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Vapor Intrusion: Investigation of Buildings. SITE BUILDING. Air Exchange. source area. 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 Center

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slide1

Vapor Intrusion: Investigation of Buildings

SITE BUILDING

Air Exchange

source area

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 Center

Monday, March 9, 2009

GSI ENVIRONMENTAL INC.

Houston, Texas

www.gsi-net.com (713) 522-6300

temchugh@gsi-net.com

slide2

Vapor Intrusion: Investigation of Buildings

lUnited States Regulatory Framework

lSpatial and Temporal Variability

lImpact of Indoor Sources on VI Investigations

Air Flow and VOC Migration Around Buildings

lControlled Investigation of Vapor Intrusion in Buildings

lConclusions and Recommendations

slide3

LowPressure

High Pressure

High Pressure

Low Pressure

Effect of Building Pressure on VOC Transport

Gas flow from subsurface into building

EXAMPLES

Lower building pressure

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

Flow in

Gas flow from building into subsurface

UPWARD VOC TRANSPORT

EXAMPLES

Higher building pressure

Building HVAC designed to maintain positive pressure

Flow out

Bi-directional flow between building and subsurface

EXAMPLES

Variable building pressure

Reversible flow

Barometric pumping; variable wind effects

DOWNWARD VOC TRANSPORT

slide4

WIND

+

+

Effect of Weather on Building Pressure

COLD WEATHER

+

+

wind

-

-

soil

subslab fill

subslab fill

soil

Stack Effect: Warm air

leaks through roof creating negative building pressure

Wind on Buildingcreates pressure gradient that results in air flow.

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

KEY POINT:

slide5

Effect of Mechanical Ventilation

Examples in Houses:

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

MECHANICAL VENTILATION

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

KEY POINT:

slide6

Pos. Pressure

Neg. Pressure

Pressure Gradient Measurements:

School Building, Houston, Texas

Pressure Transducer

KEY POINT:

Differential Pressure (Pascals)

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

Time (July 14-15, 2005)

slide7

Pos. Pressure

Neg. Pressure

Pressure Gradient Measurements:

Tropical Storm Cindy

Positive pressure: HVAC

High south wind

Pressure Transducer

Differential Pressure (Pascasl)

High north wind & low atmospheric pressure

Test Site

Storm Track: TS Cindy

Time (July 5-6, 2005)

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

KEY POINT:

slide8

Interpretation of VOC Measurements

PRESSURE CONDITION

INTERPRETATION OF VOC DATA

Negative Pressure

“ Worst Case” VI conditions.

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

Positive Pressure

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

Pressure Reversal

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

KEYPOINT:

slide9

Typical 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:

slide10

S

Vapor Sampling: No Vapor Intrusion

VOC Concentration (ug/m3) at Residence in Illinois

INDOOR AIR

AMBIENT AIR

BELOW SLAB

slide11

Common indoor sources of VOCs

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

p-Dichloro-benzene

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

BTEX

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

1,2-DCA

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

KEY POINT:

1,2-DCA = 1,2-dichloroethane

slide12

VOC Transport Model: Bidirectional Flow

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

Positive Pressure

Negative Pressure

slide13

Model Results: Transient Indoor VOC Source

VOC Conc. vs. Time: Transient Source

Indoor

PRESSURE

Sub-Slab

BIDIRECTIONAL VOC TRANSPORT

KEY POINT:

VOCs from building can be trapped below slab.

Vapors trapped below slab

slide14

Vapor Intrusion: Investigation of Buildings

lUnited States Regulatory Framework

lSpatial and Temporal Variability

lImpact of Indoor Sources on VI Investigations

lAir Flow and VOC Migration Around Buildings

Controlled Investigation of Vapor Intrusion in Buildings

lConclusions and Recommendations

slide15

s

s

Study Design: Sampling Program

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

MEASUREMENT PROGRAM:

Samples per Building

Analyses

MEDIUM

SF6

VOCs, Radon

Ambient Air

1 - 3

1.5

s

VOCs, Radon, SF6

Indoor Air

3 - 5

Radon

VOCs, Radon, SF6

Sub-slab

3 - 5

slide16

0.5

-2.5

Building Pressure

Building Pressure

TIME

TIME

Study Design: Building Pressure

Sample Event 2: Induced Negative Pressure

Sample Event 1: Baseline Conditions

subslab fill

soil

soil

slide17

Study Design: Test Site

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

TEST SITE:

slide18

7.00

(Depressure/Baseline)

6.00

AER Ratio

5.00

4.00

3.00

2.00

1.00

0.00

Res. #1

Res. #2

Res. #3

Study Results: Impact of Depressurization on Air Flow

Cross-Foundation Pressure Gradient

Change in Air Exchange Rate (AER)

Baseline Depressure

Gradient (Pa)

subslab fill

soil

KEYPOINT:

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

slide19

Study Results: Chemical Concentration Ratios

Baseline Samples

Depressurization Samples

SS Source

Indoor Source

SS Source

Indoor Source

Concentration Ratio

(Sub-slab/Indoor air)

Concentration Ratio

(Sub-slab/Indoor air)

Residence #1

Residence #2

Residence #3

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:

slide20

Study Results: Volatile Chemical Detection Frequency

Indoor Air Samples

Sub-slab Gas Samples

Detection Frequency

Detection Frequency

Baseline Samples

Depressurization Samples

KEYPOINT:

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

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

slide21

Concentration Ratio

Baseline)

(Depressurization/

10

Concentration Ratio

1

Baseline)

(Depressurization/

0.1

Res. #1

Res. #2

Res. #3

Location

Study Results: Impact of Depressurization on VOC Concentration

Indoor Source

Subsurface Source

10

10

Radon

TCE

1,2-DCA

PCE

VOCConc. in indoor air

Concentration Ratio

1

1

Baseline)

(Depressurization/

0.1

0.1

Res. #1

Res. #2

Res. #3

Res. #1

Res. #2

Res. #3

Location

Location

10

Radon

TCE

SF6

Benzene

VOCConc.in sub-slab gas

Concentration Ratio

1

(Depressurization/

Baseline)

0.1

Res. #1

Res. #2

Res. #3

Location

slide22

BUILDING

Air Exchange

Study Results: Impact on VOC Conc.

VOCs from subsurface source

VOCs from indoor source

(DCA, PCE, SF6, Benzene)

(TCE, Radon)

VOCconc. in indoor air

VOCconc. in sub-slab gas

slide23

Cia

LowPressure

High Pressure

Building Depressurization: Project Findings

“Worst Case”

Vapor Intrusion

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

Impact of Building Pressure on Evaluation of Vapor Intrusion

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

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

KEYPOINT:

slide24

Vapor Intrusion: Investigation of Buildings

lUnited States Regulatory Framework

lSpatial and Temporal Variability

lImpact of Indoor Sources on VI Investigations

lAir Flow and VOC Migration Around Buildings

lControlled Investigation of Vapor Intrusion in Buildings

Recommendations

slide25

Vapor Intrusion: Recommendations

lGeneral Strategy

lGroundwater Sampling

lSoil Gas Sampling

lIndoor Air Sampling

lNon-VOC Measurements

lTypical Building Sampling Program

slide26

Summa Canister

VOCs: Practical Tips from the Field

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

n Use radon as a tracer to control for background.

It’s Background, Stupid

For Petroleum,

Run Full VOC Scan

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

n Sorbent cartridges affected by moisture, less repeatable.

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

Cartridges are Funky, Summas are Re-Used

accounting for variability
Accounting for Variability

Understand variability in VOC concentration:

Single sample can accurately characterize well-mixed space.

1) Indoor Air:

  • Consider multiple measurement locations and sample events:
  • Separate sample events by months
  • Evaluate uncertainly based on observed variability

2) Subsurface:

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

KEY POINT:

slide28

Vapor Intrusion: Recommendations

lGeneral Strategy

lGroundwater Sampling

lSoil Gas Sampling

lIndoor Air Sampling

lNon-VOC Measurements

lTypical Building Sampling Program

slide29

Groundwater Interface

Key Physical Processes at GW Interface

Evapotranspiration

slide30

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.

slide31

Groundwater Sampling: Key Considerations

- Understand physical processes at water table.

- For vapor intrusion, collect water samples from top of water table.

KEY POINT:

slide32

Vapor Intrusion: Recommendations

lGeneral Strategy

lGroundwater Sampling

lSoil Gas Sampling

lIndoor Air Sampling

lNon-VOC Measurements

lTypical Building Sampling Program

slide33

Soil Gas Sampling: Considerations

Where Does Your Sample Come From?

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

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.

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

KEY POINT:

slide35

Soil Gas Sampling: Sample Collection

Pressure gauge

Flow controller

Shallower Sample Point

Deeper Sample Point

slide36

Photo from Blayne Hartman

Photo from Todd McAlary

Soil Gas Sampling: Leak Tracers

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)

Liquid Tracer

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

Gas Tracer

  • • Examples: Helium, SF6
  • • On-site analysis (helium)
  • Potentially more quantitative

DFA = 1,1-difluoroethane, SF6 = sulfur hexafluoride

slide37

Soil Gas Sampling: Gas Phase Leak Tracer

Leak Tracer Gas

Sample Point Shroud

Field Meter for Leak Tracer

slide38

Soil Gas Sampling: Summas vs. Sorbent Tubes

  • Most accepted in U.S.
  • Simple to use
  • Less available outside U.S.
  • Canisters are re-used, subject to carry-over contamination

Summa Canisters

  • More available world wide
  • Better for SVOCs*
  • Use is more complex- pump calibration- backpressure - breakthrough of COC- selection of sorbent

Sorbent Tubes

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

slide39

PHOTO PROVIDED BY:

beacon-usa.com

1-800-878-5510

Summa vs Sorbent: Side-by-Side

Results Comparison: Summa / Sorbent (ug/m3)

SG-04

SG-03

SG-02

TCE

20.5 / 10.5

292 / 149

<2.7 / <1.7

PCE

3070 / 1357

22,200 / 5917

187 / 225

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

KEYPOINT:

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.

slide40

Vapor Intrusion: Recommendations

lGeneral Strategy

lGroundwater Sampling

lSoil Gas Sampling

lIndoor Air Sampling

lNon-VOC Measurements

lTypical Building Sampling Program

slide41

Indoor Sampling:Overview

  • Sample Location Considerations
  • Recommend sampling in lowest level and consider sampling next highest level
    • Investigate COC patterns
  • Consider sampling near potential indoor sources or preferential pathways
    • Attached garage, industrial source
    • Basement sump, bathroom pipes
  • Collect at least one outdoor sample
    • Compare indoor and outdoor
  • Consider collection subslab samples (concurrent with indoor air samples)
    • Compare indoor and subslab or near-slab
slide42

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

NOTE:

Indoor Sampling:Sample Locations

  • Placement of samplers
  • Place at breathing-level height
  • Avoid registers, drafts
  • Remember to sample for appropriate length of time
    • Typically 24 hours for residential
    • Typically 8-24 hours for occupational
  • Collect indoor and subslab samples concurrently
  • QA Samples: Collect greater of one duplicate per day or one per 20 samples. (Collect additional QA samples if required by regs.)
slide43

Sample Collection

Sub-Slab Sampling

Outdoor Air Sampling

Measure VOC concentration below building foundation

Document ambient conditions

slide44

Vapor Intrusion: Recommendations

lGeneral Strategy

lGroundwater Sampling

lSoil Gas Sampling

lIndoor Air Sampling

lNon-VOC Measurements

lTypical Building Sampling Program

slide45

VI Investigation Methods: Non-VOC Measurements

Naturally occurring tracer gas measures attenuation through building foundation.

Radon

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

Building Pressure

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

Air Exchange

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

KEY POINT:

slide46

Radon: Measurement Options

Cost/Sample

$10-50

$100

$100

$25-50

nHome Test Methods:Charcoal Canister, electret, alpha detector

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

Indoor Air

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

nElectret:Placed over hole in foundation (questionable accuracy)

Sub-Foundation

Key Point:

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

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

slide47

Test Results

AF Calculation

Indoor Ra =0.9 pCi/L

Ambient Ra =0.3 pCi/L

AFss-ia =

= 0.00048

Sub-slab Ra =833 pCi/L

0.9 - 0.3

833

Radon (Ra) as Tracer for Foundation Attenuation

  • 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).

BENEFITS:

slide48

BUILDING

Air Exchange

ASHRAE

Std.

62.1-2004

SF 6

Air Exchange: What ‘n How

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

What

ESTIMATION METHODS

Recommended ventilation rates for commercial building.

Ventilation Standards

Measure dilution of tracer gas to determine air exchange rate

Tracer Gas

nBetter understand observed VOC attenuation.

nUse value model or mass flux calculation.

WHY:

J&E = Johnson and Ettinger model.

slide49

Building Type

Air Exchanges(per day)

Recommended Building Ventilation Rates

ANSI / ASHRAE Standard 62.1 – 2004

Ventilation for Acceptable Indoor Air Quality

USEPA Default (Residential)

6

Office Space

12

Supermarket

17

Classroom

68

High Building Ventilation

Restaurant

102

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

KEYPOINT:

slide50

Air Exchange: Measured Values

How:

Test Building

nRelease tracer gas (SF6or helium) into building at constant rate.

nMeasure steady-state concentration of gas in building.

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

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

KEY POINT:

slide51

Vapor Intrusion: Recommendations

lGeneral Strategy

lGroundwater Sampling

lSoil Gas Sampling

lIndoor Air Sampling

lNon-VOC Measurements

lTypical Building Sampling Program

slide52

s

s

Residential Building Investigation: Recommended Sampling Program

GAS MEASUREMENTS:

Samples per Building

Analyses

MEDIUM

VOCs, Radon

Ambient Air

1

1.5

s

1 - 2 (lowest level)

Indoor Air

VOCs, Radon

Radon

Sub-slab Gas

VOCs, Radon

3 - 5

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

BUILDING PRESSURE:

slide53

Swell !

3

2

S

>Std?

1

air

Guidelines for Vapor Intrusion Evaluation

Identifying Sites Needing VI Mitigation

Indoor Air > Risk Limit?

Indoor air conc’s. > applicable limits.

Subslab Vapors > Risk Limit

Subslab vapors > applicable limits.

>Std?

Building Pressure Supports VI

Pressure gradient supports soil gas flow into building

SG

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

KEY POINT:

slide54

Swell !

3

6

2

5

Rn

Rn

S

S

>Std?

Rn

1

4

air

air

Guidelines for Vapor Intrusion Evaluation

Identifying Sites Needing VI Mitigation

Indoor Air > Risk Limit?

Cause = Indoor/Ambient Source?

Indoor air conc’s. > applicable limits.

Data set shows clear indoor/ambient source.

Subslab Vapors > Risk Limit

Radon Data Suggest Actual VI?

Subslab vapors > applicable limits.

Rn attenuation factor suggests VOCs may enter house, too.

>Std?

Building Pressure Supports VI

Pressurization shows Actual VI ?

Pressure gradient supports soil gas flow into building

Pressurization and depressurization of bldg. show VI through slab.

P

SG

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

KEY POINT:

special thanks to
Special Thanks to:

Acknowledgements

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”)

Tim Nickels and Danny Bailey (GSI)

Sam Brock (AFCEE)

Kyle Gorder (Hill AFB)

Blayne HartmanDavid Folks (Envirogroup), Todd McAlary (Geosyntec)