional VI Assessment
• Evacuated canisters
• Active thermal desorption tubes
• Grab (SS) or time averaged 8‐24 hr samples (IA)
CSS,1
CIA,1 CIA,2
CSS,2
CIA = indoor air (IA) concentration
CSS = subslab (SS) concentration
How many samples? How many rounds of sampling?
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NEMC – AUGUST 6, 2019 4
Technical Challenges
CSS,1
CSG,DEEP
CGW
CIA,1CIA,3
CIA,2
CSS,2
• Temporal variability in indoor air concentrations
• Background sources of volatile organic compounds
• Spatial variability in sub‐slab concentrations
• Preferential Pathways
Degreasers, Gun cleaners
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NEMC – AUGUST 6, 2019 5
Key Factors Influencing VI
Wind CombustionStack Effect
P = Building Pressure minus Exterior Pressure
P + P ‐P ‐ P ‐
P +
P + P ‐
P + P ‐
‐Pslab = VI
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NEMC – AUGUST 6, 2019 6
Cross‐Slab Pressure Differential (Pss)
Pss characterizes building susceptibility to subsurface vapor entry
Depressurized
CyclicNeutral
Pressurized
+P ‐
+P ‐+
P ‐
+P ‐
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NEMC – AUGUST 6, 2019 7
Sampling Approaches that Consider Pss• Monitor P:
• Indicates whether and when the building was susceptible to VI during sampling
• Simple, minimal cost, high data value‐to‐cost ratio
• Manipulate P (Building Pressure Control (BPC)):• Induce depressurized building conditions and sample to characterize VI impacts
• Induce positive pressure building conditions and sample to characterize background source emissions.
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NEMC – AUGUST 6, 2019 8
Case Studies (SERDP ESTCP ER‐201503)
Vandenberg AFB, CA• Building 11193• Former dry cleaner facility & gym
• Area: 11,000 ft2
• Height: 13.2 ft• Volume: 145,000 ft3
Raritan Arsenal, NJ• Building 200• Medical office• Area: 2,100 ft2,• Height: 8 ft• Volume: 16,800 ft3
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NEMC – AUGUST 6, 2019 9
0.00
0.50
1.00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
Concen
tration (ug/m3)
Indoor Air Concentrations: TCE ‐ 11/27/2016
Building Pressure Control – Data
0
1000
2000
3000
4000
5000
6000
7000
‐60
‐50
‐40
‐30
‐20
‐10
0
10
12:00
13:00
14:00
15:00
16:00
17:00
18:00
Fan Flow
Rate (CFM
)
Cross‐Bu
ilding Pressure (P
a)
Differential Pressure and Flow: 11/27/2016
‐10
‐20
‐50
‐10
1300
3700
2100
1300
‐60
‐50
‐40
‐30
‐20
‐10
0
10
11:00
12:00
13:00
14:00
15:00
16:00
17:00
Pressure Differen
tial (Pa
)
SSP 2
SSP 3
SSP 4
SSP 7
Baseline
‐50
‐20
‐10 ‐10
Cross Building P and Flow
Cross Slab P
Indoor Air Concentrations
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NEMC – AUGUST 6, 2019 10
Cross‐building pressure differential and flow relationships…
… provide information about building envelope leakiness.
y = 0.5216x0.545
R² = 0.9998
y = 0.8781x0.7064
R² = 0.9997
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
0 10 20 30 40 50 60
Air E
xcha
nge RA
te (1
/hr)
Cross Building Pressure Differential (‐Pa)
Building‐Specific Depressurization and AER
B‐200
B‐11193
y = 0.5216x0.545
R² = 0.9998
y = 0.8781x0.7064
R² = 0.9997
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
0 10 20 30 40 50 60
Air E
xcha
nge RA
te (1
/hr)
Cross Building Pressure Differential (‐Pa)
Building‐Specific Depressurization and AER
B‐200
B‐11193
Air Exchange Rate vs ∆P
Air E
xcha
nge
Rate
Cross Building Pressure Differential (∆P)
0
1000
2000
3000
4000
5000
6000
7000
‐60
‐50
‐40
‐30
‐20
‐10
0
10
12:00
13:00
14:00
15:00
16:00
17:00
18:00
Fan Flow
Rate (CFM
)
Cross‐Bu
ilding Pressure (P
a)
Differential Pressure and Flow: 11/27/2016
‐10
‐20
‐50
‐10
1300
3700
2100
1300
0
1000
2000
3000
4000
5000
6000
7000
‐60
‐50
‐40
‐30
‐20
‐10
0
10
12:00
13:00
14:00
15:00
16:00
17:00
18:00
Fan Flow
Rate (CFM
)
Cross‐Bu
ilding Pressure (P
a)
Differential Pressure and Flow: 11/27/2016
‐10
‐20
‐50
‐10
1300
3700
2100
1300
100
1000
10000
1.0 10.0 100.0
Flow
CFM
)
Cross‐Building Pressure Differential (‐Pa)
B200: Building Leakage Curves
100
1000
10000
1.0 10.0 100.0
Flow
CFM
)
Cross‐Building Pressure Differential (‐Pa)
B200: Building Leakage Curves
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NEMC – AUGUST 6, 2019 11
Indoor air sampling combined with BPC
0
1000
2000
3000
4000
5000
6000
7000
‐60
‐50
‐40
‐30
‐20
‐10
0
10
12:00
13:00
14:00
15:00
16:00
17:00
18:00
Fan Flow
Rate (CFM
)
Cross‐Bu
ilding Pressure (P
a)
Differential Pressure and Flow: 11/27/2016
0.00
0.50
1.00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
Concen
tration (ug/m3)
Indoor Air Concentrations: TCE ‐ 11/27/2016
‐10
‐20
‐50
‐10
1300
3700
2100
1300
0
1000
2000
3000
4000
5000
6000
7000
‐60
‐50
‐40
‐30
‐20
‐10
0
10
12:00
13:00
14:00
15:00
16:00
17:00
18:00
Fan Flow
Rate (CFM
)
Cross‐Bu
ilding Pressure (P
a)
Differential Pressure and Flow: 11/27/2016
0.00
0.50
1.00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
Concen
tration (ug/m3)
Indoor Air Concentrations: TCE ‐ 11/27/2016
‐10
‐20
‐50
‐10
1300
3700
2100
1300
….provides:• Reasonable upper bound indoor air concentrations from vapor intrusion• Vapor intrusion mass loading (ML) through the slab: (ML = Conc. X Flow)• Emission rates from background sources
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NEMC – AUGUST 6, 2019 12
Application to VI Risk Assessment
• Short term and reasonable maximum exposures: • Indoor air (IA) concentrations measured under upper‐bound, natural range of depressurized building conditions.
• Long term average exposures: • IA concentrations calculated from building mass loading (MLBPC) at average air exchange rates (AER):
IA = MLBPC / (VBLDG AERAVG)
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Cross slab pressure differential monitoring under depressurized conditions…
‐60
‐50
‐40
‐30
‐20
‐10
0
10
Pressure Di
fferential (P
a)
SSP 2
SSP 3
SSP 4
SSP 7
Baseline
‐50
‐20
‐10 ‐10
• …characterizes relative leakiness of floor slab.
B200
B11193
-20
-30
Baseline
BaselineCross‐slab
pressure diffe
rential
Cross‐slab
pressure diffe
rential
‐10 Cross‐building envelope pressure differential
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NEMC – AUGUST 6, 2019 14
Cross‐slab and cross‐building pressure relationships…
• …identify heterogeneities in floor leakiness, andareas with greater potential for vapor entry.
0
1
2
3
4
0 10 20 30 40
Cross‐Slab
Pressure Differen
tial (Pa
)
Cross‐Building Pressure Differential (Pa)
Building 11193
SS‐1
SS‐2
SS‐3
SS‐4
SS‐1
SS‐2 SS‐3
SS‐4
PID Readings
Source: ESTCP ER‐201322
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NEMC – AUGUST 6, 2019 15
BPC Ballpark Costs
• ~ $4,000 ‐ $8,000
• Similar to costs for 2 rounds of conventional IA and SS sampling
• A one day test in a typical residential or small commercial building; 1 to 2 days for larger buildings
• Baseline, depressurization, and pressurization monitoring
• 6 Summa® canister samples
• Experienced mid‐level professionals; 10 hour work days; travel
• Repeat seasonal sampling not needed
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NEMC – AUGUST 6, 2019 16
Regulatory Acceptance of BPC• Approved everywhere we have proposed it.• EPA Regions: 2, 3, 4, 8, 9• States: CA, GA, IN, KY, NC, NJ, TN, UT, WV
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NEMC – AUGUST 6, 2019 17
Technology Applications
• Real Estate Transactions • Environmental due diligence
• Liability assessment
• Environmental site investigation
• Remedy performance evaluation
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Building Pressure Control – Benefits
• Potential for VI impacts can be effectively evaluated with one day of testing.
• Faster & less costly than multiple (>2) conventional monitoring events
• No need for repeat sampling
• Better define building specific conditions for risk management decisions.
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NEMC – AUGUST 6, 2019 19
Temporal Variability Long-Term Passive Sampling
Building Pressure Control
Spatial Variability High Volume Subslab Sampling
Background Sources Compound Ratio Analysis
Compound-Specific Isotope Analysis
Portable Mass Spectrometers
Preferential Pathways Pneumatic Testing and Leakance Analysis
VI Challenges Innovative Solutions
Building Pressure Control
Building Pressure Control
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NEMC – AUGUST 6, 2019 20
QUESTIONS?
Helen E. Dawson, Ph.D.Geosyntec ConsultantsWashington, D.C. USA