x>EPA
United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/625/XXX/001
September 1995
Manual
Bioventing Principles and
Practice
Volume II: Bioventing Design
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EPA/540/R-95/534a
September 1995
Manual
Principles and Practices of Bioventing
Volume II: Bioventing Design
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 Site Characterization 1
1.1 Existing Data and Site History Review 2
1.2 Soil Gas Survey 3
1.2.1 Soil Gas Chemistry 3
1.2.2 Collection and Analysis of Soil Gas Samples 4
1.2.3 Interpretation of Soil Gas Survey Results 7
1.3 Soil Characterization 9
1.3.1 Soil Borings 10
1.3.2 Soil Analyses 11
1.4 In Situ Respiration Testing 11
1.4.1 In Situ Respiration Test Procedures 11
1.4.2 Interpretation of in Situ Respiration Test Results 12
1.4.3 Factors Affecting Observed in Situ Biodegradation Rates 16
1.5 Soil Gas Permeability and Radius of Influence 17
1.5.1 Radius of Influence Determination Based on Pressure Measurements 18
1.5.2 Interpretation of Soil Gas Permeability Testing Results 19
Chapter 2 System Design 21
2.1 Determination of Air Flow System 21
2.1.1 Air Injection 21
2.1.2 Air Extraction 23
2.1.3 Determining Use of Injection Versus Extraction 25
2.1.4 Design of Air Flow To Protect Structures 26
2.2 Determining Required Air Flow Rates 26
2.3 Well Spacing 28
2.4 Blowers and Blower Sizing 29
2.4.1 Centrifugal Blowers 30
2.4.2 Rotary Positive Displacement Blowers 31
2.4.3 Blower Selection and Sizing 31
2.5 Vent Well Construction 32
2.6 Monitoring Point Construction 33
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Contents (continued)
Page
Chapter 3 Performance Monitoring 37
3.1 Soil Gas Monitoring 37
3.2 In Situ Respiration Testing 37
3.3 Quantification of Biodegradation and Volatilization of Hydrocarbons During Extractive
Bioventing 38
3.4 Surface Emissions Sampling 39
3.5 Optional Monitoring: Qualitative Validation of Biodegradation Through Stable Carbon
Isotope Monitoring 40
3.6 Operation and Maintenance 40
Chapter 4 Process Evaluation/Site Closure 43
4.1 In Situ Respiration Testing 43
4.2 Soil Sampling 43
Chapter 5 Costs 47
Chapter 6 References 49
Appendix A Glossary 51
Appendix B Equipment Specifications and Manufacturers 55
B.1 Soil Gas Survey Equipment 55
B.2 Vent Well Installation Equipment 57
B.3 Soil Gas Monitoring Point Equipment 58
B.4 Air Permeability Test Equipment 61
B.5 In Situ Respiration Test Equipment 62
B.6 Miscellaneous Items 64
B.7 Optional Items 64
Appendix C Example Procedures for Conducting Bioventing Treatability Studies 67
C.1 Example Procedures for Collecting, Labeling, Packing, and Shipping Soil Samples 67
C.1.1 Sample Collection 67
C.1.2 Sample Label and Log 68
C.1.3 Sample Packing and Shipping 68
C.1.4 Quality Control 68
C.2 Example Procedures for in Situ Respiration Testing 68
C.2.1 Field Instrumentation and Measurement 68
C.2.2 In Situ Respiration Test Procedures 69
C.2.3 Quality Control 69
IV
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Contents (continued)
Page
C.3 Example Procedures for Soil Gas Permeability Testing 70
C.3.1 Field Instrumentation and Measurement 70
C.3.2 Soil Gas Permeability Test Procedures 71
C.3.3 Quality Control 71
C.4 References 72
Appendix D Off-Gas Treatment Options 73
D.1 Introduction 73
D.2 Limiting Off-Gas Production 74
D.3 Direct Discharge 74
D.4 Off-Gas Reinjection 74
D.5 Biofiltration 75
D.6 Adsorption on Carbon or Resin 75
D.7 Catalytic Oxidation 76
D.8 Flame Incineration 77
D.9 Internal Combustion Engines 77
D.10 Emerging Vapor Treatment Technologies 79
D.11 References 80
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Figures
Figure Page
1-1 Conceptual decision tree for determining the potential applicability of bioventing at a contaminated site . . 1
1-2 Site map showing well locations and TPH soil concentrations at AOC A, Keesler AFB, Mississippi 3
1-3 Schematic of a soil gas sampling system using the stainless steel soil gas probe 4
1-4 Schematic of a soil gas sampling system for collection of soil gas from low-permeability soils 6
1 -5 Sample soil boring log 10
1-6 In situ respiration test apparatus 12
1-7 In situ respiration test results with linear oxygen concentration versus time at AOC A,
Keesler AFB, Mississippi 15
1-8 In situ respiration test results with nonlinear oxygen concentration versus time at SWMU 66,
Keesler AFB, Mississippi 15
1-9 In situ respiration test results with acceptable data based on the helium concentration for
monitoring point S1, Tinker AFB, Oklahoma 16
1-10 In situ respiration test results with unacceptable data based on the helium concentration
for monitoring point K3, Kenai, Alaska 16
1-11 Determination of radius of influence at the Saddle Tank Farm, Galena AFS, Alaska 19
2-1 Expanded bioreactor created during air injection 22
2-2 Oxygen utilization rates, averaged over depth, versus distance from the injection well at Site 280,
Hill AFB, Utah 22
2-3 Mass of TPH degraded versus distance from the injection well at Site 280, Hill AFB, Utah 22
2-4 Hydrocarbon volatilization and biodegradation rates as a function of air flow rate 23
2-5 Water table depression during air injection and air extraction 23
2-6 Air injection configuration for a bioventing system 24
2-7 Radius of influence during air injection and extraction in the control test plot at a depth of 6 ft at
Site 20, Eielson AFB, Alaska 25
2-8 Schematic of a basic air extraction system 25
2-9 Extracted BTEX and TPH soil gas concentrations at Patrick AFB, Florida 26
2-10 Schematic of an air injection system with reinjection of extracted soil gas 27
2-11 Schematic of subslab depressurization 27
2-12 Schematic of the extraction with reinjection system at AOC A, Keesler AFB, Mississippi 28
2-13 Soil gas extraction to isolate a subsurface structure at Site 48, Eielson AFB, Alaska 29
2-14 Schematic of blower types 30
2-15 Performance curves for three different-sized blowers 32
2-16 Schematic of a typical vent well 33
2-17 Schematic of a typical monitoring point construction 35
VI
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Figures (continued)
Figure Page
3-1 Schematic of a surface emissions monitoring device 39
3-2 Carbon isotopic compositions of soil gas carbon dioxide at Site 20, Eielson AFB,
Alaska, August 1993 40
5-1 Comparison of costs for various remedial technologies for fuel-contaminated soils 48
VII
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Tables
1-1 Results From a Soil Gas Survey at AOC A, Keesler AFB, Mississippi 8
1-2 Results From a Soil Gas Survey at Building 1813, Hanscom AFB, Massachusetts 8
1-3 Results from a Soil Gas Survey at the Aquasystem Site, Westover AFB, Massachusetts 9
1-4 Results From a Soil Gas Survey at an Oil/Water Leak at Cape Canaveral AFS, Florida 9
1-5 Soil Analyses Based on Bioventing Initiative Results 11
1-6 Oxygen Density Versus Temperature 13
1-7 Bulk Density of Various Soils 13
1-8 Initial Soil Gas Readings at Monitoring Points at AOC A, Keesler AFB, Mississippi 14
1-9 Raw Data From an in Situ Respiration Test at
AOC A, Keesler AFB, Mississippi 14
1-10 Oxygen Utilization and Carbon Dioxide Production Rates During the in Situ Respiration Test
at AOC A, Keesler AFB, Mississippi 15
1-11 Raw Data From an in Situ Respiration Test at SWMU 66, Keesler AFB, Mississippi 15
1-12 Soil Gas Permeability Values 17
2-1 Permeability and Radius of Influence Values at Eielson AFB, Alaska: Injection and Extraction Mode .... 24
2-2 Air Injection Versus Extraction Considerations 26
2-3 Recommended Spacing for Monitoring Points 34
3-1 Surface Emissions Sampling at Bioventing Sites 40
4-1 Cumulative t Distribution 44
4-2 Number of Observations for t Test of Mean 45
4-3 Calculation of the Number of Samples Required To Show a Statistical Difference Between Means of
Two Sampling Events 46
4-4 Selected z Values for Estimation of Final Soil Sample Number 46
5-1 Typical Full-Scale Bioventing Costs 47
5-2 Cost Comparison of in Situ Bioremediation Technologies Used at Fuel Spill Sites 47
VIM
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List of Examples
Example Page
1-1 Review of Existing Data and Site History 2
1-2 Soil Gas Survey Conducted at Keesler AFB 7
1-3 Soil Gas Survey at Building 1813, Hanscom AFB, Massachusetts 8
1-4 Soil Gas Survey at the Aquasystem Site, Westover AFB, Massachusetts 8
1-5 Soil Gas Survey at an Oil/Water Separator Leak at Cape Canaveral AFS, Florida 9
1-6 Results From an in Situ Respiration Test Conducted at Keesler AFB 14
1-7 Calculation of Oxygen Utilization Rates From Nonlinear Data 15
1-8 Evaluation of Helium Loss During an in Situ Respiration Test 16
1-9 Temperature Adjustment of Oxygen Utilization Rate 17
1-10 Calculation of the Radius of Influence Based on Pressure Measurements 19
2-1 Biodegradation of Petroleum Hydrocarbons in the Uncontaminated and Contaminated Regions at
Site 280, Hill AFB 21
2-2 Determination of Required Air Flow Rate 27
2-3 Calculation of Radius of Influence 29
2-4 Selection and Sizing of a Blower 31
2-5 Selection of Depth Intervals for Monitoring Points 34
3-1 Calculation of Volatilization and Biodegradation of Contaminants During Extraction 38
4-1 Calculation of Remediation Time Based on in Situ Respiration Rates 43
4-2 Statistical Evaluation of Contaminant Data 44
4-3 Calculation of Final Number of Soil Samples for Site Closure 45
IX
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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
AOC area of concentration
BTEX benzene, toluene, ethylbenzene, and
xylenes
cfm cubic feet per minute
CRT cone penetrometer
DNAPL dense nonaqueous phase liquid
EPA U.S. Environmental Protection Agency
FID flame ionization detector
GAG granular activated carbon
ICE internal combustion engine
LEL lower explosive limit
LNAPL less dense nonaqueous phase liquid
MP monitoring point
MW monitoring well
MAS Naval Air Station
NFPA National Fire Protection Association
NPT national pipe thread
PAH polycyclic aromatic hydrocarbon
PCB polychlorinated biphenyl
PID photoionization detector
PVC polyvinyl chloride
RD&A research, development, and acquisition
scfm standard cubic feet per minute
SGS soil gas survey
SVE soil vacuum extraction
TCE trichloroethylene
TKN total Kjeldahl nitrogen
TPH total petroleum hydrocarbon
UCL upper confidence limit
UST underground storage tank
VOC volatile organic carbon
Cs
Cv
Kd
KS
kT
MW
Pv
R
R
RI
S
t
Tabs
%
X
Y
quantity sorbed to the solid matrix
(gx/9soii)
volumetric concentration in the vapor
phase (gx/Lvapor)
saturated vapor concentration (gx/Lvapor)
volumetric concentration in the
aqueous phase (gx/Laque0us)
activation energy (cal/mole)
organic carbon fraction
maximum rate of substrate utilization
(gs/gx-min)
biodegradation rate (mg hydrocarbon/
kg soil-day)
endogenous respiration rate (day1)
sorption coefficient (Laqueous/gsoii)
baseline biodegradation rate
(% 02/day)
octanol/water partition coefficient
Monod half-velocity constant (gs/L)
temperature-corrected biodegradation
rate (% O2/day)
molecular weight (gx/molex)
vapor pressure of pure contaminant at
temperature T (atm)
gas constant (1.987 cal/°K-mol)
gas constant (L-atm/mole-°K)
radius of influence
concentration of the primary substrate
(contaminant) (gs/L)
solubility in water (gx/Lwater)
time (minutes)
absolute temperature (°K)
mole fraction (dimensionless)
concentration of microorganisms (gx/L)
cell yield (mg biomass/mg hydrocarbon)
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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
XI
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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.
XII
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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; and site closure. This
second volume focuses on bioventing design and process monitoring. The first volume describes
basic principles of bioventing.
XIII
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Chapter 1
Site Characterization
Site characterization is an important step in determining
the feasibility of bioventing and in providing information
for a full-scale bioventing design. Chapter 1 discusses
site characterization methods that are recommended for
bioventing sites based on field experience and a statis-
tical analysis of Bioventing Initiative data. These pa-
rameters have proven to be the most useful in predicting
the potential applicability of bioventing at a contami-
nated site. Figure 1-1 summarizes the sequence of
events for site characterization of a typical site. Each
step presented in Figure 1-1 is discussed in the following
sections.
Site characterization activities to be conducted at a
potential bioventing site should include the following:
• Review of existing site data (Section 1.1).
• Soil gas survey (Section 1.2).
• Soil characterization (Section 1.3).
• In situ respiration testing (Section 1.4).
• Soil gas permeability testing, and radius of influence
(Section 1.5).
Low
Respiration
Rates <0,1%
a/day
No Limiting
Factors Can
Be Identified
R, < Length
of Screen or
Permeability
<0.01 Darcy*
Full-Scale Design
and Installation
Figure 1-1. Conceptual decision tree for determining the potential applicability of bioventing at a contaminated site.
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1.1 Existing Data and Site History
Review
The first step in designing and installing a bioventing
system is to review the existing site data. An initial
review of site data provides preliminary information for
determining whether bioventing is a feasible option for
a specific site. Also, the initial data review helps to
identify any additional information that is needed to
complete the bioventing design.
Information to be obtained during the data review, if
possible, should include the following:
• Types of contaminants.
• Quantity and distribution of free product (if present).
• Historical water table levels.
• Three-dimensional distribution of contaminant.
• Potential for a continuing source of contamination
because of leaking pipes or tanks.
• Particle size distribution or soil gas permeability.
• Surface features such as concrete or asphalt.
At this stage, the most important information is type of
contaminant. Bioventing is applicable only to com-
pounds that are biodegraded aerobically, such as petro-
leum hydrocarbons.1 Compounds such as chlorinated
solvents tend to degrade more readily under anaerobic
conditions. In most cases, the contaminant is petroleum
hydrocarbons; however, bioventing also may potentially
be applied at some sites contaminated with both chlo-
rinated solvents and petroleum hydrocarbons.
If significant free product is present, removal must be
addressed either before or simultaneously with
bioventing. Bioventing alone is not sufficient to reme-
diate sites with large quantities of free product. Bios-
lurping technology combines bioventing and free
product removal and is currently under development
by the Air Force (Kittel et al., 1995).
Historical water table levels also are important to deter-
mine whether contamination is available for bioventing
or is present below the water table. If significant con-
tamination is present below the water table, dewatering
may be needed to complete site remediation. At some
sites, bioventing may be feasible only during periods of
seasonal low water tables.
The three-dimensional distribution of the contaminant
provides information necessary for generating an initial
estimate of the screen depths and the size of the
bioventing system that will be required. This initial esti-
mate provides a guideline for conducting the soil gas
1 See Volume I for a discussion of compounds degraded through
bioventing.
survey and for collecting initial soil samples necessary
to estimate the initial mass of contamination at the site.
The potential for a continuing source of contamination
must be addressed at every site. Often, contaminated
sites are created from leaking underground pipes or
tanks. These sources must be eliminated for bioventing
to achieve cleanup.
If available, data on particle size distribution or perme-
ability are useful for determining the potential for apply-
ing bioventing. Because the success of bioventing
depends on the ability to move air through the soil,
particle size or permeability measurements are crucial
parameters. Unless these values are extreme (satu-
rated clay), however, initial treatability studies should be
conducted to determine bioventing applicability.
If surface features such as concrete or asphalt are
present, excavation methods would be too disruptive, so
bioventing is the only cost-effective treatment option
available. If contamination is present beneath buildings,
the bioventing system must be designed to ensure that
contaminants do not rise up into the buildings.
Example 1-1. Review of Existing Data and Site History:
Bioventing is being considered at area of concern (AOC)
A at Keesler Air Force Base (AFB), Mississippi, and the
following information is known:
• The soil was contaminated from leaking underground
gasoline storage tanks.
• Storage tanks were removed in 1991.
• A site map (Figure 1-2) was provided with limited total
petroleum hydrocarbon (TPH) soil sample results.
• The soils are very sandy.
After examining the existing site data, the following con-
clusions are made:
• The type of contaminant is gasoline, a very good
candidate for bioventing. Based on this information,
a soil gas survey is scheduled.
• No information was provided on free product or on
water levels. Given that ground-water monitoring
wells are shown in Figure 1-2, some information
probably exists. Although further attempts will be
made to find the additional information, collection of
free product and water level measurements will also
take place during the soil gas survey phase.
• The quantity of the release is unknown because con-
tamination occurred over a long period; however, the
limited soil sampling provides a general guideline for
the area in which to conduct a soil gas survey.
• The storage tanks were removed, so a continuing
source of contamination is not a factor.
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Scale
0 75 150 Feet
Key
• Monitor Well
T Deep Well
8 Soil Sample After
Tank Removal
Meadows Drive
/^*\
1 Telecom
ding
01
Manhole
No. 5
Q] DW-4
O
£
s
Building
2222
S
M UN
TPH '
(mg/kg)
Sample ID
12 13 14 15 16 17 18
85.6 77.6 - 1030 1010 540
Building
2221
19 20 West North East South
741 814 - 1850 1640 758
Figure 1-2. Site map showing well locations and TPH soil concentrations at AOC A, Keesler AFB, Mississippi.
Particle size distribution was known; soils are sandy,
making this site an excellent candidate for bioventing.
1.2 Soil Gas Survey
At sites where the contamination is at sufficiently shal-
low depths (typically less than 20 ft [6.1 m]), a soil gas
survey should be conducted initially to determine
whether oxygen-limited conditions exist. Oxygen-limited
conditions are a good indicator of whether bacteria are
present that are capable of degrading the contaminants
of concern because soil gas in uncontaminated vadose
zone soils generally exhibits oxygen concentrations
equivalent to ambient air. The soil gas survey also as-
sists in delineating the extent of contamination and lo-
cating suitable areas for vent well and monitoring point
placement. Data on soil gas concentrations of oxygen,
carbon dioxide, and TPH can provide valuable insight
into the extent of subsurface contamination and the
potential for in situ bioventing. The procedures outlined
in this section assist in the collection and interpretation
of soil gas information, with the ultimate goal of promoting
a more cost-effective approach to fuel-contaminated soil
remediation
1.2.1 Soil Gas Chemistry
The chemical composition of soil gas can vary consid-
erably from atmospheric composition as a result of bio-
logical and mineral reactions in the soil. Many
compounds and elements may be present in soil gas
because of site-specific geochemistry, but three indica-
tors are of particular interest for bioventing systems:
respiration gases (oxygen and carbon dioxide) and hy-
drocarbon vapors. The soil gas concentrations of these
indicators in relation to atmospheric air and uncon-
taminated background soils can provide valuable in-
formation on the ongoing natural biodegradation of
hydrocarbon contaminants and the potential for biovent-
ing to enhance the rate of natural biodegradation.
1.2.1.1 Respiration Gases
Oxygen serves as a primary electron acceptor for soil
microorganisms employed in the degradation of both
refined and natural hydrocarbons. Following a hydrocar-
bon spill, if active microbial populations are present, soil
gas oxygen concentrations are usually low (typically
less than 5 percent) and soil gas carbon dioxide (a
metabolite of hydrocarbon degradation) may be high
(typically greater than 10 percent). Oxygen concentra-
tions generally are lower in the vicinity of the contami-
nated soils than in clean soils, indicating that aerobic
biodegradation is depleting oxygen. As the population of
fuel-degrading microorganisms increases, the supply of
soil gas oxygen is often depleted, creating an anaerobic
volume of contaminated soil. Under anaerobic condi-
tions, fuel biodegradation generally proceeds at signifi-
cantly slower rates than when oxygen is available for
metabolism. In some cases, aerobic biodegradation
continues because the diffusion or advection of oxygen
into soils from the atmosphere exceeds biological oxy-
gen utilization rates. Under these circumstances, the
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site is naturally aerated, and the hydrocarbons are natu-
rally attenuated overtime.
Carbon dioxide is produced as a by-product of the com-
plete aerobic biodegradation of hydrocarbons and can
also be produced or buffered by the soil carbonate cycle
(Ong et al., 1991). Carbon dioxide levels in soil gas are
generally elevated in fuel contaminated soils compared
with levels in clean background soils. In many soils,
higher carbon dioxide concentrations correlate with low
oxygen levels; however, this is not always true. Because
of the buffering capacity of alkaline soils, the relationship
between contaminant biodegradation and carbon diox-
ide production is not always a reliable indicator. Carbon
dioxide can form carbonates rather than gaseous carbon
dioxide, particularly in soils with pH over 7.5 and high
reserve alkalinity. In acidic soils, such as exist at Tyndall
AFB, Florida, carbon dioxide production is directly pro-
portional to oxygen utilization (Miller and Hinchee,
1990).
Soil gas survey results in a contaminated area should
be compared with those obtained from an uncontami-
nated area. Typically, soil gas concentrations in an un-
contaminated area are significantly different, with
oxygen concentrations approximately equal to ambient
concentrations and very low carbon dioxide (less than
0.5 percent).
1.2.1.2 Hydrocarbon Vapors
Volatile hydrocarbons found in soil gas can also provide
valuable information on the extent and magnitude of
subsurface contamination. Fuels such as gasoline,
which contain a significant fraction of C6 and lighter
compounds, are easily detected using soil gas monitor-
ing techniques. Heavier fuels, such as diesel, contain
fewer volatiles and are more difficult to locate based on
volatile hydrocarbon monitoring. Methane is frequently
produced as a by-product of anaerobic biodegradation
and, like oxygen depletion, has been used to locate the
most contaminated soils at a site. Extensive literature is
available on soil gas survey techniques for using volatile
hydrocarbons as indicators of contamination (Rivett and
Cherry, 1991; Downey and Hall, 1994).
7.2.2 Collection and Analysis of Soil Gas
Samples
This section describes the test equipment and methods
used to conduct field soil gas surveys, to monitor soil
gas for bioventing systems, and to install temporary soil
gas monitoring points. The procedures and equipment
described in this section are only guidelines. Because
of widely varying site conditions, site-specific applica-
tions are necessary. In some regulatory jurisdictions, soil
gas survey monitoring points must comply with well
installation or other regulations.
Whenever possible, soil gas surveys should be con-
ducted at potential bioventing sites before locating the
pilot test vent well(s) and monitoring points. The soil gas
survey is used to determine the necessity of bioventing
whether anaerobic soil gas conditions exist and by pro-
viding an initial indication of the extent of contamination.
If sufficient oxygen is naturally available and distributed
throughout the subsurface, bioventing may not enhance
biodegradation rates. The soil gas survey can also help
to determine the areal extent and, in the case of shallow
contamination, the vertical extent of soil contamination.
Information about contaminant distribution helps to lo-
cate the vent well and soil gas monitoring points and to
determine the optimum depths of screened intervals.
The soil gas survey points should be arranged in a grid
pattern centered on the known or suspected contami-
nated area. The soil gas probes are positioned at each
grid intersection, and the survey begins near the center
of the grid and progresses outward to the limits of sig-
nificant detectable soil contamination. At times, soil gas
measurements are taken at several depths at each lo-
cation to determine the vertical distribution of contami-
nation and oxygen supply. At shallow sites, a soil gas
sampling grid should be completed with samples col-
lected from multiple depths if the contaminated interval
exceeds 3 ft (0.91 m) or if contamination is suspected in
different soil types.
A soil gas survey can be conducted using small-diame-
ter (typically 5/8- to 1-in. [1.6- to 2.5-cm] outside
diameter steel probes. The typical probe consists of a
drive point with a perforated tip that is threaded onto a
series of drive rod extensions. Figure 1-3 shows a typi-
cal setup for monitoring soil gas.2
Soil conditions and depth of contamination dictate the
method of probe installation. Utility clearances from the
local utility companies and digging permits (required at
2 See Appendix B for recommended specifications and manufacturers
for soil gas sampling equipment.
Male Quick Couple
Female Quick Couple
^Tubing
- Soil Probe
Figure 1-3. Schematic of a soil gas sampling system using the
stainless steel soil gas probe.
-------
military installations) should be obtained before probe
installation. Temporary probes are installed using either
a handheld electric hammer or a hydraulic ram. The
maximum depth for hammer-driven probes is typically
10 ft to 15 ft (3 m to 4.6 m), depending on soil texture.
Hydraulic rams are capable of driving the probes over
30 ft (9.1 m) in a variety of soil conditions. If hydraulic
rams are not sufficient, aGeoProbeorsimilarequipment
can be used and also can collect soil samples.
At sites with deeper contamination, where soil texture
precludes the use of a hammer or hydraulic ram or
where a permanent monitoring system is required, per-
manent soil gas monitoring points may be installed us-
ing either a portable or a truck-mounted drill rig.
Gaseous concentrations of carbon dioxide and oxygen
can be analyzed using an oxygen/carbon dioxide ana-
lyzer. The analyzer generally has an internal, battery-
powered sampling pump and range settings of 0 percent
to 25 percent for both oxygen and carbon dioxide. Be-
fore taking measurements, the analyzer should be
checked for battery charge level; it should also be cali-
brated daily using atmospheric concentrations of oxy-
gen and carbon dioxide (20.9 percent and 0.05 percent,
respectively) and a gas standard containing 0.0 percent
oxygen and 5.0 percent carbon dioxide, and 95 percent
nitrogen.
Several types of instruments are available for field
measurement of TPH concentrations in air. The selected
instrument must be able to measure hydrocarbon con-
centrations in the range of 1 to 10,000 parts per million,
volume per volume (ppmv) and be able to distinguish
between methane and nonmethane hydrocarbons.
Flame ionization detectors are the most accurate field
screening instruments for fuel hydrocarbons. Instru-
ments using a platinum catalyst detector system are
also acceptable and are easier to use in the field. Pho-
toionization detectors are not recommended for the high
levels of volatile hydrocarbons found at many sites.
Before taking measurements with any field instrument,
the battery charge level should be checked and the
analyzer should be calibrated against a hexane calibra-
tion gas to ensure proper operation.
The analyzer should also have a selector switch to
change the response to eliminate the contribution of
methane gas to the TPH readings. Methane gas is a
common constituent of anaerobic soil gas and is gener-
ated by degrading manmade hydrocarbons or natural
organics. Methane is commonly produced in swampy
areas or in fill areas containing organic material. If meth-
ane is not excluded from the TPH measurement, TPH
results may indicate erroneously high levels of petro-
leum hydrocarbon contamination in the soil. The methane
content can also be estimated by placing a large carbon
trap in front of the hydrocarbon analyzer. The carbon
retains the heavier hydrocarbons, while methane and
other lighter molecular weight hydrocarbons pass
through to the detector.
Electric motor-driven sampling pumps are used to purge
and collect samples from monitoring points and soil gas
probes. The pumps should be either oil-less rotary-vane
or diaphragm pumps capable of delivering approxi-
mately 1 cubic ft per minute (cfm) (28 L/min) of air at a
maximum vacuum of 270"H2O (6.7 x 104 Pa). The
pumps have oil-less filters to eliminate particulates from
the air stream. Low-flow, battery-operated pumps may
be favored in high-permeability soils to minimize short-
circuiting.
Differential vacuum gauges are used to monitor the
vacuum in the sampling point during purging and as an
indicator of relative permeability. Typical vacuum ranges
of the gauges are 0 to 50"H2O (0 to 1.2 x 104 Pa) and 0
to 250"H2O (6.2 x 104 Pa) for sites with sandy and clayey
soils, respectively.
Purging the soil gas probe is a prerequisite for obtaining
representative soil gas samples. A typical purging sys-
tem consists of a 1-cfm (28-L/min) sampling pump, a
vacuum gauge, and an oxygen/carbon dioxide meter.
The vacuum side of the pump is connected to the soil
gas probe. A vacuum gauge is attached to a tee in the
vacuum side of the system to monitor the vacuum pro-
duced during purging, and the oxygen/carbon dioxide
analyzer is connected to a tee in the outlet tubing to
monitor oxygen/carbon dioxide concentrations in the
extracted soil gas. The magnitude of vacuum measured
during purging is inversely proportional to soil perme-
ability and determines the method of sample collection.
After the purging system is attached to the soil gas
probe or monitoring point, the valve or hose clamp is
opened and the pump is turned on. Purging continues
until oxygen and carbon dioxide concentrations stabi-
lize, indicating the purging is complete. Before turning
off the pump, a hose clamp or valve is used to close the
sampling tubing to prevent fresh air from being drawn
into the soil gas probe.
Sampling methods for high-permeability soils (sand and
silt) should be followed if the vacuum measured during
purging is less than 10"H2O (2.5 x 103 Pa). Soil gas
sampling and analysis are performed using the same
equipment used for purging, minus the vacuum gauge.
After opening the sampling point valve or hose clamp,
the sampling pump is turned on, and the extracted soil
gas is analyzed for stable oxygen/carbon dioxide and
TPH concentrations.
Adifferent sampling procedure can be followed to collect
soil gas samples from low-permeability soils. The higher
vacuums required for sampling increase the risk of vac-
uum leaks introducing fresh air and diluting the soil gas
sample. One method that may be used in low-perme-
ability soils is described below.
-------
After purging the sampling point, a soil gas sample is
collected in a Tedlar bag before analysis. The evacuated
Tedlar bag should be placed inside an airtight chamber.
The chamber is then connected to the sampling point
via a hose barb that passes through the chamber wall.
The chamber is then closed, sealed, and connected to
the pump inlet with flexible tubing. The sampling system
is shown in Figure 1-4. To collect the sample, the moni-
toring point valve is opened, the pump is turned on, and
the pressure relief port on the chamber is sealed using
either a valve orthe sampler's finger. The partial vacuum
within the chamber created by the pump draws soil gas
into the Tedlar bag. When the Tedlar bag is nearly filled,
the sampling point valve or hose clamp is closed, and
the pump is turned off. The chamber is then opened, the
Tedlar bag valve is closed, and the bag is removed from
the chamber. The soil gas sample is then analyzed by
attaching the oxygen/carbon dioxide and TPH analyzers
directly to the Tedlar bag. The advantage of this method
is that the sampling pump is no longer in line, thereby
minimizing the sampling train and subsequent sample
dilution.
Most problems encountered during soil gas sampling
and purging can be divided into three categories: (1)
difficulty extracting soil gas from the sampling point, (2)
water being drawn from the sampling point, and (3) high
oxygen readings in areas of known soil contamination.
Some of the more common problems and solutions are
discussed below.
Difficulty extracting soil gas from a sampling point is
typically caused by low-permeability (clayey and/or
nearly saturated) soils. Collecting soil gas samples from
low-permeability soils is facilitated by slowing the soil
gas extraction rate, which allows the use of less vac-
uum. Difficulty extracting soil gas from a soil gas probe
can also be caused by the screen being fouled by
fine-grained soil or heavy petroleum residuals. The
probe should be removed from the soil, and the screen
should be either cleaned or replaced if visibly fouled.
Water being drawn from the sampling point by the purge
pump may be the result either of the point being installed
in the saturated zone or, in the case of permanent
monitoring points, the filter pack being saturated with
water during construction. In the former case, a tempo-
rary probe can be pulled up to a shallower depth above
the saturated zone and resampled. With a permanent
monitoring point installed within the saturated zone,
sampling must be delayed until either the water table
drops because of seasonal variations orthe water table
is artificially depressed by a dewatering operation.
If the screened interval in a permanent monitoring point
is installed above the saturated zone but the filter pack
was saturated with water during construction, sampling
may still be possible if the water is pumped from the
monitoring point. This method will only work if the
screened interval is at a depth of less than approxi-
mately 22 ft (6.7 m), which is the practical limit of suction
lift.
Tubing
Pressure Relief
Port
Vacuum Desiccator
Tedlar Sample Bag
(inside Desiccator)
Outlet
Land Surface
1/8" Flexible Tubing
Soil Probe Extensions
T
V
Soil Probe Drive Tip
Figure 1-4. Schematic of a soil gas sampling system for collection of soil gas from low-permeability soils.
-------
Water also may be drawn into the point in unsaturated
soils as the result of the creation of a vacuum in excess
of capillary pressure. In this case, the extracted flow
typically is a mixture of water and soil gas. Frequently,
a water trap before the sampling pump can be used to
remove the water; thus, collecting and analyzing a soil
gas sample is still possible.
High soil gas oxygen readings in areas of known soil
contamination may indicate a leak in the sampling or
purging system. The potential for leakage, and the re-
sulting dilution of the sample with atmospheric air, is
higher in low-permeability soils where higher vacuums
are required for purging and sampling. If a leak is sus-
pected, all connections in the sampling system and the
seal around the monitoring point or soil gas probe
should be inspected for leaks. Seals around a soil gas
probe or monitoring point can be checked for leaks by
inspecting for air bubbles while injecting air with a sam-
pling pump after adding water around the probe or moni-
toring point. Any observed or suspected leaks should be
corrected by tightening connections, repositioning the
soil gas probe, or attempting to repair the monitoring
point seal.
1.2.3 Interpretation of Soil Gas Survey
Results
The purpose of gathering soil gas data during bioventing
investigations is to locate areas where addition of oxy-
gen will most efficiently enhance fuel biodegradation.
Low soil gas oxygen concentrations are a preliminary
indication that bioventing may be feasible at the site, so
proceeding to in situ respiration testing is appropriate. If
soil gas oxygen concentrations are high (greater than 5
percent to 10 percent), yet contamination is present,
other factors may be limiting biodegradation. The most
common limiting factor is low moisture level. If a pilot
test is to be completed, the soil gas survey should focus
on locating areas with the lowest oxygen concentra-
tions. For full-scale applications, it is useful to determine
the entire areal extent and depth of soils with an oxygen
deficit (for practical purposes, less than 5 percent oxygen).
In very shallow, permeable soils, diffusion, biometric
pumping, or water table fluctuations may enhance air
movement into the soil and provide a natural oxygen
supply.3 Soil gas data are useful for determining which
sites are naturally aerated and therefore do not require
mechanical bioventing systems.
If high oxygen concentrations are observed on the site,
the existence of significant contamination should be
questioned. Lower levels of contamination (e.g., less
than 1,000 mg/kg TPH) could potentially be biodegraded
3 See Volume I for a discussion of factors affecting the bioventing
process.
by the natural oxygen supply, and no active remediation
would be necessary. If higher levels of hydrocarbons are
present (above 1,000 mg/kg), the natural oxygen supply
will likely be inadequate to sustain biodegradation and,
more likely, some other factor is limiting. In the authors'
experience, soil containing both high oxygen and high
hydrocarbon concentrations only occurs at moisture-lim-
ited sites (the most common case) or sites with toxicity
problems (trichloroethylene [TCE] in one case and phe-
nolics in another). In only two cases familiar to the
authors, these factors could not explain the lack of
oxygen utilization. This occurred at a JP-5 jet fuel site
on Fallen Naval Air Station (MAS) in Nevada and a JP-4
Spill Site at Davis-Monthan AFB in Arizona. The problem
sites are not moisture limited; however, no clear expla-
nation has arisen to date (Engineering-Science, 1994;
Kittel et al., 1995). A series of examples of soil gas
survey results and an interpretation of the data are
presented here to illustrate the principles discussed in
this section.
Example 1-2. Soil Gas Survey Conducted at Keesler
AFB: At the site described in Example 1-1, a soil gas
survey was conducted. First, depth to ground water and
free product thickness were measured at all of the
ground-water monitoring wells (MWs). Ground-water
depths were as follows: MW8-1 at 6.8 ft (2.1 m), MW8-2
at 8.0 ft (2.4 m), MW8-3 at 8.2 ft (2.5 m), and MW8-11
at 8.25 ft (2.5 m). No free product was detected in any
of the wells, so free product removal was not a factor at
this site.
A limited soil gas survey was conducted because the
area of contamination had recently been defined. Soil
gas samples were collected at depths ranging from 2 ft
to 6 ft (.61 m to 1.8 m). Because ground water was
measured at 6.8 ft (2.1 m), soil gas probes were not
driven deeper.
Results from this survey are shown in Table 1-1. At most
locations, oxygen was limiting, with concentrations less
than 5 percent, and carbon dioxide and TPH concentra-
tions were relatively high. The exception was at location
SGS-D-6.0'. At this point, oxygen was measured at 20.1
percent, carbon dioxide at 0.1 percent, and TPH at 120
ppm. These levels were more representative of ambient
air than of the soil gas concentrations measured at other
points at the site, indicating that significant dilution of this
sample may have occurred. Because of these measure-
ments, the sampling pump was thoroughly examined
and loose connections were tightened. Upon resam-
pling, soil gas concentrations were more representative
of other soil gas concentrations. If resampling were to
give the same initial results, it could be possible that this
monitoring point was plugged, causing the sampling
train to leak, and/or atmospheric air was short circuiting
-------
Table 1-1. Results From a Soil Gas Survey at AOC A, Keesler
AFB, Mississippi
Soil Gas
Survey Point
SGS-A
SGS-B
SGS-C
SGS-D
Depth (ft)
2.0
4.0
6.0
2.0
4.0
6.0
2.0
4.0
6.0
2.0
4.0
6.0
6.0
Oxygen
(%)
4.8
0.3
0.5
1.5
0.5
0.9
0.4
0.8
0.4
0.4
0.3
20.1
0.4
SOS = Soil gas survey.
to the point. In either case, results
be discarded as invalid.
Carbon
Dioxide
(%)
9.8
12
11
12
12
12
11
11
11
11
11
0.1
11
from this
TPH (ppmv)
>1 00,000
>1 00,000
>1 00,000
>1 00,000
>1 00,000
>1 00,000
28,000
30,000
32,000
47,000
56,000
120
60,000
point should
Table 1-2. Results From a Soil Gas Survey at Building 1813,
Hanscom AFB, Massachusetts
Soil Gas
Survey
Point
PT1
PT2
PT3
PT4
PT6
PT7
PT8
Depth
(ft)
3.0
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
7.0
6.0
8.0
Oxygen
(%)
20.5
20.5
20.6
19.0
19.0
19.2
19.0
20.5
20.5
20.0
19.8
19.0
19.5
20.5
Carbon
Dioxide
(%)
0.8
1.0
0.5
2.0
2.0
2.2
2.4
0.8
0.8
0.5
1.5
1.0
1.5
0.5
TPH
(ppmv)
62
60
42
80
78
80
93
46
44
82
61
70
60
48
Results of this soil gas survey indicate that this site is
an excellent candidate for bioventing.
Example 1-3. Soil Gas Survey at Building 1813, Han-
scom AFB, Massachusetts: This site comprises an un-
derground storage tank (UST) containing diesel fuel that
had leaked. The tank was removed, but an unknown
quantity of fuel-contaminated soil remained at the site.
Site soils are sandy to ground water, which occurred at
8 ft to 9 ft (2.4 m to 2.7 m).
A soil gas survey was conducted at seven locations and
at multiple depths. Soil gas results are presented in
Table 1-2.
Low levels of TPH indicate that little diesel-contami-
nated soil remained at the site or that residual fuels were
highly weathered. Near-atmospheric oxygen levels at all
depths indicated that remaining hydrocarbons were be-
ing biodegraded with oxygen supplied by natural diffu-
sion. Carbon dioxide was found at levels above the
atmospheric concentration of 0.03 percent, indicating
some biological respiration was occurring. Higher carb-
on dioxide levels and slightly depressed oxygen levels
at point 3 (PT3) and PT4 indicated remaining fuel was
probably located in this area of the site. Natural aeration
appeared to provide sufficient oxygen for biodegrada-
tion of remaining fuel residuals.
Example 1-4. Soil Gas Survey at the Aquasystem Site,
Westover AFB, Massachusetts: This site consisted of
USTs that, when removed, revealed soil contamination.
An unknown quantity of mixed fuels contamination re-
mained in the soil. Site soils were predominantly sand,
with ground water at approximately 13 ft (4.0 m) below
the surface.
A soil gas survey consisting of a 12-point grid was
completed in and downgradient of the former tank pit.
All points were sampled at multiple depths. Results of
the survey are provided in Table 1-3.
Low levels of TPH were detected in the soil gas at this
site. Oxygen levels were significantly depleted below
atmospheric concentrations in soils near PT7 and
PT17, and generally decreased with depth. The 8
percent to 9 percent of oxygen available in this area,
however, was more than sufficient to sustain in situ
biodegradation. Carbon dioxide ranged from 2 per-
cent to 8.5 percent and generally increased with
depth. The available data suggested that significant
natural biodegradation was occurring at the site. More
oxygen-depleted soil might exist in the capillary fringe,
and engineered bioventing could accelerate biodegra-
dation if this anaerobic zone exists. The decision to
biovent this site should be based on other factors,
such as the impact and potential risk that soil contami-
nation poses to ground water.
-------
Table 1-3.
Soil Gas
Survey
Point
PT1
PT2
PT3
PT4
PT5
PT7
PT8
PT9
PT11
PT12
PT16
PT17
Example
Results from a Soil Gas Survey at the
Site, Westover
Depth
(ft)
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
3.0
6.0
9.0
12.0
6.0
7.5
6.0
9.0
1-5. Soil Gas
Aquasystem
AFB, Massachusetts
Oxygen
(%)
16
12.5
15.5
13
18
12
16
11.5
14.8
11
14
8.5
12
11
11.5
11
16
15
18.5
15.5
15
13
17
13
11.8
11
Survey at an
Carbon
Dioxide
(%)
3.2
5
4.3
6
2.6
6.2
4
5
4
5.2
7
8.5
5.5
6.5
6
6.2
3.5
4
2.5
4.2
4.8
5.6
2
3.5
6.5
6.5
TPH
(ppmv)
60
60
72
74
74
84
86
80
76
72
105
69
75
76
90
78
84
94
80
91
90
92
94
80
92
96
Oil/Water Separator
Table 1-4. Results From a Soil Gas Survey at an Oil/Water
Leak at Cape Canaveral AFS, Florida
Soil Gas Carbon
Survey Depth Oxygen Dioxide TPH
Point (ft) (%) (%) (ppmv)
PT1 2.5 15.5 4.0 82
5.5 12.5 6.0 82
PT2 2.5 14.0 5.0 76
5.5 5.5 9.5 77
PT3 2.5 13.0 5.5 73
5.5 10.0 7.0 75
PT4 2.5 19.0 2.0 60
5.5 18.5 2.5 66
PT5 2.5 19.5 1.0 57
5.5 19.0 2.0 60
PT6 2.5 18.5 2.5 64
5.5 17.5 3.0 74
PT7 2.5 20.0 1.0 36
5.5 20.0 1.0 35
PT8 2.5 20.5 0.5 34
5.5 20.2 0.8 43
biodegradation was proceeding in the vicinity of the
oil/water separator. More oxygen-depleted soil might
exist in the capillary fringe, and engineered bioventing
could accelerate biodegradation, if this anaerobic zone
exists. The decision to biovent this site should be based
on other factors, such as the impact and potential risk
that soil contamination poses to ground water. One ad-
ditional note: if the oil/water separator were connected
to a sanitary line, the biological oxygen demand might
be the result of leaking sewage. An analysis of soil gas
for benzene, toluene, ethylbenzene, and total xylenes
(BTEX) could help to determine if the oxygen demand
were fuel related.
Leak at Cape Canaveral AFS, Florida: This site con-
sisted of an oil/water separator leak located near a
diesel transfer station at Cape Canaveral AFS, Florida.
Site soils consisted of sandy soil with shell fragments.
Ground water was approximately 6 ft (1.8 m) below the
surface.
A soil gas survey was conducted at eight locations. An
attempt was made to sample soil gas at two depths. Soil
gas results are presented in Table 1-4.
Low levels of TPH indicate that little diesel-contami-
nated soil remained at the site or it was highly weath-
ered. Oxygen levels were significantly depleted near
PT2 and generally decreased with depth in points near
the oil/water separator. Carbon dioxide levels were ele-
vated in areas with low oxygen, indicating that in situ
1.3 Soil Characterization
Soil characterization is a crucial component of the site
characterization process. Of primary importance is deter-
mining the concentration and distribution of contaminants.
Because of large variations in the distribution of contami-
nants at a site, a relatively large number of soil samples
must be collected to adequately delineate the vertical and
lateral extent of contamination. Described in the following
sections are techniques for locating and drilling soil bor-
ings.4 The soil analytical protocol is also discussed.
4 See Appendix B for recommended specifications and manufacturers
for the soil sampling equipment.
-------
1.3.1 Soil Borings
Soil borings should be located based on either the re-
view of existing site data or the results of the soil gas
survey. Soil borings can serve two purposes: the collec-
tion of soil samples and the installation of vent wells and
monitoring points. Soil borings have the advantage of
allowing for collection of many soil samples from a single
location and allowing for subsequent installation of the
vent wells and monitoring points in the borings. Disad-
vantages include the generation of soil cuttings and the
fact that drilling may require subcontracting and a large
amount of time. Alternative methods, such as a Geo-
Probe system or cone penetrometer, may be used for
collection of soil samples and may be suitable for install-
ing soil gas monitoring points.
The hollow-stem auger method is generally preferred for
drilling in unconsolidated soils; however, a solid-stem
auger also is acceptable in more cohesive soils. The
final diameter of the borehole depends on the diameter
selected for the vent wells but typically should be at least
two times greater than the vent well's outside diameter.
All drilling and sample collection activities should be
observed and recorded on a geologic boring log (Figure
1-5) to record soil sample interval, sample recovery,
visual presence (or absence) of contamination, soil de-
scription, and lithology. Soil samples should be labeled
and properly stored immediately after collection. An ex-
ample procedure for soil sample collection, labeling,
packing, and shipping is provided in Appendix C.
All boreholes should preferably be completed as vent
wells or monitoring points. If this is not possible, bore-
holes must be abandoned according to applicable state
or federal regulations. Typically, borehole abandonment
is accomplished by backfilling with bentonite or grout.
Battelle Soil Boring Information
Client:
Project:
Size:
Site Information
Elevation Datum :
Elevation (Ground
Surface (OS)) (ft):
Elevation (Top of
Casing (TOC)) (ft):
Date Start:
Date Finished:
Driller:
Notes by:
Comments:
Groundwater Readings
Well I.D.
Date
Time
Depth to
Water (ft)
Depth to
Product (ft)
Well Pipe: Type Diameter (in) Slot Size (in)
Pro. Casing: Type Diameter (in) key: Y/N
Depth
(Ft. & Tenths,
e.g. 10.2-)
Sample
No. &
Label
TPH
ODOR
(Y/N)
Sample
Describtion
VW/MP X-Section
Sketch
Figure 1-5. Sample soil boring log.
10
-------
1.3.2 SoilAnalyses
A summary of soil analyses is provided in Table 1-5.
Methods in this table are not the only methods available
but are those currently used by the Air Force currently
uses. Based on results from the Bioventing Initiative,
recommended parameters to be measured include the
aromatic hydrocarbons (BTEX), TPH, moisture content,
and particle size. Total Kjeldahl nitrogen (TKN) was
found to be a statistically significant factor in the statis-
tical analyses of Bioventing Initiative data;5 however, no
evidence exists to date that addition of nitrogen en-
hances site remediation. Therefore, an analysis for TKN
is only recommended if all other explanations for poor
bioventing performance have been exhausted (i.e., per-
meability, moisture content).
Measurements of BTEX and TPH are necessary for
delineation of the contaminant plume. In addition, BTEX
and TPH typically are of regulatory concern; therefore,
these concentrations must be established.
Moisture content has been found to limit biodegradation
in extreme environments. At a site in California, moisture
content averaged approximately 2 percent and irrigation
substantially improved biodegradation rates.6
TKN is a nutrient required for microbial growth and
respiration. Low TKN levels may affect microbial respi-
ration; however, although a statistically significant rela-
tionship has been observed between TKN and oxygen
utilization rates, the relationship is weak and unlikely to
have practical significance.
Particle size distribution is an important indicator of
permeability. High clay content soils may be difficult to
5 See Chapters of Volume I fora discussion of the statistical analyses
of Bioventing Initiative data.
6 See Section 3.2.2.2 of Volume I for a discussion of this site.
Table 1-5. Soil Analyses3 Based on Bioventing Initiative Results
biovent because of the inability to move air through the
soil, particularly when high moisture levels exist. In ad-
dition, clay particles can be sites of significant contami-
nant adsorption and as such can significantly affect
contaminant sorption and bioavailability.
1.4 In Situ Respiration Testing
The in situ respiration test was developed to provide
rapid field measurement of in situ biodegradation rates
to determine the potential applicability of bioventing at a
contaminated site and to provide information for a full-
scale bioventing system design. This section describes
the test as developed by Hinchee and Ong (1992). This
respiration test has been used at numerous sites
throughout the United States, including all Bioventing
Initiative sites. The in situ respiration test described in
this document is essentially the same, with minor modi-
fications.
1.4.1 In Situ Respiration Test Procedures
The in situ respiration test consists of placing narrowly
screened soil gas monitoring points into the unsaturated
zone of contaminated soils and venting these soils with
air containing an inert tracer gas (typically helium) for a
given period. The apparatus for the respiration test is
illustrated in Figure 1-6.7 An example procedure for
conducting an in situ respiration test is provided in Ap-
pendix C.
As part of the Bioventing Initiative, respiration rates in
uncontaminated areas of similar geology to the contami-
nated test site were evaluated. These results showed
that measurement of background respiration rates was
not necessary because little significant respiration had
7 See Appendix B for recommended specifications and manufacturers
for the in situ respiration testing equipment.
Analysis
Aromatic
Method Comments
Purge and trap GC Handbook method
Sample Volume, Container,
Preservation
Collect 100 g of soil in a glass
Field or Analytical
Laboratory
Analytical laboratory
TPH
Moisture content
TKNa
Modified GC method
SW8015
ASTM D-2216
EPA 351.4
Handbook method;
reference is the California
LUFTC manual
Handbook method
Handbook method
container with Teflon-lined cap or
in brass sleeves'3; cool to 4°C
Collect 100 g of soil in a glass
container with Teflon-lined cap or
in brass sleeves'3; cool to 4°C
Collect in a 4-oz glass container
with Teflon-lined cap
Collect in a 4-oz glass container
with Teflon-lined cap
Analytical laboratory
Analytical laboratory
Analytical laboratory
a Recommended soil analysis is based on experience and analyses of petroleum-contaminated sites. Additional data may be required at sites
contaminated with other compounds.
b One sample in the brass sleeves provides sufficient volume for analyses of both aromatic hydrocarbons and TPH.
c LUFT = State of California Leaking Underground Fuel Tank Field Manual, 1988 edition.
d Not recommended for an initial analysis but only if bioventing performance is poor and other factors such as permeability and moisture content
do not account for the poor performance.
11
-------
Pressure
Gage
^_ 9 ri
TV
\^ J Source
i
.
\
3-Way Valving [
Gas Sampling ^
K""~ Port f
] Rotometer
Ground Surface \^
•* Small Diameter
Tubing
<- — Screen
1
/
J Rotometer
-------
These terms may be derived through either direct meas-
urement or estimation. The oxygen utilization rate, ko, is
directly measured in the in situ respiration test. The ratio
of hydrocarbons to oxygen required for mineralization,
C, can be calculated based upon stoichiometry (see
Equation 1-1 for hexane) but generally falls between
0.29 and 0.33. This neglects any conversion to biomass,
which probably is small and difficult, if not impossible, to
measure. The density of oxygen may be obtained from
a handbook for a given temperature and pressure, or
calculated from the ideal gas law. Table 1-6 provides
some useful oxygen density information. The bulk den-
sity of soil is difficult to measure accurately because of
the difficulty in collecting an undisturbed sample; how-
ever, it may be reasonably estimated from the literature.
Table 1-7 lists useful literature values for bulk density.
The gas-filled porosity, 9a, is the single parameter in
Equation 1-2 with the most variability. Theoretically, it
can be related to the total porosity, soil bulk density, and
moisture content. A doubling of the air-filled porosity
results in a doubling of the estimated hydrocarbon
degradation rate. Gas-filled porosity may be as high as
Table 1-6. Oxygen Density Versus Temperature
Temperature Temperature Density Density
(°C) (°F) (mg/L)a (Ib/ft3)a
-33 -27.4 1,627b 0.1 Ob
-3 26.6 1,446C 0.090C
0 32 1,429C 0.089C
5 41 1,403C 0.088C
10 50 1,378C 0.086C
15 59 1,354C 0.084C
20 68 1,331C 0.083C
27 80.6 1,301b 0.082b
30 86 1,287C 0.080C
35 95 1,266C 0.079C
40 104 1,246C 0.078C
57 134.6 1,1 82b 0.074b
87 188.6 1,083b 0.067b
127 260.0 975b 0.061 b
Table 1-7. Bulk Density of Various Soils"
Soil Bulk Density
PK
Soil Description Porosity (dry g/cm )
Uniform sand, loose 0.46 1.43
Uniform sand, dense 0.34 1.75
Mixed-grain sand, loose 0.40 1 .59
Mixed-grain sand, dense 0.30 1 .86
Windblown silt (loess) 0.50 1 .36
Glacial till, very mixed-grained 0.20 2.12
Soft glacial clay 0.55 1.22
Stiff glacial clay 0.37 1 .70
Soft slightly organic clay 0.66 0.93
Soft very organic clay 0.75 0.68
Soft montmorillonitic clay 0.84 0.43
(calcium bentonite)
aFrom Pecketal. (1962).
0.5 to 0.6 in some very dry clays and is zero in saturated
soil. To collect soil gas samples, the gas-filled porosity
must be sufficient to allow gas flow. Therefore, an in situ
respiration test could be conducted at very low gas-filled
porosity. At most bioventing sites, 9a ranges from 0.1 to
0.4. Soil in a core or split spoon sample will be com-
pressed, thereby reducing 9a. It can be estimated as
follows:
9a = 9-9w (Eq. 1-3)
where:
9 = total porosity (cm3/cm3)
9W = water-filled porosity (cm3/cm3)
The total void volume may be estimated as:
e-^P* (Eq. 1-4)
PT
where:
pk = soil bulk density (g dry soil/cm3) (from
a Oxygen density at standard pressure.
b Density values from Braker and Mossmon (1980).
c Density calculated using the second viral coefficient to the equation
of state for oxygen gas:
v
v
where P = pressure (atm), R = gas constant, V = molar volume,
and B = second viral coefficient. The temperature dependence of
B was calculated from:
The constants A' were obtained from Lide and Kehianian (1994).
Table 1-7)
pT = soil mineral density (g/cm3), estimated at
2.65
The water-filled void volume then can be calculated as:
a _ iwi -PA (Eq. 1-5)
PT
where:
M = soil moisture (g moisture/g soil)
13
-------
Because the water-filled porosity (9W) is a difficult pa-
rameter to estimate accurately, an assumption is fre-
quently made of 0.2 or 0.3.
Using several assumptions, values for 9a, po2, C, and
pk can be calculated and substituted into Equation 1-2.
Assumptions used for these calculations are:
• Gas-filled porosity (9a) of 0.25.
• Soil bulk density (p^ of 1.4 g/cm.
• Oxygen density (p02) of 1,330 mg/L.
• C, hydrocarbon-to-oxygen ratio of 0.29 from Equation
1-1 for hexane.
The resulting equation is:
kR =
- (k0) (0.25) (1,330) (0.29) (0.01)
14
= -0.68 k0
(Eq. 1-6)
The biodegradation rates measured by the in situ respi-
ration test appear to be representative of those for a
full-scale bioventing system. Miller (1990) conducted a
9-month bioventing pilot project at Tyndall AFB at the
same time Hinchee et al. (1991 a) conducted an in situ
respiration test. The oxygen utilization rates (Miller,
1990) measured from nearby active treatment areas
were virtually identical to those measured in the in situ
respiration test. Oxygen utilization rates greater than 1.0
percent/day are a good indicator that bioventing may be
feasible at the site and proceeding to soil gas perme-
ability testing is appropriate. If oxygen utilization rates
are less than 1.0 percent/day, yet significant contamina-
tion is present, other factors may be involved in limiting
biodegradation. In this case, other process variables, as
discussed in Section 3.3, should be considered as lim-
iting biodegradation. Identifying these other process
variables may require additional soil sampling and
analysis. If none of these other process variables can
be identified as potentially limiting microbial degrada-
tion, alternative technologies may have to be employed
for site remediation.
Example 1-6. Results From an in Situ Respiration Test
Conducted at Keesler AFB: At the site described in
Example 1-1, an in situ respiration test was conducted.
After the soil gas survey, three-level monitoring points
were installed at each soil gas survey point location
because these areas were highly contaminated and
were oxygen-limited. Initial soil gas readings were taken
at each monitoring point and are shown in Table 1-8.
Because all locations were oxygen-limited, a decision
was made to inject air at the deepest level of each
monitoring point (MP) (K1-MPA-7.0', K1-MPB-7.0', K1-
MPC-7.0', and K1-MPD-7'1").
Table 1-9 contains data collected at each monitoring
point during the in situ respiration test. The oxygen
utilization rate is determined as the slope of the percent
Table 1-8. Initial Soil Gas Readings at Monitoring Points at
AOC A, Keesler AFB, Mississippi
Monitoring
Point
K1-MPA
K1-MPB
K1-MPC
K1-MPD
Background
Table 1-9.
Time
(hr)
0
5
10
25
37
50
75
99
Time
(hr)
0
5
10
25
37
50
75
99
Carbon
Depth Oxygen Dioxide
(ft) (%) (%)
3.0
5.0
7.0
2.5
4.0
7.0
3.0
5.0
7.0
3.0
5.0
7'1"
Raw Data From
AOC A, Keesler
K1-MPA-5.0'
O2 CO2
20.7 0
20.6 0
20.1 0.1
19.0 0
17.8 0
16.9 0.6
15.2 1.2
14.0 2.0
K1-MPB-5.0'
20.6 0
20.2 0
19.4 0
16.9 0
14.8 0
12.9 1.0
9.9 2.6
8.0 3.0
0.1
0.4
0.6
0.5
0.5
0.8
0.4
0.1
0.5
0.6
0.5
0.5
16.8
an in
AFB,
He
1.4
1.6
1.4
1.75
1.4
1.4
1.6
1.4
1.6
1.8
14
1.6
1.4
1.4
1.2
1.2
16
15
15
15
15
15
14
15
15
14
15
15
4.6
TPH
(ppmv)
>1 00,000
>1 00,000
>1 00,000
>1 00,000
>1 00,000
>1 00,000
28,000
30,000
29,000
45,000
54,000
58,000
140
Situ Respiration Test at
Mississippi
K1-MPA-7
O2 CO2
20.5 0
20.6 0
20.3 0.1
20.1 0
19.5 0
18.7 0.2
17.3 1.2
16.3 1.2
K1-MPC-7
20.8 0
20.5 0.2
20.2 0.2
19.5 0
18.1 0.6
16.9 1.5
13.9 3.0
11.0 4.0
.0'
He
1.4
1.4
1.4
1.6
1.4
1.25
1.6
1.4
.0'
1.3
1.5
1.4
1.3
1.2
1.2
1.0
1.0
O2 = oxygen.
CO2 = carbon dioxide.
He = helium.
14
-------
oxygen versus time curve. Only data beginning with that
taken at t = 0 that appear linear with time were used to
calculated the slope. A zero-order respiration rate as
seen in these data is typical of most sites (Figure 1-7).
Calculated oxygen utilization rates and corresponding
biodegradation rates for these data are shown in Table
1-10.
Results of this test indicate that this site is an excellent
candidate for bioventing.
Oxygen Utilization Rale = 1.7 %/day
. • Oxygen
13 ~ • Carbon Dioxide
A Helium
1 £
40 60
Time (Hours)
Figure 1-7. In situ respiration test results with linear oxygen
concentration versus time at AOC A, Keesler AFB,
Mississippi.
Table 1-10. Oxygen Utilization and Carbon Dioxide
Production Rates During the in Situ Respiration
Test at AOC A, Keesler AFB, Mississippi
Sample Name
K1-MPA-5.0'
K1-MPA-7.0'
K1-MPB-5.0'
K1-MPC-7.0'
Background
Oxygen
Utilization Rate
(%/hour)
0.071
0.045
0.13
0.099
0.012
Estimated
Biodegradation
Rate (mg/kg-day)
1.16
0.73
2.12
1.62
0.20
Example 1-6 illustrates calculation of oxygen utilization
data that are linear with time. In some instances, how-
ever, this relationship is not linear, and only selected
data should be used to calculate the oxygen utilization
rate. Example 1-7 illustrates calculation of the oxygen
utilization rate from nonlinear data.
Example 1-7. Calculation of Oxygen Utilization Rates
From Nonlinear Data: Table 1-11 contains sample data
from Solid Waste Management Unit (SWMU) 66,
Keesler AFB. The oxygen utilization rate is determined
as the slope of the percentage of oxygen versus time
curve. Only data beginning with that taken at t = 0 that
appear linear with time should be used to calculate the
slope. A fairly rapid change in oxygen levels was ob-
served at Keesler AFB (Figure 1-8). In this case, the
oxygen utilization rate was obtained from the initial lin-
ear portion of the respiration curve, which included data
from t = 0 to t = 30.5 hours. As shown, after this point,
oxygen concentrations dropped below 5 percent and
were limiting. The calculated oxygen utilization rate was
11 percent/day.
Table 1-11. Raw Data From an
SWMU 66, Keesler
Time Oxygen
(Hours) (%)
0 20.5
6.3 18.1
9.3 16.5
15 14
22 11
31 6.8
48 3.7
57 2.9
ft 20' *v
|-\
Q 10 T \
o
0 10 20
in Situ Respiration Test at
AFB, Mississippi
Carbon Helium
Dioxide (%) (%)
0 1.6
.05 1.6
1.0 1.6
2.2 1.
3
3.2 1.5
5.0 1.5
5.1 1.5
5.1 1.5
Oxygen Utilization rate = 11 %day
• Oxygen
• Carbon Dioxide
T Helium
-
X ^-— -
30 40 50 6
4
3 ^
"c
8
E
0
0
Time (Honrs)
Figure 1-8. In situ respiration test results with nonlinear oxy-
gen concentration versus time at SWMU 66, Keesler
AFB, Mississippi.
The helium data collected at a site provide insight into
whether observed oxygen utilization rates are caused by
microbial utilization or by other effects such as leakage
or diffusion. As a rough estimate, diffusion of gas mole-
cules is inversely proportional to the square root of the
molecular weight of the gas. Based on the molecular
weights of 4 g/mole and 32 g/mole for helium and oxy-
gen, respectively, helium diffuses about 2.8 times faster
than oxygen. Thus, although helium is a conservative
tracer, its concentration should decrease with time. As a
general rule of thumb, any in situ respiration test in
15
-------
which the rate of helium loss is less than the oxygen loss
rate should be considered an acceptable test. If the
helium loss rate is greater than the oxygen loss rate,
disregard the test from that monitoring point. The helium
loss rate is not used to correct the oxygen utilization rate.
Example 1-8. Evaluation of Helium Loss During an in
Situ Respiration Test: Figures 1-9 and 1-10 show helium
data for two test wells. The helium concentration at
monitoring point S1 at Tinker AFB (Figure 1-9), initially
at 1.5 percent, dropped to 1.1 percent after 108 hours
(a fractional loss of approximately 0.25); this repre-
sented an acceptable concentration drop. In contrast,
for Kenai K3 (Figure 1-10), the change in helium was
rapid (a fractional drop of about 0.8 in 7 hours), indicat-
ing possible short circuiting at this monitoring point. This
suggested that the data from this monitoring point were
unreliable, so these data were not used in calculating
degradation rates.
10 20 30
40 50 60 TO 80 90 100 110 120
Time (Hours)
Figure 1-9. In situ respiration test results with acceptable data
based on the helium concentration for monitoring
point S1, Tinker AFB, Oklahoma.
10
20 30
Time (Hours)
50
Figure 1-10. In situ respiration test results with unacceptable
data based on the helium concentration for moni-
toring point K3, Kenai, Alaska.
1.4.3 Factors Affecting Observed in Situ
Biodegradation Rates
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 also
affect measured biodegradation rates. The factors that
may most influence soil gas oxygen and carbon dioxide
concentrations are soil pH, soil alkalinity, and iron con-
tent. In addition, any environmental parameter that may
affect microbial activity also may affect observed oxygen
utilization rates. Soil temperature often is a significant
factor at bioventing sites.
At several sites, oxygen utilization has proven to be a
more useful measure of biodegradation rates than carb-
on dioxide production. The biodegradation rate in mg of
hexane-equivalent/kg of soil per day based on carbon
dioxide production usually is less than can be accounted
for by the oxygen disappearance. At virtually all Biovent-
ing Initiative sites, oxygen utilization rates have been
higher than carbon dioxide production rates. A study
conducted at Tyndall AFB, however, was an exception.
That site had low-alkalinity soils and low-pH quartz sands,
and carbon dioxide production actually resulted in a slightly
higher estimate of biodegradation (Miller, 1990).
In the case of the higher pH and higher alkalinity soils
at Fallen MAS and Eielson AFB, little or no gaseous
carbon dioxide production was measured (Hinchee et
al., 1991b; Leeson et al., 1995). This may be the result
of the formation of carbonates from the gaseous evolu-
tion of carbon dioxide produced by biodegradation at
these sites. Van Eyk and Vreeken (1988) encountered
a similar phenomenon in their attempt to use carbon
dioxide evolution to quantify biodegradation associated
with soil venting.
Iron is a nutrient required for microbial growth, but the
iron also may react with oxygen to form iron oxides.
Theoretically, if a significant amount of iron oxidation
were to occur, the observed oxygen utilization rate
would reflect both iron oxidation and microbial activity.
Therefore, calculated biodegradation rates would be an
overestimate of actual biodegradation rates. In data col-
lected from the Bioventing Initiative study, however, iron
concentrations have varied greatly, with concentrations
from less than 100 mg/kg to greater than 100,000
mg/kg, with no apparent impact on oxygen utilization
rates. Iron impact on oxygen utilization rates has been
observed at only one site with very high iron concentra-
tions—on the Marine Base at Kaneohe, Hawaii, where
soil iron concentrations are in the 100,000 mg/kg range.
An important consideration is whether the respiration rate
was measured at the time of year when microbial rates
were at their maximum (summer) or if it was measured
when activity was low (winter). Investigations at many sites
16
-------
have shown that rates can vary by as much as an order
of magnitude between peak periods. For design of oxy-
gen delivery systems, respiration rates should be meas-
ure during the peak season, typically during late
summer.
If oxygen utilization rates were determined during peri-
ods of low activity, it is necessary to adjust the rates to
the maximum level before making size calculations. The
van't Hoff-Arrhenius equation can be used to predict
oxygen utilization rates given an initial rate and tempera-
ture.8 The activation energy, Ea, must be known for the
site. Alternatively, Ea found from another site can be
used, recognizing the temperature-adjusted rate is only
a rough estimate. The following example illustrates a
typical adjustment.
Example 1-9. Temperature Adjustment of Oxygen Utili-
zation Rate: The oxygen utilization rate was measured
in January at a site in Cheyenne, Wyoming. The rate
was determined to be 0.75 percent/day (0.031 per-
cent/hour). The temperature in the soil was measured at
4°C. Previous temperature measurements at the site
have indicated that soil temperatures in August average
approximately 24°C (i.e., 20°C higher than the tempera-
ture measured during January). The temperature adjust-
ment to the rate for sizing calculations is as follows:
Using the van't Hoff-Arrhenius equation (Metcalf & Eddy,
1979):
dk Ea
dT RT2
Integration of this equation between the limits T! (277°K)
and T2 (297°K) gives:
kT Ea (T2 - T,)
where:
kT =
k0 =
Ea =
R =
T! =
T2 =
_
k
temperature-corrected oxygen utilization
rate (% O2/day)
baseline reaction rate = 0.75%/day
activation energy9 = 13.4 kcal/mole
gas constant = 1 .987 cal/°K-mole
absolute temperature for ko = 277°K
absolute temperature for kT = 297°K
' See Volume I for a discussion of the effect of temperature on micro-
bial activity.
' Calculated from a different field site. See Example 3-2 in Volume I
for a description of the calculation of the activation energy.
day
(13,400 cal/mole) (297°K - 277°K)
(1.987
kT = 3.9
cal
°K-mole
•) (297°K)(277°K)
day
As seen in this calculation, the site would require ap-
proximately five times greater oxygen delivery rate in the
summer.
1.5 Soil Gas Permeability and Radius of
Influence
In situ respiration rates may be used to calculate the
required air flow rate to satisfy oxygen demand at a
given site;10 however, determining the distance air can
physically be moved also is necessary. An estimate of
the soil's permeability to fluid flow (k) and the radius of
influence (R,) of venting wells are both important ele-
ments of a full-scale bioventing design. Onsite testing
provides the most accurate estimate of soil gas perme-
ability. Onsite testing also can be used to determine the
radius of influence that can be achieved for a given well
configuration and flow rate. These data are used to
design full-scale systems, specifically to space venting
wells, to size blower equipment, and to ensure that the
entire site receives a supply of oxygen-rich air to sustain
in situ biodegradation.
Soil gas permeability, or intrinsic permeability, can be
defined as a soil's capacity for fluid flow and varies
according to grain size, soil uniformity, porosity, and
moisture content. The value of k is a physical property
of the soil; k does not change with different extraction/in-
jection rates or different pressure levels.
Soil gas permeability is generally expressed in the units
cm2 or darcy (1 darcy = 1 x 10"8 cm2). Like hydraulic
conductivity, soil gas permeability may vary by more
than an order of magnitude on the same site because
of soil variability. Table 1-12 illustrates the range of
typical k values to be expected with different uniform soil
types. Actual soils contain a mixture of grain sizes, which
generally increases the observed darcy values based on
pilot testing.
Table 1-12. Soil Gas Permeability Values (Johnson et al., 1990)
Soil Type k in Darcy
Coarse sand
Medium sand
Fine sand
Silts/clay
100 to 1,000
1 to 100
0.1 to 1.0
10 See Section 2.2 for a presentation of the calculation of required air
flow rates.
17
-------
Several field methods have been developed for deter-
mining soil gas permeability (EPA, 1991b). The most
favored field test method probably is the modified field
drawdown method developed by Paul Johnson at Ari-
zona State University and former associates at the Shell
Development Company. This method involves the injec-
tion or extraction of air at a constant rate from a single
venting well while measuring the pressure/vacuum
changes over time at several monitoring points in the
soil away from the venting well.11
The field drawdown method is based on Darcy's law and
equations for steady-state radial flow to or from a vent
well. A full mathematical development of this method
and supporting calculations are provided by Johnson et
al. (1990). Johnson developed the Hyperventilate com-
puter program to store field data and to compute soil gas
permeability. This or other commercially available pro-
grams can be used to speed the calculation and data
presentation process.
Two solution methods may be used for soil gas perme-
ability as described in Johnson et al. (1990). The first
solution is based on carefully measuring the dynamic
response of the soil to a constant injection or extraction
rate. The second solution forsoil gas permeability is based
on steady-state conditions and the measurement or esti-
mation of the radius of influence at steady state. Whenever
possible, field data should be collected to support both
solution methods because one or both of the solution
methods may be appropriate, depending on site-specific
conditions. An example procedure for conducting a soil
gas permeability test is provided in Appendix C.
1.5.1 Radius of Influence Determination
Based on Pressure Measurements
At a bioventing site, the radius of influence is defined in
two ways, as the oxygen radius of influence or the
pressure radius of influence. The oxygen radius of influ-
ence is defined as the maximum distance from the air
extraction or injection well where a sufficient supply of
oxygen for microbial respiration can be delivered. The
pressure radius of influence is the maximum distance
from the air extraction or injection well where vacuum or
pressure (soil gas movement) occurs. Under heteroge-
neous conditions, the pressure radius of influence is
theoretically infinite; for practical purposes, however, it
usually is considered to be the maximum extent to which
pressure changes can be measured.
The oxygen and pressure radius of influence is a func-
tion of soil properties but also is dependent on the
configuration of the venting well and extraction or injec-
tion flow rates and is altered by soil stratification. The
oxygen radius of influence also is dependent on micro-
bial oxygen utilization rates. On sites with shallow con-
tamination, the oxygen and pressure radius of influence
also may be increased by impermeable surface barriers
such as asphalt or concrete. These paved surfaces may
or may not act as vapor barriers. Without a tight seal to
the native soil surface,12 the pavement will not signifi-
cantly affect soil gas flow.
At a bioventing site, the oxygen radius of influence is the
true radius of influence for system design. A connection
exists between the pressure radius of influence and the
oxygen radius of influence; however, many variables
exist that are not fully understood. Empirically, during a
soil gas permeability test, an increase in oxygen con-
centration has been found at contaminated sites wher-
ever pressure changes are measured. Also, the
pressure radius of influence has been found to be a
conservative measure of the oxygen radius of influence.
The oxygen radius of influence may be directly deter-
mined by measuring the distance from the vent well at
which a change in oxygen concentration can be de-
tected. Several days or weeks may pass, however, be-
fore equilibrium is reached and an accurate oxygen
radius of influence is measured.
In addition, if microbial acclimation occurs, microbial
activity may increase, effectively reducing the oxygen
radius of influence because of increased oxygen con-
sumption. Therefore, the best approach is to measure
the oxygen radius of influence at times of peak microbial
activity. Alternatively, the pressure radius of influence
may be determined very quickly, generally within 2 hours
to 4 hours. Therefore, the pressure radius of influence
typically is used to design bioventing systems.
The pressure radius of influence should be determined
at three different flow rates, with a 1-hour to 2-hour test
per flow rate during the permeability test. Determining
the radius of influence at different flow rates allows for
more accurate blower sizing.13 Recommended flow
rates for the permeability test are 0.5 cfm, 1.5 cfm, and
3 cfm (14 L/min, 42 L/min, and 85 L/min) per ft (0.3 m)
of well screen.
The pressure radius of influence may be estimated by
determining pressure change versus distance from the
vent well. The log of the pressure is plotted versus the
distance from the vent well. The radius of influence is
that distance at which the curve intersects a pressure of
0.1"H2O (25 Pa). This value was determined empirically
from Bioventing Initiative sites. Example 1-10 illustrates
calculating the radius of influence in this manner.
11 See Appendix B for recommended specifications and manufacturers
for the soil gas permeability testing equipment.
12 In the authors' experience, this seal does not occur at most sites.
13 See Section 2.4 for a discussion of blower sizing.
18
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Example 1-10. Calculation of the Radius of Influence
Based on Pressure Measurements: Soil gas permeabil-
ity results from the Saddle Tank Farm Site at Galena
AFS, Alaska, are shown in Figure 1-11 with the log of
the steady-state pressure response at each monitoring
point plotted versus the distance from the vent well. The
radius of influence is taken to be the intersection of the
resulting slope of the curve at a pressure of 0.1 "H2O (25
Pa). Therefore, in this instance, the pressure radius of
influence would be estimated at 92 ft (28 m).
10
o.i
20 40 60 80
Distance From Vent Well (Feet)
100
Figure 1-11. Determination of radius of influence at the Saddle
Tank Farm, Galena AFS, Alaska.
The estimated radius of influence actually is an estimate
of the radius in which measurable soil gas pressures are
affected and does not always equate to gas flow. In
highly permeable gravel, for example, significant gas flow
can occur well beyond the measurable radius of influence.
On the other hand, in a low-permeability clay, a small
pressure gradient may not result in significant gas flow.
1.5.2 Interpretation of Soil Gas Permeability
Testing Results
The technology of bioventing has not advanced far
enough to provide firm quantitative criteria for determin-
ing the applicability of bioventing based solely on values
of soil permeability or the radius of influence. In general,
the soil permeability must be sufficiently high to allow
movement of oxygen in a reasonable timeframe (1 to 10
days) from either the vent well, in the case of injection,
or the atmosphere or uncontaminated soils, in the case
of extraction. If such a flow rate cannot be achieved,
oxygen cannot be supplied at a rate to match its de-
mand. Closer vent well spacing or high injection/extrac-
tion rates may be required.
If either the soil gas permeability or the radius of influ-
ence is high (greaterthan 0.01 darcyora Rigreaterthan
the screened interval of the vent well), this is a good
indicator that bioventing may be feasible at the site and
proceeding to soil sampling and full-scale design is
appropriate. If either the soil gas permeability or the
radius of influence is low (less than 0.01 darcy or a R,
less than the screened interval of the vent well), this may
indicate that bioventing is not feasible. This situation
necessitates an evaluation of the cost-effectiveness of
bioventing over other alternative technologies for site
remediation. The cost involved in installing a bioventing
system at a low-permeability site is driven primarily by
the necessity of installing more vent wells, using a
blower with a higher delivery pressure, or installing hori-
zontal wells.
19
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Chapter 2
System Design
The design of a bioventing system is based upon the
results of site characterization and pilot testing efforts
described in Chapter 1. The objective is to design a
system that results in aeration of the contaminated soils
with little or no volatilization. Aeration may be accom-
plished through air injection, gas extraction, or a combi-
nation of the two. Soil vacuum extraction (SVE) (also
known as soil venting, soil gas extraction, or vacuum
vapor extraction) is a related technology in which soil
gas is extracted to remove contaminants by volatiliza-
tion. In contrast, bioventing is designed to minimize
volatilization and optimize biodegradation. As a result,
bioventing typically uses much lower air flow rates and
often does not involve air extraction.
The basic steps involved in designing a bioventing sys-
tem are as follows:
• Determine required air flow system (injection, extrac-
tion, or both [Section 2.1]).
• Determine required air flow rates (Section 2.2).
• Determine the working radius of influence.
• Determine well spacing (Section 2.3).
• Provide detailed design of blower, vent wells, and
piping (Section 2.4).
• Determine vent well requirements (Section 2.5).
• Determine monitoring point requirements (Section 2.6).
2.1 Determination of Air Flow System
In general, if safe and feasible, air injection is the pre-
ferred configuration for full-scale bioventing systems. If
properly designed, air injection results in minimal dis-
charge of volatile organics to the atmosphere and is less
expensive to operate and maintain than air extraction
systems.
Under some circumstances, the use of soil gas extrac-
tion systems may need to be incorporated into an air
injection system design. For example, whenever the
radius of influence of a vent well reaches basements,
utility corridors, or occupied surface structures, an air
extraction system may be used to reduce the risk of
moving gases into these areas. This precaution pre-
vents the accumulation of explosive or toxic vapors in
these structures.
2.1.1 Air Injection
Air injection involves the introduction of air under pres-
sure into the contaminated zone. If the contaminants are
volatile, some will migrate in the gas phase into sur-
rounding soil, where they can biodegrade. This has the
advantage of creating an expanded in situ bioreactoras
illustrated in Figure 2-1. Given adequate oxygen, the
volatilized hydrocarbons will biodegrade in these sur-
rounding uncontaminated soils, increasing the fraction
of contaminants biodegraded compared with an air ex-
traction configuration. This concept is illustrated in Ex-
ample 2-1.
Example 2-1. Biodegradation of Petroleum Hydrocar-
bons in the Uncontaminated and Contaminated Regions
at Site 280, HillAFB:M this site, high vapor-phase TPH
concentrations were detected within a radius of approxi-
mately 50 ft (15 m) from the injection well. TPH concen-
trations decreased with increasing distance from the
well. Likewise, in situ respiration rates were observed to
decrease with increasing distance from the injection well
(Figure 2-2). Calculations were made to compare total
TPH mass degraded in each region based on these in
situ respiration rates. These results, shown in Figure
2-3, illustrate that even though relatively low in situ
respiration rates were measured at monitoring points
located far from the injection well (220 ft [67 m]), in fact,
the majority of the contaminant degradation was occur-
ring in this area. These results illustrate the availability
of vapor-phase hydrocarbons for biodegradation and
the significant contribution an expanded bioreactor can
have on contaminant removal.
Miller (1990) found at the Tyndall AFB site that hydro-
carbon vapors biodegrade at a rate approximately equal
to one-third the rate observed in contaminated soils.
Kampbell (1993) found that the vapor-phase biodegra-
dation in an air injection system was greatest in shallow
root zone soils. The concept is analogous to an in situ
biofilter. In general, air can be injected at flow rates low
21
-------
Air Injection Expanded Bioreactor
Figure 2-1. Expanded bioreactor created during air injection.
number* = mg-hexane/kg-solfday
0,15
0 14 38 S163T3 100 114 220
Distance From Injection Well (ft)
Figure 2-2. Oxygen utilization rates, averaged over depth, versus distance from the injection well at Site 280, Hill AFB, Utah.
0 14 36 616373 100 114
220
Distance From Injection Well (ft)
Figure 2-3. Mass of TPH degraded versus distance from the injection well at Site 280, Hill AFB, Utah.
22
-------
enough to avoid surface emissions. As the air injection
rate increases, hydrocarbon volatilization increases
(Figure 2-4). Therefore, the objective is to inject suffi-
cient air to meet oxygen demand for biodegradation but
not to cause emissions to the atmosphere. This is gen-
erally possible at sites contaminated with JP-4 or JP-5
jet fuel, diesel, and other contaminants of similar or
lesser volatility. It is more difficult with gasoline, although
successful systems using only air injection have been re-
ported at gasoline-contaminated sites (Kampbell, 1993).1
In addition to creating an expanded bioreactor, air injec-
tion could potentially expose a significant portion of
capillary fringe contaminated soil to treatment via water
table depression. As air is injected into the vadose zone,
a positive pressure is created, resulting in depression of
the water table. Figure 2-5 illustrates the water table
depression observed at Site 20, Eielson AFB, Alaska.
This water table depression has important implications.
At many sites, the capillary fringe is highly contami-
nated, and lowering the water table allows for more
effective treatment of the capillary fringe. In addition, this
dewatering effect frequently results in an increased ra-
dius of influence and greater soil gas permeability.
a. air injection
Air Flow Rate
b. air extraction
Air Flow Rate
Figure 2-4. Hydrocarbon volatilization and biodegradation
rates as a function of air flow rate.
A schematic diagram of a basic air injection system is
illustrated in Figure 2-6. The system is relatively simple,
involving a blower or compressor and a distribution
system. Explosion-proof blowers are recommended for
safety. Properly designed and operated injection sys-
tems do not produce significant air emissions or require
aboveground vapor phase treatment.
2.1.2 Air Extraction
Air injection is the preferred bioventing configuration;
however, air extraction may be necessary at sites where
movement of vapors into subsurface structures or air
emissions is difficult to control. If a building or other
structure is located within the radius of influence of a
site, or if the site is near a property boundary beyond
which hydrocarbon vapors cannot be pushed, air extrac-
tion may be considered. A significant disadvantage of
the air extraction configuration is that it limits biodegra-
dation to the contaminated soil volume because vapors
do not move outward, creating an expanded bioreactor.
The result is less biodegradation and more volatilization.
In general, increasing extraction rates increase volatili-
zation and biodegradation rates until the site becomes
aerated, above which the rate of biodegradation no
air extraction
13'
air injection
10'
Reisinger, J. 1994. Personal communication between J. Reisinger, 1ST, Figure 2-5. Water table depression during air injection and air
Inc., Atlanta, Georgia, and Battelle Memorial Institute, Columbus, Ohio. extraction.
23
-------
Lov
Airl
! ' '
I
c
c
Biodegradation
of Vapors
J < L
Soil Gas
^ Mnnitrvrlnn ^
\ /•-''}
I
v^l
s
/ ,f /
?"'
VR
ije
=
§=
"=
ate
ction
^
Contaminated Soil
w-|
: )
i
.--
Figure 2-6. Air injection configuration for a bioventing system.
longer increases. Volatilization generally continues to
increase with increasing extraction rates until the con-
taminated soil system becomes diffusion limited. The
optimal air flow rate for injection and extraction is the
minimum required to satisfy oxygen demand. Extraction
systems result in some volatilization regardless of the
extraction rate. Figure 2-4 illustrates this concept. The
relative removal attributed to biodegradation and vola-
tilization is quite variable and site dependent. At a JP-4
jet fuel contaminated site at Tyndall AFB, Miller et al.
(1991) found that at the optimal air injection level it was
possible to achieve approximately 85 percent of removal
due to biodegradation at the optimal flow rate.
Air extraction creates a partial vacuum in the soil, result-
ing in a water table and capillary fringe rise or upwelling.
The soil venting literature has illustrated this phenome-
non (Johnson etal., 1990). Because the bulk of contami-
nation is often several inches or feet above or below the
water table (smear zone), this upconing can saturate
much of the contaminated soil and reduce treatment
efficiency. The upconing also increases soil moisture in
the capillary fringe and thus reduces soil gas permeabil-
ity and radius of influence.
An example of this phenomenon was observed at Eiel-
son AFB. An extraction air permeability test was con-
ducted at Eielson AFB to observe the effect of the
bioventing configuration on the site air permeability and
well radius of influence. Table 2-1 compares the results
of extraction and injection tests at Site 20, Eielson AFB.
The permeability (k) calculated for the extraction test
was 0.27 darcy, approximately one-half the result for the
air injection test. The radius of influence observed at the
6-ft monitoring depth also was reduced approximately
one-third to 42 ft (13 m) (Figure 2-7). This reduction in
Table 2-1. Permeability and Radius of Influence Values at
Eielson AFB, Alaska: Injection and Extraction Mode
Permeability (darcy)
Depth (ft)
2
4
6
Injection
NR
0.53
0.56
Extraction
NR
0.27
0.27
Air Radius of
Influence (ft)
Injection
<7.0
45
68
Extraction
<6.0
34
42
NR = No response.
permeability and radius of influence was a result of the
water table rising illustrated in Figure 2-5.
Figure 2-8 is a schematic of a basic air extraction sys-
tem. In contrast to an injection system, an extraction
system usually requires an explosion-proof blower with
explosion-proof wiring. Extracted soil gas typically con-
tains moisture at or near saturation, and a knockout
(air/water separator) usually is required to collect con-
densate, which must be treated or disposed of. Also,
during winter months in regions with sustained tempera-
tures below freezing, insulation and/or heat tape may be
required to maintain piping at temperatures above freez-
ing to avoid clogged pipes.
Air extraction systems usually result in point source emis-
sions that may require permitting and treatment. Air treat-
ment affects remediation costs significantly. Appendix D
contains information on options for off-gas treatment.
Currently, only six sites out of 125 Bioventing Initiative
sites use air extraction as a method for oxygenation.
Two of the sites (Capehart Service Station, McClellan
AFB, and BX Service Station, Patrick AFB) operated in
24
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• Injection Mode
T Extraction Mode
0.001
0 10 20 30 40 50 60 70 80 90 100 110 120
Distance From Vent Well (ft)
Figure 2-7. Radius of influence during air injection and extraction in the control test plot at a depth of 6 ft at Site 20, Eielson AFB,
Alaska.
To
Atmosphere
Knockout
Drum
Figure 2-8. Schematic of a basic air extraction system.
extraction mode for 60 to 120 days, at which time the
system was reconfigured for air injection because vapor
concentrations had significantly decreased. At Patrick
AFB, initial vapor concentrations of TPH were as high
as 27,000 ppmv (Figure 2-9). After approximately 75
days of operation, concentrations decreased to 1,600
ppmv and the bioventing system was reconfigured for
injection (Downey, 1994). The Base Service Station at
Vandenberg AFB contained high concentrations of more
volatile components of gasoline and is an active service
station. As such, the possibility of vapor migration into
the service station was possible. This bioventing system
was operated in an extraction configuration in two
phases (Downey et al., 1994a). During Phase I, ex-
tracted soil gas was passed through a PADRE vapor
treatment system, where high concentrations of volatiles
were adsorbed and condensed to liquid fuel. The treated
soil gas was then recirculated through the soil using air
injection, biofilter trenches located along the perimeter
of the site. Phase II was initiated when TVH concentra-
tions decreased to less than 1,000 ppmv. At this time,
the PADRE system was taken off line, and the extracted
soil gas was reinjected directly into the biofilter trenches.
2.1.3 Determining Use of Injection Versus
Extraction
Safety considerations usually drive the selection of in-
jection versus extraction systems. Air injection should
not be used unless a system can be designed that does
25
-------
100,000-1
i- 25,000
TVH
10,000-
- 2,500
Q.
Q.
1,000-
-250
10 20
BTEX
30 40 50 60
Days of Operation
70
77
Figure 2-9. Extracted BTEX and TPH soil gas concentrations at Patrick AFB, Florida.
not push hazardous vapors into structures. Table 2-2
summarizes some of the considerations that affect the
decision.
Numerous options are available that may allow air injec-
tion at sites with structures at risk or with property
boundaries nearby (Phelps, 1995). These options in-
clude monitoring the atmosphere in the structure to
verify that no contaminants enter using air extraction
coupled with reinjection to protect the building (Figure
2-10), or using subslab depressurization.
2.1.4 Design of Air Flow To Protect
Structures
Subslab depressurization can be used to protect struc-
tures while still allowing for air injection to provide opti-
mal oxygenation. Subslab depressurization involves
extracting air within or around the perimeter of a building
during simultaneous air injection. Vapors extracted from
beneath the building may be released to the atmos-
phere, treated then released, or reinjected into the sub-
surface for further biotreatment. A schematic of such a
system is shown in Figure 2-11.
At AOC A, Keesler AFB, Mississippi, a subslab depres-
surization system is currently in operation as part of the
Bioventing Initiative. A schematic of the site is shown in
Figure 2-12. Soil vapor is continually withdrawn from air
extraction wells located around the perimeter of the
building and reinjected into the vent wells. Makeup air
is added to the injection gas to provide sufficient oxygen
to aerate the site. No vapor migration into the building
has been detected at this site, and the site soils are well
oxygenated.
Table 2-2. Air Injection Versus Extraction Considerations
Favor Injection Favor Extraction
Low vapor pressure contaminants High vapor pressure
contaminants
Deep contamination
Low permeability soils
Significant distance from
structures/property boundaries
Surface emissions
Structures/property boundaries
within the radius of influence
At Site 48, Eielson AFB, Alaska, an actively used utilidor
runs through the site. The potential for migration of
vapors into the utilidor was high. To eliminate the migra-
tion of vapors into this structure, a horizontal perforated
pipe was installed next to the utilidor. A vertical extrac-
tion well was connected to the horizontal pipe to extract
gas from along the utilidor for vapor control. The ex-
tracted soil gas was then reinjected into a contaminated
area at the site (Figure 2-13).
2.2 Determining Required Air Flow Rates
The flow rate required to operate the bioventing system
is dependent on the oxygen demand of the indigenous
microorganisms. This is best determined from maximum
oxygen utilization rates measured during an in situ res-
piration test. Equation 2-1 is used to estimate the re-
quired air flow rate:
Q:
k0V9a
(Eq. 2-1)
(20.9% - 5%) x 60
mm
hr
26
-------
Sol I Gas
Monitoring
Figure 2-10. Schematic of an air injection system with reinjection of extracted soil gas.
Monitoring Point
Utilized During Blower
Pilot Test Optional
o ; > >
Iff S . . .S
i
~t
KJ
To Injection
v
Figure 2-11. Schematic of subslab depressurization.
where:
Q = flow rate (ft3/min)
k0 = oxygen utilization rate (%/hr)
V = volume of contaminated soil (ft3)
9a = gas-filled porosity (fraction, i.e., 0.2 or 0.3)
Example 2-2 illustrates the use of this calculation.
Example 2-2. Determination of Required Air Flow Rate:
Given a volume of contaminated soil of approximately
170,000 ft3 (4,760 m3), an air-filled void volume (9a) at
this site of 0.36,2 and an oxygen utilization rate of 0.25
percent/hr, the flow rate is calculated as follows:
Q:
(0.25%/hr)(170,000 ft3)(0.36) (Eq. 2-2)
(20.9%-5%)x60mirYhr
2 See Section 1.4.2 on using moisture content to estimate this
parameter.
Therefore,therequiredflowrateisapproximately16cfm
(453L/min).
The flow rate calculated and used must be confirmed
duringoperationofthebioventingsystembymonitoring
soilgas composition to ensureadequateoxygen levels
atalllocations.
Datafrom numerous sites contaminated with various
types and mixtures of contaminants haveshownthat
microbial activity is not oxygen limited aboveoxygen
concentrationsofapproximately1percentto2percent.
Toensurethepresenceofadequateoxygen levels! nthe
27
-------
9 Injection Well
O Extraction Well
• Monitoring Point
« Building Monitoring Points
® Monitoring Well
Building 1504
O EW-l (GS-6)
(JEW-3
MPB
MPA
O EW-2 (GS-3)
©
MWA-11
Extraction Line
MPDl
Reinjection Line
'VW-l (GS-7)
1 MPE
» VW-2 ((
Service Road
vk'AWJHI
IS-5)
•g
o
O
CO
O
a
;s-4)
'GS-l
0MW8-3
*GS-2
0MW8-2
Meadows Drive
Figure 2-12. Schematic of the extraction with reinjection system at AOC A, Keesler AFB, Mississippi.
entire treatment cell, a minimum level of 5 percent
should be maintained.
2.3 Well Spacing
To determine the required number of wells and appro-
priate spacing, an estimate of the radius of influence is
necessary. Many approaches to obtaining this estimate
are possible, but those normally in use are:
• Based upon measured pressure in monitoring points
during a soil gas permeability test.
• Estimated from air flow and oxygen consumption.
• Measured empirically.
Estimating the radius of influence based on pressure
measurements during an in situ permeability test is a
common approach used in soil venting or soil vapor
extraction and is probably the fastest method. This cal-
culation is normally performed by plotting the log of
pressure versus distance, as described in Section 1.5.1.
The limitation to this approach is that it only incorporates
one of the three factors affecting the radius of influence.
To determine more exactly the radius of oxygen influ-
ence, air flow rate and oxygen utilization need to be
considered. In low-permeability soils, a pressure effect
may be seen in a monitoring point, but air flow rates to
that point may be too low to supply adequate oxygen.
Conversely, in a high-permeability soil, air flow rates
sufficient to supply oxygen may occur at pressure differ-
entials that cannot be measured. In the authors' experi-
ence, if a pressure criterion of 0.1" H2O (25 Pa) is used,
the estimated radius of influence will be conservative for
well spacing and site aeration.
Radius of influence can be estimated fora given airflow
rate based on oxygen utilization. Assuming the use of a
vertical well so that air flow can be described in cylindri-
cal coordinates and assuming that the radius of influ-
ence is much greater than the well radius, the following
equation may be used:
28
-------
E3-MPA
Power Plant Area
Cross Section Not to Scale
=
1
—
—
Vertical Air
s Injection Line
Horizontal f~\
Air Extraction ***
Line
V-f1 '
^
P 8
0 0
0 °
Utilidor
O ooo
Blower'
Air Flow
• Injection/Extraction Wells
B2 Blower for Site 48 - E2
B3 Blower for Site 48 - E3
4- Monitoring Point
^
Roadway
-*-—""" ~p/ " ^ Utildor Horizontal
\\ f ) hxtraction
L@ T@ |"i£T| Line
Air Injection
Line
3 E2-MPC
E2-MPB4-
E2-MPD
E2-MPA4-
Not to Scale
Figure 2-13. Soil gas extraction to isolate a subsurface structure at Site 48, Eielson AFB, Alaska.
Ri =
.9% - 5%)
; h kn 9a
where:
RI = radius of influence (ft)
Q = air flow rate (ft3/day)
20.9% - 5% = oxygen %
h = aerated thickness (ft)
k0 = oxygen utilization rate (%/day)
9a = air filled porosity (cm3air/cm3soi|)
Example 2-3. Calculation of Radius of Influence. To
calculate the radius of influence at Dover AFB, Equation
2-3 is used with the following parameters:
Q = 20 cfm (570 L/min) = 28,800 ft3/day (820,800 L/day);
k0 = 4 %/day; 9a = 0.25; h = 20 ft (6.1 m)
R,=
28,800
day
(20.9% - 5%)
IT (20 ft)(4%/day)(0.25)
Therefore, the radius of influence at this site is equal to
(Eq. 2-3) approximately 85 ft (26 m).
In practice, the best approach is to estimate the radius of
influence from both pressure measurements and oxygen
utilization. This incorporates all three of the key factors: pres-
sure connection, airflow, and oxygen utilization. The authors
have never found in practice a site where this combined
approach has overestimated the radius of influence.
The most conclusive determination of radius of influence
is empirical measurement. The blower can be started
and oxygen levels measured in monitoring points. The
problem with this approach is that a minimum of several
days is required to reach steady state. At some sites,
more than 30 days are required.
Well spacing typically is 1 to 1.5 times the radius of
influence. When multiple wells are installed, some con-
sideration may be given to air flow patterns. In theory,
air flow lines may develop that create "dead zones";
however, given vertical and horizontal flow paths and
diffusion, these dead zones are unlikely to occur, so
compensating for them is not routinely recommended.
2.4 Blowers and Blower Sizing
A blower provides the driving force to move air through the
(Eq. 2-4) bioventing system. In selecting a blower size, important
29
-------
points to consider are the required air flow rate and the
total system pressure drop. System pressure drop in-
cludes the back pressure due to the vent wells and
formation in an air injection configuration (or the vacuum
induced in the wells and formation in an extraction con-
figuration) plus any pressure drop in the system piping
and off-gas treatment system. This section describes
the procedure for sizing a blower and uses a specific
example to illustrate the procedure.
The two basic types of blowers are centrifugal machines
and positive displacement machines. Positive displace-
ment blowers are further subdivided into rotating ma-
chines and reciprocating machines (Figure 2-14).
Selection of the appropriate type and size is based on
the air flow requirement and the suction and discharge
pressures presented to the blower during operation at
the design air flow rate. Centrifugal blowers are gener-
ally favored when air flow requirements are high and/or
the system pressure drop is low. Rotating positive dis-
placement blowers generally provide lower air flow ca-
pacity and higher pressures than centrifugal blowers but
can generate moderate to high vacuum at the blower
inlet. Because of their vacuum capability, rotating posi-
tive displacement blowers may be used for systems
operating in an extraction configuration. Reciprocating
positive displacement machines are typically used for
applications requiring very high pressure. Except for
single-action diaphragm pumps used for soil gas sam-
pling, reciprocating positive displacement pumps are
rarely used in bioventing applications and are not dis-
cussed further. The required pressure or vacuum in the
well is a function of the soil gas permeability, which is
determined through field tests as described in Section 1.5.
2.4.1 Centrifugal Blowers
Centrifugal blowers impart energy to the air stream by
means of a rapidly rotating impeller or propeller. The
moving impeller imparts kinetic energy to the fluid. Part
of the added kinetic energy is then converted to pres-
sure head in the blower casing as the fluid leaves the
impeller. Examples of centrifugal blowers include radial
blowers, regenerative radial blowers, multistage radial
blowers, and axial blowers.
In a radial blower, air enters at the center of the housing
and is picked up by an impeller vane near the axis of
rotation (low-velocity area). Air is pushed radially away
from the axis of rotation and accelerated by the impeller
vane. Air exits the tip of the vane at high speed and
Centrifugal Blowers
Air Inlet
Air Outlet
Air Inlet ' " >- Air Outlet
Single Stage Radial Blower Regenerative Blower
Rotary Positive Displacement Blowers
Air Inlet
Air Inlet
•>• Air Outlet
Air Outlet
Sliding Vane Blower
Twin Lobe Blower
Air Inlet
Air Outlet
Water Ring
Water Ring Vacuum Pump
Figure 2-14. Schematic of blower types.
30
-------
enters the volute casing where the air velocity drops,
converting kinetic energy into pressure head.
Regenerative centrifugal blowers provide efficient air
movement in the flow rate and pressure drop ranges
encountered in soil vapor extraction and bioventing
applications and can produce moderate vacuum at the
suction port. They are available in nonsparking explo-
sion-proof designs. As a result of these capabilities, the
regenerative centrifugal blower is widely used in soil
vapor extraction and bioventing systems. Unlike stand-
ard single-stage radial centrifugal blowers, the regen-
erative design uses a short-bladed turbine impeller. As
the regenerative blower impeller rotates, centrifugal ac-
celeration moves the air from the base of the blade to
the blade tip. The fast-moving air leaving the blade tip
flows around the housing contour and back down to the
base of the next blade, where the flow pattern repeats.
This repeated acceleration allows a regenerative blower
to produce higher differential pressure than a conven-
tional single-stage radial flow design. The regenerative
blowers can also produce higher vacuum at the suction
port compared with a pure radial flow design (but are not
able to reach the high vacuum conditions provided by
rotary positive displacement blowers).
2.4.2 Rotary Positive Displacement Blowers
Rotary positive displacement blowers impart energy to
the air stream by means of a rotating element displacing
a fixed volume with each revolution. Examples of rotary
positive displacement blowers include twin-lobe blow-
ers, water ring vacuum pumps, sliding vane blowers,
and flexible vane blowers. Sliding vane and flexible vane
blowers may be used for soil gas sampling or other
low-flow applications but have too low an airflow capac-
ity to act as the air handler in a bioventing system. Lobe
blowers and water ring vacuum pumps have been used
in soil vapor extraction and bioventing systems where
moderate to high vacuum is needed.
In a twin-lobe blower, two figure-eight-shaped lobe im-
pellers, mounted on parallel shafts, rotate in opposite
directions. As each impeller lobe passes the pump inlet,
it traps a volume of gas and carries it around the case
to the pump outlet. The rotation speed of the two impel-
lers is controlled so that the volume created at the inlet
side of the casing is larger than the volume at the outlet
side of the casing, resulting in compression of the air
trapped by the impeller lobe.
A water ring vacuum pump uses a rotating vaned impel-
ler in a cylindrical pump casing. The impeller axis of
rotation is off center with respect to the pump housing.
A uniformly thick layer of water forms on the inside of
the pump casing as a result of the rotary action of the
impeller. Because the impeller is off center, the cavity
formed between two impeller vanes and the water seal
changes size as the vanes move around the pump
housing. Air enters the pump where the cavity formed
by the vanes and the water seal is large and is dis-
charged where the cavity is small, thus increasing the
pressure of the pumped gas.
2.4.3 Blower Selection and Sizing
Proper sizing and selection of a blower is essential to
ensure that the unit can deliver the required air flow and
that the unit operates properly. Choosing the wrong
blower can result in an inability to deliver sufficient oxy-
gen or a significantly shortened blower life. Care must
be taken to select the type of blower that can deliver the
required air flow at the expected pressure. The best
approach is to select a blower that allows operation near
the middle of its performance range. A blower operating
near its maximum pressure/vacuum is running ineffi-
ciently and under stressed conditions, thereby increas-
ing operating costs and shortening blower life. Selection
of an oversized blower also reduces operating efficiency
and unnecessarily increases capital costs. Example 2-4
illustrates a typical decision process for selection and
sizing of a blower.
Example 2-4. Selection and Sizing of a Blower: For the
site described in Example 2-2, 16 cfm (453 L/min) of air
must be delivered to the example treatment cell. Based
on the soil gas permeability test conducted at the site,
operating pressures of 10"H2O (2.5 x 103 Pa) were re-
quired to deliver 16 cfm (453 L/min). A regenerative air
blower is selected because it operates efficiently at the
specified flow rate and pressure. Blower performance
curves were obtained for three different-sized blowers
(1/10, 1/8, and 21/2 hp, respectively), all of which might
be expected to produce 16 cfm (453 L/min). The curves
are shown in Figure 2-15.
The performance curves indicate that Blower #1 is too
small and would not be able to provide 16 cfm (453
L/min) at 10"H2O (2.5 x103 Pa). Although Blower #3
could provide 16 cfm (453 L/min) at 10"H2O (2.5 x 103
Pa), it would be operating at the lower end of perform-
ance and would be too big. The performance curve for
Blower #2 shows that it would be a good choice. Blower
#2 is rated to deliver as much as 21 cfm (595 L/min) at
10"H2O (2.5 x 103 Pa). The excess air flow can be by-
passed to the atmosphere, allowing adjustment for the
16 cfm (453 L/min) flow into the vent. If volatilization is
not a concern and the additional air flow is not a problem,
the entire flow can be injected into the vent well.
The example described above is a simplified case to
show how to select and size a blower for use with
bioventing. Situations in the field may become more
complicated if significant seasonal variations occur in
soil gas permeability or if other parameters exist that
31
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20
B 15
& 10
I
CO
0)
I 5
Blower #1: 1/10 hp
Design AP
5 10 15 20 25
Free Air Flow (CFM)
Blower #2: 1/8 hp
25
20
15
10
5
n
•- —
\
Design
\
AP
\
\
\
\
\
10 15 20 25
Free Air Flow (CFM)
Blower #3: 2.5 hp
30
£ 8°
•§ 60
c
§an
40
i
0
~~^-
Deslg
•\
n AP
X
\
\
\
\
\
25 50 75 100 125 150 175
Free Air Flow (CFM)
Figure 2-15. Performance curves for three different-sized blow-
ers (1/10, 1/8, and 2.5 hp, respectively).
affect gas flow and oxygen demand. The key design
consideration is to select and size a blower based on
conditions when oxygen demand is highest and soil gas
permeability is lowest. Incorporating a bypass into the
system plumbing reduces the air flow delivered to the
soil. Air flow cannot be increased above the perform-
ance of the blower, so the blower should be selected for
the most demanding conditions. The operating princi-
ples of several blower types are outlined in the following
sections. Further information on pumps and blowers
may be found in Pumping Manual, 1989; Karassiketal.,
1991; and Graham, 19494
2.5 Vent Well Construction
Vent well construction is fairly standard, and general
guidelines are provided here. If existing ground-water
monitoring wells at the site are screened above the
water table, they can be used as vent wells. This option
is appropriate for air injection systems but is less suc-
cessful for air extraction systems because the applied
vacuum causes a rise in the water table that could
submerge the screened interval.
The diameter of the vent well typically is between 2 in.
and 4 in. (5.1 cm and 10 cm), although larger and
smaller diameters have been successfully used. Vent
well diameter depends on the soil type, ease of drilling,
and area and depth of the contaminated volume. In most
shallow or sandy soils, a 2-in. diameter (5.1-cm) vent
well provides adequate air flow for bioventing. For sites
with contamination extending below 30 ft (9.1 m) or in
low-permeability soils, a 3-in. or4-in. (7.6-cm or 10-cm)
vent well is recommended because it allows for greater
air flow to aerate a greater volume. As the depth of well
increases, the fractional cost of well construction mate-
rials per ft of well decreases significantly.5
The vent well typically is constructed of schedule 40
polyvinyl chloride (PVC) and should be screened with a
slot size that maximizes air flow through the soil. The
screened interval should extend through as much of the
contaminated profile as possible, with the bottom of the
screen corresponding to the lowest historical level of the
water table. When designing a screen for an extraction
well, the potential for water table upconing must be
considered. If the bottom of the screened interval is close to
the water table, water will be pulled into the vent well, reduc-
ing its effectiveness. If screening below the water table is
necessary, additional screened length above the water
table may be necessary to offset water table upconing.
Hollow-stem augering is the most common drilling
method; however, a solid-stem auger is acceptable in
more cohesive soils. The AFCEE is also investigating
the use of cone penetrometer (CRT) wells for bioventing.
Many other drilling techniques are also appropriate. In
shallow, softer soils, hand-augering may be feasible.
Wherever possible, the diameter of the borehole should
be at least two times greater than the vent well outside
diameter. The annularspace corresponding to the screened
interval should be filled with silica sand or an equivalent.
The annularspace above the screened interval should be
sealed with a bentonite and grout slurry to prevent short-
circuiting of air to or from the surface. The construction
detail of a typical vent well is shown in Figure 2-16.
4 See Appendix B for recommended specifications and manufacturers
for the blowers.
5 See Appendix B for recommended specifications and manufacturers
for vent well construction materials.
32
-------
2-4" Dia. SCH 40 PVC
Header Sloped to
Well
1
i
'A
v
X
'////^
:xX^xx
//////
<\\\\\
$W$N
5'
(Minimum)
6'
\
5'
^ O
^ t
i "^
^k
^0
p»
$°>
f f
/ ^
\
'j&X
/
|S|E
= = =
EE!S
E^E
|=E
==E
=====
==E
= = E
= = E
= ==: =
= = =
x\ *^
^ To Blower
i » <
> «»j<
:> * <
d3
S/
'I
— rf$k • r ' "!<—
///W/XVO\sX\
/y/V^XooOvvv\
s /VVVVV^^
V to Surface
9-A" Din ^PH dn PVf* Picinn
^ D^M»*.«:»» O—..I
(2' Minimum)
2-1" Dia SCH 10 PVC Screen
/ Undisturbed Soil
-CvX5
^r End Cap
Not to Scale
Figure 2-16. Schematic of a typical vent well.
To maintain the integrity of the vent well seal, as a rule
of thumb, do not allow injection pressures measured in
water depth to exceed the total grouted and sealed
length. For example, in a well with 3 ft (0.91 m) of
bentonite seal and 3 ft (0.91 m) of grout, do not exceed
an injection pressure of 72"H2O (1.8x104 Pa). High
pressures also can damage seals. If the injection pres-
sure exceeds the bearing capacity of the soil, fracturing
is possible. Care must be taken with injection wells to
obtain a good seal. Injection wells should be installed
with a bentonite and grout slurry. Dry bentonite chips do
not provide an adequate seal unless the chips are con-
tinuously hydrated during installation.
2.6 Monitoring Point Construction
Soil gas monitoring points are used for pressure and soil
gas measurements and are a very important component
of a bioventing system. Proper construction of monitoring
points is essential for monitoring localized pressure and
soil gas concentrations. To the extent possible, the
monitoring points must be located in contaminated soils
with greater than 1,000 mg/kg of total petroleum hydro-
carbon. If monitoring points are not located in contami-
nated soil, meaningful in situ respiration data cannot be
collected.
In addition, location of monitoring points should consider
soil gas permeability testing and radius of influence
determination. Monitoring points should be located at
varying distances from the vent well. The distances from
the vent well vary depending on soil type; suggested
monitoring point spacing is shown in Table 2-3.
In practice, each monitoring point cluster usually is
screened to at least three depths. The deepest screen
should be placed either at or near the bottom of contami-
nation if a water table is not encountered, or a minimum
of 2 ft to 3 ft (0.61 m to 0.91 m) above the water table if
33
-------
Table 2-3. Recommended Spacing for Monitoring Points
Depth to Top of Vent Spacing
Soil Type
Coarse sand
Medium sand
Fine sand
Silts
Clay
Well Screen (ft)a
5
10
>15
5
10
>15
5
10
>15
5
10
>15
5
10
>15
Interval (ft)b
5-1 0-20
10-30-50
20-30-70
1 0-20-30
15-25-45
20-40-70
1 0-20-40
15-30-50
20-40-60
1 0-20-40
15-30-50
20-40-60
1 0-20-30
10-20-40
10-25-50
it is encountered. Consideration should be given to po-
tential seasonal water table fluctuations and soil type in
finalizing the depth. In more permeable soil, the moni-
toring point can be screened closer to the water table.
In less permeable soil, it must be screened further above
the water table. The shallowest screen normally is 3 ft
to 5 ft (0.91 m to 1.5 m) below land surface. The inter-
mediate screen should be placed at a reasonable inter-
val at a depth corresponding to the center to upper
quarter of the depth of the vent well screen. In some
cases, additional screened depths may be desirable to
more fully monitor the contaminated interval, to monitor
differing stratigraphic intervals, or to adequately monitor
deeper sites with broadly screened vent wells.
Example 2-5. Selection of Depth Intervals for Monitoring
Points: Site soils are sandy, with ground water at 30 ft
(9.1 m). The vent well was screened from 17.5 ft to 27.5
ft (5.3 m to 8.4 m) below land surface. Therefore, moni-
toring point depth intervals chosen were 28 ft (8.5 m),
22.5 ft (6.9 m), and 3 ft (0.91 m). For sites with vent wells
deeper than 30 ft (9.1 m), more depths may be
screened, depending on stratigraphy.
Monitoring point construction varies depending on the
depth of drilling and the drilling technique. Monitoring
points consist of a small-diameter 1/4-in. (0.64-cm) tube
to the specified depth with a screen approximately 6 in.
(15 cm) long and 1 in. (2.5 cm) in diameter. In shallow,
open-hole installations, rigid tubing (i.e., schedule 80
1/4-inch [0.64 cm] PVC) terminating in the center of a
gravel or sand pack may be adequate. The gravel or
sand pack normally should extend for an interval of 1 ft
to 2 ft (0.30 m to 0.61 m), with the screen centered. In
low-permeability soils, a larger gravel pack may be de-
sirable. In wet soils, a longer gravel pack with the screen
near the top may be desirable. A bentonite seal at least
2 ft (0.31 m) thick normally is required above and below
the gravel pack. Figure 2-17 shows the construction
detail of a typical monitoring point installation.6 For rela-
tively shallow installations in more permeable soils, a
hand-driven system may be used. In such a system, a
sacrificial drive point with Tygon, Teflon, or other appro-
priate tubing is driven to the desired depth. Then the
steel outertubing is retrieved, leaving the drive point and
the inner flexible tubing in place. Because this type of
installation allows little or no sand pack or seal place-
ment, it should be used only in relatively permeable soils
where sample collection will not be a problem or in soils
that will "self-heal" to prevent short-circuiting. Surface
completion of the hand-driven points should be the
same as for those installed in borings.
Monitoring points typically are used to collect soil gas
for carbon dioxide and oxygen analysis in the 0 percent
to 25 percent range, and for hydrocarbons greater than
100 ppmv. The tubing material must have sufficient
strength and be nonreactive. Materials used include
nylon and Tygon. Sorption and gas interaction with the
tubing materials have not been significant problems for
this application. If a monitoring point will be used to
monitor specific organics in the low-ppm or ppb range,
Teflon or stainless steel may be necessary. This is un-
common, however.
A sufficient number of monitoring points should be in-
stalled to ensure representative sampling. The actual
number installed is site-specific and is driven primarily
by plume size and cost of installing and monitoring
additional monitoring points. If air injection is being con-
sidered in the bioventing test, a nest of monitoring points
must be located between the vent well and any buildings
that may be at risk to ensure that they are well beyond
the radius of influence or that vapor-phase hydrocar-
bons biodegrade before air reaches the structure.
Temperature monitoring typically is conducted by at-
taching thermocouples to monitoring points. Type J or K
thermocouples can be used and should be attached to
the monitoring point depth of interest. In general, soil
temperatures vary little across a site but do vary with
depth to the ground surface; therefore, few thermocou-
ples are required for adequate soil temperature monitor-
ing at a given site.
' See Appendix B for recommended specifications and manufacturers
for monitoring point construction materials.
34
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WATERTIGHT CAST IRON WELL BOX
FINISH CONCRETE
TO DRAIN AWAY
FROM BOX
QUICK COUPLES
GRAVEL
(FOR BOX DRAINAGE)
BENTONITE
SAND
BENTONITE
BENTONITE
1/4" NYLON TUBING
OR OTHER MATERIAL
1" DIAMETER X 6" LONG
SCREENED LENGTH
SAND
BOX SET IN
ABOVE-GROUND
CONCRETE FINISH
FINISH AT GRADE
ALSO ACCEPTABLE
BOREHOLE
THERMOCOUPLE
WITH LEADS
Figure 2-17. Schematic of a typical monitoring point construction.
35
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Chapter 3
Performance Monitoring
The following sections provide suggestions for monitor-
ing bioventing systems. These methods provide a
means of tracking the performance of a bioventing sys-
tem overtime. Methods discussed include:
• Soil gas monitoring
• In situ respiration testing
• Surface emissions sampling
• Operation and maintenance of the bioventing system
In addition, the following nonroutine or optional methods
are discussed:
• Quantification of biodegradation and volatilization of
hydrocarbons during extractive bioventings.
• Qualitative validation of biodegradation through sta-
ble carbon isotope monitoring.
3.1 Soil Gas Monitoring
Periodic soil gas monitoring should be conducted to
ensure that the bioventing site is well oxygenated.1 In-
itially, soil gas should be monitored weekly until the site
becomes fully aerated. Once full aeration is achieved,
bioventing system operation can be optimized. After this
initial period, soil gas monitoring normally is conducted
semiannually for the first year, during the warmest and
coldest months, and annually thereafter. If conducting
an in situ respiration test during different seasons is not
possible, then it should be conducted during the same
seasons as the initial test. Because of the relative sim-
plicity of most bioventing systems, frequent soil gas moni-
toring rarely is necessary to ensure proper operation.
3.2 In Situ Respiration Testing
In situ respiration testing should be conducted peri-
odically as a means of monitoring the progress of site
remediation.2 As the site remediation progresses and
contaminant concentrations decrease, in situ respiration
rates should approach those measured in the uncon-
1 See Sections 1.2, "Soil Gas Survey," and 1.4, "In Situ Respiration
Testing," for more detail on sampling and analyzing soil gases.
2 See Section 1.4, "In Situ Respiration Testing," for additional detail.
taminated area. Frequent in situ respiration tests are not
necessary. In situ respiration tests normally are conducted
quarterly for the first year and annually thereafter.
In situ respiration tests for performance are conducted
somewhat differently than the test for site charac-
terization described in Section 1.3. During system op-
eration, an in situ respiration test is conducted by first
measuring soil gas concentrations of oxygen, carbon
dioxide, and total hydrocarbons during system opera-
tion. After these measurements are collected, the
bioventing system is turned off, and soil gas monitoring
is conducted periodically to measure oxygen disappear-
ance and carbon dioxide production. No inert tracer gas
is added at this time because the initial testing should
have determined whether diffusion or monitoring point
leakage was occurring. Calculation of biodegradation
rates is accomplished in the same manner as described
in Section 1.3.
In situ respiration testing should be used as the primary
indicator for site closure. A good indication that the site
is remediated and that final soil sampling can be con-
ducted is an in situ respiration rate in the contaminated
area similar to that in the uncontaminated area. In situ
respiration testing to determine remediation success is
economically significant because soil sampling is not
relied upon as the sole indicator of site remediation, thus
eliminating the high cost of intermediate soil sampling.
In situ respiration rates can be expected to vary with
time. Generally, temperature is the most significant
driver of short-term (within 1 year) changes. Over longer
periods, contaminant reduction decreases rates. One
frequently observed phenomenon is a substantial de-
cline in rates from the initial in situ respiration rates to
subsequent measurements. This phenomenon seems
to result from placement of monitoring points in less
contaminated soils. NAPL contamination usually is dis-
tributed in a very heterogeneous manner. Under non-
venting conditions, volatilization spreads hydrocarbons
in soil gas, resulting in more heterogeneous contamina-
tion. Soil contaminated in this fashion, however, has a
much lower total concentration because sorbed hydro-
carbons are present at much lower levels than in soils
actually containing NAPLs. If a monitoring point is
37
-------
placed in this soil with only sorbed and vapor-phase
contamination, the initial rates will be high; however,
remediation will rapidly reduce the sorbed concentra-
tions and the in situ respiration rates will fall quickly,
often by a factor of 5 to 10 in a few months. One
indication of this is a low-rate apparent first-order oxy-
gen decay curve, resulting in misleading rate data.
Eliminating this problem is difficult; however, placement
of monitoring points in the most highly contaminated soil
can limit the problem.
3.3 Quantification of Biodegradation
and Volatilization of Hydrocarbons
During Extractive Bioventing
Biodegradation and volatilization of hydrocarbons can
be quantified during extractive bioventing through direct
measurement of off-gas concentrations of oxygen and
carbon dioxide. Bioventing systems that are operating
in injection mode have been reconfigured briefly to pro-
vide these data. Note, however, that in the case of
injection mode systems, reconfiguration to extraction
mode provides an overestimate of the mass of hydro-
carbons volatilized because the size of the in situ biore-
actor is reduced.3
The mass of hydrocarbons volatilized can be calculated
as follows:
HCVO, =
x Q x phexane x MWhexane x
1,440min (Eq. 3-1)
1 ,000 g day
where:
HCVO| = mass of hydrocarbons volatilized
(kg/day)
CV.HC = concentration of hydrocarbons in
extracted off-gas (ppmv)
Q = flow rate (L/min or cfm)
Phexane = density of hexane (moles/L)
MWhexane = molecular weight of hexane (g/mole)
The mass of hydrocarbons biodegraded can be calcu-
lated as follows:
HCbio -
•'V.bkgd ~ W,O2
Too
1,000g
x Q x C x po2 x MWo2 x
1,440 min (Eq. 3-2)
day
where:
HCbio = mass of hydrocarbons biodegraded
(kg/day)
Cy.bkgd = concentration of oxygen in background,
uncontaminated area (%)
Cv,o2 = concentration of oxygen in extracted off-
gas (%)
C = mass ratio of hydrocarbon to oxygen
degraded based on stoichiometry4 (1/3.5)
Example 3-1 illustrates these calculations.
Example 3-1. Calculation of Volatilization and Biodegra-
dation of Contaminants During Extraction: At a site un-
dergoing extraction, concentrations of oxygen and TPH
in the extracted soil gas at steady state are 19 percent
and 140 ppmv, respectively. The system is operating at
a flow rate of 4 cfm (113 L/min). Background oxygen
concentrations are consistently at 20.9 percent. First,
the mass of hydrocarbons volatilized must be calculated.
Given the following parameters:
CV.HC = 14° PPmv; Q = 4 cfm (113 L/min); phexane = 0.042
moles/L; and MWhexane = 84 g/mole.
Using Equation 3-1:
Solving, the mass of hydrocarbons volatilized is 0.081
kg/day (0.1 8 Ib/day).
ft3
_ fUQtfhexaneY..
vol~ 106ft3air mm
V A
28.3L
- r —
ft3
n ... mole"!
0.042 — ; —
L
/
84
g
kg Y1,440 min
mole 1,000g day
A A
To calculate the mass of hydrocarbons biodegraded,
use Equation 3-2:
20.9-19.OY, ft3 28.3 I_Y 1 g HC ^
min
3.5 g02
0 042
0.042
Solving, the mass of hydrocarbons biodegraded is ap-
proximately 1.2 kg/day (2.6 Ib/day), or nearly an order
of magnitude greater than the amount volatilized.
See Section 2.1 for a discussion of these issues.
1 See Section 1.4.2 for a discussion of stoichiometry.
38
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The fraction of total removal by biodegradation is larger
for injection systems because the opportunity for biodegra-
dation is greater. In an injection mode, vapors are pushed
through the contaminated zone into the uncontaminated
zone, allowing for additional biodegradation. When the
system is operated in an extraction mode, however,
much of the vapor is removed from the soil before
biodegradation can occur.
3.4 Surface Emissions Sampling
Surface emissions sampling is not necessary at most
bioventing sites. Under the Bioventing Initiative, it was
conducted at only five of 125 sites to quantify volatiliza-
tion of contaminants attributed to air injection. Although
surface emissions typically do not occur or are very low
at bioventing sites because of low airflow rates, possible
surface emissions often are a regulatory concern and
surface emission rates may need to be quantified to
obtain regulatory approval for bioventing. Note, how-
ever, that according to the EPA document Estimation of
Air Impacts for Bioventing Systems Used at Superfund
Sites (U.S. EPA, 1993), emissions from bioventing sites
operating in an injection mode are thought to be mini-
mal. Thus, they are not discussed in this document.
One standard surface emission sampling protocol using
isolation flux chamber procedures is described by Dupont
(1988) and EPA (1986) and is illustrated in Figure 3-1.
The system consists of a square Teflon box that covers
a surface area of approximately 0.45 m2. The box is
fitted with inlet and outlet ports for the entry and exit of
high-purity air. Inside the box is a manifold that delivers
the air uniformly across the soil surface. The same type
of manifold is fitted to the exit port of the box. This
configuration delivers an even flow of air across the
entire soil surface under the box to generate a repre-
sentative sample.
The air exiting the Teflon box is directed to a sampling
box that contains a sorbent tube and a pump. Also
attached to the box is a purge line that accommodates
the excess flow from the Teflon box that is not drawn into
the sorbent tube. A Magnehelic gauge is used to indicate
if zero pressure is being maintained on the entire system.
In all cases, a totally inert system is employed. Teflon
tubing and stainless steel fittings prevent any contribu-
tion to or removal of organics from the air stream. The
pump is located on the back side of the sorbent trap so
that it is not in a position to contaminate the sample flow.
To calculate the actual emission rates of organic com-
pounds from the soil surface into the atmosphere, the
following formula for dynamic enclosure techniques is
employed (EPA, 1991 a):
CyVr (Eq. 3-3)
where:
F = flux in mass/area-time (g/nf-min)
Cv = concentration of the gas in units of
mass/volume (g/m3)
Vr = volumetric flow rate of sweep gas (m3/min)
A = soil surface area covered by enclosure (m2)
Flow Meter
High-Grade
Compressed Air
Heated Box
Tubing
N
Pump \ sorbent J^^eiic Gauge
\ \ i (/} Teflon Box Quick Couoles
_,
Pump
Exhaust
jL-v- i
O^^±
, ^ \ \
J>-\ -- — HI H
Helium
V « '- — ' k. J
Figure 3-1. Schematic of a surface emissions monitoring device.
39
-------
At bioventing sites where surface emissions have been
measured, surface emissions rates of BTEX and TPH
have been several orders of magnitude below regulatory
levels. These results have provided strong support for
continued operation of bioventing systems in injection
mode. As an example, Table 3-1 illustrates surface emis-
sions results from six bioventing sites. In general, surface
emissions are very low, with TPH emission rates less than
1 Ib/day. These emission rates are well below most regu-
latory limits and illustrate that properly designed bioventing
systems create no significant air emissions.
3.5 Optional Monitoring: Qualitative
Validation of Biodegradation
Through Stable Carbon Isotope
Monitoring
Measurement of stable carbon isotope ratios may help
substantiate biodegradation (Aggarwal and Hinchee,
Table 3-1. Surface Emissions Sampling at Bioventing Sites
1991). Carbon dioxide produced by hydrocarbon degra-
dation may be distinguished from that produced by other
processes based on the carbon isotopic composi-
tions characteristic of the source material and/or the
fractionation accompanying microbial metabolism
(Suchomel et al., 1990; Stahl, 1980; McMahon et al.,
1990). As shown in Figure 3-2, carbon dioxide gener-
ated from natural organic material has a 813C of approxi-
mately -10 to -15, whereas carbon dioxide generated
from petroleum hydrocarbons has a 813C of approxi-
mately -20 to -30. This measurement is not required to
validate biodegradation since the in situ respiration test
is used for this purpose; therefore, it should only be
conducted if dictated by regulatory concerns.
3.6 Operation and Maintenance
Bioventing systems are very simple, with minimal me-
chanical and electrical parts. If the system is operated
Base
Beale AFB, CA
Boiling AFB, DC
Eielson AFB, AK
Fairchild AFB, WA
McClellan AFB, CA
Pittsburgh AFB, NY
Site Type
Fire Training Pit
Diesel Spill
JP-4 Spill
JP-4 Spill
JP-4 Spill
Fire Training Pit
Air Injection
Depth (ft)
10-25
10-15
6.5 - 13
5 - 10
10-55
10-35
Air
Injection
Rate (cfm)
30
20
30
15
50
13
Area of
Influence
(ft2)
6,500
5,100
43,600
5,100
9,700
11,500
Total Flux
Estimate
(Ib/day)
0.15
0.44
0.011
0.33
0.066
0.44
Petroleum and Coal
r* - "H
,^ Organisms ^ ,
H
i^ Carbonate Rock
1* '
i Air 1 Atmo
B2
B2a
i
0 -1
r i
b
B2c
' i
MP
H
sphere
MPP6a
' T
r 1
S1b
MP
' i
"\
A2b
MPP6C
MPSSc
M
i/IPA6b
MPMb
,1
1 1 1
0 -20 -30 -40
13Cin "/a,
Figure 3-2. Carbon isotopic compositions of soil gas carbon dioxide at Site 20, Eielson AFB, Alaska, August 1993.
40
-------
in an injection mode, a simple visual system check
would be required to ensure that the blower is operating
within its intended flow rate and pressure range. Weekly
system checks are desirable. Often, someone on site
can conduct these system checks because little techni-
cal knowledge of the process is required. Minor mainte-
nance such as replacing filters, flow meters, or gauges
may be necessary.
If an extraction system or an extraction/reinjection
bioventing system is installed, more intensive mainte-
nance is likely to be required. Extraction systems have
knockout drums that require draining and treatment of
condensate. In addition, in the case of extraction-only
systems, off-gas may need to be monitored regularly to
ensure that emissions are within regulatory guidelines.
Off-gas treatment systems also require periodic checks
to ensure proper operation.
Blowers used for bioventing systems typically last for
several years and should not need replacement. To
date, two bioventing systems have been operating for 3
years with the original blower in place (Battelle, 1994;
Leeson et al., 1995), and of the 125 blowers installed to
date under the Bioventing Initiative, only three have
required repair or replacement.
41
-------
Chapter 4
Process Evaluation/Site Closure
4.1 In Situ Respiration Testing
In situ respiration testing should be used as the primary
indicator for site closure. As discussed in Section 3.2,
as site remediation progresses and contaminants are
degraded, the measured in situ respiration rates ap-
proach background respiration rates. When the in situ
respiration rate in the contaminated area is similar to
that in the uncontaminated area, this is a good indication
that the site is remediated and final soil sampling can be
conducted. Initially, the amount of time necessary for
cleanup of the site can be estimated on in situ respira-
tion rates, as shown in Example 4-1.
Example 4-1. Calculation of Remediation Time Based
on in Situ Respiration Rates/This example assumes an
average oxygen utilization rate of 6 percent oxygen per
day and an initial average soil concentration of 6,000 mg
TPH/kg soil. The oxygen utilization is related to hydro-
carbon degraded by the following equations:
C6H14 + 9.5O2 -» 6CO2 + 7H2O
kB = -0.68
Using the above assumptions, an oxygen utilization rate
of 6 percent oxygen per day would correspond to a
biodegradation rate of approximately 4.1 mg/kg-day.
Given that the initial soil concentration is 6,000 mg/kg,
an estimate of cleanup time is calculated as follows:
Q
-j-2- = cleanuptime
6,000 mg/kg
4.1 mg/kgday
= 1,500 days ~ 4 years
This calculation provides a reasonable "ballpark" esti-
mate of the amount of time necessary to remediate the
site. This method tends to underestimate treatment time
because kB decreases overtime. At the same time, this
calculation overestimates treatment time because it
does not consider treatment in the expanded bioreactor.
Therefore, the calculation must be coupled with process
monitoring to provide field-based evidence that the site
actually is remediated within this time. Because of
widely variable contaminant concentrations, the aver-
age biodegradation rate does not reflect actual biode-
gradation rates throughout the site; biodegradation rates
also may fluctuate with season and as contaminant
concentrations decrease. Therefore, process monitoring
is an important parameter in determining treatment time.
4.2 Soil Sampling
Soil sampling should not be used as a process monitor-
ing technique. Because of the inherently high variability
of hydrocarbons in soils, the number of samples re-
quired to produce a meaningful result is prohibitive until
contamination levels approach 90 percent to 99 percent
cleanup. The amount of soil sampling conducted at a
site has a tremendous impact on the cost of the project.
Minimizing soil sampling makes a remediation effort
much more cost-effective. With bioventing systems, in
situ respiration testing can indicate when the site is
clean and, therefore, when to collect final soil samples.
Regulatory issues usually drive the number of final soil
samples collected.
The Department of Natural Resources of the State of
Michigan published a guidance document for verification
of soil remediation. It also provides several methods for
statistical sampling strategies (Michigan Department of
Natural Resources, 1994). In addition, it provides informa-
tion on design of the sampling grid and determination of
the upper confidence limit (UCL) of the final mean. The
UCL is calculated from the following equation:
where:
UCL
X
bracketed
term
Sx
UCL = X + [t = 0.95(n-1)]Sx (Eq. 4-1)
upper confidence limit
average contaminant concentration
one-tailed t-test at n-1 degrees of
freedom (see Table 4-1 for values)
standard error of the mean, which is
calculated as follows:
43
-------
Table 4-1. Cumulative t Distribution
One-
Tailed
Two-
Tailed
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0.550
0.100
0.158
0.142
0.137
0.134
0.132
0.131
0.130
0.130
0.129
0.129
0.129
0.128
0.128
0.128
0.128
0.750
0.500
1.000
0.816
0.765
0.741
0.727
0.718
0.711
0.706
0.703
0.700
0.697
0.695
0.694
0.692
0.691
0.080
0.600
1.376
1.061
0.978
0.941
0.920
0.906
0.896
0.889
0.883
0.879
0.876
0.873
0.870
0.868
0.866
0.900
0.800
3.078
1.886
1.638
1.533
1.476
1.440
1.415
1.397
1.383
1.372
1.363
1.356
1.350
1.345
1.341
0.950
0.900
6.314
2.920
2.353
2.132
2.015
1.943
1.895
1.860
1.833
1.812
1.796
1.782
1.771
1.761
1.753
0.975
0.950
12.706
4.303
3.182
2.776
2.571
2.447
2.365
2.306
2.262
2.228
2.201
2.179
2.160
2.145
2.131
0.990
0.980
31.821
6.925
4.541
3.747
3.365
3.143
2.998
2.896
2.821
2.764
2.718
2.681
2.650
2.624
2.602
0.995
0.990
63.657
9.925
5.841
4.604
4.032
3.707
3.499
3.355
3.250
3.169
3.106
3.055
3.012
2.977
2.947
o
(Eq. 4-2)
A/n
where:
S = standard deviation
n = sample size
If the UCL is higher than the regulatory threshold, then
the lambda relationship is used to calculate the appro-
priate sample size:
RT-X
(Eq. 4-3)
where:
A, =
RT =
X =
S =
Example 4-2. Statistical Evaluation of Contaminant
Data: At this site, three preliminary soil samples were
collected to estimate a sample mean and standard de-
viation. The initial sample mean was 90 mg/kg TPH with
a standard deviation of 30 mg/kg. The regulatory thresh-
old is 100 mg/kg TPH. Calculating the UCL:
UCL = 90 + (2.920) x (^=\= 141 mg/kg
(Eq. 4-4)
Given that this value is above the regulatory threshold,
the lambda calculation is performed to determine how
many additional samples are required to verify cleanup:
statistical parameter (see Table 4-2 for values)
regulatory threshold
average contaminant concentration
standard deviation
100-90
30
=0'33
(Eq. 4-5)
Once X is calculated, by referring to Table 4-2, the number
of additional samples required to verify cleanup can be
determined. This calculation is shown in Example 4-2.
From Table 4-2, fora = 0.05 and p = 0.05, a sample size
of between 90 and 122 additional samples is required.
Ott (1984) provides an alternative method for estimating
final sample size. This method determines the required
44
-------
Table 4-2. Number of Observations for t Test of Mean
Single-Sided a = 0.01
Double-Sided a = 0.02
X P 0.011 0.05 0.1 0.2
0.05
0.10
0.15
0.20
0.25
0.30 115
0.35 109 85
0.40 101 85 66
0.45 110 81 68 53
0.50 90 66 55 43
0.55 75 55 46 36
0.60 63 47 39 31
0.65 55 41 34 27
0.70 47 35 30 24
0.75 42 31 27 21
0.80 37 28 24 19
0.85 33 25 21 17
0.90 29 23 19 16
0.95 27 21 18 14
1.00 25 19 16 13
number of soil samples to show a statistical difference
between initial and final contaminant concentrations:
o2(za+zp)2
n - ~ (,cq. t- iu;
(Mo - M)2
where:
n = number of final soil samples to collect
o2 = population variance of the initial soil
sampling event
za = probability of a Type I error
zp = probability of a Type II error
u,0 = mean of the initial soil sampling event
u, = estimated mean of the final soil sampling
event
Level for t test
a = 0.05
a =0.10
0.5 0.01 0.05 0.1 0.2 0.5
122
139 70
90 139 101 45
63 122 97 71 32
47 90 72 52 24
37 101 70 55 40 19
30 80 55 44 33 15
25 65 45 36 27 13
21 54 38 30 22 11
18 46 32 26 19 9
16 39 28 22 17 8
14 34 24 19 15 8
13 30 21 17 13 7
12 27 19 15 12 6
11 24 17 14 11 6
10 21 15 13 10 5
9 19 14 11 9 5
9 18 13 11 85
show a statistical difference in the two means. This
concept is illustrated in Example 4-3.
Example 4-3. Calculation of Final Number of Soil Sam-
ples for Site Closure. At this site, 83 initial soil samples
were collected with a mean TPH concentration of 6,000
mg/kg and a standard deviation of 8,000 mg/kg (typical
of many bioventing sites). The average biodegradation
rate at this site was 4.1 mg/kg-day. Given that the sys-
tem had been operating for 3.5 years, the final mean
TPH concentration can be estimated as follows:
4.1 mg/kg-day x 1,278 days =
5,240 mg/kg TPH degraded ^tq- 4'n1'
Estimated final [TPH] = (Eq. 4-12)
As the difference between the initial and final means
increases, the number of samples required to show a
statistical difference between the two sampling events
decreases. As shown in Table 4-3, as hydrocarbons are
further degraded, fewer soil samples are required to
6,000 mg/kg - 5,240 mg/kg = 760 mg/kg
Using this estimate of the final mean TPH concentration,
the number of samples to be collected to provide statis-
tically significant data can be calculated using Equation
(4-4) and the following parameters:
45
-------
Table 4-3. Calculation of the Number of Samples Required To
Show a Statistical Difference Between Means of
Two Sampling Events
o = (8,000)2; za = 1.645 (for a = 0.05);
zp = 2.33 (for B = 0.01); u,0 = 6,000 mg/kg;
mg/kg
Estimated
Time From Amount of
Initiation of Hydrocarbon
Bioventing Degraded
(days) (mg/kg)
180
365
540
730
Table 4-4.
z
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3a
2.4
2.5
1,440
2,920
4,320
5,840
Selected z Values for
0.00
0.0000
0.0398
0.0793
0.1179
0.1554
0.1915
0.2257
0.2580
0.2881
0.3159
0.3413
0.3643
0.3849
0.4032
0.4192
0.4332
0.4452
0.4554
0.4641
0.4731
0.4772
0.4821
0.4861
0.4893
0.4918
0.4938
Am'o'unt'S Selected z values an
Hydrocarbon Number of are determined by fin
Remaining Samples anc| (Q 5 - B) respec
(mg/kg) Required
4,560
3,080
1,680
160
Estimation of Final
0.01
0.0040
0.0438
0.0832
0.1217
0.1591
0.1950
0.2291
0.2611
0.2910
0.3186
0.3438
0.3665
0.3869
0.4049
0.4207
0.4345
0.4463
0.4564
0.4649
0.4719
0.4778
0.4826
0.4864
0.4896
0.4920
0.4940
731
178
81 Therefore
44 collected
Soil Sample Number (Ott,
0.02
0.0080
0.0478
0.0871
0.1255
0.1628
0.1985
0.2324
0.2642
0.2939
0.3212
0.3461
0.3686
0.3888
0.4066
0.4222
0.4357
0.4474
0.4573
0.4656
0.4726
0.4783
0.4830
0.4868
0.4898
0.4922
0.4941
(8.
nv
—
e shown in Table 4-4. The zaand zp
ding areas corresponding to (0.5 -a)
:tively:
lOOO)2(1.645+2.33)2 (Eq. 4-13)
(6,000 - 760)2
, the number of final soil samples
is 37.
1984)
0.03a
0.0120
0.0517
0.0910
0.1293
0.1664
0.2019
0.2357
0.2673
0.2967
0.3238
0.3485
0.3708
0.3907
0.4082
0.4236
0.4370
0.4484
0.4582
0.4664
0.4732
0.4788
0.4734
0.4871
0.49013
0.4925
0.4943
0.04b
0.0160
0.0557
0.0948
0.1331
0.1700
0.2054
0.2398
0.2704
0.2995
0.3264
0.3508
0.3729
0.3925
0.4099
0.4251
0.4382
0.4495b
0.4591
0.4671
0.4738
0.4793
0.4838
0.4875
0.4904
0.4927
0.4945
that must be
0.05b
0.0199
0.0596
0.0987
0.1368
0.1736
0.2088
0.2422
0.2734
0.3023
0.3289
0.3531
0.3749
0.3944
0.4115
0.4265
0.4394
0.4505b
0.4599
0.4678
0.4744
0.4798
0.4842
0.4878
0.4906
0.4829
0.4846
3 Corresponds to determining zp.
b Corresponds to determining za.
46
-------
Chapter 5
Costs
Based on Air Force and recent commercial applications
of this technology, the total cost of in situ soil remediation
using the bioventing technology is $10 to $60 per yd3
(Downey et al., 1994b). At sites with over 10,000 yd3 of
contaminated soil, costs of less than $10 per yd3 can be
achieved. Costs greater than $60 per yd3 are associated
with smaller sites, but bioventing can still offer significant
advantages over more disruptive excavation options.
Operations and maintenance costs are minimal, particu-
larly when base personnel are willing to perform simple
system checks and routine maintenance. Table 5-1 pro-
vides a detailed cost breakdown of remediation of 5,000
yd3 of soil contaminated with an average concentration
of 3,000 mg of JP-4 jet fuel per kg of soil.
Ward (1992) compared costs of bioventing with costs of
other in situ bioremediation technologies (Table 5-2).
Costs shown in Table 5-2 reflect actual costs for these
three technologies at fuel spills in Traverse City, Michigan.
Table 5-1. Typical Full-Scale Bioventing Costs (Downey et al.,
1994b)
Task
Total Cost ($)
Site visit/planning
Work plan preparation
Pilot testing
Regulatory approval
Full-scale construction
Design
Drilling/sampling3
Installation/startup
Two-year monitoring
Two-year power
Soil sampling at 2 years
Total
5,000
6,000
27,000
3,000
7,500
15,000
4,000
6,500
2,800
13,500
90,300
Even though the area treated through bioventing was
larger than that treated with hydrogen peroxide or ni-
trate, total costs for bioventing were significantly lower
than for the other technologies.
Figure 5-1 provides a comparison of estimated unit
costs for several technologies commonly used for reme-
diation of fuel-contaminated soils. All costs are based on
the treatment of soil contaminated with 3,000 mg of JP-4
jet fuel per kg of soil. Costs are provided for the following
remediation scenarios: 2 years of in situ bioventing; 1
year of soil vapor extraction with thermal vapor treat-
ment; excavation and 1 year of on-base landfarming
with leachate controls; and excavation followed by low-
temperature thermal desorption. The cost of recon-
structing excavated areas is not included. At many sites
with contamination beneath concrete and buildings, bio-
venting is the only cost-effective treatment option available.
Table 5-2. Cost Comparison of in Situ Bioremediation
Technologies Used at Fuel Spill Sites (Ward, 1992)
Total Costs ($/m3 of Contaminated
Earth)
Task
Construction13
Labor/monitoring
Chemicals
Electricity
Total
Hydrogen
Peroxide
45
72
500
24
641
Nitrate
118
96
30
12
256
Bioventing3
26
40
0.44
6.8
73
a Values reflect only first 4 months of demonstration.
b Prorated to a 5-year service life on buildings, pumps, and blowers.
'Assumes four air injection wells drilled to a depth of 15 ft.
47
-------
Comparison of Unit Costs
100
90
80
70
T> 60
£
| 50
% 40
30
20
10
2 Years Bioventing
Soil Vapor Extraction with
Thermal Vapor Treatment
Land Farming with
Leachate Controls
Excavation and
Low-Tern peratu re
Thermal Desorption
I I I
I
I
500 2,000 3,500 5,000 6,500 8,000 9,500 11,000 12,500 14,000 15,500 17,000 18,500 20,000
Cubic Yards of Soil
* Based on treatment of soil contaminated with 3,000 mg of JP-4 jet fuel per kg of soil.
Costs do not include the cost of reconstructing excavated sites.
Figure 5-1. Comparison of costs for various remedial technologies for fuel-contaminated soils (Downey et al., 1994b).
48
-------
Chapter 6
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U.S. EPA. 1991 a. Current and developing analytical technologies for
quantifying biogenic gas emissions (June). EPA/600/3-91/044.
Washington, DC.
U.S. EPA. 1991b. Soil vapor extraction: Air permeability testing and
estimation methods. In: Proceedings of the 17th RREL Hazardous
Waste Research Symposium. EPA/600/9-91/002. Washington, DC
(April).
U.S. EPA. 1986. Evaluation of the volatilization of hazardous constitu-
ents at hazardous waste land treatment sites. EPA/600/2-86/071.
Washington, DC.
van Eyk, J., and C. Vreeken. 1988. Venting-mediated removal of
petrol from subsurface soil strata as a result of stimulated evapo-
ration and enhanced biodegradation. Med. Fac. Landbouww. Ri-
iksuniv. Gent 53(4b): 1873-1884.
Ward, C.H. 1992. Performance and cost evaluation of bioremediation
techniques for fuel spills. In: Proceedings of In Situ Bioremediation
Symposium '92. pp. 15-21.
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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
51
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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
52
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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
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Appendix B
Equipment Specifications and Manufacturers
The products and manufacturers listed in this document
are meant as a guidance for environmental managers
and consulting engineers. Products or manufacturers
are not endorsed by the U.S. Air Force or EPA.
B.1 Soil Gas Survey Equipment
Calibration Gases
Calibration gases include helium, carbon dioxide, oxy-
gen, and hexane. They are available in the appropriate
concentrations for each instrument and may require a
special regulator depending on the cylinder type.
The calibration gases are used to standardize the gas
analyzing instruments.
The gases are sold through Scott Specialty Gases in
Troy, Michigan, 313 589-2950. The gases cost approxi-
mately $124 depending on the cylinder size and gas
desired.
Tedlar Sampling Bag
The 1-L bag is made from transparent Tedlar and has a
polypropylene fitting. The bag is approximately 7x7 in.
and is sold in packages of 10. The fitting is opened and
closed by twisting the cap, which can also be locked into
place.
The Tedlar bag is used to store soil gas samples and
calibration gases until they can be analyzed by an ap-
propriate gas meter.
The Tedlar bags are supplied by SKC, Eighty Four,
Pennsylvania, 800 752-8472. The cost is approximately
$82 for 10 bags.
Latex Rubber Tubing
Latex or amber tubing is connected to the Tedlar bag
tubing fitting for filling the bag. Tubing is normally cut
approximately 4 in. in length. Size of tubing is 1/4-in.
outside diameter x 3/16-in. inside diameter and can be
purchased from any VWR Scientific location.
Wire/Cable Ties
Nylon cable ties are used like a hose clamp for securing
the latex tubing to the Tedlar bag fitting. Cable ties can
be purchased from Grainger or any hardware store. The
catalog number is 6X750; ties are sold in packs of 100
at $1.91/pack.
Oxygen/Carbon Dioxide Gas Sampling Meter
This handheld instrument has a rechargeable battery
that lasts up to 16 hours. It has an oxygen and carbon
dioxide range of 0 percent to 25 percent. The meter has
an analog scale readout with audible and visual alarms
for low and high warning levels. The meter analyzes
oxygen content through an electrochemical cell and
carbon dioxide through an infrared sensor. An external
filter and an internal filter are employed for high reliability
and preventive maintenance. An internal diaphragm
pump is provided.
The gas sampling meter is used to determine the oxy-
gen and carbon dioxide content of the ambient air or of
the gas within the soil. Calibrations must be performed
regularly with gas standards.
The meter is sold by Cascade Associates in Young-
stown, Ohio, 216 758-6649. It costs approximately
$3,200.
Carry Case for Gas Sampling Meter
The case is of heavy plastic construction with foam
cushioning inside and can be secured with locks.
It is capable of protecting and carrying both the Trace-
Techtor and the gas sampling meter.
The case is sold by Cascade Associates in Youngstown,
Ohio, 216 758-6649. It costs approximately $250.
Combustibles Sampling Meter
This meter has a digital display screen with audible and
visual alarms for high- and low-level combustibles/
hydrocarbons. They are measured from 0 percent to 100
percent lower explosive limit (LEL) and 0 ppm to 10,000
ppm in 20-ppm increments. The meter uses both inter-
nal and external filters and includes an internal pump. In
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addition, it has a data logging function, which allows the
meter to be connected with an IBM-compatible com-
puter. It can be operated with alkaline or nicad batteries
that hold a 9-hour charge. The platinum catalyst sensor
has a flame arrester.
The meter is used to determine the level of hydrocar-
bons or combustibles in the ambient air or sampled soil
gas. It is a new model that replaces the Trace-Techtor
meter.
The meter is sold by Cascade Associates in Young-
stown, Ohio, 216 758-6649. It costs approximately
$1,475.
1:1 Diluter
The diluter is an external fitting that attaches to the inlet
of the Trace-Techtor meter. It has a metal construction
and is about 3 in. long. A diluter is required when the
oxygen levels of the gas sample drop below 12 percent.
At this low oxygen level, the platinum catalyst cannot
combust the gas sample properly.
The function of the 1:1 diluter is to reduce the gas
sample flow by one-half. This dilution reduces the con-
centration by one-half. Once a concentration reading is
obtained from the meter, it is multiplied by a factor of two
to compensate for the dilution.
The diluter is sold by Cascade Associates in Young-
stown, Ohio, 216 758-6649. It costs approximately $150.
10:1 Diluter
This diluter is also an external fitting that attaches to the
inlet of the Trace-Techtor meter and is small enough to
hold in the hand. The diluter has two rotameters built
into it to permit a dilution factor up to 10. A diluter is
required when the oxygen levels of the gas sample drop
below 12 percent. At this low oxygen level, the platinum
catalyst cannot combust the gas sample properly. The
10:1 diluter can be used if the concentration of the
sample is still too high to be read after using a 1:1 diluter.
This is evident when the gas analysis instrument is
pegged on its highest setting.
The function of the 10:1 diluter is to reduce the gas
sample flow up to a factor of 10. The dilution factor is
set by adjusting the two rotameters until the ratio of the
two flows is equal to the dilution ratio. This reduces the
concentration by the same factor. Once a concentration
reading is obtained from the meter, it is multiplied by the
ratio to compensate for the dilution.
The diluter is sold by Cascade Associates in Young-
stown, Ohio, 216 758-6649. It costs approximately $250.
Trace-Techtor Meter
This handheld instrument has a rechargeable battery
that lasts for 10 hours. It can measure petroleum-based
hydrocarbon vapors (BTEX) up to 10,000 ppm. It has an
analog scale readout with audible and visual alarms for
low and high concentration levels. The meter analyzes
the vapor through an electrochemical cell with a plati-
num catalyst. An external filter and an internal filter are
employed for preventive maintenance and high reliabil-
ity. An internal diaphragm pump is also supplied.
The gas sampling meter is used to determine the petro-
leum hydrocarbon content of the ambient air or of the
gas within the soil. Calibrations must be performed regu-
larly with hexane. The instrument can also be equipped
to detect methane or natural gas.
The meter was sold and manufactured by GasTech in
Newark, California, 415 794-1973. The price was ap-
proximately $1,500. The Trace-Techtor is no longer
manufactured, however.
Interface Probe
It is constructed in the shape of a disk, which stores a
100-ft measuring tape and a sensor probe. It weighs 16
Ib, is 16x18x6 in., and is battery operated. The interface
probe resembles a common tape measure, only larger.
The interface probe is very useful when used alone with
soil gas probes during site investigation. The probe is
used in wells to detect the level at which both oil and
water are present. This is accomplished through the use
of audible alarms. The probe can detect an oil layer as
thin as 0.05 ft.
The interface probe is made by ORS Environmental
Systems in Greenville, New Hampshire, 800 228-2310.
It costs approximately $2,000.
150-Ft Tape Measure
A 150-ft fiberglass reel tape is needed for site mapping
during soil gas survey and is also used when measuring
borehole depths and monitoring point construction.
It is available from Grainger. The catalog number is
6C192, and the cost is $57.70.
So/7 Gas Probes and Well Points (The Macho
System)
These are electric-powered sampling systems for driv-
ing soil gas probes. The deluxe system includes a vari-
able-speed hammer drill and the capability to sample
soil gas to a depth of approximately 10 ft. This is a good
starter set; however, additional shafts, slotted well
points, and hollow probe nipples are also recom-
mended. The system is available from KVA Analytical
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Systems in Falmouth, Massachusetts, 508 540-0561.
The Macho System costs approximately $3,065.
Bulkhead Quick Coupler (Parker)
These brass fittings are threaded into the top of the soil
gas probe after driving to the desired depth. The fitting
gives the sampler an airtight connection between the
probe and the vacuum sampling pump, which pulls the
soil gas sample from the soil. The coupler is sold by
Forberg Scientific in Columbus, Ohio, 800 209-9575.
Diaphragm Pump (Vacuum/Air Compressor)
The pumps are usually wired for 110 volts for the
1/16-hp, 1/8-hp, and 1/3-hp versions. Cast produces
pumps and compressors that are preferred because of
their reliability and easy maintenance.
The pumps are used to draw soil gas from deep moni-
toring points and soil gas probes. We recommend the
1/3-hp pump because of the available air produced at
20 psi.
The pump is sold by Grainger in Columbus, Ohio, 800
323-0620. The cost depends on the size of the pump;
for the 1/3-hp pump, the catalog number is 4Z024, and
the cost is $228.
Probe Puller Adapter
The probe puller adaptor was made by Battelle staff. It
is a piece of square steel tubing approximately 4x4x2 in.
wide. A solid probe nipple is then welded in the middle
of one outside edge. The adaptor is threaded onto the
top of a soil gas probe when sampling is completed. A
large utility jack is placed inside the square tube, and
the probe is removed.
Utility Jack
The utility jack is used for removing soil gas probes
when sampling is completed. The jack is sold by Grain-
ger, Columbus, Ohio, 800 323-0620. The catalog num-
ber is 5Z156, and the cost is $100.
Miscellaneous Supplies for Soil Gas Survey
Miscellaneous supplies include work gloves, safety
glasses, small measuring tape, crescent wrenches, pipe
wrenches, vise grips, field record book, cleaning sup-
plies for cleaning soil gas probes, razor blades (single
edge), electrical tape, electrical extension cords, oil, and
fuel for the generator.
B.2 Vent Well Installation Equipment
Contracted Drilling Services
If a contract driller is installing the vent well and soil gas
monitoring points, the driller provides monitoring vent
well and well construction materials (sand and ben-
tonite); however, the soil gas monitoring points need to
be furnished to the driller. If a contract driller is not used,
then items in this section will be necessary.
Hand Augering and Soil Sampling Equipment
A vent well can be installed by hard augering if soil
conditions permit. The following is a list of hard augering
equipment and equipment needed for collecting soils for
laboratory analysis.
Auger Head
It is constructed of stainless steel to resist corrosion and
contamination of soil samples. The head is approxi-
mately 1 ft long and is open on both ends to accommo-
date a soil sample liner. The bottom of the head is flared
to allow easy penetration into the ground, while the top
has a single bar with a male pipe thread. The male pipe
thread attaches to the auger's extension rods.
The auger head is used to house the liner while the soil
is being sampled. It is designed to sample the soil with
minimal disturbance and effort.
The auger head is supplied by Enviro-Tech Services in
Martinez, California, 800 468-8921. It costs approxi-
mately $85.
Core Sampler With Slide Hammer
The core sampler is a metal pole with a soil sampler at
one end. On the other end is the slide hammer, a weight
that slides up and down the pole of the core sampler.
The core sampler is another way to obtain undisturbed
soil samples. The slide hammer drives the sampler into
the ground and eliminates the need for the auger head.
The items are supplied by Enviro-Tech Services in
Martinez, California, 800 468-8921. They cost approxi-
mately $225.
Sampling Extensions, Extension Cross Handle,
and Carry Case
The sampling extensions are long, metal poles that
connect the auger head to the cross handle with
threaded ends.
The extension cross handle is placed at the top of the
auger and is used for leverage to turn the auger into the
ground. It may have a rubber handle for increased grip.
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The metal carry case is about 6 ft long and 1 ft tall and
holds the complete auger, disassembled. It has a foam
lining for protection during travel.
The equipment is supplied by Enviro-Tech Services in
Martinez, California, 800 468-8921. It costs approxi-
mately $400 for all three items.
Brass Sleeves and Plastic End Caps
The sleeve is a cylinder that is open at both ends. It
comes in various diameters and lengths. The caps are
orange and made from plastic to fit over each end of the
sleeve after being filled with soil.
The sleeve is placed inside the auger head and used as
a core sample liner. It contains the soil that is removed
by the auger. The end caps are placed on each end of
the sleeve after it is removed from the auger head. Brass
sleeves are also used in the core sampler with slide
hammer.
The sleeves and caps are supplied by Enviro-Tech Serv-
ices in Martinez, California, 800 468-8921. The cost for
both items is approximately $3.
PVC Well Screen
Well screen constructed of polyvinyl chloride (PVC) is
flush-threaded at both ends to accommodate a threaded
plug and the riser pipe or blank well casing. Screens are
available in 10-, 20-, and 30-slot openings. Well screen
is also available in stainless steel.
The screen is sold by Environmental Well Products
Company in Dayton, Ohio, 800 777-0977. Price varies
with size and length.
PVC Riser
PVC riser or blank casing is also flush-threaded and has
no openings. It is merely an extension of pipe from the
well screen to the ground surface. It is sold by Environ-
mental Well Products Company or any drilling supply
company.
Bentonite Chips
The chips are available in coarse grades or pellets in
small sizes. Common sizes include 0.375-in. and 0.75-
in. chips or pellets. They are made from dry bentonite
clay and sold in 50-lb bags. The bentonite is chemically
stable and can absorb large amounts of moisture.
The bentonite chips are placed around the necessary
equipment within the borehole to form a seal and act as
a general filler for the void space. Bentonite was se-
lected because of its high water retention levels. It also
interfaces well with Portland cement.
The bentonite is sold by Environmental Well Products
Company in Dayton, Ohio, 800 777-0977. The price is
approximately $10 for 50 Ib.
Silica Sand
The sand contains silica powder for increased chemical
stabilization. It is commonly found in the 10x20 graded
form.
The silica sand is another form of packing used in well
construction. The granular sand is added to boreholes
around the screened interval of the vent well and soil
gas monitoring points.
The sand is sold by Environmental Well Products Com-
pany in Dayton, Ohio, 800 777-0977. The price is ap-
proximately $6 for 50 Ib.
Concrete Mix
The concrete requires only the addition of water and
sets quickly. The concrete is readily available in large
quantities throughout the country.
Concrete mix is placed around the manhole at ground
level of the well. This ensures its stability during ex-
tended absences.
The concrete is sold by Environmental Well Products
Company in Dayton, Ohio, 800 777-0977. The price is
approximately $4 for 50 Ib. It is also available at most
building supply stores and hardware stores.
Manhole (Flushmount Well Cover)
Many companies manufacture manholes, some with
bolts to secure the top. They are usually sold in 8x12-in.
or 12x12-in. sizes and are made of iron, steel, or stain-
less steel. The bottom is designed to fit over the riser
pipe or soil gas monitoring points.
The manhole serves as a marker and gives added
protection to the well and the monitoring points.
The manhole is sold by Environmental Well Products
Company in Dayton, Ohio, 800 777-0977. The price is
approximately $50.
B.3 Soil Gas Monitoring Point Equipment
Contracted Drilling Services
If a contract driller is installing the vent well and soil gas
monitoring points, the driller provides monitoring vent
well and well construction materials (sand and ben-
tonite); however, the soil gas monitoring points need to
be furnished to the driller. If a contract driller is not used,
then items in this section will be necessary.
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Hand Augering and Soil Sampling
A vent well can be installed by hand augering if soil
conditions permit. The following is a list of hand augering
equipment and equipment needed for collecting soils for
laboratory analysis.
Auger Head
It is constructed of stainless steel to resist corrosion and
contamination of soil samples. The head is approxi-
mately 1 ft long and is open on both ends to accommo-
date a soil sample liner. The bottom of the head is flared
to allow easy penetration into the ground, while the top
has a single bar with a male pipe thread. The male pipe
thread attaches to the auger's extension rods.
The auger head is used to house the liner while the soil
is being sampled. It is designed to sample the soil with
minimal disturbance and effort.
The auger head is supplied by Enviro-Tech Services in
Martinez, California, 800 468-8921. It costs approxi-
mately $85.
Core Sampler With Slide Hammer
The core sampler is a metal pole with a soil sampler at
one end. On the other end is the slide hammer, a weight
that slides up and down the pole of the core sampler.
The core sampler is another way to obtain undisturbed
soil samples. The slide hammer drives the sampler into
the ground and eliminates the need for the auger head.
The items are supplied by Enviro-Tech Services in
Martinez, California, 800 468-8921. They cost approxi-
mately $225.
Sampling Extensions, Extension Cross Handle,
and Carry Case
The sampling extensions are long, metal poles that
connect the auger head to the cross handle with
threaded ends.
The extension cross handle is placed at the top of the
auger and is used for leverage to turn the auger into the
ground. It may have a rubber handle for increased grip.
The metal carry case is about 6 ft long and 1 ft tall and
holds the complete auger, disassembled. It has a foam
lining for protection during travel.
The equipment is supplied by Enviro-Tech Services in
Martinez, California, 800 468-8921. The cost for all three
items is approximately $400.
Brass Sleeves and Plastic End Caps
The sleeve is a cylinder that is open at both ends. It
comes in various diameters and lengths. The caps are
orange and made from plastic to fit over each end of the
sleeve after being filled with soil.
The sleeve is placed inside the auger head and is used
as a core sample liner. It contains the soil that is re-
moved by the auger. The end caps are placed on each
end of the sleeve after it is removed from the auger
head. Brass sleeves are also used in the core sampler
with slide hammer.
The sleeves and caps are supplied by Enviro-Tech Serv-
ices in Martinez, California, 800 468-8921. The cost for
both items is approximately $3.
Suction Strainer
The suction strainer resembles an oxygen diffuser used
in fish tanks. It is approximately 0.75 in. in diameter and
8 in. long, constructed of a nylon frame with number 50
mesh screen to permit the flow of gases. The strainers
must be tapped with 3/8-in. national pipe thread (NPT)
to install the connector and nylon tubing.
The strainers are filled with aquarium gravel to ensure
the complete mixture of the soil gas as it is sampled. The
strainers are placed at the end of the nylon tubing and
set in the monitoring wells. There, they are used to
withdraw soil gas from the ground, free of dirt and
particulate.
The strainer is sold by Grainger in Columbus, Ohio, 800
323-0620. It costs approximately $7.
NEWLOC Male Connector
The male pipe thread connector is made of plastic and
has an opening on the end for0.25-in. tubing. The other
end has 0.375-in. male pipe thread.
The connector is used to attach the suction strainer to
the nylon tubing in the monitoring wells.
The connector is supplied by New Age Industries in
Willow Grove, Pennsylvania, 215 657-3151. It costs
approximately $1.60.
Nylon Tubing
Often called Nylotube, it is made from nylon and sold in
various colors for identification purposes. Most common
applications of the tube involve the 0.25-in. size.
The tubing transports gases from monitoring points to
the surface for soil gas sampling and can be used on
some pieces of field equipment for similar purposes.
This type of tubing is favorable because it is inexpen-
sive, is chemically resistant to hydrocarbons, and is
available in many colors. The tubing will adsorb some
small amount of hydrocarbons, however.
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The tubing is supplied by New Age Industries in Willow
Grove, Pennsylvania, 215 657-3151. It costs approxi-
mately $0.36 per ft and is sold in 100-ft rolls.
Quick Connectors (Parker)
Male and female quick connectors and quick connector
plugs are compatible with different tube sizes. They are
made of brass or stainless steel. The quick connectors
offer easy access to monitoring points for taking soil gas
samples.
The quick connectors are attached to tubing when quick
and convenient access is desired. They also are in-
stalled on gas sampling instruments and on tubing found
at the monitoring wells. In addition, they provide a strong
seal to prevent leaking. The quick connector solid plugs
are placed in the female quick connectors to prevent
corrosion and other forms of damage.
The connectors are sold by Forberg Scientific in Colum-
bus, Ohio, 614 294-4600. The price forthe male connector
is approximately $6, and the female is approximately
$11.
Thermocouple Cable, K Type
The thermocouple cable is a 24-gauge wire insulated
with PVC. It can withstand temperatures up to 105°C. It
is usually sold by the foot.
The thermocouple is responsible for measuring tem-
peratures, often within a soil gas monitoring point or an
outlet stream from a piece of field equipment. The cable
transmits the temperature through a current and is re-
corded using an electronic thermometer.
The cable is supplied by Cole-Parmer in Miles, Illinois,
800 323-4340. It costs approximately $0.80 per foot.
Thermocouple Minimale Plug
The type K minimale plug has two different prongs and
is attached to the thermocouple cable. It acts as a cable
termination. It is slightly smaller than a normal electrical
plug but serves the same purpose.
The plug is used to connect the thermocouple to the
electronic thermometer for data collection of tempera-
tures.
The plug is supplied by Cole-Parmer in Miles, Illinois,
800 323-4340. It costs approximately $5.
Brass Tags
The tags are available in 1-in. to 2-in. sizes and in either
square or round shape. They are usually constructed of
19-gauge brass. The tags can be purchased with or
without labeling.
The tags are stamped, if unlabeled, using a kit and are
then placed on wells for identification purposes. They
may also be used to label items such as pipes and
valves.
The brass tags are manufactured by Seton Identification
in New Haven, Connecticut, 800 754-7360. They are
sold in packages of 25, for approximately $20 per package.
Tag Stamping Kit
Stamping kits are sold in sizes from 0.125 in. to 0.5 in.
They contain numbers and letters made from steel.
A hammer or mallet is used to stamp the tags with the
kit for custom identification.
The stamping kit is manufactured by Seton Identification
in New Haven, Connecticut, 800 754-7360. The kit costs
approximately $80.
Bentonite Chips
The chips are available in coarse grades or pellets in
small sizes. Common sizes include 0.375-in. and 0.75-
in. chips or pellets. They are made from dry bentonite
clay and sold in 50-lb bags. The bentonite is chemically
stable and can absorb large amounts of moisture.
The bentonite chips are placed around the necessary
equipment within the borehole to form a seal and act as
a general filler for the void space. Bentonite was se-
lected because of its high water retention levels. It also
interfaces well with Portland cement.
The bentonite is sold by Environmental Well Products
Company in Dayton, Ohio, 800 777-0977. The price is
approximately $10 for 50 Ib.
Silica Sand
The sand contains silica powder for increased chemical
stabilization. It is commonly found in the 10x20 graded
form.
The silica sand is another form of packing used in well
construction. The granular sand is added to boreholes
around the screened interval of the vent well and soil
gas monitoring points.
The sand is sold by Environmental Well Products Com-
pany in Dayton, Ohio, 800 777-0977. The price is ap-
proximately $6 for 50 Ib.
Concrete Mix
The concrete requires only the addition of water and
sets quickly. The concrete is readily available in large
quantities throughout the country.
Concrete mix is placed around the manhole at the
ground level of the well. This ensures its stability during
extended absences.
60
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The concrete is sold by Environmental Well Products
Company in Dayton, Ohio, 800 777-0977. The price is
approximately $4 for 50 Ib. It is also available at most
building supply stores and hardware stores.
Manhole (Flushmount Well Cover)
Many companies manufacture manholes, some with
bolts to secure the top. They are usually sold in 8x12-in.
or 12x12-in. sizes and are made of iron, steel, or stain-
less steel. The bottom is designed to fit over the riser
pipe or soil gas monitoring points.
The manhole serves as a marker and gives added
protection to the well and the monitoring points.
The manhole is sold by Environmental Well Products
Company in Dayton, Ohio, 800 777-0977. The price is
approximately $50.
150-Ft Tape Measure
A 150-ft fiberglass reel tape is needed for site mapping
and measuring borehole depths and during monitoring
point sand and bentonite additions.
It is sold by Grainger in Columbus, Ohio, 800 323-0620.
The catalog number is 6C192, and the cost is $57.70.
Miscellaneous
Cable ties and electrical tape are useful for securing
thermocouple wires and nylon tubes together before
placing in open boreholes.
B.4 Air Permeability Test Equipment
Portable Generator
Several brands are available, and one with a maximum
of 5,500 watts is recommended. They may be available
with wheeled carts. Most have single-phase power
available in the two voltage ranges. Most smaller gen-
erators run on gasoline, while the larger have diesel
engines.
A portable generator is essential in a field operation
where electrical access is limited. It can power equip-
ment such as external lighting, pumps, and powertools.
The generator is sold by Grainger in Columbus, Ohio,
800 323-0620. It costs approximately $2,200.
Blowers
Cast manufactures the recommended blowers. They
are oilless regenerative blowers that have a mounted
motor. The motors are equipped for different voltage
requirements.
The blowers are used during the injection or extraction
of air at a monitoring site. They should be equipped with
explosion-proof circuitry and mufflers where flammable
contamination exists.
The blower is sold by Isaacs in Columbus, Ohio, 614
885-8540. Blower costs vary according to size and
power. For example, a 2-hp, 145-cfm open flow blower
costs $1,100.
Rotameters/Flow Meters
Rotameters are transparent flow meters with the ability
to regulate flow. The tubes may be constructed from
plastic or glass. Each end has a female pipe thread
made from brass or plastic. The rotameters are available
for various liquid and gas flow levels. Both must be
installed in a vertical position for accurate readings.
The rotameter is designed to control the gas or liquid
flow rate. A flow meter indicates only the rate at which
liquid or gas is flowing.
The rotameter and flow meter are manufactured and
sold by King Instrument Company in Huntington Beach,
California, 714 841-3663. The prices vary by type but
are generally $100 to $200.
Fluke Thermocouple Thermometer
This handheld, electronic instrument is the size of a
large calculator and has a digital readout with an accu-
racy of 0.1 percent. It operates on a 9-volt battery and
has two ports for type K, minimale plugs. The thermome-
ter has dual-point and differential capability.
The Fluke thermometer is used to record temperature
data from the thermocouples.
It is supplied by several companies, including Grainger
in Columbus, Ohio, 800 323-0620. It costs approxi-
mately $200.
Dwyer Magnehelic Gauges
Magnehelic gauges are used for recording negative or
positive pressure changes over time during the air per-
meability test. Four gauges mounted in a panel stand or
board should be plumbed in series to cover a wide range
of pressures. They are sold by Grainger in Columbus,
Ohio, 800 323-0620. Catalog numbers are 3T314,
3T317, 3T319, and 3T321, and the cost is approximately
$51 per gauge.
Five-Way Valves (Swage I ok)
The five-way valve is installed on the magnehelic gauge
panel, which gives the sampler the ability to record
pressures from three points, one after another, simply
by turning the valve handle. The valve is sold by Scioto
Valve, 614 891-2617. The part number is B-43ZF2, and
the cost is approximately $90.
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Male Nonvalved Quick Couple Plug (Parker)
The fitting is connected to tubing from the five-way
valve. This plug plugs into the fitting, which is attached
to a soil gas monitoring point for measuring pressure
during the test. It is supplied by Forberg Scientific in
Columbus, Ohio, 614 294-4600. The part number is
4Z-Q4P-B, and the cost is $6.
Stopwatches
A stopwatch is necessary for each sampler who is re-
cording pressures at a soil gas monitoring well. Pres-
sures are recorded overtime during the air permeability
test. Stopwatches can be purchased at most sporting
good stores or at Radio Shack. The cost is about $20.
B.5 In Situ Respiration Test Equipment
Portable Generator
Several brands are available, and one with a maximum
of 5,500 watts is recommended. They may be available
with wheeled carts. Most have single-phase power
available in the two voltage ranges. Most smaller gen-
erators run on gasoline, while the larger have diesel
engines.
A portable generator is essential in a field operation
where electrical access is limited. It can power equip-
ment such as external lighting, pumps, and powertools.
The generator is sold by Grainger in Columbus, Ohio,
800 323-0620. It costs approximately $2,200.
Diaphragm Pump (Vacuum/Air Compressor)
The pumps are usually wired for 110 volts for the 1/16-
hp, 1/8-hp, and 1/3-hp versions. Cast produces the
pumps and compressors. They are preferred because
of their reliability and easy maintenance.
The pumps are used to draw soil gas from deep moni-
toring points and soil gas probes. The 1/3-hp pumps are
recommended because of the available air produced at
20 psi.
The pump is sold by Grainger in Columbus, Ohio, 800
323-0620. The cost depends on the size of the pump.
For the recommended 1/3-hp pump, the catalog number
is 4Z024, and the cost is $228.
Rotameters/Flow Meters
Rotameters are transparent flow meters with the ability
to regulate flow. The tubes may be constructed from
plastic or glass. Each end has a female pipe thread
made from brass or plastic.
The rotameters indicate the rate at which gas is flowing.
The flow meter used for in situ respiration testing is
connected to the backside of a 1/3-hp diaphragm pump.
The flow meter normally used is a 0.4-scfm to 4.0-scfm
meter sold by King Instruments Company, 714 841-
3663. The cost is approximately $48.
Helium Leak Detector
The helium leak detector is a rechargeable instrument
that can detect helium from 0.01 percent to 100 percent.
It operates in a three-stage process where the sample
enters the portable instrument, is analyzed, then is
purged to the atmosphere. The helium leak detector is
approximately 14x12x5 in. and weighs 7 Ib. The instru-
ment must be calibrated with helium gas.
The helium leak detector is used to detect the presence
of helium. Helium gas is injected into the ground during
a tracer test. From this test, an underground model of
the gas dispersion can be developed. The detector ana-
lyzes soil gas samples from the monitoring wells sur-
rounding the helium injection site.
The leak detector is sold by Mark Products, Incorpo-
rated, in Sunnyvale, California, 800 621-4600. The price
is approximately $4,500.
Compressed Gas Helium 220 Ft3
Helium is mixed with the injection air for the in situ
respiration test at approximately 2-percent helium. He-
lium can be purchased from compressed gas suppliers
or a welding supplier. The cost per cylinder is $60.
Helium Cylinder Regulator
A two-stage cylinder regulator is necessary for connect-
ing and dispensing the compressed helium gas. The
correct connection for cylinder to regulator is a GA 580.
Regulators can be purchased through the compressed
gas supplier. The cost is approximately $180.
Helium/Air Mixing Manifold
The 2-percent helium mix in air is accomplished by using
a 1-in. inside diameter pipe closed at one end with four
tubing connectors, which would be plumbed to the dia-
phragm pumps. The open end of the pipe is where
atmospheric air is drawn in for the diaphragm pumps; a
tubing connection is installed into the pipe at about 6 in.
from the open end. This connection is for the helium
supply to enter the manifold and be swept by incoming
air. Helium concentrations need to be measured at the
pressure side of the diaphragm pump; if concentration
is too high or low, adjust at the helium regulator. This
item is not commercially available.
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Calibration Gases
Calibration gases include helium, carbon dioxide, oxy-
gen, and hexane. They are available in the appropriate
concentrations for each instrument and may require a
special regulator depending on the cylinder type.
The calibration gases are used to standardize the gas
analyzing instruments.
The gases are sold through Scott Specialty Gases in
Troy, Michigan, 313 589-2950. The gases cost approxi-
mately $124 depending on the cylinder size and gas
desired.
Tedlar Sampling Bag
The 1-L bag is made from transparent Tedlar and has a
polypropylene fitting. The bag is approximately 7x7 in.
and is sold in packages of 10. The fitting is opened and
closed by twisting the cap, which can also be locked into
place.
The Tedlar bag is used to store soil gas samples and
calibration gases until they can be analyzed by an ap-
propriate gas meter.
The Tedlar bags are supplied by SKC, Eighty Four,
Pennsylvania, 800 752-8472. The cost is approximately
$82 for 10 bags.
Fluke Thermocouple Thermometer
This handheld, electronic instrument is the size of a
large calculator and has a digital readout with an accu-
racy of 0.1 percent. It operates on a 9-volt battery and
has two ports for type K, minimale plugs. The thermome-
ter has dual-point and differential capability.
The Fluke thermometer is used to record temperature
data from the thermocouples.
The Fluke meter is supplied by several companies in-
cluding Grainger in Columbus, Ohio, 800 323-0620. It
costs approximately $200.
Pressure and Vacuum Gauges
Pressure gauges are installed with the flow meters for
air injection. When flow is recorded, the pressure needs
to be recorded as well. Vacuum gauges are used on the
diaphragm pump that is used for withdrawing soil gas
samples from monitoring points; the vacuum is also
recorded while collecting soil gas sample. The gauges
are sold by Grainger in Columbus, Ohio, 800 323-0620.
The catalog number is 1A318, and the cost is less than
$20 per gauge.
Oxygen/Carbon Dioxide Gas Sampling Meter
This handheld instrument has a rechargeable battery
that lasts up to 16 hours. It has an oxygen and carbon
dioxide range of 0 percent to 25 percent. The meter has
an analog scale readout with audible and visual alarms
for low and high warning levels. The meter analyzes
oxygen content through an electrochemical cell and
carbon dioxide through an infrared sensor. An external
filter and an internal filter are employed for high reliability
and preventive maintenance. An internal diaphragm
pump is also provided.
The gas sampling meter is used to determine the oxy-
gen and carbon dioxide content of the ambient air or of
the gas within the soil. Calibrations must be performed
regularly with gas standards.
The meter is sold by Cascade Associates in Young-
stown, Ohio, 216 758-6649. It costs approximately
$3,200.
Carry Case for Gas Sampling Meter
The case is of heavy plastic construction with foam
cushioning inside and can be secured with locks.
It is capable of protecting and carrying both the Trace-
Techtor and the gas sampling meter.
The case is sold by Cascade Associates in Youngstown,
Ohio, 216 758-6649. It costs approximately $250.
Combustibles Sampling Meter
This meter has a digital display screen with audible and
visual alarms for high- and low-level combustibles/
hydrocarbons. They are measured from 0 percent to 100
percent LEL and 0 ppm to 10,000 ppm in 20-ppm incre-
ments. The meter uses both internal and external filters
and includes an internal pump. In addition, it has a data log-
ging function, which permits the meter to be connected
with an IBM-compatible computer. It can be operated
with alkaline or nicad batteries that hold a 9-hour charge.
The platinum catalyst sensor has a flame arrester.
The meter is used to determine the level of hydrocar-
bons or combustibles in the ambient air or sampled soil
gas. It is a new model that replaces the Trace-Techtor
meter.
The meter is sold by Cascade Associates in Young-
stown, Ohio, 216 758-6649. It costs approximately
$1,475. For information on other distributors of GasTech
Instruments, call GasTech at 510 794-6200.
1:1 Diluter
The diluter is an external fitting that attaches to the inlet
of the Trace-Techtor meter. It has a metal construction
and is about 3-in. long. A diluter is required when the
oxygen levels of the gas sample drop below 12 percent.
At this low oxygen level, the platinum catalyst cannot
combust the gas sample properly.
63
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The function of the 1:1 diluter is to reduce the gas
sample flow by one-half. This dilution reduces the con-
centration by one-half. Once a concentration reading is
obtained from the meter, it is multiplied by a factor of two
to compensate for the dilution.
The diluter is sold by Cascade Associates in Young-
stown, Ohio, 216 758-6649. It costs approximately $150.
10:1 Diluter
This diluter is also an external fitting that attaches to the
inlet of the Trace-Techtor meter and is small enough to
hold in the hand. The diluter has two rotameters built
into it to permit a dilution factor up to 10. A diluter is
required when the oxygen levels of the gas sample drop
below 12 percent. At this low oxygen level, the platinum
catalyst cannot combust the gas sample properly. The
10:1 diluter can be used if the concentration of the
sample is still too high to be read after using a 1:1 diluter.
This is evident when the gas analysis instrument is
pegged on its highest setting.
The function of the 10:1 diluter is to reduce the gas
sample flow up to a factor of 10. The dilution factor is
set by adjusting the two rotameters until the ratio of the
two flows is equal to the dilution ratio. This reduces the
concentration by the same factor. Once a concentration
reading is obtained from the meter, it is multiplied by the
ratio to compensate for the dilution.
The diluter is sold by Cascade Associates in Young-
stown, Ohio, 216 758-6649. It costs approximately
$250.
B.6 Miscellaneous Items
Teflon Thread Tape
The white tape is made of Teflon and comes in rolls of
0.25-in., 0.5-in., and 1-in. widths.
The tape is wrapped over pipe threading to prevent
leaking of liquids and gases.
The tape is supplied by U.S. Plastics Corporation in
Lima, Ohio, 800 357-9724. It costs approximately $1.
PVC Piping Supplies
PVC pipe is needed in various diameters up to 6 in. Most
piping used is schedule 40 and in 10-ft or20-ft lengths.
Some of the supplies, including valves, tees, and cou-
plings, may be needed as schedule 80 PVC.
The PVC piping is used to transport gases, usually air,
to vent wells or to transport liquids from contaminated
wells.
The items are supplied by U.S. Plastics Corporation in
Lima, Ohio, 800 357-9724. The costs are dependent
upon the specific piping size, length, and schedule
required.
PVC Pipe Cement and Primer
The PVC primer is a volatile, clear liquid that is applied
using a small sponge. The PVC cement is a viscous,
gray liquid also applied with a sponge. Both have a
strong odor that can be harmful if the primer is used
without proper ventilation.
The primer is used to clean and prime the PVC before
assembly. After the primer dries, the cement is applied
to connect the PVC pieces. The PVC cement is quick
to set.
The items are supplied by U.S. Plastics Corporation in
Lima, Ohio, 800 357-9724. For both the cement and
primer, the cost is approximately $20.
Pipe Fittings
Many different types and sizes of pipe fitting are needed
for pump connections and tubing connections. Grainger
has a large selection in its catalog of steel and brass
pipe fittings that are reasonably priced.
B.7 Optional Items
So/7 Moisture Meter
The soil moisture meter is an electronic, handheld in-
strument that operates from a 9-volt battery. Two spring
terminals are at the top of the meter for connecting the
moisture blocks.
The meter gives a digital display of the soil moisture
content in a percentage obtained from the soil moisture
blocks.
The meter is supplied by Soilmoisture Equipment Cor-
poration in Santa Barbara, California, 805 964-3525. It
costs approximately $310.
So/7 Moisture Blocks
They consist of a lead wire connected to the gypsum
block, which is in the shape of a 1-in. diameter cylinder.
The blocks have a life expectancy of 3 to 5 years. The
gypsum can compensate for varying salinity conditions.
The blocks are placed in the soil to transmit the soil
moisture content to the soil moisture meter using an
electric current. They are available in different lengths
and are installed along with the soil gas monitoring
points.
The block is supplied by Soilmoisture Equipment Cor-
poration in Santa Barbara, California, 805 964-3525. It
costs approximately $15.
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Bailer be dry to install the screens and suction strainers. Oth-
„ , , . ,-.-,, .-...^ ... , . ,. . .. erwise, no soil gas sampling can occur because of the
Constructed of Teflon, PVC, or stainless steel, the bail- ,,. ,. ... ,M a
.. . , , * * i * * , xu -r a • presence of the hquid(s).
ers are available from 1-ft to 4-ft lengths. Teflon is pre- ^ -i \ /
ferred for its chemical inert properties and low cost. T. . .. . ... ._ . , .,,,,..,-, . . ^
K K The bailer is sold by Environmental Well Products Com-
The bailers are lowered into the wells with cords or rope pany in Dayton, Ohio, 800 777-0977. The price is ap-
to remove water or other standing liquids. The well must proximately $140.
65
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Appendix C
Example Procedures for Conducting Bioventing Treatability Studies
C.1 Example Procedures for Collecting,
Labeling, Packing, and Shipping Soil
Samples
C. 1.1 Sample Collection
Soil samples are usually collected from split-spoon sam-
plers during soil-boring operations or with handheld soil
augers. Regardless of how samples are collected, all
equipment must be decontaminated before and after
collection of each sample.
C.1.1.1 Equipment Decontamination
• Sampler is thoroughly washed.
• Sampler is rinsed with deionized or distilled water.
• Sampler is rinsed with methanol and allowed to air dry.
• Rinsates are disposed of in an environmentally sound
manner.
C.1.1.2 Sample Collection
• At a minimum, rubber or vinyl gloves should be worn
to collect the sample. If higher levels of contamination
are anticipated, nitrile or nitrocellulose gloves should
be worn in addition to other appropriate safety gear
as indicated in the site health and safety plan.
• During processing of soil samples, the work area
should be covered with vinyl or plastic. Between sam-
ples, the work area should be cleaned of soil resi-
dues. The work area should be positioned upwind of
the test area or drill rig.
• For split-spoon sampling, the soil core is usually re-
tained in the stainless steel or brass sampling tube.
The tube should be capped top and bottom after a
Teflon liner or its equivalent has been placed over the
exposed soil.
• If the soil is to be transferred to other containers such
as those listed below for various analysis types, the
sample should be scooped directly into the sample
container. If organic analyses are to be performed,
the scoop should be stainless steel. A soil core sam-
ple should be spooned or scooped directly from the
container (e.g., coring tube, split spoon) into the sam-
ple container.
• If a gloved hand comes into contact with the sample,
then new gloves should be used for each sample. In
addition, a background sample that contacts a glove
should be collected as a control.
C.1.1.3 Split Samples
A homogeneous mix for a split soil sample can be
obtained by mixing soil in a stainless steel pan and filling
both sample containers with alternate spoonfuls. If a
sample is collected for trace volatile analysis, however,
too much sample agitation and mixing can drive off the
compounds of concern. Consequently, if a split spoon or
other soil sample for volatile organic analysis is to be
split and concern arises that the above homogenization
would result in the loss of trace volatile compounds, an
alternate splitting technique should be used. The undis-
turbed core or soil should be spooned directly into the
two jars by alternating spoonfuls between the sample
and the split container. This ensures a fairly even split
while reducing the agitation and exposure of the sample
surface area.
C.1.1.4 Sample Containers and Sample Size
Soil samples should be stored in appropriate containers
as indicated in the site test plant or as directed by the
analytical laboratory. For sample size requirements, re-
fer to the site test plan or ask personnel in the analytical
laboratory. Some suggested container types and sam-
ple sizes include:
• Volatiles: Glass jar, wide mouth, Teflon-faced cap,
125-mL capacity, 100-g sample volume minimum.
• Semivolatiles: Glass jar, wide mouth, Teflon-faced
cap, 125-mL capacity, 100-g sample volume minimum.
• Metals: High-density polyethylene (HOPE) or glass
wide-mouth jar.
• Other: For other soil analysis types, including parti-
cle-size analysis, nutrient analysis, and moisture de-
termination, samples can be stored in metal, plastic,
or glass containers.
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C. 1.2 Sample Label and Log
A sample must be labeled with all information that would
be required by personnel working with the sample. Refer
to the test/project plan for labeling instructions. At a
minimum, the samples should be labeled with the fol-
lowing information:
• Test site where sample was collected.
• Soil boring number or identification number.
• Soil sampling depth.
• Initials of sampler.
• Date and time of collection.
• Information to be recorded in the log/record book:
specific equipment used, sampler, date and time, and
any observations about the sampled material or me-
ter readings taken.
C. 1.3 Sample Packing and Shipping
• The soil samples should be placed in plastic bags
and put in a refrigerator, ice chest, or insulated box
on ice immediately after being placed in an appropri-
ate container and labeled. Ensure that sample con-
tainers and bags are tightly closed and that they
contain sufficient ice to maintain refrigerated condi-
tions until samples arrive at the laboratory.
• Control samples and field blanks should not be
shipped with contaminated samples.
• Chain-of-custody forms should be completed for each
cooler.
• Samples should be shipped to arrive within 24 hours
whenever possible. Shipment should be made by
Federal Express (when possible), using Priority Over-
night Service with Saturday deliveries specified if ap-
plicable.
• Recipients should be notified about specifics of
shipment.
C. 1.4 Quality Control
• Descriptions and dates of all of the above activities
should be documented in study records.
• Soil analysis information should be included in the
study records. Photographs should be taken peri-
odically and retained with the study records.
• Records should be kept as indicated in this procedure
and should be periodically reviewed by the study/task
leader.
C.2 Example Procedures for in Situ
Respiration Testing
C.2.1 Field Instrumentation and
Measurement
C.2.1.1 Oxygen and Carbon Dioxide
Gaseous concentrations of carbon dioxide and oxygen
should be analyzed using a GasTech model 3252OX
carbon dioxide/oxygen analyzer or equivalent. The bat-
tery charge level should be checked to ensure proper
operation. The air filters should be checked and, if nec-
essary, cleaned or replaced before starting the experi-
ment. The instrument should be turned on and
equilibrated for at least 30 minutes before conducting
calibration or obtaining measurements. The sampling
pump of the instrument should be checked to ensure
that it is functioning properly. Low flow of the sampling
pump may indicate that the battery level is low or that
some fines are trapped in the pump or tubing.
Each day before use, meters should be calibrated
against purchased carbon dioxide and oxygen calibra-
tion standards. These standards should be in the con-
centration range of the soil gas to be sampled. The
carbon dioxide calibration should be performed against
atmospheric carbon dioxide (0.05 percent) and a 5 per-
cent standard. The oxygen should be calibrated using
atmospheric oxygen (20.9 percent) and against a 5
percent and 0 percent standard. Standard gases should
be purchased from a specialty gas supplier. To calibrate
the instrument with standard gases, a Tedlar bag (ca-
pacity approximately 1 L) should be filled with the stand-
ard gas and the valve on the bag should be closed. The
inlet nozzle of the instrument should be connected to the
Tedlar bag, and the valve on the bag should be opened.
The instrument should then be calibrated against the
standard gas according to the manufacturer's instruc-
tions. Next, the inlet nozzle of the instrument should be
disconnected from the Tedlar bag, and the valve on the
bag should be shut off. The instrument should be re-
checked against atmospheric concentration. If recalibra-
tion is required, the above steps should be repeated.
C.2.1.2 Hydrocarbon Concentration
Petroleum hydrocarbon concentrations should be ana-
lyzed using a GasTech Trace-Techtor hydrocarbon ana-
lyzer (or equivalent) with range settings of 100 ppm,
1,000 ppm, and 10,000 ppm. The analyzer should be
calibrated against two hexane calibration gases (500
ppm and 4,400 ppm). The Trace-Techtor has a dilution
fitting that can be used to calibrate the instrument in the
low-concentration range.
Calibration of the GasTech Trace-Techtor is similar to
the GasTech Model 32402X, except that a mylar bag is
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used instead of a Tedlar bag. The oxygen concentration
must be above 10 percent for the Trace-Techtor ana-
lyzer to be accurate. When the oxygen drops below 10
percent, a dilution fitting must be added to provide ade-
quate oxygen for analysis.
Hydrocarbon concentrations can also be determined
with a flame ionization detector (FID), which can detect
low (below 100 ppm) concentrations. A photoionization
detector (PID) is not acceptable.
C.2.1.3 Helium Monitoring
Helium in the soil gas should be measured with a Marks
Helium Detector Model 9821 or equivalent with a mini-
mum sensitivity of 100 ppm (0.01 percent). Calibration
of the helium detector follows the same basic procedure
described for oxygen calibration, except that the setup
for calibration is different. Helium standards used are
100 ppm (0.01 percent), 5,000 ppm (0.5 percent), and
10,000 ppm (1 percent).
C.2.1.4 Temperature Monitoring
In situ soil temperature should be monitored using
Omega Type J or K thermocouples (or equivalent). The
thermocouples should be connected to an Omega OM-
400 Thermocouple Thermometer (or equivalent). The
contractor should calibrate each thermocouple against
ice water and boiling water before field installation.
C.2.1.5 Air Flow Measurement
Before initiating respiration tests at individual monitoring
points, air should be pumped into each monitoring point
using a small air compressor. Air flow rates of 1 cfm to
1.5 cfm should be used, and flow should be measured
using a Cole-Palmer Variable Area Flowmeter No.
N03291-4 (or equivalent). Helium should be introduced
into the injected air at a 1 percent concentration. A
helium flow rate of approximately 0.01 cfm to 0.015 cfm
(0.6 cfm to 1.0 cfh) is required to achieve this concen-
tration. A Cole-Palmer Model L-03291-00 flow meter or
equivalent should be used to measure the flow rate of
the helium feed stream.
C.2.2 In Situ Respiration Test Procedures
The in situ respiration test should be conducted using a
minimum of four screened intervals of the monitoring
points and a background well. The results from this test
determine if in situ microbial activity is occurring and if
it is oxygen-limited.
C.2.2.1 Test Implementation
Air with 1 percent to 2 percent helium should be injected
into the monitoring points and background well. Follow-
ing injection, the change of oxygen, carbon dioxide,
total hydrocarbon, and helium in the soil gas should be
measured overtime. Helium should be used as an inert
tracer gas to assess the extent of diffusion of soil gases
within the aerated zone. If the background well is
screened over an interval of greater than 10 ft, the
required air injection rate may be too high to allow
helium injection. The background monitoring point
should be used to monitor natural degradation of organic
matter in the soil.
The oxygen, carbon dioxide, and total hydrocarbon lev-
els will be measured at the monitoring points before air
injection. Normally, air is injected into the ground for at
least 20 hours at rates ranging from 1.0 cfm to 1.7 cfm
(60 cfh to 100 cfh). Blowers should be diaphragm com-
pressors Model 4Z024 from Grainger (or equivalent)
with a nominal capacity of 1.7 cfm (100 cfh) at 10 psi.
The helium used as a tracer should be 99 percent or
greater purity, which is available from most welding
supply stores. The flow rate of helium should be ad-
justed to 0.6 cfh to 1.0 cfh to obtain about 1 percent in
the final air mixture that is injected into the contaminated
area. Helium in the soil gas should be measured with a
Marks Helium Detector Model 9821 (or equivalent) with
a minimum sensitivity of 0.01 percent.
After air and helium injection is completed, the soil gas
should be measured for oxygen, carbon dioxide, helium,
and total hydrocarbon. Soil gas should be extracted from
the contaminated area with a soil gas sampling pump
system. Typically, measurement of the soil gas should
be conducted after 2, 4, 6, and 8 hours and then every
4 to 12 hours, depending on the rate of the oxygen use.
If oxygen uptake is rapid, more frequent monitoring is
required. If it is slower, less frequent readings are ac-
ceptable.
At shallow monitoring points, atmospheric air might be
pulled in during purging and sampling. Excessive purg-
ing and sampling may result in erroneous readings.
Oversampling offers no benefits, so care should be
taken to minimize the volume of air extraction when
sampling shallow points. In these cases, a low-flow
extraction pump of about 0.03 cfm to 0.07 cfm (2.0 cfh
to 4.0 cfh) should be used. Field judgment is required at
each site in determining the sampling frequency.
The in situ respiration test should be terminated when
the oxygen level is about 5 percent, or after 5 days of
sampling. The temperature of the soil before air injection
and after the in situ respiration test should be recorded.
C.2.2.2 Data Interpretation
Data from the in situ respiration tests should be summa-
rized and their oxygen utilization rates computed.
C.2.3 Quality Control
• Descriptions and dates of all of the above activities
should be documented in study records.
69
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• Soil analysis information should be included in the
study records. Photographs should be taken peri-
odically and retained with the study records.
• Records should be kept as indicated in this procedure
and should be periodically reviewed by the study/task
leader.
C.3 Example Procedures for Soil Gas
Permeability Testing
C. 3.1 Field Instrumentation and
Measurement
C.3.1.1 Oxygen and Carbon Dioxide
Gaseous concentrations of carbon dioxide and oxygen
should be analyzed using a GasTech model 3252OX
carbon dioxide/oxygen analyzer or equivalent. The bat-
tery charge level should be checked to ensure proper
operation. The air filters should be checked and, if nec-
essary, cleaned or replaced before starting the experi-
ment. The instrument should be turned on and
equilibrated for at least 30 minutes before conducting
calibration or obtaining measurements. The sampling
pump of the instrument should be checked to ensure
that it is functioning properly. Low flow of the sampling
pump can indicate that the battery level is low or that
some fines are trapped in the pump or tubing.
Each day before use, meters should be calibrated
against purchased carbon dioxide and oxygen calibra-
tion standards. These standards should be in the con-
centration range of the soil gas to be sampled. The
carbon dioxide calibration should be performed against
atmospheric carbon dioxide (0.05 percent) and a 5 per-
cent standard. The oxygen should be calibrated using
atmospheric oxygen (20.9 percent) and against a 5
percent and 0 percent standard. Standard gases should
be purchased from a specialty gas supplier. To calibrate
the instrument with standard gases, a Tedlar bag (ca-
pacity approximately 1 L) should be filled with the stand-
ard gas and the valve on the bag should be closed. The
inlet nozzle of the instrument should be connected to the
Tedlar bag, and the valve on the bag should be opened.
The instrument should then be calibrated against the
standard gas according to the manufacturer's instruc-
tions. Next, the inlet nozzle of the instrument should be
disconnected from the Tedlar bag, and the valve on the
bag should be shut off. The instrument should be re-
checked against atmospheric concentration. If recalibra-
tion is required, the above steps should be repeated.
C.3.1.2 Hydrocarbon Concentration
Petroleum hydrocarbon concentrations should be ana-
lyzed using a GasTech Trace-Techtor hydrocarbon ana-
lyzer (or equivalent) with range settings of 100 ppm,
1,000 ppm, and 10,000 ppm. The analyzer should be
calibrated against two hexane calibration gases (500
ppm and 4,400 ppm). The Trace-Techtor has a dilution
fitting that can be used to calibrate the instrument in the
low-concentration range.
Calibration of the GasTech Trace-Techtor is similar to
the GasTech Model 32402X, except that a mylar bag is
used instead of a Tedlar bag. The oxygen concentration
must be above 10 percent for the Trace-Techtor ana-
lyzer to be accurate. When the oxygen drops below 10
percent, a dilution fitting must be added to provide ade-
quate oxygen for analysis.
Hydrocarbon concentrations can also be determined
with a flame ionization detector (FID), which can detect
low (below 100 ppm) concentrations. A photoionization
detector (PID) is not acceptable.
C.3.1.3 Pressure/Vacuum Monitoring
Changes in soil gas pressure during the air permeability
test should be measured at monitoring points using
Magnehelic or equivalent gauges. Tygon or equivalent
tubing should be used to connect the pressure/vacuum
gauge to the quick-disconnect on the top of each moni-
toring point. Similar gauges should be positioned before
and after the blower unit to measure pressure at the
blower and at the head of the venting well. Pressure
gauges are available in a variety of pressure ranges,
and the same gauge can be used to measure either
positive or negative (vacuum) pressure by switching
inlet ports. Gauges are sealed and calibrated at the
factory and should be rezeroed before each test. The
following pressure ranges (in inches H2O) typically are
available for this field test:
0-1", 0-5", 0-10", 0-20", 0-50", 0-100", and 0-200"
Air pressure during injection for the in situ respiration
test should be measured using a pressure gauge with a
minimum range of 0 psig to 30 psig.
C.3.1.4 Air Flow Measurement
During the air permeability test, an accurate estimate of
flow (Q) entering or exiting the vent well is required to
determine kand R,. Several airflow measuring devices
are acceptable for this test procedure.
Pitot tubes or orifice plates combined with an inclined
manometer or differential pressure gauge are accept-
able for measuring flow velocities of 1,000 ft/min or
greater (approximately 20 scfm in a 2-in. pipe). For lower
flow rates, a large rotameter provides a more accurate
measurement. If an inclined manometer is used, the
manometer must be rezeroed before and after the test
to account for thermal expansion/contraction of the
water. Devices to measure static and dynamic pressure
must also be installed in straight pipe sections according
70
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to manufacturer's specifications. All flow rates should be
corrected to standard temperature and ambient pres-
sure (altitude) conditions.
C.3.2 Soil Gas Permeability Test Procedures
This section describes the field procedures that will be
used to gather data to determine k and to estimate R,.
Before initiating the soil gas permeability test, the site
should be examined for any wells (or other structures)
that will not be used in the test but may serve as vertical
conduits for gas flow. These should be sealed to prevent
short-circuiting and to ensure the validity of the soil gas
permeability test.
C.3.2.1 System Check
Before proceeding with this test, soil gas samples
should be collected from the vent well, the background
well, and all monitoring points, and analyzed for oxygen,
carbon dioxide, and volatile hydrocarbons. After the
blower system has been connected to the vent well and
the power has been hooked up, a brief system check
should be performed to ensure proper operation of the
blower and the pressure and air flow gauges, and to
measure an initial pressure response at each monitoring
point. This test is essential to ensure that the proper
range of Magnehelic gauges is available for each moni-
toring point at the onset of the soil gas permeability test.
Generally, a 10-minuteto 15-minute period of air extrac-
tion or injection is sufficient to predict the magnitude of
the pressure response and the ability of the blower to
influence the test volume.
C.3.2.2 Soil Gas Permeability Test
After the system check, and when all monitoring point
pressures have returned to zero, the soil gas permeabil-
ity test should begin. Two people are required during the
initial hour of this test. One person reads the Magnehelic
gauges, and the other person records pressure (P)
versus time on the example data sheet. Designating one
person for each test improves the consistency in reading
the gauges and reduces confusion. Typically, the follow-
ing test sequence is followed:
1. Connect the Magnehelic gauges to the top of each
monitoring point with the stopcock opened. Return
the gauges to zero.
2. Turn the blower unit on, and record the starting time
to the nearest second.
3. At 1-minute intervals, record the pressure at each
monitoring point, beginning at t = 60 s.
4. After 10 minutes, extend the interval to 2 minutes.
Return to the blower unit, and record the pressure
reading at the well head, the temperature readings,
and the flow rate from the vent well.
5. After 20 minutes, measure P' at each monitoring
point in 3-minute intervals. Continue to record all
blower data at 3-minute intervals during the first hour
of the test.
6. Continue to record monitoring point pressure data at
3-minute intervals until the 3-minute change in P is
less than 0.1 in. of H2O. At this time, a 5-minute to
20-minute interval can be used. Review data to en-
sure accurate data were collected during the first 20
minutes. If the quality of these data is in question,
turn off the blower, allow all monitoring points to
return to zero pressure, and restart the test.
7. Begin to measure pressure at any ground-water
monitoring points that have been converted to moni-
toring points. Record all readings, including zero
readings and the time of the measurement. Record
all blower data at 30-minute intervals.
8. Once the interval of pressure data collection has
increased, collect soil gas samples from monitoring
points and the blower exhaust (if extraction system),
and analyze for oxygen, carbon dioxide, and hydro-
carbons. Continue to gather pressure data for 4 to 8
hours. The test normally continues until the outer-
most monitoring point with a pressure reading does
not increase by more than 10 percent over a 1-hour
interval.
9. Calculate the values of k and R, with the data from
the completed test; use of the Hyperventilate com-
puter program is recommended.
C.3.2.3 Soil Gas Monitoring After the
Permeability Test
Immediately after completion of the permeability test,
soil gas samples should be collected from the vent well,
the background well, and all monitoring points, and
analyzed for oxygen, carbon dioxide, and hydrocarbons.
If the oxygen concentration in the vent well has in-
creased by 5 percent or more, oxygen and carbon diox-
ide should be monitored in the vent well in a manner
similar to that described for the monitoring points in the
in situ respiration test. (Initial monitoring may be less
frequent.) The monitoring should provide additional in
situ respiration data for the site.
C.3.3 Quality Control
• Descriptions and dates of all of the above activities
should be documented in study records.
• Soil analysis information should be included in the
study records. Photographs should be taken peri-
odically and retained with the study records.
• Records should be kept as indicated in this procedure
and should be periodically reviewed by the study/task
leader.
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C.4 References
Hinchee, R.E., and S.K. Ong. 1992. A rapid in situ respiration test for Johnson, P.O., M.W. Kemblowski, and J.D. Colthart. 1990. Quantita-
measuring aerobic biodegradation rates of hydrocarbons in soil, tive analVsis for tne cleanuP of hydrocarbon-contaminated soils
J. Air & Waste Management Association 42(10):1305-1312. bV in-situ soil Ventin9- Ground ^^ 28(3)-
Hinchee, R.E., S.K. Ong, R.N. Miller, D.C. Downey, and R. Frandt. U.S. EPA. 1991. Soil vapor extraction: Air permeability testing and
1992. Test plan and technical protocol for a field treatability test estimation methods. In: Proceedings of the 17th RREL Hazardous
for bioventing, Rev. 2. U.S. Air Force Center for Environmental Waste Research Symposium. EPA/600/9-91/002. Washington,
Excellence, Brooks Air Force Base, TX. DC.
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Appendix D
Off-Gas Treatment Options
D.1 Introduction
Off-gas treatment typically is not a component of
bioventing systems. Bioventing systems are usually
configured to inject air into the in situ soil mass. The
injected air then moves through the soil to act as an
oxygen source for microbial activity. The bioventing in-
jection air flow rate is low and is selected to minimize
discharge from the surface while providing an adequate
supply of oxygen for the organisms.
Air injection is the preferred bioventing configuration;
however, air extraction may be necessary at sites where
air emissions or movement of vapors into subsurface
structures are difficult to control. If a building or other
structure is located within the radius of influence of a
site, or if the site is near a property boundary beyond
which hydrocarbon vapors cannot be pushed, air extrac-
tion may be considered. A significant disadvantage of
the air extraction configuration is that biodegradation is
limited to the contaminated soil because vapors do not
move outward and create an expanded bioreactor. The
result is less biodegradation and more volatilization. In
general, increasing extraction rates increases both vola-
tilization and biodegradation rates until the site becomes
aerated. At this point, increasing the flow rate does not
increase biodegradation but does continue to increase
volatilization. The optimal input air flow is the minimum
extraction rate that satisfies the oxygen demand. Some
volatilization occurs regardless of the extraction rate.
The relative removal attributed to biodegradation and
volatilization is quite variable and site dependent. At a
JP-4 jet fuel contaminated site at Tyndall AFB, Miller et
al. (1991) found that biodegradation could achieve
about 85-percent contaminant removal at the optimal air
flow rate.
Currently, only 6 of 120 Bioventing Initiative sites use air
extraction to oxygenate the site. Two of the sites (Davis
Global Communications Site, near McClellan AFB, and
BX Service Station, Patrick AFB) operated in extraction
mode for 60 to 90 days, at which time the system was
reconfigured for air injection because vapor concentra-
tions had significantly decreased. At Patrick AFB, initial
vapor concentrations of TPH were as high as 27,000
ppmv. After approximately 75 days of operation, concen-
trations decreased to 1,600 ppmv and the bioventing
system was reconfigured for injection. Another site that
has used extraction is the Base Service Station at Van-
denberg AFB. This site contains high concentrations of
the more volatile fuel components and is an active serv-
ice station. As such, the possibility of vapors migrating
into the building on site is possible. This bioventing
system was operated in an extraction configuration in
two phases (Downey et al., 1994). During Phase I,
extracted soil gas was passed through a PADRE vapor
treatment system, where high concentrations of volatiles
were adsorbed and condensed to liquid fuel. The treated
soil gas was then recirculated through the soil using air
injection, biofilter trenches located along the perimeter
of the site. Phase II was initiated once TVH concentra-
tions decreased to less than 1,000 ppmv. At this time,
the PADRE system was taken off-line, and the extracted
soil gas was reinjected directly into the biofilter trenches.
This appendix discusses minimization of the off-gas flow
rate, seven commercially available alternatives for treat-
ing organic vapors in an air stream, and some emerging
vapor treatment technologies. The vapor treatment
technology discussions in this appendix derive from
information on remedial technologies published by
AFCEE (1992 and 1994) and a description of off-gas
treatment in Soil Vapor Extraction Technology: Refer-
ence Handbook (U.S. EPA, 1991). Figure 1 shows the
general ranges of applicability for some commonly used
off-gas treatment methods. The organic vapor treatment
options discussed in the following sections are:
• Limiting off-gas production
• Direct discharge
• Off-gas reinjection
• Biofiltration
• Adsorption on carbon or resin
• Catalytic oxidation
• Flame incineration
• Thermal destruction in internal combustion engines
• Emerging vapor treatment technologies
73
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Many of these methods have been used in industrial
applications to control point source VOC emissions.
Figure 1 shows that most of these alternatives may be
used over a range of concentrations that spans several
orders of magnitude. Usually, however, each option is
cost-effective over only a small part of that range. For
example, granular activated carbon (GAG) adsorption
could be used to treat a vapor stream containing 10,000
ppmv of hydrocarbon vapors, but the cost for carbon
regeneration would be prohibitive.
As shown in Figure 1, thermal treatment methods are
more cost-effective for treating off-gas containing higher
concentrations of vapor contaminants. No distinct guide-
lines exist for selecting thermal treatment units for spe-
cific applications, but the tradeoff between capital and
operating costs sets general ranges of applicability for
thermal treatment methods. Catalytic oxidation units
usually have higher initial cost but lower fuel require-
ments than flame incinerators. As a result, the catalytic
oxidation units are usually economical for influent con-
taining less than 5,000 ppmv of contaminants. The capi-
tal cost of internal combustion engine (ICE) treatment
units is similar to catalytic oxidation units. The ICE is not
limited to operating with an inlet combustible vapor con-
centration below 25 percent of the lower explosive limit
(LEL). The ICE units, therefore, gain a significant advan-
tage when the vapor concentration is over 25 percent of
the LEL.
D.2 Limiting Off-Gas Production
Design and operating features can be used to minimize
the volume of off-gas released by bioventing systems.
This source reduction approach to pollution prevention
should be used whenever possible at bioventing sites.
Options for minimizing off-gas production include using
the lowest air flow rate possible while still supplying
sufficient air and/or using air injection instead of air
extraction configurations to aerate the contaminated
area. Bioventing systems can be operated at much
lower air flow rates than standard soil vapor extraction
systems. A well-designed and operated bioventing sys-
tem can minimize off-gas releases without compromis-
ing oxygenation of the contaminated area. As discussed
above, air injection systems are preferred unless site
conditions require air extraction to control movement or
accumulation of contaminant vapors.
D.3 Direct Discharge
Direct discharge involves releasing air that contains
organic vapors directly through a stack. The stack dis-
perses the vapors, but no removal or destruction of
contaminants occurs. When the organic vapor concen-
tration in the extraction well off-gas stream is low, or in
localities with less stringent air treatment standards,
treatment may not be required. Direct discharge of va-
pors to the atmosphere can be a viable option where
consistent with good environmental practice and local
permitting requirements. The concentration of the con-
taminants, the off-gas release rate, and the location and
type of nearby receptors are considered when evaluat-
ing direct discharge options.
D.4 Off-Gas Reinjection
Reinjection of off-gas for further biodegradation can be
a cost-effective and environmentally sound treatment
option. Off-gas reinjection configurations offer the ad-
vantages of low surface emissions and no point source
. Technology Effective;
Cost May Be Prohibitive
Direct Disc
GAC
large
Biofiltration
Th<
Catal)
Cerami
rmal Incinerat
tic Oxidation
ICE
; Beads
or
0.1
10 100 1000 10000 100000
Extracted Vapor Concentration (ppmv)
Figure 1. Applicability of vapor treatment options.
74
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generation. The reinjection treatment option consists of
distributing extracted air with contaminant vapors back
into the soil to allow in situ aerobic biodegradation to
destroy the contaminants. Reinjection is accomplished
by piping the discharge of the extraction blowers to air
distribution wells or trenches, where the air infiltrates
back into the soil. In situ respiration and soil gas perme-
ability data must be available for the site. These data
indicate the expected biodegradation rate and radius of
influence needed to determine the design capacity for
the reinjection point. The available soil volume must be
sufficient to accept the off-gas air flow and allow biode-
gradation of the contaminant mass flow in the off-gas.
Reinjection wells should be located and designed to
ensure that the reinjection process destroys contami-
nants rather than increasing contaminant migration. Af-
ter reinjection is established, surface emission testing
may be performed to ensure contaminants are not es-
caping at the site surface. Soil gas monitoring should be
performed to ensure that contaminant migration is not
being increased. Monitoring of migration is particularly
important at sites where air extraction is necessary be-
cause of the presence of buildings.
D.5 Biofiltration
Biofiltration can be used to destroy a variety of volatile
organic contaminants in an off-gas stream. The biofiltra-
tion process uses microorganisms immobilized as a
biofilm on a porous filter substrate, such as peat or
compost. As the air and vapor contaminants pass
through the filter, contaminants transfer from the gas
phase to the biolayer, where they are metabolized. In-
fluent contaminant concentrations less than about 1,000
ppmv can be treated with a typical contact time of 15 to
90 seconds (Skladany et al., 1994). Vendordata indicate
that biofiltration is most effective for gasoline hydrocar-
bon vapor concentrations in the range of 50 ppmv to
5,000 ppmv (U.S. EPA, 1994).
Saberiyan et al. (1992) studied the use of a biofilter for
treatment of air containing gasoline vapors. Sphagnum
moss was used as the packing material. The system
initially was inoculated with a hydrocarbon-degrading
bacterial culture, then exposed to gasoline vapors. The
biofilter removed up to 90 percent of the initial 50-ppmv
gasoline vapor concentration. These studies also
sought to demonstrate the linear relationship between
flow rate and packing material volume.
Biofiltration of vapor streams is a fairly well-established
treatment technology in Europe (Leson and Winer,
1991). Medina et al. (1995) have studied the use of
biofilters to treat ethanol and gasoline vapor streams.
Bench-scale and pilot-scale reactors have been
studied.
D.6 Adsorption on Carbon or Resin
Adsorption refers to the process by which molecules
collect on and adhere to the surface of an adsorbent
solid (U.S. EPA, 1988). This adsorption is the result of
chemical and/or physical forces. Physical adsorption
(the more common type in this application) is the result
of Van derWaals'forces, which are common to all matter
and result from the motion of electrons. Surface area is
a crucial factor in adsorption because adsorption capac-
ity is proportional to surface area. Commercially avail-
able adsorbents include activated carbon and synthetic
resins.
GAG is the most commonly used vapor-phase treatment
method. Activated carbon adsorbents provide a high
surface area in a low unit cost material because of the
carbon's complex internal pore structure. Commercially
available GAG typically has a surface area of 1,000
m2/gram to 1,400 m2/gram.
GAG is the most cost-effective organic vapor treatment
method for a wide range of applications because of
its relative ease of implementation and operation,
its established performance history in commercial appli-
cations, its ability to be regenerated for repeated use,
and its applicability to a wide range of contaminants
at a wide range of flow rates. Many vendors sell or
lease prefabricated, skid-mounted units that can be put
into operation with a few days' notice. Carbon adsorp-
tion, however, is economical only for lower mass re-
moval rates. When the vapor concentration is high,
carbon replacement or regeneration may be prohibi-
tively expensive.
An alternative to replacing the carbon with offsite dis-
posal or reactivation is onsite regeneration of the carb-
on. Such systems regenerate the carbon in place, using
steam or hot gas to desorb the contaminants. The con-
taminants recovered in liquid form may then be disposed
of or, in some cases, recovered as solvent or used as
fuel.
Information on GAG design parameters is available from
the carbon vendors. Calgon Carbon Corporation (Pitts-
burgh, Pennsylvania), Carbtrol Corporation (Westport,
Connecticut), Nucon (Columbus, Ohio), and many oth-
ers supply adsorption isotherms and pressure drop
curves for the GAG types they supply. The pressure drop
curves are developed as a function of flow rate. Many
vendors supply modular, prefabricated GAG units of
200 Ib to 2,000 Ib of activated carbon that may accom-
modate flow rates from below 400 scfm to more than
1,000 scfm.
As a rule of thumb, the adsorptive capacity of activated
carbon for most hydrocarbons in the vapor stream is
about 1 Ib hydrocarbon:10 Ib activated carbon, and the
cost of activated carbon is about $3/lb (all costs in-
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eluded, not just carbon purchase, in 1993 dollars), so
the cost of activated carbon treatment can be roughly
estimated at $30/lb of hydrocarbon to be treated.
Specialized resin adsorbents have been developed and
are now entering commercial application for treatment
of organic vapors in off-gas streams. These synthetic
resin adsorbents have a high tolerance to water vapor.
Air streams with relative humidities greater than 90 per-
cent can be processed with little reduction in the adsorp-
tion efficiency for organic contaminants. The resin
adsorbents are amenable to regeneration on site. Skid-
mounted modules are available, consisting of two resin-
adsorbent beds. The design allows one bed to be on-line
treating off-gas, while the other bed is being regener-
ated. During the desorption cycle, all organic contami-
nants trapped on the resin are removed, condensed,
and transferred to a storage tank. The desorption proc-
ess used to regenerate the resin is carried out under
vacuum, using a minimum volume of nitrogen purge
gas. A heat exchanger in the bed heats the resin during
regeneration. The same heat exchanger is used to cool
the bed to increase sorption capacity while it is on-line
treating off-gas (Downey et al., 1994).
D.7 Catalytic Oxidation
Catalytic oxidation is an incineration process that uses
catalysts to increase the oxidation rate of organic con-
taminants, allowing equivalent destruction efficiency at
a lower temperature than flame incineration. In catalytic
oxidation, the vapor stream is heated and passed
through a combustion unit where the gas stream con-
tacts the catalyst. The catalyst accelerates the chemical
reaction without undergoing a chemical change itself.
The catalyst increases the oxidation reaction rate by
adsorbing the contaminant molecules on the catalyst
surface. Sorption phenomena on the catalyst serve to
increase the local concentration of organic contami-
nants at the catalyst surface and, for some organic
contaminants, reduce the activation energy of the oxi-
dation reaction. Increased concentration and reduced
activation energy increase the rate of oxidation of the
organics (Kiang, 1988). Figure 2 shows a schematic of
a catalytic incinerator unit.
The active catalytic material typically is a precious metal
(e.g., palladium, platinum) that provides the surface con-
ditions needed to facilitate the transformation of the
contaminant molecules into carbon dioxide and water.
The catalyst metal is supported on a lower cost, high
surface area metallic or ceramic support medium.
The metal catalyst and support are exposed to the
heated off-gas in a catalytic oxidation unit. The catalytic
oxidation unit uses either a fixed-bed or a fluidized-bed
system. Fixed-bed systems include metallic mesh, wire,
or ribbon or ceramic honeycomb supporting the catalyst
metal or a packed bed of catalyst-impregnated pellets.
Fluidized beds also use catalyst-impregnated ceramic
pellets but operate at sufficiently high flow to move and
mix the pellets during treatment (U.S. EPA, 1986).
The main advantage of catalytic oxidation versus ther-
mal incineration is the much lower temperature required
with a catalyst. These systems typically operate at
600°F to 900°F (CSM Systems, 1989), versus tempera-
tures of 1,400°F or higher for flame incineration. The
lower temperature results in lower fuel costs, less se-
vere service conditions for the incinerator materials of
construction, and reduced NO* production. Natural gas
or propane is a typical fuel used for supplemental heat-
ing when the contaminated vapor streams do not con-
tain sufficient heat value for self-sustaining incineration.
Energy costs can be further reduced by reclaiming heat
from the exhaust gases (i.e., using the exhaust gas flow
to preheat the influent vapor stream).
Careful monitoring of extraction gas concentration and
reactor temperature is required to prevent overheating
of the catalyst. Overheating can damage the catalyst
metal surface and/or the support-reducing catalytic ac-
tivity. The allowed influent organic vapor concentration
depends on the heat value and LEL of the influent vapor
stream. Concentrations over 3,000 ppmv VOCs nor-
mally are diluted with air to prevent excessive energy
release rates and to control the temperature in the cata-
lytic unit. Safety is also a concern with these units, as
with any incineration method. The maximum permissible
total hydrocarbon concentration varies by site but usu-
ally is below 25 percent of the LEL. The total hydrocar-
bon concentration in the vapor is continuously
measured at the inlet to the catalytic unit to control the
dilution airflow.
Treating off-gas-containing chlorinated compounds, sul-
fur-containing compounds, or nitrogen-containing com-
pounds deactivates the catalyst because of the
chemical reaction of the catalyst metal with halogens or
strong sorption of SOX and NOX on the catalyst. Some
catalysts are specially designed to treat chlorinated
compounds. New technologies potentially capable of
treating chlorinated compounds by catalytic oxidation
currently are under development and are beginning to
become available on the market (Trowbridge and Malot,
1990; Buck and Hauck, 1992).
The significant cost elements of a catalytic oxidizer are
the capital cost (or rental) of the unit, operations and
monitoring, maintenance, and makeup fuel cost. A cata-
lytic oxidation unit for treatment of 100-cfm off-gas flow
would have a capital cost of approximately $40,000 to
$60,000 (in 1991 dollars) (AFCEE, 1992). Operations,
maintenance, and monitoring costs are site specific.
Makeup fuel is required if the hydrocarbon concentration
falls below the level necessary to maintain the required
temperature. At the Hill AFB 914 site (Smith etal., 1991),
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Treated
Air
Outlet
Contaminated
Air Inlet
Figure 2. Schematic of catalytic incinerator unit.
the extracted hydrocarbon concentration was approxi-
mately 600 ppmv and the flow rate was 1,500 cfm. To
maintain the minimum temperature, an average of 1,500
gal of propane was used every month at an average cost
of $2,000 per month. All thermal oxidation processes
require makeup fuel to treat low-concentration waste
streams, and the makeup fuel generally is proportional
to the operating temperature. Some fuel may be saved
by heat recuperation.
D.8 Flame Incineration
Flame incineration is a process that uses high-tempera-
ture direct flame combustion to produce rapid oxidation
of organic contaminants. Flame incinerators for treat-
ment of organic vapors in off-gas are typically single-
chamber, refractory-lined units containing an open
burner. Flame incinerators are often equipped with heat
exchangers where hot combustion gases leaving the
incinerator are used to preheat the incoming off-gas
stream. Heat recovered from the combustion gas im-
proves thermal efficiency and reduces fuel costs. When
operated with an adequate temperature and residence
time, flame incineration treatment oxidizes hydrocarbon
contaminants to carbon dioxide and water. For most
contaminants, acceptable contaminant destruction effi-
ciency is achieved with an operating temperature in the
range of 1,400°F to 1,600°F and a residence time of 1
second (AFCEE, 1992). Makeup fuel is usually neces-
sary to maintain the temperature required to ensure
adequate mineralization. Natural gas or propane typi-
cally serves as the supplemental fuel. Destruction of the
contaminants is a major advantage of this technique
over carbon adsorption, which only concentrates the
contaminants onto the carbon, which must then be re-
generated or disposed of.
Safety is a major design requirement for flame incinera-
tors and other thermal destruction units. Requirements
for safety provisions are derived from National Fire Pro-
tection Association (NFPA) standards and applicable
state requirements. In most applications, influent con-
centrations are limited to 25 percent of the LEL (AFCEE,
1992). The LEL for gasoline is between 12,000 ppmv
and 15,000 ppm, depending on the gasoline grade (Lit-
tle, 1987).
Direct incineration is not appropriate for influent vapor
streams containing chlorinated compounds. Complete
combustion of these compounds generates corrosive
hydrochloric acid vapors. Partial or incomplete combus-
tion of chlorinated compounds could result in the pro-
duction of chlorinated products.
The capital cost of a flame incinerator typically is less
than that of a catalytic incinerator. Because of the higher
operating temperature, however, fuel use is higher with
a flame incinerator. When the flammable contaminant
vapor concentration is sufficiently high, the heating
value from oxidation of the contaminant reduces fuel
use; therefore, at higher hydrocarbon concentrations,
flame incineration may be less costly than catalytic in-
cineration. At lower vapor concentrations, the cost of
makeup fuel is much greater than for catalytic incinera-
tion and the overall cost is probably higher than for
catalytic incineration. Flame incineration is generally fa-
vored over catalytic oxidation when the combustible
organic vapor concentration is higher than about 1,000
ppmv to 5,000 ppmv (AFCEE, 1992).
D.9 Internal Combustion Engines
ICE treatment destroys organic contaminants through
oxidation in a conventional engine. ICEs have been
used for years to destroy landfill gas. Application of ICEs
to destruction of hydrocarbon vapors in air streams is
more recent. The first operational unit was installed in
1986.
The ICE used for this technique is an ordinary industrial
or automotive engine with its carburetor modified to
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accept vapors rather than liquid fuel. The airflow capac-
ity of the ICE is determined by the cubic inch displace-
ment of the engine, the engine speed, and the engine
vacuum. The capacity (scfm) can be estimated as:
(Eq. D-1)
\ /
where:
RPM = engine speed in revolutions per minute
CID = engine displacement in cubic inches
EV = vacuum at the engine intake in inches of
mercury
P = local air pressure in inches of mercury
Therefore, a 140-in.3 displacement, four-cylinder engine
running at 2,250 rpm and 10 in. Hg engine vacuum with
an atmospheric pressure of 30 in. of mercury would
have an off-gas treatment capacity of 52 scfm. ICE
treatment units are available in sizes from 140 in.3 to 460
in.3 Currently available ICE treatment units operate the
engine near idle conditions. The off-gas capacity could
be increased by applying a load to the engine to in-
crease engine speed and decrease engine vacuum.
Engine loading by attaching a generator to supply site
power has been proposed but is not routinely practiced.
A second required modification to the engines is the
addition of a supplemental fuel input valve when the
intake hydrocarbon concentration is too low to sustain
engine operation. Propane is used almost universally,
although one vendor reported that natural gas, when
available, can reduce energy cost by 50 percent to 75
percent.
The engines are also equipped with a valve to bleed in
ambient air to maintain the required oxygen concentra-
tion. Soil vapor may have very low concentrations of
oxygen, especially during the initial stages of operation.
Ambient air is added to the engine, via an intake valve,
at a ratio sufficient to bring the oxygen content up to the
stoichiometric requirement for combustion.
A catalytic converter is an integral component of the
system, providing an important polishing step to reach
the low discharge levels required by many regulatory
agencies. A standard automobile catalytic converter, us-
ing a platinum-based catalyst, is normally used. Data
from the South Coast Air Quality Management District,
the air quality regulatory body for Los Angeles and the
surrounding area, show that the catalyst reduced con-
centrations of TPH from 478 ppmv to 89 ppmv and from
1,250 ppm to 39 ppm, resulting in important additional
contaminant removal (U.S. EPA, 1991). The South
Coast Air Quality Management District requires a cata-
lytic converter to permit this type of system. Catalysts
have a finite life span (typically expressed in hours of
operation) and must be monitored as that time ap-
proaches to ensure that the catalyst is working properly.
The length of operation of the catalyst depends on the
vapor concentration and whether lead or other potential
catalyst poisons are present in the off-gas contaminants.
One equipment vendor suggests a range of 750 to 1,500
hours (about 1 to 2 months) of operation. A deactivated
catalyst can be replaced easily with any automobile cata-
lytic converter, available at most automobile parts stores.
To date, ICE use appears to be most widespread in
California, mostly in the South Coast Air Quality Man-
agement District in southern California, which has some
of the most stringent air discharge regulations in the
country. The South Coast Air Quality Management Dis-
trict has permitted more than 100 ICEs for use in their
district. RSI, Inc. (Oxnard, California), has installed more
than 30 ICE systems, all in California.
Data obtained from ICE operators and regulators show
that ICEs are capable of destruction efficiencies of well
over 99 percent (U.S. EPA, 1991). ICEs are especially
useful for treating vapor streams with high concentra-
tions of TPH (up to 30-percent volume) to levels below
50 ppm. Tests of BTEX destruction by ICE treatment
show that nondetectable levels of contaminants can be
achieved in the outlet off-gas in some cases, and outlet
concentrations below 1 ppmv can be achieved in many
cases. The total destruction capacity may be expressed
as mass removal rate. One ICE operator reported a
mass removal and destruction rate of over 1 ton per day
(about 12 gal/hour).
ICE off-gas treatment units can handle high concentra-
tions of organic contaminants in the extracted air. As
discussed above, incineration units (e.g., catalytic oxi-
dation units, flame incinerators) usually are limited to
inlet vapor concentrations of 25 percent of the LEL. The
inlet concentration for an ICE unit can be in the combus-
tible range, so these units can accept vapor concentra-
tions as high as 40,000 ppmv with no dilution air. As a
result, the ICE treatment units have a significant advan-
tage over incineration units when the vapor concentra-
tion is higher than 25 percent of the LEL. Inlet vapor
concentrations as high as 300,000 ppmv have been
reported (U.S. EPA, 1991). The off-gas must still be
diluted with air to allow the ICE unit to treat off-gas
containing more than about 40,000 ppmv of organics,
but only one-quarter as much dilution air flow is needed
for the ICE unit compared with an incineration unit.
ICEs also can effectively treat low concentrations (i.e.,
inlet vapor concentration below 1,000 ppm), although
supplemental fuel use increases as the inlet concentra-
tion drops below 14,000 ppmv and the cost-effective-
ness decreases at reduced intake concentrations. The
removal efficiency compares favorably with other treat-
ment methods based on data available from actual sys-
tem installations.
The use of ICEs as vapor treatment devices for ex-
tracted soil vapors offers advantages over conventional
78
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treatment methods (carbon, thermal oxidation, or cata-
lytic oxidation), at least for some applications. One ad-
vantage of ICEs is the ability to produce power that can
provide useful work output. Self-contained units are
available that use the ICE to power the blower. The
extraction blower consumes only about 25 percent of the
useful work produced by the engine. Other uses of the
power have included lighting the site, heating a field
trailer, or similar ideas. Using the engine as a vacuum
source increases the engine vacuum, which has the
undesirable effect of reducing air flow capacity (see
Equation D-1). As a result, the ICE is usually coupled to
a blower to supply the well head vacuum. An added
benefit of this system is that vapors cannot be extracted
unless treatment also is occurring, eliminating the pos-
sibility of vapors bypassing the treatment system.
Another advantage of ICEs is their portability and simple
monitoring and maintenance. Typically, the self-con-
tained units are skid-mounted or put on a trailer and can
go from site to site very easily. The site requirements
may also favor ICEs over other oxidation methods. ICE
units are smaller and less noticeable than direct thermal
incineration units and may be more appropriate for ar-
eas that are intended to remain low profile. Units also
have been developed that can be monitored via modem,
eliminating costly onsite monitoring.
Noise associated with engine operation could be a
concern in areas near residential zones or occupied
buildings. Noise can be abated by adjusting engine
speed during certain periods, installing a noise sup-
pression fence, or purchasing special low noise ICE
models (AFCEE, 1994).
The capital cost of currently available ICE units appears
to be somewhat higher but is certainly in the same
general range as catalytic incineration and thermal in-
cineration. The costs of ICE treatment units with maxi-
mum flow capacities of 65 scfm, 250 scfm, and 500 scfm
are $40,450, $73,450, and $98,880, respectively (in
1994 dollars). Propane or natural gas fuel is needed
when the inlet vapor concentration is below about
40,000 ppmv. The quantity of added fuel needed in-
creases as the inlet vapor concentration declines. Fuel
costs for treating 65 scfm, 250 scfm, and 500 scfm
off-gas flow, when all energy is supplied by propane
supplemental fuel, are $20/day, $70/day, and $140/day,
respectively (AFCEE, 1994). Operations and mainte-
nance costs are site specific. Because ICEs use a much
more widely understood technology, gaining regulatory
acceptance appears to be easier than for other tech-
nologies, and as a result, permitting and monitoring
costs should be lower.
D.10 Emerging Vapor Treatment
Technologies
This section briefly describes the operating features of
several emerging technologies for destruction or con-
centration of organic contaminants in an off-gas stream.
The technologies described are packed-bed thermal
treatment, photocatalytic oxidation, and membrane
separation.
Packed-bed thermal treatment oxidizes organic con-
taminants by passing the off-gas stream through a
heated bed of ceramic beads. The packed bed in-
creases mixing to promote the oxidation reaction. A
vapor stream passes through the packed bed that ther-
mally destroys contaminants. The packing geometry
combined with uniform high temperature of the ceramic
beads is reported to provide high destruction efficiency
for organic vapors in air, without using an open flame.
The ceramic beads are heated electrically to bring them
to the operating temperature of 1,800°F No additional
energy input is required if the heat value of the vapors
is sufficient. This point is near a concentration of 2,000
ppmv. If the concentration is below this value, natural
gas or propane can be bled in with influent to maintain
the proper temperature. As with any incineration tech-
nique, excess air is added to dilute the concentration to
safe levels if the influent is too rich. Packed-bed thermal
processing has been used to destroy vapor contami-
nants in the off-gas from several chemical and other
industrial plants.
The vendor of the packed-bed technology currently is
investigating its applicability to the remediation market
(U.S. EPA, 1991). The vendor indicates that this tech-
nology has several desirable characteristics for treat-
ment of vapors in off-gas from remediation systems. The
removal efficiency is reported to be high and stable over
varying operating conditions. Tests have shown efficien-
cies of 99.99+ percent, and this removal is attained
continuously. Another reported advantage is the ability
to mineralize chlorinated compounds without the pro-
duction of chlorinated products of incomplete combus-
tion or degradation of the ceramic beads. Mineral acid
vapors would still be produced.
In the photocatalytic oxidation process, VOCs are con-
verted to carbon dioxide and water by exposure to UV
light. When chlorinated organics are present, hydrogen
chloride gas and/or chlorine are also produced. The
off-gas stream enters the photocatalyst unit, where the
contaminants are trapped on a catalyst surface. The
catalyst surface is continuously exposed to high-inten-
sity UV light. The combination of surface effects from the
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catalyst and energy input from the UV light allows rapid
oxidation of the contaminants. The reported residence
time required for 95-percent to 99-percent destruction
efficiency is 0.2 seconds (Kittrel et al., 1995).
Gas semipermeable membrane systems are available
to concentrate dilute organic vapor streams. The mem-
brane systems do not destroy the organic contaminants
and would, therefore, be used as a pretreatment step to
increase the efficiency of a second treatment process.
The membranes used have dramatically different per-
meability for air and organic vapor molecules. The dif-
ference in permeability allows the organics to
concentrate on one side of the membrane and the air on
the other side. The concentrated vapor stream can then
be further processed to condense and collect the or-
ganics or destroy them (U.S. EPA, 1994).
D.11 References
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bustion engines for the destruction of hydrocarbon vapors from
fuel-contaminated soils. Environmental Services Office, Air Force
Center for Environmental Excellence, Brooks Air Force Base, TX.
AFCEE. 1992. Remedial technology design, performance, and cost
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Buck, F.A.M, and C.W. Hauck, 1992, Vapor extraction and catalytic
oxidation of chlorinated VOCs. In: Proceedings of the 11th Annual
Incineration Conference. Albuquerque, NM (May).
CSM Systems. 1989. Company literature. Brooklyn, NY.
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Downey, D.C., C.J. Pluhar, L.A. Dudus, P.G. Blystone, R.N. Miller,
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Smith, G.J., R.R. Dupont, and R.E. Hinchee. 1991. Final report on
Hill AFB JP-4 site (building 914) remediation. Report submitted to
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Trowbridge, B.E., and J.J. Malot. 1990. Soil remediation and free
product removal using in-situ vacuum extraction with catalytic oxi-
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