xvEPA
United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/540/R-95/534a
September 1995
Manual
Bioventing Principles and
Practice
Volume I: Bioventing Principles
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EPA/540/R-95/534a
September 1995
Manual
Principles and Practices of Bioventing
Volume I: Bioventing Principles
U.S. Air Force Environics U.S. Air Force Center for
Directorate of the Environmental Excellence
Armstrong Laboratory Technology Transfer Division
Tyndall AFB, FL Brooks AFB, TX
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Center for Environmental Research Information
Cincinnati, Ohio
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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 endorse-
ment or recommendation for use.
This document is equivalent to U.S. Air Force document AL/EQ-TR-1995-0037.
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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
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Contents (continued)
Page
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
IV
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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
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Figures (continued)
Figure Page
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
VI
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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
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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
VIM
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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
MAS 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
kB
Kd
KS
kT
MW
Pv
R
RI
S
t
Tabs
%
X
Y
volumetric concentration in the
vapor phase
saturated vapor concentration
volumetric concentration in the
aqueous phase
activation energy
organic carbon fraction
maximum rate of substrate utilization
endogenous respiration rate
baseline biodegradation rate
biodegradation rate
sorption coefficient
octanol/water partition coefficient
Monod half-velocity constant
temperature-corrected
biodegradation rate
molecular weight
vapor pressure of pure contaminant
at temperature T
gas constant
radius of influence
concentration of the primary
substrate (contaminant)
solubility in water
time
absolute temperature (°K)
mole fraction
concentration of microorganisms
cell yield
IX
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Conversion Factors
To convert . . .
cubic feet
cubic feet
cubic inches
cubic yards (tons)
cubic yards (tons)
darcy
darcy
degrees Fahrenheit
degrees Fahrenheit
feet
horsepower
inches
kilocalories
millimeters of mercury (°C)
parts per million
parts per million
pounds
pounds per square inch
square inches
tons
U.S. gallons
to ...
cubic meters
liters
cubic centimeters
cubic meters
kilograms
square centimeter
square meter
degrees Celsius
degrees Kelvin
meters
kilowatts
centimeters
joules
Pascals
milligrams per liter
grams per liter
kilograms
kiloPascals
square centimeters
metric tons
liters
multiply by ...
0.02831685
0.03531
610.2
0.7646
907.1843
9.869233 x10'9
9.869233 X10'13
t.c = (t.F- 32)71.8
t.K = (t.F - 523.67)71 .8
0.3048
0.7457
2.54
4,186.8
133.322
1
1,000
0.45354237
6.895
6.4516
0.90718474
3.785
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A cknowledgments
This manual was prepared by Andrea Leeson and Robert Hinchee of Battelle Memorial Institute,
Columbus, Ohio, forthe 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
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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 Bioremedia-
tion 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.
EPAs 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 com-
pound. 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
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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 imple-
mented 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 pe-
troleum-contaminated sites. This document is a culmi-
nation of the experience gained from these sites and
provides specific guidelines on the principles and prac-
tices 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
!?a'fr Residual
Table saturation
discharged or reinjected. Although useful for preventing
continued migration of contaminants, these systems
rarely achieved typical cleanup goals. Bioventing sys-
tems are designed to remove the contaminant source in
the vadose zone, thereby preventing future and/or con-
tinued contamination of the ground water.
Atypical bioventing system is illustrated in Figure 1-2.
Although bioventing is related to the process of soil
vacuum extraction (SVE), these processes have differ-
ent 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 biodegra-
dation of aerobically biodegradable compounds, regard-
less of their molecular weight, with some volatilization
occurring. The major distinction between these tech-
nologies 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 prin-
ciples of bioventing in relation to physical, chemical, and
microbial processes occurring in the field. An overview
of the development of bioventing, including develop-
ment 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 docu-
ment to illustrate principles of bioventing as determined
from field testing.
Figure 1-1. Hydrocarbon distribution at a contaminated site.
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i
Biodegradation
of Vapor*
Soil Gas
Monitoring
Low Rate
Air Injection
4—t
Contaminated Soil
Figure 1-2. Schematic of a typical bioventing system.
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Chapter 2
Development ofBioventing
This chapter provides a framework for the document, de-
scribing this development and structure of the Bioventing
Initiative, and ultimately, of this document. This chapter
provides an overview of bioventing, covering oxygen sup-
ply in situ (the dominant issue in the evolution of biovent-
ing), early bioventing studies that led to development of the
Bioventing Initiative, final structure of the treatability stud-
ies and bioventing system design used for the Bioventing
Initiative, and finally, emerging techniques that are being
investigated as modifications to the conventional biovent-
ing 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 proc-
esses used water to carry oxygen or an alternative
electron acceptor to the contaminated zone. This proc-
ess was common, whether the contamination was pre-
sent 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 1 0 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 2-1 1 can be used to calculate the
quantity of water that must be delivered to provide suf-
ficient oxygen for biodegradation.
2 /E 2-l)
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 require-
ments 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 con-
sumed. On a mass basis:
1moleC6H14 1 mole O2 86gC6H14
• x —r=—~— x •
9.5 molesO2 32 g O2 1 mole C6H14
86 g C6H14 1 g C6H14
304 g O2 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 390 L H2O
9 mg O2 1 g
1 L H2O x 1,000 mg
or, to degrade 1 Ib:
390 L H2O 1 gal 1,QQQg
1 g C6H14 X 3.8 L X 2.2 Ib
1 g C6H14
47,000gal H2O
1 lbC6H14
Table 2-1. Oxygen Requirements Based on Supplied Form
Oxygen Form
Volume to
Oxygen Degrade 1 Ib
Concentration in H2O Hydrocarbon
Air-saturated H2O 8 mg/L to 10 mg/L
Oxygen-saturated h^O 40 mg/L to 50 mg/L
Hydrogen peroxide Up to 500 mg/L
47,000 gal
(180,000 L)
11,000 gal
(42,000 L)
1,600 gal
(6,100 L)
Air
NA (21 % vol./vol. in air) 170 fr (4,800 L)
See Section 3.2 for development of this equation.
NA = not applicable.
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Because of the low aqueous solubility of oxygen, hydro-
gen peroxide has been tested as an oxygen source in
laboratory studies and at several field sites (Hinchee et
al., 1991 a; 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 waterthat 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:
H,O
2^2
(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 spe-
cies 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 ex-
ceeds the rate of microbial oxygen utilization, gase-
ous 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 ground-
water 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 re-
sults (American Petroleum Institute, 1987; Brown et al.,
1984; Downey et al., 1988; EPA, 1990; Morgan and
Watkinson, 1992).
Hinchee et al. (1991 a) 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 coarse-
grained 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-con-
taining nutrient solution. As in previous studies, hydro-
gen 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 per-
oxide 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 ap-
pears 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 Ib (0.45 kg) of hydrocar-
bon (Table 2-1). Because costs associated with water-
based delivery of oxygen can be relatively high, the use
of gas-phase delivery significantly reduces the cost as-
sociated 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 diffu-
sion cannot realistically be expected to aid significantly
in water-based bioreclamation, diffusion of oxygen in a
gas-phase system is a significant mechanism for oxy-
gen delivery to less permeable zones.
Given the advantages of using air rather than water as
the oxygen source, several investigators began explor-
ing 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 biode-
gradation 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 effective-
ness 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).
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1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
Figure 2-1. Historical perspective on the development of bioventing.
Subsequently, a column study was conducted to deter-
mine 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 biodegra-
dation 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 effec-
tiveness of bioventing for treating hydrocarbon-contami-
nated 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 un-
saturated 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, Benned-
sen et al. (1987) concluded that soil venting provides
large quantities of oxygen to the unsaturated zone, pos-
sibly stimulating aerobic degradation. They suggested
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that water and nutrients also would be required for
significant degradation and encouraged additional in-
vestigation into this area.
Biodegradation enhanced by soil venting has been ob-
served at several field sites. Investigators claim that at
a soil venting site for remediation of gasoline-contami-
nated soil, significant biodegradation occurred (meas-
ured 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 tem-
perature, 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 de-
crease 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 be-
cause toluene concentrations decayed near the oxygen-
ated ground surface, soil venting is an attractive
remediation alternative for biodegrading light volatile hy-
drocarbon 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 biodegra-
dation, nutrient addition did not. Final soil sampling dem-
onstrated 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-contami-
nated soils. The study also showed, however, that addi-
tional 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 Flor-
ida. 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 mi-
crobial 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 illus-
trated the effectiveness of bioventing.
The studies conducted at Hill and Tyndall AFBs pro-
vided valuable information on bioventing. These stud-
ies 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 con-
taminated 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 petro-
leum hydrocarbons from JP-4 jet fuel, heating oils,
waste oils, gasoline, and/or diesel; however, some fire
training areas also were studied where significant con-
centrations of solvents were present. This manual rep-
resents 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 2-26 The scale of application and con-
taminant 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 opti-
mized 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 volatili-
zation may occur. SVE systems operate at flow rates
optimized for volatilization, although some biodegrada-
tion 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.
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•• Johnston Atoll
Figure 2-2. Locations of Bioventing Initiative sites.
The following section describes the basic structure for
field studies conducted as part of the Bioventing Initia-
tive. 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 consis-
tent data from 125 sites, which provided a strong data-
base 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 sam-
ples for analysis of BTEX, TPH, and soil physico-
chemical characteristics.
• Field treatability studies, including an in situ respira-
tion test and a soil gas permeability test.
• Identification of a background, uncontaminated area
for comparison with the contaminated area of back-
ground respiration rates and nutrient levels.
• Installation of a blower for 1 year of operation (typi-
cally 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 analy-
ses 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 activ-
ity is difficult to assess in the field because of interfer-
ence and interactions among these parameters. The in
situ respiration test integrates all factors to assess
whether the microorganisms are metabolizing the fuel.
7 See Section 1.4 of Volume II for methods for conducting the in situ
respiration test and analyses of test data.
-------
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
Eielson AFB, AK
Pilot scale
Pilot scale
Acetone, toluene,
benzene, naphthalene
JP-4 jet fuel
1.5-26
Leeson et al., 1994
Hinchee and Ong, 1992
Leeson et al., 1995
EPA, 1994c
Fallen MAS, NE
Galena AFS, AK, Saddle Tank
Farm
Hill AFB, Utah, Site 914
Hill AFB, Utah, Site 280
Eglin AFB, FL
Kenai, Alaska, Site 1-33
Kenai, Alaska, Site 3-9
Massachusetts
Minnesota
The Netherlands
The Netherlands
The Netherlands
Patuxent River NAS, MD
Prudhoe Bay
St. Louis Park, MN, Reilly Tar
Site
Seattle, WA
Southern CA
Tinker AFB, OK
Tyndall AFB, FL
Undefined
Undefined
Undefined
Valdez, Site A
In situ respiration test
Pilot scale
Full scale, 2 years
Full scale
Full scale
Pilot scale
Pilot scale
Full scale
Full scale
Full scale
Undefined
Field pilot, 1 year
In situ respiration test
Pilot scale
Pilot scale
Full scale
Full scale
In situ respiration test
Field pilot, 1-year and
in situ respiration test
Full scale
Full scale
Full scale
Pilot scale
JP-5 jet fuel
Diesel
JP-4 jet fuel
JP-4 jet fuel
Gasoline
Crude oil, petroleum
Crude oil
Gasoline
Gasoline
Gasoline
Undefined
Diesel
JP-5 jet fuel
Diesel
PAH
Diesel
Gasoline, hydraulic oil
JP-4 and mixed fuels
JP-4 jet fuel
Gasoline and diesel
Diesel
Fuel oil
Crude oil
4.2
11-30
Up to 8.5
0.27 (site average)
4.0
2.7-25
0.64-12
Not measured
15, 4.9,3.1, 0.20
570 kg of
hydrocarbon
removed during
2-year study
1 .6-4.2
6.9
2.6
8.6-11
0.55-2.2 mg
PAH/kg-day
6.0
0.14
2.3-15
1.6-16
50 kg/(well day)
100 kg/(well day)
60 kg/(well day)
0.90-15.6
Hinchee et al., 1991b
Ong et al., 1994
Hinchee et al., 1994
Battelle, 1994
EPA, 1991b
Downey et al., 1994
Hinchee, unpublished
data
Hinchee, unpublished
data
Brown and Crosbie, 1994
Newman et al., 1993
van Eyk, 1994
Urlingset al., 1990
van Eyk and Vreeken,
1989b
Hinchee et al., 1991b
Ong et al., 1994
Alleman et al., 1995
Baker et al., 1993
Zachary and Everett, 1993
Hinchee and Smith, 1991
Miller, 1990
Hinchee et al., 1991b
Ely and Heffner
Ely and Heffner, 1988
Ely and Heffner, 1988
Hinchee, unpublished data
Data from the in situ respiration test and site measure-
ments 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 con-
structed 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 oper-
ated in the extraction configuration, similar to SVE
systems. Research at Hill and Eielson AFB's, however,
demonstrated that air injection was a feasible, more effi-
cient alternative to air extraction, resulting in a greater
proportion of hydrocarbon biodegradation rather than
volatilization and reduced air emissions8 Therefore, the
See Section 2.1 of Volume II for a discussion of air injection versus
extraction considerations.
-------
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 guide-
lines 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 applica-
ble 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 tech-
nique 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 hydrocar-
bons (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 biode-
gradation 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 fu-
ture 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.
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Chapter 3
Principles ofBioventing
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 dif-
ferent processes will lead to more efficient bioventing
design and operation. Specific topics addressed in this
chapter include:
• Soil gas permeability, contaminant diffusion and dis-
tribution, and zone of oxygen influence.
• Environmental factors that affect microbial proc-
esses, such as electron acceptor conditions, moisture
content, pH, temperature, nutrient supply, contami-
nant 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 diffu-
sion 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 vol-
umes 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 approxi-
mately 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 low-
permeability 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-permeabil-
ity soils, such as a silty clay site at Fallen Naval Air
Station (MAS), 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 fine-
grained 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
75-100
Figure 3-1. Distribution of fine-grained soils (silt and clay) at
Bioventing Initiative sites.
11
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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 analy-
sis. The greatest limitation to bioventing at Bioventing
Initiative sites has been excessive soil moisture. A com-
bination 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 subsur-
face contaminant distribution is a necessity. Many sites
at which bioventing can be applied are contaminated
with immiscible liquids, such as petroleum hydrocar-
bons. 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 ex-
posed 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 ground-
water 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 non-
aqueous phase liquids (LNAPLs) if their density is less
than water or dense nonaqueous phase liquids
(DNAPLs) if their density is greater than water. In gen-
eral, 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 re-
tained 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 subsur-
face environment. Fluids can move through the subsur-
face 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 un-
less 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 be-
tween an immiscible and a vapor phase:
Cv = ?cCvsat (Eq. 3-1)
where:
Cv = volumetric concentration of the contaminant
(x) in the vapor phase (gx/Lvapor)
% = mole fraction of the contaminant
(dimensionless)
CVsat = saturated vapor concentration of the
contaminant (gx/Lvapor)
Cvsat is further defined as:
(MWX) Pv
(Eq. 3-2)
RT,
abs
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
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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, de-
pending on the solubility of specific components. Once
in the ground water, contaminants can migrate through
the subsurface in response to a gradient in the aqueous-
phase 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 =
(Eq. 3-3)
where:
Cv = volumetric concentration of the contaminant x
in the aqueous phase (gx/Laqueous)
% = mole fraction of the contaminant
(dimensionless)
sx = solubility of pure contaminant x in water
(Qx/Uvater)
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 hydrocar-
bons, 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 subsur-
face (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 Lang-
muir isotherm describes the sorbed contaminant con-
centration as increasing linearly with concentration, then
Linear
Freundlich
Langmuir
Dissolved Concentration, C, (ng/ml)
Figure 3-2. Sorption isotherms.
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 concentra-
tions 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 iso-
therm is relatively simple and is valid for dissolved
compounds at less than one-half of their solubility (Ly-
man et al., 1992). This isotherm is typically valid to
describe hydrocarbon sorption.
The linear isotherm is expressed mathematically as:
- Kd Cw
(Eq. 3-4)
where:
Cs = quantity of contaminant x sorbed to the solid
matrix (gx/gsoN)
Kd = sorption coefficient (Laqueous/gsoN)
Cw = volumetric concentration of contaminant x in
the aqueous phase (gx/Laqueous)
The sorption coefficient may be determined experimen-
tally, estimated based on values published in the litera-
ture 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:
f0,
(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 immis-
cible 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
Solubility Vapor Pressure
Kow (mg/L) (mm Hg)a
Benzene
Ethylbenzene
Heptane
Hexane
Toluene
o-xylene
m-xylene
p-xylene
131.82
1,349
—
—
489.9
891
1,585
1,513.6
1 ,750b
152b
50
20
537C
152b
158b
198b
75
10
40
150
20
7
9
9
79°F
65°F
a Vapor pressure at 68°F unless noted.
b Calculated at 20°C.
c Calculated at 20°C.
13
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not occupied,1 the vapor- or aqueous-phase concentra-
tion is a function of the sorbed concentration. This rela-
tionship is illustrated in Figure 3-3.
This relationship typically follows a Langmuirtype curve.
If the concentration in the soil is in excess of the sorption
capacity of the soil,2 the aqueous-phase and the vapor-
phase concentrations are Raoult's Law-driven and are
independent of the hydrocarbon concentration in the
soil. This is an important concept in attempting to inter-
pret 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 ap-
plying 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, how-
ever. Limited oxygenation is anticipated because of
water-filled pore space. If significant contamination ex-
ists below the water table, dewatering should be consid-
ered 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
ft
Is
o
o
li
Raoulfs Law Concentration
Immiscible Phase
Absent, Sorption Driven
Immiscible Phase Present,
Raoult's Law Driven
100-1,000 mg/kg
Soil Concentration (mg/kg)
Figure 3-3. Relationship between sorbed contaminant concen-
trations 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.
well documented, and many parameters are still un-
known concerning its applicability and effectiveness.
3.1.3 Oxygen Radius of Influence
An estimate of the oxygen radius of influence (F^) of venting
wells is an important element of a full-scale bioventing de-
sign. This measurement is used to design full-scale sys-
tems, 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 influ-
ence 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 per-
meable 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 influ-
ence 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 esti-
mate 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 ap-
proaches 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 treat-
ment. In addition, microbial processes allow treatment of
4 Based on the author's experience, this seal does not occur at most
sites.
14
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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 depend-
ent upon, thereby potentially affecting the efficacy of
bioventing.
3.2.1 Microbial Kinetics
In biological processes, microorganisms degrade or-
ganic 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 + 7.87502 + 0.25N03 -»
CH2Oo.5N0.25(biomass) +
5C02 + 6H20 (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 pro-
duced, Equation 3-6 reduces to:
C6H14 + 9.5O2 -> 6CO2 + 7H2O (Eq. 3-7)
Based on Equation 3-7, 9.5 moles of oxygen are re-
quired for every mole of hydrocarbon consumed, or, on
a weight basis, approximately 3.5 g of oxygen are re-
quired for every 1 g of hydrocarbon consumed.
Predicting the amount of time needed to bioremediate
a site requires an understanding of the microbial kinet-
ics of substrate (contaminant) utilization. Most sub-
strate 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 proc-
ess, primary substrate utilization generally describes
the kinetics of the reactions taking place; however, in
some instances, cometabolic processes also may oc-
cur. 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
(Eq. 3-8)
where:
S = concentration of the primary substrate
(contaminant) (gs/L)
t = time (minutes)
k = maximum rate of substrate utilization (gs/gx-
min)
X = concentration of microorganisms (gx/L)
Ks = Monod half-velocity constant (gs/L)
At high substrate concentrations (S is greaterthan Kg), the
rate of substrate utilization is at a maximum, limited by
some other factor such as oxygen, nutrients, or the char-
acteristics 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 concentra-
tion. Conversely, when the primary substrate concentra-
tion 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 sys-
tem, kinetics based on oxygen utilization are zero-order.
The rate based on petroleum or other contaminant re-
moval may be described, however, by Monod or inhibition
kinetics.
Monod kinetics have been widely applied to conven-
tional wastewater treatment, where the compounds be-
ing 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 typi-
cal 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 contami-
nants, driven at least in part by solubilization. Because
microorganisms exist in pore water, contaminants must
partition into the pore water to be available for degrada-
tion. Although high soil contaminant concentrations may
be present, the actual concentration of hydrocarbon
dissolved in the pore water and available to the micro-
organisms 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 op-
timal conditions for active growth. Several factors may
15
-------
affect a microorganism's ability to degrade contami-
nants, 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 measure-
ments 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 con-
structed 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 pro-
vided 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 biode-
gradability 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 an-
aerobic conditions in the subsurface soil. Although hy-
drocarbons 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 etal., 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 proc-
esses and for solubilization of energy and nutrient sup-
plies. 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 mois-
ture is that excess moisture has led to significant reduc-
tions in soil gas permeability. One major objective of the
Bioventing Initiative was to assess the effects of mois-
ture on biodegradation.
The range of soil moisture content measured at Biovent-
ing 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 mois-
ture content and oxygen utilization rate, although a slight
positive relationship has been observed.5
a 10 -
<5 540 10-15 15-20 20-25 >25
Moisture Content (% by weight)
Figure 3-4. Soil moisture content measurements at Bioventing
Initiative sites.
50
45
'S
5 40
i"*
I30
§ 25
Lo
S 15
10 15 20 25
Moisture Content (% by weight)
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 be-
tween moisture content and oxygen utilization rates.
16
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At a desert site at the Marine Corps Air Ground Combat
Center, Twentynine Palms, California, soil moisture con-
tent 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, necessi-
tating humidification of the injection air. A simple calcu-
lation, however, as shown in Example 3-1, illustrates
that moisture loss is minimal over a 3-year period. Dry-
ing 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 In-
jection and Water Generated During Biodegradation:
For this test:
Vapor pressure (Pwater)
Flow rate (Q)
Volume of treatment
area (V)
Biodegradation rate (kB)
Initial moisture content
Soil bulk density
17.5 mm Hg
1 pore volume/day
(typical of bioventing)
12,300 m3
3 mg/kg-day
15 percent by weight
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 x 1 '44° kg = 1.8 x 107 kg soil
m3
Therefore, the initial mass of water is:
(1.8 x 107 kg soil) x 0.15 = 2.7 x 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:
' See Equation 3-7 for the stoichiometry of this calculation.
20'
s?
^ 15
c
r>
Concentrati<
o
c
u
M
^
0 5
n '
^\ • Oxygen /,
N. v Carbon Dioxide j
^ Air Injection Initiated 1 —
w' ~~~~~ ~~~ 1
Blower Off 1
.___ _J
^x~v~ \
/ Irrigation Initiated 1 \
/ (11/8 and 11/29-12/5) \
/T \
rx
I
j
f''
1
"t
o
(I
•
Blower Off 1
!
-
-
^
/
' ^ /
T -
i -
\
' * i
14
12 ^
S"
10 .0
1
8 1
o
o
3
4 B
^
nj
2 U
hn
June July August September October November December,, January .
1994 1995
Figure 3-6. Oxygen and carbon dioxide concentrations before and after irrigation at Twentynine Palms, California.
17
-------
Total water removal in 3 years:
Moles H2O removed_ Pwater V
day RT
17.5 mm Hgx 12,300m3
0.0623 m3"mm?
mole- K
Moles H2O removed
day
= 11,600 = 210
_kg_
day
210
—— x 1,095 days = 230,000 kg removed
day y ' v
Thiswaterlossrepresentsafairlysmall percentage, or:
230,000 kg evaporated
2.7 x106 initial mass
- = 0.086 = 8.6% H20 loss
This is equivalent to a soil moisture drop from approxi-
mately 15 percent to 13.7 percent. Assuming a contami-
nated 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 hydrocar-
bons degraded over 3 years:
x 1,095 days x (1.8 x 107 kg soil) x
= 59,000 kg hydrocarbordegraded
Based on the stoichiometry in Equation 2-1, if 1.5 kg of
water are generated for every kg of hydrocarbon de-
graded, the amount of water generated would be:
59,000 kg hydrocarbon x
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.
survive. Most bacteria function best in a pH range be-
tween 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 obser-
vations suggest that pH is not a concern when biovent-
ing at most sites.7
<5.0 5.0-6.0 6.0-6.5 6.5-7.0 7.0-7.5 7.5-8.0 8.0-8.5 8.5-9.0 >9.0
pH
Figure 3-7. Soil pH measurements at Bioventing Initiative sites.
•
0L
4.5
***
•••ts ;•••«•
1 JM*V7«y|»L
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
PH
3.2.2.3 Soil pH
Soil pH also may affect the bioremediation process be-
cause microorganisms require a specific pH range to
Figure 3-8. Correlation between oxygen utilization rate and soil
pH at Bioventing Initiative sites.
7 See Section 5.2 for a discussion of the statistical relationship be-
tween pH and oxygen utilization rates.
18
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3.2.2.4 Soil Temperature
Soil temperature may significantly affect the bioremedia-
tion process. Microbial activity has been reported at tem-
peratures varying from -12°C to 100°C (10°F to 212°F)
(Brock et al., 1984); however, the optimal range for biode-
gradation of most contaminants is generally much nar-
rower. 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, microorgan-
isms in a subarctic environment may exhibit optimal
growth at 10°C (50°F), whereas microorganisms in a sub-
tropical 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 tem-
perature. The van't Hoff-Arrhenius equation expresses
this relationship quantitatively as:
(Eq. 3-9)
= k0 6
where:
kT = temperature-corrected biodegradation rate
(percentage of O2/day)
k0 = 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 accu-
rately 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 be-
tween oxygen utilization rate and temperature and be-
tween 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 re-
sulted in a wide range of temperatures and biodegrada-
tion 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:
0.6
0.5
0.4
a
I 0.3
a
j§ 0.2
0.0
5 10 15 20
Temperature (°C)
25
3.35 3.40 3.45 3.50 3.55 3.60 3.65 3.70
1/T (°K) * 1000
Figure 3-9. Soil temperature versus oxygen utilization and
biodegradation rate at Site 20, Eielson AFB, Alaska.
The slope of the linear regression of inverse tempera-
ture versus oxygen utilization rate is -6,740 °K (Figure
3-9). Therefore,
^ = -6,740
Ea
1.987-
cal
-6,740
K-mole
! 3,390
mole
1 3.4
x-6,740 =
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 degra-
dation (Leeson et al., 1995). Selection of a soil warming
technique depends on a comparison of cost considera-
tions versus remediation time requirements.8 Although
' See Section 4.4 for a discussion of the cost benefit of soil warming.
19
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warm water infiltration or heat tape can significantly
increase biodegradation rates, the cost is significantly
higher than simply using surface insulation or no heat-
ing 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/co-
factors are known to be required in order to support
microbial growth: calcium, cobalt, copper, iron, magne-
sium, manganese, molybdenum, nitrogen, phosphorus,
potassium, sodium, sulfur, and zinc. Nitrogen and phos-
phorus 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, sug-
gested by John T Wilson of the EPA Ada Laboratory, can
be made based on microbial kinetics. Starting with:
— = Kb Y - Kd X
(Eq. 3-10)
where:
X
kB
Y
kd
biomass (mg biomass/kg soil)
biodegradation rate (mg hydrocarbon/kg
soil-day)
cell yield (mg biomass/mg hydrocarbon)
endogenous respiration rate (day1)
Assuming that the biomass concentration achieves
steady state during bioventing,
Solving:
X = -
KbY
Kd
(Eq. 3-11)
(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-^x0.5^
kg-day mg
0.05
day
100^9.
kg
To sustain 100 mg/kg of biomass, the nutrient require-
ments 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:nitro-
gen:phosphorus is assumed. This ratio yields a nutri-
ent 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 phos-
phorus 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
26
24
.-. 22
I 20
«
£ 18
I 16
I 14
£• 12
I 10
I 8
<50 50-100 100-200 200-300 300-400 400-500 500-600 600-700 >700
Figure 3-10. TKN measurements at Bioventing Initiative sites.
20
-------
50
45
| 40
o" i«
ts 35
3 30
S 25
.a
400 600
TKN (mg/kg)
800 15002000
Figure 3-11. Correlation between oxygen utilization rate and
TKN at Bioventing Initiative sites.
^ 10
I" 8
<100 100-200 200-300 300-400 400-500 500-600 600-700 >700
ToLal Phosphorus (mg/kg)
Figure 3-12. Total phosphorus measurements at Bioventing In-
itiative sites.
50
45
•I" 40
£ 35
I 3C
a 25
I 20
5
S 15
0 200 400 600 800 1,000 1,200 1,400 1,600 3,000
Total Phosphorus (
Figure 3-13. Correlation between oxygen utilization rate and to-
tal phosphorus at Bioventing Initiative sites.
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 Fig-
ures 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 utiliza-
tion rates, again emphasizing that natural ambient nutri-
ent levels seem sufficient for microbial activity.10
Figure 3-14 illustrates the range of iron concentrations
measured at Bioventing Initiative sites. Iron concentra-
tions 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 ob-
served oxygen utilization rate11 would not reflect micro-
bial 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 utiliza-
tion rates (Figure 3-15).
3.2.2.6 Contaminant Concentration
Contaminant concentration also may affect biodegrada-
tion of the contaminant itself. Excessive quantities of a
< 2,000
2,000-4,000
4,000-8,000
12,000-16,000
20,000-25,000
8,000-12,000
Iron {mg/kg)
16,000-20,000
>25,000
Figure 3-14. Iron concentration measurements at Bioventing
Initiative sites.
the corresponding relationship between oxygen utiliza-
tion rates are shown in Figures 3-10 through 3-13. Al-
though optimal ratios of carbon, nitrogen, and
phosphorus were not available at all sites, the natural
nutrient levels were sufficient to sustain some level of
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 be-
tween nutrients and oxygen utilization rates.
11 As measured by in situ soil gas oxygen concentrations.
21
-------
I
o
•
•
0 5000 10000 15000 20000 25000 30000 35000 40000 100000
Total Iron (mg/kg)
Figure 3-15. Correlation between oxygen utilization rates and
iron content at Bioventing Initiative sites.
contaminant can result in a reduction in biodegradation
rate because of a toxicity effect. Conversely, very low
concentrations of a contaminant also may reduce over-
all degradation rates because contact between the con-
taminant 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., pheno-
lics) or less biodegradable compounds (i.e., TCE)
may exhibit a toxicity effect, and reports indicate that
pure benzene may be toxic. Although a general rela-
tionship 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 hydro-
carbon concentration. Certainly, the NAPL distribution
can affect the proportion of the soil in a site in which
biodegradation is occurring, and at lower concentra-
tions, 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 degrad-
able and more mobile compounds (i.e., benzene, tolu-
ene, 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 contami-
nant^) of concern. Bioavailability is a term that de-
scribes 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 microorgan-
isms 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 petro-
leum hydrocarbons, potentially can be degraded though
bioventing. To date, bioventing has been applied primarily
to petroleum hydrocarbons (Table 2-2); however, biovent-
ing 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 volatiliza-
tion. This will occur most often in cases where the
contaminant is a fresh, highly volatile fuel. An unsuc-
cessful 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 opera-
tion.12 Figure 3-16 illustrates the relationship between
a compound's physicochemical properties and its po-
tential 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 com-
pounds are gases at ambient temperatures. These com-
pounds 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 be-
tween 1 and 760 mm Hg may be amenable to either
volatilization or biodegradation. Within this intermediate
12 See Section 2.1 of Volume II fora discussion of air injection versus
extraction considerations.
13 For the purposes of this discussion, compounds with vapor pres-
sures below approximately 1 mm Hg are considered low, and
compounds with vapor pressures above approximately 760 mm Hg
are considered high.
22
-------
103-
10
2_
(0
0)
101-
10'1-
10* H
0.
to
o
1 10-3-
(0
<0
a)
o
a,
10-*-
10-6-
10*-
1(T7-|
10-8-
Gasollr
Vapor Pressure
Too High to Easily Biovent
Vapor Pressure
Amendable to
Bioventing or
Vapor Pressure
Too Low to Volatize
i i i i i i i i i
10 10"* 1Q-6 10"4 10"3 10'2 10'1 1 10 100 1000
Aqueous Solubility (mmoles/litre)
H - Henry's Law Coefficient (atm • rrrVmole)
Figure 3-16. Relationship between contaminant physicochemical properties and potential for bioventing.
range lie many of the petroleum hydrocarbon com-
pounds 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 pre-
viously, are typically present in low overall concentra-
tions and are attenuated rapidly. Most of the diesel
constituents are sufficiently nonvolatile to preclude vola-
tilization, 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 com-
pounds need not biodegrade as rapidly as high vapor
pressure compounds for bioventing to be successful.
Figure 3-17 illustrates this relationship. The actual fea-
sibility 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 poly chlorinated biphenyls
(PCBs) and chlorinated hydrocarbons. Through a
23
-------
-1,000,000,000
-100,000,000
-10,000,000
-1,000,000
-100,000
"3 -10,000
•i- -1,000
I -100
\ -10
I" -1
0
1
10
100
1,000
1 3-Chloropropene
2 Dlchlcromethane
3 Isoprene
4 Melhyl chloride
5 2,6-Dlnltrotoluene
6 N-Nltrosodlmelhylamlne
7 2.3,4,6-Telfachlorophenol
8 Chloroform
9 cls-l,2-DlchloroethylBne
10 1,1 -Dimethyl hydrazlne
11 lrans-1,2-0lchloroelhylane
12 Vinyl chloride
ene v
ene «*
Benzo[ ghijfluoranlhei
Dibenz[a,h)anlhracene
Benzo[k]fluoranlhene
Benzo[a]anlhracena v
Benzo[a]pyrene
Chiysene
gamma-Hexachlorocyclohexane (LlndaneJ
0-Xyli
m-Xylene
p-Xyli
Pentachlorophenol ~.
Haptachlorx
Dielhyl phthalata
2-Nllrophanol^
1,2,4-Trimethylbenzene.
• Dleldrin
Benzo[b]fluoranthene •)
Fluoranlhena •
\
Chlordane
\
Penlachlorobenzene
I
E
Ol
m
1-Butanol
Melhyl Isobutyl ketona
Fonnic acid
Melhyl ethyl kelone
Elhanol
Melhanol
Acetone
hexachloroethane
0 2,4 Dlnltraphenol
1,2-Dlchk>fObanzene « Pyrane
2,6-DlnlIrotoluene
Tetrachloroethylene
1,2-Wchloropropane
Trtchloraelhylena
Cartoon telrachlo ride
1,1,1-Tricntoroethane
1 Day
1 Month
Aerobic Half Life
1 Year
5 Years
Figure 3-17. Relationship between contaminant pressure and aerobic biodegradability.
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) demon-
strated 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 poten-
tial for cometabolic degradation of chlorinated com-
pounds 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 com-
pounds 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 illus-
trated in a study at Tyndall AFB14 and has been con-
firmed 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 concentra-
tion. Low-molecular-weight compounds such as BTEX,
however, decreased by more than 90 percent (Figure
3-18). Low-molecular-weight compounds were prefer-
entially 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 com-
pounds often initially are relatively low at many fuel-con-
taminated 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 contami-
nated with heavier weight contaminants. Only 19 of 125
Bioventing Initiative sites were contaminated by gaso-
line or aviation gas (AVGAS).
14 See Section 4.2 for a case history of the bioventing study at Tyndall
AFB, Florida.
24
-------
300
Figure 3-18. Results of soil analysis before and after venting from Plot V2 at Tyndall AFB, Florida.
5.
>,
§•
~>
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Benzene
Toluene
-Ethylbenzene
Total Xylenes
200
BTEX (mg/kg)
Figure 3-19. Contaminant distribution at Bioventing Initiative sites.
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 docu-
ment. 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 de-
signed 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 short-
term (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 pre-
sented in this chapter. This site was included in the
Bioventing Initiative, but additional samples were col-
lected at the end of the 1-year study as part of a sepa-
rate 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 exam-
ples 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 oc-
curred 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 ap-
proximately 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 per-
cent by weight in the contaminated soils.
The collected soil samples had JP-4 jet fuel concentra-
tions of up to 20,000 mg/kg, with an average concentra-
tion of approximately 400 mg/kg (Oak Ridge National
Laboratory, 1989). Contaminants were unevenly distrib-
uted 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 forma-
tion 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 biodegra-
dation 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 x 104 L/min) as hydrocarbon concentrations
dropped. During the period between December 1988
and November 1989, more than 3.5 x 108 ft3 (9.9 x 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 approxi-
mately $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 ad-
dition clearly stimulated biodegradation; nutrient addi-
tion 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 ob-
served change; and/or nutrients simply may have not
been limiting.
During extraction, oxygen and hydrocarbon concentra-
tions 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 minerali-
zation.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
Ib volatilized and 93,000 Ib biodegraded (Figure 4-1).
120
After a 2-year period, cleanup and regulatory closure
were achieved (Figure 4-2).
The results of this study indicated that aerobic biodegra-
dation 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, de-
signed to volatilize the fuel, stimulated in situ biode-
gradation with no added nutrients or moisture. In this
study, approximately 15 percent of the documented
field removal observed at the site resulted from micro-
bial-mediated mineralization to carbon dioxide. Addi-
tional 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 biodegra-
dation in unsaturated soils were needed to better under-
stand 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 stud-
ies 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
- 50
JFMAMJJASOND
J F M A M J JASON
1990
Date
Figure 4-1. Cumulative hydrocarbon removal and the effect of moisture and nutrient addition at Site 914, Hill AFB, Utah.
See Section 3.3 of Volume II fora discussion of this calculation.
28
-------
20
•S
I
40
/zj
/zj
XZZJ
XV/.I
/ZzJ
<5
<5 970
//////////A 5 g 7^8
'
<5
<5
<5 754
/ZZJ
/ZZJ
x^^
<5
<5
<5
(sjajsui) indaci
O "1
> 10 -< — <
10 ' 100
Hydrocarbon Concentration (mg/kg)
Initial Concentration
1000
\///\ Final Concentration
Figure 4-2. Results of soil analysis before and after treatment at Site 914, Hill AFB, Utah.
nature and volume of fuel spilled or leaked were un-
known. The site soils were a fine- to medium-grained
quartz sand. The depth to ground water was 2 ft to 4 ft
(0.61 mto 1.2m).
The field study was designed with the following objectives:
• To determine whether bioventing enhanced biodegra-
dation 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 biode-
gradation 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 uncontami-
nated soils. Test cells were constructed and operated in
the following manner:
• V1 (uncontaminated): Venting for approximately 8
weeks, followed by moisture addition for approxi-
mately 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 nu-
trient addition at rates similar to V2, with injection of
hydrocarbon-contaminated off-gas from V1. Opera-
tion was conducted at a series of flow rates and
retention times.
• V4 (uncontaminated): Venting with moisture and nu-
trient addition at rates similar to V2.
Initial site characterization indicated the mean soil hy-
drocarbon levels were 5,100 mg and 7,700 mg of hex-
ane-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 approxi-
mately 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 tempera-
tures, 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 hy-
drocarbon reduction of approximately 2,900 mg/kg was
observed. This represented a reduction in total hydro-
carbons 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 pro-
vided an excellent model of temperature effects. In the
Tyndall AFB study, soil temperature varied by only ap-
proximately 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).
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-ele-
vation 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 fixa-
tion. 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 maxi-
mized 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 airflow rates and biodegradation and
volatilization. Researchers found that extracting air at the
optimal rate for biodegradation resulted in 90 percent re-
moval by biodegradation and 10 percent removal by vola-
tilization. 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 con-
sumption 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 biode-
gradation and decrease the percentage of removal by
volatilization.
The study was terminated because the process moni-
toring 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-mo-
lecular-weight aromatics (the BTEX components) were
reduced by more than 90 percent (Figure 3-18). Appar-
ently, 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 impor-
tance of airflow 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-con-
taminated soils while minimizing or eliminating volatili-
zation. 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
100
ao-
«P 60
40
Moisture Addition
toV1
Nutrient Addition
toV1
0 30 SO 90 120 1SO 180 210
Venting Time Ways)
Figure 4-3. Cumulative percentage of hydrocarbon removal and the effect of moisture and nutrient addition at Tyndall AFB, Florida.
30
-------
• SMP = Surface Monitoring Point
O CW = Soil Vapor Cluster Well
A-A's Cross Section Trace
<•• Projection of Cluster Weil onto Cross Section Trace
Figure 4-4. Schematic showing locations of soil gas monitoring points, surface monitoring points, and injection wells at Site 20,
Hill AFB, Utah.
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
100ft.
From November 1992 through January 1995, many
studies were conducted to evaluate low-intensity biore-
mediation 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 airflow 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
31
-------
4790
4770-
475O- .
4730-
4710
4690
4670 - Q
A (West)
WW9 CW9 WW7 CW7
Injection A' (East)
Well CW1 CW5
4790
-4770
- 4750
473O
- 4710
- 4690
- 4670
PH - Sand with Gravel and Clay
U|-SlltySand
r~l-Sand
D = Screened Interval
—v._ ° Perched Water
(Approx. Surface)
CW • Soil Gas Cluster Well
142 - TPH In Soil (mg/kg)
13 mg/L - TPH Cctn. In Ground Water
Figure 4-5.
Geologic cross-section showing known geologic features and soil TPH concentrations (mg/kg) at Site 280, Hill AFB,
Utah.
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 airflow 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 injec-
tion 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 peri-
ods 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 excep-
tion 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 investi-
gate 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 de-
gree 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 loca-
tion also received air injection but no soil warming to
monitor natural background respiration rates. The site
32
-------
1000
100 -
10 -
initial Concentration
Final Concentration
1
0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100
Depth (ft)
a. BTEX Concentration Within a 25 to 75 ft Radius of the Injection Well
1000
20-30 30-40 40-50 50-60 60-70 80-90 90-100
Depth (ft)
b. BTEX Concentration Within a 0 to 25 ft Radius of the Injection Well
Figure 4-6. Site average initial and final BTEX soil sample results at Site 280, Hill AFB, Utah.
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 installa-
tions as well.
Differences in soil temperatures have been significant
among the four test plots (Figure 4-9). When in opera-
tion, 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 sum-
mer months, compared with average temperatures of
approximately 10°C (SOT) 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 signifi-
cantly increased the period of rapid microbial degrada-
tion. 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. Signifi-
cant microbial activity was consistently measured in the
control test plot, however, even in winter when soil
temperatures are just below freezing (Figure 4-10). Res-
piration 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.
33
-------
1000
100
10
initial Concentration
l Final Concentration
0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100
Depth (ft)
a. TPH Concentration Within a 25 to 75 ft Radius of the Injection Well
10000
20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100
Depth (ft)
b. TPH Concentration Within a 0 to 25 ft Radius of the Injection Well
Figure 4-7. Site average initial and final TPH soil sample results at Site 280, Hill AFB, Utah.
Warm water circulation was discontinued in fall 1993,
and as the soil temperature dropped, no significant mi-
crobial 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 tempera-
tures 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. Signifi-
cant microbial activity was measured, comparable to the
control test plot, indicating either readaptation or recolo-
nization 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 con-
ducted 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). Al-
though capital costs were higher in the active and sur-
face warming test plots, the rapid remediation time
results in lowertotal 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
34
-------
- Plastic Sheeting
- Styrofoam Insulation
Plywood
i— Vinyl Cover
Three-Level
Thermocouples
Air Infection/Withdrawal Well
Three-level
Soil gas probe
>ft<««««^
ft«ftiv<%
-------
10
t
§ 4
m
• Active Wanning
T Passive Wanning
• Contaminated Control
* Surface Warming
OCT ,,JAN APR AUG NOV,,JAN MAY JULY NOV ,, JAN APR JULY
1991 1992 1993
Figure 4-10. Biodegradation rates in four test plots at Site 20, Eielson AFB, Alaska.
1994
Table 4-1. Cost Analysis of Soil Warming Techniques at Site 20, Eielson AFB, Alaska3
Task
Basic Bioventing
(No Warming) ($) Active Warming ($) Passive Warming ($) Surface Warming ($)
Site visit/planning
Work plan preparation
Pilot testing
Regulatory approval
Full-scale construction
Design
Drilling/Sampling
Installation/Startup
Remediation time required0
Monitoring
Power
Final soil sampling
Cost per ydc
5,000
6,000
27,000
3,000
7,500
15,000
4,000
9.4 years
30,550
13,160
13,500
25.50
5,000
6,000
27,000
6,000
7,500
20,000b
26,000
2.8 years
9,800
9,800
13,500
26.12
5,000
6,000
27,000
3,000
7,500
15,000
10,500
6.9 years
24,150
9,660
13,500
24.86
5,000
6,000
27,000
3,000
7,500
15,000
13,000
3.4 years
11,050
17,000
13,500
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.
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 biode-
gradation 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 in-
creased biological activity in these areas. In the active
and surface warming test plot, despite problems caused
by high oil moisture content, biodegradation rates con-
sistently 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.
36
-------
120
100
1 80
i
60
40
20
0
NS
ND
• ND| ND^ND BNOBNoB
ND
Initial BTEX
Final BTEX
ND NS NS
ND_ ND ND_ ND ND ND
4.5-5.0 5.5-6.0 6.5-7.0 7.5-8.0 8.5-9.0 9.5-10 10.5-11
Depth (ft)
Figure 4-11. Site average initial and final BTEX soil sample results at Site 20, Eielson AFB, Alaska.
300
250
-3) 200
on
a.
150
100
50
i
Initial TPH
Final TPH
X
4.5-5.0
5.5-6.0
6.5-7.0
7.5-8.0
Depth (ft)
8.5-9.0
9.5-10
10.5-11
Figure 4-12. Site average initial and final TPH soil sample results at Site 20, Eielson AFB, Alaska.
4.5 Fire Training Area, Battle Creek
ANGB, Michigan
The Fire Training Area, Battle Creek ANGB, was in-
cluded 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
37
-------
w
ID
0
U.
w
C
0
NO
920-1
910-
900-
890-
BU-MPU BC-MPB BC-MPA BC-VW
* ® 0 ^Injection
Well
*TH ^Berm SOL
/ I
:•- i
4
a ' ,
. «
6 •
*p—
'21 . • , ' • • •
J8iv .''.;.' Vj
, • ' <-.-T--T,:T-:"-
is-; • •;>a;-:4
•. .* • -~",^_ • • , .
3-; •."••V'^JJ
.• .. • • .- .v .•
6 ..•'•.'« * • ' .
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* . • « .
• • o ' • % ' *
-^U:J^^ ; \ ,v
«2' \ . ' • ", ' •
j>oi.' -• • /f
rV~^~" » . . • • 6 ' r"rr?--
l^Sll- ..'•».'• •'.<>'. •' .' > ','
7T2l^. ~ ~7-r:
te --f^Hfl
~ir:.>.- -.js..
y'.;.-<5\vv
«6f •;> ',•;;•.;•
Ul^r4'^:.'-?']
'40 •; ' " • • '• '
n'4i24 • . ; . ;
r1 6,800 -^-.rr^
•""" • .I.-*.'- « rj
J>V*IL •'••'? •-'..*-'
">ip^oo-v.c.. . "":
^^":
Uq;''.-^. ;.»";.:
j^i.V-l^il:;
'.,•",-,•' '/• "* • . ". ;'. • . . -i ;". / ; _ T~J- , , • "'y * •
• .'?. •', ,'.'••'..'. I •'.'',' '^, , ' '.i ,?",• i "•'''/• "' ' J ' ' ' " 'i'
'4.38VC,' '
2666 VC- .
;jgjOOoj q '. *';
" ' . " * "
- ' » , » .. ]_^
I 3248 • 7
:i.V, .'-I'/;':'
-• . .' • , .;
. • i •
- 1Q28 ,*.'..
•»• v .•»..•
-920
-810
-900
890
FEET
LITHOLOGIC DESCRIPTION
SAND
SAND & GRAVEL
SAND & SILT
LEGEND
RP MPA
^.
« MONITORING POINT
A INJECTION WELL
W FIELD SCREENING RESULTS FOR
TOTAL VOLATILE HYDROCARBONS (ppnw)
TjQl LABORATORY RESULTS FOR SOIL TOTAL
—I PETROLEUM HYDROCARBONS (mg*g)
VC VISUAL CONTAMINATION
GROUNDWATER ELEVATION
GEOLOGIC CONTACT,
DASHED WHERE INFERRED
i MONITORING POINT
T SCREENED INTERVAL
INJECTION WELL
SCREENED INTERVAL
Figure 4-13 Hydrogeologic cross-section of the Fire Training Area, Battle Creek, ANGB, Michigan.
influence of greater than 50 ft. These results indicated and soil gas samples were collected2 Although the
that both the microbial activity and the permeability were number of soil3 and soil gas samples collected was not
conducive to an effective bioventing operation. sufficient to allow for statistically significant comparison
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
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 con-
centrations 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.
30000
Initial Concentration
Final Concentration
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
respiration rates and site closure.
detailed discussion of in situ
39
-------
60
50
40
30
20 -
10
0
• Initial
H Final
NS = Not sampled
ND = Not detected
NS NO NS ND NS ND NS ND • ND
I
ND NS ND NS ND NS ND NS ND NS ND NS ISJ NS ND NS
2-2.5
4-4.5
10-10.5 18-19
Depth (ft)
21.5-22.5
27-27.5
45000
40000
35000
30000
25000
20000
15000
10000
5000
n
NS
;*
s.
NS
FT!
:-:-:
1
I
i
1
|
|
1
X
• Initial
El Final
NS = Not sampled
NO = Not detected
NS [. NSND • Kl NSND NS
I* \ 1BT51 iK-3 .
"
;
-
NSND NSND NS NSND NS FT] NSND
2-2.5 4-4.5 7 10-10.5 18-19
Depth (ft)
21.5-22.5
27-27.5
Figure 4-15. Initial and final soil concentrations at the Fire Training Area, Battle Creek, Michigan.
40
-------
Chapter 5
Analyses ofBioventing 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 in-
creased 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 in-
stallation. Sites are located in 35 states and in all 10 EPA
regions. Figure 2-2 illustrates the locations ofBioventing
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 re-
sults, and soil gas permeability testing results.
• Six-month in situ respiration testing results.
• One-year soil and soil gas sampling and in situ res-
piration 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 impli-
cations 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 num-
ber 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 biovent-
ing 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 statis-
tical 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 col-
lection 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 conclu-
sive indicators of bioventing progress or evidence of the
success or failure of this technology.
41
-------
Initial Concentration
Final Concentration
<0.1 0.1-1 1-5 5-10 10-25 25-100 100-250250-500 >500
Concentration (ppmv)
Figure 5-1. Soil gas BTEX concentrations at Bioventing Initiative sites: initial and 1-year data.
40
35
30
25
20
15
a 10
a.
5 -
0
J Initial Concentration
Final Concentration
<10 50-100 500-1000 2500-5000 10,000-20,000 > 50,000
10-50 100-500 1000-2500 5000-10000 20000-50000
100-500 1000-2500 5000-10,000 20,000-50,000
TPH Concentration (ppmv)
Figure 5-2. Soil gas TPH concentrations at Bioventing Initiative sites: initial and 1-year data.
70
60 -
I 50
20 -
.....
-
-
^
/
I,
^
^
\
/
^
^
^
\
/,
y
;/
/
$.
^m/
^^| Initial Concentration
Y//A Final Concentration
1 1 1 ; 1' I- •' 1- 1. 1 1- 1 :
<0.1 1-5 10-20 30-40 50-75 100-200 >500
0.1-1.0 5-10 20-30 40-50 75-100 200-500
Concentration (mg/kg)
Figure 5-3. Soil BTEX concentrations at Bioventing Initiative sites: initial and 1-year data.
42
-------
50
45
to
•5 30
I 25
| 20
I 15
£ 10
5
0
-
-
-
-
7
x
X
X
x
^
\
/
?
^
1
y
/
/
/
^
^
C7]
/
X
X
X
X
/
X
H Initial TPH Concentration (mg/kg)
1/^>XJ Final TPH Concentration (mg/kg)
JJ
I
\u\im- n
<5 50-250 500-1000 2000-5000 7500-10,000 15,000-20,000 25,000-30,000
5-50 250-500 1000-2000 5000-7500 10,000-15,000 20,000-25,000 > 30,000
Concentration (mg/kg)
Figure 5-4. Soil TPH concentrations at Bioventing Initiative sites: initial and 1-year data.
26,000
TPH BTEX
^H Initial Concentration
TPH BTEX
l-Yeat Concentration
Figure 5-5. Average soil and soil gas BTEX and TPH concentrations at Bioventing Initiative sites: initial and 1-year data.
50
ffl
Initial Concentration (mg/kg)
Final Concentration (mg/kg)
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 preferen-
tially overTPH. The potential for bioventing to preferen-
tially 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.
Mill.I
1-5 5-10 10-20 20-50 50-100 100-200 >200
Total BTEX (mg/kg)
Figure 5-7. Average BTEX concentrations at Bioventing Initia-
tive sites.
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 di-
rect comparison of results across sites. Results of the
statistical analyses can be used to evaluate which soil
measurements should be taken and, if bioventing per-
formance is poor, which parameters can be adjusted to
improve performance.
Data generated from the Bioventing Initiative were sub-
jected 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 cal-
culating the oxygen utilization and carbon dioxide
production rates from the in situ respiration data.
• To characterize the oxygen utilization rate as a func-
tion 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 contami-
nated sites with those at uncontaminated background
areas.
Averages for oxygen utilization and carbon dioxide pro-
duction 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 trans-
formations performed on these parameters wherever
necessary.
Data were stored in Statistical Analysis System (SAS)
databases, and all statistical manipulations and analy-
ses 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 cal-
culate oxygen utilization and carbon dioxide production
rates. Alineartime-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:
See Section 4.2 for a presentation of this case history.
RI = OC +
j < to
(Eq. 5-1)
44
-------
Table 5-1. Data Parameters Included in the Statistical Analyses
Category
In Situ Respiration Rates
Soil Parameters
Other
Parameter
Oxygen utilization rate
Carbon dioxide production rate
Ratio of the carbon dioxide
production rate to oxygen
utilization rate
Soil gas TPH
Soil gas BTEX
Soil TPH
Soil BTEX
PH
Alkalinity
Iron content
Nitrogen content
Phosphorus content
Moisture content
Gravel
Sand
Silt
Clayc
Soil gas permeability
Soil temperature
Season (time of year)
Units
%/hr
%/hr
No units
ppmv
ppmv
mg/kg
mg/kg
No units
mg/kg as CaCOs
mg/kg
mg/kg
mg/kg
% weight
% weight
% weight
% weight
% weight
Darcy
Celsius
Day
Transformation3
Log
None
Square root
Log
Log
Log
Log
Log
Log
Log
Log
Log
None
None
None
None
None and log
Log
None
None
Acronymb
02
C02
Ratio
tphsg
btexsg
tphs
btexs
PH
ALK
IRN
NIT
PHO
MOI
GRA
SAN
SIL
CLA
PRM
TMP
Season
3 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.
i = (a + pt0) + (p + S) ft -10) t| > 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 t| (%)
a = oxygen or carbon dioxide level at initial time (%)
P = rate of change of oxygen or carbon dioxide
level with time (%/hr)
8 = 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 us-
ing the nonlinear regression procedure (NLIN proce-
dure) in the SAS software package.
The parameter 8 in the above model measures the
increase or decrease in the slope at time IQ. 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, p,
wherever 8 was statistically significant at the 0.05 sig-
nificance level. For example, Figure 5-8 presents the
piecewise linear model fitted to oxygen data at a moni-
toring point at Site FSA-1, AFP 4, where p was esti-
mated to be -1.1 percent/hr.
In cases where 8 was not significant at the 0.05 level, a
linear regression model of the following form was fitted
to the data:
RI = a + pt|
for all t| (Eq. 5-3)
where:
the rate of oxygen utilization (or carbon dioxide produc-
tion) was determined from the slope of the straight line,
P.
For cases in which six or fewer observations were avail-
able 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 inspec-
tion 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.
45
-------
20.0 r-
15.0
10.0
5.0
0.0
Observed Oxygen Level
Predicted Oxygen Level
Base AFP 4
Site Site FSA-1
%x Oxygen Rate = 1.1 %/hour
\
\
V
I
I
I
I
"1 1 1 L
10 15 20 25 30 35 40 45 50 55
Time (hours)
60 65 70 75
Figure 5-8. Use of piecewise analysis of oxygen utilization data from Site FSA-1, AFP 4, Texas.
This model accounted for the effects of the soil parame-
ters and their interactions. To reduce the effect of multi-
collinearity 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 con-
cluded that the effect of soil gas BTEX levels on the
oxygen utilization rate can almost completely be ex-
plained 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 redun-
dant 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 oxy-
gen utilization rates were examined in detail. Seven
sites in the analyses had extremely high oxygen utiliza-
tion 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 overthe seven sites was different
from the corresponding average for the remaining sites.
This analysis revealed statistically significant differ-
ences 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 utiliza-
tion rates were atypical with respect to their levels of
particle size, soil gas permeability, and soil TPH concen-
trations.
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
Silt
Clay
Soil gas permeability
Soil TPH
Lower
Higher
Higher
Lower
Lower
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 utiliza-
tion rates near zero, however, are artificially inflated in
importance as a result of the transformation. To elimi-
nate 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 nor-
mality and by observing histograms and normal prob-
ability plots.
As a preliminary step to determine the influence of soil
parameters on oxygen utilization rate, correlations be-
tween each soil parameter and the oxygen utilization
rate were examined. This was conducted to examine
strong relationships between oxygen utilization rates
46
-------
02
rat io
IRN
NIT
PHO
MO I
PH
ALK
02 « log 02 Rat* Ratio * (C02 Rate/02 Rato)u IRN =* log Iron NIT - log Nitrogen
PHO » log Phosphorus MOI = Moisture PH = log pH ALK = log Alkalinity
Z1
90%
60%
30%
0%
Koy to Correlation Scatterplots.
Figure 5-9. Oxygen utilization rates, oxygen to carbon dioxide rate ratios, element concentrations, moisture content, pH, and
alkalinity site average correlation scatterplot.
47
-------
02
rat io
btexsg
tphsg
btexs
-F
tphs
TUP
MO I
02 = log 02 Rate Ratio = (C02 Rate/02 Rate)* btax*g = log BTEX in Soil Gas tphsg = log TPH in Soil Ga»
btexs « tog BTEX in Soil tphs = log TPH in Soil IMP - Soil Temperature MOI = Moisture
Z1
90%
60%
30%
0%
Key to Correlation Scatterplot*.
Figure 5-10. Oxygen utilization rates, oxygen to carbon dioxide rate ratios, contaminant concentrations, temperature, and moisture
content site average correlation scatterplot.
48
-------
02
rat io
-H-
GRA
-H-
SAN
Sit
CIA
UOI
PRU
02 = tog 02 Rate Ratio = (CO2 Rate/02 Rat«)H 6RA = Gravel SAN » Sand SIL = Silt
CLA « Clay MOI = Moisture PRM = log Soil Gas Permeability
Z1
90%
60%
30%
0%
Key to Correlation Scatterplots.
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
-------
IRN
NIT
PHO
GRA
SAN
SIL
CLA
IRN - log Iron NIT - log Nitrogen PHO * log Phosphorus GRA = Gravel
SAN - Sand SIL = Silt CLA - Clay
Z1
90%
60%
30%
0%
Key to Correlation Seatterplots.
Figure 5-12. Element concentrations and particle size site average correlation scatterplot.
50
-------
btexsg
tphsg
-p
blexs
tphs
GRA
SAN
SIL
I-H-
CLA
btexsg » log BTEX in Soil Gas tphsg = log TPH in Soil Gas btexs = log BTEX Soil
tons = log TPH in Soil GRA = Gravel SAN - Sand SIL « Silt CLA » Clay
Z1
90%
60%
30%
0%
Key to Correlation Scatterplots.
Figure 5-13. Contaminant concentrations and particle size site average correlation scatterplot.
51
-------
PH
-h
ALK
GRA
+
SAN
-t-
+
$11
CLA
PH = tog pH ALK * log Alkalinity GRA - Gravel SAN = Sand SIL - Silt CLA - Clay
Z1
90%
60%
30%
0%
Key to Correlation Scatterplots.
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 transfor-
mation of the oxygen utilization rate and some of the soil
parameters was taken to obtain more normally distrib-
uted data on each parameter (Table 5-1). After these
transformations, the data for each parameter were plot-
ted 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, Fig-
ures 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 be-
tween soil parameters. In each figure, ellipses are drawn
on each plot containing 95 percent of the estimated
bivariate distribution. The plots with narrow ellipses rep-
resent pairs of elements that have a strong observed
correlation. Pairs of elements that are positively corre-
lated have the ellipse with the major axis running from
the lower left to the upper right, while negative correla-
tions are indicated by the major axis running from the
lower right to the upper left. The magnitude of the cor-
relation can be inferred from the shape of the ellipse by
comparing it with the key figure. In the key figure, com-
parable ellipses are displayed for distributions with
known correlations of 90 percent, 60 percent, 30 per-
cent, 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 lev-
els 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, how-
ever. In other words, microorganisms in Alaska show
peak activity in summer months with comparable oxy-
gen utilization rates to those of organisms from more
temperate climates; however, soil temperatures are sig-
nificantly different. Therefore, correlating rates with tem-
perature 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 sea-
sonal 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(02) = -2.7 + 0.39 log(NIT) - 0.108 (MOI) +
0.017log(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 ap-
pearing 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 oxy-
gen 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 un-
explained 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 in-
directly through measurements of soil gas oxygen and
carbon dioxide concentrations, abiotic processes that
affect oxygen and carbon dioxide concentration will af-
fect measured biodegradation rates. The factors that may
most influence soil gas oxygen and carbon dioxide con-
centrations 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 hexane-
equivalent/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-al-
kalinity soils and low-pH quartz sands, and carbon diox-
ide 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 Fallen MAS and Eielson AFB, little or no
53
-------
a
3.
i -
o.i -
0.01
0.01
0.1 1
Actual Oxygen Utilization Rate (%/hr)
Figure 5-15. Actual versus model-predicted oxygen utilization rates.
gaseous carbon dioxide production was measured
(Hinchee et al., 1989; Leeson et al., 1995). This may
result from the formation of carbonates from the gase-
ous evolution of carbon dioxide produced by biodegra-
dation 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 carb-
on dioxide production rates at Bioventing Initiative sites,
an analysis of the ratio of oxygen utilization to carbon
dioxide production versus soil parameters was per-
formed. Because of stoichiometry,2 the ratio of the oxy-
gen 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 di-
oxide 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 distribu-
tion. Figures 5-9 through 5-11 display the bivariate rela-
tionships 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 pre-
liminary step, a square root transformation of the ratio
and log transformation of some soil parameters were
taken to obtain more normally distributed data. All trans-
formations 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 parame-
ters (except season) and their interactions. Finally, the
effect of a cyclic seasonal component on the residuals
obtained from the fitted model was determined by incor-
porating the date of the initial in situ respiration test.
The final model for the ratio of the carbon dioxide pro-
duction rate to the oxygen utilization rate is as follows:
(CO
rate = 1 -28- 0.38log(pH) - 0.095log(clay)
0.0007log(tphs) * TMP
(Eq. 5-5)
! See Section 3.2.1 for the stoichiometry of hydrocarbon degradation.
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 ob-
served and model-predicted transformed ratios. The ef-
fects of pH on the ratio as predicted by the model are
presented in Figure 5-16.
The complicated nature of the fitted regression model
forthe 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.
54
-------
0.8
0.7
o
E 0.6
K
c 0.5
0.4
o
o
0.2
0.1
0.0
Observed Ratio
Predicted Ratio
7
PH
10
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.
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 mois-
ture 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 in-
terest in the modeling were moisture content and parti-
cle 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 permeabil-
ity. The effect of clay on soil gas permeability as pre-
dicted 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 back-
ground and contaminated sites, transformations of the
data parameters were considered. These transforma-
tions 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 in-
terest in TKN concentrations. Measurement of TKN ac-
counts for nitrogen sources within cellular material;
therefore, it is possible that TKN concentrations may be
higher in contaminated areas, where microbial popula-
tions may be higher, than in uncontaminated areas. To
date, no significant difference exists between TKN con-
centrations 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, how-
ever. Namely, nitrogen, moisture, and soil gas TPH
concentration appear to be the most important char-
acteristics influencing observed field oxygen utiliza-
tion 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.
55
-------
PRM
GRA
4- +
SAN
SIL
CLA
MOI
PRM - log Soil Gas Permeability GRA - Gravel SAN = Sand SIL • Silt CLA - Clay MOI = Moisture
Z1
90%
60%
30%
0%
Key to Correlation Scatterplot*.
Figure 5-17. Soil gas permeability, moisture content, and particle size site average correlation scatterplot.
56
-------
100 +*
Observed Permeability
Predicted Permeability
30
Clay (%)
Figure 5-18. Variation of clay and the effect on soil gas permeability based on model predictions.
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 signifi-
cant microbial activity and would therefore respond well
to bioventing.
57
-------
Chapter 6
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bioreclamation: Applications and investigations for hydrocarbon
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Miller, R.N. 1990. Afield scale investigation of enhanced petroleum
hydrocarbon biodegradation in the vadose zone combining soil
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Ph.D. Dissertation. Utah State University, Logan, UT
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61
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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 pres-
ence 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 ab-
sence of oxygen
aquifer water-bearing layer of permeable rock, sand,
or gravel
bentonite clay composed of volcanic ash decompo-
sition, 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 (usu-
ally 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 immobi-
lized 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, contami-
nants 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 proc-
esses such as microbial metabolism to degrade soil and
water contaminants and decontaminate sites
bioslurping technology application that teams vac-
uum-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 volatili-
zation 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 re-
action; catalysts are not consumed in the reaction; en-
zymes are catalysts
catalytic oxidation incineration process that uses
catalysts to increase the oxidation rate of organic con-
taminants, allowing equivalent destruction efficiency at
a lower temperature than flame incineration
clay fine-grained soil that can exhibit putty-like prop-
erties within a range of water content and is very strong
when air-dried
63
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cometabolic process metabolism of a less-favored
substrate occurring during the metabolism of the pri-
mary substrate
cone of depression area of lowered water table
around a well site because of active pumping
contaminant something that makes material in con-
tact with it impure, unfit, or unsafe; a pollutant
diffusion process of passive transport through a me-
dium motivated by a concentration gradient
diffusivity diffusion coefficient; the amount of mate-
rial, in grams, that diffuses across an area of 1 cm2 in 1
second because of a unit concentration gradient (articu-
lar to compound and medium pair)
electron acceptor relatively oxidized compound that
takes electrons from electron donors during cellular res-
piration, 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 anaero-
bic respiration, depending on environment
head pressure difference between two places; an en-
ergy 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 full-
scale 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 atmos-
pheric nitrogen by soil microorganisms and release of
the nitrogen for plant use upon the death of the micro-
organisms
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 move-
ment 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
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remediation activity involved with reducing the haz-
ard 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-molecular-
weight 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 tempera-
tures
volatilization process of vaporizing a liquid into a gas
65
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Appendix B
Data From Bioventing Initiatives Sites
Table B-1. Bioventing Initiative Results: Soil Chemical Characterization
Air Force Base
AFP 4
AFP PJKS
Battle Creek
Beale
Boiling
Camp Pendleton
Cannon
Cape Canaveral
Charleston
Davis Monthan
Dover
Dyess
Edwards
Eglin
Eielson
Site
FSB-1
FSA-3
ST-35
Fire Training Area
Site 3
Site 18
Site 11
Building 18
Former Storage Tank Farm
Site 1
SWMU 70
FTA-2
Facility 1748
Facility 44625D
Facility 44625E
FT-03
Site ST-27
Site SS-41
Site 35
Site 36
ST-04
North Storage Tank Farm
Site FT40
Site FT41
Site 21
Site 16
Site 43
FTA Hurleburt Field
Old Eglin FTA
ST-10
Site 48-E2
Site 48-E3
PH
8.8
7.7
7.5
8.2
7.7
7.4
8.2
4.9
8.1
7.7
8.4
7.7
8.5
9.2
8.8
7.1
6.7
4.7
8.3
8.1
5.3
5.5
8.7
8.8
9.3
9.6
8.9
8.2
7.5
6.3
7.8
7.5
Alkalinity
(mg/kg)
210
365
NS
170
87
67
240
<50
910
120
1,150
165
400
265
350
280
130
<50
360
220
36
<50
3,130
2,790
730
640
500
300
170
<50
240
230
TKN
(mg/kg)
33
190
490
73
105
42
15
48
100
73
190
18
110
74
54
350
62
61
32
57
48
410
180
240
26
22
150
74
<43
390
320
690
Total
Phosphorus
(mg/kg)
270
340
46
165
400
250
820
85
170
46
76
280
310
190
270
350
75
37
760
450
270
100
200
280
650
630
360
33
24
7.4
650
790
Iron
Content
(mg/kg)
7,450
9,800
NS
5,050
27,500
26,400
17,500
15,300
9,610
3,360
6,570
860
900
1,380
970
2,940
8,400
530
15,700
12,700
4,700
8,740
16,900
19,500
9,960
12,500
1 3,400
670
1,600
10,400
17,400
16,700
67
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Table B-1. Bioventing Initiative Results: Soil Chemical Characterization (Continued)
Air Force Base
Ellsworth
Elmendorf
FE Warren
Galena
Hanscom
Hickam
Hill
Johnston Island
Keesler
Kelly
Kirtland
Kl Sawyer
Kodiak Island
Little Rock
Los Angeles
March
Site
Area D Bulk Fuel Storage
Building 102 Base Fuel
Station
43/45 Valve Pit
ST-61
ST-71
43/55 Pumphouse
Fire Training Pit
Spill Site
Saddle Tank Farm
Power Plant
Million Gallon Hill
Campion POL Leak Site
Building 1639
Building 1812
Area H
Area K
Site 2 FSA
Site 204.1
Site 214.1
Site 228
Site 924
Site 1705
Site 388
Site 40002
Site 510.8
Old Fire Training Area
Former POL Tank Farm
Storage Tanks 260 and 261
SWMU 66
AOCA
Site S-4
Site FC-2
Site B-2093
Site D-10
Fire Training Area 13
Fire Training Area 14
POL Area
Tank 191
Fire Training Site 1
Spill Site 18
Building 125
Building 241
Gate 3
IRP Site 35c
PH
8.5
8.6
7.2
7.7
7.8
7.5
7.8
8.2
7.5
7.8
NS
8.1
6.0
6.6
9.0
8.3
4.7
7.8
NS
NS
8.0
NS
6.8
NS
8.7
8.9
9.0
9.0
7.5
7.0
7.5
8.2
8.2
7.7
8.4
7.0
7.9
7.0
6.1
6.1
8.7
7.5
8.4
8.2
Alkalinity
(mg/kg)
1,150
640
100
160
200
87
1,300
340
520
490
NS
300
<50
58
1,500
860
35
740
NS
NS
74
NS
52
NS
340
540
405
355
260
250
500
750
1,100
1,100
340
380
98
260
86
<50
440
830
310
21
TKN
(mg/kg)
320
24
64
78
110
66
1,300
55
800
620
NS
710
630
60
30
1,700
38
140
NS
NS
120
NS
350
NS
100
440
185
140
102
43
690
590
310
640
58
200
22
590
710
390
87
120
65
130
Total
Phosphorus
(mg/kg)
500
1,000
3.5
1,200
3.1
1,200
440
320
730
710
NS
570
320
530
3,400
2,300
470
NS
NS
NS
710
NS
NS
390
2,200
370
520
340
190
35
620
790
880
310
300
1,000
140
930
130
140
1,200
1,600
1,400
280
Iron
Content
(mg/kg)
15,000
36,800
24,800
23,700
28,000
25,300
20,200
11,200
21 ,400
24,200
NS
15,200
7,620
6,810
75,100
34,100
99,000
5,270
NS
NS
6,500
NS
9,380
NS
4,700
270
115
84
4,300
2,100
16,000
1 3,400
14,000
13,300
11,200
26,200
2,190
24,900
53,000
36,300
8,900
33,800
18,700
32,200
68
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Table B-1. Bioventing Initiative Results: Soil Chemical Characterization (Continued)
Air Force Base
McClellan
McGuire
Mt. Home
Nellis
Newark
Offutt
Patrick
Pease
Pittsburgh
Pope
Randolph
Robins
Shaw
Tinker
Travis
Vandenburg
Westover
Wright Patterson
Site
Building 720
Davis Site
Capehart Gas Station
PRL T-46
Study Area 6
Tank Farm #2
Tank Farm #4
Bulk Fuel Storage
POL Yard
Site 27
Site 28
Site 44
Facility 27
Facility 89
Facility 14
Low Point Drain
Building 30
Building 406
POL Storage Area
FTA-2
BX Service Station
Bulk Fuel Storage Area
Site 2
Fire Training Area 1
Fire Training Pit 4
Fire Training Areas 2 and 3
IRP Site ST-08
Tank 20 Site
UST 173
SS10
Site FT-01
Site SS-15
POL Storage Area C
Fuel Storage Area G
South Gas Station
Service Station
JP-4 Site
Building 7701
Building 7705
Fire Training Area
Spill Sites 2 and 3
PH
7.5
8.0
5.8
7.4
8.0
7.8
7.4
6.1
8.4
8.8
8.6
8.5
7.8
7.8
7.9
8.0
8.7
7.8
7.9
8.8
8.4
6.6
5.7
6.6
6.4
7.6
6.7
8.1
5.2
5.3
5.6
5.2
7.3
7.4
7.9
6.9
6.1
6.1
6.8
7.2
8.1
Alkalinity
(mg/kg)
22.5
350
95
46
71
120
100
37
2,100
1,600
410
800
370
460
320
330
1,600
360
470
220
160
140
22.5
84
22
120
200
340
<50
<50
22
22
<50
120
120
20
180
<50
22
730
340
TKN
(mg/kg)
44
260
54
50
10
47
74
480
76
260
100
53
35
360
200
190
250
220
750
32
60
190
59
75
36
49
<40
230
90
46
190
20
30
79
210
103
57
61.5
200
680
<20
Total
Phosphorus
(mg/kg)
260
400
180
5.9
590
1,100
150
217
5.0
170
290
210
515
540
260
480
680
720
600
260
290
730
630
<1.0
330
160
110
920
84
78
38
260
55
220
300
100
100
580
190
570
310
Iron
Content
(mg/kg)
11,400
40,200
26,700
21,300
28,400
26,700
25,200
5,830
21,100
6,950
5,800
6,800
15,400
16,100
16,400
7,500
13,700
18,500
9,800
440
360
21 ,000
39,100
4,500
4,500
4,200
3,000
12,400
6,000
3,600
4,100
13,900
3,210
28,400
22,100
2,920
9,700
6,835
4,900
16,200
6,900
NS = not sampled.
69
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Table B-2. Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations
Soil Analysis
Air Force Base
AFP 4
AFP PJKS
Battle Creek
Beale
Boiling
Camp Pendleton
Cannon
Cape Canaveral
Charleston
Davis Monthan
Dover
Dyess
Edwards
Eglin
Eielson
Ellsworth
Site
FSA-1
FSA-3
ST-35
Fire Training Area
Site 3
Site 1 8
Site 11
Building 18
Former Storage
Tank Farm
Site 1
SWMU 70
FTA-2
Facility 1 748
Facility 44625D
Facility 44625E
FT-03
ST-27
Site SS-41
Site 35
Site 36
ST-04
North STF
Site FT40
Site FT41
Site 21
Site 16
Site 43
FTA Hurleburt Field
Old Eglin FTA
ST-10
Site 48-E2
Site 48-E3
Area D Bulk Fuel
Storage
Building 102 Base
Fuel Station
Time
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Initial
Final
Initial
Initial
Initial
Initial
Final
Initial
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Benzene
(mg/kg)
0.36
BDL
2.7
BDL
BDL
BDL
0.43
BDL
1.5
BDL
BDL
BDL
1.4
0.6
BDL
BDL
0.27
0.064
0.028
1.5
BDL
BDL
0.58
0.35
0.40
BDL
BDL
BDL
0.70
3.3
20
0.90
BDL
BDL
BDL
BDL
BDL
0.05
BDL
BDL
BDL
0.24
BDL
BDL
BDL
0.97
3.8
BDL
BDL
1.4
BDL
BDL
BDL
8.2
0.842
0.18
BDL
Toluene
(mg/kg)
1.3
BDL
9.1
BDL
BDL
BDL
3.0
BDL
4.8
BDL
1.1
BDL
50
0.61
BDL
BDL
8.4
BDL
0.072
14
4.2
BDL
0.58
0.35
0.51
2.0
BDL
0.0056
28
16
100
1.1
BDL
0.33
0.25
BDL
BDL
0.05
BDL
0.13
BDL
0.29
BDL
BDL
BDL
14
7.5
230
0.015
4.4
BDL
4.3
BDL
8.9
BDL
0.60
BDL
Ethyl-
benzene
(mg/kg)
12
BDL
7.1
BDL
0.73
BDL
2.6
BDL
3.5
0.41
2.5
BDL
24
4.4
2.0
BDL
1.5
0.12
0.45
14
2.6
BDL
2.0
0.35
0.61
0.82
BDL
0.0033
2.2
14
63
1.7
BDL
13
0.080
BDL
BDL
0.05
BDL
1.6
BDL
2.3
BDL
0.12
BDL
7.3
11
41
0.0071
11
0.34
BDL
BDL
37
1.8
0.78
11
Total
Xylenes
(mg/kg)
31
BDL
60
BDL
1.5
BDL
12
0.016
17
1.4
6.0
BDL
175
240
1.8
BDL
3.7
0.22
0.50
53
6.6
BDL
5.7
1.3
7.1
2.3
BDL
0.015
17
23
140
8.7
BDL
37
0.19
0.93
BDL
0.07
BDL
6.5
BDL
12
BDL
0.68
BDL
48
32
340
0.0050
45
1.4
4.6
BDL
190
10
4.3
44
Total
BTEX
(mg/kg)
45
BDL
79
BDL
2.2
BDL
23
0.016
26.20
1.81
9.6
BDL
253
246
3.80
BDL
13.87
0.40
1.05
83
13.40
BDL
8.86
2.4
8.62
5.12
BDL
0.02
47.90
56
323.00
12.40
BDL
50.33
0.52
0.93
BDL
0.22
BDL
6.20
BDL
14.59
BDL
0.95
BDL
70.27
54.30
611.00
0.027
62
1.7
8.90
BDL
244.10
12
5.86
55
TPH
(mg/kg)
29
680
140
84
1,100
130
7,200
1,800
1 4,000
10,100
17,000
5,600
400
1,600
1,800
4,100
72
160
3,400
2,700
300
1,100
17,200
10,500
9,200
1,100
790
15
730
530
2,700
8.7
BDL
1,200
650
450
160
930
200
110
23
24
5.1
540
74
9,600
4,100
4,100
52
5,400
1,200
2,600
21
2,800
2,800
11
651
Moisture
Content
(%)
13.7
14.7
16.2
15.4
8.9
11.9
4.8
5.0
23.8
20.9
22.8
19.8
16.8
12.5
16.0
6.1
15.7
15.5
11.0
12.4
14.3
NR
9.2
6.4
6.4
15.8
8.1
13.9
14.6
9.4
7.2
11.7
14.2
24.9
22.0
17.2
17.0
16.6
15.4
11.1
10
13.7
13.3
9.4
1.65
6.6
6.9
12.3
2.7
14.9
6.2
27.8
36.9
17.7
16
7.2
9.8
70
-------
Table B-2. Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations (Continued)
Soil Analysis
Air Force Base
Elmendorf
FE Warren
Fort Drum
Galena
Hanscom
Hickam
Hill
Johnston Atoll
Keesler
Kelly
Site
43/45 Valve Pit
ST-61
ST-71
43/55 Pumphouse
Fire Training Pit
Spill Site
Area 1595
Saddle Tank Farm
Power Plant
Million Gallon Hill
Campion POL
Leak Site
Building 1639
Building 1812
Area H
Area K
Site 2 FSA
Site 204.1
Site 214.1
Site 228
Site 924
Site 1705
Site 388
Site 40002
Site 510.8
Old Fire Training
Area
Former POL Tank
Farm
Storage Tanks 260
and 261
SWMU 66
AOC A
Site S-4
Site FC-2
Time
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Initial
Initial
Final
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Benzene
(mg/kg)
BDL
BDL
BDL
BDL
BDL
BDL
1.7
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
NS
0.028
0.57
0.032
BDL
BDL
2.8
0.078
1.1
BDL
0.6
0.93
0.021
BDL
3.3
BDL
0.64
BDL
BDL
BDL
BDL
BDL
1.9
0.045
50
32
BDL
BDL
BDL
BDL
BDL
4.7
BDL
0.10
BDL
BDL
BDL
BDL
0.014
Toluene
(mg/kg)
BDL
32
0.019
0.098
BDL
0.001
41
BDL
0.46
BDL
4.1
BDL
0.85
BDL
BDL
NS
0.25
1.5
0.57
0.026
0.016
5.3
0.013
12
BDL
11
3.5
0.16
0.01
3.7
BDL
9.2
BDL
BDL
BDL
BDL
BDL
43
0.046
470
410
BDL
BDL
0.65
BDL
BDL
35
0.018
0.039
0.0017
9.1
0.94
8.0
0.13
Ethyl-
benzene
(mg/kg)
BDL
32
0.30
0.22
BDL
BDL
52
BDL
0.66
4.8
BDL
3.4
BDL
BDL
BDL
NS
BDL
0.58
0.073
BDL
BDL
5.5
0.0049
10
BDL
7.4
11
0.54
BDL
5.3
BDL
7.1
BDL
BDL
0.0068
BDL
BDL
25
0.54
160
78
BDL
BDL
BDL
3.5
15
16
BDL
0.22
BDL
BDL
BDL
BDL
0.014
Total
Xylenes
(mg/kg)
BDL
140
0.34
0.75
BDL
0.00053
241
BDL
1.4
31
10
25
3.7
BDL
BDL
NS
0.19
4.2
0.3
0.047
0.023
7.5
0.0046
19
BDL
38
12
5.1
0.089
9.1
BDL
240
BDL
BDL
0.029
0.12
BDL
250
4
1,300
1,200
BDL
0.1
BDL
2.5
14
116
0.0050
0.080
0.0020
13
1.5
22
0.022
Total
BTEX
(mg/kg)
BDL
200
0.66
1.1
BDL
0.0015
330
BDL
2.5
36
14
28
4.6
BDL
BDL
NS
0.47
6.85
0.98
0.03
0.039
21.10
0.10
34.04
BDL
71.74
27
5.82
0.099
21
BDL
256.94
BDL
BDL
0.036
0.12
BDL
320
4.6
1,977.00
1,700
0.06
0.10
0.45
6.0
29.00
171.70
0.023
0.44
0.0037
20.20
2.4
30.00
0.18
TPH
(mg/kg)
4.9
6,000
790
2,400
32
26
3,900
4.9
3,000
400
700
15,000
270
97
BDL
NS
760
13
130
6,500
1,800
12
4.8
20
47
1,100
1,400
960
4,500
12,100
550
5,800
BDL
BDL
BDL
4,400
600
7,500
1,100
28,100
12,300
5,200
2,600
7,700
13,000
265
3,300
2,500
87
19
920
590
1,600
64
Moisture
Content
(%)
5.6
9.8
8.4
11.6
4.6
5.1
8.1
4.6
20.7
20.8
19
10.6
21.9
22.3
5.8
NS
12.3
16.6
15.3
4.7
3.1
24.6
24.1
15.5
13.7
33.7
31.8
6.2
7.7
19
NS
11.7
8
6.7
16.7
8.3
6.3
8.7
6.9
23.5
27
8.1
6.9
11.0
10.7
12.5
11.5
34.1
8.4
9.0
21.1
22.9
20
20.5
71
-------
Table B-2. Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations (Continued)
Soil Analysis
Air Force Base
Kirtland
Kl Sawyer
Kodiak UCSG
Little Rock
Los Angeles
Malmstrom
March
McClellan
McGuire
Mt. Home
Nellis
Newark
Offutt
Site
Site B-2093
Site D-10
Fire Training
Area 13
Fire Training
Area 14
POL Area
FTA-06
FTA-07
Tank 191
Fire Training Site 1
Spill Site 18
Building 125
Building 241
Gate 3
Pumphouse 2
Bulk POL
IRP Site 35c
Building 720
Capehart Gas
Station
Davis Site
PRL T-46
Study Area 6
Tank Farm #2
Tank Farm #4
Bulk Fuel Storage
POL Yard
Site 27
Site 28
Site 44
Facility 27
Facility 89
Low Point Drain
Building 406
Building 30
Time
Initial
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Initial
Final
Initial
Initial
Initial
Initial
Final
Initial
Initial
Final
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Final
Benzene
(mg/kg)
13
BDL
BDL
BDL
BDL
BDL
BDL
BDL
0.72
0.84
BDL
BDL
BDL
BDL
BDL
BDL
BDL
0.0054
0.031
BDL
BDL
4.7
0.011
BDL
0.10
1.0
0.13
BDL
0.0022
BDL
4.2
0.098
0.0065
BDL
0.017
BDL
5.6
BDL
84
0.39
8.1
14
2.2
1.2
0.40
BDL
0.0028
BDL
BDL
0.11
2.2
0.048
BDL
BDL
Toluene
(mg/kg)
130
0.0096
BDL
9.1
2.2
BDL
40
BDL
7.5
2.2
0.48
0.047
0.027
BDL
BDL
BDL
BDL
0.018
0.23
0.71
0.067
130
0.011
BDL
0.10
1.6
0.13
BDL
0.0022
BDL
18
0.11
1.6
BDL
0.029
BDL
110
0.92
440
1.9
33
65
11
53
2.6
BDL
0.0079
BDL
0.014
1.8
1.4
0.88
0.0029
0.0041
Ethyl-
benzene
(mg/kg)
39
BDL
BDL
9.5
7.2
0.79
9.7
0.35
7.8
3.6
1.7
0.75
BDL
BDL
0.53
BDL
BDL
0.35
1.4
1.6
0.21
22
0.050
BDL
0.10
0.12
0.13
0.077
0.94
BDL
14
0.51
0.12
0.11
0.017
BDL
120
3.1
82
1.0
18
30
8.1
28
1.1
BDL
BDL
BDL
BDL
1.0
21
0.034
BDL
BDL
Total
Xylenes
(mg/kg)
200
BDL
BDL
57
38
3.7
27
7.8
36
11
19
2.6
BDL
0.43
0.74
BDL
BDL
0.36
2.3
3.7
0.13
120
0.16
BDL
8.2
0.84
0.25
0.15
1.2
BDL
27
1.1
0.57
BDL
1.1
BDL
200
12
930
4.7
67
130
25
110
5.5
BDL
0.0019
BDL
0.0011
6.3
35
1.8
0.014
0.00053
Total
BTEX
(mg/kg)
382.00
0.01
BDL
76
47
4.49
77.70
8.2
52
18
21
3.4
0.027
0.43
1.27
BDL
BDL
0.73
3.96
6.0
0.41
280
0.23
BDL
8.50
3.56
0.64
0.23
2.14
BDL
63.20
1.8
2.30
0.11
1.16
BDL
435.30
16
1,536.00
7.99
130
239.00
46
192.20
9.6
BDL
0.013
BDL
0.015
9.2
60
2.8
0.02
0.0046
TPH
(mg/kg)
53
86
250
1,800
4,800
7,900
1,300
2,600
6,700
8,200
250
4,000
6.3
990
8.2
BDL
560
3,700
4,000
240
84.6
2,700
1,000
8.6
3,800
5.4
6,000
1,200
3,100
61
1,200
BDL
37
98
41
BDL
2,100
1,600
5,800
50
7,800
2,200
1,500
300
140
43
92
12
6
15
730
1,600
6.6
BDL
Moisture
Content
(%)
18.7
22.5
9.3
10.3
11.4
11.3
13.3
10.6
5.8
4.9
5.7
6.6
5.9
19.0
16.3
16.1
9.6
17.1
15.4
22
ND
NS
3.5
3.2
12
17.1
18.3
17.6
21.3
14.2
17.0
20.1
15.3
13.5
20.7
22.5
15.7
14.9
15.7
14.0
19.4
24.1
21.2
24.9
18.9
16.1
NR
18.9
NR
15.7
23.0
20.0
24.3
22.4
72
-------
Table B-2. Preliminary Bioventing Initiative Results: Average BTEX and TPH Soil Concentrations (Continued)
Soil Analysis
Air Force Base
Patrick
Pease
Pittsburgh
Pope
Randolph
Robins
Shaw
Tinker
Travis
Vandenburg
Westover
Wright Patterson
Site
POL Storage Area
FTA-2
BX Service Station
Bulk Fuel Storage
Area
Site 2
Fire Training Areas
2 and 3
Fire Training Pit 4
Fire Training Area 1
Site ST-08
Tank 20 Site
UST173
SS10
Site FT-01
Site SS-15
POL Storage
Area C
Fuel Storage
Area G
South Gas Station
Service Station
JP-4 Site
Building 7701
Building 7705
Fire Training Area
Spill Sites 2 and 3
Time
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Initial
Final
Initial
Final
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Benzene
(mg/kg)
0.0042
BDL
3.4
BDL
4.5
0.60
0.33
BDL
0.024
BDL
BDL
0.85
1.8
BDL
BDL
NS
BDL
BDL
0.018
7.3
0.31
1.7
1.9
0.0012
0.26
BDL
4.6
BDL
0.44
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
Toluene
(mg/kg)
0.00082
BDL
26
BDL
0.72
0.067
1.1
BDL
3.2
0.026
BDL
0.85
30
BDL
4.7
NS
0.00067
BDL
20
21
1.7
3.8
45
0.0015
0.69
BDL
22
5.4
2.0
BDL
BDL
0.47
0.20
0.026
BDL
0.016
BDL
Ethyl-
benzene
(mg/kg)
0.019
0.004
190
0.034
3.0
0.07
5.2
BDL
0.057
0.0042
0.94
16
20
BDL
3.3
NS
0.11
0.82
14
21
3.6
7.1
53
0.0049
9.1
13
13
4.9
1.8
BDL
BDL
BDL
0.087
0.0028
BDL
BDL
BDL
Total
Xylenes
(mg/kg)
0.028
0.0073
920
BDL
18
0.2
15
BDL
0.68
0.14
1.5
80
135
BDL
33
NS
1.0
0.73
76
100
3.2
36
83
0.037
13
88
71
46
6.4
BDL
BDL
0.73
0.35
0.015
BDL
0.0054
BDL
Total
BTEX
(mg/kg)
0.05
0.011
1,100
0.034
26
0.94
21.63
BDL
3.96
0.17
2.4
97.70
186.80
BDL
41.00
NS
1.11
1.6
110.02
150
8.81
48.60
138.59
0.045
22.72
100
110.60
56.30
11
BDL
BDL
1.22
0.64
0.04
BDL
0.02
BDL
TPH
(mg/kg)
4.3
5.5
930
6,500
10,500
63
310
210
17
5,200
5,200
4,500
2,500
3,200
230
NS
1,900
340
3,100
3,600
4,500
2,400
2,300
BDL
64
5,400
20
230
6.2
BDL
BDL
22
BDL
19.5
BDL
BDL
BDL
Moisture
Content
(%)
19
21
6.6
8.3
4.1
7.6
12.3
12.5
11.0
3.8
10.5
8.3
8.2
12.9
10.5
NS
14.3
11.2
9.9
12.0
10.2
11.0
9.4
11
15.2
14.6
17.3
16.6
13.1
4.7
NR
9.8
8.9
19.0
17.0
6.6
4.2
BDL = below detection limit.
NR = not reported
NS = not sampled.
73
-------
Table B-3. Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations
Soil Gas Analysis
Air Force
Base
AFP 4
AFP PJKS
Battle Creek
Beale
Boiling
Camp
Pendleton
Cannon
Cape
Canaveral
Charleston
Davis Monthan
Dover
Dyess
Edwards
Eglin
Eielson
Ellsworth
Elmendorf
Site
FSA-1
FSA-3
ST-35
Fire Training Area
Site 3
Site 1 8
Site 11
Building 18
Former Storage Tank
Farm
Site 13115
SWMU 70
FTA-2
Facility 1748
Facility 44625D
Facility 44625E
FT-03
ST-27
Site SS-41
Site 35
Site 36
ST-04
North STF
Site FT40
Site FT41
Site 21
Site 1 6
Site 43
FTA Hurleburt Field
Old Eglin FTA
ST-10
Site 48-E2
Site 48-E3
Area D Bulk Fuel
Storage
Building 102 Base Fuel
Station
43/45 Valve Pit
Time
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Initial
Final
Initial
Initial
Initial
Initial
Final
Initial
Initial
Initial
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Benzene
(ppmv)
BDL
0.24
BDL
0.28
8.2
BDL
50
BDL
2.3
0.27
11
4.7
350
1.3
0.056
BDL
0.21
BDL
0.34
30
1.5
0.016
1.5
0.36
0.059
BDL
BDL
126
0.30
693
583
65
5.4
0.015
BDL
0.016
BDL
190
0.26
230
0.8
BDL
BDL
36
146
567
BDL
66
0.32
4.6
BDL
140
0.0091
320
BDL
13
Toluene
(ppmv)
BDL
0.094
BDL
0.21
8.8
0.004
18
0.0027
1.9
0.60
1.6
BDL
530
13
0.18
0.0033
7.9
BDL
1.2
18
0.11
0.011
0.021
0.20
0.53
BDL
BDL
557
0.30
681
665
44
4.8
0.08
0.002
0.19
0.018
16
0.24
26
0.83
0.0088
0.006
46
179
150
1.6
51
2.1
0.25
BDL
13
0.017
48
0.074
80
Ethylbenzene
(ppmv)
21
0.23
6.4
0.65
6.5
0.026
2.8
BDL
0.71
0.87
2.0
0.80
37
7.3
0.30
0.016
4.0
BDL
1.2
7.4
3.6
0.026
3.4
0.015
0.33
0.061
0.0013
81
4.87
93
118
13.4
2.5
0.011
BDL
0.14
BDL
12
0.72
20
2
0.091
0.012
12
29
4.0
BDL
3.4
2.5
0.45
1.8
12.9
2
6.7
6.7
7.5
Total
Xylenes
(ppmv)
19
0.67
12.5
0.93
14
0.070
11
BDL
2.3
2.0
1.8
1.7
300
180
0.74
0.058
5.2
BDL
3.4
23
4.8
0.071
3.3
1.6
2.2
0.11
BDL
253
9.8
153
254
47
5.4
0.042
0.012
0.26
0.013
38
1.7
89
5.3
0.48
0.11
78
120
43
4.4
12
26
1.1
4.2
30
8.4
39
32
28
Total
BTEX
(ppmv)
40.96
1.2
19.03
2.1
37.50
0.10
81.40
0.0027
3.74
3.7
16.40
7.2
1,215.00
200
1.28
0.077
17.31
BDL
6.1
78
10.01
0.12
8.22
2.18
3.12
0.17
0.0013
1,017.00
15.27
1 ,620.00
1,620.00
169.40
61.30
0.15
0.014
0.61
0.031
253.00
2.9
365.00
8.9
0.59
0.13
172.00
474.00
764.00
6.0
132.40
31
6.40
6.0
128.50
10
416.70
39
128.50
TPH
(ppmv)
25,000
290
12,800
480
2,300
11
10,900
7.9
3,000
270
3,600
1,600
59,300
2,800
317
15
11,900
12,700
460
9,000
3,900
210
750
397
303
410
6.7
118,333
19,667
46,098
39,667
33,500
6,150
49
1.5
320
1.6
49,000
220
63,000
575
380
0.95
17,667
16,000
48,000
2,100
6,000
1,200
1,866
610
35,000
780
79,000
840
13,550
74
-------
Table B-3. Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations (Continued)
Soil Gas Analysis
Air Force
Base
FE Warren
Fort Drum
Galena
Hanscom
Hickam
Hill
Johnston Atoll
Keesler
Kelly
Site
ST-61
ST-71
43/55 Pumphouse
Fire Training Pit
Spill Site
Area 1595
Saddle Tank Farm
Power Plant
Million Gallon Hill
Campion POL Leak Site
Building 1639
Building 1812
Area H
Area K
Site 2 FSA
Site 204.1
Site 214.1
Site 228
Site 924
Site 1705
Site 388
Site 40002
Site 510.8
Old Fire Training Area
Former POL Tank Farm
Storage Tanks 260 and
261
SWMU 66
AOCA
Site S-4
Site FC-2
Site B-2093
Site D-10
Time
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Initial
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Benzene
(ppmv)
0.053
BDL
BDL
BDL
19
0.87
0.92
180
BDL
BDL
40
0.059
0.060
6.4
BDL
0.022
8.1
8.3
NS
BDL
BDL
85
BDL
16
BDL
0.026
0.0025
0.010
BDL
0.81
0.021
34
0.0025
0.012
BDL
175
2.3
BDL
1.2
BDL
BDL
0.016
0.1
0.059
23
1,100
42
200
0.041
38
BDL
175
0.003
BDL
Toluene
(ppmv)
0.32
0.22
BDL
0.004
64
0.86
2.5
28
0.012
7.2
8.3
1.1
BDL
5.7
BDL
0.040
10
9
NS
BDL
BDL
BDL
BDL
29
BDL
0.11
0.0047
0.039
BDL
2.2
0.029
80
0.0045
0.019
0.0025
180
97
280
140
0.18
BDL
0.47
0.11
0.066
44
550
220
22
0.88
15
0.6
323
0.051
0.016
Ethylbenzene
(ppmv)
0.4
0.95
0.22
0.032
15
5.1
1.9
24
0.049
2.7
2.7
3.8
1.4
0.64
3.5
0.054
3.6
0.47
NS
28
0.0067
22
2
12
7.4
0.085
BDL
0.26
0.036
0.85
0.016
3.6
BDL
0.011
0.0017
8.9
25
12
9.7
0.06
0.065
0.95
3.03
1.5
4.5
51
53
22
0.3
18
0.15
25
0.18
0.003
Total
Xylenes
(ppmv)
1.1
1.3
1.12
0.033
50
33
5.1
110
0.27
16
6.4
3.5
3.2
2.5
10
0.22
17
5.5
NS
22
0.0053
48
5.3
40
18
0.39
0.0023
0.26
0.18
4.7
0.13
34
BDL
0.053
0.035
80
260
110
150
0.43
0.20
2.8
2.3
2.0
20
120
230
19
0.63
15
0.34
87
0.34
0.015
Total
BTEX
(ppmv)
1.87
2.5
1.35
0.069
150
40
10.42
348.00
0.33
26
57.40
8.5
4.7
15
14
0.34
38.70
23
NS
56.80
0.012
155.70
7.3
97.00
25
0.61
0.0095
0.57
0.22
8.48
0.20
150
0.0070
0.10
0.039
440.90
380
303.59
300
0.69
0.27
4.24
5.54
3.63
91.50
1,800
550
265.00
1.9
86.00
1.1
610.00
0.57
0.034
TPH
(ppmv)
1,000
200
390
3.2
19,700
2,700
1,059
15,400
33
2,300
2,745
897
390
2,000
1,000
254
7,000
1,900
NS
240,000
73
26,300
15,900
13,800
6,400
220
3.2
480
620
1,300
20
2,900
1.5
44
1.2
26,000
9,000
11,100
7,800
660
340
450
3,833
1,588
8,183
130,000
22,300
36,500
430
1 2,400
100
9,467
54
1.1
75
-------
Table B-3. Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations (Continued)
Soil Gas Analysis
Air Force
Base
Kirtland
K.I. Sawyer
Little Rock
Los Angeles
Malmstrom
March
McClellan
McGuire
Mt. Home
Nellis
Newark
Offutt
Patrick
Pease
Pittsburgh
Site
Fire Training Area 13
Fire Training Area 14
POL Area
FTA-06
FTA-07
Fire Training Site 1
Spill Site 18
Building 125
Building 241
Gate 3
Pumphouse 2
Bulk POL
IRP Site 35c
Building 720
Davis Site
PRL T-46
Study Area 6
Tank Farm #2
Tank Farm #4
Bulk Fuel Storage
POL Yard
Site 27
Site 28
Site 44
Facility 27
Facility 89
Facility 14
Low Point Drain
Building 30
Building 406
POL Storage Area
FTA-2
BX Service Station
Bulk Fuel Storage Area
Fire Training Pits 2 and 3
Fire Training Pit 4
Fire Training Area 1
Time
Initial
Final
Initial
Initial
Initial
Final
Initial
Final
Initial
Initial
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Initial
Initial
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Initial
Benzene
(ppmv)
19
0.011
NS
393
8.6
0.16
3.1
1.2
NS
BDL
0.026
0.065
0.026
6.6
BDL
BDL
BDL
0.035
NS
0.0053
BDL
0.18
0.34
165
3.8
0.68
BDL
0.11
BDL
73
10
550
543
6.0
520
203
0.019
0.0072
NS
88
BDL
BDL
290
BDL
67
BDL
BDL
0.048
BDL
0.027
117
4.4
BDL
11
6.01
Toluene
(ppmv)
56
BDL
NS
178
7.2
0.13
6.2
10
NS
BDL
0.026
0.31
0.026
BDL
BDL
12
BDL
0.035
NS
0.004
0.0045
0.18
3.0
124
7.2
28
0.38
0.11
BDL
190
22
25
372
14
547
753
0.023
0.015
NS
153
BDL
BDL
BDL
BDL
11
BDL
BDL
0.003
44
0.002
9.7
10
0.016
18
20
Ethylbenzene
(ppmv)
8.3
0.1
NS
9.1
0.53
0.23
0.40
4.0
NS
8.7
0.089
0.59
0.57
9.1
0.15
12
2
0.41
NS
0.39
0.0050
3.3
2.8
13
4.8
7.9
7.0
5.3
0.046
17
5.1
560
37
5.1
55
68
0.0097
0.0045
NS
29
BDL
BDL
44
6.5
4
BDL
1.5
0.024
24
0.0045
18
2.1
0.0045
24
4.2
Total
Xylenes
(ppmv)
34
0.56
NS
15
2.6
0.68
2.2
22
NS
16
0.2
0.91
1.17
12
0.28
38
4.2
0.67
NS
0.67
0.10
1.84
6.0
81
36
30
13
5.7
0.15
58
45
270
100
16
185
377
0.11
0.0088
NS
77
1.4
BDL
51
28
9.5
0.36
5.2
0.058
200
0.23
22
14
0.013
82
15
Total
BTEX
(ppmv)
117.30
0.67
NS
595.10
19
1.2
12
37
NS
25
0.34
1.88
1.79
28
0.43
62
6.2
1.15
NS
1.07
0.11
5.50
12
383.00
52
66.58
20
11.22
0.20
340
82
1,400
1,052.00
41
1,307.00
1,401.00
0.16
0.04
0.00
347.00
311.00
BDL
382.92
35
304.00
0.36
267.60
0.13
7.18
0.26
166.70
30.50
0.034
140
45.21
TPH
(ppmv)
13,000
690
NS
41 ,067
1,300
20
820
710
NS
23,700
2,200
340
857
8,800
65
46,000
580
136
NS
245
230
7,167
930
39,264
900
29,333
11,900
2,370
27
54,000
4,900
67,000
81,667
1,400
72,000
29,333
1,043
28
NS
29,750
8,200
170
18,300
2,300
13,500
860
10,400
68
62,000
4.3
48,000
4,312
9.9
7,200
8,348
76
-------
Table B-3. Preliminary Bioventing Initiative Results: BTEX and TPH Soil Gas Concentrations (Continued)
Soil Gas Analysis
Air Force
Base
Pope
Randolph
Robins
Shaw
Tinker
Travis
Vandenburg
Westover
Wright Patterson
Site
Site ST-08
Tank 20 Site
UST173
SS10
Site SS-15
POL Storage Area C
Fuel Storage Area G
South Gas Station
Service Station
JP-4 Site
Building 7701
Building 7705
Fire Training Area
Spill Sites 2 and 3
Time
Initial
Initial
Final
Initial
Final
Initial
Final
Initial
Initial
Final
Initial
Final
Initial
Initial
Initial
Initial
Final
Initial
Final
Initial
Initial
Benzene
(ppmv)
BDL
16
BDL
0.0013
0.086
270
57
210
53
0.018
1,300
7.1
1,650
160
NS
NS
610
BDL
BDL
0.23
0.07
Toluene
(ppmv)
25
0.53
BDL
0.028
0.011
109
40
200
100
0.022
550
11
1,125
84
NS
NS
BDL
BDL
0.0093
0.42
2.59
Ethylbenzene
(ppmv)
4.0
6.1
0.048
0.17
BDL
16
15
32
11
0.73
100
6.4
61
28
NS
NS
0.13
0.12
0.0063
0.21
1.92
Total
Xylenes
(ppmv)
10
18
0.21
1.04
0.016
84
67
120
36
1
97
31
240
139
NS
NS
0.031
0.087
0.023
0.29
6.76
Total
BTEX
(ppmv)
39
40.63
0.26
1.24
0.11
479.00
180
560
202.00
1.8
2,048.00
56
3,076.00
411.00
NS
NS
610
0.23
0.039
1.15
11.34
TPH
(ppmv)
3,800
19,667
50
206
1.1
55,000
13,000
69,700
11,500
190
110,000
2,300
145,000
19,467
NS
NS
0.57
92
0.34
1,147
2,398
NS = not sampled.
BDL = below detection limit.
77
-------
Table B-4. In Situ Respiration Test Results at Bioventing Initiative Sites
Initial
6-Month
1-Year
Air Force Base
AFP 4
AFP PJKS
Battle Creek
Beale
Boiling
Camp Pendleton
Cannon
Cape Canaveral
Charleston
Davis Monthan
Dover
Dyess
Edwards
Eglin
Eielson
Ellsworth
Elmendorf
FE Warren
Galena
Hanscom
Site
FSA-1
FSA-3
ST-35
Fire Training Area
Site 3
Site 18
Site 11
Building 18
Former Storage Tank Farm
Site 1
SWMU 70
FTA-2
Facility 1748
Facility 44625D
Facility 44625E
FT-03
Site SS-41
Site 35
Site 36
ST-04
North STF
Site FT40
Site FT41
Site 21
Site 16
Site 43
FTA Hurleburt Field
Old Eglin FTA
ST-10
Site 48-E2
Site 48-E3
Area D Bulk Fuel Storage
Building 102 Base Fuel
Station
43/45 Pumphouse
ST-61
ST-71
43/55 Pumphouse
Fire Training Pit
Spill Site
Saddle Tank Farm
Power Plant
Million Gallon Hill
Campion POL Leak Site
Building 1639
Building 1812
%/hr
0.32
0.91
0.52
0.39
0.14
0.74
0.12
0.11
1.4
0.021
0.53
0.18
0.16
0.39
0.17
0.54
0.38
0.009
0.078
0.18
0.30
0.010
NC
0.16
0.031
0.033
0.18
0.18
0.29
0.18
NC
1.1
0.034
0.51
0.38
0.056
0.34
0.62
1.4
1.05
1.4
0.44
0.99
0.78
NC
mg/kg-
day
5.22
14.85
8.49
6.36
2.28
12.08
1.96
1.80
22.85
0.34
8.65
2.94
2.61
6.36
2.77
8.81
6.20
0.15
1.27
2.94
4.90
0.16
NC
2.61
0.51
0.54
2.94
2.94
4.73
2.94
NC
17.95
0.55
8.32
6.20
0.91
5.55
10.12
22.85
17.14
22.85
7.18
16.16
12.73
NC
%/hr
0.058
0.36
0.17
0.12
0.043
0.078
0.031
0.011
1.5
NC
NC
NC
NC
NC
NC
0.0059
NC
NC
NC
NC
NC
NC
NC
0.016
0.0051
0.0060
NC
NC
0.22
0.046
0.067
0.068
0.0096
0.09
0.072
0.015
0.0066
NC
0.052
NC
NC
NC
NC
0.26
0.036
mg/kg-
day
0.95
5.88
2.77
1.96
0.70
1.27
0.51
0.18
24.48
NC
NC
NC
NC
NC
NC
0.10
NC
NC
NC
NC
NC
NC
NC
0.26
0.08
0.10
NC
NC
3.59
0.75
1.09
1.11
0.16
1.47
1.18
0.24
0.11
NC
0.85
NC
NC
NC
NC
4.24
0.59
%/hr
0.059
0.54
0.33
0.16
0.016
0.069
0.033
0.080
0.98
NC
NC
NC
NC
NC
NC
0.084
NC
NC
NC
NC
NC
NC
NC
0.23
0.059
0.019
NC
NC
0.10
0.11
0.11
0.074
0.0056
0.32
0.44
0.06
0.16
NC
0.018
NC
0.059
0.11
NC
0.048
NC
mg/kg-
day
0.96
8.81
5.39
2.61
0.26
1.13
0.54
1.31
15.99
NC
NC
NC
NC
NC
NC
1.37
NC
NC
NC
NC
NC
NC
NC
3.75
0.96
0.31
NC
NC
1.63
1.80
1.80
1.21
0.09
5.22
7.89
1.23
2.61
NC
0.29
NC
9.63
1.80
NC
0.78
NC
78
-------
Table B-4. In Situ Respiration Test Results at Bioventing Initiative Sites (Continued)
Initial
6-Month
1-Year
Air Force Base
Hickam
Hill
Johnston Atoll
Keesler
Kelly
Kirtland
Kl Sawyer
Little Rock
Los Angeles
Malmstrom
March
McClellan
McGuire
Mt. Home
Nellis
Newark
Offutt
Site
Area H
Area K
Site 2 FSA
Site 204.1
Site 214.1
Site 228
Site 924
Site 1705
Site 388
Site 40002
Site 510.8
Old Fire Training Area
Former POL Tank Farm
Storage Tanks 260 and 261
SWMU 66
AOC A
Site S-4
Site FC-2
Site D-10
Fire Training Area 13
Fire Training Area 14
POL Area
FTA-06
FTA-07
Spill Site 18
Building 125
Building 241
Gate 3
Pumphouse II
POLSA
IRP Site 35c
Davis Site
PRL T-46
Study Area 6
Tank Farm #2
Tank Farm #4
Bulk Fuel Storage
POL Yard
Site 27
Site 28
Site 44
Facility 27
Facility 89
Low Point Drain
Building 406
Building 30
POL Storage Area
%/hr
0.71
1.2
0.6
0.98
0.31
0.54
0.56
NC
0.42
0.22
0.022
0.42
0.24
0.64
0.65
0.081
2.4
1.9
1.1
0.061
0.0055
0.11
0.13
0.074
2.04
0.33
0.25
0.27
3.2
1.1
0.29
0.37
0.91
0.32
0.31
0.33
1.2
0.32
0.048
0.21
0.69
0.026
0.021
0.86
5.6
4.9
0.1
mg/kg-
day
11.59
19.58
9.79
15.99
5.06
8.81
9.14
NC
6.85
3.59
0.36
6.85
3.92
10.44
10.61
1.32
39.17
31.01
17.95
1.00
0.09
1.80
2.12
1.21
33.29
5.39
4.08
4.41
52.22
17.95
4.73
6.04
14.85
5.22
5.06
5.39
19.58
5.22
0.78
3.43
11.26
4.24
0.34
14.04
91.39
79.97
1.63
%/hr
0.093
0.45
0.27
0.057
0.015
0.031
0.043
NC
0.090
0.016
0.021
NC
NC
NC
0.41
0.097
0.28
0.72
0.057
0.012
0.0043
0.11
0.047
0.021
NC
NC
NC
NC
0.29
0.34
NC
0.12
0.19
0.016
0.030
0.011
0.28
NC
0.0035
0.038
0.028
NC
0.0096
NC
0.33
0.051
NC
mg/kg-
day
1.52
7.34
4.41
0.93
0.24
0.51
0.70
NC
1.47
0.26
0.34
NC
NC
NC
6.69
1.58
4.57
11.75
0.93
0.20
0.07
1.80
0.77
0.34
NC
NC
NC
NC
4.73
5.55
NC
1.96
3.10
0.26
0.49
0.18
4.57
NC
0.06
0.62
0.46
NC
0.16
NC
5.39
0.83
NC
%/hr
0.012
0.38
0.53
0.096
0.015
0.059
0.007
NC
0.39
0.083
0.091
0.44
0.22
0.23
0.60
0.083
0.11
0.58
0.070
0.0083
NC
0.16
0.029
0.012
NC
NC
NC
NC
NC
0.25
NC
0.50
0.37
0.11
0.064
0.099
0.72
NC
0.031
0.016
0.022
0.015
0.021
NC
0.26
0.039
0.46
mg/kg-
day
0.20
6.20
8.65
1.57
0.24
0.96
0.12
NC
6.36
1.35
1.49
7.2
3.5
3.7
9.79
1.35
1.80
9.47
1.14
0.13
NC
2.61
0.47
0.20
NC
NC
NC
NC
NC
4.08
NC
8.16
6.04
1.80
1.04
1.62
11.75
NC
0.51
0.26
0.36
0.24
0.34
NC
4.24
0.64
7.51
79
-------
Table B-4. In Situ Respiration Test Results at Bioventing Initiative Sites (Continued)
Initial
6-Month
1-Year
Air Force Base
Patrick
Pease
Pittsburgh
Randolph
Robins
Shaw
Tinker
Travis
Vandenburg
Westover
Wright Patterson
Site
FTA-2
BX Service Station
Bulk Fuel Storage Area
Fire Training Areas 2 and 3
Fire Training Pit 4
Tank 20 Site
UST 173
SS10
Site FT-01
Site SS-15
POL Storage Area C
Fuel Storage Area G
South Gas Station
Service Station
Building 7701
Building 7705
Fire Training Area
Spill Sites 2 and 3
%/hr
0.34
0.16
3.57
0.84
0.20
0.41
0.029
0.18
0.43
0.16
0.18
3.6
2.47
0.24
0.33
0.12
0.19
0.26
mg/kg-
day
5.55
2.61
58.26
13.71
3.26
6.69
0.47
2.94
7.02
2.61
2.94
58.75
40.31
3.92
5.39
1.96
3.10
4.24
%/hr
0.41
0.21
NC
0.17
NC
0.15
0.0023
0.031
NC
NC
0.038
0.79
NC
NC
0.0098
NC
NC
NC
mg/kg-
day
6.69
3.43
NC
2.77
NC
2.45
0.04
0.51
NC
NC
0.62
12.89
NC
NC
0.16
NC
NC
NC
%/hr
0.33
0.028
NC
0.094
NC
0.28
0.013
0.020
NC
NC
0.056
0.86
NC
NC
0.052
0.05
NC
NC
mg/kg-
day
5.39
0.46
NC
1.53
NC
4.57
0.21
0.33
NC
NC
0.91
14.04
NC
NC
0.85
0.82
NC
NC
NC = not conducted.
80
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