United States Office of Solid Waste an el
Environmental Protection Eroerifncy Response EPA-542-R-97-OQ7
Agemcy (51028) " September 198?
EPA Analysis of Selected
Enhancements for
Soil Vapor Extraction
"i ?-=-
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CONTENTS
Chapter
FOREWARD ABS-1
EXECUTIVE SUMMARY ES^
1.0 INTRODUCTION l.l
1.1 BACKGROUND j.j
1.2 OBJECTIVES 12
1.3 APPROACH ][\\ 1-3
1.4 REPORT ORGANIZATION ','.'................. 1-4
2.0 BACKGROUND: SOIL VAPOR EXTRACTION ENHANCEMENT TECHNOLOGIES ..2-1
3.0 AIR SPARGING 3.4
3.1 TECHNOLOGY OVERVIEW 3_1
3.2 APPLICABILITY '.'.'.'.'.'.'.'.'.'.'.'. 3-2
3.3 ENGINEERING DESCRIPTION 3-3
3.3.1 Air Flow Within the Subsurface 3.4
3.3.2 Equipment Requirement's and Operational Parameters 3-6
3.3.2.1 Air Sparging Wells and Probes 3_6
3.3.2.2 Manifolds, Valves, and Instrumentation 3-10
3.3.2.3 Air Compressor or Blower 3-11
3.3.3 Monitoring of System Performance 3_12
3.4 PERFORMANCE AND COST ANALYSIS 3-14
3.4.1 Performance 3_15
3.4.1.1 U.S. Department of Energy Savannah River Integrated
Demonstration Site 3_15
3.4.1.2 Toluene Remediation at a Former Industrial Facility 3-16
3.4.1.3 Electro-Voice, Inc., Demonstration Site 3-17
3.4.2 Cost Analysis 3_18
3.4.2.1 Cost for Department of Energy-Patented In Situ
Bioremediation System 3-18
3.4.2.2 Cost for Subsurface Volatilization Ventilation System 3-19
3.5
VENDORS 3_2i
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CONTENTS (Continued)
Chapter
3.5 VENDORS 3'21
3.6 STRENGTHS AND LIMITATIONS 3-21
3.7 RECOMMENDATIONS 3-22
3.8 REFERENCES 3-23
4.0 DUAL-PHASE EXTRACTION 4-1
4.1 TECHNOLOGY OVERVIEW 4-1
4.2 APPLICABILITY 4-2
4.2.1 Contaminant Properties 4-2
4.2.2 Contaminant Phases 4-3
4.2.3 Soil Characteristics 4-4
4.3 ENGINEERING DESCRIPTION 4-5
4.3.1 Dual-Phase Extraction System Design 4-5
4.3.1.1 Pilot Testing 4-5
4.3.1.2 Extraction Well Design 4-6
4.3.1.3 Extraction Equipment Design 4-7
4.3.1.4 System Monitoring 4-9
4.3.2 Dual-Phase Extraction System Characteristics 4-9
4.3.2.1 Drop-Tube Entrainment Extraction 4-9
4.3.2.2 Well-Screen Entrainment 4-11
4.3.2.3 Downhole-Pump Extraction 4-13
4.4 PERFORMANCE AND COST ANALYSIS 4-14
4.4.1 Performance 4-14
4.4.1.1 Underground Storage Tank Release from a Gasoline
Station in Houston, Texas 4-14
4.4.1.2 Underground Storage Tank Release from a Former Car Rental
Lot in Los Angeles, California 4-15
4.4.1.3 Release From An Electronics Manufacturing Facility In Texas .... 4-16
4.4.1.4 Underground Storage Tank Release from a Gasoline
Station in Indiana 4-17
4.4.1.5 Release from a Gasoline Underground Storage Tank for a
Vehicle Fueling Station at a Hospital in Madison, Wisconsin 4-18
u
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CONTENTS (Continued)
Chapter
4.5 VENDORS 4-19
4.6 STRENGTHS AND LIMITATIONS 4-19
4.7 RECOMMENDATIONS 4-20
4.8 REFERENCES 4-21
5.0 DIRECTIONAL DRILLING 5-1
5.1 TECHNOLOGY OVERVIEW 5-1
5.2 APPLICABILITY 5.3
5.2.1 Geologic Conditions 5-4
5.2.2 Distances Achieved 5.4
5.3 ENGINEERING DESCRIPTION 5-5
5.3.1 Drill Rigs 5.5
5.3.2 Drilling Assembly 5-6
5.3.2.1 Tri-Cone Type Drilling Tools 5-6
5.3.2.2 Hydraulically Assisted, Jet-Style Drilling Tools 5-7
5.3.2.3 Compaction Tools 5-7
5.3.3 Drilling Fluids 5-7
5.3.4 Guidance Systems 5-8
5.3.5 Directionally Drilled Well Installation 5-9
5.3.5.1 Well Materials 5-9
5.3.5.2 Well Screens 5-9
5.3.5.3 Well Casings 5-10
5.3.5.4 Well Installation 5-10
5.3.6 Design Considerations 5-10
5.3.6.1 Radius of Curvature 5-11
5.3.6.2 Air Flow Patterns 5-11
5.3.7 Common Problems 5-12
5.4 PERFORMANCE AND COST ANALYSIS 5-13
5.4.1 Performance 5-13
5.4.1.1 U.S. Department of Energy Savannah River Site
Integrated Demonstration Site 5-13
in
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CONTENTS (Continued)
Chapter
5.4.1.2 Alberta Gas Plant 5-14
5.4.1.3 Hastings East Industrial Park 5-15
5.4.1.4 John F. Kennedy Airport 5-18
5.4.2 Cost Analysis 5-21
5.5 VENDORS 5-21
5.6 STRENGTHS AND LIMITATIONS 5-22
5.7 RECOMMENDATIONS 5-23
5.8 REFERENCES 5-23
5.8.1 Cited References 5-24
5.8.2 Professional Contacts 5-26
6.0 PNEUMATIC AND HYDRAULIC FRACTURING 6-1
6.1 TECHNOLOGY OVERVIEW 6-1
6.2 APPLICABILITY 6-2
6.2.1 Geologic Conditions 6-3
6.2.2 Contaminants 6-4
6.2.3 Technologies Enhanced by Fracturing 6-5
6.3 ENGINEERING DESCRIPTION 6-5
6.3.1 Injection Media 6-6
6.3.2 Fracturing Equipment 6-7
6.3.3 Injection Pressure and Rate 6-8
6.3.4 Fracture Size and Shape 6-8
6.3.5 Site Conditions 6-9
6.3.6 Monitoring the Formation of Fractures 6-10
6.3.7 Well Completion 6-11
6.3.8 Pneumatic Fracturing 6-11
6.3.9 Hydraulic Fracturing 6-12
6.4 PERFORMANCE AND COST ANALYSIS 6-13
6.4.1 Performance 6-13
6.4.1.1 Pneumatic Fracturing Enhancement of SVE and
Hot Gas Injection in Shale 6-13
6.4.1.2 Pneumatic Fracturing Enhancement of SVE in Clay 6-15
6.4.1.3 Hydraulic Fracturing Enhancement of DPE in Clayey Silts . 6-16
IV
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CONTENTS (Continued)
Chapter
6.4.1.4 Pilot-Scale Testing of Hydraulic Fracturing at
Linemaster Switch Superfund Site 6-17
6.4.2 Cost Analysis 6-18
6.4.2.1 Costs of Pneumatic Fracturing 6-18
6.4.2.2 Costs of Hydraulic Fracturing 6-20
6.5 VENDORS 6-21
6.6 STRENGTHS AND LIMITATIONS 6-21
6.7 RECOMMENDATIONS 6-22
6.8 REFERENCES 6-23
6.8.1 Cited References 6-23
6.8.2 Professional Contacts 6-24
7.0 THERMAL ENHANCEMENT 7-1
7.1 TECHNOLOGY OVERVIEW 7-1
7.2 APPLICABILITY 7-3
7.3 ENGINEERING DESCRIPTION 7-3
7.3.1 Steam Injection/Stripping 7-5
7.3.1.1 Steam Injection Through Injection Wells 7-5
7.3.1.2 Steam Injection Through Drill Auger 7-6
7.3.2 Hot Air Injection 7-7
7.3.3 Radio-Frequency Heating 7-8
7.3.4 Electrical Resistance Heating 7-11
7.3.5 Thermal Conduction Heating 7-12
7.4 PERFORMANCE AND COST ANALYSIS 7-13
7.4.1 Performance 7-13
7.4.1.1 Rainbow Disposal Site 7-13
7.4.1.2 Savannah River Site 7-15
7.4.1.3 Former Gasoline Station Near St. Paul, Minnesota 7-17
7.4.2 Cost Analysis 7-18
7.4.2.1 Steam Injection/Stripping Costs 7-18
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Chapter
7.5
7.6
7.7
7.8
7.4.3
CONTENTS (Continued)
Additional Cost Studies 7-20
VENDORS
STRENGTHS AND LIMITATIONS
7.6.1 Steam Injection/Stripping
7.6.2 Hot Air Injection
7.6.3 Radio-Frequency Heating
7.6.4 Electrical Resistance
RECOMMENDATIONS
REFERENCES
7.8.1 Cited References
7.8.2 Professional Contacts
7-21
7-21
7-21
7-22
7-22
7-23
7-23
7-24
7-24
,7-25
Appendices
A PHOTOGRAPHIC LOG
B BIBLIOGRAPHY
VI
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FIGURES
Figure page
3-1 TYPICAL AIR SPARGING ENHANCEMENT TO SOIL VAPOR
EXTRACTION SYSTEM 3_26
3-2 HORIZONTAL AIR SPARGING AND SOIL VAPOR EXTRACTION
WELL SYSTEM 3_2?
3-3 3-YEAR REMEDIATION COST BREAKDOWN 3-28
3-4 REMEDIATION COST BREAKDOWN FOR IN SITU BIOREMEDIATION
AND PUMP-AND-TREAT/SOIL VAPOR EXTRACTION 3-29
4-1 SCHEMATIC OF A DUAL-PHASE EXTRACTION SYSTEM 4-23
4-2 DROP-TUBE ENTRAINMENT EXTRACTION WELL 4-24
4-3 DOWNHOLE-PUMP EXTRACTION WELL 4-25
4-4 EXTRACTION SYSTEM PERFORMANCE 4-26
5-1 HORIZONTAL WELL NETWORK INSTALLED BENEATH A
BUILDING TO REMEDIATE SOIL AND GROUND WATER 5-28
5-2 BLIND BOREHOLE COMPLETION 5-29
5-3 CONTINUOUS WELL COMPLETION 5-30
5-4 PILOT HOLE ADVANCEMENT 5-31
5-5 BACK REAMING AND WELL CASING INSTALLATION 5-32
5-6 TYPICAL DOWNHOLE HARDWARE FOR DIFFERENT DRILLING PHASES 5-33
5-7 HASTINGS EAST INDUSTRIAL PARK SITE PLAN SHOWING
HORIZONTAL AND VERTICAL WELL AIR SPARGING/SOIL
VAPOR EXTRACTION SYSTEM 5-34
5-8 TCE CONCENTRATIONS IN SIX GROUND WATER MONITORING WELLS
DOWNGRADIENT FROM THE HORIZONTAL SPARGING WELL 5-35
5-9 TCE CONCENTRATIONS IN THREE GROUND WATER MONITORING
WELLS NEAR THE VERTICAL SPARGING WELL 5-36
vn
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FIGURES (continued)
Figure Page
5-10 HORIZONTAL WELL LAYOUT FOR AIR SPARGING AND SOIL
VAPOR EXTRACTION AT TERMINAL 1A, JOHN F. KENNEDY
INTERNATIONAL AIRPORT 5-37
5-11 HORIZONTAL WELL LAYOUT FOR AIR SPARGING AND SOIL VAPOR
EXTRACTION AT THE INTERNATIONAL ARRIVALS BUILDING,
JOHN F. KENNEDY INTERNATIONAL AIRPORT 5-38
5-12 AIR SPARGING PILOT TEST, NOVEMBER 1995 AT THE INTERNATIONAL
ARRIVALS BUILDING, JOHN F. KENNEDY INTERNATIONAL AIRPORT 5-39
5-13 SOIL VAPOR EXTRACTION PILOT TEST NOVEMBER 1995 AT THE
INTERNATIONAL ARRIVALS BUILDING, JOHN F. KENNEDY
INTERNATIONAL AIRPORT 5-40
6-1 SCHEMATIC OF PNEUMATIC FRACTURING FOR ENHANCED
VAPOR EXTRACTION 6-26
6-2 SCHEMATIC OF HYDRAULIC FRACTURING 6-27
6-3 APPLICATION GUIDELINES FOR PNEUMATIC FRACTURING 6-28
6-4 EFFECTS OF PNEUMATIC FRACTURING 6-29
6-5 SEQUENCE OF OPERATIONS FOR CREATING HYDRAULIC FRACTURES 6-30
6-6 COMPARISON OF TCE MASS REMOVAL ENHANCED BY
PNEUMATIC FRACTURING 6-31
6-7 PREFRACTURE CONTAMINANT REMOVAL CONCENTRATIONS 6-32
6-8 POST-FRACTURE CONTAMINANT REMOVAL CONCENTRATIONS 6-33
6-9 CUMULATIVE GROUND WATER REMOVAL BEFORE
HYDRAULIC FRACTURING 6-34
6-10 CUMULATIVE GROUND WATER REMOVAL AFTER
HYDRAULIC FRACTURING 6-35
7-1 RELATIONSHIP BETWEEN INCREASING TEMPERATURE AND VAPOR
PRESSURE FOR SEVERAL CHEMICALS 7-26
Vlll
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FIGURES (continued)
Figure
7-2
7-3
7-4
7-5
7-6
Page
TYPICAL SOIL VAPOR EXTRACTION ENHANCEMENT
WITH STEAM INJECTION SYSTEM 7-27
HOT AIR INJECTION THROUGH DRILL AUGER 7-28
SOIL VAPOR EXTRACTION ENHANCEMENT WITH RADIO-FREQUENCY
HEATING AT SANDIA NATIONAL LABORATORY 7-29
COST ANALYSIS OF THE STEAM-ENHANCED RECOVERY PROCESS 7-30
COST COMPARISON OF THERMAL ENHANCEMENT AND
CONVENTIONAL TREATMENT TECHNOLOGIES
7-31
IX
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TABLES
Table Page
1-1 SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION 1-5
3-1 AIR SPARGING SYSTEM CHARACTERISTICS 3-30
3-2 FACTORS AFFECTING APPLICABILITY OF AIR SPARGING 3-31
3-3 SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES 3-32
3-4 PERFORMANCE OF SUBSURFACE VOLATILIZATION VENTILATION SYSTEM
FOR REDUCTION IN TARGET CONSTITUENTS IN SOIL HORIZONS IN THE
VADOSE ZONE AT THE ELECTRO-VOICE, INC., DEMONSTRATION SITE 3-35
3-5 PERFORMANCE OF SUBSURFACE VOLATILIZATION VENTILATION SYSTEM
FOR REDUCTION IN INDIVIDUAL TARGET CONSTITUENTS IN THE VADOSE
ZONE AT ELECTRO-VOICE, INC., DEMONSTRATION SITE 3-36
3-6 SUMMARY OF COST DATA FOR IN SITU BIOREMEDIATION
AS WELL AS PUMP-AND-TREAT WITH SOIL VAPOR EXTRACTION 3-37
3-7 ESTIMATED COST FOR TREATMENT USING THE SUBSURFACE
VOLATILIZATION VENTILATION SYSTEM PROCESS OVER A
3-YEAR APPLICATION 3-38
3-8 VENDORS OF AIR SPARGING TECHNOLOGIES 3-39
4-1 COSTDATA 4-27
4-2 VENDORS OF DUAL-PHASE EXTRACTION TECHNOLOGIES 4-28
5-1 VENDORS OF HORIZONTAL WELLS AND DIRECTIONAL
DRILLING TECHNOLOGY 5-41
6-1 REMEDIATION TECHNOLOGIES ENHANCED BY FRACTURING 6-36
6-2 SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES
ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING 6-37
6-3 COMPARISON OF HYDROCARBON CONDENSATE RECOVERY RATES
BEFORE AND AFTER FRACTURING 6-41
6-4 COST DATA FOR SOIL VAPOR EXTRACTION ENHANCED WITH
PNEUMATIC FRACTURING 6-42
6-5 COST DATA FOR HYDRAULIC FRACTURING 6-43
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TABLES (continued)
Table Page
6-6 PNEUMATIC AND HYDRAULIC FRACTURING TECHNOLOGY VENDORS 6-44
6-7 COMPARISON OF PNEUMATIC FRACTURING AND HYDRAULIC
FRACTURING 6-46
7-1 THERMAL ENHANCEMENT PERFORMANCE DATA 7-32
7-2 HUGHES STEAM-ENHANCED RECOVERY PROCESS COST SUMMARY 7-35
7-3 SIX PHASE SOIL HEATING COST SUMMARY 7-36
7-4 THERMAL ENHANCEMENT TECHNOLOGY VENDORS 7-37
7-5 WASTE APPLICATIONS 7.39
XI
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ACRONYMS AND ABBREVIATIONS
fig/L Micrograms per liter
AAEE American Academy of Environmental Engineers
AC Alternating current
Accutech Accutech Remedial Systems, Inc.
AS/SVE Air sparging and soil vapor extraction
bgs Below ground surface
BTEX Benzene, toluene, ethylbenzene, and xylene
ฐC Degrees Celsius
cfm Cubic feet per minute
cfm/ft Cubic feet per minute per foot
cm/s Centimeters per second
CPVC Chlorinated polyvinyl chloride
DNAPL Dense nonaqueous-phase liquid
DOE U.S. Department of Energy
DPE Dual-phase extraction
Echo Echo-Scan, Inc.
Electro-Voice Electro-Voice, Inc.
EPA U.S. Environmental Protection Agency
ER Electrical resistance
ERT Electrical resistance tomography
ฐF Degrees Fahrenheit
Frac Frac Rite Environmental, Ltd
FRX FRX, Inc.
GAG Granular activated carbon
gpm Gallons per minute
GRO Gasoline range organics
HDPE High density polyethylene
Hz Hertz
in/sec Inches per second
ISB In situ bioremediation
Xll
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ACRONYMS AND ABBREVIATIONS (Continued)
JFK John F. Kennedy Airport
K Hydraulic conductivity
KAI KAI Technologies, Inc.
kVA Kilovolt-ampere
kW Kilowatts
LNAPL Light nonaqueous-phase liquid
MHz Mega-hertz
mg/kg Milligrams per kilogram
mg/L Milligrams per liter
mm Hg Millimeter of mercury
MPE Multi phase extraction
NAPL Nonaqueous-phase liquids
PCB Polychlorinated biphenyls
PCE Tetrachloroethene
ppb Parts per billion
psi Pounds per square inch
PT/SVE Pump-and-treat system combined with soil vapor extraction
PVC Polyvinyl chloride
RFH Radio-frequency heating
scfm Standard cubic feet per minute
SERP Hughes Steam Enhanced Recovery Process
SITE Superfund Innovative Technology Evaluation
SPSH Six phase soil heating
SRS Savannah River site
SVE Soil vapor extraction
SVOC Semivolatile organic compounds
SVVSฎ Subsurface Volatilization and Ventilation System
TCA Trichloroethane
TCE Trichloroethene
Tetra Tech Tetra Tech EM Inc.
TIO Technology Innovation Office
xiii
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ACRONYMS AND ABBREVIATIONS (Continued)
TOU Thermal oxidation unit
TPH Total petroleum hydrocarbons
UST Underground storage tank
V Volts
VEP Vacuum enhanced pumping
VISITT Vendor Information System for Innovative Treatment Technologies
VOC Volatile organic compound
WDNR Wisconsin Department of Natural Resources
yd3 Cubic yard
xiv
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NOTICE
This document was prepared for the U.S. Environmental Protection Agency (EPA) by Tetra Tech EM
Inc. (Tetra Tech) under Contract No. 68-W5-0055. Reference herein to any specific commercial product,
process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply
endorsement, recommendation, or favoring by EPA.
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FOREWARD
Soil vapor extraction (SVE) has been used at many sites to remove volatile organic compounds (VOC)
from soil in the vadose zone. The effectiveness of SVE, however, is limited at sites with complex
geology or by the distribution of contaminants in the subsurface and saturated soils. In recent years,
research and field demonstrations have been conducted using innovative technologies and procedures to
enhance the treatment effectiveness and removal rates of VOCs from vadose zone soil and of VOCs
dissolved in groundwater and adsorbed to saturation zone soils. This report assists the site manager
considering SVE as a treatment remedy by providing an evaluation of the current status of enhancement
technologies. The five SVE enhancement technologies evaluated in this report are air sparging,
dual-phase extraction, directional drilling, pneumatic and hydraulic fracturing, and thermal enhancement.
The report discusses the background and applicability; provides an engineering evaluation; evaluates
performance and cost; provides a list of vendors; discusses strengths and limitations; presents
recommendations for future use and applicability; and lists references cited for each SVE enhancement
technology.
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EXECUTIVE SUMMARY
This report provides an engineering analysis of, and status report on, selected enhancements for soil
vapor extraction (SVE) treatment technologies. The report is intended to assist project managers
considering an SVE treatment system by providing them with an up-to-date status of enhancement
technologies; an evaluation of each technology's applicability to various site conditions; a presentation of
cost and performance information; a list of vendors specializing in the technologies; a discussion of
relative strengths and limitations of the technologies; recommendations to keep in mind when
considering the enhancements; and a compilation of references.
The performance of an SVE system depends on properties of both the contaminants and the soil. SVE is
generally applicable to compounds with a vapor pressure of greater than 1 millimeter of mercury at 20 ฐC
and a Henry's Law constant of greater than 100 atmospheres per mole fraction. SVE is most effective at
sites with relatively permeable contaminated soil and with saturated hydraulic conductivities of greater
than 1 x 10"3 or 1 x 10"2 centimeter per second (cm/s). SVE by itself does not effectively remove
contaminants in saturated soil. However, SVE can be used as an integral part of some treatment schemes
that treat both groundwater and the overlying vadose zone.
Enhancement technologies should be considered when contaminant or soil characteristics limit the
effectiveness of SVE or when contaminants are present in saturated soil. The five enhancement
technologies covered in this report are as follows and are described in the following subsections:
Air Sparging
Dual-phase Extraction
Directional Drilling
Pneumatic and Hydraulic Fracturing
Thermal Enhancement
ES-1
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AIR SPARGING
This popular technology expands the remediation capabilities of SVE to the saturated zone. One of the
limitations of SVE alone is that it does not effectively address contaminated soils within the capillary
fringe and below the groundwater table. Air sparging can enhance the remediation capabilities of SVE in
the capillary fringe zone to include remediation of chemicals with lower volatilities and/or chemicals that
are tightly sorbed. This technique also enhances biodegradation of aerobically-degradable contaminants
and can significantly reduce the remediation time for contaminated sites.
Air sparging is a process during which air is injected into the saturated zone below or within the areas of
contamination. Air injection can be performed through vertical or horizontal wells or sparging probes.
The choice is largely determined by the site geology, site location, depth to groundwater, contaminant
distribution, operational considerations, and a cost comparison analysis. As the injected air rises through
the formation, it may volatilize and remove adsorbed volatile organic compounds (VOC) in soils within
the saturated zone as well as strip dissolved contaminants from groundwater. Air sparging is most
effective at sites with homogeneous, high-permeability soils and unconfined aquifers contaminated with
VOCs. Air sparging also oxygenates the groundwater and soils, thereby enhancing the potential for
biodegradation at sites with contaminants that degrade aerobically.
The effectiveness of air sparging for remediating contaminated sites is highly dependent on site-specific
conditions. Less difficult at sites with homogeneous, high-permeability soils and unconfined aquifers, air
sparging has been used at sites with heterogeneous, less-permeable soils and soils containing
low-permeability layers with some effectiveness. Before selecting air sparging as an enhancement to
SVE, site-specific groundwater, soil, and contaminant conditions as well as cleanup goals and project
objectives should be assessed.
DUAL-PHASE EXTRACTION
Like air sparging, dual-phase extraction (DPE) combines soil and groundwater treatment for cleaning up
VOC contamination. By removing both contaminated water and soil gases from a common extraction
well under vacuum conditions, simultaneous treatment can be achieved, reducing both the time and cost
of treatment. DPE provides a means to accelerate removal of nonaqueous-phase liquids (NAPL) and
ES-2
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dissolved groundwater contamination, remediate capillary fringe and smear zone soils, and facilitate
removal of vadose zone soil contaminants. DPE is most effectively implemented in areas with saturated
soils exhibiting moderate to low hydraulic conductivity (silty sands, silts, and clayey silts). Lower
permeability soils enable formation of deeper water table cones of depression, exposing more saturated
soils and residual contamination to extraction system vapor flow. By lowering the groundwater table at
the point of vapor extraction, DPE enables venting of soil vapors through previously saturated and
semisaturated (capillary fringe) soils. High vacuums typically associated with DPE systems enhance
both soil vapor and groundwater recovery rates.
Three basic types of DPE have been developed including:
Drop-tube entrainment extraction. Extraction of total fluids (liquid and soil vapors) via vacuum
applied to a tube inserted in the extraction well. Groundwater and vapors are removed from the
extraction well in a common pipe manifold, separated in a gas/liquid separator, and treated.
Well-screen entrainment extraction. Extraction of groundwater and soil vapors from a common
borehole screened in the saturated and vadose zones. Groundwater is aspirated into the vapor
stream at the well screen, transported to the treatment system in a common pipe manifold,
separated in a gas/liquid separator, and treated.
Downhole-pump extraction. Extraction of groundwater using a downhole pump with concurrent
application of vacuum to the extraction well. Groundwater and soil vapors are removed in
separate pipe manifolds and treated.
Variations to each type of DPE have been developed to enhance overall system performance. The type
of DPE most suitable to any site is dictated by soil hydraulic and pneumatic properties, contaminant
characteristics and distribution, and site-specific remediation goals. Relative costs for the different types
are also largely determined by these factors.
Use of DPE for remediation of contaminated sites is most advantageous for sites contaminated with
volatile compounds and for soils with moderate to low hydraulic conductivity. The presence of existing
monitoring wells in strategic locations may provide an opportunity for minimizing system capital costs
through conversion of the wells for extraction. Before a DPE system is implemented, efforts should be
undertaken to assess groundwater and soil characteristics as well as project objectives for determining
which type of DPE is appropriate for the site.
ES-3
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DIRECTIONAL DRILLING
Directional drilling employs the use of specialized drill bits to advance curved boreholes in a controlled
arc (radius) for installation of horizontal wells or manifolds for SVE and sparging technologies.
Horizontal wells can be used for enhancement of groundwater extraction, air sparging, SVE, and free
product removal systems. The number of horizontal wells installed for environmental remediation
projects has increased dramatically in recent years; more than 400 new horizontal wells were projected to
be installed in 1996 (Wilson 1995a). Horizontal directional drilling, when applied to appropriate
geologic environments and contaminants, can result in better performance and lower overall cost than
vertical wells.
Horizontal wells can be installed in most geologic materials that are suitable for soil vapor extraction and
air sparging, including unconsolidated sands, silts, and clays, as well as bedrock. Borehole lengths of
between 200 and 600 feet, with depths of less than 50 feet are most common; however, longer and deeper
boreholes have been successfully installed.
There are two types of directionally drilled boreholes: blind and continuous. Blind boreholes terminate
in the subsurface; the well is installed from the entrance of the borehole. Continuous boreholes are
reoriented upward and return to the ground surface. In continuous boreholes, the well is installed from
the exit point and pulled into the borehole by the drill rig. An overview of a horizontal well installation
by directional drilling is as follows:
A pilot hole is advanced. Upon arriving at a target depth, the drilling tool is reoriented to drill a
horizontal borehole. Electronic sensors in the drill tool guidance system provide orientation,
location, and depth data to the driller.
The hole is enlarged using a reaming drill bit, by pushing or pulling the bit through the pilot hole.
In a continuous borehole, the reaming drill bit tool is inserted into the borehole at the exit point
and pulled back to the drill rig.
The well is installed by pushing or pulling the well casings into the borehole. In continuous
boreholes, well installation generally occurs during the reaming phase described previously.
Installation of horizontal wells may be more expensive than installation of vertical wells. A careful
analysis should be conducted to determine the costs and benefits of a horizontal well drilling program.
ES-4
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PNEUMATIC AND HYDRAULIC FRACTURING
Pneumatic and hydraulic fracturing are recognized methods adapted from the petroleum industry that
induce fractures to improve the performance of extraction or injection wells. The two enhancement
technologies involve the injection of either gases (typically air) or fluids (either water or slurries) to
increase the permeability of the area around an injection well, thereby allowing increased removal or
degradation rates of contaminants and potentially more cost-effective remediation. Pneumatic and
hydraulic fracturing enhancement technologies are most applicable to low-permeability geologic
materials, such as fine-grained soils, including silts, clays, and bedrock. The typical application of
pneumatic and hydraulic fractures is to improve the performance of wells used during SVE remediation.
Fracturing also can increase the recovery of free-phase fluids by increasing the discharge of recovery
wells. Such applications closely resemble the recovery of oil from petroleum reservoirs. In addition,
pneumatic and hydraulic fracturing also are being developed and used to enhance remediation
technologies, such as DPE, in situ bioremediation including bioventing, thermal treatment including hot
gas injection, in situ vitrification, free product recovery, and groundwater pump-and-treat systems.
Pneumatic fracturing typically involves the injection of highly pressurized air into soil, sediments, or
bedrock to extend existing fractures and create a secondary network of conductive subsurface fissures
and channels. The pore gas exchange rate, often a limiting factor during vapor extraction, can be
increased significantly as a result of pneumatic fracturing, thereby allowing accelerated removal of
contaminants. Recent application to saturated zones has provided evidence that the process also can
effectively enhance remediation of saturated zones.
In hydraulic fracturing, water or a slurry of water, sand, and a thick gel is used to create distinct,
subsurface fractures that may be filled with sand or other granular material. The fractures are created
through the use of fluid pressure to dilate a well borehole and open adjacent cracks. Once fluid pressure
exceeds a critical value, a fracture begins to propagate. Fractures may remain open naturally, or they
may be held open by permeable materials, known as "proppants" (typically sand), injected during
fracture propagation. Hydraulic fractures injected beneath the water table have shown to effectively
enhance remediation of saturated zones.
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To apply pneumatic or hydraulic fracturing effectively, the basic principles of fracturing, as well as the
site geology, hydrology, and contaminant distribution must be understood. Thorough site
characterization is necessary since fracturing may be an unnecessary step at sites that have high natural
permeabilities. When fractures are to be induced for SVE remediation, design variables such as the
selection of proppants and well completion specifications must be considered. Because of the great
variability of geologic materials, conducting pilot-scale field tests is advisable before full-scale fracturing
installations are implemented.
Although most environmental applications of pneumatic and hydraulic fracturing involve fluid injection
to induce fractures and improve the performance of wells, a few cases have involved the use of
detonating explosives to enhance permeability of crystalline bedrock and improve contaminant recovery.
Environmental applications of blast-enhanced fracturing techniques have been adapted from the mining
and geothermal industries and are well documented in the literature. To date, blast-enhanced fracturing
has been used only with pump-and-treat methods, but it also may be useful in improving the performance
of certain in situ technologies used at sites with naturally fractured aquifers in coherent bedrock. This
technology is not suitable or useful for fracturing soils or shallow aquifers, or near buildings or other
structures that cannot withstand vibrational impacts.
THERMAL ENHANCEMENT
Thermal enhancements for SVE involve transferring heat to the subsurface to increase the vapor pressure
of VOCs or semivolatile organic compounds (SVOC) or to increase air permeability in the subsurface
formation by drying it out. The removal of contaminants by SVE is controlled by a number of transport
and removal mechanisms including gas advection, chemical partitioning to the vapor phase, gas-phase
contaminant diffusion, sorption of contaminant on soil surfaces, and chemical or biological
transformation. Thermal enhancement technologies raise the soil temperature to increase the reaction
kinetics for one or all of these removal and transport mechanisms. In general, thermal enhancement
technologies should be considered during soil remediation for one or more of the following applications:
removal of sorbed organic compounds with low vapor pressures, reduction of treatment time for difficult
matrices, treatment of NAPLs, and enhancement of biological activity in soil.
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Thermal enhancement technologies include hot air or steam injection, radio-frequency heating (RFH),
electrical resistance (ER) heating, and thermal conduction heating. Past applications of steam injection
technologies have focused primarily on moving and vaporizing free petroleum product in the subsurface
toward extraction wells for removal. Hot air injection has been used to increase the vapor pressure of
VOCs and SVOCs in the vadose zone, thus decreasing remediation time and increasing contaminant
removal. Use of ER heating and RFH has primarily focused on increasing mass removal rates of
contaminants in low-permeability soil. Thermal conduction heating enhances conventional SVE
treatment by heating the soil surface to volatilize contaminants. These thermal enhancement
technologies are described in the following paragraphs.
Steam injection: This technology enhances conventional SVE treatment by injecting steam into the
contaminated region. Contaminants are pushed ahead of the condensing water vapor toward the
extraction wells. Additionally, some of the contaminants are vaporized or solubilized by the injection of
steam and are moved toward vacuum extraction wells or a vacuum well at the soil surface. Steam
injection technology is typically more applicable to regions with medium- to high-permeability soils,
where the condensate front can move through the formation more freely. The subsurface geology must
provide a confining layer below the depth of contamination to not allow contamination to migrate
vertically downwards. In addition, a low permeability surface layer may be needed to prevent steam
breakthrough for shallow soil applications.
Hot Air Injection: This technology is similar to steam injection, but hot air is used in place of steam.
Hot air is used to volatilize the contaminants for removal at an extraction well. The resulting off-gas is
then treated. The main strength of hot air injection technologies is their comparatively low cost.
However, hot air injection is not a very efficient means for delivering heat to the subsurface because of
the relatively low heat capacity of air. Because both steam injection and hot air injection involve
injecting a fluid under pressure into the subsurface, the same geological concerns apply for hot air
injection as with steam injection.
Radio-Frequency Heating: For RFH, energy is delivered to the contaminated region using electrodes
or antennae that emit radio-frequency waves. These radio waves increase molecular motion, which heats
the soil. Electrodes are either placed on the surface at the contaminated area or inserted into holes drilled
into the contaminated area. The vaporized contaminants resulting from the heated soil are then
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transported to the extraction wells by an applied vacuum. RFH is effective for treating VOCs in
low-permeability soil in the vadose zone.
Electrical Resistance Heating: This technology uses the soil as a conduction path for electrical current.
The energy dissipated because of resistance is transformed into heat. A typical application of ER heating
involves an array of metal pipes inserted into the contaminated region by drilling. An electrical current is
then passed through these pipes to heat the contaminated region and drive off soil moisture and target
contaminants. The volatilized gas is then collected under vacuum by extraction wells. ER heating is
effective for treating VOCs in low-permeability soil in the vadose zone.
Thermal Conduction Heating: In thermal conduction heating, a heat source is placed on the surface of
the contamination or inserted into the formation, and heat is supplied to the contaminants by conduction.
The supplied heat volatilizes the target contaminants collected under vacuum by extraction wells or
surface shroud. There has been limited application of this thermal enhancement technology to remediate
hazardous waste sites. Thermal conduction heating can be used to remove VOCs in medium- to
low-permeability soil. This technology is easily implemented and is relatively inexpensive; however,
heat conduction by this method is very slow and inefficient and requires that a large temperature gradient
be maintained for acceptable heating rates to be achieved.
Thermal enhancement technologies can enhance treatment efficiency and removal rates if certain site or
contaminant characteristics constrain SVE treatment efficiency. Steam injection/stripping should be
considered for sites that contain free petroleum product or high concentrations of total petroleum
hydrocarbons (TPH). Additionally, some of the contaminants are vaporized or solubilized by the
injection of steam and are moved toward the extraction wells by an applied vacuum. However,
application of steam injection/stripping systems is limited to medium- to high-permeability soils. ER
heating is more appropriate for heating and drying low-permeability soil in the vadose zone. RFH and
ER heating can be used to heat soil if site conditions restrict the use of injection wells.
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CHAPTER 1.0
INTRODUCTION
Under Contract No. 68-W5-0055 with the U.S. Environmental Protection Agency's (EPA) Office of Solid
Waste and Emergency Response Technology Innovation Office (TIO), Tetra Tech EM Inc. (Tetra Tech),
has prepared this engineering analysis of and status report on selected enhancements for soil vapor
extraction (SVE) treatment technologies. TIO was established to advocate the development and use of
innovative treatment technologies for remediation and corrective action related to hazardous waste. This
report provides additional information on SVE technologies as presented in EPA's document, SVE
Enhancement Technology Resource Guide (EPA/542-B-95-003, October 1995).
1.1 BACKGROUND
SVE has been used at many sites to remove volatile organic compounds (VOC) from soil in the vadose
zone; however, the treatment effectiveness of SVE is limited at sites with complex geology or by the
distribution of contaminants in the subsurface. In recent years, research and field demonstrations have
been conducted using innovative technologies and procedures designed to enhance the treatment
effectiveness and removal rates of VOCs from vadose zone soil and of VOCs dissolved in groundwater.
Evaluating the current status of enhancements for SVE technologies will assist site managers who may
be considering SVE as part of an integrated treatment remedy. The five enhancements that are evaluated
in this report are air sparging, dual-phase extraction (DPE), directional drilling, pneumatic and hydraulic
fracturing, and thermal enhancement. Table 1-1 presents a summary of the five SVE enhancement
technologies presented in this report.
This report evaluates engineering methodologies related to SVE technologies. Recent advancements of
in-situ bioremediation techniques have demonstrated that SVE technologies greatly enhance and sustain
the aerobic bioremediation processes by providing oxygen (or heat) to naturally occurring soil
microbials. This report does not address the evaluation and implementation of SVE systems to promote
biodegradation of site contaminants. It is important to recognize the biochemical dynamics of a
contaminated site and design a remediation technology that addresses both site characteristics and
biochemical characteristics. Engineers and site managers should consider the physical and biochemical
processes in the site characterization and design phases of remediation projects. Other technologies may
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enhance SVE treatment effectiveness (for example, bioventing); however, this report focuses solely on
the enhancements listed above.
Lasted below are some general SVE reference manuals that have proven to be helpful for the technologies
discussed in this report.
American Academy of Environmental Engineers. 1994. Innovative Site Remediation Technology.
Volume 1 - Bioremediation; Volume 2 - Chemical Treatment; Volume 3 - Soil Washing/Soil Flushing;
Volume 4 - Stabilization/Solidification; Volume 5 - Solvent/Chemical Extraction; Volume 6 - Thermal
Desportion; Volume 7 - Thermal Destruction; Volume 8 - Vacuum Vapor Extraction.
William Anderson, ed.
Battelle Memorial Inst. 1994. Air Sparging for Site Remediation. February 23.
Battelle Memorial Inst. 1994. Applied Biotechnology for Site Remediation. March 8.
Nyer, Evan. 1996. In Situ Treatment Technology. Geraghty & Miller. April 3.
Soesilo, J. Andy and Stephanie Wilson. 1997. Site Remediation Planning and Management. Lewis
Publishers. January 14.
Suthersan, Suthan S. 1996. Remediation Engineering Design Concepts. Lewis Publishers. October 24.
U.S. Army Corps of Engineers. 1995. Soil Vapor Extraction and Bioventing Engineering Manual -
Engineering and Design. EM 1110-1-4001. November.
EPA. 1991. Soil Vapor Extraction Technology Reference Handbook. Office of Research and
Development. EPA/540/2-91/003. February.
EPA. 1994. Design, Operation, and Monitoring of In Situ Soil Vapor Extraction Systems. Office of
Research and Development. EPA/600/F-94/037. September.
1.2 OBJECTIVES
The following five specific objectives have been developed for this report:
Describe the background, applicability, and assessment of SVE enhancements
Perform an engineering evaluation of each technology to evaluate performance, cost, strengths,
and weaknesses
Evaluate the current status of each technology
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Compile a vendor list for each technology
Make recommendations for future use and applicability of each technology
The general approach used to meet these objectives is discussed in Section 1.3.
1.3 APPROACH
A five-step approach was used to identify, collect, and review information to fulfill the objectives listed
in Section 1.2 for each of the five SVE enhancements. The approach consisted of conducting the
following five tasks:
Conduct literature reviews - Studies conducted by academic institutions, Federal agencies,
state programs, and other entities were reviewed to identify previous applications of
enhancement technologies
Collect performance information - Performance information was collected from the literature
reviewed for each technology, as well as through database queries, such as the Vendor
Information System for Innovative Treatment Technologies (VISITT)
Collect cost information - Because the benefits of implementing enhancement technologies
must be weighed against the costs of the technologies, cost information was collected from
literature searches and other sources whenever possible to assess the costs of implementing SVE
alone versus the costs of implementing SVE with an enhancement technology
Contact and interview experts in the field - SVE enhancement experts familiar with the
outcome of field demonstrations were contacted to collect additional insight into implementing
enhancement technologies at sites and to determine the state of the art in each technology
Contact and interview vendors - Technology vendors were contacted to collect additional,
unpublished performance and cost data to supplement information collected during the literature
review
One objective for preparing this document was to identify vendors for each technology. However, the
list of vendors identified for each technology should not be considered to be a comprehensive
representation of all vendors that exist for each technology. The list of vendors were identified by the
following methods:
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Initially, technology vendors were identified by accessing the Vendor Information System for
Innovative Treatment Technologies (VISIT!) database (EPA 1996). The VISITT database
provides vendor information for innovative treatment technologies.
Vendors were also identified through a networking process. These vendors were interviewed by
phone to confirm their services. In many instances, vendor contacts provided the names of
additional vendors providing technology services in the same field. In these cases, additional
vendors were also contacted, interviewed, and added to the lists.
The term "vendor" is more appropriate for some technologies than others. Some technologies, such as
dual-phase extraction and air sparging, are systems commonly designed and installed by a number of
environmental companies. For other technologies, such as directional drilling and pneumatic and
hydraulic fracturing, vendors are technology-specific and provide services specific to these systems.
1.4 REPORT ORGANIZATION
This report contains seven chapters, including this introduction. Chapter 2 presents a background
discussion of SVE and the enhancement technologies. Chapters 3 through 7 present in-depth
assessments of the five SVE enhancement technologies: air sparging, DPE, directional drilling,
pneumatic and hydraulic fracturing, and thermal enhancement, respectively. The in-depth assessments
provide information as follows:
The applicability of the enhancement
Cost and performance information
List of technology vendors
Strengths and limitations
List of references
Figures
Tables (including cost and vendor information)
Appendix A contains a photographic log displaying examples of the technologies presented in this report.
Appendix B contains a bibliography of published works collected during the course of research for topics
presented in this report.
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TABLE 1-1
SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION
(Page 1 of 3)
TecbiMogj?
Air Sparging.
Dual
Direettcwial Drilling
Pneumatic and
Hydraulic Fratfuraag
" & f , > ^
Thermal Enhancement
Description
Injection of air occurs
below or within
contaminated zones through
wells or sparging probes.
The injected air removes
adsorbed VOCs in soil and
dissolved contaminants in
groundwater as the air rises
through the formation. The
increase in dissolved
oxygen can also increase
biodegradation of
aerobically degradable
contaminants.
Removal of contaminated
water and soil gases from a
common extraction well
takes place under vacuum
conditions. Groundwater
extraction exposes soil
formerly in the capillary
fringe and saturated zones
to the extraction system
vapor flow. The three
primary methods used are
drop-tube entrainment, well-
screen entrainment, and
downhole-pump extraction.
Installation of extraction or
injection wells in the most
beneficial location relative
to the area of contamination,
and soil anisotropy
maximizes the results of an
SVE system. This
technology increases the
useful zone of influence of
the well and reduces short
circuiting problems in
vertical boreholes.
Injection of gases (typically
air) or fluids (either water or
slurries) into low-permeable
soil and sediments increases
the performance of
extraction or injection wells
used in SVE. Development
of fractures may occur in
saturated sediments as well
as in the vadose zone.
The transfer of heat to the
subsurface improves or
speeds up contaminant
transport and removal
mechanisms such as gas
advection, chemical
partitioning to the vapor
phase, gas phase
contaminant diffusion,
sorption of contaminant on
soil surfaces, and chemical
or biological transformation.
Methods include steam or
hot air injection, radio-
frequency heating, electrical
resistance heating, and
thermal conduction.
Status
In use at many sites in the
United States and Europe
since the 1980s.
Currently in use at many
sites in the United States.
First applied to
environmental remediation
in 1988; the number of
horizontal wells used for
environmental remediation
has increased dramatically
in recent years.
Adapted from the petroleum
industry in 1990; a number
of pilot- and full-scale
applications of fracturing
enhancement SVE
conducted in recent years.
Several full-scale
applications of steam and
hot air injection and
electrical resistance
technologies conducted in
recent years; commercial
systems available. Several
pilot-scale applications of
radio-frequency heating and
electrical heating have also
been conducted, but
commercial systems are
relatively limited.
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TABLE 1-1
SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION
(Page 2 of 3)
Technology
Air Sparging
Dual-Phase Extraction
Directional Drilling
Pneumatic and
Hydraulic Fracturing
Thermal Enhancement
Applicable Situations
Most effective at removing
volatile contaminants from
the saturated zone at sites
with homogeneous, high-
permeability soils and
unconfined aquifers; also,
used with some success in
heterogeneous, less-
permeable soil and in soil
with low-permeable layers.
Most applicable at sites with
multiple phase (soil and
groundwater or soil,
groundwater, and free
product) contamination and
low to moderate hydraulic
conductivity soils. High
vacuum enhances soil vapor
and groundwater recovery
rates in low-permeable soil
formations.
Suitable in many geologic
materials ranging from
unconsolidated sands and
silt. Often used where
access for vertical wells is
limited, the contaminant
zone is long and thin, or the
geologic materials are very
anisotropic.
Generally used at sites with
low-permeable soil and
sediment, such as clay, silt,
or sedimentary bedrock,
where fracturing may
increase permeability and
improve fluid flow during
the remediation process.
Often used in situations
involving sorbed organic
compounds with low vapor
pressure, difficult matrices,
or nonaqueous phase
liquids. Also used to
enhance biological activity
in soil.
Limiting Factors
Distribution of air channels
may be affected by
lithologjcal and operational
control of air flow.
Diffusion of contaminants
into channels is slow;
however, cycling or pulsing
may reduce diffusion
limitations. Performance
may be difficult to measure
or interpret.
Hydraulic and pneumatic
properties of soil determine
which type of dual-phase
extraction system would be
most effective.
Groundwater extraction
rates required for effective
operation in permeable soils
may be prohibitive, and
extraction depths may be
limited.
Installation in clay and
bedrock can be difficult
because of smearing along
the borehole wall and slow
drilling rates. Highly
fluctuating water tables can
cause problems in
horizontal well SVE
systems.
Geology and site conditions
control the size, shape,
orientation, and
effectiveness of the
fractures.
Site geology typically
controls which thermal
enhancement method is
appropriate.
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TABLE 1-1
SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION
(Page 3 of 3)
Technology
Air Sparging
Dual-Phase Extraction
Directional Drilling
Pneumatic land.
Hydraulic Fracturing
Thermal Enhancement
Site-specific
Considerations
Soil heterogeneity greatly
affects the distribution of air
channels and the
effectiveness of air
sparging.
Operating costs may be high
in permeable soil formations
because of high water
extraction rates and
resulting treatment
requirements.
The initial installation of
horizontal wells may be
more expensive than the
installation of vertical wells,
but other efficiency
improvements may
compensate for some of this
difference in cost. Careful
site characterization studies
are necessary to correctly
place and design well
screens.
Most effective in low-
permeable, over-
consolidated soil, sediment,
or sedimentary bedrock,
such as shale and siltstone.
Steam injection is limited to
medium- to high-permeable
soil. Electrical resistance
heating is effective in low-
permeable soil in the vadose
zone. Thermal conduction
can be used in medium- to
low-permeable soil, but is
sometimes slow and
inefficient. Radio-
frequency or electrical
resistance heating can be
used at sites where the use
of injection wells is
restricted.
Technological
Advancements
Air sparging is becoming
increasingly more important
in providing oxygen to
aerobic, in situ
bioremediation projects.
Dual-phase extraction is an
aggressive technology that
is uniquely suited to sites
with multiple-phase
contamination. Soil and
groundwater contamination,
as well as free-phase liquids
and capillary fringe/smear
zone contamination, can be
addressed.
The cost of horizonal wells
continues to decline.
Horizontal wells will be
used more routinely in the
near future.
Pneumatic and hydraulic
fracturing are becoming
increasingly more important
in improving soil
permeabilities for the
delivery or extraction of
fluids from low-permeable
environments. Fracturing
likely will be applied more
routinely to many in situ
remediation technologies in
the future.
Steam and hot air injection
are being used at full-scale
to decrease the tune
required for remediation.
Radio-frequency and
electrical resistance heating
require process automation
to reduce costs and operator
requirements.
Notes: NAPL
SVE
VOC
Nonaqueous-phase liquid
Soil vapor extraction
Volatile organic compound
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CHAPTER 2.0
BACKGROUND: SOIL VAPOR EXTRACTION ENHANCEMENT TECHNOLOGIES
SVE is an in situ remediation technique used to remove VOCs from vadose zone soil. Air flow is
induced through contaminated soil by applying a vacuum to vapor extraction vents and creating a
pressure gradient in the soil. As the soil vapor migrates through the soil pores toward the extraction
vents, VOCs are volatilized and transported out of subsurface soil. Advantage of SVE systems over
other remediation technologies for soil contaminated with organics are the relative simplicity of
installing and operating the system and the minimal amount of equipment required.
The performance of an SVE system depends on properties of both the contaminants and the soil. The
most important contaminant property is its volatility, which can be measured by its vapor pressure and its
Henry's Law constant. Vapor pressure is the pressure exerted by a vapor phase constituent and the
Henry's Law constant is the ratio of the partial pressure of a chemical's concentration in solution at
equilibrium. SVE is applicable to compounds with a vapor pressure of greater than 1 millimeter of
mercury (mm Hg) at 20 ฐC and a Henry's Law constant of greater than 100 atmospheres per mole
fraction (EPA 1991). SVE is most effective at sites with relatively permeable contaminated soil. SVE
systems are installed above the water table and thus do not affect contaminated soil within the saturated
zone. Air sparging systems installed below the water table are effective in removing contaminants from
the groundwater but do not remove contaminants in the saturated soil per se (although desorption and
equilibration with the water phase follow).
Enhancement technologies should be considered when contaminant or soil characteristics limit the
effectiveness of SVE, or when contaminants are present in saturated soil. The five enhancement
technologies covered in this report are as follows:
Air sparging - Air sparging can be used with SVE to treat VOC contamination, such as gasoline,
solvents, and other volatile contaminants, present in the saturated zone. Air sparging involves
injecting air into the saturated zone below the contaminated area. The air rises through channels
in the saturated zone and carries volatilized contaminants up into unsaturated soils, where the
contaminants are subsequently removed using SVE. Air sparging also increases the dissolved
oxygen levels in the groundwater, thereby enhancing subsurface biodegradation of contaminants
that are aerobically degradable.
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DPE - DPE enhances contaminant removal by extracting both contaminated vapors and
groundwater from the subsurface. DPE involves the removal of contaminated vapors and
groundwater from the same borehole. A vacuum applied to the borehole extracts contaminated
vapors from unsaturated soils and simultaneously entrains contaminated groundwater. The
groundwater is subsequently separated from the vapors and treated using standard aboveground
treatment methods. The groundwater table within the zone of influence of a DPE well is
lowered, exposing the capillary fringe and previously saturated soils to the extraction vacuum
and enabling more effective remediation of these soils than traditional SVE systems.
Directional drilling - Directional drilling technologies allow SVE to be conducted in areas not
easily accessed by vertical drilling techniques. Directional drilling, along the geometry of the
contaminated zone, may increase the zone of influence of a single extraction or injection well.
Directional drilling also enhances SVE by reducing air short-circuiting within the borehole in
vertical well systems.
Pneumatic and hydraulic fracturing - Pneumatic and hydraulic enhancement technologies
increase SVE efficiency in low-permeability soils by creating cracks or sand-filled fractures.
Pneumatic fracturing involves injecting air into low permeability soils to create fractures, thus
increasing the permeability of the soil. Hydraulic fracturing creates sand-filled fractures which
also enhance the permeability of the subsurface formation. These enhancements can allow the
application of SVE in low-permeability, silty clay formations where in situ cleanup may be
impossible without enhancing soil permeability.
Thermal enhancement - Thermal enhancements for SVE may involve a number a different
technologies aimed at transferring heat to the subsurface to (1) increase the vapor pressure of
VOCs or semivolatile organic compounds (SVOC) to enhance their removal via SVE or (2) dry
soil to increase air permeability. Thermal enhancement technologies include hot air or steam
injection, electrical resistance (ER) heating, radio-frequency heating (RFH), and thermal
conduction heating.
The site geology, contaminant characteristics, and surface features determine which enhancement
technology will be the most effective. Thermal processes can raise the vapor pressure of a contaminant,
thus making it more amenable to removal by SVE. Pneumatic and hydraulic fracturing, directional
drilling, and thermal processes may increase the air permeability of low permeability soil. Pneumatic
and hydraulic fracturing increase permeability by injecting a fluid under pressure into the soil, whereas
directional drilling uses mechanical processes to increase soil permeability. Thermal processes use heat
to dry soil and increase air permeability. Air sparging and DPE should be considered if contamination is
present in saturated soil at a site and conventional SVE is limited by the rate of vaporization of VOCs
from groundwater in the saturated soil.
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As shown above, several enhancements may be appropriate for modifying contaminant or site
characteristics to increase SVE effectiveness; therefore, the following considerations describing the
applicability of SVE and the selected enhancements are suggested:
1. Excavate and treat contaminated soil ex situ, if the source is small and near the surface.
2. Biovent, if the source is amenable to aerobic bioremediation.
3. Apply SVE if contaminants are volatile and bioventing and excavation are not practical.
Directional drilling should be considered during remedial design of the SVE system and
not necessarily as an enhancement per se.
4. Apply pneumatic or hydraulic fracturing if the soil permeability is low (hydraulic
conductivity of less than 10'6 centimeters per second [cm/s]).
5. Apply thermal enhancement if the vapor pressures of the contaminant of concern are low
(less than 0.5 mm Hg at ambient conditions), or where high soil moisture content
prevents adequate air exchange.
6. Apply DPE if light nonaqueous phase liquid (LNAPL) is present or if the capillary fringe
is targeted for cleanup.
7. Air sparge to distribute oxygen in the groundwater and vadose zone and to induce
bioremediation and contaminant stripping in groundwater if desired.
Specific recommendations for application of each enhancement are discussed in Chapters 3 through 7.
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CHAPTER 3.0
AIR SPARGING
Air sparging is an innovative treatment technology that expands the remediation capabilities of SVE to
the saturated zone. One of the limitations of SVE alone is that it does not effectively address
contaminated soils within the capillary fringe and below the groundwater table or contaminated
groundwater. Air sparging enhances the remediation of deeper soils and groundwater. Air sparging can
significantly reduce the remediation time frames for contaminated sites as compared with conventional
SVE systems.
Air sparging was first used in Germany in the mid-1980s. The technology spread to other parts of
Europe and the United States in the late 1980s. Air sparging has become popular for remediating
contaminated sites in recent years and is currently being used at many sites throughout the United States.
The following sections provide an overview of air sparging and its use with SVE, describe conditions
under which the technology is applicable, outline the engineering factors considered in designing and
operating an air sparging system, summarize the performance and costs of case studies, discuss vendors
that provide air sparging services, outline strengths and limitations of the technology, and provide
recommendations for using the technology at contaminated sites. Cited figures and tables follow
references at the end of the chapter.
3.1 TECHNOLOGY OVERVIEW
Air sparging, also known as "in situ air stripping" and "in situ volatilization," is a process in which air is
injected into the saturated zone below or within the areas of contamination through a system of wells. As
the injected air rises through the formation, it may volatilize and remove adsorbed VOC in soils as well
as strip dissolved contaminants from groundwater. Air sparging is most effective at sites with
homogeneous, high-permeability soils and unconfined aquifers contaminated with VOCs.
SVE is commonly used with air sparging to capture the volatiles that air sparging strips from soil and
groundwater. The volatile contaminants are transported in the vapor phase to the vadose zone, where
they are drawn to extraction wells and treated using a standard off-gas treatment system. Air sparging
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can remediate contaminants in the vadose zone that would not be remediated by vapor extraction alone
(that is, chemicals with lower volatilities and/or chemicals that are tightly sorbed) (EPA 1995).
Air sparging also oxygenates the groundwater and soils, thereby enhancing the potential for
biodegradation at sites with contaminants that degrade aerobically. At one fuel spill site, approximately
70 percent of the contaminants was remediated through biodegradation and 30 percent through
volatilization (Billings and others 1994). In general, the primary removal mechanism for highly volatile
contaminants is volatilization, and the primary removal mechanism for low volatility contaminants is
biodegradation (Brown and others 1994). Vapor extraction appears to be the more dominant removal
mechanism during the early phases of treatment, while biostimulation processes dominate during later
phases.
An air sparging system includes the following components:
Air sparging wells or probes to inject air into the saturated zone
A manifold, valves, and instrumentation to transport and control the air flow
An air compressor or blower to push air into the saturated zone through the air sparging wells or
probes
A properly designed SVE system to capture the contaminated vapors in the vadose zone
A cross-section of a typical air sparging system design, including vertical sparge and SVE wells arid
surface treatment units, is shown in Figure 3-1. A similar system using horizontal sparge and SVE wells
is shown in Figure 3-2. Air sparging system characteristics are summarized in Table 3-1 and discussed in
subsequent sections.
3.2 APPLICABILITY
Air sparging is most effective at sites with homogeneous, high-permeability soils and unconfined
aquifers contaminated with halogenated or nonhalogenated and aerobically biodegradable VOCs. The
technology can also be effective at less ideal sites, such as those with heterogeneous, low to medium
permeability, stratified soils. Table 3-2 summarizes the factors affecting the applicability of air sparging.
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Modifications to injection of air in a sparging system include the following:
Supplemental injection of nutrients to enhance biodegradation
Substitution of nitrogen for air to reduce the formation of ferric oxide in the pore spaces of
aquifers with high iron concentrations
Supplemental injection of air with other gases such as ozone or oxygen or substitution of oxygen
for air to increase the availability of oxygen for biodegradation
Supplemental injection of methane as a cometabolizer for chlorinated solvents
Supplemental injection of toluene as a cometabolizer for trichloroethene (TCE)
Air sparging can be used in conjunction with other innovative enhancement technologies such as hot air
injection, fracturing, and RFH.
3.3 ENGINEERING DESCRIPTION
Proper design and operation of an air sparging system requires knowledge of the site conditions, as well
as an understanding of the way air sparging enhances the remediation of contaminated sites. Even
though air sparging is being used at many sites throughout the country, air flow in the subsurface,
especially within the saturated zone, is not well understood. Information from research and remediation
of contaminated sites is continually refining the concepts of air flow in the subsurface, and therefore, the
ways in which air sparging systems are designed and operated.
This section addresses important air flow concepts as well as design and operational components of an
air sparging system. Section 3.3.1 discusses subsurface air flow and operational methods that can reduce
the limitations posed by low air flow. Section 3.3.2 describes the engineering components of an air
sparging system, including the types, design, and operation of the equipment. Section 3.3.3 describes
methods typically used to monitor the performance of an air sparging and soil vapor extraction (AS/SVE)
system.
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3.3.1
Air Flow Within the Subsurface
The flow of injected air in both the horizontal and vertical directions in a contaminated aquifer is of
primary importance during air sparging. Anything that controls the air flow, whether it is operational or
lithological, can influence the effectiveness of the system (Brown and others 1994).
Air injected into aquifer materials has been shown to typically migrate in channels, and little airflow
moves in the form of bubbles as proposed in earlier studies (Hinchee 1994; Wisconsin Department of
Natural Resources [WDNR] 1995). If bubbles do form and move, the bubbles would likely induce
advective water flow, resulting in substantial contact between the air and aquifer materials. Research
indicates that an average grain size of 2.0 millimeters or larger is necessary for bubble flow to occur; this
is found at a small percentage of sites. If bubbles do not form at a site, air will flow in channels and
primarily have contact with the contaminated soil and groundwater within the channels.
There is a growing amount of research that indicates that the ability of an in situ air sparging system to
clean an aquifer is a function of the air channel density in a formation (WDNR 1995). Increasing the air
flow rate can greatly increase air channel density, but not necessarily the zone of influence of the well.
Generally, a more desirable air channel distribution is achieved in uniform, coarse-grained soils.
Sparging in fine-grained or highly stratified soils can require pressures that approach or exceed soil
fracturing pressures. The creation of fractures in the soil matrix can result in a loss of system efficiency
or in some cases can actually improve channel distribution; however, when fracturing occurs, the effects
are likely irreversible (Marley 1995).
The distribution of channels and thus the effectiveness of air sparging can be greatly affected by slight
heterogeneities in the soil matrix. Since air flow in the subsurface will follow the path of least resistance,
the majority of air channels form in the most permeable zones (Marley 1995). Thus, transfer of volatile
contaminants into air channels and oxygen into the aquifer can only be accomplished in the bulk of the
formation by diffusion processes. When diffusion works alone, the process is slow. The contaminants
must migrate several inches to several feet (that is, the typical distance between air channels) by
diffusion to reach an air channel (WDNR 1995). The air channel diameter is typically quite small
(approximately the size of the pore space between the soil particles); therefore, the surface area of the air
and water interface of each air channel is extremely small, resulting in limited mass exchange rates. In
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addition, the groundwater at a distance from the air channel can be quite high in VOC content, while the
water in the air channel will have reduced VOC content. This often creates a concentration gradient
within the groundwater regime.
Cycling or pulsing of the air flow during operation of an air sparging system promotes mixing of the
water in the treatment zone, effectively increasing the contact between the air and contaminated aquifer
materials and reducing the effects of diffusion limitations and contaminant concentration gradients that
form during continuous operation (WDNR1995; Marley 1995). This allows for increased volatilization
as well as enhanced biodegradation. Although there is some speculation that pulsing the system creates
new air channels in the formation, studies indicate that air channels appear to be stable and do not seem
to move over time or because of varying air flow rates (Johnson 1994). Varying the pressure within the
air channels, however, could result in changed channel diameters, thus inducing some water flow and
improving the effectiveness of air sparging (Hinchee 1994). Cycling has the potential to cause buildup of
fines, potentially clogging the well (WDNR 1995). This effect can be reduced by installing a check
valve on each well to reduce back flow. Biofouling of the well screen or sparging probe is also a concern
under the increased oxygen concentrations associated with this technology (Johnson 1994).
By manipulating air flow to the sparging wells at a site, cycling can reduce air emissions from the SVE
system, thereby potentially reducing the costs of off-gas treatment (WDNR 1995). Reducing air flow
through cycling or lower injection rates can increase the effect of biodegradation relative to
volatilization. Biodegradation can reduce the costs of remediation by reducing the amount of
contaminants that the SVE system must remove and treat, especially during later phases of treatment.
The need for off-gas treatment typically increases operational costs by a factor of 1.5 to 2 (EPA 1995).
Reducing air flow to optimize biodegradation and minimize off-gas treatment, however, could result in
longer remediation times, thereby potentially increasing costs. Cycling the air flow at a site can also
reduce capital and energy costs.
The site geology can greatly affect the flow of air in a formation. A low permeability layer above the
saturated zone can limit vertical air flow to the SVE system placed in the unsaturated zone, resulting in
substantial lateral migration of contaminated vapors from the sparge well. The potential for uncontrolled
migration of sparge vapors increases with increasing sparge depth because of the potential for channeling
along subsurface features. One technique used to increase the vertical permeability of a stratified
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formation is through the use of sand chimneys (EPA 1995; Tetra Tech 1996a). Sand chimneys are
sand-packed borings installed through low permeability layers. They provide passive air flow between
the subsurface layers, increasing both SVE and biodegradation rates.
3.3.2
Equipment Requirements and Operational Parameters
The basic equipment needed to conduct air sparging at a contaminated site includes air sparging wells or
probes, a manifold, valves, instrumentation, an air compressor, a vacuum blower, an air/water separator,
and air emissions treatment equipment (Figure 3-1).
Pilot tests are often conducted at a site to determine air sparging system design parameters such as air
entry pressures, vacuum requirements, air flow rates, and effective zones of influence for the sparging
and extraction components. Alternatively, it can be more cost effective at some sites to use existing
information about the site conditions to conservatively design an air sparging system with increased well
density, rather than conduct pilot tests, especially at sites where a shallow installation depth minimizes
the cost of installing additional wells (Tetra Tech 1996a, b).
Both pilot testing and full-scale air sparging operations at a site are initiated by operating the extraction
system without air sparging to establish a baseline for vapor extraction capability and emissions, as well
as to avoid buildup of vapors in the formation. After a few hours to a few days, the air sparging system is
turned on. Operation of the air sparging system requires ongoing monitoring and system adjustment to
maximize performance.
3.3.2.1
Air Sparging Wells and Probes
Air is injected through vertical wells, nested wells, horizontal wells, combined horizontal/vertical wells,
or direct push sparging probes. The type of well chosen depends on the site conditions and cost
effectiveness of each method.
The placement of sparging wells or probes at a site will depend primarily on the areal delineation of the
remediation area and the soil-specific zone of influence. The zone of influence is often estimated during
pilot testing by measuring parameters such as dissolved oxygen or contaminant concentrations in
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monitoring wells; oxygen, carbon dioxide, and contaminant concentrations in SVE off-gas or soil vapor
probes; and/or changes in the water table elevation caused by a water table rise in response to air
injection. Tracer gas mapping of air channel distribution and SVE system capture effectiveness is also
used to estimate the zone of influence. The depth at which air will be injected and the screen length are
determined by the site geology, depth to groundwater, contaminant type and distribution, and well type.
Another option is to construct and install the equipment in phases, and use the first phase installation to
conduct a pilot test. The results of the pilot test can then be used to complete the design and installation
of the system.
The use of neutron probes to assess air flow in the subsurface during pilot testing and operation is
increasing, although wide spread use of this technology may be limited by cost and the regulatory
requirements of using the probes that contain a low-level radioactive source (Baker et al 1996).
Electrical resistivity tomography can also be used to assess the air flow by measuring the resistivity of
the subsurface between two or more boreholes (Lundegard et al 1996). This technique is also becoming
more popular yet still is not used routinely at air sparging sites.
The following paragraphs describe vertical and horizontal wells, typical zones of influence, effective
sparging depth, and screen configuration for each type of well. Direct push sparging probes are also
discussed.
Vertical Wells
; are
Vertical air sparging wells are the most commonly used type of wells (Figure 3-1). These wells
installed using conventional drilling techniques such as hollow-stem auger methods. The well diameter
is typically 2 inches or greater to allow the use of conventional well development equipment. Air is
injected into the wells either through a manifold system or sparging probes installed in the wells.
Vertical wells have been installed in aquifers up to about 150 feet deep; however, a depth limitation for
vertical wells was not reported. Multiple-depth completions, which allow air injection at different
depths, can be used at sites with groundwater levels that fluctuate significantly.
Placement of vertical wells is largely determined by the estimated or calculated injection zone of
influence at the site. Zones of influence of 5 to 30 feet (measured radially) have been observed in coarse
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soils and 60 feet or greater in stratified soils (Marley 1995). At sites with zones of influence of 60 feet or
greater, preferential lateral air flow was probably occurring. Sparging well spacings of greater than
30 feet may not be successful (Tetra Tech 1996c).
The majority of sparge air flows out of the well screen near the top of the screen where the pressure head
is at a minimum and follows a path determined largely by the site geology. The top of the well screen
should be located no less than 5 feet below the vertically delineated remediation zone (Marley 1995). If
the sparge point is placed shallower than this, the zone of influence is very limited, and an excessive
number of sparge points is required to remediate a unit volume of contaminated soil. Alternatively, the
top of the screen should be set 5 feet below the seasonal low static water table (WDNR 1993). Sparging
well screen lengths of 1 to 5 feet are recommended (WDNR 1993; Marley 1995).
At sites where lateral displacement of contaminated groundwater is a concern, an array of defensive
sparging wells or an intercepting sparging trench downgradient of the remediation area can be used to
prevent spreading of the contamination as an alternative to the pump-and-treat technology.
Horizontal Wells
Horizontal wells are installed using innovative horizontal trenching or drilling techniques (Figure 3-2).
Horizontal wells can be used to remediate contamination under buildings and into other hard-to-reach
areas. These wells are particularly effective at sites that present shallow aquifers and long, thin
contaminant plumes, such as those caused by leaking pipelines.
Horizontal wells are generally installed perpendicular to the groundwater flow direction so that the
groundwater flows through the wells. High flow rates must be used to inject air through long lengths of
horizontal screen; still, it is possible that more air will exit the well at the air injection end of the screen
and less air will reach the far end of the screen (Tetra Tech 1996c). A more even distribution of air flow
can be achieved by using design techniques to allow control of the air flow trajectory.
The use of horizontal sparging within an aquifer increases the surface area exposed to the injected air,
thus providing a greater zone of influence than vertical wells (Tetra Tech 1996c). Heterogeneities in the
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soil matrix, however, can cause the air to flow out of the screen in discrete zones along the length of the
screen, reducing the effective zone of influence of the well.
Both horizontal air sparging and extraction wells can be used to remediate a contaminated site.
Alternatively, because the zone of influence of extraction wells is generally greater than that of air
sparging wells, it can be more cost effective to use vertical extraction wells in combination with
horizontal injection wells (Tetra Tech 1996c). The depth of the wells required at a site is a primary
factor in comparing the cost effectiveness of installing vertical or horizontal wells. Horizontal trenching
techniques can be used to install wells to depths up to 30 feet below grade (Tetra Tech 1996d). Drilling
techniques similar to those used to install utility lines can be used to install horizontal sparging wells to
depths of about 40 feet below grade. These horizontal drilling techniques can be cost competitive with
vertical well installation. More costly horizontal drilling techniques must be used for wells greater than
40 feet in depth. These techniques are discussed in Chapter 5.0. Installation of vertical wells generally
tends to be more cost effective than horizontal wells for depths between 40 and 100 feet, and installation
of horizontal wells tends to be more cost effective between 100 and 150 feet (Tetra Tech 1996c).
Direct Push Sparging Probes
Direct push techniques can be used to install sparging probes into the subsurface without installing a
groundwater well. Typically, a 2-inch casing equipped with a fall-off bottom is driven into the ground
with a hammer assembly. After a sparging probe and air tube are installed in the casing, the casing is
withdrawn, and the boring is backfilled. The. sparging probe air tube is then connected to an
aboveground air supply.
The depth to which direct push techniques can be used is limited by geological restrictions on penetrating
the subsurface. Greater depths can be attained in porous soils. Use of sonic waves can encourage easier
penetration. Probes can typically be installed to about 40 feet below grade using direct push techniques
and have reportedly been used up to 100 feet below grade (Tetra Tech 1996c).
Probes installed directly into the subsurface can reportedly be as effective at remediating a site as probes
installed in groundwater wells (Tetra Tech 1996c). Soil and water samples can be collected during either
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well or direct push probe installation. Groundwater wells may be subsequently be used for water and
vapor monitoring.
33.2.2
Manifolds, Valves, and Instrumentation
The manifold is typically buried underground and constructed of 2-inch or larger diameter steel,
polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), or high density polyethylene pipe
(HDPE). If pressures higher than 15 pounds per square inch (psi) are anticipated, use of manifold
materials at anticipated operational temperatures and pressures should be evaluated to prevent damage to
the manifold from excessive pressure and temperatures. PVC and CPVC may not withstand elevated
temperatures or pressures. PVC pipe is not recommended by many pipe suppliers for compressed air
service. In addition, if the manifold is buried within the frost zone or placed above ground, it may need
to be protected with insulation and/or heat tape.
Several devices can be installed to optimize operation of the sparging system. The following devices
may be included in the system design:
A filter on the air intake of the compressor to prevent particulates from damaging the air
compressor or entering the air stream.
A check valve between each well and the manifold to prevent temporary high pressure in the
screened interval from forcing air and water back into the manifold system after the system is
shut off
A throttle valve at each well to allow the well to be isolated from the system or to adjust the air
flow rate to the well
A solenoid valve on each well to allow the well to be cycled several times per day (requires
installation of a control panel with a timing device)
A port at each well to temporarily attach a flow meter for measurement of air flow at each well
A port to allow temporary attachment of a pressure gauge and thermometer at each well or well
cap or at the manifold near each well to monitor the air injection pressure and air temperature at
each well
A manual pressure relief valve immediately after the air compressor outlet to exhaust excess air
from the manifold
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A permanent pressure gauge, thermometer, and flow meter between the manifold system and the
manual pressure relief valve to measure total system flow, temperature, and pressure
An automatic pressure relief valve to prevent excessive pressure from damaging the manifold or
fracturing the aquifer in the event of a system blockage
In addition, installation of devices that would automatically shut down the air sparging system in the
event of air extraction equipment failure is recommended (WDNR 1995). Operation of the air sparging
system in the absence of the extraction system could spread the contamination in the formation or cause
the migration of vapors into buildings or utility conduits, creating an explosion hazard. A sensor placed
on a gas probe near critical structures to monitor for negative soil gas pressure or on the SVE stack to
monitor for positive pressure can continuously monitor the soil venting system.
Operation of the AS/SVE system requires ongoing monitoring and system adjustment to maximize
performance. Computer systems can be used to completely or partially automate the monitoring and/or
system adjustments.
3.3.2.3
Air Compressor or Blower
The air compressor or blower chosen for a site should be large enough to inject sufficient pressure and
flow to at least one well and possibly to multiple wells simultaneously (WDNR 1993). The air
compressor or blower should produce sufficient pressure to depress the water level in all wells below the
top of the screen during both seasonal high and low water table conditions. Air compressors and blowers
should be rated for continuous duty. Common air compressor types include oil-free reciprocating and
rotary screw compressors, rotary lobe blowers, centrifugal blowers, and regenerative blowers.
Compressors and blowers should not use lubricants or fluids that could enter the air stream and reach the
groundwater.
Air injection pressures are determined by the static water head above the sparge point, the required air
entry pressure of the saturated soils, and the air injection flow rate (Marley 1995). Higher pressures will
produce higher air injection flow rates and will likely produce additional air channels. Too high an
injection pressure can displace contaminated vapors and water and spread the contamination to
previously unaffected areas. Minimum air-entry pressures of 1 to 2 psi in excess of the hydrostatic head
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at the top of the injection well screen are recommended (Marley 1995). Fine-grained soils generally
require higher air-entry pressures (factor of 2 or more than the minimum).
Over pressuring may create fractures in the sparging well annular seal or within the soil. Forty to
50 percent porosity in the soil matrix should be assumed, and a 5 psi safety factor should be included to
calculate the air pressure for a site (WDNR 1995). Alternatively, the maximum pressure should be 60 to
80 percent of the calculated pressure exerted by the weight of the soil column above the top of the screen
(WDNR 1995).
The rate at which air will be injected must be determined after considering the site geology, contaminant
type and distribution, and remediation goals. Higher air flow rates increase the volatilization component
of remediation, and lower rates increase the biodegradation component of remediation. Air flow of at
least 5 standard cubic feet per minute (scfm) per well should be injected. If the permeability is too low to
allow 5 scfm, in situ air sparging may not be the appropriate remedial method for the site (WDNR 1995).
The relationship between air injection and air extraction varies from a recommended air injection to air
extraction ratio of 1 to 4 (WDNR 1995) to an air flow maintained at 80 percent of the vacuum rate
(EPA 1995).
There is growing evidence that the ability of an in situ air sparging system to clean an aquifer is a
function of the air channel density in the soil (WDNR 1995). Increasing the air injection rate can greatly
increase the air channel density within the zone of influence of a sparging well; however, the zone of
influence of the well is not significantly affected by the increase in injection rate or channel density
(WDNR 1995; Marley 1995).
33.3
Monitoring of System Performance
System adjustments are made based on monitoring of changing subsurface conditions. Monitoring
includes measurement of parameters related to volatilization, air flow, and bioactivity (such as carbon
dioxide and oxygen). The parameters typically used to monitor the performance of an air sparging
system include the following:
Dissolved oxygen and contaminant concentrations in groundwater
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Oxygen, carbon dioxide, and contaminant concentrations in extracted air
Microbial populations and activity (including in situ respiration tests)
Air flow and extraction rates
Air flow regions using neutron probe measurements or electrical resistivity tomography
Sparging and vacuum pressure measurements
Changes in the water table elevation caused by a water table rise in response to air injection
Tracer gas mapping of air channel distribution and SVE system capture effectiveness
Zone of influence for both vacuum and sparging wells
Continuity of blower and compressor operation
There is growing evidence that pilot tests and full-scale operations often provide overly optimistic results
if those results are based only on groundwater samples from monitoring wells (WDNR 1995; Hinchee
1994). This is especially true if dissolved oxygen in monitoring wells is the basis for estimating
effectiveness. The vast majority of air channels are found in the most permeable zones, and monitoring
well filter packs are typically more permeable than the native soils; therefore, air channels formed during
the in situ air sparging process will preferentially intersect and flow through monitoring well filter packs.
As a result, the water in monitoring well filter packs and the wells themselves usually receive much more
air flow than the rest of the aquifer, resulting in more aggressive treatment. Determining monitoring
system performance using chemistry changes in monitoring wells yields overly optimistic results. These
changes are generally not representative of the aquifer as a whole.
Practitioners often measure the effectiveness of air sparging by monitoring the oxygen, carbon dioxide,
and/or contaminant levels in air extracted from the vadose zone before operating the air sparging system
and comparing these data to measurements taken after air sparging is initiated. Typically, the data
indicate an increase in the remediation rate with air sparging, followed by a drop in the rate as the
subsurface reaches equilibrium. At one site, the remediation rate showed a 10-fold increase and reached
an equilibrium equivalent to a three-fold increase over SVE alone (Terra Vac, Inc. 1995). The extent to
which this effect is caused by the removal of contaminants from the aquifer or by improved removal from
the vadose zone is not known (Hinchee 1994). At some sites, contaminant concentrations in air extracted
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from the SVE system may decrease or remain the same with the addition of air sparging (Tetra Tech
1997). This effect may be due to dilution of the extracted air by the addition of sparged air into the
subsurface.
Monitoring air pressure in the vadose zone does provide some indication of the influence of air sparging
on the vadose zone but does not appear to correlate with the effect on the underlying aquifer (Hinchee
1994). Similarly, the water table rise observed during air sparging seems to correlate with the area in
which air is injected; however, the way this can be expected to correlate with the area of effective
treatment is not clear.
The best indicator of system performance or the effectiveness of an air sparging system is the long-term
improvement in soil and groundwater quality after the system has been shut down for a period of time
(Clark and others 1995). A site is often monitored following completion of air sparging operations
because of the possibility of rebounding groundwater contaminant concentrations (Tetra Tech 1996e).
Regulatory agencies are often reluctant to officially close a site based on water, soil gas, or SVE off-gas
data. Collection and analysis of soil samples at the site are sometimes required to confirm that the
contaminants in the subsurface have been removed.
3.4 PERFORMANCE AND COST ANALYSIS
Air sparging has been selected to remediate many contaminated sites across the country, including fuel
service stations, industrial sites, and government facilities. Many projects are still in the design or
operational phase. Many sites have met or are approaching the closure requirements of the regulatory
agencies. Some level of performance and cost data is available for many sites; however, comprehensive
data are often difficult to obtain. Table 3-3 lists 29 sites remediated by air sparging. It provides data on
soil types, contaminant types, reported contaminant concentrations in groundwater (initial and final), and
the time needed to achieve those final contaminant concentrations.
This section presents three case studies from the literature and discussions with technology experts and
vendors. The evaluation of the performance and cost at each site is based on the data available.
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3.4.1
Performance
The performance of the air sparging technology at three sites is described in the following subsections.
3.4.1.1
U.S. Department of Energy Savannah River Integrated Demonstration Site
Air sparging was used to remediate chlorinated VOCs at the U.S. Department of Energy (DOE)
Savannah River "M Area" Integrated Demonstration Site in Aiken, South Carolina, using the
DOE-patented In Situ Bioremediation (ISB) system (DOE 1996). The demonstration site is located
within a much larger plume that is actively being treated using pump-and-treat technologies. Process
wastewater containing chlorinated solvents was released from a process sewer into an unlined settling
basin and nearby stream between 1954 and 1985. High concentrations of solvents were detected in soil
and groundwater near the original discharge locations. TCE and tetrachloroethene (PCE) comprised
99 percent of the total contaminant mass.
Before the application of the ISB system at the demonstration site, the TCE and PCE concentrations in
groundwater ranged from 10 to 1,031 micrograms per liter (/ug/L) and 3 to 124 Aig/L, respectively. TCE
sediment concentrations ranged from 0.67 to 6.29 milligrams per kilogram (mg/kg) and 0.44 to
1.05 mg/kg, respectively. The soils at the site are relatively permeable sands with thin lenses of clayey
sediments. The groundwater table is at 120 feet below grade.
A horizontal injection well with a screened length of 310 feet was placed below the water table at a depth
of 175 feet. A horizontal extraction well with a screened length of 205 feet was placed in the vadose
zone semiparallel to the injection well at a depth of 80 feet (see Figure 3-2 for general reference). A
vacuum was initially applied at 240 scfm, and air injection was then applied at 200 scfm. Several
different modes of gaseous nutrient injection were applied during the demonstration, including
continuous injection of methane, pulsed injection of methane, and pulsed injection of methane plus
continuous injection of nitrous oxide and triethyl phosphate to supply nitrogen and phosphate for
enhanced biodegradation. Monitoring and system control were nearly completely automated.
The demonstration was operated for about 13 months from February 1992 to April 1993. During this
time, 16,934 pounds of VOCs was removed or degraded. The vacuum component removed
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12,096 pounds of VOCs, and the bioremediation component degraded and mineralized an additional
4,848 pounds of VOCs. Mass balance calculations indicate that 41 percent more VOCs were destroyed
using methane and nutrient injection than with air sparging alone. Biostimulation was greatest with
pulsed methane injection, as evidenced by increases in microbial populations with a decrease in TCE
levels (Hazen and others 1994).
Overall TCE and PCE concentrations in groundwater decreased by as much as 95 percent, reaching
concentrations below detectable limits (that is, less than 2 yWg/L in some wells) and well below drinking
water standards of 5 fJ.gfL (Hazen and others 1994). Soil gas TCE and PCE declined by more than
99 percent. Total sediment concentrations of TCE and PCE declined from 0.100 mg/kg to nondetectable
concentrations at most areas. Overall, the site was considered about 80 to 90 percent clean following the
13-month demonstration project (Tetra Tech 1996c).
3.4.1.2
Toluene Remediation at a Former Industrial Facility
A former industrial facility in Massachusetts used and stored toluene as part of a shoe adhesive
manufacturing process (Envirogen, Inc. 1996). Toluene was accidentally released from site operations,
and dissolved and free phase toluene were detected in vadose and saturated soils and groundwater. The
soils at the site are homogeneous medium to coarse sands. The water table fluctuates seasonally from
3 to 7 feet below grade.
Following completion of pilot tests, a remedial design was developed for a 3/4-acre remedial target area.
The design included 70 air sparging points and 70 SVE wells. In addition to sparging and SVE wells
within the target area, the system included a defensive line of sparging and SVE wells near the site
perimeter to prevent downgradient contaminant migration. The system used a total air injection rate of
100 cubic feet per minute (cfm) and a total extraction rate of 300 cfm.
The system operated between May 1993 and early 1996. Approximately 20,881 pounds of toluene-range
hydrocarbons was removed in the first 23 months of operation from the bulk of the site. The system
continued operating to remove contaminants from hot spots. Closure of the site was obtained in early
1996 based on the analytical results of soil, soil gas, and groundwater samples collected from the site.
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3.4.1.3
Electro-Voice, Inc., Demonstration Site
Air sparging was used to perform a Superfund Innovative Technology Evaluation (SITE) demonstration
at the Electro-Voice, Inc. (Electro-Voice), facility in Buchanan, Michigan (EPA 1995), using the
Subsurface Volatilization and Ventilation System (SWSฎ). The Electro-Voice facility actively
manufactures audio equipment. The demonstration site was an open area near the facility where paint
shop wastes had been discharged to the subsurface via a dry well between 1964 and 1973. During
previous remedial investigation studies at the site, organic and inorganic contaminants were detected in
soil and groundwater associated with the former dry well area.
Eleven vertical SVE wells and nine vertical air injection wells were installed in the treatment area. The
vacuum extraction wells were installed with a 5-foot section of screen set to intersect a sludge layer
found at 12 to 18 feet below grade in a clay-rich horizon. The air injection wells were installed with a
1-foot screened interval positioned approximately 10 feet beneath the 46-foot deep water table. Sand
chimneys were installed to facilitate vertical air circulation in the highly stratified soils at the site. The
air flow rate was maintained at about 80 percent of the vacuum flow rate. Monitoring and system control
were mostly automated, with minimal operator control required.
Pretreatment data were collected from 20 boreholes randomly positioned in the treatment area, which
included approximately 2,300 cubic yards (yd3) of contaminated soil. The data indicated that a portion of
the site contained target VOC concentrations near or below the detection limits; therefore, only the
portion of the site at which significant contaminant concentrations were detected, referred to as the "hot
zone," was selected for assessment of the performance of the S WSฎ system. The hot zone included
approximately 800 yd3 of contaminated soil and encompassed four extraction wells and three sparging
wells. The previously installed system was operated over the entire treatment area.
The demonstration operated from August 1992 through July 1993. The reduction in the sum of target
VOC components in vadose zone soils averaged 80.6 percent over the 1-year period. This greatly
exceeded the developer's claim of a 30 percent reduction. The sludge layer in which the highest
pretreatment concentrations were detected was the only horizon that did not undergo almost complete
remediation. The pretreatment and posttreatment concentrations of the target VOC components in
3-17
-------
vadose zone soil horizons are summarized in Table 3-4. The data for individual target VOC components
are summarized in Table 3-5.
VOC contamination in saturated zone soils was reduced by 99.3 percent. Contamination was not
detected in groundwater during system operation; therefore, the remedial capabilities of the SVVSฎ
system for groundwater at the site were not assessed during the demonstration.
Operation of the SVVSฎ over the entire treatment area did not affect the performance of the system in the
hot zone. However, installation of the system in noncontaminated soils was not an effective use of
resources and emphasizes the importance of accurately defining the location and extent of contamination
before implementing a remedial system.
3.4.2
Cost Analysis
The air sparging technology is applicable to sites contaminated with gasoline, diesel fuels, and other
hydrocarbons, including halogenated compounds to enhance SVE. The technology can be applied to
contaminated soils, sludges, free-phase hydrocarbon product, and groundwater. A number of factors
could affect the estimated cost of treatment. Among them were the type and concentration of
contaminants, the extent of contamination, groundwater depth, soil moisture, air permeability of the soil,
site geology, geographic site location, physical site conditions, site accessibility, required support
facilities and availability of utilities, and treatment goals. It is important to thoroughly and properly
characterize the site before implementing this technology to insure that treatment is focused on
contaminated areas. Cost analysis for two case studies are provided to understand the variability in costs
in applying this technology.
3.4.2.1
Cost for Department of Energy-Patented In Situ Bioremediation System
The cost analysis for ISB is based on data provided by the Savannah River Site (SRS) VOCs in soils and
groundwater at nonarid sites integrated demonstration and was performed by the Los Alamos National
Laboratory. The conventional technology of pump-and-treat system combined with soil vapor extraction
(PT/SVE) was used as the baseline technology against which ISB was compared. To compare the two
remediation systems, a number of assumptions were made:
3-18
-------
PT/SVE would remove the same amount of VOCs as the vacuum component of ISB when
operated for the same time period
Four vertical SVE and four pump-and-treat wells would have the same zone of influence as
two horizontal wells used for ISB
Volatilized contaminants from both technologies are sent to a catalytic oxidation system for
destruction
Capital equipment costs are amortized over the useful life of the equipment, which is assumed to
be 10 years, not over the length of time required to remediate a site
Capital and operating costs for ISB and PT/SVE are summarized in Table 3-6.
Capital costs for the baseline technology are comparable with the innovative technology of ISB. The
cost to install horizontal wells for ISB exceeds installation costs of vertical wells. However, horizontal
drilling costs are decreasing as the technology becomes more widely used and accepted. If horizontal
wells can clean a site faster, operating costs will decrease significantly. Fixed equipment costs for ISB
include gas mixing and injection equipment for providing the nutrients required for stimulation of the
bioremediation portion of the innovative technology. The cost to biodegrade as little as 900 pounds of
TCE/PCE would offset the additional bioenhancement costs (that is, methane and trace nutrient
supplements and methane monitoring equipment) compared to air sparging alone (Hazen and others
1994).
The annual operating costs are comparable between the baseline and the innovative remediation
technology. However, the treatment time is estimated to be 10 years to remediate the demonstration site
using the baseline PT/SVE and only 3 years using ISB. Actual treatment times are estimates, and field
experience indicates that the PT/SVE estimate is on the optimistic side, since the objective is the Safe
Drinking Water Act maximum of 5 //g/L for TCE/PCE. Consumable and labor costs are approximately
85 percent of the total cost per pound of the VOCs remediated for both technologies. Figure 3-4 shows
the relative importance of each category on overall costs for both ISB and PT/SVE.
3.4.2.2
Cost for Subsurface Volatilization Ventilation System
The cost analysis for the SVVSฎ is based on assumptions and costs provided by Brown & Root
Environmental, the operator of the system at the site, and on results and experiences from the SITE
3-19
-------
demonstration operated over a 1-year period at the Electro-Voice facility. The cost associated with
treatment by the SWSฎ process, as presented in this economic analysis, is defined by 12 cost categories
that reflect typical cleanup activities performed at Superfund sites. These 12 cost categories are as
follows:
Site preparation
Permitting and regulatory requirements
Capital equipment (amortized over 10 years)
Startup
Consumables and supplies
Labor
Utilities
Effluent treatment and disposal costs
Residuals and waste shipping, handling, and storage services
Analytical services
Maintenance and modifications
Demobilization
Table 3-7 shows the itemized costs for each of the 12 cost categories on a year-by-year basis for a
hypothetical 3-year full-scale remediation of the Electro-Voice facility. The total cost to remediate
21,300 yd3 of soil was estimated to be $220,737 or $10.36/yd3. This figure does not include any
treatment of the off-gases. If effluent treatment costs are included, it would increase costs to $385,237 or
$18.09/yd3.
Figure 3-3 shows the relative importance of each category on overall costs. It shows that the largest cost
component without effluent treatment was site preparation (28 percent), followed by analytical services
(27 percent), and residuals and waste shipping, handling, and storage (13 percent). Labor accounted for a
relatively small percentage (9 percent), excluding travel, per diem, and car rental expenses. These four
categories alone accounted for 77 percent of the costs. Utilities and capital equipment accounted for
6 and 8 percent respectively, and the remaining cost categories each accounted for 4 percent or less.
Effluent treatment costs would have accounted for 43 percent of the total cleanup cost if it had been
conducted at the Electro-Voice site. Cost figures provided here are "order-of-magnitude" estimates and
are generally accurate to plus 50 percent to minus 30 percent.
3-20
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3.5 VENDORS
Many companies are involved in various aspects of air sparging technology, including equipment
manufacture and installation as well as the design and operation of air sparging systems. Some
companies have patented air sparging techniques or process name trademarks. Vendors of air sparging
technology that were identified are included in Table 3-8.
3.6 STRENGTHS AND LIMITATIONS
The following list outlines some of the strengths of using air sparging with SVE at sites contaminated
with VOCs:
Air sparging expands remediation capabilities of SVE to the saturated zone.
In air sparging, both volatilization and biodegradation processes contribute to remediation of
VOCs.
By using air sparging, biodegradation can be potentially further enhanced by supplementing air
with other gases and/or nutrients.
Air sparging eliminates the need to remove and treat large quantities of groundwater using
expensive pump-and-treat methods.
Air sparging has been shown to be more cost effective than conventional PT/SVE.
Air sparging effectively creates a crude air stripper in the subsurface, with the soil acting as the
"packing."
In air sparging, the sparged air elevates the dissolved-oxygen content in the subsurface, thus
enhancing natural biodegradation.
Cycling or pulsing the air flow during air sparging can increase mixing in the saturated zone, thus
increasing volatilization and biodegradation of contaminants.
The following list outlines some of the limitations of using air sparging at sites contaminated with VOCs:
Air flow dynamics in the subsurface, and therefore the mechanisms of air sparging remediation,
are not well understood.
Limited performance data are available.
3-21
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Operational and lithological controls influence the air flow in the subsurface, thereby controlling
the remediation potential of air sparging.
A low permeability layer above the saturated zone in stratified soils can limit vertical air flow,
resulting in substantial lateral migration of contaminated vapors from the sparge well.
Excess subsurface pressure can aggravate the spread of contaminated vapors, free phase product,
or dissolved contaminants and may create fractures in the sparging well annular seal or within
the formation.
The usefulness of standard monitoring practices for assessing the performance of air sparging is
not clearly understood.
As a rule of thumb, performance of air sparging decreases in less permeable soils.
Preferential air channeling and poor air distribution are expected to increase significantly in less
permeable soils and increase with soil heterogeneity.
Clogging of the aquifer, sparging probes, or well screens due to enhanced bacterial growth or
precipitation of metals under increased oxygen levels can reduce the permeability at a site.
There is a potential for rebound of contaminant concentrations after air sparging is discontinued.
3.7 RECOMMENDATIONS
The effectiveness of air sparging for remediating contaminated sites is highly dependent on site-specific
conditions. Before selecting air sparging as an enhancement to SVE, the site-specific groundwater, soil,
and contaminant conditions, as well as cleanup goals and project objectives, should be assessed.
Consideration of air sparging as the remedial choice should include a comparison of the cost
effectiveness of air sparging to other technologies.
Air sparging is most effective at sites with homogeneous, high-permeability soils and unconfined
aquifers that are contaminated with halogenated or nonhalogenated, aerobically biodegradable VOCs.
Air sparging is less effective, but also has been used at sites with heterogeneous, less-permeable soils and
soils containing low-permeability layers.
3-22
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The methods of injecting air into the saturated zone should be compared. Air injection can be performed
through vertical or horizontal wells or sparging probes. The choice is largely determined by the site
geology, site location, depth to groundwater, contaminant distribution, operational considerations, and a
cost comparison analysis. Vertical wells have been used to depths of 150 feet below grade. Horizontal
wells can be used to greater depths and are effective at remediating contamination under buildings and in
elongated plumes. Sparging probes can typically be used to depths of 40 feet below grade using direct
push techniques and have been used to 100 feet below grade.
Operation of an air sparging system at a contaminated site should focus on-going monitoring and system
adjustment to respond to the changing subsurface conditions. The available data are too limited to
determine whether a continuous or pulsed operating strategy is best. If mass transfer limitations prove to
govern air sparging system behavior, continuous operation will probably be the preferred option. Should
the pulsing of the air injection flow rate enhance mixing in the subsurface, a properly timed pulsed
operation could deliver enhanced performance.
3.8 REFERENCES
This section includes references cited in Chapter 3.0. A comprehensive bibliography is provided in
Appendix B.
Baker, Ralph S., R. Pemmireddy, and D. McKay. 1996. Evaluation of Air-Entry Pressure During In Situ
Air Sparging: A Potentially Rapid Method of Feasibility Assessment. Proceeding of the First
International Symposium on In-Situ Air Sparging. Las Vegas, Nevada. October 24-25,1996.
Billings, and Associates, Inc. 1996a. Project Description for Firehouse Site. Available on World Wide
Web. July 28.
Billings and Associates, Inc. 1996b. Project Description for BF1 Site. Available on World Wide Web
July 28.
Billings and Associates, Inc. 1996c. Project Description for Bloomfield Site. Available on World Wide
Web. July 29.
Billings, J.F., A.I. Cooley, and O.K. Billings. 1994. Microbial and Carbon Dioxide Aspects of
Operating Air-Sparging Sites. Air Sparging for Site Remediation, ed. Robert E. Hinchee. Lewis
Publishers. Ann Arbor, Michigan. Pages 112-119.
3-23
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Brown, R.A., R.J. Hicks, and P.M. Hicks. 1994. Use of Air Sparging for In Situ Remediation. Air
Sparging for Site Remediation, ed. Robert E. Hinchee. Lewis Publishers. Ann Arbor, Michigan.
Pages 38-55.
Clark, T.R, R.E. Chaudet, and R.L. Johnson. 1995. Assessing UST Corrective Action Technologies:
Lessons Learned about In Situ Air Sparging at the Dennison Avenue Site, Cleveland, Ohio. U.S.
Environmental Protection Agency Project Summary. EPA/600/SR-95/040. March. Risk Reduction
Engineering Laboratory. Cincinnati, Ohio.
Envirogen, Inc. 1996. Project Summary: Former Industrial Facility Remediation, Massachusetts for
Confidential Chemical Company. October 1992 to June 1996.
Hazen, T.C., K.H. Lombard, B.B. Looney, M.V. Enzien, J.M. Dougherty, C.B. Fliermans, J. Wear, and
C.A. Eddy-Dilek. 1994. Summary of In-Situ Bioremediation Demonstration (Methane Biostimulation)
via Horizontal Wells at the Savannah River Site Integrated Demonstration Project. In-Situ Remediation:
Scientific Basis for Current and Future Technologies, Thirty-Third Hanford Symposium on Health and
the Environment. Battelle Press. November 7 through 11,1994.
Hinchee, Robert E. 1994. Air Sparging State of the Art. Air Sparging for Site Remediation, ed. Robert
E. Hinchee. Lewis Publishers. Ann Arbor, Michigan. Pages 1-13.
Johnson, R.L. 1994. Enhancing Biodegradation with In Situ Air Sparging: A Conceptual Model. Air
Sparging for Site Remediation, ed. Robert E. Hinchee. Lewis Publishers. Ann Arbor, Michigan.
Pages 14-22.
Loden, MaryE. 1992. A Technology Assessment of Soil Vapor Extraction and Air Sparging. Prepared
for the U.S. Environmental Protection Agency, Risk Reduction Engineering Laboratory. Cincinnati,
Ohio. April.
Lundegard, Paul D., D. La Brecque. 1996. Integrated Geophysical and Hydrologic Monitoring of Air
Sparging Flow Behavior. Proceedings of the First International Symposium on In-Situ Air Sparging.
Las Vegas, Nevada. October 24-25,1996.
Marley, Michael C. 1995. Unpublished. The State of the Art in Air Sparging Technology.
Tetra Tech EM Inc. (Tetra Tech). 1996a. Personal Communication between Dawn Cosgrove of Tetra
Tech and Rick Billings of Billings and Associates, Inc. August 22.
Tetra Tech. 1996b. Personal Communication between Dawn Cosgrove of Tetra Tech and Dr. Gale
Billings of Billings and Associates, Inc. July 18.
Tetra Tech. 1996c. Personal Communication between Dawn Cosgrove of Tetra Tech and Brian Looney
of Westinghouse Savannah River Company. August 23.
Tetra Tech. 1996d. Personal Communication between Dawn Cosgrove of Tetra Tech and Donald
Justice of Horizontal Technologies, Inc. July 19.
3-24
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Tetra Tech. 1996e. Personal Communication between Dawn Cosgrove of Tetra Tech and Dom DiGuilo
of the U.S. Environmental Protection Agency, National Risk Management Research Laboratory,
Subsurface Protection and Remediation Division. August 23.
Tetra Tech. 1996f. Personal Communication between Dawn Cosgrove of Tetra Tech and Alia Werner of
Envirogen, Inc. August 29.
Tetra Tech. 1997. Personal Communication between Dawn Cosgrove of Tetra Tech and Dave Becker of
the U.S. Army Corps of Engineers. May 7.
Terra Vac Corporation. 1995a. Project Description for Underground Storage Tanks-Irvine, California.
July 23.
Terra Vac Corporation. 1995b. Project Description for Fabricated Metal Products-New Paris, Indiana.
May 5.
Terra Vac, Inc. 1995c. Project Summary: Gasoline Service Station - Fremont, California.
May 5.
U.S. Army Corps of Engineers. 1995. Soil Vapor Extraction and Bioventing Engineering and Design.
EMI 110-1-4001. November 30.
U.S. Department of Energy. 1996. Innovative Technology Summary, In Situ Bioremediation Using
Horizontal Wells, U.S. Department of Energy Savannah River M Area Process Sewer Integrated
Demonstration Site, Aiken, South Carolina. Available on the World Wide Web. June 27.
U.S. Environmental Protection Agency. 1995. Subsurface Volatilization Ventilation System (S WS)ฎ,
Innovative Technology Evaluation Report. Office of Research and Development. Washington D C.
EPA/540/R-94/529. August.
Wisconsin Department of Natural Resources (WDNR). 1993. Guidance for Design, Installation, and
Operation of In Situ Air Sparging Systems. September.
WDNR. 1995. Errata Sheet for the Guidance for Design, Installation, and Operation of In Situ Air
Sparging Systems, dated September 1993. August 11.
3-25
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Atmospheric
Air
Soil Vapor
Extraction
Well
Vent to
Atmosphere
Air
Filter
NX\\
Soil Vapor
Extraction
Well
OF ENGINEERS 199E
TYPICAL AIR SPARGING ENHANCEMENT
TO SOIL VAPOR EXTRACTION SYSTEM
FIGURE
3-1
-------
Atmospheric
Air
Vent to
Atmosphere
Air
Filter
Soil Vapor
Extraction
Wei
SOURCE: MODIFIED FROM U.S. ARMY CORPS OF ENGINEERS 1995
HORIZONTAL AIR SPARGING AND SOIL
VAPOR EXTRACTION WELL SYSTEM
FIGURE
3-2
-------
Without Effluent Treatment
Analytical 27.2%
Residuals 12.9%
Site Preparation 28.3%
Demobilization 1.1%
Consumables &
Supplies 1.4%
Startup 3.6%
Permitting 2.5%
Labor 8.6%
Utilities 6.2%
Capital Equipment 8.2%
With Effluent Treatment
Effluent Treatment 42.7%
Site Preparation 16.2%
Consumables & Supplies 0.8%
Demobilization 0.6%
Startup 2.6%
Permitting 2.3%
Utilities 3.8%
Analytical 15.6%
Capital Equipment 3.1%
Labor 4.9%
Residuals 7.4%
SOURCE: MODIFIED FROM EPA 1995
3-YEAR REMEDIATION
COST BREAKDOWN
FIGURE
3-3
3-28
-------
In Situ Bioremediation ($21/lb Remediated)
Equipment
18%
Consumables
37%
Pump-and-Treat/Soil Vapor Extraction ($31/lb Remediated)
Equipment
12%
Consumables
34%
SOURCE: MODIFIED FROM DOE 1996
REMEDIATION COST BREAKDOWN FOR
IN SITU BOREMEDIATION AND PUMP-AND-
TREAT/SOIL VAPOR EXTRACTION
FIGURE
3-4
3-29
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TABLE 3-1
AIR SPARGING SYSTEM CHARACTERISTICS
Topic
Geological Applicability
Contaminant Applicability
System Components
Monitoring Parameters
Cleanup Capabilities
Costs
Description' ' ; f. ,'''. 'j ',^
Ideal site: homogeneous, high-permeability soils and
unconfined aquifers
Average site: moderately heterogeneous soils with
minimal low-permeability layers
Volatile organic compounds that are aerobically
biodegradable
None or thin layer of free-phase product
Vertical or horizontal extraction and injection wells or
sparging probes
Manifold, valves, and instrumentation
Air compressor or blower
Properly designed SVE system
Dissolved oxygen and contaminant concentrations in
groundwater
Oxygen, carbon dioxide, and contaminant concentrations
in SVE off-gas or soil vapor
Microbial populations and activity
Air flow and extraction rates
Air pressure measurements
Water levels
Tracer gas mapping of air flow in subsurface
Capable of achieving maximum contaminant levels for
volatile constituents in groundwater
Estimated cleanup time is 1 to 4 years8
$15 to $120 per cubic yard"
Notes:
a Range of estimated cleanup times is based on case studies. Actual cleanup time depends on many factors,
including site-specific contaminant, geologic conditions, and cleanup goals.
b The range of cost per cubic yard is based on case studies and vendor claims and estimates. The total actual
cost to remediate a site is highly dependent on site-specific contaminant and geologic conditions as well as
cleanup goals. The cost range includes capital, operation, and maintenance costs. Note that these costs are
based on estimates of in situ volumes.
SVE soil vapor extraction
3-30
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TABLE 3-2
FACTORS AFFECTING APPLICABILITY OF AIR SPARGING
factor
Contaminant
Geology
"I Paran*$:ei* \ '"
Volatility
Solubility
Biodegradability
Presence of free product
Soil type
Heterogeneity
Permeability in the saturated
zone
Hydraulic conductivity
Depth to groundwater
Aquifer type
Saturated thickness
, Desired Range or Coaditioiis
High (KH >1 x lO'5 atm-m3/mole)
Low (<20,000 mg/L)
High (BOD5 >0.01 mg/L)
None or thin layer
Coarse-grained soils
No impervious layers above sparge interval
Permeability increases towards grade if
layering present
>1 x 10"s cm2 if horizontahvertical is <2:1
>1 x 10'4 cm2 if horizontal:vertical is >3:1
>1 x lO'3 cm/sb
>5 feet
Unconfined
5 to 30 feet
Sources: Modified from Brown and others 1994, Loden 1992, Wisconsin Department of Natural Resources 1995
Notes:
a
b
c
d
From Loden 1992.
From Brown and others 1994.
From Wisconsin Department of Natural Resources 1995
One practitioner has used air sparging on sites with permeabilities as low as 1 x 10"12 cm2 (Tetra Tech EM
Inc. 1996f).
e One practitioner claims to have cleaned site with hydraulic conductivities as low as 1 x 10'6 cm/s
(EPA 1995).
f Although air sparging is most suited to shallow aquifers, it has been effective in aquifers 150 feet below
grade (Loden 1992).
cm centimeters
cm/s centimeters per second
BOD biological oxygen demand
KH Henry's Law coefficient
atm-m3 atmosphere-cubic meter
mg/L milligrams per liter
3-31
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TABLE 3-3
SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES
(Page 1 of 3)
Site
'sleta
Conservancy
3uddy Beene
Bernalillo
Los Chavez
Arenal
BF1
Bloomfield
Firehouse
Dry Cleaning Facility
Savannah River
Former Industrial
Facility
Citation
Ardito& Billings
1990
Billings 1990
Billings 1991
Billings 1990
Billings 1990
Billings 1990
Billings and
Associates, Inc.
1996b
Billings and
Associates, Inc.
1996c
Billings and
Associates, Inc.
1996a
Brown 1991
U.S. Department of
Energy 1996
Envirogen, Inc. 1996
Soil Type
Alluvial sands, silts, clays
Silty sand
Interfacing clay layer
Clay
Clay
MR
NR
NR
Coarse sand
Natural clay barrier
Sands, thin clay lenses
Sands
Contaminants
Leaded gasoline
Gasoline
Gasoline
Gasoline
Gasoline
Gasoline
Fuel
Fuel
Fuel
PCE, TCE, DCE,
TPH
TCE, PCE
Toluene
Cleanup
Time"
(months)
2
5
2
17
9
10
12
48
30
4
13
23
Initial Groundwater
Concentration (mg/L)
MW-1, -3, -5
BTEX: 4, 18, 25
Benzene: 3 to 6
Benzene: >30
Benzene: 22,000 to 32,000
NR
Benzene: 400 to 600
Total VOCs: 41
TCE: 10 to 1,031
PCE: 3 to 124
NR
final Groundwater
Concentration (mg/L)
MW-1, -3, -5
BTEX: 0.25,8,6
59% average benzene
reduction after 5 months
8.5% reduction/month
BTEX and MTBE: <5.5
40% benzene, xylenes
reduction, 60% toluene
reduction, 30% ethylbenzene
reduction
Benzene: <5
Benzene: 29 to 50
BTEX below cleanup
standards
Benzene: 0.5 to 4
Total VOCs: 0.897
TCE: <5
PCE: <5
NR
ts>
-------
TABLE 3-3
SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES
(Page 2 of 3)
, ' ฐ Site '
Electro-Voice
Berlin
Bielefeld, Nordrhein
-Westfalen
Munich, Bavaria
Nordrhein, Westfalen
Bergisches Land
Pluderhausen, Baden
- Wurtternburg
Mannheim -
Kaesfertal
Gasoline service
station
Savannah River
Gasoline service
station
Solvent spill
Solvent leak at
degreasing facility
Chemical
manufacturer
Citation v
EPA 1995
Harress 1989
Harress 1989
Harress 1989
Harress 1989
Harress 1989
Harress 1989
Herrling 1991
Kresge 1991
Looney 1991
Marley 1990
Middleton 1990
Middleton 1990
Middleton 1990
>f ! \ " ^ '
; . ,Sgjptyte
NR
Sand, silty lenses
Aquitard-clay
Fill, sand, silt
Aquitard-siltstone
Fill, gravel, sand
Aquitard-clayey silt
Clayey silt, sand
Aquitard-siltstone
Fractured limestone
Fill, silt, gravel
Aquitard-clay
Sand
Sand and silt
Sand, silt, and clay
Fine-coarse sand, gravel
Quaternary sand and
gravel
Fill, sandy and clayey silts
Sandy gravel
Aquitard-clay
2
PCE: 27; TCE: 4.3; TCA: 0.7
PCE: 2.2; TCE: 0.4; TCA:
0.15
Location A THH: 1.5 to 4.5
Location B THH: 10 to 12
THH: 80
1.20
Total BTEX: 6 to 24
TCE: 0.5 to 1.81
PCE: 0.085 to 0.184
Total BTEX: 21
Total VOCs: 33
0.200-12
THH: 1.9 to 5.417
?ฐ
. BSnal Gronndwater '
Concentration {rog/L) - \
NMb
c-l,2-DCE: >0.440
Total VOCs: 1.207
PCE: 0.539; TCE: 0.012;
TCA: 0.002
Location A THH: 0.010
Location B THH: 0.200
THH: 0.4
0.23
Total BTEX: 0.380 to 7.6
TCE: 0.010 to 1.031
PCE: 0.003 to 0.124
Total BTEX: <1
Total VOCs: 0.27
<0.010-0.023
THH: 0.185 to 0.320
-------
TABLE 3-3
SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES
(Page 3 of 3)
Site
Truck distribution
facility
Irvine
New Paris
Citation
MWR 1990
Terra Vac, Inc.
1995a
Terra Vac, Inc.
1995b
Soil Type
Sands
Clays, sandy silts, clayey
sands and silts, gravel
Sand with some gravel,
clay layers
Contaminants
Gasoline & diesel
fuel
Gasoline
PCE, TCE
Cleanup
Time*
(months)
Ongoing
9
18
Initial Groundwater
Concentration fmg/L)
Total BTEX: 30
NR
PCE: 250
Final Groundwater
Concentration (mg/L)
below cleanup standards
PCE: 9
OJ
Notes:
Cleanup times represent the time interval between initial and final groundwater concentration reported in the table. Actual remediation time may be longer.
Demonstration assessed remediation capabilities for vadose zone soils only.
BTEX Benzene, toluene, ethylbenzene, and xylenes
DCE Dichloroethene
EPA U.S. Environmental Protection Agency
MTBE Methyl tert-butyl ether
MW Monitoring well
NM Not measured
NR Not reported
PCE Tetrachloroethene
TCA Trichloroethane
TCE Trichloroethene
THH Total halogenated hydrocarbons
TPH Total petroleum hydrocarbons
VOC Volatile organic compounds
-------
TABLE 3-4
PERFORMANCE OF SUBSURFACE VOLATILIZATION VENTILATION SYSTEM
FOR REDUCTION IN TARGET CONSTITUENTS IN SOIL HORIZONS
IN THE VADOSE ZONE AT THE ELECTRO-VOICE, INC., DEMONSTRATION SITE
' ' ^ 1 ^
v-' " V-: <
" * ^
Treatmeitf Horizon1*
Upper horizon
Sludge layer
Lower horizon Al
Lower horizon A2
Lower horizon B
Critical VOCConeentration
^ * (Wgfo8)\..
it1*"" "" '
Pref reatment
Sampling }
321.77
1,661.03
96.42
37.68
13.57
< ป' ^ *
Posttreatment
Sampling
0.74
307.69
0.98
0.42
0.30
Perceiit'R^idttctiojtt
99.77
81.48
98.99
98.99
97.79
Source: Modified from U.S. Environmental Protection Agency 1995
Notes:
a Sum of benzene, toluene, ethylbenzene, xylenes, 1,1-dichloroethene, trichloroethene,
and tetrachloroethene
b The hot zone was delineated into horizons based on lithology and contaminant
levels.
VOC Volatile organic compound
mg/kg milligrams per kilogram
3-35
-------
TABLE 3-5
PERFORMANCE OF SUBSURFACE VOLATILIZATION VENTILATION SYSTEM
FOR REDUCTION IN INDIVIDUAL TARGET CONSTITUENTS IN THE VADOSE ZONE
AT ELECTRO-VOICE, INC., DEMONSTRATION SITE
Target Constituents
Benzene
Toluene
Ethylbenzene
Xylenes
1,1-Dichloroethene
Trichloroethene
Tetrachloroethene
Sum of the Weighted Mean
Concentration (rag/kg) ,
Pretreatment
Sampling
0.01
92.84
37.41
205.50
0.01
0.36
5.37
Posttreatraent
Sampling;
0.00
14.42
6.06
45.28
0.00
0.00
0.44
-* >f "v ,
Percent fteAttction
NC
84.47
83.81
77.97
NC
NC
91.81
Source: Modified from U.S. Environmental Protection Agency 1995
Notes:
mg/kg Milligrams per kilogram
NC Not calculated; a meaningful percent reduction cannot be provided because of
low pretreatment concentrations.
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TABLE 3-6
SUMMARY OF COST DATA FOR/JVS/TT/BIOREMEDIATION
AS WELL AS PUMP-AND-TREAT WITH SOIL VAPOR EXTRACTION
Costs; \ / " \ ^ " ;.< _s "
. ISB{$).
PT/SVE($)
Capital
Site Cost
Equipment Cost
Design and Engineering
Mobile Equipment
Well Installation
Other Fixed Equipment
Mobilization Cost
Total Capital Equipment and Mobilization Costs
Cost per Pound of Contaminant
5,400
9,200
10,000
18,000
183,000
183,732
43,075
452,407
21
7,500
32,000
10,000
18,000
50,690
168,665
64,613
341,468
31
Operation and Maintenance
Monitoring/Maintenance
Consumable Cost
Demobilization Costs
Total Operational and Maintenance Costs
71,175
122,215
43,075
$236,465
71,175
123,595
64,613
$259,383
Notes:
ISB
PT/SVE
In situ bioremediation (includes vacuum extraction; see Section 3.4.1)
Pump-and-treat system combined with soil vapor extraction
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TABLE 3-7
ESTIMATED COST FOR TREATMENT USING THE SUBSURFACE VOLATILIZATION
VENTILATION SYSTEM PROCESS OVER A 3-YEAR APPLICATION
Cost Category
1. Site Preparation
Well Drilling & Preparation
Building Enclosure (10' by 15')
Utility Connections
System Installation
Total Costs
2. Permitting & Regulatory Requirements
3. Capital Equipment (amortized over 10 years)
Vacuum Pump
Blower
Plumbing
Building Heater
Total Costs
4. Startup
5. Consumables
Health and Safety Gear
6. Labor
7. Utilities
Electricity (Blower and Pump)
Electricity (Heater)
Total Costs
8. Effluent Treatment and Disposal Costs
9. Residuals and Waste Shipping and Handling
Contaminated Drill Cuttings
Contaminated Personal Protective Equipment
Total Costs
10. Analytical Services
11. Maintenance and Modifications
12. Demobilization
TOTAL ANNUAL COSTS
TOTAL REMEDIATION COSTS
First Year.
$32,500
$10,000
$5,000
$15,000
$62,500
$10,000
$450
$450
$3,333
$333
$4,566
$7,957
$1,000
$6,300
$3,900
$660
$4,560
N/A
$12,500
$6,000
$18,500
$20,000
N/A
$135,383
Second Year "
$450
$450
$3,333
$333
$4,566
$1,000
$6,300
$3,900
$660
$4,560
N/A
$1,000
$1,000
$20,000
N/A
$37,426
fhii^Year:
$450
$450
$3,334
$334
$4,568
$1,000
$6,300
$3,900
$660
$4,560
N/A
$6,000
$3,000
$9,000
$20,000
N/A
$2,500
$47,928
$220,737
Source: Modified from Department of Energy 1996
Notes: N/A Not available
Not applicable
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TABLE 3-8
VENDORS OF AIR SPARGING TECHNOLOGIES0
vf -N^me of, V-oador1'* - 1'*
Billings and Associates, Inc.
Terra Vac, Inc.
Envirogen, Inc.
IT Corporation
Quaternary Investigations, Inc.
Horizontal Technologies, Inc.
Groundwater Control, Inc.
KVA Analytical Systems
H2Oil
, \A
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CHAPTER 4.0
DUAL-PHASE EXTRACTION
DPE technologies involve removal of contaminated groundwater and soil vapors from a common
extraction well under vacuum conditions. DPE provides a means to accelerate removal of nonaqueous
phase liquid (NAPL) and dissolved groundwater contamination, remediate capillary fringe and smear
zone soils, and facilitate removal of vadose zone soil contaminants. When applied to sites with soil,
groundwater, and free-phase product contamination, DPE is often referred to as multi-phase extraction
(MPE) or total fluids extraction.
The following sections provide a brief overview of the technology, discuss the applicability of DPE to
various contaminant types and site characteristics, describe engineering aspects of DPE, examine
performance and costs of typical DPE systems, provide a list of vendors that have designed and installed
full-scale systems, outline strengths and limitations of DPE technology, and provide recommendations
for using DPE. Cited figures and tables appear at the end of the chapter.
4.1 TECHNOLOGY OVERVIEW
DPE involves concurrent extraction of groundwater and soil vapors from a common borehole. DPE
enables venting of soil vapors through previously saturated and semisaturated (capillary fringe) soils by
lowering the groundwater table at the point of vapor extraction. High vacuums typically associated with
DPE systems enhance both soil vapor and groundwater recovery rates. Water extraction rate increases of
up to tenfold over conventional downhole pump systems have been reported.
Three basic types of DPE have been developed. Differentiation among the types is based on methods
used for extraction of each medium. Following is a brief description of each type:
Drop-tube entrainment extraction. Extraction of total fluids (liquid and soil vapors) via vacuum
applied to a tube inserted in the extraction well. Groundwater and soil vapors are removed from
the extraction well in a common pipe manifold, separated in a gas/liquid separator, and treated.
Well-screen entrainment extraction. Extraction of groundwater and soil vapors from a common
borehole screened in the saturated and vadose zones. Groundwater is aspirated into the vapor
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stream at the well screen, transported to the treatment system in a common pipe manifold,
separated in a gas/liquid separator, and treated.
Downhole-pump extraction. Extraction of groundwater using a downhole pump with concurrent
application of vacuum to the extraction well. Groundwater and soil vapors are removed in
separate pipe manifolds and treated.
Variations to each type of DPE have been developed to enhance overall system performance. Ultimately,
the type of DPE most suitable to any site is dictated by soil hydraulic and pneumatic properties,
contaminant characteristics and distribution, and site-specific remediation goals. Relative costs for the
different types are also largely determined by these factors.
4.2 APPLICABILITY
DPE is applicable to sites with the following characteristics:
VOC contamination
Soil, groundwater, and free-product contaminant phases
Low to moderate hydraulic conductivity soils
The following subsections address contaminant properties and phases as well as soil characteristics for
which DPE is most effective.
4.2.1
Contaminant Properties
DPE is most effective for remediation of volatile contaminants, such as those typically targeted by SVE
systems. Contaminant types commonly treated using DPE include chlorinated and nonchlorinated
solvents and degreasers and petroleum hydrocarbons.
Vapor pressure is a commonly used indicator of volatility. Compounds with vapor pressures exceeding
1 mm Hg are generally considered suitable for application of DPE. Another important indicator of
volatility is Henry's Law constant, which indicates the extent to which a compound will volatilize when
dissolved in water. Because much of the contamination in a soil matrix is dissolved in pore water, the
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Henry's Law constant is an indicator of how readily dissolved vadose zone contaminants will volatilize
by a vapor extraction system.
Less volatile petroleum hydrocarbons may also be treated by DPE. Introduction of oxygen into the
subsurface during the vapor extraction process stimulates aerobic biodegradation of nonchlorinated (and
some chlorinated) hydrocarbon compounds and can promote in situ remediation of soil contaminants that
would not typically be volatilized and removed by the extraction system. Biological processes have been
shown to play a significant role in remediation of petroleum hydrocarbons at sites employing DPE (Roth
and others 1995).
4.2.2
Contaminant Phases
DPE systems can be implemented to target all phases of contamination associated with a typical NAPL
spill site. These systems remove residual vadose zone soil contamination residing in soil gas, dissolved
in soil pore-space moisture, and adsorbed to soil particles. DPE also effectively removes dissolved and
free-phase (both light and dense NAPL [LNAPL and DNAPL]) contamination in groundwater.
Remediation capabilities of DPE in the vadose zone are similar to those of SVE. Because it uses in-well
groundwater extraction, however, higher vacuums can typically be applied at DPE sites without concerns
related to groundwater upwelling. As a result, DPE may also accelerate volatilization and removal of
vadose zone contaminants over traditional SVE.
DPE can be implemented for remediation of the capillary fringe and smear zone. VOC concentrations
are typically highest in capillary fringe soils because of the tendency of LNAPL to accumulate at the
water table. Changes in water level move any accumulation of free product on the surface of the water
table and create a smear zone of residual contamination. SVE systems are typically ineffective at
volatilizing contaminants in the capillary fringe and smear zone because of their high water content and
low effective air-filled porosity of these soils. In addition, water table upwelling at the point of
extraction in an SVE system can submerge residual contamination and prevent removal by the vapor
extraction system.
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Dewatering from the extraction well itself not only counters upwelling effects but results in a cone of
groundwater depression. A cone of depression allows soil vapor flow induced by the extraction well
vacuum to desiccate previously saturated and partially saturated soils in the capillary fringe and smear
zone. As a result of exposure to soil vapor flow, capillary fringe and smear zone contamination can be
volatilized and removed by the extraction system. DPE can also expedite removal of saturated soil
contaminants in the dewatered zone. VOCs with limited water solubility and high affinity for soil carbon
can be more effectively removed by exposure to soil venting and volatilization than by desorption and
recovery in a groundwater extraction system.
DPE can accelerate treatment of dissolved groundwater contamination and free-phase product.
Groundwater and free product recovery rates are enhanced by the additive effects of hydraulic and
pneumatic gradients generated by concurrent extraction of groundwater and soil vapors from the
extraction well. Thus, more rapid removal and treatment of contaminants is possible. Vacuum also tends
to counteract capillary forces holding LNAPL in soil pore spaces, enabling recovery of free-phase
product that would not otherwise be extractable (Baker and Bierschenk 1995).
4.23
Soil Characteristics
DPE is most effectively implemented in areas with saturated soils exhibiting moderate to low hydraulic
conductivity (silty sands, silts, and clayey silts). Lower permeability soils enable formation of deeper
water table cones of depression, exposing more saturated soils and residual contamination to extraction
system vapor flow.
DPE systems installed in soils with higher hydraulic conductivities generally require higher equipment
and operating costs for effective implementation due to higher water extraction rates and the resulting
treatment and disposal requirements. The more broad, shallow cones of depression formed in permeable
soils may not adequately expose capillary fringe soils to soil venting. Thus, soils remaining below the
water table may act as a continued source of groundwater contamination until the slower process of
desorption and removal by groundwater extraction is complete.
As with conventional groundwater extraction systems, depth of saturated soils to a confining medium
affects the ability of a DPE system to capture and remediate a groundwater plume.
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4.3
ENGINEERING DESCRIPTION
Implementation of DPE involves construction of extraction wells (or modification of existing monitoring
wells) and installation of extraction and treatment equipment. Figure 4-1 presents a schematic of a
typical DPE system. Generally, the technology required for design and construction of a DPE system is
well established and is largely based on experience gained from implementation of separate SVE and
groundwater extraction systems. Specific design factors related to the method of DPE employed
ultimately determine the physical as well as operating characteristics of the system and influence its
ability to achieve site-specific remediation goals. The following subsections discuss general DPE system
design and describe characteristics of the three types of DPE systems.
4.3.1
Dual-Phase Extraction System Design
DPE system design considerations include extraction well construction, anticipated vapor and water flow
rates, vapor/liquid separation requirements, and vapor and liquid treatment requirements. Site
characteristics, including soil pneumatic and hydraulic conductivities, contaminant vertical and
horizontal distributions, potential groundwater treatment and discharge requirements, and the presence of
existing monitoring or extraction facilities, largely determine which type of DPE will meet remedial
design objectives most effectively.
4.3.1.1
Pilot Testing
Well placement and extraction system capacity and design are usually based on the results of pilot
testing. Pilot test activities focus on both water and vapor extraction characteristics. Frequently, aquifer
hydraulic properties are determined by aquifer step testing followed by pump testing. A conventional
vapor extraction test may also be conducted to determine soil vapor flow characteristics and vadose zone
of influence. DPE pilot testing is then conducted to determine both step and steady-state characteristics
of the extraction system. Parameters that may be monitored during testing include the following:
Induced vacuum versus distance
Water drawdown versus distance
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Wellhead vacuum
Vapor extraction rates
Groundwater extraction rates
Vapor hydrocarbon content
Extracted groundwater quality
Following the pilot test, additional monitoring may be conducted to assess the rate at which system
characteristics return to equilibrium.
Analysis of vapor extraction data obtained during pilot testing is similar to that for SVE pilot testing.
Parameters related to groundwater extraction, such as extraction flow rate and water table drawdown, are
also analyzed. Groundwater modeling data may be used to determine required well spacing. To address
varying soil characteristics across a site, full-scale systems may be designed, built, and operated in a
phased approach to capitalize on operating data obtained from wells installed during earlier phases (Tetra
Tech 1996a).
Smaller full-scale systems may be designed using available physical and theoretical data to avoid
incurring costs associated with pilot testing. Typically, when a pilot test is not conducted, both well
spacing and extraction equipment are conservatively sized to ensure that the system will perform at
expectations or better.
43.1.2
Extraction Well Design
Generally, DPE wells are designed with screened intervals above and below the groundwater table at the
location of greatest contamination. Selected screen depths must consider the hydrogeology and extent of
dewatering required. The lower portion of the extraction well screen and filter pack are generally sized
using guidelines for groundwater extraction (WDNR 1993) to prevent entrainment of fines into the
extraction system. Well diameter is based on site-specific design factors similar to those for SVE and on
requirements of the type of DPE employed; the diameter must be large enough to accommodate any
downhole apparatus associated with extraction system requirements. Existing monitoring wells with
sufficient diameter and adequate design characteristics (appropriately-sized screen slots) can be
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converted for use as extraction wells. Downhple pump systems generally require larger diameter wells
than either well-screen or drop-tube entrainment systems.
Full-scale DPE systems have been installed to approximately 100 feet below ground surface (bgs).
Specific limits on well installation depth have not been reported.
Extraction well spacing is determined by results of pilot testing and by remedial objectives. For sites
with dissolved-phase contamination, well spacing is largely based on the groundwater capture radius, or
the distance from a well where drawdown is sufficient to overcome the regional water table gradient
(Hackenberg and others 1993). Extraction well spacing must provide for adequate dewatering of the
contaminated area. Well spacing in areas with free product is generally based on the product capture
zone of influence (Tetra Tech 1996b) or the distance from the well where the slope of the free water
surface approaches zero. (LNAPL will theoretically not flow toward the well beyond this distance
[Hackenberg and others 1993].) For highly contaminated vadose zone source areas, well spacing may be
based on an SVE design zone of influence. The SVE design zone of influence is generally more
conservative than the actual zone of influence obtained during pilot testing and is selected to achieve
accelerated remediation of vadose zone soils.
High vacuums associated with DPE systems may promote short circuiting of air flow at the wellhead
from ground surface, particularly in shallow formations. This problem can be circumvented by use of a
surface seal. Surface seals are typically constructed by placing an impermeable liner over the extraction
area.
4.3.1.3
Extraction Equipment Design
Typical components of the extraction system include an extraction blower, vapor/liquid separator, vapor
phase treatment, and liquid phase treatment. Design of extraction system equipment is generally based
on desired extraction vacuum, anticipated vapor and groundwater extraction rates, and anticipated vapor
and groundwater concentrations and compositions.
The vapor extraction rate from each extraction well is dictated by local soil pneumatic characteristics,
well design and screen length, and applied system vacuum. Overall vapor extraction system capacity is
4-7
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frequently determined by multiplying the vapor extraction rate for a single well (as determined through
pilot testing or software modeling) by the total number of wells to be installed.
The groundwater extraction rate is affected by water drawdown within the well itself and soil hydraulic
characteristics as well as the applied system vacuum. Lowering the water table at the well creates a
hydraulic gradient, which induces groundwater (and free product, if any) flow into the well. Vacuum
applied at the point of water extraction introduces an additional pneumatic gradient, which can enhance
the overall rate of groundwater and free product recovery.
The system groundwater treatment capacity is generally determined by multiplying the groundwater
extraction rate for a single well by the total number of wells to be installed. Data from additional aquifer
testing or existing operating extraction wells within the treatment system area may also be incorporated
into assessment of system groundwater treatment capacity requirements.
The free water surface in the vicinity of a DPE well is a combination of the cone of depression resulting
from groundwater extraction and the upwelling caused by vacuum extraction. The shape of the free
water surface is critical at sites requiring remediation of capillary fringe soils. Vapor and groundwater
extraction rates must be balanced to ensure that the free water surface elevation at any distance from the
well does not rise above static water levels as a result of excessive vapor extraction system influence
(Hackenberg and others 1993).
Vacuum requirements largely dictate the type of vacuum blower or pump incorporated into the extraction
system. Applied DPE vacuums can range up to 28 inches of mercury (approximately 32 feet of water).
Types of vacuum pumps commonly used at DPE sites include liquid ring pumps, rotary lobe
compressors, and regenerative blowers. Vacuum pumps are selected based on desired operating
characteristics (inlet flow rate and achievable vacuum) and desired efficiency. Lower vacuums tend to
be associated with downhole pump type systems, which are more common at sites with higher yielding
aquifers. High vacuums are more common at sites using well-screen entrainment and drop tube
entrainment.
Vapor/liquid separation is generally accomplished upstream of the vacuum blower or pump but can be
accomplished downstream of a liquid ring vacuum pump, which can use extracted water as seal fluid if
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generated in sufficient quantities. Use of extracted water for seal fluid generally requires close
monitoring to prevent overheating and failure of the vacuum pump. Placement of the air/water separator
upstream of the vacuum pump prevents carryover of silts or sediments into the pump. For sites with
floating product, an oil/water separator may also be required.
Vapor and liquid treatment processes are designed to conform with air emission and water discharge
requirements. Common vapor treatment technologies used at DPE sites include carbon adsorption and
thermal or catalytic oxidation. Water is often treated using air stripping and/or liquid granular activated
carbon (GAC) adsorption, as required.
Extraction system materials of construction are determined based on contaminant types and
concentrations and on economic factors. Commonly used materials of construction include stainless
steel, PVC, and HOPE.
4.3.1.4
System Monitoring
Parameters monitored during full-scale DPE system operation typically include vapor, groundwater, and
product recovery rates; system and wellhead vacuums; extracted vapor and groundwater contaminant
concentrations; and other parameters required of the vapor and water treatment systems. At sites with
aerobically biodegradable hydrocarbons, extracted vapors may also be monitored for parameters related
to in situ bioactivity, such as methane, carbon dioxide and oxygen. In situ respiration tests may also be
conducted to assess the extent of bioremediation occurring.
4.3.2
Dual-Phase Extraction System Characteristics
This subsection discusses design and operating features of each type of DPE and the unique benefits and
drawbacks of each type of system.
4.3.2.1
Drop-Tube Entrainment Extraction
Drop-tube entrainment DPE systems are constructed by inserting a suction tube into the sealed wellhead
of an extraction well. As vacuum is applied to the suction tube, soil vapor entering from the unsaturated
4-9
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soils entrains groundwater at the tube tip. Soil vapor and entrained groundwater are transported in a
common extraction manifold piping system to an air/water separator, from which vapors are routed to a
treatment system. Groundwater drawn off the separator is treated (if necessary) before discharge. A
schematic of a drop-tube entrainment extraction well is presented in Figure 4-2.
During startup of an extraction system incorporating drop tubes, it may be necessary to prime the
extraction well with air to induce vapor flow through the drop tube if well depth exceeds the applied
vacuum (expressed in feet of water). Priming involves the introduction with air into the bottom of the
drop tube when it is below the water level in the well to create an air-lifting effect. Self-priming
drop-tube designs have been developed to enable automatic priming of the system upon startup. One
patented drop-tube design incorporates single or multiple perforations, which enable vapor flow to
reduce fluid column density in the well, thus allowing air lift of water from depths greater than the
applied vacuum (expressed in feet of water) (Tetra Tech 1996b). Another method involves insertion of
an air-bleed tube exposed to atmospheric or compressed air inside the drop tube (Hackenberg and
others 1993). Manual priming can be conducted by slowly lowering the drop tube into the extraction
well, entraining water at the water level interface until the well is dewatered to design-tube extraction
depth.
As the extraction area is dewatered during operation of a drop-tube type system, increases in saturated
zone thickness and soil vapor flow are accompanied by a decrease in manifold vacuum at the
vapor/liquid separator. As a result, unbalanced conditions may occur in which vacuum at some
extraction wells drops below that required to entrain water. Water column buildup in these wells may cut
off vapor flow and result in short circuiting. Rebalancing of system vacuums may be necessary to restore
vapor flow to all extraction wells.
Liquid and vapor removal in drop-tube type systems is limited by pressure loss through the drop tube.
Wellhead vacuum may be reduced by as much as 30 to 50 percent through the suction tube (Brown and
others 1994). The ability of a drop-tube system to air lift groundwater from a given depth is a function of
applied wellhead vacuum in the annulus between the drop tube and well screen, the air and groundwater
flow rates, and the inner diameter of the drop tube (Stenning and Martin 1968).
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Drop-tube type systems are generally inefficient for high flow rate groundwater removal and are more
effective in soils with low hydraulic conductivity and low groundwater yield. Generally, extraction well
yields of 5 gallons per minute (gpm) or less are considered suitable for entrainment extraction. Within a
range of approximately 5 to 20 gpm, use of entrainment extraction may be appropriate based on
site-specific factors and design goals. At higher water extraction rates, vacuum pump energy
requirements increase, and downhole-pump systems may be more appropriate.
During the extraction process, contaminant mass transfer occurs from the liquid to the vapor phase
because high system vacuum, high vapor/liquid ratio, and turbulence in the suction tube and extraction
piping manifold. This "stripping" action results in reduced extracted groundwater contaminant
concentrations and enables more efficient vapor-phase treatment of the contaminants. Groundwater
treatment requirements may be reduced or potentially eliminated. Reported stripping efficiencies of
approximately 90 percent are common.
Use of a drop-tube type system minimizes DPE equipment as well as instrumentation and controls
requirements. A common blower extracts water and vapors; thus, no downhole pump is necessary for
groundwater removal. Only one piping manifold is required to transport the extracted media to the
treatment system. Existing monitoring wells can be converted to drop-tube type wells.
Removal of free product using a drop-tube entrainment extraction system may be complicated by poor
water quality or high hardness content. Emulsification of free product and water can occur in the
air/water separator discharge pump or in the vacuum pump if they are situated upstream of the
vapor/liquid separator (Tetra Tech 1996b). Hard water can also cause scaling in extraction system piping
and equipment.
Several patents apply to various aspects of drop-tube type entrainment extraction, some of which may
have overlapping features. Patent holders include Xerox Corporation, International Technologies
Corporation, and James Malot of Terra Vac Incorporated.
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4.3.2.2
Well-Screen Entrainment
In well-screen entrainment DPE systems, vacuum is applied to a well screened in the vadose and
saturated zones. Vapor flow aspirates groundwater at the well screen for entrainment of groundwater.
Generally, small diameter wells (2 inch or less) are most effective for this type of DPE (Brown and
others 1994), although 4-inch well screens can be used (Tetra Tech 1996c).
For systems in which well depth exceeds applied vacuum (expressed in feet of water), priming may be
necessary to induce vapor flow on startup. Priming is achieved by inserting a tube into the extraction
well below the water surface to introduce air flow into the well. Reduced fluid column density resulting
from introduction of air enables two-phase flow from the well. Groundwater and soil vapors are
extracted in the annular space between the primer tube and well casing. After the well is primed, vapor
flow from the formation provides the air lift necessary to entrain water in the extracted stream. Low
permeability soils may require continued use of a primer to maintain two-phase flow. System hydraulics
may facilitate the use of ambient air for priming or may dictate the use of an air compressor to initiate air
flow.
Injection of air into the well enhances formation of liquid droplets, which become entrained in the
extracted soil vapor. Priming may also be used to enhance mass transfer of DNAPLs by injecting air
near the confining layer (EPA 1994). Well-screen entrainment systems benefit from the stripping action
of high-extraction vacuum and turbulence in the extraction well and manifold piping. Similar to
drop-tube type extraction, water contaminant reductions of approximately 90 percent have been reported.
This type of DPE is the simplest to implement; however, it may have limited effectiveness for water
removal from deep wells. Extraction-well entrainment is most effective at sites with shallow
groundwater (less than 10 feet bgs) (Brown and others 1994), but it has been used to depths of
approximately 27 feet (Tetra Tech 1996c).
Advantages of extraction-well entrainment include simplicity of design and construction. Because a
common blower removes both soil vapor and groundwater, downhole pumps and associated controls and
instrumentation are not necessary. Systems that do not incorporate continuous priming require only one
4-12
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piping manifold (for extraction). Systems incorporating priming, however, do require installation of an
additional piping manifold as well as use of a compressor for air injection.
Clogging of the well screen can decrease extraction effectiveness (Brown and others 1994). Entrainment
of silts and solids may occur in wells that are screened too coarsely or do not have properly sized or
graded gravel pack. Systems incorporating existing monitoring wells often require regular maintenance
to remove accumulated fines from collection points, primarily the air/water separator.
Patents apply to various aspects of well screen entrainment extraction. Patent holders include Xerox
Corporation and Dames & Moore Incorporated.
4.3.2.3
Downhole-Pump Extraction
DPE systems incorporating downhole pumps are constructed by lowering a submersible pump into each
extraction well and applying vacuum to the sealed wells. Dual-pipe manifolds are constructed for vapor
and water removal. A schematic of a downhole-pump extraction well is presented in Figure 4-3.
Operation of the downhole pump is usually based on extraction well water level. Single speed pumps are
used to maintain water levels between high and low targets. Variable-speed drive pumps can be set to
match groundwater yield and maintain constant water level in the well or can be set to match treatment
system capacity. Capital costs for variable-speed drive pumps and associated controls/instrumentation
are higher than for single-speed pumps.
Use of downhole pumps is more efficient than entrainment extraction for removal of groundwater
(Brown and others 1994). Generally, downhole-pump systems are installed in soils with higher hydraulic
conductivities or wells yielding greater than 15 to 20 gpm. For moderate well yields of approximately 5
to 15 gpm, other factors, including design and remedial action objectives and water discharge limitations,
may determine whether a downhole-pump system or one of the types of entrainment extraction is used.
Downhole-pump extraction may be more effective than entrainment extraction for systems requiring deep
well installation.
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Downhole-pump systems do not benefit from the stripping action associated with entrainment extraction
systems. Groundwater treatment requirements are therefore similar to those expected from conventional
pump and treat systems.
4.4 PERFORMANCE AND COST ANALYSIS
The following subsections discuss the performance and cost of five example DPE systems.
4.4.1
Performance
DPE has been implemented at a variety of sites contaminated with gasoline-range petroleum
hydrocarbons and VOCs. The following case studies describe the design and performance of five
full-scale DPE systems. Three of the case studies involve drop-tube entrainment type systems, one
involves well-screen entrainment, and one involves downhole-pump extraction.
4.4.1.1
Underground Storage Tank Release from a Gasoline Station in Houston, Texas
Vacuum enhanced pumping (VEP), a form of drop-tube entrainment extraction, was implemented for
remediation of a groundwater contaminant plume at a gasoline station (Mastroianni and others 1994).
The VEP system design incorporated a self-priming drop tube in each extraction well and included nine
extraction wells, a vacuum blower, a vapor/liquid separator, and an oil separation and water treatment
system. Vapor treatment was accomplished using a thermal oxidation system equipped with auto
dilution. The vacuum blower was operated at approximately 300 scfm at 12 inches of mercury.
Site soils were overlain by asphalt as well as concrete and consisted of clay to a depth of approximately
16 feet, becoming silty below 13 feet and interbedded silts and sands between 16 and 25 feet. Silty clay
extended between 25 and at least 27 feet below grade. Contamination of concern consisted of a
groundwater benzene, toluene, ethylbenzene, and xylene (BTEX) plume and an associated free-product
plume. The aerial extent of the groundwater plume was approximately 50,000 square feet. BTEX
concentrations in a majority of the plume exceeded 30 milligrams per liter (mg/L). The maximum free
product thickness was approximately 3 feet.
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The system used both new and existing monitoring wells for extraction. The wells were installed to depths
of approximately 30 feet with spacings generally between 30 and 50 feet. Initially, recovery and treatment
operations for soil vapor, LNAPL, and groundwater were conducted from one extraction well to avoid
overloading treatment capacity of the thermal oxidizer used for vapor treatment. As the hydrocarbon
content of the process stream from the initial extraction well decreased, additional extraction wells were
brought on line. All wells were brought on line within the first 500 hours of system operation.
After 7,000 hours (approximately 290 days) of operation, two small BTEX plumes with concentrations
below 2 and 5 mg/L remained. Free product had been completely removed. Cumulative contaminant mass
removed from the site was approximately 36,000 pounds (approximately 5,400 gallons). Approximately
1.62 million gallons of groundwater were removed and treated. Following system shutdown, monitoring
was conducted at the site until its closure in 1996.
Remediation goals of the system were 50 mg/L TPH, 1 mg/L total BTEX, and 0.5 mg/L benzene.
4.4.1.2 Underground Storage Tank Release from a Former Car Rental Lot in Los Angeles,
California
A drop-tube entrainmont system was installed to remediate hydrocarbon contamination resulting from
leaking underground storage tanks (UST) at a former car rental lot (Trowbridge and Ott 1991). The
extraction well network initially consisted of 29 extraction wells incorporating drop tubes, but was later
expanded twice to a total of 46 wells to address migration of the contaminant plume. The treatment system
consisted of a vapor/liquid separator, vacuum blowers, and catalytic oxidation for vapor treatment. The
vacuum blowers were capable of a combined flow of 1,000 scfm at an inlet vacuum of 15 inches of
mercury. Water from the separator was treated using liquid-phase GAC. Photographs 4-1, 4-2, and 4-3
(provided courtesy of Terra Vac Incorporated) show an extraction wellhead and the extraction treatment
system for this site.
Site soils consisted of brown silty clay to approximately 50 feet bgs. A perched groundwater table was
present at depths of approximately 25 to 30 feet bgs. Gasoline-range hydrocarbon contamination at the
site ranged in depth from 10 to 35 feet below the surface and covered an area of approximately 280 feet
4-15
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by 450 feet. The highest contaminant concentration detected was 1,400 mg/kg, with an average
concentration of 100 mg/kg. Monitoring wells at the site contained up to 3 feet of floating product.
Extraction wells were typically screened from approximately 20 to 35 feet bgs, although some screens
extended up to 10 feet bgs, and others extended down to 50 feet bgs. Well spacing was approximately
40 feet, with closer spacings used in areas with higher contaminant concentrations. An average of
20 scfm was obtained from each well at a wellhead vacuum of 10 inches of mercury. After 10 weeks of
operation, measured groundwater levels were an average of 5 feet lower than before operations began.
During the 28 weeks of system operation, more than 17,000 pounds of contaminant was removed
(2,600 gallons of gasoline equivalent), and 89,000 gallons of groundwater had been extracted and treated.
Seventy-five percent of soil samples collected contained nondetectable levels of benzene, and detections
in the remaining samples were approximately 0.17 mg/kg. Confirmatory groundwater samples collected
from three wells contained nondetectable levels of BTEX and total volatile hydrocarbons. Site closure
was obtained in 1991.
4.4.1.3
Release From An Electronics Manufacturing Facility In Texas
A drop-tube entrainment system was installed to remediate VOC contamination at the site of a closed
surface impoundment at an electronics facility (GSI1997). The extraction well network consists of
14 wells incorporating drop tubes. The wells were installed to 25 feet below ground surface and are
spaced approximately 20 feet apart. The extraction system includes an air-cooled rotary lobe blower, a
liquid/vapor separator, a centrifugal silt removal unit, a groundwater transfer pump, a scale inhibitor
addition system, and piping and accessories necessary to form a connection to existing treatment plant
facilities. The system vacuum blower was operated at approximately 20 scfm at 20 inches of mercury.
Soils at the site consist of four principle strata. The uppermost unit is a sandy, silty clay with an
approximate thickness of 10 to 15 feet (Unit I). Underlying the uppermost unit is a 5 to 8 foot thick layer
of silty, clayey, fine sand (Unit IT), followed by a 10 to 12 foot layer of sandy, silty, stiff, laminated clay
(Unit ID). Beneath the upper three layers is a fossiliferous, silty shale. Groundwater in the vicinity of
the site occurs within the silty layer (Unit II). At most well locations, the static water level is at a depth
of approximately 10 feet below grade. The hydraulic conductivity of the saturated silty sand unit
4-16
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averages approximately 6.1 x 10'5 cm/sec. At the start of system operation, the affected groundwater
plume ranged in depth from 15 to 22 feet and extended over an approximate area of 205,000 square feet.
The plume contained a maximum concentration of 225 mg/L of chlorinated solvents. Contaminants of
concern included phenol (5.83 mg/L), 1,2-dichloroethane (118 mg/L), methylene chloride (88 mg/L),
trichloroethylene (8.44 mg/L), and BTEX (0.074 mg/L benzene, 0.305 mg/L toluene, 0.018 mg/L
ethylbenzene, and 2.95 mg/L xylene, respectively).
Operation of the system is ongoing; performance information is not available at this time. Remediation
goals include <0.001 mg/L (phenol), 0.003 mg/L (1,2-dichloroethane), <0.005 mg/L (methylene chloride,
toluene, ethyl benzene, and xylene), and 0.005 mg/L (trichloroethylene and benzene).
4.4.1.4
Underground Storage Tank Release from a Gasoline Station in Indiana
Two-phase vacuum extraction, a form of well-screen entrainment extraction, was implemented to
remediate contamination resulting from UST leakage at a gasoline station (Lindhult and others 1995). A
soil VOC plume was detected during an environmental audit at a nearby shopping mall. Subsequent
investigations revealed that two groundwater plumes were associated with the soil contamination and that
one of the plumes had migrated off site from the gasoline station.
The extraction system included a vapor/liquid separator, a vacuum blower, and vapor and water
treatment. Five extraction wells were initially installed at depths of approximately 25 feet, and two wells
were installed subsequently to address additional areas of contamination. The extraction wells were
screened in the vadose and saturated zones. Vacuum of approximately 23 inches of mercury was applied
directly to the wells for removal of vapor and groundwater.
Site soils consisted of fairly uniform clays. Results of a soil gas survey indicated that a significant
portion of site soils contained VOCs at concentrations exceeding 1,000 mg/kg, and two areas contained
concentrations exceeding 10,000 mg/kg. Two groundwater BTEX plumes were associated with the soil
contamination: one with maximum BTEX concentrations exceeding 1,000 (j.gfL and one with maximum
BTEX concentrations exceeding 16,000 ^g/L. A thin layer of free product was found in one monitoring
well.
4-17
-------
After several weeks of operation, the thin layer of free product in the monitoring well disappeared.
During the initial 142 days of operation, BTEX removal efficiencies in the recovery wells ranged from
93 to greater than 99 percent. After 407 days of operation, total BTEX concentrations in all recovery
wells decreased by greater than 97 percent, except for one, which was at 88 percent. Periodic increases
in concentrations in the monitoring well were attributed to potential capture of pockets of groundwater
that had migrated past the recovery wells. At the time of reporting, the system had reduced BTEX
concentrations to below the alternate cleanup criteria of 250 //g/L benzene and 1,000 yUg/L total BTEX
for on site wells, and 150 and 500 ,ug/L for benzene and total BTEX, respectively, for off-site wells.
Approximately 2,500 pounds of contaminant (334 gallons as gasoline) and 1,051,700 gallons of
groundwater were removed and treated.
Water discharged from the system vapor/liquid separator contained total BTEX concentrations ranging
from 7 to 1,300 jug/L. Discharge criteria to a publicly owned treatment works was 3,000 (j.gfL.
4.4.1.5 Release from a Gasoline Underground Storage Tank for a Vehicle Fueling Station
at a Hospital in Madison, Wisconsin
A downhole-pump extraction system was implemented for remediation of gasoline contamination
resulting from leaking USTs at a hospital (Miller and Gan 1995). The system consisted of one 6-inch
diameter vertical extraction well screened from 5 to 30 feet bgs with a 3-foot sump at the bottom to trap
sediment. Vapors were extracted from the well using a blower operated at 30 cfm at a vacuum of
40 inches of water column. Contaminated groundwater was recovered using a submersible centrifugal
pump with a design flow rate of 10 gallons per minute (gpm) and treated by an air stripper before
discharge to an on-site storm sewer.
Site soils consisted of sandy fill from ground surface to 10 to 19 feet bgs. The fill was underlain by a 3-
to 4-foot layer of organic silt and peat. Depth to groundwater was approximately 13 to 20 feet.
The system began operation in June 1994. Approximately 8,500,000 gallons of groundwater and
120 pounds of contaminant were removed during the first 1.5 years of operation. Groundwater benzene
concentrations dropped from 276 pgfL to 8 ,ug/L after 6 months of operation and to 2 ptg/L after 1.5 years
of operation.
4-18
-------
The system was shut down in January 1996. Benzene concentrations at the extraction well were found to
fluctuate around the cleanup standard of 5 Mg/L and had risen to 8 /wg/L approximately 6 months after
shutdown. The concentration increase was attributed to the presence of residual contamination in the
capillary fringe. In spite of a 10 gpm pumping rate from the well, drawdown 5 feet from the recovery
well was less than 1 foot. Future plans for the site include increasing the groundwater extraction rate to
20 gpm to enhance dewatering of the capillary fringe.
4.4.2
Cost Analysis
Costs for implementing a DPE system are highly variable and depend on site-specific factors including
site soil characteristics, nature and extent of the contaminant plume, and vapor and liquid treatment and
discharge requirements.
Table 4-1 presents cost data available for these four case studies. Figure 4-4 relates the cost per pound of
contaminant removed and cost per gallon of groundwater removed/treated for Case Study 1.
4.5 VENDORS
DPE systems are often similar to SVE systems in construction and operation, and do not generally
employ uniquely developed and manufactured equipment items (beyond patented items such as self-
priming drop tubes). Further, consultants without patents related to DPE can design, install, and operate
DPE systems contingent upon payment of applicable licensing fees or royalties. Therefore, in addition to
patent holders, DPE vendors include companies with experience in design, installation, and operation of
DPE systems. Table 4-2 presents a list of such vendors, including identified patent holders who were
contacted during preparation of this report.
4.6 STRENGTHS AND LIMITATIONS
The following list outlines the primary strengths of DPE for remediation of sites contaminated with
VOCs:
Increases water extraction rates in low permeability settings
4-19
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Increases the vapor extraction zone of influence
Addresses smear zone and saturated soil contamination
Enhances removal of free-phase and residual NAPL
Potentially reduces ex situ groundwater treatment by in-well stripping in entrainment extraction
wells
Potentially eliminates the need for downhole pumps and associated controls and instrumentation
through the use of entrainment extraction
The following list outlines the primary limitations of DPE for remediation of sites contaminated with
VOCs:
Less cost-effective for permeable soil types
Operating costs may be high depending upon blower horsepower requirements and groundwater
treatment requirements
Short-circuiting of airflow from the surface may limit effectiveness
4.7 RECOMMENDATIONS
DPE capitalizes on synergistic effects produced by simultaneous lowering of the groundwater table and
increasing extraction well vacuum. Use of DPE for remediation of contaminated sites is most
advantageous for sites contaminated with volatile compounds and with moderate to low hydraulic
conductivity soils. The presence of existing monitoring wells in strategic locations may provide an
opportunity for minimizing system capital costs through conversion of the wells for extraction. DPE can
be a cost effective method of rapidly remediating both soil and groundwater contaminated with VOCs.
This technology provides for the remediation of the vadose zone, capillary fringe, smear zone, and
existing water table by extracting both water and air through the same borehole.
Before a DPE system is implemented, efforts should be undertaken to assess groundwater and soil
characteristics and project objectives to determine which type of DPE is appropriate for the site. Any
patents that may apply to the technology should be thoroughly researched, and, if necessary, the
appropriate licensing and fees should be assessed and included in the project cost estimate.
4-20
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4.8 REFERENCES
This section includes a list of references cited in Chapter 4. A comprehensive bibliography is provided
in Appendix B.
Baker, Ralph S., and J. Bierschenk. 1995. Vacuum-Enhanced Recovery of Water and NAPL: Concept
and Field Test. Journal of Soil Contamination. 4(l):57-76.
Brown, Richard A, R.J. Falotico, and D.M. Peterson. 1994. Dual Phase Vacuum Extraction Systems for
Groundwater Treatment: Design and Utilization. Superfund XV Conference and Exhibition
Proceedings.
Groundwater Service, Inc. (GSI). 1997. Summary of Representative Project Experience. May.
Hackenberg, T.N., JJ. Mastroianni, C.E. Blanchard, J.G. Morse. 1993. Analysis Methods and Design of
Vacuum Enhanced Pumping Systems to Optimize Accelerated Site Cleanup.
Kruseman, G.P., and N.A. de Ridder. 1991. Analysis and Evaluation of Pumping Test Data. ILRI,
Wageningen, The Netherlands. 1991. Second Edition.
Lindhult, Eric C., J.M. Tarsavage, and K.A. Foukaris. 1995. Remediation in Clay using Two-Phase
Vacuum Extraction. National Conference on Innovative Technologies for site Remediation and
Hazardous Waste Management Proceedings.
Mastroianni, J., C. Blanchard, T. Hackenberg, and J. Morse. 1994. Equipment Design Considerations
and Case Histories for Accelerated Clean-up Using Vacuum Enhanced Pumping.
Miller, Anthony W., and D. R. Gan. 1995. Soil and Groundwater Remediation Using Dual-Phase
Extraction Technology. Superfund 16 Conference and Exhibition Proceedings.
Tetra Tech EM Inc. (TetraTech). 1996a. Personal Communication Between Ronna Ungs of Tetra Tech
and James Malot of Terra Vac Corporation. August 14.
Tetra Tech. 1996b. Personal Communication Between Ronna Ungs of Tetra Tech and John Mastroianni
of IT Corporation. August 27.
Tetra Tech. 1996c. Personal Communication Between Ronna Ungs of Tetra Tech and Dan Guest of
Smith Environmental Technologies Corporation. August 30.
Roth, Robert, P. Bianco, M. Rizzo, N. Pressly, and B. Frumer. 1995. Phase I Remediation of Jet Fuel
Contaminated Soil and Groundwater at JFK International Airport Using Dual-Phase Extraction and
Bioventing. Superfund 16 Conference and Exhibition Proceedings.
Stenning, A.H., and C.B. Martin. 1968. An Analytical and Experimental Study of Air-Lift Pump
Performance. Transactions of the ASME Journal of Engineering for Power. April. Pages 106-110.
4-21
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Trowbridge, Bretton R, and D.E. Ott. 1991. The Use of In-Situ Dual Extraction for Remediation of Soil
and Groundwater. National Groundwater Association and National Water Well Association.
U.S. Environmental Protection Agency (EPA). 1994. Vendor Information System for Innovative
Treatment Technologies (VISITT), Version 4.0. Database Prepared by Office of Solid Waste and
Emergency Response, Technology Innovation Office. Cincinnati, Ohio.
Wisconsin Department of Natural Resources. 1993. Guidance for Design, Installation, and Operation of
Soil Venting Systems. PUBL-SW185-93. July.
4-22
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to
U)
Discharge
Extracted Vapor
and Groundwater
From Other
DualPhase
Extraction Wells
DualPhase Extraction Well
(Well Screen Entrainment Type)
iOURCE: MODIFIED FROM McCOY AND ASSOCIATES, INC 1992
SCHEMATIC OF A DUAL-PHASE
EXTRACTION SYSTEM
FIGURE
4-1
-------
Residual VOC
Contamination >
SOURCE; MODIFIED FROM KOERNER AND LONG 1994
Extracted Soil Vapor
and Groundwater to
Extraction Pump and
Air/Water Separator
Screen
Soil Vapor and
Entrained
Groundwater
DROP-TUBE ENTRAINMENT
EXTRACTION WELL
FIGURE
4-2
4-24
-------
Extracted Groundwater
to Groundwater
Treatment
V
Soil Vapor-
Extracted Soil
Vapor to Vapor
Treatment
Screen
Residual VOC
Contamination
Pump
SOURCE: MODIFIED FROM KOERNER AND LONG 1994
DOWNHOLE-PUMP
EXTRACTION WELL
FIGURE
4-3
4-25
-------
$18.00 -1
- 40,000
os
C
o
Q_
i_
01
a
CO
o
O
a>
en
D
$8.00
r1 0,000
- 5,000
CO
D
C
o
a
o
o
0)
to
CO
o
I
U-*
_D
D
E
|
o
"I 1 1 1 1 1 1 1 1 T
500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000
Legend
A Cost per Pound
Mass Removed
Hours of System Operation
EXTRACTION SYSTEM PERFORMANCE
FIGURE
4-4
-------
TABLE 4-1
COST DATA FOR DUAL-PHASE EXTRACTION TECHNOLOGIES
Case -
Study
1
2
3
4
5
^ *" ^
, VeMor/Censultant
IT Corporation
Terra Vac
Groundwater Services,
Inc.
Dames & Moore
Eder Associates, Inc.
Total Cost
($) '
380,000
600,000
331,600
v
Capital
Cost ($>:
60,000
58,000
C&stpfcrpotirid;
of contaminant *
,reraซved ($)
10
40
130
Cost pet gallon of
groupdwater (f )
0.23
7.00
0.31
Note:
Information is not available
4-27
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TABLE 4-2
VENDORS OF DUAL-PHASE EXTRACTION TECHNOLOGIES
Name of Vendor
Dames & Moore
Eder Associates, Inc.
First Environment, Inc.
Fluor Daniels GTI, Inc.
Groundwater Services, Inc.
International Technologies
Corporation (IT)
Radian International
Smith Environmental
Technologies Corporation
Terra Vac Incorporated
Wayne Perry, Inc.
Address and Phone Number -
2325 Maryland Road
Willow Grove, PA 19090
(215) 657-7134
8025 Excelsior Drive
Madison, WI 53717
(608) 836-1500
90 Riverdale Road
Riverdale,NJ 07457
(201) 616-9700
100 River Ridge Drive
Norwood, MA 02062
(800) 635-0053
2211 Norfolk, Suite 1600
Houston, TX 77098
(713) 522-6300
2925 Briar Park
Houston, TX 77042
(713) 784-2800
2455 Horsepen Road, Suite 250
Herndon,VA 20171
(703) 713-6493
One Plymouth Meeting
Plymouth Meeting, PA 19462
(610) 825-3800
1555 Williams Drive, Suite 102
Marietta, GA 30066-6282
(404) 421-8008
8281 Commonwealth Avenue
Buena Park, CA 90621
(714) 826-0352
Point of Contact
Joseph Tarsavage
Anthony Miller
Rick Dorrler
David Peterson
John Connor
John Mastroianni
Christopher
Koerner
Dan Guest
Charles Pineo
Don Pinkerton
Note: This list is not inclusive of all vendors capable of providing dual-phase extraction
technologies. This list reflects those vendors contacted during the preparation of this
report.
4-28
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CHAPTER 5.0
DIRECTIONAL DRILLING
This chapter focuses on the application of directionally-drilled horizontal wells to enhance SVE
bioventing/biosparging, and air sparging technologies. Horizontal wells are gaining popularity for use in
SVE and air sparging remedial systems. This is a result of recent advances in drilling mud formulation,
screen design and drill rig availability. Horizontal wells are being used to remediate shallow soil and
groundwater in areas where access is limited by airport tarmacs, buildings, tanks and subsurface debris.
One horizontal well can take the place of as many as 20 vertical wells eliminating the need for redundant
hardware for SVE and groundwater pumping.
The following sections provide an overview of directional drilling, describe conditions under which the
technology is applicable, contain a detailed description of directional drilling methods, highlight
performance data, list vendors that provide directional drilling services, outline the strengths and
limitations of the technology, and provide recommendations for using the technology. Cited figures and
tables follow references at the end of the chapter.
5.1 TECHNOLOGY OVERVIEW
The first directionally drilled horizontal wells for environmental remediation were installed in 1988 as
part of horizontal extraction and injection remediation systems at the DOE Savannah River Site (SRS)
Integrated Site Technology Demonstration. Seven wells were installed at the SRS to demonstrate
innovative in situ remediation technologies. Between 1988 and 1993, the DOE's Office of Science and
Technology supported the development and deployment of directional drilling technology for
environmental applications at the SRS. The DOE also funded the development and demonstration of
directional drilling technologies at the Sandia National Laboratory in Albuquerque, New Mexico,
between 1991 and 1995 (Kaback and others 1996).
Today, the use of horizontal wells for SVE and air sparging has moved into the private sector.
Horizontal directional drilling is considered an acceptable technology; in appropriate geologic
environments and for appropriate contaminants, it can result in better performance and lower overall cost
than vertical wells. Horizontal wells can be used to access areas generally not accessible using vertical
5-1
-------
well drilling technologies, such as under buildings and airport tarmacs. Figure 5-1 illustrates a
hypothetical horizontal well network installed beneath a building to access contaminated soil and
groundwater.
Two recent, large-scale applications of this technology occurred at the John F. Kennedy (JFK) Airport
(Tetra Tech 1996a), where more than 50 horizontal wells totaling more than 20,000 feet in length were
installed to remediate a jet fuel plume under the tarmac. Additionally, about 25 horizontal wells have
been installed at a Dow Chemical Company Louisiana Division plant located in Plaquemine, Louisiana
(Tetra Tech 1996b).
The number of horizontal wells installed for environmental remediation projects has increased
dramatically in recent years. In 1994, there were only 55 documented horizontal wells in the U.S., and in
1995, there were 117 (Kaback and others 1996). More than 400 new horizontal wells nationwide are
projected during 1996 (Wilson 1995a).
Improvements in technologies borrowed from the oil and gas industry and utility industry drilling
technologies, combined with an increase in competitiveness among drilling contractors, has contributed
to the increase in popularity of horizontal wells. These improvements, which have focused on downhole
drilling motors, drill bit steering, accuracy in drill tool guidance systems, drilling fluids, and screen
designs, are continuing to sustain a cost competitive marketplace for horizontal wells in environmental
remediation.
Directional drilling employs the use of specialized drill bits to advance curved boreholes in a controlled
arc (radius) for installation of horizontal wells or manifolds for SVE and sparging technologies. The
borehole is initiated at a shallow angle typically 5 to 30 degrees to the ground surface. After arrival at a
target depth, the drilling tool is reoriented to drill a horizontal borehole. Electronic sensors located in the
drill tool guidance system provide orientation, location, and depth data to the driller. Drilling fluids are
generally used to convey cuttings as well as lubricate and maintain the integrity of the borehole while
enlarging its diameter or installing a well. There are two types of directionally drilled boreholes: blind
and continuous. Blind boreholes terminate in the subsurface, and the well is installed from the entrance
of the borehole. Figure 5-2 illustrates a blind borehole completion. Continuous boreholes are reoriented
5-2
-------
upward and return to the ground surface. In continuous boreholes, the well is installed from the exi*
point and pulled into the borehole by the drill rig. Figure 5-3 illustrates a continuous well completion.
An overview of a horizontal well installation is as follows:
Advance a pilot hole
Enlarge the hole using a reaming drill bit, by pushing or pulling the bit through the pilot hole. In
a continuous borehole, the reaming drill bit tool is inserted into the borehole at the exit point and
pulled back to the drill rig.
Install the well by pushing or pulling the well casings into the borehole. In continuous boreholes,
well installation generally occurs during the reaming phase (second bullet).
Figure 5-4 illustrates advancing a pilot hole, and Figure 5-5 illustrates backreaming and well casing
installation.
5.2
APPLICABILITY
Directional drilling is applicable for installation of horizontal wells to enhance a variety of remedial
systems. Horizontal wells have been shown to be effective for SVE, air sparging, groundwater
extraction, and free product removal. Of the approximately 370 documented horizontal wells in the
United States today, 35 percent were installed for SVE, 33 percent for groundwater extraction, 21 percent
for air sparging remedial applications, and 11 percent for other purposes (Kaback and Oakley 1996).
Horizontal wells have also been used as gravity drainage systems for groundwater extraction to allow for
gravity pumping and injection, eliminating costly aboveground treatment and disposal fees (Tetra
Tech 1996c).
There are several benefits to using horizontal wells. These include:
Horizontal wells can have as much as a 50 percent larger zone of influence than vertical wells
because they can provide a linear, constant, and uniform air delivery or vacuum to the formation.
Horizontal wells can increase the performance of remedial systems (such as SVE, bioventing,
and air sparging) because horizontal wells conform closer to the distribution of the contaminant
than vertical wells.
5-3
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In air sparging systems, horizontal wells can be oriented perpendicular to the groundwater flow
direction. In this manner, groundwater can be exposed to a curtain of oxygen as the groundwater
flows by the sparge well.
Horizontal wells can reduce the limitations of anisotropic hydraulic conductivities common in
most stratified sediments by being oriented in the direction of the higher horizontal hydraulic
conductivity tensor.
Horizontal wells are well suited for cleanup of soil particles, soil vapor, and groundwater using an
integrated scheme in which the wells are located both above and below the water table (Downs 1996).
The largest example of such an integrated remedial scheme is at New York's JFK: approximately
36 horizontal air sparging and 18 SVE wells have been installed to remediate a large plume of jet fuel in
both subsurface soils and groundwater. In this system, two to three air sparging wells are located
adjacent to (and below) an associated SVE well (see Section 5.4.1.4 for details).
The application of horizontal wells to extract free product in areas where the elevation of the water table
is variable may be limited because the elevation of the free product plume may move above and below
the elevation of the horizontal well.
5.2.1
Geologic Conditions
Horizontal wells can be installed in most geologic materials that are suitable for SVE and air sparging,
including unconsolidated sands, silts, and clays, as well as bedrock. Installation in silts and clays can be
difficult because of the reduction of the specific capacity of the well caused by the smearing of silts and
clays against the borehole wall, which can result in lower effective permeabilities. Costs rise with
increased drilling difficulty (for example, in cobble and coarse gravels).
5.2.2
Distances Achieved
Horizontal boreholes as long as 2,600 feet and to depths of 235 feet have been installed (Kaback and
Oakley 1996); however, borehole lengths of between 200 and 600 feet, with depths of less than 50 feet,
are most common.
5-4
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5.3
ENGINEERING DESCRIPTION
Directional drilling methodologies were first developed and used by the utility industry for the
installation of buried utility conduits (sewer pipes, power lines, etc.). Large, river-crossing drill rigs were
developed in the 1970s for installing utility conduits underneath rivers with this technology. These large
and powerful rigs can drill boreholes up to 60 inches in diameter and thousands of feet long.
Approximately 25 percent of the boreholes for environmental remediation projects have been installed by
directional drilling using these larger drill rigs. The remaining 75 percent of the boreholes for
environmental remediation projects have been installed by directional drilling with the use of drill rigs
used by the utility industry.
The following sections describe the directional drill rigs, drilling assembly, drilling fluids, guidance
system, well construction materials, and design considerations for directional drilling as well as the
common problems encountered during directional drilling projects.
5.3.1
Drill Rigs
Directional drill rigs typically consist of a carriage that slides on a frame holding the drill rods at an angle
of 0 to 45 degrees. The rigs are generally powered by a hydraulically driven motor on the carriage which
rotates the drill rods (photographs 5-1 through 5-4). A chain drive, rack and pinion drive, or hydraulic
cylinder may push or pull the carriage to advance or retract the drill string. A pump on the rig capable of
handling various drilling fluids is required (EPA 1994).
The drill rig provides thrust to the drilling tool, providing the force to advance the drill string the length
of the borehole and providing sufficient pulling force to retract the casing into the completed borehole.
Horizontal drill rigs must be anchored to the ground by staking or attaching it to a buried or surface
weight. This provides an opposing force to the thrust or pull-back. The drill rig must also provide torque
to the drill strings. Most drilling methods require that the drill string be rotated while it is advanced into
the borehole to reduce drag friction on the drill string.
Drill rigs are available in a range of sizes. They are classified according to their torque and force they
push and pull with. Mini and midi type drill rigs are most commonly used for shallow SVE boreholes.
5-5
-------
Mini and midi drill rigs (photographs 5-1 through 5-3) can be very compact (for example, a typical
gasoline station can remain open during drilling operations). Maxi rigs, on the other hand, take up
considerable space and require several large trucks to mobilize and setup on the site. Photograph 5-4
shows a maxi rig.
Mini drill rigs are mounted on a trailer, a truck, or a self-propelled tracked vehicle. The drilling fluid
system is limited; water or a dilute bentonite based fluid are commonly used. A mini drill rig's
maximum thrust force is less than 40,000 pounds. Their use is limited to small diameter (4-inch range)
pipe installations at depths of less than 30 feet in semiconsolidated sediments.
Midi drill rigs are mounted on a trailer or a self-propelled tracked vehicle. These rigs have a maximum
thrust force of less than 80,000 pounds. They are used to drill continuous or blind boreholes and install
pipes up to 8 inches in diameter. The drilling fluid systems are larger and can accommodate all types of
drilling fluids.
Maxi drill rigs are mounted on trailers. These rigs have a maximum thrust force of up to
800,000 pounds. Maxi rigs can accommodate any type of drilling fluid, have been used to drill up to
60-inch boreholes, and can be used to install pipes of up to 14 inches in diameter. The large river
crossing drill rigs fall into this category (May 1994).
5.3.2
Drilling Assembly
The drilling assembly used during horizontal drilling consists of a drilling tool, a bent subassembly, and a
guidance system. The drilling tool is preferentially oriented in the borehole by the bent subassembly to
drill in the desired direction. The guidance system provides the orientation and location of the drill string
to the driller. There are three kinds of drilling tools, namely tri-cone type drilling tool, hydraulically
assisted, job-style drilling tool, and compaction tools. These drilling tools are described below.
5.3.2.1
Tri-Cone Type Drilling Tools
A tri-cone type drilling tool uses a downhole mud motor (tri-cone type drill bit), a water jet, a compaction
hammer, or a combination of these to drill a borehole by cutting the formation. The trajectory is curved
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by using a tool (the bent subassembly) that is eccentric relative to the drill rod or has a bevel in the
drilling tool face itself. Figure 5-6 shows typical drilling assembly for the different drilling phases.
Downhole mud motors (or tri-cone type drill bits) are powered by drilling fluid that is pumped down the
drill pipe. The drilling fluid (either a bentonite or organic polymer-based drilling fluid) facilitates the
turning of the drill bit. The drilling fluid is removed by development and using sodium hypochlorite.
Downhole mud motors and water are the most commonly used tools in the environmental drilling
industry.
5.3.2.2
Hydraulically Assisted, Jet-Style Drilling Tools
Hydraulically assisted, jet-style (slant head fluid-assisted drill bit) drilling tools are the most commonly
used drill tools today. Hydraulically assisted, jet-style drilling tools use hydraulic pressure to cut the
geologic formation. The hydraulic jet is directed from a bent housing or from a drilling fluid port on a
drill bit attached to a bent subassembly. To drill the curved section, the bent subassembly and the
hydraulic jet are placed in the direction of the borehole deviation. To drill the straight segment, the drill
string is rotated by the driller. The rotation prevents the hydraulic jet from having a preferred
orientation.
5.3.2.3
Compaction Tools
Compaction tools work on the same principle as wood chisels. Compaction tools are wedge-shaped and
move in the direction of the slant on the face of the wedge. The drill string is pushed if the borehole
direction is to be changed and rotated and pushed if the borehole direction is to be straight. Compaction
tools are restricted to unconsolidated materials and to boreholes that are less than 50 feet deep.
Compaction tools can press cuttings into the side of the borehole and damage formation permeability.
5.3.3
Drilling Fluids
Drilling fluids are used to clean cuttings from the drill bit, to suspend cuttings for transport to the surface,
to lubricate the drill string, to cool the drill bit, and to prevent the loss of drilling fluids to the formation.
Drilling fluids are either bentonite clay based, or synthetic or natural polymer based. Selection of the
proper drilling fluid is essential for a successful drilling project. Recent advances in drilling fluid
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formulations have resulted in mixed metal hydroxide bentonite fluids and xantham polymer systems that
have a high gel strength to carry drill cuttings and filtration control to seal the borehole.
Special well development fluids are used to remove the drilling fluids from the well (for example, mixed
metal hydroxide drilling fluids require well development using sodium acid polyphosphate to flocculate
the bentonite and clean the well). Xantham polymer-based drilling fluid breaks down and is easily
removed using sodium hypochlorite during well development. Xantham polymer-based drilling fluid
also breaks down over time. This type of drilling fluid has been shown to increase the success rate of
horizontal wells by reducing borehole damage (reduced borehole wall permeability) that can be caused
by bentonite based drilling fluids. It can also lower well installation costs by reducing well development
time.
53.4
Guidance Systems
The guidance system allows the driller to control the orientation, pitch, and depth of the drilling tool. It
is located in the downhole assembly behind the drilling tool and the bent subassembly. There are three
common types of guidance systems as follows:
Radio beacon-receiver systems
Magnetometer-accelerometer systems
Inertial (gyroscopic) systems
Each system provides location and depth data. The radio beacon method uses a surface tool to "walk
along" the ground surface while following the drilling tool during drilling. It is limited to depths of up to
25 feet. The magnetometer-accelerometer system orients using a surface imposed magnetic field and a
computer to navigate. The inertial system uses gyroscopes to orient with the earth's magnetic north and a
computer to interpret navigational data.
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5.3.5
Directionally Drilled Well Installation
Directionally drilled well materials, screens, casing, and installation steps are described in the following
subsections.
5.3.5.1
Well Materials
The well screen and riser pipe design for a horizontal well is similar to that of a vertical well with the
exception that horizontal wells require materials with higher tensile strength while maintaining
flexibility. Horizontal well materials are subject to high tensile stresses resulting from skin friction along
the borehole wall, particularly at curved sections of the borehole. Selection of riser pipe and well screen
material depends on the soil characteristics, contaminant type, and radius of the curvature of the
borehole. HOPE and fiberglass/epoxy resin are well suited to short radius boreholes because of their
flexibility. Stainless steel and carbon steel can also be used in boreholes with medium and large radii.
PVC is not well suited for use in horizontal wells because it has neither the high tensile strength nor the
flexibility necessary (Mast and Koerner 1996).
5.3.5.2
Well Screens
Traditional prepacked dual well screens, single well screens enveloped in a geotextile filter material, and
porous polyethylene pipes are commonly used. Filter packs are generally impractical in horizontal wells
because of the difficulties of installation. Other screen designs such as wire-wrapped screens, geotextile
fabric wrapping and louvered stainless steel, multilayered stainless steel and sintered HDPE and stainless
steel have been used. Wire-wrapped screens are only available in PVC and steel. Wire-wrapped screens
are not made from HDPE because of the low melting point of the material. A porous HDPE screen is
fairly new on the market and is designed specifically for horizontal well installations. The screen
consists of pure spherical shaped polyethylene beads that are heated and molded into a pipe. The heating
process does not melt the spheres completely, allowing the pipe to be porous. By controlling the size of
the polyethylene beads, the permeability can be varied. The open area of this material averages 30
percent and has 3 times the collapse strength of HDPE slotted screen (Bardsley 1995).
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5.3.5.3
Well Casings
Carrying casings are commonly used to install the screens and riser pipes. Carrying casings are installed
after the pilot hole is advanced by pulling it into the borehole during the reaming phase of the drilling.
The well materials are placed into the carrying casing during installation or afterwards. Once the screen
and riser are placed into the borehole, the carrying casing is withdrawn from the well, leaving the well
screen and riser pipe in place.
53.5.4
Well Installation
The steps of installation of directionally drilled horizontal wells are as follows:
Installation of the pilot hole and exit trenches. The pilot holes are generally drilled with an
approach angle of less than 25 degrees (Wilson 1995b). Figure 5-4 illustrates the installation of
the pilot hole.
Continuous Boreholes: switch drill bits at the exit point and enlarge the borehole using a
reaming tool. A carrier casing is generally pulled into the borehole with the reaming drill bit.
Blind Boreholes: washover pipe equipped with a reaming bit is advanced over the pilot
hole drill string. This step helps clean the borehole wall and enlarges the hole to allow
casing installation. The pilot hole drill string is removed, and the washover casing
remains to be used to install the well materials. Figure 5-5 illustrates the backreaming
and casing installation process.
The screen and riser are installed in the carrier casing or washover pipe
The casing is removed, and the well material is left in the formation
The well is developed with water and special drilling mud removal solutions
Install SVE and air sparging system components
53.6
Design Considerations
The important design considerations for directional drilling are described below.
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5.3.6.1
Radius of Curvature
The radius of curvature is an important design consideration in horizontal wells. Medium and long radii
of curvature boreholes are preferable over shorter radii because of the reduced drilling and installation
stress on the drill string and casing. Longer radii can be drilled by a variety of drill rigs. However,
longer radii increase the drilling footage and increases cost. The "step off distance," or the distance
required to accommodate the angle of entry and achieve the desired depth, should also be considered.
Generally, a minimum of a three to one ratio of horizontal distance to depth (approximately 18 degrees)
is required (Tetra Tech 1996d). The design process must consider space availability, drill rig
capabilities, well materials, and cost to arrive at the approach angle and radius of curvature.
5.3.6.2
Air Flow Patterns
A common problem with horizontal vapor extraction and air sparging wells is that the air delivery may
not be uniform throughout the screen interval. Nonuniform airflow will result from permeability
variations within the formation surrounding the screen interval, faulty well installation, or poor well
screen design. Preferential exit of air at the blower-end of the well can occur if there is excessive
pressure drop along the screen interval, or if there is failure in the annular seal. Excessive pressure drop
within the screen interval can occur if the slot size is too large or if the open area is too great. Research
conducted during the preparation of this report indicate that the use of a uniform slot size will likely
result in nonuniform air flow. Designing the well screen to correct for nonuniform air flow is one of the
most important factors in well screen design.
Lundegard and others (1996) conducted an air sparging pilot test using horizontal wells at the Guadalupe
Oil Field in California. A careful screen design resulted in uniform air flow patterns. These
investigators estimated air flow rates for a well in the design phase using the model TETRAD (Vinsome
and Shook 1993; Lundegard and Andersen 1996). Using the derived flow rates from TETRAD,
applicable pipe size and hole spacing were calculated for a well design. The hole sizes and spacings
were designed using sparger design equations and guidance described by Perry and Chilton (1975) and
Knaebel (1981).
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Significant research and evaluation on screen design to eliminate nonuniform airflow was also conducted
at JFK. This is described in Section 5.4.1.4.
5.3.7
Common Problems
Common problems in directional drilling projects result primarily from poor planning by the engineering
contractor, and a lack of experience and preparation by the drilling contractor. Historical problems have
occurred for various reasons as follows (Wilson 1995b):
Not fully characterizing the horizontal well site geology and geochemistry
Not fully researching the credentials of the drilling company
Not planning and researching the drilling fluid and screen materials and design carefully
Not developing the well adequately
Not evaluating carefully the potential for pressure drops due to slope, geology or well loss
Not using a contractor experienced in planning, procuring, and implementing a horizontal well
installation program
Not retaining a driller who understands the intricacies of drilling in the specific geologic
environment
Not providing close oversight to the drilling contractor
Drilling contractors providing undersized and undermaintained equipment for the job
Drilling contractors drilling the pilot hole too quickly and not creating a smooth uniform
curvature to the borehole
Not maintaining a consistent pressure along the length of the horizontal well
Two solutions to the problem of inconsistent pressure are to reduce the diameter of the well screen
toward the exhaust end of the screen or to use a sintered HOPE screen that can be custom made to have
varying pore size while maintaining the same open area along its length.
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5.4 PERFORMANCE AND COST ANALYSIS
Performance and cost data are presented in this section for four case studies. These are SRS, Alberta Gas
Plant, Hastings East Industrial Park, and JFK. The JFK case study presents the most ambitious and up-
to-date information regarding the use of horizontal wells for SVE and air sparging.
5.4.1
Performance
The availability of data comparing the performance of horizontal to that of vertical wells are limited.
The majority of work with this technology is being conducted at confidential private industrial and
Department of Defense facilities. Because of the relative newness and proprietary nature of this
technology, the bulk of the performance data are contained in pilot study, installation, and performance
monitoring reports prepared by contractors. Contractor reports were difficult to obtain. Only a few of
the available references contained performance data. These are presented as case studies below.
Personal communication with several experts in the field was conducted as part of this analysis. These
individuals are listed in Section 5.8.2. A unanimous consensus by these individuals indicated that
horizontal wells can have as much as a 50 percent larger zone of influence than vertical wells because
they can provide a linear, constant, and uniform air delivery or vacuum to the formation. Performance of
remedial systems (such as SVE, bioventing, and air sparging) with the use of horizontal wells increases
because horizontal wells can be installed more precisely in the contaminant plume than vertical wells. In
addition, horizontal wells can optimize typical anisotropic hydraulic conductivities common in most
stratified sediments by being oriented in the direction of the higher horizontal hydraulic conductivity
tensor.
5.4.1.1
U.S. Department of Energy Savannah River Site Integrated Demonstration Site
DOE pioneered the use of horizontal wells at the SRS for environmental remediation purposes for their
Integrated Site Technology Demonstration program. An abandoned process sewer line at the SRS leaked
approximately 2.2 million pounds of TCE and PCE into the soil and groundwater between 1958 and 1985
(DOE 1995). A pump and treat groundwater extraction and treatment system in operation since 1984
removed approximately 230,000 pounds of solvents from the groundwater. However, solvents have
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continued to leach into the groundwater from the vadose zone. The depth to groundwater is 135 feet.
Extensive site characterization (geology, geochemistry, and bioavailability) has been conducted at this
site (Kaback and others 1991).
Air injection, SVE, and ISB using horizontal wells have been demonstrated at this site. The in situ
AS/SVE strategy involved the installation of two parallel horizontal wells. These wells were aligned
with the orientation of the process sewer line.
The two horizontal wells were installed in 1989 using technology borrowed from the petroleum industry.
One 300-foot-long air sparging well was installed below the water table at a depth of 150 to 175 feet.
The 200-foot-long SVE well was installed to a depth of 75 feet.
A 20-week pilot test was conducted. During the pilot test, the two wells operated concurrently. Three
different air injection rates at two different temperatures were used. Helium tracer tests were also
conducted to evaluate vapor flow pathways and aquifer heterogeneities. The SVE wells operated at 580
scfm during the test. The air sparging wells operated at a range of 170 to 270 scfm.
Almost 16,000 pounds of solvents was removed during the pilot test (Kaback and others 1996; Looney
and others 1991).
The VOC extraction rate averaged 110 pounds of VOCs per day when the SVE well operated alone.
Extraction rates increased to 130 pounds per day when both wells operated concurrently. The
concentration of TCE at the two wells decreased from 1,600 and 1,800 ^g/L to 200 and 300 //g/L,
respectively. Additionally, the activity of indigenous microorganisms increased during the pilot test by
an order of magnitude. These same horizontal wells were also used to evaluate ISB. The results of this
study are presented by DOE (1995), and discussed in Chapter 3 of this report. The SVE well capture
zone within the vadose zone was 200 by 300 feet.
5.4.1.2
Alberta Gas Plant
Armstrong and others (1995) conducted a comparison of the performance of horizontal versus vertical
wells. These investigators used a numerical model (Mendoza 1992) calibrated against existing horizontal
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wells to evaluate well performance. Two cases were evaluated; a horizontal well installed using
trenching and a horizontal well installed using drilling. The performance of the horizontal drilling case is
presented here. This case evaluated the zone of influence of a 275-foot-long well with a 190-foot-long
screen, installed at depths ranging from 6 to 13 feet bgs, in a silty sand to sandy silt soil. Air flow tests
were conducted at the horizontal well and at a vertical air extraction well using air monitoring points
within the formation to collect pressure and flow data for use in the model. Air permeabilities were back
calculated. The model was then used to calculate the theoretical zone of influence of the vertical and
horizontal wells.
The modeling results showed that the zone of influence of the vertical and horizontal wells at a vacuum
pressure of 25 Pascal were 4.7 and 12.3 meters, respectively, indicating that one 60-meter, horizontal
well could provide the same areal coverage as 22 vertical wells. A cost evaluation indicated that, based
on well installation costs alone, a 60-meter-long well would cost the same as 15 to 20 vertical wells.
This cost evaluation only considered well installation and did not consider surface equipment associated
with each well such as blowers, manifolding, and piping. When these costs are factored in, the cost
effectiveness of horizontal wells would be realized.
5.4.1.3
Hastings East Industrial Park
Wade and others (1996), under direction of the U.S. Army Corps of Engineers, conducted a 1-year pilot
study of an air sparging system with one horizontal and one vertical sparging well at the Hastings East
Industrial Park near Hastings, Nebraska. The site is part of a former naval ammunition depot that was
decommissioned in 1967. The agency responsible for the pilot study was the U.S. Army Corps of
Engineers. Widespread soil and groundwater contamination exists at the site. The contaminants of
concern at this facility are chlorinated solvents, primarily TCE at concentrations as high as 16,000 /^g/L
in groundwater. A full-scale remedial system, incorporating air sparging using both horizontal and
vertical wells, was designed, installed, and extensively tested over a period of 1 year. Figure 5-7 presents
the site plan showing the zone of contamination, the locations of monitoring points, and vertical and
horizontal air sparging wells.
The system installed at this site is a deep system by most standards. The depth to groundwater at this
facility is 100 to 130 feet bgs. The geology includes deposits of silty clay loess, sand, and gravel with
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interbeds of silt and clay to the water table. The geology of the aquifer includes sand and gravel. The
aquifer is anisorropic, and the horizontal and vertical hydraulic conductivities are estimated at
7 x 10'2 cm/s and at 1 x 10"7 cm/s, respectively.
This system was designed as an integrated approach using the horizontal well as both a method of
containment and a device for contaminant mass removal by installing it perpendicular to the groundwater
gradient across the width of the contaminant plume. With this orientation, a vertical curtain of sparged
air aligned perpendicular to the groundwater flow direction was created so the air can strip the TCE from
the groundwater as it flows by the horizontal well.
The horizontal well was placed approximately 370 feet downgradient from the source of the plume. The
borehole for the well was drilled with a 600-foot-radius of curvature (considered to be a large radius).
No information regarding drill rig type or other specifics of the drilling phase was available. The
horizontal well has a 6-inch diameter and a 200-foot-long well screen, and it was drilled to a depth of
125 feet (13 feet below the water table). The total length of the well is 600 feet. A standard,
continuously wound, stainless steel, prepacked well screen was used. The slot size was selected using
standard water well industry screen design criteria. An air diffuser pipe was installed within the screen
to help distribute the air evenly along the screen. A blower capable of injecting air at approximately 320
scfm while maintaining a wellhead pressure of 11 psi was installed. The well was developed by jetting,
pumping, and surging the screen. In addition, phosphates were jetted through the screen to destroy the
gel properties of the bentonite-based drilling mud. The well was then videotaped to confirm adequate
development.
The vertical well was installed at the center of the contaminant plume in the same stratigraphic horizon
as the horizontal well. This well has a 4-inch diameter and a 5-foot-long, continuously wound, stainless
steel screen.
In addition to the sparging wells, the system design incorporated SVE wells screened in the vadose zone.
These wells served a dual purpose of capturing the sparged gas and remediating the vadose zone sands
and gravel. A total of 24 vertical SVE wells, 15 vertical vadose zone monitoring wells, and 22 vertical
groundwater monitoring wells were installed.
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The system was operated in five phases for a period of 1 year during the pilot test. The first two phases
operated using a constant air injection, and the last three phases at cycled air flow. The goal of the pilot
test was to optimize groundwater cleanup and prevent the plume from spreading around the zone of
sparging. There was a concern that long periods of sparging at a high flow rate at the horizontal well
could spread the plume because of the reduction of water hydraulic conductivity within the sparge zone.
The horizontal well operated at flow rates of 160 to 320 scfm, and the vertical well operated at flow rates
of 15 to 30 scfm. Extensive soil vapor and groundwater sampling during the course of the year was
conducted to measure the performance of the system.
The zone of sparging around each well was determined by observing air in the groundwater monitoring
wells, TCE concentration in monitoring wells, and changes in TCE concentrations in the SVE wells. The
zone of influence was about twice as large around the horizontal well as the vertical well. The zone of
sparging was 60 feet around the horizontal well and 26 feet around the vertical well at the maximum air
flow rates.
The effectiveness of each well in reducing TCE in the groundwater was also evaluated. Groundwater
quality data from nearby downgradient groundwater monitoring wells were used to evaluate the
performance of the horizontal and vertical air sparging well; these data are shown on Figures 5-8 and 5-9,
respectively. TCE concentrations were reduced by more than 90 percent at the groundwater monitoring
wells screened at the top of the water table. Wells screened toward the bottom of the 15-foot-thick
aquifer showed much less TCE reduction; water moving below the horizontal well was not exposed to
the sparge curtain. The groundwater sampling results showed that the plume did not spread around the
sparging curtain.
TCE concentrations were reduced in the groundwater monitoring wells adjacent to the vertical sparging
well; groundwater cleanup resulting from the vertical well was much less significant than groundwater
cleanup resulting from the horizontal well. However, it does not appear that those wells are located
directly downgradient from the sparging well. Direct comparison with the horizontal well may not be an
accurate representation of the well efficiencies immediately downgradient of the sparge well.
Wade and others (1996) cited that the horizontal well created a uniform sparge curtain that would be
unlikely with vertical wells. They noted that the horizontal well had a sparging capacity of more than 10
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times that of the vertical well under the same injection pressure. The zone of influence around the
horizontal well was greater than the vertical well by a factor of 2 under maximum injection rates. Cost
effectiveness was not evaluated in literature cited.
5.4.1.4
John F. Kennedy Airport
The Port Authority of New York and New Jersey has installed the most ambitious AS/SVE project to
date using horizontal wells at the JFK airport. More than 50 horizontal wells, to lengths reaching more
than 600 feet, have been installed in two separate areas. The system combines about 36 air sparging
wells and 18 SVE wells. Figures 5-10 and 5-11 illustrate the layout of the system. The system uses
approximately 13,000 feet of horizontal SVE wells and 7,000 feet of horizontal air sparging wells. The
design of the horizontal SVE and horizontal air sparging wells was based on a pilot study and was
followed by a full-scale test. The system is augmented by 28 vertical air sparging and 15 vertical SVE
wells. The SVE and air sparging wells will operate continuously while the groundwater is being
intermittently sparged, extracted, and treated by liquid phase activated carbon and discharged into the
storm water. Postinstallation monitoring for soil and groundwater is also underway as a part of this
system design.
The soil and groundwater at JFK are contaminated with jet fuel that spilled and/or leaked from the
hydrant fueling system. A small fraction of the contamination is also from USTs that leaked motor oil,
heating oil, or ethylene glycol. The compounds of concern at JFK are VOCs (ethylbenzene and toluene),
and SVOCs (primarily base neutral compounds). The concentrations of VOCs and SVOCs in soil ranged
from nondetected to 148,000 mg/kg and nondetected to 584,000 mg/kg, respectively. The concentration
of BTEX and SVOCs in groundwater ranged from nondetected to 6,000 ^g/L and nondetected to
4,000 f^g/L, respectively (Roth and Pressly 1996).
The geology at JFK includes hydraulic fill consisting of fine to medium sand with trace silt to depths of
10 to 16 feet bgs. The fill is underlain by a thin, low permeability, clayey-peat layer. The depth to
groundwater ranges from 6 to 8 feet bgs (Roth and Pressly 1996).
The remedial system was a result of intensive laboratory and field studies by the Port Authority of New
York and New Jersey. Two pilot studies were used to collect predesign data. The first pilot test used a
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260-foot long horizontal SVE well constructed with 3-inch diameter HDPE. The horizontal SVE well
was installed about 3.5 feet bgs and has a varying slot size of 160 feet of 0.01 inch and 100 feet of
0.020 inch slot opening. The horizontal air sparging well was 190 feet long with 80 feet of screen
installed at 12 feet bgs. A pilot test for each well was conducted independently to determine the zone of
influence, air flow rates, and distribution of air flow rates. Figures 5-12 and 5-13 show results from the
air sparging and SVE pilot tests, respectively. The results of these pilot tests were evaluated to look at
the relationships between vacuum pressure and flow and the resulting geometric distribution of pressure
vacuum as measured by pressure and vacuum monitoring points around the wells. Horizontal SVE air
flow versus vacuum data were plotted and linearly regressed to solve for flow per foot of screen interval
as a function of vacuum at the center of the screen. Vacuum line loss versus flow were also plotted and
linearly regressed to solve for the change in vacuum as a function of flow. These evaluations were used
to design the screen slot size and distance between the horizontal SVE and horizontal air sparging wells
in the full-scale pilot test and remediation system.
The objective for the full-scale test was to affect a 150-foot radius with the horizontal SVE well having 1
to 2 scfm per foot of well screen with an air pressure at the well end equivalent to 10 inches of water.
For the full scale horizontal air sparging well, the objective was to affect a 50-foot zone of influence with
a 0.4 to 0.8 scfm per foot of well screen having a pressure of 3.89 psi at the well end.
A full-scale pilot test was conducted to verify the findings of the pilot test and collect additional data for
the design of the remediation system. The horizontal SVE well used in the full-scale test was installed to
a depth of 3.5 feet with a total length of 660 feet and a 530-foot long well screen. The screen used a
0.25-inch slotted well screen with the distance between slots varying from 0.25 to 0.875 inch with the
larger spacing being located nearer the blower end of the well. The horizontal air sparging well had a
total length of 680 feet with a screen length of 480 feet installed 12 feet bgs. Pressure and vapor
monitoring points were installed on either side of the wells to determine zone of influence. Figures 5-12
and 5-13 illustrate the soil vacuum and sparge pressure at the maximum blower rates.
Results of the full-scale pilot test showed that the maximum zone of influence for SVE ranged from 250
feet at the beginning of the screen (closest to the blower) to 120 feet at the middle and 185 feet at the end
of the screen. The flow rate from the horizontal SVE well ranged from 220 to 720 cfm. The SVE air
flow per foot of screen length ratio was 0.42 to 1.37 cubic feet per minute per foot (cfm/ft). The goal of
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1.13 cfm/ft along the entire length of screen was not realized. The investigators determined the air flow
rate per section of screen using the streamline and equipotential distribution of vacuum and pressure for
each test.
The zone of influence for the air sparging well was a maximum of 52 feet. The distribution of air
sparging pressure was elliptical as in the horizontal SVE well test. The maximum zone of influence
observed was 52, 30, and 10 feet at the beginning, middle, and end of the screen, respectively. The air
sparging flow rate ranged from 60 to 480 cfm, and air flow per foot of screen length ratio was 0.13 to
1.01 cfm/ft. The goal for zone of influence of the air sparging well was 40 feet with an air flow per foot
of screen length ration of 0.9.
The flow rate in the screen portion of the well closest to the SVE blower was 3 times greater than the
flow rate further from the blower. This information was used to design the screen for the remediation
system. The goal of the final design was to have even air flow along the length of the horizontal SVE
and horizontal air sparging well. To compensate for this air flow variation along the screen section, the
screens for the full-scale remediation were designed to have the open area of the screens toward the end
of the well. The open area is approximately 2 times greater than the area at the beginning of the well.
The pilot test also demonstrated reduction of significant concentrations of VOCs in groundwater as well
as VOC extraction rates within the soil vapor.
The full system of the horizontal SVE and horizontal air sparging wells were installed over a 3-month
period at the International Arrivals Building. Logistical considerations were intensive at an active airport
with the requirements of minimal disruption of traffic at the tarmac and at the gates. A 2-month
reconnaissance and scheduling effort was undertaken just to locate the borehole paths. Fifteen horizontal
SVE wells were installed to screen depths of about 3.5 to 5 feet bgs. Twenty seven horizontal air
sparging wells were installed with screen depths at about 12 feet bgs. More than 3,700 feet of
interconnecting subsurface manifolds and piping was installed to connect the well fields to the three
treatment system buildings constructed for the project. In addition, 15 vertical SVE and 28 vertical air
sparging wells were installed.
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The results of the remediation during the first 2 months of operation show that the systems have extracted
about 18,600 pounds of vapor phase VOCs. The concentration of VOCs and methane have steadily
decreased with time, indicating the system effectiveness. Several wells within the system have air flow
per foot of screen rates within the design specifications. However, several wells are operating with air
flow per foot of screen rates below design specification. In addition, many wells have pressure and air
flow drops from the blower to the ends of the screen lengths. It is anticipated that these rates will
increase as the residual drilling fluid in the wells biodegrade and pore water in the vadose zone
evaporates.
5.4.2
Cost Analysis
Obtaining cost data from vendors was difficult. In general, they would not release specific information
on their cost structure. Cost information based on interview responses obtained from the vendors and
experts seem to agree on a price range of 100 to 150 dollars per foot for an installation of horizontal
wells using HDPE well materials. This compares to a price range of 30 to 50 dollars per foot for a
vertical well. This cost would be representative of a turnkey installation including all well installation
materials, surface completions, and development. Using stainless steel or prepack screens can increase
this cost by 100 dollars per foot.
When comparing the cost of horizontal to vertical well installations, it is important to consider the entire
system costs and not just well installation. Horizontal wells can be shown to be more efficientfrom a
performance standpoint and less costly to install and operate than vertical wells when the costs of
blowers, downhole pumps, manifolding and piping and surface treatments units are considered.
5.5
VENDORS
Table 5-1 presents a list of vendors that were identified and contacted as part of this investigation. The
vendors presented here represent a list of vendors who supply directional drilling services for the
environmental community. This list is likely a subset of vendors with the capability to install a
horizontal well for environmental purposes. Additionally, with recent advancements in drilling mud
formulations and screen design plus a training program recently developed by Ditch Witch, Inc., in Perry,
Oklahoma, drilling companies that currently provide directional drilling services to the utility industry
5-21
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are expected to emerge as having the capability to conduct environmental drilling services. When
seeking a directional drilling contractor, it is important to conduct a search for contractors who have
experience in drilling boreholes in the local geologic framework. In doing so, a project team has a
greater level of confidence that the drilling contractor will install the well to meet the project
specifications.
5.6 STRENGTHS AND LIMITATIONS
The following list outlines some of the strengths of using horizontal well technology for environmental
remediation:
Boreholes can follow the geometric trend of the contaminant plume since the boreholes can be
guided in the horizontal plane. One horizontal well can remediate a surface area many times that
of a single vertical well because contaminant plumes are generally vertically thin and
horizontally extensive. This is because horizontal hydraulic conductivities are generally several
times those of vertical hydraulic conductivities.
Horizontal wells can access contaminated areas that cannot be reached by conventional remedial
methods.
Horizontal wells cause minimal impact to activities at the ground surface such as vehicle traffic,
plant operations, and flight lines.
Horizontal wells technology is nondestructive in that it does not damage existing land
improvements.
Horizontal wells can be completed in most geologic environments by the use of alternative
drilling mud fluids.
ซ Although installation costs are more expensive on a per footage basis, a network of horizontal
wells can be more cost effective when indirect factors are considered (for example, surface
piping networks, downhole pump requirements, and effective area of influence of the well).
Pilot testing at the DOE SRS demonstrated that horizontal wells for vapor extraction can be up to
5 times more efficient than vertical wells because of a larger effective zone of influence (Looney
and others 1991).
The following list outlines some of the limitations of using horizontal well technology for environmental
remediation:
5-22
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The vertical capture zone of a horizontal well is limited by the vertical hydraulic conductivity of
the formation. If the contamination is distributed across several geologic strata, the effectiveness
of horizontal wells may be reduced.
Areas with highly fluctuating water tables can cause problems with SVE systems if the water
table variability is not fully understood.
Drilling fluids can disturb and alter the borehole surface and reduce the effective permeability of
the geologic formation, limiting the zone of influence of the well.
Installation of horizontal wells is several times more expensive than installation of vertical wells.
A careful cost analysis must be conducted to determine the feasibility of a horizontal well
drilling program.
Installation of horizontal wells requires knowledge of all potential subsurface obstacles along its
path. Detailed mapping along the borehole path may be required.
Others limitations and considerations include: impacts of drilling fluids on SVE well efficiency,
difficulties in well development, uniform air delivery/recovery, drilling fluid breakout, and
potential drainage to surface features (invasion).
5.7 RECOMMENDATIONS
Air sparging and SVE horizontal wells are most applicable to conducting remedial activities in the
following situations: in areas where access is limited to install a vertical well network; where the
contaminant zone is less than 80 bgs (due to high costs associated with deeper installations); where the
contaminant has a linear/ellipsoid geometry; and where the contaminant is located within a single
stratigraphic horizon. Horizontal wells are best suited to be installed in silty sand, sand and fine gravel
lithologies. The costs increase dramatically in geologic environments that include bedrock, clay, glacial
till, cobbles, and boulders. In remedial systems which specify a trench or cut off wall as the preferred
alternative, a horizontal well may be able to create a permeable zone when used with sparging.
Horizontal wells can eliminate the need for excavation in areas where space is limited.
5.8 REFERENCES
This section includes a list of references cited in Chapter 5 (Subsection 5.8.1) and a table presenting
professional contacts (Subsection 5.8.2). A comprehensive bibliography is provided in Appendix B.
5-23
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5.8.1
Cited References
Armstrong, I.E., C.A. Mendoza, BJ. Moore, and P.E. Hardisty. 1995. A Comparison of Horizontal
Versus Vertical Wells for Soil Vapour Extraction. Presented at Solutions '95, International Association
of Hydrogeologist Congress XXVI. Edmonton, Alberta. June 4 -10.
Bardsley, D.S. 1995. Horizontal Well Materials. World Wide Web Home Page
(http//:www.horizontalwell.com). Environmental Consultants LLC.
Downs, C.E. 1996. Multimedia Remediation Applications of Horizontal Wells. In: Proceedings of the
Tenth National Outdoor Action Conference and Exposition, Las Vegas, Nevada. National Ground Water
Association. Las Vegas, Nevada. Pages 237-243. May 13-15.
Kaback, D.D., B.B. Looney, C.A. Eddy, and T.C. Hazen 1991. Innovative Ground Water and Soil
Remediation: In Situ Air Stripping Using Horizontal Wells, Westinghouse Savannah River Company,
Savannah River Site, Aiken South Carolina. In Proceedings of the Fifth National Outdoor Action
Conference and Exposition. Las Vegas, Nevada. National Ground Water Association.
Kaback, D.D., and D. Oakley. 1996. Horizontal Environmental Wells in the United States: A Catalogue.
Colorado Center for Environmental Management. 999 18th Street, Suite 2750, Denver, Colorado 80202.
(303)297-0180. April.
Knaebel, K.S. 1981. Simplified Sparger Design. Chemical Engineering. March 9. Pages 116-117.
Looney, B.B., T. Hazen, D. Kaback, and C. Eddy. 1991. Full-Scale Field Test of the In Situ Air
Stripping Process at the Savannah River Integrated Demonstration Test Site. WSRC-RD-91-22. Aiken,
South Carolina. Westinghouse Savannah River Company. July 29.
Lundegard, P.D., and G. Anderson. 1996. Multi-Phase Numerical Simulation of Air Sparging
Performance: Groundwater. Volume 34(3). Pages 451-460.
Lundegard, P.D., Chaffee, B. and D. LaBrecque. 1996. Effective Design of a Horizontal Air Sparging
Well. Presented at the St. International Conference on Air Sparging, International Network of
Environmental Training, Inc. October 24.
Mast, V.A., and C.E. Koerner. 1996. Environmental Horizontal Directional Drilling Technology.
No-Dig Engineering, Volume 3, Number 2. Pages 17-21. March and April.
May, D.W. 1994. The Use of Horizontal Wells for Subsurface Soil and Aquifer Restoration, Drilling
Technology. In: J.P. Vozniak, ed,. American Society of Mechanical Engineers, New York, New York.
PD-Volume 56. Pages 227-239.
Mendoza, C.A. 1992. VapourT Users Guide. Department of Geology, University of Alberta,
Edmonton.
Perry, R.H., and C.H. Chilton, ed. 1975. Chemical Engineers Handbook. Fifth Edition. McGrawHill.
New York.
5-24
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Tetra Tech EM Inc. (Tetra Tech) 1996a. Personal Communication between Paul Frankel,
Hydrogeologist, and Marvin Kirshner, Chief Environmental Engineer, Port Authority of NY and NJ.
September.
Tetra Tech. 1996b. Personal Communication between Paul Frankel, Hydrogeologist, and Eric Meyer,
Design Engineer, Radian Corporation. September.
Tetra Tech. 1996c. Personal Communication between Paul Frankel, Hydrogeologist, and Charlie
Downs, Design Engineer, Pollution Prevention Associates. September.
Tetra Tech. 1996d. Personal Communication between Paul Frankel, Hydrogeologist, and Michael
Lubrecht, Marketing Director, Directed Technologies Drilling, Inc. September.
Roth, R. J., and N.C. Pressly. 1996. Remediation of Jet-Fuel-Contaminated Soil and Groundwater at JFK
International Airport Using Horizontal Air Sparging and Soil Vapor Extraction. Presented at the First
International Conference on Air Sparging. International Network of Environmental Training, Inc.
October 24.
U.S. Department of Energy. 1995. In Situ Bioremediation Using Horizontal Wells, Innovative
Technology Summary Report. Prepared by Colorado Center for Environmental Management. Denver,
CO.
U.S. Environmental Protection Agency. 1994. Alternative Methods for Fluid Delivery and Recovery.
EPA/625/R-94/003.
Vinsome, P.D.W., and G.M. Shook. 1993. Multi-Purpose Simulation. Journal of Petroleum Science and
Engineering. Volume 9. Pages 29-38.
Wade, A., G.W. Wallace, S.F. Siegwald, W.A. Lee, and K.C. McKinney. 1996. Performance
Comparison Between a Horizontal and a Vertical Air Sparging Well: A Full-Scale One-Year Pilot Study.
In: Proceedings of the Tenth National Outdoor Action Conference and Exposition, Las Vegas, Nevada.
National Ground Water Association. Pages 189-206. May 13-15.
Wilson, D. D. 1995a. Introduction to 1995 NGWA Environmental Horizontal Well Seminar. World
Wide Web Home Page (http//:www.horizontalwell.com). October.
Wilson, D.D. 1995b. Environmental Horizontal Well Drilling and Installation Methods. World Wide
Web Home Page (http//:www.horizontalwell.com), by Environmental Consultants, LLC.
5-25
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5.8.2
Professional Contacts
Name
Armstrong, James
(403) 247-0200
Birdwell, Dale
(405) 235-3371
Cox, Bob
(510) 227-1105 x420
Downs, Charlie, Ph.D.
(303) 936-4002
Fournier, Louis B.
(610) 558-2121
Kaback, Dawn
(303) 297-0180 xlll
Kirshner, Marv
Ph: (212) 435-8255
Fx: (212) 435-8276
Alt Ph: (201) 961-6600 x8255
Layne, Roger
1-800-654-6481
Meyer, Eric
(504) 922-4450
Pressly, Nick
(516) 286-5890
Wilson, David D.
(303) 422-1302
: ' "'Affiliation , ' , '> -h'Y '"" '' - "*,'.',:.'
Komex International, Ltd.
Genesis Environmental
OHM, Inc.
Private Consultant, Pollution Prevention Associates
STAR Environmental
Colorado Center for Environmental Management
Port Authority of New York and New Jersey
Ditch Witch, Inc., The Charles Machine Works, Inc.
Radian Corporation, Baton Rouge
Pressly & Associates, Inc.
Horizontal Well and Environmental Consultants, Inc.
5-26
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INFORMATION CENTERS
, ' * Organization *
National Ground Water
Association
1-800-551-7379
Remedial Action Program
Information Center
(423) 241-3098
"Contact Name
Mark Shepherd
x.594
Mary Bales
* " , Services^
Provide database search for issues related to
groundwater
Collect documentation on issues related to
decontamination, decommissioning, and
remediation of sites
5-27
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Ul
tb
oo
SOURCE: MODIFIED FROM WEMPLE AND OTHERS 1994
HORIZONTAL WELL NETWORK
INSTALLED BENEATH A BUILDING TO
REMEDIATE SOIL AND GROUNDWATER
FIGURE
5-1
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10
'' :';/:t?:-Wel:i/ 'Screen-;.;"
Illll Illll Illll II Illll Illll
Illll Illll Illll II Illll Illll
inn inn inn ii mil inn
SOURCE: MODIFIED FROM DIRECTED TECHNOLOGIES DRILLING, INC. 1996
BLIND BOREHOLE COMPLETION
FIGURE
5-2
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(J\
OJ
o
Launch
Pit
SOURCE: MODIFIED FROM DIRECTED TECHNOLOGIES DRILUNG, INC. 1996
CONTINUOUS WELL COMPLETION
FIGURE
5-3
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Directional
Drilling Unit
Exit Pit
SOURCE: MODIFIED FROM DIRECTED TECHNOLOGIES DRILLING, INC. 1996
PILOT HOLE ADVANCEMENT
FIGURE
5-4
-------
(Jl
d>
tsi
Well Screen
and Casing
Directional
Drilling Unit"
-Backreaming Tool
SOURCE: MODIFIED FROM DIRECTED TECHNOLOGIES DRILLING, INC. 1996
BACKREAMING AND WELL
CASING INSTALLATION
FIGURE
5-5
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(A
fe
w
Steering Tool
House
Flex Sub
Drill Bit-
-15' to 20' Nonmagnetic
Drill Rods
Drilling Assembly
Reamer
Drill Rod
Entrance Portal
A
Drill Rod
i i
I V-
Exit Portal
Reaming Assembly
Reamer
Flexible
Link
Pulling
Plug
Drill Rod
SOURCE: MODIFIED FROM WEMPLE AND OTHERS 1994
Reaming and Casing Fullback Assembly
Fiberglass
Casing
TYPICAL DOWNHOLE HARDWARE
FOR DIFFERENT DRILLING PHASES
FIGURE
5-6
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Vertical Sparging Well (ASW-1)
Soil Cos Plume
ฉ
O470
-Centerline of Screened
Portion of Horizontal
Sparging Well (ASW-2)
AMW-131B
AMW-144B
A
El
MW-134B H
I IE!
A A
1400O
\IW-133B
MW-136B,
"Proces?
Building
A
Axis of Groundwater
Contamination Plume
-1000/ig/L-
Groundwater
Plume
Legend
220 C
Soil Vapor Extraction Well
Groundwater Monitoring Well
Soil Gas Monitoring Well
Vertical Air Injection Well
Groundwater Sampling Location and TCE
Concentration (ug/L) in Groundwater at
(Bo
Groundwater Flow Direction
1000/ig/L-
100 Mg XL-
The Water Table (Borehole Sample, Plume
Investigation May to July 1993)
SOURCE: MODIFIED FROM WADE AND OTHERS 1996
Contour of TCE Concentration in
Groundwater Before Pilot Study Began
- Contour of TCE Concentration in
Soil Gas Before Pilot Study Began
NOTE:
Manhole containing contaminated soil, sludge, and liquids was
the suspected source of VOCs in the vadose zone and
groundwater.
0 50' 100'
SCALE: 1" = 100'
HASTINGS EAST INDUSTRIAL PARK SITE PLAN
SHOWING HORIZONTAL AND VERTICAL WELL AIR
SPARGING/SOIL VAPOR EXTRACTIONS SYSTEM
FIGURE
5-7
-------
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TCE Concentration (jJ.g/L~)
-------
Air Sparging Well Location
Soil Vapor Extraction Well
Approximate Extent of
Jet Fuel Contamination
75' 0 75' 150'
Approximate Scale in Feet
SOURCE: MODIFIED FROM THE PORT AUTHORITY OF NEW YORK AND NEW JERSEY 1995
HORIZONTAL WELL LAYOUT FOR AIR SPARGING
AND SOIL VAPOR EXTRACTION AT TERMINAL 1A,
JOHN F. KENNEDY INTERNATIONAL AIRPORT
FIGURE
5-10
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(J\
k
oo
International
Arrivals Building
Air Sparging Well Location
Soil Vapor Extraction Well
Approximate Extent of
Jet Fuel Contamination
o 75' 150'
Approximate Scale in Feet
SOURCE: MODIFIED FROM THE PORT AUTHORITY OF NEW YORK AND NEW JERSEY 1995
HORIZONTAL WELL LAYOUT FOR AIR SPARGING
AND SOIL VAPOR EXTRACTION AT THE INTERNATIONAL
ARRIVALS BUILDING, JOHN F. KENNEDY INTERNATIONAL AIRPORT
FIGURE
*" -1 _J
o-n
-------
HAS1-4
HSVE1-4
Subsurface Pressure in
Inches of Water
Horizontal Air Sparge Well,
Area No. 1, Well No. 4
Horizontal Soil Vapor Extraction
Well, Area No. 1, Well No. 4
Screened Section of Well
Vacuum Monitoring Probe
Pressure Monitoring Probe
Approximate Extent of
Jet Fuel Contamination
International
Arrivals
Building
075' 150'
Approximate Scale in Feet
SOURCE: MODIFIED FROM THE PORT AUTHORITY OF NEW YORK AND NEW JERSEY 1995
AIR SPARGING PILOT TEST, NOVEMBER 1995
AT THE INTERNATIONAL ARRIVALS BUILDING,
JOHN F. KENNEDY INTERNATIONAL AIRPORT
FIGURE
5-12
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r
HAS1-4
HSVE1-4
International
Arrivals
Building
Vacuum in Inches of Water
Horizontal Air Sparge Well,
Area No. 1, Well No. 4
Horizontal Soil Vapor Extraction
Well, Area No. 1, Well No. 4
Screened Section of Well
Vacuum Monitoring Probe
Pressure Monitoring Probe
Approximate Extent of
Jet Fuel Contamination
SOURCE: MODIFIED FROM THE PORT AUTHORITY OF NEW YORK AND NEW JERSEY 1995
75' 0 75' 150'
Approximate Scale in Feet
SOIL VAPOR EXTRACTION PILOT TEST,
NOVEMBER 1995 AT THE INTERNATIONAL ARRIVALS
BUILDING, JOHN F. KENNEDY INTERNATIONAL AIRPORT
FIGURE
5-13
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TABLE 5-1
VENDORS OF HORIZONTAL WELLS AND DIRECTIONAL DRILLING TECHNOLOGY"
(Page 1 of 3)
,' ' * Namcof,Vendor V ';,X
Address, Phone,
Point of .Contact
American Augers, Inc.
(Drill Rig Manufacturer)
135 U.S. Route 42
P.O. Box 814
West Salem, OH 44287
Ph: (419) 869-7107
Fx: (419) 869-7425
1-800-324-4930
Gary Stewart
Davis Horizontal Drilling, Inc.
7204 Timberlake
Mustang, OK 73064
Ph: (405) 376-2702
Fx: (405) 376-3807
Roland Davis
Directed Technologies Drilling, Inc.
1315 South Central Ave, Suite G
Kent, WA 98032
1-800-239-5950
Ph: (206) 850-2848
Fx: (206) 850-2824
mlubrecht@accessone.com
Michael Lubrecht
Directional Drilling, Inc.
P.O. Box 159
Oakwood, GA 30566 or
3536 Atlanta Highway
Flowery Branch, GA 30542
Ph: (770) 534-0083
Fx: (770)531-9553
Jim McEntire
Ditch Witch, Inc., The Charles Machine
Works, Inc.
(Drill Rig Manufacturer)
P.O. Box 66
Perry, OK 73077
Ph: (405) 336-4402
1-800-654-6481
Fx: (405) 336-3458
Roger Layne
Drilex Inc.
15151 Sommermeyer
Houston, TX 77041
Ph: (713) 957-5470
Fx: (713) 957-5483
David Bardsley
Fishburn Environmental Drilling
5013 State Route 229
P.O. Box 278
Marengo, OH 43334
Stuart Brown
5-41
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TABLE 5-1
VENDORS OF HORIZONTAL WELLS AND DIRECTIONAL DRILLING TECHNOLOGY"
(Page 2 of 3)
Name of Vendor
GTS Horizontal Drilling Co.
Horizontal Drilling Technologies
Horizontal Subsurface Technologies, Inc.
Horizontal Technologies, Inc.
Kelly Corp.
KVA Slantwell Installations/KVA
Analytical Systems
Mears/HDD, Inc.
Michels Environmental Services
OHM Remediation Services Group
Pledger, Inc.
Address,, Phone,JEax , " '
1231 B East Main Street, Suite 189
Meriden, CT 06450
1-800-239-8079
2414 S. Hoover Road
Wichita, KS 67215
Ph: (316) 942-3031
634 West Clarks Landing Road
Egg Harbor, NJ 08215
1-800-965-0024
2309 Hancock Bridge Parkway
P.O. Box 150820
Cape Coral, FL 33915
Ph: (204) 544-9462
15 Carlson Lane
Falmouth, MA 02540
Ph: (508) 540-0561
Fx: (508) 457-4810
4500 North Mission Road
Rosebush, MI 48878-0055
1-800-632-7727
Fx: (517) 433-5433
817 West Main Street
(main office)
Brownsville, WI 53006
Ph: (414) 583-3132
Fx: (414) 583-3429
5731 W. Las Positas Blvd
Pleasanton, CA 94588
Ph: (510) 227-1105
12848 SE Suzanne Drive
Kobe Sound, FL 33455
Ph: (407) 546-4848
Fx: (407) 546-3211
Point of .Contact
Tom Bryant
Mark Mesner
Donald Justice
Ken Kelly
Steve or Pat
Dick Gibbs
Tim McGuire
Ph: (303) 423-5761
Fx: (303) 423-1947
Robert Cox
Steve McLaughlin
5-42
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TABLE 5-1
VENDORS OF HORIZONTAL WELLS AND DIRECTIONAL DRILLING TECHNOLOGY0
(Page 3 of 3)
Fhone, Fax
Poiatof Contact
SCHUMASOILฎ
Schumacher Filters America, Inc.
P.O. Box 8040
Asheville, NC 28814
Ph: (704) 252-9000
Fx: (704) 253-7773
Anne Ogg
Stearns Drilling
6974 Hammond S.E.
Dutton, MI 49316
Ph: (616) 698-7770
Fx: (616) 698-9886
Roland Clapp
Trenchless Technology Center
Department of Civil Engineering
P.O. Box 10348
Louisiana Technical University
Ruston, LA 71272
Vermeer Manufacturing
(Drill Rig Manufacturer)
Route 1
P.O. Box 200
Pella,IA 50219
Ph: (515) 628-3141
David Whampler
Note: a This list is not inclusive of all vendors capable of providing horizontal wells and
directional drilling technologies. This list reflects vendors identified who provided
horizontal drilling and support services during the preparation of this report.
5-43
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CHAPTER 6.0
PNEUMATIC AND HYDRAULIC FRACTURING
This chapter discusses pneumatic and hydraulic fracturing technologies used to enhance SVE, as well as
other remediation technologies. Environmental applications of blast fracturing techniques have to date
only been used to enhance a limited number of pump-and-treat methods (Miller 1996) and, therefore, will
not be included in this discussion on SVE enhancement technologies. Interested readers are referred to
the literature citations in the bibliography section for more information on this topic. The following
sections provide an overview of pneumatic and hydraulic fracturing, describe conditions under which the
technology is applicable, contain a detailed description of fracturing methods, highlight performance
data, list vendors that provide pneumatic and hydraulic fracturing services, outline the strengths and
limitations of the technology, and provide recommendations for using the technology.
6.1 TECHNOLOGY OVERVIEW
Pneumatic and hydraulic fracturing are recognized methods adapted from the petroleum industry to
induce fractures to improve the performance of extraction or injection wells. The two enhancement
technologies involve the injection of either gases (typically air) or fluids (either water or slurries) to
increase the permeability of the area around an injection well, thereby allowing increased removal or
degradation rates of contaminants and potentially more cost-effective remediation.
Pneumatic fracturing typically involves the injection of highly pressurized air into soil, sediments, or
bedrock to extend existing fractures and create a secondary network of conductive subsurface fissures
and channels. The enhanced network of fractures increases the exposed surface area of the contaminated
soil, as well as its permeability to liquids and vapors. The pore gas exchange rate, often a limiting factor
during vapor extraction, can be increased significantly as a result of pneumatic fracturing, thereby
allowing accelerated removal of contaminants. Figure 6-1 illustrates in a cross section the effects of
pneumatic fracturing enhanced vapor extraction (EPA 1993a).
In hydraulic fracturing, water or a slurry of water, sand, and a thick gel is used to create distinct,
subsurface fractures that may be filled with sand or other granular material. The fractures are created
through the use of fluid pressure to dilate a well borehole and open adjacent cracks. Once fluid pressure
6-1
-------
exceeds a critical value, a fracture begins to propagate. The fracture continues to grow until injection
ceases or pressure dissipates, the fracture intersects a barrier, a permeable channel or the ground surface,
or the injected fluid leaks out through the boundary walls of the formation being fractured. Fractures
may remain open naturally, or they may be held open by permeable materials, known as "proppants"
(typically sand), injected during fracture propagation. The resultant fracture interval is designed to be
more permeable than the adjacent geologic formation. Figure 6-2 illustrates the shape of hydraulic
fracture in three dimensions and in cross section, as inferred from exposures of fracture created beneath
level ground (Murdoch and others 1990).
Pneumatic and hydraulic fracturing enhancement technologies are most applicable to low-permeability
geologic materials, such as fine-grained soils and over consolidated sediments, including silts and clays,
as well as bedrock. Both technologies can enhance the in situ remediation of any chemical contaminants
usually treated by the specific technology with which fracturing is combined. Pneumatic and hydraulic
fracturing are being developed and used to enhance such remediation technologies as SVE, DPE, in situ
bioremediation including bioventing, oxidation, thermal treatment including hot gas injection, in situ
vitrification, and free product recovery, as well as groundwater pump-and-treat systems.
In general, the costs of pneumatic and hydraulic fracturing are estimated to be roughly equal, although
pneumatic fracturing may be less expensive in some cases since it does not require the added capital
costs of equipment for mixing injection slurries. Unpropped fractures may, however, close with time. In
making price comparisons, users should make certain that vendors provide cost estimates that are based
on comparable remediation activities and include all costs including mobilization. Typically, the factors
that have the most significant effect on the unit price of fracturing are such site-specific factors as
characteristics of the soil, depth of contamination, depth to groundwater, and size of the area of
contamination.
62 APPLICABILITY
The primary application of pneumatic and hydraulic fracturing technologies is to improve the
performance of wells by increasing the flow of air or fluids into or out of the area affected by a well.
Pneumatic and hydraulic fracturing techniques can improve the performance of most in situ remedial
technologies that involve fluid flow. The following subsections describe the applicability of fracturing to
6-2
-------
various geologic conditions, the contaminants of concern, and remediation technologies that can be
enhanced through the use of pneumatic or hydraulic fracturing.
6.2.1
Geologic Conditions
Pneumatic and hydraulic fractures can be created in most naturally occurring materials, from rock to
unlithified sediments or soil. Fracturing techniques have been developed to increase the permeability of
fine-grained soils and rocks, such as silts, clays, and shales, because in situ remediation technologies are
not usually applicable when hydraulic conductivities are less than 1 x 10"4 cm/s or pneumatic
conductivities are less than 1 x 10'5 cm/s (Schuring and others 1995). Figure 6-3 shows general
guidelines for the application of pneumatic fracturing in various geologic materials (Schuring and
others 1995). In formations that have moderate permeabilities, pneumatic fracturing may be useful for
rapid aeration and delivery of supplemental liquids or dry media, though it may not be cost-effective.
To a great extent, geologic conditions control the effectiveness of fractures, which must be significantly
more permeable than the enveloping geologic formation to have a major effect on well discharge or
injection. Therefore, the relative improvement resulting from pneumatic and hydraulic fractures
increases as the hydraulic conductivity or permeability of the geologic formation decreases. Pneumatic
and hydraulic fracturing are most effective in geologic formations containing abundant silt and clay
because they have the lowest initial hydraulic conductivities or permeabilities (EPA 1994; Frank and
Barkley 1995).
The state of stress in a geologic formation will affect the orientation of a fracture once it has propagated
from the borehole. Fracturing is particularly suited to sites underlain by soils in which the lateral
component of stress exceeds the vertical stress applied by the weight of the overburden (such soils are
termed "over consolidated"). Fractures are usually flat-lying if horizontal formation stresses are greater
than vertical stresses, and they tend to be steeply dipping if vertical stresses are greatest. The state of
stress of soils and unlithified sediments depends on several factors, including history of consolidation
and history of wetting and drying. The effect of bedding within a geologic formation can be
unpredictable; fractures follow contacts along interbedded sediments or partings between rock beds in
some cases and crosscut beds in others.
6-3
-------
The strength of the geologic formation plays an important role in determining whether fractures will stay
open naturally or whether they should be filled, or propped, with a granular material, such as sand
(Murdoch and others 1991; EPA 1994; Schuring and others 1995). In general, the strength of
fine-grained soil decreases with increasing water content or decreasing consolidation. Therefore,
fractures may stay open in dry soils but may close when the soil becomes saturated. The stress driving
closure of a fracture is the stress that the geologic formation applies (for a horizontal fracture, the unit
weight of the geologic formation times the depth), plus the amount of suction applied to the fracture
during vapor extraction. Fractures may be propped naturally when soil or rock is strong relative to the
closure stress. However, if strength decreases, depth increases, or suction increases past a critical value,
fractures should be propped with granular materials.
6.2.2
Contaminants
Because pneumatic and hydraulic fracturing technologies are not in themselves remediation technologies,
they are applicable to a wide range of contaminant groups, with no particular target group (Frank and
Barkley 1995; EPA 1994; Schuring and others 1995). The types of treatable contaminants will depend
on the primary technologies used. For example, SVE is applicable to VOCs and SVOCs, and
bioremediation theoretically is capable of degrading any organic compound. Integrating pneumatic and
hydraulic fracturing with those technologies will not change the basic applicability of the technologies,
but it can extend the areal range of treatable contamination. For example, fracturing may make thermal
injection feasible at an SVE site by improving the heat flow and transfer characteristics of the geologic
formation. As a result, SVE could be used to treat compounds with lower vapor pressures that would
otherwise not be suitable for such treatment. Similarly, the ability to inject biological solutions
containing microbes and nutrients directly into a geologic formation may increase the biodegradation rate
and the number of organic compounds that are treatable with bioremediation.
Contaminants that form complexes with the soil matrix are not always remediated effectively with the aid
of enhancement fracturing; however, researchers and developers in both pneumatic and hydraulic
fracturing technologies are rapidly expanding their research efforts to enhance the in situ remediation of
inorganic and non-VOCs. The use of pneumatic or hydraulic fracturing to enhance the remediation of
contaminants from the production of explosives remains inconclusive.
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6.2.3
Technologies Enhanced by Fracturing
The typical application of pneumatic and hydraulic fractures is to improve the performance of wells used
in remediation. Table 6-1 presents examples of in situ remediation technologies that can be enhanced by
fracturing and the benefits of creating fractures (Frac Rite Environmental, Ltd [Frac] 1996). Currently,
enhancement of SVE is the most common environmental application of pneumatic or hydraulic
fracturing. Fracturing also can increase the recovery of free-phase fluids, such as LNAPLs and DNAPLs,
by increasing the discharge of recovery wells. Such applications closely resemble the recovery of oil
from petroleum reservoirs. DPE is the simultaneous recovery of vapor and liquid from wells with
induced fractures near saturated zones. Other common applications of pneumatic and hydraulic
fracturing enhancement include the injection of nutrients or oxygen-bearing fluids into the subsurface to
promote bioremediation.
In addition, the application of pneumatic and hydraulic fracturing as an enhancement for remediation
using electroosmosis is currently under investigation. Injection of graphite into the subsurface can create
fractures that are electrically conductive. This process is similar to maintaining a pressure difference
between two fractures to drive flow except that in fine-grained soils, migration by electroosmosis can be
faster than migration by hydraulic flow. Research currently is also underway to combine fracturing with
in situ vitrification, soil washing, and thermal treatment technologies. The development of such diverse
in situ treatment methods, within targeted zones or specific geologic formations and horizons, may
provide low-maintenance systems that offer major cost reductions, compared with current methods
(Accutech Remedial Systems, Inc. [Accutech] 1996; Frac 1996; FRX Inc. [FRX] 1996).
6.3 ENGINEERING DESCRIPTION
For pneumatic and hydraulic fracturing technologies, the fundamentals of inducing fractures by injecting
gases or fluids into the subsurface are similar (EPA 1994). The following subsections discuss the major
factors that affect the creation of subsurface fractures by injection and provide detailed descriptions of
the specific processes involved in the application of pneumatic and hydraulic fracturing.
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6.3.1
Injection Media
The major considerations that affect the choice of injection media for creating fractures include the
equipment required for injection, safety concerns, the potential to mobilize contaminants, and the ability
to transport solid grains into the fracture.
Air is the primary gas used in creating pneumatic fractures, although other gases have applications under
specific conditions, such as cases in which anaerobic conditions are desired. Air injection requires
relatively simple equipment (EPA 1993a; EPA 1993b). High injection pressures, however, demand
special safety precautions. With air injection, there is relatively little possibility of mobilizing liquid
phases, but there is a strong possibility of mobilizing vapor phases. Local governments may regulate
injection of air into the subsurface. Fine-grained particles or powders can be transported into fractures
by injecting air. However, the ability to transport particles decreases with increasing grain size and
density, an effect that limits the capability to inject significant volumes of coarse-grained materials.
Through research efforts, development of specialized equipment and proppants is currently underway to
improve the transport of proppant, such as sand and other materials, during air injection (EPA 1994;
Accutech 1996).
Creating fractures with water requires relatively simple pumps, although pressures in excess of 700 psi
may be needed to initiate the fracture (EPA 1994). Safety precautions are required because of such
potentially high pressures. In some locations, injection of water is restricted by regulations. Injected
water will have limited effect on the mobilization of vapors, although it may mobilize fluids. In most
cases, the injected water and any fluids mobilized as a result of the injection should be recovered through
the resulting fractures. Water can be used to transport solid grains into a fracture; however, the best
results are achieved through the use of plastic particles that have a density similar to that of water
(EPA 1994).
Guar gum gel is a viscous fluid commonly used in creating hydraulic fractures (Murdoch and
others 1991; Frank and Barkley 1995). Guar gum, a food additive derived from the guar bean, is mixed
with water to form a short-chain polymer with the consistency of mineral oil. Adding a cross linker
causes the guar gum polymer chains to link and form a thick gel capable of suspending high
concentrations of coarse-grained sand. That property makes guar gum gel ideal for filling fractures with
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solid material. An enzyme added to the gel breaks the polymer chains, allowing recovery of the thinned
fluid from the fracture.
Hydraulic fracturing with guar gum requires several specialized pieces of equipment (EPA 1993c). A
mixer is required to blend the gel, cross linker, and enzyme, as well as sand or other solids. The method
also requires a pump capable of handling a slurry that contains high concentrations of granular material.
The safety precautions necessary are similar to those for cases in which pressurized water is used.
Injection of guar gum gel does not affect the mobilization of vapors significantly, but liquids may be
slightly mobilized after the gel breaks down. The fracture confines the gel during injection; therefore,
prompt recovery of the gel should eliminate interaction with pore fluids. Local authorities that regulate
subsurface injection may regulate the injection of guar gum gel, as well. Because in situ organisms
metabolize the organic components of guar gum gel, its use commonly is avoided when fractures are
created to enhance discharge from drinking-water wells. The major benefit of the use of guar gum gel is
its capability to suspend a high concentration of coarse-grained materials, such as sand (10 to 15 pounds
of sand per gallon of gel), as a slurry in the gel (EPA 1994).
6.3.2
Fracturing Equipment
The equipment used to create fractures consists of both an aboveground system that must be capable of
injecting the desired fracture medium at the required pressures and rates and a below-ground system that
must be capable of isolating the zone where injection will take place. The type of medium to be injected
largely determines the specifications of the aboveground equipment. Sections 6.3.8 and 6.3.9 discuss
specific requirements for aboveground equipment for pneumatic and hydraulic fracturing. Both
pneumatic and hydraulic fracturing can use straddle packers that allow spacing of fractures
approximately every 1.5 feet along an open borehole. Straddle packers are appropriate in rock and in
some unlithified sediments.
An alternative to the use of straddle packers during hydraulic fracturing of unlithified sediments is the
driving of a casing with an inner pointed rod to the specified depth (Murdoch and others 1990). After the
rod is removed, a high-pressure pump injects a water jet to cut a notch in the sediments at the bottom of
the borehole. The notch reduces the pressure required to start propagation and ensures that the fracture
starts in a horizontal plane at the bottom of the casing. A fracture can be created at the bottom of the
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casing by injecting a liquid or slurry. After the fracture is created, the rod can be reinserted and driven to
greater depths to create another fracture, or the casing can be left in place for access to the fracture
during recovery. Use of this approach in unlithified sediments allows advancement of the casing by
either hammering (with a drop weight, pneumatic, or hydraulic hammer) or direct pushing (using the
weight of a drill rig or cone penetrometer).
6.3.3
Iiyection Pressure and Rate
The pressure required to initiate a fracture in a borehole depends on several factors, including confining
stresses, toughness of the enveloping geologic formation, initial rate of injection, size of incipient or
existing fractures, and the presence of pores or defects in the borehole wall. In general, the injection
pressure increases with increasing depth, injection rate, and fluid viscosity. For example, propagating a
fracture by injecting a liquid into soil at 20 gallons per minute and at a 6-foot depth requires
approximately 8 to 12 psi of pressure, the pressure required increases approximately 1 psi for each
additional foot of depth. In contrast, the pressure required to create a fracture by injecting air, with
injection rates of 700 to 1,000 cfm, is in the range of 70 to 150 psi (EPA 1994). The pressure during
propagation decreases in most operations; however, the specifics of the pressure history depend on a
variety of factors. For example, slight increases in pressure may occur because of an increase in the
concentration of sand in the slurry during injection.
6.3.4
Fracture Size and Shape
The effectiveness of pneumatic and hydraulic fractures largely depends on the size and shape of the
fracture with respect to the borehole. Propagation could continue indefinitely if the fracture were created
in infinitely impermeable material, but, in real materials, several factors limit the size and shape of
fractures. The volume of injected fluids and the rate at which they are injected are the primary
controllable variables that affect the size of the fracture.
Some of the injected fluid flows out through the walls of the fractures and into the pores of enveloping
soil or rock, a process known as "leakoff" (EPA 1994). The rate of leakoff increases as the fracture
grows and offers more surface area through which the injected fluid can flow. Other factors that affect
the leakoff rate include the relative permeability of the geologic formation and the viscosity and pressure
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of the fluid. The rate of fracture propagation decreases as the rate of leakoff increases, and horizontal
propagation ceases entirely when the leakoff rate equals the rate of injection.
Leakoff generally controls the size of pneumatic fractures. For example, injecting gas at 800 to
1,800 cfm into sandstone for approximately 20 seconds typically results in fractures approximately 20 to
70 feet in maximum dimension (EPA 1994). A longer injection period does not greatly affect the
dimensions of the fracture; however, increasing the rate of injection will generally increase the size of the
fracture. Therefore, in pneumatic fracturing, the rate of injection is a critical design variable that affects
the size of the fracture.
The volume of injected fluid determines the size of the resulting fracture. Maximum dimensions of
fractures created by gases (air) or liquids are limited by the tendency of the fracture to climb and intersect
the ground surface or by the loss of fluid through the fracture walls. The maximum horizontal dimension
of a fracture also increases with increasing depth and decreasing permeability of the formation. At a
depth in the range of 5 to 16 feet in over consolidated silty clay, the typical maximum dimension of a
fracture is approximately 3 to 4 times its depth (EPA 1994).
The shape of a fracture created by pneumatic and hydraulic fracturing largely depends on the fracturing
technique, including the type of fluid used during injection, the rate and pressure of injection, and the
configuration of the borehole, as well as the site conditions (Murdoch and others 1990; Murdoch and
others 1991; EPA 1994; Schuring and others 1995). Critical site conditions that affect the shape of a
fracture include loading at the ground surface from structures, such as buildings, reservoirs, landfills, or
heavy equipment; the permeability and heterogeneity of the geologic formation; and the presence of
subsurface borings. In general, fractures range in shape from steeply dipping, elongated fractures to
flat-lying circular or disk-shaped fractures. The flat-lying fractures are most useful in many
environmental applications because such fractures can grow to significant size without intersecting the
ground surface.
6.3.5
Site Conditions
In addition to geological conditions at a specific site, as discussed in Section 6.2.1, surface and
subsurface structures, such as buildings, pavement, buried utilities, other wells in the vicinity, and
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backfilled excavations, must be considered in the design and creation of effective pneumatic or hydraulic
fractures (EPA 1994; Frank and Barkley 1995; Schuring and others 1995). Inducing fractures beneath
such structures may cause vertical displacement of these structures. Fracturing typically results in
ground surface elevation increases or "heaving" of up to 1 centimeter or more. In cases in which surface
displacements are not desired, real-time monitoring of ground surface elevations is advisable so that the
procedure can be terminated before the structures are significantly displaced.
Surface structures also may affect the propagation of fractures by loading the ground surface. Fractures
created adjacent to buildings most likely will propagate away from the buildings in response to the
surface loading by the structure. Propagation of a fracture may change dramatically or terminate
altogether if the fracture intersects a backfilled excavation or other deep features, such as wells,
piezometers, or grouted sampling holes. The severity of such effects depends on individual site
conditions and can be evaluated only after those specific conditions are known.
6.3.6
Monitoring the Formation of Fractures
The most widely used method of monitoring the location of fractures in the subsurface is measurement of
the vertical displacement of the ground surface (Murdoch and others 1991). Net displacements can be
determined by surveying a field of measuring staffs with finely graduated scales, before and after
fracturing. This method is inexpensive and provides reliable data on final displacements.
As an alternative, tilt sensors that detect changes in electrical resistivity can measure extremely gentle
slopes of the ground surface in real time, while a fracture is being created. Although a complete
description of the deformation includes strain, displacement, and tilt fields, measurements of the tilt field
are the easiest to perform at the very high levels of resolution necessary to provide useful information.
Resistivity measurements and calculation of displacement fields are seldom better than parts per million,
while calculated strain measurements are reliable to parts per 100 million, and tilt can be monitored
routinely at parts per billion (Echo-Scan Corporation [Echo] 1996).
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6.3.7
Well Completion
The type of post fracture well completion affects the flexibility of subsurface control, versatility in
creating additional fractures, and cost. Some methods of completion provide access to each fracture or
group of fractures, while others simultaneously access all the fractures in a well. Individual completions
provide versatility by allowing the use of each fracture or set of fractures for either injection or recovery
of fluids. For example, this method can allow alternating between air inlet and suction of adjacent
fractures or can provide the capabilities of dewatering from lower fractures arid vapor recovery from
upper fractures (EPA 1994). The method also can improve recovery of NAPL because it allows the user
to direct aqueous and nonaqueous phases to separate pumps.
Completion techniques that access all fractures simultaneously resemble standard well completion
methods (Clark 1988). To provide individual access, a grouted zone along the borehole can isolate each
fracture or set of fractures. Individual completions, however, are more costly than simultaneous
continuous screening of all fractures. As an alternative, casings driven to create fractures in unlithified
sediments can be left in place to allow access to the fracture during recovery. In certain cases, it may be
necessary to return to a well to create additional fractures. Additional fractures can be created in wells
that consist of open boreholes, and fracture size can be increased when completions consist of driven
casing. It is difficult to use wells that have already been completed with a screen and gravel pack to
create fractures.
6.3.8
Pneumatic Fracturing
During pneumatic fracturing, wells are typically drilled into the contaminated vadose zone and left
uncased (EPA 1993b; Frank and Barkley 1995). Each well is divided into several small intervals of
about 2 feet using a straddle packer system, as described in Section 6.3.2. Short bursts (about 20 seconds
in duration) of compressed air are injected sequentially into each interval to fracture the adjacent
geologic formation. The fracturing extends and enlarges existing fissures, primarily in the horizontal
direction, and may induce new fractures. Figure 6-4 illustrates the effects of pneumatic fracturing on two
different geologic formations (Schuring and others 1995).
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Pneumatic fracturing requires equipment that rapidly delivers air to the.siubฃurface. Injecting air directly
from a compressor may induce fractures under some circumstances; howey^r,'filters or specialized
compressors may be required to eliminate traces of oil in the air stream. In addition, compressors
typically cannot supply the pressure or the rate that pressurized gas cylinders are capable of. Therefore,
the applicability of such equipment may be limited to relatively permeable formations in which leakoff
limits the size of the fractures created by injection at moderate rates. The most versatile equipment
developed to date employs a series of high-pressure gas cylinders with a pressure regulator to control
injection. Air is injected into the subsurface at rates of approximately 800 to 1,800 cfm and at pressures
of 70 to 300 psi. The process can be tailored to site conditions and is particularly suitable for delivering
air at high rates. Moreover, the method can use gases other than air to create fractures (EPA 1994).
Recent application to saturated zones has provided evidence that the process can also effectively enhance
remediation of saturated zones (Keffer and others, 1996). The characteristics that are changed include an
aquifer's transmissivity, hydraulic conductivity, and relative storage function. When pneumatic
fracturing has been applied to saturated zones containing significant volumes of free product, the
magnitude of the change in product recovery rates has been observed to be several orders of magnitude.
63.9
Hydraulic Fracturing
Figure 6-5 illustrates the steps necessary to create hydraulic fractures (EPA 1993c); 6- or 8-inch
hollow-stem augers are used to drill an initial borehole to just above the fracture interval. Individual
segments of steel rod and casing are threaded together, as required for the depth of the fracture. The tip
of a fracturing lance is driven through the casing to a depth at which the fracture is to be located. Only
the lance is removed, leaving soil exposed just below the bottom of the casing. Water under high ;
pressure is injected through the casing to cut a disk-shaped notch 6 inches outward from the lanced
borehole. The notch serves as the starting point for the fracture. Water is injected into the notch until a
critical pressure is attained and a fracture is created. If the fracture is to be propped, a slurry of water,
sand, guar gum gel, cross linker, and an enzyme breaker is pumped at high pressure into the borehole to
propagate the fracture. The residual gel biodegrades, and the resultant fracture is a highly permeable
sand-filled lens. The process is repeated at varying depths, typically from 5 to 30 feet, to create a stack
of sand-filled hydraulic fractures. Fractures are created in a radius of 10 to 60 feet of the borehole and up
to 1 inch in thickness. The sand-filled fractures serve as avenues for the extraction of soil vapors,
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injection of air, or recovery ofgroundwater and contaminants. These fractures also can improve
pumping efficiency and the delivery efficiency for other in situ processes. Various granular materials,
such as graphite, may be used instead of sand to create fractures that have different properties than sand
within the surrounding formation. Hydraulic fractures injected beneath the water table have shown to
effectively enhance remediation of saturated zones.
The equipment required for hydraulic fractures created by injecting water alone consists primarily of a
high-pressure, positive displacement pump with pressure relief devices (EPA 1994). For hydraulic
fractures filled with sand or other granular proppant, a mixer is needed to create the slurry. Batch mixers
consisting of one or two open tanks fitted with agitators or continuous mixers that blend metered streams
of guar gum gel, cross linker, enzyme breaker, water, and sand can be used to create the slurry.
Continuous mixers require a larger capital investment than batch mixers; however, continuous mixers
reduce the time and labor required to create fractures, thereby reducing the cost. Positive displacement
pumps and duplex and triplex piston pumps, as well as progressive cavity pumps, are used widely to
inject slurries into boreholes.
6.4 PERFORMANCE AND COST ANALYSIS
This section provides recent performance and cost data for remediation technologies enhanced by
pneumatic and hydraulic fracturing during field demonstrations.
6.4.1
Performance
Table 6-2 summarizes selected remediation technologies, technology developers and vendors, site
locations and geologic formation types, contaminants treated, and the results of field performance tests.
Four of these field demonstrations are discussed as case studies in greater detail below.
6.4.1.1
Pneumatic Fracturing Enhancement of SVE and Hot Gas Injection in Shale
Pneumatic fracturing combined with SVE and hot gas injection was evaluated under EPA's SITE
demonstration program as a means of remediating a contaminated vadose zone overlying contaminated
groundwater at an industrial park in Somerville, New Jersey (EPA 1993a; EPA 1993b; EPA 1995;
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Accutech 1996). The geologic formation consists of 4 to 6 feet of weathered shale overlying fractured
shale bedrock. Contaminants of concern are VOCs and SVOCs, including TCE, PCE, and benzene.
The remedial action objectives of this demonstration were to increase the permeability of the vadose zone
formations by creating new horizontal fractures or enlarging existing fractures, determine the effect of
fracturing on the rate of removal of VOCs, and evaluate the effects of hot gas injection on the transfer of
heat through the formation and on the rate of removal of VOCs through vapor extraction. Fracture wells
were drilled into the contaminated vadose zone to a depth of approximately 20 feet. To create an
intensely fractured vadose zone, short bursts of air were injected at successive intervals of depth of the
fracture wells. Each injection extended and enlarged existing fractures in the formation and created new
fractures, primarily in the horizontal direction.
Pneumatic fracturing increased the flow of extracted air by 400 to 700 percent compared with rates
achieved before fracturing. Even greater increases in the rate of extracted air flow (190 times) were
observed when one or more of the monitoring wells were opened to serve as passive air inlets to the
formation. The effective area of influence was observed to increase from approximately 380 square feet
to at least 1,250 square feet, more than a threefold increase. Pressure data, collected at perimeter
monitoring wells and measurements of surface heave indicate that the propagation of fractures extended
past the most distant monitoring wells to at least 35 feet.
Figure 6-6 compares TCE mass flow rates over a 4-hour test before and after pneumatic fracturing. Even
though concentrations of TCE in the air stream remained approximately constant before and after
fracturing at approximately 50 mg/kg, the increased rate of air flow resulted in an increase in TCE mass
removal of 675 percent (EPA 1993a). When wells were opened to passive air inflow, the increase in
TCE mass removal was 23,000 percent after pneumatic fracturing. In addition, chemical analysis of the
extracted air during post-fracturing tests showed high concentrations of organic compounds that had been
detected in only trace amounts before fracturing. Therefore, pneumatic fracturing effectively opened
access to pockets of VOCs that previously had been trapped.
The effect of the injection of hot gas into the fractured formation, in terms of heat transfer, air flow,
volatilization, and TCE mass removal, were inconclusive. In one experiment, increases in well
temperature (to approximately 65 to 85ฐ Fahrenheit) were observed, but TCE mass removal decreased.
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A second experiment provided^ contradictory results: increased TCE mass removal rates at increased
injected (and extracted) air flow rates were observed, but no elevated temperatures were measured in the
extraction wells. The presence of perched water in the wells may explain some of the inconsistencies in
the air flow rate and temperature results from the hot gas injection experiments conducted during the
demonstration.
6.4.1.2
Pneumatic Fracturing Enhancement of SVE in Clay
Pneumatic fracturing combined with SVE was demonstrated at an abandoned tank farm in Richmond,
Virginia (EPA 1993a; Schuring and others 1995). The geologic formation at the site consisted of highly
over consolidated clays overlain by clayey silts. The aboveground tanks had been removed, and only a
6-inch-thick slab of concrete remained. Soil samples from the vadose zone beneath the slab showed two
principal VOCs in the clay: methylene chloride and trichloroethane (TCA). VOC concentrations, as
determined by headspace analysis of spoon samples and gas chromatograph analysis of soil samples,
ranged up to 8,500 mg/kg and 485 rag/kg, respectively. An adjacent sump appeared to be the source of
the contamination.
The remedial action objectives for this demonstration were to increase the permeability of the clay
formation and to evaluate the effects of the enhancement on the removal of VOCs by SVE. Baseline
conditions were established for flow rates of air extraction and removal of contaminants. Initial flow
rates were less than 0.00071 cubic feet per minute. Figure 6-7 shows that removal concentrations for
both contaminants peaked at approximately 23 mg/kg and neared nondetectable levels after 35 minutes
(EPA 1993a) before pneumatic fracturing.
All fracture injections were made between 5 and 10 feet below the surface of the concrete slab within the
clay horizon. During pneumatic injection, surface heave was measured at more than 1 inch in some
areas. Although the concrete slab did deflect some of the injection influence, fractures were detected
beneath the concrete slab using surface measurements. Following the pneumatic fracture injections, the
permeability of the formation increased substantially, as indicated by a 4,900 percent increase in flow
rates of extracted air. Post fracture concentrations of contaminants extracted peaked at 8,677 mg/kg for
methylene chloride and 4,050 mg/kg for TCA, as Figure 6-8 shows. The concentration of methylene
chloride leveled off to approximately 200 mg/kg, which remains far higher than the concentrations
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detected before pneumatic fracturing (EPA 1993a). The results indicated that pneumatic fracturing
significantly increased the removal rate of contaminants in low permeability soils.
6.4.1.3
Hydraulic Fracturing Enhancement of DPE in Clayey Silts
Hydraulic fracturing was used to enhance the extraction of hydrocarbon condensate using pneumatic
pumps and free-phase hydrocarbons from contaminated groundwater underlying a former gas plant and
compressor station in northwestern Alberta, Canada (Frac 1996). Condensate discharged to a flare pit at
the facility had contaminated soil and groundwater, both on site and a considerable distance beyond the
property boundary. Contaminated soils consist of clayey silts and silty, fine sands at a depth of
approximately 20 to 40 feet. The groundwater table is located at 30 feet bgs. Free-phase hydrocarbon
condensate was identified on the groundwater surface at apparent thicknesses greater than 10 feet.
The remedial action objectives for this project were to mitigate further contaminant migration and
recover the hydrocarbon condensate and free-phase hydrocarbons in a cost-effective manner and thereby
reduce the risks to an acceptable level. Forty-eight fractures (six fractures per well) were created at the
site. A surfactant was incorporated into the sand-laden fracture fluid to assist in the mobilization of
hydrocarbons to the extraction wells by improving its relative permeability to water.
Echo of North Carolina provided noninvasive, near-real-time monitoring and mapping of the hydraulic
fracturing process with surface sensors. Maps of 30 hydraulic fractures over a 72-hour period were
provided shortly after the fractures were created. Maps of the induced fractures provided the basis for
optimizing the number and pattern of wells and the fracture design and execution for the remainder of the
contaminated area (Echo 1996).
Table 6-3 compares average permeability (K values), zone of influence, and hydrocarbon condensate
recovery rates in gallons per day before and after fracturing. Hydraulic conductivity before fracturing
was calculated from an average of results of rising head and aquifer pumping tests, and hydraulic
conductivity after fracturing was calculated from an average of values from aquifer pumping and
recharge tests.
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The hydraulic fracturing program at this site successfully induced fractures 0.02 to 0.07 inches in
thickness and improved the zpne of influence by a factor of four. After fracturing, the hydraulic
conductivity increased by 1 order of magnitude, and the volumetric rate of hydrocarbon condensate
recovered increased by a factor of approximately seven. Liquid recovery rates were approximately
6 times greater after fracturing, and the proportion of hydrocarbon condensate removed increased from
18 to 77 percent in the fractured wells. Another result was the relatively rapid rate of postpumping
recharge of the hydrocarbon condensate in the fractured wells, compared with that for a nonfractured
well. For example, within 24 hours of the time the pump was turned off at a fractured well, the thickness
of condensate had returned to approximately 50 percent of the original thickness, while the condensate in
a nonfractured well recovered only 25 percent of its original thickness over the same period.
Using a high-suction MPE system, the rate of removal of hydrocarbon vapor was improved from
2.9 kg/day to more than 200 kg/day in the fractured well, and the radius of vacuum influence typically
doubled from 7 to 13 meters (23 to 43 feet). The hydraulic gradient and drawdown measured in one area
of the facility indicate that plume capture in that area has been reasonably effective as a result of the
remediation efforts. The influence of SVE was much greater when applied at fractured wells than at
unfractured wells, and MPE was much more efficient than SVE or conventional pumping in removing
condensate.
6.4.1.4
Pilot-Scale Testing of Hydraulic Fracturing at Linemaster Switch Superfund Site
Pilot-scale testing of hydraulic fracturing at the Linemaster Switch Superfund Site in Woodstock,
Connecticut, was conducted to assess the capability of fracturing to enhance SVE and groundwater
extraction (FRX 1996; Fuss and O'Neill, Inc. 1996). The site is contaminated with TCE, paint thinner,
and other VOCs used at the facility. The contaminants penetrated the underlying 40 feet of clay soil and
entered a weathered bedrock system that serves as a drinking-water aquifer for the area. Pump-and-treat
operations have stabilized the contaminant plume in the aquifer, but the contaminated clay soils are a
persistent source of groundwater contamination.
The objectives for this pilot-scale study included demonstrating the ability to propagate fractures,
estimating the effect of fracture heave on the facility, evaluating fluid recovery rates before and after
fracturing, and evaluating the full-scale feasibility of hydraulic fracturing at the site.
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Two hydraulically fractured recovery wells were installed, with four fractures in one well and eight in the
other. Fractures were spaced at approximately 10-foot increments, beginning at 8 feet bgs for the first
well, and at 5-foot increments for the second well, also beginning at 8 feet bgs. The fractures were
propped with a guar gum gel and sand slurry.
The feasibility of propagating the fractures was demonstrated through the use of uplift maps and the
detection of sand in split-spoon samples. Field tests before and after fracturing, as well as modeling of
groundwater and air flow rates, showed that post-fracture groundwater extraction rates were
approximately 4 to 6 times greater than those in conventional wells at the site. Figure 6-9 shows the
cumulative amount of groundwater removed in gallons before fracturing, and Figure 6-10 shows the total
flow after hydraulic fracturing. The results indicate that hydraulic fracturing increased the groundwater
extraction rate by approximately 10 times. In addition, extracted air flow rates were higher than
expected.
6.4.2
Cost Analysis
This section provides data on the cost of pneumatic and hydraulic fracturing and describes how those
costs are determined so that reasonable cost estimates can be made for similar contaminated sites. Two
cost scenarios are presented below, one for pneumatic fracturing and the other for hydraulic fracturing.
6.4.2.1
Costs of Pneumatic Fracturing
Since pneumatic fracturing has been commercialized only recently, data on production costs are limited.
The costs presented here are drawn from the SITE demonstration project conducted by Accutech in
Somerville, New Jersey. An economic analysis of the costs of the demonstration enabled the projection
of annual operating costs for a full-scale remediation effort under similar conditions. Table 6-4
summarizes the cost categories that were considered and the percentage of the total cost that each
subcategory represents (EPA 1993a). The three major factors in determining costs were labor, capital
equipment, and emissions control. The cost figures include several assumptions that were made
regarding TCE removal rates at the Somerville site; the reader is advised to refer to vendors and the
literature cited for an in-depth analysis of the cost projections for specific sites.
6-18
-------
For Accutech's pneumatic fracturing and vapor extraction process, the cost for 1 year of operation, during
which 2,660 pounds of TCE were removed, is estimated at $371,364, or approximately $140 per pound
of TCE removed (EPA 1993a). A direct comparison with conventional vapor extraction was not made
because conventional vapor extraction would not have been possible at the site without fracturing. In
cases like this, potential cost savings can be weighed against the cost of excavating the site and hauling
away the contaminated soil or rock. Present costs of excavation and hauling range from $200 to $800 per
yd3 (Schuring and others 1995).
In general, the cost of pneumatic fracturing will vary with the size of the project and the conditions at the
site. On the basis of 1995 projections, the incremental production cost of pneumatic fracturing in excess
of primary remediation is expected to range from $8 to $20 per yd3 of soil or rock fractured (Schuring
and others 1995). Volume measurements are made by multiplying the treatment area by the height of the
actual fracture zone. For example, if a 500-foot by 500-foot site is to be fractured, starting at a depth of
10 feet and extending down to a depth of 20 feet, the volume and cost would be:
Volume = [500 ft x 500 ft x (20 ft-10 ft)]/27 ft3 per yd3 = 92,593 yd3
Cost range = 92,593 yd3 x $8 to $20 = $740,740 to $1,851,852.
The cost of applying pneumatic fracturing to a site must be weighed against the potential cost savings
and other factors. The use of pneumatic fracturing reduces both the capital costs and the operating costs
of remediation projects, primarily because the technology enhances formation permeability. Because the
zone of influence of each extraction well is increased, the well spacings can be increased and thus, the
number of wells required for remediation is reduced. For example, at a site that has an initial low
permeability, wells for standard vapor extraction may be spaced on a grid of 10 feet. With fracturing, the
spacing probably could be increased to as much as 20 to 25 feet. At a spacing of 20 feet, a savings of as
much as 75 percent in the cost of drilling wells could be realized. At a spacing of 25 feet, the savings
would range as high as 84 percent (Schuring and others 1995).
The direct application of pneumatic fracturing to the zones of contamination speeds up the rate of mass
removal, typically reducing the time required for remediation. A savings in operation costs therefore, can
be realized. For example, if the treatment time is reduced from 10 years to 5, potential savings in
6-19
-------
operation costs, in present dollars, are 36 percent (calculated at a compound annual interest rate of
12 percent). If the remediation time is reduced to 3 years, potential savings in operation costs increase to
57 percent. Therefore, although annual costs may be slightly higher with some pneumatic fracturing
systems, the removal efficiencies result in life-cycle costs that are 2 to 3 times lower than conventional
remediation technologies, such as pump-and-treat (Green and Dorrler 1996).
6.4.2.2
Costs of Hydraulic Fracturing
Economic data for hydraulic fracturing are even more limited than those for pneumatic fracturing;
however, many of the principles discussed above also apply to hydraulic fracturing. Table 6-5 shows
cost data obtained from EPA's SITE demonstration of hydraulic fracturing conducted at Oak Brook,
Illinois, in 1993 and used to determine estimated costs of hydraulic fracturing at other hazardous waste
sites (EPA 1993c). Again, the reader is cautioned to keep in mind the implications of the assumptions
made in the SITE demonstration report when applying the cost figures to other remediation sites. The
reason to be cautious is because five cost categories out of the 12 typically associated with cleanup
activities at Superfund and RCRA-corrective action sites were not applicable to the hydraulic fracturing
technology demonstration. The cost categories included start-up costs, utility costs, effluent and
treatment disposal, residuals and waste shipping and handling, equipment maintenance, and
modifications.
Capital equipment costs for this project included the costs for an equipment trailer on which the slurry
mixer, pumps, tanks, and hoses were mounted; a fracturing lance with a wellhead assembly; a pressure
transducer and display; and uplift survey instruments. The total capital equipment cost was $92,900.
The cost of rental of capital equipment assumes 30 rentals per year and depreciation of the capital costs
over 3 years. Supplies and consumables include sand, guar gum gel, enzyme, and diesel fuel or gasoline
for operating the pumps. The total cost per fracture was estimated at approximately $950 to $1,425.
Other factors that influence the cost of hydraulic fracturing include preferences of the client and
mobilization charges that will vary depending on the scale of the remediation project. In general, in
1996, the cost of hydraulic fracturing ranges from $1,500 to more than $2,500 per fracture (FRX 1996;
Frac 1996). That cost may be small in light of the benefits of enhanced remediation and the reduction in
the number of wells needed to complete remediation.
6-20
-------
6.5
VENDORS
Many companies are involved in various aspects of pneumatic and hydraulic fracturing, including
equipment, installation, and operation. Vendors of pneumatic and hydraulic fracturing used for the
development of this report are identified in Tables 6-6 and 6-7.
6.6 STRENGTHS AND LIMITATIONS
The following list outlines some of the strengths of using pneumatic and hydraulic fracturing
technologies for environmental remediation:
Pneumatic and hydraulic fracturing can increase well discharge many times over discharge rates
achieved with conventional, unfractured wells.
The relative increase in performance is greatest in the tightest formations, where the performance
of conventional wells is poorest.
In low-permeability formations, pneumatic and hydraulic fractures can improve the performance
of hydraulic control and containment at a site, or they can be combined with other remediation
technologies to accelerate recovery.
Solid compounds that improve the remedial process, such as nutrients or electrically conductive
compounds, can be delivered to the subsurface.
In SVE applications, changes in soil vacuum applied to horizontal fractures can induce controlled
communication between horizontal fractures, by creating vertical or inclined fractures between
the horizontal ones.
The following list outlines some of the limitations of using pneumatic and hydraulic fracturing
technologies for environmental remediation:
Pneumatic and hydraulic fracturing may not solve all the problems of remediation in tight
formations.
Fracturing is ineffective in normally consolidated soils and sediments in which the horizontal
stress is less than the vertical stress.
The presence of water decreases the efficiency of SVE; therefore, fracturing to enhance SVE is
best suited to unsaturated, over-consolidated geologic formations that have low permeabilities.
6-21
-------
Table 6-7 compares pneumatic and hydraulic fracturing (FRX 1996; Keffer and others 1996).
6.7 RECOMMENDATIONS
To apply pneumatic and hydraulic fracturing effectively, a good understanding of the basic principles of
fracturing is helpful (see Sections 6.2 and 6.3). Pressures required to initiate and sustain subsurface
fractures are difficult to predict because they are a complex function of depth of overburden, tensile
strength of the soil matrix, fluid pore pressure, and matrix stresses in the soil. Therefore, thorough site
characterization is necessary since fracturing may be an unnecessary step at sites with high natural
permeabilities. In addition, because of the great variability of geologic materials, the conduct of
pilot-scale field tests is advisable before implementation of full-scale fracturing installations.
Specific variables to consider when implementing fracturing to enhance fluid flow will vary depending
on the intended application of the pneumatic or hydraulic fractures to be created (EPA 1994). For
example, when fractures are to be induced for SVE remediation, design variables that must be considered
are the selection of proppants and well completion specifications. In addition, simultaneous recovery of
vapor and liquid is inevitable when extracting near-saturated zones and may occur when accelerating the
recovery of liquids by placing a vacuum on a well. Such a dual-phase recovery approach requires the use
of a well that has an inner tube attached to the vacuum pump so that the system induces vapor flow
during normal operations and also aspirates and removes any liquid that enters the well. For steam
injection applications, wells require steel rather than plastic casing because of the high temperature of the
steam. For the enhancement of bioremediation, the rate of injection of nutrients, oxygen-bearing fluids,
or simply ambient air must be considered to optimize the performance of the treatment.
The effects of pneumatic and hydraulic fracturing on nearby structures and utilities depend on the type of
construction and on the amount of deformation of the ground. Experience with fracturing in the vicinity
of structures is limited; therefore, caution is recommended when fracturing in close proximity to
structures. Geotechnical analyses should be performed to establish tolerable movements for a particular
project, and the fracture injections should be designed appropriately (Schuring and others 1995).
For hydraulic fracturing, design considerations must ensure that fractures are not spaced vertically so
close to one another that adjacent fractures intersect. Likewise, the fracture wells must be spaced
6-22
-------
sufficiently far apart laterally to prevent the intersection of fractures from adjacent wells. The sand in a
fracture should be thick enough to provide a large contrast with the permeability of the geologic
formation. However, once the sand in a fracture is several millimeters thick, creating a thicker sand pack
to obtain additional contrast provides only minor improvement in well performance. Therefore, a
decision must be made whether the cost of additional sand is worth the incremental benefit achieved by a
thicker fracture (EPA 1994).
6.8 REFERENCES
This section includes references cited in Chapter 6 (Subsection 6.8.1) and a list of professional experts in
the fields of pneumatic and hydraulic fracturing (Subsection 6.8.2), while a comprehensive bibliography
is included in Appendix B.
6.8.1
Cited References
Accutech Remedial Systems, Inc. 1996. Pneumatic Fracturing Project Summaries and Photographs
Submitted by Mike Galbraith. Keyport, NJ. August 5.
Clark, L.J. 1988. The Field Guide to Water Wells and Boreholes. John Wiley and Sons, Inc., New
York. Page 155.
Echo-Scan Corporation. 1996. Fracture Monitoring and Mapping Project Summaries Submitted by
M. Deryl Wood. Gary, NC. August 16.
Frac Rite Environmental Ltd. 1996. Hydraulic Fracturing Project Summaries Submitted by Gordon H.
Bures. Calgary, Canada. July 31.
Frank, U. and N. Barkley. 1995. Remediation of Low-permeability Subsurface Formations by
Fracturing Enhancement of Soil Vapor Extraction. Journal of Hazardous Materials, Volume 40. Pages
191-201.
FRX Inc. 1996. Hydraulic Fracturing Project Summaries and Photographs Submitted by William W.
Slack and Larry C. Murdoch. Cincinnati, OH. July 24.
Fuss and O'Neill, Inc. 1996. Hydraulic Fracturing Project Summary Submitted by David L. Bramley.
Manchester, CT. July 12.
Green, S.R. and R.C. Dorrler. 1996. Four Bullets Shoot down Costs: Combined Technology Approach
Cleans up Faster and Cheaper than Pump-and-Treat. Soil and Groundwater Cleanup. March.
6-23
-------
Keffer, E.B., J.J. Liskowitz, and C.D. Fitzgerald. 1996. The Effect of Pneumatic Fracturing When
Applied to Groundwater Aquifers. In: Proceedings of the Sixth West Coast Conference on
Contaminated Soils and Groundwater. Pages 1-21.
Miller, R.R. 1996. Blast-Enhanced Fracturing. Technology Summary Report. TS-96-01. Ground-
Water Remediation Technologies Analysis Center. Pittsburgh, PA.
Murdoch, L.C., G. Losonsky, I. Klich, and P. Cluxton. 1990. Hydraulic Fracturing to Increase Fluid
Flow. In: F. Arendt and Others, eds. Contaminated Soil. Kluwer Academic Publishers, Netherlands.
Pages 1087-1094.
Murdoch, L.C., G. Losonsky, P. Cluxton, B. Patterson, I. Klich, and B. Braswell. 1991. Feasibility of
Hydraulic Fracturing of Soil to Improve Remedial Actions. Project Summary. EPA/600/S2-91/012.
>
Schuring, J.R., P.C. Chan, and T.M. Boland. 1995. Using Pneumatic Fracturing for In-situ Remediation
of Contaminated Sites. Remediation. Spring. Pages 77-89.
U.S. Environmental Protection Agency (EPA). 1993a. Accutech Pneumatic Fracturing and Hot Gas
Injection, Phase 1. Application Analysis Report. EPA/540/AR-93/509. Office of Research and
Development, Washington, DC.
EPA. 1993b. Technology Evaluation Report: Accutech Pneumatic Fracturing Extraction and Hot Gas
Injection, Phase 1. Volume 1. EPA/540/R-93/509. Office of Research and Development, Cincinnati,
OH.
EPA. 1993c. Applications Analysis and Technology Evaluation Report. Hydraulic Fracturing
Technology. EPA/540/R-93/505. Office of Research and Development, Washington, DC.
EPA. 1994. Alternative Methods for Fluid Delivery and Recovery. Manual. EPA/625/R-94/003. Office
of Research and Development, Washington, DC.
EPA. 1995. In Situ Remediation Technology Status Report: Hydraulic and Pneumatic Fracturing.
EPA-542-K-94-005. Office of Solid Waste and Emergency Response, Technology Innovation Office,
Washington, DC.
6.8.2
Professional Contacts
Table 6-6 presents information that is useful in determining the capabilities of vendors in enhancing
SVE, as well as other remediation technologies using pneumatic and hydraulic fracturing technologies.
Listed below are the names and telephone numbers of well-known experts and developers in pneumatic
and hydraulic fracturing technologies, respectively.
6-24
-------
^fe^::^^$fBr^l
li&SIHgfli|^ Affiliation' , , , ,,'-,'
Pneumatic Fracturing
Uwe Frank
(908) 321-6626
John Schuring, Ph.D.
(201) 596-5849
David Kosson, Ph.D.
(908) 445-4346
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Hazardous Substance Management Research Center
New Jersey Institute of Technology
Department of Chemical and Biological Engineering
Rutgers, The State University of New Jersey
Hydraulic Fracturing
Michael Roulier, Ph.D.
(513) 569-7796
Larry C. Murdoch, Ph.D.
(864) 656-2597
William W. Slack, Ph.D.
(513) 556-2526
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Department of Geology
Clemson University
Center for Geo-Environmental Science and Technology
University of Cincinnati, Engineering Research Division
6-25
-------
Air
Existing Soil
Fractures
Minimal Extracted Air Flow
Minimal Existing Fractures
NAPL Pockets Remaining After Treatment
Slow, Incomplete Contaminant Removal
Multiple Extraction Wells Required
VAPOR EXTRACTION IN NORMAL "TIGHT" FORMATION
Air Pressure
Surge
Increased Extracted Air Flow
Multiple Fractures Created or Enlarged
NAPL Pockets Accessed During Treatment
More Rapid VOC Removal
Minimum Number of Extraction Wells
Soil Fractures After
1' Pneumatic Fracturing
PNEUMATIC FRACTURING ENHANCED VAPOR EXTRACTION
SOURCE: MODIFIED FROM EPA 1993c
SCHEMATIC OF PNEUMATIC FRACTURING
ENHANCED VAPOR EXTRACTION
FIGURE
6-1
6-26
-------
Load due to
Weight of Backhoe
OBLIQUE VIEW
Load due to
Weight of Backhoe
ZONE 4
Vent to Surface
ZONE 2
Horizontal fracture
ZONE 3
Inclined fracture
ZONE 1
Vertical fracture
Vent to Surface
CROSS SECTION ALONG MAJOR AXIS OF THE FRACTURE
SOURCE: MODIFIED FROM MURDOCH AND OTHERS 1990
SCHEMATIC OF
HYDRAULIC FRACTURING
FIGURE
6-2
6-27
-------
TYPES OF TREATABLE SOIL AND ROCK
Natural Pneumatic Conductivity (cm/sec)
10
-2
10"
Soil Type
Sand
10
-6
10
-8
Fine Sand
Silt
Highly
Fractured
oo
Apply Pneumatic Fraturing
For Rapid Aeration (Aerates Pores)
Moderately
Fractured
Clay
Slightly
Fractured
Apply Pneumatic Fracturing
To Improve Air Permeability (Creates Fractures)
Note:
To convert from pneumatic conductivity to hydraulic conductivity,
multiply by 30. For example, if Kp=1.0 x 10 cm/sec, the
corresponding Kh=3.0 x 10~4 cm/sec.
SOURCE: MODIFIED FROM SCHURING AND OTHERS 1995
( ?.-
APPLICATION GUIDELINES FOR
PNEUMATIC FRACTURING
FIGURE
6-3
-------
ON
Note:
Alternatives for compressed air source are
compressed gas cylinders or compressor with
receiver tank.
o o
D CO
BEFORE FRACTURE AFTER FRACTURE
(Diffusion Controlled) (Convection & Diffusion Controlled)
DETAIL "Af
Vapor Movement in Soil Microstructure
FINE-GRAINED SOILS
SOURCE: MODIFIED FROM SCHURING AND OTHERS 1995
See Detail "B
BEFORE FRACTURE
AFTER FRACTURE
Existing
Discontinuities
Joint
Filling
Joint
Filling
Partially
Cleared
DETAIL fB"
Effect of Fracturing on Rock Discontinuities
ROCK FORMATIONS
Aperture
Widened
EFFECTS OF PNEUMATIC
FRACTURING
FIGURE
6-4
-------
1
Casing
1
-Cop
Rod
Lance tip
Steel tubing
-Water
-Cutting jet
SOURCE: MODIFIED FROM EPA 1993b
Extension
rod
, Removal
of lance
-Sand slurry
Pressure from soil
seals casing
'ivx- Notch
Fracture
SEQUENCE OF OPERATIONS FOR
CREATING HYDRAULIC FRACTURES
FIGURE
6-5
-------
ON
180-
170-
160-
150-
140-
130-
^ 120-
^ 110-
"o 100-
S 90-
o
" BO-
CO
1 70-
^ 60-
50-
40-
30-
20-
10-
o-
(
\
\
\
\
\
\
\
\
\
. Postfracture
Prefracture Restart
Prefracture
I I I I I I I I I I I I
) 20 40 60 80 100 120 140 160 180 200 220 240
Elapsed Time (Minutes)
SOURCE: MODIFIED FROM EPA 1993a
COMPARISON OF TCE MASS REMOVAL
ENHANCED BY PNEUMATIC FRACTURING
FIGURE
6-6
-------
Zฃ-9
I
0
o o
m
33
>
re
Q
CD
D
Q.
Concentration (mg/kg)
n> o
o >
M co
m O
O
O
ง
3
0)
(0
w
-------
ฃฃ-9
o
o
z m
ฐo
5o
CO
Concentration (mg/kg)
a> O
o >
M on
rn O
o
a
0)
o
o
o
(D
Q
O
O
? ~
9- o-
^- =1
3
0)
(D
CO
-------
o\
tn
o
O
CD
D
T3
C
O
O
8,000-.
7,000-
6,000-
5,000-
4,000-
3,000-
2,000-
1,000-
0-
100 200 300 400 500 600 700 800
Time (Hours)
SOURCE: MODIFIED FROM FUSS AND O'NEILL, INC. 1996
CUMULATIVE GROUNDWATER REMOVAL
BEFORE HYDRAULIC FRACTURING
FIGURE
6-9
-------
se-9
O
c
"^ r=
H >
s|
x m
o O
> O
El
O
O) 3]
I CD
' f C
O33
m
X)
m
S
O
<
>
Groundwater Removed (Gallons)
3
CD
O
-------
TABLE 6-1
REMEDIATION TECHNOLOGIES ENHANCED BY FRACTURING
(Page 1 of 1)
Contaminated
Media
Soil
Groundwater
Remediation
Technology
Soil vapor extraction
Dual vapor-phase
extraction
Bioremediation
Soil flushing
Electroosmosis
Thermal treatment
Vitrification
Pump and treat
Free product
recovery
Bioremediation
Air sparging
Chemical treatment
Physical treatment
Technology Description
Removal of VOCs from unsaturated zone soils using subsurface air flow
Removal of VOCs simultaneously from both soils in the saturated and
the unsaturated zones
Injection and infiltration of fluids, including air, into soils to enhance
biodegradation of subsurface residual contaminants
Injection and infiltration of solutions such as solvents or surfactants to
concentrate contaminants into the liquid phase to enhance pump and treat
Migration of contaminants in the subsurface through the application of
an electric field
Removal of contaminants through volatilization into the gas phase by
both vapor-liquid equilibrium effects and heat
Subsurface containment of contaminants through melting of soils to form
a stable glass structure with low leaching characteristics
Removal of contaminated groundwater or immiscible contaminants and
subsequent treatment or reprocessing
Removal of free-phase contaminants from an aquifer
Injection and infiltration of fluids into the saturated zone to enhance
biodegradation of dissolved contaminants
Injection of air into the saturated zone to remove organic contaminants
by volatilization and biodegradation
Injection of chemical reagents to the saturated zone to enhance the
chemical treatment of contaminants, for example, oxidation/reduction
Injection of hot air or steam to enhance the physical treatment of
contaminants, for example in situ heating and air stripping
Benefits of Fracturing
Greater access to contaminants, increased removal rates, and fewer
wells
Greater access to contaminants, increased removal rates, and fewer
wells
Improved fluid injection and infiltration rates, as well as improved
access of microbes to contaminants
Improved injection and infiltration, as well as improved recirculation
rates
Fractures act as contaminant collection pathways
Greater permeability for heat distribution and volatilization
Greater permeability for heat distribution and melting
Larger capture zone, greater recovery rates, and fewer wells required
Larger capture zone, greater recovery rates, and fewer wells required
Improved fluid injection and infiltration rates, as well as improved
access of microbes to contaminants .,',-'
Increased delivery of air, greater rates of biodegradation and removal
of volatile compounds, and fewer injection wells required
Improved access to contaminants and greater injection rates
Greater in situ flow rates
CA
Source: Modified from Frac Rite Environmental, Ltd. 1996.
-------
TABLE 6-2
SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES
ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING
(Page 1 of 4)
Technology ^" "' ,
Pneumatic Fracturing and
SVE with Hot Gas Injection
Pneumatic Fracturing
and SVE
Pneumatic Fracturing and
DPE
Pneumatic Fracturing and
Fuel Recovery
Pneumatic Fracturing and
In Situ Bioremediation
Pneumatic Fracturing and In
Situ Bioremediation
Pneumatic Fracturing
and SVE
Pneumatic Fracturing
and SVE
Developer or
' Vendor ?'; <
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
' . - ^fe '<-v
'Location-'' 4-
Somerville, New
Jersey
Santa Clara,
California
Highland Park,
New Jersey
Oklahoma City,
Oklahoma
Oklahoma City,
Oklahoma
Flemington, New
Jersey
Columbia City,
Indiana
Coffeyville,
Kansas
, -" .Geologic :
IbrmattoriType
Shale
Silty clay, sandy
silts, and clays
Shale
Shale and
sandstone
Sandy, silty shale,
and clay stone
Shale
Clay
Silty clay
\ Contaminants i
' ,*':.. Treated; '/.
VOCs, primarily TCE
VOCs, primarily TCE
VOCs, primarily TCE
No. 2 Fuel oil as free
product
VOCs, primarily
BTEXandTCE
VOCs, primarily TCE
VOCs, including TCE,
DCE, and vinyl
chloride
VOCs, primarily TCE
>,- ; ^TecjtaoIogy-PerformaiidB, ' ^*-
V " x i Aftertraetiiring : \ ">
\
Rate of air flow increased by more than 600 percent.
Rate of TCE mass removal increased by
approximately 675 percent.
Rate of air flow increased 3.5 times. Permeability
increased as much as 510 tunes.
Rate of TCE mass removal in clay zones increased
as much as 46,000 times.
TCE mass removal increased 3 times.
Rate of recovery of free product increased by
approximately 1,600 percent.
Transmissivity increased by approximately
400 percent.
Transmissivity increased by 85 percent.
Rate of air flow increased 2 times.
Rate of air flow increased more than 5 times.
-------
TABLE 6-2
SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES
ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING
(Page 2 of 4)
Technology
Pneumatic Fracturing
and DPE
Pneumatic Fracturing
and DPE
Pneumatic Fracturing and
In Situ Bioremediation
Pneumatic Fracturing
andSVE
Pneumatic Fracturing
and DPE
Hydraulic Fracturing
andSVE
Developer or
Vendor
Terra Vac, Inc.
Terra Vac, Inc.
New Jersey
Institute
of Technology
New Jersey
Institute
of Technology
First Environment,
Inc.
University of
Cincinnati
Site
Location
New York, New
York
Monroe, Louisiana
Marcus Hook,
Pennsylvania
Richmond,
Virginia
Greenville,
South Carolina
Oak Brook,
Illinois
Geologic
Formation Type
Clay soils
Clay soils
Clay soils
Clay
Biotite gneiss and
schist
Silty clay
Contaminants
Treated
TCE, PCE, BTEX,
and other VOCs
TCE, PCE, BTEX,
and other VOCs
BTEX
VOCs, primarily
methylene chloride
and TCA
Chlorinated solvents
TCE, TCA, DCA, and
PCE
Technology Performance
After Fracturing
Rate of air flow did not increase appreciably.
Concentration of VOCs in the extracted air stream
increased 10 times.
Rate of air flow increased by 6 to 8 standard cubic
feet per minute.
Rate of extraction of VOCs more than doubled.
Soil permeability increased 40 times.
Rate of removal of BTEX increased by more than 82
percent.
Rate of air flow increased 1,000 times.
Concentration of VOCs in the extracted air stream
increased 200 times.
Recovery rate increased as much as 10 times.
Average rate of extraction increased 15 to 20 times.
Concentration of contaminants recovered increased
10 times.
03
oo
-------
TABLE 6-2
SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES
ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING
(Page 3 of 4)
Technology - "
Hydraulic Fracturing and
In Situ Bioremediation
Hydraulic Fracturing
andSVE
Hydraulic Fracturing
and SVE
Hydraulic Fracturing and In
Situ Bioremediation
Hydraulic Fracturing
and SVE
Hydraulic Fracturing
and SVE
Hydraulic Fracturing and
Electroosmosis
Hydraulic Fracturing
and DPE
' Developer or ' /
. Vendor
University of
Cincinnati
University of
Cincinnati
Fuss and O'Neill,
Inc.
and FRX Inc.
FRX Inc.
FRX Inc.
FRX Inc.
FRX Inc.
Golder Applied
Technologies, Inc.
.site;,
s Location ' ,.-
Dayton, Ohio
Beaumont, Texas
Woodstock,
Connecticut
Denver, Colorado
Lima, Ohio
Oakfield,
Maine
Columbus, Ohio
Atlanta, Georgia
Geologic '
ForaoationType
Sandy and silty
clay
Clay
Silty clay
Shale and clay
Clay and silty clay
Clay and silty clay
Clay and silty clay
Clay
Contaminants
' '', Treated * l
BTEX and TPH
Gasoline and
cyclohexane
VOCs, primarily paint
thinner
TPH
Gasoline
Gasoline and diesel
fuel
Unspecified water
soluble contaminants
Chlorinated solvents
;:*.< \, TซebnOtogy Peiformai|c - . /'
-r ' After Fractuiing , ' ป > ' -
Rate of fluid flow increased 25 to 40 tunes.
Level of contaminant reduction was 89,percent
greater for BTEX and 77 percent greater for TPH.
Rate of recovery of LNAPL increased 10 times.
Rate of fluid flow increased as much as 6 times.
Reduction of concentrations of TPH in soils was
approximately 90 percent in 5 months.
Rate of fluid flow increased more than 10 tunes.
Rate of fluid flow increased as much as ten times.
Graphite filled fractures created an electrical field
required to induce electroosmotic migration of water
and contaminants.
Average product recovery rate increased 4 times.
O\
VO
-------
TABLE 6-2
SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES
ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING
(Page 4 of 4)
o
Technology
Hydraulic Fracturing
and DPE
Hydraulic Fracturing
andSVE
Developer or
Vendor
Frac Rite
Environmental, Ltd.
and Echo-Scan
Corporation
Remediation
Technologies, Inc.
Site
Location
Alberta, Canada
Bristol, Tennessee
Geologic
Formation Type
Clayey silt, silty
sands
Sedimentary
bedrock
Contaminants
Treated
Hydrocarbon
condensate and
Free-phase
hydrocarbons
TCE
Technology Performance
After Fracturing
Hydraulic conductivity increased 10 tunes and the
zone of influence increased 4 times.
Volumetric rate of recovery of condensate increased
approximately 7 times.
Rate of extraction increased by as much as 6 tunes.
Rate of TCE extraction increased by as much as 700
liters per minute.
-------
TABLE 6-3
COMPARISON OF HYDROCARBON CONDENSATE RECOVERY RATES
BEFORE AND AFTER FRACTURING
Before Hydraulic Fracturing *
"We
(feet/day)
0.1
'Zom-ot '
, Influence
s (feซt)
3 to 5
Condensate
Recovery
^ (gaFday)',;
13
After HvdtraulicFractarinflf
" - *&
(feel/day)
1.1
Zone of
Influence
(feet)
>1.5
Condensate
'Re'eovery
" ซ X^aVday)^ *
95
Source: Modified from Frac Rite Environmental, Ltd. 1996
Note: K,ve Average permeability
6-41
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TABLE 6-4
COST DATA FOR SOIL VAPOR EXTRACTION
ENHANCED WITH PNEUMATIC FRACTURING
Cost Item
Site preparation
Permitting/regulatory requirements
Capital equipment (1.5 years)
Startup
Labor
Consumables/supplies
Utilities
Emission control
Disposal of residues (water)
Analytical services
Repair/replacement
Demobilization
Total
Total Cost
($)
42,000
1,750
82,074
8,200
107,640
4,000
17,000
70,000
37,200
NA
NA
1,500
$371,364
Cost/Ib .
"TCE <$/lb)
15.79
0.66
30.85
3.08
40.47
1.50
6.39
26.32
13.98
0.56
$139.60
Percent of ,
' Total (ป).,
11.3
0.5
22.1
2.2
29.0
1.1
4.6
18.8
10.0
0.4
$100.0
Source: Modified from U.S. Environmental Protection Agency 1993a and 1993b
Note: NA Not available
Not applicable
TCE Trichloroethene
6-42
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TABLE 6-5
COST DATA FOR HYDRAULIC FRACTURING
> ^ , __ ~, "<"< '- - , '"'-.' , x "
: i " "ฐ " ฃest Category , C ฐ\
Site preparation
Permitting/regulatory requirements"
Capital equipment rentalb
Startup
Labor
Supply and consumables
Utilities
Treatment and disposal effluent
Shipping and handling of residues and waste
Analytical services and monitoring
Maintenance and modifications
Demobilization3
Total one-time costs
Total daily costs
Estimated cost per fracture0
Estimated &ฃ
(1^>3 Dollars)
1,000
5,000
1,000
0
2,000
1,000
0
0
0
700
0
400
5,400
5,700
$950 to $1,425
Source: Modified from U.S. Environmental Protection Agency 1993c
Notes:
a
b
One-time costs
Capital equipment includes: equipment trailer; slurry mixer and pump; mixing
pumps, tanks, and hose; fracturing lance and wellhead assembly; notching pump
and accessories; pressure transducer and display; uplift survey equipment; scale;
and miscellaneous tools and hardware. Rental cost is based on 30 rentals per
year and a depreciation of the $92,900 capital cost over 3 years.
Total daily costs (excluding one-time costs) divided by four or six fractures per
day
6-43
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TABLE 6-6
PNEUMATIC AND HYDRAULIC FRACTURING TECHNOLOGY VENDORS"
(Page 1 of 2)
Name of Vendor
Address and Phone Number
Point of Contact
Pneumatic Fracturers
Accutech Remedial Systems, Inc.
First Environment, Inc.
McLaren/Hart Environmental
Engineers, Inc.
Terra Vac, Inc.
Cass Street and Highway 35
Keyport, NJ 07735
Phone: 908-739-6444
Fax: 908-739-0451
90 Riverdale Road
Riverdale, NJ 07457
Phone: 201-616-9700
Fax: 201-616-1930
25 Independence Boulevard
Warren, NJ 07059
Phone: 908-647-8111
Fax: 908-647-8162
92 North Main Street
Windsor, NJ 08561
Phone: 609-371-0070
Fax: 609-371-9446
John Liskowitz
Richard Dorrler
James Mack
Loren Martin
Hydraulic Fracturers
EMCON
ERM-Southwest, Inc.
Fluor Daniels GTI, Inc.
3300 North San Fernando Boulevard
Burbank, CA 91504
Phone: 818-841-1160
Fax: 818-846-9280
16300 Katy Freeway - Suite 300
Houston, TX 77094-1609
Phone: 713-579-8999
Fax: 713-579-8988
2000-200 Manner Avenue
Torrance, CA 90503
Phone: 310-371-1394
Fax: 310-371-4782
Donald L. Marcus
H. Reiffert Hedgcoxe
John F. Dablow III
6-44
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TABLE 6-6
PNEUMATIC AND HYDRAULIC FRACTURING TECHNOLOGY VENDORS"
(Page 2 of 2)
F$ปtof Contact
Frac Right Environmental, Ltd.
6 Stanley Place S.W.
Calgary, Alberta
Canada T2S 1B2
Phone: 403-620-5533
Fax: 403-287-7092
Gordon H. Bures
FRXInc.
P.O. Box 37945
Cincinnati, OH 45222
Phone: 513-469-6040
Fax: 513-556-2522
Larry C. Murdoch,
Ph.D. and
William W. Slack,
Ph.D.
Fuss and O'Neill, Inc.
146 Hartford Road
Manchester, CT 06040
Phone: 203-646-2469
Fax: 203-643-6313
David L. Bramley
Golder Applied Technologies, Inc.
3730 Chamblee Tucker Road
Atlanta, GA 30340
Phone: 770-496-1893
Fax: 770-934-9476
Grant Hocking
Gregg Drilling and Testing, Inc.
2475 Cerritos Avenue
Signal Hill, CA 90806
Phone: 310-427-6899
Fax: 310-427-3314
John Gregg
Remediation Technologies, Inc.
23 Old Town Square - Suite 250
Fort Collins, CO 80524
Phone: 970-493-3700
Fax: 970-493-2328
Ann Colpitts
Note: a This list is not inclusive of all vendors capable of providing pneumatic and hydraulic
fracturing technologies. This list reflects vendors contacted during the preparation of this
report.
6-45
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TABLE 6-7
COMPARISON OF PNEUMATIC FRACTURING AND HYDRAULIC FRACTURING
Features
Fracture pattern
Injection medium
Injection interval
Fracture aperture
Radial extent of fractures
Radial extent of influence
Maximum depth
Injection time to create
fracture
Well completion
Geologic formations that
favor successful
application
Pneumatic Fracturing . ,
Dense network of micro-fractures
around the injection point with one
or two major fractures that migrate
outward into the formation per
injection interval.
Air or other gases with or without
fine grained proppants.
2 to 3 feet
0.5 to 1.0 mm
20 to 70 feet
20 to 70 feet
At depths greater than 75 feet
self-propping decreases; however,
propping agents can be used.
20 seconds
Typically a single well screen
across all fractures at one location.
All fractures in a well either inlet
or recovery.
Over-consolidated or bedded
sediments and bedrock
'H 'Hytiv^zWrn^^ty*^ ^
One or two major fractures that
migrate outward into the
formation per injection interval
with secondary fractures in
overlying formation.
Water or slurries of water, sand,
and other additives.
0.5 to 5 feet
1 to 2 cm
10 to 25 feet
10 to 70 feet
Up to several hundred feet, with
or without propping agents.
5 to 15 minutes
Typically a casing for each
fracture. Where well contains
multiple fractures, use each
fracture for either air inlet or
recovery.
Over-consolidated or bedded
sediments
Source: Modified from Keffer, Liskowitz, and Fitzgerald 1996 and FRX Inc. 1996.
6-46
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CHAPTER 7.0
THERMAL ENHANCEMENT
This chapter describes use of thermal enhancements for increasing overall performance of SVE systems.
The following sections provide an overview of thermal enhancements, describe conditions under which
the technology is applicable, contain a detailed description of thermal enhancements, highlight
performance data, list vendors that provide thermal enhancement services, outline the strengths and
limitations of this technology, and provide recommendations for using the technology. Cited figures and
tables follow references at the end of the chapter.
7.1 TECHNOLOGY OVERVIEW
Thermal enhancements for SVE may involve a number of different technologies aimed at transferring
heat to the subsurface to (1) increase the vapor pressure of VOCs or SVOCs to enhance their removal via
SVE or (2) to increase air permeability. Vaporized contaminants are removed by SVE extraction wells.
Thermal enhancement technologies include steam or hot air injection, ER heating, RFH, and thermal
conduction heating. Past applications of steam injection technologies have focused primarily on moving
and vaporizing free petroleum product in the subsurface toward extraction wells for removal. Hot air
injection has been used to increase the vapor pressure of VOCs and SVOCs in the vadose zone, thus
decreasing remediation time and increasing contaminant removal. Use of ER heating and RFH has
primarily focused on increasing mass removal rates of contaminants in low-permeability soil. ER heating
and RFH remove soil moisture, thus increasing air permeability in the soil and increasing contaminant
removal in low-permeability soil formations. Thermal conduction heating enhances conventional SVE
treatment by heating the soil surface to volatilize contaminants.
Steam injection technologies enhance conventional SVE treatment by injecting steam into the
contaminated region. Contaminants are pushed ahead of the condensing water vapor toward the typical
extraction wells. Additionally, some of the contaminants are vaporized or solubilized by the injection of
steam and are moved toward the extraction wells by an applied vacuum. Three common methods of
delivering the steam into the contaminated region are use of injection wells, injection through drill
augers, and injection below the area of contamination. Steam injection technology is typically more
applicable to regions with medium to high-permeability soils, where the condensate front can more freely
7-1
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move through the formation. In addition, a low-permeability surface layer may be needed to prevent
steam breakthrough for shallow soil applications. The costs of steam injection applications range from
$46/yd3 to $166/yd3.
Hot air technologies are similar to steam injection, but hot air is used in place of steam. The hot air can
be supplied either through an injection well or by injecting hot air through a large mixing auger. The
main strength of hot air injection technologies is their comparatively inexpensive cost. Hot air can be
much easier to provide than high quality steam. However, hot air injection is not a very efficient means
for delivering heat to the subsurface because of the relatively low heat capacity of air. Because both
steam injection and hot air injection involve injecting a fluid under pressure into the subsurface, the same
geological concerns apply for hot air injection as with steam injection. The costs of hot air injection
application range from $75/yd3 to $100/yd3.
For RFH, energy is delivered to the contaminated region using electrodes or antennae that emit radio-
frequency waves. These radio waves increase molecular motion, which heats the soil. These electrodes
are either placed on the surface at the contaminated area or inserted into holes drilled into the
contaminated area. The energy given off by the electrodes excites the contaminated region and raises the
temperature. RFH is effective for treating VOCs in low-permeability soil in the vadose zone. The costs
of RFH application range from $195/yd3 to $336/yd3.
ER heating uses the soil as a conduction path for electrical current. The energy dissipated because of
resistance is transformed into heat. Past applications of ER heating have involved inserting an array of
metal pipes into the contaminated region by drilling. An electrical current is then passed through these
pipes to heat up the contaminated region and drive off soil moisture and target contaminants. ER heating
is effective for treating VOCs in low-permeability soil in the vadose zone. The cost of a previous
application of ER heating is $100/yd3.
In thermal conduction heating, a heat source is placed on the surface of the contamination or inserted into
the formation, and heat is supplied to the contaminants by conduction. Typically, a common ER heater is
used as the heat source. Thermal conduction heating can be used to remove VOCs in medium to
low-permeability soil. An advantage of this technology is its ease of implementability and relatively
inexpensive cost. However, heat conduction by this method is very slow and inefficient and requires a
7-2
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large temperature gradient to be maintained for acceptable heating rates to be achieved. Based on the
limited application of thermal conduction heating, no representative costs are presented.
7.2
APPLICABILITY
In general, thermal enhancement technologies should be considered during soil remediation for one or
more of the following applications:
Removal of sorbed organic compounds with low vapor pressures SVE generally is not
effective for removing organic compounds whose vapor pressures are less than 0.1 mm Hg to 1.0
mm Hg at ambient temperatures. The range of applicability for SVE can be extended by
employing thermal enhancement technologies. This has the effect of increasing contaminant
vapor pressures, which make the contaminants more volatile and therefore, more susceptible to
SVE treatment.
Reduction of treatment time for difficult matrices Some thermal enhancement technologies,
such as RFH and ER heating, have been used to decrease treatment time for VOCs in clayey and
silty soils. Soil heating first creates steam, which induces stripping of VOCs from soil, and then
dries the soil to increase advection. Decreased treatment times can significantly decrease
remediation costs, as well as allow property to be transferred more quickly.
Treatment of NAPL Some sites contain LNAPL or DNAPL that complicate remediation
strategies and lengthen treatment times. Thermal enhancement technologies, especially steam
stripping, may be used to solubilize or vaporize NAPL for subsequent removal by SVE.
Enhancement of biological activity in soil Increases in soil temperature may stimulate
biological activity in the soil. In general, biodegradation rates are expected to double for every
10 degrees Celsius (ฐC) rise temperature increase. Thermal enhancement technologies such as
soil surface modification, fiber optic heating, and warm water injection may be used to provide
relatively small (2 to 10 ฐC) increases in soil temperature.
7.3 ENGINEERING DESCRIPTION
Thermal enhancement technologies have been studied and developed to augment the performance of
SVE systems for removing VOCs and SVOCs. The removal of VOCs and SVOCs by SVE is controlled
by a number of transport and removal mechanisms which include:
Gas advection
Chemical partitioning to the vapor phase
7-3
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Gas-phase contaminant diffusion
Sorption of contaminant on soil surfaces
Chemical or biological transformation
Thermal enhancement technologies raise the soil temperature to increase the reaction kinetics for one or
all of these removal and transport mechanisms. Gas advection involves the bulk movement of volatilized
contaminants in the vapor phase as air is drawn through the soil. Advection through low-permeability
soils is relatively slow and can be thermally enhanced by drying soil to increase the air permeability of
the soil.
Thermal enhancement increases chemical partitioning from liquids to gases. As temperature increases,
the vapor pressure of a pure chemical also increases, as depicted in Figure 7-1. The increased rate of
vaporization at higher temperatures significantly increases the rate at which chemicals in the liquid form
in soil are removed, particularly in areas that contain soil with medium to high permeabilities.
In areas where concentration gradients exist between pores being swept by the flowing air and
contaminated soil not in communication with the air stream, contaminants will move by diffusion toward
the flowing air. Gas-phase diffusion is typically much slower than advection in less permeable zones and
will be the limiting factor for system performance in situations in which air flow does not pass
sufficiently near contamination to allow advection. Therefore, the objective of an SVE system is to
minimize the length of the diffusion path the volatilized contaminants must take to enter the air flow. In
diffusion-limited formations, beneficial effects in addition to the vapor pressure increase result from
increases in temperature. Temperature increases enhance the rate of vapor transport from
low-permeability zones to regions of high-vapor flow (American Academy of Environmental Engineers
[AAEE] 1994). In addition, for temperature increases above 100 ฐC, the steam is produced and the
steam's pressure-driven flow to regions of high-vapor flow can help drive contaminant vapors out of
low-permeability zones at a rate much higher than the natural contaminant diffusion rate.
When combined with conventional SVE, a variety of in situ thermal process options can enhance the
removal of contaminants through the transport and removal mechanisms described above. These include
steam injection and stripping, hot air injection, RFH, ER heating, and thermal conduction heating.
7-4
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7.3.1
Steam Injection/Stripping
Steam injection (also called steam stripping) technology is used to enhance typical SVE treatment
systems by injecting steam into the contaminated region. The steam increases chemical partitioning as
the contaminants are pushed ahead of the condensing water vapor toward the typical extraction wells.
Additionally, some of the contaminants are vaporized or solubilized by the injection of steam and are
moved toward the extraction wells by an applied vacuum. Steam injection technology is typically more
applicable to regions with medium- to high-permeability soils, where the condensate front can more
freely move through the formation. Steam injection has limited applicability to sites contaminated with
pesticides, dioxins, furans, and polychlorinated biphenyls (PCB). It is particularly well suited for the
treatment of petroleum contaminants and NAPLs.
The typical steam injection system, as shown in Figure 7-2, delivers steam through injection wells into
the contaminated region to heat up the zone and vaporize the contaminants. The steam also creates a
pressure gradient that controls the movement of the contaminants and condensed steam front to a
recovery well. After injection, the steam front travels some distance into the contaminated region before
condensing. The increase in temperature volatilizes the contaminants (because of increased vapor
pressures) or dissolves them in the condensed steam (because of increased solubilities). The flow of
steam is controlled to limit the possibility of contaminant mobilization into previously uncontaminated
areas.
Uniform steam distribution, control of the condensate front, and vapor containment are all desirable for
steam stripping. The surface of the treatment area is often covered with an impermeable surface to help
control the flow of the contaminants. There are two common methods of delivering the steam including
the use of injection wells and injection through drill augers.
7.3.1.1
Steam Injection Through Injection Wells
Injection wells are drilled so the steam can be injected at or below the contaminant zone. Typically, a
series of wells are drilled to evenly distribute steam to the contaminated region. The spacing of the steam
injection wells is dependent on the soil permeability of the soil. The permeability of a particular
formation could be increased by combining this technology with pneumatic fracturing. If such a
7-5
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treatment scheme was implemented, the number of delivery wells may be reduced. The vaporized
contaminants are then collected using a vacuum apparatus, such as vacuum extraction wells or a vacuum
bell at the soil surface.
The method of steam delivery described above can be used to target oily wastes. Injection and recovery
wells are drilled to cover and treat the contaminated area. The steam is injected below the contaminated
region, and the steam condenses and pushes the oily waste into a hot water stream. Alternatively, steam
is injected directly into the contaminated region to move contaminants radially to extracting wells. This
hot water stream is injected above impermeable barriers and is designed to mobilize the rising
contaminants. The resulting hot water/oily waste mixture is then withdrawn through extraction wells for
treatment.
Steam injection has been widely used in the petroleum industry and can be used to recover semivolatile
and volatile compounds. The organic compounds are often collected for reprocessing and reuse. The
application of steam heat places an upper temperature limit of 100 aC and is, therefore, not as efficient
for higher boiling point compounds. Steam injection might not be as effective in areas with impermeable
regions because of limited flows through these regions. If the area is layered with impermeable and
permeable regions, the contaminants will move along the bed, expanding the area of contamination.
Heating the contaminated area with steam will reduce the treatment time, depending on site
characteristics, compared to treatment at ambient temperatures.
7.3.1.2
Steam Injection Through Drill Auger
Steam may also be injected into the subsurface through drilling augers (see Figure 7-3). A process tower
is used that supports cutting blades at the end of a hollow shaft. The process tower consists of five major
components: a treatment shroud, kelly bars, cutter bits, and a rotary table and crowd assembly.
Together, these components loosen the soil, inject the steam, and collect the stripped VOCs from the soil.
The cutter bits are attached to the end of each kelly bar. A set of mixing blades is also attached above the
cutter bits. Each kelly bar is thus equipped with two sets of opposing blades (cutter bits and mixing
blades) positioned at 90 degrees from each other, as shown in Figure 7-3. The cutter bits have nozzles
7-6
-------
for injection of steam into the soil. Mechanical power is provided to the kelly bars by a rotary table and
crowd assembly.
The steam raises the temperature of the soil mass to between 170 and 180 degrees Fahrenheit (ฐF),
thereby increasing the vapor pressure of the VOCs, volatilizing them away from the soil particles, and
allowing them to be transported to the soil surface by the action of the steam and an applied vacuum in
the treatment shroud. The cutter bits are moved vertically to selectively treat areas of greater organic
contamination. The treatment cycle may be repeated until the contaminant levels in the soil are
satisfactorily reduced. The treatment procedure facilitates overlapping treatment of all depths of the
block to ensure adequate exposure of the VOC-contaminated soil to the steam.
7.3.2
Hot Air Injection
Hot air injection is used to enhance typical SVE application through gas advection. The introduction of
hot air to the contaminated region raises the ambient soil temperature and volatilizes the contaminants to
a gas phase. The vapor is then mobilized to the extraction wells through the applied vacuum. The
contaminants not in direct contact with the flowing vapor will undergo diffusion into the vapor phase
from the soil. This is a slower transport mechanism than the advection process, but it has the same net
effect. Hot air injection becomes more effective as the soil medium dries through its application. As the
soil dries, soil permeability is increased, and the vapors can flow more freely. Hot air injection has
limited applicability to dioxins, furans, and PCBs. It is also relatively less effective for the extraction of
SVOCs as compared to steam injection because of lower temperatures. Hot air injection is particularly
effective for VOCs in lower permeability soils.
Hot air injection is similar in implementation to steam injection, but hot air is used in place of steam.
The hot air can be supplied either through an injection well or by injecting hot air through a large mixing
auger (see Figure 7-3). The system is designed to work in a manner similar to the steam treatment; the
contaminants are volatilized for removal at an extraction well. The resulting off-gas can then be treated.
Hot air injection can also be used in conjunction with other thermal enhancement technologies. Hot air
injection can follow a steam injection process to keep the mobilized contaminants volatilized. One
7-7
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vendor uses hot air injection as a means of removing moisture from the contaminated region before
treating the soil using oxidation.
Wells used in hot air injection are typically constructed of steel casing perforated at the bottom and
cemented in place (EPA 1994). Heated, compressed air is injected into the wells, and the volatilized
contaminants rise toward the surface, where they are trapped beneath an impermeable cover. Heating air
may be provided by a burner and blower assembly, or heated air from a thermal or catalytic oxidation
unit used to treat extracted soil vapors may be used. The vacuum extraction well captures the rising
vapors because of the induced pressure gradient. When an auger configuration is used, the process is
similar to the steam injection auger method. The hot air is injected through the auger as it penetrates and
mixes the soil. A movable cover is used over the mixing area to reduce the chance of contaminant
emissions. The volatilized contaminants are then collected with vapor extraction wells and treated.
The required input temperature puts constraints on the well materials that can be implemented
successfully. As a result, more expensive well construction materials are typically required, since
bentonite (a typical sealing material) loses its effectiveness at temperatures above 100ฐC (AAEE 1994).
Additionally, for long pipe runs, insulation for the air delivery system would be required to minimize
heat losses caused by thermal radiation. Finally, cyclical heating and cooling of the injection wells
would induce expansion and contraction of the steel and could fatigue the concrete or cement seal.
73.3
Radio-Frequency Heating
RF heating is used to enhance the SVE application by heating the contaminated soil matrix to
temperatures above those of steam injection processes and volatilizing contaminants. The heating
efficiency is decreased as the soil matrix dries. The heating of the soil increases the chemical
partitioning to the vapor phase enhancing the contaminant removal. The vaporized contaminants are then
transported to the extraction wells by an applied vacuum. RFH is applicable to sites with
low-permeability soils. It has limited applicability to dioxins, furans, and NAPLs. RFH is particularly
applicable to sites contaminated with VOCs and SVOCs in soil.
RF heating has the ability to raise soil temperatures well above levels attainable by steam extraction and
is more applicable to higher boiling point compounds. This fact also leads to a reduction in removal
7-8
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times. Typically, energy is delivered to the contaminated region using electrodes or antennae that emit
radio-frequency waves. These radio waves increase molecular motion, which heats the soil.
The components of the RFH systems have two general purposes: transmission of RF energy and
collection of vapors. RF energy is transmitted to the soil using an RF generator, a matching network,
electrodes or applicators, temperature measuring devices, and an RF shield. These components are
discussed briefly below:
RF generator - The RF generator is designed to convert three-phase alternating current (AC)
power to RF energy. The RFH generators used during several previous pilot-scale
demonstrations have ranged from 25 to 125 kilowatts (kW). Trailers containing 10 kW and 20
kW RF generators are commercially available. The radio transmitter powered by the generator
provides continuous RF wave at a frequency allocated for industrial, scientific, and medical
equipment, including 6.78 mega-hertz (MHz), 13.56 MHz, 27.12 MHz, 40.68 MHz, and seven
higher frequencies.
Matching network - RF energy from the generator flows to the matching network, which is used
to adjust the electrical characteristics of the RF energy being transmitted into the soil and
maximize the fraction of power absorbed by the soil. This is important to increase energy
efficiency of the system and to prevent unadsorbed power from reflecting back to the generator
and other electrical components and overheating the components.
Electrodes or applicators - RF energy is transmitted through the matching network to an
electrode array or to applicators, which convey the energy into the soil. For applications using an
electrode array, RH energy is transmitted to rows of copper electrodes, known as exciter
electrodes. The electrodes are placed in boreholes and backfilled with material similar to the
surrounding soil. Rows of aluminum electrodes, known as ground electrodes, are installed
parallel to and on either side of the exciter electrode row. The electrode configuration is
designed to direct the flow of RF energy through the soil and contain the energy within the
treatment zone.
For sites where applicators are used, energy from the RF generator flows through the matching
network to the applicators, which convey the energy into the soil. The applicators are 3.5-inch-
diameter antennae that are constructed with aluminum, stainless steel, Teflon, ceramic, brass, and
copper components. The applicators are connected with rigid copper transmission lines that are
pressurized with nitrogen to increase high voltage handling capability. The applicators are
alternately selected with a remote-controlled coaxial switch.
Temperature measuring devices - Temperature measuring devices such as thermocouples, fiber
optic temperature probes, and infrared sensors are positioned throughout the treatment zone at
various depths to ensure adequate heating of the contaminated soil.
RF shield - If magnetic field monitoring indicates that the treatment system is not complying with
all regulations concerning magnetic fields, an RF shield should be constructed over the treatment
7-9
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area to limit exposure to the RF energy that escapes the system. A corrugated aluminum arch or
other structure has been used previously during pilot-scale studies.
RF systems require a vapor barrier and soil vapor extraction and treatment system. The vapor barrier can
be designed similar to conventional SVE surface seals; however, an insulating barrier may be desired to
reduce heat loss from the treatment area. Vapor treatment will depend on contaminant types and
concentrations, and will typically consist of condensation and thermal or catalytic oxidation.
The electrodes or antennae used in this process are powered by a radio-frequency generator that operates
in the industrial, medical, and scientific band. The frequency is chosen based on dielectric properties of
the soil and area of contamination. These electrodes are either placed on the surface at the contaminated
area or inserted into holes drilled into the contaminated area. The energy given off by the electrodes
excites the contaminated region and raises the temperature. This heating occurs through two different
mechanisms, ohinic and dielectric effects. Figure 7-4 illustrates how an RFH system was implemented at
the Sandia National Laboratory in New Mexico.
The ohmic mechanism results from an induced voltage drop that causes electrons to flow up into the
conduction band and through the contaminated region causing resistance heating (AAEE 1994). The
most efficient and uniform heating is obtained by limiting the induced voltage drop in the contaminated
region. The dielectric heating mechanism results from the interaction between the applied electric field
and distortions of molecular structure. Polar substances present in the contaminated region have dipole
moments that are randomly oriented. By applying an electric field, the dipole moments of the molecules
begin to align, causing molecular distortions. The resistance to this distortion heats the soil.
The radio-frequency generator can be used to heat the contaminated soil up to 150 to 200 QC. At such
temperatures, the range of conventional SVE is extended to organic compounds with vapor pressures in
the 5- to 10-mm Hg range. Some vendors claim this range can be extended further because the generator
used in their system is capable of heating soils to 400 SC (EPA 1995a). As the soil formation is
continually heated, soil moisture is driven off, which results in a decrease in removal efficiency. This is
caused by the decreased conductivity of air compared to water. The moisture content of the soil is
critical to the removal efficiency and is reflected through the soil dielectric constant. To maintain
adequate removal efficiencies, the frequency of the RF signal can be varied. Alternatively, if the system
was combined with a steam injection system, the soil moisture content could be controlled.
7-10
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7.3.4
. - .. E c ^ _ f ......
Electrical Resistance Heating
ER heating is used to enhance SVE processes by a similar transport mechanism as RFH. However, ER
heating is slightly less efficient because of uneven heating and decreased efficiency as the soil dries near
the electrodes. The transport process increases the chemical partitioning to the vapor phase, enhancing
the contaminant removal. The vaporized contaminants are then removed by extraction wells under an
applied vacuum. ER heating is applicable to low-permeability soils contaminated primarily with VOCs.
It is generally less applicable for sites contaminated with dioxins, furans, and PCBs (AAEE 1994).
ER heating uses the soil as a conduction path for electrical current. The energy dissipated because of
resistance is transformed into heat. ER heating suffers the same limitation as RFH in terms of soil
moisture content. As discussed above, with decreasing soil moisture, the removal efficiency is also
decreased. With a constant voltage supply, the soil nearest the electrodes dries at a faster rate than the
bulk of the soil, causing increased resistances and decreased removal efficiencies. This also leads to an
unevenness in heating.
Past applications of ER heating have included six-phase soil heating (SPSH) or EM heating. SPSH splits
conventional three-phase electricity into six separate electrical phases, producing an improved subsurface
heat distribution. Each phase is delivered to a single electrode, each of which is placed in a hexagonal
pattern. To maintain soil conduction, the electrodes are backfilled with graphite, and small amounts of
water containing an electrolyte are added to maintain moisture. The rate of water addition depends on
the soil type. A trailer-mounted power plant supplies three-phase power to a six-phase power
transformer.
SPSH reduces the moisture content of the soil and makes the soil more permeable for gas flow. The
electricity supplied is then increased to oxidize and cleave any remaining nonvolatile organic
compounds. Soil moisture and volatized contaminants are collected under vacuum by an extraction well
located in the center of the hexagon.
Components of EM heating are similar to RFH; however, powerline frequency (60 hertz [Hz]) energy is
passed through the soil using the conductive path of the residual soil water. At the Sandia National
Laboratory, EM heating was conducted using the same system configuration as RFH heating
7-11
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(Photographs 7-1,7-2, and 7-3). Powerline frequency energy input is controlled through a multi-tap
transformer to allow for the changing impedance of the soil as soil water is removed. Voltages begin at
approximately 200 volts (V) and can be increased in steps up to 1,600 V. Water is added to the excitor
electrodes to moderate the increased soil resistance caused by the removal of soil water adjacent to the
electrodes. EM heating is capable of heating soil to between 80 and 90 ฐC.
73.5
Thermal Conduction Heating
Conduction heating enhances typical SVE treatment by heating the soil surface to volatilize
contaminants. It uses the same transport mechanism as RFH and ER heating, namely by increasing
chemical partitioning to the vapor phase, enhancing the contaminant removal. This particular
enhancement would be most effective for sites with medium- to low-permeability soils contaminated
with VOCs. It is a less efficient heating mechanism than those described previously; therefore, it is not
applicable to higher boiling point compounds (although higher boiling point compounds such as PCBs
will be mobilized in the first few feet bgs).
In conductive heating, a heat source is placed on the surface of the contamination or inserted into the
formation, and heat is supplied to the contaminants by conduction. Typically, a common ER heater such
as a thermal blanket is used as the heat source. The thermal blanket is placed on the contaminated soil
and heat is conducted from the blanket/soil surface interface vertically into the soil, thus volatilizing
organics in the soil. The blanket also acts as a surface seal. Down-the-hole heaters have also been used
to enhance oil recovery operations. The supplied heat would volatilize the target contaminants and be
collected under vacuum by a surface bell arrangement or an actual extraction well. However, limited
application of this technique as applied to remediation has been documented.
A thermal blanket system developed by Shell Technology Ventures, Inc. was demonstrated in 1996 at the
South Glens Falls Dragstrip in South Glens Falls, New York. The thermal blanket system contained
heating elements that heated the ground surface up to 800ฐ to 1000ฐC, and a vacuum system that drew
soil vapors toward and through the blankets. Although the thermal blanket system did not use SVE
wells, the system reduced average PCB concentrations of more than 500 mg/kg to less than 2 mg/kg in
the treatment zone. Most contaminants were destroyed in the soil near the heat source. Treatment times
ranged from more than 24 hours to treat the upper 6 inches of soils to approximately 4 days to treat
7-12
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contaminants 12 to 18 inches deep. For deeper contamination, the technology uses ER heating in vertical
or horizontal boreholes in conjunction with the thermal blanket(s) (Soil & Groundwater Cleanup 1997).
Conduction heating has several advantages and disadvantages with respect to other thermal enhancement
technologies. An advantage of this technology is its ease of implementability and relatively inexpensive
cost; however, heat conduction by this method is very slow and inefficient and requires that a large
temperature gradient be maintained for acceptable heating rates to be achieved.
7.4 PERFORMANCE AND COST ANALYSIS
This section provides recent performance and cost data for remediation involving thermal enhancement.
7.4.1
Performance
A number of pilot- and full-scale applications of thermal enhancement technologies have been conducted
in recent years. The treatment performance of 13 thermal enhancement technology applications are
summarized in Table 7-1. This section discusses the treatment and operational performance of steam
injection and stripping and ER technologies using three case studies. Cost performance of thermal
enhancement technologies is discussed in Section 7.4.2.
7.4.1.1
Rainbow Disposal Site
A representative full-scale demonstration of steam injection and stripping technologies was performed at
the Rainbow Disposal site in Huntington Beach, California, by Hughes Environmental Systems, Inc. The
Rainbow Disposal site is an active municipal trash transfer facility that was contaminated with diesel
fuel, and contained a high-permeability formation and a lower confining layer. In 1984, an underground
fuel line was punctured during digging operations, and an estimated 70,000 to 135,000 gallons of No. 2
diesel fuel leaked into the surrounding soil. Free product was present in most monitoring wells in the
zone of contamination.
The Rainbow Disposal site geology is characterized by alternating layers of high-permeability sand and
low-permeability clay. The fuel flowed downward under gravity through each sand layer and flowed
7-13
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laterally at each sand/clay interface until a break in the clay layer allowed further downward movement.
A perched aquifer in a sand layer at 25 to 40 feet bgs prevented further downward movement of
contamination. Because of the depth of contamination, excavation and ex situ treatment were not
considered practical. In addition, the large amount of free product present at the site and the location of
the diesel in a perched aquifer made treatment by SVE impractical. Therefore, the Hughes steam
enhanced recovery process (SERF) was selected to treat the contaminated soil at the Rainbow Disposal
site.
Treatment using the SERF process began in August 1991 and was evaluated under EPA's SITE program
in August and September of 1993. SERF was applied to a lateral treatment area of approximately
2.3 acres at the Rainbow Disposal site. The system was designed with 35 steam injection wells and
38 vapor/liquid extraction wells that were placed in an arrangement with one extraction well surrounded
by four injection wells (EPA 1995b). The spacing between the well arrangements depended on the soil
permeability and the size and depth of the contamination area. For this implementation, the extraction
wells were placed 45 feet from the injection wells, and injection wells were spaced approximately 60 feet
apart. The wells were installed to a depth of 40 feet. The extraction system was equipped with a
condensation system and a thermal oxidation unit (TOU) to treat vapors removed from the extraction
wells.
The treatment objective at the Rainbow Disposal site was to treat TPH to concentrations of less than
1,000 mg/kg. Low levels of BTEX compounds were also present in the soil; however, there were no
specific treatment objectives for BTEX compounds at the Rainbow Disposal site. The treatment results
indicate that the SERP's removal efficiency was less than expected. Pretreatment samples collected at
the site indicated a weighted average concentration of 3,790 mg/kg of TPH, and post-treatment samples
had a weighted average concentration of 2,290 mg/kg. This reduction corresponds to a removal
efficiency of approximately 40 percent. Forty-five percent of the post-treatment soil sample results were
above the cleanup criterion of 1,000 mg/kg. There was a large variability in the posttreatment soil
sampling results, probably because of the heterogeneity of the pre-treatment soil contamination. BTEX
compounds were not detected in posttreatment soil samples; however, treatment efficiency results for
BTEX compounds were inconclusive based on the low concentrations and infrequent detections of
BTEX compounds in the untreated soil.
7-14
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It was estimated that approximately 16,000 gallons of the diesel fuel spill was removed during treatment
with the SERF, Since the estimated release was 70,000 to 135,000 gallons and since 4,000 gallons was
recovered before the SERF implementation, 12 to 24 percent of the original spill volume has been
removed (EPA 1995b). About 5 percent of the recovered diesel was condensed in the SERP's
aboveground condensation unit and 95 percent of the diesel was combusted in the TOU.
The reduced efficiencies reported in this demonstration are largely attributable to the soil conditions and
uneven temperature distribution. The site geology was not constant over the entire treatment area. The
same alternating layers of sand and clay that directed the flow of contamination in the site soil also
influenced the treatment process. Removal of contamination trapped in the less-permeable clay layers
was difficult because the steam and heat could not penetrate these areas easily, and flow patterns could
not be developed to bypass less-permeable areas.
Based on soil temperature profiles from several areas of the site, heating of the soil took much longer
than originally anticipated, and high soil temperatures were not maintained in many areas. This may
have been because of the hours of operation (16 hours per day, 5 days per week) and excessive
operational downtime. The heating rate improved later during the application when the process was
operated on a 24-hour-per-day, 6-day-per-week cycle. The unreliable heating of the soil may have led to
the failure of the SERP technology to achieve the cleanup criterion for the site.
In summary, steam injection and stripping may be used to remove significant amounts of contamination
from the subsurface; however, treatment times may be hard to predict because of the heterogeneity of soil
types and uneven heating of soil. In addition, it may be difficult to meet treatment goals with steam
injection and stripping systems; however, improved operation of the systems will likely improve
treatment efficiency and may reduce contaminant concentration to below treatment goals.
7.4.1.2
Savannah River Site
ER heating methods are potentially effective for removing VOCs from less permeable formations. A
representative project is the application of SPSH at the SRS in Aiken, South Carolina. The
demonstration site at SRS was located at one of the source areas, the M Area, within the 1-square-mile
VOC groundwater plume. The M Area operations resulted in the release of process wastewater to an
7-15
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unlined settling basin. Vadose zone contamination is primarily associated with a leaking process sewer
line, solvent storage tank area, settling basin, and the outfall from the settling basin to a branch of the
Savannah River. The contaminated target zone was a 10-foot-thick clay layer at a depth of approximately
40 feet bgs in the vadose zone.
SPSH was used to remove VOCs during this technology demonstration. SPSH splits conventional
three-phase electricity into six separate electrical phases, producing an improved subsurface heat
distribution. Each phase is delivered to a single electrode, each of which is placed in a hexagonal
pattern. To maintain soil conduction, the electrodes are backfilled with graphite, and small amounts of
water containing an electrolyte are added to maintain moisture. The rate of water addition depends on
the soil type. At SRS, 1 to 2 gallons/hour of water with 500 mg/L sodium chloride was added at each
electrode. A 750 kilovolt-ampere (kVA) trailer-mounted power plant supplied 480 volts of three-phase
power to a six-phase power transformer. The six-phase transformer was rated at 950 kVA. Total power
applied during the demonstration averaged 200 kilowatts.
The vapor extraction well, which removes the contaminants, air, and steam from the subsurface, is
located in the center of the hexagon. At the SRS site, the diameter of the hexagon was 30 feet. Moisture
in the extracted air was condensed, and the VOC vapors were treated by electrical catalytic oxidation.
Before treatment using SPSH, the untreated target clay zone contained TCE and PCE at concentrations
ranging from nondetected to 181 /zg/kg and nondetected to 4,529 ,ug/kg, respectively. No target cleanup
goals were specified for the demonstration. Analytical tests conducted on the treated soil indicate that
the median removal of PCE within the electrode array was 99.7 percent. Outside the electrode array,
93 percent of the PCE contamination was removed at a distance of 8 feet from the array. The mass
removal rate of PCE increased threefold after the treatment zone was heated and dried.
ER tomography (ERT) was used during the field demonstration to monitor electrical conductivity in the
clay treatment zone. The ERT monitoring indicated that the clay layer increased in electrical
conductivity (up to twice initial values) during the first 3 weeks of treatment as the soil heated and ER
decreased. After that time, conductivity decreased to as low as 40 percent of the pretest value as a result
of the drying of the soil and the increased air permeability. Approximately 19,000 gallons of water were
7-16
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removed as steam during the field demonstration, indicating that the soil was dried substantially during
the test.
Several operational problems were encountered during the SPSH demonstration. Operational difficulties
encountered included drying out of the electrodes and shorting of the thermocouples. Further field
experience is expected to facilitate improvement in the design of the system to overcome these
difficulties.
In summary, the field demonstration of SPSH at SRS indicates that ER heating has potential to enhance
the performance of SVE by heating and drying contaminated soil, thus (1) creating steam to strip
contaminants and (2) increasing advection through increased air permeability. Soil drying may lead to
increased mass removal rates and faster site remediations, particularly in low-permeability soils where
contaminant removal is limited by diffusion.
7.4.1.3
Former Gasoline Station Near St. Paul, Minnesota
During March 1996, KAI Technologies, Inc. (KAI) conducted a three-week pilot-scale demonstration of
RFH-enhanced SVE at the site of a former gasoline station near St. Paul, Minnesota. Soil and
groundwater at the site were contaminated with petroleum hydrocarbons from a release from an
underground dispensing system. From 1991 to 1996, much of the petroleum hydrocarbon contamination
was removed from the site by pumping groundwater and using SVE; however, residual petroleum
hydrocarbon levels near the underground dispensing system exceeded health risk limits established by
the Minnesota Department of Health.
The RFH demonstration equipment, consisting of one RFH well containing a 9-foot antennae applicator,
two soil vapor vents, three soil vapor probes, and one groundwater vent, were positioned in the area of
the site that contained the highest contaminant concentrations. Analytical data indicated that soil in the
three-foot layer encompassing the capillary fringe contained the highest concentrations of petroleum
hydrocarbons. The applicator was positioned from 6 feet to 15 feet bgs in the well. The water table was
located approximately 10 feet bgs. A 25-kW RF generator supplied RF energy during the demonstration.
7-17
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During the 3-week demonstration period, soil and groundwater were heated using RFH at a power level
of 5 kW and a frequency of 27.12 MHz. Approximately 2,300 kWh of RF energy was delivered to the
soil and groundwater at the site. As a result of the application of RFH, soil temperatures were raised
from an ambient temperature of approximately 8 ฐC to 100 ฐC in the immediate vicinity of the RFH
applicator and to 40 ฐC at a radial distance of 5 feet from the applicator at a depth of 8.5 feet bgs. During
the demonstration, the concentration of gasoline-range organics (GRO) in soil were reduced by an
approximate factor of two. At the location of the highest predemonstration GRO soil concentration, the
GRO concentration was reduced from 2,300 mg/kg to 1,000 mg/kg. However, GRO soil concentrations
increased at some sampling locations, which was attributed to redistribution of contaminants during the
demonstration and/or heterogeneities in contaminant distribution at the site.
Groundwater concentrations also were reduced during the 3-week demonstration period. At most
sampling locations, GRO concentrations were reduced by an order of magnitude. The largest reduction
in GRO concentration occurred at a sampling location approximately 13.5 feet from the RFH well. At
this location, GRO concentration was reduced from 29 mg/L to 0.1 mg/L in the groundwater.
7.4.2
Cost Analysis
This section presents costs developed from past applications of thermal enhancement technologies.
These costs were derived from cost analyses conducted for the field demonstrations of the steam
injection/stripping and ER case studies discussed in Section 7.4.1. Where possible, cost comparisons are
presented to show the difference in costs between using conventional SVE treatment and using SVE with
a thermal enhancement. Costs for the use of steam injection/stripping at the Rainbow Disposal site and
for the use of ER at the SRS site are presented below.
7.4.2.1
Steam Injection/Stripping Costs
Because of the nature of contamination at the Rainbow Disposal site, operation of a conventional SVE
system would not have been practical to remediate the site. Contaminants were present as free product at
the site in saturated soil. Therefore, no cost comparison can be made between remediation of the site
with conventional SVE and with steam injection/stripping.
7-18
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Treatment costs were developed for 12 cost categories as part of the SITE demonstration at the Rainbow
Disposal site (EPA 1995b). Cost were developed for the actual costs developed during two years of
operation at the Rainbow Disposal site; however, because the SERF system had significant (50 percent)
downtime during this period, costs were also developed for an "ideal" (0 percent downtime) case and for
a "typical" (25 percent downtime) case. For each of the three cost analyses, it was assumed that
95,000 yd3 of soil would be treated. The results of the economic analysis for the actual, ideal, and typical
cases are presented in Table 7-2. Figure 7-5 presents the costs per yd3 for each of the 12 cost categories
for the typical case.
As shown in Table 7-2, the soil treatment cost ranges from about $29/yd3 to $43/yd3 for the ideal and
actual cases, respectively. Labor is the largest cost for use of SERF, accounting for about one third of the
total cost. Since labor costs are directly proportional to the duration of remediation, factors that would
increase or decrease the remediation time would impact the total cost most significantly. Startup costs
and utilities are also significant costs for use of SERF, together accounting for about one-third of the
total cost. The cost per yd3 is significantly less than the cost of excavating and treating the soil; however,
as discussed in Section 7.4.1.1, SERF did not meet the treatment goal, and additional treatment may be
necessary. Continued treatment would have increased the total cost and the cost per yd3 for the site. .
7.4.2.2
Electrical Resistance Costs
The targeted zone of contamination treated during the field demonstration of the SPSH technology at the
SRS site is in the vadose zone and is amenable to conventional SVE treatment; therefore, a cost
comparison can be made between remediation with conventional SVE and with SVE used with SPSH.
An independent cost analysis prepared for the DOE by the Los Alamos National Laboratory (DOE 1995)
presents costs for SPSH and compares costs for treatment using SVE alone and treatment using SVE
enhanced with SPSH. The results of the cost analysis are presented below.
Costs were developed for a hypothetical site that contained a 100-foot diameter area that was
contaminated with VOCs and SVOCs from 20 to 120 feet bgs. It was assumed that off-gases from the
SVE extraction well would be destroyed in a catalytic oxidation system. It was also assumed that capital
costs would be amortized over a 10-year period.
7-19
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The estimated costs for SPSH are presented in Table 7-3. The total capital costs were estimated to be
$1,278,000, and the total annual operation and maintenance costs were estimated to be $204,000. The
power source for the SPSH system and the vacuum extraction system are the largest capital costs,
accounting for about two-thirds of the capital costs. For the 29,000 yd3 of soil at the hypothetical site
described previously, capital costs account for about $44/yd3.
The DOE (1995) cost analysis indicates that the total cost of SPSH would be $86/yd3 of treated soil and
that the total cost of SVE would be $576/yd3 of treated soil. The cost analysis assumed that the site
would be remediated in 5 years using SPSH and in 50 years using conventional SVE; however, the basis
of this assumption is not given. The time required to remediate the site is critical for any cost
comparison and may be estimated from modeling contaminant removal rates and field testing. The field
study indicated that mass removal rates measured in the extraction vent tripled after soil temperatures
reached about 100 ฐC. Results of a recent report that compared costs of thermal enhancement
technologies and conventional treatment technologies are also presented.
7.4.3
Additional Cost Studies
A recent report also compares the costs for thermal enhancement technologies with conventional
treatment technologies (Bremser and Booth 1996). The report studied costs for thermal enhancement and
conventional treatment technologies for five different types of contamination as presented below:
Type of Contamination
Shallow vadose zone
contamination
Deep vadose zone VOC
contamination
Deep vadose zone
SVOC contamination
Deep vadose zone with
groundwater contamination
Restricted access contamination
Thermal Enhancement
Technology
Thermally enhanced vapor
extraction system (TEVES)
3-Phase soil heating
6-Phase soil heating
RF heating
Dynamic underground stripping
(DUS)
RF heating using dipole
antennae (RFD)
Couyentional Treatment'' ,
Technology-', / , I
Excavation and Treatment
SVE
SVE
SVE
PT/SVE
SVE
7-20
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The report is based on results of demonstrations of thermal enhancement technologies at DOE sites. The
report concluded that in every treatment case described above, the thermal enhancement technologies
were significantly less expensive than the conventional technologies. The report suggests that the
thermal technologies save money by remediating the contaminants in an estimated 6 months due to the
increased mass removal rate, as compared to conventional SVE treatment that is estimated to take 5 years
to complete. Figure 7-6 presents the cost comparisons, on a cost per yd3 treated basis, for the five
treatment scenarios described above.
7.5
VENDORS
A number of vendors or companies provide thermal enhancement technologies or services. Some
technologies, such as steam injection and hot air injection, use standard equipment such as injection
wells and boilers that can be designed and constructed to meet site-specific needs. These technologies
can be implemented by a relatively large number of companies. Other technologies, such as six-phase
heating and RFH, require more specialized equipment that are provided by a more limited number of
vendors. Table 7-4 presents a list of vendors of thermal enhancement technologies. Table 7-5 presents
potential contaminants and media that can be treated by the thermal enhancement technologies.
7.6 STRENGTHS AND LIMITATIONS
The various types of thermal enhancement technologies have different strengths and limitations. The
strength and limitations of each type of thermal treatment technology are provided below.
7.6.1
Steam Injection/Stripping
The primary strengths of steam injection technologies include:
They provide both heat and pressure to a formation to remove contaminants in the vapor,
aqueous, and NAPL phases. When used in combination with vacuum vapor extraction wells, the
steam injection system can provide a large differential pressure to move contaminants toward the
extraction wells.
Steam injection is more mature than other thermal enhancement technologies to remove NAPLs.
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The primary limitations of steam injection technologies include:
Site geology may limit the performance of steam injection/stripping technologies. The soil
should have moderate to high permeability to allow the steam front to move through the soil.
Impermeable soil formations such as clay materials may not be suitable for steam injection
treatment.
The subsurface geology must provide a confining layer below the depth of contamination to
prevent contamination from migrating vertically downwards. A confining layer is especially
important for applications when steam stripping is used to remove DNAPL. In addition, a
low-permeability surface layer may be needed to prevent steam breakthrough for shallow soil
applications.
Data from the application of steam technologies suggest that soil will remain at elevated
temperatures for an extended period of time. High soil temperatures can delay use of the site or
inhibit natural biodegradation of the residual contamination.
7.6.2
Hot Air Injection
The primary strength of hot air injection technologies include:
Hot air injection is comparatively inexpensive. Hot air can be much easier to provide than
high-quality steam. For example, heated air from a TOU can be reinjected into the subsurface.
The primary limitations of hot air injection technologies include:
Hot air injection is not a very efficient means for delivering heat to the subsurface because of the
relatively low heat capacity of air and the high energy losses in the piping systems.
7.6.3
Radio-Frequency Heating
The primary strengths of RFH technologies include:
With RFH, much faster heating rates and uniform heating can potentially be obtained than with
competing technologies.
The technology does not involve any type of fluid injection and is operated under vacuum
containment conditions, so chances of contaminant spreading is minimized.
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The primary limitations of RFH technologies include:
7.6.4
The high temperatures associated with RFH inhibit biological activity and may induce some
fracturing of the soil structure as the soil dries.
Electrical Resistance
The primary strengths of ER heating technologies include:
The process uses common AC electricity, lowering capital costs and making the technology cost
competitive with RFH.
The technology can be used to enhance bioremediation by increasing biodegradation rates
through heating the soil. The electrodes used in this process are typically thin, and it therefore
requires little soil disturbance to install them.
The primary limitations of ER heating technologies include:
The ER heating system is limited to the temperature that can be applied to the contaminated
region. This process is capable of achieving maximum temperatures of 100 2C.
The effectiveness of the technology depends on soil moisture. Once the soil has been dried by
the electrodes, heating becomes uneven, and efficiencies decrease.
7.7 RECOMMENDATIONS
Thermal enhancement technologies can enhance treatment efficiency and removal rates if certain site or
contaminant characteristics constrain SVE treatment efficiency. Thermal enhancement technologies can
also be used to increase removal rates, thereby decreasing required treatment time. Steam
injection/stripping should be considered for sites that contain nonaqueous phase liquids or high
concentrations of SVOCs and TPH because contaminants are pushed ahead of the condensing water
vapor toward the typical extraction wells. Additionally, some of the contaminants are vaporized or
solubilized by the injection of steam and are moved toward the extraction wells by an applied vacuum.
However, application of steam injection and stripping systems is limited to medium- to high-permeability
soils. ER heating is more appropriate for heating and drying low-permeability soil in the vadose zone.
RFH and ER heating can be used to heat soil if site conditions restrict the use of injection wells.
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7.8 REFERENCES
This section includes a list of references cited in Chapter 7 (Subsection 7.8.1) and a table presenting
professional contacts in the field of thermal enhancement technologies (Subsection 7.8.2).
7.8.1
Cited References
American Academy of Environmental Engineers. 1994. Innovative Site Remediation Technology:
Vacuum Vapor Extraction. WASTECH. Volume 1 of 8.
Bremser, John and Booth, Steven R. 1996. Cost Studies of Thermally Enhanced In Situ Soil
Remediation Technologies. Prepared for Los Alamos National Laboratory Environmental Technology
Costs-Savings Analysis Project. LA-UR-96-1683. May.
Dablow, Jay. 1996. Memorandum Regarding Vendor Information and Performance Data. To Mike
Johnson, Tetra Tech EM Inc. September 6.
EPA. 1994. Vendor Information System for Innovative Treatment Technologies (VISITT), Version 4.0,
Database Prepared by Office of Solid Waste and Emergency Response, Technology Innovation Office.
Cincinnati, Ohio.
EPA. 1995a. Radio Frequency Heating, KAI Technologies, Inc.: Innovative Technology Evaluation
Report. Office of Research and Development. Washington, DC. EPA/540/R-94/528. April.
EPA. 1995b. In Situ Steam Enhanced Recovery Process Hughes Environmental Systems, Inc.:
Innovative Technology Evaluation Report. Office of Research and Development. Washington, DC.
EPA/540/R-94/510. July.
EPA. 1995c. IITRI Radio Frequency Heating Technology: Innovative Technology Evaluation Report.
Office of Research and Development. Washington, DC. EPA/540/R-94/527. June.
Soil &Groundwater Cleanup. 1997. May.
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7.8.2
Professional Contacts
A list of thermal enhancement technology experts is provided in the table below.
cฃฃy$^$?
Dr. Roger Aines
(510) 423-7184
John F. Dablow III
(310) 371-1394
Paul de Percin
(513)569-7797
Harsh Dev
(312) 567-4257
Raymond Kasevich
(603) 431-2266
Laurel Staley
(513) 569-4257
Michelle Simon
(513) 569-7469
Theresa Bergman
(509) 376-3638
Lawrence Livermore National Laboratory
Fluor Daniels GTI, Inc.
EPA National Risk Management Research Laboratory
in Research Institute
KAI Technologies, Inc.
EPA National Risk Management Research Laboratory
EPA National Risk Management Research Laboratory
Battelle Pacific Northwest Laboratory
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7-26
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] Softened Water /
"" V Cleaned
^
' C -*
oiler Feed Tank steam Boi|er
Heat Recovery vafor
Heat Exchangers f ฃ
1 |
| (Stack Vacuum "^
_ Blower ฃ
1 1 Thermnl ^- -^ !
Oxi<
U
rj-. Air Cooled
K Heat Exchanger
K Condensate
Mic
, -, r;u
L |_^ c
[ ' ' 1 Mil " ' 1 | ,-
i o
di.fr x-S
nit
Knock Out M
Drum
v_y
ron 'ง I
ers _. . *: >
n_nJ7 \ S
\\\\l Treated Water o
II II \ / to Storm nrnin
^ Oil/Water 4,000-Gal. Tank Holding Tank Carbon^^^^^^^^^
<; Separator (Recovered Diesel) (Separated Water) Filters s s s^
L
\
1995c
EGEND Extraction
Well
'apor Stream
iquid Stream
~~ i
1
il
2
if
-* Injection
Well
TYPICAL SOIL VAPOR EXTRACTION ENHANCEMENT
WITH STEAM INJECTION SYSTEM
FIGURE
7-2
-------
I
1
Shroud
~4
oo
\
Mix.ng
Kelly Bars.
Auger
SOURCE: MODIFIED FROM EPA 1991
Cutter
Bits
Mixing
' Blade
Auger
Steam
Generator
Water to
Cooling Tower
Process
Train
Condensed Organics
Collection Tank
Recycle Air
Compressors
HOT AIR INJECTION
THROUGH DRILL AUGER
FIGURE
7-3
-------
tsJ
VO
RF Exciter
Electrode
Vapor
Contaminment
Cover
Waste Zone
Contaminated
Soil
Guard
Electrodes
On-Site
Vapor Recovery
and Treatment
Vapor .
Extraction
SOURCE: MODIFIED FROM EPA 1995b
SOIL VAPOR EXTRACTION ENHANCEMENT
WITH RADIO FREQUENCY HEATING
AT SANDIA NATIONAL LABORATORY
FIGURE
7-4
-------
Effluent Treatment
and Disposal
($0.50)
Sampling
and Analytical
(12.34)
Facility
Modification
($0.82)
Site
Demobilization
($1.04)
Site
Preparation
($3.54)
Permitting and
Regulatory
($0.15)
ฃ
o
Residuals Disposal
($0.65)
Utilities
($5.19)
Consumables and
Supplies
($0.34)
Nondepreciable
Equipment
($5.52)
Startup and Fixed
($4.59)
Labor
($10.88)
Note: Costs shown are cost per cubic yard.
SOURCE: MODIFIED FROK' EPA 1995c
COST ANALYSIS OF THE STEAM-
ENHANCED RECOVERY PROCESS
FIGURE
-------
$3,000
$2,500
$2,000
$1,500
$1,000
$500
- 1^* Itestrjcjed t
' ^ ,* Access '1
Shallow .
Vadose Zone
Contamination
^4- ,
.f '
-------
TABLE 7-1
THERMAL ENHANCEMENT PERFORMANCE DATA
(Page 1 of 3)
Vendor
Battelle Pacific
Northwest
laboratories
Geo-Con, Inc.
?lour-Daniels
GTI (FD GH)
FDGTI
FDGTI
Hrubetz
Environmental
Services, Inc.
(Hrubetz)
Hrubetz
Hughes
Environmental
Systems, Inc.
Thermal
Enhancement
Six Phase Soil
Heating
Hot air
injection
Steam
Sparging
Hot Air
Sparging
Electrokinetic
Heating
Hot air
injection
Hot air
injection
Steam recovery
Scale
Field
Demo
Full
Full
Full
Full
Full
EPA
demo
Full
Date
of
Demo
NA
NA
1995
1993
1994
1990
NA
1991
Location
Aiken,
South Carolina
Piketon, Ohio
Bremerton,
Washington
Union,
Massachusetts
Netherlands
Ottawa, Ontario
Canada
Kelly Air Force
Base, Texas
Huntington
Beach, California
Target
Contaminant
PCE
TCE
TCE
No. 6 Fuel Oil
Diesel Fuel
Chlorinated
Solvents
BTEX
Diesel Fuel
Jet Fuel
Jet Fuel (JP-4)
TPH (diesel fuel)
Concentration
Before
Treatment
ND to 500 mg/kg
ND to 200 mg/kg
1 to 100 mg/kg
88,000 mg/kg TPH
100 mg/kg soil
lOmg/L
groundwater (gw)
BTEX(gw):
13,400 //g/L
Diesel (gw):
7,300 Aig/L
TPH (soil):
9,000 mg/L
21,000 mg/L
NA
3,790 mg/kg
Concentration
After
Treatment
ND to 0.5
mg/kg
ND to 0.5
mg/kg
10 mg/kg
Ongoing
Ongoing
BTEX(gw):
ND
Diesel (GW):
<50 Aig/L
TPH (soil): 9 to
220 mg/L
ND to 215 mg/L
12,799 Ib
removed
2,290 mg/kg
Volume
Treated
1,100 yd3
20,000 yd3
25,000 yd3
30,000 yd3
10,500 yd3
300 yd3
890 yd3
150,000 yd3
Soil Type
clayey soil
clayey soil
sandy till
glacial till
sandy clay
NA
NA
layered
sand/clay
Treatment
Time
18 days
NA
Ongoing
Ongoing
24 weeks
90 days
18 days
730 days
Source
EPA 1994
EPA 1994
Tetra Tech
1996
Tetra Tech
1996
Tetra Tech
1996
EPA 1994
EPA 1994
EPA1995b
-------
TABLE 7-1
THERMAL ENHANCEMENT PERFORMANCE DATA
(Page 2 of 3)
Vendor
IIT Research
Institute (IITRI)
IITRI
IITRI
KAI
Technologies,
Inc. (KAI)
KAI
Lawrence
Livermore
National
Laboratory
(LLNL)
Novaterra, Inc.
, Tfiermal
Enhancement
RF Heating
RF heating
RF heating
RF heating
RF heating
Steam
stripping and
electrical
heating
Steam
stripping
Scale
EPA
Demo
Pilot
Pilot
Pilot
EPA
Demo
Full
Full
Bate,
,flf
Demo
1994
1992
1989
1996
1994
1993
1988
, Location '
Kelly Air Force
Base, Texas
Rocky Mountain
Arsenal,
Colorado
VolkAir
National Guard
Base, Wisconsin
St. Paul,
Minnesota
Kelly Air Force
Base, Texas
LLNL
San Pedro,
California
t argot
Contaminant
Aromatics
Nonaromatics
Aldrin
Dieldrin
Endrin
Isodrin
Aromatic VOCs
Aliphatic VOCs
Aromatic SVOCs
Aliphatic SVOCs
Hexadecane
TPH (gasoline)
TRPH
BTEX
TPH (gasoline)
DCA
DCE
Bis(2-ethylhexyl)
phthalate
Aromatics
Butyl carbitol
Concentration
' "" ,' ; Before "
' ฐ Treafnient
40mg/kg
200 mg/kg
1,100 mg/kg
490 mg/kg
630 mg/kg
2,000 mg/kg
212 mg/kg
.4,189 mg/kg
252 mg/kg
1,663 mg/kg
31.5 mg/kg
2,300 mg/kg
1,238 mg/kg
4,800 mg/kg
8,600 gallons
10 to 200 mg/kg
20 to 100 mg/kg
100 to 80,000
mg/kg
1,200 mg/kg
6,000 mg/kg
sCeiit*tttrati0a*
';ฃ&*
, .Treatnieat
2.84 mg/kg
7.2 mg/kg
11 mg/kg
3.2 mg/kg
2.8 mg/kg
2.8 mg/kg
0.88 mg/kg
28 mg/kg
2.3 mg/kg
95 mg/kg
5.4 mg/kg
1,000 mg/kg
636.9 mg/kg
140 mg/kg
1000 gallons
0.47 to 0.82
mg/kg
0.23 to 2.41
mg/kg
52.67 mg/kg
10.77 mg/kg
4.20 mg/kg
Voluwe '
, Created
44yd3
30yd3
19yd3
Not
available
56yd3
100,000 yd3
30,000 yd3
-> s s
- f f
-------
r
TABLE 7-1
THERMAL ENHANCEMENT PERFORMANCE DATA
(Page 3 of 3)
Vendor
Praxis
Environmental
Technologies,
Inc.
R.E. Wright
Environmental,
Inc.
SIVE Services
Thermal
Enhancement
Steam
extraction
Steam
stripping
Steam
Scale
Pilot
Pilot
Full
Date
of
Demo
1988
NA
1989
Location
McClellanAir
Force Base,
California
Bradford,
Pennsylvania
San Jose,
Target
Contaminant
TCE
TPH
VOCs
Concentration
Before
Treatment
ND to 40 mg/L
50,000 to 100,000
mg/kg
NA
Concentration
After
Treatment
ND to 0.05
mg/L
4,500 mg/kg
70,000 Ib
removed
Volume
Treated
5,000yd3
330 yd3
30,000 yd3
Soil Type
NA
NA
NA
Treatment
Time
NA
45 days
400 days
Source
EPA 1994
EPA 1994
EPA 1994
Notes:
Demo
NA
PCE
TCE
ND
Demonstration
Not applicable
Tetrachloroethene
Trichloroethene
Nondetect
TPH Total petroleum hydrocarbon
DCE Dichloroethene
DCA Dichloroethane
Ib Pound
yd3 Cubic yard
mg/L Milligram per liter
mg/kg Milligram per kilogram
VOC Volatile organic compound
SVOC Semivolatile organic compound
BTEX Benzene, toluene, ethylbenzene, and total xylenes
-------
TABLE 7-2
HUGHES STEAM-ENHANCED RECOVERY PROCESS COST SUMMARY
> , S '^ ',* , - * > > *> r * ^* *, - 0 *'**"ซ
> "' < - < ) 0 X ~ *< j. "" V *<".ซ", ' =
, , . (.>.,- / Cost,Catgory " - -f ; ' U* ' '
Site Preparation
Permitting and Regulatory
Non-Depreciable Equipment
Startup and Fixed
Labor
Consumables and Supplies
Utilities
Effluent Treatment and Disposal
Residuals and Waste Handling and Disposal
Sampling and Analytical
Facility Modification, Repair, and Replacement
Site Demobilization
Total
Approximate Actual Costs
for the Rainbow ^jfpiisal:
; [ -' site " \ --'
' 'T0tal#,x
338,000
16,000
523,000
759,000
1,362,000
43,000
631,000
71,000
67,000
300,000
151,000
139,000
. 4,400,000
, .^/y#"5.
3.56
0.17
5.51
7.99
14.34
0.46
6.65
0.75
0.71
3.16
1.59
1.47
46.36
Estimated Id<
>' the Rainbow
, - . " ' Sit<
;" .Total $7 '
326,000
11,000
522,000
414,000
776,000
24,000
280,000
36,000
49,000
196,000
58,000
99,000
2,791,000
:alCos,tfor
t Disposal ,
k f '
ปf>;$/yf v
3.43
0.12
5.50
4.35
8.16
0.26
2.95
0.37
0.52
2.06
0.61
1.04
29.37
- &tijBtafeiisCost'jfwa;
%pfealSitebfJhe,
<''' Saiae'Size , "$ \
.;~'T,0tal$%.
336,000
14,000
524,000
436,000
1,034,000
32,000
493,000
47,000
61,000
222,000
78,000
99,000
3,376,000
'.**?:
3.54
0.15
5.52
4.59
10.88
0.34
5.19
0.50
0.65
2.34
0.82
1.04
35.56
Source: Modified from U.S. Environmental Protection Agency 1995b.
Notes:
yd3 Cubic yard
-------
TABLE 7-3
SIX PHASE SOIL HEATING COST SUMMARY
Cost Description
Total Cost ($)
Capital Costs
Mobilization
Power Source
Water Source
Alternating Current (AC) Applications Well
Site Characterization and Well Installation
Soil Vapor Extraction Pilot Testing
Permitting
Vacuum System
Treatment System
Dismantlement and Demobilization
Startup
Subtotal
Construction Management
Engineering, Design, and Inspection
Project Management
Contingency
Total Capital Cost
9,000
286,000
24,000
54,000
53,000
13,000
16,000
175,000
51,000
23,000
21,000
725,000
73,000
181,000
44,000
255,000
1,278,000
Annual Operation and Maintenance (O&M) Costs
Field Monitoring
Monitoring and Reporting
System Operation and Maintenance
Total Annual O&M Costs
76,000
58,000
70,000
204,000
7-36
-------
TABLE 7-4
THERMAL ENHANCEMENT TECHNOLOGY VENDORS"
(Page 1 of 2)
Name of Vendor " "
Battelle Pacific Northwest
Laboratories
Flour Daniels GTI
Geo-Con, Inc.
Hbrubetz Environmental Services,
Inc.
IIT Research Institute
KAI Technologies, Inc.
Millgard Environmental
Corporation
Praxis Environmental
Technologies, Inc.
R.E. Wright Environmental, Inc.
(REWEI)
Address, Phone, Fax
Battelle Boulevard, P.O. Box 999, Mailstop Bl-40
Richland, Washington 99352
(509) 376-3638
20000/200 Mariner Ave.
Torrance, California 90503
(310) 371-1394
4075 Monroeville Boulevard
Corporate One, Building II, Suite 400
Monroeville, Pennsylvania 15146
(412) 856-7700
5949 Sherry Lane, Suite 525
Dallas, Texas 75225
(214) 363-7833
10 West 35th Street
Chicago, Illinois 60616
(312) 567-4257
170 West Road #7
Portsmouth, New Hampshire 03801
(603) 431-2266
12900 Stark Road
Livonia, Michigan 48150
(313) 261-9760
1440 Rollins Road
Burlingame, California 94010
(415) 548-9288
3240 Schoolhouse Road
Middletown, Pennsylvania 17057
(717) 944-5501
Point of Contact
Theresa Bergsman
Jay Dablow
Linda M. Ward
Barbara Hrubetz
Harsh Dev
Raymond S.
Kasevich
Jim Brannigan
Dr. Lloyd Stewart
Richard C. Cronee,
Ph.D.
7-37
-------
TABLE 7-4
THERMAL ENHANCEMENT TECHNOLOGY VENDORS"
(Page 2 of 2)
Name of Vendor
SIVE Services
Terra Vac, Inc.
Address, Phone, Fax
555 Rossi Drive
Dixon, California 95620
(916) 678-8358
1555 Williams Drive, Suit 102
Marrieta, Georgia 30066-6282
(770) 421-8008
PoMt of Contact.
Douglas K. Dieter
Charles Prince
Note: a This list is not inclusive of all vendors capable of providing thermal enhancement technologies. This list
reflects those vendors that had been contacted in preparation of this report.
7-38
-------
TABLE 7-5
WASTE APPLICATIONS
- , '..'..'. Conta^ifnaatssftidCeirtaiHiBaHtGrBH
"f -. ->' ; Vender. ฐ-. '",
BATTELLE PACIFIC NORTHWEST LABORATORIES
FLOUR DANIEL GTI
GEO-CON.INC.
HRUBETZ ENVIRONMENTAL SERVICES, INC.
IIT RESEARCH INSTITUTE
KAI TECHNOLOGIES, INC.
PRAXIS ENVIRONMENTAL TECHNOLOGIES, INC.
R.E. WRIGHT ENVIRONMENTAL, INC.
STVF. sp.Rvrrps
Halogenated
WCs,
A
A
A
P
A
A
A
P
A
Halogenated
svocr-
p
A
A
P
A
A
A
P
p
VOCs
p
A
p
A
A
A
A
A
A
SVONgs
p
A
P
A
A
P
A
A
p
Besticide
p
p
A
P
A
NA
NA
P
p
psTreated ' ฐ * > ' - >'*
Dioxins/
Furans
p
NA
NA
P
NA
NA
NA
P
p
Idte'
NA
P
NA
P
P
P
P
P
p
> 0
Solvents
A
A
A
A
A
A
A
P
A '
BH2X
p
A
NA
A
A
P
A
A
A
Acefoiiitrile
NA
NA
A
P
NA
P
NA
NA
p
f '<
Organic
Adds
NA
P
A
P
NA
P
NA
P
p
Reference
'Sources
EPA 1994
Dablow 1996
EPA 1994
EPA 1994
EPA 1994
EPA 1994
EPA 1994
EPA 1994
FPA 1094
jj
VO
~ ." . , \, ,
" ," ^ ' s<
N = > ? 0
:',.* v\Vs
Sludge
p
P
NA
NA
P
P
P
NA
NA
ypesTreaiai" e ,- '- ' ,, , I , - < -
Solid
NA
A
P
NA
NA
P
NA
NA
NA
=x
'Natural
Sediment
(in situ)
A
P
A
P
P
P
A
P
P
Matoral*
Sediment
rex?sista)
NA
P
NA
NA
NA
P
NA
P
NA
r ' I > ฐ '
Gtwndtfater
"tasitii) '<
p
A
NA
P
NA
NA
P
A
p
.DHAPL
p
A
NA
NA
P
P
P
P
A
LNAFL
p
A
NA
P
P
P
A
A
A
V ป
Reference
' Sources
EPA 1994
Dablow 1996
EPA 1994
EPA 1994
EPA 1994
EPA 1994
EPA 1994
EPA 1994
FPA 1994
Notes:
A - Actually treated
P - Potentially treatable
NA-Not Applicable
-------
-------
Appendix A
-------
-------
PHOTOGRAPHIC RECORD
Air Sparging
.^uXt 'unjinaj!!Ks: J
Photograph: 3-1
Description:
Source: Billings and Associates, Inc.
Manifold line
1996
layout.
Photograph:' 3-2
Description:
Source: Billings and Associates, Inc.
Valving
1996
for controlling
the air flow.
-------
PHOTOGRAPHIC RECORD
Air Sparging
Photograph: 3-3 Description: Air sparging control equipment center.
Source: Billings and Associates, Inc. 1996
Photograph: 3-4 Description: Air sparging control equipment.
Billings and Associates, Inc. 1996
-------
PHOTOGRAPHIC RECORD
Photograph: 3-5 | Description: Computer control system at an air sparging site.
Source: Billings and Associates, Inc. 1996
Photograph: 3-6
Description: Two air sparging probes (one
removed from a petroleum-contaminated hole)
typically installed using direct push techniques.
Source: Transglobal Environmental
Geochemistry, Hawaii 1996
-------
PHOTOGRAPHIC RECORD
Air Sparging
Photograph: 3-7
Description: Backfilling of a hole in which an air sparging probe has
push techniques.
Source: Transglobal Environmental Geochemistry, Hawaii 1996
been installed using direct
Photograph: 3-8
Description: Final stage of air sparging probe
installation using direct push techniques.
Source: Transglobal Environmental
Geochemistry. Hawaii 1996
-------
PHOTOGRAPHIC RECORD
Dual Phase Extraction
Photograph: 4-1 | Description: Case Study 1, dropping of the tube entrainment extraction well head.
Source: Terra Vac Corporation 1996
I
Photograph: 4-2
Description:
Source: Terra Vac Corporation 1996
Case Study 1, dropping of the tube entrainment extraction
system equipment.
-------
PHOTOGRAPHIC RECORD
Dual Phase Extraction
Photograph: 4-3
Description: Case Study 1, dropping of the tube
entrainment extraction system equipment.
Source: Terra Vac Corporation 1996
-------
PHOTOGRAPHIC RECORD
Directional Drilling
^^^^^^g=gg^---^-..-._.,__.,. - <,g -. " *v
Photograph:
Source:
5-1
Description:
The Ditch Witch RC
drives a
motors.
high-torque
8/60
Jet Trac
bit for greater
mini system
productivity
, including a
special drill pipe that
than traditional downhole
mud
Ditch Witch 1996
-------
I
PHOTOGRAPHIC RECORD
Directional Drilling
Photograph:
Source:
5-2
Description: The Vermeerฎ D24a NAVIGATOR mini system,
performance for longer bore, larger pipe, or tough
which delivers
conditions.
powerful torque and pullback
Vermeer 1996
-------
PHOTOGRAPHIC RECORD
Directional Drilling
Photograph:
5-3
Description:
Source: Photo courtesy American Augers,
The DD-60 midi system used by American Augers, Inc. (the midi system fills in the gap between
the mini and maxi system rigs) provides the performance of the maxi systems without all the
trailers.
Inc. 1996
-------
PHOTOGRAPHIC RECORD
Directional Drilling
Photograph: 5-4
Description: Here is an example of a maxi system with four custom-built trailer-mounted rig
components that set up compactly in an area of 50 feet by 100 feet.
Source: Drilex 1996
-------
PHOTOGRAPHIC RECORD
Pneumatic and Hydraulic Fracturing
iftS'.:Aซ!al--i"-*1p
- - ' : fejl,ป,>. :..,,*ป ป. ,.,> .l.^,..'...*^.-.
Photograph: 6-1
Description: Installation of piping below ground for the full-scale remediation system using
pneumatic fracturing-enhanced dual vapor-phase extraction.
Source: Accutech Remedial Systems, Inc. 1996
Photograph:
Source:
6-2
Description:
Accutech Remedial
Systems,
Groundwater transfer pumps,
extraction manifold housed in
network of fracture wells.
Inc. 1996
flow meters,
the treatment
vacuum gauges, and a
building on a concrete
vacuum
pad above
the
-------
PHOTOGRAPHIC RECORD
Pneumatic and Hydraulic Fracturing
Photograph: 6-3
Description: Pilot-scale pneumatic fracturing-
enhanced bioremediation system showing fracture
hoses, pressure gauges, and a biopump that deliver
microbes into the fracture stream below ground
through the well in the background.
Source: Accutech Remedial Systems. Inc. 1996
-------
PHOTOGRAPHIC RECORD
Pneumatic and Hydraulic Fracturing
Photograph: 6-4
Description:
Researchers from the
fracturing.
University of Cincinnati at a field demonstration of hydraulic
Source: PRC Environmental Management, Inc. 1996
Photograph:
6-5
Description:
Demonstration of the subsurface device used to create the
hydraulic fractures are initiated.
initial notch from which
Source: PRC Environmental Management, Inc. 1996
-------
PHOTOGRAPHIC RECORD
Pneumatic and Hydraulic Fracturing
Photograph:
6-6
Description:
Hydraulic
fracturing
fractures
in clean soils exposed by trenching to study the results of
Source: PRC Environmental Management, Inc. 1996
**R
Photograph: 6-7 I Description: Trench wall exposure of three layers of sand-filled hydraulic fractures.
Source: PRC Environmental Management, Inc. 1996
-------
PHOTOGRAPHIC RECORD
Pneumatic and Hydraulic Fracturing
Photograph:
6-8
Description:
Hydraulic fracturing unit showing the screw mixer, guar gum storage containers,
and delivery hose.
Source: FRX Inc. 1996
.
t- ~* *. -:,.. '-JBaric-
-n-s.^, ป! fsij"---...-:...::_
t .^"-; ;*::*. ^^ ^---"^
Photograph:
6-9
Description:
Hydraulic
fracturing unit
Source: FRX Inc. 1996
showing
power
generation
engines and discharge
nozzles.
-------
PHOTOGRAPHIC RECORD
Thermal Enhancements
Photograph: 7-1
Description: Radio frequency heating zone (beneath aluminum enclosure).
Source: Sandia National Laboratory 1997
Photograph: 7-2
Description: Radio frequency heating unit (20kW).
Source: KAI Technologies, Inc. 1997
-------
PHOTOGRAPHIC RECORD
Thermal Enhancements
Photograph: 7-3
Description: Catalytic oxidation vapor recovery and combustion unit.
Source: Sandia National Laboratory 1997
-------
-------
Appendix B
-------
-------
1.0 BIBLIOGRAPHY
The following subsections list all bibliographic references consulted while preparing this document,
including those specifically cited earlier in the text. The references are listed by chapter.
1.1
CHAPTER 1
EPA. 1996. VISITT 5.0 Bulletin. Vendor Information System for Innovative Treatment Technologies
An Electronic Yellow Pages of Innovative Treatment Technologies and Vendors. EPA-542-N-96-006.
Office of Solid Waste and Emergency Response. Technology Innovation Office. Washington, DC.
1.2
CHAPTERS
Ahlfeld, D.P., A. Dahmani, and W. Ji. 1994. A Conceptual Model of Field Behavior of Air Sparging
and Its Implications for Application. Groundwater Monitoring and Remediation. Fall 1994
Pages 132-139.
Baker, Ralph S., R. Pemmireddy, and D. McKay. 1996. Evaluation of Air-Entry Pressure during In Situ
Air Sparging: A Potentially Rapid Method of Feasibility Assessment. Proceeding of the First
International Symposium on In-Situ Air Sparging, Las Vegas, Nevada, October 24-25,1996.
Barrera, J.A. 1994. Air Sparging and Vapor Extraction as a Means of Removing Chlorinated and BTEX
Compounds in Complex Groundwater Conditions. Superfund XIV Conference and Exhibition
Conference Proceedings. Volume 1.
Billings and Associates, Inc. 1996. Project Description for Firehouse Site. Available on World Wide
Web. at http://www.aristotle.com/sparging/sites. July.
Billings and Associates, Inc. 1996. Project Description for BF1 Site. Available on World Wide Web. at
http://www.aristotle.com/sparging/sites. July.
Billings and Associates, Inc. 1996. Project Description for Bloomfield Site. Available on World Wide
Web. at http://www.aristotle.com/sparging/sites. July.
Terra Vac, Inc. 1995a. Project Description for Underground Storage Tanks - Irvine, California. July.
Terra Vac, Inc. 1995b. Project Description for Fabricated Metal Products - New Paris, Indiana. May.
Brown, R.A. and R. Fraxedas. 1991. Air Sparging - Extending Volatilization to Contaminated Aquifers.
Prepublication draft presented at the Symposium on Soil Venting. Robert S. Kerr, Environmental
Research Laboratory. Houston, Texas. April 29 - May 1.
B-l
-------
Dahmani, M.A., D.P. Ahlfeld, W. Ji, and M. Parrel. 1994. Air Sparging Laboratory Study. Air Sparging
for Site Remediation, ed. Robert E. Hinchee. Lewis Publishers. Ann Arbor, MI. Pages 108-111.
Hinchee, RE. 1994. Air Sparging for Site Remediation. Lewis Publishers. Ann Arbor, MI.
Holt, W. 1994. LNAPL Remediation by Soil Vapor Extraction and Air Sparging. Ground Water.
Volume 32, No. 5. September/October.
Ji, W., A. Dahmani, D.P. Ahlfeld, J.D. Lin, and E.H. Hill. 1993. Laboratory Study of Air Sparging: Air
Flow Visualization. Groundwater Monitoring and Remediation. Fall. Pages 115-126.
Johnson, R.L., P.C. Johnson, R.E. McWhorter, R.E. Hinchee, and I. Goodman. 1993. An Overview of In
Situ Air Sparging. Groundwater Monitoring and Remediation. Fall. Pages 127-135.
Lundegard, Paul D., D. La Brecque. 1996. Integrated Geophysical and Hydrologic Monitoring of Air
Sparging Flow Behavior. Proceedings of the First International Symposium on In-Situ Air Sparging, Las
Vegas, NV, October 24-25,1996.
Marley, M.C. 1992. Air Sparging in Conjunction with Vapor Extraction for Source Removal at VOC
Spill Sites. Hazardous Contaminated Soils. Chapter 34, Pages 579-589.
Marley, M.C, P.J. Hazenbrouck, and M.T. Walsh. 1992. The Application of In Situ Air Sparging as an
Innovative Soils and Groundwater Remediation Technology. Groundwater Monitoring Review.
Volume 12 (2). Spring.
Marley, M.C., and F. Li. 1994. Air Sparging: An Efficient Groundwater and Soils Remediation
Technology. Air Sparging for Site Remediation, ed. Robert E. Hinchee. Pages 23-37. Lewis Publishers.
Ann Arbor, MI.
Marley, Michael C, and C.J. Bruel. 1995. In Situ Air Sparging: Evaluation of Petroleum Industry Sites
and Consideration for Applicability, Design, and Operation. American Petroleum Institute. API
Publication 4609.
Pijls, C.B.G.M., L.G.C.M.Urlings, H.B.R.J. van Vree, and F. Spuij. 1994. Applications of In Situ Soil
Vapor Extraction and Air Injection. Air Sparging for Site Remediation, (ed.) Robert E. Hinchee.
Pages 128-136. Lewis Publishers. Ann Arbor, MI.
Tetra Tech EM Inc. 1997. Personal Communication between Dawn Cosgrove of Tetra Tech EM Inc.
and Dave Becker of the U.S. Army Corps of Engineers. May.
U.S. Environmental Protection Agency (EPA). 1995. Soil Vapor Extraction (SVE) Enhancement
Technology Resource Guide. EPA/542-B-95-003. Office of Solid Waste and Emergency Response.
Technology Innovation Office. Washington, DC.
EPA. 1992. A Technology Assessment of Soil Vapor Extraction and Air Sparging. EPA/600/R-92/173.
Office of Research and Development. Washington, DC.
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-------
EPA. 1993. An Overview of Underground Storage Tank Remediation Options. EPA 510-F-93-029.
Office of Underground Storage Tanks. Washington, DC. October.
Wade, A., B. Holland, and G. Wallace. 1993. Air Sparging and Groundwater Flow: Optimizing
Remedial Potential of Air Sparging through a Horizontal Well. Journal of Environmental Health.
Volume 56 (3). October.
Wehrle, K., and J. Brauns. 1994. Groundwater Circulation Due to Air Injection: General Aspects and
Experimental Results for Layered Subsoil. Air Sparging for Site Remediation, ed. Robert E. Hinchee.
Lewis Publishers. Pages 20-127. Ann Arbor, MI.
1.3
CHAPTER 4
Baker, R.S., and J. Bierschenk. 1995. Vacuum-Enhanced Recovery of Water and NAPL: Concept and
Field Test. Journal of Soil Contamination. Volume 4(1). Pages 57-76.
Brown, R.A., RJ. Falotico, and D.M. Peterson. 1994. Dual Phase Vacuum Extraction Systems for
Groundwater Treatment: Design and Utilization. Superfund XV Conference and Exhibition
Proceedings.
Dodson, M.E., B.E. Trowbridge, and D. Ott. 1994. Use of In-Situ Dual Vacuum Extraction for
Remediation of Soil and Ground Water. Thirty-Third Hanford Symposium on Health and the
Environment~In-Situ Remediation: Scientific Basis for Current and future Technologies. November.
Ghalib, S., and K.H. Kastman. 1995. DNAPL Remediation Using Dual-Phase Extraction. Superfund 16
Conference and Exhibition Proceedings.
Groundwater Service, Inc. (GSI). 1997. Summary of Representative Project Experience. May.
Hackenberg, T.N., J.J. Mastroianni, C.E. Blanchard, J.G. Morse. 1993. Analysis Methods and Design of
Vacuum Enhanced Pumping Systems to Optimize Accelerated Site Cleanup.
Koerner, C.E., and J.D. Long. 1994. Two-Phase Groundwater and Soil Vapor Extraction. In Hazmacon
Conference, San Jose, CA.
Kruseman, G.P., and N.A. de Ridder. 1991. Analysis and Evaluation of Pumping Test Data. ILRI,
Wageningen, The Netherlands. 1991. Second Edition.
Lindhult, E.G., J.M. Tarsavage, and K.A. Foukaris. 1995. Remediation in Clay using Two-Phase
Vacuum Extraction. National Conference on Innovative Technologies for site Remediation and
Hazardous Waste Management Proceedings.
Mastroianni, J., C. Blanchard, T. Hackenberg, and J. Morse. 1994. Equipment Design Considerations
and Case Histories for Accelerated Clean-up Using Vacuum Enhanced Pumping.
B-3
-------
McCoy and Associates, Inc. 1992. Special Feature: Innovative In Situ Cleanup Processes. The
Hazardous Waste Consultant. September/October.
Miller, A.W., and D. R. Gan. 1995. Soil and Groundwater Remediation Using Dual-Phase Extraction
Technology. Superfund 16 Conference and Exhibition Proceedings.
Roth, R., P. Bianco, M. Rizzo, N. Pressly, and B. Frumer. 1995. Phase I Remediation of Jet Fuel
Contaminated Soil and Groundwater at JFK International Airport Using Dual-Phase Extraction and
Bioventing. Superfund 16 Conference and Exhibition Proceedings.
Roy, K.A. 1991. Dual Vacuum Extraction Sinks Below the Surface in Groundwater Cleanup. Hazmat
World. November.
Safrin, T. 1996. Dual-Phase Treatment Reduces Cleanup Time and Cost. Environmental Technology.
May/June.
Stenning, A.H., and C.B. Martin. 1968. An Analytical and Experimental Study of Air-Lift Pump
Performance. Transactions of the ASME Journal of Engineering for Power. Pages 106-110. April.
Tornatore, P.M. 1994. Remediating Low Permeability sites with 2-Phase Extraction - Case Studies.
Superfund XV Conference and Exhibition Proceedings.
Trowbridge, B.E., and D.E. Ott. 1991. The Use of In-Situ Dual Extraction for Remediation of Soil and
Groundwater. National Gfoundwater Association and National Water Well Association.
EPA. 1991. Soil Vapor Extraction Technology Reference Handbook. EPA/540/2-91/003. Office of
Solid Waste and Emergency Response. Technology Innovation Office. Washington, DC.
EPA. 1996. Vendor Information System for Innovative Treatment Technologies (VISITT), Version 5.0.
Database. Office of Solid Waste and Emergency Response. Technology Innovation Office.
Washington, DC.
Wcllensiek, M.R., K.T. McCreanor. 1993. Accelerated Implementation of a Dual-Phase Soil Vapor
Extraction System. Superfund XIV Conference and Exhibition Proceedings.
Wisconsin Department of Natural Resources. 1993. Guidance for Design, Installation, and Operation of
Soil Venting Systems. PUBL-SW185-93. July.
1.4
CHAPTERS
Armstrong, J.E., C.A. Mendoza, B.J.Moore, and P.E. Hardisty. 1994. A Comparison of Horizontal
Versus Vertical Wells for Soil Vapour Extraction. Calgary, Alberta. September 21-28.
B-4
-------
Baker, J.N., et. al. 1993. Use of a Horizontal Air-Dispersion System to Enhance Biodegradation of
Diesel Fuel Contaminated Soils. In: Proceedings of the Conference on Petroleum Hydrocarbons and
Organic Chemicals in Ground Water: Prevention, Detection, and Restoration. The Westin Galleria,
Houston, Texas (Ground Water Management Book 17). Pages 383-395. November 10-12.
Bardsley, D.S. 1995. Horizontal Well Materials. World Wide Web Home Page
(http//:www.horizontalwell.com). By Environmental Consultants LLC.
Barrow, J.C. 1994. The Resonant Sonic Drilling Method: An Innovative Technology for Environmental
Restoration Programs. Ground Water Monitoring Review. Volume 14(2). Pages 153-161.
Conger, R.M. and K. Trichel. 1993. A Ground-Water Pumping Application for Remediation of a
Chlorinated Hydrocarbon Plume with Horizontal Well Technology. In: Proceedings of the Seventh
National Outdoor Action Conference and Exposition, Las Vegas, Nevada. Dublin, Ohio. National
Ground Water Association. Pages 47-61.
Dickinson, W.W., R.W. Dickinson, P.A. Mote, and J.S. Nelson. 1987. Horizontal Radials for
Geophysics and Hazardous Waste Remediation. Presented at Superfund '87. Silver Spring, Maryland.
Hazardous Waste Control Research Institute. Pages 371-375.
Downs, C.E. 1996. Multimedia Remediation Applications of Horizontal Wells. In: Proceedings of the
Tenth National Outdoor Action Conference and Exposition, Las Vegas, Nevada. National Ground Water
Association. Pages 237-243. May 13-15.
Gaillot, G. 1996. Operation of Horizontal Wells for In Situ Leachate Collection. In: Proceedings of
the Tenth National Outdoor Action Conference and Exposition, Las Vegas, Nevada. National Ground
Water Association. Pages 207-220. May 13-15.
Ghandehari, M.H., and others. 1994. In Situ Remediation of Groundwater Using Horizontal Well Air
Injection. In: Proceedings of the Conference on Petroleum Hydrocarbons and Organic Chemicals in
Ground Water: Prevention, Detection, and Restoration. The Westin Galleria, Houston, Texas Pages
221-235. November 2-4.
Horizontal News. 1995. Published by Colorado Center for Environmental Management for the
Department of Energy Office of Technology Development. Volume 1, Number 1, Winter.
Horizontal News. 1995. Published by Colorado Center for Environmental Management for the
Department of Energy Office of Technology Development. Volume 1, Number 2, Fall.
Horizontal Wells are Cost-Effective for In Situ Air Stripping (no author). 1992. Ground Water
Monitoring Review. Volume 12. Number 3. Page 55.
Johnson, R.L., and others. 1993. An Overview of In Situ Air Sparging. Ground Water Monitoring and
Remediation. Volume 13. Number 4. Pages 127-135.
Joshi, S.A. 1991. Horizontal Well Technology. Tulsa, Oklahoma. Pennwell Books.
B-5
-------
Kaback, D.D., B.B. Looney, C.A. Eddy, and T.C. Hazen. Innovative Ground Water and Soil
Remediation: In Situ Air Stripping Using Horizontal Wells, Westinghouse Savannah River Company,
Savannah River Site, Aiken South Carolina.
Kaback, D., and D. Oakley. 1996. Horizontal Environmental Wells in the United States: A Catalogue.
Colorado Center for Environmental Management. April.
Karlsson, H. and Ditto, R. 1990. New Horizontal Well Bore System for Monitor and Remedial Wells.
Presented at Superfund '90, Washington D.C., November 26-28.
Karlsson, H. 1993. Horizontal Systems Technology for Shallow Site Remediation. Journal of
Petroleum Technology. February.
Knaebel, K.S. 1981. Simplified Sparger Design. Chemical Engineering. Pages 116-117. March 9.
Looney, B.B., T. Hazen, D. Kaback, and C. Eddy. 1991. Full-Scale Field Test of the In Situ Air
Stripping Process at the Savannah River Integrated Demonstration Test Site. WSRC-RD-91-22. Aiken,
South Carolina. Westinghouse Savannah River Company. July.
Losonsky, G., and others. 1996. Comparing Horizontal Groundwater Extraction Well Efficiencies at
hazardous Waste Sites - Implications for Well Planning and Development. In: Proceedings of the Tenth
National Outdoor Action Conference and Exposition, Las Vegas, Nevada. National Ground Water
Association. Pages 183-188. May 13-15.
Lowe, G.A., H, and W.S. Watkins. 1994. Viability of Horizontal Directional Drilling Utilization for Soil
and Groundwater Remediation. In: Proceedings of the Energy-Sources Technology Conference, New
Orleans, Louisiana. American Society of Mechanical Engineers. New York, NY. PD-Volume 56.
Pages 215-219.
Lundegard, P.D. and G. Anderson. 1996. Multi-Phase Numerical Simulation of Air Sparging
Performance: Groundwater. Volume 34(3). Pages 451-460.
Lundegard, P.D., Chaffee, B and D. LaBrecque, 1996. Effective Design of a Horizontal Air Sparging
Well. Presented at the St. International Conference on Air Sparging, International Network of
Environmental Training, Inc. October.
Maccagno, M.D., S.D. Ross, and P.E. Hardisty. 1996. Containment of a Dissolved-Phase Plume Using a
Horizontal Well. In: Proceedings of the Tenth National Outdoor Action Conference and Exposition, Las
Vegas, Nevada. National Ground Water Association. Pages 221-236. May 13-15.
Mast, V.A. and K.E. Koerner. 1996. Environmental Horizontal Directional Drilling Technology.
No-Dig Engineering, Volume 3 (2). Pages 17-21. March/April.
May, D.W. 1994. The Use of Horizontal Wells for Subsurface Soil and Aquifer Restoration, Drilling
Technology. In: J.P. Vozniak, ed,. American Society of Mechanical Engineers, New York, NY.
PD-Volume 56. Pages 227-239.
Mcndoza, C.A. 1992. VapourT Users Guide. Department of Geology, University of Alberta, Edmonton.
B-6
-------
Morgan, J.H. 1992. Horizontal Drilling Applications of Petroleum Technologies for Environmental
Purposes. Ground Water Monitoring Review. Volume 12 (3). Pages 98-102.
Oakley, D., et. al. 1992. The Use of Horizontal Wells in Remediating and Containing a Jet Fuel Plume:
Preliminary Findings. In: Proceedings of the Conference on Petroleum Hydrocarbons and Organic
Chemicals in Ground Water: Prevention, Detection, and Restoration. The Westin Galleria, Houston,
Texas. Ground Water Management Book 14. 13 Pages. November 4-6.
Perry, R.H. and C.H. Chilton, ed. 1975. Chemical Engineers Handbook. Fifth Edition. McGrawHill.
New York.
Roth, R.J., P.V. Bianco, and C. Palmer. 1995. Pilot Study Report International Arrivals Building JFK
International Airport, Jamaica, NY. Prepared by TerraVac. November 17.
Roth, R.J., and N.C. Pressly 1996. Remediation of Jet-Fuel-Contaminated Soil and Groundwater at JFK
International Airport Using Horizontal Air Sparging and Soil Vapor Extraction. Presented at the First
International Conference on Air Sparging. International Network of Environmental Training Inc
October 24.
Sale, T.C. and D. Applegate. 1994. Oil Recovery at a Former Wood Treating Facility. Proceedings of
the Innovative Solutions for Contaminated Site Management, Water Environment Federation, Miami, FL.
Schroeder, J.D., et al. 1992. In Situ Air Stripping: Cost Effectiveness of a Remediation Technology
Field Tested at the Savannah River Integrated Demonstration Site. LA-UR-92-1927. Los Alamos
National Laboratory, New Mexico.
Staller, G.E., R.P. Wenyde, and R.R. Layner. 1994. Casing Pull Tests for Directionally Drilled
Environmental Wells. Sandia Report SAND94-2387 UC-2000. Albuquerque, NM. Sandia National
Laboratories. November.
Swanson, G. J. 1996. New Product Enters Environmental Drilling Market. Water Well Journal
Volume L (5). Pages 62-64.
Ta Inglis, T.A. 1987. Directional Drilling, Petroleum Engineering, and Development Studies.
Volume 2. Graham and Trotman. Boston, MA.
Tarshish, M. 1992. Combined Mathematical Model of Flow in an Aquifer-Horizontal Well System.
GroundWater. Volume 30(6). Pages 931-935.
Treadway, C. 1996. Horizontal Direction DriUing: Environmental Applications. Water Well Journal
Volume L (5). Pages 57-61.
U.S. Army Corps of Engineers. 1995. Soil Vapor Extraction and Bioventing, Engineer Manual
EM 1110-1-4001. November.
U.S. Department of Energy 1995. In Situ Bioremediation Using Horizontal Wells, Innovative
Technology Summary Report, prepared by Colorado Center for Environmental Management.
Denver, CO.
B-7
-------
EPA. 1994. Alternative Methods for Fluid Delivery and Recovery. EPA/625/R-94/003. Office of
Research and Development. Washington, DC.
EPA. 1996. Vendor Information System for Innovative Treatment Technologies (VISITT), Version 4.0.
Database Prepared by Office of Solid Waste and Emergency Response. Technology Innovation Office.
Washington, D.C.
Vinsome, P.D.W., and G.M. Shook. 1993. Multi-Purpose Simulation. Journal of Petroleum Science and
Engineering. Volume 9. Pages 29-38.
Wade, A., and others. 1996. Performance Comparison Between a Horizontal and a Vertical Air
Sparging Well: A Full-Scale One-Year Pilot Study. In: Proceedings of the Tenth National Outdoor
Action Conference and Exposition, Las Vegas, Nevada. National Ground Water Association.
Pages 189-206. May 13-15.
Wcmple, R.P., and others. 1994. Final Report for SOL/NM Environmental Drilling Project. Sandia
Report SAND94-2388 UC-2000. Albuquerque, NM and Livermore, CA. Sandia National Laboratories.
November.
Westinghouse Savannah River Company (WSRC). 1989. Well Completion Report on Installation of
Horizontal Wells for In Situ Remediation Tests. WSRC-RP-89-784. Aiken,SC. Westinghouse
Savannah River Company. August.
WSRC. 1992. Demonstration of Utility Industry Horizontal Drilling System: Horizontal Well AMH-5
Installation Report. WSRC-TR-93-008. Aiken, SC. Westinghouse Savannah River Company.
December.
WSRC. 1992. Demonstration of Eastman Christensen Horizontal Drilling System, Integrated
Demonstration Site, Savannah River Site. WSRC-TR-92-577. Aiken, SC. Westinghouse Savannah
River Company. December.
WSRC 1993. Demonstration of River Crossing Technology for Installation of Environmental
Horizontal Wells: AMH-6 and AMH-7 Installation Report. WSRC-TR-93-387. Aiken, SC.
Westinghouse Savannah River Company. May.
WSRC. 1993. Summary Report of the Drilling Technologies Tested at the Integrated Demonstration
Site. WSRC-TR-93-565. Aiken, SC. Westinghouse Savannah River Company. October.
Westmoreland,!. 1994. Evaluation of an Air Drilling Cutting Containment System. Sandia Report
SAND94-0214 UC-721. Albuquerque, NM. Sandia National Laboratories. April.
Wilson, D.D. 1994. Horizontal Wells. Water Well Journal. Volume 48 (9). Pages 45-47.
Wilson, D. D. 1995a. Introduction to 1995 NGWA Environmental Horizontal Well Seminar. World
Wide Web Home Page (http//:www.horizontalwell.com). October.
Wilson, D.D. 1995b. Environmental Horizontal Well Drilling and Installation Methods. World Wide
Web Home Page (http//:www.horizontalwell.com), by Environmental Consultants, LLC.
B-8
-------
Wilson, D.D., and D.S. Kaback. 1993. Industry Survey for Horizontal Wells. Final Report.
WSRC-TR-93-511. Aiken, SC. Westinghouse Savannah River Company. July.
Wilson, D.D., and D.S. Kaback. 1993. Results of a Survey of Horizontal Environmental Well
Installations. In: Vozniak, J.P. ed., Drilling Technology 1994. American Society of Mechanical
Engineers. New York, NY. PD-Volume 56. Pages 193-199.
Wilson, D.D., and D.S. Kaback. 1993. Horizontal Wells Improve Access for VOC Remediation:
Stretching the Limit for the Utility Industry. In: Abstract from the 1993 National Ground Water
Association National Convention. Ground Water. Volume 31 (5). Pages 853-854.
Wu, J., and H. Juvkan-Wold. 1994. The Effect of Wellbore Curvature on Tubular Buckling and Lockup,
Drilling Technology. In: Vozniak, J.P., ed., American Society of Mechanical Engineers. New York,
NY. PD-Volume 56. Pages 17-25.
1.5
CHAPTER 6
Accutech Remedial Systems, Inc. 1996. Pneumatic Fracturing Project Summaries and Photographs
Submitted by Mike Galbraith. Keyport, NJ. August.
Anderson, D.B., B.M. Peyton, JJ. Liskowitz, C. Fitzgerald, and J.R. Schuring. 1995. Enhancing In Situ
Bioremediation with Pneumatic Fracturing. Report prepared by Battelle Memorial Institute under DOE
contract DE-AC06-76RLO 1830. Pages 1-12.
Baker, I.E. and B. Leach. 1995. Soil Fracturing Cracks Soil Remediation Barriers. Environmental
Solutions. Volume 8 (3). Pages 26-27.
Baker, J.E. and S.L. Wells. 1995. Use of Hydraulic Fracturing to Enhance Soil Vapor Extraction - a
Case Study. In: Emerging Technologies in Hazardous Waste Management Vii. Tedder, D.W., ed.
American Chemical Society Special Symposium. Pages 559.
Begor, K.F., M.A. Miller, and R.W. Sutch. 1989. Creation of an Artificially Produced Fractured Zone to
Percent Contaminated Ground Water Migration, Ground Water Volume 27 (1). Pages 57-65.
Clark, L.J. 1988. The Field Guide to Water Wells and Boreholes. John Wiley and Sons, Inc., New York
155 p.
Davis-Hoover, W.J., SJ. Vesper, and L.C. Murdoch. 1992. Delivery Techniques and Enhancement of
Bioremediation for in Situ Restoration of Contaminated Subsurface Soils. Subsurface Restoration
Conference, Dallas. Pages 1-3. June.
Davis-Hoover, W.J., L.C. Murdoch, SJ. Vesper, H.R. Pahren, O.L. Sprokel, C.L. Chang, A. Hussain, and
W.A. Ritschel. 1993. Hydraulic Fracturing to Improve Nutrient and Oxygen Delivery for In Situ
Bioreclamation. In: In Situ Bioreclamation. Hinchee, R.E. and R.F. Olfenbuttel, (eds.)
Butterworth-Heinemann Publisher. Pages 67-82.
B-9
-------
Dorrler, R.C. and S.R. Green. 1993. Innovative System Combines Technologies: Pneumatic Fracturing
and Air Injection Blow Old-fashion Pump-and-Treat Method out of the Water. Soils. Pages 26-29.
October.
Du, Y., A. Aydin, and L.C. Murdoch. 1993. Incremental Growth of a Shallow Hydraulic Fracture at a
Waste Remediation Site, Oakbrook, Illinois from Inversion of Elevation Changes. Int. J. Rock Mech.
Min. Sci. Volume 30 (7). Pages 1273-1279.
Echo-Scan Corporation. 1996. Fracture Monitoring and Mapping Project Summaries Submitted by M.
Deryl Wood. Gary, NC. August.
Frac Rite Environmental Ltd. 1996. Hydraulic Fracturing Project Summaries Submitted by Gordon H.
Bures. Calgary, Canada. July.
Frank, U. 1994. U.S. Environmental Protection Agency's Superfund Innovative Technology Evaluation
of Pneumatic Fracturing Extraction. J. Air and Waste Management Assoc. Volume 44.
Pages 1219-1223.
Frank, U. and N. Barkley. 1995. Remediation of Low-permeability Subsurface Formations by
Fracturing Enhancement of Soil Vapor Extraction. Journal of Hazardous Materials, Volume 40. Pages
191-201.
FRX Inc. 1996. Hydraulic Fracturing Project Summaries and Photographs Submitted by William W.
Slack and Larry C. Murdoch. Cincinnati, OH. July.
Fuss and O'Neill, Inc. 1996. Hydraulic Fracturing Project Summary Submitted by David L. Bramley.
Manchester, CT. July.
Green, S.R. and R.C. Dorrler. 1996. Four Bullets Shoot down Costs: Combined Technology Approach
Cleans up Faster and Cheaper than Pump-and-Treat. Soil and Groundwater Cleanup. March.
Keffer, E.B., J. J. Liskowitz, and C.D. Fitzgerald. 1996. The Effect of Pneumatic Fracturing When
Applied to Groundwater Aquifers. In: Proceedings of the Sixth West Coast Conference on
Contaminated Soils and Groundwater. Pages 1-21.
Liskowitz, J., J. Schuring, and J.P. Mack. 1993. Application of Pneumatic Fracturing Extraction for the
Effective Removal of VOCs in Low Permeable Formations. Ground Water Management. Volume 16.
Pages 249-265.
Lundy, D.A., CJ. Carleo, and M.M. Westerheim. 1994. Hydrofracturing Bedrock to Enhance DNAPL
Recovery. Proceedings of the Eighth National Outdoor Action Conference and Exposition. Minneapolis,
MN. Pages 129-143.
Mack, J.P. and H.N. Apsan. 1993. Using Pneumatic Fracturing Extraction to Achieve Regulatory
Compliance and Enhance VOC Removal from Low-permeability Formations. Remediation. Summer.
Pages 309-326.
B-10
-------
Miller, R.R 1996. Blast-Enhanced Fracturing. Technology Summary Report. TS-96-01. Ground-Water
Remediation Technologies Analysis Center. Pittsburgh, PA.
Murdoch, L.C. 1993. Hydraulic Fracturing of Soil During Laboratory Experiments, Parts I,II and III
Geotechnique. Volume 43 (2). Pages 255-287.
Murdoch, L.C., G. Losonsky, I. Klich, and P. Cluxton. 1990. Hydraulic Fracturing to Increase Fluid
Flow. In: F. Arendt and Others, (eds.) Contaminated Soil. Kluwer Academic Publishers Netherlands
Pages 1087-1094.
Murdoch, L.C., G. Losonsky, P. Cluxton, B. Patterson, I. Klich, and B. Braswell. 1991. Feasibility of
Hydraulic Fracturing of Soil to Improve Remedial Actions. Project Summary. EPA/600/S2-91/012.
Office of Research and Development. Cincinnati, OH.
Pisciotta, T., D. Pry, J.R. Schuring, P.C. Chan, and J. Chang. 1994. Enhancement of Volatile Organic
Extraction in Soil at an Industrial Site. In: Proceedings of FOCUS Conference on Eastern Regional
Ground Water Issues. Pages 1-13.
Tetra Tech EM Inc. 1996. Hydraulic Fracturing Photographs Submitted by Roger Argus and Inerid
Klich. Vienna, VA. July.
Schuring, J.R., P.C. Chan, and T.M. Boland. 1995. Using Pneumatic Fracturing for In-Situ Remediation
of Contaminated Sites. Remediation. Spring. Pages 77-89.
Smith, L.P. and R.E. Heeks. 1992. Innovative Remedial Technologies Applied to Chlorinated Solvents
in Fractured Rock. Proceedings 5th Annual Hazardous Materials and Environmental Management
Conference. Chicago, IL.
U.S. Environmental Protection Agency (EPA). 1991. Stabilization Technologies for RCRA Corrective
Actions. EPA/625/6-91/026.
EPA. 1993a. Accutech Pneumatic Fracturing and Hot Gas Injection, Phase 1. Application Analysis
Report. EPA/540/AR-93/509. Office of Research and Development. Washington, DC.
EPA. 1993b. Technology Evaluation Report: Accutech Pneumatic Fracturing Extraction and Hot Gas
Injection, Phase 1. Volume 1. EPA/540/R-93/509. Office of Research and Development. Cincinnati,
OH.
EPA. 1993c. Applications Analysis and Technology Evaluation Report. Hydraulic Fracturing
Technology. EPA/540/R-93/505. Office of Research and Development. Washington, DC.
EPA. 1993d. Technology Demonstration Summary: Hydraulic Fracturing Technology.
EPA/540/SR-93/505. Center for Environmental Research Information. Cincinnati, OH.
EPA. 1994. Alternative Methods for Fluid Delivery and Recovery. Manual. EPA/625/R-94/003.
Office of Research and Development. Washington, DC.
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-------
EPA 1995 In Situ Remediation Technology Status Report: Hydraulic and Pneumatic Fracturing.
EPAS42-K-94-005. Office of Solid Waste and Emergency Response. Technology Innovation Office.
Washington, DC.
EPA 1996 Vendor Information System for Innovative Treatment Technologies (VISITT) Version 5.0.
Database. Office of Solid Waste and Emergency Response. Technology Innovation Office.
Washington, DC.
Wolf, A. and L.C. Murdoch. 1993. A Field Test of the Effect of Sand-filled Hydraulic Fractures on Air
Flow'in Silty Clay. Ground Water Management. Volume 15. Pages 161-175.
1.6
CHAPTER?
American Academy of Environmental Engineers. 1994. Innovative Site Remediation Technology:
Vacuum Vapor Extraction. Volume 1 of 8. WASTECH.
Bremser J and S.R. Booth. 1996. Cost Studies of Thermally Enhanced In Situ Soil Remediation
Technologies. Prepared for Los Alamos National Laboratory Environmental Technology Costs-Savings
Analysis Project. LA-UR-96-1683. May.
Dablow.Jay. 1996. Memorandum Regarding Vendor Information and Performance Data. To Mike
Johnson, Tetra Tech EM Inc. September.
Perry, R.H., ed. 1963. Perry's Chemical Engineers'Handbook, 4th Edition. McGraw-Hill, Inc. New
York. Pages 3-47 through 3-60.
EPA 1991. Toxic Treatments, In Situ Steam/Hot-Air Stripping Technology: Applications Analysis
Report. EPA/540/A5-90/008. Office of Research and Development. Washington, DC.
EPA. 1993. Superfund Innovation Technology Evaluation Program Technology Profiles. Sixth Edition.
EPA/540/R-93/526. Office of Research and Development. Washington, DC.
EPA 1995a. Radio Frequency Heating, KAI Technologies, Inc.: Innovative Technology Evaluation
Report. EPA/540/R-94/528. Office of Research and Development. Washington, DC.
EPA. 1995b. DTTRI Radio Frequency Heating Technology: Innovative Technology Evaluation Report.
EPA/540/R-94/527. Office of Research and Development. Washington, DC.
EPA 1995c In Situ Steam Enhanced Recovery Process Hughes Environmental Systems, Inc.:
Innovative Technology Evaluation Report. EPA/540/R-94/510. Office of Research and Development.
Washington, DC.
B-12
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