Indoor Air Background Concentration Trends

AEHS West Coast ConferenceSan Diego, California

March 23, 2016

PRESENTED BY:Robert Ettinger

Geosyntec Consultants, Inc.

Vapor Intrusion Investigation Trends

• Recent regulatory guidance is leading toward more frequent indoor air sampling

• Impact of background sources on sample results is recognized, but representativeness of literature values has been questioned

• Forensic methods to assess background are available, but understanding “typical” values can help in risk based decision making and risk communication.

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Indoor Air Background (1990-2005)

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From USEPA, 2011. Background Indoor Air Concentrations of Volatile Organic Compounds in North American Residences (1990-2005): A Compilation of Statistics for Assessing Vapor Intrusion

Approach

• Review data from recent data sets– Residential indoor air investigations– Data collected after 2011– 24-hr to 7-day samples

• Compare concentration distributions– USEPA data summary to assess temporal changes– Indoor to outdoor air– Chemical-specific findings

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Recent Background Data Sets

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SoCalSample Period:  2015# IA Samples:  209#OA Samples:  52  

No. RockiesSample Period:  2012# IA Samples:  50#OA Samples:  0  

So. RockiesSample Period:  2011‐2015# IA Samples:  510#OA Samples:  16  

Southeast BSample Period:  2014‐2015# IA Samples:  110#OA Samples:  110  

Southeast ASample Period:  2014‐2015# IA Samples:  150#OA Samples:  150  

Petroleum Hydrocarbons

• Benzene• Naphthalene• Toluene• Ethylbenzene• Xylenes• Trimethylbenzenes

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Benzene

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Comparison with USEPA 2011 Study

0.097

RBSL

Naphthalene

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Comparison with USEPA 2011 Study

0.083

RBSL

Petroleum Hydrocarbons

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Comparison with USEPA 2011 Study

1.1RBSL

100RBSL

300RBSL

7.3RBSL

Chlorinated VOCs

• Trichloroethene• Tetrachloroethene• 1,2-Dichloroethane• Carbon tetrachloride• Chloroform• 1,4-Dichlorobenzene

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Trichloroethene

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Chlorinated VOCs

0.01

0.1

1

10

100USEPA Bkgrd_low USEPA Bkgrd_High SoCal IA North Rockies IA South Rockies IA

Con

cent

ratio

n (u

g/m

3)TCE

90th

75th

25th

median

10th

0.48

RBSL

Tetrachloroethene

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Chlorinated VOCs

0.01

0.1

1

10

100USEPA Bkgrd_low USEPA Bkgrd_High SoCal IA North Rockies IA South Rockies IA Southeast_A IA Southeast_B IA

Con

cent

ratio

n (u

g/m

3)

PCE

90th

75th

25th

median

10th

0.48

RBSL

1,2-Dichloroethane

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Chlorinated VOCs

0.01

0.1

1

10

100USEPA Bkgrd_low USEPA Bkgrd_High SoCal IA North Rockies IA South Rockies IA Southeast_A IA Southeast_B IA

Con

cent

ratio

n (u

g/m

3)

1,2-Dichloroethane

90th

75th

25th

median

10th

0.11

RBSL

Carbon Tetrachloride

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Chlorinated VOCs

0.01

0.1

1

10

100USEPA Bkgrd_low USEPA Bkgrd_High SoCal IA North Rockies IA Southeast_A IA Southeast_B IA

Con

cent

ratio

n (u

g/m

3)Carbon Tetrachloride

90th

75th

25th

median

10th

0.067

RBSL

Chloroform

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Chlorinated VOCs

0.01

0.1

1

10

100USEPA Bkgrd_low USEPA Bkgrd_High SoCal IA North Rockies IA Southeast_A IA Southeast_B IA

Con

cent

ratio

n (u

g/m

3)Chloroform

90th

75th

25th

median

10th

0.12

RBSL

1,4-Dichlorobenzene

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Chlorinated VOCs

0.01

0.1

1

10

100USEPA Bkgrd_low USEPA Bkgrd_High SoCal IA North Rockies IA Southeast_A IA Southeast_B IA

Con

cent

ratio

n (u

g/m

3)

Exposure Areas

1,4-Dichlorobenzene

90th

75th

25th

median

10th

0.26

RBSL

Outdoor Air Contribution to Background

• Compare distribution of VOCs in indoor and outdoor air to assess the effect of outdoor air on indoor air quality

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Benzene

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Indoor-Outdoor Concentration Comparison

Petroleum Hydrocarbons

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Indoor-Outdoor Concentration Comparison

Trichloroethene

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Indoor-Outdoor Concentration Comparison

Carbon Tetrachloride

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Indoor-Outdoor Concentration Comparison

Chloroform

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Indoor-Outdoor Concentration Comparison

1,2-Dichloroethane

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Indoor-Outdoor Concentration Comparison

1,4-Dichlorobenzene

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Indoor-Outdoor Concentration Comparison

Key Points

• Background concentrations for several compounds are greater than RBSLs

• Recent data generally within range of historical literature values– some background levels slightly lower (petroleum compounds,

TCE), – some higher (chloroform, 1,2-DCA, 1,2-DCB)– Some unchanged (carbon tetrachloride)

• Indoor air concentrations are higher than outdoor air concentrations for many chemicals

• Consider these factors when planning indoor air sampling and communicating with stakeholders.

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