Vapor Intrusion: Investigation of Buildings

Vapor Intrusion: Investigation of Buildings

Migration of VOCs through the building foundation and lessons learned from the detailed field investigation of the vapour

intrusion process at Altus and Hill Air Force Bases

Vingsted CenterMonday, March 9, 2009

GSI ENVIRONMENTAL INC.Houston, Texaswww.gsi-net.com (713) 522-6300 [email protected]

source area

Air Exchange

SITE BUILDING

2

Vapor Intrusion: Investigation of BuildingsVapor Intrusion: Investigation of Buildings

United States Regulatory Framework

Spatial and Temporal Variability

Impact of Indoor Sources on VI Investigations

Air Flow and VOC Migration Around Buildings

Controlled Investigation of Vapor Intrusion in Buildings

Conclusions and Recommendations







4

Effect of Building Pressure on VOC Transport

Lower building pressure

Residence in winter(chimney effect); bathroom, kitchen vents

Flow in

EXAMPLES

Gas flow from subsurface into building

High Pressure

Low Pressure

DOWNWARD VOC TRANSPORT

LowPressure

High Pressure

UPWARD VOC TRANSPORT

Higher building pressure

Building HVAC designed to maintain positive pressure

Flow out

EXAMPLES

Gas flow from building into subsurface

Variable building pressure

Barometric pumping; variable wind effects

Reversible flow

EXAMPLES

Bi-directional flow between building and subsurface

5

Effect of Weather on Building Pressure

COLD WEATHERCOLD WEATHER

Temperature and wind create pressure gradients that influence air movement in and around buildings.

Stack Effect: Warm airleaks through roof creating negative building pressure

Stack Effect: Warm airleaks through roof creating negative building pressure

soilsoil subslab fill

+ +

- -

WINDWIND

Wind on Building creates pressure gradient that results in air flow.

Wind on Building creates pressure gradient that results in air flow.

soilsoil

wind

++

++

subslab fill

KEY POINT:

6

Effect of Mechanical Ventilation

Mechanical ventilation can create localized or building-wide pressure differences that drive air flow.

KEY POINT:

MECHANICAL VENTILATION

Examples in Houses:- HVAC system

- Exhaust fans (kitchen, bath)- Furnace- Other combustion appliances (water heater, cloths dryer, etc)

7

Pressure Gradient Measurements:School Building, Houston, Texas

Dif

fere

nti

al P

ress

ure

(P

asca

ls)

Time (July 14-15, 2005)

-40

-30

-20

-10

0

10

20

30

40

6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00

Neg. Pressure

Pos. Pressure

Pressure gradient frequently switches between positive and negative within a single day.

KEY POINT:

Pressure Transducer

8

Pressure gradients potentially influenced by wide variety of factors. Measurements document non-representative sampling conditions.

Pressure Gradient Measurements:Tropical Storm Cindy

KEY POINT:

Pressure Transducer

Dif

fere

nti

al

Pre

ssu

re

(Pas

casl

)

-80

-60

-40

-20

0

20

40

60

80

13:00 17:48 22:36 3:24 8:12 13:00 17:48

Time (July 5-6, 2005)

High south wind

High north wind & low

atmospheric pressure

Positive pressure:

HVAC

Neg. Pressure

Pos. Pressure

Test Site

Storm Track: TS Cindy

9

Negative PressureNegative Pressure

Positive PressurePositive Pressure

“ Worst Case” VI conditions.

No current VOC transport from subsurface. Indoor VOCs due to background sources.

Bi-directional VOC transport. Carefully consider potential sources of measured indoor and sub-slab VOCs.

Pressure ReversalPressure Reversal

-8

-6

-4

-2

0

2

4

6

0.00 10.00 20.00

-6

-4

-2

0

2

4

6

0.00 10.00 20.00

-6

-4

-2

0

2

4

6

0.00 10.00 20.00

Interpretation of VOC Measurements

PRESSURE CONDITION

INTERPRETATION OF VOC DATA

Pressure gradients drive VOC transport. Multiple indoor VOC sampling events may be needed to measure VI.

KEYPOINT:KEYPOINT:

10

Typical Building VI Investigation: Outdoor, Indoor, and Sub-Slab SamplingTypical Building VI Investigation: Outdoor, Indoor, and Sub-Slab Sampling

Sub-Slab Sampling Dataat Apartment Complex

Concurrent sampling of sub-slab, indoor air, and outdoor air.

KEY POINT:

11

0.1

1

10

100

1000

10000

Vapor Sampling: No Vapor IntrusionVapor Sampling: No Vapor Intrusion

INDOOR AIR

VOC Concentration (ug/m3) at Residence in Illinois

S

BELOW SLAB

AMBIENT AIR

12

KEY POINT:

Common indoor sources of VOCs

p-Dichloro-benzene

Used as air freshener and indoor pesticide for moths and carpet beetles.

Petroleum-based solvents, paints, glues, gasoline from attached garages.

BTEX

Even at sites with no subsurface source, these chemicals will commonly be detected in indoor air and sub-slab samples.

Emitted from molded plastic objects (e.g., toys, Christmas decorations).

1,2-DCA

1,2-DCA = 1,2-dichloroethane

13

VOC Transport Model: Bidirectional Flow

Model simulates advective transport of chemicals between building air and subsurface soil through building slab.

Positive PressurePositive Pressure

Negative PressureNegative Pressure

14

Model Results: Transient Indoor VOC SourceModel Results: Transient Indoor VOC Source

VOCs from building can be trapped below slab.

KEY POINT:

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0 1 2 3 4 5

Time (days)

Predicted VOC

Concentration (ug/m3)

Indoor Air

Subsurface

Detection limit

Phase 1 Phase 2 Phase 3

Phase 4

VOC Conc. vs. Time: Transient SourceIndoor

Sub-Slab

BIDIRECTIONAL VOC TRANSPORT

Vapors trapped below slab

PRESSURE

15














16

Study Design: Sampling Program

MEASUREMENT PROGRAM:

Measure VOC concentrations in and around building under baseline and induced negative pressure conditions.

1.5ss ss ss

SF6SF6

RadonRadon

VOCs, Radon

VOCs, Radon, SF6

VOCs, Radon,

SF6

Analyses

Ambient Air

Indoor Air

Sub-slab

MEDIUMSamples

per Building

1 - 3

3 - 5

3 - 5

17

Study Design: Building Pressure

Sample Event 1: Baseline ConditionsSample Event 1: Baseline Conditions

Sample Event 2: Induced Negative PressureSample Event 2: Induced Negative Pressure

soilsoilsubslab fill

-2.50.5

TIME

Bu

ild

ing

Pre

ssu

re

TIME

Bu

ild

ing

Pre

ssu

re

18

Study Design: Test Site

TEST SITE:

Three single-family residences over a TCE plume near Hill AFB in Utah

19

Study Results: Impact of Depressurization on Air Flow

soilsoil

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

Res. #1

Res. #2

Res. #3

AE

R R

atio

(Dep

res

sure

/B

asel

ine)

subslab fill

Cross-Foundation Pressure GradientCross-Foundation Pressure Gradient

-1.5

-1

-0.5

0

0.5

1

1.5

4/30/2007

12:00

4/30/2007

18:00

5/1/2007

0:00

5/1/2007

6:00

5/1/2007

12:00

5/1/2007

18:00

5/2/2007

0:00

5/2/2007

6:00

5/2/2007

12:00

5/2/2007

18:00

5/3/2007

0:00

Time

Gra

die

nt

(Pa)

Baseline Depressure

Change in Air Exchange

Rate (AER)

Induction of negative building pressure resulted in 3 to 6-fold increase in air exchange rate.

KEYPOINT:KEYPOINT:

20

Study Results: Chemical Concentration Ratios

Sub-slab to indoor air concentration ratio provides an indication of the likely source of the chemical. However, multiple sources may contribute to indoor air impact.

KEYPOINT:KEYPOINT:

Co

nce

ntr

atio

n R

atio

(Su

b-s

lab

/In

do

or

air)

Baseline Samples Depressurization Samples

Residence #1 Residence #2

0.01

0.1

1

10

100

1000

RadonTCE SF6

1,2-DCA

PCE

Benzene

SS Source Indoor Source

0.01

0.1

1

10

100

1000

RadonTCE SF6

1,2-DCA

PCE

Benzene

Co

nce

ntr

atio

n R

atio

(Su

b-s

lab

/In

do

or

air) SS Source Indoor Source

Residence #3

21

Study Results: Volatile Chemical Detection Frequency

All chemicals commonly detected in indoor air samples. Chemicals w/ subsurface sources (Radon and TCE) more commonly detected in sub-slab samples.

KEYPOINT:KEYPOINT:

0%10%20%30%40%50%60%70%80%90%

100%

RadonTCE SF6

1,2-DCA

PCE

Benzene

0%10%20%30%40%50%60%70%80%90%

100%

RadonTCE SF6

1,2-DCA

PCE

Benzene

Det

ecti

on

Fre

qu

ency

Det

ecti

on

Fre

qu

ency

Indoor Air Samples Sub-slab Gas Samples

Baseline Samples Depressurization Samples

Note: Detection frequency is for combined sample set from all three residences.

22

Study Results: Impact of Depressurization on VOC Concentration

Res. #1 Res. #2 Res. #3

Location

0.1

1

10

Co

nc

en

tra

tio

n

Ra

tio

(De

pre

ss

uri

zati

on

/B

as

eli

ne

)

Location

0.1

1

10

Res. #1 Res. #2 Res. #3

Co

nc

en

tra

tio

n R

ati

o

(De

pre

ss

uri

zati

on

/B

as

eli

ne

)0.1

1

10

Res. #1 Res. #2 Res. #3

Location

Co

nc

en

tra

tio

n

Ra

tio

(De

pre

ss

uri

zati

on

/B

ase

lin

e)

0.1

1

10

Res. #1 Res. #2 Res. #3

Location

Co

nc

en

tra

tio

n R

ati

o

(De

pre

ss

uri

zati

on

/B

as

eli

ne

)

1,2-DCAPCE

SF6

Benzene

RadonTCE

RadonTCE

Subsurface Source Indoor Source

VOCConc.

in sub-slab gas

VOCConc.

in indoor

air

23

BUILDING

Air Exchange

Study Results: Impact on VOC Conc.

VOCconc. in sub-slab

gas

VOCconc. in indoor

air

VOCs from indoor source

VOCs from subsurface

source(DCA, PCE, SF6,

Benzene)(TCE, Radon)

24

Building depressurization does NOT appear to increase the magnitude of vapor intrusion.

Building depressurization improves ability to detect vapor intrusion by increasing the contrast between VOCs from indoor vs. subsurface sources.

Impact of Building

Pressure on Evaluation of Vapor Intrusion

Building Depressurization: Project Findings

“Worst Case”Vapor

Intrusion

CiaCia

LowPressure

High Pressure

Use building depressurization to increase contrast between indoor and subsurface sources of VOCs.

KEYPOINT:KEYPOINT:

25







Recommendations






Recommendations

26

Vapor Intrusion: RecommendationsVapor Intrusion: Recommendations

General Strategy

Groundwater Sampling

Soil Gas Sampling

Indoor Air Sampling

Non-VOC Measurements

Typical Building Sampling Program

General Strategy


Soil Gas Sampling

Indoor Air Sampling



27

VOCs: Practical Tips from the Field

VOCs are pervasive. You will always find hits in indoor air.

Use radon as a tracer to control for background.

It’s Background,

Stupid

Cartridges are Funky,

Summas are Re-Used

Run full Method T0-15 scan to be able to distinguish petroleum hydrocarbon composition of soil vapor vs. indoor air.

For Petroleum,Run Full VOC Scan

Sorbent cartridges affected by moisture, less repeatable.

Summa canister preferable, but have individually-certified clean. Summa

CanisterSumma Canister

Understand variability in VOC concentration:

1) Indoor Air:

2) Subsurface:

Single sample can accurately characterize well-mixed space.

Consider multiple measurement locations and sample events:

- Separate sample events by months

- Evaluate uncertainly based on observed variability

Accounting for Variability

Skip samples to don’t increase knowledge: (e.g., multiple indoor samples; daily resamples.)

KEY POINT:

29


General Strategy


Soil Gas Sampling

Indoor Air Sampling



General Strategy


Soil Gas Sampling

Indoor Air Sampling



30

Key Physical Processes at GW InterfaceGroundwater InterfaceGroundwater Interface

Aquifer

SourceArea

SourceArea

Clean waterlense

Aquifer

Evapotranspiration

31

Distribution of TCE in Shallow Groundwater

Based on >150 water table samples

VOC distribution at water table is difficult to predict and may be very different from deeper GW plume.

KEY POINT:

Graphic from presentation by Bill Wertz (NYSDEC) made at ESTCP-SERDP Conference, December 2008.

32

Groundwater Sampling: Key Considerations

Aquifer

SourceArea

SourceArea

Clean waterlense

Aquifer

- Understand physical processes at water table.- For vapor intrusion, collect water samples

from top of water table.

KEY POINT:

33


General Strategy


Soil Gas Sampling

Indoor Air Sampling



General Strategy


Soil Gas Sampling

Indoor Air Sampling



34

Soil Gas Sampling: Considerations

Sample Volume: Lab often needs only 50 mL of sample. Use ≤1L sample vessel (not 6L Summa), if available.

Purge Volume: Use small diameter sample lines to minimize purge volume.

Sample Rate: Use lower flow rate in fine grain soils to minimize induced vacuum.

Goal: Minimize the flow of gas in subsurface due to sample collection

Where Does Your Sample Come From?

Flexibility required to allow use of newly validated sample collection and analysis methods.

KEY POINT:

35

Soil Gas Sample Collection:Scheme for Summa Canister

36

Soil Gas Sampling: Sample Collection

Shallower Sample Point

Pressure gauge

Flow controller

Deeper Sample Point

37

Liquid Tracer

Apply to towel and place in enclosure or wrap around fittings.

• Examples: DFA, isopropyl alcohol, pentane

• High concentrations in samples may cause elevated detection limits for target analytes(Check w/ lab before using)

Gas Tracer

Inject periodically or continuously into enclosure around fittings and sample point:

• Examples: Helium, SF6

• On-site analysis (helium)• Potentially more quantitative

DFA = 1,1-difluoroethane, SF6 = sulfur hexafluoride Photo from Todd McAlary

Photo from Blayne Hartman

Soil Gas Sampling: Leak Tracers

38

Sample Point Shroud

Leak Tracer Gas

Field Meter for Leak Tracer

Soil Gas Sampling: Gas Phase Leak Tracer

39

Summa Canisters

Soil Gas Sampling: Summas vs. Sorbent Tubes

Sorbent Tubes

Most accepted in U.S. Simple to use

Less available outside U.S. Canisters are re-used,

subject to carry-over contamination

More available world wide Better for SVOCs*

Use is more complex- pump calibration- backpressure - breakthrough of COC- selection of sorbent

* = Analysis for SVOCs not typically required, but sometimes requested by regulators.

40

Results Comparison: Summa / Sorbent (ug/m3)

Summa vs Sorbent: Side-by-Side

beacon-usa.com1-800-878-5510

PHOTO PROVIDED BY:Reference: Odencrantz et al., 2008, Canister v. Sorbent Tubes: Vapor Intrusion Test Method Comparison, Proceedings of the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, May 2008.

TCE

PCE

SG-02 SG-03

20.5 / 10.5 292 / 149

3070 / 1357 22,200 / 5917

<2.7 / <1.7

187 / 225

SG-04

KEYPOINT:

Even skilled practitioners see up to 4x difference between Summa and sorbettube results.

41


General Strategy


Soil Gas Sampling

Indoor Air Sampling



General Strategy


Soil Gas Sampling

Indoor Air Sampling



42

Sample Location ConsiderationsSample Location Considerations

■ Collect at least one outdoor sampleCollect at least one outdoor sample► Compare indoor and outdoorCompare indoor and outdoor

■ Consider collection subslab samples Consider collection subslab samples (concurrent with indoor air samples)(concurrent with indoor air samples)

► Compare indoor and subslab or near-slabCompare indoor and subslab or near-slab

■ Recommend sampling in lowest level and consider Recommend sampling in lowest level and consider sampling next highest levelsampling next highest level

► Investigate COC patternsInvestigate COC patterns

■ Consider sampling near potential indoor sources Consider sampling near potential indoor sources or preferential pathwaysor preferential pathways

► Attached garage, industrial sourceAttached garage, industrial source► Basement sump, bathroom pipesBasement sump, bathroom pipes

Indoor Sampling: Overview

43

■ Placement of samplersPlacement of samplers

NOTE:Little value to collect multiple samples in a single building zone (e.g. same room), unless collecting QA duplicates.

■ Place at breathing-level heightPlace at breathing-level height■ Avoid registers, draftsAvoid registers, drafts■ Remember to sample for appropriate Remember to sample for appropriate

length of timelength of time► Typically 24 hours for residentialTypically 24 hours for residential► Typically 8-24 hours for occupationalTypically 8-24 hours for occupational

Collect indoor and subslab samples Collect indoor and subslab samples concurrentlyconcurrently

QA SamplesQA Samples: : Collect greater of one Collect greater of one duplicate per day or one per 20 samples. duplicate per day or one per 20 samples. (Collect additional QA samples if required by regs.)(Collect additional QA samples if required by regs.)

Indoor Sampling: Sample Locations

44

Sub-Slab Sampling

Sample CollectionSample Collection

Measure VOC concentration below building foundation

Outdoor Air Sampling

Document ambient conditions

45


General Strategy


Soil Gas Sampling

Indoor Air Sampling



General Strategy


Soil Gas Sampling

Indoor Air Sampling



46

VI Investigation Methods: VI Investigation Methods: Non-VOC MeasurementsNon-VOC Measurements

Non-VOC measurements can be used to evaluate vapor intrusion while avoiding background VOC issues.

Non-VOC measurements can be used to evaluate vapor intrusion while avoiding background VOC issues.

KEY POINT:KEY POINT:

RadonRadon

Building PressureBuilding Pressure

Naturally occurring tracer gas measures attenuation through building foundation.

Magnitude and duration of building pressure fluctuations: negative vs. positive building pressure.

Air ExchangeAir Exchange

Rate of ambient air entry into building. Supports mass flux evaluations.

47

Home Test Methods:Charcoal Canister, electret, alpha detector

Air Samples:Radon concentration measured at off-site lab *

Sub-Foundation

Indoor Air

Air Sample:Radon concentration measured at off-site lab *

Electret:Placed over hole in foundation (questionable accuracy)

* Off-site analysis provided by Dr. Doug Hammond, University of Southern California

Radon: Measurement OptionsRadon: Measurement Options

Cost/Sample

$10-50

$100

$100

$25-50

Key Point:Key Point:

Radon analysis less expensive than VOC analysis ($200-250/sample for VOCs by TO-15).

Radon analysis less expensive than VOC analysis ($200-250/sample for VOCs by TO-15).

48

BENEFITS:BENEFITS:

No common indoor sources of radon.

Lower analytical costs compared to VOCs.

Less bias caused by non-detect results indoors.

Can be used for long-term testing (up to 6 months).

Radon (Ra) as Tracer for Foundation Attenuation

Indoor Ra =0.9 pCi/L

Sub-slab Ra =833 pCi/L

Test Results AF Calculation

AFss-ia = 0.9 - 0.3

833

= 0.00048

Ambient Ra =

0.3 pCi/L

49

Rate at which indoor air is replaced by ambient (fresh) air.

What

ASHRAEStd.

62.1-2004

SF 6SF 6

Air Exchange: What ‘n How

WHY: Better understand observed VOC attenuation. Use value model or mass flux calculation.

Recommended ventilation rates for commercial building.

Ventilation Standards

Tracer Gas

Measure dilution of tracer gas to determine air exchange rate

ESTIMATION METHODS

J&E = Johnson and Ettinger model.

Air Exchange

BUILDING

50

Recommended Building Ventilation Rates

KEYPOINT:

Buildings designed for high density use will have high air exchange rates.

ANSI / ASHRAE Standard 62.1 – 2004Ventilation for Acceptable Indoor Air Quality

Building Type

Building Type

Air Exchanges(per day)

Air Exchanges(per day)

USEPA Default (Residential)

Office Space

Supermarket

Classroom

Restaurant

6

12

17

68

102

High Building Ventilation

51

KEY POINT:

Site-specific measurement provides most accurate measure of air exchange under current operating conditions.

Test Building

How:

Release tracer gas (SF6 or helium) into building at constant rate.

Measure steady-state concentration of gas in building.

Calculate air exchange based on release rate, concentration, and building volume.

Air Exchange: Measured Values

52


General Strategy


Soil Gas Sampling

Indoor Air Sampling



General Strategy


Soil Gas Sampling

Indoor Air Sampling



53

Residential Building Investigation: Recommended Sampling Program

BUILDING PRESSURE:

For more definitive results, conduct sampling program under induced negative pressure and positive pressure building conditions.

1.5ss ss ss

RadonRadon

VOCs, Radon

VOCs, Radon

VOCs, Radon

Analyses

Ambient Air

Indoor Air

Sub-slab Gas

MEDIUMSamples

per Building

1

1 - 2 (lowest level)

3 - 5

GAS MEASUREMENTS:

54

Guidelines for Vapor Intrusion Evaluation

Identifying Sites Needing VI Mitigation

KEY POINT:

Step-wise approach can help distinguish VI sources from indoor sources.

Swell !

Indoor Air > Risk Limit?

> Std?Indoor air conc’s. > applicable limits.

Subslab Vapors > Risk LimitSubslab vapors > applicable limits. >Std?

Pressure gradient supports soil gas flow into building

Building Pressure Supports VI

S

3

2

1

SG

air

55

Guidelines for Vapor Intrusion Evaluation

Identifying Sites Needing VI Mitigation

KEY POINT:

Step-wise approach can help distinguish VI sources from indoor sources.

Cause = Indoor/Ambient Source?Data set shows clear indoor/ambient source.Radon Data Suggest Actual VI?Rn attenuation factor suggests VOCs may enter house, too.

Pressurization and depressurization of bldg. show VI through slab.

Pressurization shows Actual VI ?

SRn

Rn

airP

Rn

Swell !

6

5

4Indoor Air > Risk Limit?

> Std?Indoor air conc’s. > applicable limits.

Subslab Vapors > Risk LimitSubslab vapors > applicable limits. >Std?

Pressure gradient supports soil gas flow into building

Building Pressure Supports VI

S

3

2

1

SG

air

Support provided by by the Environmental Security Technology Certification Program (ESTCP) Projects ER-0423 and ER-0707

Project Reports: www.estcp.org (Search “0423” & “0707”)

Special Thanks to:

Acknowledgements

Tim Nickels and Danny Bailey (GSI)Sam Brock (AFCEE)Kyle Gorder (Hill AFB)Blayne HartmanDavid Folks (Envirogroup), Todd McAlary (Geosyntec)

Documents

Vapor Intrusion: Investigation of Buildings