United States Office of Research and EPA/625/XXX/001

Environmental Protection Development September 1995

Agency Washington, DC 20460

1EPA Manual

Bioventing Principles and

Practice

Volume II: Bioventing Design
EPA/540/R-95/534a

September 1995

Manual

Principles and Practices of Bioventing

Volume II: Bioventing Design

U.S. Environmental Protection Agency

Office of Research and Development

National Risk Management Research Laboratory

Center for Environmental Research Information

Cincinnati, Ohio

U.S. Air Force Center for

Environmental Excellence

Technology Transfer Division

Brooks AFB, TX

U.S. Air Force Environics 

Directorate of the

Armstrong Laboratory

Tyndall AFB, FL
Notice

The information in this document has been funded wholly, or in part, by the U.S. Environmental

Protection Agency (EPA). This document has been subjected to EPA’s peer and administrative

review and has been approved for publication as an EPA document. The methods presented in this

document are ones often used by the U.S. Air Force and EPA but are not necessarily the only

methods available. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

This document is equivalent to U.S. Air Force document AL/EQ-TR-1995-0037.

ii
Contents

Page

Chapter 1 Site Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Existing Data and Site History Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Soil Gas Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.1 Soil Gas Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.2 Collection and Analysis of Soil Gas Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.3 Interpretation of Soil Gas Survey Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.3 Soil Characterization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.3.1 Soil Borings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.3.2 Soil Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.4 In Situ Respiration Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.4.1 In Situ Respiration Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.4.2 Interpretation of in Situ Respiration Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1.4.3 Factors Affecting Observed in Situ Biodegradation Rates . . . . . . . . . . . . . . . . . . . 16

1.5 Soil Gas Permeability and Radius of Influence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1.5.1 Radius of Influence Determination Based on Pressure Measurements. . . . . . . . . 18

1.5.2 Interpretation of Soil Gas Permeability Testing Results . . . . . . . . . . . . . . . . . . . . . 19

Chapter 2 System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.1 Determination of Air Flow System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.1.1 Air Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.1.2 Air Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.1.3 Determining Use of Injection Versus Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.1.4 Design of Air Flow To Protect Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.2 Determining Required Air Flow Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.3 Well Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.4 Blowers and Blower Sizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.4.1 Centrifugal Blowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.4.2 Rotary Positive Displacement Blowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2.4.3 Blower Selection and Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2.5 Vent Well Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2.6 Monitoring Point Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

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Chapter 3 Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.1 Soil Gas Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.2 In Situ Respiration Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.3 Quantification of Biodegradation and Volatilization of Hydrocarbons During Extractive 

Bioventing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.4 Surface Emissions Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.5 Optional Monitoring: Qualitative Validation of Biodegradation Through Stable Carbon 

Isotope Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.6 Operation and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Chapter 4 Process Evaluation/Site Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.1 In Situ Respiration Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.2 Soil Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Chapter 5 Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Chapter 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Appendix A Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Appendix B Equipment Specifications and Manufacturers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

B.1 Soil Gas Survey Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

B.2 Vent Well Installation Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

B.3 Soil Gas Monitoring Point Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

B.4 Air Permeability Test Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

B.5 In Situ Respiration Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

B.6 Miscellaneous Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

B.7 Optional Items. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Appendix C Example Procedures for Conducting Bioventing Treatability Studies . . . . . . . . . . . . . . . . . 67

C.1 Example Procedures for Collecting, Labeling, Packing, and Shipping Soil Samples. . . . . 67

C.1.1 Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

C.1.2 Sample Label and Log. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

C.1.3 Sample Packing and Shipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

C.1.4 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

C.2 Example Procedures for in Situ Respiration Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

C.2.1 Field Instrumentation and Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

C.2.2 In Situ Respiration Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

C.2.3 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Contents (continued)

Page

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C.3 Example Procedures for Soil Gas Permeability Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

C.3.1 Field Instrumentation and Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

C.3.2 Soil Gas Permeability Test Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

C.3.3 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

C.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Appendix D Off-Gas Treatment Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

D.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

D.2 Limiting Off-Gas Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

D.3 Direct Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

D.4 Off-Gas Reinjection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

D.5 Biofiltration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

D.6 Adsorption on Carbon or Resin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

D.7 Catalytic Oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

D.8 Flame Incineration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

D.9 Internal Combustion Engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

D.10 Emerging Vapor Treatment Technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

D.11 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Contents (continued)

Page

v
Figures

Figure Page

1-1 Conceptual decision tree for determining the potential applicability of bioventing at a contaminated site . . 1

1-2 Site map showing well locations and TPH soil concentrations at AOC A, Keesler AFB, Mississippi . . . . . . 3

1-3 Schematic of a soil gas sampling system using the stainless steel soil gas probe . . . . . . . . . . . . . . . . . . . . 4

1-4 Schematic of a soil gas sampling system for collection of soil gas from low-permeability soils . . . . . . . . . . 6

1-5 Sample soil boring log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1-6 In situ respiration test apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1-7 In situ respiration test results with linear oxygen concentration versus time at AOC A, 

Keesler AFB, Mississippi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1-8 In situ respiration test results with nonlinear oxygen concentration versus time at SWMU 66, 

Keesler AFB, Mississippi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1-9 In situ respiration test results with acceptable data based on the helium concentration for 

monitoring point S1, Tinker AFB, Oklahoma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1-10 In situ respiration test results with unacceptable data based on the helium concentration 

for monitoring point K3, Kenai, Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1-11 Determination of radius of influence at the Saddle Tank Farm, Galena AFS, Alaska . . . . . . . . . . . . . . . . . 19

2-1 Expanded bioreactor created during air injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2-2 Oxygen utilization rates, averaged over depth, versus distance from the injection well at Site 280, 

Hill AFB, Utah . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2-3 Mass of TPH degraded versus distance from the injection well at Site 280, Hill AFB, Utah . . . . . . . . . . . . 22

2-4 Hydrocarbon volatilization and biodegradation rates as a function of air flow rate . . . . . . . . . . . . . . . . . . . 23

2-5 Water table depression during air injection and air extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2-6 Air injection configuration for a bioventing system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2-7 Radius of influence during air injection and extraction in the control test plot at a depth of 6 ft at 

Site 20, Eielson AFB, Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2-8 Schematic of a basic air extraction system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2-9 Extracted BTEX and TPH soil gas concentrations at Patrick AFB, Florida . . . . . . . . . . . . . . . . . . . . . . . . . 26

2-10 Schematic of an air injection system with reinjection of extracted soil gas . . . . . . . . . . . . . . . . . . . . . . . . . 27

2-11 Schematic of subslab depressurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2-12 Schematic of the extraction with reinjection system at AOC A, Keesler AFB, Mississippi. . . . . . . . . . . . . . 28

2-13 Soil gas extraction to isolate a subsurface structure at Site 48, Eielson AFB, Alaska. . . . . . . . . . . . . . . . . 29

2-14 Schematic of blower types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2-15 Performance curves for three different-sized blowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2-16 Schematic of a typical vent well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2-17 Schematic of a typical monitoring point construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

vi
3-1 Schematic of a surface emissions monitoring device. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3-2 Carbon isotopic compositions of soil gas carbon dioxide at Site 20, Eielson AFB, 

Alaska, August 1993 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5-1 Comparison of costs for various remedial technologies for fuel-contaminated soils . . . . . . . . . . . . . . . . . . 48

Figures (continued)

Figure Page

vii
Tables

1-1 Results From a Soil Gas Survey at AOC A, Keesler AFB, Mississippi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1-2 Results From a Soil Gas Survey at Building 1813, Hanscom AFB, Massachusetts . . . . . . . . . . . . . . . . . . . 8

1-3 Results from a Soil Gas Survey at the Aquasystem Site, Westover AFB, Massachusetts . . . . . . . . . . . . . . 9

1-4 Results From a Soil Gas Survey at an Oil/Water Leak at Cape Canaveral AFS, Florida . . . . . . . . . . . . . . . 9

1-5 Soil Analyses Based on Bioventing Initiative Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1-6 Oxygen Density Versus Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1-7 Bulk Density of Various Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1-8 Initial Soil Gas Readings at Monitoring Points at AOC A, Keesler AFB, Mississippi . . . . . . . . . . . . . . . . . . 14

1-9 Raw Data From an in Situ Respiration Test at 

AOC A, Keesler AFB, Mississippi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1-10 Oxygen Utilization and Carbon Dioxide Production Rates During the in Situ Respiration Test 

at AOC A, Keesler AFB, Mississippi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1-11 Raw Data From an in Situ Respiration Test at SWMU 66, Keesler AFB, Mississippi . . . . . . . . . . . . . . . . . 15

1-12 Soil Gas Permeability Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2-1 Permeability and Radius of Influence Values at Eielson AFB, Alaska: Injection and Extraction Mode . . . . 24

2-2 Air Injection Versus Extraction Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2-3 Recommended Spacing for Monitoring Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3-1 Surface Emissions Sampling at Bioventing Sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4-1 Cumulative t Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4-2 Number of Observations for t Test of Mean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4-3 Calculation of the Number of Samples Required To Show a Statistical Difference Between Means of 

Two Sampling Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4-4 Selected z Values for Estimation of Final Soil Sample Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

5-1 Typical Full-Scale Bioventing Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5-2 Cost Comparison of in Situ Bioremediation Technologies Used at Fuel Spill Sites. . . . . . . . . . . . . . . . . . . 47

viii
List of Examples

Example Page

1-1 Review of Existing Data and Site History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1-2 Soil Gas Survey Conducted at Keesler AFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1-3 Soil Gas Survey at Building 1813, Hanscom AFB, Massachusetts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1-4 Soil Gas Survey at the Aquasystem Site, Westover AFB, Massachusetts . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1-5 Soil Gas Survey at an Oil/Water Separator Leak at Cape Canaveral AFS, Florida. . . . . . . . . . . . . . . . . . . . 9

1-6 Results From an in Situ Respiration Test Conducted at Keesler AFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1-7 Calculation of Oxygen Utilization Rates From Nonlinear Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1-8 Evaluation of Helium Loss During an in Situ Respiration Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1-9 Temperature Adjustment of Oxygen Utilization Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1-10 Calculation of the Radius of Influence Based on Pressure Measurements. . . . . . . . . . . . . . . . . . . . . . . . . 19

2-1 Biodegradation of Petroleum Hydrocarbons in the Uncontaminated and Contaminated Regions at 

Site 280, Hill AFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2-2 Determination of Required Air Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2-3 Calculation of Radius of Influence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2-4 Selection and Sizing of a Blower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2-5 Selection of Depth Intervals for Monitoring Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3-1 Calculation of Volatilization and Biodegradation of Contaminants During Extraction . . . . . . . . . . . . . . . . . 38

4-1 Calculation of Remediation Time Based on in Situ Respiration Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4-2 Statistical Evaluation of Contaminant Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4-3 Calculation of Final Number of Soil Samples for Site Closure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

ix
List of Symbols and Acronyms

AFB Air Force Base

AFCEE U.S. Air Force Center for

Environmental Excellence

AL/EQ Armstrong Laboratory Environics

Directorate

AOC area of concentration

BTEX benzene, toluene, ethylbenzene, and

xylenes

cfm cubic feet per minute

CPT cone penetrometer

DNAPL dense nonaqueous phase liquid

EPA U.S. Environmental Protection Agency

FID flame ionization detector

GAC granular activated carbon

ICE internal combustion engine

LEL lower explosive limit

LNAPL less dense nonaqueous phase liquid

MP monitoring point

MW monitoring well

NAS Naval Air Station

NFPA National Fire Protection Association

NPT national pipe thread

PAH polycyclic aromatic hydrocarbon

PCB polychlorinated biphenyl

PID photoionization detector

PVC polyvinyl chloride

RD&A research, development, and acquisition

scfm standard cubic feet per minute

SGS soil gas survey

SVE soil vacuum extraction

TCE trichloroethylene

TKN total Kjeldahl nitrogen

TPH total petroleum hydrocarbon

UCL upper confidence limit

UST underground storage tank

VOC volatile organic carbon

CS quantity sorbed to the solid matrix

(gx/gsoil)

CV volumetric concentration in the vapor

phase (gx/Lvapor)

Cvsat saturated vapor concentration (gx/Lvapor)

CW volumetric concentration in the

aqueous phase (gx/Laqueous)

Ea activation energy (cal/mole)

foc organic carbon fraction

k maximum rate of substrate utilization

(gS/gX-min)

kB biodegradation rate (mg hydrocarbon/

kg soil-day)

kd endogenous respiration rate (day-1)

Kd sorption coefficient (Laqueous/gsoil)

ko baseline biodegradation rate

(% O2/day)

Kow octanol/water partition coefficient

KS Monod half-velocity constant (gS/L)

kT temperature-corrected biodegradation

rate (% O2/day)

MW molecular weight (gx/molex)

PV vapor pressure of pure contaminant at

temperature T (atm)

R gas constant (1.987 cal/°K-mol)

R gas constant (L-atm/mole-°K)

RI radius of influence

S concentration of the primary substrate

(contaminant) (gS/L)

sx solubility in water (gx/Lwater)

t time (minutes)

Tabs absolute temperature (°K)

χ mole fraction (dimensionless)

X concentration of microorganisms (gX/L)

Y cell yield (mg biomass/mg hydrocarbon)

x
Conversion Factors

To convert . . . to . . . multiply by . . .

cubic feet cubic meters 0.02831685

cubic feet liters 0.03531

cubic inches cubic centimeters 610.2

cubic yards (tons) cubic meters 0.7646

cubic yards (tons) kilograms 907.1843

darcy square centimeter 9.869233 x 10-9

darcy square meter 9.869233 x 10-13

degrees Fahrenheit degrees Celsius t°C = (t°F - 32)/1.8

degrees Fahrenheit degrees Kelvin t°K = (t°F - 523.67)/1.8

feet meters 0.3048

horsepower kilowatts 0.7457

inches centimeters 2.54

kilocalories joules 4,186.8

millimeters of mercury (°C) Pascals 133.322

parts per million milligrams per liter 1

parts per million grams per liter 1,000

pounds kilograms 0.45354237

pounds per square inch kiloPascals 6.895

square inches square centimeters 6.4516

tons metric tons 0.90718474

U.S. gallons liters 3.785

xi
Acknowledgments

This manual was prepared by Andrea Leeson and Robert Hinchee of Battelle Memorial Institute,

Columbus, Ohio, for the U.S. Environmental Protection Agency’s (EPA’s) National Risk Management

Research Laboratory, Cincinnati, Ohio; the U.S. Air Force Environics Directorate of the Armstrong

Laboratory, Tyndall AFB, Florida; and the U.S. Air Force Center for Environmental Excellence,

Technology Transfer Division, Brooks AFB, Texas.

The project managers for this manual were Lt. Colonel Ross Miller, U.S. Air Force Center for

Environmental Excellence; Gregory Sayles, EPA National Risk Management Research Laboratory;

and Catherine Vogel, U.S. Air Force Environics Directorate, Armstrong Laboratory. These individuals

also contributed to the content of the manual.

The manual was peer reviewed by:

 Ryan Dupont, Utah State University

 Chi-Yuan Fan, U.S. EPA National Risk Management Research Laboratory

 Paul Johnson, Arizona State University

 Jack van Eyck, Delft Geotechnic

Acknowledgments are also given to the following individuals who contributed to this document:

 Bruce Alleman, Battelle Memorial Institute

 Douglas Downey, Parsons Engineering Science

 Gregory Headington, Battelle Memorial Institute

 Jeffrey Kittel, Battelle Memorial Institute

 Priti Kumar, Battelle Memorial Institute

 Say Kee Ong, Iowa State University

 Lawrence Smith, Battelle Memorial Institute

Eastern Research Group, Inc., Lexington, Massachusetts, copy edited and prepared camera-ready

copy of this manual.

xii
This document is a product of the bioventing research and development efforts sponsored by the

U.S. Air Force Armstrong Laboratory, the Bioventing Initiative sponsored by the U.S. Air Force

Center for Environmental Excellence (AFCEE) Technology Transfer Division, and the Bioremediation Field Initiative sponsored by the U.S. Environmental Protection Agency (EPA).

The Armstrong Laboratory Environics Directorate (AL/EQ), an element of the Air Force Human

Systems Center, began its bioventing research and development program in 1988 with a study at

Hill Air Force Base (AFB), Utah. Follow-up efforts included field research studies at Tyndall AFB,

Florida; Eielson AFB, Alaska; and F.E. Warren AFB, Wyoming, to monitor and optimize process

variables. The results of these research efforts led to the Bioventing Initiative and are discussed in

this document.

The AFCEE’s Bioventing Initiative has involved conducting field treatability studies to evaluate

bioventing feasibility at over 125 sites throughout the United States. At those sites where feasibility

studies produced positive results, pilot-scale bioventing systems were installed and operated for 1

year. Results from these pilot-scale studies culminated in the production of this document.

EPA’s Bioremediation Field Initiative was established to provide EPA and state project managers,

consulting engineers, and industry with timely information regarding new developments in the

application of bioremediation at hazardous waste sites. This program has sponsored field research

to enable EPA laboratories to more fully document newly developing bioremediation technologies.

As part of the EPA Bioremediation Field Initiative, EPA has contributed to the Air Force Bioventing

Initiative in the development of the test plan for conducting the pilot-scale bioventing studies and

assisted in the development of this manual.

The results from bioventing research and development efforts and from the pilot-scale bioventing

systems have been used to produce this two-volume manual. Although this design manual has been

written based on extensive experience with petroleum hydrocarbons (and thus, many examples use

this contaminant), the concepts here should be applicable to any aerobically biodegradable compound. The manual provides details on bioventing principles; site characterization; field treatability

studies; system design, installation, and operation; process monitoring; and site closure. This

second volume focuses on bioventing design and process monitoring. The first volume describes

basic principles of bioventing.

xiii
Chapter 1

Site Characterization

Site characterization is an important step in determining

the feasibility of bioventing and in providing information

for a full-scale bioventing design. Chapter 1 discusses

site characterization methods that are recommended for

bioventing sites based on field experience and a statistical analysis of Bioventing Initiative data. These parameters have proven to be the most useful in predicting

the potential applicability of bioventing at a contaminated site. Figure 1-1 summarizes the sequence of

events for site characterization of a typical site. Each

step presented in Figure 1-1 is discussed in the following

sections.

Site characterization activities to be conducted at a

potential bioventing site should include the following:

• Review of existing site data (Section 1.1).

• Soil gas survey (Section 1.2).

• Soil characterization (Section 1.3).

• In situ respiration testing (Section 1.4).

• Soil gas permeability testing, and radius of influence

(Section 1.5).

Figure 1-1. Conceptual decision tree for determining the potential applicability of bioventing at a contaminated site.

1
1.1 Existing Data and Site History

Review

The first step in designing and installing a bioventing

system is to review the existing site data. An initial

review of site data provides preliminary information for

determining whether bioventing is a feasible option for

a specific site. Also, the initial data review helps to

identify any additional information that is needed to

complete the bioventing design.

Information to be obtained during the data review, if

possible, should include the following:

• Types of contaminants.

• Quantity and distribution of free product (if present).

• Historical water table levels.

• Three-dimensional distribution of contaminant.

• Potential for a continuing source of contamination

because of leaking pipes or tanks.

• Particle size distribution or soil gas permeability.

• Surface features such as concrete or asphalt.

At this stage, the most important information is type of

contaminant. Bioventing is applicable only to compounds that are biodegraded aerobically, such as petroleum hydrocarbons.1

 Compounds such as chlorinated

solvents tend to degrade more readily under anaerobic

conditions. In most cases, the contaminant is petroleum

hydrocarbons; however, bioventing also may potentially

be applied at some sites contaminated with both chlorinated solvents and petroleum hydrocarbons.

If significant free product is present, removal must be

addressed either before or simultaneously with

bioventing. Bioventing alone is not sufficient to remediate sites with large quantities of free product. Bioslurping technology combines bioventing and free

product removal and is currently under development

by the Air Force (Kittel et al., 1995).

Historical water table levels also are important to determine whether contamination is available for bioventing

or is present below the water table. If significant contamination is present below the water table, dewatering

may be needed to complete site remediation. At some

sites, bioventing may be feasible only during periods of

seasonal low water tables.

The three-dimensional distribution of the contaminant

provides information necessary for generating an initial

estimate of the screen depths and the size of the

bioventing system that will be required. This initial estimate provides a guideline for conducting the soil gas

survey and for collecting initial soil samples necessary

to estimate the initial mass of contamination at the site.

The potential for a continuing source of contamination

must be addressed at every site. Often, contaminated

sites are created from leaking underground pipes or

tanks. These sources must be eliminated for bioventing

to achieve cleanup.

If available, data on particle size distribution or permeability are useful for determining the potential for applying bioventing. Because the success of bioventing

depends on the ability to move air through the soil,

particle size or permeability measurements are crucial

parameters. Unless these values are extreme (saturated clay), however, initial treatability studies should be

conducted to determine bioventing applicability.

If surface features such as concrete or asphalt are

present, excavation methods would be too disruptive, so

bioventing is the only cost-effective treatment option

available. If contamination is present beneath buildings,

the bioventing system must be designed to ensure that

contaminants do not rise up into the buildings.

Example 1-1. Review of Existing Data and Site History:

Bioventing is being considered at area of concern (AOC)

A at Keesler Air Force Base (AFB), Mississippi, and the

following information is known:

• The soil was contaminated from leaking underground

gasoline storage tanks.

• Storage tanks were removed in 1991.

• A site map (Figure 1-2) was provided with limited total

petroleum hydrocarbon (TPH) soil sample results.

• The soils are very sandy.

After examining the existing site data, the following conclusions are made:

• The type of contaminant is gasoline, a very good

candidate for bioventing. Based on this information,

a soil gas survey is scheduled.

• No information was provided on free product or on

water levels. Given that ground-water monitoring

wells are shown in Figure 1-2, some information

probably exists. Although further attempts will be

made to find the additional information, collection of

free product and water level measurements will also

take place during the soil gas survey phase.

• The quantity of the release is unknown because contamination occurred over a long period; however, the

limited soil sampling provides a general guideline for

the area in which to conduct a soil gas survey.

• The storage tanks were removed, so a continuing

source of contamination is not a factor.

1 See Volume I for a discussion of compounds degraded through

bioventing.

2
• Particle size distribution was known; soils are sandy,

making this site an excellent candidate for bioventing.

1.2 Soil Gas Survey

At sites where the contamination is at sufficiently shallow depths (typically less than 20 ft [6.1 m]), a soil gas

survey should be conducted initially to determine

whether oxygen-limited conditions exist. Oxygen-limited

conditions are a good indicator of whether bacteria are

present that are capable of degrading the contaminants

of concern because soil gas in uncontaminated vadose

zone soils generally exhibits oxygen concentrations

equivalent to ambient air. The soil gas survey also assists in delineating the extent of contamination and locating suitable areas for vent well and monitoring point

placement. Data on soil gas concentrations of oxygen,

carbon dioxide, and TPH can provide valuable insight

into the extent of subsurface contamination and the

potential for in situ bioventing. The procedures outlined

in this section assist in the collection and interpretation

of soil gas information, with the ultimate goal of promoting

a more cost-effective approach to fuel-contaminated soil

remediation

1.2.1 Soil Gas Chemistry

The chemical composition of soil gas can vary considerably from atmospheric composition as a result of biological and mineral reactions in the soil. Many

compounds and elements may be present in soil gas

because of site-specific geochemistry, but three indicators are of particular interest for bioventing systems:

respiration gases (oxygen and carbon dioxide) and hydrocarbon vapors. The soil gas concentrations of these

indicators in relation to atmospheric air and uncontaminated background soils can provide valuable information on the ongoing natural biodegradation of

hydrocarbon contaminants and the potential for bioventing to enhance the rate of natural biodegradation.

1.2.1.1 Respiration Gases

Oxygen serves as a primary electron acceptor for soil

microorganisms employed in the degradation of both

refined and natural hydrocarbons. Following a hydrocarbon spill, if active microbial populations are present, soil

gas oxygen concentrations are usually low (typically

less than 5 percent) and soil gas carbon dioxide (a

metabolite of hydrocarbon degradation) may be high

(typically greater than 10 percent). Oxygen concentrations generally are lower in the vicinity of the contaminated soils than in clean soils, indicating that aerobic

biodegradation is depleting oxygen. As the population of

fuel-degrading microorganisms increases, the supply of

soil gas oxygen is often depleted, creating an anaerobic

volume of contaminated soil. Under anaerobic conditions, fuel biodegradation generally proceeds at significantly slower rates than when oxygen is available for

metabolism. In some cases, aerobic biodegradation

continues because the diffusion or advection of oxygen

into soils from the atmosphere exceeds biological oxygen utilization rates. Under these circumstances, the

Figure 1-2. Site map showing well locations and TPH soil concentrations at AOC A, Keesler AFB, Mississippi.

3
site is naturally aerated, and the hydrocarbons are naturally attenuated over time.

Carbon dioxide is produced as a by-product of the complete aerobic biodegradation of hydrocarbons and can

also be produced or buffered by the soil carbonate cycle

(Ong et al., 1991). Carbon dioxide levels in soil gas are

generally elevated in fuel contaminated soils compared

with levels in clean background soils. In many soils,

higher carbon dioxide concentrations correlate with low

oxygen levels; however, this is not always true. Because

of the buffering capacity of alkaline soils, the relationship

between contaminant biodegradation and carbon dioxide production is not always a reliable indicator. Carbon

dioxide can form carbonates rather than gaseous carbon

dioxide, particularly in soils with pH over 7.5 and high

reserve alkalinity. In acidic soils, such as exist at Tyndall

AFB, Florida, carbon dioxide production is directly proportional to oxygen utilization (Miller and Hinchee,

1990).

Soil gas survey results in a contaminated area should

be compared with those obtained from an uncontaminated area. Typically, soil gas concentrations in an uncontaminated area are significantly different, with

oxygen concentrations approximately equal to ambient

concentrations and very low carbon dioxide (less than

0.5 percent).

1.2.1.2 Hydrocarbon Vapors

Volatile hydrocarbons found in soil gas can also provide

valuable information on the extent and magnitude of

subsurface contamination. Fuels such as gasoline,

which contain a significant fraction of C6 and lighter

compounds, are easily detected using soil gas monitoring techniques. Heavier fuels, such as diesel, contain

fewer volatiles and are more difficult to locate based on

volatile hydrocarbon monitoring. Methane is frequently

produced as a by-product of anaerobic biodegradation

and, like oxygen depletion, has been used to locate the

most contaminated soils at a site. Extensive literature is

available on soil gas survey techniques for using volatile

hydrocarbons as indicators of contamination (Rivett and

Cherry, 1991; Downey and Hall, 1994).

1.2.2 Collection and Analysis of Soil Gas

Samples

This section describes the test equipment and methods

used to conduct field soil gas surveys, to monitor soil

gas for bioventing systems, and to install temporary soil

gas monitoring points. The procedures and equipment

described in this section are only guidelines. Because

of widely varying site conditions, site-specific applications are necessary. In some regulatory jurisdictions, soil

gas survey monitoring points must comply with well

installation or other regulations.

Whenever possible, soil gas surveys should be conducted at potential bioventing sites before locating the

pilot test vent well(s) and monitoring points. The soil gas

survey is used to determine the necessity of bioventing

whether anaerobic soil gas conditions exist and by providing an initial indication of the extent of contamination.

If sufficient oxygen is naturally available and distributed

throughout the subsurface, bioventing may not enhance

biodegradation rates. The soil gas survey can also help

to determine the areal extent and, in the case of shallow

contamination, the vertical extent of soil contamination.

Information about contaminant distribution helps to locate the vent well and soil gas monitoring points and to

determine the optimum depths of screened intervals.

The soil gas survey points should be arranged in a grid

pattern centered on the known or suspected contaminated area. The soil gas probes are positioned at each

grid intersection, and the survey begins near the center

of the grid and progresses outward to the limits of significant detectable soil contamination. At times, soil gas

measurements are taken at several depths at each location to determine the vertical distribution of contamination and oxygen supply. At shallow sites, a soil gas

sampling grid should be completed with samples collected from multiple depths if the contaminated interval

exceeds 3 ft (0.91 m) or if contamination is suspected in

different soil types.

A soil gas survey can be conducted using small-diameter (typically 5/8- to 1-in. [1.6- to 2.5-cm] outside

diameter steel probes. The typical probe consists of a

drive point with a perforated tip that is threaded onto a

series of drive rod extensions. Figure 1-3 shows a typical setup for monitoring soil gas.2

Soil conditions and depth of contamination dictate the

method of probe installation. Utility clearances from the

local utility companies and digging permits (required at

Figure 1-3. Schematic of a soil gas sampling system using the

stainless steel soil gas probe.

2 See Appendix B for recommended specifications and manufacturers

for soil gas sampling equipment.

4
military installations) should be obtained before probe

installation. Temporary probes are installed using either

a handheld electric hammer or a hydraulic ram. The

maximum depth for hammer-driven probes is typically

10 ft to 15 ft (3 m to 4.6 m), depending on soil texture.

Hydraulic rams are capable of driving the probes over

30 ft (9.1 m) in a variety of soil conditions. If hydraulic

rams are not sufficient, a GeoProbe or similar equipment

can be used and also can collect soil samples.

At sites with deeper contamination, where soil texture

precludes the use of a hammer or hydraulic ram or

where a permanent monitoring system is required, permanent soil gas monitoring points may be installed using either a portable or a truck-mounted drill rig.

Gaseous concentrations of carbon dioxide and oxygen

can be analyzed using an oxygen/carbon dioxide analyzer. The analyzer generally has an internal, batterypowered sampling pump and range settings of 0 percent

to 25 percent for both oxygen and carbon dioxide. Before taking measurements, the analyzer should be

checked for battery charge level; it should also be calibrated daily using atmospheric concentrations of oxygen and carbon dioxide (20.9 percent and 0.05 percent,

respectively) and a gas standard containing 0.0 percent

oxygen and 5.0 percent carbon dioxide, and 95 percent

nitrogen.

Several types of instruments are available for field

measurement of TPH concentrations in air. The selected

instrument must be able to measure hydrocarbon concentrations in the range of 1 to 10,000 parts per million,

volume per volume (ppmv) and be able to distinguish

between methane and nonmethane hydrocarbons.

Flame ionization detectors are the most accurate field

screening instruments for fuel hydrocarbons. Instruments using a platinum catalyst detector system are

also acceptable and are easier to use in the field. Photoionization detectors are not recommended for the high

levels of volatile hydrocarbons found at many sites.

Before taking measurements with any field instrument,

the battery charge level should be checked and the

analyzer should be calibrated against a hexane calibration gas to ensure proper operation.

The analyzer should also have a selector switch to

change the response to eliminate the contribution of

methane gas to the TPH readings. Methane gas is a

common constituent of anaerobic soil gas and is generated by degrading manmade hydrocarbons or natural

organics. Methane is commonly produced in swampy

areas or in fill areas containing organic material. If methane is not excluded from the TPH measurement, TPH

results may indicate erroneously high levels of petroleum hydrocarbon contamination in the soil. The methane

content can also be estimated by placing a large carbon

trap in front of the hydrocarbon analyzer. The carbon

retains the heavier hydrocarbons, while methane and

other lighter molecular weight hydrocarbons pass

through to the detector.

Electric motor-driven sampling pumps are used to purge

and collect samples from monitoring points and soil gas

probes. The pumps should be either oil-less rotary-vane

or diaphragm pumps capable of delivering approximately 1 cubic ft per minute (cfm) (28 L/min) of air at a

maximum vacuum of 2709H2O (6.7 × 104

 Pa). The

pumps have oil-less filters to eliminate particulates from

the air stream. Low-flow, battery-operated pumps may

be favored in high-permeability soils to minimize shortcircuiting.

Differential vacuum gauges are used to monitor the

vacuum in the sampling point during purging and as an

indicator of relative permeability. Typical vacuum ranges

of the gauges are 0 to 509H2O (0 to 1.2 × 104

 Pa) and 0

to 2509H2O (6.2 × 104

 Pa) for sites with sandy and clayey

soils, respectively.

Purging the soil gas probe is a prerequisite for obtaining

representative soil gas samples. A typical purging system consists of a 1-cfm (28-L/min) sampling pump, a

vacuum gauge, and an oxygen/carbon dioxide meter.

The vacuum side of the pump is connected to the soil

gas probe. A vacuum gauge is attached to a tee in the

vacuum side of the system to monitor the vacuum produced during purging, and the oxygen/carbon dioxide

analyzer is connected to a tee in the outlet tubing to

monitor oxygen/carbon dioxide concentrations in the

extracted soil gas. The magnitude of vacuum measured

during purging is inversely proportional to soil permeability and determines the method of sample collection.

After the purging system is attached to the soil gas

probe or monitoring point, the valve or hose clamp is

opened and the pump is turned on. Purging continues

until oxygen and carbon dioxide concentrations stabilize, indicating the purging is complete. Before turning

off the pump, a hose clamp or valve is used to close the

sampling tubing to prevent fresh air from being drawn

into the soil gas probe.

Sampling methods for high-permeability soils (sand and

silt) should be followed if the vacuum measured during

purging is less than 109H2O (2.5 × 103

 Pa). Soil gas

sampling and analysis are performed using the same

equipment used for purging, minus the vacuum gauge.

After opening the sampling point valve or hose clamp,

the sampling pump is turned on, and the extracted soil

gas is analyzed for stable oxygen/carbon dioxide and

TPH concentrations.

A different sampling procedure can be followed to collect

soil gas samples from low-permeability soils. The higher

vacuums required for sampling increase the risk of vacuum leaks introducing fresh air and diluting the soil gas

sample. One method that may be used in low-permeability soils is described below.

5
After purging the sampling point, a soil gas sample is

collected in a Tedlar bag before analysis. The evacuated

Tedlar bag should be placed inside an airtight chamber.

The chamber is then connected to the sampling point

via a hose barb that passes through the chamber wall.

The chamber is then closed, sealed, and connected to

the pump inlet with flexible tubing. The sampling system

is shown in Figure 1-4. To collect the sample, the monitoring point valve is opened, the pump is turned on, and

the pressure relief port on the chamber is sealed using

either a valve or the sampler’s finger. The partial vacuum

within the chamber created by the pump draws soil gas

into the Tedlar bag. When the Tedlar bag is nearly filled,

the sampling point valve or hose clamp is closed, and

the pump is turned off. The chamber is then opened, the

Tedlar bag valve is closed, and the bag is removed from

the chamber. The soil gas sample is then analyzed by

attaching the oxygen/carbon dioxide and TPH analyzers

directly to the Tedlar bag. The advantage of this method

is that the sampling pump is no longer in line, thereby

minimizing the sampling train and subsequent sample

dilution.

Most problems encountered during soil gas sampling

and purging can be divided into three categories: (1)

difficulty extracting soil gas from the sampling point, (2)

water being drawn from the sampling point, and (3) high

oxygen readings in areas of known soil contamination.

Some of the more common problems and solutions are

discussed below.

Difficulty extracting soil gas from a sampling point is

typically caused by low-permeability (clayey and/or

nearly saturated) soils. Collecting soil gas samples from

low-permeability soils is facilitated by slowing the soil

gas extraction rate, which allows the use of less vacuum. Difficulty extracting soil gas from a soil gas probe

can also be caused by the screen being fouled by

fine-grained soil or heavy petroleum residuals. The

probe should be removed from the soil, and the screen

should be either cleaned or replaced if visibly fouled.

Water being drawn from the sampling point by the purge

pump may be the result either of the point being installed

in the saturated zone or, in the case of permanent

monitoring points, the filter pack being saturated with

water during construction. In the former case, a temporary probe can be pulled up to a shallower depth above

the saturated zone and resampled. With a permanent

monitoring point installed within the saturated zone,

sampling must be delayed until either the water table

drops because of seasonal variations or the water table

is artificially depressed by a dewatering operation.

If the screened interval in a permanent monitoring point

is installed above the saturated zone but the filter pack

was saturated with water during construction, sampling

may still be possible if the water is pumped from the

monitoring point. This method will only work if the

screened interval is at a depth of less than approximately 22 ft (6.7 m), which is the practical limit of suction

lift.

Figure 1-4. Schematic of a soil gas sampling system for collection of soil gas from low-permeability soils.

6
Water also may be drawn into the point in unsaturated

soils as the result of the creation of a vacuum in excess

of capillary pressure. In this case, the extracted flow

typically is a mixture of water and soil gas. Frequently,

a water trap before the sampling pump can be used to

remove the water; thus, collecting and analyzing a soil

gas sample is still possible.

High soil gas oxygen readings in areas of known soil

contamination may indicate a leak in the sampling or

purging system. The potential for leakage, and the resulting dilution of the sample with atmospheric air, is

higher in low-permeability soils where higher vacuums

are required for purging and sampling. If a leak is suspected, all connections in the sampling system and the

seal around the monitoring point or soil gas probe

should be inspected for leaks. Seals around a soil gas

probe or monitoring point can be checked for leaks by

inspecting for air bubbles while injecting air with a sampling pump after adding water around the probe or monitoring point. Any observed or suspected leaks should be

corrected by tightening connections, repositioning the

soil gas probe, or attempting to repair the monitoring

point seal.

1.2.3 Interpretation of Soil Gas Survey

Results

The purpose of gathering soil gas data during bioventing

investigations is to locate areas where addition of oxygen will most efficiently enhance fuel biodegradation.

Low soil gas oxygen concentrations are a preliminary

indication that bioventing may be feasible at the site, so

proceeding to in situ respiration testing is appropriate. If

soil gas oxygen concentrations are high (greater than 5

percent to 10 percent), yet contamination is present,

other factors may be limiting biodegradation. The most

common limiting factor is low moisture level. If a pilot

test is to be completed, the soil gas survey should focus

on locating areas with the lowest oxygen concentrations. For full-scale applications, it is useful to determine

the entire areal extent and depth of soils with an oxygen

deficit (for practical purposes, less than 5 percent oxygen).

In very shallow, permeable soils, diffusion, biometric

pumping, or water table fluctuations may enhance air

movement into the soil and provide a natural oxygen

supply.3

 Soil gas data are useful for determining which

sites are naturally aerated and therefore do not require

mechanical bioventing systems.

If high oxygen concentrations are observed on the site,

the existence of significant contamination should be

questioned. Lower levels of contamination (e.g., less

than 1,000 mg/kg TPH) could potentially be biodegraded

by the natural oxygen supply, and no active remediation

would be necessary. If higher levels of hydrocarbons are

present (above 1,000 mg/kg), the natural oxygen supply

will likely be inadequate to sustain biodegradation and,

more likely, some other factor is limiting. In the authors’

experience, soil containing both high oxygen and high

hydrocarbon concentrations only occurs at moisture-limited sites (the most common case) or sites with toxicity

problems (trichloroethylene [TCE] in one case and phenolics in another). In only two cases familiar to the

authors, these factors could not explain the lack of

oxygen utilization. This occurred at a JP-5 jet fuel site

on Fallon Naval Air Station (NAS) in Nevada and a JP-4

Spill Site at Davis-Monthan AFB in Arizona. The problem

sites are not moisture limited; however, no clear explanation has arisen to date (Engineering-Science, 1994;

Kittel et al., 1995). A series of examples of soil gas

survey results and an interpretation of the data are

presented here to illustrate the principles discussed in

this section.

Example 1-2. Soil Gas Survey Conducted at Keesler

AFB: At the site described in Example 1-1, a soil gas

survey was conducted. First, depth to ground water and

free product thickness were measured at all of the

ground-water monitoring wells (MWs). Ground-water

depths were as follows: MW8-1 at 6.8 ft (2.1 m), MW8-2

at 8.0 ft (2.4 m), MW8-3 at 8.2 ft (2.5 m), and MW8-11

at 8.25 ft (2.5 m). No free product was detected in any

of the wells, so free product removal was not a factor at

this site.

A limited soil gas survey was conducted because the

area of contamination had recently been defined. Soil

gas samples were collected at depths ranging from 2 ft

to 6 ft (.61 m to 1.8 m). Because ground water was

measured at 6.8 ft (2.1 m), soil gas probes were not

driven deeper.

Results from this survey are shown in Table 1-1. At most

locations, oxygen was limiting, with concentrations less

than 5 percent, and carbon dioxide and TPH concentrations were relatively high. The exception was at location

SGS-D-6.0’. At this point, oxygen was measured at 20.1

percent, carbon dioxide at 0.1 percent, and TPH at 120

ppm. These levels were more representative of ambient

air than of the soil gas concentrations measured at other

points at the site, indicating that significant dilution of this

sample may have occurred. Because of these measurements, the sampling pump was thoroughly examined

and loose connections were tightened. Upon resampling, soil gas concentrations were more representative

of other soil gas concentrations. If resampling were to

give the same initial results, it could be possible that this

monitoring point was plugged, causing the sampling

train to leak, and/or atmospheric air was short circuiting

3 See Volume I for a discussion of factors affecting the bioventing

process.

7
to the point. In either case, results from this point should

be discarded as invalid.

Results of this soil gas survey indicate that this site is

an excellent candidate for bioventing.

Example 1-3. Soil Gas Survey at Building 1813, Hanscom AFB, Massachusetts: This site comprises an underground storage tank (UST) containing diesel fuel that

had leaked. The tank was removed, but an unknown

quantity of fuel-contaminated soil remained at the site.

Site soils are sandy to ground water, which occurred at

8 ft to 9 ft (2.4 m to 2.7 m).

A soil gas survey was conducted at seven locations and

at multiple depths. Soil gas results are presented in

Table 1-2.

Low levels of TPH indicate that little diesel-contaminated soil remained at the site or that residual fuels were

highly weathered. Near-atmospheric oxygen levels at all

depths indicated that remaining hydrocarbons were being biodegraded with oxygen supplied by natural diffusion. Carbon dioxide was found at levels above the

atmospheric concentration of 0.03 percent, indicating

some biological respiration was occurring. Higher carbon dioxide levels and slightly depressed oxygen levels

at point 3 (PT3) and PT4 indicated remaining fuel was

probably located in this area of the site. Natural aeration

appeared to provide sufficient oxygen for biodegradation of remaining fuel residuals.

Example 1-4. Soil Gas Survey at the Aquasystem Site,

Westover AFB, Massachusetts: This site consisted of

USTs that, when removed, revealed soil contamination.

An unknown quantity of mixed fuels contamination remained in the soil. Site soils were predominantly sand,

with ground water at approximately 13 ft (4.0 m) below

the surface.

A soil gas survey consisting of a 12-point grid was

completed in and downgradient of the former tank pit.

All points were sampled at multiple depths. Results of

the survey are provided in Table 1-3.

Low levels of TPH were detected in the soil gas at this

site. Oxygen levels were significantly depleted below

atmospheric concentrations in soils near PT7 and

PT17, and generally decreased with depth. The 8

percent to 9 percent of oxygen available in this area,

however, was more than sufficient to sustain in situ

biodegradation. Carbon dioxide ranged from 2 percent to 8.5 percent and generally increased with

depth. The available data suggested that significant

natural biodegradation was occurring at the site. More

oxygen-depleted soil might exist in the capillary fringe,

and engineered bioventing could accelerate biodegradation if this anaerobic zone exists. The decision to

biovent this site should be based on other factors,

such as the impact and potential risk that soil contamination poses to ground water.

Table 1-2. Results From a Soil Gas Survey at Building 1813,

Hanscom AFB, Massachusetts

Soil Gas

Survey

Point

Depth

(ft)

Oxygen 

(%)

Carbon

Dioxide

(%)

TPH

(ppmv)

PT1 3.0 20.5 0.8 62

PT2 3.0 20.5 1.0 60

6.0 20.6 0.5 42

PT3 3.0 19.0 2.0 80

6.0 19.0 2.0 78

PT4 3.0 19.2 2.2 80

6.0 19.0 2.4 93

PT6 3.0 20.5 0.8 46

6.0 20.5 0.8 44

PT7 3.0 20.0 0.5 82

6.0 19.8 1.5 61

7.0 19.0 1.0 70

PT8 6.0 19.5 1.5 60

8.0 20.5 0.5 48

Table 1-1. Results From a Soil Gas Survey at AOC A, Keesler

AFB, Mississippi

Soil Gas

Survey Point Depth (ft)

Oxygen 

(%)

Carbon

Dioxide

(%) TPH (ppmv)

SGS-A 2.0 4.8 9.8 >100,000

4.0 0.3 12 >100,000

6.0 0.5 11 >100,000

SGS-B 2.0 1.5 12 >100,000

4.0 0.5 12 >100,000

6.0 0.9 12 >100,000

SGS-C 2.0 0.4 11 28,000

4.0 0.8 11 30,000

6.0 0.4 11 32,000

SGS-D 2.0 0.4 11 47,000

4.0 0.3 11 56,000

6.0 20.1 0.1 120

6.0 0.4 11 60,000

SOS = Soil gas survey.

8
Example 1-5. Soil Gas Survey at an Oil/Water Separator

Leak at Cape Canaveral AFS, Florida: This site consisted of an oil/water separator leak located near a

diesel transfer station at Cape Canaveral AFS, Florida.

Site soils consisted of sandy soil with shell fragments.

Ground water was approximately 6 ft (1.8 m) below the

surface.

A soil gas survey was conducted at eight locations. An

attempt was made to sample soil gas at two depths. Soil

gas results are presented in Table 1-4.

Low levels of TPH indicate that little diesel-contaminated soil remained at the site or it was highly weathered. Oxygen levels were significantly depleted near

PT2 and generally decreased with depth in points near

the oil/water separator. Carbon dioxide levels were elevated in areas with low oxygen, indicating that in situ

biodegradation was proceeding in the vicinity of the

oil/water separator. More oxygen-depleted soil might

exist in the capillary fringe, and engineered bioventing

could accelerate biodegradation, if this anaerobic zone

exists. The decision to biovent this site should be based

on other factors, such as the impact and potential risk

that soil contamination poses to ground water. One additional note: if the oil/water separator were connected

to a sanitary line, the biological oxygen demand might

be the result of leaking sewage. An analysis of soil gas

for benzene, toluene, ethylbenzene, and total xylenes

(BTEX) could help to determine if the oxygen demand

were fuel related.

1.3 Soil Characterization

Soil characterization is a crucial component of the site

characterization process. Of primary importance is determining the concentration and distribution of contaminants.

Because of large variations in the distribution of contaminants at a site, a relatively large number of soil samples

must be collected to adequately delineate the vertical and

lateral extent of contamination. Described in the following

sections are techniques for locating and drilling soil borings.4

 The soil analytical protocol is also discussed.

4 See Appendix B for recommended specifications and manufacturers

for the soil sampling equipment.

Table 1-4. Results From a Soil Gas Survey at an Oil/Water

Leak at Cape Canaveral AFS, Florida

Soil Gas

Survey

Point

Depth

(ft)

Oxygen

(%)

Carbon

Dioxide

(%)

TPH

(ppmv)

PT1 2.5 15.5 4.0 82

5.5 12.5 6.0 82

PT2 2.5 14.0 5.0 76

5.5 5.5 9.5 77

PT3 2.5 13.0 5.5 73

5.5 10.0 7.0 75

PT4 2.5 19.0 2.0 60

5.5 18.5 2.5 66

PT5 2.5 19.5 1.0 57

5.5 19.0 2.0 60

PT6 2.5 18.5 2.5 64

5.5 17.5 3.0 74

PT7 2.5 20.0 1.0 36

5.5 20.0 1.0 35

PT8 2.5 20.5 0.5 34

5.5 20.2 0.8 43

Table 1-3. Results from a Soil Gas Survey at the Aquasystem

Site, Westover AFB, Massachusetts

Soil Gas

Survey

Point

Depth

(ft)

Oxygen 

(%)

Carbon

Dioxide

(%)

TPH

(ppmv)

PT1 3.0 16 3.2 60

6.0 12.5 5 60

PT2 3.0 15.5 4.3 72

6.0 13 6 74

PT3 3.0 18 2.6 74

6.0 12 6.2 84

PT4 3.0 16 4 86

6.0 11.5 5 80

PT5 3.0 14.8 4 76

6.0 11 5.2 72

PT7 3.0 14 7 105 

6.0 8.5 8.5 69

PT8 3.0 12 5.5 75

6.0 11 6.5 76

PT9 3.0 11.5 6 90

6.0 11 6.2 78

PT11 3.0 16 3.5 84

6.0 15 4 94

PT12 3.0 18.5 2.5 80

6.0 15.5 4.2 91

9.0 15 4.8 90

12.0 13 5.6 92

PT16 6.0 17 2 94

7.5 13 3.5 80

PT17 6.0 11.8 6.5 92

9.0 11 6.5 96

9
1.3.1 Soil Borings

Soil borings should be located based on either the review of existing site data or the results of the soil gas

survey. Soil borings can serve two purposes: the collection of soil samples and the installation of vent wells and

monitoring points. Soil borings have the advantage of

allowing for collection of many soil samples from a single

location and allowing for subsequent installation of the

vent wells and monitoring points in the borings. Disadvantages include the generation of soil cuttings and the

fact that drilling may require subcontracting and a large

amount of time. Alternative methods, such as a GeoProbe system or cone penetrometer, may be used for

collection of soil samples and may be suitable for installing soil gas monitoring points.

The hollow-stem auger method is generally preferred for

drilling in unconsolidated soils; however, a solid-stem

auger also is acceptable in more cohesive soils. The

final diameter of the borehole depends on the diameter

selected for the vent wells but typically should be at least

two times greater than the vent well’s outside diameter.

All drilling and sample collection activities should be

observed and recorded on a geologic boring log (Figure

1-5) to record soil sample interval, sample recovery,

visual presence (or absence) of contamination, soil description, and lithology. Soil samples should be labeled

and properly stored immediately after collection. An example procedure for soil sample collection, labeling,

packing, and shipping is provided in Appendix C.

All boreholes should preferably be completed as vent

wells or monitoring points. If this is not possible, boreholes must be abandoned according to applicable state

or federal regulations. Typically, borehole abandonment

is accomplished by backfilling with bentonite or grout.

Figure 1-5. Sample soil boring log.

10
1.3.2 Soil Analyses

A summary of soil analyses is provided in Table 1-5.

Methods in this table are not the only methods available

but are those currently used by the Air Force currently

uses. Based on results from the Bioventing Initiative,

recommended parameters to be measured include the

aromatic hydrocarbons (BTEX), TPH, moisture content,

and particle size. Total Kjeldahl nitrogen (TKN) was

found to be a statistically significant factor in the statistical analyses of Bioventing Initiative data;5

 however, no

evidence exists to date that addition of nitrogen enhances site remediation. Therefore, an analysis for TKN

is only recommended if all other explanations for poor

bioventing performance have been exhausted (i.e., permeability, moisture content).

Measurements of BTEX and TPH are necessary for

delineation of the contaminant plume. In addition, BTEX

and TPH typically are of regulatory concern; therefore,

these concentrations must be established.

Moisture content has been found to limit biodegradation

in extreme environments. At a site in California, moisture

content averaged approximately 2 percent and irrigation

substantially improved biodegradation rates.6

TKN is a nutrient required for microbial growth and

respiration. Low TKN levels may affect microbial respiration; however, although a statistically significant relationship has been observed between TKN and oxygen

utilization rates, the relationship is weak and unlikely to

have practical significance.

Particle size distribution is an important indicator of

permeability. High clay content soils may be difficult to

biovent because of the inability to move air through the

soil, particularly when high moisture levels exist. In addition, clay particles can be sites of significant contaminant adsorption and as such can significantly affect

contaminant sorption and bioavailability.

1.4 In Situ Respiration Testing

The in situ respiration test was developed to provide

rapid field measurement of in situ biodegradation rates

to determine the potential applicability of bioventing at a

contaminated site and to provide information for a fullscale bioventing system design. This section describes

the test as developed by Hinchee and Ong (1992). This

respiration test has been used at numerous sites

throughout the United States, including all Bioventing

Initiative sites. The in situ respiration test described in

this document is essentially the same, with minor modifications.

1.4.1 In Situ Respiration Test Procedures

The in situ respiration test consists of placing narrowly

screened soil gas monitoring points into the unsaturated

zone of contaminated soils and venting these soils with

air containing an inert tracer gas (typically helium) for a

given period. The apparatus for the respiration test is

illustrated in Figure 1-6.7

 An example procedure for

conducting an in situ respiration test is provided in Appendix C.

As part of the Bioventing Initiative, respiration rates in

uncontaminated areas of similar geology to the contaminated test site were evaluated. These results showed

that measurement of background respiration rates was

not necessary because little significant respiration had

Table 1-5. Soil Analysesa Based on Bioventing Initiative Results

Analysis Method Comments

Sample Volume, Container,

Preservation

Field or Analytical

Laboratory

Aromatic

hydrocarbons (BTEX)

Purge and trap GC

method SW8020

Handbook method Collect 100 g of soil in a glass

container with Teflon-lined cap or

in brass sleevesb

; cool to 4°C

Analytical laboratory

TPH Modified GC method

SW8015

Handbook method;

reference is the California

LUFTc

 manual

Collect 100 g of soil in a glass

container with Teflon-lined cap or

in brass sleevesb

; cool to 4°C

Analytical laboratory

Moisture content ASTM D-2216 Handbook method Collect in a 4-oz glass container

with Teflon-lined cap

Analytical laboratory

TKNd EPA 351.4 Handbook method Collect in a 4-oz glass container

with Teflon-lined cap

Analytical laboratory

a Recommended soil analysis is based on experience and analyses of petroleum-contaminated sites. Additional data may be required at sites

contaminated with other compounds. b One sample in the brass sleeves provides sufficient volume for analyses of both aromatic hydrocarbons and TPH.

c

 LUFT = State of California Leaking Underground Fuel Tank Field Manual, 1988 edition. d Not recommended for an initial analysis but only if bioventing performance is poor and other factors such as permeability and moisture content

do not account for the poor performance.

5 See Chapter 5 of Volume I for a discussion of the statistical analyses

of Bioventing Initiative data.

6 See Section 3.2.2.2 of Volume I for a discussion of this site.

7 See Appendix B for recommended specifications and manufacturers

for the in situ respiration testing equipment.

11
occurred. Instead, oxygen and carbon dioxide should be

measured in an uncontaminated location of similar geology. Only if these measurements indicate significant

oxygen depletion should a background in situ respiration

test be conducted to determine whether significant

background respiration is occurring.

In a typical experiment, a cluster of three to four soil gas

probes are placed in the contaminated soil of the test

location. These soil gas probes must be located in the

center of contaminated areas where low soil gas oxygen

concentrations and high TPH concentrations have been

measured. If the monitoring points are not located in contaminated areas, the in situ respiration test will not produce

meaningful results. Additional detail on monitoring point

location and construction is provided in Section 2.6.

Measurements of carbon dioxide and oxygen concentrations in the soil gas are taken before air and inert gas

injection. A 1 percent to 3 percent concentration of inert

gas is added to the injection air, which is injected for

approximately 24 hours at flow rates ranging from 1.0

cfm to 1.7 cfm (28 L/min to 48 L/min). The air provides

oxygen to the soil, and the inert gas measurements

provide data on the diffusion of oxygen from the ground

surface and the surrounding soil and ensure that the soil

gas sampling system does not leak. The background

control location is placed in similar soils in an uncontaminated area to monitor natural background respiration

rates.

After air and inert gas injection are turned off, oxygen,

carbon dioxide, and inert gas concentrations are monitored over time. Before a reading is taken, the probe is

purged for a few minutes until the carbon dioxide and

oxygen readings are constant. Initial readings are taken

every 2 hours and then progressively over 4-hour to

8-hour intervals. If oxygen uptake is rapid, more frequent

monitoring may be required. If it is slow, less frequent

readings may be acceptable. The experiment usually is

terminated when the soil gas oxygen concentration is

approximately 5 percent.

As discussed in Section 1.2, shallow monitoring points

pose a risk of pulling in atmospheric air in the process

of purging and sampling. Excessive purging and sampling may result in erroneous readings. Oversampling

produces no benefits and, when sampling shallow

points, care must be taken to minimize the volume of air

extraction. In these cases, a low-flow extraction pump

of about 0.03 cfm to 0.07 cfm (0.85 L/min to 2.0 L/min)

should be used.

1.4.2 Interpretation of in Situ Respiration

Test Results

Oxygen utilization rates are determined from data obtained during the in situ respiration test. The rates are

calculated as the zero-order relationship between percentage of oxygen versus time. Typically, a rapid linear

decrease in oxygen occurs, followed by a lag period

once oxygen concentrations drop below approximately

5 percent. To calculate oxygen utilization rates, only the

first linear portion of the data is used because this

represents oxygen utilization when oxygen is not limiting, as is the case during active bioventing.

To estimate biodegradation rates of hydrocarbon from

the oxygen utilization rates, a stoichiometric relationship

for the oxidation of the contaminant is used. For hydrocarbons, hexane is used as the representative hydrocarbon. If a site is contaminated with compounds other then

petroleum hydrocarbons, a suitable compound should

be used to determine stoichiometry. The stoichiometric

relationship used to determine petroleum degradation

rates is:

C6H14 + 9.5O2 → 6CO2 + 7H2O (Eq. 1-1)

Based on the utilization rates (percentage of oxygen per

day), the biodegradation rate in terms of mg hexaneequivalent per kg of soil per day is estimated using

Equation 1-2:

−kB =

− ko

100 θa

1L

1,000 cm3 ρO2

 C

ρk







1 kg

1,000 g







=

−ko θa ρO2

 C (0.01)

ρk

(Eq. 1-2)

where:

kB = biodegradation rate (mg/kg-day)

ko = oxygen utilization rate (%/day)

θa = gas-filled pore space (volumetric content

at the vapor phase, m3

 gas/cm3 soil)

ρO2 = density of oxygen (mg/L)

C = mass ratio of hydrocarbons to oxygen

required for mineralization (1:3.5)

ρk = soil bulk density (g/cm3

)

Figure 1-6. In situ respiration test apparatus.

12
These terms may be derived through either direct measurement or estimation. The oxygen utilization rate, ko, is

directly measured in the in situ respiration test. The ratio

of hydrocarbons to oxygen required for mineralization,

C, can be calculated based upon stoichiometry (see

Equation 1-1 for hexane) but generally falls between

0.29 and 0.33. This neglects any conversion to biomass,

which probably is small and difficult, if not impossible, to

measure. The density of oxygen may be obtained from

a handbook for a given temperature and pressure, or

calculated from the ideal gas law. Table 1-6 provides

some useful oxygen density information. The bulk density of soil is difficult to measure accurately because of

the difficulty in collecting an undisturbed sample; however, it may be reasonably estimated from the literature.

Table 1-7 lists useful literature values for bulk density.

The gas-filled porosity, θa, is the single parameter in

Equation 1-2 with the most variability. Theoretically, it

can be related to the total porosity, soil bulk density, and

moisture content. A doubling of the air-filled porosity

results in a doubling of the estimated hydrocarbon

degradation rate. Gas-filled porosity may be as high as 0.5 to 0.6 in some very dry clays and is zero in saturated

soil. To collect soil gas samples, the gas-filled porosity

must be sufficient to allow gas flow. Therefore, an in situ

respiration test could be conducted at very low gas-filled

porosity. At most bioventing sites, θa ranges from 0.1 to

0.4. Soil in a core or split spoon sample will be compressed, thereby reducing θa. It can be estimated as

follows:

θa = θ − θW (Eq. 1-3)

where:

θ = total porosity (cm3

/cm3)

θW = water-filled porosity (cm3/cm3

)

The total void volume may be estimated as:

θ = 1 − ρk

ρT

(Eq. 1-4)

where:

ρk = soil bulk density (g dry soil/cm3) (from

Table 1-7)

ρT = soil mineral density (g/cm3

), estimated at

2.65

The water-filled void volume then can be calculated as:

θ = M ρk

ρT

(Eq. 1-5)

where:

M = soil moisture (g moisture/g soil)

Table 1-7. Bulk Density of Various Soilsa

Soil Description Porosity

Soil Bulk Density 

rk

(dry g/cm3

)

Uniform sand, loose 0.46 1.43

Uniform sand, dense 0.34 1.75

Mixed-grain sand, loose 0.40 1.59

Mixed-grain sand, dense 0.30 1.86

Windblown silt (loess) 0.50 1.36

Glacial till, very mixed-grained 0.20 2.12

Soft glacial clay 0.55 1.22

Stiff glacial clay 0.37 1.70

Soft slightly organic clay 0.66 0.93

Soft very organic clay 0.75 0.68

Soft montmorillonitic clay

(calcium bentonite)

0.84 0.43

a From Peck et al. (1962).

Table 1-6. Oxygen Density Versus Temperature

Temperature

(°C)

Temperature

(°F)

Density

(mg/L)a Density 

(lb/ft3

)

a

-33 -27.4 1,627b 0.10b 

 -3 26.6 1,446c 0.090c

 0 32 1,429c 0.089c

 5 41 1,403c 0.088c

10 50 1,378c 0.086c

15 59 1,354c 0.084c

20 68 1,331c 0.083c

27 80.6 1,301b 0.082b

30 86 1,287c 0.080c

35 95 1,266c 0.079c

40 104 1,246c 0.078c

57 134.6 1,182b 0.074b

87 188.6 1,083b 0.067b

127 260.0 975b 0.061b

a Oxygen density at standard pressure.

b Density values from Braker and Mossmon (1980).

c

 Density calculated using the second viral coefficient to the equation

of state for oxygen gas:

 P = RT

V







1 +

B(T)

V







where P = pressure (atm), R = gas constant, V = molar volume,

and B = second viral coefficient. The temperature dependence of

B was calculated from:

 B(T) = ∑

i = 1

n

Ai







T0

T − 1





i −1

 The constants Ai were obtained from Lide and Kehianian (1994).

13
Because the water-filled porosity (θW) is a difficult parameter to estimate accurately, an assumption is frequently made of 0.2 or 0.3.

Using several assumptions, values for θa, ρO2

, C, and

ρk can be calculated and substituted into Equation 1-2.

Assumptions used for these calculations are:

• Gas-filled porosity (θa) of 0.25.

• Soil bulk density (ρk) of 1.4 g/cm.

• Oxygen density (ρO2) of 1,330 mg/L.

• C, hydrocarbon-to-oxygen ratio of 0.29 from Equation

1-1 for hexane.

The resulting equation is:

kB = − (ko) (0.25) (1,330) (0.29) (0.01)

1.4 = −0.68 ko

(Eq. 1-6)

The biodegradation rates measured by the in situ respiration test appear to be representative of those for a

full-scale bioventing system. Miller (1990) conducted a

9-month bioventing pilot project at Tyndall AFB at the

same time Hinchee et al. (1991a) conducted an in situ

respiration test. The oxygen utilization rates (Miller,

1990) measured from nearby active treatment areas

were virtually identical to those measured in the in situ

respiration test. Oxygen utilization rates greater than 1.0

percent/day are a good indicator that bioventing may be

feasible at the site and proceeding to soil gas permeability testing is appropriate. If oxygen utilization rates

are less than 1.0 percent/day, yet significant contamination is present, other factors may be involved in limiting

biodegradation. In this case, other process variables, as

discussed in Section 3.3, should be considered as limiting biodegradation. Identifying these other process

variables may require additional soil sampling and

analysis. If none of these other process variables can

be identified as potentially limiting microbial degradation, alternative technologies may have to be employed

for site remediation.

Example 1-6. Results From an in Situ Respiration Test

Conducted at Keesler AFB: At the site described in

Example 1-1, an in situ respiration test was conducted.

After the soil gas survey, three-level monitoring points

were installed at each soil gas survey point location

because these areas were highly contaminated and

were oxygen-limited. Initial soil gas readings were taken

at each monitoring point and are shown in Table 1-8.

Because all locations were oxygen-limited, a decision

was made to inject air at the deepest level of each

monitoring point (MP) (K1-MPA-7.08, K1-MPB-7.08, K1-

MPC-7.08, and K1-MPD-7819).

Table 1-9 contains data collected at each monitoring

point during the in situ respiration test. The oxygen

utilization rate is determined as the slope of the percent

Table 1-8. Initial Soil Gas Readings at Monitoring Points at

AOC A, Keesler AFB, Mississippi

Monitoring

Point

Depth 

(ft)

Oxygen

(%)

Carbon

Dioxide

(%)

TPH

(ppmv)

K1-MPA 3.0 0.1 16 >100,000

5.0 0.4 15 >100,000

7.0 0.6 15 >100,000

K1-MPB 2.5 0.5 15 >100,000

4.0 0.5 15 >100,000

7.0 0.8 15 >100,000

K1-MPC 3.0 0.4 14 28,000

5.0 0.1 15 30,000

7.0 0.5 15 29,000

K1-MPD 3.0 0.6 14 45,000

5.0 0.5 15 54,000

7819 0.5 15 58,000

Background 16.8 4.6 140

Table 1-9. Raw Data From an in Situ Respiration Test at 

AOC A, Keesler AFB, Mississippi

K1-MPA-5.0′ K1-MPA-7.0′

Time

(hr)

O2

(%)

CO2

(%) 

He

(%)

O2

(%)

CO2

(%)

He

(%)

 0 20.7 0 1.4 20.5 0 1.4

 5 20.6 0 1.6 20.6 0 1.4

10 20.1 0.1 1.4 20.3 0.1 1.4

25 19.0 0 1.75 20.1 0 1.6

37 17.8 0 1.4 19.5 0 1.4

50 16.9 0.6 1.4 18.7 0.2 1.25

75 15.2 1.2 1.6 17.3 1.2 1.6

99 14.0 2.0 1.4 16.3 1.2 1.4

Time

(hr)

K1-MPB-5.0′ K1-MPC-7.0′

 0 20.6 0 1.6 20.8 0 1.3

 5 20.2 0 1.8 20.5 0.2 1.5

10 19.4 0 14 20.2 0.2 1.4

25 16.9 0 1.6 19.5 0 1.3

37 14.8 0 1.4 18.1 0.6 1.2

50 12.9 1.0 1.4 16.9 1.5 1.2

75 9.9 2.6 1.2 13.9 3.0 1.0

99 8.0 3.0 1.2 11.0 4.0 1.0

O2 = oxygen.

CO2 = carbon dioxide.

He = helium.

14
oxygen versus time curve. Only data beginning with that

taken at t = 0 that appear linear with time were used to

calculated the slope. A zero-order respiration rate as

seen in these data is typical of most sites (Figure 1-7).

Calculated oxygen utilization rates and corresponding

biodegradation rates for these data are shown in Table

1-10.

Results of this test indicate that this site is an excellent

candidate for bioventing.

Example 1-6 illustrates calculation of oxygen utilization

data that are linear with time. In some instances, however, this relationship is not linear, and only selected

data should be used to calculate the oxygen utilization

rate. Example 1-7 illustrates calculation of the oxygen

utilization rate from nonlinear data.

Example 1-7. Calculation of Oxygen Utilization Rates

From Nonlinear Data: Table 1-11 contains sample data

from Solid Waste Management Unit (SWMU) 66,

Keesler AFB. The oxygen utilization rate is determined

as the slope of the percentage of oxygen versus time

curve. Only data beginning with that taken at t = 0 that

appear linear with time should be used to calculate the

slope. A fairly rapid change in oxygen levels was observed at Keesler AFB (Figure 1-8). In this case, the

oxygen utilization rate was obtained from the initial linear portion of the respiration curve, which included data

from t = 0 to t = 30.5 hours. As shown, after this point,

oxygen concentrations dropped below 5 percent and

were limiting. The calculated oxygen utilization rate was

11 percent/day.

The helium data collected at a site provide insight into

whether observed oxygen utilization rates are caused by

microbial utilization or by other effects such as leakage

or diffusion. As a rough estimate, diffusion of gas molecules is inversely proportional to the square root of the

molecular weight of the gas. Based on the molecular

weights of 4 g/mole and 32 g/mole for helium and oxygen, respectively, helium diffuses about 2.8 times faster

than oxygen. Thus, although helium is a conservative

tracer, its concentration should decrease with time. As a

general rule of thumb, any in situ respiration test in

Figure 1-7. In situ respiration test results with linear oxygen

concentration versus time at AOC A, Keesler AFB,

Mississippi.

Table 1-10. Oxygen Utilization and Carbon Dioxide

Production Rates During the in Situ Respiration

Test at AOC A, Keesler AFB, Mississippi

Sample Name

Oxygen

Utilization Rate

(%/hour)

Estimated

Biodegradation

Rate (mg/kg-day)

K1-MPA-5.0′ 0.071 1.16

K1-MPA-7.0′ 0.045 0.73

K1-MPB-5.0′ 0.13 2.12

K1-MPC-7.0′ 0.099 1.62

Background 0.012 0.20

Figure 1-8. In situ respiration test results with nonlinear oxygen concentration versus time at SWMU 66, Keesler

AFB, Mississippi.

Table 1-11. Raw Data From an in Situ Respiration Test at

SWMU 66, Keesler AFB, Mississippi

Time

(Hours)

Oxygen

(%)

Carbon

Dioxide (%)

Helium

(%)

0 20.5 0 1.6

6.3 18.1 .05 1.6

9.3 16.5 1.0 1.6

15 14 2.2 1.8

22 11 3.2 1.5

31 6.8 5.0 1.5

48 3.7 5.1 1.5

57 2.9 5.1 1.5

15
which the rate of helium loss is less than the oxygen loss

rate should be considered an acceptable test. If the

helium loss rate is greater than the oxygen loss rate,

disregard the test from that monitoring point. The helium

loss rate is not used to correct the oxygen utilization rate.

Example 1-8. Evaluation of Helium Loss During an in

Situ Respiration Test: Figures 1-9 and 1-10 show helium

data for two test wells. The helium concentration at

monitoring point S1 at Tinker AFB (Figure 1-9), initially

at 1.5 percent, dropped to 1.1 percent after 108 hours

(a fractional loss of approximately 0.25); this represented an acceptable concentration drop. In contrast,

for Kenai K3 (Figure 1-10), the change in helium was

rapid (a fractional drop of about 0.8 in 7 hours), indicating possible short circuiting at this monitoring point. This

suggested that the data from this monitoring point were

unreliable, so these data were not used in calculating

degradation rates.

1.4.3 Factors Affecting Observed in Situ

Biodegradation Rates

Because in situ biodegradation rates are measured indirectly through measurements of soil gas oxygen and

carbon dioxide concentrations, abiotic processes that

affect oxygen and carbon dioxide concentration also

affect measured biodegradation rates. The factors that

may most influence soil gas oxygen and carbon dioxide

concentrations are soil pH, soil alkalinity, and iron content. In addition, any environmental parameter that may

affect microbial activity also may affect observed oxygen

utilization rates. Soil temperature often is a significant

factor at bioventing sites. 

At several sites, oxygen utilization has proven to be a

more useful measure of biodegradation rates than carbon dioxide production. The biodegradation rate in mg of

hexane-equivalent/kg of soil per day based on carbon

dioxide production usually is less than can be accounted

for by the oxygen disappearance. At virtually all Bioventing Initiative sites, oxygen utilization rates have been

higher than carbon dioxide production rates. A study

conducted at Tyndall AFB, however, was an exception.

That site had low-alkalinity soils and low-pH quartz sands,

and carbon dioxide production actually resulted in a slightly

higher estimate of biodegradation (Miller, 1990).

In the case of the higher pH and higher alkalinity soils

at Fallon NAS and Eielson AFB, little or no gaseous

carbon dioxide production was measured (Hinchee et

al., 1991b; Leeson et al., 1995). This may be the result

of the formation of carbonates from the gaseous evolution of carbon dioxide produced by biodegradation at

these sites. Van Eyk and Vreeken (1988) encountered

a similar phenomenon in their attempt to use carbon

dioxide evolution to quantify biodegradation associated

with soil venting.

Iron is a nutrient required for microbial growth, but the

iron also may react with oxygen to form iron oxides.

Theoretically, if a significant amount of iron oxidation

were to occur, the observed oxygen utilization rate

would reflect both iron oxidation and microbial activity.

Therefore, calculated biodegradation rates would be an

overestimate of actual biodegradation rates. In data collected from the Bioventing Initiative study, however, iron

concentrations have varied greatly, with concentrations

from less than 100 mg/kg to greater than 100,000

mg/kg, with no apparent impact on oxygen utilization

rates. Iron impact on oxygen utilization rates has been

observed at only one site with very high iron concentrations—on the Marine Base at Kaneohe, Hawaii, where

soil iron concentrations are in the 100,000 mg/kg range.

An important consideration is whether the respiration rate

was measured at the time of year when microbial rates

were at their maximum (summer) or if it was measured

when activity was low (winter). Investigations at many sites

Figure 1-9. In situ respiration test results with acceptable data

based on the helium concentration for monitoring

point S1, Tinker AFB, Oklahoma.

Figure 1-10. In situ respiration test results with unacceptable

data based on the helium concentration for monitoring point K3, Kenai, Alaska.

16
have shown that rates can vary by as much as an order

of magnitude between peak periods. For design of oxygen delivery systems, respiration rates should be measure during the peak season, typically during late

summer.

If oxygen utilization rates were determined during periods of low activity, it is necessary to adjust the rates to

the maximum level before making size calculations. The

van’t Hoff-Arrhenius equation can be used to predict

oxygen utilization rates given an initial rate and temperature.8

 The activation energy, Ea, must be known for the

site. Alternatively, Ea found from another site can be

used, recognizing the temperature-adjusted rate is only

a rough estimate. The following example illustrates a

typical adjustment.

Example 1-9. Temperature Adjustment of Oxygen Utilization Rate: The oxygen utilization rate was measured

in January at a site in Cheyenne, Wyoming. The rate

was determined to be 0.75 percent/day (0.031 percent/hour). The temperature in the soil was measured at

4°C. Previous temperature measurements at the site

have indicated that soil temperatures in August average

approximately 24°C (i.e., 20°C higher than the temperature measured during January). The temperature adjustment to the rate for sizing calculations is as follows:

Using the van’t Hoff-Arrhenius equation (Metcalf & Eddy,

1979):

dk

dT = Ea

RT2

Integration of this equation between the limits T1 (277°K)

and T2 (297°K) gives:

ln

kT

ko

= Ea (T2 − T1)

RT1T2

where:

kT = temperature-corrected oxygen utilization

rate (% O2/day)

ko = baseline reaction rate = 0.75%/day

Ea = activation energy9

 = 13.4 kcal/mole

R = gas constant = 1.987 cal/°K-mole

T1 = absolute temperature for ko = 277°K

T2 = absolute temperature for kT = 297°K

kT = 





0.75 %

day







 e











(13,400 cal/mole) (2977K − 2777K)

(1.987 cal

7K−mole) (2977K)(2777K)











kT = 3.9 %

day

As seen in this calculation, the site would require approximately five times greater oxygen delivery rate in the

summer.

1.5 Soil Gas Permeability and Radius of

Influence

In situ respiration rates may be used to calculate the

required air flow rate to satisfy oxygen demand at a

given site;10 however, determining the distance air can

physically be moved also is necessary. An estimate of

the soil’s permeability to fluid flow (k) and the radius of

influence (RI

) of venting wells are both important elements of a full-scale bioventing design. Onsite testing

provides the most accurate estimate of soil gas permeability. Onsite testing also can be used to determine the

radius of influence that can be achieved for a given well

configuration and flow rate. These data are used to

design full-scale systems, specifically to space venting

wells, to size blower equipment, and to ensure that the

entire site receives a supply of oxygen-rich air to sustain

in situ biodegradation.

Soil gas permeability, or intrinsic permeability, can be

defined as a soil’s capacity for fluid flow and varies

according to grain size, soil uniformity, porosity, and

moisture content. The value of k is a physical property

of the soil; k does not change with different extraction/injection rates or different pressure levels.

Soil gas permeability is generally expressed in the units

cm2

 or darcy (1 darcy = 1 x 10-8 cm2). Like hydraulic

conductivity, soil gas permeability may vary by more

than an order of magnitude on the same site because

of soil variability. Table 1-12 illustrates the range of

typical k values to be expected with different uniform soil

types. Actual soils contain a mixture of grain sizes, which

generally increases the observed darcy values based on

pilot testing.

Table 1-12. Soil Gas Permeability Values (Johnson et al., 1990)

Soil Type k in Darcy

Coarse sand 100 to 1,000

Medium sand 1 to 100

Fine sand 0.1 to 1.0

Silts/clay <0.1

10 See Section 2.2 for a presentation of the calculation of required air

 flow rates.

8 See Volume I for a discussion of the effect of temperature on microbial activity.

9 Calculated from a different field site. See Example 3-2 in Volume I

for a description of the calculation of the activation energy.

17
Several field methods have been developed for determining soil gas permeability (EPA, 1991b). The most

favored field test method probably is the modified field

drawdown method developed by Paul Johnson at Arizona State University and former associates at the Shell

Development Company. This method involves the injection or extraction of air at a constant rate from a single

venting well while measuring the pressure/vacuum

changes over time at several monitoring points in the

soil away from the venting well.11

The field drawdown method is based on Darcy’s law and

equations for steady-state radial flow to or from a vent

well. A full mathematical development of this method

and supporting calculations are provided by Johnson et

al. (1990). Johnson developed the HyperVentilate computer program to store field data and to compute soil gas

permeability. This or other commercially available programs can be used to speed the calculation and data

presentation process.

Two solution methods may be used for soil gas permeability as described in Johnson et al. (1990). The first

solution is based on carefully measuring the dynamic

response of the soil to a constant injection or extraction

rate. The second solution for soil gas permeability is based

on steady-state conditions and the measurement or estimation of the radius of influence at steady state. Whenever

possible, field data should be collected to support both

solution methods because one or both of the solution

methods may be appropriate, depending on site-specific

conditions. An example procedure for conducting a soil

gas permeability test is provided in Appendix C.

1.5.1 Radius of Influence Determination

Based on Pressure Measurements

At a bioventing site, the radius of influence is defined in

two ways, as the oxygen radius of influence or the

pressure radius of influence. The oxygen radius of influence is defined as the maximum distance from the air

extraction or injection well where a sufficient supply of

oxygen for microbial respiration can be delivered. The

pressure radius of influence is the maximum distance

from the air extraction or injection well where vacuum or

pressure (soil gas movement) occurs. Under heterogeneous conditions, the pressure radius of influence is

theoretically infinite; for practical purposes, however, it

usually is considered to be the maximum extent to which

pressure changes can be measured.

The oxygen and pressure radius of influence is a function of soil properties but also is dependent on the

configuration of the venting well and extraction or injection flow rates and is altered by soil stratification. The

oxygen radius of influence also is dependent on microbial oxygen utilization rates. On sites with shallow contamination, the oxygen and pressure radius of influence

also may be increased by impermeable surface barriers

such as asphalt or concrete. These paved surfaces may

or may not act as vapor barriers. Without a tight seal to

the native soil surface,12 the pavement will not significantly affect soil gas flow.

At a bioventing site, the oxygen radius of influence is the

true radius of influence for system design. A connection

exists between the pressure radius of influence and the

oxygen radius of influence; however, many variables

exist that are not fully understood. Empirically, during a

soil gas permeability test, an increase in oxygen concentration has been found at contaminated sites wherever pressure changes are measured. Also, the

pressure radius of influence has been found to be a

conservative measure of the oxygen radius of influence.

The oxygen radius of influence may be directly determined by measuring the distance from the vent well at

which a change in oxygen concentration can be detected. Several days or weeks may pass, however, before equilibrium is reached and an accurate oxygen

radius of influence is measured.

In addition, if microbial acclimation occurs, microbial

activity may increase, effectively reducing the oxygen

radius of influence because of increased oxygen consumption. Therefore, the best approach is to measure

the oxygen radius of influence at times of peak microbial

activity. Alternatively, the pressure radius of influence

may be determined very quickly, generally within 2 hours

to 4 hours. Therefore, the pressure radius of influence

typically is used to design bioventing systems.

The pressure radius of influence should be determined

at three different flow rates, with a 1-hour to 2-hour test

per flow rate during the permeability test. Determining

the radius of influence at different flow rates allows for

more accurate blower sizing.13 Recommended flow

rates for the permeability test are 0.5 cfm, 1.5 cfm, and

3 cfm (14 L/min, 42 L/min, and 85 L/min) per ft (0.3 m)

of well screen.

The pressure radius of influence may be estimated by

determining pressure change versus distance from the

vent well. The log of the pressure is plotted versus the

distance from the vent well. The radius of influence is

that distance at which the curve intersects a pressure of

0.19H2O (25 Pa). This value was determined empirically

from Bioventing Initiative sites. Example 1-10 illustrates

calculating the radius of influence in this manner.

12 In the authors’ experience, this seal does not occur at most sites.

13 See Section 2.4 for a discussion of blower sizing.

11 See Appendix B for recommended specifications and manufacturers

 for the soil gas permeability testing equipment.

18
Example 1-10. Calculation of the Radius of Influence

Based on Pressure Measurements: Soil gas permeability results from the Saddle Tank Farm Site at Galena

AFS, Alaska, are shown in Figure 1-11 with the log of

the steady-state pressure response at each monitoring

point plotted versus the distance from the vent well. The

radius of influence is taken to be the intersection of the

resulting slope of the curve at a pressure of 0.1"H2O (25

Pa). Therefore, in this instance, the pressure radius of

influence would be estimated at 92 ft (28 m).

The estimated radius of influence actually is an estimate

of the radius in which measurable soil gas pressures are

affected and does not always equate to gas flow. In

highly permeable gravel, for example, significant gas flow

can occur well beyond the measurable radius of influence.

On the other hand, in a low-permeability clay, a small

pressure gradient may not result in significant gas flow.

1.5.2 Interpretation of Soil Gas Permeability

Testing Results

The technology of bioventing has not advanced far

enough to provide firm quantitative criteria for determining the applicability of bioventing based solely on values

of soil permeability or the radius of influence. In general,

the soil permeability must be sufficiently high to allow

movement of oxygen in a reasonable timeframe (1 to 10

days) from either the vent well, in the case of injection,

or the atmosphere or uncontaminated soils, in the case

of extraction. If such a flow rate cannot be achieved,

oxygen cannot be supplied at a rate to match its demand. Closer vent well spacing or high injection/extraction rates may be required. 

If either the soil gas permeability or the radius of influence is high (greater than 0.01 darcy or a RI greater than

the screened interval of the vent well), this is a good

indicator that bioventing may be feasible at the site and

proceeding to soil sampling and full-scale design is

appropriate. If either the soil gas permeability or the

radius of influence is low (less than 0.01 darcy or a RI

less than the screened interval of the vent well), this may

indicate that bioventing is not feasible. This situation

necessitates an evaluation of the cost-effectiveness of

bioventing over other alternative technologies for site

remediation. The cost involved in installing a bioventing

system at a low-permeability site is driven primarily by

the necessity of installing more vent wells, using a

blower with a higher delivery pressure, or installing horizontal wells.

Figure 1-11. Determination of radius of influence at the Saddle

Tank Farm, Galena AFS, Alaska.

19
Chapter 2

System Design

The design of a bioventing system is based upon the

results of site characterization and pilot testing efforts

described in Chapter 1. The objective is to design a

system that results in aeration of the contaminated soils

with little or no volatilization. Aeration may be accomplished through air injection, gas extraction, or a combination of the two. Soil vacuum extraction (SVE) (also

known as soil venting, soil gas extraction, or vacuum

vapor extraction) is a related technology in which soil

gas is extracted to remove contaminants by volatilization. In contrast, bioventing is designed to minimize

volatilization and optimize biodegradation. As a result,

bioventing typically uses much lower air flow rates and

often does not involve air extraction.

The basic steps involved in designing a bioventing system are as follows:

• Determine required air flow system (injection, extraction, or both [Section 2.1]).

• Determine required air flow rates (Section 2.2).

• Determine the working radius of influence.

• Determine well spacing (Section 2.3).

• Provide detailed design of blower, vent wells, and

piping (Section 2.4).

• Determine vent well requirements (Section 2.5).

• Determine monitoring point requirements (Section 2.6).

2.1 Determination of Air Flow System

In general, if safe and feasible, air injection is the preferred configuration for full-scale bioventing systems. If

properly designed, air injection results in minimal discharge of volatile organics to the atmosphere and is less

expensive to operate and maintain than air extraction

systems.

Under some circumstances, the use of soil gas extraction systems may need to be incorporated into an air

injection system design. For example, whenever the

radius of influence of a vent well reaches basements,

utility corridors, or occupied surface structures, an air

extraction system may be used to reduce the risk of

moving gases into these areas. This precaution prevents the accumulation of explosive or toxic vapors in

these structures.

2.1.1 Air Injection

Air injection involves the introduction of air under pressure into the contaminated zone. If the contaminants are

volatile, some will migrate in the gas phase into surrounding soil, where they can biodegrade. This has the

advantage of creating an expanded in situ bioreactor as

illustrated in Figure 2-1. Given adequate oxygen, the

volatilized hydrocarbons will biodegrade in these surrounding uncontaminated soils, increasing the fraction

of contaminants biodegraded compared with an air extraction configuration. This concept is illustrated in Example 2-1.

Example 2-1. Biodegradation of Petroleum Hydrocarbons in the Uncontaminated and Contaminated Regions

at Site 280, Hill AFB: At this site, high vapor-phase TPH

concentrations were detected within a radius of approximately 50 ft (15 m) from the injection well. TPH concentrations decreased with increasing distance from the

well. Likewise, in situ respiration rates were observed to

decrease with increasing distance from the injection well

(Figure 2-2). Calculations were made to compare total

TPH mass degraded in each region based on these in

situ respiration rates. These results, shown in Figure

2-3, illustrate that even though relatively low in situ

respiration rates were measured at monitoring points

located far from the injection well (220 ft [67 m]), in fact,

the majority of the contaminant degradation was occurring in this area. These results illustrate the availability

of vapor-phase hydrocarbons for biodegradation and

the significant contribution an expanded bioreactor can

have on contaminant removal.

Miller (1990) found at the Tyndall AFB site that hydrocarbon vapors biodegrade at a rate approximately equal

to one-third the rate observed in contaminated soils.

Kampbell (1993) found that the vapor-phase biodegradation in an air injection system was greatest in shallow

root zone soils. The concept is analogous to an in situ

biofilter. In general, air can be injected at flow rates low

21
Figure 2-1. Expanded bioreactor created during air injection.

Figure 2-2. Oxygen utilization rates, averaged over depth, versus distance from the injection well at Site 280, Hill AFB, Utah.

Figure 2-3. Mass of TPH degraded versus distance from the injection well at Site 280, Hill AFB, Utah.

22
enough to avoid surface emissions. As the air injection

rate increases, hydrocarbon volatilization increases

(Figure 2-4). Therefore, the objective is to inject sufficient air to meet oxygen demand for biodegradation but

not to cause emissions to the atmosphere. This is generally possible at sites contaminated with JP-4 or JP-5

jet fuel, diesel, and other contaminants of similar or

lesser volatility. It is more difficult with gasoline, although

successful systems using only air injection have been reported at gasoline-contaminated sites (Kampbell, 1993).1

In addition to creating an expanded bioreactor, air injection could potentially expose a significant portion of

capillary fringe contaminated soil to treatment via water

table depression. As air is injected into the vadose zone,

a positive pressure is created, resulting in depression of

the water table. Figure 2-5 illustrates the water table

depression observed at Site 20, Eielson AFB, Alaska.

This water table depression has important implications.

At many sites, the capillary fringe is highly contaminated, and lowering the water table allows for more

effective treatment of the capillary fringe. In addition, this

dewatering effect frequently results in an increased radius of influence and greater soil gas permeability.

A schematic diagram of a basic air injection system is

illustrated in Figure 2-6. The system is relatively simple,

involving a blower or compressor and a distribution

system. Explosion-proof blowers are recommended for

safety. Properly designed and operated injection systems do not produce significant air emissions or require

aboveground vapor phase treatment.

2.1.2 Air Extraction

Air injection is the preferred bioventing configuration;

however, air extraction may be necessary at sites where

movement of vapors into subsurface structures or air

emissions is difficult to control. If a building or other

structure is located within the radius of influence of a

site, or if the site is near a property boundary beyond

which hydrocarbon vapors cannot be pushed, air extraction may be considered. A significant disadvantage of

the air extraction configuration is that it limits biodegradation to the contaminated soil volume because vapors

do not move outward, creating an expanded bioreactor.

The result is less biodegradation and more volatilization.

In general, increasing extraction rates increase volatilization and biodegradation rates until the site becomes

aerated, above which the rate of biodegradation no

Figure 2-4. Hydrocarbon volatilization and biodegradation

rates as a function of air flow rate.

1 Reisinger, J. 1994. Personal communication between J. Reisinger, IST,

Inc., Atlanta, Georgia, and Battelle Memorial Institute, Columbus, Ohio. Figure 2-5. Water table depression during air injection and air

extraction.

23
longer increases. Volatilization generally continues to

increase with increasing extraction rates until the contaminated soil system becomes diffusion limited. The

optimal air flow rate for injection and extraction is the

minimum required to satisfy oxygen demand. Extraction

systems result in some volatilization regardless of the

extraction rate. Figure 2-4 illustrates this concept. The

relative removal attributed to biodegradation and volatilization is quite variable and site dependent. At a JP-4

jet fuel contaminated site at Tyndall AFB, Miller et al.

(1991) found that at the optimal air injection level it was

possible to achieve approximately 85 percent of removal

due to biodegradation at the optimal flow rate.

Air extraction creates a partial vacuum in the soil, resulting in a water table and capillary fringe rise or upwelling.

The soil venting literature has illustrated this phenomenon (Johnson et al., 1990). Because the bulk of contamination is often several inches or feet above or below the

water table (smear zone), this upconing can saturate

much of the contaminated soil and reduce treatment

efficiency. The upconing also increases soil moisture in

the capillary fringe and thus reduces soil gas permeability and radius of influence.

An example of this phenomenon was observed at Eielson AFB. An extraction air permeability test was conducted at Eielson AFB to observe the effect of the

bioventing configuration on the site air permeability and

well radius of influence. Table 2-1 compares the results

of extraction and injection tests at Site 20, Eielson AFB.

The permeability (k) calculated for the extraction test

was 0.27 darcy, approximately one-half the result for the

air injection test. The radius of influence observed at the

6-ft monitoring depth also was reduced approximately

one-third to 42 ft (13 m) (Figure 2-7). This reduction in

permeability and radius of influence was a result of the

water table rising illustrated in Figure 2-5.

Figure 2-8 is a schematic of a basic air extraction system. In contrast to an injection system, an extraction

system usually requires an explosion-proof blower with

explosion-proof wiring. Extracted soil gas typically contains moisture at or near saturation, and a knockout

(air/water separator) usually is required to collect condensate, which must be treated or disposed of. Also,

during winter months in regions with sustained temperatures below freezing, insulation and/or heat tape may be

required to maintain piping at temperatures above freezing to avoid clogged pipes.

Air extraction systems usually result in point source emissions that may require permitting and treatment. Air treatment affects remediation costs significantly. Appendix D

contains information on options for off-gas treatment.

Currently, only six sites out of 125 Bioventing Initiative

sites use air extraction as a method for oxygenation.

Two of the sites (Capehart Service Station, McClellan

AFB, and BX Service Station, Patrick AFB) operated in

Figure 2-6. Air injection configuration for a bioventing system.

Table 2-1. Permeability and Radius of Influence Values at

Eielson AFB, Alaska: Injection and Extraction Mode

Permeability (darcy)

Air Radius of

Influence (ft)

Depth (ft) Injection Extraction Injection Extraction

2 NR NR <7.0 <6.0

4 0.53 0.27 45 34

6 0.56 0.27 68 42

NR = No response.

24
extraction mode for 60 to 120 days, at which time the

system was reconfigured for air injection because vapor

concentrations had significantly decreased. At Patrick

AFB, initial vapor concentrations of TPH were as high

as 27,000 ppmv (Figure 2-9). After approximately 75

days of operation, concentrations decreased to 1,600

ppmv and the bioventing system was reconfigured for

injection (Downey, 1994). The Base Service Station at

Vandenberg AFB contained high concentrations of more

volatile components of gasoline and is an active service

station. As such, the possibility of vapor migration into

the service station was possible. This bioventing system

was operated in an extraction configuration in two

phases (Downey et al., 1994a). During Phase I, extracted soil gas was passed through a PADRE vapor

treatment system, where high concentrations of volatiles

were adsorbed and condensed to liquid fuel. The treated

soil gas was then recirculated through the soil using air

injection, biofilter trenches located along the perimeter

of the site. Phase II was initiated when TVH concentrations decreased to less than 1,000 ppmv. At this time,

the PADRE system was taken off line, and the extracted

soil gas was reinjected directly into the biofilter trenches.

2.1.3 Determining Use of Injection Versus

Extraction

Safety considerations usually drive the selection of injection versus extraction systems. Air injection should

not be used unless a system can be designed that does

Figure 2-7. Radius of influence during air injection and extraction in the control test plot at a depth of 6 ft at Site 20, Eielson AFB,

Alaska.

Figure 2-8. Schematic of a basic air extraction system.

25
not push hazardous vapors into structures. Table 2-2

summarizes some of the considerations that affect the

decision.

Numerous options are available that may allow air injection at sites with structures at risk or with property

boundaries nearby (Phelps, 1995). These options include monitoring the atmosphere in the structure to

verify that no contaminants enter using air extraction

coupled with reinjection to protect the building (Figure

2-10), or using subslab depressurization.

2.1.4 Design of Air Flow To Protect

Structures

Subslab depressurization can be used to protect structures while still allowing for air injection to provide optimal oxygenation. Subslab depressurization involves

extracting air within or around the perimeter of a building

during simultaneous air injection. Vapors extracted from

beneath the building may be released to the atmosphere, treated then released, or reinjected into the subsurface for further biotreatment. A schematic of such a

system is shown in Figure 2-11.

At AOC A, Keesler AFB, Mississippi, a subslab depressurization system is currently in operation as part of the

Bioventing Initiative. A schematic of the site is shown in

Figure 2-12. Soil vapor is continually withdrawn from air

extraction wells located around the perimeter of the

building and reinjected into the vent wells. Makeup air

is added to the injection gas to provide sufficient oxygen

to aerate the site. No vapor migration into the building

has been detected at this site, and the site soils are well

oxygenated.

At Site 48, Eielson AFB, Alaska, an actively used utilidor

runs through the site. The potential for migration of

vapors into the utilidor was high. To eliminate the migration of vapors into this structure, a horizontal perforated

pipe was installed next to the utilidor. A vertical extraction well was connected to the horizontal pipe to extract

gas from along the utilidor for vapor control. The extracted soil gas was then reinjected into a contaminated

area at the site (Figure 2-13).

2.2 Determining Required Air Flow Rates

The flow rate required to operate the bioventing system

is dependent on the oxygen demand of the indigenous

microorganisms. This is best determined from maximum

oxygen utilization rates measured during an in situ respiration test. Equation 2-1 is used to estimate the required air flow rate:

Q = ko V θa

(20.9% − 5%) × 60 min

hr

(Eq. 2-1)

Figure 2-9. Extracted BTEX and TPH soil gas concentrations at Patrick AFB, Florida.

Table 2-2. Air Injection Versus Extraction Considerations

Favor Injection Favor Extraction

Low vapor pressure contaminants High vapor pressure

contaminants

Deep contamination Surface emissions

Low permeability soils Structures/property boundaries

within the radius of influence

Significant distance from

structures/property boundaries

26
where:

Q = flow rate (ft3

/min)

ko = oxygen utilization rate (%/hr)

V = volume of contaminated soil (ft3

)

θa = gas-filled porosity (fraction, i.e., 0.2 or 0.3)

Example 2-2 illustrates the use of this calculation.

Example 2-2. Determination of Required Air Flow Rate:

Given a volume of contaminated soil of approximately

170,000 ft3

 (4,760 m3), an air-filled void volume (θa) at

this site of 0.36,2

 and an oxygen utilization rate of 0.25

percent/hr, the flow rate is calculated as follows:

Q = (0.25%/hr)(170,000 ft3

)(0.36)

(20.9% − 5%) × 60 min/hr

(Eq. 2-2)

Therefore, the required flow rate is approximately 16 cfm

(453 L/min).

The flow rate calculated and used must be confirmed

during operation of the bioventing system by monitoring

soil gas composition to ensure adequate oxygen levels

at all locations.

Data from numerous sites contaminated with various

types and mixtures of contaminants have shown that

microbial activity is not oxygen limited above oxygen

concentrations of approximately 1 percent to 2 percent.

To ensure the presence of adequate oxygen levels in the

Figure 2-10. Schematic of an air injection system with reinjection of extracted soil gas.

Figure 2-11. Schematic of subslab depressurization.

2 See Section 1.4.2 on using moisture content to estimate this

parameter.

27
entire treatment cell, a minimum level of 5 percent

should be maintained.

2.3 Well Spacing

To determine the required number of wells and appropriate spacing, an estimate of the radius of influence is

necessary. Many approaches to obtaining this estimate

are possible, but those normally in use are:

• Based upon measured pressure in monitoring points

during a soil gas permeability test.

• Estimated from air flow and oxygen consumption.

• Measured empirically.

Estimating the radius of influence based on pressure

measurements during an in situ permeability test is a

common approach used in soil venting or soil vapor

extraction and is probably the fastest method. This calculation is normally performed by plotting the log of

pressure versus distance, as described in Section 1.5.1.

The limitation to this approach is that it only incorporates

one of the three factors affecting the radius of influence.

To determine more exactly the radius of oxygen influence, air flow rate and oxygen utilization need to be

considered. In low-permeability soils, a pressure effect

may be seen in a monitoring point, but air flow rates to

that point may be too low to supply adequate oxygen.

Conversely, in a high-permeability soil, air flow rates

sufficient to supply oxygen may occur at pressure differentials that cannot be measured. In the authors’ experience, if a pressure criterion of 0.19 H2O (25 Pa) is used,

the estimated radius of influence will be conservative for

well spacing and site aeration.

Radius of influence can be estimated for a given air flow

rate based on oxygen utilization. Assuming the use of a

vertical well so that air flow can be described in cylindrical coordinates and assuming that the radius of influence is much greater than the well radius, the following

equation may be used:

Figure 2-12. Schematic of the extraction with reinjection system at AOC A, Keesler AFB, Mississippi.

28
RI = √ Q(20.9% p 5%)

π h ko θa

(Eq. 2-3)

where:

RI = radius of influence (ft)

Q = air flow rate (ft3

/day)

20.9% - 5% = oxygen %

h = aerated thickness (ft)

ko = oxygen utilization rate (%/day)

θa = air filled porosity (cm3

air/cm3soil)

Example 2-3. Calculation of Radius of Influence: To

calculate the radius of influence at Dover AFB, Equation

2-3 is used with the following parameters:

Q = 20 cfm (570 L/min) = 28,800 ft3

/day (820,800 L/day);

ko = 4 %/day; θa = 0.25; h = 20 ft (6.1 m)

RI =

√ 





28,800 ft3

day







(20.9% − 5%)

π (20 ft)(4%/day)(0.25)

(Eq. 2-4)

Therefore, the radius of influence at this site is equal to

approximately 85 ft (26 m).

In practice, the best approach is to estimate the radius of

influence from both pressure measurements and oxygen

utilization. This incorporates all three of the key factors: pressure connection, air flow, and oxygen utilization. The authors

have never found in practice a site where this combined

approach has overestimated the radius of influence.

The most conclusive determination of radius of influence

is empirical measurement. The blower can be started

and oxygen levels measured in monitoring points. The

problem with this approach is that a minimum of several

days is required to reach steady state. At some sites,

more than 30 days are required.

Well spacing typically is 1 to 1.5 times the radius of

influence. When multiple wells are installed, some consideration may be given to air flow patterns. In theory,

air flow lines may develop that create “dead zones”;

however, given vertical and horizontal flow paths and

diffusion, these dead zones are unlikely to occur, so

compensating for them is not routinely recommended.

2.4 Blowers and Blower Sizing

A blower provides the driving force to move air through the

bioventing system. In selecting a blower size, important

Figure 2-13. Soil gas extraction to isolate a subsurface structure at Site 48, Eielson AFB, Alaska.

29
points to consider are the required air flow rate and the

total system pressure drop. System pressure drop includes the back pressure due to the vent wells and

formation in an air injection configuration (or the vacuum

induced in the wells and formation in an extraction configuration) plus any pressure drop in the system piping

and off-gas treatment system. This section describes

the procedure for sizing a blower and uses a specific

example to illustrate the procedure.

The two basic types of blowers are centrifugal machines

and positive displacement machines. Positive displacement blowers are further subdivided into rotating machines and reciprocating machines (Figure 2-14).

Selection of the appropriate type and size is based on

the air flow requirement and the suction and discharge

pressures presented to the blower during operation at

the design air flow rate. Centrifugal blowers are generally favored when air flow requirements are high and/or

the system pressure drop is low. Rotating positive displacement blowers generally provide lower air flow capacity and higher pressures than centrifugal blowers but

can generate moderate to high vacuum at the blower

inlet. Because of their vacuum capability, rotating positive displacement blowers may be used for systems

operating in an extraction configuration. Reciprocating

positive displacement machines are typically used for

applications requiring very high pressure. Except for

single-action diaphragm pumps used for soil gas sampling, reciprocating positive displacement pumps are

rarely used in bioventing applications and are not discussed further. The required pressure or vacuum in the

well is a function of the soil gas permeability, which is

determined through field tests as described in Section 1.5.

2.4.1 Centrifugal Blowers

Centrifugal blowers impart energy to the air stream by

means of a rapidly rotating impeller or propeller. The

moving impeller imparts kinetic energy to the fluid. Part

of the added kinetic energy is then converted to pressure head in the blower casing as the fluid leaves the

impeller. Examples of centrifugal blowers include radial

blowers, regenerative radial blowers, multistage radial

blowers, and axial blowers.

In a radial blower, air enters at the center of the housing

and is picked up by an impeller vane near the axis of

rotation (low-velocity area). Air is pushed radially away

from the axis of rotation and accelerated by the impeller

vane. Air exits the tip of the vane at high speed and

Figure 2-14. Schematic of blower types.

30
enters the volute casing where the air velocity drops,

converting kinetic energy into pressure head.

Regenerative centrifugal blowers provide efficient air

movement in the flow rate and pressure drop ranges

encountered in soil vapor extraction and bioventing

applications and can produce moderate vacuum at the

suction port. They are available in nonsparking explosion-proof designs. As a result of these capabilities, the

regenerative centrifugal blower is widely used in soil

vapor extraction and bioventing systems. Unlike standard single-stage radial centrifugal blowers, the regenerative design uses a short-bladed turbine impeller. As

the regenerative blower impeller rotates, centrifugal acceleration moves the air from the base of the blade to

the blade tip. The fast-moving air leaving the blade tip

flows around the housing contour and back down to the

base of the next blade, where the flow pattern repeats.

This repeated acceleration allows a regenerative blower

to produce higher differential pressure than a conventional single-stage radial flow design. The regenerative

blowers can also produce higher vacuum at the suction

port compared with a pure radial flow design (but are not

able to reach the high vacuum conditions provided by

rotary positive displacement blowers).

2.4.2 Rotary Positive Displacement Blowers

Rotary positive displacement blowers impart energy to

the air stream by means of a rotating element displacing

a fixed volume with each revolution. Examples of rotary

positive displacement blowers include twin-lobe blowers, water ring vacuum pumps, sliding vane blowers,

and flexible vane blowers. Sliding vane and flexible vane

blowers may be used for soil gas sampling or other

low-flow applications but have too low an air flow capacity to act as the air handler in a bioventing system. Lobe

blowers and water ring vacuum pumps have been used

in soil vapor extraction and bioventing systems where

moderate to high vacuum is needed.

In a twin-lobe blower, two figure-eight-shaped lobe impellers, mounted on parallel shafts, rotate in opposite

directions. As each impeller lobe passes the pump inlet,

it traps a volume of gas and carries it around the case

to the pump outlet. The rotation speed of the two impellers is controlled so that the volume created at the inlet

side of the casing is larger than the volume at the outlet

side of the casing, resulting in compression of the air

trapped by the impeller lobe.

A water ring vacuum pump uses a rotating vaned impeller in a cylindrical pump casing. The impeller axis of

rotation is off center with respect to the pump housing.

A uniformly thick layer of water forms on the inside of

the pump casing as a result of the rotary action of the

impeller. Because the impeller is off center, the cavity

formed between two impeller vanes and the water seal

changes size as the vanes move around the pump

housing. Air enters the pump where the cavity formed

by the vanes and the water seal is large and is discharged where the cavity is small, thus increasing the

pressure of the pumped gas.

2.4.3 Blower Selection and Sizing

Proper sizing and selection of a blower is essential to

ensure that the unit can deliver the required air flow and

that the unit operates properly. Choosing the wrong

blower can result in an inability to deliver sufficient oxygen or a significantly shortened blower life. Care must

be taken to select the type of blower that can deliver the

required air flow at the expected pressure. The best

approach is to select a blower that allows operation near

the middle of its performance range. A blower operating

near its maximum pressure/vacuum is running inefficiently and under stressed conditions, thereby increasing operating costs and shortening blower life. Selection

of an oversized blower also reduces operating efficiency

and unnecessarily increases capital costs. Example 2-4

illustrates a typical decision process for selection and

sizing of a blower.

Example 2-4. Selection and Sizing of a Blower: For the

site described in Example 2-2, 16 cfm (453 L/min) of air

must be delivered to the example treatment cell. Based

on the soil gas permeability test conducted at the site,

operating pressures of 109H2O (2.5 × 103

 Pa) were required to deliver 16 cfm (453 L/min). A regenerative air

blower is selected because it operates efficiently at the

specified flow rate and pressure. Blower performance

curves were obtained for three different-sized blowers

(1/10, 1/8, and 21⁄2 hp, respectively), all of which might

be expected to produce 16 cfm (453 L/min). The curves

are shown in Figure 2-15.

The performance curves indicate that Blower #1 is too

small and would not be able to provide 16 cfm (453

L/min) at 109H2O (2.5 × 103

 Pa). Although Blower #3

could provide 16 cfm (453 L/min) at 109H2O (2.5 × 103

Pa), it would be operating at the lower end of performance and would be too big. The performance curve for

Blower #2 shows that it would be a good choice. Blower

#2 is rated to deliver as much as 21 cfm (595 L/min) at

109H2O (2.5 × 103

 Pa). The excess air flow can be bypassed to the atmosphere, allowing adjustment for the

16 cfm (453 L/min) flow into the vent. If volatilization is

not a concern and the additional air flow is not a problem,

the entire flow can be injected into the vent well.

The example described above is a simplified case to

show how to select and size a blower for use with

bioventing. Situations in the field may become more

complicated if significant seasonal variations occur in

soil gas permeability or if other parameters exist that

31
affect gas flow and oxygen demand. The key design

consideration is to select and size a blower based on

conditions when oxygen demand is highest and soil gas

permeability is lowest. Incorporating a bypass into the

system plumbing reduces the air flow delivered to the

soil. Air flow cannot be increased above the performance of the blower, so the blower should be selected for

the most demanding conditions. The operating principles of several blower types are outlined in the following

sections. Further information on pumps and blowers

may be found in Pumping Manual, 1989; Karassik et al.,

1991; and Graham, 1949.4

2.5 Vent Well Construction

Vent well construction is fairly standard, and general

guidelines are provided here. If existing ground-water

monitoring wells at the site are screened above the

water table, they can be used as vent wells. This option

is appropriate for air injection systems but is less successful for air extraction systems because the applied

vacuum causes a rise in the water table that could

submerge the screened interval.

The diameter of the vent well typically is between 2 in.

and 4 in. (5.1 cm and 10 cm), although larger and

smaller diameters have been successfully used. Vent

well diameter depends on the soil type, ease of drilling,

and area and depth of the contaminated volume. In most

shallow or sandy soils, a 2-in. diameter (5.1-cm) vent

well provides adequate air flow for bioventing. For sites

with contamination extending below 30 ft (9.1 m) or in

low-permeability soils, a 3-in. or 4-in. (7.6-cm or 10-cm)

vent well is recommended because it allows for greater

air flow to aerate a greater volume. As the depth of well

increases, the fractional cost of well construction materials per ft of well decreases significantly.5

The vent well typically is constructed of schedule 40

polyvinyl chloride (PVC) and should be screened with a

slot size that maximizes air flow through the soil. The

screened interval should extend through as much of the

contaminated profile as possible, with the bottom of the

screen corresponding to the lowest historical level of the

water table. When designing a screen for an extraction

well, the potential for water table upconing must be

considered. If the bottom of the screened interval is close to

the water table, water will be pulled into the vent well, reducing its effectiveness. If screening below the water table is

necessary, additional screened length above the water

table may be necessary to offset water table upconing.

Hollow-stem augering is the most common drilling

method; however, a solid-stem auger is acceptable in

more cohesive soils. The AFCEE is also investigating

the use of cone penetrometer (CPT) wells for bioventing.

Many other drilling techniques are also appropriate. In

shallow, softer soils, hand-augering may be feasible.

Wherever possible, the diameter of the borehole should

be at least two times greater than the vent well outside

diameter. The annular space corresponding to the screened

interval should be filled with silica sand or an equivalent.

The annular space above the screened interval should be

sealed with a bentonite and grout slurry to prevent shortcircuiting of air to or from the surface. The construction

detail of a typical vent well is shown in Figure 2-16.

Figure 2-15. Performance curves for three different-sized blowers (1/10, 1/8, and 2.5 hp, respectively).

5 See Appendix B for recommended specifications and manufacturers

for vent well construction materials.

4 See Appendix B for recommended specifications and manufacturers

for the blowers.

32
To maintain the integrity of the vent well seal, as a rule

of thumb, do not allow injection pressures measured in

water depth to exceed the total grouted and sealed

length. For example, in a well with 3 ft (0.91 m) of

bentonite seal and 3 ft (0.91 m) of grout, do not exceed

an injection pressure of 729H2O (1.8 × 104

 Pa). High

pressures also can damage seals. If the injection pressure exceeds the bearing capacity of the soil, fracturing

is possible. Care must be taken with injection wells to

obtain a good seal. Injection wells should be installed

with a bentonite and grout slurry. Dry bentonite chips do

not provide an adequate seal unless the chips are continuously hydrated during installation.

2.6 Monitoring Point Construction

Soil gas monitoring points are used for pressure and soil

gas measurements and are a very important component

of a bioventing system. Proper construction of monitoring

points is essential for monitoring localized pressure and

soil gas concentrations. To the extent possible, the

monitoring points must be located in contaminated soils

with greater than 1,000 mg/kg of total petroleum hydrocarbon. If monitoring points are not located in contaminated soil, meaningful in situ respiration data cannot be

collected.

In addition, location of monitoring points should consider

soil gas permeability testing and radius of influence

determination. Monitoring points should be located at

varying distances from the vent well. The distances from

the vent well vary depending on soil type; suggested

monitoring point spacing is shown in Table 2-3.

In practice, each monitoring point cluster usually is

screened to at least three depths. The deepest screen

should be placed either at or near the bottom of contamination if a water table is not encountered, or a minimum

of 2 ft to 3 ft (0.61 m to 0.91 m) above the water table if

Figure 2-16. Schematic of a typical vent well.

33
it is encountered. Consideration should be given to potential seasonal water table fluctuations and soil type in

finalizing the depth. In more permeable soil, the monitoring point can be screened closer to the water table.

In less permeable soil, it must be screened further above

the water table. The shallowest screen normally is 3 ft

to 5 ft (0.91 m to 1.5 m) below land surface. The intermediate screen should be placed at a reasonable interval at a depth corresponding to the center to upper

quarter of the depth of the vent well screen. In some

cases, additional screened depths may be desirable to

more fully monitor the contaminated interval, to monitor

differing stratigraphic intervals, or to adequately monitor

deeper sites with broadly screened vent wells.

Example 2-5. Selection of Depth Intervals for Monitoring

Points: Site soils are sandy, with ground water at 30 ft

(9.1 m). The vent well was screened from 17.5 ft to 27.5

ft (5.3 m to 8.4 m) below land surface. Therefore, monitoring point depth intervals chosen were 28 ft (8.5 m),

22.5 ft (6.9 m), and 3 ft (0.91 m). For sites with vent wells

deeper than 30 ft (9.1 m), more depths may be

screened, depending on stratigraphy.

Monitoring point construction varies depending on the

depth of drilling and the drilling technique. Monitoring

points consist of a small-diameter 1⁄4-in. (0.64-cm) tube

to the specified depth with a screen approximately 6 in.

(15 cm) long and 1 in. (2.5 cm) in diameter. In shallow,

open-hole installations, rigid tubing (i.e., schedule 80

1⁄4-inch [0.64 cm] PVC) terminating in the center of a

gravel or sand pack may be adequate. The gravel or

sand pack normally should extend for an interval of 1 ft

to 2 ft (0.30 m to 0.61 m), with the screen centered. In

low-permeability soils, a larger gravel pack may be desirable. In wet soils, a longer gravel pack with the screen

near the top may be desirable. A bentonite seal at least

2 ft (0.31 m) thick normally is required above and below

the gravel pack. Figure 2-17 shows the construction

detail of a typical monitoring point installation.6

 For relatively shallow installations in more permeable soils, a

hand-driven system may be used. In such a system, a

sacrificial drive point with Tygon, Teflon, or other appropriate tubing is driven to the desired depth. Then the

steel outer tubing is retrieved, leaving the drive point and

the inner flexible tubing in place. Because this type of

installation allows little or no sand pack or seal placement, it should be used only in relatively permeable soils

where sample collection will not be a problem or in soils

that will “self-heal” to prevent short-circuiting. Surface

completion of the hand-driven points should be the

same as for those installed in borings.

Monitoring points typically are used to collect soil gas

for carbon dioxide and oxygen analysis in the 0 percent

to 25 percent range, and for hydrocarbons greater than

100 ppmv. The tubing material must have sufficient

strength and be nonreactive. Materials used include

nylon and Tygon. Sorption and gas interaction with the

tubing materials have not been significant problems for

this application. If a monitoring point will be used to

monitor specific organics in the low-ppm or ppb range,

Teflon or stainless steel may be necessary. This is uncommon, however.

A sufficient number of monitoring points should be installed to ensure representative sampling. The actual

number installed is site-specific and is driven primarily

by plume size and cost of installing and monitoring

additional monitoring points. If air injection is being considered in the bioventing test, a nest of monitoring points

must be located between the vent well and any buildings

that may be at risk to ensure that they are well beyond

the radius of influence or that vapor-phase hydrocarbons biodegrade before air reaches the structure.

Temperature monitoring typically is conducted by attaching thermocouples to monitoring points. Type J or K

thermocouples can be used and should be attached to

the monitoring point depth of interest. In general, soil

temperatures vary little across a site but do vary with

depth to the ground surface; therefore, few thermocouples are required for adequate soil temperature monitoring at a given site.

Table 2-3. Recommended Spacing for Monitoring Points

Soil Type

Depth to Top of Vent

Well Screen (ft)a SpacingInterval (ft)b

Coarse sand 5 5-10-20

10 10-30-50

>15 20-30-70

Medium sand 5 10-20-30

10 15-25-45

>15 20-40-70

Fine sand 5 10-20-40

10 15-30-50

>15 20-40-60

Silts 5 10-20-40

10 15-30-50

>15 20-40-60

Clay 5 10-20-30

10 10-20-40

>15 10-25-50

6 See Appendix B for recommended specifications and manufacturers

for monitoring point construction materials.

34
Figure 2-17. Schematic of a typical monitoring point construction.

35
Chapter 3

Performance Monitoring

The following sections provide suggestions for monitoring bioventing systems. These methods provide a

means of tracking the performance of a bioventing system over time. Methods discussed include:

• Soil gas monitoring

• In situ respiration testing

• Surface emissions sampling

• Operation and maintenance of the bioventing system

In addition, the following nonroutine or optional methods

are discussed:

• Quantification of biodegradation and volatilization of

hydrocarbons during extractive bioventings.

• Qualitative validation of biodegradation through stable carbon isotope monitoring.

3.1 Soil Gas Monitoring

Periodic soil gas monitoring should be conducted to

ensure that the bioventing site is well oxygenated.1

 Initially, soil gas should be monitored weekly until the site

becomes fully aerated. Once full aeration is achieved,

bioventing system operation can be optimized. After this

initial period, soil gas monitoring normally is conducted

semiannually for the first year, during the warmest and

coldest months, and annually thereafter. If conducting

an in situ respiration test during different seasons is not

possible, then it should be conducted during the same

seasons as the initial test. Because of the relative simplicity of most bioventing systems, frequent soil gas monitoring rarely is necessary to ensure proper operation.

3.2 In Situ Respiration Testing

In situ respiration testing should be conducted periodically as a means of monitoring the progress of site

remediation.2

 As the site remediation progresses and

contaminant concentrations decrease, in situ respiration

rates should approach those measured in the uncontaminated area. Frequent in situ respiration tests are not

necessary. In situ respiration tests normally are conducted

quarterly for the first year and annually thereafter.

In situ respiration tests for performance are conducted

somewhat differently than the test for site characterization described in Section 1.3. During system operation, an in situ respiration test is conducted by first

measuring soil gas concentrations of oxygen, carbon

dioxide, and total hydrocarbons during system operation. After these measurements are collected, the

bioventing system is turned off, and soil gas monitoring

is conducted periodically to measure oxygen disappearance and carbon dioxide production. No inert tracer gas

is added at this time because the initial testing should

have determined whether diffusion or monitoring point

leakage was occurring. Calculation of biodegradation

rates is accomplished in the same manner as described

in Section 1.3.

In situ respiration testing should be used as the primary

indicator for site closure. A good indication that the site

is remediated and that final soil sampling can be conducted is an in situ respiration rate in the contaminated

area similar to that in the uncontaminated area. In situ

respiration testing to determine remediation success is

economically significant because soil sampling is not

relied upon as the sole indicator of site remediation, thus

eliminating the high cost of intermediate soil sampling.

In situ respiration rates can be expected to vary with

time. Generally, temperature is the most significant

driver of short-term (within 1 year) changes. Over longer

periods, contaminant reduction decreases rates. One

frequently observed phenomenon is a substantial decline in rates from the initial in situ respiration rates to

subsequent measurements. This phenomenon seems

to result from placement of monitoring points in less

contaminated soils. NAPL contamination usually is distributed in a very heterogeneous manner. Under nonventing conditions, volatilization spreads hydrocarbons

in soil gas, resulting in more heterogeneous contamination. Soil contaminated in this fashion, however, has a

much lower total concentration because sorbed hydrocarbons are present at much lower levels than in soils

actually containing NAPLs. If a monitoring point is

1 See Sections 1.2, “Soil Gas Survey,” and 1.4, “In Situ Respiration

Testing,” for more detail on sampling and analyzing soil gases.

2 See Section 1.4, “In Situ Respiration Testing,” for additional detail.

37
placed in this soil with only sorbed and vapor-phase

contamination, the initial rates will be high; however,

remediation will rapidly reduce the sorbed concentrations and the in situ respiration rates will fall quickly,

often by a factor of 5 to 10 in a few months. One

indication of this is a low-rate apparent first-order oxygen decay curve, resulting in misleading rate data.

Eliminating this problem is difficult; however, placement

of monitoring points in the most highly contaminated soil

can limit the problem.

3.3 Quantification of Biodegradation

and Volatilization of Hydrocarbons

During Extractive Bioventing

Biodegradation and volatilization of hydrocarbons can

be quantified during extractive bioventing through direct

measurement of off-gas concentrations of oxygen and

carbon dioxide. Bioventing systems that are operating

in injection mode have been reconfigured briefly to provide these data. Note, however, that in the case of

injection mode systems, reconfiguration to extraction

mode provides an overestimate of the mass of hydrocarbons volatilized because the size of the in situ bioreactor is reduced.3

The mass of hydrocarbons volatilized can be calculated

as follows:

HCvol = CV,HC

106 × Q × ρhexane × MWhexane ×

kg

1,000 g × 1,440 min

day

(Eq. 3-1)

where:

HCvol = mass of hydrocarbons volatilized

(kg/day)

CV,HC = concentration of hydrocarbons in

extracted off-gas (ppmv)

Q = flow rate (L/min or cfm)

ρhexane = density of hexane (moles/L)

MWhexane = molecular weight of hexane (g/mole)

The mass of hydrocarbons biodegraded can be calculated as follows:

HCbio =







CV,bkgd − CV,O2

100







× Q × C × ρO2 × MWO2 ×

kg

1,000 g × 1,440 min

day

(Eq. 3-2)

where:

HCbio = mass of hydrocarbons biodegraded

(kg/day)

CV,bkgd = concentration of oxygen in background,

uncontaminated area (%)

CV,O2 = concentration of oxygen in extracted offgas (%)

C = mass ratio of hydrocarbon to oxygen

degraded based on stoichiometry4

 (1/3.5)

Example 3-1 illustrates these calculations.

Example 3-1. Calculation of Volatilization and Biodegradation of Contaminants During Extraction: At a site undergoing extraction, concentrations of oxygen and TPH

in the extracted soil gas at steady state are 19 percent

and 140 ppmv, respectively. The system is operating at

a flow rate of 4 cfm (113 L/min). Background oxygen

concentrations are consistently at 20.9 percent. First,

the mass of hydrocarbons volatilized must be calculated.

Given the following parameters:

CV,HC = 140 ppmv; Q = 4 cfm (113 L/min); ρhexane = 0.042

moles/L; and MWhexane = 84 g/mole.

Using Equation 3-1:

Solving, the mass of hydrocarbons volatilized is 0.081

kg/day (0.18 lb/day).

HCvol = 





140 ft3

 hexane

106

 ft3 air













4 ft3

min ×

28.3 L

ft3













0.042 mole

L













84 g

mole













kg

1,000 g













1,440 min

day







To calculate the mass of hydrocarbons biodegraded,

use Equation 3-2:

HCbio = 





20.9 − 19.0

100













4 ft3

min ×

28.3 L

ft3













1 g HC

3.5 g O2













0.042 mole

L













32 g

mole













kg

1,000 g













1,440 min

day







Solving, the mass of hydrocarbons biodegraded is approximately 1.2 kg/day (2.6 lb/day), or nearly an order

of magnitude greater than the amount volatilized.

3 See Section 2.1 for a discussion of these issues. 4 See Section 1.4.2 for a discussion of stoichiometry.

38
The fraction of total removal by biodegradation is larger

for injection systems because the opportunity for biodegradation is greater. In an injection mode, vapors are pushed

through the contaminated zone into the uncontaminated

zone, allowing for additional biodegradation. When the

system is operated in an extraction mode, however,

much of the vapor is removed from the soil before

biodegradation can occur.

3.4 Surface Emissions Sampling

Surface emissions sampling is not necessary at most

bioventing sites. Under the Bioventing Initiative, it was

conducted at only five of 125 sites to quantify volatilization of contaminants attributed to air injection. Although

surface emissions typically do not occur or are very low

at bioventing sites because of low air flow rates, possible

surface emissions often are a regulatory concern and

surface emission rates may need to be quantified to

obtain regulatory approval for bioventing. Note, however, that according to the EPA document Estimation of

Air Impacts for Bioventing Systems Used at Superfund

Sites (U.S. EPA, 1993), emissions from bioventing sites

operating in an injection mode are thought to be minimal. Thus, they are not discussed in this document.

One standard surface emission sampling protocol using

isolation flux chamber procedures is described by Dupont

(1988) and EPA (1986) and is illustrated in Figure 3-1.

The system consists of a square Teflon box that covers

a surface area of approximately 0.45 m2

. The box is

fitted with inlet and outlet ports for the entry and exit of

high-purity air. Inside the box is a manifold that delivers

the air uniformly across the soil surface. The same type

of manifold is fitted to the exit port of the box. This

configuration delivers an even flow of air across the

entire soil surface under the box to generate a representative sample.

The air exiting the Teflon box is directed to a sampling

box that contains a sorbent tube and a pump. Also

attached to the box is a purge line that accommodates

the excess flow from the Teflon box that is not drawn into

the sorbent tube. A Magnehelic gauge is used to indicate

if zero pressure is being maintained on the entire system.

In all cases, a totally inert system is employed. Teflon

tubing and stainless steel fittings prevent any contribution to or removal of organics from the air stream. The

pump is located on the back side of the sorbent trap so

that it is not in a position to contaminate the sample flow.

To calculate the actual emission rates of organic compounds from the soil surface into the atmosphere, the

following formula for dynamic enclosure techniques is

employed (EPA, 1991a):

F = CV Vr

A

(Eq. 3-3)

where:

F = flux in mass/area-time (g/m2

-min)

CV = concentration of the gas in units of

mass/volume (g/m3

)

Vr = volumetric flow rate of sweep gas (m3

/min)

A = soil surface area covered by enclosure (m2

)

Figure 3-1. Schematic of a surface emissions monitoring device.

39
At bioventing sites where surface emissions have been

measured, surface emissions rates of BTEX and TPH

have been several orders of magnitude below regulatory

levels. These results have provided strong support for

continued operation of bioventing systems in injection

mode. As an example, Table 3-1 illustrates surface emissions results from six bioventing sites. In general, surface

emissions are very low, with TPH emission rates less than

1 lb/day. These emission rates are well below most regulatory limits and illustrate that properly designed bioventing

systems create no significant air emissions.

3.5 Optional Monitoring: Qualitative

Validation of Biodegradation

Through Stable Carbon Isotope

Monitoring

Measurement of stable carbon isotope ratios may help

substantiate biodegradation (Aggarwal and Hinchee,

1991). Carbon dioxide produced by hydrocarbon degradation may be distinguished from that produced by other

processes based on the carbon isotopic compositions characteristic of the source material and/or the

fractionation accompanying microbial metabolism

(Suchomel et al., 1990; Stahl, 1980; McMahon et al.,

1990). As shown in Figure 3-2, carbon dioxide generated from natural organic material has a δ13C of approximately -10 to -15, whereas carbon dioxide generated

from petroleum hydrocarbons has a δ13C of approximately -20 to -30. This measurement is not required to

validate biodegradation since the in situ respiration test

is used for this purpose; therefore, it should only be

conducted if dictated by regulatory concerns.

3.6 Operation and Maintenance

Bioventing systems are very simple, with minimal mechanical and electrical parts. If the system is operated

Table 3-1. Surface Emissions Sampling at Bioventing Sites

Base Site Type

Air Injection

Depth (ft)

Air

Injection

Rate (cfm)

Area of

Influence

(ft2

)

Total Flux

Estimate

(lb/day)

Beale AFB, CA Fire Training Pit 10 - 25 30 6,500 0.15 

Bolling AFB, DC Diesel Spill 10 - 15 20 5,100 0.44 

Eielson AFB, AK JP-4 Spill 6.5 - 13 30 43,600 0.011

Fairchild AFB, WA JP-4 Spill 5 - 10 15 5,100 0.33 

McClellan AFB, CA JP-4 Spill 10 - 55 50 9,700 0.066

Plattsburgh AFB, NY Fire Training Pit 10 - 35 13 11,500 0.44 

Figure 3-2. Carbon isotopic compositions of soil gas carbon dioxide at Site 20, Eielson AFB, Alaska, August 1993.

40
in an injection mode, a simple visual system check

would be required to ensure that the blower is operating

within its intended flow rate and pressure range. Weekly

system checks are desirable. Often, someone on site

can conduct these system checks because little technical knowledge of the process is required. Minor maintenance such as replacing filters, flow meters, or gauges

may be necessary.

If an extraction system or an extraction/reinjection

bioventing system is installed, more intensive maintenance is likely to be required. Extraction systems have

knockout drums that require draining and treatment of

condensate. In addition, in the case of extraction-only

systems, off-gas may need to be monitored regularly to

ensure that emissions are within regulatory guidelines.

Off-gas treatment systems also require periodic checks

to ensure proper operation.

Blowers used for bioventing systems typically last for

several years and should not need replacement. To

date, two bioventing systems have been operating for 3

years with the original blower in place (Battelle, 1994;

Leeson et al., 1995), and of the 125 blowers installed to

date under the Bioventing Initiative, only three have

required repair or replacement.

41
Chapter 4

Process Evaluation/Site Closure

4.1 In Situ Respiration Testing

In situ respiration testing should be used as the primary

indicator for site closure. As discussed in Section 3.2,

as site remediation progresses and contaminants are

degraded, the measured in situ respiration rates approach background respiration rates. When the in situ

respiration rate in the contaminated area is similar to

that in the uncontaminated area, this is a good indication

that the site is remediated and final soil sampling can be

conducted. Initially, the amount of time necessary for

cleanup of the site can be estimated on in situ respiration rates, as shown in Example 4-1.

Example 4-1. Calculation of Remediation Time Based

on in Situ Respiration Rates: This example assumes an

average oxygen utilization rate of 6 percent oxygen per

day and an initial average soil concentration of 6,000 mg

TPH/kg soil. The oxygen utilization is related to hydrocarbon degraded by the following equations:

C6H14 + 9.5O2 → 6CO2 + 7H2O

kB = −0.68 kο

Using the above assumptions, an oxygen utilization rate

of 6 percent oxygen per day would correspond to a

biodegradation rate of approximately 4.1 mg/kg-day.

Given that the initial soil concentration is 6,000 mg/kg,

an estimate of cleanup time is calculated as follows:

Cο

kB

= cleanup time

6,000 mg/kg

4.1 mg/kgpday = 1,500 days ≈ 4 years

This calculation provides a reasonable “ballpark” estimate of the amount of time necessary to remediate the

site. This method tends to underestimate treatment time

because kB decreases over time. At the same time, this

calculation overestimates treatment time because it

does not consider treatment in the expanded bioreactor.

Therefore, the calculation must be coupled with process

monitoring to provide field-based evidence that the site

actually is remediated within this time. Because of

widely variable contaminant concentrations, the average biodegradation rate does not reflect actual biodegradation rates throughout the site; biodegradation rates

also may fluctuate with season and as contaminant

concentrations decrease. Therefore, process monitoring

is an important parameter in determining treatment time.

4.2 Soil Sampling

Soil sampling should not be used as a process monitoring technique. Because of the inherently high variability

of hydrocarbons in soils, the number of samples required to produce a meaningful result is prohibitive until

contamination levels approach 90 percent to 99 percent

cleanup. The amount of soil sampling conducted at a

site has a tremendous impact on the cost of the project.

Minimizing soil sampling makes a remediation effort

much more cost-effective. With bioventing systems, in

situ respiration testing can indicate when the site is

clean and, therefore, when to collect final soil samples.

Regulatory issues usually drive the number of final soil

samples collected.

The Department of Natural Resources of the State of

Michigan published a guidance document for verification

of soil remediation. It also provides several methods for

statistical sampling strategies (Michigan Department of

Natural Resources, 1994). In addition, it provides information on design of the sampling grid and determination of

the upper confidence limit (UCL) of the final mean. The

UCL is calculated from the following equation:

UCL = X

__

+ [t = 0.95(n − 1)] SX (Eq. 4-1)

where:

UCL = upper confidence limit

X = average contaminant concentration

bracketed

 term

= one-tailed t-test at n-1 degrees of

freedom (see Table 4-1 for values)

SX = standard error of the mean, which is

calculated as follows:

43
SX = S

√n

(Eq. 4-2)

where:

S = standard deviation

n = sample size

If the UCL is higher than the regulatory threshold, then

the lambda relationship is used to calculate the appropriate sample size:

λ = RT − X

__

S

(Eq. 4-3)

where:

λ = statistical parameter (see Table 4-2 for values)

RT = regulatory threshold

X = average contaminant concentration

S = standard deviation

Once λ is calculated, by referring to Table 4-2, the number

of additional samples required to verify cleanup can be

determined. This calculation is shown in Example 4-2.

Example 4-2. Statistical Evaluation of Contaminant

Data: At this site, three preliminary soil samples were

collected to estimate a sample mean and standard deviation. The initial sample mean was 90 mg/kg TPH with

a standard deviation of 30 mg/kg. The regulatory threshold is 100 mg/kg TPH. Calculating the UCL:

UCL = 90 + (2.920) × 





30

√3







= 141 mg/kg

(Eq. 4-4)

Given that this value is above the regulatory threshold,

the lambda calculation is performed to determine how

many additional samples are required to verify cleanup:

λ = 100 − 90

30 = 0.33 (Eq. 4-5)

From Table 4-2, for α = 0.05 and β = 0.05, a sample size

of between 90 and 122 additional samples is required.

Ott (1984) provides an alternative method for estimating

final sample size. This method determines the required

Table 4-1. Cumulative t Distribution

p

OneTailed 0.550 0.750 0.080 0.900 0.950 0.975 0.990 0.995

TwoTailed 0.100 0.500 0.600 0.800 0.900 0.950 0.980 0.990

 1 0.158 1.000 1.376 3.078 6.314 12.706 31.821 63.657

 2 0.142 0.816 1.061 1.886 2.920 4.303 6.925 9.925

 3 0.137 0.765 0.978 1.638 2.353 3.182 4.541 5.841

 4 0.134 0.741 0.941 1.533 2.132 2.776 3.747 4.604

 5 0.132 0.727 0.920 1.476 2.015 2.571 3.365 4.032

 6 0.131 0.718 0.906 1.440 1.943 2.447 3.143 3.707

 7 0.130 0.711 0.896 1.415 1.895 2.365 2.998 3.499

 8 0.130 0.706 0.889 1.397 1.860 2.306 2.896 3.355

 9 0.129 0.703 0.883 1.383 1.833 2.262 2.821 3.250

10 0.129 0.700 0.879 1.372 1.812 2.228 2.764 3.169

11 0.129 0.697 0.876 1.363 1.796 2.201 2.718 3.106

12 0.128 0.695 0.873 1.356 1.782 2.179 2.681 3.055

13 0.128 0.694 0.870 1.350 1.771 2.160 2.650 3.012

14 0.128 0.692 0.868 1.345 1.761 2.145 2.624 2.977

15 0.128 0.691 0.866 1.341 1.753 2.131 2.602 2.947

44
number of soil samples to show a statistical difference

between initial and final contaminant concentrations:

n = σ2 (zα + zβ)

2

(μο − μ)2 (Eq. 4-10)

where:

n = number of final soil samples to collect

σ2 = population variance of the initial soil

sampling event

zα = probability of a Type I error

zβ = probability of a Type II error

μο = mean of the initial soil sampling event

μ = estimated mean of the final soil sampling

event

As the difference between the initial and final means

increases, the number of samples required to show a

statistical difference between the two sampling events

decreases. As shown in Table 4-3, as hydrocarbons are

further degraded, fewer soil samples are required to

show a statistical difference in the two means. This

concept is illustrated in Example 4-3.

Example 4-3. Calculation of Final Number of Soil Samples for Site Closure: At this site, 83 initial soil samples

were collected with a mean TPH concentration of 6,000

mg/kg and a standard deviation of 8,000 mg/kg (typical

of many bioventing sites). The average biodegradation

rate at this site was 4.1 mg/kg-day. Given that the system had been operating for 3.5 years, the final mean

TPH concentration can be estimated as follows:

4.1 mg/kg-day × 1,278 days = 

5,240 mg/kg TPH degraded (Eq. 4-11)

Estimated final [TPH] = 

6,000 mg/kg - 5,240 mg/kg = 760 mg/kg

(Eq. 4-12)

Using this estimate of the final mean TPH concentration,

the number of samples to be collected to provide statistically significant data can be calculated using Equation

(4-4) and the following parameters:

Table 4-2. Number of Observations for t Test of Mean

 Level for t test

Single-Sided

Double-Sided

α = 0.01

α = 0.02

α = 0.05

α = 0.10

λ β 0.011 0.05 0.1 0.2 0.5 0.01 0.05 0.1 0.2 0.5

0.05

0.10

0.15 122 

0.20 139 70

0.25 90 139 101 45

0.30 115 63 122 97 71 32

0.35 109 85 47 90 72 52 24

0.40 101 85 66 37 101 70 55 40 19

0.45 110 81 68 53 30 80 55 44 33 15

0.50 90 66 55 43 25 65 45 36 27 13

0.55 75 55 46 36 21 54 38 30 22 11

0.60 63 47 39 31 18 46 32 26 19 9

0.65 55 41 34 27 16 39 28 22 17 8

0.70 47 35 30 24 14 34 24 19 15 8

0.75 42 31 27 21 13 30 21 17 13 7

0.80 37 28 24 19 12 27 19 15 12 6

0.85 33 25 21 17 11 24 17 14 11 6

0.90 29 23 19 16 10 21 15 13 10 5

0.95 27 21 18 14 9 19 14 11 9 5

1.00 25 19 16 13 9 18 13 11 8 5

45
σ = (8,000)2

; zα = 1.645 (for α = 0.05);

zβ = 2.33 (for β = 0.01); μο = 6,000 mg/kg; 

μ = 525 mg/kg

Selected values are shown in Table 4-4. The zα and zβ

are determined by finding areas corresponding to (0.5 - α)

and (0.5 - β), respectively:

n = (8,000)

2

(1.645+ 2.33)

2

(6,000 − 760)

2

(Eq. 4-13)

Therefore, the number of final soil samples that must be

collected is 37.

Table 4-3. Calculation of the Number of Samples Required To

Show a Statistical Difference Between Means of

Two Sampling Events

Time From

Initiation of

Bioventing

(days)

Estimated

Amount of

Hydrocarbon 

Degraded

(mg/kg)

Estimated

Amount of

Hydrocarbon 

Remaining

(mg/kg)

Number of

Samples

Required

180 1,440 4,560 731

365 2,920 3,080 178

540 4,320 1,680 81

730 5,840 160 44

Table 4-4. Selected z Values for Estimation of Final Soil Sample Number (Ott, 1984)

z 0.00 0.01 0.02 0.03a 0.04b 0.05b

0.0 0.0000 0.0040 0.0080 0.0120 0.0160 0.0199

0.1 0.0398 0.0438 0.0478 0.0517 0.0557 0.0596

0.2 0.0793 0.0832 0.0871 0.0910 0.0948 0.0987

0.3 0.1179 0.1217 0.1255 0.1293 0.1331 0.1368

0.4 0.1554 0.1591 0.1628 0.1664 0.1700 0.1736

0.5 0.1915 0.1950 0.1985 0.2019 0.2054 0.2088

0.6 0.2257 0.2291 0.2324 0.2357 0.2398 0.2422

0.7 0.2580 0.2611 0.2642 0.2673 0.2704 0.2734

0.8 0.2881 0.2910 0.2939 0.2967 0.2995 0.3023

0.9 0.3159 0.3186 0.3212 0.3238 0.3264 0.3289

1.0 0.3413 0.3438 0.3461 0.3485 0.3508 0.3531

1.1 0.3643 0.3665 0.3686 0.3708 0.3729 0.3749

1.2 0.3849 0.3869 0.3888 0.3907 0.3925 0.3944

1.3 0.4032 0.4049 0.4066 0.4082 0.4099 0.4115

1.4 0.4192 0.4207 0.4222 0.4236 0.4251 0.4265

1.5 0.4332 0.4345 0.4357 0.4370 0.4382 0.4394

1.6 0.4452 0.4463 0.4474 0.4484 0.4495b 0.4505b

1.7 0.4554 0.4564 0.4573 0.4582 0.4591 0.4599

1.8 0.4641 0.4649 0.4656 0.4664 0.4671 0.4678

1.9 0.4731 0.4719 0.4726 0.4732 0.4738 0.4744

2.0 0.4772 0.4778 0.4783 0.4788 0.4793 0.4798

2.1 0.4821 0.4826 0.4830 0.4734 0.4838 0.4842

2.2 0.4861 0.4864 0.4868 0.4871 0.4875 0.4878

2.3a 0.4893 0.4896 0.4898 0.4901a 0.4904 0.4906

2.4 0.4918 0.4920 0.4922 0.4925 0.4927 0.4829

2.5 0.4938 0.4940 0.4941 0.4943 0.4945 0.4846

a Corresponds to determining zβ. b Corresponds to determining zα.

46
Chapter 5

Costs

Based on Air Force and recent commercial applications

of this technology, the total cost of in situ soil remediation

using the bioventing technology is $10 to $60 per yd3

(Downey et al., 1994b). At sites with over 10,000 yd3 of

contaminated soil, costs of less than $10 per yd3

 can be

achieved. Costs greater than $60 per yd3

 are associated

with smaller sites, but bioventing can still offer significant

advantages over more disruptive excavation options.

Operations and maintenance costs are minimal, particularly when base personnel are willing to perform simple

system checks and routine maintenance. Table 5-1 provides a detailed cost breakdown of remediation of 5,000

yd3

 of soil contaminated with an average concentration

of 3,000 mg of JP-4 jet fuel per kg of soil.

Ward (1992) compared costs of bioventing with costs of

other in situ bioremediation technologies (Table 5-2).

Costs shown in Table 5-2 reflect actual costs for these

three technologies at fuel spills in Traverse City, Michigan.

Even though the area treated through bioventing was

larger than that treated with hydrogen peroxide or nitrate, total costs for bioventing were significantly lower

than for the other technologies.

Figure 5-1 provides a comparison of estimated unit

costs for several technologies commonly used for remediation of fuel-contaminated soils. All costs are based on

the treatment of soil contaminated with 3,000 mg of JP-4

jet fuel per kg of soil. Costs are provided for the following

remediation scenarios: 2 years of in situ bioventing; 1

year of soil vapor extraction with thermal vapor treatment; excavation and 1 year of on-base landfarming

with leachate controls; and excavation followed by lowtemperature thermal desorption. The cost of reconstructing excavated areas is not included. At many sites

with contamination beneath concrete and buildings, bioventing is the only cost-effective treatment option available.

Table 5-1. Typical Full-Scale Bioventing Costs (Downey et al.,

1994b)

Task Total Cost ($)

Site visit/planning 5,000

Work plan preparation 6,000

Pilot testing 27,000

Regulatory approval 3,000

Full-scale construction

 Design 7,500

 Drilling/samplinga 15,000

 Installation/startup 4,000

Two-year monitoring 6,500

Two-year power 2,800

Soil sampling at 2 years 13,500

Total 90,300

a Assumes four air injection wells drilled to a depth of 15 ft.

Table 5-2. Cost Comparison of in Situ Bioremediation

Technologies Used at Fuel Spill Sites (Ward, 1992)

Total Costs ($/m3 of Contaminated

Earth)

Task

Hydrogen

Peroxide Nitrate Bioventinga

Constructionb 45 118 26 

Labor/monitoring 72 96 40 

Chemicals 500 30 0.44

Electricity 24 12 6.8 

Total 641 256 73 

a Values reflect only first 4 months of demonstration.

b Prorated to a 5-year service life on buildings, pumps, and blowers.

47
Figure 5-1. Comparison of costs for various remedial technologies for fuel-contaminated soils (Downey et al., 1994b).

48
Chapter 6

References

Aggarwal, P.K., and R.E. Hinchee. 1991. Monitoring in situ biodegradation of hydrocarbons by using stable carbon isotopes. Env.

Science and Tech. 25:1178-1180.

Battelle. 1994. Bioremediation of hazardous wastes at CERCLA and

RCRA: Hill AFB 280 site low-intensity bioreclamation. Report prepared for EPA, Cincinnati, OH.

Braker, W., and A.L. Mossmon. 1980. Matheson gas data book,

6th ed. Lyndhurst, NJ.

Downey, D.C., and J.F. Hall. 1994. Addendum one to test plan and

technical protocol for a field treatability test for bioventing-Using

soil gas surveys to determine bioventing feasibility and natural

attenuation potential. U.S. Air Force Center for Environmental Excellence, Brooks Air Force Base, TX.

Downey, D.C., J.F. Hall, R.N. Miller, A. Leeson, and R.E. Hinchee.

1994b. Bioventing performance and cost summary, February,

1994. U.S. Air Force Center for Environmental Excellence, Brooks

Air Force Base, TX.

Downey, D.C., C.J. Pluhar, L.A. Dudus, P.G. Blystone, R.N. Miller,

G.L. Lane, and S. Taffinder. 1994a. Remediation of gasoline-contaminated soils using regenerative resin vapor treatment and in

situ bioventing. In: Proceedings of the Petroleum Hydrocarbons

and Organic Chemicals in Ground Water: Prevention, Detection,

and Restoration Conference, Houston, TX (November).

Dupont, R.R. 1988. A sampling system for the detection of specific

hazardous constituent emissions from soil systems. In: Hazardous

waste: Detection control treatment. Amsterdam, The Netherlands:

Elsevier Science Publisher, BV. pp. 581-592.

Engineering-Science. 1994. Interim pilot test results report for Site

ST-35 Fuel Pumphouse No. J3 and Site ST-36 Underground Fuel

Line Davis-Monthan AFB, Arizona. Report prepared for the U.S.

Air Force Center for Environmental Excellence, Brooks AFB, Texas.

Hinchee, R.E., D.C. Downey, R.R. Dupont, P. Aggarwal, and R.N.

Miller. 1991a. Enhancing biodegradation of petroleum hydrocarbon through soil venting. J. Hazardous Materials 27:315-325.

Hinchee, R.E., D.C. Downey, and P. Aggarwal. 1991b. Use of hydrogen peroxide as an oxygen source for in situ biodegradation:

Part I, Field studies. J. Hazardous Materials 27:287-299.

Hinchee, R.E., and S.K. Ong. 1992. A rapid in situ respiration test for

measuring aerobic biodegradation rates of hydrocarbons in soil.

J. Air & Waste Management Association 42(10):1305-1312.

Johnson, P.C., C.C. Stanley, M.W. Kemblowski, D.L. Byers, and J.D.

Colthart. 1990. A practical approach to the design, operation, and

monitoring of in situ soil-venting systems. Groundwater Monitoring

Review 10(2):159-178.

Kampbell, D. 1993. U.S. EPA air sparging demonstration at Traverse

City, Michigan. In: Environmental Restoration Symposium. Sponsored by the U.S. Air Force Center for Environmental Excellence,

Brooks AFB, TX.

Karassik, I.J., W.C. Krutsch, W.H. Fraser, and J.P. Messina. Pump

handbook. pp. 2-202, 3-70 to 3-99.

Kittel, J.A., R.E. Hinchee, and M. Raj. 1994. Full-scale startup of a

soil venting-based in situ bioremediation field pilot study at Fallon

NAS, Nevada. Report prepared for the Naval Facilities Engineering Services, Port Hueneme, CA (February).

Leeson, A., R.E. Hinchee, J.A. Kittel, E.A. Foote, G. Headington, and

A. Pollack. 1995. Bioventing feasibility study at the Eielson AFB

Site. Report prepared for the Environics Directorate of the Armstrong Laboratory, Tyndall AFB, FL (September).

Lide, D.R., and H.V. Kehianian. 1994. CRC handbook of thermophysical and thermochemical data. Boca Raton, FL: CRC Press.

McMahon, P.B., D.F. Williams, and J.T. Morris. 1990. Ground water

28:693-702.

Metcalf & Eddy. 1979. Wastewater engineering, treatment, disposal,

reuse. New York, NY: McGraw Hill.

Michigan Department of Natural Resources. 1994. Guidance document: Verification of soil remediation. Report prepared by the Environmental Response Division and Waste Management Division

of the Department of Natural Resources (April).

Miller, R.N. 1990. A field scale investigation of enhanced petroleum

hydrocarbon biodegradation in the vadose zone combining soil

venting as an oxygen source with moisture and nutrient additions.

Ph.D. dissertation. Utah State University, Logan, UT.

Miller, R.N., and R.E. Hinchee. 1990. A field scale investigation of

enhanced petroleum hydrocarbon biodegradation in the vadose

zone-Tyndall AFB, FL. In: Proceedings NWWA/API Conference on

Petroleum Hydrocarbons and Organic Chemicals in Ground

Water, Houston, TX.

Miller, R.N., C.C. Vogel, and R.E. Hinchee. 1991. A field-scale investigation of petroleum hydrocarbon biodegradation in the vadose

zone enhanced by soil venting at Tyndall AFB, Florida. In:

Hinchee, R.E., and R.F. Olfenbuttel, eds. In situ bioreclamation.

Stoneham, MA: Butterworth-Heinemann. pp. 283-302.

Ong, S.K., R. Hinchee, R. Hoeppel, and R. Scholze. 1991. In situ

respirometry for determining aerobic degradation rates: In:

Hinchee, R.E., and R.F. Olfenbuttel, eds. In situ bioreclamation

applications and investigations for hydrocarbon and contaminated

site remediation. Boston, MA.

Ott, L. 1984. An introduction to statistical methods and data analysis.

2nd ed. Boston, MA: Duxbury Press.

Phelps, M.B., F.T. Stanin, and D.C. Downey. 1995. In: Hinchee, R.E.,

R.N. Miller, and P.C. Johnson, eds. In situ aeration: Air sparging,

bioventing and related remediation processes. Columbus, OH:

Battelle Press. pp. 277-282.

Pumping manual, 1st ed. 1989. Morden, Surrey, England: Trade &

Technical Press Ltd. pp. 120, 122.

49
Rivett, M.O., and J.A. Cherry. 1991. The effectiveness of soil gas

surveys in delineation of groundwater contamination: Controlled

experiments at the Borden Field Site. In: Proceedings of the Petroleum Hydrocarbons and Organic Chemicals in Ground Water:

Prevention, Detection, and Restoration Conference, Houston, TX

(November).

Stahl, W.J. 1980. Geochim. Cosmochim. Acta 44:1903-1907.

Suchomel, K.H., D.K. Kreamer, and A. Long. 1990. Environ. Sci. Tech.

24:1824-1831.

U.S. EPA. 1993. Estimation of air impacts for bioventing systems used

at Superfund sites. EPA/451/R-93/003. Washington, DC.

U.S. EPA. 1991a. Current and developing analytical technologies for

quantifying biogenic gas emissions (June). EPA/600/3-91/044.

Washington, DC.

U.S. EPA. 1991b. Soil vapor extraction: Air permeability testing and

estimation methods. In: Proceedings of the 17th RREL Hazardous

Waste Research Symposium. EPA/600/9-91/002. Washington, DC

(April).

U.S. EPA. 1986. Evaluation of the volatilization of hazardous constituents at hazardous waste land treatment sites. EPA/600/2-86/071.

Washington, DC.

van Eyk, J., and C. Vreeken. 1988. Venting-mediated removal of

petrol from subsurface soil strata as a result of stimulated evaporation and enhanced biodegradation. Med. Fac. Landbouww. Riiksuniv. Gent 53(4b): 1873-1884.

Ward, C.H. 1992. Performance and cost evaluation of bioremediation

techniques for fuel spills. In: Proceedings of In Situ Bioremediation

Symposium ’92. pp. 15-21.

50
Appendix A

Glossary

abiotic not relating to living things, not alive

acidity measure of the hydrogen ion concentration of

a solution

adsorption process by which molecules collect on

and adhere to the surface of an adsorbent solid because

of chemical and/or physical forces

aeration process of supplying or introducing air into a

medium such as soil or water

aerobic living, active, or occurring only in the presence of oxygen

air sparging technology of introducing gases, usually

air, beneath the water table to promote site remediation;

air sparging can be divided into two distinct processes:

in-well aeration and air injection

alkalinity measure of the hydroxide ion concentration

of a solution

alluvial relating to flowing water, as in a stream or

river

anaerobic living, active, or occurring only in the absence of oxygen

aquifer water-bearing layer of permeable rock, sand,

or gravel

bentonite clay composed of volcanic ash decomposition, which is used to seal wells

bioavailability accessibility of contaminants to the

degrading populations; consists of (1) a physical aspect

related to phase distribution and mass transfer and (2)

a physiological aspect related to the suitability of the

contaminant as a substrate

biodegradable material or compound that can be

broken down by natural processes of living things such

as metabolization by microorganisms

biodegradation act of breaking down material (usually into more innocuous forms) by natural processes of

living things such as metabolization by microorganisms

biofilm structure in which bacteria fixed to a surface

produce a protective extracellular polysaccharide layer

biofiltration process using microorganisms immobilized as a biofilm on a porous filter substrate, such as

peat or compost, to separate contaminants; as air and

vapor contaminants pass through the filter, contaminants transfer from the gas phase to the biolayer, where

they are metabolized

biomass amount of living matter (in a specified area)

bioreactor container or area in which a biological

reaction or biological activity takes place

bioreclamation process of making a contaminated

site usable again through biological processes

bioremediation technology of using biological processes such as microbial metabolism to degrade soil and

water contaminants and decontaminate sites

bioslurping technology application that teams vacuum-assisted free-product recovery with bioventing to

simultaneously recover free product and remediate the

vadose zone

bioventing process of aerating subsurface soils by

means of installed vents to stimulate in situ biological

activity and optimize bioremediation, with some volatilization occurring

capillarity action by which a liquid is held to a solid

by surface tension

capillary fringe first layer of rock above a layer in

which water is held by capillarity

catalyst substance that initiates a chemical reaction,

allows a reaction to proceed under different conditions

than otherwise possible, or accelerates a chemical reaction; catalysts are not consumed in the reaction; enzymes are catalysts

catalytic oxidation incineration process that uses

catalysts to increase the oxidation rate of organic contaminants, allowing equivalent destruction efficiency at

a lower temperature than flame incineration

clay fine-grained soil that can exhibit putty-like properties within a range of water content and is very strong

when air-dried

51
cometabolic process metabolism of a less-favored

substrate occurring during the metabolism of the primary substrate

cone of depression area of lowered water table

around a well site because of active pumping

contaminant something that makes material in contact with it impure, unfit, or unsafe; a pollutant

diffusion process of passive transport through a medium motivated by a concentration gradient

diffusivity diffusion coefficient; the amount of material, in grams, that diffuses across an area of 1 cm2

 in 1

second because of a unit concentration gradient (articular to compound and medium pair)

electron acceptor relatively oxidized compound that

takes electrons from electron donors during cellular respiration, resulting in the release of energy to the cell

electron donor organic carbon, or reduced inorganic

compound, that gives electrons to electron acceptors

during cellular respiration, resulting in the release of

energy to the cell

enzyme biologically produced, protein-based catalyst

ex situ refers to a technology or process for which

contaminated material must be removed from the site of

contamination for treatment

facultative microbial trait enabling aerobic or anaerobic respiration, depending on environment

head pressure difference between two places; an energy term expressed in length units

immiscible refers to liquids that do not form a single

phase when mixed (e.g., oil and water)

in situ refers to a technology or treatment process

that can be carried out within the site of contamination

in situ respiration test test used to provide rapid

field measurement of in situ biodegradation rates to

determine the potential applicability of bioventing at a

contaminated site and to provide information for a fullscale bioventing system design

in-well aeration process of injecting gas into a well to

produce an in-well airlift pump effect

miscible refers to liquids that form a single phase

when mixed (e.g., ethanol and water)

nitrogen fixation metabolic assimilation of atmospheric nitrogen by soil microorganisms and release of

the nitrogen for plant use upon the death of the microorganisms

nutrients constituents required to support life and

growth

off-gas gas that leaves a site, typically from a point

source during extraction operations

oxidation chemical process that results in a net loss

of electrons in an element or compound

oxygen utilization rate rate of reduction of the in situ

oxygen content of soil gas because of biological and

chemical action

ozonation injection of ozone into a contaminated site

packed-bed thermal treatment process that oxidizes

organic contaminants by passing the off-gas stream

through a heated bed of ceramic beads, resulting in

destruction of the organic compounds

perched aquifer unconfined ground water separated

from an underlying main body of ground water by a

low-permeability rock layer that blocks vertical movement of water

permeability measure of the ability of liquid or gas to

move through pores and openings in a material

pH measure of the alkalinity or acidity of a solution;

the negative log of the hydrogen ion concentration

photocatalytic oxidation process by which volatile

organic compounds are converted to carbon dioxide and

water by exposure to ultraviolet light

pore space open space in a material through which

liquid and gas can move

porosity measure of the amount of available space in

a material through which liquid and gas can move

primary substrate substrate that provides most of

the growth and energy requirements for cells

pump and treat technology treatment method in

which the contaminated water is pumped out of the

contaminated site, then treated off site before being

returned

radius of influence maximum distance from the air

extraction or injection well where vacuum or pressure

(soil gas movement) occurs

radius of oxygen influence radius to which oxygen

has to be supplied to sustain maximal biodegradation; a

function of air flow rates and oxygen utilization rates

and, therefore, depends on site geology, well design,

and microbial activity

Raoult’s law physical chemical law that states that

the vapor pressure of a solution is equal to the mole

fraction of the solvent multiplied by the vapor pressure

of the pure solvent

reduction chemical process that results in a net gain

of electrons to an element or compound

52
remediation activity involved with reducing the hazard from a contaminated site

sand unconsolidated rock and mineral particles with

diameters ranging from 1/16 mm to 2 mm

silt unconsolidated rock and mineral particles with

diameters ranging from 0.0002 mm to 0.05 mm

soil gas permeability soil’s capacity for fluid flow;

varies according to grain size, soil uniformity, porosity,

and moisture content

soil vacuum extraction (SVE) process designed and

operated to maximize the volatilization of low-molecularweight compounds, with some biodegradation occurring

sorb to take up or hold by means of adsorption or

absorption

substrate base on which an organism lives; reactant in

microbial respiration reaction (electron donor, nutrient)

surfactant substance that lowers the surface tension

of a liquid

treatability ability of a site to be remediated

vacuum-enhanced pumping use of a vacuum pump

to lift ground water, or other liquids or gases, from a well

while producing a reduced pressure in the well

vadose zone zone of soil below the surface and

above the permanent water table

volatile easily vaporized at relatively low temperatures

volatilization process of vaporizing a liquid into a gas

53
Appendix B

Equipment Specifications and Manufacturers

The products and manufacturers listed in this document

are meant as a guidance for environmental managers

and consulting engineers. Products or manufacturers

are not endorsed by the U.S. Air Force or EPA.

B.1 Soil Gas Survey Equipment

Calibration Gases

Calibration gases include helium, carbon dioxide, oxygen, and hexane. They are available in the appropriate

concentrations for each instrument and may require a

special regulator depending on the cylinder type.

The calibration gases are used to standardize the gas

analyzing instruments.

The gases are sold through Scott Specialty Gases in

Troy, Michigan, 313 589-2950. The gases cost approximately $124 depending on the cylinder size and gas

desired.

Tedlar Sampling Bag

The 1-L bag is made from transparent Tedlar and has a

polypropylene fitting. The bag is approximately 7x7 in.

and is sold in packages of 10. The fitting is opened and

closed by twisting the cap, which can also be locked into

place.

The Tedlar bag is used to store soil gas samples and

calibration gases until they can be analyzed by an appropriate gas meter.

The Tedlar bags are supplied by SKC, Eighty Four,

Pennsylvania, 800 752-8472. The cost is approximately

$82 for 10 bags.

Latex Rubber Tubing

Latex or amber tubing is connected to the Tedlar bag

tubing fitting for filling the bag. Tubing is normally cut

approximately 4 in. in length. Size of tubing is 1/4-in.

outside diameter x 3/16-in. inside diameter and can be

purchased from any VWR Scientific location.

Wire/Cable Ties

Nylon cable ties are used like a hose clamp for securing

the latex tubing to the Tedlar bag fitting. Cable ties can

be purchased from Grainger or any hardware store. The

catalog number is 6X750; ties are sold in packs of 100

at $1.91/pack.

Oxygen/Carbon Dioxide Gas Sampling Meter

This handheld instrument has a rechargeable battery

that lasts up to 16 hours. It has an oxygen and carbon

dioxide range of 0 percent to 25 percent. The meter has

an analog scale readout with audible and visual alarms

for low and high warning levels. The meter analyzes

oxygen content through an electrochemical cell and

carbon dioxide through an infrared sensor. An external

filter and an internal filter are employed for high reliability

and preventive maintenance. An internal diaphragm

pump is provided.

The gas sampling meter is used to determine the oxygen and carbon dioxide content of the ambient air or of

the gas within the soil. Calibrations must be performed

regularly with gas standards.

The meter is sold by Cascade Associates in Youngstown, Ohio, 216 758-6649. It costs approximately

$3,200.

Carry Case for Gas Sampling Meter

The case is of heavy plastic construction with foam

cushioning inside and can be secured with locks.

It is capable of protecting and carrying both the TraceTechtor and the gas sampling meter.

The case is sold by Cascade Associates in Youngstown,

Ohio, 216 758-6649. It costs approximately $250.

Combustibles Sampling Meter

This meter has a digital display screen with audible and

visual alarms for high- and low-level combustibles/

hydrocarbons. They are measured from 0 percent to 100

percent lower explosive limit (LEL) and 0 ppm to 10,000

ppm in 20-ppm increments. The meter uses both internal and external filters and includes an internal pump. In

55
addition, it has a data logging function, which allows the

meter to be connected with an IBM-compatible computer. It can be operated with alkaline or nicad batteries

that hold a 9-hour charge. The platinum catalyst sensor

has a flame arrestor.

The meter is used to determine the level of hydrocarbons or combustibles in the ambient air or sampled soil

gas. It is a new model that replaces the Trace-Techtor

meter.

The meter is sold by Cascade Associates in Youngstown, Ohio, 216 758-6649. It costs approximately

$1,475.

1:1 Diluter

The diluter is an external fitting that attaches to the inlet

of the Trace-Techtor meter. It has a metal construction

and is about 3 in. long. A diluter is required when the

oxygen levels of the gas sample drop below 12 percent.

At this low oxygen level, the platinum catalyst cannot

combust the gas sample properly.

The function of the 1:1 diluter is to reduce the gas

sample flow by one-half. This dilution reduces the concentration by one-half. Once a concentration reading is

obtained from the meter, it is multiplied by a factor of two

to compensate for the dilution.

The diluter is sold by Cascade Associates in Youngstown, Ohio, 216 758-6649. It costs approximately $150.

10:1 Diluter

This diluter is also an external fitting that attaches to the

inlet of the Trace-Techtor meter and is small enough to

hold in the hand. The diluter has two rotameters built

into it to permit a dilution factor up to 10. A diluter is

required when the oxygen levels of the gas sample drop

below 12 percent. At this low oxygen level, the platinum

catalyst cannot combust the gas sample properly. The

10:1 diluter can be used if the concentration of the

sample is still too high to be read after using a 1:1 diluter.

This is evident when the gas analysis instrument is

pegged on its highest setting.

The function of the 10:1 diluter is to reduce the gas

sample flow up to a factor of 10. The dilution factor is

set by adjusting the two rotameters until the ratio of the

two flows is equal to the dilution ratio. This reduces the

concentration by the same factor. Once a concentration

reading is obtained from the meter, it is multiplied by the

ratio to compensate for the dilution.

The diluter is sold by Cascade Associates in Youngstown, Ohio, 216 758-6649. It costs approximately $250.

Trace-Techtor Meter

This handheld instrument has a rechargeable battery

that lasts for 10 hours. It can measure petroleum-based

hydrocarbon vapors (BTEX) up to 10,000 ppm. It has an

analog scale readout with audible and visual alarms for

low and high concentration levels. The meter analyzes

the vapor through an electrochemical cell with a platinum catalyst. An external filter and an internal filter are

employed for preventive maintenance and high reliability. An internal diaphragm pump is also supplied.

The gas sampling meter is used to determine the petroleum hydrocarbon content of the ambient air or of the

gas within the soil. Calibrations must be performed regularly with hexane. The instrument can also be equipped

to detect methane or natural gas.

The meter was sold and manufactured by GasTech in

Newark, California, 415 794-1973. The price was approximately $1,500. The Trace-Techtor is no longer

manufactured, however.

Interface Probe

It is constructed in the shape of a disk, which stores a

100-ft measuring tape and a sensor probe. It weighs 16

lb, is 16x18x6 in., and is battery operated. The interface

probe resembles a common tape measure, only larger.

The interface probe is very useful when used alone with

soil gas probes during site investigation. The probe is

used in wells to detect the level at which both oil and

water are present. This is accomplished through the use

of audible alarms. The probe can detect an oil layer as

thin as 0.05 ft.

The interface probe is made by ORS Environmental

Systems in Greenville, New Hampshire, 800 228-2310.

It costs approximately $2,000.

150-Ft Tape Measure

A 150-ft fiberglass reel tape is needed for site mapping

during soil gas survey and is also used when measuring

borehole depths and monitoring point construction.

It is available from Grainger. The catalog number is

6C192, and the cost is $57.70.

Soil Gas Probes and Well Points (The Macho

System)

These are electric-powered sampling systems for driving soil gas probes. The deluxe system includes a variable-speed hammer drill and the capability to sample

soil gas to a depth of approximately 10 ft. This is a good

starter set; however, additional shafts, slotted well

points, and hollow probe nipples are also recommended. The system is available from KVA Analytical

56
Systems in Falmouth, Massachusetts, 508 540-0561.

The Macho System costs approximately $3,065.

Bulkhead Quick Coupler (Parker)

These brass fittings are threaded into the top of the soil

gas probe after driving to the desired depth. The fitting

gives the sampler an airtight connection between the

probe and the vacuum sampling pump, which pulls the

soil gas sample from the soil. The coupler is sold by

Forberg Scientific in Columbus, Ohio, 800 209-9575.

Diaphragm Pump (Vacuum/Air Compressor)

The pumps are usually wired for 110 volts for the

1/16-hp, 1/8-hp, and 1/3-hp versions. Gast produces

pumps and compressors that are preferred because of

their reliability and easy maintenance.

The pumps are used to draw soil gas from deep monitoring points and soil gas probes. We recommend the

1/3-hp pump because of the available air produced at

20 psi.

The pump is sold by Grainger in Columbus, Ohio, 800

323-0620. The cost depends on the size of the pump;

for the 1/3-hp pump, the catalog number is 4Z024, and

the cost is $228.

Probe Puller Adapter

The probe puller adaptor was made by Battelle staff. It

is a piece of square steel tubing approximately 4x4x2 in.

wide. A solid probe nipple is then welded in the middle

of one outside edge. The adaptor is threaded onto the

top of a soil gas probe when sampling is completed. A

large utility jack is placed inside the square tube, and

the probe is removed.

Utility Jack

The utility jack is used for removing soil gas probes

when sampling is completed. The jack is sold by Grainger, Columbus, Ohio, 800 323-0620. The catalog number is 5Z156, and the cost is $100.

Miscellaneous Supplies for Soil Gas Survey

Miscellaneous supplies include work gloves, safety

glasses, small measuring tape, crescent wrenches, pipe

wrenches, vise grips, field record book, cleaning supplies for cleaning soil gas probes, razor blades (single

edge), electrical tape, electrical extension cords, oil, and

fuel for the generator.

B.2 Vent Well Installation Equipment

Contracted Drilling Services

If a contract driller is installing the vent well and soil gas

monitoring points, the driller provides monitoring vent

well and well construction materials (sand and bentonite); however, the soil gas monitoring points need to

be furnished to the driller. If a contract driller is not used,

then items in this section will be necessary.

Hand Augering and Soil Sampling Equipment

A vent well can be installed by hard augering if soil

conditions permit. The following is a list of hard augering

equipment and equipment needed for collecting soils for

laboratory analysis.

Auger Head

It is constructed of stainless steel to resist corrosion and

contamination of soil samples. The head is approximately 1 ft long and is open on both ends to accommodate a soil sample liner. The bottom of the head is flared

to allow easy penetration into the ground, while the top

has a single bar with a male pipe thread. The male pipe

thread attaches to the auger’s extension rods.

The auger head is used to house the liner while the soil

is being sampled. It is designed to sample the soil with

minimal disturbance and effort.

The auger head is supplied by Enviro-Tech Services in

Martinez, California, 800 468-8921. It costs approximately $85.

Core Sampler With Slide Hammer

The core sampler is a metal pole with a soil sampler at

one end. On the other end is the slide hammer, a weight

that slides up and down the pole of the core sampler.

The core sampler is another way to obtain undisturbed

soil samples. The slide hammer drives the sampler into

the ground and eliminates the need for the auger head.

The items are supplied by Enviro-Tech Services in

Martinez, California, 800 468-8921. They cost approximately $225.

Sampling Extensions, Extension Cross Handle,

and Carry Case

The sampling extensions are long, metal poles that

connect the auger head to the cross handle with

threaded ends.

The extension cross handle is placed at the top of the

auger and is used for leverage to turn the auger into the

ground. It may have a rubber handle for increased grip.

57
The metal carry case is about 6 ft long and 1 ft tall and

holds the complete auger, disassembled. It has a foam

lining for protection during travel.

The equipment is supplied by Enviro-Tech Services in

Martinez, California, 800 468-8921. It costs approximately $400 for all three items.

Brass Sleeves and Plastic End Caps

The sleeve is a cylinder that is open at both ends. It

comes in various diameters and lengths. The caps are

orange and made from plastic to fit over each end of the

sleeve after being filled with soil.

The sleeve is placed inside the auger head and used as

a core sample liner. It contains the soil that is removed

by the auger. The end caps are placed on each end of

the sleeve after it is removed from the auger head. Brass

sleeves are also used in the core sampler with slide

hammer.

The sleeves and caps are supplied by Enviro-Tech Services in Martinez, California, 800 468-8921. The cost for

both items is approximately $3.

PVC Well Screen

Well screen constructed of polyvinyl chloride (PVC) is

flush-threaded at both ends to accommodate a threaded

plug and the riser pipe or blank well casing. Screens are

available in 10-, 20-, and 30-slot openings. Well screen

is also available in stainless steel.

The screen is sold by Environmental Well Products

Company in Dayton, Ohio, 800 777-0977. Price varies

with size and length.

PVC Riser

PVC riser or blank casing is also flush-threaded and has

no openings. It is merely an extension of pipe from the

well screen to the ground surface. It is sold by Environmental Well Products Company or any drilling supply

company.

Bentonite Chips

The chips are available in coarse grades or pellets in

small sizes. Common sizes include 0.375-in. and 0.75-

in. chips or pellets. They are made from dry bentonite

clay and sold in 50-lb bags. The bentonite is chemically

stable and can absorb large amounts of moisture.

The bentonite chips are placed around the necessary

equipment within the borehole to form a seal and act as

a general filler for the void space. Bentonite was selected because of its high water retention levels. It also

interfaces well with Portland cement.

The bentonite is sold by Environmental Well Products

Company in Dayton, Ohio, 800 777-0977. The price is

approximately $10 for 50 lb.

Silica Sand

The sand contains silica powder for increased chemical

stabilization. It is commonly found in the 10x20 graded

form.

The silica sand is another form of packing used in well

construction. The granular sand is added to boreholes

around the screened interval of the vent well and soil

gas monitoring points.

The sand is sold by Environmental Well Products Company in Dayton, Ohio, 800 777-0977. The price is approximately $6 for 50 lb.

Concrete Mix

The concrete requires only the addition of water and

sets quickly. The concrete is readily available in large

quantities throughout the country.

Concrete mix is placed around the manhole at ground

level of the well. This ensures its stability during extended absences.

The concrete is sold by Environmental Well Products

Company in Dayton, Ohio, 800 777-0977. The price is

approximately $4 for 50 lb. It is also available at most

building supply stores and hardware stores.

Manhole (Flushmount Well Cover)

Many companies manufacture manholes, some with

bolts to secure the top. They are usually sold in 8x12-in.

or 12x12-in. sizes and are made of iron, steel, or stainless steel. The bottom is designed to fit over the riser

pipe or soil gas monitoring points.

The manhole serves as a marker and gives added

protection to the well and the monitoring points.

The manhole is sold by Environmental Well Products

Company in Dayton, Ohio, 800 777-0977. The price is

approximately $50.

B.3 Soil Gas Monitoring Point Equipment

Contracted Drilling Services

If a contract driller is installing the vent well and soil gas

monitoring points, the driller provides monitoring vent

well and well construction materials (sand and bentonite); however, the soil gas monitoring points need to

be furnished to the driller. If a contract driller is not used,

then items in this section will be necessary.

58
Hand Augering and Soil Sampling

A vent well can be installed by hand augering if soil

conditions permit. The following is a list of hand augering

equipment and equipment needed for collecting soils for

laboratory analysis.

Auger Head

It is constructed of stainless steel to resist corrosion and

contamination of soil samples. The head is approximately 1 ft long and is open on both ends to accommodate a soil sample liner. The bottom of the head is flared

to allow easy penetration into the ground, while the top

has a single bar with a male pipe thread. The male pipe

thread attaches to the auger’s extension rods.

The auger head is used to house the liner while the soil

is being sampled. It is designed to sample the soil with

minimal disturbance and effort.

The auger head is supplied by Enviro-Tech Services in

Martinez, California, 800 468-8921. It costs approximately $85.

Core Sampler With Slide Hammer

The core sampler is a metal pole with a soil sampler at

one end. On the other end is the slide hammer, a weight

that slides up and down the pole of the core sampler.

The core sampler is another way to obtain undisturbed

soil samples. The slide hammer drives the sampler into

the ground and eliminates the need for the auger head.

The items are supplied by Enviro-Tech Services in

Martinez, California, 800 468-8921. They cost approximately $225.

Sampling Extensions, Extension Cross Handle,

and Carry Case

The sampling extensions are long, metal poles that

connect the auger head to the cross handle with

threaded ends.

The extension cross handle is placed at the top of the

auger and is used for leverage to turn the auger into the

ground. It may have a rubber handle for increased grip.

The metal carry case is about 6 ft long and 1 ft tall and

holds the complete auger, disassembled. It has a foam

lining for protection during travel.

The equipment is supplied by Enviro-Tech Services in

Martinez, California, 800 468-8921. The cost for all three

items is approximately $400.

Brass Sleeves and Plastic End Caps

The sleeve is a cylinder that is open at both ends. It

comes in various diameters and lengths. The caps are

orange and made from plastic to fit over each end of the

sleeve after being filled with soil.

The sleeve is placed inside the auger head and is used

as a core sample liner. It contains the soil that is removed by the auger. The end caps are placed on each

end of the sleeve after it is removed from the auger

head. Brass sleeves are also used in the core sampler

with slide hammer.

The sleeves and caps are supplied by Enviro-Tech Services in Martinez, California, 800 468-8921. The cost for

both items is approximately $3.

Suction Strainer

The suction strainer resembles an oxygen diffuser used

in fish tanks. It is approximately 0.75 in. in diameter and

8 in. long, constructed of a nylon frame with number 50

mesh screen to permit the flow of gases. The strainers

must be tapped with 3/8-in. national pipe thread (NPT)

to install the connector and nylon tubing.

The strainers are filled with aquarium gravel to ensure

the complete mixture of the soil gas as it is sampled. The

strainers are placed at the end of the nylon tubing and

set in the monitoring wells. There, they are used to

withdraw soil gas from the ground, free of dirt and

particulate.

The strainer is sold by Grainger in Columbus, Ohio, 800

323-0620. It costs approximately $7.

NEWLOC Male Connector

The male pipe thread connector is made of plastic and

has an opening on the end for 0.25-in. tubing. The other

end has 0.375-in. male pipe thread.

The connector is used to attach the suction strainer to

the nylon tubing in the monitoring wells.

The connector is supplied by New Age Industries in

Willow Grove, Pennsylvania, 215 657-3151. It costs

approximately $1.60.

Nylon Tubing

Often called Nylotube, it is made from nylon and sold in

various colors for identification purposes. Most common

applications of the tube involve the 0.25-in. size.

The tubing transports gases from monitoring points to

the surface for soil gas sampling and can be used on

some pieces of field equipment for similar purposes.

This type of tubing is favorable because it is inexpensive, is chemically resistant to hydrocarbons, and is

available in many colors. The tubing will adsorb some

small amount of hydrocarbons, however.

59
The tubing is supplied by New Age Industries in Willow

Grove, Pennsylvania, 215 657-3151. It costs approximately $0.36 per ft and is sold in 100-ft rolls.

Quick Connectors (Parker)

Male and female quick connectors and quick connector

plugs are compatible with different tube sizes. They are

made of brass or stainless steel. The quick connectors

offer easy access to monitoring points for taking soil gas

samples.

The quick connectors are attached to tubing when quick

and convenient access is desired. They also are installed on gas sampling instruments and on tubing found

at the monitoring wells. In addition, they provide a strong

seal to prevent leaking. The quick connector solid plugs

are placed in the female quick connectors to prevent

corrosion and other forms of damage.

The connectors are sold by Forberg Scientific in Columbus, Ohio, 614 294-4600. The price for the male connector

is approximately $6, and the female is approximately

$11.

Thermocouple Cable, K Type

The thermocouple cable is a 24-gauge wire insulated

with PVC. It can withstand temperatures up to 105°C. It

is usually sold by the foot.

The thermocouple is responsible for measuring temperatures, often within a soil gas monitoring point or an

outlet stream from a piece of field equipment. The cable

transmits the temperature through a current and is recorded using an electronic thermometer.

The cable is supplied by Cole-Parmer in Niles, Illinois,

800 323-4340. It costs approximately $0.80 per foot.

Thermocouple Minimale Plug

The type K minimale plug has two different prongs and

is attached to the thermocouple cable. It acts as a cable

termination. It is slightly smaller than a normal electrical

plug but serves the same purpose.

The plug is used to connect the thermocouple to the

electronic thermometer for data collection of temperatures.

The plug is supplied by Cole-Parmer in Niles, Illinois,

800 323-4340. It costs approximately $5.

Brass Tags

The tags are available in 1-in. to 2-in. sizes and in either

square or round shape. They are usually constructed of

19-gauge brass. The tags can be purchased with or

without labeling.

The tags are stamped, if unlabeled, using a kit and are

then placed on wells for identification purposes. They

may also be used to label items such as pipes and

valves.

The brass tags are manufactured by Seton Identification

in New Haven, Connecticut, 800 754-7360. They are

sold in packages of 25, for approximately $20 per package.

Tag Stamping Kit

Stamping kits are sold in sizes from 0.125 in. to 0.5 in.

They contain numbers and letters made from steel.

A hammer or mallet is used to stamp the tags with the

kit for custom identification.

The stamping kit is manufactured by Seton Identification

in New Haven, Connecticut, 800 754-7360. The kit costs

approximately $80.

Bentonite Chips

The chips are available in coarse grades or pellets in

small sizes. Common sizes include 0.375-in. and 0.75-

in. chips or pellets. They are made from dry bentonite

clay and sold in 50-lb bags. The bentonite is chemically

stable and can absorb large amounts of moisture.

The bentonite chips are placed around the necessary

equipment within the borehole to form a seal and act as

a general filler for the void space. Bentonite was selected because of its high water retention levels. It also

interfaces well with Portland cement.

The bentonite is sold by Environmental Well Products

Company in Dayton, Ohio, 800 777-0977. The price is

approximately $10 for 50 lb.

Silica Sand

The sand contains silica powder for increased chemical

stabilization. It is commonly found in the 10x20 graded

form.

The silica sand is another form of packing used in well

construction. The granular sand is added to boreholes

around the screened interval of the vent well and soil

gas monitoring points.

The sand is sold by Environmental Well Products Company in Dayton, Ohio, 800 777-0977. The price is approximately $6 for 50 lb.

Concrete Mix

The concrete requires only the addition of water and

sets quickly. The concrete is readily available in large

quantities throughout the country.

Concrete mix is placed around the manhole at the

ground level of the well. This ensures its stability during

extended absences.

60
The concrete is sold by Environmental Well Products

Company in Dayton, Ohio, 800 777-0977. The price is

approximately $4 for 50 lb. It is also available at most

building supply stores and hardware stores.

Manhole (Flushmount Well Cover)

Many companies manufacture manholes, some with

bolts to secure the top. They are usually sold in 8x12-in.

or 12x12-in. sizes and are made of iron, steel, or stainless steel. The bottom is designed to fit over the riser

pipe or soil gas monitoring points.

The manhole serves as a marker and gives added

protection to the well and the monitoring points.

The manhole is sold by Environmental Well Products

Company in Dayton, Ohio, 800 777-0977. The price is

approximately $50.

150-Ft Tape Measure

A 150-ft fiberglass reel tape is needed for site mapping

and measuring borehole depths and during monitoring

point sand and bentonite additions.

It is sold by Grainger in Columbus, Ohio, 800 323-0620.

The catalog number is 6C192, and the cost is $57.70.

Miscellaneous

Cable ties and electrical tape are useful for securing

thermocouple wires and nylon tubes together before

placing in open boreholes.

B.4 Air Permeability Test Equipment

Portable Generator

Several brands are available, and one with a maximum

of 5,500 watts is recommended. They may be available

with wheeled carts. Most have single-phase power

available in the two voltage ranges. Most smaller generators run on gasoline, while the larger have diesel

engines.

A portable generator is essential in a field operation

where electrical access is limited. It can power equipment such as external lighting, pumps, and power tools.

The generator is sold by Grainger in Columbus, Ohio,

800 323-0620. It costs approximately $2,200.

Blowers

Gast manufactures the recommended blowers. They

are oilless regenerative blowers that have a mounted

motor. The motors are equipped for different voltage

requirements.

The blowers are used during the injection or extraction

of air at a monitoring site. They should be equipped with

explosion-proof circuitry and mufflers where flammable

contamination exists.

The blower is sold by Isaacs in Columbus, Ohio, 614

885-8540. Blower costs vary according to size and

power. For example, a 2-hp, 145-cfm open flow blower

costs $1,100.

Rotameters/Flow Meters

Rotameters are transparent flow meters with the ability

to regulate flow. The tubes may be constructed from

plastic or glass. Each end has a female pipe thread

made from brass or plastic. The rotameters are available

for various liquid and gas flow levels. Both must be

installed in a vertical position for accurate readings.

The rotameter is designed to control the gas or liquid

flow rate. A flow meter indicates only the rate at which

liquid or gas is flowing.

The rotameter and flow meter are manufactured and

sold by King Instrument Company in Huntington Beach,

California, 714 841-3663. The prices vary by type but

are generally $100 to $200.

Fluke Thermocouple Thermometer

This handheld, electronic instrument is the size of a

large calculator and has a digital readout with an accuracy of 0.1 percent. It operates on a 9-volt battery and

has two ports for type K, minimale plugs. The thermometer has dual-point and differential capability.

The Fluke thermometer is used to record temperature

data from the thermocouples.

It is supplied by several companies, including Grainger

in Columbus, Ohio, 800 323-0620. It costs approximately $200.

Dwyer Magnehelic Gauges

Magnehelic gauges are used for recording negative or

positive pressure changes over time during the air permeability test. Four gauges mounted in a panel stand or

board should be plumbed in series to cover a wide range

of pressures. They are sold by Grainger in Columbus,

Ohio, 800 323-0620. Catalog numbers are 3T314,

3T317, 3T319, and 3T321, and the cost is approximately

$51 per gauge.

Five-Way Valves (Swagelok)

The five-way valve is installed on the magnehelic gauge

panel, which gives the sampler the ability to record

pressures from three points, one after another, simply

by turning the valve handle. The valve is sold by Scioto

Valve, 614 891-2617. The part number is B-43ZF2, and

the cost is approximately $90.

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Male Nonvalved Quick Couple Plug (Parker)

The fitting is connected to tubing from the five-way

valve. This plug plugs into the fitting, which is attached

to a soil gas monitoring point for measuring pressure

during the test. It is supplied by Forberg Scientific in

Columbus, Ohio, 614 294-4600. The part number is

4Z-Q4P-B, and the cost is $6.

Stopwatches

A stopwatch is necessary for each sampler who is recording pressures at a soil gas monitoring well. Pressures are recorded over time during the air permeability

test. Stopwatches can be purchased at most sporting

good stores or at Radio Shack. The cost is about $20.

B.5 In Situ Respiration Test Equipment

Portable Generator

Several brands are available, and one with a maximum

of 5,500 watts is recommended. They may be available

with wheeled carts. Most have single-phase power

available in the two voltage ranges. Most smaller generators run on gasoline, while the larger have diesel

engines.

A portable generator is essential in a field operation

where electrical access is limited. It can power equipment such as external lighting, pumps, and power tools.

The generator is sold by Grainger in Columbus, Ohio,

800 323-0620. It costs approximately $2,200.

Diaphragm Pump (Vacuum/Air Compressor)

The pumps are usually wired for 110 volts for the 1/16-

hp, 1/8-hp, and 1/3-hp versions. Gast produces the

pumps and compressors. They are preferred because

of their reliability and easy maintenance.

The pumps are used to draw soil gas from deep monitoring points and soil gas probes. The 1/3-hp pumps are

recommended because of the available air produced at

20 psi.

The pump is sold by Grainger in Columbus, Ohio, 800

323-0620. The cost depends on the size of the pump.

For the recommended 1/3-hp pump, the catalog number

is 4Z024, and the cost is $228.

Rotameters/Flow Meters

Rotameters are transparent flow meters with the ability

to regulate flow. The tubes may be constructed from

plastic or glass. Each end has a female pipe thread

made from brass or plastic.

The rotameters indicate the rate at which gas is flowing.

The flow meter used for in situ respiration testing is

connected to the backside of a 1/3-hp diaphragm pump.

The flow meter normally used is a 0.4-scfm to 4.0-scfm

meter sold by King Instruments Company, 714 841-

3663. The cost is approximately $48.

Helium Leak Detector

The helium leak detector is a rechargeable instrument

that can detect helium from 0.01 percent to 100 percent.

It operates in a three-stage process where the sample

enters the portable instrument, is analyzed, then is

purged to the atmosphere. The helium leak detector is

approximately 14x12x5 in. and weighs 7 lb. The instrument must be calibrated with helium gas.

The helium leak detector is used to detect the presence

of helium. Helium gas is injected into the ground during

a tracer test. From this test, an underground model of

the gas dispersion can be developed. The detector analyzes soil gas samples from the monitoring wells surrounding the helium injection site.

The leak detector is sold by Mark Products, Incorporated, in Sunnyvale, California, 800 621-4600. The price

is approximately $4,500.

Compressed Gas Helium 220 Ft3

Helium is mixed with the injection air for the in situ

respiration test at approximately 2-percent helium. Helium can be purchased from compressed gas suppliers

or a welding supplier. The cost per cylinder is $60.

Helium Cylinder Regulator

A two-stage cylinder regulator is necessary for connecting and dispensing the compressed helium gas. The

correct connection for cylinder to regulator is a GA 580.

Regulators can be purchased through the compressed

gas supplier. The cost is approximately $180.

Helium/Air Mixing Manifold

The 2-percent helium mix in air is accomplished by using

a 1-in. inside diameter pipe closed at one end with four

tubing connectors, which would be plumbed to the diaphragm pumps. The open end of the pipe is where

atmospheric air is drawn in for the diaphragm pumps; a

tubing connection is installed into the pipe at about 6 in.

from the open end. This connection is for the helium

supply to enter the manifold and be swept by incoming

air. Helium concentrations need to be measured at the

pressure side of the diaphragm pump; if concentration

is too high or low, adjust at the helium regulator. This

item is not commercially available.

62
Calibration Gases

Calibration gases include helium, carbon dioxide, oxygen, and hexane. They are available in the appropriate

concentrations for each instrument and may require a

special regulator depending on the cylinder type.

The calibration gases are used to standardize the gas

analyzing instruments.

The gases are sold through Scott Specialty Gases in

Troy, Michigan, 313 589-2950. The gases cost approximately $124 depending on the cylinder size and gas

desired.

Tedlar Sampling Bag

The 1-L bag is made from transparent Tedlar and has a

polypropylene fitting. The bag is approximately 7x7 in.

and is sold in packages of 10. The fitting is opened and

closed by twisting the cap, which can also be locked into

place.

The Tedlar bag is used to store soil gas samples and

calibration gases until they can be analyzed by an appropriate gas meter.

The Tedlar bags are supplied by SKC, Eighty Four,

Pennsylvania, 800 752-8472. The cost is approximately

$82 for 10 bags.

Fluke Thermocouple Thermometer

This handheld, electronic instrument is the size of a

large calculator and has a digital readout with an accuracy of 0.1 percent. It operates on a 9-volt battery and

has two ports for type K, minimale plugs. The thermometer has dual-point and differential capability.

The Fluke thermometer is used to record temperature

data from the thermocouples.

The Fluke meter is supplied by several companies including Grainger in Columbus, Ohio, 800 323-0620. It

costs approximately $200.

Pressure and Vacuum Gauges

Pressure gauges are installed with the flow meters for

air injection. When flow is recorded, the pressure needs

to be recorded as well. Vacuum gauges are used on the

diaphragm pump that is used for withdrawing soil gas

samples from monitoring points; the vacuum is also

recorded while collecting soil gas sample. The gauges

are sold by Grainger in Columbus, Ohio, 800 323-0620.

The catalog number is 1A318, and the cost is less than

$20 per gauge.

Oxygen/Carbon Dioxide Gas Sampling Meter

This handheld instrument has a rechargeable battery

that lasts up to 16 hours. It has an oxygen and carbon

dioxide range of 0 percent to 25 percent. The meter has

an analog scale readout with audible and visual alarms

for low and high warning levels. The meter analyzes

oxygen content through an electrochemical cell and

carbon dioxide through an infrared sensor. An external

filter and an internal filter are employed for high reliability

and preventive maintenance. An internal diaphragm

pump is also provided.

The gas sampling meter is used to determine the oxygen and carbon dioxide content of the ambient air or of

the gas within the soil. Calibrations must be performed

regularly with gas standards.

The meter is sold by Cascade Associates in Youngstown, Ohio, 216 758-6649. It costs approximately

$3,200.

Carry Case for Gas Sampling Meter

The case is of heavy plastic construction with foam

cushioning inside and can be secured with locks.

It is capable of protecting and carrying both the TraceTechtor and the gas sampling meter.

The case is sold by Cascade Associates in Youngstown,

Ohio, 216 758-6649. It costs approximately $250.

Combustibles Sampling Meter

This meter has a digital display screen with audible and

visual alarms for high- and low-level combustibles/

hydrocarbons. They are measured from 0 percent to 100

percent LEL and 0 ppm to 10,000 ppm in 20-ppm increments. The meter uses both internal and external filters

and includes an internal pump. In addition, it has a data logging function, which permits the meter to be connected

with an IBM-compatible computer. It can be operated

with alkaline or nicad batteries that hold a 9-hour charge.

The platinum catalyst sensor has a flame arrestor.

The meter is used to determine the level of hydrocarbons or combustibles in the ambient air or sampled soil

gas. It is a new model that replaces the Trace-Techtor

meter.

The meter is sold by Cascade Associates in Youngstown, Ohio, 216 758-6649. It costs approximately

$1,475. For information on other distributors of GasTech

Instruments, call GasTech at 510 794-6200.

1:1 Diluter

The diluter is an external fitting that attaches to the inlet

of the Trace-Techtor meter. It has a metal construction

and is about 3-in. long. A diluter is required when the

oxygen levels of the gas sample drop below 12 percent.

At this low oxygen level, the platinum catalyst cannot

combust the gas sample properly.

63
The function of the 1:1 diluter is to reduce the gas

sample flow by one-half. This dilution reduces the concentration by one-half. Once a concentration reading is

obtained from the meter, it is multiplied by a factor of two

to compensate for the dilution.

The diluter is sold by Cascade Associates in Youngstown, Ohio, 216 758-6649. It costs approximately $150.

10:1 Diluter

This diluter is also an external fitting that attaches to the

inlet of the Trace-Techtor meter and is small enough to

hold in the hand. The diluter has two rotameters built

into it to permit a dilution factor up to 10. A diluter is

required when the oxygen levels of the gas sample drop

below 12 percent. At this low oxygen level, the platinum

catalyst cannot combust the gas sample properly. The

10:1 diluter can be used if the concentration of the

sample is still too high to be read after using a 1:1 diluter.

This is evident when the gas analysis instrument is

pegged on its highest setting.

The function of the 10:1 diluter is to reduce the gas

sample flow up to a factor of 10. The dilution factor is

set by adjusting the two rotameters until the ratio of the

two flows is equal to the dilution ratio. This reduces the

concentration by the same factor. Once a concentration

reading is obtained from the meter, it is multiplied by the

ratio to compensate for the dilution.

The diluter is sold by Cascade Associates in Youngstown, Ohio, 216 758-6649. It costs approximately

$250.

B.6 Miscellaneous Items

Teflon Thread Tape

The white tape is made of Teflon and comes in rolls of

0.25-in., 0.5-in., and 1-in. widths.

The tape is wrapped over pipe threading to prevent

leaking of liquids and gases. 

The tape is supplied by U.S. Plastics Corporation in

Lima, Ohio, 800 357-9724. It costs approximately $1.

PVC Piping Supplies

PVC pipe is needed in various diameters up to 6 in. Most

piping used is schedule 40 and in 10-ft or 20-ft lengths.

Some of the supplies, including valves, tees, and couplings, may be needed as schedule 80 PVC.

The PVC piping is used to transport gases, usually air,

to vent wells or to transport liquids from contaminated

wells.

The items are supplied by U.S. Plastics Corporation in

Lima, Ohio, 800 357-9724. The costs are dependent

upon the specific piping size, length, and schedule

required.

PVC Pipe Cement and Primer

The PVC primer is a volatile, clear liquid that is applied

using a small sponge. The PVC cement is a viscous,

gray liquid also applied with a sponge. Both have a

strong odor that can be harmful if the primer is used

without proper ventilation.

The primer is used to clean and prime the PVC before

assembly. After the primer dries, the cement is applied

to connect the PVC pieces. The PVC cement is quick

to set.

The items are supplied by U.S. Plastics Corporation in

Lima, Ohio, 800 357-9724. For both the cement and

primer, the cost is approximately $20.

Pipe Fittings

Many different types and sizes of pipe fitting are needed

for pump connections and tubing connections. Grainger

has a large selection in its catalog of steel and brass

pipe fittings that are reasonably priced.

B.7 Optional Items

Soil Moisture Meter

The soil moisture meter is an electronic, handheld instrument that operates from a 9-volt battery. Two spring

terminals are at the top of the meter for connecting the

moisture blocks.

The meter gives a digital display of the soil moisture

content in a percentage obtained from the soil moisture

blocks.

The meter is supplied by Soilmoisture Equipment Corporation in Santa Barbara, California, 805 964-3525. It

costs approximately $310.

Soil Moisture Blocks

They consist of a lead wire connected to the gypsum

block, which is in the shape of a 1-in. diameter cylinder.

The blocks have a life expectancy of 3 to 5 years. The

gypsum can compensate for varying salinity conditions.

The blocks are placed in the soil to transmit the soil

moisture content to the soil moisture meter using an

electric current. They are available in different lengths

and are installed along with the soil gas monitoring

points.

The block is supplied by Soilmoisture Equipment Corporation in Santa Barbara, California, 805 964-3525. It

costs approximately $15.

64
Bailer

Constructed of Teflon, PVC, or stainless steel, the bailers are available from 1-ft to 4-ft lengths. Teflon is preferred for its chemical inert properties and low cost.

The bailers are lowered into the wells with cords or rope

to remove water or other standing liquids. The well must

be dry to install the screens and suction strainers. Otherwise, no soil gas sampling can occur because of the

presence of the liquid(s).

The bailer is sold by Environmental Well Products Company in Dayton, Ohio, 800 777-0977. The price is approximately $140.

65
Appendix C

Example Procedures for Conducting Bioventing Treatability Studies

C.1 Example Procedures for Collecting,

Labeling, Packing, and Shipping Soil

Samples

C.1.1 Sample Collection

Soil samples are usually collected from split-spoon samplers during soil-boring operations or with handheld soil

augers. Regardless of how samples are collected, all

equipment must be decontaminated before and after

collection of each sample.

C.1.1.1 Equipment Decontamination

• Sampler is thoroughly washed.

• Sampler is rinsed with deionized or distilled water.

• Sampler is rinsed with methanol and allowed to air dry.

• Rinsates are disposed of in an environmentally sound

manner.

C.1.1.2 Sample Collection

• At a minimum, rubber or vinyl gloves should be worn

to collect the sample. If higher levels of contamination

are anticipated, nitrile or nitrocellulose gloves should

be worn in addition to other appropriate safety gear

as indicated in the site health and safety plan.

• During processing of soil samples, the work area

should be covered with vinyl or plastic. Between samples, the work area should be cleaned of soil residues. The work area should be positioned upwind of

the test area or drill rig.

• For split-spoon sampling, the soil core is usually retained in the stainless steel or brass sampling tube.

The tube should be capped top and bottom after a

Teflon liner or its equivalent has been placed over the

exposed soil.

• If the soil is to be transferred to other containers such

as those listed below for various analysis types, the

sample should be scooped directly into the sample

container. If organic analyses are to be performed,

the scoop should be stainless steel. A soil core sample should be spooned or scooped directly from the

container (e.g., coring tube, split spoon) into the sample container.

• If a gloved hand comes into contact with the sample,

then new gloves should be used for each sample. In

addition, a background sample that contacts a glove

should be collected as a control.

C.1.1.3 Split Samples

A homogeneous mix for a split soil sample can be

obtained by mixing soil in a stainless steel pan and filling

both sample containers with alternate spoonfuls. If a

sample is collected for trace volatile analysis, however,

too much sample agitation and mixing can drive off the

compounds of concern. Consequently, if a split spoon or

other soil sample for volatile organic analysis is to be

split and concern arises that the above homogenization

would result in the loss of trace volatile compounds, an

alternate splitting technique should be used. The undisturbed core or soil should be spooned directly into the

two jars by alternating spoonfuls between the sample

and the split container. This ensures a fairly even split

while reducing the agitation and exposure of the sample

surface area.

C.1.1.4 Sample Containers and Sample Size

Soil samples should be stored in appropriate containers

as indicated in the site test plant or as directed by the

analytical laboratory. For sample size requirements, refer to the site test plan or ask personnel in the analytical

laboratory. Some suggested container types and sample sizes include:

• Volatiles: Glass jar, wide mouth, Teflon-faced cap,

125-mL capacity, 100-g sample volume minimum.

• Semivolatiles: Glass jar, wide mouth, Teflon-faced

cap, 125-mL capacity, 100-g sample volume minimum.

• Metals: High-density polyethylene (HDPE) or glass

wide-mouth jar.

• Other: For other soil analysis types, including particle-size analysis, nutrient analysis, and moisture determination, samples can be stored in metal, plastic,

or glass containers.

67
C.1.2 Sample Label and Log

A sample must be labeled with all information that would

be required by personnel working with the sample. Refer

to the test/project plan for labeling instructions. At a

minimum, the samples should be labeled with the following information:

• Test site where sample was collected.

• Soil boring number or identification number.

• Soil sampling depth.

• Initials of sampler.

• Date and time of collection.

• Information to be recorded in the log/record book:

specific equipment used, sampler, date and time, and

any observations about the sampled material or meter readings taken.

C.1.3 Sample Packing and Shipping

• The soil samples should be placed in plastic bags

and put in a refrigerator, ice chest, or insulated box

on ice immediately after being placed in an appropriate container and labeled. Ensure that sample containers and bags are tightly closed and that they

contain sufficient ice to maintain refrigerated conditions until samples arrive at the laboratory.

• Control samples and field blanks should not be

shipped with contaminated samples.

• Chain-of-custody forms should be completed for each

cooler.

• Samples should be shipped to arrive within 24 hours

whenever possible. Shipment should be made by

Federal Express (when possible), using Priority Overnight Service with Saturday deliveries specified if applicable.

• Recipients should be notified about specifics of

shipment.

C.1.4 Quality Control

• Descriptions and dates of all of the above activities

should be documented in study records.

• Soil analysis information should be included in the

study records. Photographs should be taken periodically and retained with the study records.

• Records should be kept as indicated in this procedure

and should be periodically reviewed by the study/task

leader.

C.2 Example Procedures for in Situ

Respiration Testing

C.2.1 Field Instrumentation and

Measurement

C.2.1.1 Oxygen and Carbon Dioxide

Gaseous concentrations of carbon dioxide and oxygen

should be analyzed using a GasTech model 3252OX

carbon dioxide/oxygen analyzer or equivalent. The battery charge level should be checked to ensure proper

operation. The air filters should be checked and, if necessary, cleaned or replaced before starting the experiment. The instrument should be turned on and

equilibrated for at least 30 minutes before conducting

calibration or obtaining measurements. The sampling

pump of the instrument should be checked to ensure

that it is functioning properly. Low flow of the sampling

pump may indicate that the battery level is low or that

some fines are trapped in the pump or tubing.

Each day before use, meters should be calibrated

against purchased carbon dioxide and oxygen calibration standards. These standards should be in the concentration range of the soil gas to be sampled. The

carbon dioxide calibration should be performed against

atmospheric carbon dioxide (0.05 percent) and a 5 percent standard. The oxygen should be calibrated using

atmospheric oxygen (20.9 percent) and against a 5

percent and 0 percent standard. Standard gases should

be purchased from a specialty gas supplier. To calibrate

the instrument with standard gases, a Tedlar bag (capacity approximately 1 L) should be filled with the standard gas and the valve on the bag should be closed. The

inlet nozzle of the instrument should be connected to the

Tedlar bag, and the valve on the bag should be opened.

The instrument should then be calibrated against the

standard gas according to the manufacturer’s instructions. Next, the inlet nozzle of the instrument should be

disconnected from the Tedlar bag, and the valve on the

bag should be shut off. The instrument should be rechecked against atmospheric concentration. If recalibration is required, the above steps should be repeated.

C.2.1.2 Hydrocarbon Concentration

Petroleum hydrocarbon concentrations should be analyzed using a GasTech Trace-Techtor hydrocarbon analyzer (or equivalent) with range settings of 100 ppm,

1,000 ppm, and 10,000 ppm. The analyzer should be

calibrated against two hexane calibration gases (500

ppm and 4,400 ppm). The Trace-Techtor has a dilution

fitting that can be used to calibrate the instrument in the

low-concentration range.

Calibration of the GasTech Trace-Techtor is similar to

the GasTech Model 32402X, except that a mylar bag is

68
used instead of a Tedlar bag. The oxygen concentration

must be above 10 percent for the Trace-Techtor analyzer to be accurate. When the oxygen drops below 10

percent, a dilution fitting must be added to provide adequate oxygen for analysis.

Hydrocarbon concentrations can also be determined

with a flame ionization detector (FID), which can detect

low (below 100 ppm) concentrations. A photoionization

detector (PID) is not acceptable.

C.2.1.3 Helium Monitoring

Helium in the soil gas should be measured with a Marks

Helium Detector Model 9821 or equivalent with a minimum sensitivity of 100 ppm (0.01 percent). Calibration

of the helium detector follows the same basic procedure

described for oxygen calibration, except that the setup

for calibration is different. Helium standards used are

100 ppm (0.01 percent), 5,000 ppm (0.5 percent), and

10,000 ppm (1 percent).

C.2.1.4 Temperature Monitoring

In situ soil temperature should be monitored using

Omega Type J or K thermocouples (or equivalent). The

thermocouples should be connected to an Omega OM400 Thermocouple Thermometer (or equivalent). The

contractor should calibrate each thermocouple against

ice water and boiling water before field installation.

C.2.1.5 Air Flow Measurement

Before initiating respiration tests at individual monitoring

points, air should be pumped into each monitoring point

using a small air compressor. Air flow rates of 1 cfm to

1.5 cfm should be used, and flow should be measured

using a Cole-Palmer Variable Area Flowmeter No.

N03291-4 (or equivalent). Helium should be introduced

into the injected air at a 1 percent concentration. A

helium flow rate of approximately 0.01 cfm to 0.015 cfm

(0.6 cfm to 1.0 cfh) is required to achieve this concentration. A Cole-Palmer Model L-03291-00 flow meter or

equivalent should be used to measure the flow rate of

the helium feed stream.

C.2.2 In Situ Respiration Test Procedures

The in situ respiration test should be conducted using a

minimum of four screened intervals of the monitoring

points and a background well. The results from this test

determine if in situ microbial activity is occurring and if

it is oxygen-limited.

C.2.2.1 Test Implementation

Air with 1 percent to 2 percent helium should be injected

into the monitoring points and background well. Following injection, the change of oxygen, carbon dioxide,

total hydrocarbon, and helium in the soil gas should be

measured over time. Helium should be used as an inert

tracer gas to assess the extent of diffusion of soil gases

within the aerated zone. If the background well is

screened over an interval of greater than 10 ft, the

required air injection rate may be too high to allow

helium injection. The background monitoring point

should be used to monitor natural degradation of organic

matter in the soil.

The oxygen, carbon dioxide, and total hydrocarbon levels will be measured at the monitoring points before air

injection. Normally, air is injected into the ground for at

least 20 hours at rates ranging from 1.0 cfm to 1.7 cfm

(60 cfh to 100 cfh). Blowers should be diaphragm compressors Model 4Z024 from Grainger (or equivalent)

with a nominal capacity of 1.7 cfm (100 cfh) at 10 psi.

The helium used as a tracer should be 99 percent or

greater purity, which is available from most welding

supply stores. The flow rate of helium should be adjusted to 0.6 cfh to 1.0 cfh to obtain about 1 percent in

the final air mixture that is injected into the contaminated

area. Helium in the soil gas should be measured with a

Marks Helium Detector Model 9821 (or equivalent) with

a minimum sensitivity of 0.01 percent.

After air and helium injection is completed, the soil gas

should be measured for oxygen, carbon dioxide, helium,

and total hydrocarbon. Soil gas should be extracted from

the contaminated area with a soil gas sampling pump

system. Typically, measurement of the soil gas should

be conducted after 2, 4, 6, and 8 hours and then every

4 to 12 hours, depending on the rate of the oxygen use.

If oxygen uptake is rapid, more frequent monitoring is

required. If it is slower, less frequent readings are acceptable.

At shallow monitoring points, atmospheric air might be

pulled in during purging and sampling. Excessive purging and sampling may result in erroneous readings.

Oversampling offers no benefits, so care should be

taken to minimize the volume of air extraction when

sampling shallow points. In these cases, a low-flow

extraction pump of about 0.03 cfm to 0.07 cfm (2.0 cfh

to 4.0 cfh) should be used. Field judgment is required at

each site in determining the sampling frequency.

The in situ respiration test should be terminated when

the oxygen level is about 5 percent, or after 5 days of

sampling. The temperature of the soil before air injection

and after the in situ respiration test should be recorded.

C.2.2.2 Data Interpretation

Data from the in situ respiration tests should be summarized and their oxygen utilization rates computed.

C.2.3 Quality Control

• Descriptions and dates of all of the above activities

should be documented in study records.

69
• Soil analysis information should be included in the

study records. Photographs should be taken periodically and retained with the study records.

• Records should be kept as indicated in this procedure

and should be periodically reviewed by the study/task

leader.

C.3 Example Procedures for Soil Gas

Permeability Testing

C.3.1 Field Instrumentation and

Measurement

C.3.1.1 Oxygen and Carbon Dioxide

Gaseous concentrations of carbon dioxide and oxygen

should be analyzed using a GasTech model 3252OX

carbon dioxide/oxygen analyzer or equivalent. The battery charge level should be checked to ensure proper

operation. The air filters should be checked and, if necessary, cleaned or replaced before starting the experiment. The instrument should be turned on and

equilibrated for at least 30 minutes before conducting

calibration or obtaining measurements. The sampling

pump of the instrument should be checked to ensure

that it is functioning properly. Low flow of the sampling

pump can indicate that the battery level is low or that

some fines are trapped in the pump or tubing.

Each day before use, meters should be calibrated

against purchased carbon dioxide and oxygen calibration standards. These standards should be in the concentration range of the soil gas to be sampled. The

carbon dioxide calibration should be performed against

atmospheric carbon dioxide (0.05 percent) and a 5 percent standard. The oxygen should be calibrated using

atmospheric oxygen (20.9 percent) and against a 5

percent and 0 percent standard. Standard gases should

be purchased from a specialty gas supplier. To calibrate

the instrument with standard gases, a Tedlar bag (capacity approximately 1 L) should be filled with the standard gas and the valve on the bag should be closed. The

inlet nozzle of the instrument should be connected to the

Tedlar bag, and the valve on the bag should be opened.

The instrument should then be calibrated against the

standard gas according to the manufacturer’s instructions. Next, the inlet nozzle of the instrument should be

disconnected from the Tedlar bag, and the valve on the

bag should be shut off. The instrument should be rechecked against atmospheric concentration. If recalibration is required, the above steps should be repeated.

C.3.1.2 Hydrocarbon Concentration

Petroleum hydrocarbon concentrations should be analyzed using a GasTech Trace-Techtor hydrocarbon analyzer (or equivalent) with range settings of 100 ppm,

1,000 ppm, and 10,000 ppm. The analyzer should be

calibrated against two hexane calibration gases (500

ppm and 4,400 ppm). The Trace-Techtor has a dilution

fitting that can be used to calibrate the instrument in the

low-concentration range.

Calibration of the GasTech Trace-Techtor is similar to

the GasTech Model 32402X, except that a mylar bag is

used instead of a Tedlar bag. The oxygen concentration

must be above 10 percent for the Trace-Techtor analyzer to be accurate. When the oxygen drops below 10

percent, a dilution fitting must be added to provide adequate oxygen for analysis.

Hydrocarbon concentrations can also be determined

with a flame ionization detector (FID), which can detect

low (below 100 ppm) concentrations. A photoionization

detector (PID) is not acceptable.

C.3.1.3 Pressure/Vacuum Monitoring

Changes in soil gas pressure during the air permeability

test should be measured at monitoring points using

Magnehelic or equivalent gauges. Tygon or equivalent

tubing should be used to connect the pressure/vacuum

gauge to the quick-disconnect on the top of each monitoring point. Similar gauges should be positioned before

and after the blower unit to measure pressure at the

blower and at the head of the venting well. Pressure

gauges are available in a variety of pressure ranges,

and the same gauge can be used to measure either

positive or negative (vacuum) pressure by switching

inlet ports. Gauges are sealed and calibrated at the

factory and should be rezeroed before each test. The

following pressure ranges (in inches H2O) typically are

available for this field test:

0-1”, 0-5”, 0-10”, 0-20”, 0-50”, 0-100”, and 0-200”

Air pressure during injection for the in situ respiration

test should be measured using a pressure gauge with a

minimum range of 0 psig to 30 psig.

C.3.1.4 Air Flow Measurement

During the air permeability test, an accurate estimate of

flow (Q) entering or exiting the vent well is required to

determine k and RI. Several air flow measuring devices

are acceptable for this test procedure.

Pitot tubes or orifice plates combined with an inclined

manometer or differential pressure gauge are acceptable for measuring flow velocities of 1,000 ft/min or

greater (approximately 20 scfm in a 2-in. pipe). For lower

flow rates, a large rotameter provides a more accurate

measurement. If an inclined manometer is used, the

manometer must be rezeroed before and after the test

to account for thermal expansion/contraction of the

water. Devices to measure static and dynamic pressure

must also be installed in straight pipe sections according

70
to manufacturer’s specifications. All flow rates should be

corrected to standard temperature and ambient pressure (altitude) conditions.

C.3.2 Soil Gas Permeability Test Procedures

This section describes the field procedures that will be

used to gather data to determine k and to estimate RI.

Before initiating the soil gas permeability test, the site

should be examined for any wells (or other structures)

that will not be used in the test but may serve as vertical

conduits for gas flow. These should be sealed to prevent

short-circuiting and to ensure the validity of the soil gas

permeability test.

C.3.2.1 System Check

Before proceeding with this test, soil gas samples

should be collected from the vent well, the background

well, and all monitoring points, and analyzed for oxygen,

carbon dioxide, and volatile hydrocarbons. After the

blower system has been connected to the vent well and

the power has been hooked up, a brief system check

should be performed to ensure proper operation of the

blower and the pressure and air flow gauges, and to

measure an initial pressure response at each monitoring

point. This test is essential to ensure that the proper

range of Magnehelic gauges is available for each monitoring point at the onset of the soil gas permeability test.

Generally, a 10-minute to 15-minute period of air extraction or injection is sufficient to predict the magnitude of

the pressure response and the ability of the blower to

influence the test volume.

C.3.2.2 Soil Gas Permeability Test

After the system check, and when all monitoring point

pressures have returned to zero, the soil gas permeability test should begin. Two people are required during the

initial hour of this test. One person reads the Magnehelic

gauges, and the other person records pressure (P′)

versus time on the example data sheet. Designating one

person for each test improves the consistency in reading

the gauges and reduces confusion. Typically, the following test sequence is followed:

1. Connect the Magnehelic gauges to the top of each

monitoring point with the stopcock opened. Return

the gauges to zero.

2. Turn the blower unit on, and record the starting time

to the nearest second.

3. At 1-minute intervals, record the pressure at each

monitoring point, beginning at t = 60 s.

4. After 10 minutes, extend the interval to 2 minutes.

Return to the blower unit, and record the pressure

reading at the well head, the temperature readings,

and the flow rate from the vent well.

5. After 20 minutes, measure P′ at each monitoring

point in 3-minute intervals. Continue to record all

blower data at 3-minute intervals during the first hour

of the test.

6. Continue to record monitoring point pressure data at

3-minute intervals until the 3-minute change in P′ is

less than 0.1 in. of H2O. At this time, a 5-minute to

20-minute interval can be used. Review data to ensure accurate data were collected during the first 20

minutes. If the quality of these data is in question,

turn off the blower, allow all monitoring points to

return to zero pressure, and restart the test.

7. Begin to measure pressure at any ground-water

monitoring points that have been converted to monitoring points. Record all readings, including zero

readings and the time of the measurement. Record

all blower data at 30-minute intervals.

8. Once the interval of pressure data collection has

increased, collect soil gas samples from monitoring

points and the blower exhaust (if extraction system),

and analyze for oxygen, carbon dioxide, and hydrocarbons. Continue to gather pressure data for 4 to 8

hours. The test normally continues until the outermost monitoring point with a pressure reading does

not increase by more than 10 percent over a 1-hour

interval.

9. Calculate the values of k and RI with the data from

the completed test; use of the HyperVentilate computer program is recommended.

C.3.2.3 Soil Gas Monitoring After the

Permeability Test

Immediately after completion of the permeability test,

soil gas samples should be collected from the vent well,

the background well, and all monitoring points, and

analyzed for oxygen, carbon dioxide, and hydrocarbons.

If the oxygen concentration in the vent well has increased by 5 percent or more, oxygen and carbon dioxide should be monitored in the vent well in a manner

similar to that described for the monitoring points in the

in situ respiration test. (Initial monitoring may be less

frequent.) The monitoring should provide additional in

situ respiration data for the site.

C.3.3 Quality Control

• Descriptions and dates of all of the above activities

should be documented in study records.

• Soil analysis information should be included in the

study records. Photographs should be taken periodically and retained with the study records.

• Records should be kept as indicated in this procedure

and should be periodically reviewed by the study/task

leader.

71
C.4 References

Hinchee, R.E., and S.K. Ong. 1992. A rapid in situ respiration test for

measuring aerobic biodegradation rates of hydrocarbons in soil,

J. Air & Waste Management Association 42(10):1305-1312.

Hinchee, R.E., S.K. Ong, R.N. Miller, D.C. Downey, and R. Frandt.

1992. Test plan and technical protocol for a field treatability test

for bioventing, Rev. 2. U.S. Air Force Center for Environmental

Excellence, Brooks Air Force Base, TX.

Johnson, P.C., M.W. Kemblowski, and J.D. Colthart. 1990. Quantitative analysis for the cleanup of hydrocarbon-contaminated soils

by in-situ soil venting. Ground Water 28(3).

U.S. EPA. 1991. Soil vapor extraction: Air permeability testing and

estimation methods. In: Proceedings of the 17th RREL Hazardous

Waste Research Symposium. EPA/600/9-91/002. Washington,

DC.

72
Appendix D

Off-Gas Treatment Options

D.1 Introduction

Off-gas treatment typically is not a component of

bioventing systems. Bioventing systems are usually

configured to inject air into the in situ soil mass. The

injected air then moves through the soil to act as an

oxygen source for microbial activity. The bioventing injection air flow rate is low and is selected to minimize

discharge from the surface while providing an adequate

supply of oxygen for the organisms.

Air injection is the preferred bioventing configuration;

however, air extraction may be necessary at sites where

air emissions or movement of vapors into subsurface

structures are difficult to control. If a building or other

structure is located within the radius of influence of a

site, or if the site is near a property boundary beyond

which hydrocarbon vapors cannot be pushed, air extraction may be considered. A significant disadvantage of

the air extraction configuration is that biodegradation is

limited to the contaminated soil because vapors do not

move outward and create an expanded bioreactor. The

result is less biodegradation and more volatilization. In

general, increasing extraction rates increases both volatilization and biodegradation rates until the site becomes

aerated. At this point, increasing the flow rate does not

increase biodegradation but does continue to increase

volatilization. The optimal input air flow is the minimum

extraction rate that satisfies the oxygen demand. Some

volatilization occurs regardless of the extraction rate.

The relative removal attributed to biodegradation and

volatilization is quite variable and site dependent. At a

JP-4 jet fuel contaminated site at Tyndall AFB, Miller et

al. (1991) found that biodegradation could achieve

about 85-percent contaminant removal at the optimal air

flow rate.

Currently, only 6 of 120 Bioventing Initiative sites use air

extraction to oxygenate the site. Two of the sites (Davis

Global Communications Site, near McClellan AFB, and

BX Service Station, Patrick AFB) operated in extraction

mode for 60 to 90 days, at which time the system was

reconfigured for air injection because vapor concentrations had significantly decreased. At Patrick AFB, initial

vapor concentrations of TPH were as high as 27,000

ppmv. After approximately 75 days of operation, concentrations decreased to 1,600 ppmv and the bioventing

system was reconfigured for injection. Another site that

has used extraction is the Base Service Station at Vandenberg AFB. This site contains high concentrations of

the more volatile fuel components and is an active service station. As such, the possibility of vapors migrating

into the building on site is possible. This bioventing

system was operated in an extraction configuration in

two phases (Downey et al., 1994). During Phase I,

extracted soil gas was passed through a PADRE vapor

treatment system, where high concentrations of volatiles

were adsorbed and condensed to liquid fuel. The treated

soil gas was then recirculated through the soil using air

injection, biofilter trenches located along the perimeter

of the site. Phase II was initiated once TVH concentrations decreased to less than 1,000 ppmv. At this time,

the PADRE system was taken off-line, and the extracted

soil gas was reinjected directly into the biofilter trenches.

This appendix discusses minimization of the off-gas flow

rate, seven commercially available alternatives for treating organic vapors in an air stream, and some emerging

vapor treatment technologies. The vapor treatment

technology discussions in this appendix derive from

information on remedial technologies published by

AFCEE (1992 and 1994) and a description of off-gas

treatment in Soil Vapor Extraction Technology: Reference Handbook (U.S. EPA, 1991). Figure 1 shows the

general ranges of applicability for some commonly used

off-gas treatment methods. The organic vapor treatment

options discussed in the following sections are:

• Limiting off-gas production 

• Direct discharge 

• Off-gas reinjection 

• Biofiltration 

• Adsorption on carbon or resin 

• Catalytic oxidation 

• Flame incineration 

• Thermal destruction in internal combustion engines 

• Emerging vapor treatment technologies

73
Many of these methods have been used in industrial

applications to control point source VOC emissions.

Figure 1 shows that most of these alternatives may be

used over a range of concentrations that spans several

orders of magnitude. Usually, however, each option is

cost-effective over only a small part of that range. For

example, granular activated carbon (GAC) adsorption

could be used to treat a vapor stream containing 10,000

ppmv of hydrocarbon vapors, but the cost for carbon

regeneration would be prohibitive.

As shown in Figure 1, thermal treatment methods are

more cost-effective for treating off-gas containing higher

concentrations of vapor contaminants. No distinct guidelines exist for selecting thermal treatment units for specific applications, but the tradeoff between capital and

operating costs sets general ranges of applicability for

thermal treatment methods. Catalytic oxidation units

usually have higher initial cost but lower fuel requirements than flame incinerators. As a result, the catalytic

oxidation units are usually economical for influent containing less than 5,000 ppmv of contaminants. The capital cost of internal combustion engine (ICE) treatment

units is similar to catalytic oxidation units. The ICE is not

limited to operating with an inlet combustible vapor concentration below 25 percent of the lower explosive limit

(LEL). The ICE units, therefore, gain a significant advantage when the vapor concentration is over 25 percent of

the LEL.

D.2 Limiting Off-Gas Production

Design and operating features can be used to minimize

the volume of off-gas released by bioventing systems.

This source reduction approach to pollution prevention

should be used whenever possible at bioventing sites.

Options for minimizing off-gas production include using

the lowest air flow rate possible while still supplying

sufficient air and/or using air injection instead of air

extraction configurations to aerate the contaminated

area. Bioventing systems can be operated at much

lower air flow rates than standard soil vapor extraction

systems. A well-designed and operated bioventing system can minimize off-gas releases without compromising oxygenation of the contaminated area. As discussed

above, air injection systems are preferred unless site

conditions require air extraction to control movement or

accumulation of contaminant vapors.

D.3 Direct Discharge

Direct discharge involves releasing air that contains

organic vapors directly through a stack. The stack disperses the vapors, but no removal or destruction of

contaminants occurs. When the organic vapor concentration in the extraction well off-gas stream is low, or in

localities with less stringent air treatment standards,

treatment may not be required. Direct discharge of vapors to the atmosphere can be a viable option where

consistent with good environmental practice and local

permitting requirements. The concentration of the contaminants, the off-gas release rate, and the location and

type of nearby receptors are considered when evaluating direct discharge options.

D.4 Off-Gas Reinjection

Reinjection of off-gas for further biodegradation can be

a cost-effective and environmentally sound treatment

option. Off-gas reinjection configurations offer the advantages of low surface emissions and no point source

Figure 1. Applicability of vapor treatment options.

74
generation. The reinjection treatment option consists of

distributing extracted air with contaminant vapors back

into the soil to allow in situ aerobic biodegradation to

destroy the contaminants. Reinjection is accomplished

by piping the discharge of the extraction blowers to air

distribution wells or trenches, where the air infiltrates

back into the soil. In situ respiration and soil gas permeability data must be available for the site. These data

indicate the expected biodegradation rate and radius of

influence needed to determine the design capacity for

the reinjection point. The available soil volume must be

sufficient to accept the off-gas air flow and allow biodegradation of the contaminant mass flow in the off-gas.

Reinjection wells should be located and designed to

ensure that the reinjection process destroys contaminants rather than increasing contaminant migration. After reinjection is established, surface emission testing

may be performed to ensure contaminants are not escaping at the site surface. Soil gas monitoring should be

performed to ensure that contaminant migration is not

being increased. Monitoring of migration is particularly

important at sites where air extraction is necessary because of the presence of buildings.

D.5 Biofiltration

Biofiltration can be used to destroy a variety of volatile

organic contaminants in an off-gas stream. The biofiltration process uses microorganisms immobilized as a

biofilm on a porous filter substrate, such as peat or

compost. As the air and vapor contaminants pass

through the filter, contaminants transfer from the gas

phase to the biolayer, where they are metabolized. Influent contaminant concentrations less than about 1,000

ppmv can be treated with a typical contact time of 15 to

90 seconds (Skladany et al., 1994). Vendor data indicate

that biofiltration is most effective for gasoline hydrocarbon vapor concentrations in the range of 50 ppmv to

5,000 ppmv (U.S. EPA, 1994).

Saberiyan et al. (1992) studied the use of a biofilter for

treatment of air containing gasoline vapors. Sphagnum

moss was used as the packing material. The system

initially was inoculated with a hydrocarbon-degrading

bacterial culture, then exposed to gasoline vapors. The

biofilter removed up to 90 percent of the initial 50-ppmv

gasoline vapor concentration. These studies also

sought to demonstrate the linear relationship between

flow rate and packing material volume.

Biofiltration of vapor streams is a fairly well-established

treatment technology in Europe (Leson and Winer,

1991). Medina et al. (1995) have studied the use of

biofilters to treat ethanol and gasoline vapor streams.

Bench-scale and pilot-scale reactors have been

studied. 

D.6 Adsorption on Carbon or Resin

Adsorption refers to the process by which molecules

collect on and adhere to the surface of an adsorbent

solid (U.S. EPA, 1988). This adsorption is the result of

chemical and/or physical forces. Physical adsorption

(the more common type in this application) is the result

of Van der Waals’ forces, which are common to all matter

and result from the motion of electrons. Surface area is

a crucial factor in adsorption because adsorption capacity is proportional to surface area. Commercially available adsorbents include activated carbon and synthetic

resins.

GAC is the most commonly used vapor-phase treatment

method. Activated carbon adsorbents provide a high

surface area in a low unit cost material because of the

carbon’s complex internal pore structure. Commercially

available GAC typically has a surface area of 1,000

m2

/gram to 1,400 m2/gram.

GAC is the most cost-effective organic vapor treatment

method for a wide range of applications because of

its relative ease of implementation and operation,

its established performance history in commercial applications, its ability to be regenerated for repeated use,

and its applicability to a wide range of contaminants

at a wide range of flow rates. Many vendors sell or

lease prefabricated, skid-mounted units that can be put

into operation with a few days’ notice. Carbon adsorption, however, is economical only for lower mass removal rates. When the vapor concentration is high,

carbon replacement or regeneration may be prohibitively expensive.

An alternative to replacing the carbon with offsite disposal or reactivation is onsite regeneration of the carbon. Such systems regenerate the carbon in place, using

steam or hot gas to desorb the contaminants. The contaminants recovered in liquid form may then be disposed

of or, in some cases, recovered as solvent or used as

fuel.

Information on GAC design parameters is available from

the carbon vendors. Calgon Carbon Corporation (Pittsburgh, Pennsylvania), Carbtrol Corporation (Westport,

Connecticut), Nucon (Columbus, Ohio), and many others supply adsorption isotherms and pressure drop

curves for the GAC types they supply. The pressure drop

curves are developed as a function of flow rate. Many

vendors supply modular, prefabricated GAC units of

200 lb to 2,000 lb of activated carbon that may accommodate flow rates from below 400 scfm to more than

1,000 scfm.

As a rule of thumb, the adsorptive capacity of activated

carbon for most hydrocarbons in the vapor stream is

about 1 lb hydrocarbon:10 lb activated carbon, and the

cost of activated carbon is about $3/lb (all costs in75
cluded, not just carbon purchase, in 1993 dollars), so

the cost of activated carbon treatment can be roughly

estimated at $30/lb of hydrocarbon to be treated.

Specialized resin adsorbents have been developed and

are now entering commercial application for treatment

of organic vapors in off-gas streams. These synthetic

resin adsorbents have a high tolerance to water vapor.

Air streams with relative humidities greater than 90 percent can be processed with little reduction in the adsorption efficiency for organic contaminants. The resin

adsorbents are amenable to regeneration on site. Skidmounted modules are available, consisting of two resinadsorbent beds. The design allows one bed to be on-line

treating off-gas, while the other bed is being regenerated. During the desorption cycle, all organic contaminants trapped on the resin are removed, condensed,

and transferred to a storage tank. The desorption process used to regenerate the resin is carried out under

vacuum, using a minimum volume of nitrogen purge

gas. A heat exchanger in the bed heats the resin during

regeneration. The same heat exchanger is used to cool

the bed to increase sorption capacity while it is on-line

treating off-gas (Downey et al., 1994).

D.7 Catalytic Oxidation

Catalytic oxidation is an incineration process that uses

catalysts to increase the oxidation rate of organic contaminants, allowing equivalent destruction efficiency at

a lower temperature than flame incineration. In catalytic

oxidation, the vapor stream is heated and passed

through a combustion unit where the gas stream contacts the catalyst. The catalyst accelerates the chemical

reaction without undergoing a chemical change itself.

The catalyst increases the oxidation reaction rate by

adsorbing the contaminant molecules on the catalyst

surface. Sorption phenomena on the catalyst serve to

increase the local concentration of organic contaminants at the catalyst surface and, for some organic

contaminants, reduce the activation energy of the oxidation reaction. Increased concentration and reduced

activation energy increase the rate of oxidation of the

organics (Kiang, 1988). Figure 2 shows a schematic of

a catalytic incinerator unit.

The active catalytic material typically is a precious metal

(e.g., palladium, platinum) that provides the surface conditions needed to facilitate the transformation of the

contaminant molecules into carbon dioxide and water.

The catalyst metal is supported on a lower cost, high

surface area metallic or ceramic support medium.

The metal catalyst and support are exposed to the

heated off-gas in a catalytic oxidation unit. The catalytic

oxidation unit uses either a fixed-bed or a fluidized-bed

system. Fixed-bed systems include metallic mesh, wire,

or ribbon or ceramic honeycomb supporting the catalyst

metal or a packed bed of catalyst-impregnated pellets.

Fluidized beds also use catalyst-impregnated ceramic

pellets but operate at sufficiently high flow to move and

mix the pellets during treatment (U.S. EPA, 1986).

The main advantage of catalytic oxidation versus thermal incineration is the much lower temperature required

with a catalyst. These systems typically operate at

600°F to 900°F (CSM Systems, 1989), versus temperatures of 1,400°F or higher for flame incineration. The

lower temperature results in lower fuel costs, less severe service conditions for the incinerator materials of

construction, and reduced NOx production. Natural gas

or propane is a typical fuel used for supplemental heating when the contaminated vapor streams do not contain sufficient heat value for self-sustaining incineration.

Energy costs can be further reduced by reclaiming heat

from the exhaust gases (i.e., using the exhaust gas flow

to preheat the influent vapor stream).

Careful monitoring of extraction gas concentration and

reactor temperature is required to prevent overheating

of the catalyst. Overheating can damage the catalyst

metal surface and/or the support-reducing catalytic activity. The allowed influent organic vapor concentration

depends on the heat value and LEL of the influent vapor

stream. Concentrations over 3,000 ppmv VOCs normally are diluted with air to prevent excessive energy

release rates and to control the temperature in the catalytic unit. Safety is also a concern with these units, as

with any incineration method. The maximum permissible

total hydrocarbon concentration varies by site but usually is below 25 percent of the LEL. The total hydrocarbon concentration in the vapor is continuously

measured at the inlet to the catalytic unit to control the

dilution air flow.

Treating off-gas-containing chlorinated compounds, sulfur-containing compounds, or nitrogen-containing compounds deactivates the catalyst because of the

chemical reaction of the catalyst metal with halogens or

strong sorption of SOx and NOx on the catalyst. Some

catalysts are specially designed to treat chlorinated

compounds. New technologies potentially capable of

treating chlorinated compounds by catalytic oxidation

currently are under development and are beginning to

become available on the market (Trowbridge and Malot,

1990; Buck and Hauck, 1992).

The significant cost elements of a catalytic oxidizer are

the capital cost (or rental) of the unit, operations and

monitoring, maintenance, and makeup fuel cost. A catalytic oxidation unit for treatment of 100-cfm off-gas flow

would have a capital cost of approximately $40,000 to

$60,000 (in 1991 dollars) (AFCEE, 1992). Operations,

maintenance, and monitoring costs are site specific.

Makeup fuel is required if the hydrocarbon concentration

falls below the level necessary to maintain the required

temperature. At the Hill AFB 914 site (Smith et al., 1991),

76
the extracted hydrocarbon concentration was approximately 600 ppmv and the flow rate was 1,500 cfm. To

maintain the minimum temperature, an average of 1,500

gal of propane was used every month at an average cost

of $2,000 per month. All thermal oxidation processes

require makeup fuel to treat low-concentration waste

streams, and the makeup fuel generally is proportional

to the operating temperature. Some fuel may be saved

by heat recuperation.

D.8 Flame Incineration

Flame incineration is a process that uses high-temperature direct flame combustion to produce rapid oxidation

of organic contaminants. Flame incinerators for treatment of organic vapors in off-gas are typically singlechamber, refractory-lined units containing an open

burner. Flame incinerators are often equipped with heat

exchangers where hot combustion gases leaving the

incinerator are used to preheat the incoming off-gas

stream. Heat recovered from the combustion gas improves thermal efficiency and reduces fuel costs. When

operated with an adequate temperature and residence

time, flame incineration treatment oxidizes hydrocarbon

contaminants to carbon dioxide and water. For most

contaminants, acceptable contaminant destruction efficiency is achieved with an operating temperature in the

range of 1,400°F to 1,600°F and a residence time of 1

second (AFCEE, 1992). Makeup fuel is usually necessary to maintain the temperature required to ensure

adequate mineralization. Natural gas or propane typically serves as the supplemental fuel. Destruction of the

contaminants is a major advantage of this technique

over carbon adsorption, which only concentrates the

contaminants onto the carbon, which must then be regenerated or disposed of.

Safety is a major design requirement for flame incinerators and other thermal destruction units. Requirements

for safety provisions are derived from National Fire Protection Association (NFPA) standards and applicable

state requirements. In most applications, influent concentrations are limited to 25 percent of the LEL (AFCEE,

1992). The LEL for gasoline is between 12,000 ppmv

and 15,000 ppm, depending on the gasoline grade (Little, 1987).

Direct incineration is not appropriate for influent vapor

streams containing chlorinated compounds. Complete

combustion of these compounds generates corrosive

hydrochloric acid vapors. Partial or incomplete combustion of chlorinated compounds could result in the production of chlorinated products.

The capital cost of a flame incinerator typically is less

than that of a catalytic incinerator. Because of the higher

operating temperature, however, fuel use is higher with

a flame incinerator. When the flammable contaminant

vapor concentration is sufficiently high, the heating

value from oxidation of the contaminant reduces fuel

use; therefore, at higher hydrocarbon concentrations,

flame incineration may be less costly than catalytic incineration. At lower vapor concentrations, the cost of

makeup fuel is much greater than for catalytic incineration and the overall cost is probably higher than for

catalytic incineration. Flame incineration is generally favored over catalytic oxidation when the combustible

organic vapor concentration is higher than about 1,000

ppmv to 5,000 ppmv (AFCEE, 1992).

D.9 Internal Combustion Engines

ICE treatment destroys organic contaminants through

oxidation in a conventional engine. ICEs have been

used for years to destroy landfill gas. Application of ICEs

to destruction of hydrocarbon vapors in air streams is

more recent. The first operational unit was installed in

1986.

The ICE used for this technique is an ordinary industrial

or automotive engine with its carburetor modified to

Figure 2. Schematic of catalytic incinerator unit.

77
accept vapors rather than liquid fuel. The air flow capacity of the ICE is determined by the cubic inch displacement of the engine, the engine speed, and the engine

vacuum. The capacity (scfm) can be estimated as:

Capacity = RPM

2 ×

CID

1,728 × 0.85 × 





1 − EV

P







 (Eq. D-1)

where:

RPM = engine speed in revolutions per minute

CID = engine displacement in cubic inches

EV = vacuum at the engine intake in inches of

mercury

P = local air pressure in inches of mercury

Therefore, a 140-in.3

 displacement, four-cylinder engine

running at 2,250 rpm and 10 in. Hg engine vacuum with

an atmospheric pressure of 30 in. of mercury would

have an off-gas treatment capacity of 52 scfm. ICE

treatment units are available in sizes from 140 in.3

 to 460

in.3

 Currently available ICE treatment units operate the

engine near idle conditions. The off-gas capacity could

be increased by applying a load to the engine to increase engine speed and decrease engine vacuum.

Engine loading by attaching a generator to supply site

power has been proposed but is not routinely practiced.

A second required modification to the engines is the

addition of a supplemental fuel input valve when the

intake hydrocarbon concentration is too low to sustain

engine operation. Propane is used almost universally,

although one vendor reported that natural gas, when

available, can reduce energy cost by 50 percent to 75

percent.

The engines are also equipped with a valve to bleed in

ambient air to maintain the required oxygen concentration. Soil vapor may have very low concentrations of

oxygen, especially during the initial stages of operation.

Ambient air is added to the engine, via an intake valve,

at a ratio sufficient to bring the oxygen content up to the

stoichiometric requirement for combustion.

A catalytic converter is an integral component of the

system, providing an important polishing step to reach

the low discharge levels required by many regulatory

agencies. A standard automobile catalytic converter, using a platinum-based catalyst, is normally used. Data

from the South Coast Air Quality Management District,

the air quality regulatory body for Los Angeles and the

surrounding area, show that the catalyst reduced concentrations of TPH from 478 ppmv to 89 ppmv and from

1,250 ppm to 39 ppm, resulting in important additional

contaminant removal (U.S. EPA, 1991). The South

Coast Air Quality Management District requires a catalytic converter to permit this type of system. Catalysts

have a finite life span (typically expressed in hours of

operation) and must be monitored as that time approaches to ensure that the catalyst is working properly.

The length of operation of the catalyst depends on the

vapor concentration and whether lead or other potential

catalyst poisons are present in the off-gas contaminants.

One equipment vendor suggests a range of 750 to 1,500

hours (about 1 to 2 months) of operation. A deactivated

catalyst can be replaced easily with any automobile catalytic converter, available at most automobile parts stores.

To date, ICE use appears to be most widespread in

California, mostly in the South Coast Air Quality Management District in southern California, which has some

of the most stringent air discharge regulations in the

country. The South Coast Air Quality Management District has permitted more than 100 ICEs for use in their

district. RSI, Inc. (Oxnard, California), has installed more

than 30 ICE systems, all in California.

Data obtained from ICE operators and regulators show

that ICEs are capable of destruction efficiencies of well

over 99 percent (U.S. EPA, 1991). ICEs are especially

useful for treating vapor streams with high concentrations of TPH (up to 30-percent volume) to levels below

50 ppm. Tests of BTEX destruction by ICE treatment

show that nondetectable levels of contaminants can be

achieved in the outlet off-gas in some cases, and outlet

concentrations below 1 ppmv can be achieved in many

cases. The total destruction capacity may be expressed

as mass removal rate. One ICE operator reported a

mass removal and destruction rate of over 1 ton per day

(about 12 gal/hour).

ICE off-gas treatment units can handle high concentrations of organic contaminants in the extracted air. As

discussed above, incineration units (e.g., catalytic oxidation units, flame incinerators) usually are limited to

inlet vapor concentrations of 25 percent of the LEL. The

inlet concentration for an ICE unit can be in the combustible range, so these units can accept vapor concentrations as high as 40,000 ppmv with no dilution air. As a

result, the ICE treatment units have a significant advantage over incineration units when the vapor concentration is higher than 25 percent of the LEL. Inlet vapor

concentrations as high as 300,000 ppmv have been

reported (U.S. EPA, 1991). The off-gas must still be

diluted with air to allow the ICE unit to treat off-gas

containing more than about 40,000 ppmv of organics,

but only one-quarter as much dilution air flow is needed

for the ICE unit compared with an incineration unit.

ICEs also can effectively treat low concentrations (i.e.,

inlet vapor concentration below 1,000 ppm), although

supplemental fuel use increases as the inlet concentration drops below 14,000 ppmv and the cost-effectiveness decreases at reduced intake concentrations. The

removal efficiency compares favorably with other treatment methods based on data available from actual system installations.

The use of ICEs as vapor treatment devices for extracted soil vapors offers advantages over conventional

78
treatment methods (carbon, thermal oxidation, or catalytic oxidation), at least for some applications. One advantage of ICEs is the ability to produce power that can

provide useful work output. Self-contained units are

available that use the ICE to power the blower. The

extraction blower consumes only about 25 percent of the

useful work produced by the engine. Other uses of the

power have included lighting the site, heating a field

trailer, or similar ideas. Using the engine as a vacuum

source increases the engine vacuum, which has the

undesirable effect of reducing air flow capacity (see

Equation D-1). As a result, the ICE is usually coupled to

a blower to supply the well head vacuum. An added

benefit of this system is that vapors cannot be extracted

unless treatment also is occurring, eliminating the possibility of vapors bypassing the treatment system.

Another advantage of ICEs is their portability and simple

monitoring and maintenance. Typically, the self-contained units are skid-mounted or put on a trailer and can

go from site to site very easily. The site requirements

may also favor ICEs over other oxidation methods. ICE

units are smaller and less noticeable than direct thermal

incineration units and may be more appropriate for areas that are intended to remain low profile. Units also

have been developed that can be monitored via modem,

eliminating costly onsite monitoring.

Noise associated with engine operation could be a

concern in areas near residential zones or occupied

buildings. Noise can be abated by adjusting engine

speed during certain periods, installing a noise suppression fence, or purchasing special low noise ICE

models (AFCEE, 1994).

The capital cost of currently available ICE units appears

to be somewhat higher but is certainly in the same

general range as catalytic incineration and thermal incineration. The costs of ICE treatment units with maximum flow capacities of 65 scfm, 250 scfm, and 500 scfm

are $40,450, $73,450, and $98,880, respectively (in

1994 dollars). Propane or natural gas fuel is needed

when the inlet vapor concentration is below about

40,000 ppmv. The quantity of added fuel needed increases as the inlet vapor concentration declines. Fuel

costs for treating 65 scfm, 250 scfm, and 500 scfm

off-gas flow, when all energy is supplied by propane

supplemental fuel, are $20/day, $70/day, and $140/day,

respectively (AFCEE, 1994). Operations and maintenance costs are site specific. Because ICEs use a much

more widely understood technology, gaining regulatory

acceptance appears to be easier than for other technologies, and as a result, permitting and monitoring

costs should be lower.

D.10 Emerging Vapor Treatment

Technologies

This section briefly describes the operating features of

several emerging technologies for destruction or concentration of organic contaminants in an off-gas stream.

The technologies described are packed-bed thermal

treatment, photocatalytic oxidation, and membrane

separation.

Packed-bed thermal treatment oxidizes organic contaminants by passing the off-gas stream through a

heated bed of ceramic beads. The packed bed increases mixing to promote the oxidation reaction. A

vapor stream passes through the packed bed that thermally destroys contaminants. The packing geometry

combined with uniform high temperature of the ceramic

beads is reported to provide high destruction efficiency

for organic vapors in air, without using an open flame.

The ceramic beads are heated electrically to bring them

to the operating temperature of 1,800°F. No additional

energy input is required if the heat value of the vapors

is sufficient. This point is near a concentration of 2,000

ppmv. If the concentration is below this value, natural

gas or propane can be bled in with influent to maintain

the proper temperature. As with any incineration technique, excess air is added to dilute the concentration to

safe levels if the influent is too rich. Packed-bed thermal

processing has been used to destroy vapor contaminants in the off-gas from several chemical and other

industrial plants.

The vendor of the packed-bed technology currently is

investigating its applicability to the remediation market

(U.S. EPA, 1991). The vendor indicates that this technology has several desirable characteristics for treatment of vapors in off-gas from remediation systems. The

removal efficiency is reported to be high and stable over

varying operating conditions. Tests have shown efficiencies of 99.99+ percent, and this removal is attained

continuously. Another reported advantage is the ability

to mineralize chlorinated compounds without the production of chlorinated products of incomplete combustion or degradation of the ceramic beads. Mineral acid

vapors would still be produced.

In the photocatalytic oxidation process, VOCs are converted to carbon dioxide and water by exposure to UV

light. When chlorinated organics are present, hydrogen

chloride gas and/or chlorine are also produced. The

off-gas stream enters the photocatalyst unit, where the

contaminants are trapped on a catalyst surface. The

catalyst surface is continuously exposed to high-intensity UV light. The combination of surface effects from the

79
catalyst and energy input from the UV light allows rapid

oxidation of the contaminants. The reported residence

time required for 95-percent to 99-percent destruction

efficiency is 0.2 seconds (Kittrel et al., 1995).

Gas semipermeable membrane systems are available

to concentrate dilute organic vapor streams. The membrane systems do not destroy the organic contaminants

and would, therefore, be used as a pretreatment step to

increase the efficiency of a second treatment process.

The membranes used have dramatically different permeability for air and organic vapor molecules. The difference in permeability allows the organics to

concentrate on one side of the membrane and the air on

the other side. The concentrated vapor stream can then

be further processed to condense and collect the organics or destroy them (U.S. EPA, 1994).

D.11 References

AFCEE. 1994. A performance and cost evaluation of internal combustion engines for the destruction of hydrocarbon vapors from

fuel-contaminated soils. Environmental Services Office, Air Force

Center for Environmental Excellence, Brooks Air Force Base, TX.

AFCEE. 1992. Remedial technology design, performance, and cost

study. Environmental Services Office, Air Force Center for Environmental Excellence, Brooks Air Force Base, TX.

Buck, F.A.M, and C.W. Hauck, 1992, Vapor extraction and catalytic

oxidation of chlorinated VOCs. In: Proceedings of the 11th Annual

Incineration Conference. Albuquerque, NM (May).

CSM Systems. 1989. Company literature. Brooklyn, NY.

DeVinny et al. 1993.

Downey, D.C., C.J. Pluhar, L.A. Dudus, P.G. Blystone, R.N. Miller,

G.L. Lane, and S. Taffinder. 1994. Remediation of gasoline-contaminated soils using regenerative resin vapor treatment and in

situ bioventing. In: Proceedings of the Petroleum Hydrocarbons

and Organic Chemicals Ground Water: Prevention, Detection, and

Restoration Conference (November 10-12).

Kiang, Y-H. 1988. Catalytic incineration. In: Freeman, H. Standard

handbook of hazardous waste treatment and disposal. New York,

NY: McGraw-Hill.

Kittrell, J.R., C.W. Quinlan, A. Gavaskar, B.C. Kim, M.H. Smith, and

P.F. Carpenter, 1995. Air stripping teams with photocatalytic technology in successful groundwater remediation demonstration. Presented at: Air and Waste Management Association Annual

Meeting. Paper number A469. San Antonio, TX.

Leson, G., and A.M. Winer. 1991. Biofiltration: An innovative air pollution control technology for VOC emissions. J. Air & Waste Management Association 41(8).

Little, A.D. 1987. The installation restoration program toxicology

guide, Vol. 3. Prepared for the Aerospace Medical Division. U.S.

Air Force Systems Command, Wright-Patterson Air Force Base,

Dayton, OH.

Medina, V.F., J.S. Devinny, and M. Ramaratnam. 1995. Biofiltration

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G.D. Sayles, and R.S. Skeen, eds. Biological unit processes for

hazardous waste treatment. Columbus, OH: Battelle Press. pp.

257-264.

Miller, R.N., C.C. Vogel, and R.E. Hinchee. 1991. A field-scale investigation of petroleum hydrocarbon biodegradation in the vadose

zone enhanced by soil venting at Tyndall AFB, Florida. In:

Hinchee, R.E., and R.F. Olfenbuttel, eds. In situ bioreclamation.

Stoneham, MA: Butterworth-Heinemann.

Saberiyan, A.G., M.S. Wilson, E.O. Roe, J.S. Andrilenas, C.T. Esler,

G.H. Kise, and P.E. Reith. 1992. Removal of gasoline volatile

organic compounds via air biofiltration: A technique for treating

secondary air emissions from vapor-extraction and air-stripping

systems. In: Hinchee, R.E., B.C. Alleman, R.E. Hoeppel, and R.N.

Miller, eds. Hydrocarbon bioremediation. Boca Raton, FL: Lewis

Publishers. pp. 1-12.

Skladany, G.J., A.P Togna, and Y. Yang, 1994. Using biofiltration to

treat VOCs and odors. Presented at: Superfund XIV Conference

and Exhibition. Hazardous Materials Control Resources Institute,

Rockville, MD.

Smith, G.J., R.R. Dupont, and R.E. Hinchee. 1991. Final report on

Hill AFB JP-4 site (building 914) remediation. Report submitted to

Hill AFB, Utah, by Battelle (July). 

Trowbridge, B.E., and J.J. Malot. 1990. Soil remediation and free

product removal using in-situ vacuum extraction with catalytic oxidation. In: Proceedings of the Fourth Annual Outdoor Action Conference on Aquifer Restoration, Ground Water Monitoring and

Geophysical Methods, Las Vegas, NV.

U.S. EPA. 1994. VISITT - Vendor Information System for Innovative

Treatment Technologies. EPA/542/R-94/003. Washington, DC.

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U.S. EPA. 1988. Cleanup of releases from petroleum USTs: Selected

technologies. EPA/530/UST-88/001. Washington, DC.

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EPA/625/6-86/014. Washington, DC.

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