United States Office of Research and EPA/540/R-95/534a

Environmental Protection Development September 1995

Agency Washington, DC 20460

1EPA Manual

Bioventing Principles and

Practice

Volume I: Bioventing Principles
EPA/540/R-95/534a

September 1995

Manual

Principles and Practices of Bioventing

Volume I: Bioventing Principles

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 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Chapter 2 Development of Bioventing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1 Oxygen Supply to Contaminated Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Bioventing Research and Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.3 Structure of Bioventing Initiative Field Treatability Studies and Bioventing 

System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.4 Emerging Techniques for Modifications to Bioventing Systems . . . . . . . . . . . . . . . . . . . . . 9

Chapter 3 Principles of Bioventing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1 Physical Processes Affecting Bioventing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1.1 Soil Gas Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1.2 Contaminant Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1.3 Oxygen Radius of Influence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.2 Microbial Processes Affecting Bioventing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.2.1 Microbial Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.2.2 Environmental Parameters Affecting Microbial Processes . . . . . . . . . . . . . . . . . . . 15

3.3 Compounds Targeted for Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.4 BTEX Versus TPH Removal in Petroleum-Contaminated Sites . . . . . . . . . . . . . . . . . . . . . 24

Chapter 4 Bioventing Case Histories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.1 Site 914, Hill AFB, Utah . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.2 Tyndall AFB, Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.3 Site 280, Hill AFB, Utah . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.4 Site 20, Eielson AFB, Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.5 Fire Training Area, Battle Creek ANGB, Michigan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Chapter 5 Analyses of Bioventing Initiative Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5.1 Estimate of Contaminant Removal at Bioventing Initiative Sites. . . . . . . . . . . . . . . . . . . . . 41

5.2 Statistical Analysis of Bioventing Initiative Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5.2.1 Procedures for Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5.2.2 Calculation of Oxygen Utilization and Carbon Dioxide Production Rates . . . . . . . 44

5.2.3 Correlation of Oxygen Utilization Rates and Environmental Parameters. . . . . . . . 45

iii
5.2.4 Correlation of Oxygen Utilization and Carbon Dioxide Production Rate Ratios 

With Environmental Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

5.2.5 Correlation of Soil Gas Permeability With Environmental Parameters . . . . . . . . . 55

5.2.6 Analyses of Data From Contaminated and Background Areas . . . . . . . . . . . . . . . 55

5.2.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Chapter 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Appendix A Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Appendix B Data From Bioventing Initiatives Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Contents (continued)

Page

iv
Figures

Figure Page

1-1 Hydrocarbon distribution at a contaminated site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1-2 Schematic of a typical bioventing system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2-1 Historical perspective on the development of bioventing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2-2 Locations of Bioventing Initiative sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3-1 Distribution of fine-grained soils (silt and clay) at Bioventing Initiative sites . . . . . . . . . . . . . . . . . . . . . . . . 11

3-2 Sorption isotherms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3-3 Relationship between sorbed contaminant concentrations and vapor- or aqueous-phase 

concentrations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3-4 Soil moisture content measurements at Bioventing Initiative sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3-5 Direct correlation between oxygen utilization rates and soil moisture content at Bioventing 

Initiative sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3-6 Oxygen and carbon dioxide concentrations before and after irrigation at Twentynine Palms, California . . 17

3-7 Soil pH measurements at Bioventing Initiative sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3-8 Correlation between oxygen utilization rate and soil pH at Bioventing Initiative sites . . . . . . . . . . . . . . . . . 18

3-9 Soil temperature versus oxygen utilization and biodegradation rate at Site 20, Eielson AFB, Alaska. . . . . 19

3-10 TKN measurements at Bioventing Initiative sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3-11 Correlation between oxygen utilization rate and TKN at Bioventing Initiative sites . . . . . . . . . . . . . . . . . . . 21

3-12 Total phosphorus measurements at Bioventing Initiative sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3-13 Correlation between oxygen utilization rate and total phosphorus at Bioventing Initiative sites . . . . . . . . . 21

3-14 Iron concentration measurements at Bioventing Initiative sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3-15 Correlation between oxygen utilization rates and iron content at Bioventing Initiative sites . . . . . . . . . . . . 22

3-16 Relationship between contaminant physicochemical properties and potential for bioventing . . . . . . . . . . . 23

3-17 Relationship between contaminant pressure and aerobic biodegradability . . . . . . . . . . . . . . . . . . . . . . . . . 24

3-18 Results of soil analysis before and after venting from Plot V2 at Tyndall AFB, Florida . . . . . . . . . . . . . . . . 25

3-19 Contaminant distribution at Bioventing Initiative sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4-1 Cumulative hydrocarbon removal and the effect of moisture and nutrient addition at 

Site 914, Hill AFB, Utah . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4-2 Results of soil analysis before and after treatment at Site 914, Hill AFB, Utah. . . . . . . . . . . . . . . . . . . . . . 29

4-3 Cumulative percentage of hydrocarbon removal and the effect of moisture and nutrient 

addition at Tyndall AFB, Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4-4 Schematic showing locations of soil gas monitoring points, surface monitoring points, and 

injection wells at Site 20, Hill AFB, Utah . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4-5 Geologic cross-section showing known geologic features and soil TPH concentrations (mg/kg) at 

Site 280, Hill AFB, Utah . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4-6 Site average initial and final BTEX soil sample results at Site 280, Hill AFB, Utah. . . . . . . . . . . . . . . . . . . 33

4-7 Site average initial and final TPH soil sample results at Site 280, Hill AFB, Utah . . . . . . . . . . . . . . . . . . . . 34

v
4-8 Cross-section showing geologic features and typical construction details of the active 

warming test plot, Site 20, Eielson AFB, Alaska. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4-9 Soil temperature in four test plots and the background area at Site 20, Eielson AFB, Alaska . . . . . . . . . . 35

4-10 Biodegradation rates in four test plots at Site 20, Eielson AFB, Alaska. . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4-11 Site average initial and final BTEX soil sample results at Site 20, Eielson AFB, Alaska. . . . . . . . . . . . . . . 37

4-12 Site average initial and final TPH soil sample results at Site 20, Eielson AFB, Alaska . . . . . . . . . . . . . . . . 37

4-13 Hydrogeologic cross-section of the Fire Training Area, Battle Creek, ANGB, Michigan . . . . . . . . . . . . . . . 38

4-14 Initial and final soil gas concentrations at the Fire Training Area, Battle Creek, Michigan . . . . . . . . . . . . . 39

4-15 Initial and final soil concentrations at the Fire Training Area, Battle Creek, Michigan . . . . . . . . . . . . . . . . . 40

5-1 Soil gas BTEX concentrations at Bioventing Initiative sites: initial and 1-year data . . . . . . . . . . . . . . . . . . 42

5-2 Soil gas TPH concentrations at Bioventing Initiative sites: initial and 1-year data. . . . . . . . . . . . . . . . . . . . 42

5-3 Soil BTEX concentrations at Bioventing Initiative sites: initial and 1-year data . . . . . . . . . . . . . . . . . . . . . . 42

5-4 Soil TPH concentrations at Bioventing Initiative sites: initial and 1-year data . . . . . . . . . . . . . . . . . . . . . . . 43

5-5 Average soil and soil gas BTEX and TPH concentrations at Bioventing Initiative sites: initial 

and 1-year data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5-6 Initial and final soil sampling results at Site 3, Battle Creek ANGB, Michigan. . . . . . . . . . . . . . . . . . . . . . . 43

5-7 Average BTEX concentrations at Bioventing Initiative sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5-8 Use of piecewise analysis of oxygen utilization data from Site FSA-1, AFP 4, Texas . . . . . . . . . . . . . . . . . 46

5-9 Oxygen utilization rates, oxygen to carbon dioxide rate ratios, element concentrations, 

moisture content, pH, and alkalinity site average correlation scatterplot . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5-10 Oxygen utilization rates, oxygen to carbon dioxide rate ratios, contaminant concentrations, 

temperature, and moisture content site average correlation scatterplot . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5-11 Oxygen utilization rates, oxygen to carbon dioxide rate ratios, particle size, moisture content, 

and soil gas permeability site average correlation scatterplot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5-12 Element concentrations and particle size site average correlation scatterplot. . . . . . . . . . . . . . . . . . . . . . . 50

5-13 Contaminant concentrations and particle size site average correlation scatterplot . . . . . . . . . . . . . . . . . . . 51

5-14 pH, alkalinity, and particle size site average correlation scatterplot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

5-15 Actual versus model-predicted oxygen utilization rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

5-16 Variation of pH and the effect on oxygen utilization to carbon dioxide rate ratio based on model 

predictions with average levels of other parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5-17 Soil gas permeability, moisture content, and particle size site average correlation scatterplot . . . . . . . . . . 56

5-18 Variation of clay and the effect on soil gas permeability based on model predictions. . . . . . . . . . . . . . . . . 57

Figures (continued)

Figure Page

vi
Tables

Table Page

2-1 Oxygen Requirements Based on Supplied Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2-2 Summary of Reported in Situ Respiration Rates and Bioventing Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3-1 Values for Key Properties of Select Petroleum Hydrocarbons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4-1 Cost Analysis of Soil Warming Techniques at Site 20, Eielson AFB, Alaska . . . . . . . . . . . . . . . . . . . . . . . . 36

5-1 Data Parameters Included in the Statistical Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

5-2 Parameters That Distinguish the Seven Sites With High Oxygen Utilization Rates 

From the Remaining Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

B-1 Bioventing Initiative Results: Soil Chemical Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

B-2 Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations . . . . . . . . . . . . . . . 70

B-3 Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations . . . . . . . . . . . . . . . . . . 74

B-4 In Situ Respiration Test Results at Bioventing Initiative Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

vii
List of Examples

Example Page

2-1 Calculation of Air-Saturated Water Mass That Must Be Delivered To Degrade Hydrocarbons . . . . . . . . . . 3

3-1 Moisture Content Change During Air Injection and Water Generated During Biodegradation . . . . . . . . . . 17

3-2 Calculation of the van’t Hoff-Arrhenius Constant From Site Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3-3 Estimation of Nutrient Requirements in Situ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

viii
List of Symbols and Acronyms

AFB Air Force Base

AFCEE U.S. Air Force Center for

Environmental Excellence

AL/EQ Armstrong Laboratory Environics

Directorate

ANGB Air National Guard Base

AVGAS aviation gas

BTEX benzene, toluene, ethylbenzene,

and xylenes

cfm cubic feet per minute

DNAPL dense nonaqueous phase liquid

EPA U.S. Environmental Protection

Agency

LNAPL less dense nonaqueous phase liquid

NAS Naval Air Station

NLIN nonlinear regression procedure

PAH polycyclic aromatic hydrocarbon

PCB polychlorinated biphenyl

RD&A Research, Development, and

Acquisition

SAS Statistical Analysis System

SVE soil vacuum extraction

TCE trichloroethylene

TKN total Kjeldahl nitrogen

TPH total petroleum hydrocarbon

TVH total volatile hydrocarbon

UST underground storage tank

VOC volatile organic carbon

CS quantity sorbed to the solid matrix

CV volumetric concentration in the

vapor phase

Cvsat saturated vapor concentration

CW volumetric concentration in the

aqueous phase

Ea activation energy

foc organic carbon fraction

k maximum rate of substrate utilization

kd endogenous respiration rate

ko baseline biodegradation rate

kB biodegradation rate

Kd sorption coefficient

Kow octanol/water partition coefficient

KS Monod half-velocity constant

kT temperature-corrected

biodegradation rate

MW molecular weight

PV vapor pressure of pure contaminant

at temperature T

R gas constant

RI radius of influence

S concentration of the primary

substrate (contaminant)

sx solubility in water

t time

Tabs absolute temperature (°K)

χ mole fraction

X concentration of microorganisms

Y cell yield

ix
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

x
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.

xi
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; site closure; and optional

technologies to combine with bioventing if warranted. This first volume describes basic principles

of bioventing. The second volume focuses on bioventing design and process monitoring.

xii
Chapter 1

Introduction

Bioventing is the process of aerating soils to stimulate

in situ biological activity and promote bioremediation.

Bioventing typically is applied in situ to the vadose zone

and is applicable to any chemical that can be aerobically

biodegraded but to date has primarily been implemented at petroleum-contaminated sites. Through the

efforts of the U.S. Air Force Bioventing Initiative and the

U.S. EPA Bioremediation Field Initiative, bioventing has

been implemented at over 150 sites and has emerged

as one of the most cost-effective, efficient technologies

currently available for vadose zone remediation of petroleum-contaminated sites. This document is a culmination of the experience gained from these sites and

provides specific guidelines on the principles and practices of bioventing.

Much of the hydrocarbon residue at a fuel-contaminated

site is found in the vadose zone soils, in the capillary

fringe, and immediately below the water table (Figure

1-1). Seasonal water table fluctuations typically spread

residues in the area immediately above and below the

water table. In the past, conventional physical treatment

involved pump and treat systems, where ground water

was pumped out of the ground, treated, then either

discharged or reinjected. Although useful for preventing

continued migration of contaminants, these systems

rarely achieved typical cleanup goals. Bioventing systems are designed to remove the contaminant source in

the vadose zone, thereby preventing future and/or continued contamination of the ground water.

A typical bioventing system is illustrated in Figure 1-2.

Although bioventing is related to the process of soil

vacuum extraction (SVE), these processes have different primary objectives. SVE is designed and operated

to maximize the volatilization of low-molecular-weight

compounds, with some biodegradation occurring. In

contrast, bioventing is designed to maximize biodegradation of aerobically biodegradable compounds, regardless of their molecular weight, with some volatilization

occurring. The major distinction between these technologies is that the objective of SVE (also called soil

venting) is to optimize removal by volatilization, while

the objective of bioventing is to optimize biodegradation

while minimizing volatilization and capital and utility

costs. Although both technologies involve venting of air

though the subsurface, the different objectives result in

different design and operation of the remedial systems.

The following chapters provide an overview of the principles of bioventing in relation to physical, chemical, and

microbial processes occurring in the field. An overview

of the development of bioventing, including development of the Bioventing Initiative, is provided as a basis

for the data presented in this document. Data from

Bioventing Initiative sites are used throughout this document to illustrate principles of bioventing as determined

from field testing.

Figure 1-1. Hydrocarbon distribution at a contaminated site.

1
Figure 1-2. Schematic of a typical bioventing system.

2
Chapter 2

Development of Bioventing

This chapter provides a framework for the document, describing this development and structure of the Bioventing

Initiative, and ultimately, of this document. This chapter

provides an overview of bioventing, covering oxygen supply in situ (the dominant issue in the evolution of bioventing), early bioventing studies that led to development of the

Bioventing Initiative, final structure of the treatability studies and bioventing system design used for the Bioventing

Initiative, and finally, emerging techniques that are being

investigated as modifications to the conventional bioventing design described in this document.

2.1 Oxygen Supply to Contaminated

Areas

One driving force behind the development of bioventing

was the difficulty of delivering oxygen in situ. Many

contaminants, especially the petroleum hydrocarbons

found in fuels, are biodegradable in the presence of

oxygen. Traditionally, enhanced bioreclamation processes used water to carry oxygen or an alternative

electron acceptor to the contaminated zone. This process was common, whether the contamination was present in the ground water or in the unsaturated zone.

Media for adding oxygen to contaminated areas have

included pure-oxygen-sparged water, air-sparged water,

hydrogen peroxide, and air.

In all cases where water is used, the solubility of oxygen

is the limiting factor. At standard conditions, a maximum

of 8 mg/L to 10 mg/L of oxygen can be obtained in water

when aerated, while 40 mg/L to 50 mg/L can be obtained

if sparged with pure oxygen, and up to 500 mg/L of

oxygen theoretically can be supplied using 1,000 mg/L

of hydrogen peroxide. The stoichiometric equation

shown in Equation 2-11

 can be used to calculate the

quantity of water that must be delivered to provide sufficient oxygen for biodegradation.

C6H14 + 9.5O2 → 6CO2 + 7H2O (Eq. 2-1)

An example of calculating the mass of water that must

be delivered for hydrocarbon degradation is shown in

Example 2-1. Table 2-1 summarizes oxygen requirements based on the supplied form of oxygen.

Example 2-1. Calculation of Air-Saturated Water Mass

That Must Be Delivered To Degrade Hydrocarbons:

Based on Equation 2-1, the stoichiometric molar ratio of

hydrocarbon to oxygen is 1:9.5. Or, to degrade 1 mole

of hydrocarbons, 9.5 moles of oxygen must be consumed. On a mass basis:

1 mole C6H14

9.5 moles O2

×

1 mole O2

32 g O2

×

86 g C6H14

1 mole C6H14

=

86 g C6H14

304 g O2

= 1 g C6H14

3.5 g O2

Given an average concentration of 9 mg/L of oxygen

dissolved in water, the amount of air-saturated water

that must be delivered to degrade 1 g of hydrocarbon is

calculated as follows:

3.5 g O2 required

9 mg O2

1 L H2O × 1 g

1,000 mg

= 390 L H2O

1 g C6H14

or, to degrade 1 lb:

390 L H2O

1 g C6H14

× 1 gal

3.8 L × 1,000 g2.2 lb = 47,000 gal H2O

1 lb C6 H14

1 See Section 3.2 for development of this equation.

Table 2-1. Oxygen Requirements Based on Supplied Form

Oxygen Form

Oxygen

Concentration in H2O

Volume to

Degrade 1 lb

Hydrocarbon

Air-saturated H2O 8 mg/L to 10 mg/L 47,000 gal

(180,000 L)

Oxygen-saturated H2O 40 mg/L to 50 mg/L 11,000 gal

(42,000 L)

Hydrogen peroxide Up to 500 mg/L 1,600 gal

(6,100 L)

Air NA (21% vol./vol. in air) 170 ft3

 (4,800 L)

NA = not applicable.

3
Because of the low aqueous solubility of oxygen, hydrogen peroxide has been tested as an oxygen source in

laboratory studies and at several field sites (Hinchee et

al., 1991a; Aggarwal et al., 1991; Morgan and Watkinson,

1992). As shown in Table 2-1, if 500 mg/L of dissolved

oxygen can be supplied via hydrogen peroxide, the

mass of water that must be delivered decreases by more

than an order of magnitude. Initially, these calculations

made the use of hydrogen peroxide appear to be an

attractive alternative to injecting air-saturated water.

Hydrogen peroxide is miscible in water and decomposes

to release water and oxygen as shown in Equation 2-2:

H2O2 → H2O +

1

2

O2 (Eq. 2-2)

Many substances commonly present in ground water

and soil act as catalysts for the decomposition of

peroxide. Important among these are aqueous species of iron and copper as well as the enzyme

catalase (Schumb et al., 1955), which has significant

activity in situ (Spain et al., 1989). If the rate of oxygen

formation from hydrogen peroxide decomposition exceeds the rate of microbial oxygen utilization, gaseous oxygen may form because of its limited aqueous

solubility. Gaseous oxygen may form bubbles, which

may not be transported efficiently in ground water,

resulting in ineffective oxygen delivery.

Phosphate is commonly used in nutrient formulations to

decrease the rate of peroxide decomposition in groundwater applications (Britton, 1985). The effectiveness,

however, of phosphate addition in stabilizing peroxide

injected into an aquifer has not been well established,

and different researchers have reported conflicting results (American Petroleum Institute, 1987; Brown et al.,

1984; Downey et al., 1988; EPA, 1990; Morgan and

Watkinson, 1992).

Hinchee et al. (1991a) conducted a field experiment to

examine the effectiveness of hydrogen peroxide as an

oxygen source for in situ biodegradation. The study was

performed at a JP-4 jet fuel-contaminated site at Eglin

AFB, Florida. Site soils consisted of fine- to coarsegrained quartz sand with ground water at a depth of 2 ft

to 6 ft (0.61 m to 1.8 m). Previous studies by Downey et

al. (1988) and Hinchee et al. (1989) at the same site had

shown that rapid decomposition of hydrogen peroxide

occurred, even with the addition of phosphate as a

peroxide stabilizer. In subsequent studies, hydrogen

peroxide was injected at a concentration of 300 mg/L,

both with and without the addition of a phosphate-containing nutrient solution. As in previous studies, hydrogen peroxide decomposition was rapid, resulting in poor

distribution of oxygen in ground water. Addition of the

phosphate-containing nutrient solution did not appear to

improve hydrogen peroxide stability.

Other attempts have been made to use hydrogen peroxide as an oxygen source. Although results indicate

better hydrogen peroxide stability than achieved by

Hinchee et al. (1989), researchers concluded that most

of the hydrogen peroxide decomposed rapidly (EPA,

1990). Some degradation of aromatic hydrocarbons appears to have occurred; however, no change in total

hydrocarbon contamination levels was detected in the

soils (Ward, 1988).

In contrast to hydrogen peroxide use, when air is used

as an oxygen source in unsaturated soil, 170 ft3

 (4,800

L) of air must be delivered to provide the minimum

oxygen required to degrade 1 lb (0.45 kg) of hydrocarbon (Table 2-1). Because costs associated with waterbased delivery of oxygen can be relatively high, the use

of gas-phase delivery significantly reduces the cost associated with supplying oxygen.2

An additional advantage of using a gas-phase process

is that gases have greater diffusivity than liquids. At

many sites, geological heterogeneities cause fluid that

is pumped through the formation to be channeled into

more permeable pathways (e.g., in an alluvial soil with

interbedded sand and clay, all fluid flow initially takes

place in the sand). As a result, oxygen must be delivered

to the less permeable clay lenses through diffusion. In

a gaseous system (as found in unsaturated soils), this

diffusion can be expected to take place at rates at least

three orders of magnitude greater than rates in a liquid

system (as is found in saturated soils). Although diffusion cannot realistically be expected to aid significantly

in water-based bioreclamation, diffusion of oxygen in a

gas-phase system is a significant mechanism for oxygen delivery to less permeable zones.

Given the advantages of using air rather than water as

the oxygen source, several investigators began exploring the feasibility of an air-based oxygen supply system

as a remedial option. A summary of the results of these

investigations is presented in the following section.

2.2 Bioventing Research and

Development

Figure 2-1 provides a historical perspective of bioventing

research and development. To the authors’ knowledge, the

first documented evidence of unsaturated-zone biodegradation resulting from forced aeration was reported

by the Texas Research Institute, Inc., in a 1980 study

for the American Petroleum Institute. A large-scale

model experiment was conducted to test the effectiveness of a surfactant treatment to enhance the recovery

of spilled gasoline. The experiment accounted for only

8 gal (30 L) of the 65 gal (250 L) originally spilled

and raised questions about the fate of the gasoline.

2 See Chapter 5 of Volume II for a comparison of costs associated

with hydrogen peroxide use versus air (bioventing).

4
Subsequently, a column study was conducted to determine a diffusion coefficient for soil venting. This column

study evolved into a biodegradation study in which

researchers concluded that as much as 38 percent

of the fuel hydrocarbons were biologically mineralized.

Researchers also concluded that venting not only

would remove gasoline by physical means but also

would enhance microbial activity and promote biodegradation of the gasoline (Texas Research Institute, 1980,

1984).

To the authors’ knowledge, the first actual field-scale

bioventing experiments were conducted by Jack van

Eyk for Shell Research. In 1982, at van Eyk’s direction,

the Shell Laboratory in Amsterdam, The Netherlands,

initiated a series of experiments to investigate the effectiveness of bioventing for treating hydrocarbon-contaminated soils. These studies were reported in a series of

papers (Anonymous, 1986; Staatsuitgeverij, 1986; van

Eyk and Vreeken, 1988, 1989a, and 1989b).

Wilson and Ward (1986) suggested that using air as a

carrier for oxygen could be 1,000 times more efficient

than using water, especially in deep, hard-to-flood unsaturated zones. They made the connection between

oxygen supply via soil venting and biodegradation by

observing that “soil venting uses the same principle to

remove volatile components of the hydrocarbon.” In a

general overview of the soil venting process, Bennedsen et al. (1987) concluded that soil venting provides

large quantities of oxygen to the unsaturated zone, possibly stimulating aerobic degradation. They suggested

Figure 2-1. Historical perspective on the development of bioventing.

5
that water and nutrients also would be required for

significant degradation and encouraged additional investigation into this area.

Biodegradation enhanced by soil venting has been observed at several field sites. Investigators claim that at

a soil venting site for remediation of gasoline-contaminated soil, significant biodegradation occurred (measured by a temperature rise) when air was supplied.

Investigators pumped pulses of air through a pile of

excavated soil and observed a consistent rise in temperature, which they attributed to biodegradation. They

claimed that the pile was cleaned up during the summer

primarily by biodegradation (Conner, 1989). They did

not, however, control for natural volatilization from the

aboveground pile, and insufficient data were published

to critically review their biodegradation claim.

Researchers at Traverse City, Michigan, observed a decrease in the toluene concentration in unsaturated zone

soil gas, which they measured as an indicator of fuel

contamination in the unsaturated zone. They assumed that

advection had not occurred and attributed the toluene loss

to biodegradation. The investigators concluded that because toluene concentrations decayed near the oxygenated ground surface, soil venting is an attractive

remediation alternative for biodegrading light volatile hydrocarbon spills (Ostendorf and Kampbell, 1989).

The U.S. Air Force initiated its research and development

program in bioventing in 1988 with a study at Site 914,3

Hill AFB, Utah. This site was initially operated as a soil

vapor extraction unit but was modified to a bioventing

system after 9 months of operation because of evidence

that biodegradation was occurring and also as part of an

attempt to decrease costs by reducing off-gas. Moisture

and nutrient addition were studied at this site; however,

although moisture addition appeared to improve biodegradation, nutrient addition did not. Final soil sampling demonstrated that benzene, toluene, ethylbenzene, and

xylenes (BTEX) and total petroleum hydrocarbon (TPH)

levels decreased to below regulatory levels, and this site

became the first Air Force site that was closed through in

situ bioremediation. This study revealed that bioventing

had great potential for remediating JP-4 jet fuel-contaminated soils. The study also showed, however, that additional research would be needed before the technology

could be routinely applied in the field.

Following the Site 914, Hill AFB study, a more controlled

bioventing study was completed at Tyndall AFB,4

 Florida. This study was designed to monitor specific process

variables and the subsequent effect on biodegradation

of hydrocarbons. Several important findings resulted

from this study, including the effect of air flow rates on

removal by biodegradation and volatilization, the effect

of temperature on biodegradation rates, the lack of microbial stimulation from the addition of moisture and

nutrients, and the importance of natural nitrogen supply

through nitrogen fixation. In addition, initial and final

contaminant measurements showed over 90 percent

removal of BTEX. This study was short-term but illustrated the effectiveness of bioventing.

The studies conducted at Hill and Tyndall AFBs provided valuable information on bioventing. These studies also showed, however, that long-term, controlled

bioventing studies were necessary to fully evaluate and

optimize the technology. In 1991, long-term bioventing

studies were initiated at Site 280, Hill AFB, Utah, and

Site 20, Eielson AFB, Alaska.5

 These studies were joint

efforts between EPA and the U.S. Air Force Environics

Directorate of the Armstrong Laboratory. These studies

have involved intensive monitoring of several process

variables, including the effect of soil temperature on

biodegradation rates, surface emission analyses, and

optimization of flow rate.

Based on the success of these previous studies, in

1992, AFCEE initiated the Bioventing Initiative, where

pilot-scale bioventing systems were installed at 125 contaminated sites located throughout the continental

United States and in Hawaii, Alaska, and Johnston Atoll

(Figure 2-2). Sites varied dramatically in climatic and

geologic conditions. Contaminants typically were petroleum hydrocarbons from JP-4 jet fuel, heating oils,

waste oils, gasoline, and/or diesel; however, some fire

training areas also were studied where significant concentrations of solvents were present. This manual represents the culmination of this study and is the product

of the data collected from these sites and other projects.

In addition to these studies, other bioventing studies have

been conducted by several researchers. A summary of

data from some sites where bioventing has been applied

is shown in Table 2-2.6

 The scale of application and contaminant type is given, as well as the biodegradation rate,

if known. The studies listed in Table 2-2 are limited to those

where the study was conducted in situ, where no inoculum

was added to site soils, and where flow rates were optimized for biodegradation, not volatilization. A distinction

must be made between bioventing and SVE systems.

Bioventing systems operate at flow rates optimized for

biodegradation, not volatilization, although some volatilization may occur. SVE systems operate at flow rates

optimized for volatilization, although some biodegradation may occur. Therefore, flow rates and configurations

of the two systems are significantly different.

3 See Section 4.1 for a detailed discussion of this study.

4 See Section 4.2 for a detailed discussion of this study.

5 See Sections 4.3 and 4.4, respectively, for a detailed discussion of

these studies.

6 Only select Bioventing Initiative sites are included in this table. A

presentation of data from all Bioventing Initiative sites is provided in

Section 4.1.

6
The following section describes the basic structure for

field studies conducted as part of the Bioventing Initiative. Data from these studies were used to generate this

document.

2.3 Structure of Bioventing Initiative

Field Treatability Studies and

Bioventing System Design

The design of the field treatability studies and final

bioventing system was developed based on experience

from previous studies at Hill, Tyndall, and Eielson AFBs.

The Test Plan and Technical Protocol for a Treatability

Test for Bioventing (Hinchee et al., 1992) was written to

standardize all field methods, from treatability tests to

well installations. This allowed for collection of consistent data from 125 sites, which provided a strong database for evaluating bioventing potential. At all sites, the

following activities were conducted:

• Site characterization, including a small-scale soil gas

survey and collection of initial soil and soil gas samples for analysis of BTEX, TPH, and soil physicochemical characteristics.

• Field treatability studies, including an in situ respiration test and a soil gas permeability test.

• Identification of a background, uncontaminated area

for comparison with the contaminated area of background respiration rates and nutrient levels.

• Installation of a blower for 1 year of operation (typically configured for air injection), if results of field

treatability studies were positive.

• Conduct of 6-month and 1-year in situ respiration

tests at sites where a blower was installed.

• Collection of final soil and soil gas samples for analyses of BTEX and TPH.

Of particular significance were the use of the in situ

respiration test to measure microbial activity and the use

of air injection instead of extraction for air delivery.

The in situ respiration test was developed to rapidly

measure aerobic biodegradation rates in situ at discrete

locations.7

 Biodegradation rates calculated from the in

situ respiration test are useful for (1) assessing the

potential application of bioremediation at a given site, (2)

estimating the time required for remediation at a given

site, and (3) providing a measurement tool for evaluating

the effects of environmental parameters on microbial

activity and ultimately on bioventing performance. The

actual effect of individual parameters on microbial activity is difficult to assess in the field because of interference and interactions among these parameters. The in

situ respiration test integrates all factors to assess

whether the microorganisms are metabolizing the fuel.

Figure 2-2. Locations of Bioventing Initiative sites.

7 See Section 1.4 of Volume II for methods for conducting the in situ

respiration test and analyses of test data.

7
Data from the in situ respiration test and site measurements were used to conduct a statistical analysis of the

observed effects of the site measurements on microbial

activity in the field. The statistical analysis was constructed to account for parameter interactions. These

results are discussed in detail in Chapter 5.

Also of note is that 120 of the 125 bioventing systems

installed were configured for air injection. Before the

bioventing studies conducted at Hill (Site 280) and

Eielson AFBs, bioventing systems were typically operated in the extraction configuration, similar to SVE

systems. Research at Hill and Eielson AFB’s, however,

demonstrated that air injection was a feasible, more efficient alternative to air extraction, resulting in a greater

proportion of hydrocarbon biodegradation rather than

volatilization and reduced air emissions.8

 Therefore, the

Table 2-2. Summary of Reported in Situ Respiration Rates and Bioventing Data

Site Scale of Application Contaminant

In Situ Respiration

Rates (mg/kg-day

Unless Marked) Reference

Albemarle County, VA Pilot scale Acetone, toluene,

benzene, naphthalene

1.5-26 Leeson et al., 1994

Eielson AFB, AK Pilot scale JP-4 jet fuel 0.82-8.2 Hinchee and Ong, 1992

Leeson et al., 1995

EPA, 1994c

Fallon NAS, NE In situ respiration test JP-5 jet fuel 4.2 Hinchee et al., 1991b

Galena AFS, AK, Saddle Tank

Farm

Pilot scale Diesel 11-30 Ong et al., 1994

Hill AFB, Utah, Site 914 Full scale, 2 years JP-4 jet fuel Up to 8.5 Hinchee et al., 1994

Hill AFB, Utah, Site 280 Full scale JP-4 jet fuel 0.27 (site average) Battelle, 1994

EPA, 1991b

Eglin AFB, FL Full scale Gasoline 4.0 Downey et al., 1994

Kenai, Alaska, Site 1-33 Pilot scale Crude oil, petroleum 2.7-25 Hinchee, unpublished

data

Kenai, Alaska, Site 3-9 Pilot scale Crude oil 0.64-12 Hinchee, unpublished

data

Massachusetts Full scale Gasoline Not measured Brown and Crosbie, 1994

Minnesota Full scale Gasoline 15, 4.9, 3.1, 0.20 Newman et al., 1993

The Netherlands Full scale Gasoline 570 kg of

hydrocarbon

removed during

2-year study

van Eyk, 1994

The Netherlands Undefined Undefined 1.6-4.2 Urlings et al., 1990

The Netherlands Field pilot, 1 year Diesel 6.9 van Eyk and Vreeken,

1989b

Patuxent River NAS, MD In situ respiration test JP-5 jet fuel 2.6 Hinchee et al., 1991b

Prudhoe Bay Pilot scale Diesel 8.6-11 Ong et al., 1994

St. Louis Park, MN, Reilly Tar

Site

Pilot scale PAH 0.55-2.2 mg

PAH/kg-day

Alleman et al., 1995

Seattle, WA Full scale Diesel 6.0 Baker et al., 1993

Southern CA Full scale Gasoline, hydraulic oil 0.14 Zachary and Everett, 1993

Tinker AFB, OK In situ respiration test JP-4 and mixed fuels 2.3-15 Hinchee and Smith, 1991

Tyndall AFB, FL Field pilot, 1-year and

in situ respiration test

JP-4 jet fuel 1.6-16 Miller, 1990

Hinchee et al., 1991b

Undefined Full scale Gasoline and diesel 50 kg/(well day) Ely and Heffner

Undefined Full scale Diesel 100 kg/(well day) Ely and Heffner, 1988

Undefined Full scale Fuel oil 60 kg/(well day) Ely and Heffner, 1988

Valdez, Site A Pilot scale Crude oil 0.90-15.6 Hinchee, unpublished data

8 See Section 2.1 of Volume II for a discussion of air injection versus

extraction considerations.

8
air injection configuration was selected for the basic

bioventing system at Bioventing Initiative sites.

The results generated from the Bioventing Initiative are

summarized in detail in Chapter 5 but also are used to

illustrate basic principles of bioventing and microbial

processes discussed in Chapter 3. The design guidelines presented in this manual are the result primarily of

the information gained from installing and operating the

125 Bioventing Initiative sites. These design guidelines

represent the basic bioventing system, which is applicable to the majority of sites suitable for bioventing. The

following section addresses emerging techniques for

modifying the basic bioventing system for use at sites

that are not amenable to standard bioventing methods.

2.4 Emerging Techniques for

Modifications to Bioventing Systems

Several techniques are being investigated as a means of

modifying the conventional bioventing system described in

this document. These techniques have not been tested

extensively in the field; therefore, their potential feasibility

is unknown. These techniques are briefly presented in this

section to illustrate their potential application.

The bioventing modifications being investigated are

designed to address specific challenges in bioventing

including:

• Injection of pure oxygen instead of air for treatment

of low-permeability soils: Because only low flow rates

are possible in low-permeability soil, injection of pure

oxygen may be useful for providing larger oxygen

concentrations for a given volume than is possible

with air injection.

• Soil warming for bioventing in cold climates: Soil

warming can be used to increase biodegradation

rates, thus decreasing remediation times. This technique has been studied in detail at Site 20, Eielson

AFB, Alaska9

 but would only be an option in extreme

environments.

• Remediation of recalcitrant compounds through

ozonation: Ozonation may be used to partially oxidize

more recalcitrant contaminants, making them more

susceptible to biodegradation. This technique would

not be necessary at petroleum-contaminated sites

but may be considered at sites contaminated with

compounds such as polycyclic aromatic hydrocarbons (PAHs) or pesticides.

• Remediation of contaminated saturated soils through

air sparging: Air sparging is being investigated as a

means of aerating saturated soil to enhance biodegradation and volatilization. Studies to date, however,

have been inconclusive concerning its effectiveness

because the studies lacked adequate controls and

measurement techniques.

The techniques described above represent potential future areas of investigation in the bioremediation field.

The following chapters describe the principles of

bioventing, which also apply to the techniques described

in this section.

9 See Section 4.4 for a discussion of this site and the cost benefits of

soil warming.

9
Chapter 3

Principles of Bioventing

In this chapter, basic principles fundamental to the

bioventing process are discussed to provide a clear

understanding of the many physical, chemical, and

biological processes that affect the ultimate feasibility of

bioventing. Recognizing the significance of these different processes will lead to more efficient bioventing

design and operation. Specific topics addressed in this

chapter include:

• Soil gas permeability, contaminant diffusion and distribution, and zone of oxygen influence.

• Environmental factors that affect microbial processes, such as electron acceptor conditions, moisture

content, pH, temperature, nutrient supply, contaminant concentration, and bioavailability.

• Subsurface distribution of an immiscible liquid.

• Compounds targeted for removal through bioventing.

• BTEX versus TPH removal during petroleum bioventing.

3.1 Physical Processes Affecting

Bioventing

Three primary physical characteristics affect bioventing.

These include soil gas permeability, contaminant diffusion and distribution, and zone of oxygen influence.

Each of these parameters is discussed in the following

sections.

3.1.1 Soil Gas Permeability

Assuming contaminants are present that are amenable

to bioventing, geology probably is the most important

site characteristic for a successful bioventing application.

Soils must be sufficiently permeable to allow movement

of enough soil gas to provide adequate oxygen for

biodegradation, approximately 0.25 to 0.5 pore volumes per day.

Soil gas permeability is a function of soil structure and

particle size, as well as moisture content. Typically,

permeability in excess of 0.1 darcy is adequate for

sufficient air exchange. Below this level, bioventing

certainly is possible, but field testing may be required

to establish feasibility.

When the soil gas permeability falls below approximately 0.01 darcy, soil gas flow is primarily through

either secondary porosity (e.g., fractures) or any more

permeable strata that may be present (e.g., thin sand

lenses). Therefore, the feasibility of bioventing in lowpermeability soils is a function of the distribution of flow

paths and diffusion of air to and from the flow paths

within the contaminated area.

In a soil that is of reasonable permeability, a minimum

separation of 2 ft to 4 ft (0.61 m to 1.2 m) between

vertical and horizontal flow paths and contaminant may

still result in successful treatment because of oxygen

diffusion. The degree of treatment, however, will be very

site-specific.

Bioventing has been successful in some low-permeability soils, such as a silty clay site at Fallon Naval Air

Station (NAS), Nevada (Kittel et al., 1995), a clayey site

at Beale AFB, California (Phelps et al., 1995), a silty site

at Eielson AFB, Alaska (Leeson et al., 1995), a silty clay

site in Albemarle County, Virginia (Leeson et al., 1994),

and many Bioventing Initiative sites. Grain size analysis

was conducted on several samples from each site in the

Bioventing Initiative. The relative distribution of finegrained soils is illustrated in Figure 3-1. Sufficient soil

gas permeability has been demonstrated at many sites

with silt and clay contents exceeding 80 percent by

weight. Approximately 50 percent of the sites tested

Figure 3-1. Distribution of fine-grained soils (silt and clay) at

Bioventing Initiative sites.

11
contained greater than 50 percent clay and silt fractions.

Oxygen distribution has generally been adequate in

soils where permeability values exceeded 0.1 darcy,

with oxygen detected at ambient levels in all nine of the

monitoring points installed. Few sites had permeability

less than 0.1 darcy; therefore, data are limited for analysis. The greatest limitation to bioventing at Bioventing

Initiative sites has been excessive soil moisture. A combination of high soil moisture content and fine-grained

soils has made bioventing impractical at only three of

the 125 test sites, however.

In general, our calculated soil gas permeability values

have exceeded suggested values reported in Johnson

et al. (1990) for silt and clay soils. This is probably

because of the heterogeneous nature of most soils,

which contain lenses of more permeable material or

fractures that aid in air distribution.

3.1.2 Contaminant Distribution

Another important factor affecting the feasibility of

bioventing is contaminant distribution throughout the

site. Because bioventing is in essence an air delivery

system designed to efficiently provide sufficient oxygen

to contaminated soils, a clear understanding of subsurface contaminant distribution is a necessity. Many sites

at which bioventing can be applied are contaminated

with immiscible liquids, such as petroleum hydrocarbons. When a fuel release occurs, the contaminants

may be present in any or all of four phases in the

geologic media:

• Sorbed to the soils in the vadose zone.

• In the vapor phase in the vadose zone.

• In free-phase form floating on the water table or as

residual saturation in the vadose zone.

• In the aqueous phase dissolved in pore water in the

vadose zone or dissolved in the ground water.

Of the four phases, dissolved petroleum contaminants

in ground water frequently are considered to be of

greatest concern due to the risk of humans being exposed to contaminants through drinking water. The

free-phase and sorbed-phase hydrocarbons, however,

act as feed stocks for ground-water contamination, so

any remedial technology aimed at reducing groundwater contamination must address these sources of

contamination. Also, hydrocarbons in the vadose zone

can produce a volatile organic carbon (VOC) threat in

subsurface buildings or structures.

Immiscible liquids are classified as less dense nonaqueous phase liquids (LNAPLs) if their density is less

than water or dense nonaqueous phase liquids

(DNAPLs) if their density is greater than water. In general, most petroleum hydrocarbons, such as gasoline,

are LNAPLs, whereas most chlorinated solvents, such

as trichloroethylene (TCE), are DNAPLs. Because of

these differences in densities, subsurface spills of

LNAPLs and DNAPLs behave differently at a given site,

with LNAPLs distributed primarily in the vadose zone

and DNAPLs distributed in both the unsaturated and

saturated zones. Because bioventing is primarily a

vadose zone treatment process, this discussion focuses

on the behavior of LNAPLs.

When a large-enough fuel spill occurs, the fuel is retained within approximately 10 percent to 20 percent of

the pore volume of the soil and may eventually come to

rest on the water table. Contaminants then partition

among the various phases existing within the subsurface environment. Fluids can move through the subsurface via various mechanisms, such as advection and

diffusion. LNAPLs are likely to migrate through the

vadose zone relatively uniformly until they reach the

capillary fringe. The LNAPLs will then spread laterally

along the saturated zone. Water table fluctuation may

result in LNAPL below the water table; however, an

LNAPL will not permeate the water-saturated zone unless a critical capillary pressure is exceeded, which is a

function of the porous medius pore sizes.

In the vadose zone, components of the LNAPL may

partition into the vapor phase or the aqueous phase

(pore water), sorb onto solids, or remain in the free

product. Contaminants in free product may partition into

the vapor phase, depending on their vapor pressures at

the temperature and pressure existing in the vadose

zone. Once in the vapor phase, these contaminants can

migrate in response to advection and diffusion. Raoult’s

Law is used to describe partitioning at equilibrium between an immiscible and a vapor phase:

Cv = χ Cvsat (Eq. 3-1)

where:

CV = volumetric concentration of the contaminant

(x) in the vapor phase (gx/Lvapor)

χ = mole fraction of the contaminant

(dimensionless)

Cvsat = saturated vapor concentration of the

contaminant (gx/Lvapor)

Cvsat is further defined as:

Cvsat = (MWx) Pv

RTabs

(Eq. 3-2)

where:

MWx = molecular weight of the contaminant

(gx/molex)

PV = vapor pressure of pure contaminant at

temperature T (atm)

R = gas constant (L-atm/mole-°K); and

Tabs = absolute temperature (°K)

12
Free product in contact with ground water may leach

contaminants into the ground water, or contaminants

may dissolve into pore water in the vadose zone, depending on the solubility of specific components. Once

in the ground water, contaminants can migrate through

the subsurface in response to a gradient in the aqueousphase total potential (i.e., advection) or by a difference

in the aqueous-phase chemical concentrations. The

equilibrium relationship between the aqueous and the

immiscible phases is described as:

Cw = χ sx (Eq. 3-3)

where:

CV = volumetric concentration of the contaminant x

in the aqueous phase (gx/Laqueous)

χ = mole fraction of the contaminant

(dimensionless)

sx = solubility of pure contaminant x in water

(gx/Lwater)

Sorption of contaminants is a complex process involving

several different phenomena, including coulomb forces,

London-van der Waals forces, hydrogen bonding, ligand

exchange, dipole-dipole forces, dipole-induced dipole

forces, and hydrophobic forces. In the case of hydrocarbons, because of their nonpolar nature, sorption most

often occurs through hydrophobic bonding to organic

matter. Hydrophobic bonding often is a dominant factor

influencing the fate of organic chemicals in the subsurface (DeVinny et al., 1990). The degree of sorption

generally is empirically related by the organic content of

the soil and the octanol-water partition coefficient of a

particular compound.

Sorption isotherms generally follow one of three shapes:

Langmuir, Freundlich, or linear (Figure 3-2). The Langmuir isotherm describes the sorbed contaminant concentration as increasing linearly with concentration, then

leveling off as the number of sites available for sorption

are filled. This isotherm accurately describes the situation

at or near the contaminant source, where concentrations are high. The Freundlich isotherm assumes an

infinite number of sorption sites, which would accurately

describe an area some distance from the contaminant

source, where concentrations are dilute. The mathematical

expression contains a chemical-specific coefficient that

may alter the linearity of the isotherm. The linear isotherm is relatively simple and is valid for dissolved

compounds at less than one-half of their solubility (Lyman et al., 1992). This isotherm is typically valid to

describe hydrocarbon sorption.

The linear isotherm is expressed mathematically as:

Cs = Kd Cw (Eq. 3-4)

where:

CS = quantity of contaminant x sorbed to the solid

matrix (gx/gsoil)

Kd = sorption coefficient (Laqueous/gsoil)

CW = volumetric concentration of contaminant x in

the aqueous phase (gx/Laqueous)

The sorption coefficient may be determined experimentally, estimated based on values published in the literature or estimated using the octanol/water partition

coefficient (Kow) and the organic carbon fraction (foc) of

the soil. The sorption coefficient can be estimated using

the following mathematical expression:

Kd = Kow foc (Eq. 3-5)

Some values for Kow are provided in Table 3-1.

In practice, at equilibrium, the concentration of most

petroleum hydrocarbon compounds of interest in the

aqueous or vapor phases is driven by the immiscible

phase, if present, and the sorbed phase, if the immiscible phase is not present. If no immiscible phase is

present, and all sorption sites on the solid soil matrix are

Table 3-1. Values for Key Properties of Select Petroleum

Hydrocarbons

Compound Kow

Solubility

(mg/L)

Vapor Pressure

(mm Hg)a

Benzene 131.82 1,750b 75

Ethylbenzene 1,349 152b 1079°F

Heptane — 50 40

Hexane — 20 150 

Toluene 489.9 537c 2065°F

o-xylene 891 152b 7

m-xylene 1,585 158b 9

p-xylene 1,513.6 198b 9

a Vapor pressure at 68°F unless noted.

b Calculated at 20°C.

c Figure 3-2. Sorption isotherms. Calculated at 20°C.

13
not occupied,1

 the vapor- or aqueous-phase concentration is a function of the sorbed concentration. This relationship is illustrated in Figure 3-3.

This relationship typically follows a Langmuir type curve.

If the concentration in the soil is in excess of the sorption

capacity of the soil,2

 the aqueous-phase and the vaporphase concentrations are Raoult’s Law-driven and are

independent of the hydrocarbon concentration in the

soil. This is an important concept in attempting to interpret soil gas or ground-water data. For example, in a

sandy site at which free product has been detected, the

highest soil hydrocarbon concentrations may exceed

25,000 mg/kg. Yet, 99 percent remediation to 250 mg/kg

may not affect the equilibrium soil gas or ground-water

hydrocarbon concentrations.

In terms of contaminant distribution, difficulties in applying bioventing arise when significant quantities of

the contaminant are in the capillary fringe or below the

water table because of ground-water fluctuations.

Treatment of the capillary fringe is possible, and

screening of venting wells below the water table is

recommended to ensure treatment of this area.3

 The

ability of bioventing to aerate the capillary fringe and

underlying water table has not been evaluated, however. Limited oxygenation is anticipated because of

water-filled pore space. If significant contamination exists below the water table, dewatering should be considered as a means of exposing any contaminated soil to

injected air. Alternatively, a combination of air sparging

and bioventing may provide more efficient air delivery to

the capillary fringe; however, air sparging has not been

well documented, and many parameters are still unknown concerning its applicability and effectiveness.

3.1.3 Oxygen Radius of Influence

An estimate of the oxygen radius of influence (RI) of venting

wells is an important element of a full-scale bioventing design. This measurement is 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.

The radius of oxygen influence is defined as the radius

to which oxygen has to be supplied to sustain maximal

biodegradation. This definition of radius of influence is

different than is typically used for SVE, where radius of

influence is defined as the maximum distance from the

air extraction or injection well where vacuum or pressure

(soil gas movement) occurs. The oxygen radius of influence is a function of both air flow rates and oxygen

utilization rates, and therefore depends on site geology,

well design, and microbial activity.

The radius of influence is a function of soil properties but

also is dependent on the configuration of the venting well,

extraction or injection flow rates, and microbial activity, and

also is altered by soil stratification. In soils with less permeable lenses adjacent to more permeable soils, injection

into the permeable layer produces a greater radius of

influence than could be achieved in homogeneous soils.

On sites with shallow contamination, the radius of influence also may be increased by impermeable surface

barriers such as asphalt or concrete. Frequently, however,

paved surfaces do not act as vapor barriers. Without a tight

seal to the native soil surface,4

 the pavement does not

significantly affect soil gas flow.

Microbial activity affects the oxygen radius of influence.

As microbial activity increases, the effective treated area

decreases. Therefore, a desirable approach is to estimate the oxygen radius of influence at times of peak

microbial activity and to design the bioventing system

based on these measurements.

3.2 Microbial Processes Affecting

Bioventing

Biological treatment approaches rely on organisms to

destroy or reduce the toxicity of contaminants. The

advantages of chemical and physical treatment approaches generally are outweighed by the ability of

microorganisms to mineralize contaminants, thereby

eliminating the process of transferring contaminants

from one medium (i.e., soil and soil vapor) into another

medium (i.e., activated carbon) that will still require treatment. In addition, microbial processes allow treatment of

Figure 3-3. Relationship between sorbed contaminant concentrations and vapor- or aqueous-phase concentrations.

1 In most soils, this is probably at a concentration of less than 100

mg/kg to 1,000 mg/kg.

2 In most soils, this is probably at a concentration of less than 100

mg/kg to 1,000 mg/kg

3 See Section 2.5 of Volume II for a discussion of vent well construction.

4 Based on the author’s experience, this seal does not occur at most

sites.

14
large areas relatively inexpensively and with relatively

noninvasive techniques. This section discusses kinetics

of microbial metabolism and environmental parameters

that affect the microbial processes bioventing is dependent upon, thereby potentially affecting the efficacy of

bioventing.

3.2.1 Microbial Kinetics

In biological processes, microorganisms degrade organic compounds either directly to obtain carbon and/or

energy, or fortuitously in a cometabolic process with no

significant benefit to the microorganism. As an example,

a stoichiometric equation describing degradation of

n-hexane is shown:

C6H14 + 7.875O2 + 0.25NO3 →

CH2O0.5N0.25(biomass) +

5CO2 + 6H2O (Eq. 3-6)

In the case of bioventing, where microorganisms are

stimulated in situ, the microorganisms are at equilibrium,

and little net biomass growth occurs. In other words,

biomass decay approximately balances biomass

growth. Consequently, where no net biomass is produced, Equation 3-6 reduces to:

C6H14 + 9.5O2 → 6CO2 + 7H2O (Eq. 3-7)

Based on Equation 3-7, 9.5 moles of oxygen are required for every mole of hydrocarbon consumed, or, on

a weight basis, approximately 3.5 g of oxygen are required for every 1 g of hydrocarbon consumed.

Predicting the amount of time needed to bioremediate

a site requires an understanding of the microbial kinetics of substrate (contaminant) utilization. Most substrate utilization falls under the heading of primary

substrate utilization, in which growth on a carbon

source supplies most of the carbon and energy for the

microorganism. In cases where a contaminant does not

supply the primary source or cannot be used for carbon

and energy, secondary substrate utilization or

cometabolism may occur. During the bioventing process, primary substrate utilization generally describes

the kinetics of the reactions taking place; however, in

some instances, cometabolic processes also may occur. For example, at sites contaminated with both fuels

and solvents, such as TCE, cometabolic bioventing

may account for degradation of TCE.

Primary substrate utilization has been described through

an empirical approach by the Monod expression:

− dS

dt = kXS

Ks + S

(Eq. 3-8)

where:

S = concentration of the primary substrate

(contaminant) (gS/L)

t = time (minutes)

k = maximum rate of substrate utilization (gS/gXmin)

X = concentration of microorganisms (gX/L)

KS = Monod half-velocity constant (gS/L)

At high substrate concentrations (S is greater than KS), the

rate of substrate utilization is at a maximum, limited by

some other factor such as oxygen, nutrients, or the characteristics of the microorganism. In this instance, the rate

of substrate utilization is first-order with respect to cell

density but zero-order with respect to substrate concentration. Conversely, when the primary substrate concentration is very low (S is less than KS), the substrate utilization

rate is first-order with respect to both cell density and

substrate concentration. In a well-designed bioventing system, kinetics based on oxygen utilization are zero-order.

The rate based on petroleum or other contaminant removal may be described, however, by Monod or inhibition

kinetics.

Monod kinetics have been widely applied to conventional wastewater treatment, where the compounds being treated generally are bioavailable and readily

degradable. Bioventing typically is applied to aerobically

biodegradable compounds; however, the maximum rate

of biodegradation (k) is much lower than for most wastes

in conventional wastewater treatment. For example,

Howard et al. (1991) estimated that benzene has an

aerobic half-life (dissolved in ground water) of 10 days

to 24 months, whereas ethanol (a compound more typical of conventional wastewater treatment) is estimated

to have a half-life of 0.5 to 2.2 days. Bioventing kinetics

are further complicated by bioavailability of the contaminants, driven at least in part by solubilization. Because

microorganisms exist in pore water, contaminants must

partition into the pore water to be available for degradation. Although high soil contaminant concentrations may

be present, the actual concentration of hydrocarbon

dissolved in the pore water and available to the microorganisms may be low.

In practice, oxygen utilization rates tend to decline

slowly with time during remediation. At many sites, this

trend may be difficult to follow over periods of less than

1 to 3 years because of other variables affecting the rate,

such as temperature and soil moisture. This decline may

not be indicative of true first-order kinetics but may

simply be the result of selective early removal of more

degradable compounds, such as benzene.

3.2.2 Environmental Parameters Affecting

Microbial Processes

Bioventing depends upon providing microorganisms optimal conditions for active growth. Several factors may

15
affect a microorganism’s ability to degrade contaminants, including:

• Availability and type of electron acceptors

• Moisture content

• Soil pH

• Soil temperature

• Nutrient supply

• Contaminant concentration

• Bioavailability and relative biodegradation

Each of these parameters was measured at Bioventing

Initiative sites. The actual effect of individual parameters

on microbial activity is difficult to assess in the field

because of interference and interactions among these

parameters. The in situ respiration test was used as a

measurement tool that integrates all factors to assess

whether the microorganisms are metabolizing the fuel.

Data from the in situ respiration test and site measurements were used to conduct a statistical analysis of the

observed effects of the site measurements on microbial

activity in the field. The statistical analysis was constructed to account for parameter interactions. These

results are discussed in detail in Chapter 5. A more

general discussion of the significance of each of these

parameters and its effect on microbial activity is provided in Sections 3.3.2.1 through 3.3.2.7.

3.2.2.1 Electron Acceptor Conditions

One of the most important factors influencing the biodegradability of a compound is the type and availability of

electron acceptors. Following a hydrocarbon spill, for

example, the microbial degradation of biodegradable

hydrocarbons results in oxygen depletion and thus anaerobic conditions in the subsurface soil. Although hydrocarbons may undergo limited biodegradation under

anaerobic conditions (Bilbo et al., 1992; Mormile et al.,

1994), aerobic conditions generally are most suitable for

relatively rapid remediation of petroleum hydrocarbons.

Therefore, oxygen supply is crucial to the success of a

bioventing system. In field studies, oxygen has been

found to be the most important factor in determining the

success of a bioventing system (Hinchee et al., 1989;

Miller et al., 1991). The Bioventing Initiative confirmed

this conclusion, finding that oxygen was the primary

factor limiting microbial activity at all but three sites

(Miller et al., 1993).

3.2.2.2 Moisture Content

Soil moisture content may affect the bioventing process

by its effect on microorganisms or soil gas permeability.

Microorganisms require moisture for metabolic processes and for solubilization of energy and nutrient supplies. Conversely, soil moisture content directly affects

soil permeability, with high moisture content resulting in

poor distribution of oxygen. In practice, soil moisture has

been found to directly limit biodegradation rates only

where bioventing has been implemented in very dry

desert environments. A more common influence of moisture is that excess moisture has led to significant reductions in soil gas permeability. One major objective of the

Bioventing Initiative was to assess the effects of moisture on biodegradation.

The range of soil moisture content measured at Bioventing Initiative sites is shown in Figure 3-4. The lowest soil

moisture content measured was 2 percent by weight,

and microbial activity still was observed in these soils.

Figure 3-5 illustrates the observed relationship between

soil moisture and oxygen utilization rates. To date, a

strong correlation has not been recorded between moisture content and oxygen utilization rate, although a slight

positive relationship has been observed.5

Figure 3-4. Soil moisture content measurements at Bioventing

Initiative sites.

Figure 3-5. Direct correlation between oxygen utilization rates

and soil moisture content at Bioventing Initiative

sites.

5 See Section 5.2 for a discussion of the statistical relationship between moisture content and oxygen utilization rates.

16
At a desert site at the Marine Corps Air Ground Combat

Center, Twentynine Palms, California, soil moisture content appeared to detrimentally affect microbial activity.

Soil moisture content ranged from 2 percent to 4 percent

by weight and, although the site was contaminated with

jet fuel, significant oxygen limitation was not observed.

An irrigation system was installed at the site in an effort

to enhance microbial activity. The site was irrigated for

1 week, then bioventing was initiated for 1 month before

conducting an in situ respiration test. In situ respiration

rates measured after irrigation were significantly higher

than those measured before irrigation (Figure 3-6). In

addition, before irrigation, oxygen was not consumed

below approximately 17 percent before microbial activity

stopped. After irrigation, activity continued until oxygen

was completely consumed to less than 1 percent. These

results demonstrated that in extreme cases, moisture

addition may improve the performance of bioventing

systems through enhanced microbial activity.

Air injection bioventing may dry out the soil to a point

that would be detrimental to microbial growth, necessitating humidification of the injection air. A simple calculation, however, as shown in Example 3-1, illustrates

that moisture loss is minimal over a 3-year period. Drying and moisture loss as a result of bioventing usually

are only a problem very near the vent well or if very high

air injection rates are used (typically not the case in

properly designed bioventing systems). Sites typically

have several moisture sources that also make drying

due to air injection negligible, such as rain and snow,

and water as a by-product of mineralization (generated

at a rate of 1.5 kg of water for every 1 kg of hydrocarbon

degraded).6

Example 3-1. Moisture Content Change During Air Injection and Water Generated During Biodegradation:

For this test:

Vapor pressure (Pwater) = 17.5 mm Hg

Flow rate (Q) = 1 pore volume/day

(typical of bioventing)

Volume of treatment

area (V)

= 12,300 m3

Biodegradation rate (kB) = 3 mg/kg-day

Initial moisture content = 15 percent by weight

Soil bulk density = 1,440 kg/m3

Assume worst case of 0 percent humidity and no

infiltration.

To calculate the total water at the site initially, the mass

of soil is first calculated:

12,300 m3 × 1,440 kg

m3 = 1.8 × 107

 kg soil

Therefore, the initial mass of water is:

(1.8 × 107

 kg soil) × 0.15 = 2.7 × 106 kg H2O

Because the flow rate is equivalent to 1 pore volume/day,

the mass of water removed per day will be equal to the

mass of water in the vapor phase of the treated area, which

can be calculated using the Ideal Gas Law:

Figure 3-6. Oxygen and carbon dioxide concentrations before and after irrigation at Twentynine Palms, California.

6 See Equation 3-7 for the stoichiometry of this calculation.

17
Total water removal in 3 years:

Moles H2O removed

day = Pwater V

RT =

17.5 mm Hg × 12,300 m3







0.0623 m3pmm Hg

molep8K







× 2988K

Moles H2O removed

day = 11,600 = 210 kg

day

210 kg

day × 1,095 days = 230,000 kg removed

This water loss represents a fairly small percentage, or:

230,000 kg evaporated

2.7 × 106

 initial mass = 0.086 ≈ 8.6% H2O loss

This is equivalent to a soil moisture drop from approximately 15 percent to 13.7 percent. Assuming a contaminated thickness of 10 ft (3 m), an infiltration rate of

approximately 2.4 inches (6.1 cm) in 3 years, or less

than 1 inch (2.5 cm) per year, would replace the lost

moisture. In practice, some drying very close to the vent

well may be observed but usually is not.

Water loss also will be replaced through biodegradation

of hydrocarbons. Calculating the total mass of hydrocarbons degraded over 3 years:

3 mg

kgpday × 1,095 days × (1.8 × 107

 kg soil) ×

kg

106

mg = 59,000 kg hydrocarbon degraded

Based on the stoichiometry in Equation 2-1, if 1.5 kg of

water are generated for every kg of hydrocarbon degraded, the amount of water generated would be:

59,000 kg hydrocarbon × 1.5 kg water

kg hydrocarbon =

88,500 kg water

Therefore, total water removal in 3 years must also

account for the water generation, where:

230,000 kg − 88,500 kg H2O = 141,500 kg H2O loss

This is equivalent to a water loss of 5.3 percent over 3

years.

3.2.2.3 Soil pH

Soil pH also may affect the bioremediation process because microorganisms require a specific pH range to

survive. Most bacteria function best in a pH range between 5 and 9 with the optimum being slightly above 7

(Dragun, 1988). A shift in pH may result in a shift in the

makeup of the microbial population because each

species exhibits optimal growth at a specific pH.

Throughout the Bioventing Initiative, pH has not been

found to limit in situ bioremediation and is probably

only of concern where contamination has radically

altered the existing pH.

Figure 3-7 illustrates the range of soil pH found at the

Bioventing Initiative sites to date. In general, the majority

of sites have fallen within the “optimal” pH range for

microbial activity of 5 to 9. Microbial respiration based

on oxygen utilization has been observed at all sites,

however, even in soils where the pH was below 5 or

above 9. Figure 3-8 illustrates the observed relationship

between pH and oxygen utilization rates. These observations suggest that pH is not a concern when bioventing at most sites.7

Figure 3-7. Soil pH measurements at Bioventing Initiative sites.

7 See Section 5.2 for a discussion of the statistical relationship between pH and oxygen utilization rates.

Figure 3-8. Correlation between oxygen utilization rate and soil

pH at Bioventing Initiative sites.

18
3.2.2.4 Soil Temperature

Soil temperature may significantly affect the bioremediation process. Microbial activity has been reported at temperatures varying from -12°C to 100°C (10°F to 212°F)

(Brock et al., 1984); however, the optimal range for biodegradation of most contaminants is generally much narrower. An individual microorganism may tolerate a

temperature peak of up to approximately 40°C (104°F). A

microorganism’s optimal growth temperature, however,

varies depending on climate. For example, microorganisms in a subarctic environment may exhibit optimal

growth at 10°C (50°F), whereas microorganisms in a subtropical environment may exhibit optimal growth at 30°C

(86°F).

Generally biodegradation rates double for every 10°C

(50°F) temperature increase, up to some inhibitory temperature. The van’t Hoff-Arrhenius equation expresses

this relationship quantitatively as:

kT = ko e 

−Ea

RTabs

(Eq. 3-9)

where:

kT = temperature-corrected biodegradation rate

(percentage of O2/day)

ko = baseline biodegradation rate (percentage of

O2/day)

Ea = activation energy (cal/mole)

R = gas constant (1.987 cal/°K-mol)

Tabs = absolute temperature (°K)

Miller (1990) found Ea equal to 8 to 13 kcal/mole for in situ

biodegradation of jet fuel. In the 17°C to 27°C (63°F to

81°F) range, the van’t Hoff-Arrhenius relationship accurately predicted biodegradation rates. A similar analysis

was conducted at Site 20, Eielson AFB, Alaska, where the

activation energy was found to be equal to 13.4 kcal/mole

(Example 3-2). Figure 3-9 illustrates the relationship between oxygen utilization rate and temperature and between biodegradation and temperature observed at Site

20, Eielson AFB, a JP-4 jet fuel-contaminated site.

Example 3-2. Calculation of the van’t Hoff-Arrhenius

Constant From Site Data: Various forms of soil warming

were tested at Site 20, Eielson AFB, Alaska. This resulted in a wide range of temperatures and biodegradation rates measured at the same site.

To calculate the van’t Hoff-Arrhenius constant, the log of

the biodegradation rate must be calculated versus the

inverse of the temperature to provide the relationship:

In 





kT

KO







= −Ea

R ×

1

T

The slope of the linear regression of inverse temperature versus oxygen utilization rate is -6,740 °K (Figure

3-9). Therefore,

Ea

R = −6,740

Ea

1.987 cal

8Kpmole

= −6,740

Ea = 1.987 cal

8Kpmole × −6,740 =

13,390 cal

mole≈ 13.4 kcal

mole

Heat addition may improve bioventing processes. Solar

warming, warm water infiltration, and buried heat tape

have been used to increase soil temperature. Their use

has increased microbial activity and contaminant degradation (Leeson et al., 1995). Selection of a soil warming

technique depends on a comparison of cost considerations versus remediation time requirements.8

 Although

Figure 3-9. Soil temperature versus oxygen utilization and

biodegradation rate at Site 20, Eielson AFB, Alaska.

8 See Section 4.4 for a discussion of the cost benefit of soil warming.

19
warm water infiltration or heat tape can significantly

increase biodegradation rates, the cost is significantly

higher than simply using surface insulation or no heating method. The use of warm water infiltration, although

effective, is limited to very permeable soils to ensure that

adequate drainage of the applied water occurs. The use

of soil heating to increase biodegradation rates may only

prove cost-effective in cold regions, such as Alaska.

3.2.2.5 Nutrient Supply

To sustain microbial growth, certain nutrients must be

available at minimum levels. The following nutrients/cofactors are known to be required in order to support

microbial growth: calcium, cobalt, copper, iron, magnesium, manganese, molybdenum, nitrogen, phosphorus,

potassium, sodium, sulfur, and zinc. Nitrogen and phosphorus are required in the greatest concentrations and

are the nutrients most likely to limit microbial growth.

The remaining chemicals are considered micronutrients

because they are required in only small quantities and

generally are available in excess in nature.

Nutrients are required as components of the microbial

biomass. The need for these nutrients is very different

from the need for oxygen (or other electron donors) and

the carbon source. Nutrients are not destroyed but are

recycled by the ecosystem. Thus, unlike oxygen, a

steady input of nutrient is not required.

An approach to estimation of nutrient requirements, suggested by John T. Wilson of the EPA Ada Laboratory, can

be made based on microbial kinetics. Starting with:

dX

dt = Kb Y − Kd X (Eq. 3-10)

where:

X = biomass (mg biomass/kg soil)

kB = biodegradation rate (mg hydrocarbon/kg

soil-day)

Y = cell yield (mg biomass/mg hydrocarbon)

kd = endogenous respiration rate (day-1)

Assuming that the biomass concentration achieves

steady state during bioventing,

dX

dt = 0 = Kb Y − Kd X (Eq. 3-11)

Solving:

X = Kb Y

Kd

(Eq. 3-12)

Little is known about the in situ cell yields or endogenous

respiration rates of hydrocarbon-degrading organisms,

but these parameters can be estimated based on ranges

reported in the wastewater treatment literature (Metcalf

and Eddy, 1979). An example for calculating required

nutrients is shown in Example 3-3.

Example 3-3. Estimation of Nutrient Requirements in

Situ: For a given site, the following is assumed:

kB = 10 mg/kg-day (typical rate found at

bioventing sites)

Y = 0.5 mg/mg

kd = 0.05/day

Solving:

X =

10 mg

kgpday × 0.5 mg

mg

0.05

day

= 100 mg

kg

To sustain 100 mg/kg of biomass, the nutrient requirements may be estimated from biomass to nutrient

ratios. A variety of ratios is found in the literature. For

this example, a 100:10:1 ratio of biomass:nitrogen:phosphorus is assumed. This ratio yields a nutrient requirement of 10 mg/kg of nitrogen and 1 mg/kg

of phosphorus. Thus, if the above assumptions hold,

a site with at least these levels of nitrogen and phosphorus initially should not be rate-limited by nitrogen

and phosphorus.

Most soils naturally contain nutrients in excess of the

concentrations calculated in Example 3-3. Therefore,

although the addition of nutrients may be desirable in

hopes of increasing biodegradation rates, field research

to date does not indicate the need for these additions

(Dupont et al., 1991; Miller et al., 1991). Therefore,

although nutrients are often added to bioremediation

projects in anticipation of increased biodegradation

rates, field data to date do not show a clear relationship

between increased rates and supplied nutrients.

Concentrations of total Kjeldahl nitrogen (TKN) and

total phosphorus at the Bioventing Initiative sites and

Figure 3-10. TKN measurements at Bioventing Initiative sites.

20
the corresponding relationship between oxygen utilization rates are shown in Figures 3-10 through 3-13. Although optimal ratios of carbon, nitrogen, and

phosphorus were not available at all sites, the natural

nutrient levels were sufficient to sustain some level of

biological respiration at all sites when the most limiting

element, oxygen, was provided.

In controlled nutrient additions at Tyndall and Hill AFBs,9

no apparent increase in microbial activity was observed.

Therefore, there appeared to be no benefit of nutrient

addition. The relationship between oxygen utilization

rates and TKN and total phosphorus are shown in Figures 3-11 and 3-13, respectively. As illustrated in these

figures, no correlation exists between phosphorus and

oxygen utilization rates and only a weak relationship

exists between TKN concentrations and oxygen utilization rates, again emphasizing that natural ambient nutrient levels seem sufficient for microbial activity.10

Figure 3-14 illustrates the range of iron concentrations

measured at Bioventing Initiative sites. Iron concentrations varied greatly, with concentrations from less than

100 mg/kg to greater than 75,000 mg/kg. Soils in Hawaii

and Alaska exhibited the highest iron contents. Although

iron is a nutrient required for microbial growth, iron also

may react with oxygen to form iron oxides. Theoretically,

if a significant amount of iron oxidation occurs, the observed oxygen utilization rate11 would not reflect microbial activity only. Calculated biodegradation rates would

therefore be an overestimate of actual biodegradation

rates. Thus, background wells in uncontaminated areas

are recommended in bioventing applications in areas of

high iron concentrations. To date, this study has shown

no correlation between iron content and oxygen utilization rates (Figure 3-15).

3.2.2.6 Contaminant Concentration

Contaminant concentration also may affect biodegradation of the contaminant itself. Excessive quantities of a

Figure 3-11. Correlation between oxygen utilization rate and

TKN at Bioventing Initiative sites.

Figure 3-12. Total phosphorus measurements at Bioventing Initiative sites.

Figure 3-13. Correlation between oxygen utilization rate and total phosphorus at Bioventing Initiative sites. Figure 3-14. Iron concentration measurements at Bioventing

Initiative sites.

 9 See Sections 4.1 and 4.2 for a detailed discussion of these sites.

10 See Section 5.2 for a discussion of the statistical relationship between nutrients and oxygen utilization rates.

11 As measured by in situ soil gas oxygen concentrations.

21
contaminant can result in a reduction in biodegradation

rate because of a toxicity effect. Conversely, very low

concentrations of a contaminant also may reduce overall degradation rates because contact between the contaminant and the microorganism is limited and the

substrate concentration is likely below Smin.

In practice, petroleum hydrocarbons in fuel mixtures

do not generally appear to be toxic to the bioventing

process. Other more soluble compounds (i.e., phenolics) or less biodegradable compounds (i.e., TCE)

may exhibit a toxicity effect, and reports indicate that

pure benzene may be toxic. Although a general relationship between bioventing rates and concentration

no doubt exists, the relationship is complex and not

fully understood. At sites where NAPLs are present

(soil concentrations above the 100 to 1,000 mg/kg

range), the bioavailable hydrocarbon is most probably

limited by solubilization, which is linked to Raoult’s

Law and, to an extent, is independent of total hydrocarbon concentration. Certainly, the NAPL distribution

can affect the proportion of the soil in a site in which

biodegradation is occurring, and at lower concentrations, less soil may be in direct contact with NAPLs.

The reduction in biodegradation rates observed over

time on many sites is likely caused, at least in part, by

changes in the hydrocarbon makeup as more degradable and more mobile compounds (i.e., benzene, toluene, ethylbenzene, and xylenes) are removed. At

lower hydrocarbon concentrations where NAPLs are

not present, a decline in rate would be expected with

time as the available substrate is removed.

3.2.2.7 Bioavailability and Relative

Biodegradability

Another important parameter affecting the extent of in

situ bioremediation is bioavailability of the contaminant(s) of concern. Bioavailability is a term that describes the accessibility of contaminants to the

degrading populations. Bioavailability 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 (U.S. EPA,

1993). Compounds with greater aqueous solubilities

and lower affinities to partition into NAPL or to sorb onto

the soil generally are bioavailable to soil microorganisms and are more readily degraded. For example,

BTEX compounds are preferentially degraded relative

to the larger alkanes found in fuels. The most likely

explanation for this is that BTEX compounds are more

mobile and more soluble in pore water and therefore are

more bioavailable.

3.3 Compounds Targeted for Removal

Any aerobically biodegradable compound, such as petroleum hydrocarbons, potentially can be degraded though

bioventing. To date, bioventing has been applied primarily

to petroleum hydrocarbons (Table 2-2); however, bioventing of PAHs (Lund et al., 1991; Hinchee and Ong, 1992;

EPA, 1994a; Alleman et al., 1995) and bioventing applied

to an acetone, toluene, and naphthalene mixture (Leeson

et al., 1994) have been implemented successfully.

The key to bioventing feasibility in most applications

is biodegradability versus volatility of the compound.

If the rate of volatilization greatly exceeds the rate of

biodegradation, bioventing is unlikely to be successful

because removal occurs primarily though volatilization. This will occur most often in cases where the

contaminant is a fresh, highly volatile fuel. An unsuccessful bioventing application is unlikely to occur due

to a lack of microbial activity. If bioventing is operated

in an injection mode, as this manual recommends,

volatilized contaminants may be biodegraded before

reaching the surface, unlike during an extraction operation.12 Figure 3-16 illustrates the relationship between

a compound’s physicochemical properties and its potential for bioventing.

In general, compounds with a low vapor pressure13

cannot be successfully removed by volatilization but can

be biodegraded in a bioventing application if they are

aerobically biodegradable. High vapor pressure compounds are gases at ambient temperatures. These compounds volatilize too rapidly to be easily biodegraded in

a bioventing system but are typically a small component

of fuels and, because of their high volatility, they will

attenuate rapidly. Compounds with vapor pressures between 1 and 760 mm Hg may be amenable to either

volatilization or biodegradation. Within this intermediate

Figure 3-15. Correlation between oxygen utilization rates and

iron content at Bioventing Initiative sites.

12 See Section 2.1 of Volume II for a discussion of air injection versus

 extraction considerations.

13 For the purposes of this discussion, compounds with vapor pressures below approximately 1 mm Hg are considered low, and

compounds with vapor pressures above approximately 760 mm Hg

are considered high.

22
range lie many of the petroleum hydrocarbon compounds of greatest regulatory interest, such as benzene,

toluene, ethylbenzene, and xylenes. As can be seen in

Figure 3-16, various petroleum fuels are more or less

amenable to bioventing. Some components of gasoline

are too volatile to biodegrade easily but, as stated previously, are typically present in low overall concentrations and are attenuated rapidly. Most of the diesel

constituents are sufficiently nonvolatile to preclude volatilization, whereas the constituents of JP-4 jet fuel are

intermediate in volatility.

To be amenable to bioventing, a compound must (1)

biodegrade aerobically at a rate resulting in an oxygen

demand greater than the rate of oxygen diffusion from

the atmosphere and (2) biodegrade at a sufficiently high

rate to allow in situ biodegradation before volatilization.

Practically, this means that low vapor pressure compounds need not biodegrade as rapidly as high vapor

pressure compounds for bioventing to be successful.

Figure 3-17 illustrates this relationship. The actual feasibility of bioventing is very site-specific, so Figures

3-16 and 3-17 should be used as general guidelines

rather than absolutes.

Bioventing generally is not considered appropriate for

treating compounds such as polychlorinated biphenyls

(PCBs) and chlorinated hydrocarbons. Through a

Figure 3-16. Relationship between contaminant physicochemical properties and potential for bioventing.

23
cometabolic process, however, enhancement of the

degradation of compounds such as TCE through

bioventing may be possible. Laboratory studies have

shown that if toluene is present to provide the primary

source of carbon, organisms that grow on toluene may

be able to cometabolize TCE (Wackett and Gibson,

1992). More recently, Hopkins et al. (1993) demonstrated TCE degradation in situ through the injection of

oxygen and phenol into an aquifer. TCE removal of 88

percent was observed in the field, indicating the potential for cometabolic degradation of chlorinated compounds in situ.

3.4 BTEX Versus TPH Removal in

Petroleum-Contaminated Sites

In many areas, treatment of petroleum hydrocarbons is

based on BTEX compounds. Typically, these compounds degrade rapidly during bioventing and, at most

sites, degrade to below detection limits within 1 year of

operation of a bioventing system. This trend was illustrated in a study at Tyndall AFB14 and has been confirmed at 81 sites completing the 1-year testing under

the Bioventing Initiative. At Tyndall AFB, two test plots

were studied with initial hydrocarbon concentrations of

5,100 and 7,700 mg/kg. After 9 months of bioventing,

TPH decreased by 40 percent from the initial concentration. Low-molecular-weight compounds such as BTEX,

however, decreased by more than 90 percent (Figure

3-18). Low-molecular-weight compounds were preferentially degraded over heavier fuel components, which

is consistent with previous research (Atlas, 1986).

If a risk-based approach to remediation is used that

focuses on removing the soluble, mobile, and more toxic

BTEX components of the fuel, remediation times can be

significantly reduced, making bioventing an attractive

technology for risk-based remediations. In addition,

Bioventing Initiative results illustrate that BTEX compounds often initially are relatively low at many fuel-contaminated sites. Data collected from the majority of the

Bioventing Initiative sites demonstrate that more than 85

percent of initial soil samples contained less than 1

mg/kg of benzene (Figure 3-19). An exception to this

may be gasoline-contaminated sites; the majority of

sites included in the Bioventing Initiative were contaminated with heavier weight contaminants. Only 19 of 125

Bioventing Initiative sites were contaminated by gasoline or aviation gas (AVGAS).

Figure 3-17. Relationship between contaminant pressure and aerobic biodegradability.

14 See Section 4.2 for a case history of the bioventing study at Tyndall

 AFB, Florida.

24
Figure 3-19. Contaminant distribution at Bioventing Initiative sites.

Figure 3-18. Results of soil analysis before and after venting from Plot V2 at Tyndall AFB, Florida.

25
Chapter 4

Bioventing Case Histories

Four of the first well-documented bioventing studies

are presented in this chapter to illustrate significant

results that have contributed to the development of

bioventing, the Bioventing Initiative, and this document. The development of the Bioventing Initiative

was largely based upon the results from these four

early studies. Site 914, Hill AFB, Utah, was one of the

first bioventing systems studied. This study was designed to examine the feasibility of biodegradation

through air injection and also to investigate the effect

of nutrient and moisture addition on biodegradation.

The second site was a bioventing system at Tyndall

AFB, Florida, initiated in 1990. This study was shortterm (9 months) but was designed to examine process

variables in more detail than was possible at Site 914,

Hill AFB. The third site discussed in this chapter was

conducted at Site 280, Hill AFB, Utah. This study was

initiated in 1991 as a bioventing site and was operated

for approximately 3 years. Research on air flow rates

and injection depth was conducted at this site. The

fourth study presented in this chapter was conducted

at Eielson AFB, Alaska. This study was initiated in 1991

as a bioventing system and was operated for 3 years.

This study was conducted to examine the feasibility of

bioventing in a subarctic climate and to evaluate the

effects of soil warming on biodegradation rates.

A case history of the Fire Training Area, Battle Creek Air

National Guard Base (ANGB), Michigan, also is presented in this chapter. This site was included in the

Bioventing Initiative, but additional samples were collected at the end of the 1-year study as part of a separate project. The results from this study illustrate typical

installations and results from a Bioventing Initiative site

and provide additional data on BTEX contamination

after 1 year of bioventing.

These case histories are not presented as design examples because these studies were designed as research

efforts. In fact, these studies have been the basis for

development of current design practice as presented in

Volume II of this document. Details of each study are

presented in the following sections.

4.1 Site 914, Hill AFB, Utah

A spill of approximately 27,000 gal of JP-4 jet fuel occurred at Site 914 when an automatic overflow device

failed. Contamination was limited to the upper 65 ft (20 m)

of a delta outwash of the Weber River. This surficial

formation extends from the surface to a depth of approximately 65 ft (20 m) and comprises mixed sand and

gravel with occasional clay stringers. Depth to regional

ground water is approximately 600 ft (180 m); however,

water occasionally may be found in discontinuous

perched zones. Soil moisture averaged less than 6 percent by weight in the contaminated soils.

The collected soil samples had JP-4 jet fuel concentrations of up to 20,000 mg/kg, with an average concentration of approximately 400 mg/kg (Oak Ridge National

Laboratory, 1989). Contaminants were unevenly distributed to depths of 65 ft (20 m). Vent wells were drilled to

approximately 65 ft (20 m) below the ground surface and

were screened from 10 to 60 ft (3 to 20 m) below the

surface. A background vent well was installed in an

uncontaminated location in the same geological formation approximately 700 ft (210 m) north of the site.

This system originally was designed for SVE, not

bioventing. During the initial 9 months of operation, it

was operated to optimize volatilization, while biodegradation was merely observed. After this period, air flow

rates were greatly reduced, and an effort was made to

optimize biodegradation and limit volatilization.

Soil vapor extraction was initiated in December 1988 at

a rate of approximately 25 cubic ft per minute (cfm) (710

L/min). The off-gas was treated by catalytic incineration,

and initially the highly concentrated gas needed to be

diluted to keep it below explosive limits and within the

incinerator’s hydrocarbon operating limits. The venting

rate was gradually increased to approximately 1,500

cfm (4.2 × 104

 L/min) as hydrocarbon concentrations

dropped. During the period between December 1988

and November 1989, more than 3.5 × 108

 ft3 (9.9 × 1010

L) of soil gas were extracted from the site.

27
In November 1989, ventilation rates were reduced to

between approximately 300 cfm and 600 cfm (8,500 to

17,000 L/min) to provide aeration for bioremediation

while reducing off-gas generation. This change allowed

removal of the catalytic incinerators, saving approximately $13,000 per month in rental and propane costs.

Hinchee and Arthur (1991) conducted bench-scale

studies using soils from this site and found that, in the

laboratory, both moisture and nutrients appeared to

become limiting after aerobic conditions had been

achieved. These findings led to the addition of first

moisture and then nutrients in the field. Moisture addition clearly stimulated biodegradation; nutrient addition did not (Figure 4-1). The failure to observe an

effect of nutrient addition could be explained by many

factors, including that the nutrients failed to move in

the soils, which is a problem particularly for ammonia

and phosphorus (Aggarwal et al., 1991); remediation

of the site was entering its final phase and nutrient

addition may have been too late to result in an observed change; and/or nutrients simply may have not

been limiting.

During extraction, oxygen and hydrocarbon concentrations in the off-gas were measured. To quantify the

extent of biodegradation at the site, the oxygen was

converted to an equivalent basis. This was based on the

stoichiometric oxygen requirement for hexane mineralization.1

 Hydrocarbon concentrations were determined

based on direct readings of a total hydrocarbon analyzer

calibrated to hexane. Based on these calculations, the

mass of the JP-4 jet fuel as carbon removed (measured

as amount of carbon removed) was approximately 1,500

lb volatilized and 93,000 lb biodegraded (Figure 4-1).

After a 2-year period, cleanup and regulatory closure

were achieved (Figure 4-2).

The results of this study indicated that aerobic biodegradation of JP-4 jet fuel did occur in the vadose zone at

Site 914. Soil venting increased biodegradation at this

site because, before venting, biodegradation appeared

to have been oxygen limited. The SVE system, designed to volatilize the fuel, stimulated in situ biodegradation with no added nutrients or moisture. In this

study, approximately 15 percent of the documented

field removal observed at the site resulted from microbial-mediated mineralization to carbon dioxide. Additional biological fuel removal by conversion to

biomass and degradation products no doubt occurred

but was not quantified.

This study showed that further studies of field biodegradation in unsaturated soils were needed to better understand the effects of such variables as oxygen content,

nutrient requirements, soil moisture, contaminant levels,

and soil type on the limitation and optimization of

bioventing of contaminated field sites. Also, further studies of gas transport in the vadose zone were needed to

ensure adequate design of air delivery systems.

Further details of this study may be found in the following

references: Dupont et al., 1991; Hinchee et al., 1991b.

4.2 Tyndall AFB, Florida

A more controlled study than was possible at Site 914,

Hill AFB, was designed at Tyndall AFB as a follow-up to

the Hill AFB research. The experimental area in the

Tyndall AFB study was located at a site where past JP-4

jet fuel storage had resulted in contaminated soils. The

Figure 4-1. Cumulative hydrocarbon removal and the effect of moisture and nutrient addition at Site 914, Hill AFB, Utah.

1 See Section 3.3 of Volume II for a discussion of this calculation.

28
nature and volume of fuel spilled or leaked were unknown. The site soils were a fine- to medium-grained

quartz sand. The depth to ground water was 2 ft to 4 ft

(0.61 m to 1.2 m).

The field study was designed with the following objectives:

• To determine whether bioventing enhanced biodegradation of JP-4 jet fuel at this site.

• To determine whether moisture addition coupled with

bioventing enhanced biodegradation rates.

• To determine whether nutrient addition coupled with

bioventing enhanced biodegradation rates.

• To evaluate flow rate manipulation to maximize biodegradation and minimize volatilization.

• To calculate specific biodegradation rate constants

from a series of respiration tests conducted during

shutdown of the air extraction system.

Four test cells were constructed to allow control of gas

flow, water flow, and nutrient addition. Test cells V1 and

V2 were installed in the hydrocarbon-contaminated

zone; test cells V3 and V4 were installed in uncontaminated soils. Test cells were constructed and operated in

the following manner:

• V1 (uncontaminated): Venting for approximately 8

weeks, followed by moisture addition for approximately 14 weeks, then moisture and nutrient addition

for approximately 7 weeks.

• V2 (uncontaminated): Venting coupled with moisture

and nutrient addition for 29 weeks.

• V3 (uncontaminated): Venting with moisture and nutrient addition at rates similar to V2, with injection of

hydrocarbon-contaminated off-gas from V1. Operation was conducted at a series of flow rates and

retention times.

• V4 (uncontaminated): Venting with moisture and nutrient addition at rates similar to V2.

Initial site characterization indicated the mean soil hydrocarbon levels were 5,100 mg and 7,700 mg of hexane-equivalent/kg in treatment plots V1 and V2,

respectively. The contaminated area was dewatered,

and hydraulic control was maintained to keep the depth

to water at approximately 5.25 ft (1.6 m). This exposed

more of the contaminated soil to aeration. During normal

operation, air flow rates were maintained at approximately one air-filled void volume per day.

Biodegradation and volatilization rates were much

higher at the Tyndall AFB site than those observed at

Hill AFB. These higher rates were likely the result of

higher average levels of contamination, higher temperatures, and higher moisture content. Biodegradation

rates during bioventing ranged from approximately 2

mg/kg-day to 20 mg/kg-day, with an average value of 5

mg/kg-day. After 200 days of aeration, an average hydrocarbon reduction of approximately 2,900 mg/kg was

observed. This represented a reduction in total hydrocarbons of approximately 40 percent.

Another important observation of this study was the

effect of temperature on the biodegradation rate. Miller

(1990) found that the van’t Hoff-Arrhenius equation provided an excellent model of temperature effects. In the

Tyndall AFB study, soil temperature varied by only approximately 7°C (44.6°F), yet biodegradation rates were

approximately twice as high at 25°C (77°F) than at 18°C

(64.4°F).

Figure 4-2. Results of soil analysis before and after treatment at Site 914, Hill AFB, Utah.

29
Operational data and biodegradation rates indicated that

soil moisture and nutrients were not limiting factors in

hydrocarbon biodegradation for this site (Figure 4-3). The

lack of moisture effect contrasts with the Hill AFB findings

but most likely results from the contrasting climatic and

hydrogeologic conditions. Hill AFB is located in a high-elevation desert with a deep water table. Tyndall AFB is

located in a moist, subtropical environment, and at the

study sites, the water table was maintained at a depth of

approximately 5.25 ft (1.6 m). The nutrient findings support

field observations made at Hill AFB that the addition of

nutrients does not stimulate biodegradation. Based on

acetylene reduction studies, Miller (1990) speculated that

adequate nitrogen was present because of nitrogen fixation. The Hill and Tyndall AFB sites had been contaminated

for several years before the bioventing studies began, and

both sites were anaerobic. Nitrogen fixation, which is maximized under these conditions, may have provided the

required nutrients. In any case, these findings show that

nutrient addition is not always required.

The Tyndall AFB study included a careful evaluation of the

relationship between air flow rates and biodegradation and

volatilization. Researchers found that extracting air at the

optimal rate for biodegradation resulted in 90 percent removal by biodegradation and 10 percent removal by volatilization. They also found that passing the contaminants

volatilized in the off-gas through clean soil resulted in

complete biodegradation of the volatilized vapors.

In situ respiration tests documented that oxygen consumption rates followed zero-order kinetics and that

rates were linear down to 2 percent to 4 percent oxygen.

Therefore, air flow rates can be minimized to maintain

oxygen levels between 2 percent and 4 percent without

fuel biodegradation, with the added benefit that lower air

flow rates increase the percentage of removal by biodegradation and decrease the percentage of removal by

volatilization.

The study was terminated because the process monitoring objectives had been met; biodegradation was still

vigorous. Although the TPH had been reduced by only

40 percent by the time of study termination, the low-molecular-weight aromatics (the BTEX components) were

reduced by more than 90 percent (Figure 3-18). Apparently, the bioventing process more rapidly removed

BTEX compounds that other JP-4 fuel constituents.

Results from this study demonstrated the effectiveness

of bioventing for remediating fuel-contaminated soils,

the ineffectiveness of moisture or nutrient addition for

increasing in situ biodegradation rates, and the importance of air flow rates for optimizing biodegradation over

volatilization. This study demonstrated, however, that a

long-term bioventing study was necessary to examine

process variables. This led to the initiation of the Site

280, Hill AFB, and the Site 20, Eielson AFB, projects

described in the following sections.

Further details of the Tyndall AFB study may be found

in the following references: Hinchee et al., 1989; Miller,

1990; Miller et al., 1991.

4.3 Site 280, Hill AFB, Utah

A key objective of the study at Site 280 was to optimize

the injection air flow rates. These efforts were intended

to maximize biodegradation rates in JP-4 jet fuel-contaminated soils while minimizing or eliminating volatilization. The site studied was a JP-4 jet fuel spill at

Hill AFB that had existed since the 1940s (Figure 4-4).

The geology was similar to Site 914, while average

Figure 4-3. Cumulative percentage of hydrocarbon removal and the effect of moisture and nutrient addition at Tyndall AFB, Florida.

30
contaminant levels were slightly higher (Figure 4-5).

Vent wells were installed to a depth of approximately 110

ft, and ground water was at a depth of approximately

100 ft.

From November 1992 through January 1995, many

studies were conducted to evaluate low-intensity bioremediation at Site 280. These efforts included (1) varying

the air injection flow rates in conjunction with in situ

respiration tests and (2) testing surface emissions to

obtain information for system optimization.

Five air flow rate evaluations were conducted at Site 280

from 1991 through 1994 (28, 67, 67, 40, and 117 cfm

[790, 1,900, 1,900, 1,100, and 3,300 L/min]). In situ

respiration testing followed each evaluation. The 67-cfm

(1,900-L/min) study was repeated to include additional

soil gas monitoring points added to the site. Monthly soil

Figure 4-4. Schematic showing locations of soil gas monitoring points, surface monitoring points, and injection wells at Site 20,

Hill AFB, Utah.

31
gas monitoring was conducted at Site 280 to measure

the concentrations of oxygen, carbon dioxide, and TPH

at each sampling point following system operation at

each of the different air flow rates.

Surface emissions tests were conducted during each air

injection test and while the air injection system was

turned off. In each surface emissions test, no significant

differences were found between the periods of air injection and no air injection. TPH soil gas levels measured

during the air injection periods averaged approximately

70 ppmv, while TPH soil gas levels during resting periods averaged 42 ppmv. These averages were not found

to be statistically different. Likewise, surface emission

rates were not significantly different at different flow rates.

Final soil sampling was conducted in December 1994.

Results of initial and final BTEX and TPH samples are

shown in Figures 4-6 and 4-7, respectively. Results

shown represent soil samples within a 0-ft to 25-ft radius

of the injection well and a 25-ft to 75-ft radius. In general,

BTEX and TPH concentrations decreased at all depths

within the 25-ft radius from the vent well, with the exception of the samples collected at a depth of 90 ft to 100

ft. Samples taken from this depth are located at the

capillary fringe, and adequate aeration probably was not

possible. Samples collected outside of the 25-ft radius

were less conclusive, indicating the lack of aeration in

this area. Further details of the Site 280, Hill AFB, study

may be found in the following reference: EPA, 1994b.

4.4 Site 20, Eielson AFB, Alaska

The objective of the Eielson AFB study was to install and

operate an in situ soil bioremediation system to investigate the feasibility of using bioventing to remediate JP-4

jet fuel contamination in a subarctic environment and to

actively increase soil temperature to determine the degree to which increased soil temperature can enhance

the biodegradation rates of JP-4 contaminants in soil.

This study comprised four test plots: (1) a test plot in

which heated ground water was circulated through the

test plot (active warming test plot), (2) a test plot in which

plastic sheeting was placed over the ground surface of

the test plot during the spring and summer months to

capture solar heat and passively warm the soil (passive

warming test plot), (3) a test plot in which heat tape was

installed in the test plot to heat the soil directly (surface

warming test plot), and (4) a control test plot, which

received air injection but no soil warming (control test

plot). In addition, an uncontaminated background location also received air injection but no soil warming to

monitor natural background respiration rates. The site

Figure 4-5. Geologic cross-section showing known geologic features and soil TPH concentrations (mg/kg) at Site 280, Hill AFB,

Utah.

32
soils were a sandy silt, with increasing amounts of sand

and gravel with depth. Ground water was typically at

approximately 7 ft. Figure 4-8 illustrates site geologic

features and typical construction details of the active

warming test pilot, which is typical of other site installations as well.

Differences in soil temperatures have been significant

among the four test plots (Figure 4-9). When in operation, the active warming test plot consistently maintained

higher temperatures than the other test plots during the

winter months. In the passive warming test plot, plastic

sheeting increased soil temperature, with average soil

temperatures as high as 18°C (64.4°F) during the summer months, compared with average temperatures of

approximately 10°C (50°F) in the control test plot. A

significant feature of this soil warming technique was

that the addition of plastic sheeting in the spring caused

a rapid increase in soil temperature, nearly 6 weeks to

8 weeks sooner than in unheated test plots. This significantly increased the period of rapid microbial degradation. During the winter months, the passive warming test

plot remained warmer than the control test plot.

Respiration rates were measured quarterly in each test

plot. Of particular interest were rates measured in the

control test plot. No substantial microbial activity was

expected to occur during the winter months in unheated

test plots because of the extreme temperatures. Significant microbial activity was consistently measured in the

control test plot, however, even in winter when soil

temperatures are just below freezing (Figure 4-10). Respiration rates in the passive warming test plot were

observed to increase nearly one order of magnitude as

soil temperature increased during the summer months,

indicating the success of using of plastic sheeting to

promote soil warming (Figure 4-10). Respiration rates

measured in the active warming test plot were higher

than those measured in the passive warming or control

test plot when warm water circulation was operating.

Figure 4-6. Site average initial and final BTEX soil sample results at Site 280, Hill AFB, Utah.

33
Warm water circulation was discontinued in fall 1993,

and as the soil temperature dropped, no significant microbial activity could be measured in the test plot during

the winter months. This phenomenon is interesting in

that it suggests that during the 2 years of soil heating,

microorganisms adapted to growth at higher temperatures yet lost the ability to remain active in colder soils.

To determine whether the microbial population could

adapt to cold temperatures given time, a final in situ

respiration test was conducted in January 1995. Significant microbial activity was measured, comparable to the

control test plot, indicating either readaptation or recolonization by the microbial population.

The surface warming test plot has shown promise as a

form of soil warming. Soil temperatures and respiration

rates were higher than temperatures or rates in either

the passive warming or control test plot and were similar

to those measured in the active warming test plot during

warm water circulation. These results indicate that the

use of heat tape may prove to be a more efficient means

of soil warming than hot water circulation because it

avoids the problem of high soil moisture content.

An evaluation of cost versus remediation time was conducted to evaluate the feasibility of soil warming. Costs

for the basic bioventing system in Table 4-1 were based

on costs calculated by Downey et al. (1994). Given that

average biodegradation rates were higher in the actively

warmed plots, overall remediation time would be more

rapid than in the unheated test plots (Table 4-1). Although capital costs were higher in the active and surface warming test plots, the rapid remediation time

results in lower total cost for power and monitoring. Final

costs based on dollars per cubic yard illustrate that costs

are comparable among the four treatment cells. These

results indicate that implementation of a soil warming

technology over basic bioventing is not necessarily

based on cost but on desired remediation time and

funds available for operation and maintenance versus

capital costs.

Final soil sampling at this site was conducted in August

1994. Results of initial and final BTEX and TPH samples

Figure 4-7. Site average initial and final TPH soil sample results at Site 280, Hill AFB, Utah.

34
Figure 4-8. Cross-section showing geologic features and typical construction details of the active warming test plot, Site 20, Eielson

AFB, Alaska.

Figure 4-9. Soil temperature in four test plots and the background area at Site 20, Eielson AFB, Alaska.

35
are shown in Figures 4-11 and 4-12, respectively. A

dramatic reduction in BTEX compounds was observed

at all sample locations, while TPH was reduced by an

average of approximately 60 percent.

Spatial variability in contaminant distribution and biodegradation rates makes quantitative comparison between

the test plots difficult; however, the results from the

active, surface, and passive warming test plots clearly

demonstrate that these forms of soil warming have increased biological activity in these areas. In the active

and surface warming test plot, despite problems caused

by high oil moisture content, biodegradation rates consistently have been higher than those measured in

either the passive warming or the control test plot, even

though the control test plot appears to be more heavily

contaminated than the active warming test plot. These

results have demonstrated the feasibility of bioventing

in a subarctic climate and the potential advantages of

soil warming to decrease remediation times.

Further details of the Site 20, Eielson AFB study may be

found in the following references: Leeson et al., 1995;

EPA, 1994c.

Figure 4-10. Biodegradation rates in four test plots at Site 20, Eielson AFB, Alaska.

Table 4-1. Cost Analysis of Soil Warming Techniques at Site 20, Eielson AFB, Alaskaa

Task

Basic Bioventing

(No Warming) ($) Active Warming ($) Passive Warming ($) Surface Warming ($)

Site visit/planning 5,000 5,000 5,000 5,000

Work plan preparation 6,000 6,000 6,000 6,000

Pilot testing 27,000 27,000 27,000 27,000

Regulatory approval 3,000 6,000 3,000 3,000

Full-scale construction

 Design 7,500 7,500 7,500 7,500

 Drilling/Sampling 15,000 20,000b 15,000 15,000

 Installation/Startup 4,000 26,000 10,500 13,000

Remediation time requiredc 9.4 years 2.8 years 6.9 years 3.4 years

Monitoring 30,550 9,800 24,150 11,050

Power 13,160 9,800 9,660 17,000

Final soil sampling 13,500 13,500 13,500 13,500

Cost per ydc 25.50 26.12 24.86 24.21

a Costs are estimated based on a 5,000-yd3 contaminated area with an initial contamination level of 4,000 mg/kg. b Requires installation and development of one well.

c

 Estimated based on average biodegradation rates in four test plots.

36
4.5 Fire Training Area, Battle Creek

ANGB, Michigan

The Fire Training Area, Battle Creek ANGB, was included as part of the Bioventing Initiative. An estimated

54,000 gal to 74,000 gal of mixed waste fuels, oils, and

solvents were burned at this site during fire training

exercises. Soils at the site consist of fine-to-coarse, silty

sand interbedded with gravel and cobbles (Figure 4-13).

Ground water is at a depth of approximately 30 ft.

As dictated by the Bioventing Initiative Protocol, one

vent well and three monitoring points were installed at

this site. The vent well was installed to a depth of 30 ft

with 20 ft of 0.04-in. slotted screen. Each monitoring

point consisted of three levels, with screens located at

depths of 8 ft, 17 ft, and 27 ft. Monitoring points were

located at distances of 15 ft, 30 ft, and 50 ft away from

the vent well.

Initial treatability tests (an in situ respiration test and a

soil gas permeability test) were conducted to determine

the feasibility of bioventing. Oxygen utilization rates ranged

from 2.9 to 22 percent/day (2.0 to 15 mg/kg-day), with

higher rates associated with more contaminated locations.

Soil gas permeability testing demonstrated an average

permeability of approximately 230 darcy and a radius of

Figure 4-12. Site average initial and final TPH soil sample results at Site 20, Eielson AFB, Alaska.

Figure 4-11. Site average initial and final BTEX soil sample results at Site 20, Eielson AFB, Alaska.

37
influence of greater than 50 ft. These results indicated

that both the microbial activity and the permeability were

conducive to an effective bioventing operation.

Initial soil and soil gas samples were collected, and a

1-hp regenerative blower was installed at the site for

continuous air injection in September 1992. The blower

was operated for 1 year, and in October 1993, final soil

and soil gas samples were collected.2

 Although the

number of soil3

 and soil gas samples collected was not

sufficient to allow for statistically significant comparison

Figure 4-13 Hydrogeologic cross-section of the Fire Training Area, Battle Creek, ANGB, Michigan.

2 Blower operation was discontinued for 1 month before collecting soil

gas samples to allow time for soil gas equilibration.

3 Three initial soil samples were collected, but 29 final soil samples

were collected as part of an intrinsic remediation study.

38
of the data, certain trends were observed. Final BTEX

and TPH soil gas concentrations were significantly lower

than initial measurements (Figure 4-14). Soil BTEX concentrations were significantly lower after 1 year of

bioventing, while soil TPH concentrations changed little,

as expected (Figure 4-15). In addition, in situ respiration

rates declined from the initial treatability test, which

indicates decreased contaminant levels.4

 These results

illustrated the effectiveness of bioventing at this site.

Because Michigan uses a risk-based standard for site

closure, this site is likely to be closed based on these

results.

Figure 4-14. Initial and final soil gas concentrations at the Fire Training Area, Battle Creek, Michigan.

4 See Chapter 4 of Volume II for a detailed discussion of in situ

respiration rates and site closure.

39
Figure 4-15. Initial and final soil concentrations at the Fire Training Area, Battle Creek, Michigan.

40
Chapter 5

Analyses of Bioventing Initiative Results

In May 1992, the U.S. Air Force began the Bioventing

Initiative to examine bioventing at 55 contaminated sites

throughout the country. In December 1992, the program

was increased to more than 130 sites because of increased demand by Air Force managers. To date, data

have been collected from 125 contaminated sites at a

total of 50 Air Force bases, one Army base, one Naval

installation, and one Department of Transportation installation. Sites are located in 35 states and in all 10 EPA

regions. Figure 2-2 illustrates the locations of Bioventing

Initiative sites to date. The selected sites represent a

wide range of contaminant types and concentrations,

soil types, contaminant depths, climatic conditions, and

regulatory frameworks. Sites were selected based on

contamination level (preferably greater than 1,000

mg/kg TPH). Selection was not biased regarding factors

such as soil type or climatic conditions so that bioventing

potential could be properly evaluated under favorable

and unfavorable conditions.

A Bioventing Test Protocol was developed to provide

strict guidelines for treatability testing and bioventing

system design. The Bioventing Test Protocol was peer

reviewed and was also reviewed by EPA Headquarters

and the EPA National Risk Management Research

Laboratory. Using the Bioventing Test Protocol, initial

testing was conducted at each site to determine the

feasibility of bioventing. Based on the initial testing, a

decision was made about whether to install a bioventing

system for 1 year of operation. At the majority of sites

(95 percent), a bioventing system was installed for the

1-year operational period. At the end of this period, each

Air Force base could either elect to keep the bioventing

system in operation or remove it if the site was deemed

to be sufficiently remediated.

At each site in which a bioventing system was installed, a

series of data was collected as described in Section 2.3:

• Initial site characterization data consisting of soil and

soil gas sampling, in situ respiration rate testing results, and soil gas permeability testing results.

• Six-month in situ respiration testing results.

• One-year soil and soil gas sampling and in situ respiration testing results. Data from the initial testing

are summarized in Appendix B and have been used

in the statistical analyses as described in Section 5.2.

A summary of the results to date and potential implications are presented in the following sections.

5.1 Estimate of Contaminant Removal at

Bioventing Initiative Sites

At all Bioventing Initiative sites in which a blower was

installed and operated for 1 year, initial and final soil and

soil gas BTEX and TPH concentrations have been

measured. The approach was to compile a limited number of samples from each site and statistically analyze

for trends to avoid known spatial variability. Distribution

of soil and soil gas BTEX and TPH concentrations from

the initial and 1-year sampling events are shown in

Figures 5-1 through 5-4, respectively. The average soil

and soil gas BTEX and TPH concentrations across all

sites are shown in Figure 5-5. In general, the most

dramatic reductions were observed in BTEX removal in

both soil and soil gas samples. As an example, soil

results from Site 3, Battle Creek ANGB, are shown in

Figure 5-6. BTEX concentrations after 1 year of bioventing operation are very low and are no longer a source

of ground water contamination; therefore, site closure is

now a viable option for this site.

The objective of the 1-year sampling event was not to

collect the large number of samples required for statistical significance for a single site. Rather, the sampling

event was conducted to give a qualitative indication of

changes in contaminant mass. Soil gas samples are

somewhat similar to composite samples in that they are

collected over a wide area. Thus, they indicate changes

in soil gas profiles (Downey and Hall, 1994). Blower

operation was discontinued 30 days before sample collection to allow for soil gas equilibration. In contrast, soil

samples are discrete point samples subject to large

variabilities over small distances/soil types. Given this

variability, coupled with known sampling and analytical

variabilities, many samples at a single site would have

to be collected to conclusively determine real changes

in soil contamination. Because of the limited number of

samples, these results should not be viewed as conclusive indicators of bioventing progress or evidence of the

success or failure of this technology.

41
Figure 5-2. Soil gas TPH concentrations at Bioventing Initiative sites: initial and 1-year data.

Figure 5-1. Soil gas BTEX concentrations at Bioventing Initiative sites: initial and 1-year data.

Figure 5-3. Soil BTEX concentrations at Bioventing Initiative sites: initial and 1-year data.

42
Figure 5-4. Soil TPH concentrations at Bioventing Initiative sites: initial and 1-year data.

Figure 5-5. Average soil and soil gas BTEX and TPH concentrations at Bioventing Initiative sites: initial and 1-year data.

Figure 5-6. Initial and final soil sampling results at Site 3, Battle Creek ANGB, Michigan.

43
If a risk-based approach to remediation is used that

focuses on removing the soluble, mobile, and more toxic

BTEX component of the fuel, remediation times can be

significantly reduced. As discussed in the Tyndall AFB

case history,1

 the BTEX fraction was removed preferentially over TPH. The potential for bioventing to preferentially remove BTEX makes this technology suitable for

risk-based remediations. In addition, the low levels of

BTEX that have been encountered at the majority of

Bioventing Initiative sites further supports an emphasis

on risk-based remediation (Figure 5-7). Over 85 percent

of the initial soil samples contained less than 1 mg/kg of

benzene.

5.2 Statistical Analysis of Bioventing

Initiative Data

One primary objective of the Bioventing Initiative was to

develop a large database of bioventing systems that

could be used to determine which parameters are most

important in evaluating the feasibility of bioventing. This

is the largest field effort to date where data have

been collected in a consistent manner, allowing for direct comparison of results across sites. Results of the

statistical analyses can be used to evaluate which soil

measurements should be taken and, if bioventing performance is poor, which parameters can be adjusted to

improve performance.

Data generated from the Bioventing Initiative were subjected to thorough statistical analyses to determine

which parameters most influenced observed oxygen

utilization rates. Procedures used for conducting the

statistical analyses and the results of these analyses are

presented in the following sections.

5.2.1 Procedures for Statistical Analysis

Data collected from 125 Bioventing Initiative sites have

been analyzed for this study. The study involved in situ

respiration test data, soil gas permeability test data, and

soil chemistry and nutrient data from each site. Several

parameters were measured in the soil samples. The

statistical analyses had five specific objectives:

• To develop a consistent statistical approach for calculating the oxygen utilization and carbon dioxide

production rates from the in situ respiration data.

• To characterize the oxygen utilization rate as a function of parameters measured during initial testing.

• To determine the relationship between carbon dioxide

production rate and pH or alkalinity by characterizing

the ratio of oxygen utilization rate to carbon dioxide

production rate as a function primarily of pH and

alkalinity.

• To characterize soil gas permeability as a function of

particle size and moisture content.

• To compare primarily TKN concentrations at contaminated sites with those at uncontaminated background

areas.

Averages for oxygen utilization and carbon dioxide production rates and soil parameters were computed for

each site. All subsequent analyses were performed on

the site averages. Table 5-1 displays the parameters

included in the statistical analyses, their units, and transformations performed on these parameters wherever

necessary.

Data were stored in Statistical Analysis System (SAS)

databases, and all statistical manipulations and analyses were conducted using the SAS software. Methods

used for characterizing the data and the final regression

model are presented in the following sections for each

of the listed objectives.

5.2.2 Calculation of Oxygen Utilization and

Carbon Dioxide Production Rates

A statistical analysis was conducted to consistently calculate oxygen utilization and carbon dioxide production

rates. A linear time-related change in oxygen and carbon

dioxide levels that is characterized by a constant (or

zero-order) rate is typical of most sites. In some sites,

however, a two-piecewise linear change is observed. An

initial rapid rate is observed followed by a leveling off.

This change in rates generally occurs once oxygen

becomes limiting, typically below 5 percent to 10 percent

oxygen.

The two-piecewise regression model, with a slope change

at time t0, was fitted to the oxygen (and carbon dioxide)

versus time data obtained at every monitoring point. The

piecewise regression model is presented below:

Ri = α + β ti

 ti ≤ t0 (Eq. 5-1)

Figure 5-7. Average BTEX concentrations at Bioventing Initiative sites.

1 See Section 4.2 for a presentation of this case history.

44
Ri = (α + βt0) + (β + δ) (ti − t0) ti

 > t0 

(Eq. 5-2)

where i = number of observations at each monitoring

point (1, 2,...), and where:

Ri = measured ith oxygen or carbon dioxide level at

time ti

 (%)

α = oxygen or carbon dioxide level at initial time (%)

β = rate of change of oxygen or carbon dioxide

level with time (%/hr)

δ = increase or decrease in the rate of change at

time t0 (%/hr)

t0 = time at which the slope change occurs (hr)

The piecewise regression model was implemented using the nonlinear regression procedure (NLIN procedure) in the SAS software package.

The parameter δ in the above model measures the

increase or decrease in the slope at time t0. Therefore,

the statistical significance of confirmed the suitability of

a two-piecewise model fitted to the data. The rate of

oxygen utilization (or carbon dioxide production) was

estimated from the slope of the first linear piece, β,

wherever δ was statistically significant at the 0.05 significance level. For example, Figure 5-8 presents the

piecewise linear model fitted to oxygen data at a monitoring point at Site FSA-1, AFP 4, where β was estimated to be -1.1 percent/hr.

In cases where δ was not significant at the 0.05 level, a

linear regression model of the following form was fitted

to the data:

Ri = α + βti

 for all ti (Eq. 5-3)

where:

the rate of oxygen utilization (or carbon dioxide production) was determined from the slope of the straight line,

β.

For cases in which six or fewer observations were available at a monitoring point, or where the oxygen levels

exhibited virtually no change over a short initial period

followed by a linear change, the piecewise analysis was

not attempted. In such cases, a linear regression model,

as described above, was fitted. In these cases, the

suitability of the linear model was confirmed by inspection of the model fit to observed data.

5.2.3 Correlation of Oxygen Utilization Rates

and Environmental Parameters

A preliminary analysis of the untransformed data was

performed in which a regression model was fitted to the

oxygen utilization rate using forward stepwise regression.

Table 5-1. Data Parameters Included in the Statistical Analyses

Category Parameter Units Transformationa Acronymb

In Situ Respiration Rates Oxygen utilization rate %/hr Log O2

Carbon dioxide production rate %/hr None CO2

Ratio of the carbon dioxide

production rate to oxygen

utilization rate

No units Square root Ratio

Soil Parameters Soil gas TPH ppmv Log tphsg

Soil gas BTEX ppmv Log btexsg

Soil TPH mg/kg Log tphs

Soil BTEX mg/kg Log btexs

pH No units Log PH

Alkalinity mg/kg as CaCO3 Log ALK

Iron content mg/kg Log IRN

Nitrogen content mg/kg Log NIT

Phosphorus content mg/kg Log PHO

Moisture content % weight None MOI

Gravel % weight None GRA

Sand % weight None SAN

Silt % weight None SIL

Clayc % weight None and log CLA

Soil gas permeability Darcy Log PRM

Soil temperature Celsius None TMP

Other Season (time of year) Day None Season

a Transformation was applied to the parameter for purposes of statistical analysis.

b Acronym is used for the parameter in this report.

c

 The correlations presented in Figures 5-9 through 5-14 and Figure 5-17 are based on untransformed clay.

45
This model accounted for the effects of the soil parameters and their interactions. To reduce the effect of multicollinearity among the parameters on the fitted model,

soil gas BTEX levels and gravel were excluded from the

modeling. In other words, soil gas BTEX was highly

correlated with soil gas TPH, and therefore, it was concluded that the effect of soil gas BTEX levels on the

oxygen utilization rate can almost completely be explained by soil gas TPH concentrations. Also, because

the particle size levels added up to a constant value (100

percent), the effect of gravel was assumed to be redundant in the modeling.

Fitting the regression model to the oxygen utilization rate

revealed that soil particle sizes and permeability had a

dominating influence on the oxygen utilization rate; that

is, low levels of permeability and sand, and high levels

of silt and clay appeared to correlate strongly with high

oxygen utilization rates.

To determine whether a handful of sites was unduly

influencing the statistical modeling, sites with high oxygen utilization rates were examined in detail. Seven

sites in the analyses had extremely high oxygen utilization rates, well above average rates from other sites. A

two-sample t-test was performed on each parameter

(e.g., sand, nitrogen) to determine whether the average

value of the parameter over the seven sites was different

from the corresponding average for the remaining sites.

This analysis revealed statistically significant differences in particle size, soil gas permeability, and soil TPH

concentrations between the two groups of sites (Table

5-2). The results of this analysis led to the determination

that the seven sites with extremely high oxygen utilization rates were atypical with respect to their levels of

particle size, soil gas permeability, and soil TPH concentrations.

To reduce the influence of these seven sites on the

model for oxygen utilization rate, the log transformation

of the oxygen utilization rate was taken. Additionally, the

log transform resulted in more normally distributed data

for the oxygen utilization rate. Sites with oxygen utilization rates near zero, however, are artificially inflated in

importance as a result of the transformation. To eliminate this artificial effect, all the log transformed values

of the oxygen rate below -2.5 were censored (i.e., set to

a constant value of -2.5). Censoring was based on visual

inspection of the log transformed data.

Subsequently, the log transform of some soil parameters

was taken if the data for the parameter were not well

represented by a normal distribution. Normality in the

data was checked using the Shapiro-Wilk test for normality and by observing histograms and normal probability plots.

As a preliminary step to determine the influence of soil

parameters on oxygen utilization rate, correlations between each soil parameter and the oxygen utilization

rate were examined. This was conducted to examine

strong relationships between oxygen utilization rates

Figure 5-8. Use of piecewise analysis of oxygen utilization data from Site FSA-1, AFP 4, Texas.

Table 5-2. Parameters That Distinguish the Seven Sites

With High Oxygen Utilization Rates From the

Remaining Sites

Parameter

Level of Parameter in Seven

Sites Relative to Other Sites

Sand Lower

Silt Higher

Clay Higher

Soil gas permeability Lower

Soil TPH Lower

46
Figure 5-9. Oxygen utilization rates, oxygen to carbon dioxide rate ratios, element concentrations, moisture content, pH, and

alkalinity site average correlation scatterplot.

47
Figure 5-10. Oxygen utilization rates, oxygen to carbon dioxide rate ratios, contaminant concentrations, temperature, and moisture

content site average correlation scatterplot.

48
Figure 5-11. Oxygen utilization rates, oxygen to carbon dioxide rate ratios, particle size, moisture content, and soil gas permeability

site average correlation scatterplot.

49
Figure 5-12. Element concentrations and particle size site average correlation scatterplot.

50
Figure 5-13. Contaminant concentrations and particle size site average correlation scatterplot.

51
Figure 5-14. pH, alkalinity, and particle size site average correlation scatterplot.

52
and measured environmental parameters to assist in

developing a statistical model describing performance

at the Bioventing Initiative sites. First, the log transformation of the oxygen utilization rate and some of the soil

parameters was taken to obtain more normally distributed data on each parameter (Table 5-1). After these

transformations, the data for each parameter were plotted against the corresponding data for each of the other

parameters.

Figures 5-9 through 5-14 display the magnitude of the

correlations among data parameters. Specifically, Figures 5-9 through 5-11 display the correlations between

the oxygen utilization rate and the soil parameters, and

Figures 5-12 through 5-14 present the correlations between soil parameters. In each figure, ellipses are drawn

on each plot containing 95 percent of the estimated

bivariate distribution. The plots with narrow ellipses represent pairs of elements that have a strong observed

correlation. Pairs of elements that are positively correlated have the ellipse with the major axis running from

the lower left to the upper right, while negative correlations are indicated by the major axis running from the

lower right to the upper left. The magnitude of the correlation can be inferred from the shape of the ellipse by

comparing it with the key figure. In the key figure, comparable ellipses are displayed for distributions with

known correlations of 90 percent, 60 percent, 30 percent, and 0 percent.

For example, Figures 5-9 through 5-11 show that the

oxygen rate is most positively correlated with nitrogen

(Figure 5-9, correlation coefficient r = 0.40), moisture

(Figure 5-9, r = 0.30), and soil gas TPH concentrations

(Figure 5-10, r = 0.20) and negatively correlated with

temperature (Figure 5-10, r = 0.25) and sand (Figure

5-11, r = 0.25). This indicates that high levels of nitrogen,

moisture, and soil gas TPH concentrations, but low levels of sand and temperature, appear to correlate with

high oxygen utilization rates.

The correlation between soil temperature and oxygen

utilization rate is of little practical significance in this

analysis, however. At a given site, temperature has been

shown to correlate well with microbial activity, having

peak activity in summer months and low activity in winter

months. This relationship is also very site-specific, however. In other words, microorganisms in Alaska show

peak activity in summer months with comparable oxygen utilization rates to those of organisms from more

temperate climates; however, soil temperatures are significantly different. Therefore, correlating rates with temperature under such different climatic conditions as was

seen at Bioventing Initiative sites is impossible.

Among the soil parameters, the correlation coefficient

between soil gas BTEX and TPH concentrations is 0.92

(Figure 5-9) and that between pH and alkalinity is 0.75

(Figure 5-8). The correlations between the particle sizes

(sand, silt, and clay), moisture, and soil gas permeability

are also pronounced.

After taking the log transformation, a second regression

model was fitted to the oxygen utilization rate using

stepwise regression. Finally, the effect of a cyclic seasonal component on residuals obtained from the fitted

regression model was investigated by including the date

of the initial in situ respiration test.

The final regression model for oxygen utilization rate is:

log(O2) = −2.7 + 0.39 log(NIT) − 0.108 (MOI) +

0.017 log (TPHsg) ∗ MOI −

0.004 log (TPHsg) ∗ TMP (Eq. 5-4)

Each effect in the above model is statistically significant

at the 0.05 significance level. Note that the effects appearing in the model are consistent with relationships

observed in the bivariate setting. The model explains 41

percent of the variability in the log-transformed oxygen

utilization rate (i.e., a 64-percent correlation between the

observed and model-predicted log transformed oxygen

rates). Figure 5-15 illustrates actual versus predicted

oxygen utilization rates based on model predictions. As

shown, the model appears to explain mid-range oxygen

utilization rates fairly well but does not predict low oxygen utilization rates as accurately. This may be due to

an effect on microbial activity that was not measured

during the Bioventing Initiative and, therefore, was unexplained in the model.

5.2.4 Correlation of Oxygen Utilization and

Carbon Dioxide Production Rate Ratios

With Environmental Parameters

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 will 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.

At nearly all sites included in the Bioventing Initiative,

oxygen utilization has proven to be a more useful

measure of biodegradation rates than carbon dioxide

production. The biodegradation rate in mg of hexaneequivalent/kg of soil per day based on carbon dioxide

production usually is less than can be accounted for by

the oxygen disappearance. A study conducted at the

Tyndall AFB site 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 higher pH and higher alkalinity soils at

such sites as Fallon NAS and Eielson AFB, little or no

53
gaseous carbon dioxide production was measured

(Hinchee et al., 1989; Leeson et al., 1995). This may

result from 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.

To determine whether pH and alkalinity influenced carbon dioxide production rates at Bioventing Initiative sites,

an analysis of the ratio of oxygen utilization to carbon

dioxide production versus soil parameters was performed. Because of stoichiometry,2

 the ratio of the oxygen utilization to carbon dioxide production rate will not

be 1 because for every 9.5 moles of oxygen consumed,

6 moles of carbon dioxide are produced. A square root

transformation of the oxygen utilization and carbon dioxide production rate ratio (ratio) and log transformation

of some of the soil parameters were taken wherever the

data were not well represented by the normal distribution. Figures 5-9 through 5-11 display the bivariate relationships between the ratio and the soil parameters after

the transformation. These figures, as expected, show a

negative correlation between the ratio and the oxygen

utilization rate (Figure 5-9, r = -0.45). The correlation of

the ratio with clay is the most pronounced (Figure 5-11,

r = -0.40). The ratio is also negatively correlated with pH

(Figure 5-9, r = -0.25) and alkalinity (Figure 5-9, r =

-0.30). As noted previously, pH and alkalinity are

strongly positively related (Figure 5-9, r = 0.75). The

correlations of the ratio with iron, moisture, permeability,

and particle sizes are between 0.20 and 0.30 (Figures

5-9 and 5-11).

The statistical methods used to model the ratio of the

oxygen utilization rate to carbon dioxide production rate

as a function of the soil parameters are similar to those

used for the oxygen utilization rate analysis. As a preliminary step, a square root transformation of the ratio

and log transformation of some soil parameters were

taken to obtain more normally distributed data. All transformations for the soil parameters except clay were

consistent with those taken previously to model the

oxygen utilization rate. A log transformation of clay was

considered as it was more correlated with the ratio.

After applying the transformation, a regression model

was fitted to the ratio using forward stepwise regression.

The model accounted for the effects of all soil parameters (except season) and their interactions. Finally, the

effect of a cyclic seasonal component on the residuals

obtained from the fitted model was determined by incorporating the date of the initial in situ respiration test.

The final model for the ratio of the carbon dioxide production rate to the oxygen utilization rate is as follows:







CO2 rate

O2 rate







1

2

= 1.28 − 0.38log(pH) − 0.095log(clay) +

0.0007log(tphs) ∗ TMP (Eq. 5-5)

Each effect in the above model is statistically significant

at the 0.05 significance level. The model explains 40

percent of the variability in the transformed ratio. This

amounts to a 63 percent correlation between the observed and model-predicted transformed ratios. The effects of pH on the ratio as predicted by the model are

presented in Figure 5-16.

The complicated nature of the fitted regression model

for the ratio makes the quantification of the effects in the

model difficult. Figure 5-16, however, shows that as pH

increases, the ratio of the carbon dioxide production rate

to the oxygen utilization rate decreases, as would be

expected given the formation of carbonates.

Figure 5-15. Actual versus model-predicted oxygen utilization rates.

2 See Section 3.2.1 for the stoichiometry of hydrocarbon degradation.

54
5.2.5 Correlation of Soil Gas Permeability

With Environmental Parameters

The bivariate relationships between log-transformed soil

gas permeability and each of the independent variables

of interest are shown in Figure 5-17. In this figure,

permeability correlates most strongly with clay (r =

-0.50). The magnitude of the correlations with both moisture and sand are less pronounced and similar.

The statistical methods used here are similar to those

described previously for the oxygen utilization rate and

the ratio. Forward stepwise regression was used to

determine a regression model for the log-transformed

soil gas permeability. The independent variables of interest in the modeling were moisture content and particle size (sand, silt, and clay).

The final model describing soil gas permeability is given

below:

log(PRM) = 3.2 − 0.064 clay (Eq. 5-6)

Based on this model, clay alone explains 21 percent of

the variability in the log-transformed soil gas permeability. The effect of clay on soil gas permeability as predicted by the model is presented in Figure 5-18. In this

figure, the soil gas permeability levels greater than 100

have been censored (i.e., they were set to a constant

value of 100). Based on the regression model it is

determined that an increase in clay of 5 units decreases

soil gas permeability by 25 percent on average.

5.2.6 Analyses of Data From Contaminated

and Background Areas

As the preliminary step to comparing the data at background and contaminated sites, transformations of the

data parameters were considered. These transformations were consistent with those taken previously to

address the other objectives of the statistical analysis.

After taking the transformation, statistical analyses were

performed separately on each parameter (e.g., nitrogen,

oxygen rate). The goal of this analysis was to determine

significant differences in the levels of each parameter at

background and contaminated sites, with particular interest in TKN concentrations. Measurement of TKN accounts for nitrogen sources within cellular material;

therefore, it is possible that TKN concentrations may be

higher in contaminated areas, where microbial populations may be higher, than in uncontaminated areas. To

date, no significant difference exists between TKN concentrations at contaminated sites (average of 232 mg/kg)

and those at background areas (average of 226 mg/kg).

5.2.7 Summary

Based on the statistical analyses presented in the previous

sections, the following overall conclusions are drawn:

• The relationships between biodegradation rates and

soil parameters are not very strong. Some significant

relative effects of the soil parameters stand out from

the statistical evaluation conducted in the study, however. Namely, nitrogen, moisture, and soil gas TPH

concentration appear to be the most important characteristics influencing observed field oxygen utilization rates.

• The ratio of the carbon dioxide production rate to the

oxygen utilization rate correlates strongly with pH and

clay levels in the soil.

• Soil gas permeability correlates with each particle size

(sand, silt, and clay) and moisture content; however,

the relative effect of clay on permeability is most

important.

Figure 5-16. Variation of pH and the effect on oxygen utilization to carbon dioxide rate ratio based on model predictions with average

levels of other parameters.

55
Figure 5-17. Soil gas permeability, moisture content, and particle size site average correlation scatterplot.

56
The Bioventing Initiative has provided a large database

of information useful in the design and implementation

of bioventing systems. The statistical analyses provide

guidelines for determining which parameters are most

important to bioventing technology. These data must be

balanced, however, by experience and site-specific

data. For example, sites with relatively low soil nitrogen

concentrations should not be discarded as bioventing

sites for this reason alone, nor should an assumption be

made that nitrogen addition at these sites will increase

oxygen utilization rates. Data collected from the U.S. Air

Force Bioventing Initiative have shown that even sites

with low soil nutrient concentrations can exhibit significant microbial activity and would therefore respond well

to bioventing.

Figure 5-18. Variation of clay and the effect on soil gas permeability based on model predictions.

57
Chapter 6

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61
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

63
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

64
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

65
Appendix B

Data From Bioventing Initiatives Sites

Table B-1. Bioventing Initiative Results: Soil Chemical Characterization

Air Force Base Site pH

Alkalinity

(mg/kg)

TKN

(mg/kg)

 Total 

Phosphorus

 (mg/kg)

Iron

Content

(mg/kg)

AFP 4 FSB-1 8.8 210 33 270 7,450

FSA-3 7.7 365 190 340 9,800

AFP PJKS ST-35 7.5 NS 490 46 NS

Battle Creek Fire Training Area 8.2 170 73 165 5,050

Beale Site 3 7.7 87 105 400 27,500

Site 18 7.4 67 42 250 26,400

Site 11 8.2 240 15 820 17,500

Bolling Building 18 4.9 <50 48 85 15,300

Former Storage Tank Farm 8.1 910 100 170 9,610

Camp Pendleton Site 1 7.7 120 73 46 3,360

Cannon SWMU 70 8.4 1,150 190 76 6,570

Cape Canaveral FTA-2 7.7 165 18 280 860

Facility 1748 8.5 400 110 310 900

Facility 44625D 9.2 265 74 190 1,380

Facility 44625E 8.8 350 54 270 970

Charleston FT-03 7.1 280 350 350 2,940

Site ST-27 6.7 130 62 75 8,400

Site SS-41 4.7 <50 61 37 530

Davis Monthan Site 35 8.3 360 32 760 15,700

Site 36 8.1 220 57 450 12,700

Dover ST-04 5.3 36 48 270 4,700

North Storage Tank Farm 5.5 <50 410 100 8,740

Dyess Site FT40 8.7 3,130 180 200 16,900

Site FT41 8.8 2,790 240 280 19,500

Edwards Site 21 9.3 730 26 650 9,960

Site 16 9.6 640 22 630 12,500

Site 43 8.9 500 150 360 13,400

Eglin FTA Hurleburt Field 8.2 300 74 33 670

Old Eglin FTA 7.5 170 <43 24 1,600

Eielson ST-10 6.3 <50 390 7.4 10,400

Site 48-E2 7.8 240 320 650 17,400

Site 48-E3 7.5 230 690 790 16,700

67
Air Force Base Site pH

Alkalinity

(mg/kg)

TKN

(mg/kg)

 Total 

Phosphorus

 (mg/kg)

Iron

Content

(mg/kg)

Ellsworth Area D Bulk Fuel Storage 8.5 1,150 320 500 15,000

Building 102 Base Fuel

Station

8.6 640 24 1,000 36,800

Elmendorf 43/45 Valve Pit 7.2 100 64 3.5 24,800

ST-61 7.7 160 78 1,200 23,700

ST-71 7.8 200 110 3.1 28,000

43/55 Pumphouse 7.5 87 66 1,200 25,300

FE Warren Fire Training Pit 7.8 1,300 1,300 440 20,200

Spill Site 8.2 340 55 320 11,200

Galena Saddle Tank Farm 7.5 520 800 730 21,400

Power Plant 7.8 490 620 710 24,200

Million Gallon Hill NS NS NS NS NS

Campion POL Leak Site 8.1 300 710 570 15,200

Hanscom Building 1639 6.0 <50 630 320 7,620

Building 1812 6.6 58 60 530 6,810

Hickam Area H 9.0 1,500 30 3,400 75,100

Area K 8.3 860 1,700 2,300 34,100

Site 2 FSA 4.7 35 38 470 99,000

Hill Site 204.1 7.8 740 140 NS 5,270

Site 214.1 NS NS NS NS NS

Site 228 NS NS NS NS NS

Site 924 8.0 74 120 710 6,500

Site 1705 NS NS NS NS NS

Site 388 6.8 52 350 NS 9,380

Site 40002 NS NS NS 390 NS

Site 510.8 8.7 340 100 2,200 4,700

Johnston Island Old Fire Training Area 8.9 540 440 370 270

Former POL Tank Farm 9.0 405 185 520 115

Storage Tanks 260 and 261 9.0 355 140 340 84

Keesler SWMU 66 7.5 260 102 190 4,300

AOC A 7.0 250 43 35 2,100

Kelly Site S-4 7.5 500 690 620 16,000

Site FC-2 8.2 750 590 790 13,400

Site B-2093 8.2 1,100 310 880 14,000

Site D-10 7.7 1,100 640 310 13,300

Kirtland Fire Training Area 13 8.4 340 58 300 11,200

Fire Training Area 14 7.0 380 200 1,000 26,200

KI Sawyer POL Area 7.9 98 22 140 2,190

Kodiak Island Tank 191 7.0 260 590 930 24,900

Little Rock Fire Training Site 1 6.1 86 710 130 53,000

Spill Site 18 6.1 <50 390 140 36,300

Los Angeles Building 125 8.7 440 87 1,200 8,900

Building 241 7.5 830 120 1,600 33,800

Gate 3 8.4 310 65 1,400 18,700

March IRP Site 35c 8.2 21 130 280 32,200

Table B-1. Bioventing Initiative Results: Soil Chemical Characterization (Continued)

68
Air Force Base Site pH

Alkalinity

(mg/kg)

TKN

(mg/kg)

 Total 

Phosphorus

 (mg/kg)

Iron

Content

(mg/kg)

McClellan Building 720 7.5 22.5 44 260 11,400

Davis Site 8.0 350 260 400 40,200

Capehart Gas Station 5.8 95 54 180 26,700

PRL T-46 7.4 46 50 5.9 21,300

Study Area 6 8.0 71 10 590 28,400

Tank Farm #2 7.8 120 47 1,100 26,700

Tank Farm #4 7.4 100 74 150 25,200

McGuire Bulk Fuel Storage 6.1 37 480 217 5,830

Mt. Home POL Yard 8.4 2,100 76 5.0 21,100

Nellis Site 27 8.8 1,600 260 170 6,950

Site 28 8.6 410 100 290 5,800

Site 44 8.5 800 53 210 6,800

Newark Facility 27 7.8 370 35 515 15,400

Facility 89 7.8 460 360 540 16,100

Facility 14 7.9 320 200 260 16,400

Offutt Low Point Drain 8.0 330 190 480 7,500

Building 30 8.7 1,600 250 680 13,700

Building 406 7.8 360 220 720 18,500

POL Storage Area 7.9 470 750 600 9,800

Patrick FTA-2 8.8 220 32 260 440

BX Service Station 8.4 160 60 290 360

Pease Bulk Fuel Storage Area 6.6 140 190 730 21,000

Site 2 5.7 22.5 59 630 39,100

Plattsburgh Fire Training Area 1 6.6 84 75 <1.0 4,500

Fire Training Pit 4 6.4 22 36 330 4,500

Fire Training Areas 2 and 3 7.6 120 49 160 4,200

Pope IRP Site ST-08 6.7 200 <40 110 3,000

Randolph Tank 20 Site 8.1 340 230 920 12,400

Robins UST 173 5.2 <50 90 84 6,000

SS10 5.3 <50 46 78 3,600

Shaw Site FT-01 5.6 22 190 38 4,100

Site SS-15 5.2 22 20 260 13,900

Tinker POL Storage Area C 7.3 <50 30 55 3,210

Travis Fuel Storage Area G 7.4 120 79 220 28,400

South Gas Station 7.9 120 210 300 22,100

Vandenburg Service Station 6.9 20 103 100 2,920

JP-4 Site 6.1 180 57 100 9,700

Westover Building 7701 6.1 <50 61.5 580 6,835

Building 7705 6.8 22 200 190 4,900

Wright Patterson Fire Training Area 7.2 730 680 570 16,200

Spill Sites 2 and 3 8.1 340 <20 310 6,900

NS = not sampled.

Table B-1. Bioventing Initiative Results: Soil Chemical Characterization (Continued)

69
Table B-2. Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations

Soil Analysis

Air Force Base Site Time

Benzene

(mg/kg)

Toluene

(mg/kg)

Ethylbenzene

(mg/kg)

Total

Xylenes

(mg/kg)

Total

BTEX

(mg/kg)

TPH

(mg/kg)

Moisture 

Content

(%)

AFP 4 FSA-1 Initial

Final

0.36

BDL

1.3

BDL

12

BDL

31

BDL

45

BDL

29

680

13.7

14.7

FSA-3 Initial

Final

2.7

BDL

9.1

BDL

7.1

BDL

60

BDL

79

BDL

140

84

16.2

15.4

AFP PJKS ST-35 Initial

Final

BDL

BDL

BDL

BDL

0.73

BDL

1.5

BDL

2.2

BDL

1,100

130

8.9

11.9

Battle Creek Fire Training Area Initial

Final

0.43

BDL

3.0

BDL

2.6

BDL

12

0.016

23

0.016

7,200

1,800

4.8

5.0

Beale Site 3 Initial

Final

1.5

BDL

4.8

BDL

3.5

0.41

17

1.4

26.20

1.81

14,000

10,100

23.8

20.9

Site 18 Initial

Final

BDL

BDL

1.1

BDL

2.5

BDL

6.0

BDL

9.6

BDL

17,000

5,600

22.8

19.8

Site 11 Initial

Final

1.4

0.6

50

0.61

24

4.4

175

240

253

246

400

1,600

16.8

12.5

Bolling Building 18 Initial

Final

BDL

BDL

BDL

BDL

2.0

BDL

1.8

BDL

3.80

BDL

1,800

4,100

16.0

6.1

Former Storage

Tank Farm

Initial

Final

0.27

0.064

8.4

BDL

1.5

0.12

3.7

0.22

13.87

0.40

72

160

15.7

15.5

Camp Pendleton Site 1 Initial 0.028 0.072 0.45 0.50 1.05 3,400 11.0

Cannon SWMU 70 Initial 1.5 14 14 53 83 2,700 12.4

Cape Canaveral FTA-2 Initial

Final

BDL

BDL

4.2

BDL

2.6

BDL

6.6

BDL

13.40

BDL

300

1,100

14.3

NR

Facility 1748 Initial 0.58 0.58 2.0 5.7 8.86 17,200 9.2

Facility 44625D Initial 0.35 0.35 0.35 1.3 2.4 10,500 6.4

Facility 44625E Initial 0.40 0.51 0.61 7.1 8.62 9,200 6.4

Charleston FT-03 Initial

Final

BDL

BDL

2.0

BDL

0.82

BDL

2.3

BDL

5.12

BDL

1,100

790

15.8

8.1

ST-27 Initial BDL 0.0056 0.0033 0.015 0.02 15 13.9

Site SS-41 Initial 0.70 28 2.2 17 47.90 730 14.6

Davis Monthan Site 35 Initial 3.3 16 14 23 56 530 9.4

Site 36 Initial 20 100 63 140 323.00 2,700 7.2

Dover ST-04 Initial

Final

0.90

BDL

1.1

BDL

1.7

BDL

8.7

BDL

12.40

BDL

8.7

BDL

11.7

14.2

North STF Initial

Final

BDL

BDL

0.33

0.25

13

0.080

37

0.19

50.33

0.52

1,200

650

24.9

22.0

Dyess Site FT40 Initial

Final

BDL

BDL

BDL

BDL

BDL

BDL

0.93

BDL

0.93

BDL

450

160

17.2

17.0

Site FT41 Initial

Final

0.05

BDL

0.05

BDL

0.05

BDL

0.07

BDL

0.22

BDL

930

200

16.6

15.4

Edwards Site 21 Initial

Final

BDL

BDL

0.13

BDL

1.6

BDL

6.5

BDL

6.20

BDL

110

23

11.1

10

Site 16 Initial

Final

0.24

BDL

0.29

BDL

2.3

BDL

12

BDL

14.59

BDL

24

5.1

13.7

13.3

Site 43 Initial

Final

BDL

BDL

BDL

BDL

0.12

BDL

0.68

BDL

0.95

BDL

540

74

9.4

1.65

Eglin FTA Hurleburt Field Initial 0.97 14 7.3 48 70.27 9,600 6.6

Old Eglin FTA Initial 3.8 7.5 11 32 54.30 4,100 6.9

Eielson ST-10 Initial

Final

BDL

BDL

230

0.015

41

0.0071

340

0.0050

611.00

0.027

4,100

52

12.3

2.7

Site 48-E2 Initial

Final

1.4

BDL

4.4

BDL

11

0.34

45

1.4

62

1.7

5,400

1,200

14.9

6.2

Site 48-E3 Initial

Final

BDL

BDL

4.3

BDL

BDL

BDL

4.6

BDL

8.90

BDL

2,600

21

27.8

36.9

Ellsworth Area D Bulk Fuel

Storage

Initial

Final

8.2

0.842

8.9

BDL

37

1.8

190

10

244.10

12

2,800

2,800

17.7

16

Building 102 Base

Fuel Station

Initial

Final

0.18

BDL

0.60

BDL

0.78

11

4.3

44

5.86

55

11

651

7.2

9.8

70
Soil Analysis

Air Force Base Site Time

Benzene

(mg/kg)

Toluene

(mg/kg)

Ethylbenzene

(mg/kg)

Total

Xylenes

(mg/kg)

Total

BTEX

(mg/kg)

TPH

(mg/kg)

Moisture 

Content

(%)

Elmendorf 43/45 Valve Pit Initial

Final

BDL

BDL

BDL

32

BDL

32

BDL

140

BDL

200

4.9

6,000

5.6

9.8

ST-61 Initial

Final

BDL

BDL

0.019

0.098

0.30

0.22

0.34

0.75

0.66

1.1

790

2,400

8.4

11.6

ST-71 Initial

Final

BDL

BDL

BDL

0.001

BDL

BDL

BDL

0.00053

BDL

0.0015

32

26

4.6

5.1

43/55 Pumphouse Initial

Final

1.7

BDL

41

BDL

52

BDL

241

BDL

330

BDL

3,900

4.9

8.1

4.6

FE Warren Fire Training Pit Initial BDL 0.46 0.66 1.4 2.5 3,000 20.7

Spill Site Initial

Final

BDL

BDL

BDL

4.1

4.8

BDL

31

10

36

14

400

700

20.8

19

Fort Drum Area 1595 Initial BDL BDL 3.4 25 28 15,000 10.6

Galena Saddle Tank Farm Initial BDL 0.85 BDL 3.7 4.6 270 21.9

Power Plant Initial

Final

BDL

BDL

BDL

BDL

BDL

BDL

BDL

BDL

BDL

BDL

97

BDL

22.3

5.8

Million Gallon Hill Initial NS NS NS NS NS NS NS

Campion POL

Leak Site

Initial 0.028 0.25 BDL 0.19 0.47 760 12.3

Hanscom Building 1639 Initial

Final

0.57

0.032

1.5

0.57

0.58

0.073

4.2

0.3

6.85

0.98

13

130

16.6

15.3

Building 1812 Initial

Final

BDL

BDL

0.026

0.016

BDL

BDL

0.047

0.023

0.03

0.039

6,500

1,800

4.7

3.1

Hickam Area H Initial

Final

2.8

0.078

5.3

0.013

5.5

0.0049

7.5

0.0046

21.10

0.10

12

4.8

24.6

24.1

Area K Initial

Final

1.1

BDL

12

BDL

10

BDL

19

BDL

34.04

BDL

20

47

15.5

13.7

Site 2 FSA Initial

Final

0.6

0.93

11

3.5

7.4

11

38

12

71.74

27

1,100

1,400

33.7

31.8

Hill Site 204.1 Initial

Final

0.021

BDL

0.16

0.01

0.54

BDL

5.1

0.089

5.82

0.099

960

4,500

6.2

7.7

Site 214.1 Initial

Final

3.3

BDL

3.7

BDL

5.3

BDL

9.1

BDL

21

BDL

12,100

550

19

NS

Site 228 Initial

Final

0.64

BDL

9.2

BDL

7.1

BDL

240

BDL

256.94

BDL

5,800

BDL

11.7

8

Site 924 Initial

Final

BDL

BDL

BDL

BDL

BDL

0.0068

BDL

0.029

BDL

0.036

BDL

BDL

6.7

16.7

Site 1705 Initial

Final

BDL

BDL

BDL

BDL

BDL

BDL

0.12

BDL

0.12

BDL

4,400

600

8.3

6.3

Site 388 Initial

Final

1.9

0.045

43

0.046

25

0.54

250

4

320

4.6

7,500

1,100

8.7

6.9

Site 40002 Initial

Final

50

32

470

410

160

78

1,300

1,200

1,977.00

1,700

28,100

12,300

23.5

27

Site 510.8 Initial

Final

BDL

BDL

BDL

BDL

BDL

BDL

BDL

0.1

0.06

0.10

5,200

2,600

8.1

6.9

Johnston Atoll Old Fire Training

Area

Initial BDL 0.65 BDL BDL 0.45 7,700 11.0

Former POL Tank

Farm

Initial BDL BDL 3.5 2.5 6.0 13,000 10.7

Storage Tanks 260

and 261

Initial BDL BDL 15 14 29.00 265 12.5

Keesler SWMU 66 Initial

Final

4.7

BDL

35

0.018

16

BDL

116

0.0050

171.70

0.023

3,300

2,500

11.5

34.1

AOC A Initial

Final

0.10

BDL

0.039

0.0017

0.22

BDL

0.080

0.0020

0.44

0.0037

87

19

8.4

9.0

Kelly Site S-4 Initial

Final

BDL

BDL

9.1

0.94

BDL

BDL

13

1.5

20.20

2.4

920

590

21.1

22.9

Site FC-2 Initial

Final

BDL

0.014

8.0

0.13

BDL

0.014

22

0.022

30.00

0.18

1,600

64

20

20.5

Table B-2. Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations (Continued)

71
Soil Analysis

Air Force Base Site Time

Benzene

(mg/kg)

Toluene

(mg/kg)

Ethylbenzene

(mg/kg)

Total

Xylenes

(mg/kg)

Total

BTEX

(mg/kg)

TPH

(mg/kg)

Moisture 

Content

(%)

Site B-2093 Initial 13 130 39 200 382.00 53 18.7

Site D-10 Initial

Final

BDL

BDL

0.0096

BDL

BDL

BDL

BDL

BDL

0.01

BDL

86

250

22.5

9.3

Kirtland Fire Training 

Area 13

Initial

Final

BDL

BDL

9.1

2.2

9.5

7.2

57

38

76

47

1,800

4,800

10.3

11.4

Fire Training 

Area 14

Initial BDL BDL 0.79 3.7 4.49 7,900 11.3

KI Sawyer POL Area Initial

Final

BDL

BDL

40

BDL

9.7

0.35

27

7.8

77.70

8.2

1,300

2,600

13.3

10.6

FTA-06 Initial

Final

0.72

0.84

7.5

2.2

7.8

3.6

36

11

52

18

6,700

8,200

5.8

4.9

FTA-07 Initial

Final

BDL

BDL

0.48

0.047

1.7

0.75

19

2.6

21

3.4

250

4,000

5.7

6.6

Kodiak UCSG Tank 191 Initial BDL 0.027 BDL BDL 0.027 6.3 5.9

Little Rock Fire Training Site 1 Initial BDL BDL BDL 0.43 0.43 990 19.0

Spill Site 18 Initial

Final

BDL

BDL

BDL

BDL

0.53

BDL

0.74

BDL

1.27

BDL

8.2

BDL

16.3

16.1

Los Angeles Building 125 Initial BDL BDL BDL BDL BDL 560 9.6

Building 241 Initial 0.0054 0.018 0.35 0.36 0.73 3,700 17.1

Gate 3 Initial 0.031 0.23 1.4 2.3 3.96 4,000 15.4

Malmstrom Pumphouse 2 Initial

Final

BDL

BDL

0.71

0.067

1.6

0.21

3.7

0.13

6.0

0.41

240

84.6

22

ND

Bulk POL Initial 4.7 130 22 120 280 2,700 NS

March IRP Site 35c Initial

Final

0.011

BDL

0.011

BDL

0.050

BDL

0.16

BDL

0.23

BDL

1,000

8.6

3.5

3.2

McClellan Building 720 Initial 0.10 0.10 0.10 8.2 8.50 3,800 12

Capehart Gas

Station

Initial 1.0 1.6 0.12 0.84 3.56 5.4 17.1

Davis Site Initial

Final

0.13

BDL

0.13

BDL

0.13

0.077

0.25

0.15

0.64

0.23

6,000

1,200

18.3

17.6

PRL T-46 Initial

Final

0.0022

BDL

0.0022

BDL

0.94

BDL

1.2

BDL

2.14

BDL

3,100

61

21.3

14.2

Study Area 6 Initial

Final

4.2

0.098

18

0.11

14

0.51

27

1.1

63.20

1.8

1,200

BDL

17.0

20.1

Tank Farm #2 Initial

Final

0.0065

BDL

1.6

BDL

0.12

0.11

0.57

BDL

2.30

0.11

37

98

15.3

13.5

Tank Farm #4 Initial

Final

0.017

BDL

0.029

BDL

0.017

BDL

1.1

BDL

1.16

BDL

41

BDL

20.7

22.5

McGuire Bulk Fuel Storage Initial

Final

5.6

BDL

110

0.92

120

3.1

200

12

435.30

16

2,100

1,600

15.7

14.9

Mt. Home POL Yard Initial 84 440 82 930 1,536.00 5,800 15.7

Nellis Site 27 Initial

Final

0.39

8.1

1.9

33

1.0

18

4.7

67

7.99

130

50

7,800

14.0

19.4

Site 28 Initial

Final

14

2.2

65

11

30

8.1

130

25

239.00

46

2,200

1,500

24.1

21.2

Site 44 Initial

Final

1.2

0.40

53

2.6

28

1.1

110

5.5

192.20

9.6

300

140

24.9

18.9

Newark Facility 27 Initial

Final

BDL

0.0028

BDL

0.0079

BDL

BDL

BDL

0.0019

BDL

0.013

43

92

16.1

NR

Facility 89 Initial

Final

BDL

BDL

BDL

0.014

BDL

BDL

BDL

0.0011

BDL

0.015

12

6

18.9

NR

Offutt Low Point Drain Initial 0.11 1.8 1.0 6.3 9.2 15 15.7

Building 406 Initial

Final

2.2

0.048

1.4

0.88

21

0.034

35

1.8

60

2.8

730

1,600

23.0

20.0

Building 30 Initial

Final

BDL

BDL

0.0029

0.0041

BDL

BDL

0.014

0.00053

0.02

0.0046

6.6

BDL

24.3

22.4

Table B-2. Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations (Continued)

72
Soil Analysis

Air Force Base Site Time

Benzene

(mg/kg)

Toluene

(mg/kg)

Ethylbenzene

(mg/kg)

Total

Xylenes

(mg/kg)

Total

BTEX

(mg/kg)

TPH

(mg/kg)

Moisture 

Content

(%)

POL Storage Area Initial

Final

0.0042

BDL

0.00082

BDL

0.019

0.004

0.028

0.0073

0.05

0.011

4.3

5.5

19

21

Patrick FTA-2 Initial

Final

3.4

BDL

26

BDL

190

0.034

920

BDL

1,100

0.034

930

6,500

6.6

8.3

BX Service Station Initial

Final

4.5

0.60

0.72

0.067

3.0

0.07

18

0.2

26

0.94

10,500

63

4.1

7.6

Pease Bulk Fuel Storage

Area

Initial

Final

0.33

BDL

1.1

BDL

5.2

BDL

15

BDL

21.63

BDL

310

210

12.3

12.5

Site 2 Initial 0.024 3.2 0.057 0.68 3.96 17 11.0

Plattsburgh Fire Training Areas

2 and 3

Initial

Final

BDL

BDL

0.026

BDL

0.0042

0.94

0.14

1.5

0.17

2.4

5,200

5,200

3.8

10.5

Fire Training Pit 4 Initial 0.85 0.85 16 80 97.70 4,500 8.3

Fire Training Area 1 Initial 1.8 30 20 135 186.80 2,500 8.2

Pope Site ST-08 Initial BDL BDL BDL BDL BDL 3,200 12.9

Randolph Tank 20 Site Initial

Final

BDL

NS

4.7

NS

3.3

NS

33

NS

41.00

NS

230

NS

10.5

NS

Robins UST 173 Initial

Final

BDL

BDL

0.00067

BDL

0.11

0.82

1.0

0.73

1.11

1.6

1,900

340

14.3

11.2

SS10 Initial

Final

0.018

7.3

20

21

14

21

76

100

110.02

150

3,100

3,600

9.9

12.0

Shaw Site FT-01 Initial 0.31 1.7 3.6 3.2 8.81 4,500 10.2

Site SS-15 Initial 1.7 3.8 7.1 36 48.60 2,400 11.0

Tinker POL Storage 

Area C

Initial

Final

1.9

0.0012

45

0.0015

53

0.0049

83

0.037

138.59

0.045

2,300

BDL

9.4

11

Travis Fuel Storage 

Area G

Initial

Final

0.26

BDL

0.69

BDL

9.1

13

13

88

22.72

100

64

5,400

15.2

14.6

South Gas Station Initial 4.6 22 13 71 110.60 20 17.3

Vandenburg Service Station Initial BDL 5.4 4.9 46 56.30 230 16.6

JP-4 Site Initial 0.44 2.0 1.8 6.4 11 6.2 13.1

Westover Building 7701 Initial

Final

BDL

BDL

BDL

BDL

BDL

BDL

BDL

BDL

BDL

BDL

BDL

BDL

4.7

NR

Building 7705 Initial

Final

BDL

BDL

0.47

0.20

BDL

0.087

0.73

0.35

1.22

0.64

22

BDL

9.8

8.9

Wright Patterson Fire Training Area Initial

Final

BDL

BDL

0.026

BDL

0.0028

BDL

0.015

BDL

0.04

BDL

19.5

BDL

19.0

17.0

Spill Sites 2 and 3 Initial

Final

BDL

BDL

0.016

BDL

BDL

BDL

0.0054

BDL

0.02

BDL

BDL

BDL

6.6

4.2

BDL = below detection limit.

NR = not reported

NS = not sampled.

Table B-2. Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations (Continued)

73
Table B-3. Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations

Soil Gas Analysis

Air Force

Base Site Time

Benzene

(ppmv)

Toluene

(ppmv)

Ethylbenzene

(ppmv)

Total

Xylenes

(ppmv)

Total

BTEX

(ppmv)

TPH

(ppmv)

AFP 4 FSA-1 Initial

Final

BDL

0.24

BDL

0.094

21

0.23

19

0.67

40.96

1.2

25,000

290

FSA-3 Initial

Final

BDL

0.28

BDL

0.21

6.4

0.65

12.5

0.93

19.03

2.1

12,800

480

AFP PJKS ST-35 Initial

Final

8.2

BDL

8.8

0.004

6.5

0.026

14

0.070

37.50

0.10

2,300

11

Battle Creek Fire Training Area Initial

Final

50

BDL

18

0.0027

2.8

BDL

11

BDL

81.40

0.0027

10,900

7.9

Beale Site 3 Initial

Final

2.3

0.27

1.9

0.60

0.71

0.87

2.3

2.0

3.74

3.7

3,000

270

Site 18 Initial

Final

11

4.7

1.6

BDL

2.0

0.80

1.8

1.7

16.40

7.2

3,600

1,600

Site 11 Initial

Final

350

1.3

530

13

37

7.3

300

180

1,215.00

200

59,300

2,800

Bolling Building 18 Initial

Final

0.056

BDL

0.18

0.0033

0.30

0.016

0.74

0.058

1.28

0.077

317

15

Former Storage Tank

Farm

Initial

Final

0.21

BDL

7.9

BDL

4.0

BDL

5.2

BDL

17.31

BDL

11,900

12,700

Camp

Pendleton

Site 13115 Initial 0.34 1.2 1.2 3.4 6.1 460

Cannon SWMU 70 Initial 30 18 7.4 23 78 9,000

Cape

Canaveral

FTA-2 Initial

Final

1.5

0.016

0.11

0.011

3.6

0.026

4.8

0.071

10.01

0.12

3,900

210

Facility 1748 Initial 1.5 0.021 3.4 3.3 8.22 750

Facility 44625D Initial 0.36 0.20 0.015 1.6 2.18 397

Facility 44625E Initial 0.059 0.53 0.33 2.2 3.12 303

Charleston FT-03 Initial

Final

BDL

BDL

BDL

BDL

0.061

0.0013

0.11

BDL

0.17

0.0013

410

6.7

ST-27 Initial 126 557 81 253 1,017.00 118,333

Site SS-41 Initial 0.30 0.30 4.87 9.8 15.27 19,667

Davis Monthan Site 35 Initial 693 681 93 153 1,620.00 46,098

Site 36 Initial 583 665 118 254 1,620.00 39,667

Dover ST-04 Initial 65 44 13.4 47 169.40 33,500

North STF Initial 5.4 4.8 2.5 5.4 61.30 6,150

Dyess Site FT40 Initial

Final

0.015

BDL

0.08

0.002

0.011

BDL

0.042

0.012

0.15

0.014

49

1.5

Site FT41 Initial

Final

0.016

BDL

0.19

0.018

0.14

BDL

0.26

0.013

0.61

0.031

320

1.6

Edwards Site 21 Initial

Final

190

0.26

16

0.24

12

0.72

38

1.7

253.00

2.9

49,000

220

Site 16 Initial

Final

230

0.8

26

0.83

20

2

89

5.3

365.00

8.9

63,000

575

Site 43 Initial

Final

BDL

BDL

0.0088

0.006

0.091

0.012

0.48

0.11

0.59

0.13

380

0.95

Eglin FTA Hurleburt Field Initial 36 46 12 78 172.00 17,667

Old Eglin FTA Initial 146 179 29 120 474.00 16,000

Eielson ST-10 Initial

Final

567

BDL

150

1.6

4.0

BDL

43

4.4

764.00

6.0

48,000

2,100

Site 48-E2 Initial

Final

66

0.32

51

2.1

3.4

2.5

12

26

132.40

31

6,000

1,200

Site 48-E3 Initial

Final

4.6

BDL

0.25

BDL

0.45

1.8

1.1

4.2

6.40

6.0

1,866

610

Ellsworth Area D Bulk Fuel

Storage

Initial

Final

140

0.0091

13

0.017

12.9

2

30

8.4

128.50

10

35,000

780

Building 102 Base Fuel

Station

Initial

Final

320

BDL

48

0.074

6.7

6.7

39

32

416.70

39

79,000

840

Elmendorf 43/45 Valve Pit Initial 13 80 7.5 28 128.50 13,550

74
Soil Gas Analysis

Air Force

Base Site Time

Benzene

(ppmv)

Toluene

(ppmv)

Ethylbenzene

(ppmv)

Total

Xylenes

(ppmv)

Total

BTEX

(ppmv)

TPH

(ppmv)

ST-61 Initial

Final

0.053

BDL

0.32

0.22

0.4

0.95

1.1

1.3

1.87

2.5

1,000

200

ST-71 Initial

Final

BDL

BDL

BDL

0.004

0.22

0.032

1.12

0.033

1.35

0.069

390

3.2

43/55 Pumphouse Initial

Final

19

0.87

64

0.86

15

5.1

50

33

150

40

19,700

2,700

FE Warren Fire Training Pit Initial 0.92 2.5 1.9 5.1 10.42 1,059

Spill Site Initial

Final

180

BDL

28

0.012

24

0.049

110

0.27

348.00

0.33

15,400

33

Fort Drum Area 1595 Initial BDL 7.2 2.7 16 26 2,300

Galena Saddle Tank Farm Initial 40 8.3 2.7 6.4 57.40 2,745

Power Plant Initial

Final

0.059

0.060

1.1

BDL

3.8

1.4

3.5

3.2

8.5

4.7

897

390

Million Gallon Hill Initial

Final

6.4

BDL

5.7

BDL

0.64

3.5

2.5

10

15

14

2,000

1,000

Campion POL Leak Site Initial 0.022 0.040 0.054 0.22 0.34 254

Hanscom Building 1639 Initial

Final

8.1

8.3

10

9

3.6

0.47

17

5.5

38.70

23

7,000

1,900

Building 1812 Initial NS NS NS NS NS NS

Hickam Area H Initial

Final

BDL

BDL

BDL

BDL

28

0.0067

22

0.0053

56.80

0.012

240,000

73

Area K Initial

Final

85

BDL

BDL

BDL

22

2

48

5.3

155.70

7.3

26,300

15,900

Site 2 FSA Initial

Final

16

BDL

29

BDL

12

7.4

40

18

97.00

25

13,800

6,400

Hill Site 204.1 Initial

Final

0.026

0.0025

0.11

0.0047

0.085

BDL

0.39

0.0023

0.61

0.0095

220

3.2

Site 214.1 Initial

Final

0.010

BDL

0.039

BDL

0.26

0.036

0.26

0.18

0.57

0.22

480

620

Site 228 Initial

Final

0.81

0.021

2.2

0.029

0.85

0.016

4.7

0.13

8.48

0.20

1,300

20

Site 924 Initial

Final

34

0.0025

80

0.0045

3.6

BDL

34

BDL

150

0.0070

2,900

1.5

Site 1705 Initial

Final

0.012

BDL

0.019

0.0025

0.011

0.0017

0.053

0.035

0.10

0.039

44

1.2

Site 388 Initial

Final

175

2.3

180

97

8.9

25

80

260

440.90

380

26,000

9,000

Site 40002 Initial

Final

BDL

1.2

280

140

12

9.7

110

150

303.59

300

11,100

7,800

Site 510.8 Initial

Final

BDL

BDL

0.18

BDL

0.06

0.065

0.43

0.20

0.69

0.27

660

340

Johnston Atoll Old Fire Training Area Initial 0.016 0.47 0.95 2.8 4.24 450

Former POL Tank Farm Initial 0.1 0.11 3.03 2.3 5.54 3,833

Storage Tanks 260 and

261

Initial 0.059 0.066 1.5 2.0 3.63 1,588

Keesler SWMU 66 Initial 23 44 4.5 20 91.50 8,183

AOC A Initial

Final

1,100

42

550

220

51

53

120

230

1,800

550

130,000

22,300

Kelly Site S-4 Initial

Final

200

0.041

22

0.88

22

0.3

19

0.63

265.00

1.9

36,500

430

Site FC-2 Initial

Final

38

BDL

15

0.6

18

0.15

15

0.34

86.00

1.1

12,400

100

Site B-2093 Initial 175 323 25 87 610.00 9,467

Site D-10 Initial

Final

0.003

BDL

0.051

0.016

0.18

0.003

0.34

0.015

0.57

0.034

54

1.1

Table B-3. Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations (Continued)

75
Soil Gas Analysis

Air Force

Base Site Time

Benzene

(ppmv)

Toluene

(ppmv)

Ethylbenzene

(ppmv)

Total

Xylenes

(ppmv)

Total

BTEX

(ppmv)

TPH

(ppmv)

Kirtland Fire Training Area 13 Initial

Final

19

0.011

56

BDL

8.3

0.1

34

0.56

117.30

0.67

13,000

690

Fire Training Area 14 Initial NS NS NS NS NS NS

K.I. Sawyer POL Area Initial 393 178 9.1 15 595.10 41,067

FTA-06 Initial

Final

8.6

0.16

7.2

0.13

0.53

0.23

2.6

0.68

19

1.2

1,300

20

FTA-07 Initial

Final

3.1

1.2

6.2

10

0.40

4.0

2.2

22

12

37

820

710

Little Rock Fire Training Site 1 Initial NS NS NS NS NS NS

Spill Site 18 Initial BDL BDL 8.7 16 25 23,700

Los Angeles Building 125 Initial 0.026 0.026 0.089 0.2 0.34 2,200

Building 241 Initial 0.065 0.31 0.59 0.91 1.88 340

Gate 3 Initial 0.026 0.026 0.57 1.17 1.79 857

Malmstrom Pumphouse 2 Initial

Final

6.6

BDL

BDL

BDL

9.1

0.15

12

0.28

28

0.43

8,800

65

Bulk POL Initial

Final

BDL

BDL

12

BDL

12

2

38

4.2

62

6.2

46,000

580

March IRP Site 35c Initial 0.035 0.035 0.41 0.67 1.15 136

McClellan Building 720 Initial NS NS NS NS NS NS

Davis Site Initial

Final

0.0053

BDL

0.004

0.0045

0.39

0.0050

0.67

0.10

1.07

0.11

245

230

PRL T-46 Initial

Final

0.18

0.34

0.18

3.0

3.3

2.8

1.84

6.0

5.50

12

7,167

930

Study Area 6 Initial

Final

165

3.8

124

7.2

13

4.8

81

36

383.00

52

39,264

900

Tank Farm #2 Initial

Final

0.68

BDL

28

0.38

7.9

7.0

30

13

66.58

20

29,333

11,900

Tank Farm #4 Initial

Final

0.11

BDL

0.11

BDL

5.3

0.046

5.7

0.15

11.22

0.20

2,370

27

McGuire Bulk Fuel Storage Initial

Final

73

10

190

22

17

5.1

58

45

340

82

54,000

4,900

Mt. Home POL Yard Initial 550 25 560 270 1,400 67,000

Nellis Site 27 Initial

Final

543

6.0

372

14

37

5.1

100

16

1,052.00

41

81,667

1,400

Site 28 Initial 520 547 55 185 1,307.00 72,000

Site 44 Initial 203 753 68 377 1,401.00 29,333

Newark Facility 27 Initial 0.019 0.023 0.0097 0.11 0.16 1,043

Facility 89 Initial 0.0072 0.015 0.0045 0.0088 0.04 28

Facility 14 Initial NS NS NS NS 0.00 NS

Offutt Low Point Drain Initial 88 153 29 77 347.00 29,750

Building 30 Initial

Final

BDL

BDL

BDL

BDL

BDL

BDL

1.4

BDL

311.00

BDL

8,200

170

Building 406 Initial

Final

290

BDL

BDL

BDL

44

6.5

51

28

382.92

35

18,300

2,300

POL Storage Area Initial

Final

67

BDL

11

BDL

4

BDL

9.5

0.36

304.00

0.36

13,500

860

Patrick FTA-2 Initial

Final

BDL

0.048

BDL

0.003

1.5

0.024

5.2

0.058

267.60

0.13

10,400

68

BX Service Station Initial

Final

BDL

0.027

44

0.002

24

0.0045

200

0.23

7.18

0.26

62,000

4.3

Pease Bulk Fuel Storage Area Initial 117 9.7 18 22 166.70 48,000

Plattsburgh Fire Training Pits 2 and 3 Initial

Final

4.4

BDL

10

0.016

2.1

0.0045

14

0.013

30.50

0.034

4,312

9.9

Fire Training Pit 4 Initial 11 18 24 82 140 7,200

Fire Training Area 1 Initial 6.01 20 4.2 15 45.21 8,348

Table B-3. Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations (Continued)

76
Soil Gas Analysis

Air Force

Base Site Time

Benzene

(ppmv)

Toluene

(ppmv)

Ethylbenzene

(ppmv)

Total

Xylenes

(ppmv)

Total

BTEX

(ppmv)

TPH

(ppmv)

Pope Site ST-08 Initial BDL 25 4.0 10 39 3,800

Randolph Tank 20 Site Initial

Final

16

BDL

0.53

BDL

6.1

0.048

18

0.21

40.63

0.26

19,667

50

Robins UST 173 Initial

Final

0.0013

0.086

0.028

0.011

0.17

BDL

1.04

0.016

1.24

0.11

206

1.1

SS10 Initial

Final

270

57

109

40

16

15

84

67

479.00

180

55,000

13,000

Shaw Site SS-15 Initial 210 200 32 120 560 69,700

Tinker POL Storage Area C Initial

Final

53

0.018

100

0.022

11

0.73

36

1

202.00

1.8

11,500

190

Travis Fuel Storage Area G Initial

Final

1,300

7.1

550

11

100

6.4

97

31

2,048.00

56

110,000

2,300

South Gas Station Initial 1,650 1,125 61 240 3,076.00 145,000

Vandenburg Service Station Initial 160 84 28 139 411.00 19,467

JP-4 Site Initial NS NS NS NS NS NS

Westover Building 7701 Initial

Final

NS

610

NS

BDL

NS

0.13

NS

0.031

NS

610

NS

0.57

Building 7705 Initial

Final

BDL

BDL

BDL

0.0093

0.12

0.0063

0.087

0.023

0.23

0.039

92

0.34

Wright Patterson Fire Training Area Initial 0.23 0.42 0.21 0.29 1.15 1,147

Spill Sites 2 and 3 Initial 0.07 2.59 1.92 6.76 11.34 2,398

NS = not sampled.

BDL = below detection limit.

Table B-3. Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations (Continued)

77
Table B-4. In Situ Respiration Test Results at Bioventing Initiative Sites

Initial 6-Month 1-Year

Air Force Base Site %/hr

mg/kgday %/hrmg/kgday %/hrmg/kgday

AFP 4 FSA-1 0.32 5.22 0.058 0.95 0.059 0.96

FSA-3 0.91 14.85 0.36 5.88 0.54 8.81

AFP PJKS ST-35 0.52 8.49 0.17 2.77 0.33 5.39

Battle Creek Fire Training Area 0.39 6.36 0.12 1.96 0.16 2.61

Beale Site 3 0.14 2.28 0.043 0.70 0.016 0.26

Site 18 0.74 12.08 0.078 1.27 0.069 1.13

Site 11 0.12 1.96 0.031 0.51 0.033 0.54

Bolling Building 18 0.11 1.80 0.011 0.18 0.080 1.31

Former Storage Tank Farm 1.4 22.85 1.5 24.48 0.98 15.99

Camp Pendleton Site 1 0.021 0.34 NC NC NC NC

Cannon SWMU 70 0.53 8.65 NC NC NC NC

Cape Canaveral FTA-2 0.18 2.94 NC NC NC NC

Facility 1748 0.16 2.61 NC NC NC NC

Facility 44625D 0.39 6.36 NC NC NC NC

Facility 44625E 0.17 2.77 NC NC NC NC

Charleston FT-03 0.54 8.81 0.0059 0.10 0.084 1.37

Site SS-41 0.38 6.20 NC NC NC NC

Davis Monthan Site 35 0.009 0.15 NC NC NC NC

Site 36 0.078 1.27 NC NC NC NC

Dover ST-04 0.18 2.94 NC NC NC NC

North STF 0.30 4.90 NC NC NC NC

Dyess Site FT40 0.010 0.16 NC NC NC NC

Site FT41 NC NC NC NC NC NC

Edwards Site 21 0.16 2.61 0.016 0.26 0.23 3.75

Site 16 0.031 0.51 0.0051 0.08 0.059 0.96

Site 43 0.033 0.54 0.0060 0.10 0.019 0.31

Eglin FTA Hurleburt Field 0.18 2.94 NC NC NC NC

Old Eglin FTA 0.18 2.94 NC NC NC NC

Eielson ST-10 0.29 4.73 0.22 3.59 0.10 1.63

Site 48-E2 0.18 2.94 0.046 0.75 0.11 1.80

Site 48-E3 NC NC 0.067 1.09 0.11 1.80

Ellsworth Area D Bulk Fuel Storage 1.1 17.95 0.068 1.11 0.074 1.21

Building 102 Base Fuel

Station

0.034 0.55 0.0096 0.16 0.0056 0.09

Elmendorf 43/45 Pumphouse 0.51 8.32 0.09 1.47 0.32 5.22

ST-61 0.38 6.20 0.072 1.18 0.44 7.89

ST-71 0.056 0.91 0.015 0.24 0.06 1.23

43/55 Pumphouse 0.34 5.55 0.0066 0.11 0.16 2.61

FE Warren Fire Training Pit 0.62 10.12 NC NC NC NC

Spill Site 1.4 22.85 0.052 0.85 0.018 0.29

Galena Saddle Tank Farm 1.05 17.14 NC NC NC NC

Power Plant 1.4 22.85 NC NC 0.059 9.63

Million Gallon Hill 0.44 7.18 NC NC 0.11 1.80

Campion POL Leak Site 0.99 16.16 NC NC NC NC

Hanscom Building 1639 0.78 12.73 0.26 4.24 0.048 0.78

Building 1812 NC NC 0.036 0.59 NC NC

78
Initial 6-Month 1-Year

Air Force Base Site %/hr

mg/kgday %/hrmg/kgday %/hrmg/kgday

Hickam Area H 0.71 11.59 0.093 1.52 0.012 0.20

Area K 1.2 19.58 0.45 7.34 0.38 6.20

Site 2 FSA 0.6 9.79 0.27 4.41 0.53 8.65

Hill Site 204.1 0.98 15.99 0.057 0.93 0.096 1.57

Site 214.1 0.31 5.06 0.015 0.24 0.015 0.24

Site 228 0.54 8.81 0.031 0.51 0.059 0.96

Site 924 0.56 9.14 0.043 0.70 0.007 0.12

Site 1705 NC NC NC NC NC NC

Site 388 0.42 6.85 0.090 1.47 0.39 6.36

Site 40002 0.22 3.59 0.016 0.26 0.083 1.35

Site 510.8 0.022 0.36 0.021 0.34 0.091 1.49

Johnston Atoll Old Fire Training Area 0.42 6.85 NC NC 0.44 7.2

Former POL Tank Farm 0.24 3.92 NC NC 0.22 3.5

Storage Tanks 260 and 261 0.64 10.44 NC NC 0.23 3.7

Keesler SWMU 66 0.65 10.61 0.41 6.69 0.60 9.79

AOC A 0.081 1.32 0.097 1.58 0.083 1.35

Kelly Site S-4 2.4 39.17 0.28 4.57 0.11 1.80

Site FC-2 1.9 31.01 0.72 11.75 0.58 9.47

Site D-10 1.1 17.95 0.057 0.93 0.070 1.14

Kirtland Fire Training Area 13 0.061 1.00 0.012 0.20 0.0083 0.13

Fire Training Area 14 0.0055 0.09 0.0043 0.07 NC NC

KI Sawyer POL Area 0.11 1.80 0.11 1.80 0.16 2.61

FTA-06 0.13 2.12 0.047 0.77 0.029 0.47

FTA-07 0.074 1.21 0.021 0.34 0.012 0.20

Little Rock Spill Site 18 2.04 33.29 NC NC NC NC

Los Angeles Building 125 0.33 5.39 NC NC NC NC

Building 241 0.25 4.08 NC NC NC NC

Gate 3 0.27 4.41 NC NC NC NC

Malmstrom Pumphouse II 3.2 52.22 0.29 4.73 NC NC

POL SA 1.1 17.95 0.34 5.55 0.25 4.08

March IRP Site 35c 0.29 4.73 NC NC NC NC

McClellan Davis Site 0.37 6.04 0.12 1.96 0.50 8.16

PRL T-46 0.91 14.85 0.19 3.10 0.37 6.04

Study Area 6 0.32 5.22 0.016 0.26 0.11 1.80

Tank Farm #2 0.31 5.06 0.030 0.49 0.064 1.04

Tank Farm #4 0.33 5.39 0.011 0.18 0.099 1.62

McGuire Bulk Fuel Storage 1.2 19.58 0.28 4.57 0.72 11.75

Mt. Home POL Yard 0.32 5.22 NC NC NC NC

Nellis Site 27 0.048 0.78 0.0035 0.06 0.031 0.51

Site 28 0.21 3.43 0.038 0.62 0.016 0.26

Site 44 0.69 11.26 0.028 0.46 0.022 0.36

Newark Facility 27 0.026 4.24 NC NC 0.015 0.24

Facility 89 0.021 0.34 0.0096 0.16 0.021 0.34

Offutt Low Point Drain 0.86 14.04 NC NC NC NC

Building 406 5.6 91.39 0.33 5.39 0.26 4.24

Building 30 4.9 79.97 0.051 0.83 0.039 0.64

POL Storage Area 0.1 1.63 NC NC 0.46 7.51

Table B-4. In Situ Respiration Test Results at Bioventing Initiative Sites (Continued)

79
Initial 6-Month 1-Year

Air Force Base Site %/hr

mg/kgday %/hrmg/kgday %/hrmg/kgday

Patrick FTA-2 0.34 5.55 0.41 6.69 0.33 5.39

BX Service Station 0.16 2.61 0.21 3.43 0.028 0.46

Pease Bulk Fuel Storage Area 3.57 58.26 NC NC NC NC

Plattsburgh Fire Training Areas 2 and 3 0.84 13.71 0.17 2.77 0.094 1.53

Fire Training Pit 4 0.20 3.26 NC NC NC NC

Randolph Tank 20 Site 0.41 6.69 0.15 2.45 0.28 4.57

Robins UST 173 0.029 0.47 0.0023 0.04 0.013 0.21

SS10 0.18 2.94 0.031 0.51 0.020 0.33

Shaw Site FT-01 0.43 7.02 NC NC NC NC

Site SS-15 0.16 2.61 NC NC NC NC

Tinker POL Storage Area C 0.18 2.94 0.038 0.62 0.056 0.91

Travis Fuel Storage Area G 3.6 58.75 0.79 12.89 0.86 14.04

South Gas Station 2.47 40.31 NC NC NC NC

Vandenburg Service Station 0.24 3.92 NC NC NC NC

Westover Building 7701 0.33 5.39 0.0098 0.16 0.052 0.85

Building 7705 0.12 1.96 NC NC 0.05 0.82

Wright Patterson Fire Training Area 0.19 3.10 NC NC NC NC

Spill Sites 2 and 3 0.26 4.24 NC NC NC NC

NC = not conducted.

Table B-4. In Situ Respiration Test Results at Bioventing Initiative Sites (Continued)

80