Vapor Intrusion: Investigation of Buildings

Vapor Intrusion: Investigation of Buildings

Overview of the US vapour intrusion framework, empirical attenuation factors, and the conceptual understanding of soil gas and

building dynamics

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: Wazzat?

KEY POINT:

Vapor intrusion is the movement of volatile chemicals into buildings from below ground.

BUILDING

GW source area

Soil source

areaVapors in

subsurface

Effect on indoor air quality?

3

Indoor SourcesIndoor Sources

False PositivesFalse Positives

Difficulty separating vapor intrusion from indoor sources of VOCs:- Affects indoor and sub-slab samples

Low levels of VOCs often detected in soil gas and indoor air samples:- Summa carry over contamination- Lab contamination- Unexpected minor sources

High VariabilityHigh Variability

LIMITATION DETAILS

VOC measurements alone often provide a confusing picture of vapor intrusion.

KEYPOINT:KEYPOINT:

Limitations of VOC Measurements

Gas

ss

ssssss

High spatial and temporal variability:- Conservative assumptions OR- Large number of samples

Summa

Canister

Summa

Canister

IntroductionIntroduction

4

Physical Barriers to Vapor Intrusion

KEY POINT:

Non-VOC measurements can provide improved understanding of vapor intrusion.

IntroductionIntroduction

A B

A B

A BGroundwater Interface:(A) Clean water lens;(B) Saturated confining layer

Vadose Zone(A) High moisture contentfine-grained soil layer

(B) Aerobic Biodegradation

Aquifer

SourceArea

UnsaturatedSoil

5

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







6

Vapor Intrusion: Regulatory FrameworkVapor Intrusion: Regulatory Framework

USEPA Framework

State Regulations

Petroleum vs. Chlorinated VOCs

Site-Specific Screening

Mass Flux Evaluations

USEPA Framework

State Regulations




7

Conceptual Model for Vapor Intrusion:

KEY POINT:

Regulatory guidance assumes vapor migration through soils and building foundation based on conservative assumptions.

Building Attenuation Due to Exchange with Ambient Air

Advection and Diffusion Through Unsaturated Soil and Building Foundation

Partitioning Between Source and Soil Vapor

Groundwater-Bearing

Unit

Air Exchange

BUILDING

Unsaturated Soil

3

2

1

Affected SoilAffected Soil

Affected GWAffected GW

Overview of USEPA VI GuidanceOverview of USEPA VI Guidance

8

NFA NFA NFA NFA NFA

Mitigation/Remediation

Typical Vapor Intrusion Screening Process

Step-wise VI investigation process recommended by most VI regulatory guidance.

KEY POINT

Chemicals could cause VI impact based on volatility and toxicity

CHEMICAL CRITERIA

GW conc. > VI screening levels

GW SCREENING

Soil gas/sub-slab conc. > VI screening levels

SOIL GAS/SUB-SLAB SCREENING

indoor air concentrations other measurements indicate vapor intrusion impact

INDOOR AIR TESTNG

No No No No

Yes Yes Yes Yes

Yes

No

Screening Steps Field Measurements

Current or future buildings within 10 - 30 m of edge of impact.

DISTANCE CRITERIA

9

Benzene

Ethylbenzene

USEPA VI Screening Values: Key COCs

Indoor Air (ug/m3)

Sub-slab (ug/m3)

0.31 3.1

2.2 22

3000MTBE 30000

Groundwater(mg/L)

Vinyl Chloride

Lindane

0.022TCE 0.22

0.28 2.8

0.0066 0.066

0.81PCE 8.1

* = Value based on MCL, risk-based number would be lower.

0.005*

0.70*

120

0.005*

0.002*

0.011

0.005*

KEY POINT:

Under EPA guidance, GW impacts above MCLs usually require VI investigation (i.e., ALL corrective action sites).

10


USEPA Framework

State Regulations




USEPA Framework

State Regulations




11

KEY POINT:

Draft or final guidance from NY, NJ, WI, CA, PA, MA, MI, NH, and others.

NJ: Screening values account for petroleum biodeg.

MA: Screening values based on indoor background.

NY: Screening based on sub-slab and indoor data only.

All: Screening values vary by >100x between states.

Approach to vapor intrusion varies widely between states. State guidance evolving rapidly.

Who

High-lights

Low-lights

State Vapor Intrusion GuidanceOverview of VI GuidanceOverview of VI Guidance

SITE BUILDINGSITE BUILDING

Affected GWAffected GWAffected GWAffected GW

Affected SoilAffected Soil

12

Benzene

Ethylbenzene

Indoor Air Limits: USEPA vs. States

USEPA VI Guide1

(ug/m3)New Jersey

(ug/m3)

0.31 2*

KEY POINT: Indoor air, soil gas, and GW screening values vary widely between states.

2.2 1,100

3000MTBE 2*

Range

Vinyl Chloride

Lindane

0.022TCE 3*

0.28 1*

0.0066 N/A

0.81PCE 3*

1) USEPA Limits based on 10-6 cancer risk, Texas limits based on 10-5 cancer risk * = Value based on TO-15 detection limit, risk-based value would be lower.

3.1

1000

94

14

2.8

0.5

42

Texas1

(ug/m3)

10x

500x

1500x

640x

10x

76x

45x

13


USEPA Framework

State Regulations




USEPA Framework

State Regulations




14

0.1

1

10

100

1000

10 100 1000 100000.001

0.01

0.1

1

10

100

1000

0.1 1 10 100 1000 10000

Observable RelationshipCia vs. Cgw ?

Chlorinated SolventsPetroleum Hydrocarbons

Ind

oo

r A

ir C

on

cen

trat

ion

( u

g/m

3)

Ind

oo

r A

ir C

on

cen

trat

ion

( u

g/m

3)

CORRELATION ? NO (p = 0.11)

CORRELATION ? YES (p <0.001)

Cgw = COC conc. In groundwater; Cia = COC conc. In indoor air; (p = 0.11) = Probability = 11% that slope of best-fit line = 0 (I.e., no trend).

GW Concentration (ug/L) GW Concentration (ug/L)

Petroleum Hydrocarbons: No

Chlorinated Solvents: Yes - Direct

Correlation Between Groundwater Concentration and Indoor Air??

Subslab to Indoor Air AF

15

Oxygen

AerobicBiodegradationPossibleCo>Co

min

No AerobicBiodegradationCo<Co

min Comin CH

max

Hydrocarbon

Vapor Source Zone

Vapor Concentration

CHmin Co

max

L

Petroleum Biodeg. AF

Petroleum Biodegradation Conceptual Model

From Roggemans et al., 2001, Vadose Zone Natural Attenuation of Hydrocarbon Vapors: An Empirical Assessment of Soil Gas Vertical Profile Data, API’s Soil and Groundwater Technical Task Force Bulletin No. 15.

KEY POINT:

Correlation between oxygen consumption and hydrocarbon attenuation.

16

KEY POINT:

For petroleum sites, vapor intrusion is generally associated with two factors acting together - shallow sources and preferential pathways.

Petroleum Vapor Intrusion: Industry Experience

Preferential pathway allows vapors to enter building.

1

NAPLNAPL

NAPLNAPL

Affected GW

Groundwater-Bearing Unit

Sump draws NAPL or dissolved hydrocarbons into building.

Shallow NAPL directly impacts building wall or floor.

BUILDING

32

Unsaturated

Soil

17


USEPA Framework

State Regulations




USEPA Framework

State Regulations




18

Site-Specific Screening: Vadose Zone

• Fine-grained soils (e.g., silt and clay) expected to inhibit vapor intrusion.

• However, available field data does not show clear relationship between soil type and vapor intrusion risk.

19


USEPA Framework

State Regulations

Petroleum vs. Chlorinated



USEPA Framework

State Regulations

Petroleum vs. Chlorinated



20

Mass Flux EvaluationsGroundwater ScreeningGroundwater Screening

Key Point:

High variability in subsurface VOC concentrations may limit use of mass flux analysis for vapor intrusion evaluation.

Mass flux into building must be < vertical mass flux out of groundwater.

MASS BALANCEAPPROACH:

source area

VGW-Bearing

Unit

Unsaturated

Soil

Fia1

L

Fsv

Fia2ERh

SITE BUILDING

Fgw1 Fgw2

Mass Balance

Fsv = Fgw1 - Fgw2

Fsv = Fia1 = Fia2

21








ss

ssssss

Distribution of VOCs

Vertical GW profile Vertical soil gas profile Sub-slab data Indoor air data Ambient air data

12345

Study Approach:

High density of data collected around individual buildings at two study sites.

Project Overview

1

23

45

6

788

1

Other Site Data

Physical soil properties Indoor air exchange Radon analysis Cross-foundation pressure gradient

67899

Altus AFB Study Site: Overview

Cluster 1

Cluster 2

Cluster 3

Sample Point Locations

Sample Point Locations

Altus AFB Study Site: Overview

Cluster 1

Cluster 2

Cluster 3

KEY POINT:

Collect at least three samples from each medium to quantify spatial variability.Collect at least three samples from each medium to quantify spatial variability.

Altus AFB Demonstration: Field Program

Field Investigation

Sample point cluster

Sub-slab point

Vertical soil gas points

Pressure transducer

Variability in Vapor Intrusion

Overview of VI Research Project

Building-Scale Spatial Variability Short and Long-Term Temporal Variability

Impact of Variability on Attenuation Factors


Building-Scale Spatial Variability in VOC Conc.

IndoorAir

Indoor Air

Sub-slab

Deeper soil gas

Ground-water

Number of Data Sets

Average Variability*

6

Spatial variability in subsurface media much higher than in indoor or ambient air.

KEY POINT:

* = Variability expressed as average of the coefficient of variation for each data set of three samples from the medium during each sampling event

Sub-slab

Deeper soil gas

Groundwater:Altus AFBHill AFB

Well Headspace

WellHeadspace

Ambient Air

AmbientAir

8

12

7

13

1064

0.55

0.26

0.96

0.96

0.92

0.901.350.21


Building-Scale Spatial Variability

Short and Long-Term Temporal Variability




Probe A3 (TCE - Normalized)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

13:50:0910:50:267:50:444:51:041:51:43

22:53:465:43:292:43:47

23:44:0420:44:2217:44:3914:44:5711:45:158:45:32

16:02:0113:02:1810:02:367:02:554:03:121:43:56

22:44:157:06:414:06:591:07:19

22:07:5819:11:25Time (3/16/07 to 4/10/07)

Normalized Concentration

Probe A3-3' (Port 9)



Short-term (3 weeks) Temporal Variability in Soil Gas TCE Concentration (from Blayne Hartmen):

<2x variation

Short-Term Temporal Variability:Timescale of days - Altus AFB

IndoorAir

Indoor Air

Sub-slab

Deeper soil gas

Ground-water

# of Paired Samples

Relative Percent Difference*

0

61% of paired subsurface gas samples had RPD <30%. 9% had RPD >100% (3x difference).

KEY POINT:

* = Relative percent difference (RPD) = (Sample 1 - Sample 2)/(Average of Sample 1 and Sample 2).

Sub-slab

Deeper soil gas

Groundwater

Well Headspace

WellHeadspace

Ambient Air

AmbientAir

1

6

11

6

7

N/A

1

0

4

3

1

< 30% 30 - 100% >100%

N/A

0

6

7

1

6

N/A

0

0

0

2

0

Long-Term (8 Years)Temporal Variability in Indoor VOC Concentration (from EnviroGroup):

5x Variation

0.01

0.1

1

10

Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04 May-05 Oct-06

Sample Date

Indoor Air DCE, ug/m3

H1 H2 H3 H4 H5

Long-Term (1 Year)Temporal Variability in Deep Soil Gas VOC Concentration (from NYDEQ): 5x Variation

IndoorAir

Indoor Air

Sub-slab

Deeper soil gas

Ground-water

Number of Data Sets

Average Variability*

0

For subsurface gas samples, longer-term temporal variability is similar to spatial variability

KEY POINT:

* = Variability expressed as average of the coefficient of variation for each data set of three samples from the medium during each sampling event

Sub-slab

Deeper soil gas

Groundwater

Well Headspace

WellHeadspace

Ambient Air

AmbientAir

0

6

10

5

6

N/A

N/A

1.02

0.80

0.96

0.52

Longer-Term Temporal Variability:Timescale of months - Altus AFB



Building-Scale Spatial Variability

Short and Long-Term Temporal Variability



Building-Scale Spatial Variability: How Many Samples?

IndoorAir

Indoor Air

Sub-slab

Deeper soil gas

Ground-water

+/- 50%

Number of Samples to Estimate True VOC Conc.*

3

Lots of sample locations required to understand VOC concentration in subsurface.

KEY POINT:

* = Number of samples = [(Z-statistic*CV)/Error]2; CV = coefficient of variation; for 90% confidence level, Z-statistic = 1.64

Sub-slab

Deeper soil gas

Groundwater:Altus AFBHill AFB

Well Headspace

WellHeadspace

Ambient Air

AmbientAir

1

10

10

9

9201

2

1

6

6

5

5111

+/- 67%

IndoorAir

Indoor Air

Sub-slab

Deeper soil gas

Ground-water

+/- 50%

Number of Samples to Estimate True VOC Conc.*

NC

Sampling effort should be balanced to characterized both spatial and temporal variability.

KEY POINT:

* = Number of samples = [(Z-statistic*CV)/Error]2; CV = coefficient of variation; for 90% confidence level, Z-statistic = 1.64

Sub-slab

Deeper soil gas

Groundwater:

Well Headspace

WellHeadspace

Ambient Air

AmbientAir

NC

11

7

10

3

NC

NC

6

4

6

2

+/- 67%

Long-Term Temporal Variability: How Many Samples?

Impact of Building-Scale Variability:

Pro

bab

ility

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

>2x >3x >5x >10x

Error for Single Measurement

Csubsurface

Error Between Single Measurement and Average VOC Concentration

Subsurface Measurements

Key Point:

Single measurement may not accurately represent subsurface vapor conditions.

Variability in VOC Concentration:

1) Indoor Air:

2) Subsurface:

Spatial: Low

Temporal: Moderate

Summary of Findings

Spatial: High

Short-Term Temporal: Low

Long-Term Temporal: High

Sampling effort should be balanced to characterized both spatial and long-term temporal variability in the subsurface.

KEY POINT:

39








40

Key Sources of VOCs in Indoor Air

Source of Background Indoor Air Impacts

REFERENCES:

USEPA, 1991, “Building Air Quality Guide”

OSHA, 1999, “Tech Manual for Indoor Air Investigation”

Ambient air Vehicles, gasoline Paints, adhesives Cleaning agents Insecticides Tobacco smoke Cosmetics, etc.

Significance of Background EffectsSignificance of Background Effects

41

0.1

1.0

10.0

100.0

1986 1991 1996 2001 2006

0.01

0.10

1.00

10.00

1986 1991 1996 2001 2006

Indoor use of chemicals has decreased. However, average background concentration remains well above USEPA risk limits.

Average Indoor Air Quality Over TimeAverage Indoor Air Quality Over Time

Note: 1) Average background indoor air concentrations reported in various studies by year of publication. 2) Indoor air limits (10-6) from USEPA Draft Vapor Intrusion Guidance, November 2002.

KEY POINT:

TRICHLOROETHENEBENZENE

Ave

rag

e B

ackg

rou

nd

C

on

cen

trat

ion

(u

g/m

3 )

Ave

rag

e B

ackg

rou

nd

C

on

cen

trat

ion

(u

g/m

3 )

USEPA INDOOR AIR LIMITUSEPA INDOOR AIR LIMIT

42

ARAMCO Art and Crafts Goop

Aleenes Patio & Garden Adhesive

Consumer Products Containing PCE

Product

Gumout Brake Cleaner

PCE Concentration

Hagerty Silversmith Spray Polish

Champion Spot it Gone

Plumbers Goop Adhesive

Liquid Wrench Lubricant w/ Teflon

Source: http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=177

Not Specified

70%

50 - 90%

67.5%

30.5%

20 - 25%

65 - 80%

KEY POINT:

Wide variety of consumer products still contain high concentrations of PCE.

Indoor AirIndoor Air

43

In 2004, background indoor and outdoor air concentrations still exceed risk-based limits for indoor air.

2004 Background vs. USEPA Risk-Based Limits2004 Background vs. USEPA Risk-Based Limits

1) Background concentrations from Sexton et al. 2004 ES&T 38(2); 423-430.2) USEPA Master Screening Values Table, September 2008

KEY POINT:

PCEBENZENE

Ran

ge

of

Rep

ort

ed B

ackg

rou

nd

C

on

cen

tra

tio

n

(ug

/m3)

0.1

1

10

100

0 0.2 0.4 0.6 0.8 1 1.2

INDOOR AIR LIMIT2

90th %

10th %

Median

90th %

10th %

Median

0.01

0.1

1

10

0 0.2 0.4 0.6 0.8 1 1.2

INDOOR LIMIT2

90th %

10th %

Median

90th %

Median

Clean GW

Bkgrnd Air

Bkgrnd Air

Ambient 1

Indoor 1

Ambient 1

Indoor 1

10th %

44

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2004 2005 2006 2007 2008

Indoor concentration of 1,2-DCA increasing over time. New indoor source = molded plastic (e.g., toys, Christmas decorations).

New Indoor Source of 1,2-DCANew Indoor Source of 1,2-DCA

Note: 1) 1,2-DCA = 1,2-dichloroethane

KEY POINT:

CONCENTRATIONDETECTION FREQUENCY

1,2-

DC

A D

etec

tio

n

Fre

qu

ency

(%

)

1,2-

DC

A C

on

cen

trat

ion

(u

g/m

3 )

USEPA INDOOR AIR LIMIT

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2004 2005 2006 2007 2008

<0.08 <0.08 <0.08

Median 1,2-DCA Conc.

90%ile 1,2-DCA Conc.

2) Indoor 1,2-DCA data from residential area in Colorado. Data provided by Jeff Kurtz, Envirogroup ([email protected])

45

TCE Background at Redfields, CO., SiteTCE Background at Redfields, CO., SiteSignificance of Background EffectsSignificance of Background Effects

Adapted from USEPA Seminar on Indoor Air Vapor Intrusion, January 2003, Dallas, Texas

- 100 100 200 300 400 500

0.01

0.1

1

10

100

Post RemedyPre-Remedy

TCE

1,1-DCE

USEPA TCE Limit

USEPA 1,1-DCE Limit

Time After Vent System Installation (Days)

Cia in

Sin

gle

Ho

me

(u

g/m

3)

1,1-DCE

TCE

Indoor Air Data

Subslab VentSubslab Vent

0

KEY FINDINGS

TCE does NOT change after vent system startup.

Indoor TCE NOT due to vapor intrusion.

46

Key Findings Re: USEPA VI Guidance

USEPA indoor air limits are < < typical background VOC conc’s in indoor air.

USEPA indoor air limits are < < typical background VOC conc’s in indoor air.

Accurate identification of vapor intrusion impacts requires careful accounting of indoor sources.

VOC = Volatile organic compound

Significance of Background EffectsSignificance of Background Effects

USEPA VI Screening Values are not accurate for the prediction of indoor air impacts. Use of screening values will result in a high false positive rate.

USEPA VI Screening Values are not accurate for the prediction of indoor air impacts. Use of screening values will result in a high false positive rate.

Risk-Based Air Limits

False Positives

BOTTOM LINE:

Vapor Intrusion: Investigation of Buildings

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