Distinguishing Vapor Intrusion Sources from Background ...

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


Topics

• Conventional approach to vapor intrusion (VI) assessment

• Key factors influencing VI

• Cross‐slab pressure differentials

• Building Pressure Control (BPC)

• Technology applications

• Regulatory acceptance


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?


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


Key Factors Influencing VI

Wind CombustionStack Effect

P = Building Pressure minus Exterior Pressure

P + P ‐P ‐ P ‐

P +

P + P ‐

P + P ‐

‐Pslab = VI


Cross‐Slab Pressure Differential (Pss)

Pss characterizes building susceptibility to subsurface vapor entry

Depressurized

CyclicNeutral

Pressurized

+P ‐

+P ‐+

P ‐

+P ‐


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.


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


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


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)


‐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)


‐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


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)


0.00

0.50

1.00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

Concen

tration (ug/m3)


‐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)


0.00

0.50

1.00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

Concen

tration (ug/m3)


‐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


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)


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


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


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


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


Technology Applications

• Real Estate Transactions • Environmental due diligence

• Liability assessment

• Environmental site investigation

• Remedy performance evaluation


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.


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




QUESTIONS?

Helen E. Dawson, Ph.D.Geosyntec ConsultantsWashington, D.C. USA

[email protected]

Distinguishing Vapor Intrusion Sources from Background ...

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