Ian Hers UBC/Golder

Measurement of BTX Vapour Intrusioninto an Experimental Building

Alberta Environmental Protection (AEP)American Petroleum Institute (API)BC Environment (BCE)Canada Mortgage Housing Corporation (CMHC)Canadian Association Petroleum Producers (CAPP)Canadian Petroleum Products Institute (CPPI)Chatterton Petrochemical Corporation (CPC)Dow ChemicalGolder Associates Ltd.Ontario Ministry of Environment (OME)

Sponsored by:

Ian HersGolder Associates Ltd. /University of British ColumbiaAugust 15, 2000

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Ian Hers UBC/Golder

Presentation Outline

Chatterton site research program overview

Why measure VOC intrusion?

Conceptual models

Mathematical models

Experimental methods

Measured BTX flux and soil gas flow rates

Model comparisons

Conclusions and research needs

Chatterton site research program overview

Why measure VOC intrusion?

Conceptual models

Mathematical models

Experimental methods

Measured BTX flux and soil gas flow rates

Model comparisons

Conclusions and research needs

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Ian Hers UBC/Golder

Research Objectives

1.Conduct field-based project at hydrocarbon (BTX) -contaminated site (“Chatterton” research site).

2.Conduct integrated study addressing both vadosezone hydrocarbon transport and building intrusion.

3.Identify key processes & conditions affecting transport.

4.Incorporate results of other case studies including building science, radon & methane research.

5.Validate available screening level models, develop new (numerical) models.

6.Develop new or improved field methods.

7.Develop guidance or protocol addressing framework, model selection and use, and input parameters.

1.Conduct field-based project at hydrocarbon (BTX) -contaminated site (“Chatterton” research site).

2.Conduct integrated study addressing both vadosezone hydrocarbon transport and building intrusion.

3.Identify key processes & conditions affecting transport.

4.Incorporate results of other case studies including building science, radon & methane research.

5.Validate available screening level models, develop new (numerical) models.

6.Develop new or improved field methods.

7.Develop guidance or protocol addressing framework, model selection and use, and input parameters.

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Ian Hers UBC/Golder

Project Scope

Comprehensive, multi-year program

Construct new building (greenhouse) with controlled building properties, monitor old building

Field program:1. Baseline characterization, lab testing2. Vadose zone monitoring3. BTX intrusion measurements

Model development (numerical model for transport & intrusion)

Model validation

Comprehensive, multi-year program

Construct new building (greenhouse) with controlled building properties, monitor old building

Field program:1. Baseline characterization, lab testing2. Vadose zone monitoring3. BTX intrusion measurements

Model development (numerical model for transport & intrusion)

Model validation

Data Typeschemical distributionchemical propertiesenvironmental/meteorologicalsoil propertiesbuilding properties

Measurement Techniquessoil vapour profilingpush-pull diffusionin-situ respirationsoil-air permeabilitycontinuous ∆P, O2, Tflux chambertracer tests

Data Quality & Quantityuncertainty/statisticsanalyticalseasonal effectstransient effects

Data Typeschemical distributionchemical propertiesenvironmental/meteorologicalsoil propertiesbuilding properties

Measurement Techniquessoil vapour profilingpush-pull diffusionin-situ respirationsoil-air permeabilitycontinuous ∆P, O2, Tflux chambertracer tests

Data Quality & Quantityuncertainty/statisticsanalyticalseasonal effectstransient effects4

Ian Hers UBC/Golder

Why Measure VOC Intrusion?

Focus for this talk is building foundation and near-surface soils

Our understanding of vapour migration through building foundations is poor (more emphasis has been placed on vadose zone transport)

Evaluate importance of building depressurization and cracks

Research may lead to practical techniques

To validate models for this pathway, reduce uncertainty

Focus for this talk is building foundation and near-surface soils

Our understanding of vapour migration through building foundations is poor (more emphasis has been placed on vadose zone transport)

Evaluate importance of building depressurization and cracks

Research may lead to practical techniques

To validate models for this pathway, reduce uncertainty

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Ian Hers UBC/Golder@ Ian Hers Golder Associates / UBC

BIODEGRADATIONBIODEGRADATIONBIODEGRADATIONBIODEGRADATION

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Ian Hers UBC/Golder

ADVECTIONADVECTIONADVECTIONADVECTION

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Advective Processes

Driving forces include:temperature difference (stack effect) - probably most significantunbalanced ventilation, heating systemswind, temperature (diurnal), barometric pressure

Site-specific factors (construction, soil type, subsurface utilites) and relative permeability of soil and foundation are critical

Driving forces include:temperature difference (stack effect) - probably most significantunbalanced ventilation, heating systemswind, temperature (diurnal), barometric pressure

Site-specific factors (construction, soil type, subsurface utilites) and relative permeability of soil and foundation are critical

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Ian Hers UBC/Golder

Mathematical Models for Soil GasAdvection through Building Foundation

1.Flow to Perimeter Crack Model (analytical sol’n steady-state 2-D flow to horizontal drain) (Soil & Foundation)

2.Flow through Foundation Model (Hagan-Pouissellerelationship for laminar flow through parallel plates or tube (Just Foundation)

Q = K b w δh / δL K = ρairgb2 / (12µ)

1.Flow to Perimeter Crack Model (analytical sol’n steady-state 2-D flow to horizontal drain) (Soil & Foundation)

2.Flow through Foundation Model (Hagan-Pouissellerelationship for laminar flow through parallel plates or tube (Just Foundation)

Q = K b w δh / δL K = ρairgb2 / (12µ)

Q = 2πkair∆Pxcrack/(µln(2zcrack/rcrack)zcrack

3. Numerical model - How to couple flow in soil with flow through small cracks ? One possibility is to adapt MODFLOW (ASTM 5719-95)

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Possible Approaches to Estimate VOC Vapour Intrusion

1. Measure VOC concentrations (indoor & outdoor air, groundwater &/or soil vapour, ventilation)

vapour attenuation ratio (α)

using mass balance approach:

– VOC mass flux

– soil gas flow rate (assumes mass flux by advection)

2. Flux chamber measurements (cracks)

VOC mass flux

soil gas flow rate

3. Tracer test (inject SF6, use radon)

infer VOC flux and soil gas flow rate

1. Measure VOC concentrations (indoor & outdoor air, groundwater &/or soil vapour, ventilation)

vapour attenuation ratio (α)

using mass balance approach:

– VOC mass flux

– soil gas flow rate (assumes mass flux by advection)

2. Flux chamber measurements (cracks)

VOC mass flux

soil gas flow rate

3. Tracer test (inject SF6, use radon)

infer VOC flux and soil gas flow rate

Background ?

Sensitivity Scale Up ?

Boundary conditions?

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Ian Hers UBC/Golder

Experimental Methods

Constructed building with controlled properties

Used VOC measurements & flux chamber tests to estimate (i) vapour attenuation ratio, (ii) BTX flux into building & (iii) soil gas flow rate into building.

Natural (“Diffusion”) Cases - η = 0.00033, 2 tests

Depressurized (“Advection”) Cases - Fan Induced

i) 2.5 Pa, η=0.0001 ii) 10 Pa, η=0.0001

iii) 10 Pa, η=0.00033 iv) 30 Pa, η=0.00033

Extensive sub-slab monitoring BTX vapour, O2, pressure, temperature

Constructed building with controlled properties

Used VOC measurements & flux chamber tests to estimate (i) vapour attenuation ratio, (ii) BTX flux into building & (iii) soil gas flow rate into building.

Natural (“Diffusion”) Cases - η = 0.00033, 2 tests

Depressurized (“Advection”) Cases - Fan Induced

i) 2.5 Pa, η=0.0001 ii) 10 Pa, η=0.0001

iii) 10 Pa, η=0.00033 iv) 30 Pa, η=0.00033

Extensive sub-slab monitoring BTX vapour, O2, pressure, temperature

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Ian Hers UBC/Golder

Flux Chamber Testing Protocol

Test flux chamber blanks - a challenge !

Depressurize greenhouse

Purge 5 chamber volumes

Adjust flux chamber flow rate to equalize pressure in building and chamber (developed Q vs. ∆P curve for various leakage elements to assist in this)

Edge Crack - Q on order of 500 ml/min @ 10 Pa (sample without replacement)

Hairline Crack - Q on order of 10 ml/min @ 10 Pa (sample with replacement)

Collect samples over several hours using sorbanttube (Supelco 300)

Test flux chamber blanks - a challenge !

Depressurize greenhouse

Purge 5 chamber volumes

Adjust flux chamber flow rate to equalize pressure in building and chamber (developed Q vs. ∆P curve for various leakage elements to assist in this)

Edge Crack - Q on order of 500 ml/min @ 10 Pa (sample without replacement)

Hairline Crack - Q on order of 10 ml/min @ 10 Pa (sample with replacement)

Collect samples over several hours using sorbanttube (Supelco 300)

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Flux Chamber Design

Valve #4

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Soil Gas Flow Through Edge Crack

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Soil Gas Flow Through Hairline Crack & Capped Drain Pipe

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BTX Vapour Intrusion Measurement Results - Natural (“Diffusion”) Case

no significant difference in indoor & outdoor BTX concentrations

no measurable flux by flux chamber

BTX vapour concentrations below slab stayed low, O2 below slab remained elevated

no significant difference in indoor & outdoor BTX concentrations

no measurable flux by flux chamber

BTX vapour concentrations below slab stayed low, O2 below slab remained elevated

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Ian Hers UBC/Golder

Benzene Vapour Concentrations Below Centre Building - Natural Conditions

NATURAL SOIL COVER

0

0.5

1

1.5

0.0001 0.01 1 100Benzene Concentration (mg/L)

Dep

th (

m)

SG-BC Mar 11/97

SG-BC May 13&14/97

SG-BC June 24/97

SG-BC July 2/97

SG-BC July 25/97

SG-BR Dec 1/97

SG-BR Mar 18/98

SG-BR Nov/98

SG-BR Feb 19/99

DL=0.001 to 0.0001 mg/L, DL plotted if BDL

BELOW BUILDING (SG-BC)

0

0.5

1

1.5

0.0001 0.01 1 100Benzene Concentration (mg/L)

Dep

th fr

om T

op o

f Sla

b (m

)

Sept 2/97Oct 21/97Nov 14/97Mar 18/98June 25/98

DL=0.001 to 0.0001 mg/L,DL plotted if BDL

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Ian Hers UBC/Golder

Oxygen Concentrations Below CentreBuilding - Natural Conditions

BELOW BUILDING (SG-BC)

0

0.5

1

1.5

0 10 20 30O2 Concentration (%)

Dep

th (

m)

Oct 3/97 Oct 17/97 Nov 19/97 Nov 19/97 June 24/98 June 24/98 Mar 9/99

NATURAL SOIL COVER (SG-BR)

0

0 .5

1

1 .5

0 10 20 30O2 Concentration (%)

Dep

th (

m)

M ay 15 /97

S ept 27/98

S ept 28/98

N ov 17 /98

N ov 30& Dec 4 /98

M ar 9/99

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∆P = 10 & 30 Pa:Sub-slab BTX vapour levels increased, O2 decreasedIndoor BTX concentrations significantly higher than outdoor concentrationsHigh BTX flux through cracks

∆P = 2.5 Pa:increase in BTX vapour and decrease in O2 only below centre of slabIndoor BTX concentrations only slightly higher outdoor concentrationsLow BTX flux through cracks

Chatterton site conditions conducive for advectivetransport of BTX into building (shallow contamination, permeable soil/slab, high ∆P)

∆P = 10 & 30 Pa:Sub-slab BTX vapour levels increased, O2 decreasedIndoor BTX concentrations significantly higher than outdoor concentrationsHigh BTX flux through cracks

∆P = 2.5 Pa:increase in BTX vapour and decrease in O2 only below centre of slabIndoor BTX concentrations only slightly higher outdoor concentrationsLow BTX flux through cracks

Chatterton site conditions conducive for advectivetransport of BTX into building (shallow contamination, permeable soil/slab, high ∆P)

BTX Vapour Intrusion Measurement Re-sults - Depressurized (“Advection”) Case

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0.0

0.5

1.0

1.5

0.0001 0.01 1 100

Benzene Concentration (mg/L)D

epth

Bel

ow

To

p o

f S

lab

(m

)

Sept 2/97Oct 21/97Nov 14/97Mar 18/98June 25/98Nov 28/97Sept 2/98

-10 Pa Depres-surization

-30 Pa Depres-surization

Effect of Depressurization on Soil Gas Benzene Profile - Dynamic Conditions

-2.5 Pa similar to 10 Pa case

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Ian Hers UBC/Golder

2000

12980

6420

430 9380 1130 1130

Vapour Probe Benzene

Conc(ug/L)

Chatterton Benzene VapourConcentrations Directly Below SlabDepressurized ∆∆∆∆P=10 Pa, ηηηη=0.0001

Edge Crack

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Ian Hers UBC/Golder

0.039

3810

0.049

0.040 790 0.049 1130

Vapour Probe Benzene

Conc(ug/L)

Chatterton Benzene VapourConcentrations Directly Below SlabDepressurized ∆∆∆∆P=2.5 Pa, ηηηη=0.0001

Edge Crack

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Benzene Flux Through Cracks Measured Using Flux Chamber

Average F lux C ham ber F low R ate Average Benzene F lux(m l/m in) (m g/m in-P a-m )

Edge C rack (~2m m ) 460 0.016H airline C rack 11 0.00023

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Soil Gas Flow into Building

Measured soil gas flow rates:mass balance approach: ~ 2.7 to 4.2 L/minflux chamber: on order of 2 to 4 L/min

Predicted soil gas flow rates:flow to perimeter crack model: 8.2 (10 Pa) to 29 L/min (30 Pa)MODFLOW simulations: 4 to 5 L/min (10 Pa)– soil permeability most important

– over 90 % through open portion of 2 mm edge crack

– remainder through hairline cracks

Measured soil gas flow rates:mass balance approach: ~ 2.7 to 4.2 L/minflux chamber: on order of 2 to 4 L/min

Predicted soil gas flow rates:flow to perimeter crack model: 8.2 (10 Pa) to 29 L/min (30 Pa)MODFLOW simulations: 4 to 5 L/min (10 Pa)– soil permeability most important

– over 90 % through open portion of 2 mm edge crack

– remainder through hairline cracks

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MODFLOW DOMAIN

Impermeable boundarySlab

Silt & sand k=1 darcy

Crack

New sand k=25 darcy

Old sand k = 10 darcy

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MODFLOW RESULTS

Equipotentials

Flow Lines

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Source αααα - Direct Measurements

TYPE SITE CONDITIONS CHEMICAL αααα

BTEX Chatterton ∆P=0 Pa η=0.00033 B&T <1.2E-6∆P=2.5 Pa η=0.0001 5.0E-7∆P=10 Pa η=0.0001 1.1E-4∆P=10 Pa η=0.00033 2.0E-5∆P=30 Pa η=0.00033 1.4E-5

Alameda ∆P~3 Pa (wind) benzene <9E-6Slab-on-grade pentane <9E-7

Paulsboro SFR w\ bsmt ∆P=? benzene <1E-6CS CDOT HDQ Apartment/SFRs Avg 4 CS 3.0E-5

90th% 4 CS 6.5E-5Redfields SFRs w\ bsmt or cs Avg DCE 7.6E-5

90th% DCE 1.2E-4Lowry AFB Apartments Sept 97 Avg TCE ~ 1E-3??

Apartments/SFRs Avg TCE <1 to 6E-5

TYPE SITE CONDITIONS CHEMICAL αααα

BTEX Chatterton ∆P=0 Pa η=0.00033 B&T <1.2E-6∆P=2.5 Pa η=0.0001 5.0E-7∆P=10 Pa η=0.0001 1.1E-4∆P=10 Pa η=0.00033 2.0E-5∆P=30 Pa η=0.00033 1.4E-5

Alameda ∆P~3 Pa (wind) benzene <9E-6Slab-on-grade pentane <9E-7

Paulsboro SFR w\ bsmt ∆P=? benzene <1E-6CS CDOT HDQ Apartment/SFRs Avg 4 CS 3.0E-5

90th% 4 CS 6.5E-5Redfields SFRs w\ bsmt or cs Avg DCE 7.6E-5

90th% DCE 1.2E-4Lowry AFB Apartments Sept 97 Avg TCE ~ 1E-3??

Apartments/SFRs Avg TCE <1 to 6E-5

CS = chlorinated solvent, SFR = single-family residence34

Ian Hers UBC/Golder

Subslab αααα - Tracer Tests & Radon Studies

TRACER SITE CONDITIONS αααα Qsoil/(Qb*∆∆∆∆P)

BTEX Chatterton ∆P >= 10 Pa 3E-4 to 6E-4 0.005 - 0.01Slab-on-grade

SF6 Alameda ∆P ~ 3 Pa 2E-4 to 4E-4 ~0.006Fischer, 96 Slab-on-grade

SF6 Central CA ∆P = 30 Pa ~0.001 0.02Hodgson. 92 SFR w\ bsmt

SF6 Ben Lomand Experimental bsmt N/A 0.04 Garbesi, 93 3 mm edge crack

Rn Spokane R. SFR slab-on highly 7.9E-3 to 1.4E-2 N/AValley Rez- permeable sand &van, 92 gravel, winter

Rn Indoor Rn SFRs 1.6E-3 N/AUSA Little ‘92

TRACER SITE CONDITIONS αααα Qsoil/(Qb*∆∆∆∆P)

BTEX Chatterton ∆P >= 10 Pa 3E-4 to 6E-4 0.005 - 0.01Slab-on-grade

SF6 Alameda ∆P ~ 3 Pa 2E-4 to 4E-4 ~0.006Fischer, 96 Slab-on-grade

SF6 Central CA ∆P = 30 Pa ~0.001 0.02Hodgson. 92 SFR w\ bsmt

SF6 Ben Lomand Experimental bsmt N/A 0.04 Garbesi, 93 3 mm edge crack

Rn Spokane R. SFR slab-on highly 7.9E-3 to 1.4E-2 N/AValley Rez- permeable sand &van, 92 gravel, winter

Rn Indoor Rn SFRs 1.6E-3 N/AUSA Little ‘92

Implication α generally < ~ 0.001 for sub-slab vapour sourceQb = building ventilation rate, Qsoil = soil gas flowrate, A = subsurface foundation area

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Comparison Measured to Predicted (J&E) αααα

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Conclusions

Techniques were developed to measure soil gas & BTX intrusion into building

Flux chamber testing challenging

Advective processes significant:natural case: while there were diurnal & barometric pumping effects, no measurable intrusionsustained depressurization > 2.5 Pa: high BTX intrusion

Advection primarily controlled by ∆P & soil permeability

Intrusion through hairline cracks does occur !

Good comparison between measured & model-predicted soil gas flow rates into building

Techniques were developed to measure soil gas & BTX intrusion into building

Flux chamber testing challenging

Advective processes significant:natural case: while there were diurnal & barometric pumping effects, no measurable intrusionsustained depressurization > 2.5 Pa: high BTX intrusion

Advection primarily controlled by ∆P & soil permeability

Intrusion through hairline cracks does occur !

Good comparison between measured & model-predicted soil gas flow rates into building

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Ian Hers UBC/Golder

Conclusions

J&E model conservative, except for ∆P > 2.5 Pa

Building properties and interaction between building and vapour fate and transport is important (∆P effects, barometric / temperature pumping)

Significant uncertainty associated with this pathway -will be difficult to reduce this uncertainty

J&E model conservative, except for ∆P > 2.5 Pa

Building properties and interaction between building and vapour fate and transport is important (∆P effects, barometric / temperature pumping)

Significant uncertainty associated with this pathway -will be difficult to reduce this uncertainty

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