Assessment of Vapor Intrusion

in Homes Near the Raymark

Superfund Site Using Basement

and Sub-Slab Air Samples
EPA/600/R-05/147

March 2006

Assessment of Vapor Intrusion in Homes 

Near the Raymark Superfund Site Using 

Basement and Sub-Slab Air Samples

Dominic C. DiGiulio and Cynthia J. Paul

U.S. Environmental Protection Agency

Office of Research and Development

National Risk Management Research Laboratory

Ground Water and Ecosystems Restoration Division

Ada, OK

Raphael Cody and Richard Willey

U.S. Environmental Protection Agency

Region I

Boston, MA

Scott Clifford and Peter Kahn

U.S. Environmental Protection Agency

Region I, New England Regional Laboratory

North Chelmsford, MA

Ronald Mosley

U.S. Environmental Protection Agency

Office of Research and Development

National Risk Management Research Laboratory

Research Triangle Park, NC

Annette Lee and Kaneen Christensen

Xpert Design and Diagnostics, LLC

Stratham, NH

Project Officer

Dominic C. DiGiulio

U.S. Environmental Protection Agency

Office of Research and Development

National Risk Management Research Laboratory

Ground Water and Ecosystems Restoration Division

Ada, OK

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF RESEARCH AND DEVELOPMENT

NATIONAL RISK MANAGEMENT RESEARCH LABORATORY

CINCINNATI, OH 45268
ii

Notice

The U.S. Environmental Protection Agency (EPA) through its Office of Research and 

Development funded and managed the research described here through in-house 

efforts and under Contract No. 68-C-02-092 to the Dynamac Corporation. It has been 

subjected to the Agency’s peer and administrative reviews and has been approved 

for publication as an EPA document. Mention of trade names or commercial products 

does not constitute endorsement or recommendation for use.

All data generated in this report were subjected to an analytical Quality Assurance 

Plan developed by EPA's New England Regional Laboratory. Also, a Quality 

Assurance Project Plan was implemented at the Ground Water and Ecosystems 

Restoration Division. Results of field-based studies and recommendations 

provided in this document have been subjected to external and internal peer 

and administrative reviews. This report provides technical recommendations, not 

policy guidance. It is not issued as an EPA Directive, and the recommendations 

of this report are not binding on enforcement actions carried out by the EPA or by 

the individual states of the United States of America. Neither the United States 

government nor the authors accept any liability or responsibility resulting from the 

use of this document. Implementation of the recommendations of the document 

and the interpretation of the results provided through that implementation are the 

sole responsibility of the user.
iii

Foreword

The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation’s land, air, 

and water resources. Under a mandate of national environmental laws, the Agency strives to formulate 

and implement actions leading to a compatible balance between human activities and the ability of natural 

systems to support and nurture life. To meet these mandates, EPA’s research program is providing data 

and technical support for solving environmental problems today and building a science knowledge base 

necessary to manage our ecological resources wisely, understand how pollutants affect our health, and 

prevent or reduce environmental risks in the future.

The National Risk Management Research Laboratory is the Agency’s center for investigation of technological 

and management approaches for reducing risks from threats to human health and the environment. The 

focus of the Laboratory’s research program is on methods for the prevention and control of pollution to air, 

land, water, and subsurface resources; protection of water quality in public water systems; remediation of 

contaminated sites and ground water; and prevention and control of indoor air pollution. The goal of this 

research effort is to catalyze development and implementation of innovative, cost-effective environmental 

technologies; develop scientific and engineering information needed by EPA to support regulatory and 

policy decisions; and provide technical support and information transfer to ensure effective implementation 

of environmental regulations and strategies.

This report describes the results of an investigation conducted to assist EPA's New England Regional 

Office in evaluating vapor intrusion in homes and a commercial building near the Raymark Superfund 

Site in Stratford, Connecticut. Methods were developed to sample sub-slab air and use basement and 

sub-slab air measurements to evaluate vapor intrusion on a building-by-building basis. Using the methods 

described in this report, volatile organic compounds detected in basement air due to vapor intrusion could 

be separated from numerous other halogenated and non-halogenated (e.g., petroleum hydrocarbons) 

compounds present in basement air.

Stephen G. Schmelling, Director

 Ground Water and Ecosystems Restoration Division

 National Risk Management Research Laboratory
iv

Abstract

This report describes the results of an investigation conducted to assist EPA’s New England Regional Office in 

evaluating vapor intrusion at 15 homes and one commercial building near the Raymark Superfund Site in Stratford, 

Connecticut. Methods were developed to sample sub-slab air and use basement and sub-slab air measurements to 

evaluate vapor intrusion on a building-by-building basis. A volatile organic compound (VOC) detected in basement 

air was considered due primarily to vapor intrusion if: (1) the VOC was detected in ground water or soil gas in the 

vicinity (e.g., 30 meters) of a building, and (2) statistical testing indicated equivalency between basement/sub-slab 

air concentration ratios of indicator VOCs and VOCs of interest. An indicator VOC was defined as a VOC detected 

in sub-slab air and known to be only associated with sub-surface contamination. Using this method of evaluation, 

VOCs detected in basement air due to vapor intrusion could easily be separated from numerous other halogenated 

and non-halogenated (e.g., petroleum hydrocarbons) VOCs present in basement air. As a matter of necessity, 

radon was used as an indicator compound at locations where an indicator VOC was not detected in basement air. 

However, when basement/sub-slab air concentration ratios were compared for radon and indicator VOCs, statistical 

non-equivalency occurred at three out of the four locations evaluated. Further research is needed to assess the 

usefulness of radon in assessing vapor intrusion. 

Holes for sub-slab probes were drilled in concrete slabs using a rotary hammer drill. Probes were designed to allow 

for collection of air samples directly beneath a slab and in sub-slab media. Three to five probes were installed in each 

basement. Placement of a probe in a central location did not ensure detection of the highest VOC concentrations. 

Schematics illustrating the location of sub-slab probes and other slab penetrations (e.g., suction holes for sub-slab 

permeability testing) were prepared for each building to document sample locations, interpret sample results, and 

design corrective measures. Basement and sub-slab air samples were collected and analyzed for VOCs using 

six-liter SilcoCan canisters and EPA-Method TO-15. Sub-slab air samples were also collected in one-liter Tedlar 

bags using a peristaltic pump and analyzed on-site for target VOCs. Open-faced charcoal canisters were used 

to sample radon gas in basement air. Scintillation cells and a peristaltic pump were used to sample radon gas in 

sub-slab air. 

Three methods were used to evaluate infiltration of basement air into sub-slab media during air extraction (purging 

+ sampling). The first method consisted of sequentially collecting five one-liter Tedlar bag samples at a flow rate 

of 1 standard liter per minute and comparing vapor concentration of four VOCs associated with vapor intrusion as 

a function of extraction volume. This was performed at three locations with little effect on sample concentration. 

This testing also indicated the absence of rate-limited mass exchange during air extraction. Replicate canister 
v

samples representing extraction volumes of 5 to 9 and 10 to14 liters were compared at two locations with similar 

results. A second method was then employed which utilized a mass balance equation and sub-slab and basement 

air concentrations. When sensitivity of the method permitted, infiltration was shown to be less than 1% at sampled 

locations. A third method involved simulating streamlines and travel time in sub-slab media during air extraction. Air 

permeability testing in sub-slab media was conducted to obtain estimates of radial and vertical air permeability to 

support air flow simulations. Simulations indicated that less than 10% of air extracted during purging and sampling 

could have originated as basement air when extracting up to 12 liters of air. Overall, extraction volumes used in 

this investigation (up to 14 liters) had little or no effect on sample results.

To assess the need for an equilibration period after probe installation, advective air flow modeling with particle 

tracking was employed to establish radial path lengths for diffusion modeling. Simulations indicated that in sub-slab 

material beneath homes at the Raymark site (sand and gravel), equilibration likely occurred in less than 2 hours. 

Sub-slab probes in this investigation were allowed to equilibrate for 1 to 3 days prior to sampling. A mass-balance 

equation was used to estimate the purging requirement prior to sampling. Simulations indicated that collection of 

5 purge volumes would ensure that the exiting vapor concentration was 99% of the entering concentration even if 

vapor concentration inside the sample system had been reduced to zero concentration prior to sampling.
vi
vii

Table of Contents

Notice .............................................................................................................................................. ii

Foreword ....................................................................................................................................... iii

Abstract ......................................................................................................................................... iv

List of Chemical Abbreviations ......................................................................................................viii

List of Figures ................................................................................................................................. ix

List of Tables .................................................................................................................................. xv

Acknowledgements ...................................................................................................................... xxi

Executive Summary .....................................................................................................................xxii

1.0 Introduction ...............................................................................................................................1

2.0 Site Description .........................................................................................................................3

3.0 Methods and Materials Used For Basement and Sub-Slab Air Sampling ................................6

 3.1 Quality Control Measures for Sampling and Analysis Using EPA Method TO-15 ..............6

 3.2 Basement and Outdoor Air Sampling for VOCs ...............................................................10

 3.3 Quality Control Measures and Data Quality for Basement Air Sampling and Analysis

 for Radon ..........................................................................................................................11

 3.4 Sub-Slab Probe Assembly and Installation ......................................................................12

 3.5 Sub-Slab Air Sample Collection for VOCs Using EPA Method TO-15 ..............................17

 3.6 Quality Control Measures and Data Quality for Sub-Slab Air Sampling Using Tedlar

 Bags and On-Site GC Analysis ........................................................................................17

 3.7 Quality Control Measures and Data Quality for Sub-Slab Air Sampling for Radon

 Using Scintillation Cells ....................................................................................................19

4.0 Methods and Materials Used for Air Permeability Testing and Sub-Slab Flow Analysis ........21

5.0 Discussion of Sampling Issues Associated with Sub-Slab Sampling .....................................25

 5.1 Assessment of Infiltration of Basement Air During Air Extraction ....................................25

 5.2 Assessment of Extraction Flow Rate ................................................................................31

 5.3 Evaluation of Equilibration Time .......................................................................................32

 5.4 Selection of Purge Volume ................................................................................................34

 5.5 Placement of Sub-Slab Vapor Probes ..............................................................................35

6.0 Use of Basement and Sub-Slab Air Measurement to Assess Vapor Intrusion .......................37

 6.1 Method of Vapor Intrusion Evaluation ...............................................................................37

 6.2 Summary of Results for Buildings Sampled in July and October 2002 ............................39

 6.3 Summary of Results for Buildings Sampled in March 2003 .............................................62

 6.4 Results of Radon Testing to Assess Vapor Intrusion ........................................................96

 6.5 Summary of Basement/Sub-Slab Concentration Ratios ...................................................98

7.0 Summary ...............................................................................................................................100

References ..................................................................................................................................105
viii

List of Chemical Abbreviations

1,1,1-TCA 1,1,1-trichloroethane

1,1-DCE 1,1-dichloroethylene

TCE trichloroethylene

c-1,2-DCE cis-1,2-dichloroethylene

1,1-DCA 1,1-dichloroethane

1,2-DCA 1,2-dichloroethane

PCE perchloroethylene

CH2Cl2 methylene chloride

CHCl3 chloroform

CCl4 carbon tetrachloride

CCl3F trichlorofluoromethane (F-11)

CCl2F2 dichlorodifluoromethane (F-12)

CHBrCl2 bromodichloromethane

CH3CH2Cl chloroethane

CCl3CF3 trichlorotrifluoroethane (F-113)

THF tetrahydrofuran

MEK methyl ethyl ketone

MIBK methyl isobutyl ketone

MTBE methyl tert-butyl ether

1,2,4-TMB 1,2,4-trimethylbenzene

1,3,5-TMB 1,3,5-trimethylbenzene

CS2 carbon disulfide
ix

List of Figures

Figure 1 Direction of ground-water flow (large arrows) and location of the residential area 

of investigation near the Raymark Superfund Site 

(modified from Tetra Tech NUS, Inc., 2000) .................................................................3

Figure 2 Location of geologic cross-sections and the residential area of investigation near the

Raymark Superfund Site (modified from Tetra Tech NUS, Inc., 2000) ........................4

Figure 3 Geologic cross-section G – G' (modified from Tetra Tech NUS, Inc., 2000) ................5

Figure 4 Geologic cross-section H – H' (modified from Tetra Tech NUS, Inc., 2000) ................5

Figure 5 Collection of a replicate basement air sample .............................................................7

Figure 6 Replicate precision as a function of mean basement concentration for the July 2002

and March 2003 sampling events ................................................................................9

Figure 7 Coefficient of variation (COV) as a function of mean basement concentration

for July 2002 and March 2003 sampling events ..........................................................9

Figure 8 Tripod and six-liter evacuated canister used to collect a 24-hour outdoor air

sample during the March 2003 sampling event .........................................................10

Figure 9 Coefficient of variation (COV) as a function of mean basement radon 

concentration ..............................................................................................................12

Figure 10 General schematic of a sub-slab vapor probe ...........................................................13

Figure 11 Brass materials used for sub-slab probe construction in homes near the Raymark

facility .........................................................................................................................13

Figure 12 Hex bushing used for probe construction when a concrete slab was less than

2.5 cm thick ................................................................................................................13

Figure 13 A comparison of VOC concentrations in outdoor air and outdoor air passing through

brass fittings used for probe construction during the July 2002 sampling event.

Dashed lines indicate detection limits. .......................................................................14

Figure 14 Stainless-steel materials now used for sub-slab probe assembly .............................14
x

List of Figures — continued

Figure 15 Drilling through a concrete slab using a rotary hammer drill .....................................15

Figure 16 "Inner" and "outer" holes drilled in a concrete slab ...................................................15

Figure 17 Typical schematic illustrating location of sub-slab vapor probes ...............................16

Figure 18 Sample train for sub-slab air collection using EPA Method TO-15 ............................17

Figure 19 Sample train for sub-slab air collection using one-liter Tedlar bags ..........................18

Figure 20 Comparison of EPA Method TO-15 and Tedlar bag sampling with on-site GC

analysis for 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE, n = 91, r 2 = 0.88 ................19

Figure 21 Sample train for sub-slab air collection for radon using scintillation cells ..................20

Figure 22 Regenerative blower used for air permeability testing ...............................................21

Figure 23 Variable-area flowmeter used for air permeability testing ..........................................22

Figure 24 Magnehelic gauges and suction hole used for vacuum measurement ......................22

Figure 25 Best-fit model results for permeability test conducted at House C with four vacuum

observation points and a flow rate of 255 SLPM

(kr /kz constrained between 1 – 2) ..............................................................................24

Figure 26a Sub-slab vapor concentration as a function of extraction volume at Probe A 

in House L using Tedlar bag sampling and on-site GC analysis ...............................26

Figure 26b Sub-slab vapor concentration as a function of extraction volume at Probe B

in House M using Tedlar bag sampling and on-site GC analysis ..............................26

Figure 26c Sub-slab vapor concentration as a function of extraction volume at Probe A

in House N using Tedlar bag sampling and on-site GC analysis. Dashed lines

denote detection limit .................................................................................................27

Figure 27a Sub-slab vapor concentration as a function of extraction volume at Probe A

in House J using EPA Method TO-15 ........................................................................27

Figure 27b Sub-slab vapor concentration as a function of extraction volume at Probe A

in House M using EPA Method TO-15 .......................................................................28

Figure 28 Simulated streamline (solid lines) and travel time (s) (dashed lines) contours

in sub-slab media when kr = 7.4E-07 cm2, kr /kz = 1.5, = 3.2E-09 cm, 

flow rate = 1 SLPM, and depth to ground water = 500 cm ........................................30
xi

List of Figures — continued

Figure 29 Simulated vacuum (Pa) (dashed lines) and pore-air velocity (solid lines) (cm/s)

in sub-slab media when kr

 = 7.4E-07 cm2, kr /kz = 1.5, = 0.35, flow rate = 1 SLPM,

and depth to ground water = 500 cm .........................................................................31

Figure 30 Time to reach C(t)/C = 0.99 as a function of diffusion path length ' ' and for TCE

when C0

 = 0, = 0.4, = 1.68 g/cm3, Da = 7.4E-02 cm2/s, Dw = 9.3E-06 cm2/s,

and H = 0.38 (no sorption) .........................................................................................34

Figure 31 Purge volume as a function of C0 /Cin and Cout /Cin .....................................................35

Figure 32 Total vapor concentration measured in one-liter Tedlar bags as a function of probe

location and house. Dark bars refer to centrally located probes. No VOCs

associated with subsurface contamination were detected at Location F. Locations

H, K, M, and P did not have a centrally located probe ..............................................36

Figure 33 Coefficient of variation (COV) as a function of mean sub-slab concentration (ppbv)

and method of analysis for VOCs associated with subsurface contamination ..........36

Figure 34 Basement/sub-slab concentration ratios using EPA Method TO-15 at House A

during the July 2002 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................42

Figure 35 Comparison of mean sub-slab air concentrations of VOCs collected in one-liter

Tedlar bags during the July and October 2002 sample events at House A. Error

bars represent one standard deviation ......................................................................44

Figure 36 Basement/sub-slab air concentration ratios using EPA Method TO-15 at House B

during the July 2002 sample event – error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................47

Figure 37 Comparison of mean sub-slab air concentrations of VOCs collected in one-liter

Tedlar bags during the July and October 2002 sample events at House B. Error

bars represent one standard deviation ......................................................................48

Figure 38 Basement/sub-slab concentration ratios using EPA Method TO-15 at House C

during the July 2002 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................51

Figure 39 Comparison of mean sub-slab air concentrations of VOCs collected in one-liter

Tedlar bags during the July and October 2002 sample events at House C. Error

bars represent one standard deviation ......................................................................53
xii

List of Figures — continued

Figure 40 Basement/sub-slab concentration ratios using EPA Method TO-15 at House D

during the July 2002 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................56

Figure 41 Comparison of mean sub-slab air concentrations of VOCs collected in one-liter

Tedlar bags during the July and October 2002 sample events at House D. Error

bars represent one standard deviation ......................................................................57

Figure 42 Basement/sub-slab concentration ratios using EPA Method TO-15 at House E

during the July 2002 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................60

Figure 43 Comparison of mean sub-slab air concentrations of VOCs collected in one-liter

Tedlar bags during the July and October 2002 sample events at House E. Error

bars represent one standard deviation ......................................................................61

Figure 44 Basement/sub-slab concentration ratios using EPA Method TO-15 at House G

during the March 2003 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................67

Figure 45 Basement/sub-slab concentration ratios using EPA Method TO-15 at House H

during the March 2003 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................71

Figure 46 Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site

GC analysis at House I during the March 2003 sample event. Error bars represent

one standard deviation ...............................................................................................73

Figure 47 Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site

GC analysis at House J during the March 2003 sample event. Error bars represent

one standard deviation ...............................................................................................76

Figure 48 Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site

GC analysis at House K during the March 2003 sample event. Error bars represent

one standard deviation ...............................................................................................79

Figure 49 Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site

GC analysis at House L during the March 2003 sample event. Error bars represent

one standard deviation ...............................................................................................82
xiii

List of Figures — continued

Figure 50 Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site

GC analysis at House M during the March 2003 sample event. Error bars represent

one standard deviation. Arrows indicate less than values due to non-detection

in basement air ..........................................................................................................85

Figure 51 Basement/sub-slab concentration ratios using EPA Method TO-15 at House N

during the March 2003 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................89

Figure 52 Basement/sub-slab concentration ratios using EPA Method TO-15 at House O

during the March 2003 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................92

Figure 53 Basement/sub-slab concentration ratios using EPA Method TO-15 at House P

during the March 2003 sample event. Error bars represent one standard deviation.

Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air ............................................................................................................96

Figure 54 Comparison of basement/sub-slab air concentration ratios for radon and indicator

VOCs associated with vapor intrusion. Samples for VOCs collected in one-liter

Tedlar bags with on-site GC analysis ........................................................................97

Figure 55 Coefficient of variation (COV) as a function of location and compound for VOCs

detected in basement air as a result of vapor intrusion .............................................98

Figure 56 Summary of average basement/sub-slab concentration ratios for VOCs

present in basement air due to vapor intrusion using one-liter Tedlar bags and

on-site GC analysis. Arrows indicate less than values due to non-detection

in basement air ..........................................................................................................99
xiv
xv

List of Tables

Table 1 Computation of maximum percent infiltration of basement air into an evacuated

canister during sampling as a function of extraction volume, location, and probe.

P[A], P[B], P[C], P[D], and P[E] denote probes evaluated at individual locations .....29

Table 2 Outdoor air concentrations of VOCs during the July 2002 and March 2003 sample

events .........................................................................................................................39

Table 3a Basement and sub-slab concentrations of VOCs at House A using EPA Method 

TO-15 during the July 2002 sample event .................................................................41

Table 3b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House A using EPA Method TO-15 during the 

July 2002 sample event .............................................................................................43

Table 3c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House A using 1-liter Tedlar bags and on-site 

GC analysis during the July 2002 sample event .......................................................43

Table 3d Sub-slab air concentrations of VOCs associated with sub-surface contamination

in House A using 1-liter Tedlar bags and on-site GC analysis during the 

October 2002 sample event .......................................................................................43

Table 4a Basement and sub-slab concentrations of VOCs at House B using EPA Method

TO-15 during the July 2002 sample event .................................................................45

Table 4b Summary of basement/sub-slab air concentration ratios of VOCs associated

with sub-surface contamination in House B using EPA Method TO-15 during the

July 2002 sample event .............................................................................................46

Table 4c Summary of basement/sub-slab air concentration ratios of VOCs associated

with sub-surface contamination in House B using 1-liter Tedlar bags and on-site

GC analysis during the July 2002 sample event .......................................................46

Table 4d Sub-slab air concentrations of VOCs associated with sub-surface contamination

in House B using 1-liter Tedlar bags and on-site GC analysis during the

October 2002 sample event .......................................................................................48
xvi

List of Tables — continued

Table 5a Basement and sub-slab air concentrations of VOCs at House C using EPA Method

TO-15 during the July 2002 sample event .................................................................50

Table 5b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House C using EPA Method TO-15 during the

July 2002 sample event .............................................................................................51

Table 5c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House C using 1-liter Tedlar bags and on-site

GC analysis during the July 2002 sample event .......................................................51

Table 5d Sub-slab air concentrations of VOCs associated with sub-surface contamination

in House C using 1-liter Tedlar bags and on-site GC analysis during the October 

2002 sample event .....................................................................................................52

Table 6a Basement and sub-slab concentrations of VOCs at House D using EPA Method

TO-15 during the July 2002 sample event .................................................................54

Table 6b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House D using EPA Method TO-15 during the

July 2002 sample event .............................................................................................55

Table 6c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House D using 1-liter Tedlar bags and on-site

GC analysis during the July 2002 sample event .......................................................55

Table 6d Sub-slab air concentrations of VOCs associated with sub-surface contamination

in House D using 1-liter Tedlar bags and on-site GC analysis during the October

2002 sample event .....................................................................................................56

Table 7a Basement/sub-slab air concentrations of VOCs at House E using EPA Method

TO-15 during the July 2002 sample event .................................................................58

Table 7b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House E using EPA Method TO-15 during the

July 2002 sample event .............................................................................................59

Table 7c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House E using 1-liter Tedlar bags and on-site

GC analysis during the July 2002 sample event .......................................................59
xvii

List of Tables — continued

Table 7d Sub-slab air concentrations of VOCs associated with sub-surface contamination

in House E using 1-liter Tedlar bags and on-site GC analysis during the

October 2002 sample event .......................................................................................61

Table 8 Basement and sub-slab air concentrations for VOCs at House F using EPA Method

TO-15 during the March 2003 sample event .............................................................63

Table 9a Basement and sub-slab air concentration of VOCs at House G using EPA Method

TO-15 during the March 2003 sample event .............................................................65

Table 9b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House G using EPA Method TO-15 during the March

2003 sample event .....................................................................................................66

Table 9c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House G using 1-liter Tedlar bags and on-site 

GC analysis during the March 2003 sample event ....................................................66

Table 9d Basement/sub-slab air concentration ratios for radon in House G using 48-hr

activated carbon canisters for basement air sampling (3/25-3/27/03) and scintillation

cells for sub-slab air sampling during the March 2003 sample event ........................67

Table 10a Basement and sub-slab air concentrations for VOCs at House H using EPA Method

TO-15 during the March 2003 sample event .............................................................69

Table 10b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House H using EPA Method TO-15 during the March

2003 sample event .....................................................................................................70

Table 10c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House H using 1-liter Tedlar bags and on-site

GC analysis during the March 2003 sample event ....................................................70

Table 10d Basement/sub-slab air concentration ratios for radon in House H using 48-hr

activated carbon canisters for basement air sampling (3/21-3/24/03) and scintillation

cells for sub-slab air sampling during the March 2003 sample event ........................70

Table 11a Basement and sub-slab air concentrations for VOCs at House I using EPA Method

TO-15 during the March 2003 sample event .............................................................72

Table 11b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House H using 1-liter Tedlar bags and on-site

GC analysis during the March 2003 sample event ....................................................73
xviii

List of Tables — continued

Table 12a Basement and sub-slab air concentrations for VOCs at House J using EPA Method

TO-15 during the March 2003 sample event .............................................................74

Table 12b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House J using 1-liter Tedlar bags and on-site GC

analysis during the March 2003 sample event ..........................................................75

Table 12c Basement/sub-slab air concentration ratios for radon in House J using 48-hr

activated carbon canisters for basement air sampling (3/21-3/24/03) and scintillation

cells for sub-slab sampling during the March 2003 sample event .............................75

Table 13a Basement air concentrations for VOCs at House K using EPA Method TO-15

during the March 2003 sample event ........................................................................77

Table 13b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House K using 1-liter Tedlar bags and on-site

GC analysis during the March 2003 sample event ....................................................78

Table 13c Basement and sub-slab air concentration ratios for radon in House K using 48-hr

activated carbon canisters for basement air sampling (3/21-3/24/03) and scintillation

cells for sub-slab air sampling during the March 2003 sample event ........................78

Table 14a Basement and sub-slab air concentrations for VOCs at House L using EPA Method

TO-15 during the March 2003 sample event .............................................................80

Table 14b Results of sequential sub-slab air sampling using 1-liter Tedlar bags and on-site

GC analysis at House L during the March 2003 sample event .................................81

Table 14c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House L using 1-liter Tedlar bags and on-site GC

analysis during the March 2003 sample event ..........................................................81

Table 14d Summary of 48-hour indoor air measurements for radon using activated charcoal

at House L ..................................................................................................................81

Table 14e Basement/sub-slab air concentration ratios for radon in House L using 48-hr

activated carbon canisters for basement air sampling (3/26-3/28/03) and scintillation

cells for sub-slab air sampling during the March 2003 sample event ........................81

Table 15a Basement and sub-slab air concentrations for VOCs at House M using EPA Method

TO-15 during the March 2003 sample event .............................................................83
xix

List of Tables — continued

Table 15b Results of sequential sub-slab air sampling using 1-liter Tedlar bags and on-site

GC analysis at House M during the March 2003 sample event ................................84

Table 15c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House M using 1-liter Tedlar bags and on-site GC

analysis during the March 2003 sample event ..........................................................84

Table 15d Basement/sub-slab air concentration ratios for radon in House M using 48-hr

activated carbon canisters for basement air sampling (3/22-3/24/03) and scintillation

cells for sub-slab air sampling during the March 2003 sample event ........................84

Table 16a Basement and sub-slab air concentrations for VOCs at House N using EPA Method

TO-15 during the March 2003 sample event .............................................................86

Table 16b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House N using EPA Method TO-15 during the March

2003 sample event .....................................................................................................87

Table 16c Results of sequential sub-slab air sampling and on-site GC analysis using 1-liter

Tedlar bags at House N during the March 2003 sample event .................................88

Table 16d Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House N using 1-liter Tedlar bags and on-site

GC analysis during the March 2003 sample event ....................................................88

Table 16e Basement/sub-slab air concentration ratios for radon in House N using 48-hr

activated carbon canisters for basement air sampling (3/25-3/27/03) and scintillation

cells for sub-slab air sampling during the March 2003 sample event ........................88

Table 17a Basement and sub-slab concentrations for VOCs at House O using EPA Method

TO-15 during the March 2003 sample event .............................................................90

Table 17b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House O using EPA Method TO-15 during the March

2003 sample event .....................................................................................................91

Table 17c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House O using 1-liter Tedlar bags and on-site

GC analysis during the March 2003 sample event ....................................................91

Table 17d Basement/sub-slab air concentration ratios for radon in House O using 48-hr

activated carbon canisters for basement air sampling (3/25-3/27/03) and scintillation

cells for sub-slab air sampling during the March 2003 sample event ........................92
xx

List of Tables — continued

Table 18a Basement and sub-slab air concentrations for VOCs at House P using EPA Method

TO-15 during the March 2003 sample event .............................................................94

Table 18b Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House P using EPA Method TO-15 during the March

2003 sample event .....................................................................................................95

Table 18c Summary of basement/sub-slab air concentration ratios of VOCs associated with

sub-surface contamination in House P using 1-liter Tedlar bags and on-site

GC analysis during the March 2003 sample event ....................................................95

Table 18d Basement/sub-slab air concentration ratios for radon in House P using 48-hr

activated carbon canisters for basement air sampling (3/26-3/28/03) and scintillation

cells for sub-slab air sampling during the March 2003 sample event ........................95
xxi

Acknowledgements

The authors would like to thank the following for their help and support in this project: Mike Jasinski,

Ron Jennings, Matt Hoagland, Mary Sanderson, and Don Berger of EPA Region I, David Burden of 

NRMRL, Ada, OK, and William Bell of the Massachusetts Department of Public Health.

The authors would also like to acknowledge the following for their formal review of this manuscript:

Dr. John E. McCray

Colorado School of Mines

Environmental Science and Engineering Division

1500 Illinois Street

Golden, CO 80401

Dr. Blayne Hartman

HP Labs

432 N. Cedros Avenue

Solana Beach, CA 92075

Dr. Brian Schumacher

U.S. EPA

Office of Research and Development

National Exposure Research Laboratory

Environmental Sciences Division

P.O. Box 93478

Las Vegas, NV 89193-3478

Dr. Helen Dawson

U.S. EPA, Region VIII

999 18th Street, Suite 300

Denver, CO 80401
xxii

Executive Summary

This report describes the results of an investigation conducted to assist EPA’s New England Regional Office 

in evaluating vapor intrusion at 15 homes and one commercial building near the Raymark Superfund Site 

in Stratford, Connecticut. Ground water beneath these homes is contaminated with 1,1,1-trichloroethane, 

1,1-dichloroethylene, trichloroethylene, cis-1,1-dichloroethylene, and 1,1-dichloroethane. Methods were 

developed to sample sub-slab air and use basement and sub-slab air measurements to evaluate vapor 

intrusion on a building-by-building basis. A volatile organic compound (VOC) detected in basement air 

was considered due primarily to vapor intrusion if: (1) the VOC was detected in ground water or soil gas 

in the vicinity (e.g., 30 meters) of a building, and (2) the null hypothesis that the basement/sub-slab air 

concentration ratio of the VOC was equal to the basement/sub-slab air concentration ratio of an indicator 

VOC could not be rejected using a one-tailed Approximate t-Test at a level of significance less than 

or equal to 0.05. An indicator VOC was defined as a VOC detected in sub-slab air and known to be 

associated only with sub-surface contamination (i.e., no outdoor or indoor air sources). The VOCs 1,1-

dichloroethylene and 1,1-dichloroethane were considered indicator VOCs in this investigation because 

they are degradation products of 1,1,1-trichloroethane and not commonly associated with commercial 

products. The VOC cis-1,2-dichloroethylene was considered an indicator VOC because it is a degradation 

product of trichloroethylene and also not commonly associated with commercial products. Using this 

method of evaluation, VOCs detected in basement air due to vapor intrusion could easily be separated 

from numerous other halogenated and non-halogenated (e.g., petroleum hydrocarbons) VOCs present 

in basement air. The variance associated with each basement/sub-slab air concentration ratio was 

calculated using the method of propagation of errors which incorporated the variance associated with 

both basement and sub-slab air measurement. An average basement/sub-slab air concentration ratio 

was computed using concentration ratios of all VOCs detected in basement air and associated with vapor 

intrusion. The method of propagation of errors was then used to calculate the variance associated with 

the average basement/sub-slab concentration ratio. 

As a matter of necessity, radon was used as an indicator compound at locations where an indicator 

VOC was not detected in basement air. However, when basement/sub-slab air concentration ratios 

were compared for radon and indicator VOCs, statistical non-equivalency occurred at three out of the 

four locations evaluated. At these three locations, the null hypothesis that the basement/sub-slab air 

concentration ratio of radon was equal to the basement/sub-slab air concentration ratio of the indicator 

VOC, 1,1-DCE, was rejected using a two-tailed Approximate t-Test at a significance level less than or 
xxiii

equal to 0.1. There was a visual dissimilarity between the basement/sub-slab air concentration ratio of 

radon and VOCs associated with vapor intrusion. This was in contrast to visual and statistical (levels of 

significance always greater than 0.1) similarity of basement/sub-slab air concentration ratios of indicator 

VOCs and other VOCs associated with vapor intrusion. These two observations indicate, at least in 

this investigation, use of indicator VOCs was preferable to radon in assessing vapor intrusion. Further 

research is needed at other sites containing indicator VOCs to determine the usefulness of radon in 

assessing vapor intrusion. 

Holes for sub-slab probes were drilled in concrete slabs using a rotary hammer drill. Probes were 

designed to allow for collection of air samples directly beneath a slab and in sub-slab media. Three to 

five probes were installed in each basement. Fifty-five probes were installed in 16 buildings which, on 

average, resulted in placement of one probe every 220 ft2

. Observation of high coefficients of variation in 

sub-slab air concentrations (greater than 100% at several locations), and the need for statistical analysis 

in assessing basement/sub-slab air concentration ratios, indicated that placement of multiple probes in 

sub-slab media was necessary to evaluate vapor intrusion. Generally, one sub-slab vapor probe was 

centrally located while two or more probes were placed within one or two meters of basement walls in 

each building. In this investigation, placement of a probe in a central location did not ensure detection of 

the highest VOC concentrations in sub-slab media. Schematics illustrating the location of sub-slab probes 

and other slab penetrations (e.g., suction holes for sub-slab permeability testing) were prepared for each 

building to document sample locations, interpret sample results, and design corrective measures. 

Basement and sub-slab air samples were collected and analyzed for VOCs using six-liter SilcoCan 

canisters and EPA-Method TO-15. Sub-slab air samples were also collected in one-liter Tedlar bags 

using a peristaltic pump and analyzed on-site for target VOCs by EPA’s New England Regional Laboratory 

within 24 hours of sample collection. Open-faced charcoal canisters were used to sample radon gas in 

basement air over a 48-hour period. Scintillation cells and a peristaltic pump were used to sample radon 

gas in sub-slab air. Scintillation cells were analyzed within four hours using a portable radiation monitor 

to count and amplify light pulses.

Three methods were used to evaluate infiltration of basement air into sub-slab media during air extraction 

(purging + sampling). The first method consisted of sequentially collecting five one-liter Tedlar bag samples 

at a flow rate of 1 standard liter per minute and comparing vapor concentration of four VOCs associated 

with vapor intrusion as a function of extraction volume. This was performed at three locations with little 

effect on sample concentration. This testing also indicated the absence of rate-limited mass exchange 

during air extraction. Replicate canister samples representing extraction volumes of 5 to 9 and 10 to 14 

liters were compared at two locations with similar results. A second method was then employed which 

utilized a mass balance equation and sub-slab and basement air concentrations. When sensitivity of the 

method permitted, infiltration was shown to be less than 1% at sampled locations. A third method involved 
xxiv

simulating streamlines and travel time in sub-slab media during air extraction. Air permeability testing in 

sub-slab media was conducted to obtain estimates of radial and vertical air permeability to support air 

flow simulations. Simulations indicated that less than 10% of air extracted during purging and sampling 

could have originated as basement air when extracting up to 12 liters of air. Overall, extraction volumes 

used in this investigation (up to 14 liters) had little or no effect on sample results. 

To assess the time required after probe installation for sampling (equilibration period), advective air flow 

modeling with particle tracking was employed to establish radial path lengths for diffusion modeling. 

Simulations indicated that in sub-slab material beneath homes at the Raymark site (sand and gravel), 

equilibration likely occurred in less than 2 hours. Sub-slab probes in this investigation were allowed to 

equilibrate for 1 to 3 days prior to sampling. A mass-balance equation was used to estimate the purging 

requirement prior to sampling. Simulations indicated that collection of 5 purge volumes would ensure 

that the exiting vapor concentration was 99% of the entering concentration even if vapor concentration 

inside the sample system had been reduced to zero concentration prior to sampling. A purge volume for 

the sample train used in homes near the Raymark site was typically less than 10 cm3.

In summary, this report constitutes an important first step in the development of a technical resource 

document on sub-slab air sampling and use of indoor and sub-slab air samples to assess vapor 

intrusion.
1

1.0 Introduction

In this report, vapor intrusion was defined as the entry 

of volatile organic or inorganic compounds (elemental 

mercury) and gases (e.g., methane) into a building 

due to contaminated subsurface media (ground water, 

soil, rock), non-aqueous phase liquids (NAPLs), or 

waste material (e.g., landfills). Vapor intrusion was 

not defined by the violation of health-based criteria 

associated with these compounds or gases which 

vary over time. 

One commonly accepted conceptual model of vapor 

intrusion involves diffusive transport of volatile organic 

compounds (VOCs) or gases from contaminated 

ground water and/or soil to sub-slab media. This 

is followed by advective-diffusive transport in subslab media through an overlying concrete slab and 

basement walls until entry into a building is achieved. 

Another conceptual model involves VOC and gas 

transport into a building via preferential pathways (e.g., 

utility conduits). Entry of methane gas from landfills 

and gasoline vapors from gas stations into buildings

via preferential pathways is well documented. Subslab sampling taken alone is likely not an appropriate 

method for assessing vapor intrusion for this latter 

conceptual model. 

Until recently, potential risk posed by vapor intrusion 

was not consistently considered during sub-surface 

investigations at sites regulated by the Comprehensive 

Environmental Response and Liability Act (CERCLA) 

and the Resource Conservation and Recovery Act 

(RCRA). Also, risk posed by vapor intrusion has not 

been consistently considered during investigations 

involving leaking underground storage tank sites or 

sites where residential or commercial construction 

is proposed over known areas of soil and/or groundwater contamination (i.e., Brownfields sites). Thus, 

the number of buildings where vapor intrusion 

has occurred, or is occurring, is unknown, and 

the magnitude of the problem remains undefined. 

Recognition of this exposure pathway necessitates its

consideration in regulatory decision making and may 

require review of past regulatory decisions involving 

VOC contamination in soil and/or ground water. 

To assess this increasingly important regulatory issue, 

the United States Environmental Protection Agency’s 

(EPA) Office of Solid Waste and Emergency Response 

developed guidance (USEPA, 2002) to facilitate 

assessment of vapor intrusion at sites regulated 

by RCRA and CERCLA - sites where halogenated 

organic compounds constitute the bulk of risk to 

human health. EPA does not consider the guidance 

applicable to underground storage tank sites where 

petroleum compounds primarily determine risk, and 

biodegradation in subsurface media may be a dominant 
2

fate process. In the guidance, EPA considers a site 

as a regulated unit potentially consisting of numerous 

buildings and subsurface monitoring points. The 

guidance was not developed to conduct building-tobuilding investigations. Recommendations provided 

in this report directly support the guidance but also 

support subsequent building-to-building investigations. 

A number of state agencies have or are in the process 

of developing state-specific guidance or advisories to 

assess vapor intrusion. 

In the guidance, EPA recommends concomitant use 

of sub-slab air sampling with indoor air sampling to 

differentiate outdoor and indoor sources of VOCs 

(e.g., cosmetics, air fresheners, gasoline storage 

or car parked in garage, cigarette smoke, solvents, 

paints, furniture polish) from VOCs emanating from 

contaminated soil or ground water. The agency, 

however, does not provide detailed recommendations 

on how to collect sub-slab air samples nor how to 

use these samples to assess vapor intrusion. Also, 

little is published in peer-reviewed literature on

sub-slab sample collection and interpretation. Subslab sampling offers an opportunity to collect air 

samples directly beneath the living space of a building 

and thereby eliminates uncertainty associated with 

interpolation or extrapolation of soil-gas and/or groundwater concentrations from monitoring points away 

from a building. Sub-slab sampling also provides 

an opportunity to evaluate the validity of claims that 

petroleum hydrocarbons of concern degrade prior to 

vapor entry into sub-slab material. 

The purpose of this report is to provide a method for 

evaluating vapor intrusion using indoor and sub-slab air 

samples. This report does not constitute guidance. It 

is, however, an important first step in the development 

of a technical resource document on sub-slab air 

sampling and interpretation. Use of recommendations 

provided in this report should increase the potential 

of collecting samples representative of “true” subslab air concentration even if the method of data 

interpretation presented here is not utilized to assess 

vapor intrusion.
3

The Raymark Superfund Site consists of 33.4 acres 

of land previously occupied by the RaybestosManhattan Company in Stratford, Connecticut, 

where the company disposed of solid-waste from 

settling lagoons during its operation. Between 1919 

and 1989, the company produced asbestos and 

asbestos compounds, metals, phenol-formaldehyde 

resins, adhesives, gasket material, sheet packing, 

clutch facings, transmission plates, and brake linings. 

Between 1993 and 1996, EPA removed fill containing 

asbestos, lead, and PCBs from a number of residential 

properties and a middle school. EPA placed the fill 

back on the facility property and isolated the waste 

beneath a cap. In 1996 and 1997, EPA demolished 

the facility buildings and placed a cap over the area 

previously occupied by the buildings. The property 

is now occupied by commercial buildings (e.g., WalMart, Home Depot). 

As illustrated in Figure 1, ground water beneath 

the residential area of this investigation generally 

flows southeast from the former facility, underneath 

a large residential community, and discharges into 

the Housatonic River which eventually discharges 

into Long Island Sound. Ground water in the vicinity 

of the former facility is contaminated with a number 

of VOCs including 1,1,1-trichloroethane (1,1,1-

TCA), trichloroethene (TCE), cis-1,2-dichloroethene

(c-1,2-DCE), 1,1-dichloroethene (1,1-DCE), and 1,1-

dichloroethane (1,1-DCA).

2.0 Site Description

Figure 1. Direction of ground-water flow (Iarge arrows) 

and location of the residential area of investigation near the 

Raymark Superfund Site (modified from Tetra Tech NUS, Inc., 

2000).
4

Figures 2, 3, and 4 illustrate glacio-fluvial deposits 

and fractured granite bedrock valleys in the vicinity 

of the residential area of investigation. The remedial 

investigation (TetraTech NUS, 2000) and subsequent 

studies financed by EPA indicate that ground-water flow 

is heavily influenced by the location and orientation 

of bedrock valleys. This results in a fairly complex 

contaminant distribution profile making interpolation 

and extrapolation of ground-water contaminant profiles 

difficult. For instance, TCE was not detected during 

ground-water sampling at well MW-215, illustrated 

in Figure 4, but was detected in basement air at a 

home less than 10 meters from this well. As will be 

discussed, the basement/sub-slab air concentration 

ratio of TCE observed at this location suggests that 

the cause of TCE in basement air was vapor intrusion. 

Non-detection of TCE in well MW-215 was likely 

caused by a bedrock knoll close to this house where 

ground-water flow may have been diverted. This 

assertion is corroborated by significant drawdown 

during sampling compared to other shallow wells.

Sub-slab and basement air samples were collected 

in 15 homes and one business near the Raymark 

Superfund Site in Stratford, Connecticut. The 

investigation consisted of three separate sample 

events. In July 2002, basement and sub-slab air 

was sampled for VOCs at five homes using six-liter 

SilcoCan canisters and EPA Method TO-15 (USEPA, 

1999) analysis. Sub-slab air was also sampled using 

one-liter Tedlar bags and analyzed on-site using gas 

chromatography (GC). In October 2002, sub-slab air 

at these five homes was re-sampled and re-analyzed 

using one-liter Tedlar bags and on-site GC analysis to 

assess temporal variability. In March 2003, basement 

and sub-slab air was sampled for VOCs at an additional 

ten homes and one commercial building using six-liter 

SilcoCan canisters and EPA Method TO-15 analysis. 

Sub-slab air was also sampled using one-liter Tedlar 

bags and on-site GC analysis. During this sample 

event, basement and sub-slab air was sampled for 

radon gas.

Figure 2. Location of geologic cross-sections and the 

residential area of investigation near the Raymark Superfund 

Site (modified from Tetra Tech NUS, Inc., 2000).
5

Figure 3. Geologic cross-section G – G' (modified from Tetra Tech NUS, Inc., 2000).

Figure 4. Geologic cross-section H – H' (modified from Tetra Tech NUS, Inc., 2000).
6

3.1 Quality Control Measures and Data 

 Quality for Sampling and Analysis 

 Using EPA Method TO-15

EPA’s Compendium of Methods for Determination of 

Toxic Organic Compounds in Ambient Air (TO Methods) 

was developed for measurement of 97 VOCs listed in 

Title III of the Clean Air Act Amendments of 1990. EPA’s 

TO Methods stipulate specific sampling and analytical 

requirements for determination of VOCs in air. A 

number of TO Methods are appropriate for indoor and 

sub-slab air sampling. However, EPA Method TO-15 

- Determination of Volatile Organic Compounds (VOCs) 

in Air Collected in Specially-Prepared Canisters and 

Analyzed by Gas Chromatography/Mass Spectrometry 

(GC/MS) (USEPA, 1999) – was used to sample and 

analyze basement and sub-slab air samples during 

this investigation. 

In EPA Method TO-15, two MS options are available. 

In the MS-SCAN mode, a GC is coupled to a MS 

programmed to scan all ions repeatedly over a specified 

mass range. In the MS-SIM (selected ion monitoring) 

mode, a GC is coupled to a MS programmed to scan 

selected ions repeatedly. The MS-SCAN mode allows 

wide identification of VOCs and detection in tenths of 

a part per billion volume (ppbv) or hundreds of parts 

per trillion volume while the MS-SIM mode allows 

identification of a few select compounds and detection 

in the tenths of parts per trillion volume. The MS-SCAN 

mode was used during this investigation because risk 

levels for VOCs of concern were generally in the low 

ppbv range, and VOCs associated with sub-surface 

contamination were suspected to be present in subslab material at concentrations ranging from tens to 

hundreds ppbv. 

EPA Method TO-15 requires that canisters be 

meticulously cleaned prior to sampling. Six-liter 

SilcoCan canisters were provided and analyzed by 

EPA’s New England Regional Laboratory. Canisters 

were cleaned in accordance with EPA’s New England 

Regional Laboratory standard operating procedure 

(USEPA, 1998). Canister cleaning involved three 

evacuation/pressurization cycles. Each cycle 

consisted of evacuation to 0.1 Pascal (Pa), heating to 

150°C, and pressurization to 206.7 kPa with humidified 

nitrogen. Canisters were then evacuated again to 0.1 

Pa and vacuum tested with a Pirani sensor for a 24 

hour period. Every canister used for basement and 

sub-slab air sampling was then re-pressurized with 

humidified, ultra-high purity nitrogen and analyzed 

for VOCs using the same GC/MS utilized for sample 

analysis. This process is known as certification. If all 

canisters are subjected to this process prior to use, 

as was the case in this investigation, there is 100% 

3.0 Methods and Materials Used for Basement and Sub-Slab Air Sampling
7

certification. Canisters were considered “clean” if 

concentrations of target VOCs were less than 0.02 

ppbv. Canisters were stored under pressure until the 

day before sampling and then evacuated once more 

to 0.1 Pa for sub-atmospheric pressure sampling 

in accordance with EPA’s New England Regional 

Laboratory standard operating procedure (USEPA, 

1996). A certification level of 100% is generally 

desirable for indoor air sampling efforts because 

risk-based concentrations are in the low ppbv range

for many compounds. However, a lower level of 

certification may be suitable for sub-slab sampling 

because vapor concentrations associated with subsurface contamination are typically one to three orders 

of magnitude higher than indoor air.

EPA Method TO-15, EPA requires the use of duplicate, 

replicate, and audit samples for quality control. 

Performance is measured by relative percent difference 

(RPD) defined by: 

where X1 and X2 are values for sample 1 and 2, 

respectively, and is a sample mean. EPA Method 

TO-15 requires duplicate and replicate precision less 

than or equal to 25%. In Method TO-15, EPA defines 

duplicate precision as a comparison between two 

samples taken from the same canister. Duplicate 

sampling is performed at an analytical laboratory 

and is used to assess analytical precision. Duplicate 

sampling was performed at EPA’s New England 

Regional Laboratory at a sampling frequency of 10%. 

Relative percent differences did not exceed 30% for 

any compound in any analysis. In Method TO-15, EPA 

defines replicate precision as a comparison between 

two canisters filled from the same air mass over the 

same period of time. Replicate sampling is performed in 

the field and can be used to assess precision associated 

with the entire sample and analytical process. As 

illustrated in Figure 5, replicate sampling consisted of 

placing two canisters side-by-side. Replicate samples 

were collected from basement air only. One replicate 

sample was collected during the July 2002 sample 

event which included 5 basement air samples and 

one outdoor air sample. Two replicate samples were 

collected during the March 2003 sampling event which 

included 11 basement and two outdoor air samples. 

Thus, replicate sampling frequency was 3 out of 19 

samples, or about 16%. 

Figure 5. Collection of replicate basement air sample.
8

As illustrated in Figure 6, RPDs for replicate 

sampling were generally less than, or near to, 25%. 

The highest RPDs were for methyl ethyl ketone and 

trichlorotrifluoroethane analyzed during the July 2002 

sample event. An alternative method of assessing 

replicate precision is to express mean concentration 

as a function of a coefficient of variability (COV) which 

is simply the standard deviation divided by the mean 

times 100. As illustrated in Figure 7, the mean COV 

for the three homes used for replicate sampling during 

the July 2002 and March 2003 sampling events was 

only 5.5%. As will be discussed, the COV for replicate 

basement air sampling was useful for statistical 

analysis in assessing vapor intrusion. 

In EPA Method TO-15, EPA defines audit accuracy 

as the difference between analyses provided in an 

audit canister and the nominal value as determined 

by an audit authority. Audit canisters containing target 

VOCs were analyzed to assess analytical accuracy. 

Relative percent differences did not exceed 30% 

for any compound. As an additional quality control 

check, ultra-high purity humidified nitrogen was 

introduced into the analytical instrument inlet line prior 

to analyzing canisters to serve as laboratory blanks 

and to demonstrate lack of background contamination 

in analytical instrumentation. A laboratory blank was 

analyzed every six canister samples. During the 

July 2002 sampling event, acetone was detected in 

17 of 21 laboratory blanks at concentrations slightly 

below reporting limits. Acetone concentrations 

were not high enough though to exceed acceptance 

criteria (observed concentration in samples less 

than 5 times the concentration in laboratory blanks). 

During the March 2003 sampling event, 12 laboratory 

blanks were analyzed. Acetone was detected in one 

laboratory blank at 0.11 ppbv. Prior to analyzing each 

canister, surrogate compounds 1,2-dichloroethane d4,

p-bromofluorobenzene, and toluene d8 were 

introduced into the analytical instrument inlet line 

to assess the accuracy of the analytical system. 

Acceptable recovery (88%-116%) was attained for 

all surrogate compounds in all samples. 

Sub-slab gas sample concentrations were typically 

much higher than basement air samples. Fifty milliliters 

(ml) of air were withdrawn from each canister for 

preliminary analysis to determine if concentrations 

were within the calibration range. If so, 500 ml were 

withdrawn from canisters for a second round of 

analysis. Otherwise, a smaller volume of sample was 

withdrawn and diluted to ensure analysis within the 

calibration range. Analytical results were reported in 

units of μg/m3

 and ppbv. A conversion from ppbv to 

μg/m3 can be obtained by use of the Ideal Gas Law:

where Mv = molecular weight of VOC (g/mole),

P = pressure (atm), T = temperature (°K), and = 

the ideal gas constant (8.204E-05 atm m3

/°K mole). 

For instance, 10 ppbv benzene (Mv

 = 78 g/mole) is 

equivalent to 32 μg/m3

 at a pressure of 1 atmosphere 

and a temperature of 298°K (25°C).
9

Figure 6. Replicate precision as a function of mean basement concentration for the July 2002 and March 2003 sampling events.

Figure 7. Coefficient of variation (COV) as a function of mean basement concentration for July 2002 and March 2003 sampling 

events.
10

3.2 Basement and Outdoor Air Sampling

for VOCs

Building surveys were conducted prior to basement 

and sub-slab sampling. Surveys provide an opportunity 

to explain the purpose and rudimentary mechanics of 

indoor air and sub-slab air sampling to homeowners 

and to check buildings for household solvents which 

could potentially hinder a vapor intrusion investigation. 

A survey guide similar to that included in EPA’s vapor 

intrusion guidance (USEPA, 2002) was used for each 

building.

Basement and outdoor air sampling was conducted 

prior to sub-slab sampling for VOCs. Figure 8

illustrates a tripod used to collect a 24-hour outdoor 

air sample during the March 2003 sampling event. 

Each evacuated canister used for basement and 

outdoor air sampling was equipped with a flow controller 

and particulate filter. A particulate filter was attached 

to the high pressure inlet port of a flow controller. 

The low pressure outlet port of the flow controller 

was connected to a canister inlet port. Vacuum was 

measured in each canister prior to sampling. Air in 

each basement was sampled by placing a six-liter 

SilcoCan canister approximately 1 to 1.5 meters (3 to 

5 feet) above the floor in a centrally located position. 

With the exception of closing basement doors and 

windows, no other precautions were taken to reduce 

air exchange in homes before or during sampling. 

During the July 2002 sample event, 5 basements 

were sampled at a flow rate of 73 to 80 ml/min over a 

1-hour period. During the March 2003 sample event, 

11 basements were sampled at a flow rate of 3.1 to 

3.3 ml/min over a 24-hour period. 

As illustrated in Figure 5, an Aalborg Electronic Mass 

Flow Meter (Model GFM-1700) was used during 

sampling of basement air to ensure that flow controllers 

maintained constant sample flow rates (±1 ml/min). 

While not performed in this investigation, flow rate can 

also be estimated by periodically measuring vacuum 

in a canister through use of the Ideal Gas Law by: 

where: = change in standard volume of air in 

canister (L), = change in time (min), TSTP and PSTP

= standard temperature (273°K), and pressure 

(1 atm), Vcan = volume of canister (L), Pcan(1 or 2)

= pressure (atm) in canister at time 1 or 2, and 

Tcan(1 or 2) = temperature (°K) in canister at time 1 or 

2. For instance, if absolute pressure in a canister is 

0.1 atm and 293°K at time (1) and 0.2 atm and 298°K 

Figure 8. Tripod and six-liter evacuated canister used to 

collect a 24-hour outdoor air sample during the March 2003 

sampling event.
11

at time (2) over a period of 60 minutes, then sample 

flow rate during this period is estimated at 0.008 

standard liters per minute (SLPM) or 8 standard cubic 

centimeters per minute. At the cessation of sampling, 

pressure was measured to document the presence 

of residual vacuum. Mechanical flow controllers have 

difficulty maintaining constant flow near atmospheric 

pressure. 

3.3 Quality Control Measures and Data 

 Quality for Basement Sampling and 

 Analysis for Radon

Radon was sampled in basement and sub-slab air to 

evaluate the feasibility of using radon as an indicator 

compound to assess vapor intrusion. In the absence 

of significant off-gassing of radon in a water supply or 

radon precursors in building materials, measurement 

of radon in sub-slab and indoor air may provide an 

indoor air/sub-slab air concentration ratio unaffected by 

source terms outside or inside a building. Radon gas 

has the potential to be widely utilized as an indicator 

compound during vapor intrusion investigations 

because it is present in virtually all sub-surface 

media, albeit at low concentrations in some areas of 

the United States. 

Open-faced, activated charcoal canisters were used to 

measure basement radon gas concentrations during 

the March 2003 sample event in accordance with 

sampling procedures outlined in EPA 402-R-93-003 

(USEPA, 1993). Cylindrical 1.5 cm diameter, 5 cm 

deep canisters containing Calgon-type 1193-coconut 

shell charcoal were supplied by AccuStar Labs in 

Medway, MA. Canisters were placed with the open 

side up 1.2 to 1.5 meters above a floor in a central 

location with unimpeded air flow and left undisturbed 

for a period of 48 hours. EPA 402-R-93-003 requires 

placement of canisters a minimum distance of 75 

cm from a floor, one meter from an exterior wall, and 

deployment for a minimum of 48 continuous hours. 

Property owners were advised to close windows and 

doors during sampling to minimize ventilation. At the 

cessation of sampling, canisters were closed with 

protective covers, resealed, and submitted to AccuStar 

Labs for analysis. 

Compliance with EPA 402-R-93-003 requires 

attainment of a lower limit of detection (sensitivity) of 

0.5 picoCuries per liter (pCi/L) for an exposure period 

of two to seven days and attainment of five primary 

quality assurance factors: (1) routine instrument 

checks, (2) calibration of canisters and equipment 

utilized to analyze canisters at least once every 12 

months, (3) agreement within ± 25% between known 

and measured concentrations at or above 4 pCi/L with 

a testing frequency of 3 per 100 samples submitted, 

(4) measurement of background concentration in 

field blanks with a testing frequency of at least 5% of 

canisters deployed, and (5) a coefficient of variation 

(COV) less than 10% for concentrations at or above 

4 pCi/L for replicate (comparison of two canisters) 

analysis with a sampling frequency of at least 10% of 

samples collected. A detection limit of 0.4 pCi/L was 

attained in this study. As illustrated in Figure 9, the 

average COV was 10%, but a COV greater than 10% 

was observed for several samples at concentrations 

greater than 4 pCi/L. 
12

3.4 Sub-Slab Probe Assembly and 

 Installation

To minimize the potential for drilling through utility 

lines, local utility companies were contacted to mark 

off entry points of water, gas, electrical, and sewer lines 

outside each building. Utility companies, however, 

will not trace utility lines inside a building. During this 

investigation, it was often possible to see points of 

entry of gas, water, and sewer lines through basement 

walls and floors. At most homes, a sewer line entered 

a basement in a central location and could be traced 

outside a building by using utility company markings. 

Tracing utility lines inside a building with a slab on 

grade would have been considerably more difficult. 

In this case, a local plumber and electrician would 

have been contracted to provide recommendations 

on safe locations to drill.

Sub-slab vapor probes were installed several days prior 

to sampling. Figure 10 illustrates general construction 

details of sub-slab vapor probes installed in concrete 

slabs. Sub-slab vapor probes were designed to lie 

flush on the upper surface of a slab to not interfere 

with daily building use and to “float” in a slab to enable 

gas sample collection from sub-slab material in direct 

contact with a slab or from an air pocket directly beneath 

a slab created by sub-slab material subsidence. Use 

of a screen was unnecessary because probes were 

not inserted directly into sub-slab material. Probes 

were assembled prior to drilling to minimize exposure 

time of sub-slab soils to an open hole. 

As illustrated in Figure 11, sub-slab vapor probes 

were assembled from 5.08 cm (2”) long, 1/8” brass 

pipe nipples having inner and outer diameters of 

0.64 cm (1/4”) and 0.95 cm (3/8”), respectively, and 

Figure 9. Coefficient of variation (COV) as a function of mean basement radon concentration.
13

2.5 cm (1”) long, 1.3 cm (1/2”) outer diameter brass 

couplings. When slab thickness was less than 2.5 

cm (1”), 0.64 cm (1/4”) long stainless-steel hex 

bushings, as illustrated in Figure 12, were used in 

lieu of pipe nipples and couplings. Both probe types 

were closed by 0.32 cm (1/8”) recessed brass socket 

plugs. To ensure that brass fittings were not a source 

of VOCs during sampling, one set of brass fittings 

was immersed in methanol for a 24-hour period. 

Gas chromatography/mass spectrometry (GC/MS) 

analysis was then conducted at EPA’s ORD Laboratory 

in Ada, Oklahoma, on the methanol, and a sample 

of a lime-based cement was used to set the probes. 

No VOCs were detected in either material. To further 

assess the potential of brass fittings as a source of 

VOCs, a sample (grab) of outside air passing through 

brass fittings was analyzed by EPA’s New England 

Laboratory using EPA Method TO-15 and compared 

with a 1-hr time integrated sample of outside air 

collected the same day. As illustrated in Figure 13, 

VOC concentrations of air exiting the brass fittings 

were generally equivalent to outside air concentrations 

indicating again that probe construction materials were 

not a source of VOCs. 

Figure 10. General schematic of a sub-slab vapor probe.

Figure 12. Hex bushing used for probe construction when a 

concrete slab was less than 2.5 cm thick.

Figure 11. Brass materials used for sub-slab probe 

construction in homes near the Raymark facility.
14

Initial probe design emphasized the use of materials 

readily available at a typical hardware store. However, 

cutting oils are often used to machine brass nipples 

and couplings and thus require analytical testing as 

described here to ensure cleanliness. Sub-slab vapor 

probes at other sites are now assembled from 2.5 cm 

(1”) long, 0.64 cm (1/4”) OD x 0.46 cm (0.18”) ID gas 

chromatography grade 316 stainless-steel tubing and 

2.5 cm (1”) long, 0.64 cm (1/4”) OD x 0.32 cm (1/8”) 

NPT Swagelok stainless-steel compression fittings. 

Use of gas chromatography grade stainless-steel 

materials minimizes potential VOC contamination due 

to probe assembly. The components of this probe 

design are illustrated in Figure 14.

Figure 13. A comparison of VOC concentrations in outdoor air and outdoor air passing through brass fittings used for probe 

construction during the July 2002 sampling event. Dashed lines indicate detection limits.

Figure 14. Stainless-steel materials now used 

for sub-slab probe assembly.
15

As illustrated in Figure 15, a Model 11224E Bosch 

1.25-inch rotary hammer drill was used to create a 2.5 

cm (1”) “outer” diameter hole approximately 2.5 cm (1”) 

into a slab. Initial depth of penetration was equivalent 

to the length of the brass couplings to ensure that the 

probes were flush with the upper surface of the slab. 

The inside of the outer hole was cleaned with a damp 

towel prior to creating a 0.95 cm (3/8”) “inner” diameter 

hole through the remainder of the concrete. The drill 

bit was then allowed to penetrate an additional 5 cm 

(2”) into sub-slab material (e.g., sand or sand and 

gravel) to create an open cavity to prevent potential 

obstruction of probes during sampling. The outer 

diameter hole was then cleaned once more with a 

damp towel to increase the potential of a good seal 

during cement application. Inner and outer holes are 

illustrated in Figure 16. Probe tubing was then inserted 

into the inner diameter hole allowing couplings or hex 

fittings to rest at the base of the outer diameter hole. 

A quick-drying, lime-based cement which expanded 

upon drying (to ensure a tight seal) was mixed with 

tap water to form a slurry and placed into the annular 

space between the probe and inside of the 2.5 cm 

(1”) diameter hole using a small metal rod. Tap water 

was not analyzed for VOCs during our investigations. 

Tap water at these homes was chlorinated and likely 

contained trihalomethanes but not VOCs of concern 

in sub-surface media. Nevertheless, it would appear 

prudent in future investigations to use VOC-free water 

for cement application. The cement was allowed to 

cure for at least 24 hours prior to sampling. Using 

this procedure, 3 probes could be installed in less 

than 2 hours. 

Figure 15. Drilling through a concrete slab using a rotary 

hammer drill.

Figure 16. "Inner" and "outer" holes drilled in a concrete slab.
16

Figure 17. Typical schematic illustrating location of sub-slab vapor probes.

prepared for each building. Schematics were used 

to document sample locations, interpret sub-slab 

sample results, and design corrective measures. 

Figure 17 illustrates a typical schematic developed 

for each building.

Schematics illustrating the location of sub-slab probes 

and other slab penetrations (e.g., suction holes for 

sub-slab permeability testing), evacuated canisters for 

basement air sampling, and other investigative devices 

(e.g., permeation tubes for air exchange testing) were 
17

3.5 Sub-Slab Air Sample Collection for 

 VOCs Using EPA Method TO-15

As illustrated in Figure 18, a brass NPT to Swagelok 

union fitting was used to connect vapor probes to a 

“T” fitting made of a stainless-steel flexible line and an 

in-line valve. A portable vacuum pump was used to 

purge vapor probes and sampling lines. Samples were 

collected by closing the in-line valve on the pump end 

of the “T” fitting and opening a valve for entry into 

a six-liter SilcoCan canister. A particulate filter was 

attached to the inlet port. Samples were collected by 

opening the canister valve and waiting until canister 

pressure approached atmospheric pressure (grab 

sampling). This took approximately two minutes. 

Time-integrated sub-slab sampling will be evaluated 

in future investigations. 

3.6 Quality Control Measures and Data 

 Quality for Sub-Slab Air Sampling 

 Using Tedlar Bags and On-Site GC 

 Analysis

In addition to sample collection in evacuated canisters, 

sub-slab air samples were collected in 1-liter Tedlar 

bags. Tedlar bags were filled in about one minute 

resulting in an average flow rate of 1 SLPM. As 

illustrated in Figure 19, sub-slab vapor samples were 

collected from the vapor probes using a threaded (1/8”) 

brass or plastic nipple, a peristaltic pump, Tygon, and 

Masterflex tubing. All tubing was disposed of after 

sampling at each probe to avoid cross contamination. 

High purity FEP-lined polyethylene tubing could be 

used in lieu of Tygon tubing because it offers very low 

vapor and gas permeability, is non-photo reactive, 

Figure 18. Sample train for sub-slab air collection using EPA 

Method TO-15.

and is a low cost alternative to fluoropolymer tubing. 

Tedlar bags were stored in a cooler without ice to 

avoid condensation and analyzed for target VOCs 

(1,1,1-TCE, 1,1-DCE, TCE, c-1,2-DCE) by EPA’s 

New England Regional Laboratory within 24 hours 

of sample collection. 

Unlike TO Methods, EPA does not have explicit quality 

assurance guidelines for on-site GC analysis. Thus, a 

site-specific quality assurance (QA) plan or standard 

operating procedure (SOP) for on-site GC analysis 

is critical to collecting defensible data. On-site GC 

analysis was conducted by EPA’s New England 

Regional Laboratory using their SOP (USEPA, 2002b). 

Hartman (2004) discusses the use of QA requirements 

in EPA Methods 8021 and 8260 (water analysis) for 

on-site vapor GC analysis.
18

A brief review of EPA’s New England Regional 

Laboratory SOP for on-site GC analysis is provided 

to document work here and to aid development of 

QA plans developed for other sites. Air samples from 

each Tedlar bag were injected into two portable GCs 

with results compared for consistency. The first GC 

was a Shimadzu 14A equipped with a 30 m, 0.53 mm 

megabore capillary column, a Photoionization Detector 

(PID), and an Electron Capture Detector (ECD). The 

second GC was a Photovac 10A10 equipped with a 

1.2 m (4 ft), 0.32 cm (1/8”) SE-30 column and a PID. 

A Hamilton 250 μl steel barrel syringe with a 2 inch, 

25-gauge needle was used to directly inject 200 μl 

of sample into both GCs. Standards were prepared 

from readily available commercial methanol stock 

solutions and diluted in VOC-free water in Class A 

volumetric glassware to a concentration of 10 μg/l. 

Standards were then immediately transferred from 

the volumetric glassware into 40 ml VOA vials and 

stored on ice. Prior to air sample analysis, 10 ml of 

standard was withdrawn from the 40 ml VOA vial to 

create a headspace above the liquid standard. After 

a period of equilibrium in an ice bath (0 – 1°C), field 

GCs were calibrated for target compounds using the 

headspace above the 10 μg/l standard. This proved 

to be a simple, quick, dependable, and inexpensive 

method for calibration. 

Figure 20presents a comparison of SilcoCan canister 

and TO-15 analysis with Tedlar bag sampling with onsite GC analysis for 1,1,1-TCA, 1,1-DCE, TCE, and 

c-1,2-DCE analysis (n = 91, r 2

 = 0.88). There is no 

systematic bias in the data set (i.e., Tedlar bag analysis 

consistently lower or higher than TO-15 analysis). 

Four out of five of the outliers were associated with 

sampling one probe during one sample event. The 

regression coefficient increased to 0.95 when these 

four points were omitted. In general, there was good 

agreement between Tedlar bag sampling with on-site 

GC analysis and EPA Method TO-15. 

Tedlar bag sampling and on-site analysis provided 

near real-time data compared to EPA Method TO-15. 

However, this method provided analysis for a limited 

number of compounds with higher detection limits. 

Detection limits for on-site analysis were 2 – 5 ppbv 

compared to 0.1 – 0.5 ppbv for EPA Method TO-15.

Figure 19. Sample train for sub-slab air collection using one-liter Tedlar bags.
19

3.7 Quality Control Measures and Data 

 Quality for Sub-Slab Air Sampling for 

 Radon Using Scintillation Cells

Scintillation cells are air-tight metal cylinders lined 

with activated silver zinc sulfide ZnS(Ag). They have 

a transparent window at one end for scintillation 

counting and connectors at the other end for sample 

intake or flow through. When an alpha particle from the 

radioactive decay of radon isotopes Rn-222, Rn-220, 

and Rn-219 strikes the lining of a scintillation cell, the 

alpha particle becomes a helium atom, and the sulfide 

de-excites by emitting photons or light pulses. The 

transparent window and a radiation monitor equipped 

with a photomultiplier tube are used to amplify and 

count light pulses.

Scintillation cells used for this investigation were 

originally purchased from the Pylon Electronic 

Development Company. Pylon Models 110A and 300A 

scintillation cells have internal volumes of 151±3 and 

270±3 ml, respectively. The larger internal volume 

of Model 300A allows greater sensitivity compared 

to Model 110A. The scintillation cells were equipped 

with two gas-tight Swagelok connectors allowing 

continuous monitoring (flow through) or grab sampling 

(vacuum collection or disconnection after a period of 

flow through or purging). 

The sub-slab sampling train is illustrated in Figure 21. 

A threaded (1/8”) barbed nipple was used to attach 

Tygon tubing to a sub-slab probe. Plastic barbed fittings 

were used to connect Tygon to Masterflex tubing used 

Figure 20. Comparison of EPA Method TO-15 Tedlar bag sampling with on-site GC analysis for 1,1,1-TCA, 1,1-DCE, TCE, and

c-1,2-DCE analysis, n = 91, r 2 = 0.88.
20

by a peristaltic pump to create vacuum 

in a probe for sample collection. A 

particulate filter was placed on the inlet 

side of a scintillation cell. Quick-connect 

assemblies were used for connection 

of Tygon tubing to Pylon cells. A flow 

meter was placed on the outlet side of a 

scintillation cell to ensure a flow rate of 

approximately 1 SLPM. The outlet end 

of the flow meter was vented outside. 

Purging ceased when 10 cell volumes 

were exchanged in each cell. 

Samples were analyzed by the MA Department of 

Public Health (Mr. William Bell) within four hours 

as recommended in EPA 402-R-93-003. A Pylon 

AB-5 portable radiation monitor was used to amplify 

and count light pulses. Counts per minute were 

determined by recording total counts over six 10 minute 

measurement intervals and dividing by total counting 

time. The relationship between the number of light 

pulses counted per time and the concentration of radon 

gas in a cell is outlined in EPA 402-R-93-003

where: CRn = concentration of radon gas (pCi/l),

cpm(s) = counts per minute for the scintillation cell after 

sample collection, cpm(bkg) = counts per minute in the 

scintillation cell prior to sample collection (background 

count), C = a correction factor for radon decay during 

the counting interval provided in EPA (1993), 3 = total 

number of alpha particle emitters, 2.22 = a conversion 

factor relating disintegrations per minute (dpm) to pCi, 

E = counting efficiency (cpm/dpm), V = volume of the 

scintillation cell (liters), and = a correction factor

for radon decay between sample collection and start 

of measurement provided in EPA (1993). Certificates 

of calibration for counting efficiencies for scintillation 

cells used in this study were included with analytical 

results. Knowledge of counting efficiency is necessary 

because not all alpha particle impacts on the activated 

zinc sulfide lining result in detection of light pulses. 

EPA 402-R-93-003 requires: (1) a lower limit of 

detection of 1.0 pCi/L or less, (2) collection of replicates 

at 10% of sample load with attainment of a coefficient 

of variation of 10% or less at concentrations 4 pCi/L 

or greater, (3) use of field blanks kept sealed in a low 

radon (less than 0.2 pCi/L) environment, and analyzed 

in the same manner as other samples at 5% of sample 

load, and (4) calibration of cells at least once every 

12 months. 

Figure 21. Sample train for sub-slab air collection for radon using scintillation cells.
21

Air permeability testing was conducted in sub-slab 

media to support design of corrective action (subslab depressurization) and air flow simulations used 

to evaluate infiltration of basement air into sub-slab 

media during sampling. A Bosch 1.25-inch capacity 

hammer drill (Model 11224E) was used to drill a 

5.08 cm (2”) diameter hole 2.5 cm (1”) through a 

slab for installation of suction points. A 2.5 cm (1”) 

diameter drill bit was then advanced through the 

remainder of a slab and 7 to 8 cm (3”) into sub-slab 

material to create an open cavity for air extraction. 

Sub-slab material consisted of coarse sand and 

gravel similar to native deposits. Suction points 

were assembled from 5.1 cm (2”) long threaded 

brass pipe having inner and outer diameters of 1.9 

cm (3/4”) and 2.5 cm (1”) respectively and 3.2 cm 

(1 1⁄4”) outer diameter brass couplings. The length 

of the threaded pipe used was determined by the 

thickness of the concrete slab. Couplings were 

installed without threaded pipe when the slab was 

less than 7 to 8 cm (3”) thick. All suction points 

were completed flush with the top of the concrete 

slab with recessed brass plugs so as not interfere 

with day-to-day use of the basements. Figure 22. Regenerative blower used for air permeability testing.

4.0 Methods and Materials Used for Air Permeability Testing

and Sub-Slab Air Flow Analysis

As illustrated in Figure 22, a small regenerative blower was 

used to extract air from sub-slab material. A variable-area 

flowmeter illustrated in Figure 23 was used to measure 

flow rate. As illustrated in Figure 24, air pressure was 

measured with magnehelic gauges. A digital manometer 

(± 1.0% of range accuracy) was also used for pressure 

measurement. 
22

Radial and vertical air permeability of sub-slab media 

was estimated using Baehr and Joss’s (1995) analytical 

solution for two-dimensional, axisymmetric, steadystate gas flow in a semi-confined domain. 

where

and = pressure squared in sub-slab media (g/cm-s2

)

2

,

 = pressure squared in air above slab (atmospheric 

pressure) (g/cm-s2

)2 , z = depth below bottom of slab 

(cm), r = radial distance from cavity created in subslab media (cm), b = depth below bottom of slab to 

an impermeable boundary (ground water) (cm), d = 

distance from bottom of slab and top of cavity in subslab media (d = 0), l = distance from bottom of slab to 

bottom of cavity created in sub-slab media (cm), kz

 = 

vertical air permeability of sub-slab media (cm2), kr = 

radial air permeability of sub-slab media (cm2), μg= 

dynamic viscosity of air (g/cm s), = average molecular 

weight of air (g/mole), Qm = mass flow of air (g/s), = 

Ideal Gas Constant (8.314E+07 g-cm2/s2-mole-°K), 

T = temperature (°K), K0

 = zero-order modified 

Bessel function of the second kind, K1

 = first-order 

modified Bessel function of the second kind, and qn

= positive solutions (n = 1,2,3,···) to tan (qn

) = h/qn.. 

As , the roots of the transcendental equation

tan (qn

) = h/qn become . Leakance or is 

used to represent flux into the simulated domain (subslab material) expressed by:

Figure 23. Variable-area flowmeter used for air permeability 

testing.

Figure 24. Magnehelic gauges and suction hole used for 

vacuum measurement.
23

Baehr and Joss (1995) represent as the vertical 

permeability of a semi-confining boundary layer divided 

by the thickness of the boundary layer. Given the 

potential of sub-slab material subsidence, can be 

taken in this application to represent a term used in 

describing lateral air flow beneath a slab but above 

sub-slab material and vertical air flow through cracks in 

a slab. Air flow through cracks is not explicitly simulated 

in this model. Also, the vertical permeability of slab 

material is not estimated in this application. 

Parameter estimation involves finding values of kr

, kz, 

and that minimize the difference between observed 

versus simulated data for pressure or the root mean 

squared error (RMSE) defined as:

where P is observed pressure and is modeled 

pressure. When there are few pressure measurements 

(some of which are of minimum usefulness because 

of near atmospheric pressure response), nonuniqueness in parameter estimation and convergence 

to a local but not global minimum RMSE can occur. That 

is, a similar pressure distribution in a domain can be 

simulated using various parameter inputs. To address 

this issue, 5000 random initial guesses were applied 

for kr 

, kz, and to determine a lowest RMSE. This 

process was repeated with decreasing intervals of kr

, 

kz, and until the same or similar RMSE values were 

obtained. A FORTRAN program, MFRLKINV (USEPA, 

2001), was used to facilitate computations. 

Figure 25 illustrates the best five fits of kr

, kr /kz, 

and for an air permeability test at House C 

consisting of four observation points conducted at 

where = volumetric air content and

Vertical volumetric specific discharge (qz

) and pore-air 

velocity vz

 (cm/s) are defined as:

where

a flow rate of 255 SLPM. Estimation of kr 

/kz was 

constrained between 1 and 2 because sand and 

gravel typically exhibit kr 

/kz values within this range 

(USEPA, 2001 - Section 5). Unconstrained estimation 

of kr 

/kz resulted in greater variation in to provide 

comparable fits to the observation points. When 

pressure measurement of the closest observation point 

was eliminated from consideration during parameter 

estimation, estimates of kr

 varied from 10-10 cm2 to 

10-7 cm2. This demonstrates the need to locate one or 

more pressure monitoring points or sub-slab probes 

fairly close (e.g., one meter) to the source of vacuum 

during sub-slab air permeability testing. 

Estimates of kr 

, kz, and were then used for air flow 

simulations. Radial volumetric specific discharge (qr

) 

and pore-air velocity (vr 

) (cm/s) are defined as:
24

For analysis of air flow during sampling, the norm 

of the radial and vertical pore-air velocity vector (v) 

(cm/s) is calculated by:

The stream function, , for axisymmetric flow with 

anisotropy may be written as:

Solving for yields:

The path of an air particle in a flow field at location 

(r0,z0) at time zero was solved by the following set of 

ordinary differential equations:

and the algorithm:

where i = 0,1,...,N. The particle tracking terminates 

when the particle reaches the probe. Total travel time 

= N . The equations were solved numerically using 

a second-order Runge-Kutta method. A FORTRAN 

program, SAIRFLOW, (USEPA, 2001) was used to 

facilitate computation of P(r,z), vr 

, vz, v, , and 

travel time to a vapor probe.

Figure 25. Best fit model results for permeability test conducted at House C with four observation points and a flow rate of 255 

SLPM (kr /kz constrained between 1 – 2).
25

5.1 Assessment of Infiltration of Basement 

 Air During Air Extraction

Generally, sub-slab air samples were collected by first 

purging two liters of air from probes at a flow rate of

1 SLPM, then collecting a sample into a one liter Tedlar 

bag at a flow of 1 SLPM, followed by purging one liter 

again at a flow rate of 1 SLPM, then finally collecting 

a five-liter sample into a six-liter evacuated canister 

over a period of approximately one minute. 

If during sub-slab sampling, basement or indoor air 

enters openings in a slab (e.g., cracks, utility entry 

locations) and is collected into a sampling vessel, then 

measured sub-slab concentrations should decrease 

for VOCs having sub-slab concentrations higher than 

basement air. The opposite effect should occur for 

VOCs having sub-slab concentrations lower than 

basement air. One way to directly evaluate infiltration 

of basement or indoor air into a sampling vessel 

during air extraction is to collect a series of sequential 

samples and measure vapor concentration as a 

function of extraction volume. Constant concentration 

in sequential samples would indicate the absence 

of significant infiltration of basement air during the 

extraction period. A reduction in concentration during 

air extraction could indicate significant infiltration 

during extraction or reduced sub-slab air concentration 

away from the probe (spatial variability). An increase 

in concentration during air extraction could indicate 

5.0 Discussion of Sampling Issues Associated with Sub-Slab Air Sampling

increased concentration away from the probe (spatial 

variability). 

Sub-slab samples were collected sequentially in a 

probe at three homes (L, M, and N) in five 1-liter Tedlar 

bags at a flow rate of 1 SLPM and analyzed on site by 

GC analysis. Results of sampling at each location are 

summarized numerically in Tables 14b, 15b, and 16c

(see pages 81, 84 and 88) and graphically in Figures 

26a, 26b, and 26c. At each location, extraction of 

5 liters at a flow rate of 1 SLPM had little effect on 

sample concentration indicating a lack of significant 

infiltration. Concrete slabs at these three buildings 

consisted of approximately 2-4” of relatively intact 

concrete (few cracks). A comparison of replicate 

canister samples was also used to assess the effect 

of extraction volume. After Tedlar bag sampling, a 

canister sample represented an extraction volume of 

5 to 9 liters. A replicate canister sample represented 

an extraction volume of 10 to 14 liters. Results of 

sampling are summarized numerically in Tables 12a

and 15a (see pages 74 and 83) and graphically in 

Figures 27a and 27b. Sampling at Probe A in House 

J indicated little difference in sample results. Sampling 

at Probe A in House M revealed a slight decrease in 

vapor concentration as a function of extraction volume 

for most VOCs. Thus, replicate sampling in canisters 

indicated little or no effect in sample concentration 

due to air extraction.
26

Figure 26a. Sub-slab vapor concentration as a function of extraction volume at Probe A in House L using Tedlar bag sampling and 

on-site GC analysis.

Figure 26b. Sub-slab vapor concentration as a function of extraction volume at Probe B in House M using Tedlar bag sampling and 

on-site GC analysis.
27

Figure 26c. Sub-slab vapor concentration as a function of extraction volume at Probe A in House N using Tedlar bag sampling and 

on-site GC analysis. Dashed lines denote detection limit.

Figure 27a. Sub-slab vapor concentration as a function of extraction volume at Probe A in House J using EPA Method TO-15.
28

A second direct method to evaluate infiltration of 

indoor air into sub-slab media during extraction is to 

compare basement and sub-slab concentrations of 

VOCs known not to be associated with subsurface 

contamination. Statistical testing to distinguish VOCs 

associated with vapor intrusion from other VOCs 

detected in indoor air is discussed in section 6.0. A 

simple mass-balance equation:

is used to express a measured sub-slab vapor 

concentration (Cmeas ) as a function of “true” sub-slab 

concentration (Css ) and indoor air concentration (Cindoor ) 

where Qleak = flow rate of air through cracks or other 

openings in the slab and Qss = sub-slab air flow to a 

vapor probe. If infiltration of indoor air into sub-slab 

media can be expressed as: 

 then 

 and

The assumption that Cmeas is due entirely to infiltration 

of indoor air into sub-slab media (Css = 0) leads 

to computation of a maximum value of I for each 

VOC detected in indoor air and not associated with 

vapor intrusion. The lowest value of I can then be

Figure 27b. Sub-slab vapor concentration as a function of extraction volume at Probe A in House M using EPA Method TO-15.
29

selected to represent maximum infiltration during air 

extraction. For instance, 1,4-dichlorobenzene (not 

a VOC associated with sub-surface contamination) 

was detected in basement air at House H at 36 ppbv 

but was not detected in a sub-slab probe (detection 

limit 0.086 ppbv). Thus, less than 0.24% of sampled 

air originated from above the slab. This method 

provides reasonable results (I < 100%) only if the ratio 

Cindoor /Cmeas is greater than 1. Table 1 summarizes 

maximum infiltration of indoor air during air extraction 

at each probe. When the sensitivity of the test was

Location Extraction

Volume (L)

P[A] P[B] P[C] P[D] P[E]

(%) (%) (%) (%) (%)

A 9 < 42 < 9.0 IND

B 9 < 2.1 < 6.7 < 0.35

C 9 IND IND IND IND

D 9 < 27 < 27 NA

E 9 < 12 < 19 < 39

F 9 < 8.6 NA < 22 NA

G 9 < 0.60 NA < 0.60 NA NA

H 9 ND < 0.24 < 0.33 NA

I 9 < 7.5 NA NA

J 14 < 3.0 NA NA NA

K NA NA NA NA

L 9 NA < 2.7 NA

M 14 < 78 NA NA

N 9 NA < 4.4 < 24

O 9 < 0.42 NA < 0.63

P 9 NA < 1.3 < 1.4 NA

NA = not analyzed IND=indeterminate

Table 1. Computation of Maximum Percent Infiltration of 

Basement Air into an Evacuated Canister During Sampling 

as a Function of Extraction Volume, Location, and Probe. 

P[A], P[B], P[C], P[D], and P[E] Denote Probes Evaluated at 

Individual Locations

satisfactory (e.g., sensitivity < 1%), infiltration during 

sampling was evidently very low. Use of this method 

however, requires detection of elevated levels of 

VOCs not associated with sub-surface contamination 

in indoor air and low levels or low detection limits for 

these compounds in sub-slab air. Sensitivity could 

be increased by enclosing an area around a probe 

with a chamber during air extraction and injecting a

tracer over a specified period of time. Infiltration then 

could be estimated by: 

where Ctracer= tracer concentration within the chamber, 

t

sample is total sampling time, and t tracer is time of tracer 

application. Tracer concentration would have to be held 

constant during the tracer application period. Also, 

flow analysis would have to be conducted to estimate 

the potential area of infiltration during testing. If a 

pure phase solvent is exposed to air within a chamber 

surrounding a sub-slab probe and equilibration within 

the chamber is assumed, Ctracer could be estimated 

in units of μg/m3 using the solvent’s saturated vapor 

concentration (Csat)

or in units of ppbv by

where Pv = vapor pressure (atm), and Mv , T, P, 

and are as previously defined. For instance, the 

saturated vapor concentration of isopropanol, which 

has a vapor pressure of 0.058 atm at 25°C and a 

molecular weight of 60.1 g/mole, is 1.43E+08 μg/m3

or 5.80E+07 ppbv at a pressure of 1 atmosphere. If 

a pure phase solvent is used as a tracer for infiltration 

testing, it would be prudent to minimize t tracer /tsample

because detection of a solvent at a high concentration 

could result in high detection limits for other VOCs of 

interest. For instance, if I = 0.01 or 1%, and t tracer /tsample

= 1, then isopropanol would be present in a sampling 

canister at a concentration of 1.43E+06 μg/m3 which 

would likely preclude detection of other VOCs of 

v
30

could have come from infiltration from basement air. Thus, 

when extracting 12 liters of air, less than 10% of air entering 

an evacuated canister could have been from infiltration of 

basement air. The results of sequential sampling and mass 

balance analysis revealed that less than 1% of air entering 

evacuated canisters during this investigation were from 

basement air. 

In this investigation, extraction volumes up to 14 liters had 

little effect on sample results. However, data generated in 

this investigation cannot be extrapolated to justify the use of 

large extraction volumes (e.g., 20, 50, or 100 liters) during 

sampling. Further research is needed in this area. 

interest. The ratio t tracer /tsample would have 

to be reduced to 0.001 (e.g., sample time 

of 10,000s, tracer time of 10s) to observe 

a concentration of 1.43E+03 μg/m3 in the 

canister.

A third, but indirect, method of evaluating 

infiltration of indoor air during air extraction 

is to simulate streamlines and particle 

transport during flow. Mean estimated 

parameters at House C (kr

 = 7.4E-07 cm2, 

kr /kz = 1.5, = 3.2E-09 cm) were used to 

generate streamlines and travel time contours 

of air particles in sub-slab material with = 

0.35 at a flow rate of 1 SLPM. Depth to a 

no flow lower boundary was set at 500 cm. 

This simulation is illustrated in Figure 28. 

Dashed contour lines for 60 and 300 seconds 

reflect collection of 1 and 5 liters of sample, 

respectively, at a flow rate of 1 SLPM. Areas 

between streamlines reflect fractional flow. 

As previously stated, air flow through the 

slab is not simulated because the leakance 

term represents a combination of lateral 

flow beneath a slab and sub-slab material 

and vertical flow through a slab. The solid 

contour lines for 0.90 and 0.95 streamlines are 

highlighted. The 0.95 streamline at the top of 

the figure indicates that approximately 5% of 

air that had exited a probe at 100 seconds (1.7 

liters) originated from above sub-slab material 

of which some fraction of this 5% could have 

been from infiltration from basement air. The 

0.90 streamline indicates that approximately 

10% of air that exited a probe at 700 seconds 

(11.7 liters) originated from above sub-slab 

material of which some fraction of this 10% 

Figure 28. Simulated streamlines (solid lines) and travel time (s) 

(dashed lines) contours in sub-slab media when kr = 7.4E-07 cm2, 

kr /kz = 1.5, = 3.2E-09 cm, flow rate = 1 SLPM, and depth to ground 

water = 500 cm.
31

5.2 Assessment of Extraction Flow 

 Rate

Laboratory- and field-scale research conducted 

on soil venting indicates that rate-limited airwater and/or solid-water mass exchange can 

occur in sub-surface media during air flow. 

Rate-limited mass exchange could decrease 

vapor concentration in a sample container 

below what would be expected from equilibrium 

partitioning. EPA (Section 9, 2001) provides 

a comprehensive summary of mass transfer 

coefficients for air-water and solids-water 

exchange determined for several soil types 

in laboratory column studies. These studies 

indicate that for sandy, non-oven dried soils 

typically found directly beneath a slab, solidswater partitioning and hence rate-limited solidswater rate-limited mass exchange should be 

insignificant. Rate-limited air-water exchange, 

however, can be significant at high pore-air 

velocities. In one case, rate-limited air-water 

exchange was observed at a pore air velocity as 

low as 0.01 cm/s. In another case, no rate-limited 

behavior was observed at a pore-air velocity as 

high as 0.16 cm/s. Rate-limited mass transfer 

is a function of media-to-media mass transfer 

coefficients and a characteristic length over 

which mass transport occurs. The transport 

length in laboratory column studies is typically 

on the order of 30 cm. The characteristic length 

in sub-slab media could be considerably longer 

(resulting in increased potential of attainment of 

local equilibrium) depending on the thickness 

and permeability of sub-slab media as illustrated 

by streamlines in Figure 28. 

Figure 29 illustrates pore-air velocity and travel time at a 

sampling at a rate of 1 SLPM for sub-slab conditions present 

at House C. Because of convergent flow to a relatively small 

probe cross-sectional area (radius = 0.32 cm, length = 5 

cm), pore-air velocity likely exceeded 0.01 cm/s throughout 

most of the domain during sampling (radius 17 cm for 5 

liters of air extracted from Figure 28). However, constant 

concentration in sequential samples indicated an absence 

of rate-limited mass transport during air extraction. This 

could be due to a long characteristic transport length and 

low extraction volume relative to the sampled domain. The 

California Environmental Protection Agency (Cal EPA) 

in conjunction with the California Department of Toxic 

Substances and Los Angeles Regional Water Quality Control 

Board recently published an advisory on soil-gas sampling 

Figure 29. Simulated vacuum (Pa) (dashed lines) and pore-air 

velocity (cm/s) (solid lines) in sub-slab media when kr

 = 7.4E-07 cm2, 

kr /kz = 1.5, = 0.35, flow rate = 1 SLPM and depth to ground water 

= 500 cm.
32

(Cal EPA, 2003) specifying maximum flow rate during 

sampling. This advisory is being used for sub-slab 

sampling. Cal EPA recommends a maximum sampling 

rate of 0.1 to 0.2 SLPM. Given simulations presented 

here, this recommendation appears reasonable.

5.3 Evaluation of Equilibration Time

The process of drilling through a concrete slab would 

be expected to reduce sub-slab vapor concentration 

in the immediate vicinity of a probe. For strictly 

diffusive transport, concentration reduction would be 

a function of chemical properties of a VOC (Henry’s 

constant, organic carbon - water partition coefficient, 

aqueous diffusion coefficient, air diffusion coefficient), 

material properties of sub-slab media (water content, 

porosity, bulk density, and organic carbon content), 

and temperature. For advective-diffusive transport, 

additional factors such as air permeability and the 

pressure differential between basement and sub-slab 

air are relevant. Concentration reduction would be 

expected to be greatest in relatively dry permeable 

material. However, these conditions would also 

expedite equilibration of the vapor concentration 

around a sub-slab probe. If sub-slab material consists 

of silt or clay, equilibration time may not necessarily 

be significantly longer because the initial vapor 

concentration perturbation may be reduced by a lower 

media permeability and lumped diffusion coefficient. 

Robust estimation of equilibration time would require 

knowledge of the extent and magnitude of vapor 

concentration reduction in sub-slab media and threedimensional advective-diffusive modeling. The problem 

can be simplified by using advective air flow modeling 

with particle tracking to estimate a maximum radius 

of perturbation for various sub-slab conditions when 

clean air flows into an open hole. This radius could 

then be utilized as a path length in diffusion modeling 

to calculate a maximum equilibration time when a 

hole is sealed. For instance, if a maximum pressure 

differential of 15 Pa (highest pressure differential or 

most conservative value used in EPA’s vapor intrusion 

guidance) is present between sub-slab media and 

basement air during probe installation and mean 

estimated parameters at House C (kr

 = 7.4E-07 cm2, 

kr /kz = 1.5, = 3.2E-09 cm) with = 0.35 are used for 

flow analysis, then this is equivalent to 0.22 SLPM of 

air flow into a probe. The radius of perturbation then 

is a function of the time in which the probe is open. 

In homes near the Raymark facility, holes drilled 

for probes were open for a maximum period of one 

hour. Using particle tracking, this results in a radius 

of perturbation of 27 cm. 

Now consider concentration C(r,t) of a VOC at radius 

‘r’ and time ‘t’ in a sphere around a sub-slab probe. 

If VOC concentration inside the sphere is initially at 

a uniform initial concentration C(r,0) or C0

 and the 

surface concentration of the sphere at radius ‘ ’ is 

maintained at a constant concentration C( ,t) or , 

then a normalized concentration at the center of the 

sphere or at the probe C(0,t) or C(t) can be estimated 

by (Crank, p.91,1975):

T is a dimensionless time defined by
33

D is a lumped diffusion coefficient (cm2/s) defined 

by

and = soil-air phase tortuosity, Da = free air diffusion 

coefficient (cm2/s), = soil-water phase tortuosity, Dw

= free water diffusion coefficient, H = dimensionless 

Henry’s constant, =volumetric air phase content,

 = volumetric water phase content, Kd

 = soil - water 

partition coefficient (cm3/g), and = bulk density of 

soil (g/cm3). Tortuosity factors can be estimated by 

Millington and Quirk (1961):

where = porosity. 

If attainment of C(t)/ = 0.99 is desired and

C0 = 0 (most conservative condition), then T approaches 

0.537. The initial concentration would be greater than 

zero if air exited a probe during installation. The 

assumption of air entry adds an additional degree 

of conservativeness. Figure 30 illustrates time to

C(t)/ = 0.99 for trichloroethylene (TCE) as a function 

of diffusion path length and when T=0.537 and

= 0.4, =1.68 g/cm3, Da = 7.4E-02 cm2/s,

Dw = 9.3E-06 cm2/s, H=0.38, and no sorption. This 

relationship is simply t = 0.537 /D. At homes near 

the Raymark site, sub-slab and underlying soils 

underlying each building consisted of relatively dry 

sand and gravel. Little or no sorption would be expected 

in this material and would be relatively low (e.g.,

 = 0.05). Figure 30 indicates that for a diffusion path 

length of 27 cm, time to C(t)/ = 0.99 would occur in 

less than 2 hours. During this investigation, sub-slab 

probes were allowed to equilibrate for 1 to 3 days. If 

probes were immediately sampled after installation 

without regard to grout setting time, approximately 

14.4 liters (hemispheric domain with a radius of

27 cm and = 0.35) of air would have to be extracted 

to remove sub-slab air potentially affected by probe 

installation. For sub-slab material consisting of silt or 

clay with kr

 = kz = 1.0E-09 cm2 and = 0.10, the radius 

of perturbation would be approximately 6 cm over an 

exposure period of 1 hour requiring an equilibration of 

time of approximately 10 hours. However, most subslab material consists of sand and gravel or sand even 

for homes built directly on clay. Thus, in most cases, 

an equilibration time of 2 hours should be sufficient 

for sampling.
34

5.4 Selection of Purge Volume

Sub-slab vapor probes and associated tubing must be 

purged prior to sampling because air in a probe and 

tubing will initially have VOC concentrations reflective 

of indoor air upon removal of recessed socket plugs. 

A purge volume consists of the total internal volume 

of: (1) sample tubing and associated fittings between 

a probe and sample container, (2) tubing and fittings 

associated with sub-slab vapor probes, (3) the open 

hole in slab below a probe, and (4) the cavity created 

in sub-slab material during drilling. Minimum purge 

volume prior to sampling can be estimated using a 

mass balance equation:

Figure 30. Time to reach C(t)/C = 0.99 as a function of diffusion path length ' ' and for TCE when C0 = 0, = 0.4,

 = 1.68 g/cm3

, Da = 7.4E-02 cm2/s, Dw = 9.3E-06 cm2/s, and H = 0.38 (no sorption).

where C is a well-mixed vapor concentration within and 

exiting the sample system, Cin= concentration entering 

the system, Cout = concentration exiting system,

Q = flow rate entering and exiting sample system, 

and V = internal volume of sampled system. When 

subject to an initial condition C(0)=C0

, (concentration 

at time zero), purge volume (tQ/V) can be expressed 

as a function of Cin and Cout by:
35

5.5 Placement of Sub-Slab Vapor Probes

Generally, during this investigation, one sub-slab vapor 

probe was centrally located, while two or more probes 

were placed within one or two meters of basement walls 

in each building. This was done to ensure detection 

of vacuum throughout the entire sub-slab during air 

permeability testing for corrective action. Figure 32

illustrates total vapor concentration of VOCs detected 

in Tedlar bags as a function of probe location in each 

building tested. There appears to be little correlation 

of probe placement with VOC concentration. That 

Figure 31. Purge volume as a function of C0 /Cin and Cout /Cin.

Figure 31 illustrates a simulation of purge volume as 

a function of C0 /Cin and Cout /Cin. Collection of 5 purge 

volumes ensures that the exiting vapor concentration 

is 99% of the entering concentration even when vapor 

concentration inside the sample system has been 

reduced to zero prior to sampling (C0

 = 0). A purge 

volume for the sample train used in homes near the 

former Raymark site was typically less than 10 cm3. 

is, placement of a probe in a central location did not 

ensure detection of the highest VOC concentrations. 

Figure 33 illustrates COVs for VOCs detected 

in sub-slab air and associated with sub-surface 

contamination. In many instances, COVs exceeded 

100%, indicating substantial spatial variability in subslab air concentration and the need for placement of 

multiple probes during a sub-slab investigation. In this 

investigation, 55 probes were installed in 16 buildings 

which on average resulted in the placement of one 

probe every 20 m2

 (220 ft2).
36

Figure 33. Coefficient of variation (COV) as a function of mean sub-slab concentration (ppbv) and method of analysis for VOCs 

associated with sub-surface contamination.

Figure 32. Total vapor concentration measured in one-liter Tedlar bags as a function of probe location and house. Dark bars refer 

to centrally located probes. No VOCs associated with subsurface contamination were detected at location F. Locations H, K, M, 

and P did not have a centrally located probe.
37

6.1 Method of Vapor Intrusion Evaluation

A dimensionless basement/sub-slab concentration 

ratio for a VOC or radon was defined by:

where Xbsmt(i) = mean concentration of a VOC in 

basement air and Xss(i) = mean concentration of a VOC 

in sub-slab air. When a VOC was detected in subslab air but not basement air, was reported to be 

less than the ratio of the detection limit in basement 

air to sub-slab air. For instance, if Xss(i) for TCE was 

48 ppbv but was not detected in basement air at a 

detection limit of 0.24 ppbv, then was reported 

as less than 5.0E-03. When a VOC was not detected 

in sub-slab air but was detected in basement air, 

was reported to be greater than the ratio of basement 

air concentration to the detection limit of sub-slab air 

measurement. When a VOC was undetected in all 

probes tested, Xss(i) was reported as less than the 

mean of each detection limit. For instance, if the 

detection limit in probes A, B, and C for m/p-xylenes 

were 4.3, 3.9, and 3.7 ppbv, respectively, and m/pxylenes were detected in basement air at 0.89 ppbv, 

then Xss(i) was reported as less than 4.0 ppbv and 

 less than 2.2E-01. In some instances, a VOC 

was detected in two probes but undetected in a third.

6.0 Use of Basement and Sub-Slab Air Measurements to Assess Vapor Intrusion

In that case, the mean of two measurements was 

used to estimate Xss(i).

Variance associated with each basement/sub-slab 

concentration ratio was calculated using the method 

of propagation of errors:

where =variance associated with measurement 

of a VOC in basement air and = variance 

associated with measurement of a VOC in sub-slab 

air. With the exception of replicate sampling at one 

location during the July 2002 sample event and two 

locations during the March 2003 sampling event, 

only one air sample was taken in each basement. 

To estimate for locations not having replicate 

samples, the coefficients of variation (COV) for each 

VOC in each replicate were calculated. Results of 

these calculations are illustrated in Figure 7. At House 

B during the July 2002 sample event, the average 

COV was 5.2%. At Houses F and H during the March 

2003 sample event, average COVs were 6.2% and 

5.2%, respectively. A global average using all three 

replicate measurements was 5.5%. A global average 

of 6% was used to estimate the standard deviation of 

basement air samples by:
38

in this investigation because they are degradation 

products of 1,1,1-trichloroethane and not commonly 

associated with commercial products. The VOC, cis1,2-dichloroethylene, was considered an indicator 

VOC because it is a degradation product of 

trichloroethylene and not commonly associated with 

commercial products. Vicinity is a subjective term 

but generally refers to a number of ground-water or 

soil-gas measurements within 30 meters of a building. 

The primary purpose of these two questions was to 

ascertain whether or not VOCs detected in basement 

air were due to vapor intrusion. Sources (e.g., indoor, 

outdoor) of VOCs not associated with vapor intrusion 

were not investigated. Evaluation of outdoor and 

indoor air source terms would require additional 

building-related information or characterization needs 

(e.g., air exchange rates). The Approximate t-Test 

for Independent Sample of Unequal Variance was 

employed for statistical testing where the test statistic 

t’ is defined as:

where is the variance of the basement/sub-slab 

concentration ratio for the indicator VOC, and n(i) 

and n*(i) are the number of sub-slab measurements 

used in determining and , respectively. The 

degrees of freedom (df) are defined as:

where

An average basement/sub-slab air concentration 

ratio ( ) was calculated using basement/sub-slab 

air concentration ratios for all VOCs associated with 

vapor intrusion by:

The variance associated with ( ) was calculated 

by:

Basement/sub-slab air concentration ratios, , and 

associated standard deviations, , were computed 

for every VOC detected in basement or sub-slab air 

and plotted. A VOC detected in basement air was 

considered due to vapor intrusion if: (1) the VOC 

was detected in ground water and/or soil gas in the 

“vicinity” of the house, and (2) the null hypothesis that 

basement/sub-slab air concentration ratio of the VOC 

was equal to the basement/sub-slab air concentration 

ratio of an indicator VOC could not be rejected using a 

one-tailed Approximate t-Test at a level of significance 

or Type I error less than or equal to 0.05. A Type I 

error is committed when the null hypothesis is rejected 

when it is true. The alternative hypothesis was that 

the basement/sub-slab air concentration ratio of the 

VOC was greater than the basement/sub-slab air 

concentration ratio of an indicator VOC. An indicator 

VOC is defined as a VOC detected in sub-slab air 

and known to be associated only with subsurface 

contamination. The VOCs, 1,1-dichloroethylene and 

1,1-dichloroethane, were considered indicator VOCs 
39

Table 2. Outdoor Air Concentrations of VOCs During July 2002 

and March 2003 Sample Events

VOC Outdoor1hr

Outdoor24hrOutdoor24hr

07/16/02 03/24/03 03/27/03

House B House K House G

(ppbv) (ppbv) (ppbv)

1,1,1-TCA 0.58 ND(0.09) ND(0.11)

1,1-DCE ND(0.25) ND(0.092) ND(0.11)

TCE ND(0.25) ND(0.092) ND(0.11)

c-1,2-DCE ND(0.25) ND(0.09) ND(0.11)

1,1-DCA ND(0.25) ND(0.092) ND(0.11)

1,2-DCA ND(0.25) ND(0.092) ND(0.11)

PCE ND(0.25) 0.12 ND(0.10)

CH2Cl2 0.44 0.19 0.70

CHCl3 0.10 ND(0.09) ND(0.11)

CCl4 0.09 0.080 ND(0.11)

CCl3F(F-11) 0.27 0.25 0.23

CCl2F2(F-12) 0.66 0.5 0.47

CHBrCl2 ND(2.2) ND(0.084) ND(0.10)

vinyl chloride ND(0.25) ND(0.09) ND(0.11)

CH3CH2Cl ND(0.25) ND(0.95) 0.95

CCl3CF3(F-113) 0.10 ND(0.09) ND(0.11)

acetone 4.50 2.0 2.0

2-hexanone ND(0.25) ND(0.086) ND(0.10)

THF ND(2.3) ND(0.088) ND(0.10)

MEK ND(0.46) 0.45 0.51

MIBK ND(0.21) 0.081 ND(0.096)

MTBE 0.23 0.46 0.61

heptane ND(0.24) 0.22 0.3

hexane 1.0 0.69 0.62

cyclohexane ND(0.50) ND(0.09) ND(0.11)

benzene 0.15 0.33 0.38

toluene 0.85 0.63 3.5

ethylbenzene 0.20 0.09 0.14

m/p-xylenes 0.65 0.23 0.45

o-xylene 0.25 0.1 0.17

styrene ND(0.23) ND(0.084) ND(0.10)

1,2,4-TMB ND(0.24) ND(0.088) 0.16

1,3,5-TMB ND(0.25) ND(0.09) ND(0.11)

1,3-butadiene ND(0.50) ND(0.18) ND(0.21)

1,3-DCB ND(0.24) ND(0.09) ND(0.11)

1,4-DCB ND(0.24) ND(0.088) ND(0.10)

4-ethyltoluene ND(0.25) 0.09 0.16

isopropyl alcohol ND(0.25) 0.31 0.93

ethyl/vinyl acetate ND(0.48) ND(0.16) ND(0.19)

CS2 ND(0.23) ND(0.086) ND(0.10)

ND ( ) = Not detected above (reporting limits)

6.2 Summary of Results for Buildings 

 Sampled in July and October 2002

Basement and sub-slab air samples were collected 

for VOC analysis in houses A, B, C, D, and E during 

the July 2002 sample event. Basement (1-hr) and 

sub-slab (grab) samples were collected in six-liter 

evacuated canisters using EPA Method TO-15. Subslab samples were also collected in one-liter Tedlar 

bags with on-site GC analyses. An outdoor air sample 

(1-hr) was collected outside of House B. The results 

of this sample, as well as two outdoor air samples 

collected during the March 2003 sample event, are 

presented in Table 2. One of the VOCs associated with 

sub-surface contamination, 1,1,1-TCA, was detected 

at 0.58 ppbv during the July 2002 sample event. 

Only sub-slab air samples using one-liter Tedlar bags 

with subsequent on-site GC analysis were collected 

during the October 2002 sample event. Mean subslab air concentrations for 1,1,1-TCA, 1,1-DCE, TCE, 

and c-1,2-DCE collected in one-liter Tedlar bags were 

compared for the July 2002 and October 2002 sample 

events using a two-tailed Approximate t-Test. The null 

hypothesis was that the mean concentration of a VOC 

during the July 2002 sample event was equal to the 

mean concentration of the VOC during the October 

2002 sample event. The alternate hypothesis was 

that the means were not equal. The rejection criteria 

was a Type I error or level of significance less than 

or equal to 0.1 (twice the level of significance for 

one-tailed tests used to assess vapor intrusion). A 

Type I error is committed when the null hypothesis is 

rejected when it is true.
40

The slabs at these houses were located approximately 

two meters below grade. All buildings tested were 

in locations of known ground-water and soil-gas 

contamination from the Raymark Superfund Site. 

During the October 2002 sample event, basement 

(48-hr activated charcoal) and sub-slab (scintillation 

cells) air samples were collected for radon analysis. 

However, since the results of radon testing in the 

October 2002 sample event were not used to assess 

vapor intrusion during the July 2002 sample event, the 

results of sub-slab air radon testing during the October 

sample event were not included in this report. 

House A

At the time of probe installation, no significant cracks or 

holes were observed in the concrete slab or in painted 

cinderblock walls. Concentrations of VOCs detected in 

basement and/or sub-slab air using EPA Method TO15 are summarized in Table 3a. The only constituent 

associated with sub-surface contamination detected 

in basement air was 1,1,1-TCA at a concentration 

of 0.20 ppbv. The detection limit for other VOCs 

associated with sub-surface contamination was 0.24 

ppbv. Other chlorinated VOCs detected in basement 

air were methylene chloride, chloroform, and carbon 

tetrachloride at concentrations of 0.78, 0.14, and 0.13 

ppbv, respectively. Freons, F-11, F-12, and F-113 were 

detected at 0.39, 0.71, and 0.12 ppbv, respectively. 

Hydrocarbons, hexane, cyclohexane, benzene, 

toluene, ethylbenzene, m/p-xylenes, o-xylene, styrene, 

1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, 

and 4-ethyltoluene were detected in basement air 

at concentrations up to 1.8 ppbv. Acetone, methyl 

isobutyl ketone, and methyl tertiary-butyl ether were 

detected in basement air at concentrations of 8.3, 

0.11, and 0.49 ppbv, respectively. 

Three probes were installed for sub-slab sampling. All 

three probes were sampled using EPA Method TO-15 

and with one-liter Tedlar bags. As indicated in Table 

3a, when sampling using EPA Method TO-15, 1,1,1-

TCA, 1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA were 

detected at maximum concentrations of 100, 62, 60, 

21, and 13 ppbv, respectively. The only other VOCs 

detected in sub-slab air using EPA Method TO-15 were 

acetone and chloroform at maximum concentrations 

of 3.8 and 1.3 ppbv, respectively. Detection limits of 

other VOCs varied from 1.8 to 18 ppbv. As indicated 

in Table 3c, when sampling with one-liter Tedlar 

bags, 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE were 

detected at maximum concentrations in Probe A at 

164, 75, 78, and 29 ppbv, respectively. 

Basement/sub-slab air concentration ratios for 

VOCs using EPA Method TO-15 are illustrated in 

Figure 34. The basement/sub-slab air concentration 

ratios for all five VOCs associated with sub-surface 

contamination were lower than basement/sub-slab 

air concentration ratios for other VOCs detected in 

basement air. However, since indicator VOCs, 1,1-

DCE , c-1,2-DCE, and 1,1-DCA, were not detected in 

basement air at the time of sampling, their basement/

sub-slab air concentration ratios and associated 

standard deviations could not be computed. All that 

can be inferred from available data is that the actual 

basement/sub-slab air concentration ratios of these 

indicator VOCs were less than the values indicated. 

The null hypothesis that the basement/sub-slab air 

concentration ratio of 1,1,1-TCA was equivalent to 

the basement/sub-slab air concentration ratios of 

indicator VOCs, 1,1-DCE , c-1,2-DCE, and 1,1-DCA 

could not be evaluated. Thus, there was insufficient 

data to determine whether or not the presence of 

1,1,1-TCA in basement air was due to vapor intrusion 
41

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov

bsmt/

sub-slab

ratio

bsmt/

sub-slab

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 stdev

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.20 0.01 99 100 43 81 29 36 2.5E-03 9.0E-04

1,1-DCE ND(0.24) IND 62 56 20 46 19 40 < 4.3E-03 IND

TCE ND(0.24) IND 60 55 28 48 14 29 < 4.2E-03 IND

c-1,2-DCE ND(0.24) IND 21 18 6.0 15 6.2 42 < 1.3E-02 IND

1,1-DCA ND(0.24) IND 13 13 4.0 10 4.6 46 < 2.0E-02 IND

1,2-DCA ND(0.24) IND ND(2.1) ND(2.1) ND(2.1) ND(<2.1) IND IND IND IND

PCE ND(0.25) IND ND(2.1) ND(2.1) ND(2.1) ND(<2.1) IND IND IND IND

CH2Cl2 0.78 0.05 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 4.1E-01 IND

CHCl3 0.14 0.01 1.0 1.3 0.73 1.0 0.29 28 1.4E-01 4.0E-02

CCl4 0.13 0.01 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 6.8E-02 IND

CCl3F(F-11) 0.39 0.02 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 2.1E-01 IND

CCl2F2(F-12) 0.71 0.04 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 3.7E-01 IND

CHBrCl2 ND(2.2) IND ND(2.1) ND(2.1) ND(2.1) ND(<2.1) IND IND IND IND

vinyl chloride ND(0.25) IND ND(2.1) ND(2.1) ND(2.1) ND(<2.1) IND IND IND IND

CH3CH2Cl ND(2.3) IND ND(2.1) ND(2.1) ND(2.1) ND(<2.1) IND IND IND IND

CCl3CF3(F-113) 0.12 0.01 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 6.3E-02 IND

acetone 8.30 0.50 3.5 3.8 ND(18) 3.7 0.21 IND 2.3E+00 1.9E-01

2-hexanone ND(2.3) IND ND(18) ND(18) ND(18) ND(<18) IND IND IND IND

THF ND(2.3) IND ND(18) ND(18) ND(18) ND(<18) IND IND IND IND

MEK ND(0.26) IND ND(1.8) ND(1.7) ND(1.6) ND(<1.7) IND IND IND IND

MIBK 0.11 0.01 ND(1.8) ND(1.7) ND(1.6) ND(<1.7) IND IND > 6.5E-02 IND

MTBE 0.49 0.03 ND(2.0) ND(1.8) ND(1.7) ND(<2.0) IND IND > 2.5E-01 IND

heptane ND(0.24) IND ND(18) ND(18) ND(18) ND(<18) IND IND IND IND

hexane 1.2 0.07 ND(2.2) ND(2.0) ND(1.9) ND(<2.0) IND IND > 6.0E-01 IND

cyclohexane 0.19 0.01 ND(4.3) ND(3.9) ND(3.7) ND(<4.0) IND IND > 4.8E-02 IND

benzene 0.25 0.02 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 1.3E-01 IND

toluene 1.8 0.11 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 9.5E-01 IND

ethylbenzene 0.26 0.02 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 1.4E-01 IND

m/p-xylenes 0.89 0.05 ND(4.3) ND(3.9) ND(3.7) ND(<4.0) IND IND > 2.2E-01 IND

o-xylene 0.27 0.02 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 1.4E-01 IND

styrene 0.12 0.01 ND(2.0) ND(1.8) ND(1.7) ND(<1.7) IND IND > 7.1E-02 IND

1,2,4-TMB 0.29 0.02 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 1.5E-01 IND

1,3,5-TMB 0.11 0.01 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND > 5.8E-02 IND

1,3-butadiene ND(0.50) IND ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND IND IND

1,3-DCB ND(0.24) IND ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND IND IND

1,4-DCB ND(0.24) IND ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND IND IND

4-ethyltoluene 0.19 0.01 ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND IND IND

isopropyl alcohol ND(0.25) IND ND(2.2) ND(2.0) ND(1.9) ND(<2.0) IND IND IND IND

ethyl/vinyl acetate ND(0.48) IND ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND IND IND

CS2 ND(0.48) IND ND(2.1) ND(1.9) ND(1.8) ND(<1.9) IND IND IND IND

ND( )=Not detected (reporting limit) IND = indeterminate

Table 3a. Basement and Sub-Slab Air Concentrations for VOCs at House A Using EPA Method TO-15 During the July 2002 

Sample Event
42

Figure 34. Basement/sub-slab concentration ratios using EPA Method TO-15 at House A during the July 2002 sample event. Error 

bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or subslab air.

at the time of sampling. However, it was evident that 

significant levels of VOCs associated with sub-surface 

contamination were present in sub-slab air at the time 

of sampling.

A statistical analysis of VOCs associated with subsurface contamination and sampled using EPA Method 

TO-15 is summarized in Table 3b. Since the basement/

sub-slab air concentration ratios of indicator VOCs, 1,1-

DCE, c-1,2-DCE, and 1,1-DCA were less than 4.3E-03, 

1.3E-02, and 2.0E-02, respectively, the basement/subslab air concentration ratio of VOCs associated with 

sub-surface contamination was less than 4.3E-03. If 

the presence of 1,1,1-TCA in basement air was not 

due to vapor intrusion at the time of sampling, then 

the basement/sub-slab air concentration ratio of VOCs 

associated with sub-surface contamination was less 

than the basement/sub-slab air concentration ratio 

of 1,1,1-TCA or 2.5E-03. Coefficients of variation in 

sub-slab air concentration ranged from 29 to 46%. 

A statistical analysis of VOCs associated with subsurface contamination and sampled using one-liter 

Tedlar bags is summarized in Table 3c. Since the 

basement/sub-slab air concentration ratio of the 

indicator VOC, 1,1-DCE, was less than 4.0E-03, the 

basement/sub-slab air concentration ratio of VOCs 

associated with sub-surface contamination was 

less than 4.0E-03. If the presence of 1,1,1-TCA in 

basement air was not due to vapor intrusion at the 

time of sampling, then the basement/sub-slab air 

concentration ratio of VOCs associated with subsurface contamination was less than the basement/

sub-slab air concentration ratio of 1,1,1-TCA or
43

1.6E-03 for the July 2002 sampling event. Coefficients 

of variation in sub-slab air concentration ranged from 

24 to 31%.

The results of sub-slab sampling using one-liter Tedlar 

bags during the October 2002 sample are summarized 

in Table 3d. A comparison of mean sub-slab air 

concentrations of 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-

DCE during the July 2002 and October 2002 sample 

events is illustrated in Figure 35. The null hypothesis 

Table 3b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House A Using EPA Method TO-15 During the July 2002 Sample Event

Table 3c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House A Using 1-Liter Tedlar Bags and On-Site GC Analysis During the July 2002 Sample Event

Table 3d. Sub-Slab Air Concentrations of VOCs Associated with Sub-Surface Contamination in House A Using 1-Liter Tedlar Bags 

and On-Site GC Analysis During the October 2002 Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov

bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev 07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.20 0.01 99 100 43 81 29 36 2.5E-03 9.0E-04

1,1-DCE ND(0.24) IND 62 56 20 46 19 40 < 4.3E-03 IND

TCE ND(0.24) IND 60 55 28 48 14 29 < 4.2E-03 IND

c-1,2-DCE ND(0.24) IND 21 18 6.0 15 6.2 42 < 1.3E-02 IND

1,1-DCA ND(0.24) IND 13 13 4.0 10 4.6 46 < 2.0E-02 IND

mean and standard deviation of basement/sub-slab ratio < 4.3E-03 IND

VOC bsmt-1hr

#1582

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov

bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev 07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.20 0.01 164 144 69 126 39 31 1.6E-03 5.0E-04

1,1-DCE ND(0.24) IND 75 65 38 59 14 24 < 4.0E-03 IND

TCE ND(0.24) IND 78 58 33 56 14 25 < 4.3E-03 IND

c-1,2-DCE ND(0.24) IND 29 20 ND(25) 25 6 26 IND IND

mean and standard deviation of basement/sub-slab ratio < 4.0E-03 IND

VOC P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov

n=3 n=3 n=3

10/30/02 10/30/02 10/30/02 10/30/02 10/30/02 10/30/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%)

1,1,1-TCA 402 256 197 285 106 37

1,1-DCE 170 102 72 115 50 44

TCE 137 75 47 86 46 53

c-1,2-DCE 48 28 15 30 17 55

that the mean sub-slab air concentrations of 1,1,1-

TCA were equivalent during the July and October 

2002 sample events was rejected using a two-tailed 

Approximate t-Test at a level of significance less than 

or equal to 0.1 (p = 0.08). The null hypotheses that the 

mean sub-slab concentrations of 1,1-DCE, TCE, and 

c-1,2-DCE were equivalent during the July and October 

2002 sample events were not rejected at significance 

levels of 0.48, 0.63, and 0.22, respectively. 
44

Figure 35. Comparison of mean sub-slab air concentrations of VOCs collected in one-liter Tedlar bags during the July and October 

2002 sample events at House A. Error bars represent one standard deviation.

House B

At the time of probe installation, no significant cracks 

or holes were observed in the visible portion of the 

concrete slab or in cinderblock walls. Most of the 

basement was finished with carpeting and paneled 

walls. Concentrations of all VOCs detected in 

basement and/or sub-slab air using EPA Method TO15 are summarized in Table 4a. A replicate sample 

was collected for basement air analysis. VOCs 

associated with sub-surface contamination, 1,1,1-

TCA, 1,1-DCE, and TCE, were detected in basement 

air at concentrations of 0.41, 0.11, and 0.41 ppbv, 

respectively. The detection limit for c-1,2-DCE and 

1,1-DCA was 0.25 and 0.26 pppv, respectively. Other 

chlorinated VOCs detected in basement air were

perchloroethylene, methylene chloride, chloroform, 

and carbon tetrachloride at concentrations of 0.53, 

6.2, 0.91, and 0.14 ppbv, respectively. Freons, F11, F-12, and F-113, were detected in basement 

air at concentrations of 0.71, 1.3, and 0.19 ppbv, 

respectively. Hydrocarbons, heptane, hexane, 

cyclohexane, benzene, toluene, ethylbenzene, m/

p-xylenes, o-xylene, 1,2,4-trimethylbenzene, 1,3,5-

trimethylbenzene, 4-ethyltoluene were detected 

in basement air at concentrations up to 58 ppbv. 

Acetone, methyl ethyl ketone, methyl isobutyl ketone, 

and methyl tertiary-butyl ether were detected in 

basement air at concentrations of 40, 2.4, 0.22, and 

9.8 ppbv, respectively. During basement sampling, the 

homeowner stated that a latex paint had been used on 

the second floor room two days prior to sampling.
45

Table 4a. Basement and Sub-Slab Air Concentrations for VOCs at House B Using EPA Method TO-15 During the July 2002 

Sample Event

VOC bsmt

1-hr

bsmt

1-hr

bsmt

mean

bsmt

stdev

bsmt

cov P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

subslab

stdev

n=2 n=2 n=2 n=3 n=3 n=3

07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.40 0.41 0.41 0.01 1.7 7.9 120 8.1 45 65 143 8.9E-03 1.3E-02

1,1-DCE 0.10 0.11 0.11 0.01 6.7 3.7 44 0.94 16 24 149 6.5E-03 9.6E-03

TCE 0.41 0.40 0.41 0.01 1.7 20 80 30 43 32 74 9.3E-03 6.9E-03

c-1,2-DCE ND(0.25) ND(0.25) ND(<0.25) IND IND 4.3 16 1.3 7.2 7.8 108 < 3.5E-02 IND

1,1-DCA ND(0.26) ND(0.26) ND(<0.26) IND IND 1.6 11 1.2 4.6 5.5 121 < 5.7E-02 IND

1,2-DCA ND(0.25) ND(0.25) ND(<0.25) IND IND ND(0.23) ND(1.9) ND(0.42) ND(<0.85) IND IND IND IND

PCE 0.53 0.52 0.53 0.01 1.3 0.37 0.79 0.30 0.49 0.27 54 1.1E+00 5.9E-01

CH2Cl2 6.2 6.2 6.2 0.00 0.0 3.6 ND(1.9) 0.15 1.9 2.4 130 3.3E+00 4.3E+00

CHCl3 0.91 0.83 0.87 0.06 6.5 4.3 7.2 32 14.5 15 105 6.0E-02 6.3E-02

CCl4 0.14 0.14 0.14 0.00 0.0 0.12 ND(1.9) ND(0.42) < 0.81 IND IND > 1.7E-01 IND

CCl3F

(F-11) 0.71 0.71 0.71 0.00 0.0 0.75 ND(1.9) 0.50 0.63 0.18 28 1.1E+00 3.2E-01

CCl2F2

(F-12) 1.3 1.3 1.3 0.00 0.0 34 11 570 205 316 154 6.3E-03 9.8E-03

CHBrCl2 ND(2.2) ND(2.2) ND(<2.2) IND IND 0.13 ND(17) 0.20 0.17 0.05 30 < 1.3E+01 IND

vinyl chloride ND(0.25) ND(0.25) ND(<0.25) IND IND ND(0.23) ND(1.9) ND(0.42) ND(<0.85) IND IND IND IND

CH3CH2Cl 0.86 0.86 0.86 0.00 0.0 ND(0.24) ND(2.0) ND(0.44) ND(<0.9) IND IND > 9.6E-01 IND

CCl3CF3

(F-113) 0.10 0.19 0.14 0.06 44.5 0.10 ND(1.9) ND(0.42) < 0.81 IND IND > 2.3E-01 IND

acetone 38 40 39 1.4 3.6 1.1 ND(18) 1.2 1.2 0.07 6.1 3.4E+01 2.4E+00

2-hexanone ND(0.25) ND(0.25) ND(<0.25) IND IND ND(0.23) ND(1.9) ND(0.42) ND(<0.85) IND IND IND IND

THF ND(2.3) ND(2.3) ND(<2.3) IND IND ND(18) ND(18) ND(18) ND(<18) IND IND IND IND

MEK 2.4 2.2 2.3 0.14 6.1 ND(0.43) ND(3.5) ND(0.79) ND(<1.6) IND IND > 1.4E+00 IND

MIBK 0.22 0.15 0.19 0.05 26.8 ND(0.20) ND(1.6) ND(0.36) ND(<0.72) IND IND > 3.1E-01 IND

MTBE 9.8 9.5 9.7 0.21 2.2 1.8 ND(1.8) 0.16 1.0 1.2 118 9.8E+00 1.2E+01

heptane 3.4 3.4 3.4 0.00 0.0 ND(0.22) ND(1.9) ND(0.42) ND(<0.85) IND IND > 4.0E+00 IND

hexane 3.8 4.1 4.0 0.21 5.4 0.44 ND(1.9) ND(0.43) < 0.92 IND IND > 4.5E+00 IND

cyclohexane 1.5 1.5 1.5 0.00 0.0 0.53 ND(3.8) ND(0.86) < 1.7 IND IND > 8.8E-01 IND

benzene 1.1 1.0 1.1 0.07 6.7 0.26 ND(1.9) ND(0.42) < 0.86 IND IND > 1.3E+00 IND

toluene 17 17 17 0.00 0.0 1.6 ND(1.9) ND(0.42) < 1.3 IND IND > 1.3E+01 IND

ethylbenzene 17 16 17 0.71 4.3 0.51 ND(1.9) ND(0.42) < 0.94 IND IND > 1.8E+01 IND

m/p-xylenes 58 56 57 1.4 2.5 1.2 ND(3.8) 0.20 L < 1.7 IND IND > 3.4E+01 IND

o-xylene 20 19 20 0.71 3.6 0.55 ND(1.9) ND(0.42) < 0.96 IND IND > 2.1E+01 IND

styrene ND(0.25) ND(0.25) ND(<0.25) IND IND ND(0.22) ND(1.9) ND(0.42) ND(<0.85) IND IND IND IND

1,2,4-TMB 1.5 1.5 1.5 0.00 0.0 ND(0.22) ND(1.9) ND(0.42) ND(<0.85) IND IND > 1.8E-01 IND

1,3,5-TMB 0.56 0.54 0.55 0.01 2.6 ND(0.23) ND(1.9) ND(0.42) ND(<0.85) IND IND > 6.6E-01 IND

1,3-

butadiene ND(0.25) ND(0.25) ND(<0.25) IND IND ND(0.23) ND(1.9) ND(0.42) ND(<0.85) IND IND IND IND

1,3-DCB ND(0.25) ND(0.25) ND(<0.25) IND IND ND(0.23) ND(1.9) ND(0.42) ND(<0.85) IND IND IND IND

1,4-DCB ND(0.25) ND(0.25) ND(<0.25) IND IND ND(0.23) ND(1.9) ND(0.42) ND(<0.85) IND IND IND IND

4-ethyltoluene 2.2 2.0 2.1 0.14 6.7 ND(0.23) ND(1.9) ND(0.43) ND(<0.84) IND IND > 2.6E+00 IND

isopropyl 

alcohol ND(0.25) ND(0.25) ND(<0.25) IND IND ND(0.23) ND(1.9) ND(0.42) ND(<0.85) IND IND IND IND

ethyl/vinyl 

acetate 12 11 12 0.71 6.1 ND(45) ND(3.7) ND(0.83) ND(<17) IND IND > 7.1E-01 IND

CS2 0.14 0.13 0.14 0.01 5.2 ND(0.21) ND(1.8) ND(0.39) ND(<0.84) IND IND > 1.7E-01 IND

ND( )=Not detected (reporting limit) IND = indeterminate mean and stdev calculated from 2 or more measurements
46

o-xylene were detected in sub-slab air at maximum 

concentrations up to 1.6 ppbv. Acetone and methyl 

tertiary-butyl ether were detected in sub-slab air 

at maximum concentrations of 1.2 and 1.8 ppbv, 

respectively. As indicated in Table 4c, when sampling 

with one-liter Tedlar bags, 1,1,1-TCA, 1,1-DCE, 

TCE, and c-1,2-DCE were detected at maximum 

concentrations in Probe B at 137, 48, 75, and 25 

ppbv, respectively. 

Basement/sub-slab air concentration ratios for VOCs 

using EPA Method TO-15 are illustrated in Figure 

36. With the exception of F-12 and chloroform, 

basement/sub-slab air concentration ratios for all five 

VOCs associated with sub-surface contamination 

were lower than other VOCs detected in basement 

air. The standard deviations of basement/sub-slab air 

concentration ratios of F-12 and chloroform exceeded 

Three probes were installed for sub-slab sampling. All 

three probes were sampled using EPA Method TO-15 

and one-liter Tedlar bags. As indicated in Table 4b, 

when sampling using EPA Method TO-15, 1,1,1-TCA, 

1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA were detected 

at maximum concentrations in Probe B at 120, 44, 80, 

16, and 11 ppbv, respectively. Other chlorinated VOCs 

detected in sub-slab air using EPA Method TO-15 were 

perchloroethylene, methylene chloride, chloroform, 

and carbon tetrachloride at maximum concentrations 

of 0.79, 3.6, 32, and 0.12 ppbv, respectively. Freons, 

F-11, F-12, and F-113, were detected in sub-slab air 

at maximum concentrations of 0.75, 570, and 0.10 

ppbv, respectively. The high concentration of F-12 

at Probe [C] may have been associated with a leak 

from the central air conditioning system located in 

the basement. Hydrocarbons, hexane, cyclohexane, 

benzene, toluene, ethylbenzene, m/p-xylenes, and 

Table 4b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House B Using EPA Method TO-15 During the July 2002 Sample Event

Table 4c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House B Using 1-Liter Tedlar Bags and On-Site GC Analysis During the July 2002 Sample Event

VOC bsmt

1-hr

bsmt

1-hr

bsmt

mean

bsmt

stdev

bsmt

cov P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev

n=2 n=2 n=2 n=3 n=3 n=3

07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.40 0.41 0.41 0.01 1.7 7.9 120 8.1 45 65 143 8.9E-03 1.3E-02

1,1-DCE 0.10 0.11 0.11 0.01 6.7 3.7 44 0.94 16 24 149 6.5E-03 9.6E-03

TCE 0.41 0.40 0.41 0.01 1.7 20 80 30 43 32 74 9.3E-03 6.9E-03

c-1,2-DCE ND(0.25) ND(0.25) ND(<0.25) IND IND 4.3 16 1.3 7.2 7.8 108 < 3.5E-02 IND

1,1-DCA ND(0.26) ND(0.26) ND(<0.26) IND IND 1.6 11 1.2 4.6 5.5 121 < 5.7E-02 IND

mean and standard deviation of basement/sub-slab ratio 8.3E-03 5.8E-03

VOC bsmt

1-hr

bsmt

1-hr

bsmt

mean

bsmt

stdev

bsmt

cov P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev

n=2 n=2 n=2 n=3 n=3 n=3

07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.40 0.41 0.41 0.01 1.7 10 137 14 54 72 135 7.5E-03 1.0E-02

1,1-DCE 0.10 0.11 0.11 0.01 6.7 ND(10) 48 ND(10) < 23 IND IND > 4.8E-03 IND

TCE 0.41 0.40 0.41 0.01 1.7 20 75 27 41 30 74 1.0E-02 7.3E-03

c-1,2-DCE ND(0.25) ND(0.25) ND(<0.25) IND IND ND(25) 25 ND(25) < 25 IND IND IND IND

mean and standard deviation of basement/sub-slab ratio 8.8E-03 6.3E-03
47

mean values. F-12 and chloroform were eliminated 

from consideration of vapor intrusion because these 

VOCs were not detected in soil gas or ground water in 

the vicinity of the building. Since the null hypotheses 

that the basement/sub-slab air concentration ratios of 

1,1,1-TCA and TCE were equivalent to the indicator 

VOC, 1,1-DCE, could not be rejected using a one-tailed 

Approximate t-Test at a level of significance less than 

or equal to 0.05 (p > 0.1), it was inferred that detection 

of 1,1,1-TCA, 1,1-DCE, and TCE in basement air was 

due to vapor intrusion at the time of sampling. 1,1,1-

TCA was detected in outside air at 0.58 ppbv during 

the July 2002 sampling event. Unlike other VOCs 

such as benzene, toluene, ethylbenzene, and xylenes, 

1,1,1-TCA was not detected in outside air during the 

March 2003 sampling event nor in previous outdoor 

sampling activities conducted by EPA’s New England 

Laboratory. 

Figure 36. Basement/sub-slab concentration rations using EPA Method TO-15 at House B during the July 2002 sample event. 

Error bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement

or sub-slab air.

Results and statistical analysis of VOCs associated 

with sub-surface contamination and sampled using 

EPA Method TO-15 are summarized in Table 4b. Use 

of basement/sub-slab air concentration ratios of 1,1,1-

TCA, 1,1-DCE, and TCE resulted in computation of 

an average basement/sub-slab air ratio of 8.3E-03 for 

VOCs associated with vapor intrusion. Coefficients 

of variation in sub-slab air samples ranged from 74 

to 149%. Results and statistical analysis of VOCs 

associated with sub-surface contamination sampled 

using one-liter Tedlar bags are summarized in Table 

4c. Use of basement/sub-slab air concentration ratios 

of 1,1,1-TCA and TCE resulted in computation of an 

average basement/sub-slab ratio of 8.8E-03 for VOCs 

associated with vapor intrusion. The coefficients of 

variation for sub-slab air sampling ranged from 74 to 

135%.
48

Figure 37. Comparison of mean sub-slab air concentrations of VOCs collected in one-liter Tedlar bags during the July and October 

2002 sample events at House B. Error bars represent one standard deviation.

The results of sub-slab sampling using one-liter 

Tedlar bags during the October 2002 sampling 

event are presented in Table 4d. A comparison of 

mean sub-slab air concentrations for 1,1,1-TCA and 

TCE for the July 2002 and October 2002 sampling 

events using one-liter Tedlar bags is illustrated in 

Table 4d. Sub-Slab Air Concentrations of VOCs Associated with Sub-Surface Contamination in House B Using 1-Liter Tedlar Bags 

and On-Site GC Analysis During the October 2002 Sample Event

VOC P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov

n=3 n=3 n=3

10/30/02 10/30/02 10/30/02 10/30/02 10/30/02 10/30/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%)

1,1,1-TCA 101 169 42 104 64 61

1,1-DCE 39 82 18 46 33 70

TCE 50 80 29 53 26 48

c-1,2-DCE 4.6 12 ND(4.1) 8 5.2 63

Figure 37. The null hypotheses that the mean subslab air concentrations of 1,1,1-TCA and TCE were 

equivalent during the July and October 2002 sample 

events were not rejected using a two-tailed Approximate 

t-Test at a level of significance of 0.1 or less. 
49

House C

During the home survey, a strong petroleum odor was 

noticed inside the basement. It was determined that 

a lawnmower was leaking gasoline from inside a shed 

attached to the house. The lawnmower was removed 

from the shed. The shed door was kept open for 

three days prior to installation of sub-slab probes and 

basement air sampling. At the time of probe installation, 

no significant cracks or holes were observed in the 

concrete slab or in unpainted cinderblock walls. 

Concentrations of VOCs detected in basement and/or 

sub-slab air using EPA Method TO-15 are summarized 

in Table 5a. All five VOCs associated with sub-surface 

contamination were detected in basement air. 1,1,1-

TCA, 1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA were 

detected at concentrations of 3.8, 2.3, 1.5, 0.57, and 

0.52 ppbv, respectively. Other chlorinated VOCs 

detected in basement air were perchloroethylene, 

methylene chloride, chloroform, carbon tetrachloride, 

1,3-dichlorobenzene, and 1,4-dichlorobenzene at 

concentrations of 0.17, 3.9, 0.34, 0.23, 0.10, and 0.15 

ppbv, respectively. Freons, F-11, F-12, and F-113, 

were detected at concentrations of 0.82, 1.1, 0.22 

ppbv, respectively. Hydrocarbons, heptane, hexane, 

cyclohexane, benzene, toluene, ethylbenzene, m/pxylenes, o-xylene, styrene, 1,2,4-trimethylbenzene, 

1,3,5-trimethylbenzene, 4-ethyltoluene were detected 

in basement air at concentrations up to 5.3 ppbv. 

Acetone, methyl ethyl ketone, and methyl tertiary-butyl 

ether were detected in basement air at concentrations 

of 5.3, 1.0, and 8.5 ppbv, respectively. The compound, 

1,3-butadiene, was detected at a concentration of 0.35 

ppbv. 

Four probes were installed for sub-slab sampling. 

All four probes were sampled using EPA Method 

TO-15 and in one-liter Tedlar bags. As indicated in 

Table 5b, when sampling using EPA Method TO-15, 

1,1,1-TCA, 1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA 

were detected at maximum concentrations in Probe 

A at 590, 410, 280, 120, and 94 ppbv, respectively. 

Total VOCs in probes exceeded 1000 ppbv. The only 

other VOCs detected in sub-slab air were acetone, 

toluene, and m/p-xylenes at 28, 4.2, and 7.0 ppbv, 

respectively. Detection limits for other VOCs ranged 

from 13 to 200 ppbv. As indicated in Table 5c, when 

sampling with one-liter Tedlar bags, 1,1,1-TCA, 1,1-

DCE, TCE, and c-1,2-DCE were detected at maximum 

concentrations in Probe [A] at 833, 486, 260, and 120 

ppbv, respectively. 

Basement/sub-slab air concentration ratios of VOCs 

detected in basement air and sampled using EPA 

Method TO-15 are illustrated in Figure 38. With the 

exception of the bromodichloromethane, which had 

a basement/sub-slab air concentration ratio at some 

value greater than 9.2E-04, basement/sub-slab air 

concentration ratios for all five VOCs associated 

with sub-surface contamination were significantly 

lower than other VOCs detected in basement air. 

Bromodichloromethane, a trihalomethane, was not 

present in ground water or soil gas in the vicinity of 

the house and thus was removed from consideration 

of vapor intrusion. Since the null hypotheses that 

basement/sub-slab air concentration ratios of 1,1,1-

TCA and TCE were equivalent to indicator VOCs, 1,1-

DCE, c-1,2-DCE, and 1,1-DCA, could not be rejected 

using a one-tailed Approximate t-Test at a level of 

significance less than or equal to 0.05 (p > 0.1), it was 

inferred that detection of 1,1,1-TCA, 1,1-DCE, TCE, 

c-1,2-DCE, and 1,1-DCA in basement air was due to 

vapor intrusion at the time of sampling.
50

Table 5a. Basement and Sub-Slab Air Concentrations for VOCs at House C Using EPA Method TO-15 During the July 2002 

Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

P[D]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

n=4 n=4 n=4 stdev

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 3.8 0.23 590 420 510 460 495 73.3 14.8 7.7E-03 1.2E-03

1,1-DCE 2.3 0.14 410 290 290 300 323 58.5 18.1 7.1E-03 1.4E-03

TCE 1.5 0.09 280 200 200 180 215 44.3 20.6 7.0E-03 1.5E-03

c-1,2-DCE 0.57 0.03 120 84 55 64 81 28.8 36 7.1E-03 2.6E-03

1,1-DCA 0.52 0.03 94 66 57 61 70 17 24 7.5E-03 1.9E-03

1,2-DCA ND(0.25) IND ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND IND IND

PCE 0.17 0.01 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 1.0E-02 IND

CH2Cl2 3.9 0.23 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 2.3E-01 IND

CHCl3 0.34 0.02 ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND > 2.0E-02 IND

CCl4 0.23 0.01 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 1.4E-02 IND

CCl3F(F-11) 0.82 0.05 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 4.8E-02 IND

CCl2F2

(F-12) 1.1 0.07 ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND > 6.5E-02 IND

CHBrCl2 0.14 0.01 ND(190) ND(180) ND(110) ND(130) ND(<152) IND IND > 9.2E-04 IND

vinyl chloride ND(0.25) IND ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND IND IND

CH3CH2Cl ND(0.25) IND ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND IND IND

CCl3CF3

(F-113) 0.22 0.01 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 1.3E-02 IND

acetone 5.3 0.32 ND(200) 28 14 20 21 7.0 34 2.5E-01 8.9E-02

2-hexanone ND(0.25) IND ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND IND IND

THF ND(2.3) IND ND(18) ND(18) ND(18) ND(18) ND(18) IND IND IND IND

MEK 1.0 0.06 ND(39) ND(36) ND(24) ND(28) ND(<32) IND IND > 3.1E-02 IND

MIBK ND(0.22) IND ND(18) ND(17) ND(11) ND(13) ND(<15) IND IND IND IND

MTBE 8.5 0.51 ND(20) ND(18) ND(12) ND(14) ND(<16) IND IND > 5.3E-01 IND

heptane 0.97 0.06 ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND > 4.6E-02 IND

hexane 2.4 0.14 ND(22) ND(20) ND(13) ND(15) ND(<18) IND IND > 1.3E-01 IND

cyclohexane 0.57 0.03 ND(43) ND(40) ND(26) ND(90) ND(<50) IND IND > 1.1E-02 IND

benzene 0.80 0.05 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 4.7E-02 IND

toluene 5.3 0.32 4.2 ND(20) ND(13) ND(15) <13 IND IND > 4.1E-01 IND

ethylbenzene 1.0 0.06 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 5.9E-02 IND

m/p-xylenes 3.7 0.22 ND(42) 7.0 ND(26) ND(30) < 21 IND IND > 1.8E-02 IND

o-xylene 1.5 0.09 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 8.8E-02 IND

styrene 0.29 0.02 ND(20) ND(19) ND(12) ND(14) ND(<16) IND IND > 1.8E-02 IND

1,2,4-TMB 2.4 0.14 ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND > 1.4E-01 IND

1,3,5-TMB 0.77 0.05 ND(21) ND(20) ND(13) ND(15) ND(<17) IND IND > 4.5E-02 IND

1,3-

butadiene 0.35 0.02 ND(43) ND(40) ND(26) ND(30) ND(<35) IND IND > 1.0E-02 IND

1,3-DCB 0.10 0.01 ND(21) ND(19) ND(13) ND(15) ND(<17) IND IND > 5.9E-03 IND

1,4-DCB 0.15 0.01 ND(20) ND(19) ND(12) ND(14) ND(<16) IND IND > 9.4E-03 IND

4-ethyltoluene 1.70 0.10 ND(22) ND(20) ND(13) ND(15) ND(<18) IND IND > 9.4E-02 IND

isopropyl

alcohol ND(0.25) IND ND(22) ND(20) ND(13) ND(15) ND(<18) IND IND IND IND

ethyl/vinyl 

acetate 1.5 0.09 ND(42) ND(39) ND(25) ND(29) ND(< 34) IND IND > 4.4E-02 IND

CS2 0.18 0.01 ND(20) ND(18) ND(12) ND(14) ND(<16) IND IND > 1.1E-02 IND

ND( ) = Not detected above reporting limits IND = indeterminate mean and stdev calculated from 2 or more measurements
51

Table 5b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House C Using EPA Method TO-15 During the July 2002 Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

P[D]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=4 n=4 n=4

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 3.8 0.23 590 420 510 460 495 73.3 14.8 7.7E-03 1.2E-03

1,1-DCE 2.3 0.14 410 290 290 300 323 58.5 18.1 7.1E-03 1.4E-03

TCE 1.5 0.09 280 200 200 180 215 44.3 20.6 7.0E-03 1.5E-03

c-1,2-DCE 0.57 0.03 120 84 55 64 81 28.8 36 7.1E-03 2.6E-03

1,1-DCA 0.52 0.03 94 66 57 61 70 17 24 7.5E-03 1.9E-03

mean and standard deviation of basement/sub-slab ratio 7.3E-03 7.9E-04

Table 5c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House C Using 1-Liter Tedlar Bags and On-Site GC Analysis During the July 2002 Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

P[D]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=4 n=4 n=4

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 3.8 0.23 833 650 757 722 741 76.1 10.3 5.1E-03 6.1E-04

1,1-DCE 2.3 0.14 486 374 423 416 425 46.2 10.9 5.4E-03 6.7E-04

TCE 1.5 0.09 260 201 249 195 226 33.0 14.6 6.6E-03 1.0E-03

c-1,2-DCE 0.57 0.03 120 98 61 74 88 26 30 6.5E-03 2.0E-03

mean and standard deviation of basement/sub-slab ratio 5.9E-03 6.0E-04

Figure 38. Basement/sub-slab concentration ratios using EPA Method TO-15 at House C during the July 2002 sample event. 

Error bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or 

sub-slab air.
52

Table 5d. Sub-Slab Air Concentrations of VOCs Associated with Sub-Surface Contamination in House C Using 1-Liter Tedlar Bags 

and On-Site GC Analysis During the October 2002 Sample Event

VOC P[A]

grab

P[B]

grab

P[C]

grab

P[D]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov

n=4 n=4 n=4

10/01/02 10/01/02 10/01/02 10/01/02 10/01/02 10/01/02 10/01/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%)

1,1,1-TCA 941 630 623 505 675 187 27.6

1,1-DCE 618 387 323 288 404 148 36.7

TCE 469 276 200 188 283 130 45.8

c-1,2-DCE 167 91 34 57 87 58 67

Results and statistical analysis of VOCs associated 

with sub-surface contamination and sampled using 

EPA Method TO-15 are summarized in Table 5b. 

Use of basement/sub-slab air concentration ratios of 

1,1,1-TCA, 1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA 

resulted in computation of an average basement/

sub-slab ratio of 7.3E-03. Coefficients of variation of 

sub-slab air concentrations varied from 15 to 36%. 

Results and statistical analysis of VOCs associated 

with sub-surface contamination and sampled using 

one-liter Tedlar bags are summarized in Table 5c. 

Use of basement/sub-slab air concentration ratios of 

1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE resulted 

in computation of an average basement/sub-slab 

air concentration ratio of 5.9E-03. Coefficients of 

variation of sub-slab air concentrations varied from 

10 to 30%. 

The results of sub-slab sampling with one-liter Tedlar 

bags during the October 2002 sample event are 

summarized in Table 5d. A comparison of mean 

sub-slab air concentrations for 1,1,1-TCA , 1,1-DCE, 

TCE, and c-1,2-DCE for the July 2002 and October 

2002 sampling events using one-liter Tedlar bags is 

illustrated in Figure 39. The null hypotheses that the 

mean sub-slab air concentrations of 1,1,1-TCA , 1,1-

DCE, TCE, and c-1,2-DCE were equivalent during the 

July and October 2002 sample events was not rejected 

using a two-tailed Approximate t-Test at significance 

less than or equal to 0.1.
53

Figure 39. Comparison of mean sub-slab air concentrations of VOCs collected in one-liter Tedlar bags during the July and October 

2002 sample events at House C. Error bars represent one standard deviation.

House D

At the time of probe installation, significant cracks 

and holes were observed in the concrete slab. At 

some locations, the slab resembled a veneer of 

plaster-like material. Concentrations of VOCs 

detected in basement and/or sub-slab air using EPA 

Method TO-15 are summarized in Table 6a. 1,1,1-

TCA and 1,1-DCE were detected in basement air at 

concentrations of 0.48 and 0.13 ppbv, respectively. 

The detection limit for TCE, c-1,2-DCE, and 1,1-DCA 

was 0.28 ppbv. Other chlorinated VOCs detected in 

basement air were methylene chloride, chloroform, 

and carbon tetrachloride at concentrations of 7.1, 

0.11, and 0.11 ppbv, respectively. Freons, F-11, F-12, 

and F-113 were detected at concentrations of 0.30, 

0.61, 0.10 ppbv, respectively. Hydrocarbons, hexane, 

cyclohexane, benzene, toluene, ethylbenzene,m /pxylenes, o-xylene, styrene, 1,2,4-trimethylbenzene, 

4-ethyltoluene were detected in basement air at 

concentrations up to 1.4 ppbv. Acetone, tetahydrofuran, 

methyl ethyl ketone, and methyl tertiary-butyl ether 

were detected at concentrations of 6.9, 3.7, 6.2, and 

0.57 ppbv, respectively. 

Three probes were installed for sub-slab sampling. All 

three probes were sampled with Tedlar bags. Only 

two probes were sampled using EPA Method TO-15 

because one probe, Probe P[B], became loose during 

sampling with a Tedlar bag. As indicated in Table 

6b, when sampling using EPA Method TO-15, 1,1,1-

TCA, 1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA were 

detected at maximum concentrations at 110, 110, 

28, 6.1, 16 ppbv, respectively. The only other VOCs 

detected in sub-slab air were acetone and chloroform at 

4.5 and 1.4 ppbv, respectively. Detection limits for other 
54

Table 6a. Basement and Sub-Slab Air Concentrations for VOCs at House D Using EPA Method TO-15 During the July 2002 

Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.48 0.03 52 110 81 41 51 5.9E-03 3.0E-03

1,1-DCE 0.13 0.01 22 110 66 62 94 2.0E-03 1.9E-03

TCE ND(0.28) IND 16 28 22 8.5 39 < 1.3E-02 IND

c-1,2-DCE ND(0.27) IND 4.6 6.1 5.4 1.1 20 < 5.0E-02 IND

1,1-DCA ND(0.28) IND 12 16 14 2.8 20 < 2.0E-02 IND

1,2-DCA ND(0.28) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

PCE ND(0.25) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

CH2Cl2 7.1 0.43 ND(1.9) ND(1.9) ND(<1.9) IND IND > 3.7E+00 IND

CHCl3 0.11 0.01 1.4 0.98 1.2 0.30 25 9.2E-02 2.4E-02

CCl4 0.11 0.01 ND(1.9) ND(1.9) ND(<1.9) IND IND > 5.8E-02 IND

CCl3F

(F-11) 0.30 0.02 ND(1.9) ND(1.9) ND(<1.9) IND IND > 1.6E-01 IND

CCl2F2

(F-12) 0.61 0.04 ND(1.9) ND(1.9) ND(<1.9) IND IND > 3.2E-01 IND

CHBrCl2 ND(2.2) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

vinyl chloride ND(0.25) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

CH3CH2Cl ND(0.25) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

CCl3CF3

(F-113) 0.10 0.01 ND(1.9) ND(1.9) ND(<1.9) IND IND > 5.3E-02 IND

acetone 6.9 0.41 2.7 4.5 3.6 1.3 35 1.9E+00 6.9E-01

2-hexanone ND(0.25) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

THF 3.7 0.22 ND(18) ND(18) ND(<18) IND IND > 2.1E-01 IND

MEK 6.2 0.37 ND(3.5) ND(3.6) ND(<3.6) IND IND > 1.7E+00 IND

MIBK ND(0.21) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

MTBE 0.57 0.03 ND(1.8) ND(1.8) ND(<1.8) IND IND > 3.2E-01 IND

heptane ND(0.24) IND ND(1.8) ND(1.8) ND(<1.8) IND IND IND IND

hexane 1.3 0.08 ND(1.9) ND(2.0) ND(<2.0) IND IND > 6.5E-01 IND

cyclohexane 0.21 0.01 ND(3.8) ND(3.9) ND(<3.9) IND IND > 5.4E-02 IND

benzene 0.28 0.02 ND(1.9) ND(1.9) ND(<1.9) IND IND > 1.5E-01 IND

toluene 1.4 0.08 ND(1.9) ND(1.9) ND(<1.9) IND IND > 7.4E-01 IND

ethylbenzene 0.39 0.02 ND(1.9) ND(1.9) ND(<1.9) IND IND > 2.1E-01 IND

m/p-xylenes 1.3 0.08 ND(3.8) ND(3.9) ND(<3.9) IND IND > 3.3E-01 IND

o-xylene 0.35 0.02 ND(1.9) ND(1.9) ND(<1.9) IND IND > 1.8E-01 IND

styrene 0.11 0.01 ND(1.8) ND(1.8) ND(<1.8) IND IND > 6.1E-02 IND

1,2,4-TMB 0.71 0.04 ND(1.9) ND(1.9) ND(<1.9) IND IND > 3.7E-01 IND

1,3,5-TMB ND(0.25) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

1,3-

butadiene ND(0.50) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

1,3-DCB ND(0.24) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

1,4-DCB ND(0.24) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

4-ethyltoluene 0.41 0.02 ND(1.9) ND(2.0) ND(<2.0) IND IND IND IND

isopropyl 

alcohol ND(0.25) IND ND(1.9) ND(1.9) ND(<1.9) IND IND > 2.1E-01 IND

ethyl/vinyl 

acetate ND(0.48) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

CS2 ND(0.23) IND ND(1.9) ND(1.9) ND(<1.9) IND IND IND IND

ND( )=Not detected (reporting limit) IND = indeterminate
55

compounds ranged from 1.8 to 18 ppbv. As indicated 

in Table 6c, when sampling with one-liter Tedlar bags, 

maximum concentrations of 1,1,1-TCA, 1,1-DCE, and 

TCE were 168, 111, and 30 ppbv, respectively. The 

detection limit for c-1,2-DCE was 25 ppbv.

Basement/sub-slab air concentration ratios of VOCs 

detected in basement air and sampled using EPA 

Method TO-15 are illustrated in Figure 40. Since 

the null hypothesis that the basement/sub-slab air 

concentration ratio of 1,1,1-TCA was equivalent to the 

indicator VOC, 1,1-DCE, could not be rejected using 

a one-tailed Approximate t-Test at a significance level 

less than or equal to 0.05 (p > 0.1), it was inferred that 

detection of 1,1,1-TCA and 1,1-DCE in basement air 

was due to vapor intrusion at the time of sampling.

Table 6b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House D Using EPA Method TO-15 During the July 2002 Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.48 0.03 52 110 81 41 51 5.9E-03 3.0E-03

1,1-DCE 0.13 0.01 22 110 66 62 94 2.0E-03 1.9E-03

TCE ND(0.28) IND 16 28 22 8.5 39 < 1.3E-02 IND

c-1,2-DCE ND(0.27) IND 4.6 6.1 5.4 1.1 20 < 5.0E-02 IND

1,1-DCA ND(0.28) IND 12 16 14 2.8 20 < 2.0E-02 IND

mean and standard deviation of basement/sub-slab ratio 3.9E-03 1.8E-03

Table 6c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House D Using 1-Liter Tedlar Bags and On-Site GC Analysis During the July 2002 Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

Tedlar

bsmt/

sub-slab

stdev n=3 n=3 n=3

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.48 0.03 77 16 168 87 76 87.9 5.5E-03 4.9E-03

1,1-DCE 0.13 0.01 22 ND(10) 111 67 63 95 2.0E-03 1.9E-03

TCE ND(0.28) IND 18 ND(6) 30 24 8 35.4 < 1.1E-02 IND

c-1,2-DCE ND(0.27) IND ND(25) ND(25) ND(25) < 25 IND IND IND IND

mean and standard deviation of basement/sub-slab ratio 3.7E-03 2.6E-03

Results and statistical analysis of VOCs associated 

with sub-surface contamination and sampled using 

EPA Method TO-15 are summarized in Table 6b. 

Use of basement/sub-slab air concentration ratios 

of 1,1,1-TCA and 1,1-DCE resulted in computation 

of an average basement/sub-slab air concentration 

ratio of 3.9E-03. Coefficients of variation of sub-slab 

air concentrations ranged from 20 to 94%. Results 

and statistical analysis of VOCs associated with 

sub-surface contamination and sampled using oneliter Tedlar bags are summarized in Table 6c. Use 

of basement/sub-slab air concentration values of 

1,1,1-TCA and 1,1-DCE resulted in computation of 

an average basement/sub-slab air concentration ratio 

of 3.7E-03. Coefficients of variation of sub-slab air 

concentrations ranged from 35 to 95%. 
56

The results of sub-slab sampling with one-liter Tedlar 

bags during the October 2002 sample event are 

summarized in Table 6d. A comparison of mean subslab sample concentrations for 1,1,1-TCA, 1,1-DCE, 

and TCE during the July and October sampling events 

is illustrated in Figure 41. The null hypotheses that 

the mean sub-slab air concentrations of 1,1,1-TCA , 

1,1-DCE, and TCE were equivalent during the July 

and October 2002 sample events were not rejected 

using a two-tailed Approximate t-Test at a level of 

significance less than or equal to 0.1. 

Figure 40. Basement/sub-slab concentration ratios using EPA Method TO-15 at House D during the July 2002 sample event. 

Error bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or 

sub-slab air.

Table 6d. Sub-Slab Air Concentrations of VOCs Associated with Sub-Surface Contamination in House D Using 1-Liter Tedlar Bags 

and On-Site GC Analysis During the October 2002 Sample Event

VOC P[A]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov

n=2 n=2 n=2

11/01/02 11/01/02 11/01/02 11/01/02 11/01/02

(ppbv) (ppbv) (ppbv) (ppbv) (%)

1,1,1-TCA 39 61 50 16 31

1,1-DCE 8.2 52 30 31 103

TCE 7.9 23 15 11 69

c-1,2-DCE ND(4) 11 11 IND IND

ND( ) = Not detected (reporting limit) IND = indeterminate
57

Figure 41. Comparison of mean sub-slab air concentrations of VOCs collected in one-liter Tedlar bags during the July and October 

2002 sample events at House D. Error bars represent one standard deviation.

House E

At the time of probe installation, there was a two 

centimeter separation between the slab and cinderblock 

walls where underlying sandy soil was exposed. A 

portion (approximately 30%) of the basement was 

finished with ceramic tile. Poured concrete walls 

were painted. An oil furnace was centrally located in 

the basement. Concentrations of VOCs detected in 

basement and/or sub-slab air using EPA Method TO-15 

are summarized in Table 7a. 1,1,1-TCA and 1,1-DCE 

were detected in basement air at concentrations of 

0.57 and 0.12 ppbv, respectively. The detection limits 

for TCE, c-1,2-DCE, and 1,1-DCA were between 0.26 

and 1.1 ppbv. Other chlorinated VOCs detected in 

basement air were methylene chloride, chloroform, 

and carbon tetrachloride at concentrations of 9.5, 

0.81, and 0.10 ppbv, respectively. Freons, F-11, F-12, 

and F-113, were detected at concentrations of 0.44, 

0.59, and 0.09 ppbv, respectively. Hydrocarbons, 

hexane, benzene, toluene, ethylbenzene, m/p-xylenes, 

o-xylene, 1,2,4-trimethylbenzene were detected in 

basement air at concentrations up to 1.2 ppbv. Acetone, 

methyl ethyl ketone, and methyl tertiary-butyl ether 

were detected at concentrations of 9.6, 1.0, and 0.27 

ppbv, respectively.

Three probes were installed for sub-slab sampling. All 

three probes were sampled using EPA Method TO15 and one-liter Tedlar bags. As indicated in Table 

7b, when sampling using EPA Method TO-15, 1,1,1-

TCA, 1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA were 
58

Table 7a. Basement and Sub-Slab Air Concentrations for VOCs at House E Using EPA Method TO-15 During the July 2002 

Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

n=3 n=3 n=3 stdev

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.57 0.03 48 78 170 99 64 64 5.8E-03 3.7E-03

1,1-DCE 0.12 0.01 13 59 170 81 81 100 1.5E-03 1.5E-03

TCE ND(0.26) IND 20 32 66 39 24 61 < 6.7E-03 IND

c-1,2-DCE ND(0.26) IND 2.5 12 26 14 12 88 < 1.9E-02 IND

1,1-DCA ND(1.1) IND 7.0 15 32 18 13 71 < 6.12E-02 IND

1,2-DCA ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

PCE ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

CH2Cl2 9.5 0.57 ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND > 4.3E+00 IND

CHCl3 0.81 0.05 0.73 1.5 1.4 1.2 0.42 35 0.67 2.4E-01

CCl4 0.10 0.01 ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND > 4.5E-02 IND

CCl3F(F-11) 0.44 0.03 0.47 ND(1.8) ND(3.7) < 2.0 IND IND > 2.2E-01 IND

CCl2F2

(F-12) 0.59 0.04 0.84 ND(1.8) ND(3.7) < 2.1 IND IND > 2.8E-01 IND

CHBrCl2 0.15 0.01 ND(9.8) ND(16) ND(33) ND(<20) IND IND > 7.3E-03 IND

vinyl chloride ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

CH3CH2Cl ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

CCl3CF3

(F-113) 0.09 0.01 ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND > 4.12E-02 IND

acetone 9.6 0.58 2.6 5.0 5.7 4.4 1.6 37 2.2E+00 8.2E-01

2-hexanone ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

THF ND(2.3) IND ND(18) ND(18) ND(18) ND(18) IND IND IND IND

MEK 1.0 0.06 ND(2.0) ND(3.3) ND(7.0) ND(<4.1) IND IND > 2.4E-01 IND

MIBK ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

MTBE 0.27 0.02 ND(1.0) ND(1.7) ND(3.5) ND(<2.1) IND IND > 1.3E-01 IND

heptane ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

hexane 1.1 0.07 ND(1.1) ND(1.8) ND(3.8) ND(<2.2) IND IND > 5.0E-01 IND

cyclohexane ND(0.50) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

benzene 0.22 0.01 ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND > 1.0E-01 IND

toluene 1.2 0.07 ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND > 5.5E-01 IND

ethylbenzene 0.14 0.01 ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND > 6.4E-02 IND

m/p-xylenes 0.37 0.02 ND(2.2) ND(3.6) ND(7.5) ND(<4.4) IND IND > 8.4E-02 IND

o-xylene 0.17 0.01 ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND > 7.7E-02 IND

styrene ND(0.23) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

1,2,4-TMB 0.19 0.01 ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND > 8.6E-02 IND

1,3,5-TMB ND(0.26) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

1,3-

butadiene ND(0.50) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

1,3-DCB ND(0.24) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

1,4-DCB ND(0.24) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

4-ethyltoluene ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

isopropyl

alcohol ND(0.25) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

ethyl/vinyl 

acetate 1.0 0.06 ND(2.2) ND(3.5) ND(7.3) ND(< 4.3) IND IND > 2.3E-01 IND

CS2 ND(0.23) IND ND(1.1) ND(1.8) ND(3.7) ND(<2.2) IND IND IND IND

ND( ) = Not detected (reporting limit) IND = indeterminate
59

detected at maximum concentrations in Probe C at 

170, 170, 66, 26, and 32 ppbv, respectively. The only 

other VOCs detected in sub-slab air were acetone, 

chloroform, F-11, and F-12 at maximum concentrations 

of 5.7, 1.5, 0.47, and 0.84 ppbv, respectively. Detection 

limits for other compounds ranged from 1.1 to 18 ppbv. 

As indicated in Table 7c, when sampling with one-liter 

Tedlar bags, 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE 

were detected at maximum concentrations at Probe 

[C] at 234, 130, 65, and 26 pppv, respectively.

Basement/sub-slab air concentration ratios of 

VOCs detected in basement air and sampled using 

EPA Method TO-15 are illustrated in Figure 42. 

Basement/sub-slab air concentration ratios for all 

five VOCs associated with sub-surface contamination 

Table 7b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House E Using EPA Method TO-15 During the July 2002 Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=3 n=3 n=3

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.57 0.03 48 78 170 99 64 64 5.8E-03 3.7E-03

1,1-DCE 0.12 0.01 13 59 170 81 81 100 1.5E-03 1.5E-03

TCE ND(0.26) IND 20 32 66 39 24 61 < 6.7E-03 IND

c-1,2-DCE ND(0.26) IND 2.5 12 26 14 12 88 < 1.9E-02 IND

1,1-DCA ND(1.1) IND 7.0 15 32 18 13 71 < 6.12E-02 IND

ND( ) = Not detected (reporting limit) IND = indeterminate mean and standard deviation 3.6E-03 2.0E-03

Table 7c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House E Using 1-Liter Tedlar Bags and On-Site GC Analysis During the July 2002 Sample Event

VOC bsmt

1-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=3 n=3 n=3

07/16/02 cov=6% 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02 07/16/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.57 0.03 59 107 234 133 90 68 4.3E-03 2.9E-03

1,1-DCE 0.12 0.01 10 44 130 61 62 101 2.0E-03 2.0E-03

TCE ND(0.26) IND 20 36 65 40 23 57 < 6.4E-03 IND

c-1,2-DCE ND(0.26) IND ND(25) ND(25) 26.00 < 25 IND IND IND IND

ND( ) = Not detected (reporting limit) IND = indeterminate mean and standard deviation 3.1E-03 1.8E-03

were significantly lower than other VOCs detected in 

basement air. The basement/sub-slab air concentration 

ratio of bromodichloromethane was some value 

greater than 7.3E-03. This VOC was eliminated from 

consideration of vapor intrusion because it was not 

detected in soil gas or ground water in the vicinity 

of the building. Since the null hypothesis that the 

basement/sub-slab air concentration ratio of 1,1,1-TCA 

was equal to the basement/sub-slab air concentration 

ratio of the indicator VOC, 1,1-DCE, could not be 

rejected using a one-tailed Approximate t-Test at a 

level of significance less than or equal to 0.05 (p = 

0.1), it was inferred that the presence of both 1,1,1-

TCA and 1,1-DCE in basement air was due to vapor 

intrusion at the time of sampling.
60

Figure 42. Basement/sub-slab concentration ratios using EPA Method TO-15 at House E during the July 2002 sample event. Error 

bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or subslab air.

Results and statistical analysis of VOCs associated 

with sub-surface contamination and sampled using 

EPA Method TO-15 are summarized in Table 7b. 

Use of basement/sub-slab air concentration ratios 

of 1,1,1-TCA and 1,1-DCE resulted in computation 

of an average basement/sub-slab ratio of 3.6E-03. 

Coefficients of variation in sub-slab air samples ranged 

from 61 to 100%. Results and statistical analysis of 

VOCs associated with sub-surface contamination and 

sampled using one-liter Tedlar bags are summarized in 

Table 7c. Use of basement/sub-slab air concentration 

values of 1,1,1-TCA and 1,1-DCE resulted in 

computation of an average basement/sub-slab ratio 

of 3.1E-03. Coefficients of variation in sub-slab air 

samples ranged from 57 to 101%.

The results of sub-slab sampling using one-liter Tedlar 

bags during the October 2002 sample event are 

summarized in Table 7d. A comparison of mean subslab sample concentrations for 1,1,1-TCA, 1,1-DCE, 

and TCE during the July and October 2002 sampling 

events is illustrated in Figure 43. The null hypotheses 

that the mean sub-slab air concentrations of 1,1,1-TCA 

, 1,1-DCE, and TCE were equivalent during the July 

and October 2002 sample events were not rejected 

using a two-tailed Approximate t-Test at a level of 

significance less than or equal to 0.1. 

Hence, a comparison of July and October 2002 sample 

events indicated that levels of VOCs associated with 

sub-surface contamination found in sub-slab air were 

statistically different (p < 0.10) in only 1 out of 16 

comparisons. This indicated little temporal variability 

in sub-slab air concentrations between the July 2002 

and October 2002 sampling events.
61

Figure 43. Comparison of mean sub-slab air concentrations of VOCs collected in one-liter Tedlar bags during the July and October 

2002 sample events at House E. Error bars represent one standard deviation.

Table 7d. Sub-Slab Air Concentrations of VOCs Associated with Sub-Surface Contamination in House E Using 1-Liter Tedlar Bags 

and On-Site GC Analysis During the October 2002 Sample Event

VOC P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov

n=3 n=3 n=3

11/01/02 11/01/02 11/01/02 11/01/02 11/01/02 11/01/02

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%)

1,1,1-TCA 30 78 370 159 184 115

1,1-DCE 10 37 198 82 102 124

TCE 13 29 152 65 76 118

c-1,2-DCE 6 18 84 36 42 117
62

6.3 Summary of Results for Buildings 

 Sampled in March 2003

Basement and sub-slab air samples were collected for 

VOC analysis in Houses F through P during the March 

2003 sample event. Basement (24-hr) and sub-slab 

(grab) samples were collected in six-liter evacuated 

canisters. Sub-slab samples were also collected in 

one-liter Tedlar bags with on-site GC analyses. Two 

outdoor air samples (24-hr) were collected outside of 

Houses G and K with results summarized in Table 2. 

(See page 39.)

During the March 2003 sample event, basement 

(48-hr activated charcoal) and sub-slab (scintillation 

cells) air samples were collected for radon analysis. 

When one or more indicator VOCs were present in 

basement air and more than one probe was sampled 

for radon, the basement/sub-slab air concentration 

ratio of radon was compared with the basement/subslab air concentration ratio of indicator VOCs using 

a two-tailed Approximate t-Test. The null hypothesis 

was that the basement/sub-slab air concentration 

ratio of radon was equal to the basement/sub-slab 

air concentration ratio of an indicator VOC. The 

alternate hypothesis was that the basement/sub-slab 

concentration ratios were not equal. The rejection 

criteria was a Type I error or level of significance less 

than or equal to 0.1 (twice the level of significance 

for one-tailed tests used to assess vapor intrusion). 

As a matter of necessity, radon was used as an 

indicator compound to assess vapor intrusion when 

indicator VOCs, 1,1-DCE, c-1,2-DCE, and 1,1-DCA, 

were not detected in basement air. Basement slabs 

were approximately 1.6 meters below ground surface.

 

House F

Concentrations of all VOCs detected in basement 

and/or sub-slab air using EPA Method TO-15 are 

summarized in Table 8. A replicate basement air 

sample was collected at House F. VOCs associated 

with sub-surface contamination were not detected 

in basement air at detection limits ranging from 

0.078 to 0.086 ppbv. Thus, assessment of vapor 

intrusion was not necessary at this location. Other 

chlorinated VOCs detected in basement air were 

methylene chloride, carbon tetrachloride, and 1,1-

dichlorobenzene at concentrations of 0.87, 0.09, 

and 0.09 ppbv, respectively. Freons, F-11, F-12, and 

F-113, were detected at concentrations of 0.40, 1.4, 

and 0.07 ppbv, respectively. Hydrocarbons, hexane, 

benzene, toluene, ethylbenzene, m/p-xylenes, oxylene, styrene, and 1,2,4-trimethylbenzene were 

detected in basement air at concentrations up to 

1.25 ppbv. Acetone, methyl ethyl ketone, and methyl 

tertiary-butyl ether were detected at concentrations of 

2.8, 0.55, and 0.32 ppbv, respectively. The compound, 

1,3-butadiene, was detected at a concentration of 

0.33 ppbv.

Four probes were installed for sub-slab sampling. 

Two probes were sampled using EPA Method TO15. All four probes were sampled using one-liter 

Tedlar bags. VOCs associated with sub-surface 

contamination were not detected using EPA Method 

TO-15. Detection limits ranged from 0.083 to 0.085 

ppbv. Other chlorinated VOCs detected in sub-slab 

air were perchloroethylene, methylene chloride, 

chloroform, and carbon tetrachloride at maximum 

concentrations of 0.13, 0.70, 0.09, and 0.09 ppbv, 

respectively. Freons, F-11 and F-12, were detected 

at maximum concentrations of 0.42 and 1.7 ppbv, 
63

Table 8. Basement and Sub-Slab Air Concentrations for VOCs at House F Using EPA Method TO-15 During the March 2003 

Sample Event

VOC bsmt

24-hr

bsmt

24-hr

bsmt

mean

bsmt

stdev P[A]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

n=2 n=2 n=2 n=2 stdev

03/26/03 03/26/03 03/26/03 03/26/03 03/28/03 03/28/03 03/28/03 03/28/03 03/28/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA ND(0.084) ND(0.082) ND(<0.083) IND ND(0.078) ND(0.082) ND(<0.080) IND IND IND IND

1,1-DCE ND(0.086) ND(0.084) ND(<0.085) IND ND(0.08) ND(0.084) ND(<0.082) IND IND IND IND

TCE ND(0.086) ND(0.084) ND(<0.085) IND ND(0.08) ND(0.084) ND(<0.082) IND IND IND IND

c-1,2-DCE ND(0.084) ND(0.082) ND(<0.083) IND ND(0.078) ND(0.082) ND(<0.080) IND IND IND IND

1,1-DCA ND(0.086) ND(0.084) ND(<0.085) IND ND(0.08) ND(0.084) ND(<0.082) IND IND IND IND

1,2-DCA ND(0.084) ND(0.082) ND(<0.083) IND ND(0.078) ND(0.082) ND(<0.080) IND IND IND IND

PCE ND(0.084) ND(0.082) ND(<0.083) IND ND(0.078) 0.13 < 0.10 IND IND IND IND

CH2Cl2 0.77 0.87 0.82 0.07 0.49 0.70 0.60 0.15 25 1.4E+00 3.6E-01

CHCl3 ND(0.084) ND(0.082) ND(<0.083) IND ND(0.078) 0.09 < 0.084 IND IND IND IND

CCl4 ND(0.086) 0.09 < 0.088 IND 0.09 0.09 0.09 0.00 0.0 < 9.6E-01 IND

CCl3F(F-11) 0.38 0.4 0.39 0.01 0.42 0.36 0.39 0.04 11 1.0E+00 1.1E-01

CCl2F2

(F-12) 1.4 1.4 1.4 0.00 1.7 1.4 1.6 0.21 14 9.0E-01 1.2E-01

CHBrCl2 ND(0.079) ND(0.077) ND(<0.078) IND ND(0.073) ND(0.077) ND(<0.075) IND IND IND IND

vinyl chloride ND(0.086) ND(0.085) ND(<0.086) IND ND(0.081) ND(0.085) ND(<0.083) IND IND IND IND

CH3CH2Cl 0.5 ND(0.87) < 0.66 IND ND(0.83) 0.38 < 0.61 IND IND IND IND

CCl3CF3

(F-113) 0.07 ND(0.082) < 0.076 IND ND(0.078) ND(0.082) ND(<0.080) IND IND IND IND

acetone 2.8 2.5 2.7 0.21 1.7 2.4 2.1 0.49 24 1.3E+00 3.3E-01

2-hexanone ND(0.081) ND(0.079) ND(<0.080) IND 0.1 0.12 0.11 0.01 13 < 7.4E-01 IND

THF ND(0.082) ND(0.08) ND(<0.081) IND ND(0.076) ND(0.08) ND(<0.078) IND IND IND IND

MEK 0.53 0.55 0.54 0.01 0.48 0.66 0.57 0.13 22 9.5E-01 2.1E-01

MIBK ND(0.076) ND(0.074) ND(<0.075) IND 0.26 0.27 0.265 0.01 2.7 < 1.6E-01 IND

MTBE 0.30 0.32 0.31 0.01 0.65 0.69 0.67 0.03 4.2 4.6E-01 2.9E-02

heptane ND(0.082) ND(0.08) ND(<0.081) IND ND(0.076) ND(0.11) ND(<0.093) IND IND IND IND

hexane 0.33 0.36 0.35 0.02 0.22 0.25 0.24 0.02 9.0 1.5E+00 1.6E-01

cyclohexane ND(0.084) ND(0.082) ND(<0.083) IND 0.08 ND(0.082) ND(<0.081) IND IND IND IND

benzene 0.41 0.45 0.43 0.03 0.11 0.33 0.22 0.16 71 2.0E+00 1.4E+00

toluene 1.2 1.3 1.25 0.07 0.51 2.2 1.4 1.2 88 9.2E-01 8.2E-01

ethylbenzene 0.16 0.17 0.17 0.01 0.08 0.12 0.1 0.03 28 1.7E+00 4.7E-01

m/p-xylenes 0.48 0.52 0.50 0.03 0.2 0.36 0.28 0.11 40 1.8E+00 7.3E-01

o-xylene 0.16 0.16 0.16 0.00 0.09 0.13 0.11 0.03 26 1.5E+00 3.7E-01

styrene 0.10 0.10 0.10 0.00 ND(0.073) ND(0.077) ND(<0.075) IND IND > 1.3E+00 IND

1,2,4-TMB 0.080 0.090 0.085 0.01 0.09 0.15 0.12 0.04 35 7.1E-01 2.6E-01

1,3,5-TMB ND(0.084) ND(0.082) ND(<0.083) IND ND(0.15) ND(0.082) ND(<0.12) IND IND IND IND

1,3-

butadiene 0.31 0.33 0.32 0.01 ND(0.17) 0.31 < 0.24 IND IND > 1.0E+00 IND

1,3-DCB ND(0.084) ND(0.082) ND(<0.083) IND ND(0.078) ND(0.082) ND(<0.080) IND IND IND IND

1,4-DCB 0.09 ND(0.08) < 0.09 IND ND(0.078) ND(0.08) ND(<0.079) IND IND IND IND

4-ethyltoluene 0.11 0.10 0.11 0.01 ND(0.078) 0.13 < 0.10 IND IND > 8.5E-01 IND

isopropyl

alcohol 2.9 4.0 3.5 0.78 0.25 0.64 0.445 0.28 62 7.8E+00 5.1E+00

ethyl/vinyl 

acetate 0.32 0.35 0.34 0.02 ND(0.14) ND(0.15) ND(< 0.15) IND IND > 2.2E+00 IND

CS2 ND(0.081) ND(0.079) ND(<0.080) IND 0.21 0.26 0.24 0.04 15 < 3.4E-01 IND

ND( ) = Not detected (reporting limit) IND = indeterminate
64

respectively. Hydrocarbons, hexane, cyclohexane, 

benzene, toluene, ethylbenzene, m/p-xylenes, oxylene, 1,2,4-trimethylbenzene, and 4-ethyltoluene 

were detected in sub-slab air at concentrations up to 

2.2 ppbv. Acetone, methyl ethyl ketone, methyl isobutyl 

ketone, and methyl tertiary-butyl ether were detected at 

maximum concentrations of 2.4, 0.66, 0.27, and 0.69 

ppbv, respectively. The compound, 1,3-butadiene, was 

detected at a maximum concentration of 0.33 ppbv. 

VOCs associated with sub-surface contamination were 

not detected in one-liter Tedlar bags with detection 

limits ranging from 2 to 5 ppbv. 

Basement/sub-slab ratios of VOCs detected in 

basement air and sampled using EPA Method TO-15 

are summarized in Table 8. Basement/sub-slab air 

concentration ratios for VOCs not associated with subsurface contamination ranged from less than 1.6E-01 

(methyl isobutyl ketone) to 7.8E+00 (isopropyl alcohol). 

Basement/sub-slab air concentration ratios were less 

than 1.0E+00 for eight compounds not associated 

with sub-surface contamination demonstrating that 

observation of a basement/sub-slab air concentration 

ratio less than 1.0E+00 does not necessarily indicate 

vapor intrusion.

House G

There were several visible cracks in the slab and two 

small diameter holes near an oil tank which serviced 

an oil furnace. The basement wall consisted of 

field stone. Concentrations of all VOCs detected 

in basement and/or sub-slab air using EPA Method 

TO-15 are summarized in Table 9a. The only VOC 

associated with sub-surface contamination detected 

in basement air was 1,1,1-TCA at a concentration 

of 0.28 ppbv. The detection limit of other VOCs 

associated with sub-surface contamination was 0.10 

ppbv. Other chlorinated VOCs detected in basement 

air were perchloroethylene and methylene chloride 

at concentrations of 0.18 and 7.4 ppbv, respectively. 

Freons, F-11 and F-12, were detected at concentrations 

of 0.30 and 0.49 ppbv, respectively. Hydrocarbons, 

hexane, benzene, toluene, ethylbenzene, m/pxylenes, o-xylene, 1,2,4-trimethylbenzene, 1,3,5-

trimethylbenzene, and 4-ethyltoluene were detected 

in basement air at concentrations up to 42 ppbv. 

Acetone, methyl ethyl ketone, and methyl tertiary-butyl 

ether were detected at concentrations of 2.0, 0.81, 

and 0.54 ppbv, respectively. 

Five probes were installed for sub-slab sampling. Two 

probes were sampled using EPA Method TO-15. All five 

probes were sampled using one-liter Tedlar bags. As 

indicated by Tables 9a and 9b, when sampling using 

EPA Method TO-15, 1,1,1-TCA, 1,1-DCE, TCE, and 

1,1-DCA were detected at maximum concentrations 

of 6.0, 0.75, 0.99, and 0.37 ppbv, respectively. Other 

chlorinated VOCs perchloroethylene, chloroform, 

and carbon tetrachloride were detected at maximum 

concentrations of 0.20, 0.73 and 0.09 ppbv, respectively. 

Freons, F-11, F-12, and F-113, were detected at 

maximum concentrations of 0.27, 0.55, and 0.08 ppbv, 

respectively. Hydrocarbons, hexane and toluene were 

detected at maximum concentrations of 0.41 and 0.25 

ppbv, respectively. Acetone, 2-hexanone, methyl ethyl 

ketone, methyl isobutyl ketone, and methyl tertiarybutyl ether were detected at maximum concentrations 

of 2.5, 0.12, 0.80, 0.30, and 0.090 ppbv, respectively. 

As indicated by Table 9c, 1,1,1-TCA and TCE were 

detected in one-liter Tedlar bag samples at maximum 

concentrations of 7.5 and 2.4 ppbv, respectively. 

Detection limits for 1,1-DCE and c-1,2-DCE were 3 

to 5 ppbv. Radon was sampled at two probes with 
65

Table 9a. Basement and Sub-Slab Air Concentrations for VOCs Detected at House G Using EPA Method TO-15 During the March

2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

n=2 n=2 n=2 stdev

03/27/03 cov=6% 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.28 0.02 6.0 2.0 4.0 2.8 71 7.0E-02 5.0E-02

1,1-DCE ND(0.10) IND 0.21 0.75 0.48 0.38 80 < 2.1E-01 IND

TCE ND(0.10) IND 0.990 0.94 1.0 0.04 3.7 < 1.0E-01 IND

c-1,2-DCE ND(0.10) IND ND(0.073) ND(0.071) ND(<0.072) IND IND IND IND

1,1-DCA ND(0.10) IND 0.37 0.25 0.31 0.08 27 < 3.2E-01 IND

1,2-DCA ND(0.10) IND ND(0.073) ND(0.071) ND(<0.072) IND IND IND IND

PCE 0.18 0.01 0.20 ND(0.071) < 0.14 IND IND > 1.3E+00 IND

CH2Cl2 7.4 0.44 ND(0.074) ND(0.073) ND(<0.074) IND IND > 1.0E+02 IND

CHCl3 ND(0.10) IND 0.73 0.19 0.46 0.38 83 < 2.2E-01 IND

CCl4 ND(0.10) IND ND(0.074) 0.090 < 0.082 IND IND IND IND

CCl3F(F-11) 0.30 0.02 0.25 0.27 0.26 0.01 5.4 1.2E+00 9.3E-02

CCl2F2

(F-12) 0.49 0.03 0.55 0.52 0.54 0.02 4.0 9.2E-01 6.6E-02

CHBrCl2 ND(0.096) IND 0.11 ND(0.067) < 0.09 IND IND IND IND

vinyl chloride ND(0.11) IND ND(0.073) ND(0.074) ND(<0.074) IND IND IND IND

CH3CH2Cl ND(1.1) IND ND(0.77) ND(0.76) ND(<0.76) IND IND IND IND

CCl3CF3

(F-113) ND(0.10) IND ND(0.073) 0.08 < 0.08 IND IND IND IND

acetone 2.0 0.12 2.5 2.1 2.3 0.28 12 8.7E-01 1.2E-01

2-hexanone ND(0.098) IND 0.10 0.12 0.11 0.01 13 < 8.9E-01 IND

THF ND(0.10) IND ND(0.071) ND(0.07) ND(<0.07) IND IND IND IND

MEK 0.81 0.05 0.80 0.70 0.75 0.07 9.4 1.1E+00 1.2E-01

MIBK ND(0.092) IND 0.25 0.30 0.28 0.04 13 < 3.3E-01 IND

MTBE 0.54 0.03 0.070 0.090 0.08 0.01 18 6.8E+00 1.3E+00

heptane ND(0.10) IND ND(0.071) ND(0.07) ND(<0.07) IND IND IND IND

hexane 0.70 0.04 0.41 0.17 0.29 0.17 59 2.4E+00 1.4E+00

cyclohexane 0.12 0.01 ND(0.073) ND(0.071) ND(<0.072) IND IND > 1.6E+00 IND

benzene 0.39 0.02 ND(0.074) ND(0.073) ND(<0.074) IND IND > 5.3E+00 IND

toluene 42 2.52 0.25 0.25 0.25 0.0 0.0 1.7E+02 1.0E+01

ethylbenzene 0.25 0.02 ND(0.073) ND(0.071) ND(<0.072) IND IND > 3.4E+00 IND

m/p-xylenes 0.59 0.04 ND(0.15) ND(0.14) ND(<0.15) IND IND > 3.9E+00 IND

o-xylene 0.35 0.02 ND(0.074) ND(0.073) ND(<0.074) IND IND > 4.7E+00 IND

styrene ND(0.096) IND ND(0.069) ND(0.067) ND(<0.068) IND IND IND IND

1,2,4-TMB 0.46 0.03 ND(0.071) ND(0.07) ND(<0.07) IND IND > 6.5E+00 IND

1,3,5-TMB 0.35 0.02 ND(0.073) ND(0.071) ND(<0.072) IND IND > 4.8E+00 IND

1,3-

butadiene ND(0.20) IND ND(0.14) ND(0.14) ND(<0.14) IND IND IND IND

1,3-DCB ND(0.10) IND ND(0.073) ND(0.071) ND(<0.072) IND IND IND IND

1,4-DCB ND(0.10) IND ND(0.071) ND(0.07) ND(<0.07) IND IND IND IND

4-ethyltoluene 1.4 0.08 ND(0.073) ND(0.071) ND(<0.072) IND IND > 1.9E+01 IND

isopropyl

alcohol 2.1 0.13 0.16 ND(0.13) < 0.15 IND IND > 1.4E+01 IND

ethyl/vinyl 

acetate 0.19 0.01 ND(0.13) ND(0.13) ND(< 0.13) IND IND > 1.5E+00 IND

CS2 ND(0.098) IND ND(0.07) 0.23 < 0.15 IND IND IND IND

ND( ) = Not detected (reporting limit) IND = indeterminate
66

mean basement/sub-slab air concentration ratio of 

radon was rejected using a one-tailed Approximate 

t-Test at a level of significance less than or equal to 

0.05 (p < 0.005), it was inferred that the presence of 

1,1,1-TCA in basement air was not primarily due to 

vapor intrusion at the time of sampling. 

Tables 9b and 9c summarize basement/sub-slab air 

concentration ratios determined using EPA Method 

TO-15 and Tedlar bag sampling for VOCs associated 

with sub-surface contamination. For EPA Method TO15 analysis, the basement/sub-slab air concentration 

ratio of 1,1,1-TCA was less than 7.0E-02. For Tedlar 

bag sampling and on-site GC analyses, the basement/

sub-slab air concentration ratio of 1,1,1-TCA was less 

than 5.4E-02.

concentrations of 916 and 1035 pCi/l and detected 

in basement air at a mean concentration of 2.3 pCi/l. 

Results and statistical analysis of sub-slab sampling 

for radon are summarized in Table 9d.

Figure 44 illustrates basement/sub-slab air 

concentration ratios for VOCs and radon detected 

in basement air. Radon was used as an indicator 

compound because indicator VOCs, 1,1-DCE, c-1,2-

DCE, and 1,1-DCA, were not detected in basement 

air. The results of Tedlar bag sampling were used 

for hypothesis testing because sampling occurred 

at five sub-slab vapor probes instead of at only two 

probes for EPA Method TO-15 analysis. Since the 

null hypothesis that the mean basement/sub-slab 

air concentration ratio of 1,1,1-TCA was equal to the 

Table 9b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House G Using EPA Method TO-15 During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2

03/27/03 cov=6% 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.28 0.02 6.0 2.0 4.0 2.8 71 7.0E-02 5.0E-02

1,1-DCE ND(0.10) IND 0.21 0.75 0.48 0.38 80 < 2.1E-01 IND

TCE ND(0.10) IND 0.990 0.94 1.0 0.04 3.7 < 1.0E-01 IND

c-1,2-DCE ND(0.10) IND ND(0.073) ND(0.071) ND(<0.072) IND IND IND IND

1,1-DCA ND(0.10) IND 0.37 0.25 0.31 0.08 27 < 3.2E-01 IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation < 7.0E-02 IND

Table 9c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House G Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

P[D]

grab

P[E]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=5 n=5 n=5

03/27/03 cov=6% 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.28 0.02 7.5 5.2 2.6 5.2 5.2 5.1 1.7 34 5.4E-02 1.9E-02

1,1-DCE ND(0.10) IND ND(5.0) ND(5.0) ND(5.0) ND(5.0) ND(5.0) ND(<5.0) IND IND IND IND

TCE ND(0.10) IND 1.1 1.4 1.4 2.4 2.4 1.7 0.6 35 < 5.9E-02 IND

c-1,2-DCE ND(0.10) IND ND(3.0) ND(3.0) ND(3.0) ND(3.0) ND(3.0) ND(<3.0) IND IND IND IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation < 5.9E-02 IND
67

Figure 44. Basement/sub-slab concentration ratios using EPA Method TO-15 at House G during the March 2003 sample event. 

Error bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or 

sub-slab air.

Table 9d. Basement/Sub-Slab Air Concentration Ratios of Radon in House G Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/25-3/27/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt

48-hr

bsmt

48-hr

bsmt-48 hr

mean

bsmt-48 hr

stdev

bsmt-48 hr

cov

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2 110A 300A n=2 n=2 n=2

3/27/2003 3/27/2003 3/27/2003 3/31/2003 3/31/2003 3/31/2003 3/31/2003 3/31/2003

(pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

2.4 2.1 2.3 0.21 9.4 916 1035 976 84.1 8.63 2.31E-03 2.95E-04

House H

There were several visible one to two millimeter 

wide cracks in the slab at House H. Basement 

walls consisted of poured concrete. Concentrations 

of all VOCs detected in basement and/or sub-slab 

air using EPA Method TO-15 are summarized in 

Table 10a. A replicate basement air sample was 

collected at House H. The only VOC associated with 

subsurface contamination detected in basement 

air was 1,1,1-TCA at a concentration of 3.7 ppbv. 

The detection limit for other VOCs associated with 

sub-surface contamination was between 0.079 and 

0.082 ppbv. Other chlorinated compounds detected 

in basement air were perchloroethylene, methylene 

chloride, chloroform, carbon tetrachloride, and 1.4-

dichlorobenzene at concentrations of 0.15, 270, 

0.17, 0.090, and 36 ppbv, respectively. Freons, 

F-11, F-12, and F-113, were detected in basement 

air at concentrations of 1.8, 0.54, and 0.070 ppbv, 
68

respectively. Hydrocarbons, heptane, hexane, 

cylcohexane, benzene, toluene, ethylbenzene, m/pxylenes, o-xylene, styrene, 1,2,4-trimethylbenzene, 

1,3,5-trimethylbenzene, and 4-ethyltoluene were 

detected at concentrations up to 14 ppbv. Acetone, 

tetrahydrofuran, methyl ethyl ketone, methyl isobutyl 

ketone, and methyl tertiary-butyl ether were detected 

at concentrations of 3.0, 0.82, 1.1, 0.17, and 1.0 ppbv, 

respectively.

Four probes were installed for sub-slab sampling. 

Two probes were sampled using EPA Method TO-15. 

All four probes were sampled using one-liter Tedlar 

bags. As indicated by Table 10b, when sampling 

using EPA Method TO-15, 1,1,1-TCA, 1,1-DCE, TCE, 

c-1,2-DCE, and 1,1-DCA were detected in sub-slab 

air at maximum concentrations of 46, 16, 24, 6.6, 

and 9.7 ppbv, respectively. Other chlorinated VOCs 

detected in sub-slab air were perchloroethylene, 

methylene chloride, chloroform, carbon tetrachloride, 

and 1,3-dichlorobenzene at maximum concentrations 

of 0.44, 14, 4.5, 0.12, and 0.48 ppbv, respectively. 

Freons, F-11, F-12, and F-113, were detected at 

maximum concentrations of 1.1, 0.59, and 0.070 

ppbv, respectively. Hydrocarbons, hexane, benzene, 

toluene, ethylbenzene, m/p-xylenes, o-xylene, 1,2,4-

trimethylbenzene, 1,3,5-trimethylbenzene, and 

4-ethyltoluene were detected at concentrations up 

to 0.69 ppbv. Acetone, 2-hexanone, methyl ethyl 

ketone, methyl isobutyl ketone, and methyl tertiarybutyl ether were detected at concentrations up to 1.8 

ppbv. Detection limits for other compounds varied 

from 0.082 to 0.17 ppbv. As indicated by Table 10c, 

when sampling with one-liter Tedlar bags, 1,1,1-TCA, 

1,1-DCE, TCE, and c-1,2-DCE were detected at 

maximum concentrations of 61, 18, 24, and 6.0 pppv, 

respectively. Radon was sampled at two probes with 

concentrations of 406 and 343 pCi/l and detected in 

basement air at a mean concentration of 0.8 pCi/l. 

Results and statistical analysis of sub-slab sampling 

for radon are summarized in Table 10d.

Figure 45 illustrates basement/sub-slab ratios for 

VOCs and radon detected in basement air at House 

H. The results of Tedlar bag sampling were used 

for hypothesis testing because sampling occurred 

at four sub-slab vapor probes instead of at only two 

probes for EPA Method TO-15 analysis. Radon was 

used as an indicator compound because indicator 

VOCs, 1,1-DCE, c-1,2-DCE, and 1,1-DCA, were not 

detected in basement air. Since the null hypothesis 

that the basement/sub-slab air concentration ratio of 

1,1,1-TCA was equal to the basement/sub-slab air 

concentration ratio of radon could be rejected using a 

one-tailed Approximate t-Test at a level of significance 

less than or equal to 0.05 (p < 0.025), it was inferred 

that the presence of 1,1,1-TCA in basement air was 

not primarily due to vapor intrusion at the time of 

sampling. 

Tables 10b and 10c summarize basement/sub-slab 

air concentration ratios determined using EPA Method 

TO-15 and Tedlar bag sampling for VOCs associated 

with sub-surface contamination. For EPA Method 

TO-15 analysis, the basement/sub-slab concentration 

ratio of 1,1-DCE was less than 4.7E-03. For Tedlar 

bag sampling and on-site GC analyses, the basement/

sub-slab air concentration ratio of TCE was less than 

5.2E-03.
69

Table 10a. Basement and Sub-Slab Air Concentrations for VOCs Detected at House H Using EPA Method TO-15 During the 

March 2003 Sample Event

VOC bsmt

24-hr

bsmt

24-hr

bsmt

mean

bsmt

stdev P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

n=2 n=2 n=2 n=2 n=2 stdev

03/25/03 03/25/03 03/25/03 03/25/03 03/27/03 03/27/03 03/27/03 03/27/03 03/27/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 3.7 3.6 3.7 0.07 15 46 31 22 72 1.2E-01 8.6E-02

1,1-DCE ND(0.082) ND(0.08) ND(<0.08) IND 9.2 16 13 4.8 38 < 6.5E-03 IND

TCE ND(0.082) ND(0.08) ND(<0.08) IND 11 24 18 9.2 53 < 4.7E-03 IND

c-1,2-DCE ND(0.081) ND(0.079) ND(<0.08) IND 3.8 6.6 5.2 2.0 38 < 1.6E-02 IND

1,1-DCA ND(0.082) ND(0.08) ND(<0.08) IND 3.5 9.7 6.6 4.4 66 < 1.2E-02 IND

1,2-DCA ND(0.081) ND(0.079) ND(<0.081) IND ND(<0.087) 0.070 < 0.079 IND IND IND IND

PCE 0.15 0.15 0.15 0.00 0.22 0.44 0.33 0.16 47 4.5E-01 2.1E-01

CH2Cl2 270 250 260 14.1 7.7 14 11 4.5 41 2.4E+01 9.9E+00

CHCl3 0.16 0.17 0.17 0.01 1.1 4.5 2.8 2.4 86 5.9E-02 5.1E-02

CCl4 0.090 0.090 0.090 0.00 ND(0.089) 0.12 < 0.10 IND IND > 8.7E-01 IND

CCl3F(F-11) 1.8 1.8 1.8 0.00 0.63 1.1 0.87 0.33 38 2.1E+00 8.0E-01

CCl2F2

(F-12) 0.51 0.54 0.53 0.02 0.54 0.59 0.57 0.04 6.3 9.3E-01 6.9E-02

CHBrCl2 ND(0.076) ND(0.074) ND(<0.075) IND ND(0.082) 0.34 < 0.21 IND IND IND IND

vinyl chloride ND(0.084) ND(0.082) ND(<0.083) IND ND(0.091) ND(0.12) ND(<0.11) IND IND IND IND

CH3CH2Cl 1.1 1.2 1.2 0.07 ND(0.92) ND(1.2) ND(<1.1) IND IND > 9.6E-01 IND

CCl3CF3

(F-113) 0.070 ND(0.079) 0.07 IND ND(0.087) 0.070 < 0.079 IND IND > 8.8E-01 IND

acetone 2.4 3.0 2.7 0.42 1.8 2.6 2.2 0.57 26 1.2E+00 3.7E-01

2-hexanone ND(0.077) 0.090 0.09 IND 0.11 0.13 0.12 0.01 12 7.5E-01 IND

THF 0.76 0.82 0.79 0.04 ND(0.086) ND(0.11) ND(<0.10) IND IND > 7.2E+00 IND

MEK 0.93 1.1 1.0 0.12 0.58 0.72 0.65 0.10 15 1.6E+00 3.0E-01

MIBK 0.14 0.17 0.16 0.02 0.49 0.19 0.34 0.21 62 4.6E-01 2.9E-01

MTBE 0.97 1.0 1.0 0.02 0.36 0.33 0.35 0.02 6 2.9E+00 1.9E-01

heptane 1.7 1.7 1.7 0.00 ND(0.086) ND(0.11) ND(<0.10) IND IND > 1.5E+01 IND

hexane 1.6 1.5 1.6 0.07 0.14 0.20 0.17 0.04 25 9.1E+00 2.3E+00

cyclohexane 0.95 1.0 1.0 0.04 ND(0.087) ND(0.11) ND(<0.10) IND IND > 8.9E+00 IND

benzene 0.63 0.68 0.66 0.04 ND(0.089) 0.14 < 0.11 IND IND > 6.0E+00 IND

toluene 2.7 2.8 2.8 0.07 0.40 0.46 0.43 0.04 10 6.4E+00 6.5E-01

ethylbenzene 0.79 0.79 0.79 0.00 ND(0.087) 0.10 < 0.09 IND IND > 7.2E+00 IND

m/p-xylenes 3.6 3.9 3.8 0.21 0.20 0.18 0.19 0.01 7.4 2.0E+01 1.8E+00

o-xylene 3.4 3.6 3.5 0.14 0.090 0.17 0.13 0.06 44 2.7E+01 1.2E+01

styrene 1.8 1.9 1.9 0.07 ND(0.082) ND(0.11) ND(<0.10) IND IND > 1.7E+01 IND

1,2,4-TMB 6.4 6.9 6.7 0.35 ND(0.086) 0.69 < 0.39 IND IND > 1.7E+01 IND

1,3,5-TMB 3.2 3.4 3.3 0.14 ND(0.087) 0.25 < 0.17 IND IND > 1.9E+01 IND

1,3-

butadiene ND(0.16) ND(0.16) ND(<0.16) IND ND(0.17) 0.16 < 0.17 IND IND IND IND

1,3-DCB ND(0.081) ND(0.079) ND(<0.080) IND ND(0.087) 0.48 < 0.28 IND IND IND IND

1,4-DCB 36 30 33 4.24 ND(0.086) ND(0.11) ND(<0.10) IND IND > 3.0E+02 IND

4-ethyltoluene 14 13 14 0.71 0.15 0.29 0.22 0.10 45 6.1E+01 2.8E+01

isopropyl

alcohol 8.2 6.5 7.4 1.20 0.20 0.33 0.27 0.09 35 2.8E+01 1.1E+01

ethyl/vinyl 

acetate 0.34 0.33 0.34 0.01 ND(0.16) 0.10 < 0.13 IND IND > 3.0E+00 IND

CS2 ND(0.077) ND(0.075) ND(<0.076) IND ND(0.084) ND(0.11) ND(<0.09) IND IND IND IND

ND( ) = Not detected (reporting limit) IND = indeterminate
70

Table 10d. Basement/Sub-Slab Air Concentration Ratios of Radon in House H Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/21-3/24/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt

48-hr

bsmt

48-hr

bsmt-48 hr

mean

bsmt-48 hr

stdev

bsmt-48 hr

cov P[A]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2 n=2 n=2 n=2

03/24/03 03/24/03 03/24/03 03/27/03 03/27/03 03/27/03 03/27/03 03/27/03

(pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

0.8 0.8 0.8 0.0 0.0 406 343 375 44.5 11.9 2.14E-03 2.54E-04

Table 10b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House H Using EPA Method TO-15 During the March 2003 Sample Event

VOC bsmt

24-hr

bsmt

24-hr

bsmt

mean

bsmt

stdev P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2 n=2 n=2

03/25/03 03/25/03 03/25/03 03/25/03 03/27/03 03/27/03 03/27/03 03/27/03 03/27/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 3.7 3.6 3.7 0.07 15 46 31 22 72 1.2E-01 8.6E-02

1,1-DCE ND(0.082) ND(0.08) ND(<0.08) IND 9.2 16 13 4.8 38 < 6.5E-03 IND

TCE ND(0.082) ND(0.08) ND(<0.08) IND 11 24 18 9.2 53 < 4.7E-03 IND

c-1,2-DCE ND(0.081) ND(0.079) ND(<0.080) IND 3.8 6.6 5.2 2.0 38 < 1.6E-02 IND

1,1-DCA ND(0.082) ND(0.08) ND(<0.08) IND 3.5 9.7 6.6 4.4 66 < 1.2E-02 IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation < 4.7E-03 IND

Table 10c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House H Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

bsmt

24-hr

bsmt

mean

bsmt

stdev P[A]

grab

P[B]

grab

P[C]

grab

P[D]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=4 n=4 n=4

03/25/03 03/25/03 03/25/03 03/25/03 03/27/03 03/27/03 03/27/03 03/27/03 03/27/03 03/27/03 03/27/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 3.7 3.6 3.7 0.07 48 22 61 22 38 20 51 9.7E-02 4.9E-02

1,1-DCE ND(0.082) ND(0.08) ND(<0.08) IND 19 11 18 11 15 4.3 29 < 5.6E-03 IND

TCE ND(0.082) ND(0.08) ND(<0.08) IND 19 10 24 9.8 16 7.0 45 < 5.2E-03 IND

c-1,2-DCE ND(0.081) ND(0.079) ND(<0.08) IND 6.0 3.6 5.5 3.3 4.6 1.3 29 < 1.8E-02 IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation < 5.2E-03 IND
71

Figure 45. Basement/sub-slab concentration ratios using EPA Method TO-15 at House H during the March 2003 sample event. 

Error bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or 

sub-slab air.

House I

There were several visible cracks in the slab which 

varied in thickness between 1 to 2.5 millimeters. 

Basement walls consisted of poured concrete. 

Concentrations of all VOCs detected in basement 

and/or sub-slab air using EPA Method TO-15 are 

summarized in Table 11a. 1,1,1-TCA, 1,1-DCE, TCE, 

c-1,2-DCE, and 1,1-DCA were detected in basement 

air at concentrations of 2.8, 2.0, 1.1, 0.54, and 0.46 

ppbv, respectively. Other chlorinated compounds 

detected in basement air were methylene chloride, 

chloroform, and vinyl chloride at concentrations of 2.5, 

0.15, and 0.17 ppbv, respectively. Freons, F-11 and 

F-12, were detected in basement air at concentrations 

of 0.42 and 1.0 ppbv, respectively. Hydrocarbons, 

hexane, cyclohexane, benzene, toluene, ethylbenzene, 

m/p-xylenes, o-xylene, 1,2,4-trimethylbenzene, 

1,3,5-trimethylbenzene, and 4-ethyltoluene were 

detected at concentrations up to 3.3 ppbv. Acetone, 

tetrahydrofuran, methyl ethyl ketone, and methyl 

tertiary-butyl ether were detected at concentrations 

of 2.6, 1.1, 1.1, and 3.5 ppbv, respectively. 

Three sub-slab probes were installed at House I. Only 

one probe was sampled using EPA Method TO-15. 

All three probes were sampled using one-liter Tedlar 

bags. Using EPA Method TO-15, 1,1,1-TCA, 1,1-

DCE, TCE, c-1,2-DCE, and 1,1-DCA were detected 

at 320, 390, 200, 74, and 73 ppbv, respectively. Other 

chlorinated compounds detected in sub-slab air were 

perchloroethylene, methylene chloride, chloroform, 
72

Table 11a. Basement and Sub-Slab Air Concentrations for 

VOCs Detected at House I Using EPA Method TO-15 During 

the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]

grab

03/26/03 cov = 6% 03/28/03

(ppbv) (ppbv) (ppbv)

1,1,1-TCA 2.8 0.17 320

1,1-DCE 2.0 0.12 390

TCE 1.1 0.07 200

c-1,2-DCE 0.54 0.03 74

1,1-DCA 0.46 0.03 73

1,2-DCA ND(0.12) IND ND(0.17)

PCE ND(0.12) IND 0.87

CH2Cl2 2.5 0.15 0.19

CHCl3 0.15 0.01 0.970

CCl4 ND(0.12) IND ND(0.17)

CCl3F(F-11) 0.42 0.03 0.26

CCl2F2

(F-12) 1.0 0.06 0.54

CHBrCl2 ND(0.11) IND ND(0.16)

vinyl chloride 0.17 0.01 0.27

CH3CH2Cl 1.2 0.07 ND(1.8)

CCl3CF3

(F-113) ND(0.12) IND ND(0.17)

acetone 2.6 0.16 2.9

2-hexanone ND(0.11) IND 0.14

THF 1.1 0.07 ND(0.16)

MEK 1.1 0.07 0.52

MIBK ND(0.11) IND 0.21

MTBE 3.5 0.21 0.26

heptane ND(0.11) IND ND(0.16)

hexane 1.6 0.10 ND(0.17)

cyclohexane 0.87 0.05 ND(0.17) 

benzene 0.65 0.04 ND(0.17)

toluene 3.3 0.20 0.3

ethylbenzene 0.71 0.04 ND(0.17)

m/p-xylenes 2.1 0.13 ND(0.33)

o-xylene 0.79 0.05 ND(0.17)

styrene ND(0.11) IND ND(0.16)

1,2,4-TMB 0.65 0.04 ND(0.16)

1,3,5-TMB 0.19 0.01 ND(0.17)

1,3-butadiene ND(0.23) IND ND(0.33)

1,3-DCB ND(0.12) IND ND(0.17)

1,4-DCB ND(0.11) IND ND(0.16)

4-ethyltoluene 0.62 0.04 ND(0.17)

isopropyl

alcohol ND(0.21) IND ND(0.30)

ethyl/vinyl 

acetate 3.8 0.23 0.36

CS2 ND(0.11) IND ND(0.16)

ND( ) = Not detected above reporting limits IND = indeterminate

and vinyl chloride at concentrations of 0.87, 0.19, 0.97, 

and 0.27 ppbv, respectively. Freons, F-11 and F-12, were 

detected in sub-slab air at concentrations of 0.26 and 

0.54 ppbv, respectively. The only hydrocarbon detected 

in sub-slab air using EPA Method TO-15 was toluene at 

0.30 ppbv. Acetone, 2-hexanone, methyl ethyl ketone, 

methyl isobutyl ketone, and methyl tertiary-butyl ether 

were detected at concentrations of 2.9, 0.14, 0.52, 0.21, 

and 0.26 ppbv, respectively. As indicated by Table 11b, 

when sampling with one-liter Tedlar bags, 1,1,1-TCA, 1,1-

DCE, TCE, and c-1,2-DCE were detected at maximum 

concentrations in Probe [B] at 430, 320, 194, and 77 

pppv, respectively. Radon was sampled at only one 

probe with a concentration of 1295 pCi/l and detected 

in basement air at a mean concentration of 13.0 pCi/l. 

Figure 46 illustrates basement/sub-slab air concentration 

ratios for sub-slab samples collected in 1-liter Tedlar 

bags and analyzed on site. Since the null hypotheses 

that the basement/sub-slab air concentration ratios of 

1,1,1-TCA and TCE were equal to the basement/subslab air concentration ratios of 1,1-DCE and c-1,2-DCE 

could not be rejected using a one-tailed Approximate 

t-Test at a level of significance less than or equal to 0.05

(p > 0.1), it was inferred that the presence of 1,1,1-TCA, 

TCE, 1,1-DCE, and c-1,2-DCE in basement air was due 

to vapor intrusion at the time of sampling. 

Table 11b summarizes basement/sub-slab air 

concentration ratios determined using Tedlar bag 

sampling for VOCs associated with sub-surface 

contamination. Use of basement/sub-slab air 

concentration ratios for 1,1,1-TCA, 1,1-DCE, TCE, 

and c-1,2-DCE resulted in computation of an average 

basement/sub-slab air concentration ratio of 8.9E-03. 

Coefficients of variation in sub-slab air concentration 

ranged from 50 to 59%.
73

Table 11b. Summary of Basement/Sub-Slab Concentration Ratios of VOCs Associated with Sub-Surface Contamination in House I 

Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=3 n=3 n=3

03/26/03 cov = 6% 03/28/03 03/28/03 03/28/03 03/27/03 03/27/03 03/27/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 2.8 0.17 380 430 131 314 160 51 8.9E-03 4.6E-03

1,1-DCE 2.0 0.12 317 320 103 247 124 50 8.1E-03 4.1E-03

TCE 1.1 0.07 173 194 52 140 76.6 55 7.9E-03 4.3E-03

c-1,2-DCE 0.54 0.03 58 77 18 51 30 59 1.1E-02 6.3E-03

mean and standard deviation 8.9E-03 2.5E-03

Figure 46. Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site GC analysis at House I during the 

March 2003 sample event. Error bars represent one standard deviation.
74

House J

There were several visible cracks in the concrete slab 

in the basement of House J. Basement walls consisted 

of poured concrete but were covered with sheet rock. 

Concentrations of all VOCs detected in basement and/or 

sub-slab air using EPA Method TO-15 are summarized in 

Table 12a. 1,1,1-TCA, 1,1-DCE, and TCE were detected 

in basement air at concentrations of 0.44, 0.20, and 

0.18 ppbv, respectively. Other chlorinated compounds 

detected in basement air were perchloroethylene, 

methylene chloride, and chloroform at concentrations of 

0.10, 15, and 0.18 ppbv, respectively. Freons, F-11 and 

F-12, were detected in basement air at concentrations of 

1.4 and 0.48 ppbv, respectively. Hydrocarbons, heptane, 

hexane, cylcohexane, benzene, toluene, ethylbenzene, 

m/p-xylenes, o-xylene, 1,2,4-trimethylbenzene, 1,3,5-

trimethylbenzene, and 4-ethyltoluene were detected at 

concentrations up to 23 ppbv. Acetone, tetrahydrofuran, 

methyl ethyl ketone, and methyl tertiary-butyl ether were 

detected at concentrations of 4.2, 2.4, 0.86, and 12 

ppbv, respectively. The compound, 1,3 butadiene, was 

detected at 0.48 ppbv.

Four sub-slab probes were installed at House J. Only 

one probe was sampled using EPA Method TO-15 

(sampled twice). All four probes were sampled using 

one-liter Tedlar bags. Using EPA Method TO-15, 1,1,1-

TCA, 1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA were 

found at concentrations of 36, 26, 15, 4.6, 12 ppbv, 

respectively. Other chlorinated compounds detected 

in sub-slab air were perchloroethylene, methylene 

chloride, and chloroform at concentrations of 0.20, 1.1, 

and 1.3 ppbv, respectively. Freons, F-11, F-12, and F113, were detected in sub-slab air at concentrations of 

0.36, 0.55, and 0.08 ppbv, respectively. Hydrocarbons, 

hexane, benzene, toluene, ethylbenzene, m/p-xylenes, 

Table 12a. Basement and Sub-Slab Air Concentrations of 

VOCs at House J Using EPA Method TO-15 During the March 

2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]

grab

P[A]

grab

P[A]

mean

n=2

03/24/03 cov = 6% 03/26/03 03/26/03 03/26/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv)

1,1,1-TCA 0.44 0.03 33 36 35

1,1-DCE 0.20 0.01 26 24 25

TCE 0.18 0.01 14 15 15

c-1,2-DCE ND(0.14) IND 4.2 4.6 4.4

1,1-DCA ND(0.14) IND 12 9.7 11

1,2-DCA ND(0.14) IND ND(0.11) ND(0.11) ND(0.11)

PCE 0.10 0.01 0.20 0.19 0.20

CH2Cl2 15 0.90 0.92 1.1 1.0

CHCl3 0.18 0.01 1.2 1.3 1.3

CCl4 ND(0.14) IND ND(0.12) ND(0.12) ND(0.12)

CCl3F(F-11) 1.4 0.08 0.33 0.36 0.35

CCl2F2

(F-12) 0.48 0.03 0.52 0.55 0.54

CHBrCl2 ND(0.13) IND ND(0.11) ND(0.11) ND(0.11)

vinyl chloride ND(0.14) IND ND(0.12) ND(0.12) ND(0.12)

CH3CH2Cl ND(1.5) IND ND(1.2) ND(1.2) ND(1.2)

CCl3CF3

(F-113) ND(0.14) IND ND(0.11) 0.08 < 0.10

acetone 4.2 0.25 2.4 2.8 2.6

2-hexanone ND(0.13) IND ND(0.11) ND(0.11) ND(0.11)

THF 2.4 0.14 0.30 ND(0.11) < 0.21

MEK 0.86 0.05 0.63 0.85 0.74

MIBK ND(0.13) IND 0.21 0.17 0.19

MTBE 12 0.72 0.54 0.50 0.52

heptane 3.7 0.22 ND(0.11) ND(0.11) ND(0.11)

hexane 6.4 0.38 0.58 0.64 0.61

cyclohexane 1.8 0.11 ND(0.11) ND(0.11) ND(0.11) 

benzene 3.9 0.23 0.52 0.48 0.50

toluene 23 1.38 1.9 1.6 1.8

ethylbenzene 2.5 0.15 0.19 0.16 0.18

m/p-xylenes 8.6 0.52 0.58 0.47 0.53

o-xylene 2.7 0.16 0.22 0.18 0.20

styrene ND(0.13) IND ND(0.11) ND(0.11) ND(0.11)

1,2,4-TMB 1.7 0.10 0.18 0.16 0.17

1,3,5-TMB 0.45 0.03 ND(0.11) ND(0.11) ND(0.11)

1,3-

butadiene 0.48 0.03 ND(0.22) ND(0.23) ND(0.23)

1,3-DCB ND(0.14) IND ND(0.11) ND(0.11) ND(0.11)

1,4-DCB ND(0.14) IND ND(0.11) ND(0.11) ND(0.11)

4-ethyltoluene 2.0 0.12 ND(0.11) 0.17 < 0.14

isopropyl

alcohol 0.63 0.04 ND(0.21) ND(0.21) ND(0.21)

ethyl/vinyl 

acetate 3.9 0.23 0.38 0.47 0.43

CS2 ND(0.13) IND 0.13 0.13 0.13

ND = Not detected (reporting limit)

o-xylene, 1,2,4-trimethylbenzene, and 4-ethyltoluene 

were detected at concentrations up to 1.6 ppbv. Acetone, 

tetrahydrofuran, methyl ethyl ketone, methyl isobutyl 

ketone, and methyl tertiary-butyl ether were detected at 

concentrations of 2.8, 0.30, 0.85, 0.21, and 0.54 ppbv, 

respectively.
75

As indicated in Table 12b, when sampling with oneliter Tedlar bags, 1,1,1-TCA, 1,1-DCE, TCE, and c1,2-DCE were found at maximum concentrations in 

Probe [A] at 43, 26, 14, and 3.0 ppbv, respectively. 

Radon was sampled at two probes with concentrations 

Table 12b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House J Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

P[D]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=4 n=4 n=4

03/24/03 cov=6% 03/26/03 03/26/03 03/26/03 03/26/03 03/26/03 03/26/03 03/26/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.44 0.03 43 8.5 17 8.5 19 16 85 2.3E-02 1.9E-02

1,1-DCE 0.20 0.01 26 5.2 9.2 5.2 11 9.9 87 1.8E-02 1.5E-02

TCE 0.18 0.01 14 2.6 4.6 2.4 5.9 5.5 93 3.1E-02 2.8E-02

c-1,2-DCE ND(0.14) IND 3.0 ND(3.0) ND(3.0) ND(3.0) <3.0 IND IND IND IND

ND = Not detected (reporting limit), IND = indeterminate mean and standard deviation 2.4E-02 1.3E-02

Table 12c. Basement/Sub-Slab Air Concentration Ratios for Radon in House J Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/21-3/24/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt

48-hr

bsmt

48-hr

bsmt

mean

bsmt

stdev

bsmt

cov P[A]

110A

P[B]

110A

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

n=2 n=2 n=2 stdev n=2 n=2 n=2

03/26/03 03/26/03 03/26/03 03/26/03 03/26/03

(pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

2.90 3.00 3.0 0.07 2.4 1029 1253 1141 158.4 13.88 2.59E-03 3.64E-04

of 1029 and 1253 pCi/l and detected in basement air 

at a mean concentration of 3.0 pCi/l. Results and 

statistical analysis of sub-slab sampling for radon are 

summarized in Table 12c.

Figure 47 illustrates basement/sub-slab air 

concentration ratios for radon and sub-slab samples 

collected in one-liter Tedlar bags and analyzed on site. 

Sub-slab air samples for VOCs from one-liter Tedlar 

bags were used for statistical testing because only 

one probe was sampled using EPA Method TO-15. 

At House J, the basement/sub-slab air concentration 

ratios for both radon and the indicator VOC, 1,1-

DCE, were available. The null hypothesis that the 

basement/sub-slab air concentration ratio of radon 

was equal to the basement/sub-slab air concentration 

ratio of 1,1-DCE could be rejected using a two-tailed 

Approximate t-Test at a level of significance of 0.1. 

The null hypotheses that the basement/sub-slab air 

concentration ratios for 1,1,1-TCE and TCE were equal 

to the basement/sub-slab air concentration ratio of 

1,1-DCE using a one-tailed Approximate t-Test could 

not be rejected at a level of significance less than or 

equal to 0.05 (p > 0.1). The null hypotheses that the 

basement/sub-slab air concentration ratios of 1,1,1-

TCA and TCE were equal to the basement/sub-slab 

air concentration ratio of radon could be rejected using 

a one-tailed Approximate t-Test at a significance level 

of 0.1 but not at a significance level of 0.05. Since 

the rejection criteria for the null hypothesis is a level 

of significance less than or equal to 0.05, use of 

both radon and the indicator VOC, 1,1-DCE, led to 

a consistent finding that the presence of 1,1,1-TCA, 
76

1,1-DCE, and TCE in basement air was due to vapor 

intrusion at the time of sampling. However, visually 

and statistically, there was more consistency in the 

use of 1,1-DCE as an indicator compound compared 

to radon.

Table 12b summarizes basement/sub-slab air 

concentration ratios determined using one-liter 

Tedlar bag sampling for VOCs associated with subsurface contamination. Use of basement/sub-slab 

concentration values for 1,1,1-TCA, 1,1-DCE, and TCE 

Figure 47. Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site GC analysis at House J during the 

March 2003 sample event. Error bars represent one standard deviation.

resulted in computation of an average basement/subslab ratio of 2.4E-02. The overall basement/sub-slab 

air concentration ratio for House J appears high relative 

to other testing locations. However, the basement/

sub-slab concentration ratio for 1,1-DCE, a VOC only 

associated with sub-surface contamination, was 1.8E02. Also, throughout this investigation, when TCE was 

detected in basement air, it was always associated 

with sub-surface contamination. At House J, TCE 

had a basement/sub-slab air concentration ratio of 

3.1E-02 which was similar to 1,1-DCE. 
77

Table 13a. Basement Air Concentrations for VOCs

at House K Using EPA Method TO-15 During the

March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

03/24/03 cov = 6%

(ppbv) (ppbv)

1,1,1-TCA 1.1 0.07

1,1-DCE 1.3 0.08

TCE 0.54 0.03

c-1,2-DCE 0.23 0.01

1,1-DCA 0.31 0.02

1,2-DCA ND(0.15) IND

PCE 0.10 0.01

CH2Cl2 3.3 0.20

CHCl3 ND(0.15) IND

CCl4 ND(0.15) IND

CCl3F(F-11) 0.38 0.02

CCl2F2(F-12) 0.54 0.03

CHBrCl2 ND(0.14) IND

vinyl chloride ND(0.15) IND

CH3CH2Cl ND(1.6) IND

CCl3CF3(F-113) ND(0.15) IND

acetone 3.3 0.20

2-hexanone ND(0.14) IND

THF 1.6 0.10

MEK 2.1 0.13

MIBK ND(0.13) IND

MTBE 0.52 0.03

heptane 0.40 0.02

hexane 0.38 0.02

cyclohexane ND(0.15) IND

benzene 0.32 0.02

toluene 3.0 0.18

ethylbenzene 1.4 0.08

m/p-xylenes 3.6 0.22

o-xylene 0.65 0.04

styrene ND(0.14) IND

1,2,4-TMB 1.6 0.10

1,3,5-TMB 0.51 0.03

1,3-butadiene ND(0.29) IND

1,3-DCB ND(0.15) IND

1,4-DCB 0.19 0.01

4-ethyltoluene 1.3 0.08

isopropyl alcohol 0.39 0.02

ethyl/vinyl acetate 6.2 0.37

CS2 ND(0.14) IND

ND( ) = Not detected (reporting limit)

IND = indeterminate

House K

There were several visible cracks and holes in the 

concrete slab in the basement of House K. The slab 

was less than 2.5 centimeters thick. Basement walls 

consisted of poured concrete. Concentrations of all 

VOCs detected in basement and/or sub-slab air using 

EPA Method TO-15 are summarized in Table 13a. All 

VOCs associated with sub-surface contamination were 

detected in basement air. 1,1,1-TCA, 1,1-DCE, TCE, c1,2-DCE, and 1,1-DCA were detected in basement air 

at concentrations of 1.1, 1.3, 0.54, 0.23, and 0.31 ppbv, 

respectively. Other chlorinated compounds detected 

in basement air were perchloroethylene, methylene 

chloride, and 1,4-dichlorobenzene at concentrations of 

0.10, 3.3, and 0.19 ppbv, respectively. Freons, F-11 and 

F-12, were detected in basement air at concentrations 

of 0.38 and 0.54 ppbv, respectively. Hydrocarbons, 

heptane, hexane, benzene, toluene, ethylbenzene, 

m/p-xylenes, o-xylene, 1,2,4-trimethylbenzene, 

1,3,5-trimethylbenzene, and 4-ethyltoluene were 

detected at concentrations up to 3.6 ppbv. Acetone, 

tetrahydrofuran, methyl ethyl ketone, and methyl 

tertiary-butyl ether were detected at concentrations 

of 3.3, 1.6, 2.1, and 0.52 ppbv, respectively. 

Three sub-slab probes were installed at House K. Subslab air was not sampled using EPA Method TO-15. All 

three probes were sampled using one-liter Tedlar bags. 

As indicated in Table 13b, maximum concentrations 

of 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE were 

found at Probe B at 947, 933, 440, and 190 ppbv, 

respectively. Radon was sampled at two probes with 

concentrations of 142 and 1144 pCi/L and detected 

in basement air at a mean concentration of 3.2 pCi/L. 

Results and statistical analysis of sub-slab sampling 

for radon are summarized in Table 13c.
78

Table 13b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House K Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=3 n=3 n=3

03/24/03 cov=6% 03/26/03 03/26/03 03/26/03 03/26/03 03/26/03 03/26/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 1.1 0.07 530 947 500 659 250 38 1.7E-03 6.4E-04

1,1-DCE 1.3 0.08 513 933 513 653 242 37 2.0E-03 7.5E-04

TCE 0.54 0.03 209 440 210 286 133 46 1.9E-03 8.8E-04

c-1,2-DCE 0.23 0.01 82 190 84 119 62 52 1.9E-03 1.0E-03

ND = Not detected (reporting limit), IND = indeterminate mean and standard deviation 1.9E-03 4.2E-04

Table 13c. Basement/Sub-Slab Air Concentration Ratios for Radon in House K Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/21-3/24/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt

48-hr

bsmt

48-hr

bsmt

mean

bsmt

stdev

bsmt

cov P[A]

110A

P[B]

110A

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2 n=2 n=2 n=2

03/24/03 03/24/03 03/24/03 03/26/03 03/26/03 03/26/03 03/26/03 03/26/03

(pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

3.0 3.4 3.2 0.28 8.8 142 1144 643 709 110 4.98E-03 5.50E-03

Figure 48 illustrates basement/sub-slab air 

concentration ratios for radon and VOCs collected 

in one-liter Tedlar bags and analyzed on site. The 

null hypotheses that the basement/sub-slab air 

concentration ratio of radon was equal to the basement/

sub-slab concentration ratios of indicator VOCs, 1,1-

DCE and c-1,2-DCE, could not be rejected using a 

two-tailed Approximate t-Test at a level of significance 

less than 0.1. This finding was in part due to the large 

standard deviation associated with the basement/

sub-slab air concentration ratio of radon (standard 

deviation larger than mean). The null hypotheses 

that the basement/sub-slab air concentration ratios 

of 1,1,1-TCA and TCE were equal to the basement/

sub-slab air concentration ratios of indicator VOCs, 

1,1-DCE and c-1,2-DCE, could not be rejected using a 

one-tailed Approximate t-test at a level of significance 

less than or equal to 0.05 (p > 0.1) inferring that the 

presence of 1,1,1-TCA, TCE, 1,1-DCE, c-1,2-DCE, 

and 1,1-DCA (indicator VOC) in basement air was 

all due to vapor intrusion at the time of sampling. 

The null hypotheses that the basement/sub-slab air 

concentration ratios of 1,1,1-TCA and TCE were equal 

to the basement/sub-slab concentration ratio of radon 

could not be rejected using a one-tailed Approximate 

t-Test at a level of significance less than or equal to 

0.05 (p > 0.1). This provided a consistent finding with 

indicator VOCs that the presence of 1,1,1-TCA and 

TCE in basement air was due to vapor intrusion at 

the time of sampling.

Table 13b summarizes basement/sub-slab air 

concentration ratios determined using Tedlar 

bag sampling for VOCs associated with subsurface contamination. Use of basement/sub-slab 

concentration values for 1,1,1-TCA, 1,1-DCE, TCE , 

and 1,2-DCE resulted in computation of an average 

basement/sub-slab ratio of 1.9E-03. Coefficients of 

variation in sub-slab air concentration ranged from 

38 to 52%.
79

Figure 48. Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site GC analysis at House K during the 

March 2003 sample event. Error bars represent one standard deviation.

House L

Basement walls at House L consisted of poured 

concrete. The basement was partitioned into finished 

and unfinished areas. Concentrations of all VOCs 

detected in basement and/or sub-slab air using EPA 

Method TO-15 are summarized in Table 14a. VOCs 

associated with sub-surface contamination, 1,1,1-TCA, 

1,1-DCE, and TCE, were detected in basement air at 

concentrations of 0.27, 0.24, and 0.20 ppbv, respectively. 

The only other chlorinated VOC detected in basement air 

was methylene chloride at a concentration of 1.1 ppbv. 

Freons, F-11, and F-12, were detected in basement air 

at concentrations of 0.28 and 0.67 ppbv, respectively. 

Hydrocarbons, heptane, hexane, benzene, toluene, 

ethylbenzene, m/p-xylenes, and o-xylene were detected in 

basement air at concentrations up to 2.0 ppbv. Acetone, 

tetrahydrofuran, methyl ethyl ketone, methyl isobutyl 

ketone, and methyl tertiary-butyl ether were detected in 

basement air at concentrations of 1.9, 0.38, 1.7, 0.82, 

and 0.23 ppbv, respectively. 

Three sub-slab vapor probes were installed at House L. 

Sub-slab air was sampled at only one probe using EPA 

Method TO-15. All probes were sampled using one-liter 

Tedlar bags. Using EPA Method TO-15, 1,1,1-TCA, 

1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA were detected 

in sub-slab air at concentrations of 170, 140, 120, 48, 

and 43 ppbv, respectively. Other chlorinated VOCs 

detected in sub-slab air using EPA Method TO-15 were 

perchloroethylene and chloroform detected at 0.44 and 1.1 

ppbv, respectively. Freons, F-11 and F-12, were detected 

at 0.26 and 0.53 ppbv, respectively. Hydrocarbons, 

hexane and toluene were detected at concentrations of 

0.19 and 0.37 ppbv, respectively. Acetone, methyl ethyl 

ketone, methyl isobutyl ketone, and methyl tertiary-butyl 

ether were detected at concentrations of 2.8, 0.81, 0.28, 

and 0.17 ppbv, respectively. 
80

Table 14a. Basement and Sub-Slab Air Concentrations for 

VOCs at House L Using EPA Method TO-15 During the March 

2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[B]

grab

03/26/03 cov = 6% 04/01/03

(ppbv) (ppbv) (ppbv)

1,1,1-TCA 0.27 0.02 170

1,1-DCE 0.24 0.01 140

TCE 0.20 0.01 120

c-1,2-DCE ND(0.10) IND 48

1,1-DCA ND(0.10) IND 43

1,2-DCA ND(0.10) IND ND(0.17)

PCE ND(0.10) IND 0.44

CH2Cl2 1.1 0.07 ND(0.18)

CHCl3 ND(0.10) IND 1.1

CCl4 ND(0.10) IND ND(0.18)

CCl3F(F-11) 0.28 0.02 0.26

CCl2F2

(F-12) 0.67 0.04 0.53

CHBrCl2 ND(0.096) IND ND(0.17)

vinyl chloride ND(0.11) IND ND(0.17)

CH3CH2Cl ND(1.1) IND ND(1.9)

CCl3CF3

(F-113) ND(0.10) IND ND(0.18)

acetone 1.9 0.11 2.8

2-hexanone ND(0.098) IND ND(0.17)

THF 0.38 0.02 ND(0.17)

MEK 1.7 0.10 0.81

MIBK 0.82 0.05 0.28

MTBE 0.23 0.01 0.17

heptane 0.75 0.05 ND(0.17)

hexane 0.23 0.01 0.19

cyclohexane ND(0.10) IND ND(0.18) 

benzene 0.28 0.02 ND(0.18)

toluene 2.0 0.12 0.37

ethylbenzene 0.19 0.01 ND(0.18)

m/p-xylenes 0.57 0.03 ND(0.35)

o-xylene 0.15 0.01 ND(0.18)

styrene ND(0.096) IND ND(0.17)

1,2,4-TMB ND(0.10) IND ND(0.17)

1,3,5-TMB ND(0.10) IND ND(0.18)

1,3-butadiene ND(0.20) IND ND(0.35)

1,3-DCB ND(0.10) IND ND(0.18)

1,4-DCB ND(0.10) IND ND(0.17)

4-ethyltoluene ND(0.10) IND ND(0.18)

isopropyl

alcohol 0.30 0.02 0.84

ethyl/vinyl 

acetate 12 0.72 ND(0.32)

CS2 ND(0.098) IND ND(0.17)

ND( ) = Not detected (reporting limit) IND = indeterminate

As indicated in Table 14b, Probe A was sampled 

sequentially five times using one-liter Tedlar bags to 

assess the impact of extraction volume on sample 

results. These results were previously discussed. As 

indicated in Table 14c, when sampling with one-liter 

Tedlar bags, 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE 

were found in sub-slab air at maximum concentrations 

of 210, 141, 123, and 43 ppbv, respectively. Radon 

was sampled at three probes with concentrations of 

695, 567, and 387 pCi/L and detected in basement 

air at a mean concentration of 2.6 pCi/L. Results and 

statistical analysis of sub-slab sampling for radon are 

summarized in Tables 14d and 14e.

Figure 49 illustrates basement/sub-slab air 

concentration ratios for radon and VOCs collected 

in one-liter Tedlar bags and analyzed on site. 

The null hypothesis that the basement/sub-slab 

air concentration ratio of radon was equal to the 

basement/sub-slab air concentration ratio of the 

indicator VOC, 1,1-DCE, could be rejected using a 

two-tailed Approximate t-Test at a significance level 

less than or equal to 0.1. The null hypotheses that 

the basement/sub-slab air concentration ratios of 

1,1,1-TCA and TCE were equal to the basement/

sub-slab concentration ratio of 1,1-DCE could not be 

rejected using a one-tailed Approximate t-Test at a 

significance level less than or equal to 0.05 (p > 0.1). 

This inferred that the presence of 1,1,1-TCA, TCE, and 

1,1-DCE in basement air was due to vapor intrusion 

at the time of sampling. Since the basement/sub-slab 

air concentration ratio for radon was greater than 

basement/sub-slab air concentration ratios for 1,1,1-

TCA and TCE, use of radon as an indicator compound 

also inferred that detection of 1,1,1-TCA and TCE in 

basement air were due to vapor intrusion at the time 

of sampling. As visually illustrated in Figure 49, there 

was greater consistency in basement/sub-slab air 
81

concentration ratios of VOCs associated with vapor 

intrusion than between VOCs associated with vapor 

intrusion and radon.

Table 14c summarizes basement/sub-slab air 

concentration ratios determined using Tedlar bag 

Table 14b. Results of Sequential Sub-Slab Air Sampling Using 1-Liter Tedlar Bags and On-Site GC Analysis at House L During the 

March 2003 Sample Event

VOC P[A]-01

grab

P[A]-02

grab

P[A]-03

grab

P[A]-04

grab

P[A]-05

grab

P[A]

mean

P[A]

stdev

P[A]

cov

n=5 n=5 n=5

04/01/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%)

1,1,1-TCA 210 210 204 207 207 207.6 2.51 1.21

1,1-DCE 145 138 138 141 141 140.6 2.88 2.05

TCE 122 122 123 124 124 123 1.00 0.81

c-1,2-DCE 44 43 43 43 44 43.4 0.55 1.26

Table 14e. Basement/Sub-Slab Air Concentration Ratios for Radon in House L Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/26-3/28/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt 48-hr

mean

bsmt

stdev

bsmt

cov P[A]

110A

P[B]

110A

P[C]

110A

sub-slab

grab mean

sub-slab

grab stdev

sub-slab

grab cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=4 n=4 n=3 n=3 n=3 03/29/03 03/29/03 04/01/03 04/01/03 04/01/03

(pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

2.6 0.78 30.3 695 567 387 550 155 28.1 4.68E-03 1.94E-03

Table 14d. Summary of 48-Hour Indoor Air Measurements for Radon Using Activated Charcoal at House L

Location Start Date End Date Conc.

(pCi/L)

1st floor 03/26/03 03/28/03 1.1

1st floor 03/26/03 03/28/03 0.9

bsmt 03/26/03 03/28/03 3.2

bsmt 03/26/03 03/28/03 3.3

bsmt-bar 03/26/03 03/29/03 1.9

bsmt-bar 03/26/03 03/29/03 1.9

Table 14c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House L Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A] mean

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=3 n=3 n=3

03/28/03 cov=6% 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.27 0.02 208 210 184 201 14 7.2 1.3E-03 1.3E-04

1,1-DCE 0.24 0.01 141 131 100 124 21 17 1.9E-03 3.5E-04

TCE 0.20 0.01 123 109 104 112 10 8.8 1.8E-03 1.9E-04

c-1,2-DCE ND(0.10) IND 43 38 31 37 6 17 < 2.7E-03 IND

ND = Not detected(reporting limit) IND = indeterminate mean and standard deviation 1.7E-03 1.4E-04

sampling for VOCs associated with sub-surface 

contamination. Use of basement/sub-slab air 

concentration ratios for 1,1,1-TCA, 1,1-DCE, and TCE 

resulted in computation of an average basement/subslab ratio of 1.7E-03. 
82

Figure 49. Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site GC analysis at House L during the 

March 2003 sample event. Error bars represent one standard deviation. Arrows indicate less than values due to non-detection in 

basement air.

House M

Basement walls at House M consisted of field stone 

and were covered with sheet rock and wood framing. 

Concentrations of all VOCs detected in basement 

and/or sub-slab air using EPA Method TO-15 are 

summarized in Table 15a. 1,1,1-TCA and 1,1-DCE 

were detected in basement air at concentrations of 

0.14 and 0.12 ppbv, respectively. The only other 

chlorinated compound detected in basement air was 

methylene chloride at a concentration of 0.20 ppbv. 

Freons, F-11 and F-12, were detected in basement air 

at concentrations of 0.27 and 0.47 ppbv, respectively. 

Hydrocarbons, heptane, hexane, benzene, toluene, 

m/p-xylenes, o-xylene, 1,2,4-trimethylbenzene, 1,3,5-

trimethylbenzene, and 4-ethyltoluene were detected 

at concentrations up to 0.66 ppbv. Acetone, methyl 

ethyl ketone, and methyl tertiary-butyl ether were 

detected at concentrations of 2.2, 0.30, and 0.44 

ppbv, respectively. 

Three sub-slab vapor probes were installed at House 

M. Sub-slab air was sampled at only one probe using 

EPA Method TO-15. This probe was sampled twice. 

All three probes were sampled using one-liter Tedlar 

bags. Using EPA Method TO-15, 1,1,1-TCA, 1,1-DCE, 

TCE, c-1,2-DCE, and 1,1-DCA were detected at 6.4, 

4.3, 5.2, 1.2, and 2.2 ppbv, respectively. The only 

other chlorinated compounds detected in sub-slab 

air were methylene chloride and 1,4-dichlorobenzene 

at concentrations of 2.9 and 1.2 ppbv, respectively. 

Freons, F-11 and F-12, were detected in sub-slab air 

at concentrations of 0.29 and 0.54 ppbv, respectively. 

Hydrocarbons, hexane, benzene, toluene, m/pxylenes, o-xylene, 1,2,4-trimethylbenzene, 1,3,5-

trimethylbenzene, and 4-ethyltoluene were detected at 
83

Table 15a. Basement and Sub-Slab Air Concentrations for 

VOCs at House M Using EPA Method TO-15 During the March 

2003 Sample Event

VOC bsmt

24-hr

scaled

stdev

P[A]-01

grab

P[A]-02

grab

P[A]

mean

n=2

03/24/03 cov = 6% 03/27/03 03/27/03 03/27/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv)

1,1,1-TCA 0.14 0.01 6.4 2.8 4.6

1,1-DCE 0.12 0.01 4.3 1.7 3.0

TCE ND(0.12) IND 5.2 3.6 4.4

c-1,2-DCE ND(0.12) IND 1.2 0.88 1.0

1,1-DCA ND(0.12) IND 2.2 1.0 1.6

1,2-DCA ND(0.12) IND ND(0.24) ND(0.21) ND(< 0.23)

PCE ND(0.12) IND ND(0.24) ND(0.21) ND(< 0.23)

CH2Cl2 0.20 0.01 2.9 1.30 2.1

CHCl3 ND(0.12) IND ND(0.24) ND(0.21) ND(< 0.23)

CCl4 ND(0.12) IND ND(0.24) ND(0.21) ND(< 0.23)

CCl3F(F-11) 0.27 0.02 0.30 0.28 0.29

CCl2F2

(F-12) 0.47 0.03 0.54 0.53 0.54

CHBrCl2 ND(0.11) IND ND(0.22) ND(0.20) ND(< 0.21)

vinyl chloride ND(0.13) IND ND(0.25) ND(0.22) ND(< 0.24)

CH3CH2Cl ND(1.3) IND ND(2.5) ND(2.2) ND(< 2.4)

CCl3CF3

(F-113) ND(0.12) IND ND(0.24) ND(0.21) ND(< 0.23)

acetone 2.2 0.13 6.20 5.10 5.65

2-hexanone ND(0.12) IND 0.28 0.28 0.28

THF ND(0.12) IND 0.30 ND(0.21) < 0.23

MEK 0.30 0.02 1.7 1.6 1.65

MIBK ND(0.11) IND 0.36 0.27 0.315

MTBE 0.44 0.03 0.36 0.33 0.345

heptane 0.19 0.01 ND(0.23) ND(0.21) ND(< 0.22)

hexane 0.33 0.02 0.58 0.53 0.555

cyclohexane ND(0.12) IND ND(0.24) ND(0.21) ND(< 0.23)

benzene 0.32 0.02 0.28 0.27 0.275

toluene 0.66 0.04 1.20 0.93 1.065

ethylbenzene ND(0.12) IND ND(0.24) ND(0.21) ND(< 0.23)

m/p-xylenes 0.35 0.02 0.66 0.92 0.79

o-xylene 0.15 0.01 0.27 0.28 0.275

styrene ND(0.11) IND ND(0.22) ND(0.20) ND(< 0.21)

1,2,4-TMB 0.42 0.03 0.53 0.64 0.585

1,3,5-TMB 0.15 0.01 ND(0.24) 0.22 < 0.23

1,3-

butadiene ND(0.24) IND ND(0.47) ND(0.42) ND(< 0.45)

1,3-DCB ND(0.12) IND 0.83 ND(0.21) < 0.52

1,4-DCB ND(0.12) IND ND(0.23) 1.2 < 0.72

4-ethyltoluene 0.29 0.02 0.73 0.76 0.75

isopropyl

alcohol ND(0.22) IND 0.64 0.54 0.59

ethyl/vinyl 

acetate 1.5 0.09 2.2 1.7 2.0

CS2 ND(0.12) IND ND(0.23) ND(0.20) ND(< 0.22)

ND = Not detected (reporting limit) IND = indeterminate

concentrations up to 1.2 ppbv. Acetone, 2-hexanone, 

tetrahydrofuran, methyl ethyl ketone, methyl isobutyl 

ketone, and methyl tertiary-butyl ether were detected 

at concentrations of 6.2, 0.28, 0.30, 1.7, and 0.36 

ppbv, respectively. 

As indicated in Table 15b, Probe B was sampled 

sequentially five times using one-liter Tedlar bags to 

assess the impact of extraction volume on sample 

results. These results were previously discussed. As 

indicated in Table 15c, when sampling with one-liter 

Tedlar bags, maximum concentrations of 1,1,1-TCA, 

1,1-DCE, TCE, and c-1,2-DCE were detected in 

Probe B at 542, 480, 189, and 46 ppbv, respectively. 

Radon was sampled at two probes with concentrations 

of 732 and 766 pCi/L and detected in basement air 

at a mean concentration of 2.4 pCi/L. Results and 

statistical analysis of sub-slab sampling for radon are 

summarized in Table 15d. 

Figure 50 illustrates basement/sub-slab air 

concentration ratios for radon and VOCs collected 

in one-liter Tedlar bags and analyzed on site. The 

null hypothesis that the basement/sub-slab air 

concentration ratio of radon was equal to the basement/

sub-slab air concentration ratio of the indicator 

VOC, 1,1-DCE, could be rejected using a two-tailed 

Approximate t-Test at a significance level less than 

or equal to 0.1 (p < 0.025). The null hypothesis that 

the basement/sub-slab air concentration ratio of 

1,1,1-TCA was equal to the basement/sub-slab air 

concentration ratio of 1,1-DCE could not be rejected 

using a one-tailed Approximate t-Test at a significance 

level less than or equal to 0.05 (p > 0.1) inferring that 

the presence of 1,1,1-TCA and 1,1-DCE in basement 

air was due to vapor intrusion at the time of sampling. 

Since the basement/sub-slab air concentration ratio 

of radon was greater than the basement/sub-slab air 

concentration ratio of 1,1,1-TCA, use of radon as an 

indicator compound also inferred that detection of 

1,1,1-TCA in basement air was due to vapor intrusion 

at the time of sampling.
84

Table 15c summarizes basement/sub-slab air 

concentration ratios determined using Tedlar bag 

sampling for VOCs associated with sub-surface 

contamination. Use of basement/sub-slab air 

concentration ratios for 1,1,1-TCA and 1,1-DCE 

resulted in computation of an overall basement/subslab ratio of 6.3E-03. 

Table 15d. Basement/Sub-Slab Air Concentration Ratios of Radon in House M Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/22-3/24/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt

48-hr

bsmt

48-hr

bsmt

mean

bsmt

stdev bsmt

cov

P[A]

pylon

P[C]

pylon

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

n=2 n=2 stdev n=2 n=2 n=2

03/27/03 03/27/03 03/27/03 03/27/03 03/27/03

(pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

2.4 2.4 2.4 0.00 0.0 732 766 749 12.0 1.60 3.20E-03 5.14E-05

Table 15b. Results of Sequential Sub-Slab Air Sampling Using 1-Liter Tedlar Bags and On-Site GC Analysis at House M During 

the March 2003 Sample Event

VOC P[B]-01

grab

P[B]-02

grab

P[B]-03

grab

P[B]-04

grab

P[B]-05

grab

P[B]

mean

P[B]

stdev

P[B]

cov

n=5 n=5 n=5

03/27/03 03/27/03 03/27/03 03/27/03 03/27/03 04/01/03 04/01/03 04/01/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%)

1,1,1-TCA 548 541 533 540 550 542 6.80 1.25

1,1-DCE 483 484 475 480 478 480 3.67 0.77

TCE 183 189 190 190 192 189 3.42 1.81

c-1,2-DCE 44 46 46 46 46 46 0.89 1.96

Table 15c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House M Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev P[A]

grab

P[B] mean

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev cov = 6% n=3 n=3 n=3

03/24/03 03/27/03 03/27/03 03/27/03 03/27/03 03/27/03 03/27/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.14 0.01 52 542 76 223 276 124 6.3E-04 7.8E-04

1,1-DCE 0.12 0.01 31 480 64 192 250 131 6.3E-04 8.2E-04

TCE ND(0.12) IND 31 189 17 79 95 121 < 1.5E-03 IND

c-1,2-DCE ND(0.12) IND 9.5 46 1.4 19 24 125 < 6.4E-03 IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation 6.3E-04 5.6E-04
85

Figure 50. Basement/sub-slab concentration ratios using one-liter Tedlar bags and on-site GC analysis at House M during the 

March 2003 sample event. Error bars represent one standard deviation. Arrows indicate less than values due to non-detection in 

basement air.

House N

Basement walls at House N consisted of poured 

concrete. The basement was equipped with a sub-slab 

depressurization system which had not been operated 

for over 3 years. Concentrations of VOCs detected 

in basement and/or sub-slab air using EPA Method 

TO-15 are summarized in Table 16a. The only VOC 

associated with subsurface contamination detected in 

basement air was 1,1,1-TCA at a concentration of 0.10 

ppbv. The detection limits of other VOCs associated 

with subsurface contamination ranged from 0.092 to 

0.094 ppbv. Other chlorinated compounds detected 

in basement air were perchloroethylene, methylene 

chloride, and chloroform at concentrations of 0.11, 

0.54, and 0.11 ppbv, respectively. Freons, F-11 and 

F-12, were detected in basement air at concentrations 

of 0.28 and 0.45 ppbv, respectively. Hydrocarbons, 

hexane, cyclohexane, benzene, toluene, m/pxylenes, o-xylene, and 1,3,5-trimethylbenzene were 

detected at concentrations up to 4.1 ppbv. Acetone, 

tetrahydrofuran, methyl ethyl ketone, and methyl 

tertiary-butyl ether were detected at concentrations 

of 3.3, 0.67, 1.1, and 0.56 ppbv, respectively. 

Three sub-slab probes were installed at House N. 

Two probes were sampled using EPA Method TO-15. 

All three probes were sampled using one-liter Tedlar 

bags. As indicated in Table 16b, using EPA Method 

TO-15, 1,1,1-TCA, 1,1-DCE, TCE, c-1,2-DCE, and 

1,1-DCA were found at maximum concentrations in 

Probe B at 32, 42, 12, 9.9, and 20 ppbv, respectively. 

Other chlorinated compounds detected in sub-slab 

air were perchloroethylene, methylene chloride, and 
86

Table 16a. Basement and Sub-Slab Air Concentrations for VOCs at House N Using EPA Method TO-15

During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

cov=6% n=2 n=2 n=2 stdev

03/28/03 03/28/03 03/28/03 03/28/03 03/28/03 03/28/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.10 0.01 32 9.7 21 16 76 4.8E-03 3.6E-03

1,1-DCE ND(0.094) IND 42 5.3 24 26 110 < 4.0E-03 IND

TCE ND(0.094) IND 12 2.5 7.3 6.7 93 < 1.3E-02 IND

c-1,2-DCE ND(0.092) IND 9.9 ND(1.0) < 5.5 IND IND IND IND

1,1-DCA ND(0.094) IND 20 6.9 13.5 9.3 69 < 7.0E-03 IND

1,2-DCA ND(0.092) IND ND(0.098) ND(1.0) ND(<0.55) IND IND IND IND

PCE 0.11 0.01 0.26 ND(1.0) < 0.63 IND IND > 1.7E-01 IND

CH2Cl2 0.54 0.03 0.24 ND(1.0) < 0.62 IND IND > 8.6E-01 IND

CHCl3 0.11 0.01 0.29 1.0 0.6 0.5 78 1.7E-01 1.3E-01

CCl4 ND(0.094) IND ND(0.10) ND(1.0) ND(<0.55) IND IND IND IND

CCl3F(F-11) 0.28 0.02 0.27 ND(1.0) < 0.64 IND IND > 4.4E-01 IND

CCl2F2

(F-12) 0.45 0.03 0.56 ND(1.0) < 0.78 IND IND > 5.8E-01 IND

CHBrCl2 ND(0.086) IND ND(0.092) ND(0.96) ND(<0.53) IND IND IND IND

vinyl chloride ND(0.095) IND ND(0.10) ND(1.1) ND(<0.55) IND IND IND IND

CH3CH2Cl ND(0.97) IND ND(1.0) ND(11) ND(<6.0) IND IND IND IND

CCl3CF3

(F-113) ND(0.092) IND ND(0.098) ND(1.0) ND(<0.55) IND IND IND IND

acetone 3.3 0.20 2.2 9.1 5.7 4.9 86 5.8E-01 5.1E-01

2-hexanone ND(0.088) IND 0.11 ND(0.98) <0.56 IND IND IND IND

THF 0.67 0.04 ND(0.096) ND(1.0) ND(<0.55) IND IND > 1.2E+00 IND

MEK 1.1 0.07 0.73 3.7 2.2 2.1 95 5.0E-01 4.7E-01

MIBK ND(0.083) IND 0.16 ND(0.92) <0.54 IND IND IND IND

MTBE 0.56 0.03 0.50 ND(0.98) <0.74 IND IND > 7.6E-01 IND

heptane ND(0.09) IND ND(0.096) ND(1.0) ND(<0.55) IND IND IND IND

hexane 1.4 0.08 0.25 1.9 1.1 1.2 109 1.3E+00 1.4E+00

cyclohexane 0.58 0.03 ND(0.098) 14 < 7.0 IND IND > 8.3E-02 IND

benzene 0.54 0.03 0.14 ND(1.0) < 0.57 IND IND > 9.5E-01 IND

toluene 4.1 0.25 0.18 ND(1.0) < 0.59 IND IND > 6.9E+00 IND

ethylbenzene 0.17 0.01 ND(0.098) ND(1.0) ND(<0.55) IND IND > 3.1E-01 IND

m/p-xylenes 0.54 0.03 ND(0.20) ND(2.0) ND(<1.1) IND IND > 4.9E-01 IND

o-xylene 0.19 0.01 ND(0.10) ND(1.0) ND(<0.55) IND IND > 3.5E-01 IND

styrene ND(0.086) IND ND(0.092) ND(0.96) ND(<0.53) IND IND IND IND

1,2,4-TMB ND(0.09) IND ND(0.096) 0.60 < 0.35 IND IND IND IND

1,3,5-TMB 0.10 0.01 ND(0.098) ND(1.0) ND(<0.55) IND IND > 1.8E-01 IND

1,3-

butadiene ND(0.18) IND ND(0.19) ND(2.0) ND(<1.1) IND IND IND IND

1,3-DCB ND(0.092) IND ND(0.098) ND(1.0) ND(<0.55) IND IND IND IND

1,4-DCB ND(0.09) IND ND(0.096) ND(1.0) ND(<0.55) IND IND IND IND

4-ethyltoluene 0.22 0.01 ND(0.098) ND(1.0) ND(<0.55) IND IND > 4.0E-01 IND

isopropyl

alcohol 0.7 0.04 ND(0.18) ND(1.9) ND(<1.0) IND IND > 7.2E-01 IND

ethyl/vinyl 

acetate 2.0 0.12 0.31 3.0 1.7 1.9 115 1.2E+00 1.4E+00

CS2 ND(0.088) IND ND(0.094) ND(0.98) ND(<0.54) IND IND IND IND

ND( ) = Not detected (reporting limit) IND = indeterminate
87

chloroform detected at concentrations of 0.24, 0.24, 

and 1.0 ppbv, respectively. Freons, F-11 and F-12, 

were detected in sub-slab air at concentrations of 0.27 

and 0.56 ppbv, respectively. Hydrocarbons, hexane, 

cyclohexane, benzene, and toluene were detected 

at concentrations of 1.9, 14, 0.14, and 0.18 ppbv, 

respectively. Acetone, 2-hexanone, methyl ethyl ketone, 

methyl isobutyl ketone, and methyl tertiary-butyl ether 

were detected at concentrations of 9.1, 0.11, 3.7, 0.16, 

and 0.50 ppbv, respectively. 

The results of sequential sampling using one-liter Tedlar 

bags at Probe A at House N to assess the impact of 

extraction volume on sample results are presented in 

Table 16c. These results were previously discussed. 

As indicated in Table 16d, when sampling with one-liter 

Tedlar bags, 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE 

were found at maximum concentrations of 47, 6.3, 14, 

and 6.4 ppbv, respectively. Radon was sampled at two 

probes with concentrations of 197 and 409 pCi/l and 

detected in basement air at a mean concentration of 

3.1 pCi/L. Results and statistical analysis of sub-slab 

sampling for radon are summarized in Table 16e. 

Figure 51illustrates basement/sub-slab air concentration 

ratios for VOCs and radon detected in basement air 

Table 16b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House N Using EPA Method TO-15 During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev cov = 6% n=2 n=2 n=2

03/28/03 03/28/03 03/28/03 03/28/03 03/28/03 03/28/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.10 0.01 32 9.7 21 16 76 4.8E-03 3.6E-03

1,1-DCE ND(0.094) IND 42 5.3 24 26 110 < 4.0E-03 IND

TCE ND(0.094) IND 12 2.5 7.3 6.7 93 < 1.3E-02 IND

c-1,2-DCE ND(0.092) IND 9.9 ND(1.0) < 5.5 IND IND IND IND

1,1-DCA ND(0.094) IND 20 6.9 13.5 9.3 69 < 7.0E-03 IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation 4.8E-03 3.6E-03

using EPA Method TO-15 for sub-slab air analysis. The 

basement/sub-slab air concentration ratio of radon was 

used to assess vapor intrusion since indicator VOCs, 

1,1-DCE, c-1,2-DCE, and 1,1-DCA, were not detected 

in basement air. A basement/sub-slab air concentration 

ratio of c-1,2-DCE was not calculated using EPA Method 

TO-15 analysis because c-1,2-DCE was detected in only 

one probe. The null hypothesis that the basement/subslab air concentration ratio of 1,1,1-TCA was equal to 

the basement/sub-slab air concentration ratio of radon 

could not be rejected using a one-tailed Approximate 

t-Test at a level of significance less than or equal to 

0.05 (p > 0.1) inferring that the presence of 1,1,1-TCA 

in basement air was due to vapor intrusion at the time 

of sampling. 

Table 16b summarizes basement/sub-slab air 

concentration ratios determined using EPA Method 

TO-15 and Tedlar bag sampling for VOCs associated 

with sub-surface contamination. For EPA Method TO15 analysis, the basement/sub-slab air concentration 

ratio of 1,1,1-TCA was 4.8E-03. Table 16dsummarizes 

basement/sub-slab air ratios using Tedlar bags 

for sampling along with on-site GC analyses. The 

basement/sub-slab air concentration ratio of 1,1,1-TCA 

was 4.0E-03. 
88

Table 16e. Basement/Sub-Slab Air Concentration Ratios of Radon in House N Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/25-3/27/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt

48-hr

bsmt

48-hr

bsmt

mean

bsmt

stdev

bsmt

cov P[A]

300A

P[B]

330A

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2 n=2 n=2 n=2

03/27/03 03/27/03 03/27/03 03/31/03 03/27/03 03/31/03 03/31/03 03/31/03

(pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

3.3 2.9 3.1 0.28 9.1 197 409 303 150 49.5 1.02E-02 5.15E-03

Table 16c. Results of Sequential Sub-Slab Air Sampling Using 1-Liter Tedlar Bags and On-Site GC Analysis at House N During 

the March 2003 Sample Event

VOC P[A]-01

grab

P[A]-02

grab

P[A]-03

grab

P[A]-04

grab

P[A]-05

grab

P[A]

mean

P[A]

stdev

P[A]

cov

n=5 n=5 n=5

03/31/03 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%)

1,1,1-TCA 13 14 15 16 15 15 1.14 7.81

1,1-DCE 5.8 6.3 6.5 6.6 6.4 6 0.31 4.93

TCE 2.5 2.5 2.5 2.5 2.7 3 0.09 3.52

c-1,2-DCE ND(3.0) ND(3.0) ND(3.0) ND(3.0) ND(3.0) ND(3.0) IND IND

ND = Not detected (reporting limit), IND = indeterminate

Table 16d. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House N Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev P[A] 

mean

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev cov = 6% n=3 n=3 n=3

03/28/03 03/31/03 03/31/03 03/31/03 03/28/03 03/28/03 03/28/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-

TCA 0.10 0.01 15 47 13 25 19 77 4.0E-03 3.1E-03

1,1-DCE ND(0.094) IND 6.3 4.6 4.8 5.2 0.9 18 < 1.8E-02 IND

TCE ND(0.094) IND 2.5 14 3.9 6.8 6.3 92 < 1.4E-02 IND

c-1,2-

DCE ND(0.092) IND ND(3.0) 6.4 ND(3.0) < 4.1 IND IND IND IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation 4.0E-03 3.1E-03
89

Figure 51. Basement/sub-slab concentration ratios using EPA Method TO-15 at House N during the March 2003 sample event. 

Error bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or 

sub-slab air.

House O

The slab appeared relatively intact with few cracks. 

Basement walls consisted of poured concrete. 

Concentrations of all VOCs detected in basement 

and/or sub-slab air using EPA Method TO-15 are 

summarized in Table 17a. No VOCs associated with 

subsurface contamination were detected in basement 

air. The detection limits of VOCs associated with 

sub-surface contamination ranged from 0.097 to 

0.099 ppbv. Other chlorinated compounds detected 

in basement air were methylene chloride, chloroform, 

carbon tetrachloride, and 1,4-dichlorobenzene at 

concentrations of 1.2, 0.22, 0.17, and 0.16 ppbv, 

respectively. Freons, F-11 and F-12, were detected 

in basement air at concentrations of 0.74 and 0.52 

ppbv, respectively. Hydrocarbons, heptane, hexane, 

cyclohexane, benzene, toluene, ethylbenzene, 

m/p-xylenes, o-xylene, 1,2,4-trimethylbenzene, 

1,3,5-trimethylbenzene, and 4-ethyltoluene were 

detected at concentrations up to 21 ppbv. Acetone, 

tetrahydrofuran, methyl ethyl ketone, and methyl 

tertiary-butyl ether were detected at concentrations of 

19, 11, 1.1, and 19 ppbv, respectively. The compound, 

1,3-butadiene, was detected in basement air at a 

concentration of 0.80 ppbv.

Three sub-slab probes were installed at House O. 

Two probes were sampled using EPA Method TO15. All three probes were sampled using one-liter 

Tedlar bags. As indicated by Table 17b, 1,1,1-TCA, 

1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA were 

found at maximum concentrations in Probe C at 7.2, 

2.2, 1.6, 0.080, and 1.3 ppbv, respectively. Other 
90

Table 17a. Basement and Sub-Slab Air Concentrations for VOCs at House O Using EPA Method TO-15 During the March 2003 

Sample Event

VOC bsmt

24-hr

scaled

stdev P[A]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

cov=6% n=2 n=2 n=2 stdev

03/26/03 03/26/03 03/26/03 03/26/03 03/26/03 03/26/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA ND(0.097) IND 5.6 7.2 6.4 1.13 18 < 1.5E-02 IND

1,1-DCE ND(0.099) IND 1.1 2.2 1.7 0.78 47 < 5.9E-02 IND

TCE ND(0.099) IND 0.56 1.6 1.1 0.74 68 < 9.0E-02 IND

c-1,2-DCE ND(0.097) IND ND(0.07) 0.080 < 0.08 IND IND IND IND

1,1-DCA ND(0.099) IND 0.930 1.3 1.1 0.26 23 < 8.7E-02 IND

1,2-DCA 0.080 0.00 ND(0.07) ND(0.071) ND(<0.07) IND IND > 1.1E+00 IND

PCE ND(0.092) IND 0.34 0.33 0.34 0.01 2.1 < 2.9E-01 IND

CH2Cl2 1.2 0.07 0.10 ND(0.073) < 0.09 IND IND > 1.3E+00 IND

CHCl3 0.22 0.01 0.82 10 5.4 6.49 120 4.1E-02 4.9E-02

CCl4 0.17 0.01 ND(0.071) ND(0.073) ND(<0.072) IND IND > 2.3E+00 IND

CCl3F(F-11) 0.74 0.04 0.30 0.29 0.30 0.01 2.4 2.5E+00 1.6E-01

CCl2F2

(F-12) 0.50 0.03 0.57 0.13 0.35 0.31 89 1.4E+00 1.3E+00

CHBrCl2 ND(0.092) IND ND(0.066) ND(0.067) ND(<0.067) IND IND IND IND

vinyl chloride ND(0.10) IND ND(0.073) ND(0.074) ND(<0.074) IND IND IND IND

CH3CH2Cl 1.5 0.09 ND(0.74) ND(0.75) ND(<0.75) IND IND > 2.0E+00 IND

CCl3CF3

(F-113) ND(0.097) IND 0.080 0.090 0.09 0.01 8.3 < 1.1E+00 IND

acetone 19 1.14 1.9 2.0 2.0 0.07 3.6 9.7E+00 6.8E-01

2-hexanone ND(0.094) IND 0.080 0.10 0.09 0.01 16 < 1.1E+00 IND

THF 11 0.66 ND(0.068) ND(0.07) ND(<0.07) IND IND > 1.6E+02 IND

MEK 1.1 0.07 0.46 0.80 0.63 0.24 38 1.7E+00 6.7E-01

MIBK ND(0.088) IND 0.17 0.15 0.16 0.01 8.8 < 5.5E-01 IND

MTBE 19 1.14 0.080 0.12 0.10 0.03 28 1.9E+02 5.5E+01

heptane 7.2 0.43 ND(0.068) ND(0.07) ND(<0.07) IND IND > 1.0E+02 IND

hexane 8.9 0.53 0.11 0.19 0.15 0.06 38 5.9E+01 2.3E+01

cyclohexane 0.94 0.06 ND(0.07) ND(0.071) ND(<0.07) IND IND > 1.3E+01 IND

benzene 3.4 0.20 ND(0.071) ND(0.073) ND(<0.072) IND IND > 4.9E+01 IND

toluene 21 1.26 0.17 0.23 0.20 0.04 21 1.1E+02 2.3E+01

ethylbenzene 2.5 0.15 ND(0.07) ND(0.071) ND(<0.07) IND IND > 3.6E+01 IND

m/p-xylenes 11 0.66 ND(0.14) ND(0.14) ND(<0.14) IND IND > 7.9E+01 IND

o-xylene 3.6 0.22 ND(0.071) ND(0.073) ND(<0.072) IND IND > 5.1E+01 IND

styrene ND(0.092) IND ND(0.066) ND(0.067) ND(<0.067) IND IND IND IND

1,2,4-TMB 4.3 0.26 ND(0.068) ND(0.07) ND(<0.07) IND IND > 6.1E+01 IND

1,3,5-TMB 1.2 0.07 ND(0.07) ND(0.071) ND(<0.071) IND IND > 1.7E+01 IND

1,3-

butadiene 0.80 0.05 ND(0.14) ND(0.14) ND(<0.14) IND IND > 5.7E+00 IND

1,3-DCB ND(0.097) IND ND(0.07) ND(0.071) ND(<0.07) IND IND IND IND

1,4-DCB 0.16 0.01 ND(0.068) ND(0.07) ND(<0.07) IND IND > 2.3E+00 IND

4-ethyltoluene 3.9 0.23 ND(0.07) ND(0.071) ND(<0.07) IND IND > 5.6E+01 IND

isopropyl

alcohol 0.36 0.02 ND(0.13) ND(0.13) ND(<0.13) IND IND > 2.8E+00 IND

ethyl/vinyl 

acetate ND(0.18) IND ND(0.13) ND(0.13) ND(<0.13) IND IND IND IND

CS2 ND(0.094) IND ND(0.067) ND(0.069) ND(<0.068) IND IND IND IND

ND( ) = Not detected (reporting limit) IND = indeterminate
91

chlorinated compounds detected in sub-slab air 

were perchloroethylene, methylene chloride, and 

chloroform at concentrations of 0.34, 0.10, and 10 

ppbv, respectively. Freons, F-11 and F-12, were 

detected in sub-slab air at concentrations of 0.30 

and 0.57 ppbv, respectively. Hydrocarbons, hexane 

and toluene were detected at concentrations of 0.19 

and 0.23 ppbv, respectively. Acetone, 2-hexanone, 

methyl ethyl ketone, methyl isobutyl ketone, and methyl 

tertiary-butyl ether were detected at concentrations of 

2.0, 0.10, 0.80, 0.17, and 0.12 ppbv, respectively. As 

indicated by Table 17c, when sampling with one-liter 

Tedlar bags, 1,1,1-TCA, 1,1-DCE, and TCE were found 

at maximum concentrations of 9.3, 2.1, and 1.4 ppbv, 

respectively. Radon was sampled at two probes with 

concentrations of 948 and 958 pCi/l and detected in 

basement air at a mean concentration of 4.8 pCi/L. 

Table 17b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House O Using EPA Method TO-15 During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev P[A]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev cov = 6% n=2 n=2 n=2

03/26/03 03/26/03 03/26/03 03/26/03 03/26/03 03/26/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA ND(0.097) IND 5.6 7.2 6.4 1.13 18 < 1.5E-02 IND

1,1-DCE ND(0.099) IND 1.1 2.2 1.7 0.78 47 < 5.9E-02 IND

TCE ND(0.099) IND 0.56 1.6 1.1 0.74 68 < 9.0E-02 IND

c-1,2-DCE ND(0.097) IND ND(0.07) 0.080 < 0.08 IND IND IND IND

1,1-DCA ND(0.099) IND 0.930 1.3 1.1 0.26 23 < 8.7E-02 IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation < 1.5E-02 IND

Table 17c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House O Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev P[A] 

grab

P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

cov = 6% ratio n=3 n=3 n=2

03/26/03 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03 03/31/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-)

1,1,1-TCA ND(0.097) IND 7.6 9.3 8.6 8.5 0.85 10 < 1.1E-02

1,1-DCE ND(0.099) IND ND(5.0) ND(5.0) 2.1 < 4.0 IND IND IND

TCE ND(0.099) IND ND(1.2) ND(1.2) 1.4 < 1.3 IND IND IND

c-1,2-DCE ND(0.097) IND ND(3.0) ND(3.0) ND(3.0) ND(3.0) IND IND IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation < 1.1E-02

Results and statistical analysis of sub-slab sampling 

for radon are summarized in Table 17d.

Figure 52 illustrates basement/sub-slab air 

concentration ratios for VOCs and radon detected in 

basement air. Table 17b summarizes basement/subslab air concentration ratios determined using EPA 

Method TO-15. Use of the lowest basement/sub-slab 

air concentration ratio for a VOC associated with 

sub-surface contamination (1,1,1-TCA) resulted in 

computation of a basement/sub-slab air concentration 

ratio of less than 1.5E-02. Table 17c summarizes 

basement/sub-slab air concentration ratios using 

Tedlar bags for sampling along with on-site GC 

analyses. Use of a basement/sub-slab concentration 

value for 1,1,1-TCA resulted in computation of a 

basement/sub-slab ratio of less than 1.1E-02. 
92

Table 17d. Basement/Sub-Slab Air Concentration Ratios for Radon in House O Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/25-3/27/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt

48-hr

bsmt

48-hr

bsmt

mean

bsmt

stdev

bsmt

cov P[B]

300A

P[C]

110A

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=2 n=2 n=2 n=2 n=2 n=2

03/24/03 03/24/03 03/24/03 03/31/03 3/27/03 3/31/03 3/31/03 3/31/03

(pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

4.9 4.6 4.8 0.21 4.5 948 958 953 7.1 0.74 5.0E-03 2.26E-04

Figure 52. Basement/sub-slab concentration ratios using EPA Method TO-15 at House O during the March 2003 sample event. 

Error bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or 

sub-slab air.
93

Location P

Location P is a commercial building. It has a concrete 

slab approximately 1.6 meters below ground surface. 

At the time of sub-slab probe installation, the slab 

appeared relatively intact with few cracks. Basement 

walls consist of field stone and mortar. 

Concentrations of VOCs detected in basement and/or 

sub-slab air using EPA Method TO-15 for sampling and 

analysis are summarized in Table 18a. The only VOC 

associated with sub-surface contamination detected 

in basement air was 1,1,1-TCA at a concentration of 

0.12 ppbv. Detection limits for other VOCs associated 

with sub-surface contamination were 0.09 ppbv. Other 

chlorinated compounds detected in basement air were 

methylene chloride, chloroform, carbon tetrachloride, 

and 1,4-dichlorobenzene at concentrations of 0.55, 

0.49, 0.17, and 0.12 ppbv, respectively. Freons, 

F-11 and F-12, were detected in basement air at 

concentrations of 0.23 and 0.46 ppbv, respectively. 

Hydrocarbons, hexane, cyclohexane, benzene, 

toluene, ethylbenzene, m/p-xylenes, o-xylene, styrene, 

1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and 

4-ethyltoluene were detected at concentrations up 2.7 

ppbv. Acetone, tetrahydrofuran, methyl ethyl ketone, 

methyl isobutyl ketone, and methyl tertiary-butyl ether 

were detected at concentrations of 7.7, 11, 33, 3.4, 

and 0.37 ppbv, respectively. 

Four sub-slab probes were installed at location P. 

Two probes were sampled using EPA Method TO-15. 

All probes were sampled using one-liter Tedlar bags. 

As indicated in Table 18b, using EPA Method TO-15, 

1,1,1-TCA, 1,1-DCE, TCE, c-1,2-DCE, and 1,1-DCA 

were found at maximum concentrations in Probe [B] 

at 250, 100, 92, 18, and 54 ppbv, respectively. Other 

chlorinated compounds detected in sub-slab air were 

perchloroethylene and chloroform at concentrations 

of 2.8 and 1.9 ppbv, respectively. Freons, F-11 and 

F-12, were detected in sub-slab air at concentrations 

of 0.37 and 0.52 ppbv, respectively. Hydrocarbons, 

hexane, toluene, m/p-xylenes, 1,2,4-trimethylbenzene, 

and 4-ethyltoluene were detected at concentrations 

of 0.19, 0.19, 0.16, 0.16, and 0.15 ppbv, respectively. 

Acetone, 2-hexanone, methyl ethyl ketone, and methyl 

isobutyl ketone were detected at concentrations of 2.6, 

0.17, 1.0, and 0.20 ppbv, respectively. As indicated 

in Table 18c, when sampling sub-slab air with oneliter Tedlar bags, 1,1,1-TCA, 1,1-DCE, TCA, and c1,2-DCE were found at maximum concentrations in 

Probe [B] at 273, 92, 77, and 15 ppbv, respectively. 

Radon was sampled at two probes with concentrations 

of 691 and 1258 pCi/l and detected in basement air 

at a mean concentration of 3.8 pCi/l. Results and 

statistical analysis of sub-slab sampling for radon are 

summarized in Table 18d.

Figure 53 illustrates calculated basement/sub-slab 

ratios for radon and VOCs using EPA Method TO-15 

analysis. Since indicator VOCs were not detected in 

basement air, the basement/sub-slab air concentration 

ratio of radon was used to assess vapor intrusion. 

The null hypothesis that the basement/sub-slab air 

concentration ratio of 1,1,1-TCA was equal to the 

basement/sub-slab air concentration ratio of radon 

could not be rejected using a one-tailed Approximate 

t-Test at a level of significance less than or equal to 

0.05 (p > 0.1) inferring that the presence of 1,1,1-TCA 

in basement air was due to vapor intrusion at the time 

of sampling.

Table 18b summarizes basement/sub-slab air 

concentration ratios determined using EPA Method 
94

TO-15. Only the upper limit of basement/sub-slab air 

concentration ratios could be calculated for 1,1-DCE, 

TCE, c-1,2-DCE, and 1,1-DCA. The basement/subslab air concentration ratio of 1,1,1-TCA was 7.2E-04. 

Table 18a. Basement and Sub-Slab Air Concentrations for VOCs at House P Using EPA Method TO-15 During the March 2003 

Sample Event

VOC bsmt

24-hr

scaled

stdev P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

cov=6% n=2 n=2 n=2 stdev

03/26/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.12 0.01 250 83 167 118 71 7.2E-04 5.1E-04

1,1-DCE ND(0.092) IND 100 22 61 55 90 < 1.5E-03 IND

TCE ND(0.092) IND 92 15 54 54 102 < 1.7E-03 IND

c-1,2-DCE ND(0.09) IND 18 0.36 9.2 12 136 < 9.8E-03 IND

1,1-DCA ND(0.092) IND 54 5.2 30 35 117 < 3.0E-03 IND

1,2-DCA ND(0.09) IND ND(0.14) ND(0.16) ND(<0.15) IND IND IND IND

PCE ND(0.09) IND 2.8 1.7 2.3 0.78 35 < 4.0E-02 IND

CH2Cl2 0.55 0.03 ND(0.14) ND(0.16) ND(<0.15) IND IND > 3.4E+00 IND

CHCl3 0.49 0.03 1.9 0.45 1.2 1.0 87 4.2E-01 3.6E-01

CCl4 0.17 0.01 ND(0.14) ND(0.16) ND(<0.15) IND IND > 1.1E+00 IND

CCl3F(F-11) 0.23 0.01 0.37 0.25 0.31 0.08 27 7.4E-01 2.1E-01

CCl2F2(F-12) 0.46 0.03 0.50 0.52 0.51 0.01 2.8 9.0E-01 6.0E-02

CHBrCl2 ND(0.076) IND ND(0.082) 0.34 <0.21 IND IND IND IND

vinyl chloride ND(0.094) IND ND(0.14) ND(0.16) ND(<0.15) IND IND IND IND

CH3CH2Cl ND(0.96) IND ND(1.5) ND(1.6) ND(<1.6) IND IND IND IND

CCl3CF3(F-113) ND(0.09) IND ND(0.14) ND(0.16) ND(<0.15) IND IND IND IND

acetone 7.7 0.46 2.6 2.5 2.6 0.07 2.8 3.0E+00 2.0E-01

2-hexanone ND(0.087) IND 0.17 ND(0.15) <0.16 IND IND IND IND

THF 11 0.66 ND(0.14) ND(0.15) ND(<0.15) IND IND > 6.9E+01 IND

MEK 33 1.98 1.0 0.76 0.88 0.17 19 3.8E+01 7.6E+00

MIBK 3.4 0.20 0.20 0.15 0.18 0.04 20 1.9E+01 4.1E+00

MTBE 0.37 0.02 ND(0.13) ND(0.15) ND(<0.14) IND IND > 2.3E+00 IND

heptane ND(0.089) IND ND(0.14) ND(0.15) ND(<0.15) IND IND IND IND

hexane 0.33 0.02 0.19 ND(0.16) <0.18 IND IND > 1.8E+00 IND

cyclohexane 0.34 0.02 ND(0.14) ND(0.16) ND(<0.15) IND IND > 2.1E+00 IND

benzene 0.26 0.02 ND(0.14) ND(0.16) ND(<0.15) IND IND > 1.6E+00 IND

toluene 5.5 0.33 0.19 0.12 0.16 0.05 32 3.5E+01 1.2E+01

ethylbenzene 0.83 0.05 ND(0.14) ND(0.16) ND(<0.15) IND IND > 5.2E+00 IND

m/p-xylenes 2.7 0.16 0.16 ND(0.31) <0.24 IND IND > 1.1E+01 IND

o-xylene 0.57 0.03 ND(0.14) ND(0.16) ND(<0.15) IND IND > 3.6E+00 IND

styrene 0.13 0.01 ND(0.13) ND(0.15) ND(<0.14) IND IND > 8.1E-01 IND

1,2,4-TMB 0.85 0.05 0.16 ND(0.15) <0.16 IND IND > 5.3E+00 IND

1,3,5-TMB 0.31 0.02 ND(0.14) ND(0.16) ND(<0.15) IND IND > 1.9E+00 IND

1,3-butadiene ND(0.18) IND ND(0.28) ND(0.31) ND(<0.30) IND IND IND IND

1,3-DCB ND(0.09) IND ND(0.14) ND(0.16) ND(<0.15) IND IND IND IND

1,4-DCB 0.12 0.01 ND(0.14) ND(0.15) ND(<0.15) IND IND > 7.5E-01 IND

4-ethyltoluene 0.85 0.05 0.15 ND(0.16) <0.16 IND IND > 5.3E+00 IND

isopropyl alcohol 4.7 0.28 ND(0.25) ND(0.28) ND(<0.27) IND IND > 1.7E+01 IND

ethyl/vinyl acetate 6.7 0.40 0.37 0.30 0.34 0.05 IND 2.0E+01 3.2E+00

CS2 ND(0.087) IND ND(0.13) ND(0.15) ND(<0.14) IND IND IND IND

ND( ) = Not detected (reporting limit) IND = indeterminate

Table 18c summarizes basement/sub-slab ratios 

using Tedlar bag and on-site GC analyses for sub-slab 

sampling. The basement/sub-slab air concentration 

ratio of 1,1,1-TCA was 1.0E-03. 
95

Table 18d. Basement/Sub-Slab Air Concentration Ratios of Radon in House P Using 48-hr Activated Carbon Canisters for 

Basement Air Sampling (3/26-3/28/03) and Scintillation Cells for Sub-Slab Air Sampling During the March 2003 Sample Event

bsmt

48-hr

bsmt

48-hr

bsmt

48-hr

bsmt

mean

bsmt

stdev

bsmt

cov P[A]

300A

P[C]

300A

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

stdev n=3 n=2 n=2 n=2 n=2 n=2

03/28/03 03/28/03 03/28/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03

(pCi/L) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (pCi/L) (pCi/L) (pCi/L) (pCi/L) (%) (-) (-)

3.8 3.8 1.4 3.0 1.4 46 691 1258 975 401 41.1 3.08E-03 1.90E-03

Table 18c. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House P Using 1-Liter Tedlar Bags and On-Site GC Analysis During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev P[A]

grab

P[B]

grab

P[C]

grab

P[D]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

cov = 6% stdev n=4 n=4 n=4

03/26/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.12 0.01 37 273 117 38 116 111 95 1.0E-03 9.9E-04

1,1-DCE ND(0.092) IND 8.4 92 28 7.8 34 40 117 < 2.7E-03 IND

TCE ND(0.092) IND 4.6 77 12 4.9 25 35 142 < 3.7E-03 IND

c-1,2-DCE ND(0.09) IND ND(3.0) 15 ND(3.0) ND(3.0) < 6.0 IND IND IND IND

ND( ) = Not detected (reporting limit), IND = indeterminate mean and standard deviation 1.0E-03 9.9E-04

Table 18b. Summary of Basement/Sub-Slab Air Concentration Ratios of VOCs Associated with Sub-Surface Contamination in 

House P Using EPA Method TO-15 During the March 2003 Sample Event

VOC bsmt

24-hr

scaled

stdev P[B]

grab

P[C]

grab

sub-slab

mean

sub-slab

stdev

sub-slab

cov bsmt/

sub-slab

ratio

bsmt/

sub-slab

cov = 6% stdev n=2 n=2 n=2

03/26/03 04/01/03 04/01/03 04/01/03 04/01/03 04/01/03

(ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (ppbv) (%) (-) (-)

1,1,1-TCA 0.12 0.01 250 83 167 118 71 7.2E-04 5.1E-04

1,1-DCE ND(0.092) IND 100 22 61 55 90 < 1.5E-03 IND

TCE ND(0.092) IND 92 15 54 54 102 < 1.7E-03 IND

c-1,2-DCE ND(0.09) IND 18 0.36 9.2 12 136 < 9.8E-03 IND

1,1-DCA ND(0.092) IND 54 5.2 30 35 117 < 3.0E-03 IND

ND( ) = Not detected(reporting limit), IND = indeterminate mean and standard deviation 7.2E-04 IND
96

6.4 Results of Radon Testing to Assess 

 Vapor Intrusion

Figure 54 provides a comparison of basement/subslab air concentration ratios for radon and indicator 

VOCs associated with vapor intrusion. At locations 

J, L, and M, the null hypothesis that the basement/

sub-slab air concentration ratio of radon was equal 

to the basement/sub-slab air concentration ratio of 

the indicator VOC, 1,1-DCE, could be rejected using 

a two-tailed Approximate t-Test at a significance level 

less than 0.1. At location K, the null hypotheses 

that the basement/sub-slab air concentration ratio 

of radon was equal to the basement/sub-slab air 

concentration ratios of the indicator VOCs, 1,1-DCE 

and c-1,2-DCE, could not be rejected using a twotailed Approximate t-Test at a significance level less 

than 0.1. As illustrated in Figures 47, 48, 49, and 50, 

for locations J, K, L, and M, respectively, there was a 

visual dissimilarity between the basement/sub-slab 

air concentration ratio of radon and VOCs associated 

with vapor intrusion. This is in contrast to visual and 

statistical (levels of significance always greater than 

0.1) similarity of basement/sub-slab concentration air 

ratios for indicator VOCs and other VOCs associated 

with vapor intrusion illustrated in Figures 36, 38, 46, 

47, 48, 49, and 50 at locations B, C, I, J, K, L, and M, 

respectively. The internal consistency of basement/

sub-slab air concentration ratios of 1,1-DCE, c-1,2-

DCE, TCE, and 1,1,1-TCA (when associated with 

vapor intrusion) relative to the basement/sub-slab 

concentration ratio of radon when compared to VOCs 

associated with sub-surface contamination, indicates 

that for this investigation, the use of indicator VOCs 

Figure 53. Basement/sub-slab concentration ratios using EPA Method TO-15 at House P during the March 2003 sample event. 

Error bars represent one standard deviation. Arrows indicate greater than or less than values due to non-detection in basement or 

sub-slab air.
97

Figure 54. Comparison of basement/sub-slab air concentration ratios for radon and indicator VOCs associated with vapor 

intrusion. Samples for VOCs collected in one-liter Tedlar bags with on-site GC analysis.

was preferable over the use of radon as an indicator 

compound to assess vapor intrusion. However, data 

for comparison of radon with indicator VOCs were 

available at only four locations. Further research

is needed at sites containing conservative VOCs to 

assess the usefulness of radon as a conservative 

compound. 

Figure 55 illustrates COVs of VOCs associated with 

vapor intrusion and radon as a function of location. 

COVs for VOCs are from Tedlar bag sampling and 

on-site GC analysis. Sub-slab air concentrations 

of radon generally do not appear to be more or less 

variable than VOCs associated with vapor intrusion. 

Thus, the number of probes used to estimate mean 

sub-slab air radon concentration should be equivalent 

to the number of probes used to estimate mean subslab air concentrations of VOCs associated with vapor 

intrusion. 
98

6.5 Summary of Basement/Sub-Slab 

 Concentration Ratios

Figure 56 summarizes the overall basement/sub-slab 

concentration ratios for VOCs associated with vapor 

intrusion at each location tested during the July 2002 

and March 2003 sample events. Basement/sub-slab 

concentration ratios of 1,1,1-TCA were removed 

from consideration of overall basement/sub-slab 

concentration ratios when statistical testing supported 

a difference between indicator VOCs and 1,1,1-TCA. 

While building construction and slab conditions were 

generally similar, basement/sub-slab concentration 

ratios varied significantly. 

In this investigation, basement/sub-slab concentration 

ratios were utilized to determine whether or not VOCs 

detected in basement air during the time of sampling 

were due to vapor intrusion. Causative factors for 

basement/sub-slab concentration ratio variation were 

not investigated. However, variation in basement/

sub-slab concentration ratios in this investigation 

indicates that it would have been unwise to select 

a generic basement/sub-slab concentration ratio 

such as 0.01 or 0.02 and measure only sub-slab air 

concentrations to assess risk. This approach would 

not have been conservative at House J where an 

overall basement/sub-slab concentration ratio of 2.4E02 ± 1.3E-02 was determined for VOCs associated 

with vapor intrusion. This approach would have been 

borderline at Houses B and I where basement/subslab concentration ratios of 8.3E-03 ± 5.3E-03, and 

8.9E-03 ± 2.5E-03, respectively, were determined 

for VOCs associated with vapor intrusion. Also, 

Figure 55. Coefficient of Variation (COV) as a function of location and compound for VOCs detected in basement air as a result of 

vapor intrusion.
99

Figure 56. Summary of average basement/sub-slab concentration ratios for VOCs present in basement air due to vapor intrusion 

using one-liter Tedlar bags and on-site GC analysis. Arrows indicate less than values due to non-detection in basement air.

basement/sub-slab concentration ratios determined 

during this investigation were specific to the time 

of sampling. Basement and sub-slab sampling at 

House B occurred during the summer (July) when 

air exchange would be expected to be greater than 

fall or winter months. 

Finally, statistical testing sometimes resulted in a 

finding that the presence of 1,1,1-TCA in basement air 

was not due to vapor intrusion despite being found in 

sub-slab air, soil gas, and ground water in the vicinity of 

a building. Also, statistical testing sometimes resulted 

in a finding that the presence of 1,1,1-TCA in basement 

air was likely due to vapor intrusion despite being 

found in outdoor air at concentrations comparable to 

basement air. When 1,1-DCE, TCE, and 1,1-DCA 

were detected in indoor air, their presence was always 

due to vapor intrusion.
100

equal to the indoor/sub-slab concentration ratio of 

an “indicator” VOC at the time of sampling. A onetailed Approximate t-test for Independent Samples of 

Unequal Variance was used with rejection of the null 

hypothesis at a level of significance (p) less than or 

equal to 0.05. An indicator VOC was defined as a VOC 

detected in sub-slab air and known to be associated 

only with subsurface contamination. The VOCs 

1,1-dichloroethylene and 1,1-dichloroethane were 

considered indicator VOCs in this investigation because 

they are degradation products of 1,1,1-trichloroethane 

and not associated with commercial products. The 

VOC cis-1,2-dichloroethylene was considered an 

indicator VOC because it is a degradation product 

of trichloroethylene and not commonly associated 

with commercial products. The variance associated 

with each basement/sub-slab concentration ratio was 

calculated using the method of propagation of errors 

which incorporated the variance associated with both 

basement and sub-slab air measurement. An average 

or overall basement/sub-slab concentration ratio was 

computed at each location using concentration ratios 

of all VOCs associated with vapor intrusion. The 

method of propagation of errors was then used to 

calculate the variance associated with the average 

basement/sub-slab concentration ratio. 

Statistical testing sometimes resulted in a finding that 

the presence of 1,1,1-trichloroethane in basement 

air was not due to vapor intrusion despite being 

7.0 Summary

There were three primary objectives in this 

investigation. The first objective was to develop a 

method of sub-slab probe installation and sampling. 

The second objective was to develop a method of 

assessing vapor intrusion using basement and sub-slab 

air samples that would be appropriate for building-tobuilding investigations and sites containing petroleum 

hydrocarbons. The third objective was to directly assist 

EPA’s New England Regional Office in evaluating 

vapor intrusion at 15 homes and one business near 

the Raymark Superfund Site in Stratford, Connecticut. 

Sub-slab air sampling offers an opportunity to collect 

samples directly beneath the living space of a building 

and thereby eliminate uncertainty associated with 

interpolation or extrapolation of soil-gas and/or groundwater concentrations from monitoring points distant 

from a building. Sub-slab sampling also provides 

an opportunity to evaluate the validity of claims that 

petroleum hydrocarbons degrade prior to vapor entry 

into sub-slab material. 

In this investigation, a VOC detected in basement 

air was considered due to vapor intrusion if: (1) the 

VOC of interest was detected in ground water and/or 

soil-gas in the “vicinity” (e.g., 30 meters) of the house, 

and (2) the results of statistical testing indicated 

that the presence of a VOC in indoor air was due 

to vapor intrusion. Statistical testing consisted of 

evaluating the null hypothesis that the indoor/subslab concentration ratio of a VOC of interest was 
101

found in sub-slab air, soil-gas, and ground water in 

the vicinity of a building. Also, hypothesis testing 

sometimes resulted in a finding that the presence 

of 1,1,1-trichloroethane in basement air was due to 

vapor intrusion despite being found in outdoor air at 

a concentration comparable to basement air. When 

1,1-dichloroethylene, trichloroethylene, and 1,1-

dichloroethane were detected in basement air, their 

presence was always due to vapor intrusion.

The usefulness of radon as an indicator compound in 

assessing vapor intrusion was evaluated by statistically 

comparing basement/sub-slab concentration ratios 

for radon and indicator VOCs. However, the data set 

for indicator VOCs versus radon comparison was 

limited, consisting of testing at only four locations. At 

three locations, the null hypothesis that the basement/

sub-slab air concentration ratio of radon was equal to 

the basement/sub-slab air concentration ratio of the 

indicator VOC, 1,1-DCE, was rejected using a twotailed Approximate t-Test at a significance level less 

than 0.1. There was a visual dissimilarity between 

the basement/sub-slab air concentration ratio of 

radon and VOCs associated with vapor intrusion. 

This is in contrast to visual and statistical (levels 

of significance always greater than 0.1) similarity 

of basement/sub-slab concentration air ratios for 

indicator VOCs and other VOCs associated with vapor 

intrusion. The internal consistency of basement/

sub-slab air concentration ratios of 1,1-DCE, c-1,2-

DCE, TCE, and 1,1,1-TCA (when associated with 

vapor intrusion) relative to the basement/sub-slab 

concentration ratio of radon when compared to VOCs 

associated with sub-surface contamination, indicate 

that for this investigation, use of indicator VOCs were 

preferable to use of radon as an indicator compound 

to assess vapor intrusion. Further research is needed 

at sites containing conservative VOCs to assess the 

usefulness of radon as a conservative compound. 

A number of specific recommendations regarding subslab probe installation and sampling are provided in 

this report. A design for a sub-slab vapor probe was 

presented which allows for multiple use and “floats” in 

a slab to enable air sample collection from sub-slab 

material in direct contact with a slab or from an air 

pocket directly beneath a slab created by subsidence. 

It was demonstrated that probe materials used in this 

investigation did not serve as a source of VOCs. 

A method of drilling through a concrete slab is presented 

where a rotary hammer drill was used to create an 

“inner” and “outer” diameter hole in a concrete slab for 

probe installation. Initial depth of penetration of the 

“outer” diameter hole was equivalent to the length of 

brass couples to ensure that probes were flush with the 

upper surface of the slab. The “inner” diameter hole 

fully penetrated the slab and extended into sub-slab 

material to create an open cavity to prevent potential 

obstruction of probes during sampling. A quick-drying, 

lime-based cement which expanded upon drying (to 

ensure a tight seal) was mixed with tap water to form a 

slurry and tapped into the annular space between the 

probe and inside of the “outer” diameter hole using a 

small metal rod. Using this procedure, 3 probes were 

typically installed in less than 2 hours. Schematics 

illustrating the location of sub-slab probes and other 

slab penetrations (e.g., suction holes for sub-slab 

permeability testing) were prepared for each building to 

document sample locations, interpret sample results, 

and design corrective measures. 

Basement air samples were collected in sixliter SilcoCan canisters and analyzed by EPA’s
102

a period of 48 hours. Sub-slab sampling and analysis 

using scintillation cells were conducted in accordance 

with the Grab Radon/Scintillation Cell Method outlined 

in EPA 402-R-93-003. Tygon tubing was attached to 

the sub-slab probes using threaded barbed nipples. 

A peristaltic pump was used to create a vacuum in 

the probe for sample collection and circulation of subslab air through scintillation cells. Barbed fittings were 

used to connect Tygon to Masterflex tubing used for 

the peristaltic pump. A flow meter was placed on the 

outlet side of a scintillation cell to ensure a flow rate 

of approximately 1 SLPM and to determine when 10 

cell volumes were exchanged in each cell. The outlet 

end of the flow meter was vented outside each house. 

A particulate filter was placed on the inlet side of the 

scintillation cell. Quick-connect assemblies were 

used for connection of Tygon tubing to scintillation 

cells. Samples were analyzed within four hours as 

recommended in EPA 402-R-93-003. 

Air permeability testing in sub-slab media was 

conducted to support corrective action (sub-slab 

depressurization) and air flow simulations used to 

help assess potential limits to extraction volume 

and flow rate during sampling and purging. A small 

regenerative blower was used to extract air from subslab material. A variable-area flowmeter was used to 

measure flow rate. Air pressure was measured with 

magnehelic gauges and a digital manometer. Radial 

and vertical air permeability of sub-slab media was 

estimated using Baehr and Joss’s (1995) analytical 

solution for two-dimensional, axisymmetric, steadystate gas flow in a semi-confined domain. Estimates of 

radial permeability, vertical permeability, and recharge 

at the top of sub-slab material along with streamline 

computation and particle tracking were used to support 

air flow simulations.

New England Regional Laboratory using EPA Method 

TO-15. One-hour samples were collected during 

the July 2003 sample event while 24-hour samples 

were collected during the March 2003 sample event. 

Sub-slab air samples were collected in evacuated 

six-liter SilcoCan canisters using EPA Method TO15 and in one-liter Tedlar bags using a peristaltic 

pump. The canisters were provided and analyzed 

by EPA’s New England Regional Laboratory. Tedlar 

bags were stored in a cooler without ice (to avoid 

condensation) and analyzed for target VOCs on-site 

by EPA’s New England Regional Laboratory within 24 

hours of sample collection. Canister samples were 

collected by using a brass NPT to Swagelok union 

fitting to connect vapor probes to a “T” fitting made of 

a stainless steel flexible line and an in-line valve. A 

portable vacuum pump was then used to purge vapor 

probes and sampling lines. Samples were collected 

by closing the in-line valve on the pump end of the 

“T” fitting and opening a valve for entry into a six liter 

SilcoCan canister. A particulate filter was attached 

to the inlet port. Samples were collected by simply 

opening the canister valve and waiting until canister 

pressure approached atmospheric pressure (grab 

sampling). This took approximately two minutes. 

Tedlar bag samples were collected using threaded 

brass or plastic nipples, a peristaltic pump, and Tygon 

and Masterflex tubing. All tubing was disposed of after 

sampling at each probe to avoid cross contamination. 

Tedlar bags were filled in about one minute resulting 

in an average flow rate of 1 SLPM.

Open-faced activated charcoal canisters were used 

to measure indoor radon gas concentrations in 

accordance with sampling procedures outlined in EPA 

402-R-93-004. Canisters were placed with the open 

side up 1.2 to 1.5 meters above a floor in a central 

location with unimpeded air flow and left undisturbed for 
103

Three methods were used to evaluate infiltration of 

indoor air flow into a sample container during air 

extraction (purging + sampling). The first method 

entailed sequentially collecting five one-liter Tedlar 

bag samples at a flow rate of 1 SLPM and monitoring 

vapor concentration as a function of extraction volume. 

This was carried out in three homes with little effect on 

sample concentration indicating insignificant infiltration. 

Concrete slabs at these three buildings consisted of 

approximately 2-4” of concrete and were relatively 

intact (few cracks). Similar testing was conducted 

with evacuated canisters representing extraction 

volumes of 5 to 9 and 10 to14 liters at two homes with 

similar results. A second method was then employed 

which utilized a simple mass balance equation and 

sub-slab and basement air concentrations. When the 

sensitivity of the test permitted assessment, infiltration 

of basement air into an evacuated canister was less 

than 1%. However, use of this method to assess 

infiltration during sampling required detection of fairly 

high levels of VOCs not associated with subsurface 

contamination in basement air and low levels or low 

detection limits for these compounds in sub-slab air. 

Sensitivity could be increased by enclosing a wide area 

around a probe with a chamber during air extraction 

and injecting a compound not present in sub-slab or 

basement air (tracer) for a specified period of time. 

However, the tracer concentration would have to be 

held constant during the application period, and air 

permeability testing and flow analysis would have 

to be conducted to estimate the potential area of 

infiltration during testing. A third method of evaluating 

infiltration of basement air into a sampling vessel 

during air extraction involved simulating streamlines 

and particle transport during air extraction using 

estimated permeability parameters. Simulations 

indicated that between 5% and 10% of air extracted 

during purging and sampling could have originated 

as basement air when extracting up to 12 liters of air. 

However, if there was subsidence of sub-slab material 

below a concrete slab, most of this airflow would have 

been lateral flow directly beneath the slab. Overall, 

the extraction volume used in this investigation had 

little effect on sample results. However, the impact 

of large extraction volumes was not evaluated, and 

results of this investigation do not justify use of large 

extraction volumes. 

The impact of rate-limited mass transport was 

evaluated during air extraction by comparing sequential 

sample results with air flow simulations using estimated 

permeability and recharge parameters. At a sampling 

rate of 1 SLPM, constant concentration in sequential 

samples indicated an absence of rate-limited mass 

transport during air extraction. The California 

Environmental Protection Agency in conjunction with 

the California Department of Toxic Substances and the 

Los Angeles Regional Water Quality Control Board (Cal 

EPA, 2003) recently published an advisory on soil-gas 

sampling specifying a maximum flow rate of 0.1 to 0.2 

SLPM during sampling. Given simulations presented 

here, this recommendation appears reasonable.

To evaluate a necessary equilibration time after probe 

installation for sampling, advective air flow modeling 

with particle tracking was used to estimate maximum 

radii of perturbation during probe installation occurring 

over a period of one hour at a pressure differential of 15 

Pa (highest pressure differential or most conservative 

value used in EPA’s vapor intrusion guidance). These 

radii were then used with a spherical diffusion model 

to estimate time to reach 99% of a steady-state 

concentration at a probe given an initial concentration in 

the modeled domain of zero (most conservative case). 
104

coefficients of variation in sub-slab air exceeded 

100% indicating substantial spatial variability in subslab air concentration and the need for placement of 

multiple probes. In this investigation, 55 probes were 

installed in 16 buildings which, on average, resulted 

in placement of one probe every 220 ft2

.

In conclusion, this work provides an extensive 

analysis of sub-slab sampling and supporting datainterpretation techniques. It represents an important 

first step in this area. Further research needs to be 

conducted to evaluate the use of radon as an indicator 

compound to assess vapor intrusion.

At homes near the former Raymark site, sub-slab and 

underlying soils underlying each building consisted 

of relatively dry sand and gravel. Little or no sorption 

would be expected in this material, and volumetric 

water content was relatively low. Simulations indicated 

that under these conditions, equilibration would occur in 

less than 2 hours. Sub-slab probes in this investigation 

were allowed to equilibrate for 1 to 3 days. For subslab material consisting of silt or clay, simulations 

indicated that an equilibration time of approximately 10 

hours would be necessary. However, most sub-slab 

material consists of a mixture of sand and gravel or 

sand even for homes built directly on clay. Thus, an 

equilibration time of two hours should be conservative 

for most cases.

A simple mass-balance equation was used to estimate 

the purging requirement prior to sampling. Simulations 

indicated that collection of 5 purge volumes should 

ensure that the exiting vapor concentration is 99% 

of the entering concentration even when vapor 

concentration inside the sample system has been 

reduced to zero prior to sampling (most conservative 

case). A purge volume for the sample train used in 

homes near the former Raymark site was typically 

less than 10 cm3. 

Generally, during this investigation, one sub-slab vapor 

probe was centrally located while two or more probes 

were placed within one or two meters of basement walls 

in each building. This was done to ensure detection 

of vacuum throughout the entire sub-slab during subslab depressurization testing. In this investigation, 

there appeared to be little correlation between probe 

placement and VOC concentration. That is, placement 

of a probe in a central location did not ensure detection 

of the highest VOC concentrations. At several houses, 
105

Baehr, A.L. and C.J. Joss. 1995. An updated model 

of induced airflow in the unsaturated zone. Water 

Resources Research 31, (2): 417-421.

California Environmental Protection Agency. 2003. 

Advisory - Active soil gas investigations. http://www.

dtsc.ca.gov/PolicyandProcedures/SiteCleanup/

SMBR_ADV_activesoilgasinvst.pdf

Crank, J. 1975. The Mathematics of Diffusion, 2nd 

Ed., Oxford University Press, New York, NY.

Hartman, B. 2004. How to collect reliable soil-gas data 

for risk-based applications - specifically vapor intrusion, 

Part 3 - Answers to frequently asked questions. 

LUSTLine Bulletin 48, November, 2004.

Millington, R.J. and J.P. Quirk. 1961. Permeability 

of porous solids. Trans. Faraday Society 57: 1200-

1207.

Tetra Tech NUS, Inc. 2000. Draft final remedial 

investigation, Raymark – OU – Groundwater, Stratford, 

CT, Response action contract (RAC), Region I, EPA 

contract No. 68-W6-0045, EPA work assignment no. 

029-RICO-01H3

U.S. Environmental Protection Agency. 2002a. Draft 

guidance for evaluating the vapor intrusion to indoor 

air pathway from groundwater and soils (subsurface 

vapor intrusion guidance). http://www.epa.gov/

correctiveaction/eis/vapor.htm. Office of Solid Waste 

and Emergency Response, Washington, D.C.

U.S. Environmental Protection Agency. 2002b. Air 

sample analysis for volatile organic compounds. 

Internal report, Feb. 12, 2002. USEPA New England 

Regional Laboratory, Lexington, MA. 

U.S. Environmental Protection Agency. 2001. 

Development of recommendations and methods to 

support assessment of soil venting performance 

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reports/epa_600_r01_070.pdf. EPA/600/R-01/070. 

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United States

Environmental Protection

Agency

EPA/600/R-05/147

March 2006

National Risk Management

 Research Laboratory

Cincinnati, OH 45268

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