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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.
2
Indoor Air Background (1990-2005)
3
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
4
Recent Background Data Sets
5
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
Chlorinated VOCs
• Trichloroethene• Tetrachloroethene• 1,2-Dichloroethane• Carbon tetrachloride• Chloroform• 1,4-Dichlorobenzene
10
Trichloroethene
11
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
12
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
13
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
14
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
15
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
16
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
17
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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