United States Office of Solid Waste and

Environmental Protection Emergency Response EPA-542-R-97-007

Agency (5102G) September 1997

Analysis of Selected

Enhancements for

Soil Vapor Extraction
i

CONTENTS

Chapter Page

FOREWORD .............................................................. . ABS-1

EXECUTIVE SUMMARY ...................................................... . ES-1

1.0 INTRODUCTION ....................................................... . 1-1

1.1 BACKGROUND .................................................. . 1-1

1.2 OBJECTIVES .................................................... . 1-2

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 ........................................................ . 3-1

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 Requirements 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 ............................. . 3-13

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 ................................ . 3-19

3.4.2.2 Cost for Subsurface Volatilization Ventilation System ........ . 3-20
CONTENTS (Continued)

Chapter Page

ii

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 ............................ . 4-13

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
CONTENTS (Continued)

Chapter Page

iii

4.4.2 Cost Analysis .............................................. . 4-19

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 ............................. . 5-7

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 ............................ . 5-12

5.4.1 Performance ............................................... . 5-13
CONTENTS (Continued)

Chapter Page

iv

5.4.1.1 U.S. Department of Energy Savannah River Site

Integrated Demonstration Site ........................... . 5-13

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 ............................... . 5-17

5.4.2 Cost Analysis .............................................. . 5-20

5.5 VENDORS ...................................................... . 5-21

5.6 STRENGTHS AND LIMITATIONS .................................. . 5-21

5.7 RECOMMENDATIONS ........................................... . 5-23

5.8 REFERENCES .................................................. . 5-23

5.8.1 Cited References ............................................ . 5-23

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 .............................................. 6-10

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 .............................. . 6-14
CONTENTS (Continued)

Chapter Page

v

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

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 ........................................ . 6-25

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 .................... . 7-6

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 ................................... . 7-16

7.4.1.3 Former Gasoline Station Near St. Paul, Minnesota ............ . 7-17

7.4.2 Cost Analysis .............................................. . 7-18
CONTENTS (Continued)

Chapter Page

vi

7.4.2.1 Steam Injection/Stripping Costs .......................... . 7-19

7.4.2.2 Electrical Resistance Costs .............................. . 7-19

7.4.3 Additional Cost Studies ....................................... . 7-20

7.5 VENDORS ...................................................... . 7-21

7.6 STRENGTHS AND LIMITATIONS .................................. . 7-22

7.6.1 Steam Injection/Stripping ..................................... . 7-22

7.6.2 Hot Air Injection ............................................ . 7-22

7.6.3 Radio-Frequency Heating ..................................... . 7-23

7.6.4 Electrical Resistance ......................................... . 7-23

7.7 RECOMMENDATIONS ........................................... . 7-24

7.8 REFERENCES .................................................. . 7-24

7.8.1 Cited References ............................................ . 7-24

7.8.2 Professional Contacts ........................................ . 7-25

Appendices

A PHOTOGRAPHIC LOG

B BIBLIOGRAPHY
vii

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 ........................................................ 3-27

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 GROUNDWATER ..................... 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 GROUNDWATER MONITORING WELLS

DOWNGRADIENT FROM THE HORIZONTAL SPARGING WELL ............... 5-35

5-9 TCE CONCENTRATIONS IN THREE GROUNDWATER MONITORING

WELLS NEAR THE VERTICAL SPARGING WELL ........................... 5-36
FIGURES (continued)

Figure Page

viii

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 GROUNDWATER REMOVAL BEFORE

HYDRAULIC FRACTURING .............................................. 6-34

6-10 CUMULATIVE GROUNDWATER REMOVAL AFTER

HYDRAULIC FRACTURING .............................................. 6-35

7-1 RELATIONSHIP BETWEEN INCREASING TEMPERATURE AND VAPOR

PRESSURE FOR SEVERAL CHEMICALS ................................... 7-26
FIGURES (continued)

Figure Page

ix

7-2 TYPICAL SOIL VAPOR EXTRACTION ENHANCEMENT

WITH STEAM INJECTION SYSTEM ....................................... 7-27

7-3 HOT AIR INJECTION THROUGH DRILL AUGER ............................ 7-28

7-4 SOIL VAPOR EXTRACTION ENHANCEMENT WITH RADIO-FREQUENCY

HEATING AT SANDIA NATIONAL LABORATORY .......................... 7-29

7-5 COST ANALYSIS OF THE STEAM-ENHANCED RECOVERY PROCESS .......... 7-30

7-6 COST COMPARISON OF THERMAL ENHANCEMENT AND

CONVENTIONAL TREATMENT TECHNOLOGIES ........................... 7-31
x

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 COST DATA ........................................................... 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
TABLES (continued)

Table Page

xi

6-5 COST DATA FOR HYDRAULIC FRACTURING .............................. 6-43

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
xii

ACRONYMS AND ABBREVIATIONS

Fg/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

C Degrees Celsius o

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

F Degrees Fahrenheit o

Frac Frac Rite Environmental, Ltd

FRX FRX, Inc.

GAC Granular activated carbon

gpm Gallons per minute

GRO Gasoline range organics

HDPE High density polyethylene

Hz Hertz

in/sec Inches per second
ACRONYMS AND ABBREVIATIONS (Continued)

xiii

ISB In situ bioremediation

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

SVVS Subsurface Volatilization and Ventilation System ®

TCA Trichloroethane

TCE Trichloroethene
ACRONYMS AND ABBREVIATIONS (Continued)

xiv

Tetra Tech Tetra Tech EM Inc.

TIO Technology Innovation Office

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

yd Cubic yard 3
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.
FOREWORD

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.
ES-1

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 20EC

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 or 1 x 10 centimeter per second (cm/s). SVE by itself does not effectively remove contaminants -3 -2

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:

C Air Sparging

C Dual-phase Extraction

C Directional Drilling

C Pneumatic and Hydraulic Fracturing

C Thermal Enhancement
ES-2

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
ES-3

treatment. DPE provides a means to accelerate removal of nonaqueous-phase liquids (NAPL) and

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
ES-4

to assess groundwater and soil characteristics as well as project objectives for determining which type of

DPE is appropriate for the site.

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:

C 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.

C 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.

C 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.
ES-5

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.

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
ES-6

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.

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
ES-7

organic compounds with low vapor pressures, reduction of treatment time for difficult matrices, treatment

of NAPLs, and enhancement of biological activity in soil.

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.
ES-8

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 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.
1-1

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 insitu 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
1-2

characterization and design phases of remediation projects. Other technologies may enhance SVE

treatment effectiveness (for example, bioventing); however, this report focuses solely on the enhancements

listed above.

Listed 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:

C Describe the background, applicability, and assessment of SVE enhancements 

C Perform an engineering evaluation of each technology to evaluate performance, cost, strengths, and

weaknesses
1-3

C Evaluate the current status of each technology

C Compile a vendor list for each technology

C 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:

C Conduct literature reviews - Studies conducted by academic institutions, Federal agencies, state

programs, and other entities were reviewed to identify previous applications of enhancement

technologies

C 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)

C 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 

C 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

C 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:
1-4

C Initially, technology vendors were identified by accessing the Vendor Information System for

Innovative Treatment Technologies (VISITT) database (EPA 1996). The VISITT database

provides vendor information for innovative treatment technologies.

C 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:

C The applicability of the enhancement

C Cost and performance information

C List of technology vendors

C Strengths and limitations

C List of references

C Figures

C 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.
1-5

TABLE 1-1

SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION

(Page 1 of 3)

Technology Air Sparging Dual-Phase Extraction Directional Drilling Hydraulic Fracturing Thermal Enhancement

Pneumatic and

Description Injection of air occurs below Removal of contaminated Installation of extraction or Injection of gases (typically The transfer of heat to the

or within contaminated water and soil gases from a injection wells in the most air) or fluids (either water subsurface improves or

zones through wells or common extraction well beneficial location relative or slurries) into low- speeds up contaminant

sparging probes. The takes place under vacuum to the area of permeable soil and transport and removal

injected air removes conditions. Groundwater contamination, and soil sediments increases the mechanisms such as gas

adsorbed VOCs in soil and extraction exposes soil anisotropy maximizes the performance of extraction advection, chemical

dissolved contaminants in formerly in the capillary results of an SVE system. or injection wells used in partitioning to the vapor

groundwater as the air rises fringe and saturated zones This technology increases SVE. Development of phase, gas phase

through the formation. The to the extraction system the useful zone of influence fractures may occur in contaminant diffusion,

increase in dissolved vapor flow. The three of the well and reduces saturated sediments as well sorption of contaminant on

oxygen can also increase primary methods used are short circuiting problems in as in the vadose zone. soil surfaces, and chemical

biodegradation of drop-tube entrainment, vertical boreholes. or biological

aerobically degradable well-screen entrainment, transformation. Methods

contaminants. and downhole-pump include steam or hot air

extraction. injection, radio-frequency

heating, electrical resistance

heating, and thermal

conduction.

Status In use at many sites in the Currently in use at many First applied to Adapted from the petroleum Several full-scale

United States and Europe sites in the United States. environmental remediation industry in 1990; a number applications of steam and

since the 1980s. in 1988; the number of of pilot- and full-scale hot air injection and

horizontal wells used for applications of fracturing electrical resistance

environmental remediation enhancement SVE technologies conducted in

has increased dramatically conducted in recent years. recent years; commercial

in recent years. systems available. Several

pilot-scale applications of

radio-frequency heating and

electrical heating have also

been conducted, but

commercial systems are

relatively limited.
1-6

TABLE 1-1

SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION

(Page 2 of 3)

Technology Air Sparging Dual-Phase Extraction Directional Drilling Hydraulic Fracturing Thermal Enhancement

Pneumatic and

Applicable Situations Most effective at removing Most applicable at sites Suitable in many geologic Generally used at sites with Often used in situations

volatile contaminants from with multiple phase (soil materials ranging from low-permeable soil and involving sorbed organic

the saturated zone at sites and groundwater or soil, unconsolidated sands and sediment, such as clay, silt, compounds with low vapor

with homogeneous, high- groundwater, and free silt. Often used where or sedimentary bedrock, pressure, difficult matrices,

permeability soils and product) contamination and access for vertical wells is where fracturing may or nonaqueous phase

unconfined aquifers; also, low to moderate hydraulic limited, the contaminant increase permeability and liquids. Also used to

used with some success in conductivity soils. High zone is long and thin, or the improve fluid flow during enhance biological activity

heterogeneous, less- vacuum enhances soil vapor geologic materials are very the remediation process. in soil.

permeable soil and in soil and groundwater recovery anisotropic.

with low-permeable layers. rates in low-permeable soil

formations.

Limiting Factors Distribution of air channels Hydraulic and pneumatic Installation in clay and Geology and site conditions Site geology typically

may be affected by properties of soil determine bedrock can be difficult control the size, shape, controls which thermal

lithological and operational which type of dual-phase because of smearing along orientation, and enhancement method is

control of air flow. extraction system would be the borehole wall and slow effectiveness of the appropriate.

Diffusion of contaminants most effective. drilling rates. Highly fractures.

into channels is slow; Groundwater extraction fluctuating water tables can

however, cycling or pulsing rates required for effective cause problems in

may reduce diffusion operation in permeable soils horizontal well SVE

limitations. Performance may be prohibitive, and systems.

may be difficult to measure extraction depths may be

or interpret. limited.
1-7

TABLE 1-1

SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION

(Page 3 of 3)

Technology Air Sparging Dual-Phase Extraction Directional Drilling Hydraulic Fracturing Thermal Enhancement

Pneumatic and

Site-specific Soil heterogeneity greatly Operating costs may be The initial installation of Most effective in low- Steam injection is limited to

Considerations affects the distribution of air high in permeable soil horizontal wells may be permeable, over- medium- to high-permeable

channels and the formations because of high more expensive than the consolidated soil, sediment, soil. Electrical resistance

effectiveness of air water extraction rates and installation of vertical wells, or sedimentary bedrock, heating is effective in lowsparging. resulting treatment but other efficiency such as shale and siltstone. permeable soil in the vadose

requirements. improvements may zone. Thermal conduction

compensate for some of this can be used in medium- to

difference in cost. Careful low-permeable soil, but is

site characterization studies sometimes slow and

are necessary to correctly inefficient. Radioplace and design well frequency or electrical

screens. resistance heating can be

used at sites where the use

of injection wells is

restricted.

Technological Air sparging is becoming Dual-phase extraction is an The cost of horizonal wells Pneumatic and hydraulic Steam and hot air injection

Advancements increasingly more important aggressive technology that continues to decline. fracturing are becoming are being used at full-scale

in providing oxygen to is uniquely suited to sites Horizontal wells will be increasingly more important to decrease the time

aerobic, in situ with multiple-phase used more routinely in the in improving soil required for remediation. 

bioremediation projects. contamination. Soil and near future. permeabilities for the Radio-frequency and

groundwater contamination, delivery or extraction of electrical resistance heating

as well as free-phase liquids fluids from low-permeable require process automation

and capillary fringe/smear environments. Fracturing to reduce costs and operator

zone contamination, can be likely will be applied more requirements.

addressed. routinely to many in situ

remediation technologies in

the future.

Notes: NAPL Nonaqueous-phase liquid

SVE Soil vapor extraction

VOC Volatile organic compound
2-1

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 EC 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:

C 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.
2-2

C 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.

C 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. 

C 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.

C 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.
2-3

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 centimeters per second [cm/s]). -6

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.
3-1

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 can
3-2

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:

C Air sparging wells or probes to inject air into the saturated zone

C A manifold, valves, and instrumentation to transport and control the air flow

C An air compressor or blower to push air into the saturated zone through the air sparging wells or

probes

C 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 and

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.
3-3

Modifications to injection of air in a sparging system include the following:

C Supplemental injection of nutrients to enhance biodegradation

C Substitution of nitrogen for air to reduce the formation of ferric oxide in the pore spaces of aquifers

with high iron concentrations 

C 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

C Supplemental injection of methane as a cometabolizer for chlorinated solvents

C 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
3-5

interface of each air channel is extremely small, resulting in limited mass exchange rates. In 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 (WDNR 1995; 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
3-6

along subsurface features. One technique used to increase the vertical permeability of a stratified

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.
3-7

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

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

Vertical air sparging wells are the most commonly used type of wells (Figure 3-1). These wells are

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
3-8

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 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
3-9

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 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
3-10

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

well or direct push probe installation. Groundwater wells may be subsequently be used for water and

vapor monitoring.

3.3.2.2 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:

C A filter on the air intake of the compressor to prevent particulates from damaging the air

compressor or entering the air stream.

C 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

C 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

C 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)

C A port at each well to temporarily attach a flow meter for measurement of air flow at each well
3-11

C 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

C A manual pressure relief valve immediately after the air compressor outlet to exhaust excess air

from the manifold

C 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

C 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. 
3-12

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 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).
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3.3.3 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:

C Dissolved oxygen and contaminant concentrations in groundwater 

C Oxygen, carbon dioxide, and contaminant concentrations in extracted air

C Microbial populations and activity (including in situ respiration tests)

C Air flow and extraction rates

C Air flow regions using neutron probe measurements or electrical resistivity tomography

C Sparging and vacuum pressure measurements

C Changes in the water table elevation caused by a water table rise in response to air injection

C Tracer gas mapping of air channel distribution and SVE system capture effectiveness

C Zone of influence for both vacuum and sparging wells

C 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. 
3-14

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 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
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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. 

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 (Fg/L) and 3 to 124 Fg/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
3-16

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 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 Fg/L in some wells) and well below drinking

water standards of 5 Fg/L (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.
3-17

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.

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 (SVVS ). 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 (yd ) of contaminated soil. The data indicated that a portion of 3

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 SVVS system. The hot zone included approximately ®

800 yd of contaminated soil and encompassed four extraction wells and three sparging wells. The 3

previously installed system was operated over the entire treatment area.
3-18

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 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 SVVS system for ®

groundwater at the site were not assessed during the demonstration. 

Operation of the SVVS 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.
3-19

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:

C PT/SVE would remove the same amount of VOCs as the vacuum component of ISB when operated

for the same time period

C Four vertical SVE and four pump-and-treat wells would have the same zone of influence as

two horizontal wells used for ISB

C Volatilized contaminants from both technologies are sent to a catalytic oxidation system for

destruction

C 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
3-20

Act maximum of 5 Fg/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 SVVS 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

demonstration operated over a 1-year period at the Electro-Voice facility. The cost associated with

treatment by the SVVS 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:

C Site preparation

C Permitting and regulatory requirements

C Capital equipment (amortized over 10 years)

C Startup

C Consumables and supplies

C Labor

C Utilities

C Effluent treatment and disposal costs

C Residuals and waste shipping, handling, and storage services

C Analytical services

C Maintenance and modifications

C 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

yd of soil was estimated to be $220,737 or $10.36/yd . This figure does not include any treatment of the 3 3

off-gases. If effluent treatment costs are included, it would increase costs to $385,237 or $18.09/yd .

3

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
3-21

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.

3.5 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:

C Air sparging expands remediation capabilities of SVE to the saturated zone.

C In air sparging, both volatilization and biodegradation processes contribute to remediation of

VOCs.

C By using air sparging, biodegradation can be potentially further enhanced by supplementing air

with other gases and/or nutrients.

C Air sparging eliminates the need to remove and treat large quantities of groundwater using

expensive pump-and-treat methods.

C Air sparging has been shown to be more cost effective than conventional PT/SVE.

C Air sparging effectively creates a crude air stripper in the subsurface, with the soil acting as the

“packing.”

C In air sparging, the sparged air elevates the dissolved-oxygen content in the subsurface, thus

enhancing natural biodegradation.

C Cycling or pulsing the air flow during air sparging can increase mixing in the saturated zone, thus

increasing volatilization and biodegradation of contaminants.
3-22

The following list outlines some of the limitations of using air sparging at sites contaminated with VOCs: 

C Air flow dynamics in the subsurface, and therefore the mechanisms of air sparging remediation, are

not well understood.

C Limited performance data are available.

C Operational and lithological controls influence the air flow in the subsurface, thereby controlling

the remediation potential of air sparging.

C 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.

C 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.

C The usefulness of standard monitoring practices for assessing the performance of air sparging is

not clearly understood.

C As a rule of thumb, performance of air sparging decreases in less permeable soils.

C Preferential air channeling and poor air distribution are expected to increase significantly in less

permeable soils and increase with soil heterogeneity.

C 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.

C 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.
3-23

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.

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.
3-24

Billings and Associates, Inc. 1996c. Project Description for Bloomfield Site. Available on World Wide

Web. July 29.

Billings, J.F., A.I. Cooley, and G.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.

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, Mary E. 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.
3-25

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.

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 Alla 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. 

EM1110-1-4001. 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 (SVVS) ,

®

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.
FIGURE 3-1

TYPICAL AIR SPARGING ENHANCEMENT TO SOIL VAPOR EXTRACTION SYSTEM
FIGURE 3-2

HORIZONTAL AIR SPARGING AND SOIL VAPOR EXTRACTION WELL SYSTEM
FIGURE 3-3

3-YEAR REMEDIATION COST BREAKDOWN

3-28
3-29

 FIGURE 3-4

REMEDIATION COST BREAKDOWN FOR IN SITU BIOREMEDIATION

AND PUMP-AND-TREAT/SOIL VAPOR EXTRACTION
3-30

TABLE 3-1

AIR SPARGING SYSTEM CHARACTERISTICS

Topic Description

Geological Applicability C Ideal site: homogeneous, high-permeability soils and

unconfined aquifers

C Average site: moderately heterogeneous soils with minimal

low-permeability layers

Contaminant Applicability C Volatile organic compounds that are aerobically

biodegradable

C None or thin layer of free-phase product

System Components C Vertical or horizontal extraction and injection wells or

sparging probes

C Manifold, valves, and instrumentation

C Air compressor or blower

C Properly designed SVE system

Monitoring Parameters C Dissolved oxygen and contaminant concentrations in

groundwater

C Oxygen, carbon dioxide, and contaminant concentrations in

SVE off-gas or soil vapor

C Microbial populations and activity

C Air flow and extraction rates

C Air pressure measurements

C Water levels

C Tracer gas mapping of air flow in subsurface

Cleanup Capabilities C Capable of achieving maximum contaminant levels for

volatile constituents in groundwater

C Estimated cleanup time is 1 to 4 yearsa

Costs C $15 to $120 per cubic yardb

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
3-31

TABLE 3-2

FACTORS AFFECTING APPLICABILITY OF AIR SPARGING

Factor Parameter Desired Range or Conditions

Contaminant Volatility High (KH >1 x 10 atm-m /mole) -5 3

Solubility Low (<20,000 mg/L)

Biodegradability High (BOD >0.01 mg/L) 5

Presence of free product None or thin layer

Geology Soil type Coarse-grained soils

Heterogeneity No impervious layers above sparge interval

Permeability increases towards grade if

layering present

Permeability in the saturated >1 x 10 cm if horizontal:vertical is <2:1

zone >1 x 10 cm if horizontal:vertical is >3:1 a

-5 2

-4 2

Hydraulic conductivity >1 x 10 cm/s -3 b

Depth to groundwater >5 feet c

Aquifer type Unconfined

Saturated thickness 5 to 30 feet

Sources: Modified from Brown and others 1994, Loden 1992, Wisconsin Department of Natural Resources 1995

Notes:

a From Loden 1992.

b From Brown and others 1994.

c From Wisconsin Department of Natural Resources 1995

d One practitioner has used air sparging on sites with permeabilities as low as 1 x 10 cm (Tetra Tech -12 2

EM Inc. 1996f).

e One practitioner claims to have cleaned site with hydraulic conductivities as low as 1 x 10 cm/s -6

(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-m atmosphere-cubic meter 3

mg/L milligrams per liter
3-32

TABLE 3-3

SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES

(Page 1 of 3)

(months) Concentration (mg/L) Concentration (mg/L)

Cleanup

Time Initial Groundwater Final Groundwater a

Site Citation Soil Type Contaminants

Isleta Ardito & Billings Alluvial sands, silts, clays Leaded gasoline 2 MW-1, -3, -5 MW-1, -3, -5

1990 BTEX: 4, 18, 25 BTEX: 0.25, 8, 6

Conservancy Billings 1990 Silty sand Gasoline 5 Benzene: 3 to 6 59% average benzene

Interfacing clay layer reduction after 5 months

Buddy Beene Billings 1991 Clay Gasoline 2 — 8.5% reduction/month

Bernalillo Billings 1990 — Gasoline 17 — BTEX and MTBE: <5.5

Los Chavez Billings 1990 Clay Gasoline 9 — 40% benzene, xylenes

reduction, 60% toluene

reduction, 30% ethylbenzene

reduction

Arenal Billings 1990 — Gasoline 10 Benzene: >30 Benzene: <5

BF1 Billings and NR Fuel 12 Benzene: 22,000 to 32,000 Benzene: 29 to 50

Associates, Inc. 

1996b

Bloomfield Billings and NR Fuel 48 NR BTEX below cleanup

Associates, Inc. standards

1996c

Firehouse Billings and NR Fuel 30 Benzene: 400 to 600 Benzene: 0.5 to 4

Associates, Inc. 

1996a

Dry Cleaning Facility Brown 1991 Coarse sand PCE, TCE, DCE, 4 Total VOCs: 41 Total VOCs: 0.897

Natural clay barrier TPH

Savannah River U.S. Department of Sands, thin clay lenses TCE, PCE 13 TCE: 10 to 1,031 TCE: <5

Energy 1996 PCE: 3 to 124 PCE: <5
3-33

TABLE 3-3

SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES

(Page 2 of 3)

(months) Concentration (mg/L) Concentration (mg/L)

Cleanup

Time Initial Groundwater Final Groundwater a

Site Citation Soil Type Contaminants

Former Industrial Envirogen, Inc. 1996 Sands Toluene 23 NR NR

Facility

Electro-Voice EPA 1995 NR VOC 12 NMb NMb

Berlin Harress 1989 Sand, silty lenses c-1,2-DCE, TCE, 24 c-1,2-DCE: >2 c-1,2-DCE: >0.440

Aquitard-clay PCE

Bielefeld, Nordrhein Harress 1989 Fill, sand, silt PCE, TCE, TCA 11 PCE: 27; TCE: 4.3; TCA: 0.7 Total VOCs: 1.207

-Westfalen Aquitard-siltstone

Munich, Bavaria Harress 1989 Fill, gravel, sand PCE, TCE, TCA 4 PCE: 2.2; TCE: 0.4; TCA: PCE: 0.539; TCE: 0.012;

Aquitard-clayey silt 0.15 TCA: 0.002

Nordrhein, Harress 1989 Clayey silt, sand Halogenated 4 Location A THH: 1.5 to 4.5 Location A THH: 0.010

Westfalen Aquitard-siltstone hydrocarbons 6 Location B THH: 10 to 12 Location B THH: 0.200

Bergisches Land Harress 1989 Fractured limestone Halogenated 15 THH: 80 THH: 0.4

hydrocarbons

Pluderhausen, Baden Harress 1989 Fill, silt, gravel TCE 2 1.20 0.23

- Wurtternburg Aquitard-clay

Mannhelm - Herrling 1991 Sand PCE, chlorinated — — —

Kaesfertal hydrocarbons

Gasoline service Kresge 1991 Sand and silt Gasoline 24 Total BTEX: 6 to 24 Total BTEX: 0.380 to 7.6

station

Savannah River Looney 1991 Sand, silt, and clay TCE, PCE 3 TCE: 0.5 to 1.81 TCE: 0.010 to 1.031

PCE: 0.085 to 0.184 PCE: 0.003 to 0.124

Gasoline service Marley 1990 Fine-coarse sand, gravel Gasoline 3 Total BTEX: 21 Total BTEX: <1

station

Solvent spill Middleton 1990 Quaternary sand and TCE, PCE 3 Total VOCs: 33 Total VOCs: 0.27

gravel
3-34

TABLE 3-3

SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES

(Page 3 of 3)

(months) Concentration (mg/L) Concentration (mg/L)

Cleanup

Time Initial Groundwater Final Groundwater a

Site Citation Soil Type Contaminants

Solvent leak at Middleton 1990 Fill, sandy and clayey silts TCE 2 0.200-12 <0.010-0.023

degreasing facility

Chemical Middleton 1990 Sandy gravel Halogenated 9 THH: 1.9 to 5.417 THH: 0.185 to 0.320

manufacturer Aquitard-clay hydrocarbons

Truck distribution MWR 1990 Sands Gasoline & diesel Ongoing Total BTEX: 30 —

facility fuel

Irvine Terra Vac, Inc. Clays, sandy silts, clayey Gasoline 9 NR below cleanup standards

1995a sands and silts, gravel

New Paris Terra Vac, Inc. Sand with some gravel, PCE, TCE 18 PCE: 250 PCE: 9

1995b clay layers

Notes:

a Cleanup times represent the time interval between initial and final groundwater concentration reported in the table. Actual remediation time may be longer.

b Demonstration assessed remediation capabilities for vadose zone soils only.

BTEX Benzene, toluene, ethylbenzene, and xylenes PCE Tetrachloroethene

DCE Dichloroethene TCA Trichloroethane

EPA U.S. Environmental Protection Agency TCE Trichloroethene

MTBE Methyl tert-butyl ether THH Total halogenated hydrocarbons

MW Monitoring well TPH Total petroleum hydrocarbons

NM Not measured VOC Volatile organic compounds

NR Not reported
3-35

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

Treatment Horizon Sampling Sampling Percent Reduction b

Critical VOC Concentration

(mg/kg)a

Pretreatment Posttreatment

Upper horizon 321.77 0.74 99.77

Sludge layer 1,661.03 307.69 81.48

Lower horizon A1 96.42 0.98 98.99

Lower horizon A2 37.68 0.42 98.99

Lower horizon B 13.57 0.30 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
3-36

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 Sampling Sampling Percent Reduction

Sum of the Weighted Mean 

Concentration (mg/kg)

Pretreatment Posttreatment

Benzene 0.01 0.00 NC

Toluene 92.84 14.42 84.47

Ethylbenzene 37.41 6.06 83.81

Xylenes 205.50 45.28 77.97

1,1-Dichloroethene 0.01 0.00 NC

Trichloroethene 0.36 0.00 NC

Tetrachloroethene 5.37 0.44 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.
3-37

TABLE 3-6

SUMMARY OF COST DATA FOR IN SITU BIOREMEDIATION 

AS WELL AS PUMP-AND-TREAT WITH SOIL VAPOR EXTRACTION

Costs ISB ($) PT/SVE($)

Capital

 Site Cost 5,400 7,500

 Equipment Cost 9,200 32,000

 Design and Engineering 10,000 10,000

 Mobile Equipment 18,000 18,000

 Well Installation 183,000 50,690

 Other Fixed Equipment 183,732 168,665

 Mobilization Cost 43,075 64,613

 Total Capital Equipment and Mobilization Costs 452,407 341,468

 Cost per Pound of Contaminant 21 31

Operation and Maintenance

 Monitoring/Maintenance 71,175 71,175

 Consumable Cost 122,215 123,595

 Demobilization Costs 43,075 64,613

 Total Operational and Maintenance Costs $236,465 $259,383

Notes:

ISB In situ bioremediation (includes vacuum extraction; see Section 3.4.1)

PT/SVE Pump-and-treat system combined with soil vapor extraction
3-38

TABLE 3-7

ESTIMATED COST FOR TREATMENT USING THE SUBSURFACE VOLATILIZATION

VENTILATION SYSTEM PROCESS OVER A 3-YEAR APPLICATION

Cost Category First Year Second Year Third Year

1. Site Preparation

Well Drilling & Preparation $32,500 — —

Building Enclosure (10' by 15') $10,000 — —

Utility Connections $5,000 — —

System Installation $15,000 — —

Total Costs $62,500 — —

2. Permitting & Regulatory Requirements $10,000 — —

3. Capital Equipment (amortized over 10 years)

Vacuum Pump $450 $450 $450

Blower $450 $450 $450

Plumbing $3,333 $3,333 $3,334

Building Heater $333 $333 $334

Total Costs $4,566 $4,566 $4,568

4. Startup $7,957 — —

5. Consumables

Health and Safety Gear $1,000 $1,000 $1,000

6. Labor $6,300 $6,300 $6,300

7. Utilities

Electricity (Blower and Pump) $3,900 $3,900 $3,900

Electricity (Heater) $660 $660 $660

Total Costs $4,560 $4,560 $4,560

8. Effluent Treatment and Disposal Costs N/A N/A N/A

9. Residuals and Waste Shipping and Handling

Contaminated Drill Cuttings $12,500 — $6,000

Contaminated Personal Protective Equipment $6,000 $1,000 $3,000

Total Costs $18,500 $1,000 $9,000

10. Analytical Services $20,000 $20,000 $20,000

11. Maintenance and Modifications N/A N/A N/A

12. Demobilization — — $2,500

TOTAL ANNUAL COSTS $135,383 $37,426 $47,928

TOTAL REMEDIATION COSTS $220,737

Source: Modified from Department of Energy 1996

Notes: N/A Not available

— Not applicable
3-39

TABLE 3-8

VENDORS OF AIR SPARGING TECHNOLOGIESa

Name of Vendor Address and Phone Number Point of Contact a

Billings and Associates, Inc. 3816 Academy Parkway N-NE Rick Billings

Albuquerque, New Mexico 87109

(505) 345-1116

Terra Vac, Inc. 1555 Williams Drive, Suite 102 Charles Pineo

Marietta, Georgia 30066-6282

(770) 421-8008

Envirogen, Inc. 480 Neponset Street Alla Werner

Canton, Massachusetts 02021

(617) 821-5560

IT Corporation 2925 Briar Park John Mastroianni

Houston, Texas 77042

(713) 784-2800

Quaternary Investigations, Inc. 300 West Olive Street, Suite A Tony Morgon

Colton, California 92324

(800) 423-0740

Horizontal Technologies, Inc. 2309 Hancock Bridge Parkway Donald Justice

(33990)

P.O. Box 150820

Cape Coral, Florida 33915-0820

Groundwater Control, Inc. 754 Harrison Avenue Jeff Haluch

Jacksonville, Florida 32220

(800) 843-6133

KVA Analytical Systems 281 Main Street, Box 574 Steve Leffert

Falmouth, Massachusetts 02541

(508) 540-0561

H2 Oil P.O. Box 9028 Troy York

Bend, Oregon 97708-9028

(541) 382-7070

Note: a This list is not inclusive of all vendors capable of providing air sparging technologies. 

This list reflects vendors contacted during the preparation of this report.
4-1

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:

C 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.

C 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
4-2

stream at the well screen, transported to the treatment system in a common pipe manifold,

separated in a gas/liquid separator, and treated.

C 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:

C VOC contamination

C Soil, groundwater, and free-product contaminant phases

C 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
4-3

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 freephase (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.

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
4-4

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).

4.2.3 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.
4-5

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:

C Induced vacuum versus distance

C Water drawdown versus distance
4-6

C Wellhead vacuum

C Vapor extraction rates

C Groundwater extraction rates

C Vapor hydrocarbon content

C 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.

4.3.1.2 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
4-7

sufficient diameter and adequate design characteristics (appropriately-sized screen slots) can be converted

for use as extraction wells. Downhole 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
4-8

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

generated in sufficient quantities. Use of extracted water for seal fluid generally requires close monitoring
4-9

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

HDPE.

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 soils

entrains groundwater at the tube tip. Soil vapor and entrained groundwater are transported in a common
4-10

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). 

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
4-11

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.

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).
4-12

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

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.
4-13

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.

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.
4-14

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.

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.
4-15

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 entrainment 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 

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.
4-16

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 (GSI 1997). 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 II), followed by a 10 to 12 foot layer of sandy, silty, stiff, laminated clay

(Unit III). 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 averages

approximately 6.1 x 10 cm/sec. At the start of system operation, the affected groundwater plume ranged -5

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).
4-17

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 Fg/L and one with maximum

BTEX concentrations exceeding 16,000 Fg/L. A thin layer of free product was found in one monitoring

well.

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 Fg/L benzene and 1,000 Fg/L total BTEX for
4-18

on site wells, and 150 and 500 Fg/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 Fg/L. Discharge criteria to a publicly owned treatment works was 3,000 Fg/L.

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 Fg/L to 8 Fg/L after 6 months of operation and to 2 Fg/L after 1.5 years

of operation.

The system was shut down in January 1996. Benzene concentrations at the extraction well were found to

fluctuate around the cleanup standard of 5 Fg/L and had risen to 8 Fg/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.
4-19

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:

C Increases water extraction rates in low permeability settings

C Increases the vapor extraction zone of influence

C Addresses smear zone and saturated soil contamination

C Enhances removal of free-phase and residual NAPL

C Potentially reduces ex situ groundwater treatment by in-well stripping in entrainment extraction

wells

C Potentially eliminates the need for downhole pumps and associated controls and instrumentation

through the use of entrainment extraction
4-20

The following list outlines the primary limitations of DPE for remediation of sites contaminated with

VOCs:

C Less cost-effective for permeable soil types

C Operating costs may be high depending upon blower horsepower requirements and groundwater

treatment requirements

C 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.
4-21

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(1):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., J.J. 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. (Tetra Tech). 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.
4-22

Trowbridge, Bretton E., 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.
FIGURE 4-1

SCHEMATIC OF A DUAL-PHASE EXTRACTION SYSTEM
4-24

FIGURE 4-2

DROP-TUBE ENTRAINMENT EXTRACTION WELL
4-25

FIGURE 4-3

DOWNHOLE-PUMP EXTRACTION WELL
FIGURE 4-4

EXTRACTION SYSTEM PERFORMANCE
4-27

TABLE 4-1

COST DATA FOR DUAL-PHASE EXTRACTION TECHNOLOGIES

Case Total Cost Capital of contaminant Cost per gallon of

Study Vendor/Consultant ($) Cost ($) removed ($) groundwater ($)

Cost per pound

1 IT Corporation 380,000 — 10 0.23

2 Terra Vac 600,000 — 40 7.00

3 Groundwater Services, — — — —

Inc.

4 Dames & Moore 331,600 60,000 130 0.31

5 Eder Associates, Inc. — 58,000 — —

Note:

— Information is not available
4-28

TABLE 4-2

VENDORS OF DUAL-PHASE EXTRACTION TECHNOLOGIES

Name of Vendor Address and Phone Number Point of Contact

Dames & Moore 2325 Maryland Road Joseph Tarsavage

Willow Grove, PA 19090

(215) 657-7134

Eder Associates, Inc. 8025 Excelsior Drive Anthony Miller

Madison, WI 53717

(608) 836-1500

First Environment, Inc. 90 Riverdale Road Rick Dorrler

Riverdale, NJ 07457

(201) 616-9700

Fluor Daniels GTI, Inc. 100 River Ridge Drive David Peterson

Norwood, MA 02062

(800) 635-0053

Groundwater Services, Inc. 2211 Norfolk, Suite 1600 John Connor

Houston, TX 77098

(713) 522-6300

International Technologies 2925 Briar Park John Mastroianni

Corporation (IT) Houston, TX 77042

(713) 784-2800

Radian International 2455 Horsepen Road, Suite 250 Christopher

Herndon, VA 20171 Koerner

(703) 713-6493

Smith Environmental One Plymouth Meeting Dan Guest

Technologies Corporation Plymouth Meeting, PA 19462

(610) 825-3800

Terra Vac Incorporated 1555 Williams Drive, Suite 102 Charles Pineo

Marietta, GA 30066-6282 

(404) 421-8008

Wayne Perry, Inc. 8281 Commonwealth Avenue Don Pinkerton

Buena Park, CA 90621

(714) 826-0352

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.
5-1

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. 
5-2

Horizontal wells can be used to access areas generally not accessible using vertical 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 upward and return
5-3

to the ground surface. In continuous boreholes, the well is installed from the exit 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:

C Advance a pilot hole

C 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.

C 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:

C 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.

C 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. 
5-4

C 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.

C 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.
5-5

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.
5-6

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. 

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.
5-7

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 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. 
5-8

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

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.

5.3.4 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:

C Radio beacon-receiver systems

C Magnetometer-accelerometer systems

C 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.
5-9

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. HDPE

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. 

5.3.5.4 Well Installation

The steps of installation of directionally drilled horizontal wells are as follows:

C 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.

C 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.

C The screen and riser are installed in the carrier casing or washover pipe 

C The casing is removed, and the well material is left in the formation 

C The well is developed with water and special drilling mud removal solutions 

C Install SVE and air sparging system components

5.3.6 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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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):

C Not fully characterizing the horizontal well site geology and geochemistry

C Not fully researching the credentials of the drilling company

C Not planning and researching the drilling fluid and screen materials and design carefully

C Not developing the well adequately

C Not evaluating carefully the potential for pressure drops due to slope, geology or well loss

C Not using a contractor experienced in planning, procuring, and implementing a horizontal well

installation program

C Not retaining a driller who understands the intricacies of drilling in the specific geologic

environment

C Not providing close oversight to the drilling contractor

C Drilling contractors providing undersized and undermaintained equipment for the job

C Drilling contractors drilling the pilot hole too quickly and not creating a smooth uniform curvature

to the borehole

C 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 HDPE screen that can be custom made to have varying

pore size while maintaining the same open area along its length. 

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-todate information regarding the use of horizontal wells for SVE and air sparging.
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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

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.
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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 Fg/L to 200 and 300 Fg/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

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.
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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 Fg/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

interbeds of silt and clay to the water table. The geology of the aquifer includes sand and gravel. The

aquifer is anisotropic, and the horizontal and vertical hydraulic conductivities are estimated at 7 x 10 cm/s -2

and at 1 x 10 cm/s, respectively. -7

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.
5-16

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.

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
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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

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
5-18

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 Fg/L and nondetected to 4,000 Fg/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

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
5-19

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

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. 
5-20

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.

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
5-21

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 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:

C 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
5-22

extensive. This is because horizontal hydraulic conductivities are generally several times those of

vertical hydraulic conductivities.

C Horizontal wells can access contaminated areas that cannot be reached by conventional remedial

methods.

C Horizontal wells cause minimal impact to activities at the ground surface such as vehicle traffic,

plant operations, and flight lines.

C Horizontal wells technology is nondestructive in that it does not damage existing land

improvements.

C Horizontal wells can be completed in most geologic environments by the use of alternative drilling

mud fluids.

C 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:

C 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.

C Areas with highly fluctuating water tables can cause problems with SVE systems if the water table

variability is not fully understood.

C 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.

C 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.

C Installation of horizontal wells requires knowledge of all potential subsurface obstacles along its

path. Detailed mapping along the borehole path may be required.
5-23

C 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.

5.8.1 Cited References

Armstrong, J.E., C.A. Mendoza, B.J. 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,
5-24

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. McGraw Hill. 

New York.

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.
5-25

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.
5-26

5.8.2 Professional Contacts

Name Affiliation

Armstrong, James Komex International, Ltd.

(403) 247-0200

Birdwell, Dale Genesis Environmental

(405) 235-3371

Cox, Bob OHM, Inc.

(510) 227-1105 x420

Downs, Charlie, Ph.D. Private Consultant, Pollution Prevention Associates

(303) 936-4002

Fournier, Louis B. STAR Environmental

(610) 558-2121

Kaback, Dawn Colorado Center for Environmental Management

(303) 297-0180 x111

Kirshner, Marv Port Authority of New York and New Jersey

Ph: (212) 435-8255

Fx: (212) 435-8276

Alt Ph: (201) 961-6600 x8255

Layne, Roger Ditch Witch, Inc., The Charles Machine Works, Inc.

1-800-654-6481

Meyer, Eric Radian Corporation, Baton Rouge

(504) 922-4450

Pressly, Nick Pressly & Associates, Inc.

(516) 286-5890

Wilson, David D. Horizontal Well and Environmental Consultants, Inc.

(303) 422-1302
5-27

INFORMATION CENTERS

Organization Contact Name Services

National Ground Water Mark Shepherd Provide database search for issues related to

Association x. 594 groundwater

1-800-551-7379

Remedial Action Program Mary Bales Collect documentation on issues related to

Information Center decontamination, decommissioning, and

(423) 241-3098 remediation of sites
FIGURE 5-1

HORIZONTAL WELL NETWORK INSTALLED BENEATH A BUILDING

TO REMEDIATE SOIL AND GROUNDWATER
FIGURE 5-2

BLIND BOREHOLE COMPLETION
FIGURE 5-3

CONTINUOUS WELL COMPLETION
FIGURE 5-4

PILOT HOLE ADVANCEMENT
FIGURE 5-5

BACK REAMING AND WELL CASING INSTALLATION
FIGURE 5-6

TYPICAL DOWNHOLE HARDWARE FOR DIFFERENT DRILLING PHASES
FIGURE 5-7

HASTINGS EAST INDUSTRIAL PARK SITE PLAN SHOWING

HORIZONTAL AND VERTICAL WELL AIR SPARGING/SOIL VAPOR EXTRACTION SYSTEM
FIGURE 5-8

TCE CONCENTRATIONS IN SIX GROUNDWATER MONITORING WELLS

DOWNGRADIENT FROM THE HORIZONTAL SPARGING WELL
FIGURE 5-9

TCE CONCENTRATIONS IN THREE GROUNDWATER MONITORING

WELLS NEAR THE VERTICAL SPARGING WELL
FIGURE 5-10

HORIZONTAL WELL LAYOUT FOR AIR SPARGING AND SOIL

VAPOR EXTRACTION AT TERMINAL 1A, JOHN F. KENNEDY INTERNATIONAL AIRPORT
FIGURE 5-11

HORIZONTAL WELL LAYOUT FOR AIR SPARGING AND SOIL VAPOR EXTRACTION AT

THE INTERNATIONAL ARRIVALS BUILDING, JOHN F. KENNEDY INTERNATIONAL AIRPORT
FIGURE 5-12

AIR SPARGING PILOT TEST, NOVEMBER 1995 AT

THE INTERNATIONAL ARRIVALS BUILDING, JOHN F. KENNEDY INTERNATIONAL AIRPORT
FIGURE 5-13

SOIL VAPOR EXTRACTION PILOT TEST NOVEMBER 1995 AT

THE INTERNATIONAL ARRIVALS BUILDING, JOHN F. KENNEDY INTERNATIONAL AIRPORT
5-41

TABLE 5-1

VENDORS OF HORIZONTAL WELLS AND DIRECTIONAL DRILLING TECHNOLOGYa

(Page 1 of 3)

Name of Vendor Address, Phone, Fax Point of Contact

American Augers, Inc. 135 U.S. Route 42 Gary Stewart

(Drill Rig Manufacturer) P.O. Box 814

West Salem, OH 44287

Ph: (419) 869-7107

Fx: (419) 869-7425

1-800-324-4930

Davis Horizontal Drilling, Inc. 7204 Timberlake Roland Davis

Mustang, OK 73064

Ph: (405) 376-2702

Fx: (405) 376-3807

Directed Technologies Drilling, Inc. 1315 South Central Ave, Suite G Michael Lubrecht

Kent, WA 98032

1-800-239-5950

Ph: (206) 850-2848

Fx: (206) 850-2824

mlubrecht@accessone.com

Directional Drilling, Inc. P.O. Box 159 Jim McEntire

Oakwood, GA 30566 or

3536 Atlanta Highway

Flowery Branch, GA 30542

Ph: (770) 534-0083

Fx: (770)531-9553

Ditch Witch, Inc., The Charles Machine P.O. Box 66 Roger Layne

Works, Inc. Perry, OK 73077

(Drill Rig Manufacturer) Ph: (405) 336-4402

1-800-654-6481

Fx: (405) 336-3458

Drilex Inc. 15151 Sommermeyer David Bardsley

Houston, TX 77041

Ph: (713) 957-5470

Fx: (713) 957-5483

Fishburn Environmental Drilling 5013 State Route 229 Stuart Brown

P.O. Box 278

Marengo, OH 43334
TABLE 5-1

VENDORS OF HORIZONTAL WELLS AND DIRECTIONAL DRILLING TECHNOLOGYa

(Page 2 of 3)

Name of Vendor Address, Phone, Fax Point of Contact

5-42

GTS Horizontal Drilling Co. 1231 B East Main Street, Suite 189 Tom Bryant

Meriden, CT 06450

1-800-239-8079

Horizontal Drilling Technologies 2414 S. Hoover Road Mark Mesner

Wichita, KS 67215

Ph: (316) 942-3031

Horizontal Subsurface Technologies, Inc. 634 West Clarks Landing Road

Egg Harbor, NJ 08215

1-800-965-0024

Horizontal Technologies, Inc. 2309 Hancock Bridge Parkway Donald Justice

P.O. Box 150820

Cape Coral, FL 33915

Kelly Corp. Ph: (204) 544-9462 Ken Kelly

KVA Slantwell Installations/KVA 15 Carlson Lane Steve or Pat

Analytical Systems Falmouth, MA 02540

Ph: (508) 540-0561

Fx: (508) 457-4810

Mears/HDD, Inc. 4500 North Mission Road Dick Gibbs

Rosebush, MI 48878-0055

1-800-632-7727

Fx: (517) 433-5433

Michels Environmental Services 817 West Main Street Tim McGuire 

(main office) Ph: (303) 423-5761

Brownsville, WI 53006 Fx: (303) 423-1947

Ph: (414) 583-3132

Fx: (414) 583-3429

OHM Remediation Services Group 5731 W. Las Positas Blvd Robert Cox

Pleasanton, CA 94588

Ph: (510) 227-1105

Pledger, Inc. 12848 SE Suzanne Drive Steve McLaughlin

Hobe Sound, FL 33455

Ph: (407) 546-4848

Fx: (407) 546-3211
TABLE 5-1

VENDORS OF HORIZONTAL WELLS AND DIRECTIONAL DRILLING TECHNOLOGYa

(Page 3 of 3)

Name of Vendor Address, Phone, Fax Point of Contact

5-43

SCHUMASOIL P.O. Box 8040 Anne Ogg ®

Schumacher Filters America, Inc. Asheville, NC 28814

Ph: (704) 252-9000

Fx: (704) 253-7773

Stearns Drilling 6974 Hammond S.E. Roland Clapp

Dutton, MI 49316

Ph: (616) 698-7770

Fx: (616) 698-9886

Trenchless Technology Center Department of Civil Engineering

P.O. Box 10348

Louisiana Technical University

Ruston, LA 71272

Vermeer Manufacturing Route 1 David Whampler

(Drill Rig Manufacturer) P.O. Box 200

Pella, IA 50219

Ph: (515) 628-3141

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.
6-1

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
6-2

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. 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. 

6.2 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
6-3

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 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 cm/s or pneumatic conductivities -4

are less than 1 x 10 cm/s (Schuring and others 1995). Figure 6-3 shows general guidelines for the -5

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;
6-4

fractures follow contacts along interbedded sediments or partings between rock beds in some cases and

crosscut beds in others.

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
6-5

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.

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
6-6

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.

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
6-7

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 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
6-8

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 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 Injection 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. 
6-9

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 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.
6-10

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 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,
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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).

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 and 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
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new fractures. Figure 6-4 illustrates the effects of pneumatic fracturing on two different geologic

formations (Schuring and others 1995).

Pneumatic fracturing requires equipment that rapidly delivers air to the subsurface. Injecting air directly

from a compressor may induce fractures under some circumstances; however, 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.

6.3.9 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. 
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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, injection of air, or recovery of

groundwater 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. 
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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;

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
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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 85E Fahrenheit) were observed, but TCE mass removal decreased. 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 mg/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. 
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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 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).
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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.

The hydraulic fracturing program at this site successfully induced fractures 0.02 to 0.07 inches in thickness

and improved the zone 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
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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.

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
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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.

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 yd of soil or rock fractured (Schuring and 3

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 ft per yd = 92,593 yd 3 3 3

Cost range = 92,593 yd x $8 to $20 = $740,740 to $1,851,852. 3

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
6-20

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 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
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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.

6.5 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:

C Pneumatic and hydraulic fracturing can increase well discharge many times over discharge rates

achieved with conventional, unfractured wells.

C The relative increase in performance is greatest in the tightest formations, where the performance

of conventional wells is poorest.

C 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.

C Solid compounds that improve the remedial process, such as nutrients or electrically conductive

compounds, can be delivered to the subsurface.

C 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.
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The following list outlines some of the limitations of using pneumatic and hydraulic fracturing technologies

for environmental remediation:

C Pneumatic and hydraulic fracturing may not solve all the problems of remediation in tight

formations.

C Fracturing is ineffective in normally consolidated soils and sediments in which the horizontal stress

is less than the vertical stress.

C 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.

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
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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 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. Cary, NC. August 16.
6-24

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.

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.
6-25

EPA. 1995. In Situ Remediation Technology Status Report: Hydraulic and Pneumatic Fracturing. EPA542-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.

Name Affiliation

Pneumatic Fracturing

Uwe Frank U.S. Environmental Protection Agency

(908) 321-6626 Risk Reduction Engineering Laboratory

John Schuring, Ph.D. Hazardous Substance Management Research Center

(201) 596-5849 New Jersey Institute of Technology

David Kosson, Ph.D. Department of Chemical and Biological Engineering

(908) 445-4346 Rutgers, The State University of New Jersey

Hydraulic Fracturing

Michael Roulier, Ph.D. U.S. Environmental Protection Agency

(513) 569-7796 Risk Reduction Engineering Laboratory 

Larry C. Murdoch, Ph.D. Department of Geology

(864) 656-2597 Clemson University

William W. Slack, Ph.D. Center for Geo-Environmental Science and Technology

(513) 556-2526 University of Cincinnati, Engineering Research Division
6-26

FIGURE 6-1

SCHEMATIC OF PNEUMATIC FRACTURING FOR ENHANCED VAPOR EXTRACTION
6-27

FIGURE 6-2

CONCEPTUAL SCHEMATIC OF HYDRAULIC FRACTURING
FIGURE 6-3

APPLICATION GUIDELINES FOR PNEUMATIC FRACTURING
FIGURE 6-4

EFFECTS OF PNEUMATIC FRACTURING
FIGURE 6-5

SEQUENCE OF OPERATIONS FOR CREATING HYDRAULIC FRACTURES
FIGURE 6-6

COMPARISON OF TCE MASS REMOVAL ENHANCED BY PNEUMATIC FRACTURING
FIGURE 6-7

PREFRACTURE CONTAMINANT REMOVAL CONCENTRATIONS
FIGURE 6-8

POSTFRACTURE CONTAMINANT REMOVAL CONCENTRATIONS
FIGURE 6-9

CUMULATIVE GROUNDWATER REMOVAL BEFORE HYDRAULIC FRACTURING
FIGURE 6-10

CUMULATIVE GROUNDWATER REMOVAL AFTER HYDRAULIC FRACTURING
6-36

TABLE 6-1

REMEDIATION TECHNOLOGIES ENHANCED BY FRACTURING

(Page 1 of 1)

Contaminated Remediation 

Media Technology Technology Description Benefits of Fracturing

Soil Soil flushing concentrate contaminants into the liquid phase to enhance pump and recirculation rates

Soil vapor extraction Removal of VOCs from unsaturated zone soils using subsurface air flow Greater access to contaminants, increased removal rates, and fewer

wells

Dual vapor-phase Removal of VOCs simultaneously from both soils in the saturated and Greater access to contaminants, increased removal rates, and fewer

extraction the unsaturated zones wells

Bioremediation Injection and infiltration of fluids, including air, into soils to enhance Improved fluid injection and infiltration rates, as well as improved

biodegradation of subsurface residual contaminants access of microbes to contaminants

Injection and infiltration of solutions such as solvents or surfactants to Improved injection and infiltration, as well as improved

treat

Electroosmosis Migration of contaminants in the subsurface through the application of Fractures act as contaminant collection pathways

an electric field

Thermal treatment Removal of contaminants through volatilization into the gas phase by Greater permeability for heat distribution and volatilization

both vapor-liquid equilibrium effects and heat

Vitrification Subsurface containment of contaminants through melting of soils to Greater permeability for heat distribution and melting

form a stable glass structure with low leaching characteristics

Groundwater

Pump and treat Removal of contaminated groundwater or immiscible contaminants and Larger capture zone, greater recovery rates, and fewer wells required

subsequent treatment or reprocessing

Free product Removal of free-phase contaminants from an aquifer Larger capture zone, greater recovery rates, and fewer wells required

recovery

Bioremediation Injection and infiltration of fluids into the saturated zone to enhance Improved fluid injection and infiltration rates, as well as improved

biodegradation of dissolved contaminants access of microbes to contaminants

Air sparging Injection of air into the saturated zone to remove organic contaminants Increased delivery of air, greater rates of biodegradation and

by volatilization and biodegradation removal of volatile compounds, and fewer injection wells required

Chemical treatment Injection of chemical reagents to the saturated zone to enhance the Improved access to contaminants and greater injection rates

chemical treatment of contaminants, for example, oxidation/reduction

Physical treatment Injection of hot air or steam to enhance the physical treatment of Greater in situ flow rates

contaminants, for example in situ heating and air stripping

Source: Modified from Frac Rite Environmental, Ltd. 1996.
6-37

TABLE 6-2

SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES

ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING

(Page 1 of 4)

Technology Vendor Location Formation Type Treated After Fracturing 

Developer or Site Geologic Contaminants Technology Performance

Pneumatic Fracturing and Accutech Remedial Somerville, New Shale VOCs, primarily TCE Rate of air flow increased by more than 600 percent.

SVE with Hot Gas Injection Systems, Inc. Jersey

Rate of TCE mass removal increased by

approximately 675 percent.

Pneumatic Fracturing Accutech Remedial Santa Clara, Silty clay, sandy VOCs, primarily TCE Rate of air flow increased 3.5 times. Permeability

and SVE Systems, Inc. California silts, and clays increased as much as 510 times.

Rate of TCE mass removal in clay zones increased

as much as 46,000 times.

Pneumatic Fracturing and Accutech Remedial Highland Park, Shale VOCs, primarily TCE TCE mass removal increased 3 times.

DPE Systems, Inc. New Jersey

Pneumatic Fracturing and Accutech Remedial Oklahoma City, Shale and No. 2 Fuel oil as free Rate of recovery of free product increased by

Fuel Recovery Systems, Inc. Oklahoma sandstone product approximately 1,600 percent.

Pneumatic Fracturing and Accutech Remedial Oklahoma City, Sandy, silty shale, VOCs, primarily Transmissivity increased by approximately

In Situ Bioremediation Systems, Inc. Oklahoma and clay stone BTEX and TCE 400 percent.

Pneumatic Fracturing and Accutech Remedial Flemington, New Shale VOCs, primarily TCE Transmissivity increased by 85 percent.

In Situ Bioremediation Systems, Inc. Jersey

Pneumatic Fracturing Accutech Remedial Columbia City, Clay VOCs, including Rate of air flow increased 2 times.

and SVE Systems, Inc. Indiana TCE, DCE, and vinyl

chloride

Pneumatic Fracturing Accutech Remedial Coffeyville, Silty clay VOCs, primarily TCE Rate of air flow increased more than 5 times.

and SVE Systems, Inc. Kansas
6-38

TABLE 6-2

SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES

ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING

(Page 2 of 4)

Technology Vendor Location Formation Type Treated After Fracturing 

Developer or Site Geologic Contaminants Technology Performance

Pneumatic Fracturing Terra Vac, Inc. New York, New Clay soils TCE, PCE, BTEX, Rate of air flow did not increase appreciably.

and DPE York and other VOCs

Concentration of VOCs in the extracted air stream

increased 10 times.

Pneumatic Fracturing Terra Vac, Inc. Monroe, Louisiana Clay soils TCE, PCE, BTEX, Rate of air flow increased by 6 to 8 standard cubic

and DPE and other VOCs feet per minute.

Rate of extraction of VOCs more than doubled.

Pneumatic Fracturing and New Jersey Marcus Hook, Clay soils BTEX Soil permeability increased 40 times.

In Situ Bioremediation Institute Pennsylvania

of Technology Rate of removal of BTEX increased by more than

82 percent.

Pneumatic Fracturing New Jersey Richmond, Clay VOCs, primarily Rate of air flow increased 1,000 times.

and SVE Institute Virginia methylene chloride

of Technology and TCA Concentration of VOCs in the extracted air stream

increased 200 times.

Pneumatic Fracturing First Environment, Greenville, Biotite gneiss and Chlorinated solvents Recovery rate increased as much as 10 times.

and DPE Inc. South Carolina schist

Hydraulic Fracturing University of Oak Brook, Silty clay TCE, TCA, DCA, and Average rate of extraction increased 15 to 20 times.

and SVE Cincinnati Illinois PCE

Concentration of contaminants recovered increased

10 times.
6-39

TABLE 6-2

SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES

ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING

(Page 3 of 4)

Technology Vendor Location Formation Type Treated After Fracturing 

Developer or Site Geologic Contaminants Technology Performance

Hydraulic Fracturing and University of Dayton, Ohio Sandy and silty BTEX and TPH Rate of fluid flow increased 25 to 40 times.

In Situ Bioremediation Cincinnati clay

Level of contaminant reduction was 89 percent

greater for BTEX and 77 percent greater for TPH.

Hydraulic Fracturing University of Beaumont, Texas Clay Gasoline and Rate of recovery of LNAPL increased 10 times.

and SVE Cincinnati cyclohexane

Hydraulic Fracturing Fuss and O'Neill, Woodstock, Silty clay VOCs, primarily paint Rate of fluid flow increased as much as 6 times.

and SVE Inc. Connecticut thinner

and FRX Inc.

Hydraulic Fracturing and In FRX Inc. Denver, Colorado Shale and clay TPH Reduction of concentrations of TPH in soils was

Situ Bioremediation approximately 90 percent in 5 months.

Hydraulic Fracturing FRX Inc. Lima, Ohio Clay and silty clay Gasoline Rate of fluid flow increased more than 10 times.

and SVE

Hydraulic Fracturing FRX Inc. Oakfield, Clay and silty clay Gasoline and diesel Rate of fluid flow increased as much as ten times.

and SVE Maine fuel

Hydraulic Fracturing and FRX Inc. Columbus, Ohio Clay and silty clay Unspecified water Graphite filled fractures created an electrical field

Electroosmosis soluble contaminants required to induce electroosmotic migration of water

and contaminants. 

Hydraulic Fracturing Golder Applied Atlanta, Georgia Clay Chlorinated solvents Average product recovery rate increased 4 times.

and DPE Technologies, Inc.
6-40

TABLE 6-2

SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES

ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING

(Page 4 of 4)

Technology Vendor Location Formation Type Treated After Fracturing 

Developer or Site Geologic Contaminants Technology Performance

Hydraulic Fracturing Frac Rite Alberta, Canada Clayey silt, silty Hydrocarbon Hydraulic conductivity increased 10 times and the

and DPE Environmental, sands condensate and zone of influence increased 4 times.

Ltd. and Echo-Scan Free-phase

Corporation hydrocarbons Volumetric rate of recovery of condensate increased

approximately 7 times.

Hydraulic Fracturing Remediation Bristol, Tennessee Sedimentary TCE Rate of extraction increased by as much as 6 times.

and SVE Technologies, Inc. bedrock

Rate of TCE extraction increased by as much as 700

liters per minute.
6-41

TABLE 6-3

COMPARISON OF HYDROCARBON CONDENSATE RECOVERY RATES 

BEFORE AND AFTER FRACTURING

Before Hydraulic Fracturing After Hydraulic Fracturing

Kave Influence Recovery K Influence Recovery

(feet/day) (feet) (gal/day) (feet/day) (feet) (gal/day)

Zone of Condensate Zone of Condensate

ave

0.1 3 to 5 13 1.1 >1.5 95

Source: Modified from Frac Rite Environmental, Ltd. 1996

Note: Kave Average permeability
6-42

TABLE 6-4

COST DATA FOR SOIL VAPOR EXTRACTION

ENHANCED WITH PNEUMATIC FRACTURING

Cost Item ($) TCE ($/lb)

Total Cost Cost/lb Percent of 

Total (%)

Site preparation 42,000 15.79 11.3

Permitting/regulatory requirements 1,750 0.66 0.5

Capital equipment (1.5 years) 82,074 30.85 22.1

Startup 8,200 3.08 2.2

Labor 107,640 40.47 29.0

Consumables/supplies 4,000 1.50 1.1

Utilities 17,000 6.39 4.6

Emission control 70,000 26.32 18.8

Disposal of residues (water) 37,200 13.98 10.0

Analytical services NA — —

Repair/replacement NA — —

Demobilization 1,500 0.56 0.4

Total $371,364 $139.60 $100.0

Source: Modified from U.S. Environmental Protection Agency 1993a and 1993b

Note: NA Not available

— Not applicable

TCE Trichloroethene
6-43

TABLE 6-5

COST DATA FOR HYDRAULIC FRACTURING

Cost Category (1993 Dollars)

Estimated Cost

Site preparation 1,000

Permitting/regulatory requirements 5,000 a

Capital equipment rental 1,000 b

Startup 0

Labor 2,000

Supply and consumables 1,000

Utilities 0

Treatment and disposal effluent 0

Shipping and handling of residues and waste 0

Analytical services and monitoring 700

Maintenance and modifications 0

Demobilization 400 a

Total one-time costs 5,400

Total daily costs 5,700

Estimated cost per fracture $950 to $1,425 c

Source: Modified from U.S. Environmental Protection Agency 1993c

Notes:

a One-time costs

b 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.

c Total daily costs (excluding one-time costs) divided by four or six fractures per

day
6-44

TABLE 6-6

PNEUMATIC AND HYDRAULIC FRACTURING TECHNOLOGY VENDORSa

(Page 1 of 2)

Name of Vendor Address and Phone Number Point of Contact

Pneumatic Fracturers

Accutech Remedial Systems, Inc. Cass Street and Highway 35 John Liskowitz

Keyport, NJ 07735

Phone: 908-739-6444

Fax: 908-739-0451

First Environment, Inc. 90 Riverdale Road Richard Dorrler

Riverdale, NJ 07457

Phone: 201-616-9700

Fax: 201-616-1930

McLaren/Hart Environmental 25 Independence Boulevard James Mack

Engineers, Inc. Warren, NJ 07059

Phone: 908-647-8111

Fax: 908-647-8162

Terra Vac, Inc. 92 North Main Street Loren Martin

Windsor, NJ 08561

Phone: 609-371-0070

Fax: 609-371-9446

Hydraulic Fracturers

EMCON 3300 North San Fernando Boulevard Donald L. Marcus

Burbank, CA 91504

Phone: 818-841-1160

Fax: 818-846-9280

ERM-Southwest, Inc. 16300 Katy Freeway - Suite 300 H. Reiffert Hedgcoxe

Houston, TX 77094-1609

Phone: 713-579-8999

Fax: 713-579-8988

Fluor Daniels GTI, Inc. 2000-200 Manner Avenue John F. Dablow III

Torrance, CA 90503

Phone: 310-371-1394

Fax: 310-371-4782
TABLE 6-6

PNEUMATIC AND HYDRAULIC FRACTURING TECHNOLOGY VENDORSa

(Page 2 of 2)

Name of Vendor Address and Phone Number Point of Contact

6-45

Frac Right Environmental, Ltd. 6 Stanley Place S.W. Gordon H. Bures

Calgary, Alberta 

Canada T2S 1B2

Phone: 403-620-5533

Fax: 403-287-7092

FRX Inc. P.O. Box 37945 Larry C. Murdoch,

Cincinnati, OH 45222 Ph.D. and 

Phone: 513-469-6040 William W. Slack,

Fax: 513-556-2522 Ph.D.

Fuss and O'Neill, Inc. 146 Hartford Road David L. Bramley

Manchester, CT 06040

Phone: 203-646-2469

Fax: 203-643-6313

Golder Applied Technologies, Inc. 3730 Chamblee Tucker Road Grant Hocking

Atlanta, GA 30340

Phone: 770-496-1893

Fax: 770-934-9476

Gregg Drilling and Testing, Inc. 2475 Cerritos Avenue John Gregg 

Signal Hill, CA 90806

Phone: 310-427-6899

Fax: 310-427-3314

Remediation Technologies, Inc. 23 Old Town Square - Suite 250 Ann Colpitts

Fort Collins, CO 80524

Phone: 970-493-3700

Fax: 970-493-2328

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.
6-46

TABLE 6-7

COMPARISON OF PNEUMATIC FRACTURING AND HYDRAULIC FRACTURING

Features Pneumatic Fracturing Hydraulic Fracturing

Fracture pattern Dense network of micro-fractures One or two major fractures that

around the injection point with one migrate outward into the

or two major fractures that migrate formation per injection interval

outward into the formation per with secondary fractures in

injection interval. overlying formation.

Injection medium Air or other gases with or without Water or slurries of water, sand,

fine grained proppants. and other additives.

Injection interval 2 to 3 feet 0.5 to 5 feet

Fracture aperture 0.5 to 1.0 mm 1 to 2 cm

Radial extent of fractures 20 to 70 feet 10 to 25 feet

Radial extent of influence 20 to 70 feet 10 to 70 feet

Maximum depth At depths greater than 75 feet Up to several hundred feet, with

self-propping decreases; however, or without propping agents.

propping agents can be used.

Injection time to create 20 seconds 5 to 15 minutes

fracture

Well completion Typically a single well screen Typically a casing for each

across all fractures at one location. fracture. Where well contains

All fractures in a well either inlet or multiple fractures, use each

recovery. fracture for either air inlet or

recovery.

Geologic formations that Over-consolidated or bedded Over-consolidated or bedded

favor successful sediments and bedrock sediments

application

Source: Modified from Keffer, Liskowitz, and Fitzgerald 1996 and FRX Inc. 1996.
7-1

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
7-2

to high-permeability soils, where the condensate front can more freely 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/yd to $166/yd .

3 3

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/yd to $100/yd . 

3 3

For RFH, energy is delivered to the contaminated region using electrodes or antennae that emit radiofrequency 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/yd to $336/yd .

3 3

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/yd .

3

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
7-3

inexpensive cost. However, heat conduction by this method is very slow and inefficient and requires a 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:

C 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.

C 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.

C 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.

C 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 ( C) rise temperature increase. Thermal enhancement technologies such as soil o

surface modification, fiber optic heating, and warm water injection may be used to provide

relatively small (2 to 10 C) increases in soil temperature. o

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:
7-4

C Gas advection

C Chemical partitioning to the vapor phase

C Gas-phase contaminant diffusion

C Sorption of contaminant on soil surfaces

C 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 C, the steam is produced and the steam’s pressure-driven flow to o

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.
7-5

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.

7.3.1 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.
7-6

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 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 oC 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.
7-7

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 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 ( F), thereby o

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.
7-8

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 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 100EC (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.

7.3.3 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.
7-9

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 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:

C 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.

C 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.

C 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. 

C 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-inchdiameter 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.

C 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.
7-10

C 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

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,

ohmic 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 oC. 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 oC (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,
7-11

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.

7.3.4 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.
7-12

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 (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 C. o

7.3.5 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 800 to 1000 C, and a vacuum system that drew soil o o
7-13

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 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
7-14

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

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 (SERP) was selected to treat the contaminated soil at the Rainbow Disposal site.

Treatment using the SERP process began in August 1991 and was evaluated under EPA’s SITE program

in August and September of 1993. SERP 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
7-15

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.

It was estimated that approximately 16,000 gallons of the diesel fuel spill was removed during treatment

with the SERP. Since the estimated release was 70,000 to 135,000 gallons and since 4,000 gallons was

recovered before the SERP 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.
7-16

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 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 Fg/kg and nondetected to 4,529 Fg/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.
7-17

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 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 threefoot layer encompassing the capillary fringe contained the highest concentrations of petroleum
7-18

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.

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 C to 100 C in the immediate vicinity of the RFH applicator and o o

to 40 C at a radial distance of 5 feet from the applicator at a depth of 8.5 feet bgs. During the o

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.
7-19

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.

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 SERP 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 yd for each of the 12 cost categories for the 3

typical case.

As shown in Table 7-2, the soil treatment cost ranges from about $29/yd to $43/yd for the ideal and 3 3

actual cases, respectively. Labor is the largest cost for use of SERP, 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 SERP, together accounting for about one-third of the total cost. 

The cost per yd is significantly less than the cost of excavating and treating the soil; however, as discussed 3

in Section 7.4.1.1, SERP did not meet the treatment goal, and additional treatment may be necessary. 

Continued treatment would have increased the total cost and the cost per yd for the site. 3

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
7-20

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.

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 yd of soil at the hypothetical site 3

described previously, capital costs account for about $44/yd .

3

The DOE (1995) cost analysis indicates that the total cost of SPSH would be $86/yd of treated soil and 3

that the total cost of SVE would be $576/yd of treated soil. The cost analysis assumed that the site would 3

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 C. o

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:
7-21

Type of Contamination Technology Technology

Thermal Enhancement Conventional Treatment

Shallow vadose zone Thermally enhanced vapor Excavation and Treatment

contamination extraction system (TEVES)

Deep vadose zone VOC 3-Phase soil heating SVE

contamination

6-Phase soil heating SVE

Deep vadose zone RF heating SVE

SVOC contamination

Deep vadose zone with Dynamic underground stripping PT/SVE

groundwater contamination (DUS)

Restricted access contamination RF heating using dipole SVE

antennae (RFD)

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 yd treated basis, for the five treatment 3

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.
7-22

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:

C 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.

C Steam injection is more mature than other thermal enhancement technologies to remove NAPLs.

The primary limitations of steam injection technologies include:

C 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.

C 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.

C 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:

C 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.
7-23

The primary limitations of hot air injection technologies include:

C 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:

C With RFH, much faster heating rates and uniform heating can potentially be obtained than with

competing technologies. 

C The technology does not involve any type of fluid injection and is operated under vacuum

containment conditions, so chances of contaminant spreading is minimized. 

The primary limitations of RFH technologies include:

C The high temperatures associated with RFH inhibit biological activity and may induce some

fracturing of the soil structure as the soil dries.

7.6.4 Electrical Resistance

The primary strengths of ER heating technologies include:

C The process uses common AC electricity, lowering capital costs and making the technology cost

competitive with RFH.

C 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:

C 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 oC.

C The effectiveness of the technology depends on soil moisture. Once the soil has been dried by the

electrodes, heating becomes uneven, and efficiencies decrease.
7-24

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. 

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.
7-25

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.

7.8.2 Professional Contacts

A list of thermal enhancement technology experts is provided in the table below.

Name Affiliation

Dr. Roger Aines Lawrence Livermore National Laboratory

(510) 423-7184

John F. Dablow III Fluor Daniels GTI, Inc.

(310) 371-1394

Paul de Percin EPA National Risk Management Research Laboratory

(513) 569-7797

Harsh Dev IIT Research Institute

(312) 567-4257

Raymond Kasevich KAI Technologies, Inc.

(603) 431-2266

Laurel Staley EPA National Risk Management Research Laboratory

(513) 569-4257

Michelle Simon EPA National Risk Management Research Laboratory

(513) 569-7469

Theresa Bergman Battelle Pacific Northwest Laboratory

(509) 376-3638
7-26

FIGURE 7-1

RELATIONSHIP BETWEEN INCREASING TEMPERATURE

AND VAPOR PRESSURE FOR SEVERAL CHEMICALS
FIGURE 7-2

TYPICAL SOIL VAPOR EXTRACTION ENHANCEMENT

WITH STEAM INJECTION SYSTEM
FIGURE 7-3

HOT AIR INJECTION THROUGH DRILL AUGER
FIGURE 7-4

SOIL VAPOR EXTRACTION ENHANCEMENT WITH RADIO-FREQUENCY

HEATING AT SANDIA NATIONAL LABORATORY
FIGURE 7-5

COST ANALYSIS OF THE STEAM-ENHANCED RECOVERY PROCESS
FIGURE 7-6

COST COMPARISON OF THERMAL ENHANCEMENT AND

CONVENTIONAL TREATMENT TECHNOLOGIES
7-32

TABLE 7-1

THERMAL ENHANCEMENT PERFORMANCE DATA

(Page 1 of 3)

Vendor Enhancement Scale Demo Location Contaminant Treatment Treatment Treated Soil Type Time Source

Thermal of Target Before After Volume Treatment

Date Concentration Concentration

Battelle Pacific Six Phase Soil Field NA Aiken, PCE ND to 500 mg/kg ND to 0.5 1,100 yd clayey soil 18 days EPA 1994

Northwest Heating Demo South Carolina TCE ND to 200 mg/kg mg/kg

Laboratories ND to 0.5

mg/kg

3

Geo-Con, Inc. Hot air Full NA Piketon, Ohio TCE 1 to 100 mg/kg 10 mg/kg 20,000 yd clayey soil NA EPA 1994

injection

3

Flour-Daniels Steam Full 1995 Bremerton, No. 6 Fuel Oil 88,000 mg/kg TPH Ongoing 25,000 yd sandy till Ongoing Tetra Tech

GTI (FD GTI) Sparging Washington Diesel Fuel 1996

3

FD GTI Hot Air Full 1993 Union, Chlorinated 100 mg/kg soil Ongoing 30,000 yd glacial till Ongoing Tetra Tech

Sparging Massachusetts Solvents 10 mg/L 1996

groundwater (gw)

3

FD GTI Electrokinetic Full 1994 Netherlands BTEX BTEX (gw): BTEX (gw): 10,500 yd sandy clay 24 weeks Tetra Tech

Heating Diesel Fuel 13,400 Fg/L ND 1996

Diesel (gw): Diesel (GW):

7,300 Fg/L <50 Fg/L

TPH (soil): TPH (soil): 9 to

9,000 mg/L 220 mg/L

3

Hrubetz Hot air Full 1990 Ottawa, Ontario Jet Fuel 21,000 mg/L ND to 215 mg/L 300 yd NA 90 days EPA 1994

Environmental injection Canada

Services, Inc.

(Hrubetz)

3

Hrubetz Hot air EPA NA Kelly Air Force Jet Fuel (JP-4) NA 12,799 lb 890 yd NA 18 days EPA 1994

injection demo Base, Texas removed

3
7-33

TABLE 7-1

THERMAL ENHANCEMENT PERFORMANCE DATA

(Page 2 of 3)

Vendor Enhancement Scale Demo Location Contaminant Treatment Treatment Treated Soil Type Time Source

Thermal of Target Before After Volume Treatment

Date Concentration Concentration

Hughes Steam Full 1991 Huntington TPH (diesel fuel) 3,790 mg/kg 2,290 mg/kg 150,000 yd layered 730 days EPA 1995b

Environmental recovery Beach, sand/clay

Systems, Inc. California

3

IIT Research RF Heating EPA 1994 Kelly Air Force Aromatics 40 mg/kg 2.84 mg/kg 44 yd silt, clay, 60 days EPA 1995c,

Institute (IITRI) Demo Base, Texas Nonaromatics 200 mg/kg 7.2 mg/kg and cobbles EPA 1994

3

IITRI RF heating Pilot 1992 Rocky Mountain Aldrin 1,100 mg/kg 11 mg/kg 30 yd sandy clays 35 days EPA 1995c,

Arsenal, Dieldrin 490 mg/kg 3.2 mg/kg and clayey EPA 1994

Colorado Endrin 630 mg/kg 2.8 mg/kg sands

Isodrin 2,000 mg/kg 2.8 mg/kg

3

IITRI RF heating Pilot 1989 Volk Air Aromatic VOCs 212 mg/kg 0.88 mg/kg 19 yd sandy soil 13 days EPA 1995c,

National Guard Aliphatic VOCs 4,189 mg/kg 28 mg/kg EPA 1994

Base, Wisconsin Aromatic SVOCs 252 mg/kg 2.3 mg/kg

Aliphatic SVOCs 1,663 mg/kg 95 mg/kg

Hexadecane 31.5 mg/kg 5.4 mg/kg

3

KAI RF heating Pilot 1996 St. Paul, TPH (gasoline) 2,300 mg/kg 1,000 mg/kg Not Not 20 days Price, et. al.

Technologies, Minnesota available available 1997

Inc. (KAI)

KAI RF heating EPA 1994 Kelly Air Force TRPH 1,238 mg/kg 636.9 mg/kg 56 yd sandy soil 45 days EPA 1995a

Demo Base, Texas

3

Lawrence Steam Full 1993 LLNL BTEX 4,800 mg/kg 140 mg/kg 100,000 yd alluvial soil 145 days EPA 1995b

Livermore stripping and TPH (gasoline) 8,600 gallons 1000 gallons w/silt clay

National electrical and gravel

Laboratory heating

(LLNL)

3
7-34

TABLE 7-1

THERMAL ENHANCEMENT PERFORMANCE DATA

(Page 3 of 3)

Vendor Enhancement Scale Demo Location Contaminant Treatment Treatment Treated Soil Type Time Source

Thermal of Target Before After Volume Treatment

Date Concentration Concentration

Novaterra, Inc. Steam Full 1988 San Pedro, DCA 10 to 200 mg/kg 0.47 to 0.82 30,000 yd NA late 1989 EPA 1994

stripping California DCE 20 to 100 mg/kg mg/kg to early

Bis(2-ethylhexyl) 0.23 to 2.41 1990

phthalate 100 to 80,000 mg/kg

Aromatics mg/kg

Butyl carbitol 1,200 mg/kg 52.67 mg/kg

6,000 mg/kg 10.77 mg/kg

4.20 mg/kg

3

Praxis Steam Pilot 1988 McClellan Air TCE ND to 40 mg/L ND to 0.05 5,000 yd NA NA EPA 1994

Environmental extraction Force Base, mg/L

Technologies, California

Inc.

3

R.E. Wright Steam Pilot NA Bradford, TPH 50,000 to 100,000 4,500 mg/kg 330 yd NA 45 days EPA 1994

Environmental, stripping Pennsylvania mg/kg

Inc.

3

SIVE Services Steam Full 1989 San Jose, VOCs NA 70,000 lb 30,000 yd NA 400 days EPA 1994

injection California removed

3

Notes:

Demo Demonstration TPH Total petroleum hydrocarbon mg/L Milligram per liter

NA Not applicable DCE Dichloroethene mg/kg Milligram per kilogram

PCE Tetrachloroethene DCA Dichloroethane VOC Volatile organic compound

TCE Trichloroethene lb Pound SVOC Semivolatile organic compound

ND Nondetect yd Cubic yard

BTEX Benzene, toluene, ethylbenzene, and total xylenes

3
7-35

TABLE 7-2

HUGHES STEAM-ENHANCED RECOVERY PROCESS COST SUMMARY

Cost Category Total $ $/yd Total $ $/yd Total $ $/yd

Approximate Actual Costs Estimated Ideal Cost for Estimated Cost for a

for the Rainbow Disposal the Rainbow Disposal Typical Site of the

Site Site Same Size

3 3 3

Site Preparation 338,000 3.56 326,000 3.43 336,000 3.54

Permitting and Regulatory 16,000 0.17 11,000 0.12 14,000 0.15

Non-Depreciable Equipment 523,000 5.51 522,000 5.50 524,000 5.52

Startup and Fixed 759,000 7.99 414,000 4.35 436,000 4.59

Labor 1,362,000 14.34 776,000 8.16 1,034,000 10.88

Consumables and Supplies 43,000 0.46 24,000 0.26 32,000 0.34

Utilities 631,000 6.65 280,000 2.95 493,000 5.19

Effluent Treatment and Disposal 71,000 0.75 36,000 0.37 47,000 0.50

Residuals and Waste Handling and Disposal 67,000 0.71 49,000 0.52 61,000 0.65

Sampling and Analytical 300,000 3.16 196,000 2.06 222,000 2.34

Facility Modification, Repair, and Replacement 151,000 1.59 58,000 0.61 78,000 0.82

Site Demobilization 139,000 1.47 99,000 1.04 99,000 1.04

Total 4,400,000 46.36 2,791,000 29.37 3,376,000 35.56

Source: Modified from U.S. Environmental Protection Agency 1995b.

Notes:

yd Cubic yard 3
7-36

TABLE 7-3

SIX PHASE SOIL HEATING COST SUMMARY

Cost Description Total Cost ($)

Capital Costs

Mobilization 9,000

Power Source 286,000

Water Source 24,000

Alternating Current (AC) Applications Well 54,000

Site Characterization and Well Installation 53,000

Soil Vapor Extraction Pilot Testing 13,000

Permitting 16,000

Vacuum System 175,000

Treatment System 51,000

Dismantlement and Demobilization 23,000

Startup 21,000

Subtotal 725,000

Construction Management 73,000

Engineering, Design, and Inspection 181,000

Project Management 44,000

Contingency 255,000

Total Capital Cost 1,278,000

Annual Operation and Maintenance (O&M) Costs

Field Monitoring 76,000

Monitoring and Reporting 58,000

System Operation and Maintenance 70,000

Total Annual O&M Costs 204,000
7-37

TABLE 7-4

THERMAL ENHANCEMENT TECHNOLOGY VENDORSa

(Page 1 of 2)

Name of Vendor Address, Phone, Fax Point of Contact

Battelle Pacific Northwest Battelle Boulevard, P.O. Box 999, Mailstop B1-40 Theresa Bergsman

Laboratories Richland, Washington 99352

(509) 376-3638

Flour Daniels GTI 20000/200 Mariner Ave. Jay Dablow

Torrance, California 90503

(310) 371-1394

Geo-Con, Inc. 4075 Monroeville Boulevard Linda M. Ward

Corporate One, Building II, Suite 400

Monroeville, Pennsylvania 15146 

(412) 856-7700

Hrubetz Environmental Services, 5949 Sherry Lane, Suite 525 Barbara Hrubetz

Inc. Dallas, Texas 75225

(214) 363-7833

IIT Research Institute 10 West 35th Street Harsh Dev

Chicago, Illinois 60616

(312) 567-4257

KAI Technologies, Inc. 170 West Road #7 Raymond S.

Portsmouth, New Hampshire 03801 Kasevich

(603) 431-2266

Millgard Environmental 12900 Stark Road Jim Brannigan

Corporation Livonia, Michigan 48150

(313) 261-9760

Praxis Environmental 1440 Rollins Road Dr. Lloyd Stewart

Technologies, Inc. Burlingame, California 94010

(415) 548-9288

R.E. Wright Environmental, Inc. 3240 Schoolhouse Road Richard C. Cronee,

(REWEI) Middletown, Pennsylvania 17057 Ph.D.

(717) 944-5501
TABLE 7-4

THERMAL ENHANCEMENT TECHNOLOGY VENDORSa

(Page 2 of 2)

Name of Vendor Address, Phone, Fax Point of Contact

7-38

SIVE Services 555 Rossi Drive Douglas K. Dieter

Dixon, California 95620

(916) 678-8358

Terra Vac, Inc. 1555 Williams Drive, Suit 102 Charles Prince

Marrieta, Georgia 30066-6282

(770) 421-8008

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.
7-39

TABLE 7-5

WASTE APPLICATIONS

Contaminants and Contaminant Groups Treated

Vendor VOCs SVOCs VOCs SVOCs Pesticide Furans PCBs Solvents BTEX Acetonitrile Acids Sources

Halogenated Halogenated Dioxins/ Organic Reference

BATTELLE PACIFIC NORTHWEST LABORATORIES A P P P P P NA A P NA NA EPA 1994

FLOUR DANIEL GTI A A A A P NA P A A NA P Dablow 1996

GEO-CON, INC. A A P P A NA NA A NA A A EPA 1994

HRUBETZ ENVIRONMENTAL SERVICES, INC. P P A A P P P A A P P EPA 1994

IIT RESEARCH INSTITUTE A A A A A NA P A A NA NA EPA 1994

KAI TECHNOLOGIES, INC. A A A P NA NA P A P P P EPA 1994

PRAXIS ENVIRONMENTAL TECHNOLOGIES, INC. A A A A NA NA P A A NA NA EPA 1994

R.E. WRIGHT ENVIRONMENTAL, INC. P P A A P P P P A NA P EPA 1994

SIVE SERVICES A P A P P P P A A P P EPA 1994

Media Types Treated

Vendor (in situ) (ex situ) Sludge Solid (in situ) (ex situ) (in situ) DNAPL LNAPL Sources

Soil Soil Sediment Sediment Groundwater Reference

Natural Natural

BATTELLE PACIFIC NORTHWEST

LABORATORIES A NA P NA A NA P P P EPA 1994

FLOUR DANIEL GTI A A P A P P A A A Dablow 1996

GEO-CON, INC. A NA NA P A NA NA NA NA EPA 1994

HRUBETZ ENVIRONMENTAL SERVICES, INC. A NA NA NA P NA P NA P EPA 1994

IIT RESEARCH INSTITUTE A NA P NA P NA NA P P EPA 1994

KAI TECHNOLOGIES, INC. A P P P P P NA P P EPA 1994

PRAXIS ENVIRONMENTAL TECHNOLOGIES, INC. A NA P NA A NA P P A EPA 1994

R.E. WRIGHT ENVIRONMENTAL, INC. A P NA NA P P A P A EPA 1994

SIVE SERVICES A NA NA NA P NA P A A EPA 1994

Notes:

A - Actually treated

P - Potentially treatable

NA - Not Applicable
Appendix A
(This appendix contains Jpeg images to be posted at a later date.)
Appendix B
B-1

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 CHAPTER 3

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-2

Dahmani, M.A., D.P. Ahlfeld, W. Ji, and M. Farrel. 1994. Air Sparging Laboratory Study. Air Sparging

for Site Remediation, ed. Robert E. Hinchee. Lewis Publishers. Ann Arbor, MI. Pages 108-111.

Hinchee, R E. 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.
B-3

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., 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.

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.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. 
B-4

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 Groundwater 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.

Wellensiek, 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

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1.4 CHAPTER 5

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