INDOOR AIR PROGRAM AND DATA EVALUATION

Marilyn S. Hajicek, P.G.

Colorado Department of Labor and EmploymentDivision of Oil and Public Safety

OPS Vapor Intrusion Program

Regulations effective 2/1/99Regulations and Guidance available at:

http://oil.cdle.state.co.us

Overview

Discussion of current programRationale for development of database Key elements of the databaseFindings to-dateFuture data evaluation and collection

Initial Screening Criteria

RBSLs in groundwater to protect indoor air exposure pathway.

Benzene – 0.015 mg/LToluene – 6.9 mg/LEthylbenzene – 18 mg/LXylenes – 14 mg/L

RBSLs apply to structures within the influence of contamination (exceptions: businesses that dispense petroleum products).

Immediate Indoor Air Sampling

In some situations, indoor air samples are collected immediately.

Presence of free product in close proximity to the structure.Presence of petroleum odors inside the structure.Complaints of possible exposure effects from building occupants.

Indoor Air BTEX Thresholds

Benzene 0.23 µg/m3 (10-6 carcinogenic risk)Toluene 120 µg/m3 (Hazard Index = 1)Ethylbenzene 300 µg/m3 (HI= 1)Xylenes 210 µg/m3 (HI= 1)

Secondary Screening Criteria

Soil vapor concentrations that exceed the RBSL for the soil vapor to indoor air exposure pathway

Benzene = 2,700 µg/m3

Advantages of Soil Vapor Sampling

Can be used to screen both soil to indoor air and groundwater to indoor pathways.Does not have the background issue that indoor air sampling poses.Does not unduly alarm potential receptors.Soil vapor concentrations represent average conditions over larger areas (than a point soil sample).Sub-slab soil vapor samples are potentially useful but may be difficult to obtain.

Attenuation Factor

Johnson & Ettinger model used to calculate attenuation factor.

vaporsoil

airindoor

RBSL

RBSLAF =

Sample Collection Locations and Depths

Locations for permanent soil vapor wellsAt source of contaminationBetween source of contamination and structure

Depths of well screensAt source of contaminationAt depth of foundationAdditional samples based on heterogeneity

Site Specific Screening Criteria

Examples of parameters that can be changed:Distance between foundation and soil vapor sourceTotal soil porosity unsaturated zoneAir and water content of unsaturated zoneTotal building area Intrinsic permeability of soil adjacent to foundation

Soil Sampling Results

Soil vapor concentrations > RBSL near structure at the depth of foundation

collect indoor air samples

Soil vapor concentrations > RBSL at source and/or at depth of contamination near structure, but < RBSL at depth of foundation near structure

continue monitoring

Background Issues

Screen for potential sources in buildingSample indoor air in other structures of similar use and construction in vicinity, outside of the influence of contaminationCollect outdoor air samples concurrently

Indoor Air Sampling

Collected from:Occupied living areasBasement, if applicable

Indoor Air Mitigation

Immediate mitigation activities are implemented at sites where indoor air samples exceed the site- specific threshold (and are not eliminated through the background screening process).

Post-Assessment Monitoring

Regular monitoring of indoor air and soil vapor will continue:

At any site where indoor air concentrations do not exceed the indoor air threshold, but soil vapor samples exceed RBSLs or SSTLs, orAt any site where indoor air samples exceed the indoor air threshold, and mitigation has been implemented.

Typical Program Scenario

Database Evaluation Goals

Identify if there are trends based on site conditions (soil types, depth to groundwater, source concentrations, etc.)Compare results with current process to identify if additional screening criteria is appropriateDetermine additional data collection needsDetermine whether vadose biodegradation can be characterized using site information in the database

Media Concentration Samples

Type of Sample Number of Sites

Soil vapor 109

Groundwater 109

Soil 103

Indoor air 22

Crawl space 2

Sub-slab 1

Physical Parameters Measured

Type of Data CollectedSites

(Total = 109)

CO2 31

O2 32

USCS Soil Type 109

Depth to water 109

FOC 14

Porosity 14

Moisture content 17

Summary of Soil Vapor Data

Total number of sites 109

Number of soil vapor wells 353

Number of sampling events at each siteRange 1 to 19

Average 7

Total number of samples collected 4025

Distribution of Soil Vapor Well Screens

94

151

105

2 10

50

100

150

1 2 3 4 5# of Screened Intervals

# of

Soi

l Vap

or L

ocat

ions

Soil Vapor Sampling Events at Sites

0%

2%

4%

6%

8%

10%

12%

14%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

# of Sampling Events

% o

f Site

s

Vapor Well Construction Methods

171

128

54

0

50

100

150

200

Geoprobe Auger Unknown

Soil Vapor Sample Collection Methods

2441

520

1064

0

500

1000

1500

2000

2500

3000

Tedlar Bag Summa Unknown

Soil Vapor Analytical Methods

1219

760622

468343

22483 64 63

179

0

200

400

600

800

1000

1200

140080

21B

TO-3

TO-1

18M

TO-1

5

TO-1

4A

CA

RB

410

8020

8260

Unk

now

n

Analytical Method

# of

Sam

ples

Air Samples

Air Sample Location Number of

Sites

Indoor air (main level) 22

Basement 11

Outdoor air (ambient air) 21

Indoor Air Collection Methods Number of

Samples

24-hr Summa 92

8-hr Summa 28

Summa (unknown duration) 7

Unknown method 123

Indoor Air Analytical Methods

128

83

5 4 2

28

0

20

40

60

80

100

120

140

TO-14A TO-15 TO-3 8260 M18 Unknown

Analytical Method

Cou

nt

Current Activities

Develop a Microsoft Access database of OPS sites that have soil vapor dataReview and summarize information in the databasePerform QA/QC evaluation of the data

Data Evaluation

Evaluate BTEX concentrations in soil vapor, groundwater, indoor air and outdoor air for all sites

Compare to RBSLs and background values

Examined sites with indoor air and soil vapor data (22 sites)

BTEX in Groundwater by Site 109 Sites

1.E-02

1.E-01

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

1.E+09

1.E+10

Benzene Toluene Ethylbenzene Xylene TPH

Compounds

Wat

er C

once

ntra

tion

(μ

g/L)

maximum

75th

25th

median

minimum

ResidentialRBSL

Ethylbenzene

Toluene

Benzene

BTEX in Soil Vapor by Site 109 Sites

1.E-02

1.E-01

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

1.E+09

1.E+10

Benzene Toluene Ethylbenzene Xylene TPH

Compound

Vapo

r Con

cent

ratio

n ( μ

g/m

3 )

BenzeneResidentialRBSL

maximum

75th

median

Benzene Concentrations in Air

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

Outdoor air(21 sites)

Indoor air above grade

(22 sites)

Basement(11 sites)

Crawl space(2 sites)

Sampling Location

Vapo

r Con

cent

ratio

n ( μ

g/m

3 )

Industrial Threshol

ResidentialThreshold

Typical CO Background

maximum

75th

25th

median

minimum

Benzene in Soil Vapor (from the 22 sites that had indoor air samples)

1.E-02

1.E-01

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

6412

9266

8982

8409

7546

5957

5269

3136

1978

1601

1479

Site ID

Vapo

r Con

cent

ratio

n (

g/m

3 )

IndustrialRBSL

ResidentialRBSL

maximum

75th

25th

median

minimum

Benzene in Indoor Air (22 Sites)

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

2534

6412

9336

9266

9249

8982

8516

8409

7928

7546

6580

5957

5359

5269

3913

3136

3118

1978

1931

1601

1511

1479

Site ID

Vapo

r Con

cent

ratio

n (

g/m

3 )

IndustrialThreshold

ResidentialThreshold

Typical CO Background

maximum

75th

25th

median

minimum

Data Evaluation Conclusions

Benzene is primary chemical of concernBenzene concentration in groundwater exceeds RBSL at more than 50% of the sample locationsBenzene concentration in soil vapor exceeds RBSL at less than 25% of sample locationsBenzene concentration in outdoor and indoor air exceeds threshold value at more than 75% of sitesBenzene concentration in outdoor and indoor air exceeds typical background values at less than 50% of sites

Data Evaluation Conclusions

Estimation of empirical attenuation factors difficult due to:

Variability in soil vapor and indoor air dataIndoor air concentrations at/near background levels

Additional evaluation and population of database warranted

Continuing Work

Continue to QA/QC the dataProvide an interim guidance document to contractors regarding requirements and methodology (currently developed and in draft form)Collect additional site data to enhance the studyIdentify if there are trends based on site conditions (soil types, depth to groundwater, source concentrations, etc.)Compare results with current process to identify if additional screening criteria is appropriateDetermine whether vadose biodegradation can be characterized using site information in the database

Guidance to Contractors

Interim vapor intrusion guidanceProgram requirements Soil vapor and sub-slab sample point constructionSoil vapor and indoor air sampling methodologyLaboratory analysesIndoor air screening checklistVapor intrusion mitigation

Enhance Existing Data

Toluene, ethylbenzene, xylenes, MTBE, and total volatile hydrocarbon analysesMeasure radon at vapor intrusion sitesAdditional information regarding lithologic profileMeasurement of O2 and CO2

Sub-slab samplingMeasure pressure gradients