Comparison of Geoprobe®

PRT and AMS GVP Soil-Gas

Sampling Systems with 

Dedicated Vapor Probes

in Sandy Soils at the

Raymark Superfund Site

EPA/600/R-06/111

November 2006

Comparison of Geoprobe® PRT and AMS GVP 

Soil-Gas Sampling Systems with Dedicated 

Vapor Probes in Sandy Soils

at the Raymark Superfund Site

Dominic DiGiulio, Cynthia Paul, and Brad Scroggins

U.S. Environmental Protection Agency

Offi ce 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

U.S. Environmental Protection Agency

Region I, New England Regional Laboratory

North Chelmsford, MA

Ronald Mosley

U.S. Environmental Protection Agency

Offi ce 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

Ravi Costa

The Shaw Group Inc.

Ada, OK

Project Offi cer

Dominic C. DiGiulio

U.S. Environmental Protection Agency

Offi ce 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
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. 

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. 

ii
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. Specifically, a study was conducted to compare results of soil-gas sampling 

using dedicated vapor probes, a truck-mounted direct-push technique, Geoprobe®

 Post-Run-Tubing 

system, and a hand-held rotary hammer technique, AMS Gas Vapor Probe kit. Testing revealed some 

statistically significant differences. However, the magnitude of variation was similar to that due to spatial 

variability on the scale of testing (1 m). Hence for practical purposes, all three sample systems were 

considered approximately equivalent. This investigation should provide confidence that the PRT and GVP 

sample systems are satisfactory for collecting soil-gas samples in sandy soils, such as those present near 

the Raymark site, to evaluate the potential for vapor intrusion. 

 Stephen G. Schmelling, Director 

 Ground Water and Ecosystems Restoration Division 

 National Risk Management Research Laboratory

iii
 

 Abstract 

A study was conducted near the Raymark Superfund Site in Stratford, Connecticut to compare results of 

soil-gas sampling using dedicated vapor probes, a truck-mounted direct-push technique - the Geoprobe 

Post-Run-Tubing (PRT) system, and a hand-held rotary hammer technique - the AMS Gas Vapor Probe 

(GVP) kit. A comparison of VOC concentrations using dedicated vapor probes and the GVP sampling kit 

indicated that the two methods provided similar results. However, at one location, VOC concentrations 

were significantly higher for dedicated vapor probes indicating potential leakage with the GVP system. 

VOC concentrations using the PRT system were higher than VOC concentrations using dedicated vapor 

probes by an average factor of 1.2. This is the same magnitude observed for spatial variability on a scale 

of 1 m (median of 1.2 and average of 1.3 for 90 sample pairs). However, this effect did not appear to be 

due to spatial variability which would result in random scatter not a consistent bias as observed. It is also 

unlikely that extraction volume or sampling sequence caused the observed bias given the results of 

extraction volume and sample sequence testing. VOC concentrations using the PRT system were also 

higher than VOC concentrations using the GVP kit by an average factor of 2.4. Similar to the comparison 

between probe and PRT sampling systems, the effect did not appear to be due to spatial variability, 

extraction volume, or sequence of sampling. Thus, utilization of the PRT system resulted in observation of 

higher concentrations of VOCs compared to the GVP kit and dedicated vapor probes. However, variation 

in concentration was relatively minor when compared to spatial variability on the scale used for comparison 

testing. Hence for practical purposes, all three sample systems can be considered approximately 

equivalent. 

iv
Table of Contents 

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

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

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

List of Abbreviations ....................................................................................................................................vi 

List of Figures ............................................................................................................................................. vii 

List of Tables ...............................................................................................................................................xi 

Acknowledgements.................................................................................................................................... xiv 

Executive Summary................................................................................................................................... E1 

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

2.0 Site Description.................................................................................................................................2

3.0 Methods and Materials......................................................................................................................6 

3.1 Soil-Gas Sampling from Dedicated Vapor Probes ................................................................6 

3.2 Soil-Gas Sampling with the GeoProbe®

 PRT System ...........................................................8 

3.3 Soil-Gas Sampling with the AMS GVP Kit ..........................................................................11 

 3.4 On-Site Soil-Gas Analysis and Data Quality .......................................................................13 

 3.5 Computation of Pre-Sample Internal Volume Exchange Requirements .............................15 

 3.6 Assessment of Extraction Volume on Sample Results .......................................................18 

 3.7 Assessment of Air Extraction at One Location on Another Location...................................21 

 3.8 Consideration of Spatial Variability on Comparison of Sampling Techniques ....................22 

4.0 Results............................................................................................................................................26 

 4.1 Results of Testing at MW302SGM......................................................................................26 

 4.2 Results of Testing at MW514SG.........................................................................................27 

 4.3 Results of Testing at MW523SGS, MW523SGM, and MW523SGD...................................29 

 4.4 Results of Testing at MW525SG.........................................................................................31 

 4.5 Results of Testing at MW526SGS, MW526SGM, and MW526SGD...................................34 

5.0 Discussion of Comparison Testing .................................................................................................38 

6.0 Summary.........................................................................................................................................41 

References .................................................................................................................................................43 

Appendix A .................................................................................................................................................45 

v
List of 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 

O2 oxygen 

CO2 carbon dioxide 

CH4 methane 

ID inner diameter 

VOC volatile organic chemical 

PRT post-run tubing 

GVP gas vapor probe 

PVC polyvinylchloride 

SLPM standard liter per minute 

GC gas chromatography 

vi
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).....................................................................................................................................2 

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) ..................................3 

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

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

Figure 5 Results of ten shallow single-well hydraulic conductivity tests at the Raymark site 

(boundary values for sand and gravel taken from Freeze and Cherry, 1979).......................4 

Figure 6 Results of a sub-slab air permeability test taken from EPA (2006).......................................5 

Figure 7 Typical construction log for dedicated vapor probes installed at the Raymark Site ..............6 

Figure 8 Photograph of valve used to seal dedicated probes, PVC barbed fitting, and Teflon tubing 

used for sampling..................................................................................................................7 

Figure 9 Photograph of peristaltic pump, flowmeter, and landfill gas meter used during purging 

dedicated vapor probes.........................................................................................................8 

Figure 10 Photograph of peristaltic pump and one-liter Tedlar bags (duplicate sample) used for 

sampling dedicated vapor probes .........................................................................................8 

Figure 11 Photograph of truck-mounted PRT system...........................................................................9 

Figure 12 Components of PRT sampling system..................................................................................9 

Figure 13 Photograph of an expendable point and expendable point holder........................................9 

Figure 14 Photograph of a PRT adapter with an O-ring and associated Teflon tubing.......................10 

Figure 15 Photograph of metal rod used to push out the expendable point........................................10 

Figure 16 Photograph of connection of PRT adapter to expendable point holder ..............................10 

Figure 17 Creation of hole in asphalt prior sampling with GVP kit ......................................................11 

Figure 18 Photograph of Retract-A-Tip ...............................................................................................11 

Figure 19 Disassembled view of Retract-A-Tip ...................................................................................11 

vii
List of Figures - continued 

Figure 20 Photograph of hammering Retract-A-Tip and support pipe using a rotary hammer drill 

and the GVP extension drive adapter .................................................................................12 

Figure 21 Retraction of Retract-A-Tip prior to sampling......................................................................12 

 

Figure 22 Proximity of dedicated vapor probe (metal cover surrounded by white concrete at 

base of Geoprobe unit), PRT, and GVP sampling systems ................................................12 

Figure 23 Comparison of EPA Method TO-15 with sample collection using a peristaltic pump 

 and Tedlar bags with on-site GC analysis of 1,1,1-TCA, 1,1-DCE, TCE, and 

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

 = 0.88).............................................................................................14 

Figure 24 Purge volume as a function of C0 /Cin and Cout /Cin ...............................................................16 

Figure 25 Vapor concentration as a function of cumulative post-sample extraction volume up to 

5.5 liters at dedicated vapor probe MW513SG ...................................................................17 

Figure 26 O2, CO2, and CH4 concentration as a function of cumulative post-sample extraction at 

dedicated vapor probe MW514SG......................................................................................18 

Figure 27 Vapor concentration as a function of cumulative pre-sample extraction volume using 

the PRT sampling system at a depth of 0.76 m near MW525SG .......................................19 

Figure 28 Vapor concentration as a function of cumulative pre-sample extraction volume at dedicated 

vapor probe MW513SG at a depth interval of 2.1 to 2.4 m.................................................20 

Figure 29 Comparison of first and third samples at dedicated probe, PRT, and GVP sample 

 locations..............................................................................................................................21 

Figure 30 Coefficient of variation (%) as a function of mean vapor concentration for first, second, and 

third samples at dedicated probe, PRT, and GVP sample locations ..................................22 

Figure 31 Photograph illustrating five PRT sample locations (orange flags) near MW213 .................23 

Figure 32 Schematic illustrating five PRT sample locations near MW213 in plan view ......................23 

Figure 33a Vapor concentration at locations S1 through S5 (one sample at each location) at a 

depth of 0.76 m ...................................................................................................................24 

Figure 33b Vapor concentration at locations S1 through S5 (one sample at each location) at a 

depth of 2.3 m .....................................................................................................................24

Figure 33c Vapor concentration at locations S1 through S5 (one sample at each location) at a 

depth of 3.2 m .....................................................................................................................25

viii
List of Figures - continued 

Figure 34 Schematic illustrating the location of sampling systems at MW302SGM in plan view........26 

Figure 35 Comparison of mean (3 samples from each sample system) vapor concentrations at 

MW302SGM at a depth of 2.3 m.........................................................................................27 

Figure 36 Schematic illustrating the location of sampling systems at MW514SG in plan view...........28 

Figure 37 Comparison of mean (3 samples from each sample system) vapor concentrations at 

MW514SG at a depth of 2.3 m............................................................................................28

Figure 38 Schematic illustrating the location of sampling systems at MW523SGS, MW523SGM, 

and MW523SGD in plan view .............................................................................................29 

Figure 39 Comparison of vapor concentrations (1 sample from each sample system) at 

MW523SGM at a depth of 2.3 m.........................................................................................30 

Figure 40 Comparison of vapor concentrations (1 sample from each sample system) at 

MW523SGD at a depth of 3.4 m.........................................................................................31 

Figure 41 Schematic illustrating the location of sampling systems at MW525SG in plan view...........32 

Figure 42 Comparison of mean (3 samples from each sample system) vapor concentrations at 

MW525SG at a depth of 0.91 m..........................................................................................32

Figure 43 Comparison of mean (3 samples from each sample system) vapor concentrations at 

MW525SG at a depth of 2.3 m............................................................................................33 

Figure 44 Schematic illustrating the location of sampling systems at MW526SGS, MW526SGM, 

and MW526SGD in plan view .............................................................................................34 

Figure 45 Comparison of mean (3 samples from each sample system) vapor concentrations at 

MW526SGS at a depth of 0.76 m .......................................................................................35 

Figure 46 Comparison of mean (3 samples from each sample system) vapor concentrations at 

MW526SGM at a depth of 0.76 m.......................................................................................35 

Figure 47 Comparison of mean (3 samples from each sample system) vapor concentrations at 

MW526SGM at a depth of 2.3 m.........................................................................................36 

Figure 48 Comparison of mean (3 samples from each sample system) vapor concentrations at 

MW526SGD at a depth of 3.2 m.........................................................................................37 

Figure 49 Comparison of probe and GVP VOC concentrations – error bars represent one 

standard deviation from three samples ...............................................................................38 

ix
List of Figures - continued 

Figure 50 Comparison of dedicated vapor probe and GVP VOC concentrations – error bars represent 

one standard deviation from three samples ........................................................................39 

Figure 51 Comparison of PRT and GVP VOC concentrations – error bars represent one 

standard deviation from three samples ...............................................................................40 

x
List of Tables 

Table 1 Depth of Fill Materials and Screened Intervals in Boreholes Containing Dedicated 

 Vapor Probe........................................................................................................................45 

Table 2 Results of Container Blanks................................................................................................45 

Table 3 Results of Field Blanks........................................................................................................45 

Table 4 Results of Probe Blanks......................................................................................................45

Table 5 Results of Travel Blanks .....................................................................................................45

Table 6 Results of Replicate Samples .............................................................................................46 

Table 7a Computation of Internal Volume of PRT Sampling System When Sampling 

at 0.76 m Near MW525SG..................................................................................................46 

Table 7b Computation of Pre-Sample Extraction and Internal Exchange Volumes of PRT 

Sample System When Sampling at 0.76 m Near MW525SG .............................................46 

Table 8a Computation of Internal Volume Dedicated Vapor Probe MW513SG When Sampling 

at a Depth Interval of 2.1 to 2.4 m.......................................................................................46 

Table 8b Computation of Pre-Sample Extraction and Internal Exchange Volumes of Dedicated Vapor 

Probe MW513SG When Sampling at a Depth Interval of 2.1 to 2.4 m ...............................47 

Table 9a Computation of Internal Volumes Using the PRT Sampling System at Five Sample 

Locations at a Depth of 0.76 m Near MW213 .....................................................................47 

Table 9b Computation of Internal Volumes Using the PRT Sampling System at Five Sample 

Locations at a Depth of 2.3 m Near MW213 .......................................................................47 

 

Table 9c Computation of Internal Volumes Using the PRT Sampling System at Five Sample 

Locations at a Depth of 3.2 m Near MW213 .......................................................................47 

Table 9d Computation of Pre-Sample Extraction and Internal Exchange Volumes and Sample 

Results Using the PRT Sampling System at a Depth of 0.76 m Near MW213 ...................48 

Table 9e Computation of Pre-Sample Extraction and Internal Exchange Volumes and Sample 

Results Using the PRT Sampling System at a Depth of 2.3 m Near MW213 .....................48 

Table 9f Computation of Pre-Sample Extraction and Internal Exchange Volumes and Sample 

Results Using the PRT Sampling System at a Depth of 3.2 m Near MW213 .....................48 

Table 10a Internal Volumes of Probe, PRT, and GVP Systems at 2.3 m Near MW302SGM..............48 

xi
List of Tables - continued 

Table 10b Cumulative Pre-Sample Internal Exchanges of Probe, PRT, and GVP Systems at 

2.3 m Near MW302SGM.....................................................................................................49 

Table 10c VOC and Gas Concentrations of Probe, PRT, and GVP Systems at 2.3 m Near 

 MW302SGM........................................................................................................................49

Table 11a Internal Volumes of Probe, PRT, and GVP Systems at 2.3 m Near MW514SG.................49 

Table 11b Cumulative Pre-Sample Internal Exchanges of Probe, PRT, and GVP Systems at 2.3 m 

 Near MW514SG..................................................................................................................50 

Table 11c VOC and Gas Concentrations of Probe, PRT, and GVP Systems at 2.3 m Near 

 MW514SG...........................................................................................................................50 

Table 12a Computation of Internal Volumes of Sample Systems at 0.8 m Near MW523SGS ............50 

Table 12b Computation of Pre-Sample Internal Exchanges and VOC Concentrations of Sample 

Systems at 0.8 m Near MW523SGS...................................................................................51 

Table 13a Computation of Internal Volumes of Sample Systems at 2.3 m Near MW523SGM............51 

Table 13b Computation of Pre-Sample Internal Exchanges and VOC Concentrations of Sample 

Systems at 2.3 m Near MW523SGM ..................................................................................51 

Table 14a Computation of Internal Volumes of Sample Systems at 3.4 m Near MW523SGD............51 

Table 14b Computation of Pre-Sample Internal Exchanges and VOC Concentrations of Sample 

Systems at 3.4 m Near MW523SGD ..................................................................................51 

Table 15a Computation of Internal Volumes of Sample Systems at 0.91 m Near MW525SG ............51 

Table 15b Computation of Pre-Sample Internal Exchanges of Sample Systems at 0.91 m Near 

 MW525SG...........................................................................................................................52 

Table 15c Summary of VOC Concentrations in PRT and GVP Systems at 0.91 m Near 

 MW525SG...........................................................................................................................52 

Table 16a Computation of Internal Volumes of Sample Systems at 2.3 m Near MW525SG ..............52 

Table 16b Computation of Pre-Sample Internal Exchanges of Sample Systems at 2.3 m Near 

 MW525SG...........................................................................................................................52 

Table 16c Summary of VOC and Gas Concentrations in PRT and GVP Systems at 2.3 m Near 

 MW525SG...........................................................................................................................53 

Table 17a Computation of Internal Volumes of Sample Systems at 0.91 m Near MW526SGS ..........53 

xii
List of Tables - continued 

Table 17b Computation of Pre-Sample Internal Exchanges of Sample Systems at 0.91 m Near 

 MW526SGS ........................................................................................................................53 

Table 17c Summary of VOC and Gas Concentrations in PRT and GVP Systems at 0.91 m Near 

 MW525SG...........................................................................................................................54

Table 18a Computation of Internal Volumes of Sample Systems at 0.91 m Near MW526SGM..........54 

Table 18b Computation of Pre-Sample Internal Exchanges of Sample Systems at 0.91 m Near 

 MW526SGM........................................................................................................................54 

Table 18c Summary of VOC and Gas Concentrations in PRT and GVP Systems at 0.91 m Near 

 MW526SGM........................................................................................................................55 

Table 19a Computation of Internal Volumes of Sample Systems at 2.3 m Near MW526SGM............55 

Table 19b Computation of Pre-Sample Internal Exchanges of Sample Systems at 2.3 m Near 

 MW526SGM........................................................................................................................55 

Table 19c Summary of VOC and Gas Concentrations in Sample Systems at 2.3 m Near 

 MW526SGM........................................................................................................................56 

Table 20a Computation of Internal Volumes of Sample Systems at 3.2 m Near MW526SGD............56 

Table 20b Computation of Pre-Sample Internal Exchanges of Sample Systems at 3.2 m Near 

 MW526SGD........................................................................................................................56 

Table 20c Summary of VOC and Gas Concentrations in Sample Systems at 3.2 m Near 

 MW526SGD........................................................................................................................57 

xiii
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, and David Burden of 

NRMRL, Ada, OK. 

 

The authors would 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 

Solano Beach, CA 92075 

Dr. Jim Weaver 

U.S. Environmental Protection Agency 

Office of Research and Development 

National Exposure Research Laboratory 

Ecosystems Research Division 

Athens, GA 30605-2700 

xiv
Executive Summary 

Soil-gas sampling is widely used as a reconnaissance tool to help delineate the areal extent of groundwater contamination and both the areal and vertical extent of vadose zone contamination by volatile 

organic compounds (VOCs). Soil-gas sampling is often followed by ground-water and/or soil sampling to 

quantify contamination in these media. Since soil-gas data is generally not used to evaluate the need for 

corrective action or attainment of remedial goals, quality assurance and control (QA/QC) considerations 

associated with soil-gas sampling are often less stringent compared to ground-water or soil sampling. 

However, EPA’s recent draft guidance on vapor intrusion (EPA, 2002) allows the quantitative use of soilgas data along with empirical attenuation factors or the Johnson-Ettinger Model (1991) to directly assess 

potential exposure from vapor intrusion. Thus, collection of representative soil-gas samples could be 

critical to this endeavor. Representative soil-gas data refers to collection of a sufficient number of properly 

located samples within an area and depth of concern subject to adequate QA/QC measures. 

Implementation of QA/QC measures ensures that observed concentrations reflect true soil-gas 

concentrations in the vicinity of a probe during sampling. 

There are a number of important QA/QC issues relevant to soil-gas sample collection. One issue not 

addressed in the literature is the equivalence of direct-push/hammer soil-gas sampling techniques with 

dedicated vapor probes. Dedicated probes are generally considered a reliable method for soil-gas 

sampling because of the use of a layer of bentonite to isolate a sand-packed screened interval. However, 

direct-push/hammer soil-gas sampling techniques have become common to support vapor intrusion 

investigations because they are more convenient (ability to sample the same day as probing) and less 

expensive compared to installation of dedicated probes. Also, direct-push/hammer techniques allow 

collection of soil-gas samples close to a building minimizing concern regarding interpolation and 

extrapolation of soil-gas concentrations beneath a building. 

In this investigation, concentrations from soil-gas samples collected using dedicated vapor probes were 

compared with samples using the Geoprobe Post-Run Tubing (PRT) system and AMS Gas Vapor Probe 

(GVP) kit. The PRT system is one of the most commonly used truck-mounted direct-push soil-gas 

sampling systems in the United States. The PRT system can be used to collect soil-gas samples to depths 

up to 20 m. The hand-held rotary hammer GVP kit is suitable for shallow soil-gas sampling (up to 4 m) but 

allows access within 1 m of a building. These two methods were selected for evaluation because of their 

common use. 

E1 
Soil-gas sampling was conducted at one to three depths at several locations near the Raymark Superfund 

site in Stratford, Connecticut. Surficial soils in the soil-gas sampling areas are very permeable consisting 

of sand or a mixture of sand and gravel. A peristaltic pump with Masterflex®

 tubing, variable-area PVC 

flowmeter, and landfill gas meter were used in line to extract air, measure flow rates, and measure gas (O2, 

CO2, and CH4 ) concentrations during purging. A peristaltic pump and one-liter Tedlar bags were used for 

sampling. Purging and sampling occurred at a flowrate of 0.5 standard liters per minute (SLPM). On-site 

gas chromatography (GC) analysis was conducted by EPA's New England Regional Laboratory using their 

standard operating procedure. Air samples from each Tedlar bag were injected into two portable GCs with 

results compared to ensure consistency. Tedlar bag sampling and on-site analysis provided near real-time 

data. Detection limits for on-site analysis were 2 – 5 ppbv for VOCs of concern. Container, field, probe, 

and travel blanks demonstrated that Tedlar bags used to collect samples, coolers used to transport 

samples, PRT and GVP sample systems used to extract samples, and atmospheric air were not a source 

of VOCs at detection limits of concern. Replicate samples indicated excellent sample precision. 

A mass-balance equation was used to estimate internal volume exchanges necessary to purge dedicated 

probe, PRT, and GVP systems prior to sample collection. Simulations indicated that if air within a sample 

system had initially been reduced to zero concentration because of direct exposure to atmospheric air, 

extraction of 2.2 to 3.0 internal volumes prior to sampling would ensure that VOC concentrations of air 

entering a sample vessel would be 90 to 95% of VOC concentrations of soil-gas entering a sampling 

system. This would be the most conservative condition and representative of PRT and GVP sample 

systems. A zero concentration would not be expected for a dedicated vapor probe which had been sealed 

for months prior to sampling. Purge testing at a dedicated vapor probe indicated concentration stabilization 

after only one internal volume exchange. In this investigation, at least 2 internal volumes of air were 

removed from dedicated vapor probes prior to sample collection. At least 3 internal volumes of air were 

removed from PRT and GVP sample systems prior to sample collection. 

To allow a comparison of dedicated probe, PRT, and GVP sampling systems, it had to be demonstrated 

that the act of sample collection did not affect sample results at the system being sampled or at other 

nearby sample locations. Increasing internal volume exchanges or pre-sample air extraction volume in 

excess of a purging requirement could increase the possibility of collecting a soil-gas sample not 

representative of some integrated volume of soil around a screened interval. If properly sampled, VOC 

concentrations should remain relatively constant unless air is drawn in from a nearby region of lower or 

higher vapor concentration. To evaluate the impact of pre-sample internal volume exchanges on sample 

results, ten soil-gas samples were collected after various (starting with zero) internal volume exchanges at 

E2 
one PRT and one dedicated vapor location sampling location. In the test using the PRT system, up to 9 

liters of air and 74 internal volume exchanges were extracted with little impact on vapor concentration. In 

the test using the dedicated vapor probe, up to 103 liters or internal volume exchanges were extracted with 

little impact on vapor concentration (1 internal exchange equaled 1 liter). Thus, it is unlikely that presample air extraction impacted sample results at the systems being sampled. 

To evaluate the potential impact of air extraction at one location on sample results at a nearby location and 

depth, three samples were taken non-sequentially from each sampling system. For example, at one 

location, the PRT system was sampled first, followed by the GVP system, followed by sampling at the 

dedicated probe. The sequence was then changed to sampling at the GVP system, followed by sampling 

at the dedicated vapor probe, followed by sampling at the PRT system and so on until three samples had 

been obtained from each system at each depth. A comparison of first and third VOC concentrations for 

locations and depths where three samples were collected indicated that sample collection at a one location 

did not impact sample results at another location. Also, coefficients of variation for the three samples were 

generally below 10% again indicating little impact. 

Another potentially complicating factor in comparing vapor concentrations from dedicated probe, PRT, and 

GVP sampling systems is spatial variability. PRT and GVP sampling locations were positioned relatively 

close (usually within 1 m) to dedicated vapor probes to minimize the effect of spatial variability on soil-gas 

concentration. To assess the presence and magnitude of spatial variability at this scale, soil-gas sampling 

was conducted at three depths at five locations separated by 0.46 m (1.5’) in a cross-like pattern using the 

PRT sampling system. In general, variation in VOC concentration with location at each depth was present 

but relatively minor. 

Sampling systems were compared using data from all locations and depths. A comparison of VOC 

concentrations using dedicated vapor probes and the GVP sampling kit indicated that the two methods 

provided similar results (p = 0.31 for two-tailed paired t-Test, p > 0.2 for two-tailed non-parametric Wilcoxon 

Signed Rank Test). However, at one location, O2, CO2, and VOC concentrations were noticeably different 

for sampling systems indicating potential leakage with the GVP system. 

VOC concentrations using the PRT system were not statistically equivalent to VOC concentrations using 

dedicated vapor probes (p = 0.009 for two-tailed paired t-Test, p < 0.01 for two-tailed non-parametric 

Wilcoxon Signed Rank Test). VOC concentrations using the PRT system were higher than VOC 

concentrations detected using dedicated vapor probes by an average factor of 1.2. This is the same 

E3 
magnitude observed for spatial variability on a scale of 1 m (median of 1.2 and average of 1.3 for 90 

sample pairs). However, this effect did not appear to be due to spatial variability which would result in 

random scatter not a consistent bias as observed. It is also unlikely that extraction volume or sampling 

sequence caused the observed bias given results from extraction volume and sample sequence testing. 

VOC concentrations using the PRT system were also not statistically equivalent to VOC concentrations 

using the GVP kit (p = 0.03 for two-tailed paired t-Test, p < 0.01 for two-tailed non-parametric Wilcoxon 

Signed Rank Test). VOC concentrations using the PRT system were higher than VOC concentrations 

detected using the GVP kit by an average factor of 2.4. Similar to the comparison between probe and PRT 

sampling systems, the effect does not appear to be due to spatial variability, extraction volume, or 

sequence of sampling. 

Thus, utilization of the PRT system resulted in observation of higher concentrations of VOCs compared to 

the GVP sampling system and dedicated vapor probes. However, the magnitude of variation was relatively 

minor especially when to compared to variation on a scale of 1 m due to spatial variability. Hence for 

practical purposes, all three sample systems can be considered approximately equivalent. 

This testing was conducted in highly permeable soils where the potential for leakage from directpush/hammer soil-gas sampling systems would be expected to be low compared to less permeable soils 

such as silt and clay. Thus, the results of this investigation should not be extrapolated to other soil textures 

where additional investigation is needed. Also, only one direct-push and one rotary hammer method was 

evaluated for comparison with dedicated vapor probes. Thus, the results of this investigation should not be 

extrapolated to other direct-push/hammer soil-gas sampling techniques. 

E4 
1.0 Introduction 

Soil-gas sampling is widely used as a reconnaissance tool to help delineate the areal extent of groundwater contamination and both the areal and vertical extent of vadose zone contamination by volatile 

organic compounds (VOCs). Soil-gas sampling is often followed by ground-water and/or soil sampling to 

quantify contamination in these media. Since soil-gas data is generally not used to evaluate the need for 

corrective action or attainment of remedial goals, quality assurance considerations associated with soil-gas 

sampling are often less stringent compared to ground-water or soil sampling. However, EPA’s recent draft 

guidance on vapor intrusion (EPA, 2002) allows the quantitative use of soil-gas data along with empirical 

attenuation factors or the Johnson-Ettinger Model (1991) to directly assess potential exposure from vapor 

intrusion. Thus, collection of representative soil-gas samples could be critical to this endeavor. 

Representative soil-gas data refers to collection of a sufficient number of properly located samples within 

an area and depth of concern subject to adequate quality assurance and control (QA/QC) measures. 

Implementation of QA/QC measures ensures that observed concentrations reflect true soil-gas 

concentrations in the vicinity of a probe during sampling. 

There are a number of important QA/QC issues relevant to soil-gas sample collection. One issue not 

addressed in the literature is the equivalence of direct-push/hammer soil-gas sampling techniques with 

dedicated vapor probes. Dedicated probes are generally considered a reliable method for soil-gas 

sampling because of the use of a layer of bentonite to isolate a sand-packed screened interval. However, 

direct-push/hammer soil-gas sampling techniques have become common to support vapor intrusion 

investigations because they are more convenient (ability to sample the same day as probing) and less 

expensive compared to installation of dedicated probes. Also, direct-push/hammer techniques allow 

collection of soil-gas samples close to a building minimizing concern regarding interpolation and 

extrapolation of soil-gas concentrations beneath a building. 

In this investigation, concentrations from soil-gas samples collected using dedicated vapor probes were 

compared with samples using the Geoprobe Post-Run Tubing (PRT) system and AMS Gas Vapor Probe 

(GVP) kit. The PRT system is one of the most commonly used truck-mounted direct-push soil-gas 

sampling systems in the United States. The PRT system can be used to collect soil-gas samples to depths 

up to 20 m. The hand-held rotary hammer GVP kit is suitable for shallow soil-gas sampling (up to 4 m) but 

allows access within 1 m of a building. These two methods were selected for evaluation because of their 

common use. 

1
2.0 Site Description 

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., Wal-Mart, 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 

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). 

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 2000). 

As illustrated in Figures 2, 3, and 4, glaciofluvial deposits 

and fractured granite bedrock valleys lie beneath 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 and soil-gas 

contaminant profiles difficult. 

2
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). 

 

Surficial soils in areas of soil-gas sampling consist of sand 

or a mixture of sand and gravel. The results of ten shallow 

single-well ground-water hydraulic conductivity tests taken 

from TetraTech NUS (2000) are illustrated in Figure 5. 

Bounds for sand and gravel are taken from Freeze and 

Cherry (1979). Values for hydraulic conductivity are typical 

of sand and vary from 1.0 x10-03 to 2.0 x 10-02 cm/s. The 

results of a sub-slab air permeability test taken from a home 

(EPA, 2006) are illustrated in Figure 6. Air permeability 

values of sub-slab materials are representative of native 

soils since concrete was simply poured on sandy soils in 

basements. The range of radial permeability of soils tested, 

7.0 x 10-07 – 8.0 x 10-07 cm2

 is typical of sandy soils. 

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

3
Figure 4

Figure 5 a r 

and and gravel taken from Freeze and Cherry, 1979). 

. Geologic cross-section H – H’ (modified from Tetra Tech NUS, Inc., 2000). 

. Results of ten shallow single-well hydraulic conductivity tests at the Raymark site (boundary v lues fo

s

4
Figure 6. Results of a sub-slab air permeability test taken from EPA (2006). 

5
 

3.0 Methods and Materials 

3.1 Soil-Gas Sampling from Dedicated Vapor Probes 

Dedicated vapor probes used in the study were installed by Tetra-Tech for U.S. EPA, Region I. A typical 

construction log for a dedicated probe is illustrated in Figure 7. 

Figure 7. Typical construction log for dedicated vapor probes installed at the Raymark Site. 

6
Boreholes for dedicated vapor probes were installed using a drill rig equipped with a hollow-stem auger. 

The diameter of boreholes varied from 8 to 13 cm (3 to 5”). A 1.9 cm (3⁄4”) inner diameter (ID) 

polyvinylchloride (PVC) riser pipe containing a metal valve at the upper end and a 30 cm (1’) long 3.8 cm 

(1.5”) ID PVC factory-slotted screen interval at the lower end was lowered into each borehole and set in 

place with a filter pack consisting of medium-grained sand. Dry bentonite chips were placed above each 

filter pack in small increments (e.g., 15 cm) and hydrated to create a seal above the sample interval. 

Medium-grained sand was placed above each bentonite seal to serve as a drainage layer. A flushmounted iron casing was then set in place at each borehole and sealed in concrete. 

Depths of fill materials and screened intervals in each borehole are summarized in Table 1 in Appendix A. 

Concrete extending from the surface to sand drain layers varied in thickness from 0.2 to 0.3 m (0.5 to 0.8’). 

Bentonite layers extending from the base sand drain layers to the top of the sand filter packs were 0.2 m 

thick (0.5’) for probes screened 0.61 – 0.91 m (2 to 3’) below grade, 0.9 to 1.1 m thick (3.0 to 3.5’) for 

probes screened 2.1 to 2.4 m (7 to 8’) below grade, and 2.0 to 2.1 m thick (6.5 to 7.0’) for probes screened 

3.0 – 3.3 m (10 to 11’) below grade. 

Figures 8, 9, and 10 illustrate purge and sample collection in dedicated vapor probes. Tetra Tech (2000) 

attached a valve with a metal barbed fitting to a riser pipe to seal all dedicated probes. A PVC barbed 

union and 0.95 cm (3/8”) ID Teflon®

 tubing was attached to the barbed fitting during purging and sample 

collection. 

Figure 8. Photograph of valve used to seal dedicated 

probes, PVC barbed fitting, and Teflon®

 tubing used for 

sampling. 

During purging, a peristaltic pump with Masterflex®

tubing, variable-area PVC flowmeter, and landfill gas 

meter were used in line to extract air, measure flow 

rate, and measure oxygen (O2 ), carbon dioxide 

(CO2 ), and methane (CH4 ) gas concentrations. 

Purge and sample collection occurred at a flow rate 

of 0.5 standard liters per minute (SLPM). To 

eliminate the potential of cross-contamination, 

flowrate was not measured during sampling but set 

during purging. Teflon®

 and Masterflex® were 

replaced after sampling at each depth and location. 

7
Figure 9. Photograph of peristaltic pump, flowmeter, a

landfill gas meter used during purging dedicated vapor 

probes. 

nd 

Figure 10. Photograph of peristaltic pump and one-liter 

Tedlar bags (replicate sample) used for sampling 

dedicated vapor probes. 

3.2 Soil-Gas Sampling with the GeoProbe PRT System 

A photograph of a Geoprobe PRT system mounted on a flat-bed truck is illustrated in Figure 11. Each 

sample location was surveyed for the presence of underground utilities prior to probing. Figures 12

through 16 illustrate components of the PRT system. Probe rods were pushed vertically into the ground 

until the desired depth was reached. The probe rods were then retracted approximately 5 cm for sampling. 

A metal rod was used to push out the expendable point. The Teflon®

 tubing containing the PRT and an 

adapter with an O-ring was then inserted into the probe rods and turned counterclockwise to 

engage the adapter threads with the expendable point holder. 

8
Figure 11. Photograph of truck-mounted PRT 

system. 

The tubing was pulled up lightly to test 

engagement of the threads. After sampling 

was completed, the tubing was pulled up firmly 

until it released from the adapter. The probe 

rods were then retracted to recover the point 

holder and PRT adapter. Teflon®

 tubing was 

replaced at each sample depth to avoid 

potential cross-contamination. 

Figure 12. Components of PRT sampling system. 

Similar to sampling at dedicated vapor probes, a peristaltic pump, flowmeter, 

and landfill gas meter were used in line to extract air and measure flow rate 

and O2, CO2, and CH4 concentrations during purging. A peristaltic pump and 

one-liter Tedlar bags were used for sampling. Flowrate during purging and 

sampling was 0.5 SLPM. 

 point holder. 

Figure 13. Photograph of an expendable point and expendable 

9
Figure 14. Photograph of a PRT adapter with an O-ring 

igure 15. Photograph of metal rod used to push out the 

Figure 16. Photograph of connection of PRT adapter to 

and associated Teflon®

 tubing. 

F

expendable point.

expendable point holder. 

10
3.3 Soil-Gas Sampling with the AMS GVP System 

As illustrated in Figure 17, if asphalt was present at the probing location, a rotary hammer drill and 

concrete bit were used to cut a 3.8 cm (11⁄2") hole prior to sampling. 

Figure 17. Creation of hole in asphalt prior sampling with GVP kit. 

A section (30 cm longer than target depth) of 0.48 cm (3/16") ID 

x 0.64 cm (1/4") OD Teflon®

 tubing was attached to the barbed 

end of an AMS Retract-A-Tip as illustrated in Figure 18. A 

disassembled view of the Retract-A-Tip is provided in Figure 

19. The Retract-A-Tip consists of a stainless-steel tip, screen, 

and housing having a 1.6 cm (5/8”) outside diameter. The tip 

was then connected to 0.91 meter (3’) sections of threaded 1.6 

cm OD stainless-steel pipe. The pipe was connected to an 

AMS extension drive adapter and hammered to a desired depth 

with a rotary hammer drill as illustrated in Figure 20. 

 

Figure 18. Photograph of Retract-A-Tip and Teflon®

 tubing. 

 Figure 19. Disassembled view of Retract-A-Tip. 

11
12

hotograph of hammering Retract-A-Tip and support 

pipe using a rotary hammer drill and the GVP extension drive 

adapter. 

As illustrated in Figure 21, prior to sampling, the Retract-Ak 

provided with the GVP kit. After sampling, the rods were 

Figure 21. Retraction of Retract-A-Tip prior to sampling. 

As illustrated in Figure 22, dedicated vapor probe, PRT, and 

GVP sampling systems were generally located within 1 m of 

 spatial variability on data 

por probe (metal cover 

 Geoprobe unit), PRT, and 

Figure 20. P

Tip and associated pipe was retracted 5 cm using a jac

removed from the ground using the AMS retrieval jack. The 

Retract-A-Tip was then cleaned prior to sampling at the next 

depth. 

Again, similar to sampling at dedicated vapor probes, a 

peristaltic pump, flowmeter, and landfill gas meter were used 

in line to extract air and measure flow rate and O2, CO2, and 

CH4 concentrations during purging. A peristaltic pump and 

one-liter Tedlar bags were used for sampling. Purging and 

sampling occurred at a flowrate of 0.5 SLPM. 

each other to minimize the effect of

interpretation. 

Figure 22. Proximity of dedicated va

surrounded by white concrete at base of

GVP sampling systems.
3.4 On-Site Soil-Gas Analysis and Data Quality 

w

using their standard operating procedure (USEPA, 2002b). 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 

electron capture detector. The second GC w

(1/8”) SE-30 column and a PID. A Hamilton 2

used to directly inject 200 μl of sample into bo

readily available commercial methanol stock s

glassware to a concentration of 10 μg/l. After preparation, standards were immediately transferred into 40 

ml VOA vials and stored in an ice bath (0 – 1°C). Prior to air sample analysis, 10 ml of standard was 

withdrawn from a 40 ml VOA vial to create

calibrated for target compounds using the hea

On-site GC analysis for 1,1,1-TCA, 1,1-DCE, 

sampling at the Raymark site (EPA, 2006). 

a

Tedlar bags. As illustrated in Figure 23, there was good agreement between this sampling and analytical 

method and EPA Method TO-15. 

Sample container blanks were collected to ensure that VOCs of concern were not present in Tedlar bags 

prior to sample collection. Four one-liter Te

laboratory-grade nitrogen gas and analyzed. T

A. Analysis of container blanks indicated that 

concern above detection limits of 2 to 4 ppbv. 

reakthrough of VOCs of concern from atmospheric air into 

s il-gas 

sampling. The results of testing are summ

indicated that there was little potential for atmospheric air to impact soil-gas sample results of VOCs of 

concern above detection limits of 2 to 4 ppbv. 

On-site gas chromatography (GC) analysis as conducted by EPA's New England Regional Laboratory 

capillary column, a photoionization detector (PID), and an 

as a Photovac 10A10 equipped with a 1.2 m (4’), 0.32 cm 

50 μl steel barrel syringe with a 2.5 cm 25-gauge needle was 

th GCs. Single concentration standards were prepared from 

olutions and diluted in VOC-free water in Class A volumetric 

 a headspace above the liquid standard. Field GCs were 

dspace above the 10 μg/l standard. 

TCE, and c-1,2-DCE was identical to that used for sub-slab 

 Sub-slab air samples collected using EPA Method TO-15 

(EPA, 1999) were compared with sub-slab ir samples collected using a peristaltic pump and one-liter

dlar bags (one from each batch received) were filled with 

he results of testing are summarized in Table 2 in Appendix 

Tedlar bags used for sampling were not a source of VOCs of 

Field blanks were collected to assess potential b

Tedlar bags during sampling. Outdoor air amples were collected each of the three days of so

arized in Table 3 in Appendix A. Analysis of field blanks 

13
 

Figure 23. Comparison of EPA Method TO-15 with sample collection using a peristaltic pump and Tedlar bags with 

on-site GC analysis of 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE (n = 91, r2

 = 0.88). 

Probe blanks were collected to ensure that components of the PRT and GVP sample systems and 

 was discarded after sampling at each location and depth to 

void potential cross-contamination. 

y) samples each day. The results of travel blanks are 

ummarized in Table 5 in Appendix A. Analysis of travel blanks for VOCs of concern indicated that 

ansport of the Tedlar bags did not impact sample results at detection limits above 2 to 4 ppbv. 

associated tubing were not the source of VOCs of concern. Atmospheric air was passed through the probe 

and tubing of GVP and PRT sampling systems several times and collected into one-liter Tedlar bags. The 

results of testing are summarized in Table 4 in Appendix A. Analysis of probe blanks indicated that neither 

GVP nor PRT sample systems and associated tubing were sources of VOCs of concern above detection 

limits of 2 to 5 ppbv. Tubing for both systems

a

Travel blanks were collected to ensure that storage of Tedlar bags in a cooler (not chilled) prior to analysis 

did not impart an analytical bias (e.g., VOC transport from one Tedlar bag to another or presence of VOCs 

in the cooler). A one-liter Tedlar bag was filled with laboratory-grade nitrogen and placed in a cooler used 

to transport (hand carry to mobile laborator

s

tr

14
Replicat ssess the 

ecision of the entire sample and analysis procedure. Figure 10 illustrates collection of replicate samples 

om a dedicated vapor probe. The results of replicate sampling are summarized in Table 6 in Appendix A. 

he relative percent difference (RPD) of 15 replicate analytical pairs (from 5 samples) with detectable 

oncentrations varied from 0.0 to 9.1% (9 out of 15 sample pairs were 0.0%). By comparison, EPA Method 

O-15 (EPA, 1999) requires replicate precision less than or equal to 25%. RPD is defined as: 

here:

e samples, which consisted of two samples from the same air stream, were collected to a

pr

fr

T

c

T

w X= sample mean and X1 and X2 are values for samples 1 and 2, respectively. 

.5 Computation of Pre-Sample Internal Volume Exchange Requirements 

he internal volume of dedicated vapor probes consisted of a 3.8 cm (1.5”) ID, 30.5 cm (1’) long slotted 

VC pipe used as a screened interval, a 1.9 cm (0.75”) ID PVC riser pipe to the surface, and 0.95 cm 

/8”) ID Teflon®

 tubing used between valves and one-liter Tedlar sample bags. The internal volume of the 

alve at the top of the riser pipe was insignificant compared to other internal volume components. The 

ction to one-liter Tedlar bags. 

le point holder and PRT adapter were similar to the Teflon®

 tubing and 

l of PRT and GVP sample systems should also be purged 

se outside air may be drawn into the screened interval during riser pipe retraction. 

X X 1 2 RPD 100

X

− =

3

T

P

(3

v

internal volume of the PRT sample system consisted of an open 2.5 cm (1”) diameter by 5 cm (2”) long

cylindrical hole created during riser pipe retraction and tubing used for conne

The internal volume of the retractab

were incorporated into the computation of the internal volume of tubing. The internal volume of the GVP 

sample system consisted of a 0.64 cm (1/4”) ID 5 cm (2”) long stainless-steel screen and 0.48 cm (3/16") 

ID Teflon®

 tubing. 

Tubing used to sample dedicated vapor probes and direct-push/hammer soil-gas sampling systems should 

be purged prior to sampling. Air inside tubing will initially have direct contact with and be representative of 

outdoor air. The relatively small screened interva

prior to sampling becau

However, the screened interval and riser pipe of a sealed dedicated vapor probe should be more reflective, 

although not necessarily the same, as nearby soil-gas concentrations if the probe was installed some time 

(e.g., days or weeks) prior to sampling. Thus, less internal volume exchanges or purge volumes may be 

necessary prior to sampling dedicated vapor probes compared to PRT and GVP sample systems. Internal 

volumes and pre-sample internal volume exchanges were calculated for each sample system at each 

depth and location and are presented in tables throughout Appendix A. 

15
Calculation of a minimum purge volume prior to sampling can be estimated using a mass balance 

equation: 

 

where Cout is a well-mixed vapor concentration within and exiting the sample system, Cin = constant 

concentration entering the system from surrounding soil-gas, Q = flow rate entering and ex

( ) out

in out

dC Q C C

dt V = −

iting sample 

ystem, t = time, and V = internal volume of n subject to an initial condition, C0

apor concentration at time zero), purge volume (tQ/V) can be expressed as a function of Cin and Cout by: 

 

s sampled system. Whe

(v

. 

− = −

in 0

in out

tQ C C ln

V CC

Purge volumes as a function of C0 /Cin and Cout /Cin are illustrated in Figure 24. 

Figure 24. Purge volume as a function of C0 /Cin and Cout /Cin. 

16
T

17

he ideal condition is that Cout /Cin =1. However, extraction of 2.2 to 3 purge volumes ensures that the 

n vapor 

ion inside the sample system has been reduced to C /Cin = 0. This would be the condition most 

ple systems. However, as previou

0 /Cin would equal zero for dedicated vapor probes. If for instance C0 /Cin = 0.4, then extraction of 1.8 to 2.5 

 Vapor concentration as a function of cumulative post-sample extraction volume up to 5.5 liters at 

edicated vapor probe MW513SG.

ne internal exchange or purge volume was calculated to be one liter. Cumulative post-sample extraction 

olume represents the summation of air extracted during and prior to sample collection. Thus, air 

xtraction did not occur prior to the first sample and five liters of air were extracted prior to the fifth sample. 

nly the first 5 samples are shown in Figure 25. To evaluate the effect of extraction volume on sample 

oncentration, a total of 10 samples were collected at MW513SG up to a cumulative post-sample volume 

f 103 liters. These results will be discussed in Section 3.6. There appears to be a slight increase in 

n for all four VOCs analyzed after the first sample. Thus, at least in this case, a purge volume 

o stabilize concentrations in dedicated 

exiting vapor concentration is approximately 90 to 95% of the entering concentration even whe

concentrat out

representative of PRT and GVP sam sly discussed, it is unlikely that 

C

purge volumes results in the exiting concentration being approximately 90 to 95% of the entering 

concentration. Figure 25 illustrates vapor concentration as a function of cumulative post-sample extraction 

volume at dedicated vapor probe MW513SG. Sample volume was 0.5 liters. 

Figure 25.

d

O

v

e

O

c

o

concentratio

of one liter or 1 internal air exchange would have been sufficient t
vapor probes. Stabilization of O2, CO2, and CH4 concentrations is sometimes used as an indicator of 

sufficient purging. Sequential sampling indicated stable O2, CO2, and CH4 concentrations at virtually all 

locations as evidenced in Appendix A. For example, Figure 26 illustrates a stable gas concentration after 

extraction of two liters of air at dedicated vapor probe MW514SG. Similar to MW513SG, sample volume 

was 0.5 liters while one internal exchange volume was calculated to be one liter. 

igure 26. O2, CO2, and CH4 concentration as a function of cumulative post-sample extraction at dedicated vapor 

robe MW514SG. 

 this investigation, at least 2 internal volumes were exchanged prior to sampling dedicated vapor probes. 

l 

 sampling. 

F

p

In

Because of the relatively small internal volumes of PRT and GVP soil-gas systems, at least 3 interna

volumes were exchanged prior to

3.6 Assessment of Extraction Volume on Sample Results 

To allow a comparison of dedicated probe, PRT, and GVP sampling systems, the act of sample collection 

should neither affect sample results from the system being sampled nor at other sample systems nearby. 

The potential for sample collection affecting sampling results from the system being sampled is discussed 

in this section. The potential for sample collection affecting sampling results at other sample systems 

nearby is discussed in Section 3.7. Increasing pre-sample air extraction volume in excess of a purging 

requirement could increase the possibility of collecting a soil-gas sample which is not representative of 

18
some integrated volume of soil around a screened interval. The most direct way to evaluate the impact of 

a pre-sample air extraction volume on sample results is to collect a number of soil-gas samples 

sequentially and observe vapor concentration as a function of extraction volume. During sample collection, 

VOC concentrations should remain relatively constant unless air is drawn in from a nearby region of lower 

or higher vapor concentration. Extraction volume testing was performed at one location using the PRT 

ampling system and at another location using a dedicated vapor probe. 

he computation of the internal volume of a PRT sampling system when sampling at a depth of 0.76 m 

.5’) near MW 525SG is summarized in Table 7a in Appendix A. The computation of cumulative postample extraction volumes and pre-sample internal exchanges is summarized in Table 7b in Appendix A. 

ince the internal volume of the PRT sampling system was only 0.122 liters, pre-sample internal volume 

xchanges were relatively high during testing at this location (up to 73.6). Vapor concentration as a 

nction of cumulative post-sample extraction volume is presented in Figure 27 which demonstrates little 

r no effect of extraction volume on sample concentration of 1,1,1-TCA, 1,1-DCE, TCE, and c-1,2-DCE. 

Figure 27. Vapor concentration as a function of cumulative pre-sample extraction volume using the PRT sampling 

s

T

(2

s

S

e

fu

o

system at a depth of 0.76 m near MW525SG.

19
Vapor concentration as a function of cumulative post-sample extraction volume at dedicated vapor probe 

MW513SG is illustrated in Figure 28. The internal volume of MW513SG having a screened interval 2.1 m 

(6.9’) to 2.4 m (7.9’) below grade was 1 liter. The computation is summarized in Table 8a in Appendix A. 

The computation of cumulative post-sample extraction volumes and pre-sample internal exchanges is 

summarized in Table 8b in Appendix A. A total of 10 samples and 103 liters of air were extracted during 

this test. Since the internal volume of MW513SG was one liter, pre-sample internal exchanges were 

equivalent to pre-sample air extraction volumes. Thus, 102.5 liters of air or 102.5 internal exchanges 

occurred prior to collecting the tenth sample. With the exception of sample results for 1,1,1-TCA which are 

somewhat erratic, it is apparent after the first one or two internal volume exchanges, sample concentration 

remained relatively constant even after extraction of over 100 liters air. With the exception of explicit 

extraction testing, the most air extracted during any sampling event was 8 liters (for deep dedicated vapor 

probes). This indicates that it is unlikely that the act of sample collection impacted sample results at any 

sample system at any depth in this study. 

Figure 28. Vapor concentration as a function of cumulative post-sample extraction volume at dedicated vapor probe 

MW513SG at a depth interval of 2.1 to 2.4 m. 

20
3.7 Assessment of Impact of Air Extraction at One Location on Another Location 

At least conceivably, excessive air extraction volume at one probe could impact vapor concentration at a 

nearby probe. To evaluate the potential impact of pre-sample extraction volume at one location on sample 

results at a nearby location and depth, three samples were taken from each sampling system at most test 

locations. For example, at MW523SGS, the PRT system was sampled first followed by the GVP system 

followed by sampling at the dedicated probe. The sequence was then changed to sampling at the GVP 

system followed by sampling at the dedicated vapor probe followed by sampling at the PRT system and so 

on. A comparison of first and third vapor concentrations for locations and depths where three samples 

were collected is presented in Figure 29. A 1:1 correlation between samples indicates that sample 

collection at one location did not impact sample results at another location. 

igure 29. Comparison of first and third samples at dedicated probe, PRT, and GVP sample locations. 

igure 30 illustrates coefficients of variation (100 x standard deviation/mean) for all locations where three 

 5 - 10 ppbv again indicating that sample collection at one 

cation did not impact sample results at another location. 

F

F

samples were collected for each sample system at each depth. Coefficients of variation were low except 

when approaching detection limits around

lo

21
F

a

igure 30. Coefficient of variation (%) as a function of mean vapor concentration for first, second, and third samples 

t dedicated probe, PRT, and GVP sample locations. 

.8 Consideration of Spatial Variability on Comparison of Sampling Techniques 

RT and GVP sampling locations were positioned relatively close (usually within 1 m) to dedicated vapor 

robes to minimize the effect of spatial variability in comparing soil-gas sampling techniques. To assess 

e presence and magnitude of spatial variability on this scale, soil-gas sampling was conducted at five 

cations and three depths near MW213 using the PRT sampling system. Figures 31 and 32 illustrate the 

cale and locations of testing. 

he computation of internal volumes using the PRT sampling system at five locations at depths of 0.76 m 

 A. Sample 

sults and computation of pre-sample internal exchanges at these depths are summarized in Tables 9d

 minor as evidenced by a median of 1.2 and 

verage of 1.3 for 90 sample pairs. 

3

P

p

th

lo

s

T

(2.5’), 2.3 m (7.5’), and 3.2 m (10.5’) are summarized in Tables 9a through 9c in Appendix

re

through 9f in Appendix A. As these tables indicate, there were 2 to 3 internal exchanges prior to sampling. 

Pre-sample O2 and CO2 concentrations were similar with depth and location. Figures 33a, 33b, and 33c

illustrate variation in concentration with depth and location. Concentration varied by a factor of 1.0 to 2.8. 

However, variation in most measurements was relatively

a

22
Figure 31. Photograph illustrating five PRT sample locations (orange flags) near MW213. 

Figure 32. Schematic illustrating five PRT sample locations near MW213 in plan view. 

23
Figure 33a. Vapor concentration at S1 through S5 (one sample at each location) at a depth of 0.76 m. 

Figure 33b. Vapor concentration at S1 through S5 (one sample at each location) at a depth of 2.3 m.

24
Figure 33c. Vapor concentration at S1 through S5 (one sample at each location) at a depth of 3.2 m.

25
The results of testing at and near each dedicated vapor probe are summarized in this section. These 

sults will be combined and discussed in further detail in Section 5. 

.1 Results of Testing at MW302SGM 

 schematic illustrating the location of the dedicated probe MW302SGM and nearby PRT and GVP 

ampling locations systems is illustrated in Figure 34. The screened interval of MW302SGM is 2.1 – 2.4 m 

 – 8’) below ground surface. Soil-gas samples were collected using the PRT and GVP systems at 2.3 m 

.5’) below ground surface. Samples were collected from each system three times. 

Figure 34. Schematic illustrating the location of sampling systems at MW302SGM in plan view. 

The computation of internal volumes and cumulative pre-sample internal exchanges is summarized in 

Tables 10a and 10b in Appendix A. Pre-sample internal exchanges for GVP, PRT, and probe systems 

varied from 6.7 – 33.6, 2.9 – 14.3, and 2.5 – 6.5 respectively. VOC and gas concentrations detected from 

sample systems at MW514SG are illustrated in Figure 35 and summarized in Table 10c in Appendix A. 

VOC concentrations of 1,1-DCE, 1,1,1-TCA, and TCE were slightly lower at the dedicated probe compared 

to PRT and GVP sample systems by a factor up to 1.3. 

4.0 Results 

re

4

A

s

(7

(7

26
igure 35. Compar at MW302SGM at a 

epth of 2.3 m. 

.2 Results of Testing at MW514SG 

 schematic of the location of dedicated probe MW514SG and nearby PRT and GVP sampling systems is 

lustrated in Figure 36. The screened interval of MW514SG is 2.1 – 2.4 m (6.9 – 7.9’) below ground 

urface. PRT and GVP were sampled at 2.3 m (7.5’) below ground surface. Samples were collected from 

ach system three times. 

e-sample internal exchanges is summarized in 

ables 11a and 11b in Appendix A. Pre-sample internal exchanges for GVP, PRT, and probe systems 

concentrations detected using the dedicated vapor probe by a factor of up to 1.9. 

F ison of mean (3 samples from each sample system) vapor concentrations 

d

4

A

il

s

e

The computation of internal volumes and cumulative pr

T

varyed from 8.1 – 40.4, 2.8 – 13.9, and 2.5 – 6.5 respectively. VOC and gas concentrations detected from 

sample systems at MW514SG are illustrated in Figure 37 and summarized in Table 11c in Appendix A. 

O2 and CO2 concentrations were very similar in all three sample systems. VOC concentrations of 1,1-DCE, 

1,1,1-TCA, TCE, and c-1,2-DCE were similar for the GVP and PRT sample systems but higher than VOC 

27
Figure 36. Schematic illustrating the location of sampling systems at MW514SG in plan view. 

Figure 37. Comparison of mean (3 samples from each sample system) vapor concentrations at MW514SG at a 

depth of 2.3 m. 

28
4.3 Results of Testing at MW523SGS, MW523SGM, and MW523SGD 

A schematic of the location of dedicated probes MW523SGS MW523SGM, and MW523SGD and nearby 

RT and

edicated vapor probes made it difficult to locate associated PRT and GVP sample systems nearby. While 

RT and GVP systems are within 0.91 m (3’) of each other, both sample systems were more than 1 m 

way from dedicated vapor probes used for comparison. 

igure 3 23SGD in 

lan view. 

he screened interval of MW523SGS is 0.6 – 0.9 m (2 – 3’) below ground surface. PRT and GVP were 

ampled at 0.8 meters (2.5 feet) below ground surface. Computation of internal volumes at MW523SGS is 

ummarized in Table 12a in Appendix A. Computation of pre-sample internal exchanges and VOC and 

as concentrations detected from sample systems at MW523SGS is summarized in Table 12b in Appendix 

. Pre-sample internal exchanges for GVP, PRT, and probe systems were 4.1, 1.8, and 3.5 respectively. 

he high CH4 concentration detected in MW523SGS was caused by a natural gas leak in the area. 

terference by CH4 caused an increase in detection limits for 1,1-DCE and c-1,2-DCE. VOC 

oncentrations were too low to discern any differences between sampling systems. 

P GVP sampling locations is illustrated in Figure 38. The separation of shallow, medium, and deep

d

P

a

F 8. Schematic illustrating the location of sampling systems at MW523SGS, MW523SGM, and MW5

p

T

s

s

g

A

T

In

c

29
The screened interval of MW523SGM is 2.1 – 2.4 m (7 – 8’) below ground surface. PRT and GVP were

ampled at 2.3 m (7.5’) below ground surface. Computation of internal volumes at MW523SGM is 

ummarized in Table 13a in Appendix A. Computation of pre-sample internal exchanges and VOC and 

ummarized in Table 13b in 

ppendix A. VOC concentrations are illustrated in Figure 39. Pre-sample internal exchanges for GVP, 

he screened interval of MW523SGD is 3.2 – 3.5 m (10.5 – 11.5’) below ground surface. The PRT system 

s

s

gas concentrations detected from sample systems at MW523SGM is s

A

PRT, and probe systems were 5.8, 2.5, and 2.5 respectively. Again, interference by CH4 caused an 

increase in detection limits for 1,1-DCE and c-1,2-DCE. VOC concentrations of 1,1,1-TCA and TCE were 

slightly higher for the dedicated probe and PRT system compared to the GVP system (by a factor of up to 

1.9). 

Figure 39. Comparison of vapor concentrations (1 sample from each sample system) at MW523SGM at a depth of 

2.3 m. 

T

was sampled at 3.4 m (11’) below ground surface. Sampling at this depth with the GVP system proved 

difficult (resistance to penetration with rotary hammer drill). Computation of internal volumes at 

MW523SGD is summarized in Table 14a in Appendix A. Computation of pre-sample internal exchanges 

and VOC and gas concentrations detected from sample systems at MW523SGM is summarized in Table 

14b in Appendix A. Vapor concentrations are illustrated in Figure 40. Pre-sample internal exchanges for 

30
PRT and probe systems were 1.8 and 2.0 respectively. The CH4 gas concentration was not as high as the 

shallower depths but still interfered with detection of 1,1-DCE and c-1,2-DCE. VOC concentrations for 

igure 4 at a depth of 

.4 m. 

.4 Results of Testing at MW525SG 

 schematic illustrating the location of the dedicated probe MW525SG and nearby PRT and GVP sampling 

’) 

ground surface. In addition to collecting soil-gas samples at 2.3 m (7.5’), samples were collected at 

of internal volumes of PRT system and GVP kit at 0.91 m is summarized in Table 15a in Appendix A. The 

1,1,1-TCA and TCE were slightly higher for the PRT system compared to the dedicated vapor probe (factor 

up to 1.7). 

F 0. Comparison of vapor concentrations (1 sample from each sample system) at MW523SGD

3

4

A

locations systems is illustrated in Figure 41. The screened interval of MW523SGS is 2.1 – 2.4 m (7 – 8

below 

0.91 m (3’) using PRT and GVP sample systems. Soil-gas samples were also collected at 3.4 m (11’) 

using the PRT system but not used or presented here for comparison purposes. The location of purge or 

extraction volume testing near MW525SG using the PRT sampling system at a depth of 0.76 m is also 

illustrated in Figure 41. The results of this test were previously discussed in Section 3.6. The computation 

31
computation of pre-sample internal exchanges is summarized in Table 15b in Appendix A while VOC and 

gas concentrations are summarized in Table 15c in Appendix A. Pre-sample internal exchanges for GVP 

and PRT systems were 8.7 – 60.9 and 1.9 – 13.4 respectively. Vapor concentrations are illustrated in 

Figure 42. Mean VOC concentrations of 1.1-DCE, 1,1,1-TCA, and TCE using the PRT system appear to 

be slightly higher (up to a factor of 1.7) compared to sampling with the GVP kit. 

Figure 41. Schematic illustrating the location of sampling systems at MW525SG in plan view. 

Figure 42. Comparison of mean (3 samples from each sample system) vapor concentrations at MW525SG at a 

depth of 0.91 m. 

32
Soil-gas samples were also collected at a depth of 2.3 m (7.5’) at nearby PRT and GVP locations. The 

computation of internal volumes and pre-sample internal exchanges is summarized in Tables 16a and 16b

in Appendix A. Pre-sample internal exchanges for GVP, PRT, and dedicated probe sample systems were 

6.0 – 30.1, 2.9 – 14.7, and 2.6 – 6.8 respectively. VOC concentrations are illustrated in Figure 43 and 

summarized in Table 16c in Appendix A. O2 concentration appeared higher and CO2 concentration lower 

using the GVP kit compared to PRT and dedicated probe sample systems. Mean CO2 concentrations in 

the PRT and dedicated vapor probe sample systems were approximately six times higher than the mean 

O2

ce between 

hat these 

arge from 

igure 4 at a 

epth of 2.3 m.

C concentration detected using the GVP kit. Mean VOC concentrations of 1,1-DCE, 1,1,1-TCA, and

TCE using the GVP kit appeared lower by a factor of 8 to 9 compared to mean VOC concentrations 

detected using the PRT and dedicated probe sample systems. Given the relatively small distan

the GVP kit and PRT (0.73 m) and dedicated probe sample systems (1.1 m), it is unlikely t

differences in concentration were due entirely to spatial variability. It appears likely that rech

atmospheric air or leakage occurred during sampling with the GVP kit at this location. 

F 3. Comparison of mean (3 samples from each sample system) vapor concentrations at MW525SG

d

33
4.5 Results of Testing at MW526SGS, MW526SGM, and MW526SGD 

igure 4 26SGD in 

lan view. 

W526SGS is screened over a depth of 0.61 to 0.91 m (2 to 3’) while soil-gas samples were collected at a 

epth of 0.76 m (2.5 ft) at nearby PRT and GVP locations. The computation of internal volumes and preample internal exchanges is summarized in Tables 17a and 17b in Appendix A. Pre-sample internal 

xchanges for GVP, PRT, and dedicated probe sample systems were 8.7 – 60.9, 2.0 – 13.8, and 3.5 – 9.6 

spectively. VOC concentrations are illustrated in Figure 45 and summarized in Table 17c in Appendix 

. Mean O2 and CO2 concentrations were similar for all three sample systems. There did not appear to be 

ny clear trends in 1,1-DCE, 1,1,1-TCA, and TCE concentrations with the three sample systems. 

owever, the concentration of 1,1-DCE in the dedicated probe was 5.8 times greater than that in the PRT 

ystem whereas concentrations of 1,1,1-TCA were nearly equivalent. 

oil-gas samples were also collected at a depth of 0.76 m (2.5’) using PRT and GVP sampling systems 

ear MW526SGM. The computation of internal volumes and pre-sample internal exchanges for these 

ampling systems is summarized in Tables 18a and 18b in Appendix A. Pre-sample internal exchanges 

r GVP and PRT sample systems were 4.5 – 31.3 and 2.0 – 14.2 respectively. VOC concentrations are 

gure 46 and summarized in Table 18c in Appendix A. Mean VOC concentrations for 1,1-

A schematic illustrating the location of the dedicated vapor probes MW526SGS, MW526SGM, and 

MW526SGD and nearby PRT and GVP sampling locations systems is illustrated in Figure 44. The 

relatively large distance between shallow, medium, and deep dedicated vapor probes necessitated the use 

of multiple PRT and GVP sampling locations. 

F 4. Schematic illustrating the location of sampling systems at MW526SGS, MW526SGM, and MW5

p

M

d

s

e

re

A

a

H

s

S

n

s

fo

illustrated in Fi

34
DCE, 1,1,1-TCA, and TCE using the PRT system appeared to be slightly higher than those using the GVP 

ystem by a factor up to 3.3. 

i

s

F

d

gure 45. Comparison of mean (3 samples from each sample system) vapor concentrations at MW526SGS at a 

epth of 0.76 m. 

Figure 46. Comparison of mean (3 samples from each sample system) vapor concentrations at MW526SGM at a 

depth of 0.76 m.

35
MW526SGM is screened over a depth of 2.1 to 2.4 m (7 to 8’). Soil-gas samples were collected at a depth 

of 2.3 m (7.5’) at nearby PRT and GVP locations. The computation of internal volumes and pre-sample 

ternal e exchanges 

r GVP, PRT, and dedicated vapor probe sample systems were 7.4 – 37.2, 3.0 – 14.9, and 2.5 – 6.5 

spectively. VOC concentrations are summarized in Figure 47 and in Table 19c in Appendix A. VOC 

oncentrations of 1,1-DCE, 1,1,1-TCA, TCE, and c-1,2-DCE using GVP and dedicated vapor systems 

ppeared similar but lower than VOC concentrations detected using the PRT sampling system by a factor 

f up to 1.4 which is within the range expected for spatial variability on the scale of 1 m. 

igure 47 M at a 

epth of 2.3 m.

W526SGD is screened over a depth of 3.0 to 3.4 m (10 to 11’). Soil-gas samples were collected at a 

epth of 3.2 m (10.5’) at a nearby PRT location. The computation of internal volumes and pre-sample 

ternal exchanges for these sampling systems is summarized in Tables 20a and 20b in Appendix A. Preample internal exchanges for PRT and dedicated vapor probe sample systems were 3.4 – 12.6 and 2.4 – 

6.0 respectively. Gas and VOC concentrations are summarized in Table 20c in Appendix A. VOC 

in xchanges is summarized in Tables 19a and 19b in Appendix A. Pre-sample internal 

fo

re

c

a

o

F . Comparison of mean (3 samples from each sample system) vapor concentrations at MW526SG

d

M

d

in

s

36
concentrations are illustrated in Figure 48. Mean O2 and CO2 concentrations were similar for both 

igure 4 at a 

epth of 3.2 m.

sampling systems. Mean VOC concentrations of 1,1-DCE, 1,1,1-TCA, TCE, and c-1,2-DCE were higher 

using the PRT system compared to dedicated vapor probes by a factor up to 1.4 which is within the range 

expected for spatial variability on the scale of 1 m. 

F 8. Comparison of mean (3 samples from each sample system) vapor concentrations at MW526SGD

d

37
A comparison of dedicated vapor probes and the GVP sampling kit is illustrated in Figure 49. The vapor 

probes were screened at depths of 0.61 – 0.91 and 2.1 – 2.4 m while soil-gas samples were collected at 

epths of 0.76 and 2.3 m. With the exception of sampling at MW525SG at a depth of 2.3 m, there was no 

 depth, O2

concentratio ared to the 

RT system and dedicated vapor probe indicating likely leakage with the GVP kit. However, use of all 

ample data reveals no statistical difference in sampling methods (p = 0.31 for two-tailed t-Test, p > 0.2 for 

o-tailed Wilcoxon Signed Rank Test). Random scatter about the 1:1 line is likely due at least in part to 

patial variability. 

Figure 49. Comparison of probe and GVP VOC concentrations – error bars represent one standard deviation from 

three samples. 

A comparison of dedicated vapor probes and PRT sampling systems is illustrated in Figure 50. The vapor 

probes were screened at depths of 0.61 – 0.91, 2.1 – 2.4, and 3.0 – 3.4 m while soil-gas samples were 

d

apparent bias in sample collection method. As previously discussed, at this location and

n was higher and CO2 concentration lower (by a factor of 6) using the GVP kit comp

5.0 Discussion of Comparison Testing 

P

s

tw

s

38
collected at depths of 0.76, 2.3, and 3.2 m using the Geoprobe®

 PRT system. Both visually and statistically 

 = 0.009 for two-tailed t- p ), VOC concentrations in 

e PRT system were higher than corresponding VOC concentrations in dedicated vapor probes. VOC 

igure 50. Comparison of dedicated vapor probe and GVP VOC concentrations – error bars represent one standard 

 comparison of PRT and GVP sampling systems is illustrated in Figure 51. Both systems were sampled 

(p Test, < 0.01 for two-tailed Wilcoxon Signed Rank Test

th

concentrations using the PRT system were higher than VOC concentrations detected using dedicated 

vapor probes by an average factor of 1.2. The effect does not appear to be due to spatial variability which 

would result in random scatter of data. It is unlikely that extraction volume or sampling sequence caused 

the observed bias given results discussed in Sections 3.6 and 3.7. Also, it is unlikely that a difference in 

screen length (5 cm for PRT and GVP system and 30 cm for dedicated vapor probes) resulted in elevated 

PRT concentrations relative to dedicated vapor probes since concentrations should be equivalent for vapor 

concentration increasing uniformly with depth. A non-uniform increase in concentration with depth (e.g., 

exponential function) would result in lower PRT concentrations relative to dedicated vapor probes. 

F

deviation from three samples. 

A

at depths of 0.76 and 2.3 m. Again, bias at location MW525SG at a depth of 2.3 m indicated leakage 

during sampling with the GVP system. Both visually and statistically (p = 0.03 for two-tailed t-Test, p < 

39
0.01 for two-tailed Wilcoxon Signed Rank Test), VOC concentrations in the PRT system were higher than 

corresponding VOC concentrations using the GVP system. VOC concentrations using the PRT system 

were higher than VOC concentrations detected using the GVP kit by an average factor of 2.4. Similar to 

the comparison between probe and PRT sampling systems, the effect does not appear to be due to spatial 

variability, extraction volume, or sequence of sampling. 

th

y 

inor when compared to variation on a scale of 1 m due to spatial variability (median of 1.2 and average of 

Figure 51. Comparison of PRT and GVP VOC concentrations – error bars represent one standard deviation from 

ree samples. 

Thus, utilization of the PRT system resulted in observation of higher concentrations of VOCs compared to 

the GVP sampling system and dedicated vapor probes. However, the magnitude of variation was relativel

m

1.3 for 90 sample pairs). 

40
A study was conducted near the Raymark Superfund Site in Stratford, Connecticut to compare results of 

soil-gas sampling using dedicated vapor probes, a truck-m

6.0 Summary 

ounted direct-push technique – Geoprobe®

 Postun-Tubing (PRT) system, and a hand-held rotary hammer technique - AMS Gas Vapor Probe (GVP) kit. 

s 

s using 

d 

consist

s 

entrations 

hus, utilization of the PRT system resulted in observation of higher concentrations of VOCs compared to 

his testing was conducted in highly permeable soils where the potential for leakage from directpush/hammer soil-gas sampling systems would be expected to be low compared to less permeable soils 

such as silt and clay. Thus, the results of this investigation should not be extrapolated to other soil textures 

where additional investigation is needed. Also, only one direct-push and one rotary hammer method was 

R

A comparison of VOC concentrations using dedicated vapor probes and the GVP sampling kit indicated

that the two methods provided similar results. However, at one location, O2, CO2, and VOC concentration

were noticeably different for sampling systems indicating potential leakage with the GVP system. 

VOC concentrations using the PRT system were not statistically equivalent to VOC concentration

dedicated vapor probes. VOC concentrations using the PRT system were higher than VOC concentrations 

detected using dedicated vapor probes by an average factor of 1.2. This is the same magnitude observe

for spatial variability on a scale of 1 m (median of 1.2 and average of 1.3 for 90 sample pairs). However, 

this effect did not appear to be due to spatial variability which would result in random scatter not a 

ent bias as observed. It is also unlikely that extraction volume or sampling sequence caused the 

observed bias given results from extraction volume and sample sequence testing. 

VOC concentrations using the PRT system were also not statistically equivalent to VOC concentration

using the GVP kit. VOC concentrations using the PRT system were higher than VOC conc

detected using the GVP kit by an average factor of 2.4. Similar to the comparison between probe and PRT

sampling systems, the effect does not appear to be due to spatial variability, extraction volume, or

sequence of sampling. 

T

the GVP sampling system and dedicated vapor probes. However, the magnitude of variation was relatively 

minor when compared to variation on a scale of 1 m due to spatial variability. Hence for practical 

purposes, all three sample systems can be considered approximately equivalent. 

T

41
evaluated for comparison with dedicated vapor probes. Thus, the results of this investigation should not be 

extrapolated to other direct-push/hammer soil-gas sampling techniques. 

42
Freeze, R. A. and J.A. Cherry. 1979. Groundwater. Prentice-Hall, Inc., Englewood Cliffs, NJ. 

Johnson, P.C. and R. A. Ettinger. 1991. Heuristic model for the intrusion rate of contaminant vapors into 

buildings. Environmental Science and Technology, 25(8):14445-1452. 

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. 1999. Compendium of methods for determination of toxic organic 

compounds in ambient air, Determination of volatile organic compounds (VOCs) in air collected in 

specially-prepared canisters and analyzed by gas chromatography/mass spectrometry (GC/MS). 

http://www.epa.gov/ttn/amtic/files/ambient/airtox/to-15r.pdf

References 

. EPA/625/R-96/010b. Office of Research and 

Development, National Risk Management Research Laboratory, Cincinnati, OH. 

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. 2006. Assessment of vapor intrusion in homes near the Raymark 

superfund site using basement and sub-slab air samples. http://www.epa.gov/ada/download/reports/

600R05147/600R05147.pdf. Office of Research and Development, National Risk Management Research 

Laboratory, Cincinnati, OH. 

43

Appendix A 

Table 1. Depth of Fill Materials and Screened Intervals in Boreholes Containing Dedicated Vapor Probes 

Depth (m) 302SG 513SG 514SG 523SGS 523SGM 523SGD 525SG 526SGS 526SGM 526SGD

Bottom of concrete seal 0.2 0.2 0.2 0.2 0.3 0.3 0.2 0.2 0.3 0.2

Bottom of sand drain layer 0.8 0.9 0.9 0.3 0.9 0.9 0.9 0.3 0.9 0.9

Bottom of bentonite 1.8 1.8 2.0 0.5 2.0 3.0 2.0 0.5 2.0 2.9

Top of screen 2.1 2.1 2.1 0.6 2.1 3.2 2.1 0.6 2.1 3.0

Bottom of screen 2.4 2.4 2.4 0.9 2.4 3.5 2.4 0.9 2.4 3.4

Bottom of sand filter 2.4 2.4 2.4 1.0 2.4 3.5 2.4 1.0 2.4 3.4

Table 2. Results of Container Blanks 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE

Identification (ppbv) (ppbv) (ppbv) (ppbv)

SSEB-01 ND(4.0) ND(3.0) ND(3.0) ND(4.0)

SSEB-02 ND(4.0) ND(3.0) ND(3.0) ND(4.0)

SSEB-03 ND(4.0) ND(3.0) ND(3.0) ND(4.0)

SSEB-04 ND(4.0) ND(3.0) ND(3.0) ND(4.0)

ND() = not detected (detection limit)

Table 3. Results of Field Blanks 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE

Identification (ppbv) (ppbv) (ppbv) (ppbv)

Ambient 1 ND(2.0) ND(3.0) ND(3.0) ND(2.0)

Ambient 2 ND(2.0) ND(3.0) ND(2.0) ND(2.0)

Ambient 3 ND(3.0) ND(3.0) ND(2.0) ND(4.0)

ND() = not detected (detection limit)

Table 4. Results of Probe Blanks 

Sample Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE

System Identification (ppbv) (ppbv) (ppbv) (ppbv)

GVP SM-A-525 ND(2.0) ND(3.0) ND(3.0) ND(2.0)

PRT SM-G-525 ND(2.0) ND(3.0) ND(3.0) ND(3.0)

PRT SM-526-G ND(2.0) ND(3.0) ND(2.0) ND(2.0)

GVP SM-526-A ND(3.0) ND(3.0) ND(2.0) ND(4.0)

PRT SM-526-G2 ND(3.0) ND(3.0) ND(5.0) ND(4.0)

ND() = not detected (detection limit)

Table 5. Results of Travel Blanks 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE

Identification (ppbv) (ppbv) (ppbv) (ppbv)

ST-5-5-03 ND(2.0) ND(3.0) ND(3.0) ND(2.0)

ST-5-6-03 ND(2.0) ND(3.0) ND(2.0) ND(2.0)

ST-5-7-03 ND(3.0) ND(3.0) ND(2.0) ND(4.0)

ND() = not detected (detection limit)

45
Table 6. Results of Replicate Samples 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE

Identification (ppbv) (ppbv) (ppbv) (ppbv)

523-8-G1 ND(30) 8.7 11 ND(25)

523-8-G1(rep) ND(30) 8.9 11 ND(25)

526-3-A2R 6.4 28 8.1 ND(3.0)

526-3-A2R(rep) 6.4 26 8.1 ND(3.0)

526-3-A3 6.7 64 21 ND(4.0)

526-3-A3(rep) 6.7 65 23 ND(4.0)

526-8-G3 82 102 33 12

526-8-G3(rep) 82 105 33 12

302SG-1 77 157 31 ND(6.0)

302SG-1(rep) 77 157 30 ND(6.0)

ND() = not detected (detection limit)

Table 7a. Computation of Internal Volume of PRT Sampling System When Sampling at 0.76 m Near MW 525SG 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

PRT 2.54 5.1 26 NR NR NR 0.64 305 96.5 0.122

NR = not relevant

Table 7b. Computation of Pre-Sample Extraction and Internal Exchange Volumes of PRT Sample System When 

Sampling at 0.76 m Near MW525SG 

Sample Pre-Sample Cumulative Cumulative Sample Cumulative 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE 

Identification Purge Pre-Sample Pre-Sample Volume Post-Sample (ppbv) (ppbv) (ppbv) (ppbv)

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

525-3-PRT1 0.0 0.0 0.0 0.50 0.5 204 436 115 20

525-3-PRT2 0.5 1.0 8.2 0.50 1.5 248 484 126 22

525-3-PRT3 0.5 2.0 16.4 0.50 2.5 229 458 119 20

525-3-PRT4 0.5 3.0 24.5 0.50 3.5 254 466 126 26

525-3-PRT5 0.5 4.0 32.7 0.50 4.5 229 474 118 20

525-3-PRT6 0.5 5.0 40.9 0.50 5.5 221 462 118 19

525-3-PRT7 0.5 6.0 49.1 0.50 6.5 230 475 128 22

525-3-PRT8 0.5 7.0 57.3 0.50 7.5 234 473 126 21

525-3-PRT9 0.5 8.0 65.5 0.50 8.5 224 443 121 20

525-3-PRT10 0.5 9.0 73.6 0.50 9.5 226 447 123 22

Table 8a. Computation of Internal Volume Dedicated Vapor Probe MW513SG When Sampling at a Depth Interval of 

2.1 to 2.4 m 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

Probe 3.81 30.5 347 1.9 213 608 0.95 61 43.4 0.999

46
Table 8b. Computation of Pre-Sample Extraction and Internal Exchange Volumes of Dedicated Vapor Probe 

MW513SG When Sampling at a Depth Interval of 2.1 to 2.4 m 

Sample Pre-Sample Cumulative Cumulative Sample Cumulative 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE 

Identification Purge Pre-Sample Pre-Sample Volume Post-Sample (ppbv) (ppbv) (ppbv) (ppbv)

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

513SG-1 0.0 0.0 0.0 0.50 0.5 579 1306 186 79

513SG-2 0.0 0.5 0.5 0.50 1.0 616 1402 239 93

513SG-3 0.5 1.5 1.5 0.50 2.0 603 1402 218 84

513SG-4 0.5 2.5 2.5 0.50 3.0 611 1363 224 84

513SG-5 2.0 5.0 5.0 0.50 5.5 611 1389 228 85

513SG-6 5.0 10.5 10.5 0.50 11.0 609 1478 255 90

513SG-7 10.0 21.0 21.0 0.50 21.5 629 1490 265 96

513SG-8 15.0 36.5 36.5 0.50 37.0 637 1446 281 96

513SG-9 25.0 62.0 62.0 0.50 62.5 619 1414 261 92

513SG-10 40.0 102.5 102.5 0.50 103.0 646 1459 293 101

Table 9a. Computation of Internal Volumes Using the PRT Sampling System at Five Sample Locations at a Depth of 

0.76 m Near MW213 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Identification ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

213-3-S1 2.54 5.1 26 NR 152 NR 0.64 332 105.2 0.131

213-3-S2 2.54 5.1 26 NR 152 NR 0.64 335 106.1 0.132

213-3-S3 2.54 5.1 26 NR 152 NR 0.64 293 92.6 0.118

213-3-S4 2.54 5.1 26 NR 152 NR 0.64 274 86.8 0.113

213-3-S5 2.54 5.1 26 NR 152 NR 0.64 305 96.5 0.122

NR = not relevant

Table 9b. Computation of Internal Volumes Using the PRT Sampling System at Five Sample Locations at a Depth of 

2.3 m Near MW213 

 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Identification ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

213-8-S1 2.54 5.1 26 NR 152 NR 0.64 418 132.2 0.158

213-8-S2 2.54 5.1 26 NR 152 NR 0.64 439 138.9 0.165

213-8-S3 2.54 5.1 26 NR 152 NR 0.64 457 144.7 0.170

213-8-S4 2.54 5.1 26 NR 152 NR 0.64 497 157.3 0.183

213-8-S5 2.54 5.1 26 NR 152 NR 0.64 430 136.0 0.162

NR = not relevant

Table 9c. Computation of Internal Volumes Using the PRT Sampling System at Five Sample Locations at a Depth of 

3.2 m Near MW213 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Identification ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

213-11-S1 2.54 5.1 26 NR 152 NR 0.64 671 212.3 0.238

213-11-S2 2.54 5.1 26 NR 152 NR 0.64 610 193.0 0.219

213-11-S3 2.54 5.1 26 NR 152 NR 0.64 616 194.9 0.221

213-11-S4 2.54 5.1 26 NR 152 NR 0.64 655 207.4 0.233

213-11-S5 2.54 5.1 26 NR 152 NR 0.64 622 196.8 0.223

NR = not relevant

47
Table 9d. Computation of Pre-Sample Extraction and Internal Exchange Volumes and Sample Results Using the 

PRT Sampling System at a Depth of 0.76 m Near MW213 

Sample Pre-Sample Pre-Sample Sample Post-Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Sequence Purge Internal Volume Extraction (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

Volume (L) Exchange (-) (L) Volume (L)

213-3-S1 0.25 1.9 0.50 0.75 3.4 25 19 ND(4.0) 20.5 0.3 0.0

213-3-S2 0.25 1.9 0.50 0.75 2.8 24 19 ND(4.0) 20 0.4 0.0

213-3-S3 0.25 2.1 0.50 0.75 2.1 20 16 ND(4.0) 20.2 0.3 0.0

213-3-S4 0.25 2.2 0.50 0.75 5.3 36 24 ND(4.0) 20.2 0.3 0.0

213-3-S5 0.25 2.0 0.50 0.75 2.3 13 12 ND(4.0) NA NA NA

NA = not analyzed ND() = not detected

Table 9e. Computation of Pre-Sample Extraction and Internal Exchange Volumes and Sample Results Using the 

PRT Sampling System at a Depth of 2.3 m Near MW213 

Sample Pre-Sample Pre-Sample Sample Post-Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification Purge Internal Volume Extraction (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

Volume (L) Exchange (-) (L) Volume (L)

213-8-S1 0.50 3.2 0.50 1.00 12 46 28 ND(4.0) 20.4 0.3 0.0

213-8-S2 0.50 3.0 0.50 1.00 9.3 41 28 ND(4.0) 20.3 0.3 0.0

213-8-S3 0.50 2.9 0.50 1.00 10 42 32 ND(4.0) 20.0 0.4 0.0

213-8-S4 0.50 2.7 0.50 1.00 10 44 30 ND(4.0) 20.3 0.3 0.0

213-8-S5 0.50 3.1 0.50 1.00 9.1 37 25 ND(4.0) NA NA NA

NA = not analyzed ND() = not detected

Table 9f. Computation of Pre-Sample Extraction and Internal Exchange Volumes and Sample Results Using the PRT 

Sampling System at a Depth of 3.2 m Near MW213 

Sample Pre-Sample Pre-Sample Sample Post-Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification Purge Internal Volume Extraction (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

Volume (L) Exchange (-) (L) Volume (L)

213-11-S1 0.50 2.1 0.50 1.00 16 50 37 ND(4.0) 20.3 0.4 0.0

213-11-S2 0.50 2.3 0.50 1.00 13 48 35 ND(4.0) 20.2 0.3 0.0

213-11-S3 0.50 2.3 0.50 1.00 12 49 30 ND(4.0) 20.0 0.4 0.0

213-11-S4 0.50 2.1 0.50 1.00 14 54 33 ND(4.0) 19.9 0.4 0.0

213-11-S5 0.50 2.2 0.50 1.00 10 40 25 ND(4.0) NA NA NA

NA = not analyzed ND() = not detected

Table 10a. Internal Volumes of Probe, PRT, and GVP Systems at 2.3 m Near MW302SGM 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NR 274 NR 0.48 408 72.7 0.074

PRT 2.54 5.1 26 NR 305 NR 0.64 469 149 0.174

Probe 3.81 30.5 347 1.9 213 608 0.95 61 43.4 0.999

NR = not relevant

48
Table 10b. Cumulative Pre-Sample Internal Exchanges of Probe, PRT, and GVP Systems at 2.3 m Near 

MW302SGM 

Sample Sample Pre-Sample Cumulative Cumulative Sample Cumulative

Method Identification Purge Pre-Sample Pre-Sample Volume Post-Sample

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

PRT 302-8-G1 0.5 0.5 2.9 0.50 1.0

GVP 302-8-A1 0.5 0.5 6.7 0.50 1.0

Probe 302SG-1 2.5 2.5 2.5 0.50 3.0

GVP 302-8-A2 0.5 1.5 20.2 0.50 2.0

Probe 302SG-2 1.5 4.5 4.5 0.50 5.0

PRT 302-8-G2 0.5 1.5 8.6 0.50 2.0

Probe 302SG-3 1.5 6.5 6.5 0.50 7.0

PRT 302-8-G3 0.5 2.5 14.3 0.50 3.0

GVP 302-8-A3 0.5 2.5 33.6 0.50 3.0

Table 10c. VOC and Gas Concentrations in Probe, PRT, and GVP Systems at 2.3 m Near MW302SGM 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

GVP

302-8-A1 84 187 40 ND(6.0) 19.7 1.3 0.0

302-8-A2 90 187 41 ND(6.0) 19.6 1.3 0.0

302-8-A3 84 181 40 ND(6.0) NA NA NA

mean 302-8-A 86 185 40 ND(6.0) 19.7 1.3 0.0

stdev 302-8-A 3.5 3.5 0.6 IND 0.1 0.0 0.0

PRT

302-8-G1 80 193 37 ND(6.0) 19.1 1.2 0.0

302-8-G2 79 192 37 ND(6.0) NA NA NA

302-8-G3 83 190 39 ND(6.0) NA NA NA

mean 302-8-G 80.7 192 38 ND(6.0) IND IND IND

stdev 302-8-G 2.1 1.5 1.2 IND IND IND IND

Probe

302SG-1 77 157 31 ND(6.0) 20.1 1.3 0.0

302SG-2 83 156 30 ND(6.0) NA NA NA

302SG-3 79 157 30 ND(6.0) NA NA NA

mean 302SG 80 157 30 ND(3.0) IND IND IND

stdev 302SG 3.1 0.6 0.6 IND IND IND IND

ND( )-not detected IND = indeterminate

Table 11a. Internal Volumes of Probe, PRT, and GVP Systems at 2.3 m Near MW514SG 

 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NR 274 NR 0.48 338 60.2 0.062

PRT 2.54 5.1 26 NR 305 NR 0.64 488 154 0.180

Probe 3.81 30.5 347 1.9 213 608 0.95 61 43.4 0.999

NR = not relevant

49
Table 11b. Cumulative Pre-Sample Internal Exchanges of Probe, PRT, and GVP Systems at 2.3 m Near MW514SG 

Sample Sample Pre-Sample Cumulative Cumulative Sample Cumulative

Method Identification Purge Pre-Sample Pre-Sample Volume Post-Sample

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

PRT 514-8-G1 0.5 0.5 2.8 0.50 1.0

GVP 514-8-A1 0.5 0.5 8.1 0.50 1.0

Probe 514SG-1 2.5 2.5 2.5 0.50 3.0

GVP 514-8-A2 0.5 1.5 24.3 0.50 2.0

Probe 514SG-2 1.5 4.5 4.5 0.50 5.0

PRT 514-8-G2 0.5 1.5 8.3 0.50 2.0

Probe 514SG-3 1.5 6.5 6.5 0.50 7.0

PRT 514-8-G3 0.5 2.5 13.9 0.50 3.0

GVP 514-8-A3 0.5 2.5 40.4 0.50 3.0

Table 11c. VOC and Gas Concentrations of Probe, PRT, and GVP Systems at 2.3 m Near MW514SG 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

GVP

514-8-A1 122 825 256 58 15.6 4.7 0.0

514-8-A2 120 917 291 65 15.6 4.8 0.0

514-8-A3 125 883 279 65 15.6 4.6 0.0

mean 514-8-A 122 875 275 63 15.6 4.7 0.0

stdev 514-8-A 2.5 46.5 17.8 4.0 0.0 0.1 0.0

PRT

514-8-G1 124 881 266 65 15.5 4.7 0.0

514-8-G2 127 911 283 66 15.4 4.8 0.0

514-8-G3 109 904 268 62 15.5 4.8 0.0

mean 514-8-G 120 899 272 64 15.5 4.8 0.0

stdev 514-8-G 9.6 15.7 9.3 2.1 0.1 0.1 0.0

Probe

514SG-1 101 728 255 36 15.2 4.9 0.0

514SG-2 103 804 247 34 15.3 5.0 0.0

514SG-3 103 795 243 33 15.3 5.0 0.0

mean 514SG 102 776 248 34 15.3 5.0 0.0

stdev 514SG 1.2 41.5 6.1 1.5 0.1 0.1 0.0

Table 12a. Computation of Internal Volumes of Sample Systems at 0.8 m Near MW523SGS 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NR 91 NR 0.48 335 59.7 0.061

PRT 2.54 5.1 26 NR 152 NR 0.64 351 111.0 0.137

Probe 3.81 30.5 347 1.9 61 174 0.95 61 43.4 0.564

NR = not relevant

50
Table 12b. Computation of Pre-Sample Internal Exchanges and VOC Concentrations of Sample Systems at 0.8 m 

Near MW523SGS 

Sample Sample Pre-Sample Pre-Sample Sample Post-Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Method Identification Purge Internal Volume Extraction (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

Volume (L) Exchange (-) (L) Volume (L)

PRT 523-3-G1 0.25 1.8 0.50 0.75 ND(30) ND(2.0) ND(4.0) ND(25) NA NA NA

GVP 523-3-A1 0.25 4.1 0.50 0.75 ND(30) 7.0 ND(5.0) ND(25) NA NA NA

Probe 523SGS-1 2.0 3.5 0.50 2.5 ND(15) ND(3.0) 5.8 ND(25) 0.0 10.8 55.5

NA = not analyzed

Table 13a. Computation of Internal Volumes of Sample Systems at 2.3 m Near MW523SGM 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NR 274 NR 0.48 479 85.2 0.087

PRT 2.54 5.1 26 NR 305 NR 0.64 561 177.5 0.203

Probe 3.81 30.5 347 1.9 213 608 0.95 61 43.4 0.999

NR = not relevant

Table 13b. Computation of Pre-Sample Internal Exchanges and VOC Concentrations of Sample Systems at 2.3 m 

Near MW523SGM 

Sample Sample Pre-Sample Pre-Sample Sample Post-Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Method Identification Purge Internal Volume Extraction (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

Volume (L) Exchange (-) (L) Volume (L)

PRT 523-8-G1 0.5 2.5 0.50 1.0 ND(30) 8.7 11 ND(25) NA NA NA

GVP 523-8-A1 0.5 5.8 0.50 1.0 ND(30) 4.4 7.2 ND(25) NA NA NA

Probe 523SGM-1 2.5 2.5 0.50 3.0 ND(30) 6.2 13 ND(25) 0.0 11.2 26.4

ND() = not detected NA = not analyzed

Table 14a. Computation of Internal Volumes of Sample Systems at 3.4 m Near MW523SGD 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

PRT 2.54 5.1 26 NR 457 NR 0.64 796 252 0.278

Probe 3.81 30.5 347 1.9 305 868 0.95 61 43.4 1.259

Table 14b. Computation of Pre-Sample Internal Exchanges and VOC Concentrations of Sample Systems at 3.4 m 

Near MW523SGD 

Sample Sample Pre-Sample Pre-Sample Sample Post-Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Method Identification Purge Internal Volume Extraction (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

Volume (L) Exchange (-) (L) Volume (L)

PRT 523-11-G1 0.5 1.8 0.5 1.0 ND(30) 19 15 ND(25) NA NA NA

Probe 523SGD-1 2.5 2.0 0.5 3.0 ND(30) 11 13 ND(25) 0.0 12.2 9.6

ND() = non-detect NA = not analyzed

Table 15a. Computation of Internal Volumes of Sample Systems at 0.91 m Near MW525SG 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NA 91 NR 0.48 152 27.1 0.029

PRT 2.54 5.1 26 NA 152 NR 0.64 332 105.2 0.131

NR = not relevant

51
Table 15b. Computation of Pre-Sample Internal Exchanges of Sample Systems at 0.91 m Near MW525SG 

Sample Sample Pre-Sample Cumulative Cumulative Sample Cumulative

Method Identification Purge Pre-Sample Pre-Sample Volume Post-Sample

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

PRT 526-3-G1 0.25 0.25 1.9 0.50 0.75

GVP 525-3-A1 0.25 0.25 8.7 0.50 0.75

PRT 525-3-G2 0.25 1.00 7.6 0.50 1.50

GVP 525-3-A2 0.25 1.00 34.8 0.50 1.50

PRT 525-3-G3 0.25 1.75 13.4 0.50 2.25

GVP 525-3-A3 0.25 1.75 60.9 0.50 2.25

Table 15c. Summary of VOC Concentrations in PRT and GVP Systems at 0.91 m near MW525SG 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

GVP

525-3-A1 148 303 52 8.0 NA NA NA

525-3-A2 151 312 58 8.5 NA NA NA

525-3-A3 151 289 58 8.5 NA NA NA

mean 525-3-A 150 301 56 8.3 NA NA NA

stdev 525-3-A 1.7 11.6 3.5 0.3 NA NA NA

PRT

525-3-G1 222 452 93 17 18.2 2.0 0.0

525-3-G2 221 444 97 17 NA NA NA

525-3-G3 219 449 95 17 18.2 1.8 0.0

mean 525-3-G 221 448 95 17 18.2 1.9 0.0

stdev 525-3-G 1.5 4.0 2.0 0.0 0.0 0.1 0.0

NA = not analyzed

Table 16a. Computation of Internal Volumes of Sample Systems at 2.3 m Near MW525SG 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NA 274 NR 0.48 457 81.4 0.083

PRT 2.54 5.1 26 NA 305 NR 0.64 457 145 0.170

Probe 3.81 30.5 347 1.9 213 608 0.95 61 0.0 0.955

NR = not relevant

Table 16b. Computation of Pre-Sample Internal Exchanges of Sample Systems at 2.3 m Near MW525SG 

Sample Sample Pre-Sample Cumulative Cumulative Sample Cumulative

Method Identification Purge Pre-Sample Pre-Sample Volume Post-Sample

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

PRT 525-8-G1 0.5 0.5 2.9 0.5 1.0

GVP 525-8-A1 0.5 0.5 6.0 0.5 1.0

Probe 525SG-1 2.5 2.5 2.6 0.5 3.0

GVP 525-8-A2 0.5 1.5 18.1 0.5 2.0

Probe 525SG-2 1.5 4.5 4.7 0.5 5.0

PRT 525-8-G2 0.5 1.5 8.8 0.5 2.0

Probe 525SG-3 1.5 6.5 6.8 0.5 7.0

PRT 525-8-G3 0.5 2.5 14.7 0.5 3.0

GVP 525-8-A3 0.5 2.5 30.1 0.5 3.0

52
Table 16c. Summary of VOC and Gas Concentrations in PRT and GVP Systems at 2.3 m Near MW525SG 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

GVP

525-8-A1 33 55 12 ND(5.0) 19.9 0.3 0.0

525-8-A2 25 41 8.1 ND(5.0) 20.1 0.2 0.0

525-8-A3 35 55 12 ND(5.0) 20.0 0.3 0.0

mean 525-8-A 31 50 11 ND(5.0) 20.0 0.3 0.0

stdev 525-8-A 5.3 8.1 2.3 IND 0.1 0.1 0.0

PRT

525-8-G1 256 450 101 22 18.2 1.9 0.0

525-8-G2 254 451 101 22 18.2 1.9 0.0

525-8-G3 254 452 100 22 18.4 2.0 0.0

mean 525-8-G 255 451 101 22 18.3 1.9 0.0

stdev 525-8-G 1.2 1.0 0.6 0.0 0.1 0.1 0.0

Probe

525SG-1 267 389 85 21 18.4 1.8 0.0

525SG-2 272 389 85 22 18.4 1.8 0.0

525SG-3 275 400 92 23 18.4 1.8 0.0

mean 525SG 271 393 87 22 18.4 1.8 0.0

stdev 525SG 4.0 6.4 4.0 1.0 0.0 0.0 0.0

Table 17a. Computation of Internal Volumes of Sample Systems at 0.91 m Near MW526SGS 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NA 91 NA 0.48 152 27.1 0.029

PRT 2.54 5.1 26 NA 152 NA 0.64 320 101.3 0.127

Probe 3.81 30.5 347 1.9 61 174 0.95 61 43.4 0.564

NR = not relevant

Table 17b. Computation of Pre-Sample Internal Exchanges of Sample Systems at 0.91 m Near MW526SGS 

Sample Sample Pre-Sample Cumulative Cumulative Sample Cumulative

Method Identification Purge Pre-Sample Pre-Sample Volume Post-Sample

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

PRT 526-3-G1 0.25 0.25 2.0 0.50 0.75

GVP 526-3-A1 0.25 0.25 8.7 0.50 0.75

Probe 526SGS-1 2.0 2.0 3.5 0.50 2.5

GVP 526-3-A2 0.25 1.00 34.8 0.50 1.50

Probe 526SGS-2 1.2 3.7 6.6 0.50 4.2

PRT 526-3-G2 0.25 1.00 7.9 0.50 1.50

Probe 526SGS-3 1.2 5.4 9.6 0.50 5.9

PRT 526-3-G3 0.25 1.75 13.8 0.50 2.25

GVP 526-3-A3 0.25 1.75 60.9 0.50 2.25

53
Table 17c. Summary of VOC and Gas Concentrations in PRT and GVP Systems at 0.91 m Near MW526SG 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

GVP

526-3-A1 11 72 22 ND(4.0) 18.2 1.3 0.0

526-3-A2 10 69 23 ND(4.0) 18.5 1.2 0.0

526-3-A3 6.7 64 21 ND(4.0) 18.4 1.2 0.0

mean 526-3-A 9.2 68 22 ND(4.0) 18.4 1.2 0.0

stdev 526-3-A 2.3 4.0 1.0 IND 0.2 0.1 0.0

PRT

526-3-G1 6.2 55 12 ND(4.0) 18.7 1.1 0.0

526-3-G2 3.9 55 12 ND(4.0) 18.7 1.1 0.0

526-3-G3 2.8 55 12 ND(4.0) 18.9 1.1 0.0

mean 526-3-G 4.3 55 12 ND(4.0) 18.8 1.1 0.0

stdev 526-3-G 1.7 0.0 0.0 IND 0.1 0.0 0.0

Probe

526SGS-1 25 55 21 ND(3.0) 19.0 1.0 0.0

526SGS-2 25 54 22 ND(3.0) 18.8 1.0 0.0

526SGS-3 25 55 22 ND(3.0) 18.8 1.0 0.0

mean 526SGS 25 55 22 ND(3.0) 18.9 1.0 0.0

stdev 526SGS 0.0 0.6 0.6 IND 0.1 0.0 0.0

ND( ) =not detected IND = indeterminate

Table 18a. Computation of Internal Volumes of Sample Systems at 0.91 m Near MW526SGM 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NR 91 NA 0.48 305 54.3 0.056

PRT 2.54 5.1 26 NR 152 NA 0.64 308 97.4 0.123

NR = not relevant

Table 18b. Computation of Pre-Sample Internal Exchanges of Sample Systems at 0.91 m Near MW526SGM

Sample Sample Pre-Sample Cumulative Cumulative Sample Cumulative

Method Identification Purge Pre-Sample Pre-Sample Volume Post-Sample

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

GVP 526-3-A1R 0.25 0.25 4.5 0.5 0.75

PRT 526-3-G1R 0.25 0.25 2.0 0.5 0.75

GVP 526-3-A2R 0.25 1.00 17.9 0.5 1.50

PRT 526-3-G2R 0.25 1.00 8.1 0.5 1.50

GVP 526-3-A3R 0.25 1.75 31.3 0.5 2.25

PRT 526-3-G3R 0.25 1.75 14.2 0.5 2.25

54
Table 18c. Summary of VOC and Gas Concentrations in PRT and GVP Systems at 0.91 m Near MW526SGM 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

GVP

526-3-A1R 6.4 29 8.1 ND(3.0) NM NM NM

526-3-A2R 6.4 28 8.1 ND(3.0) NM NM NM

526-3-A3R 8.6 28 8.1 ND(3.0) NM NM NM

mean 525-3-AR 7.1 28 8.1 ND(4.0) NM NM NM

stdev 525-3-AR 1.3 0.6 0.0 IND NM NM NM

PRT

526-3-G1R 10 49 26 ND(4.0) NM NM NM

526-3-G2R 11 50 27 ND(4.0) NM NM NM

526-3-G3R 12 50 28 ND(4.0) NM NM NM

mean 526-3-GR 11 50 27 ND(4.0) NM NM NM

stdev 526-3-GR 1.0 0.6 1.0 IND NM NM NM

ND( )-not detected NM - not measured IND - indeterminate

Table 19a. Computation of Internal Volumes of Sample Systems at 2.3 m Near MW526SGM 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

GVP 0.64 5.1 1.6 NR 274 NA 0.48 369 65.7 0.067

PRT 2.54 5.1 26 NR 305 NA 0.64 448 142 0.168

Probe 3.81 30.5 347 1.9 213 608 0.95 61 43.4 0.999

NR = not relevant

Table 19b. Computation of Pre-Sample Internal Exchanges of Sample Systems at 2.3 m Near MW526SGM 

Sample Sample Pre-Sample Cumulative Cumulative Sample Cumulative

Method Identification Purge Pre-Sample Pre-Sample Volume Post-Sample

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

PRT 526-8-G1 0.5 0.5 3.0 0.5 1.0

GVP 526-8-A1 0.5 0.5 7.4 0.5 1.0

Probe 526SGM-1 2.5 2.5 2.5 0.5 3.0

GVP 526-8-A2 0.5 1.5 22.3 0.5 2.0

Probe 526SGM-2 1.5 4.5 4.5 0.5 5.0

PRT 526-8-G2 0.5 1.5 9.0 0.5 2.0

Probe 526SGM-3 1.5 6.5 6.5 0.5 7.0

PRT 526-8-G3 0.5 2.5 14.9 0.5 3.0

GVP 526-8-A3 0.5 2.5 37.2 0.5 3.0

55
Table 19c. Summary of VOC and Gas Concentrations in Sample Systems at 2.3 m Near MW526SGM 

 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

GVP

526-8-A1 62 80 27 7.9 19.3 0.8 0.0

526-8-A2 61 79 27 7.8 19.2 0.8 0.0

526-8-A3 61 77 26 7.9 19.3 0.8 0.0

mean 526-8-A 61 79 27 7.9 19.3 0.8 0.0

stdev 526-8-A 0.6 1.5 0.6 0.1 0.1 0.0 0.0

PRT

526-8-G1 74 101 32 11 19.3 0.7 0.0

526-8-G2 80 104 34 12 19.2 0.7 0.0

526-8-G3 82 102 33 12 19.3 0.7 0.0

mean 526-8-G 79 102 33 12 19.3 0.7 0.0

stdev 526-8-G 4.2 1.5 1.0 0.6 0.1 0.0 0.0

Probe

526SGM-1 56 72 26 8.7 19.3 0.9 0.0

526SGM-2 56 73 26 8.2 19.3 0.9 0.0

526SGM-3 57 72 23 8.4 19.3 0.9 0.0

mean 526SGM 56 72 25 8.4 19.3 0.9 0.0

stdev 526SGM 0.6 0.6 1.7 0.3 0.0 0.0 0.0

Table 20a. Computation of Internal Volumes of Sample Systems at 3.2 m Near MW526SGD 

Sample Screen Screen Screen Riser Riser Riser Tubing Tubing Tubing Internal

Method ID Length Volume ID Length Volume ID Length Volume Volume

(cm) (cm) (cm3

) (cm) (cm) (cm3) (cm) (cm) (cm3) (L)

PRT 2.54 5.1 26 NR 457 NR 0.64 610 193 0.219

Probe 3.81 30.5 347 1.9 305 868 0.95 61 43.4 1.259

NR = not relevant

Table 20b. Computation of Pre-Sample Internal Exchanges of Sample Systems at 3.2 m Near MW526SGD

Sample Sample Pre-Sample Cumulative Cumulative Sample Cumulative

Method Identification Purge Pre-Sample Pre-Sample Volume Post-Sample

Volume Extraction Internal (L) Extraction

(L) Volume (L) Exchanges (-) Volume (L)

PRT 526-11-G1 0.75 0.75 3.4 0.5 1.3

Probe 526SGD-1 3.0 3.0 2.4 0.5 3.5

PRT 526-11-G2 0.5 1.75 8.0 0.5 2.3

Probe 526SGD-2 1.8 5.3 4.2 0.5 5.8

PRT 526D-11-G3 0.5 2.8 12.6 0.5 3.3

Probe 526SGD-3 1.8 7.6 6.0 0.5 8.1

56
Table 20c. Summary of VOC and Gas Concentrations in Sample Systems at 3.2 m Near MW526SGD 

Sample 1,1-DCE 1,1,1-TCA TCE c-1,2-DCE O2 CO2 CH4 

Identification (ppbv) (ppbv) (ppbv) (ppbv) (%) (%) (%)

PRT

526-11-G1 85 120 38 16 18.9 0.8 0.0

526-11-G2 85 121 40 18 19.0 0.8 0.0

526-11-G3 92 124 45 19 19.1 0.9 0.0

mean 526-11-G 87 122 41 18 19.0 0.8 0.0

stdev 526-11-G 4.0 2.1 3.6 1.5 0.1 0.1 0.0

Probe

526SGD-1 68 87 32 14 19.2 0.9 0.0

526SGD-2 68 87 32 14 19.2 0.9 0.0

526SGD-3 66 87 33 14 19.2 0.9 0.0

mean 526SGD 67 87 32 14 19.2 0.9 0.0

stdev 526SGD 1.2 0.0 0.6 0.0 0.0 0.0 0.0

57

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