RPIC: Federal Contaminated Sites Workshop

May 2012

Lindsay Smith-Munoz, Ian Hers, Meghan Roushorne,

Jo-Ann Aldridge, Asish Mohapatra

Comparison of Observed Vapour Attenuation versus Model Predicted for Sites

Contaminated with Chlorinated Solvents

Summary

•  Goal of study was to compare modeled vapour intrusion attenuation factors to those calculated from site data

•  Data was gather from multiple sources, and needed to be filtered to control quality, and the influence of background

•  Compared to Health Canada’s vapour intrusion model which is based on the Johnson and Ettinger model

•  Model was not found to be consistently conservative, but data issues may be partially responsible

2

3

Indoor Air Concentration = Source Concentration X Attenuation

Study Description

•  Compare model predictions to measured values

•  Chlorinated Solvents

•  Northern Regions

• Gathered data through informal networks, combined with US EPA database

4

Data Characteristics

•  Different countries, years, techniques

•  Sites with subsurface and indoor air samples (3 months)

•  Important details missing or inferred

 Sample depth, soil type, screen intervals etc.

5

Filtering

•  Remove Influence of Background   Source Strength

  Consistency between multiple chemicals

  Detection Limit

0.01

0.1

1

10

100

1000

1 100 10000 1000000

Background

No Background

Source Vapour Concentration (ug/m3)

Indo

or A

ir C

once

ntra

tion

Filtering For Source Strength

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

Att

enua

tion

Fact

or

Soil vapor f rom groundwater (ug/m3)

IA > RLIA < RLRes CG 1mRes CG 30mRes-FG-1mRes FG 30m

G

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08

Att

enu

atio

n F

acto

r

Soil Vapour from Groundwater (ug/m3)

IA > RLIA < RLRes CG 1mRes CG 30mRes-FG-1mRes FG 30m

G

Model Comparisons

•  Is the 75th percentile appropriate?

Health Canada’s Vapour Intrusion Model

•  Partitioning into soil pore space vapour, diffusive and advective transport into buildings, mixing in building

•  Model uses an empirical flow rate into building

•  No adjustments to model predictions for partitioning or biodegradation

•  More conservative than CCME for BTEX, wanted model to be more widely applicable, and to be applicable at sites where there is not sufficient data to determine if biodegradation is occurring.

9

Results -- Groundwater

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00 Residential

Coarse Residential

Fine Commercial Coarse and

Fine

Predicted Attenuation (1-10m depth) Empirical Attenuation (25-75%iles)

Median

95th Percentile

Atte

nuat

ion

Fact

or

Results - Soil Vapour

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00 Residential

Coarse Residential Fine Commercial

Coarse and Fine

Predicted Attenuation (1-10m depth) Empirical Attenuation (25-75%iles)

Median

95th Percentile

Atte

nuat

ion

Fact

or

Results – Subslab Samples

12

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00 Subslab Empirical

Attenuation (25-75%iles)

Recommended Subslab Attenuation Factor (0.02)

95th Percentile

Atte

nuat

ion

Fac

tor

Recommendations

•  The importance of adequate, good quality data can not be underestimated

•  Predict within 10x acceptable risk   Review data (2 samples, 2 sides of building, 2 seasons)

  Fill data gaps, consider multiple lines of evidence, subslab sampling

  For commercial buildings, check building parameters for correspondance with model assumptions (may need DQRA spreadsheet)

Acknowledgements

•  Health Canada: Odette Bose, Heather Jones-Otazo, Frederic Valcin, Deborah Schoen, Bertrand Langlet, Michelle Giddings

•  Alaska DEC: Todd Blessing, Rich Sundet, Janice Weigers, Ann Farris

•  OMOE: Camilo Martinez

•  NB Dept of Environment: Michel Poirier

•  Golder Associates: Theresa Repaso-Subyang, Lena Torin (Göteborg)

•  Department of Defense: Julie Dalgard

•  Oasis Environmental: Ben Martich

•  US EPA