WATERSHED QUAL MGMT
WATERSHED QUAL MGMT ESM 224
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ESM 224 Expected information in Deliverable 5 The objective in this section is to describe the current monitoring data available for your watershed any existing WQ monitoring programs if they are documented online and more importantly propose a comprehensive monitoring plan for your watershed in support of the WMP effort Provide a short introduction to your report and a summary The core of the report is the characterization of current monitoring and your proposed plan 1 Flow monitoring Follow the instructions in the User s Guide Section 73 to obtain information about the various USGS gage stations in your watershed Note that you may have already downloaded the data for these gage stations using BASINS 40 but the USGS NIWS website can help you to determine the dates in which the gage stations were active and therefore which stations will be most useful for your analysis In some cases even a station that has been discontinued may be useful since it may be the only info available to estimate flows in a particular catchment For your analysis create a table with the gage stations available from the USGS indicating the period of record Provide a map with the location of the stations Using either the graphics from the USGS website or processing gage station data in Excel provide a few key hydrographs for your watershed with the mean min and max flows for that location over the time period of interest hopefully several years 10 would be useful Compare these flows to the precipitation data that you obtained from NOAA for your WARMF model in terms of timing of storms vs observed peak flows It doesn t have to be on the same graph although you can do it if you prefer 2 Current Water Quality monitoring Follow the instructions in the User s Guide Section 74 to obtain information about the various STORET WQ stations in your watershed Use the approach in Section 742 to gather the info for the various stations For your analysis create a table with the STORET WQ stations available indicating the agency that collected the data the period of record and the WQ parameters that are being monitored Provide a map with the location of the stations Given the information available from the 303d listings plot WQ data related to these impairments for a few key locations in your watershed Key means that they are in the main stem of the river and passing through regions where one would expect higher impact from the land uses These would be integrator stations they integrate information from various areas in the watershed If there are other WQ monitoring efforts in your watershed from some of the stakeholder groups you identified in Section 1 provide some details type of monitoring agency volunteer locations frequency parameters United States Office of Solid Waste and Environmental Protection Emergency Response EPA542R97007 Agency 51026 September 1997 EPA Analysis of Selected Enhancements for Soil Vapor Extraction CONTENTS Chapter Page FOREWORD ABS1 EXECUTIVE SUMMARY ES1 10 INTRODUCTION 11 11 BACKGROUND 11 12 OBJECTIVES 12 13 APPROACH 13 14 REPORT ORGANIZATION 14 20 BACKGROUND SOIL VAPOR EXTRACTION ENHANCEMENT TECHNOLOGIES 21 AIR SPARGING 31 31 TECHNOLOGY OVERVIEW 31 32 APPLICABILITY 32 33 ENGINEERING DESCRIPTION 33 331 Air Flow Within the Subsurface 34 332 Equipment Requirements and Operational Parameters 36 3321 Air Sparging Wells and Probes 36 3322 Manifolds Valves and Instrumentation 310 3323 Air Compressor or Blower 311 333 Monitoring of System Performance 313 34 PERFORMANCE AND COST ANALYSIS 314 341 Performance 315 3411 US Department of Energy Savannah River Integrated Demonstration Site 315 3412 Toluene Remediation at a Former Industrial Facility 316 3413 ElectroVoice Inc Demonstration Site 317 342 Cost Analysis 318 3421 Cost for Department of EnergyPatented In Situ Bioremediation System 319 3422 Cost for Subsurface Volatilization Ventilation System 320 CONTENTS Continued Chapter 40 35 VENDORS 36 STRENGTHS AND LIMITATIONS 37 RECOMMENDATIONS 38 REFERENCES DUALPHASE EXTRACTION 41 TECHNOLOGY OVERVIEW 42 APPLICABILITY 421 Contaminant Properties 422 Contaminant Phases 423 Soil Characteristics 43 ENGINEERING DESCRIPTION 431 DualPhase Extraction System Design 4311 Pilot Testing 4312 Extraction Well Design 4313 Extraction Equipment Design 4314 System Monitoring DualPhase Extraction System Characteristics 4321 DropTube Entrainment Extraction 4322 WellScreen Entrainment 4323 Downhole Pump Extraction 44 PERFORMANCE AND COST ANALYSIS 441 Performance 4411 Underground Storage Tank Release from a Gasoline Station in Houston Texas Underground Storage Tank Release from a Former Car Rental Lot in Los Angeles California Release From An Electronics Manufacturing Facility In Texas Underground Storage Tank Release from a Gasoline Station in Indiana Release from a Gasoline Underground Storage Tank for a Vehicle Fueling Station at a Hospital in Madison Wisconsin 4412 4413 4414 4415 Page 321 321 322 323 41 41 42 42 44 45 45 45 46 47 49 49 49 411 413 414 415 416 417 418 Chapter CONTENTS Continued 442 Cost Analysis 45 46 47 48 VENDORS STRENGTHS AND LIMITATIONS RECOMMENDATIONS REFERENCES DIRECTIONAL DRILLING 51 52 TECHNOLOGY OVERVIEW APPLICABILITY 521 Geologic Conditions 522 Distances Achieved 53 ENGINEERING DESCRIPTION 531 532 Drill Rigs Drilling Assembly 5321 TriCone Type Drilling Tools 5322 Hydraulically Assisted JetStyle Drilling Tools 5323 Compaction Tools 533 534 535 Drilling Fluids Guidance Systems Directionally Drilled Well Installation 5351 Well Materials 5352 Well Screens 5353 Well Casings 5354 Well Installation Design Considerations 5361 Radius of Curvature 5362 Air Flow Patterns 537 Common Problems 54 PERFORMANCE AND COST ANALYSIS 541 Performance iii Page 4 19 4 19 4 19 420 421 51 51 53 54 54 55 55 56 57 57 57 57 58 59 59 59 510 510 510 511 511 Chapter CONTENTS Continued Page 5411 US Department of Energy Savannah River Site Integrated Demonstration Site 513 5412 Alberta Gas Plant 514 5413 Hastings East Industrial Park 515 5414 John F Kennedy Airport 517 542 Cost Analysis 520 55 VENDORS 521 56 STRENGTHS AND LIMITATIONS 521 57 RECOMMENDATIONS 523 58 REFERENCES 523 581 Cited References 523 582 Professional Contacts 526 PNEUMATIC AND HYDRAULIC FRACTURING 61 61 TECHNOLOGY OVERVIEW 61 62 APPLICABILITY 62 621 Geologic Conditions 63 622 Contaminants 64 623 Technologies Enhanced by Fracturing 65 63 ENGINEERING DESCRIPTION 65 631 Injection Media 66 632 Fracturing Equipment 67 633 Injection Pressure and Rate 68 634 Fracture Size and Shape 68 635 Site Conditions 610 636 Monitoring the Formation of Fractures 610 637 Well Completion 611 638 Pneumatic Fracturing 611 639 Hydraulic Fracturing 612 64 PERFORMANCE AND COST ANALYSIS 613 641 Performance 613 6411 Pneumatic Fracturing Enhancement of SVE and Hot Gas Injection in Shale 614 Chapter 70 CONTENTS Continued Page 6412 Pneumatic Fracturing Enhancement of SVE in Clay 615 6413 Hydraulic Fracturing Enhancement of DPE in Clayey Silts 616 6414 PilotScale Testing of Hydraulic Fracturing at Linemaster Switch Superfund Site 617 642 Cost Analysis 618 6421 Costs of Pneumatic Fracturing 618 6422 Costs of Hydraulic Fracturing 620 65 VENDORS 621 66 STRENGTHS AND LIMITATIONS 621 67 RECOMMENDATIONS 622 68 REFERENCES 623 681 Cited References 623 682 Professional Contacts 625 THERMAL ENHANCEMENT 71 71 TECHNOLOGY OVERVIEW 71 72 APPLICABILITY 73 73 ENGINEERING DESCRIPTION 73 731 Steam InjectionStripping 75 7311 Steam Injection Through Injection Wells 76 7312 Steam Injection Through Drill Auger 76 732 HotAirInjection 77 733 RadioFrequency Heating 78 734 Electrical Resistance Heating 711 735 Thermal Conduction Heating 712 74 PERFORMANCE AND COST ANALYSIS 713 741 Performance 713 7411 Rainbow Disposal Site 713 7412 Savannah River Site 716 7413 Former Gasoline Station Near St Paul Minnesota 717 742 Cost Analysis 718 Chapter 75 76 77 78 Appendices CONTENTS Continued Page 7421 Steam InjectionStripping Costs 719 7422 Electrical Resistance Costs 719 743 Additional Cost Studies 720 VENDORS 721 STRENGTHS AND LIMITATIONS 722 761 Steam InjectionStripping 722 762 Hot Air Injection 722 763 RadioFrequency Heating 723 764 Electrical Resistance 723 RECOMMENDATIONS 724 REFERENCES 724 781 Cited References 724 782 Professional Contacts 725 A PHOTOGRAPIHC LOG B BIBLIOGRAPHY Vi FIGURES TYPICAL AIR SPARGING ENHANCEMENT TO SOIL VAPOR EXTRACTION SYSTEM HORIZONTAL AIR SPARGING AND SOIL VAPOR EXTRACTION WELL SYSTEM 3YEAR REMEDIATION COST BREAKDOWN REMEDIATION COST BREAKDOWN FOR IN SITU BIOREMEDIATION AND PUMPANDTREAT SOIL VAPOR EXTRACTION SCHEMATIC OF A DUALPHASE EXTRACTION SYSTEM DROPTUBE ENTRAINMENT EXTRACTION WELL DOWNHOLEPUMP EXTRACTION WELL EXTRACTION SYSTEM PERFORMANCE HORIZONTAL WELL NETWORK INSTALLED BENEATH A BUILDING TO REMEDIATE SOIL AND GROUNDWATER BLIND BOREHOLE COMPLETION CONTINUOUS WELL COMPLETION PILOT HOLE ADVANCEMENT BACK REAMING AND WELL CASING INSTALLATION TYPICAL DOWNHOLE HARDWARE FOR DIFFERENT DRILLING PHASES HASTINGS EAST INDUSTRIAL PARK SITE PLAN SHOWING HORIZONTAL AND VERTICAL WELL AIR SPARGING SOIL VAPOR EXTRACTION SYSTEM TCE CONCENTRATIONS IN SIX GROUNDWATER MONITORING WELLS DOWNGRADIENT FROM THE HORIZONTAL SPARGING WELL TCE CONCENTRATIONS IN THREE GROUNDWATER MONITORING WELLS NEAR THE VERTICAL SPARGING WELL 424 533 512 610 FIGURES continued Page HORIZONTAL WELL LAYOUT FOR AIR SPARGING AND SOIL VAPOR EXTRACTION AT TERMINAL 1A JOHN F KENNEDY INTERNATIONAL AIRPORT 537 HORIZONTAL WELL LAYOUT FOR AIR SPARGING AND SOIL VAPOR EXTRACTION AT THE INTERNATIONAL ARRIVALS BUILDING JOHN F KENNEDY INTERNATIONAL AIRPORT 538 AIR SPARGING PILOT TEST NOVEMBER 1995 AT THE INTERNATIONAL ARRIVALS BUILDING JOHN F KENNEDY INTERNATIONAL AIRPORT 539 SOIL VAPOR EXTRACTION PILOT TEST NOVEMBER 1995 AT THE INTERNATIONAL ARRIVALS BUILDING JOHN F KENNEDY INTERNATIONAL AIRPORT 540 SCHEMATIC OF PNEUMATIC FRACTURING FOR ENHANCED VAPOR EXTRACTION 626 SCHEMATIC OF HYDRAULIC FRACTURING 627 APPLICATION GUIDELINES FOR PNEUMATIC FRACTURING 628 EFFECTS OF PNEUMATIC FRACTURING 629 SEQUENCE OF OPERATIONS FOR CREATING HYDRAULIC FRACTURES 630 COMPARISON OF TCE MASS REMOVAL ENHANCED BY PNEUMATIC FRACTURING 631 PREFRACTURE CONTAIVIINANT REMOVAL CONCENTRATIONS 632 POSTFRACTURE CONTAIVIINANT REMOVAL CONCENTRATIONS 633 CUMULATIVE GROUNDWATER REMOVAL BEFORE HYDRAULIC FRACTURING 634 CUMULATIVE GROUNDWATER REMOVAL AFTER HYDRAULIC FRACTURING 635 RELATIONSIHP BETWEEN INCREASING TEMPERATURE AND VAPOR PRESSURE FOR SEVERAL CHEMICALS 726 Viii FIGURES continued TYPICAL SOIL VAPOR EXTRACTION ENHANCEMENT WITH STEAM INJECTION SYSTEM HOT AIR INJECTION THROUGH DRILL AUGER SOIL VAPOR EXTRACTION ENHANCEMENT WITH RADIOFREQUENCY HEATING AT SANDIA NATIONAL LABORATORY COST ANALYSIS OF THE STEAMENHANCED RECOVERY PROCESS COST COMPARISON OF THERMAL ENHANCEMENT AND CONVENTIONAL TREATMENT TECHNOLOGIES 730 73 1 TABLES Page SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION 15 AIR SPARGING SYSTEM CHARACTERISTICS 330 FACTORS AFFECTING APPLICABILITY OF AIR SPARGING 331 SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES 332 PERFORMANCE OF SUB SURFACE VOLATILIZATION VENTILATION SYSTEM FOR REDUCTION IN TARGET CONSTITUENTS IN SOIL HORIZONS IN THE VADOSE ZONE AT THE ELECTROVOICE INC DEMONSTRATION SITE 335 PERFORMANCE OF SUB SURFACE VOLATILIZATION VENTILATION SYSTEM FOR REDUCTION IN INDIVIDUAL TARGET CONSTITUENTS IN THE VADOSE ZONE AT ELECTROVOICE INC DEMONSTRATION SITE 336 SUMMARY OF COST DATA FOR IN SIT U BIOREMEDIATION AS WELL AS PUMPANDTREAT WITH SOIL VAPOR EXTRACTION 337 ESTIMATED COST FOR TREATIVIENT USING THE SUBSURFACE VOLATILIZATION VENTILATION SYSTEM PROCESS OVER A 3YEAR APPLICATION 338 VENDORS OF AIR SPARGING TECHNOLOGIES 339 COST DATA 427 VENDORS OF DUALPHASE EXTRACTION TECHNOLOGIES 428 VENDORS OF HORIZONTAL WELLS AND DIRECTIONAL DRILLING TECHNOLOGY 541 REMEDIATION TECHNOLOGIES ENHANCED BY FRACTURING 636 SELECTED EXAMPLES OF REMEDIATION TECHNOLOGIES ENHANCED BY PNEUMATIC AND HYDRAULIC FRACTURING 637 COMPARISON OF HYDROCARBON CONDENSATE RECOVERY RATES BEFORE AND AFTER FRACTURING 641 COST DATA FOR SOIL VAPOR EXTRACTION ENHANCED WITH PNEUMATIC FRACTURING 642 TABLES continued Egg COST DATA FOR HYDRAULIC FRACTURING 643 PNEUMATIC AND HYDRAULIC FRACTURING TECHNOLOGY VENDORS 644 COMPARISON OF PNEUMATIC FRACTURING AND HYDRAULIC FRACTURING 646 THERMAL ENHANCEMENT PERFORMANCE DATA 7 32 HUGHES STEAMENHANCED RECOVERY PROCESS COST SUMMARY 7 35 SIX PHASE SOIL HEATING COST SUMMARY 736 THERMAL ENHANCEMENT TECHNOLOGY VENDORS 7 37 WASTE APPLICATIONS 7 39 Xi Mgl AAEE AC Accutech ASSVE Echo ElectroVoice EPA ER ERT Frac FRX GAC GRO HDPE insec ACRONYMS AND ABBREVIATIONS Micrograms per liter American Academy of Environmental Engineers Alternating current Accutech Remedial Systems Inc Air sparging and soil vapor extraction Below ground surface Benzene toluene ethylbenzene and xylene Degrees Celsius Cubic feet per minute Cubic feet per minute per foot Centimeters per second Chlorinated polyvinyl chloride Dense nonaqueousphase liquid US Department of Energy Dualphase extraction EchoScan Inc ElectroVoice Inc US Environmental Protection Agency Electrical resistance Electrical resistance tomography Degrees Fahrenheit Frac Rite Environmental Ltd FRX Inc Granular activated carbon Gallons per minute Gasoline range organics High density polyethylene Hertz Inches per second ISB JFK KAI kVA kW LNAPL mgkg mgL mm Hg MPE NAPL PCB PCE Ppb psi PTSVE PVC RFH scfm SERP SITE SPSH SRS SVE SVOC SVVS TCA TCE ACRONYMS AND ABBREVIATIONS Continued In situ bioremediation John F Kennedy Airport Hydraulic conductivity KAI Technologies Inc Kilovoltampere Kilowatts Light nonaqueousphase liquid Megahertz Milligrams per kilogram Milligrams per liter Millimeter of mercury Multi phase extraction Nonaqueousphase liquids Polychlorinated biphenyls Tetrachloroethene Parts per billion Pounds per square inch Pumpandtreat system combined with soil vapor extraction Polyvinyl chloride Radiofrequency heating Standard cubic feet per minute Hughes Steam Enhanced Recovery Process Superfund Innovative Technology Evaluation Six phase soil heating Savannah River site Soil vapor extraction Semivolatile organic compounds Subsurface Volatilization and Ventilation System Trichloroethane Trichloroethene xiii Tetra Tech TIO TOU TPH UST V VEP VISITT VOC WDNR yd3 ACRONYMS AND ABBREVIATIONS Continued Tetra Tech EM Inc Technology Innovation Of ce Thermal oxidation unit Total petroleum hydrocarbons Underground storage tank Volts Vacuum enhanced pumping Vendor Information System for Innovative Treatment Technologies Volatile organic compound Wisconsin Department of Natural Resources Cubic yard NOTICE This document was prepared for the US Environmental Protection Agency EPA by Tetra Tech EM Inc Tetra Tech under Contract No 68W50055 Reference herein to any speci c 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 eld 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 ve SVE enhancement technologies evaluated in this report are air sparging dualphase 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 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 uptodate status of enhancement technologies an evaluation of each technology s applicability to various site conditions a presentation of cost and performance information a list of vendors specializing in the technologies a discussion of relative strengths and limitations of the technologies recommendations to keep in mind when considering the enhancements and a compilation of references The performance of an SVE system depends on properties of both the contaminants and the soil SVE is generally applicable to compounds with a vapor pressure of greater than 1 millimeter of mercury at 20 C 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 10393 or 1 X 10392 centimeter per second cms SVE by itself does not effectively remove contaminants in saturated soil However SVE can be used as an integral part of some treatment schemes that treat both groundwater and the overlying vadose zone Enhancement technologies should be considered when contaminant or soil characteristics limit the effectiveness of SVE or when contaminants are present in saturated soil The ve enhancement technologies covered in this report are as follows and are described in the following subsections Air Sparging Dualphase Extraction Directional Drilling Pneumatic and Hydraulic Fracturing Thermal Enhancement ESl AIR SPARGIN G 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 andor chemicals that are tightly sorbed This technique also enhances biodegradation of aerobicallydegradable contaminants and can signi cantly 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 V OC in soils within the saturated zone as well as strip dissolved contaminants from groundwater Air sparging is most effective at sites with homogeneous highpermeability 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 sitespeci c conditions Less dif cult at sites with homogeneous highpermeability soils and unconfined aquifers air sparging has been used at sites with heterogeneous lesspermeable soils and soils containing lowpermeability layers with some effectiveness Before selecting air sparging as an enhancement to SVE sitespeci c groundwater soil and contaminant conditions as well as cleanup goals and project objectives should be assessed DUAL PHASE EXTRACTION Like air sparging dualphase 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 ES2 treatment DPE provides a means to accelerate removal of nonaqueousphase 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 ow By lowering the groundwater table at the point of vapor extraction DPE enables venting of soil vapors through previously saturated and sernisaturated 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 Droptube entrainment extraction Extraction of total uids 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 gasliquid separator and treated Wellscreen 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 gasliquid separator and treated Downholepump 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 sitespeci c remediation goals Relative costs for the different types are also largely determined by these factors Use of DPE for remediation of contaminated sites is most advantageous for sites contaminated with volatile compounds and for soils with moderate to low hydraulic conductivity The presence of existing monitoring wells in strategic locations may provide an opportunity for minimizing system capital costs through conversion of the wells for extraction Before a DPE system is implemented efforts should be undertaken to assess groundwater and soil characteristics as well as project objectives for determining which type of DPE is appropriate for the site DIRECTIONAL DRILLING Directional drilling employs the use of specialized drill bits to advance curved boreholes in a controlled arc radius for installation of horizontal wells or manifolds for SVE and sparging technologies Horizontal wells can be used for enhancement of groundwater extraction air sparging SVE and free product removal systems The number of horizontal wells installed for environmental remediation projects has increased dramatically in recent years more than 400 new horizontal wells were projected to be installed in 1996 Wilson 1995a Horizontal directional drilling when applied to appropriate geologic environments and contaminants can result in better performance and lower overall cost than vertical wells Horizontal wells can be installed in most geologic materials that are suitable for soil vapor extraction and air sparging including unconsolidated sands silts and clays as well as bedrock Borehole lengths of between 200 and 600 feet with depths of less than 50 feet are most common however longer and deeper boreholes have been successfully installed There are two types of directionally drilled boreholes blind and continuous Blind boreholes terminate in the subsurface the well is installed from the entrance of the borehole Continuous boreholes are reoriented upward and return to the ground surface In continuous boreholes the well is installed from the exit point and pulled into the borehole by the drill rig An overview of a horizontal well installation by directional drilling is as follows A pilot hole is advanced Upon arriving at a target depth the drilling tool is reoriented to drill a horizontal borehole Electronic sensors in the drill tool guidance system provide orientation location and depth data to the driller The hole is enlarged using a reaming drill bit by pushing or pulling the bit through the pilot hole In a continuous borehole the reaming drill bit tool is inserted into the borehole at the exit point and pulled back to the drill rig The well is installed by pushing or pulling the well casings into the borehole In continuous boreholes well installation generally occurs during the reaming phase described previously Installation of horizontal wells may be more expensive than installation of vertical wells A care ll analysis should be conducted to determine the costs and bene ts 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 uids 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 costeffective remediation Pneumatic and hydraulic fracturing enhancement technologies are most applicable to lowpermeability geologic materials such as fmegrained 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 freephase uids 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 biorernediation including bioventing thermal treatment including hot gas injection in situ vitri cation free product recovery and groundwater pumpandtreat 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 ssures and channels The pore gas exchange rate often a limiting factor during vapor extraction can be increased signi cantly 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 lled with sand or other granular material The fractures are created through the use of uid pressure to dilate a well borehole and open adjacent cracks Once uid pressure exceeds a critical value a fracture begins to propagate Fractures may remain open naturally or they may ESS be held open by permeable materials known as proppan 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 I 439 139 439 r 1 well must be 391 1 Because of the great variability of geologic materials conducting pilotscale eld tests is advisable before fullscale fracturing installations are implemented Although most environmental applications of pneumatic and hydraulic fracturing involve uid 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 blastenhanced fracturing techniques have been adapted from the mining and geothermal industries and are well documented in the literature To date blastenhanced fracturing has been used only with pumpandtreat 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 sernivolatile 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 gasphase 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 ES6 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 radiofrequency 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 lowpermeability 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 highpermeability 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 offgas 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 uid under pressure into the subsurface the same geological concerns apply for hot air injection as with steam injection Radio Frequency Heating For RFH energy is delivered to the contaminated region using electrodes or antennae that emit radiofrequency 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 lowpermeability 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 lowpermeability 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 rernediate hazardous waste sites Thermal conduction heating can be used to remove VOCs in medium to lowpermeability soil This technology is easily implemented and is relatively inexpensive however heat conduction by this method is very slow and inef cient 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 inj ectionstripping 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 injectionstripping systems is limited to medium to highpermeability soils ER heating is more appropriate for heating and drying lowpermeability soil in the vadose zone RFH and ER heating can be used to heat soil if site conditions restrict the use of injection wells ES8 CHAPTER 10 INTRODUCTION Under Contract No 68W50055 with the US Environmental Protection Agency39s EPA Of ce of Solid Waste and Emergency Response Technology Innovation Of ce 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 EPA39s document S VE Enhancement T eehnology Resource Guide EPA542B 95003 October 1995 11 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 eld 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 ve enhancements that are evaluated in this report are air sparging dualphase extraction DPE directional drilling pneumatic and hydraulic fracturing and thermal enhancement Table 11 presents a summary of the ve SVE enhancement technologies presented in this report This report evaluates engineering methodologies related to SVE technologies Recent advancements of in situ bioremediation techniques have demonstrated that SVE technologies greatly enhance and sustain the aerobic bioremediation processes by providing oxygen or heat to naturally occurring soil microbials This report does not address the evaluation and implementation of SVE systems to promote biodegradation of site contaminants It is important to recognize the biochemical dynamics of a contaminated site and design a remediation technology that addresses both site characteristics and biochemical characteristics Engineers and site managers should consider the physical and biochemical processes in the site characterization and design phases of remediation projects Other technologies may 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 Biorernediation Volume 2 Chemical Treatment Volume 3 Soil WashingSoil Flushing Volume 4 StabilizationSolidi cation Volume 5 SolventChemical 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 amp 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 US Army Corps of Engineers 1995 Soil Vapor Extraction and Bioventing Engineering Manual Engineering and Design EM 111014001 November EPA 1991 Soil Vapor Extraction Technology Reference Handbook Of ce of Research and Development EPA540291003 February EPA 1994 Design Operation and Monitoring of In Situ Soil Vapor Extraction Systems Of ce of Research and Development EPA600F94037 September 12 OBJECTIVES The following ve speci c objectives have been developed for this report Describe the background applicability and assessment of SVE enhancements Perform an engineering evaluation of each technology to evaluate performance cost strengths and weaknesses Evaluate the current status of each technology Compile a vendor list for each technology Make recommendations for future use and applicability of each technology The general approach used to meet these objectives is discussed in Section 13 13 APPROACH A vestep approach was used to identify collect and review information to ful ll the objectives listed in Section 12 for each of the ve SVE enhancements The approach consisted of conducting the following ve tasks Conduct literature reviews Studies conducted by academic institutions Federal agencies state programs and other entities were reviewed to identify previous applications of enhancement technologies Collect performance information Performance information was collected from the literature reviewed for each technology as well as through database queries such as the Vendor Information System for Innovative Treatment Technologies VISITT Collect cost information Because the bene ts of implementing enhancement technologies must be weighed against the costs of the technologies cost information was collected from literature searches and other sources whenever possible to assess the costs of implementing SVE alone versus the costs of implementing SVE with an enhancement technology Contact and interview experts in the eld SVE enhancement experts familiar with the outcome of eld demonstrations were contacted to collect additional insight into implementing enhancement technologies at sites and to determine the state of the art in each technology Contact and interview vendors Technology vendors were contacted to collect additional unpublished performance and cost data to supplement information collected during the literature review One objective for preparing this document was to identify vendors for each technology However the list of vendors identi ed 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 identi ed by the following methods 13 Initially technology vendors were identi ed by accessing the Vendor Information System for Innovative Treatment Technologies VISITT database EPA 1996 The VISITT database provides vendor information for innovative treatment technologies Vendors were also identi ed through a networking process These vendors were interviewed by phone to con rm their services In many instances vendor contacts provided the names of additional vendors providing technology services in the same eld 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 dualphase 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 technologyspeci c and provide services speci c to these systems 14 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 indepth assessments of the ve SVE enhancement technologies air sparging DPE directional drilling pneumatic and hydraulic fracturing and thermal enhancement respectively The indepth assessments provide information as follows The applicability of the enhancement Cost and performance information List of technology vendors Strengths and limitations List of references Figures Tables including cost and vendor information Appendix A contains a photographic log displaying examples of the technologies presented in this report Appendix B contains a bibliography of published works collected during the course of research for topics presented in this report TABLE 1 1 SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION Page 1 of 3 Technology Air Sparging Dual Ph ase Extraction Directional Drilling Pneumatic and Hydraulic Fracturing Thermal Enhancement Description Injection of air occurs below or within contaminated zones through wells or sparging probes The injected air removes adsorbed VOCs in soil and dissolved contaminants in as the air rises 1 through the formation The increase in dissolved oxygen can also increase biodegradation of quot degradable Rem oval of contaminated water and soil gases from a common extraction well takes place under vacuum 4139 n 1 Installation of extraction or injection wells in the most beneficial location relative to the area 0 39 39 and soil extraction exposes soil formerly in the capillary fringe and saturated zones to the extraction system vapor flow The three primary methods used are droptube entrainment wellscreen entrainment and downholepump extraction anisotropy maximizes the results of an SVE system This technology increases the useful zone of in uence of the well and reduces short circuiting problems in vertical boreholes Injection of gases typically air or fluids either water or slurries into low permeable soil and sediments increases the performance of extraction or injection wells used in SVE Development of fractures may occur in saturated sediments as well as in the vadose zone The transfer of heat to the subsurface improves or speeds up contaminant transport and rem oval mechanisms such as gas advection chemical partitioning to the vapor phase gas phase contaminant diffusion sorption of contaminant on soil surfaces and chemical or biological transformation Methods include steam or hot air injection radiofrequency heating electrical resistance heating and therma conduction Status In use at many sites in the United States and Europe since the 19805 Currently in use at many sites in the United States First applied to environmental remediation in 198839 the number of horizontal wells used for environmental remediation has increased dramatically in recent years Adapted from the petroleum industry in 199039 a number of pilot and fullscale applications of fracturing enhancement SVE conducted in recent years Several fullscale applications of steam and hot air injection and electrical resistance technologies conducted in recent years commercial systems available Several pilotscale applications of radiofrequency heating and electrical heating have also been conducted but commercial systems are relatively limited 9391 TABLE 1 1 SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION Page 2 of 3 Technology Air Sparging Dual Ph ase Extraction Directional Drilling Pneumatic and Hydraulic Fracturing Thermal Enhancement Applicable Situations Most effective at removing volatile contaminants from the saturated zone at sites with homogeneous high permeability soils and unconfined aquifers also used with some success in heterogeneous less permeable soil and in soil with lowpermeable layers Most applicable at sites with multiple phase soil and groundwater or soil groundwater and free product contamination and low to moderate hydraulic conductivity soils High vacuum enhances soil vapor and groundwater recovery rates in lowpermeable soil formations Suitable in many geologic materials ranging from unconsolidated sands and silt Often used where access for vertical wells is limited the contaminant zone is long and thin or the geologic materials are very anisotropic Generally used at sites with lowpermeable soil and sediment such as clay silt or sedimentary bedrock where fracturing may increase permeability and improve uid flow during the remediation process Often used in situations involving sorbed organic compounds with low vapor pressure difficult matrices or nonaqueous phase liquids Also used to enhance biological activity in soil Limiting Factors Distribution of air channels may be affected by lithological and operational control of air ow Diffusion of contaminants into channels is slow however cycling or pulsing may reduce diffusion limitations Performance may be difficult to measure or interpret Hydraulic and pneumatic properties of soil determine which type of dualphase extraction system would be most effective Groundwater extraction rates required for effective operation in permeable soils may be prohibitive and extraction depths may be limited Installation in clay and bedrock can be difficult because of smearing along the borehole wall and slow drilling rates Highly fluctuating water tables can cause problems in horizontal well SVE systems Geology and site conditions control the size shape orientation and effectiveness of the fractures Site geology typically controls which thermal enhancement method is appropriate L39I TABLE 1 1 SUMMARY OF ENHANCEMENTS FOR SOIL VAPOR EXTRACTION Page 3 of 3 Air Sparging Dual Ph ase Extraction Directional Drilling Pneumatic and Hydraulic Fracturing Thermal Enhancement Soil heterogeneity greatly affects the distribution of air of air Operating costs may be high in permeable soil formations because of high water extraction rates and resulting treatment requirements The initial installation of horizontal wells may be more expensive than the installation of vertical wells but other efficiency improvements may compensate for some of this difference in cost Careful site characterization studies are necessary to correctly place and design well screens Most effective in low permeable over consolidated soil sediment or sedimentary bedrock such as shale and siltstone Steam injection is limited to medium to highpermeable soil Electrical resistance heating is effective in low permeable soil in the vadose zone Thermal conduction can be used in medium to lowpermeable soil but is sometimes slow and inefficient Radio frequency or electrical resistance heating can be used at sites where the use of injection wells is restricted Air sparging is becoming more important in providing oxygen to biorem ediation projects Dualphase extraction is an aggressive technology that is uniquely suited to sites with multiplephase contamination Soil and groundwater contamination as well as freephase liquids and capillary fringesmear zone contamination can be addressed The cost of horizonal wells continues to decline Horizontal wells will be used more routinely in the near future Pneumatic and hydraulic fracturing are becoming increasingly more important in improving soi permeabilities for the delivery or extraction of uids from lowpermeable environments Fracturing likely will be applied more routinely to many in situ remediation technologies in the future Steam and hot air injection are being used at fullscale to decrease the time required for remediation Radiofrequenc and electrical resistance heating require process automation to reduce costs and operator requirements Nonaqueousphase liquid Soil vapor extraction Technology Sitespeci c Considerations channels and the sparging Technological A r aerobic 1n srtu Notes NAPL VOC Volatile organic compound CHAPTER 20 BACKGROUND SOIL VAPOR EXTRACTION ENHANCEMENT TECHNOLOGIES SVE is an in situ remediation technique used to remove VOCs from vadose zone soil Air ow 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 C 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 ve enhancement technologies covered in this report are as follows Air sparging Air sparging can be used with SVE to treat VOC contamination such as gasoline solvents and other volatile contaminants present in the saturated zone Air sparging involves injecting air into the saturated zone below the contaminated area The air rises through channels in the saturated zone and carries volatilized contaminants up into unsaturated soils where the contaminants are subsequently removed using SVE Air sparging also increases the dissolved oxygen levels in the groundwater thereby enhancing subsurface biodegradation of contaminants that are aerobically degradable 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 in uence of a DPE well is lowered exposing the capillary fringe and previously saturated soils to the extraction vacuum and enabling more effective remediation of these soils than traditional SVE systems Directional drilling Directional drilling technologies allow SVE to be conducted in areas not easily accessed by vertical drilling techniques Directional drilling along the geometry of the contaminated zone may increase the zone of in uence of a single extraction or injection well Directional drilling also enhances SVE by reducing air shortcircuiting within the borehole in vertical well systems Pneumatic and hydraulic fracturing Pneumatic and hydraulic enhancement technologies increase SVE efficiency in lowpermeability soils by creating cracks or sand lled fractures Pneumatic fracturing involves injecting air into low permeability soils to create fractures thus increasing the permeability of the soil Hydraulic fracturing creates sand lled fractures which also enhance the permeability of the subsurface formation These enhancements can allow the application of SVE in lowpermeability silty clay formations where in situ cleanup may be impossible without enhancing soil permeability Thermal enhancement Thermal enhancements for SVE may involve a number a different technologies aimed at transferring heat to the subsurface to 1 increase the vapor pressure of VOCs or sernivolatile 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 radiofrequency 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 uid 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 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 10396 centimeters per second cms 5 Apply thermal enhancement if the vapor pressures of the contaminant of concem are low less than 05 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 biorernediation and contaminant stripping in groundwater if desired Speci c recommendations for application of each enhancement are discussed in Chapters 3 through 7 CHAPTER 30 AIR SPARGIN G 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 signi cantly reduce the remediation time frames for contaminated sites as compared with conventional SVE systems Air sparging was first used in Germany in the mid1980s 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 gures and tables follow references at the end of the chapter 31 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 highpermeability 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 offgas treatment system Air sparging can rernediate contaminants in the vadose zone that would not be remediated by vapor extraction alone that is chemicals with lower volatilities andor chemicals that are tightly sorbed EPA 1995 Air sparging also oxygenates the groundwater and soils thereby enhancing the potential for biodegradation at sites with contaminants that degrade aerobically At one fuel spill site approximately 70 percent of the contaminants was remediated through biodegradation and 30 percent through volatilization Billings and others 1994 In general the primary removal mechanism for highly volatile contaminants is volatilization and the primary removal mechanism for low volatility contaminants is biodegradation Brown and others 1994 Vapor extraction appears to be the more dominant removal mechanism during the early phases of treatment while biostimulation processes dominate during later phases An air sparging system includes the following components Air sparging wells or probes to inject air into the saturated zone A manifold valves and instrumentation to transport and control the air ow An air compressor or blower to push air into the saturated zone through the air sparging wells or probes A properly designed SVE system to capture the contaminated vapors in the vadose zone A crosssection of a typical air sparging system design including vertical sparge and SVE wells and surface treatment units is shown in Figure 31 A similar system using horizontal sparge and SVE wells is shown in Figure 32 Air sparging system characteristics are summarized in Table 31 and discussed in subsequent sections 32 APPLICABILITY Air sparging is most effective at sites with homogeneous highpermeability 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 strati ed soils Table 32 summarizes the factors affecting the applicability of air sparging Modi cations to injection of air in a sparging system include the following Supplemental injection of nutrients to enhance biodegradation Substitution of nitrogen for air to reduce the formation of ferric oxide in the pore spaces of aquifers with high iron concentrations Supplemental injection of air with other gases such as ozone or oxygen or substitution of oxygen for air to increase the availability of oxygen for biodegradation Supplemental injection of methane as a cometabolizer for chlorinated solvents Supplemental injection of toluene as a cometabolizer for trichloroethene TCE Air sparging can be used in conjunction with other innovative enhancement technologies such as hot air injection fracturing and RFH 33 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 ow in the subsurface especially within the saturated zone is not well understood Information from research and remediation of contaminated sites is continually re ning the concepts of air ow in the subsurface and therefore the ways in which air sparging systems are designed and operated This section addresses important air ow concepts as well as design and operational components of an air sparging system Section 331 discusses subsurface air ow and operational methods that can reduce the limitations posed by low air ow Section 332 describes the engineering components of an air sparging system including the types design and operation of the equipment Section 333 describes methods typically used to monitor the performance of an air sparging and soil vapor extraction ASSVE system 331 Air Flow Within the Subsurface The ow 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 ow whether it is operational or lithological can in uence the effectiveness of the system Brown and others 1994 Air injected into aquifer materials has been shown to typically migrate in channels and little air ow 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 ow resulting in substantial contact between the air and aquifer materials Research indicates that an average grain size of 20 millimeters or larger is necessary for bubble ow to occur this is found at a small percentage of sites If bubbles do not form at a site air will ow 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 ow 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 coarsegrained soils Sparging in negrained or highly strati ed 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 ow in the subsurface will follow the path of least resistance the majority of air channels form in the most permeable zones Marley 1995 Thus transfer of volatile contaminants into air channels and oxygen into the aquifer can only be accomplished in the bulk of the formation by diffusion processes When diffusion works alone the process is slow The contaminants must migrate several inches to several feet that is the typical distance between air channels by diffusion to reach an air channel WDNR 1995 The air channel diameter is typically quite small approximately the size of the pore space between the soil particles therefore the surface area of the air and water interface of each air channel is extremely small resulting in limited mass exchange rates In 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 ow 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 ow rates Johnson 1994 Varying the pressure within the air channels however could result in changed channel diameters thus inducing some water ow and improving the effectiveness of air sparging Hinchee 1994 Cycling has the potential to cause buildup of nes potentially clogging the well WDNR 1995 This effect can be reduced by installing a check valve on each well to reduce back ow Biofouling of the well screen or sparging probe is also a concem under the increased oxygen concentrations associated with this technology Johnson 1994 By manipulating air ow to the sparging wells at a site cycling can reduce air emissions from the SVE system thereby potentially reducing the costs of offgas treatment WDNR 1995 Reducing air ow 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 offgas treatment typically increases operational costs by a factor of 15 to 2 EPA 1995 Reducing air ow to optimize biodegradation and minimize offgas treatment however could result in longer remediation times thereby potentially increasing costs Cycling the air ow at a site can also reduce capital and energy costs The site geology can greatly affect the ow of air in a formation A low permeability layer above the saturated zone can limit vertical air ow to the SVE system placed in the unsaturated zone resulting in substantial lateral migration of contaminated vapors from the sparge well The potential for uncontrolled migration of sparge vapors increases with increasing sparge depth because of the potential for channeling along subsurface features One technique used to increase the vertical permeability of a strati ed formation is through the use of sand chimneys EPA 1995 Tetra Tech 1996a Sand chimneys are sandpacked borings installed through low permeability layers They provide passive air ow between the subsurface layers increasing both SVE and biodegradation rates 332 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 airwater separator and air emissions treatment equipment Figure 31 Pilot tests are often conducted at a site to determine air sparging system design parameters such as air entry pressures vacuum requirements air ow rates and effective zones of in uence 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 fullscale 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 3321 Air Sparging Wells and Probes Air is injected through vertical wells nested wells horizontal wells combined horizontalvertical wells or direct push sparging probes The type of well chosen depends on the site conditions and cost effectiveness of each method The placement of sparging wells or probes at a site will depend primarily on the areal delineation of the remediation area and the soilspeci c zone of in uence The zone of in uence 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 offgas or soil vapor probes andor 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 in uence 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 ow 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 lowlevel radioactive source Baker et al 1996 Electrical resistivity tomography can also be used to assess the air ow 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 in uence effective sparging depth and screen con guration 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 31 These wells are installed using conventional drilling techniques such as hollowstern auger methods The well diameter is typically 2 inches or greater to allow the use of conventional well development equipment Air is injected into the wells either through a manifold system or sparging probes installed in the wells Vertical wells have been installed in aquifers up to about 150 feet deep however a depth limitation for vertical wells was not reported Multipledepth completions which allow air injection at different depths can be used at sites with groundwater levels that uctuate signi cantly Placement of vertical wells is largely determined by the estimated or calculated injection zone of in uence at the site Zones of in uence of 5 to 30 feet measured radially have been observed in coarse soils and 60 feet or greater in strati ed soils Marley 1995 At sites with zones of in uence of 60 feet or greater preferential lateral air ow was probably occurring Sparging well spacings of greater than 30 feet may not be successful Tetra Tech 1996c The majority of sparge air ows 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 in uence 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 pumpandtreat technology Horizontal Wells Horizontal wells are installed using innovative horizontal trenching or drilling techniques Figure 32 Horizontal wells can be used to remediate contamination under buildings and into other hardtoreach 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 ow direction so that the groundwater ows through the wells High ow 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 38 less air will reach the far end of the screen Tetra Tech 1996c A more even distribution of air ow can be achieved by using design techniques to allow control of the air ow trajectory The use of horizontal sparging within an aquifer increases the surface area exposed to the injected air thus providing a greater zone of in uence than vertical wells Tetra Tech 1996c Heterogeneities in the soil matrix however can cause the air to ow out of the screen in discrete zones along the length of the screen reducing the effective zone of in uence of the well Both horizontal air sparging and extraction wells can be used to rernediate 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 l996d 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 50 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 2inch casing equipped with a falloff 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 back lled The sparging probe air tube is then connected to an aboveground air supply The depth to which direct push techniques can be used is limited by geological restrictions on penetrating the subsurface Greater depths can be attained in porous soils Use of sonic waves can encourage easier penetration Probes can typically be installed to about 40 feet below grade using direct push techniques and have reportedly been used up to 100 feet below grade Tetra Tech 1996c Probes installed directly into the subsurface can reportedly be as effective at remediating a site as probes installed in groundwater wells Tetra Tech 1996c Soil and water samples can be collected during either well or direct push probe installation Groundwater wells may be subsequently be used for water and vapor monitoring 3322 Manifolds Valves and Instrumentation The manifold is typically buried underground and constructed of 2inch 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 andor heat tape Several devices can be installed to optimize operation of the sparging system The following devices may be included in the system design A lter on the air intake of the compressor to prevent particulates from damaging the air compressor or entering the air stream A check valve between each well and the manifold to prevent temporary high pressure in the screened interval from forcing air and water back into the manifold system after the system is shut off A throttle valve at each well to allow the well to be isolated from the system or to adjust the air ow rate to the well A solenoid valve on each well to allow the well to be cycled several times per day requires installation of a control panel with a timing device A port at each well to temporarily attach a ow meter for measurement of air ow at each well 310 A port to allow temporary attachment of a pressure gauge and thermometer at each well or well cap or at the manifold near each well to monitor the air injection pressure and air temperature at each well A manual pressure relief valve immediately after the air compressor outlet to exhaust excess air from the manifold A permanent pressure gauge thermometer and ow meter between the manifold system and the manual pressure relief valve to measure total system ow temperature and pressure An automatic pressure relief valve to prevent excessive pressure from damaging the manifold or fracturing the aquifer in the event of a system blockage In addition installation of devices that would automatically shut down the air sparging system in the event of air extraction equipment failure is recommended WDNR 1995 Operation of the air sparging system in the absence of the extraction system could spread the contamination in the formation or cause the migration of vapors into buildings or utility conduits creating an explosion hazard A sensor placed on a gas probe near critical structures to monitor for negative soil gas pressure or on the SVE stack to monitor for positive pressure can continuously monitor the soil venting system Operation of the ASSVE system requires ongoing monitoring and system adjustment to maximize performance Computer systems can be used to completely or partially automate the monitoring andor system adjustments 3323 Air Compressor or Blower The air compressor or blower chosen for a site should be large enough to inject sufficient pressure and ow 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 oilfree reciprocating and rotary screw compressors rotary lobe blowers centrifugal blowers and regenerative blowers Compressors and blowers should not use lubricants or uids that could enter the air stream and reach the groundwater Air injection pressures are determined by the static water head above the sparge point the required air entry pressure of the saturated soils and the air injection ow rate Marley 1995 Higher pressures will produce higher air injection ow 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 airentry pressures of 1 to 2 psi in excess of the hydrostatic head at the top of the injection well screen are recommended Marley 1995 Finegrained soils generally require higher airentry 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 ow rates increase the volatilization component of remediation and lower rates increase the biodegradation component of remediation Air ow of at least 5 standard cubic feet per minute scfm per well should be injected Ifthe 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 ow 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 in uence of a sparging well however the zone of in uence of the well is not signi cantly affected by the increase in injection rate or channel density WDNR 1995 Marley 1995 312 333 Monitoring of System Performance System adjustments are made based on monitoring of changing subsurface conditions Monitoring includes measurement of parameters related to volatilization air ow and bioactivity such as carbon dioxide and oxygen The parameters typically used to monitor the performance of an air sparging system include the following Dissolved oxygen and contaminant concentrations in groundwater Oxygen carbon dioxide and contaminant concentrations in extracted air Microbial populations and activity including in situ respiration tests Air ow and extraction rates Air ow regions using neutron probe measurements or electrical resistivity tomography Sparging and vacuum pressure measurements Changes in the water table elevation caused by a water table rise in response to air injection Tracer gas mapping of air channel distribution and SVE system capture effectiveness Zone of in uence for both vacuum and sparging wells Continuity of blower and compressor operation There is growing evidence that pilot tests and fullscale 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 lter packs are typically more permeable than the native soils therefore air channels formed during the in situ air sparging process will preferentially intersect and ow through monitoring well lter packs As a result the water in monitoring well lter packs and the wells themselves usually receive much more air ow than the rest of the aquifer resulting in more aggressive treatment Determining monitoring system performance using chemistry changes in monitoring wells yields overly optimistic results These changes are generally not representative of the aquifer as a whole Practitioners o en 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 10fold increase and reached an equilibrium equivalent to a threefold 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 in uence 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 longterm 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 of cially close a site based on water soil gas or SVE offgas data Collection and analysis of soil samples at the site are sometimes required to confirm that the contaminants in the subsurface have been removed 34 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 dif cult to obtain Table 33 lists 29 sites remediated by air sparging It provides data on 314 soil types contaminant types reported contaminant concentrations in groundwater initial and nal and the time needed to achieve those nal 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 341 Performance The performance of the air sparging technology at three sites is described in the following subsections 3411 US Department of Energy Savannah River Integrated Demonstration Site Air sparging was used to remediate chlorinated VOCs at the US Department of Energy DOE Savannah River M Area Integrated Demonstration Site in Aiken South Carolina using the DOEpatented In Situ Biorernediation ISB system DOE 1996 The demonstration site is located within a much larger plume that is actively being treated using pumpandtreat 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 1031 micrograms per liter ugL and 3 to 124 ugL respectively TCE sediment concentrations ranged from 067 to 629 milligrams per kilogram mgkg and 044 to 105 mgkg 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 serniparallel to the injection well at a depth of 80 feet see Figure 32 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 315 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 16934 pounds of VOCs was removed or degraded The vacuum component removed 12096 pounds of VOCs and the bioremediation component degraded and mineralized an additional 4848 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 PCB concentrations in groundwater decreased by as much as 95 percent reaching concentrations below detectable limits that is less than 2 ugL in some wells and well below drinking water standards of 5 ugL Hazen and others 1994 Soil gas TCE and PCB declined by more than 99 percent Total sediment concentrations of TCE and PCB declined from 0100 mgkg to nondetectable concentrations at most areas Overall the site was considered about 80 to 90 percent clean following the 13month demonstration project Tetra Tech 1996c 3412 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 uctuates seasonally from 3 to 7 feet below grade Following completion of pilot tests a remedial design was developed for a 34acre 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 316 The system operated between May 1993 and early 1996 Approximately 20881 pounds of toluenerange 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 3413 Electro Voice Inc Demonstration Site Air sparging was used to perform a Superfund Innovative Technology Evaluation SITE demonstration at the ElectroVoice Inc ElectroVoice facility in Buchanan Michigan EPA 1995 using the Subsurface Volatilization and Ventilation System SVVS The ElectroVoice 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 5foot section of screen set to intersect a sludge layer found at 12 to 18 feet below grade in a clayrich horizon The air injection wells were installed with a 1foot screened interval positioned approximately 10 feet beneath the 46foot deep water table Sand chimneys were installed to facilitate vertical air circulation in the highly strati ed soils at the site The air ow rate was maintained at about 80 percent of the vacuum ow 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 2300 cubic yards yd3 of contaminated soil The data indicated that a portion of the site contained target VOC concentrations near or below the detection limits therefore only the portion of the site at which signi cant 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 yd3 of contaminated soil and encompassed four extraction wells and three sparging wells The previously installed system was operated over the entire treatment area 317 The demonstration operated from August 1992 through July 1993 The reduction in the sum of target VOC components in vadose zone soils averaged 806 percent over the 1year 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 and 1 1 of the target VOC components in vadose zone soil horizons are summarized in Table 34 The data for individual target VOC components are summarized in Table 35 VOC contamination in saturated zone soils was reduced by 993 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 342 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 freephase 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 318 3421 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 pumpandtreat system combined with soil vapor extraction PTSVE was used as the baseline technology against which ISB was compared To compare the two remediation systems a number of assumptions were made PTSVE would remove the same amount of VOCs as the vacuum component of ISB when operated for the same time period Four vertical SVE and four pumpandtreat wells would have the same zone of in uence as two horizontal wells used for ISB Volatilized contaminants from both technologies are sent to a catalytic oxidation system for destruction Capital equipment costs are amortized over the useful life of the equipment which is assumed to be 10 years not over the length of time required to rernediate a site Capital and operating costs for ISB and PTSVE are summarized in Table 36 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 signi cantly Fixed equipment costs for ISB include gas mixing and injection equipment for providing the nutrients required for stimulation of the biorernediation portion of the innovative technology The cost to biodegrade as little as 900 pounds of TCEPCE would offset the additional bioerlhancement costs that is methane and trace nutrient supplements and methane monitoring equipment compared to air sparging alone Hazer1 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 rernediate the demonstration site using the baseline PTSVE and only 3 years using ISB Actual treatment times are estimates and eld experience indicates that the PTSVE estimate is on the optimistic side since the objective is the Safe Drinking Water 319 Act maximum of 5 ugL for TCEPCE Consumable and labor costs are approximately 85 percent of the total cost per pound of the VOCs remediated for both technologies Figure 34 shows the relative importance of each category on overall costs for both ISB and PTSVE 3422 Cost for Subsurface Volatiliz ation Ventilation System The cost analysis for the SVVS is based on assumptions and costs provided by Brown amp Root Environmental the operator of the system at the site and on results and experiences from the SITE demonstration operated over a 1year period at the ElectroVoice facility The cost associated with treatment by the SVVS process as presented in this economic analysis is defined by 12 cost categories that re ect typical cleanup activities performed at Superfund sites These 12 cost categories are as follows Site preparation Permitting and regulatory requirements Capital equipment amortized over 10 years Startup Consumables and supplies Labor Utilities Effluent treatment and disposal costs Residuals and waste shipping handling and storage services Analytical services Maintenance and modi cations Demobilization Table 37 shows the itemized costs for each of the 12 cost categories on a yearbyyear basis for a hypothetical 3year fullscale remediation of the ElectroVoice facility The total cost to rernediate 21300 yd3 of soil was estimated to be 220737 or 1036yd3 This gure does not include any treatment of the offgases If effluent treatment costs are included it would increase costs to 385237 or 1809yd3 Figure 33 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 320 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 ElectroVoice site Cost gures provided here are orderofmagnitude estimates and are generally accurate to plus 50 percent to minus 30 percent 35 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 identi ed are included in Table 38 36 STRENGTHS AND LIMITATIONS The following list outlines some of the strengths of using air sparging with SVE at sites contaminated with VOCs Air sparging expands remediation capabilities of SVE to the saturated zone In air sparging both volatilization and biodegradation processes contribute to remediation of s By using air sparging biodegradation can be potentially further enhanced by supplementing air with other gases andor nutrients Air sparging eliminates the need to remove and treat large quantities of groundwater using expensive pumpandtreat methods Air sparging has been shown to be more cost effective than conventional PTSVE Air sparging effectively creates a crude air stripper in the subsurface with the soil acting as the packing In air sparging the sparged air elevates the dissolvedoxygen content in the subsurface thus enhancing natural biodegradation Cycling or pulsing the air ow during air sparging can increase mixing in the saturated zone thus increasing volatilization and biodegradation of contaminants 321 The following list outlines some of the limitations of using air sparging at sites contaminated with VOCs Air ow dynamics in the subsurface and therefore the mechanisms of air sparging remediation are not well understood Limited performance data are available Operational and lithological controls in uence the air ow in the subsurface thereby controlling the remediation potential of air sparging A low permeability layer above the saturated zone in strati ed soils can limit vertical air ow resulting in substantial lateral migration of contaminated vapors from the sparge well Excess subsurface pressure can aggravate the spread of contaminated vapors free phase product or dissolved contaminants and may create fractures in the sparging well annular seal or within the formation The usefulness of standard monitoring practices for assessing the performance of air sparging is not clearly understood As a rule of thumb performance of air sparging decreases in less permeable soils Preferential air channeling and poor air distribution are expected to increase signi cantly in less permeable soils and increase with soil heterogeneity Clogging of the aquifer sparging probes or well screens due to enhanced bacterial growth or precipitation of metals under increased oxygen levels can reduce the permeability at a site There is a potential for rebound of contaminant concentrations after air sparging is discontinued 37 RECOMNIENDATION S The effectiveness of air sparging for remediating contaminated sites is highly dependent on sitespeci c conditions Before selecting air sparging as an enhancement to SVE the sitespeci c 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 322 Air sparging is most effective at sites with homogeneous highpermeability 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 lesspermeable soils and soils containing lowpermeability 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 rernediating 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 ongoing 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 ow rate enhance mixing in the subsurface a properly timed pulsed operation could deliver enhanced performance 38 REFERENCES This section includes references cited in Chapter 30 A comprehensive bibliography is provided in Appendix B Baker Ralph S R Pernmireddy and D McKay 1996 Evaluation of AirEntry Pressure During In Situ Air Sparging A Potentially Rapid Method of Feasibility Assessment Proceeding of the First International Symposium on InSitu Air Sparging Las Vegas Nevada October 2425 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 BFl Site Available on World Wide Web July 28 323 Billings and Associates Inc 1996c Project Description for Bloom eld Site Available on World Wide Web July 29 Billings JF AI Cooley and GK Billings 1994 Microbial and Carbon Dioxide Aspects of Operating AirSparging Sites Air Sparging for Site Remediation ed Robert E Hinchee Lewis Publishers Ann Arbor Michigan Pages 112119 Brown RA RJ Hicks and PM 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 3855 Clark TR RE Chaudet and RL Johnson 1995 Assessing UST Corrective Action Technologies Lessons Learned about In Situ Air Sparging at the Dennison Avenue Site Cleveland Ohio US Environmental Protection Agency Project Summary EPA 600 SR95 040 March Risk Reduction Engineering Laboratory Cincinnati Ohio Envirogen Inc 1996 Project Summary Former Industrial Facility Remediation Massachusetts for Con dential Chemical Company October 1992 to June 1996 Hazen TC KH Lombard BB Looney MV Enzien J M Dougherty CB Fliermans J Wear and CA EddyDilek 1994 Summary of InSitu Bioremediation Demonstration Methane Biostimulation via Horizontal Wells at the Savannah River Site Integrated Demonstration Project InSitu Remediation Scienti c Basis for Current and Future Technologies ThirtyThird 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 113 Johnson RL 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 1422 Loden Mary E 1992 A Technology Assessment of Soil Vapor Extraction and Air Sparging Prepared for the US 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 InSitu Air Sparging Las Vegas Nevada October 2425 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 Cos grove of Tetra Tech and Rick Billings of Billings and Associates Inc August 22 Tetra Tech 1996b Personal Communication between Dawn Cos grove of Tetra Tech and Dr Gale Billings of Billings and Associates Inc July 18 324 Tetra Tech 1996c Personal Communication between Dawn Cos grove of Tetra Tech and Brian Looney of Westinghouse Savannah River Company August 23 Tetra Tech 1996d Personal Communication between Dawn Cos grove 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 US 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 Cos grove of Tetra Tech and Dave Becker of the US Army Corps of Engineers May 7 Terra Vac Corporation 1995a Project Description for Underground Storage TanksIrvine California July 23 Terra Vac Corporation 1995b Project Description for Fabricated Metal ProductsNew Paris Indiana May 5 Terra Vac Inc 1995c Project Summary Gasoline Service Station Fremont California May 5 US Army Corps of Engineers 1995 Soil Vapor Extraction and Bioventing Engineering and Design EM111014001 November 30 US Department of Energy 1996 Innovative Technology Summary In Situ Biorernediation Using Horizontal Wells US Department of Energy Savannah River M Area Process Sewer Integrated Demonstration Site Aiken South Carolina Available on the World Wide Web June 27 US Environmental Protection Agency 1995 Subsurface Volatilization Ventilation System SVVS Innovative Technology Evaluation Report Office of Research and Development Washington DC EPA540R 94529 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 11 325 FIGURE 3 1 TYPICAL AIR SPARGING ENHANCEMENT TO SOIL VAPOR EXTRACTION SYSTEM Atmosphe 39c Air Vent to Atmosphere Air FiIter Contaminant AirWater Free Air Separator Vacuum Blower Blower or Compressor 39 Extracted Weller to Treatment gt 7 Agt ltI A Extracted Air 3 V v x v 9x SoII Va or lt Sod Vapor ExtracllI39on 39 Sparqe Extraction Wen eH Well lgt Water Table V 39 I quot onIchnat39ed zon TYPICAL AIR SPARGING ENHANCEMENT TO SOIL VAPOR EXTRACTION SYSTEM 31 SOURCE MCOIF39IED FROM US ARMV CORPS OF ENGINEERS I995 FIGURE 32 HORIZONTAL AIR SPARGING AND SOIL VAPOR EXTRACTION WELL SYSTEM Atmospheric Air Vent to Atmosphere Air Filter ContaminantA AirWater Free Air Separator Vacuum Blower Blower or Compressor Water to Treatment Soil Vapor Extraction Well llll lllllllllllll llllllllllllllllllllllllWllllllllllllllllllllllllllllllllllllllllllll I Water Table gt V lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll SOURCE MODIFIED FROM US ARMY CORPS OF ENGINEERS 1995 HORIZONTAL AIR SPARGING AND SOIL VAPOR EXTRACTION WELL SYSTEM FIGURE 32 FIGURE 33 3YEAR REMEDIATION COST BREAKDOWN Without Effluent Treatment Site Preparation 283 Residuals 129 39 Utilities 62 Labor 86 Capital Equipment 82 Analytical 272 Demobilizotion 1 1 Consumables 8c Supplies 14 Startup 36 Permitting 25 With Effluent Treatment Effluent Treatment 427 Site Preparation 162 Consumables 8c Supplies 08 Demobilization 06 Startup 26 Permitting 23 Utilities 38 Capital Equipment 31 Analytical 156 Labor 49 Residuals 74 SOURCE MODIFIED FROM EPA 1995 3YEAR REMEDIATION COST BREAKDOWN FlGURE 33 328 FIGURE 34 REMEDIATION COST BREAKDOWN FOR IN SITU BIOREMEDIATION AND PUMPANDTREATSOIL VAPOR EXTRACTION In Situ Bioremediation 21Ib Remediated Eqmpment 18 Labor 45 Consumobms 37 PumpandTreatSoil Vapor Extraction 31Ib Remediated Eqmpnmnt 12 Consumobbs lllll 34 Labor 54 SOURCE MODIFIED FROM DOE 1996 REMEDIATION COST BREAKDOWN FOR IN SITU BOREMEDIATION AND PUMPAND TREATSOIL VAPOR EXTRACTION FIGURE 34 329 TABLE 3 1 AIR SPARGING SYSTEM CHARACTERISTICS Topic Description Geological Applicability Ideal site homogeneous highpermeability soils and unconfined aquifers Average site moderately heterogeneous soils with minimal lowpermeability layers Contaminant Applicability Volatile organic compounds that are aerobically biodegradable None or thin layer of freephase product System Components Vertical or horizontal extraction and injection wells or sparging probes Manifold valves and instrumentation Air compressor or blower Properly designed SVE system Monitoring Parameters Dissolved oxygen and contaminant concentrations in groundwater Oxygen carbon dioxide and contaminant concentrations in SVE offgas or soil vapor Microbial populations and activity Air ow and extraction rates Air pressure measurements Water levels Tracer gas mapping of air ow in subsurface Cleanup Capabilities Capable of achieving maximum contaminant levels for volatile constituents in groundwater Estimated cleanup time is l to 4 years Costs 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 sitespecific 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 sitespecific 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 TABLE 3 2 FACTORS AFFECTING APPLICABILITY OF AIR SPARGING Factor Parameter Desired Range or Conditions Contaminant Volatility High KH gtl X 10395 atm 3mole Solubility Low lt20000 mgL Biodegradability High BOD5 gt00l mgL Presence of free product None or thin layer Geology Soil type Coarsegrained soils Heterogeneity No impervious layers above sparge interval Permeability increases towards grade 1f layering present gtl X 10395 cm2 if horizontalve1tical is lt2l gtl X 10394 cm2 if horizontalve1tical is gt3l Permeability in the saturated zone Hydraulic conductivity gtl X 10393 cmsb Depth to groundwaterc gt5 feet Aquifer type Unconfmed Saturated thickness 5 to 30 feet Notes a b c d 12 cms BOD atm m m gL ources Modified from Brown and others 1994 Loden 1991 Wisconsin Department of Natural Resources 1995 From Loden 1992 From Brown and others 1994 From Wisconsin Department of Natural Resources 1995 One practitioner has used air sparging on sites with permeabilities as low as 1 X 103912 cm2 Tetra Tech EM Inc 19960 One practitioner claims to have cleaned site with hydraulic conductivities as low as 1 X 10396 cms EPA 1995 Although air sparging is most suited to shallow aquifers it has been effective in aquifers 150 feet below grade Loden 1992 centimeters centimeters per second biological oxygen demand Henry s Law coefficient atm ospherecubic meter milligrams per liter ZE39E TABLE 3 3 SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES Page 1 of 3 Cleanup ime2 Initial Groundwater Final Groundwater 539 Cmmoquot soquot Type Contamlnams months Concentration mgL Concentration mgL Is1eta Ardito amp Billings Alluvial sands si1ts c1ays Leaded gasoline 2 MWI 3 5 MWI 3 5 1990 BTEX 4 18 25 BTEX 025 8 6 Conservancy Billings 1990 i1ty sand Gasoline 5 Benzene 3 to 6 59 average benzene Interfacing c1ay layer reduction a er 5 months Buddy Beene Billings 1991 Clay Gasoline 2 i 85 reductionmonth Bernalillo Billings 1990 i Gasoline 17 i BTEX and MTBE lt55 Los Chavez Billings 1990 Clay Gasoline 9 i 40 benzene xylenes reduction 60 toluene reduction 30 ethylbenzene reduction Arenal Billings 1990 i Gasoline 10 Benzene gt30 Benzene lt5 BF1 Billings and NR Fuel 12 Benzene 22000 to 32000 Benzene 29 to 50 Associates Inc 1996b Bloom eld Billings and NR Fuel 48 NR BTEX below cleanup Associates Inc standards 1996c Firehouse Billings and NR Fuel 30 Benzene 400 to 600 Benzene 05 to 4 Associates Inc 1996a Dry Cleaning Facility Brown 1991 Coarse sand PCE TCE DCE 4 Total VOCs 41 Total VOCs 0897 Natural c1ay barrier TPH Savannah River US Department of Sands thin c1ay lenses TCE PCE 13 TCE 10 to 1031 TCE lt5 Energy 1996 PCE 3 to 124 PCE lt5 EE39E TABLE 3 3 SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES Page 2 of 3 Cleanup ime2 Initial Groundwater Final Groundwater 539 Cmmoquot soquot Type Contamlnams months Concentration mgL Concentration mgL Former Industrial Envirogen Inc 1996 Sands Toluene 23 NR NR Facility ElectroVoice EPA 1995 NR VOC 12 NM 3 NM 3 Berlin Harress 1989 Sand silty lenses c12DCE TCE 24 c12DCE gt2 c12DCE gt0440 Aquitard clay PCE Bielefeld Nordrhein Harress 1989 Fill sand silt PCE TCE TCA 11 PCB 2739 TCE 4339 TCA 07 Total VOCs 1207 Westfalen Aquitardsiltstone Munich Bavaria Harress 1989 Fill gravel sand PCE TCE TCA 4 PCB 2239 TCE 0439 TCA PCE 053939 TCE 001239 Aquitard clayey silt TCA 0002 Nordrhein Harress 1989 Clayey silt sand Halogenated 4 Location A THH 15 to 45 Location A THH 0010 Westfalen Aquitardsiltstone hydrocarbons 6 Location B THH 10 to 12 Location B THH 0200 Bergisches Land Harress 1989 Fractured limestone Halogenated 15 THH 80 THH 04 hydrocarbons Baden Harress 1989 Fill silt gravel TCE 2 120 023 Wurtternburg Aquitard clay Mannhelm Herrling 1991 Sand PCE chlorinated i i i Kaesfertal hydrocarbons Gasoline service Kresge 1991 Sand and silt Gasoline 24 Total BTEX 6 to 24 Total BTEX 0380 to 76 station Savannah River Looney 1991 Sand silt and clay TCE PCE 3 TCE 05 to 181 TCE 0010 to 1031 PCE 0085 to 0184 PCE 0003 to 0124 Gasoline service Marley 1990 Finecoarse sand gravel Gasoline 3 Total BTEX 21 Total BTEX lt1 station Solvent spill Middleton 1990 TCE PCE 3 Total VOCs 33 Total VOCs 027 Quaternary sand and gravel VE39E TABLE 3 3 SUMMARY OF PUBLISHED INFORMATION ON AIR SPARGING SITES Page 3 of 3 Cleanup ime2 Initial Groundwater Final Groundwater 539 Cmmoquot soquot Type Contamlnams months Concentration mgL Concentration mgL Solvent leak at Middleton 1990 Fill sandy and clayey silts TCE 2 020012 lt00100023 degreasing facility Chemical Middleton 1990 Sandy gravel Halogenated 9 THH 19 to 5417 THH 0185 to 0320 f Aquitard clay hydrocarbons Truck distribution MWR 1990 Sands Gasoline amp diesel Ongoing Total BTEX 30 i facility fuel Irvine Terra Vac Inc Clays sandy si1ts clayey Gasoline 9 NR below cleanup standards 1995a sands and si1ts gravel New Paris Terra Vac Inc Sand with some gravel PCE TCE 18 PCB 250 PCE 9 1995b clay layers Notes a Cleanup times represent the time interval between initial and nal groundwater concentration reported in the table Actual remediation time may be longer b Demonstration assessed remediation capabilities for vadose zone soils only DCE Dichloroethene EPA US Environmental Protection Agency Methyl tertbutyl ether MW Monitoring well NM Not measured NR Not reported Benzene toluene ethylbenzene and xylenes PCE TCA TCE THH TPH VOC Tetrachloroethene Trichloroethane Trichloroethene Total halogenated hydrocarbons Total petroleum hydrocarbons Volatile organic compounds PERFORMANCE OF SUBSURFACE VOLATILIZATION VENTILATION SYSTEM TABLE 3 4 FOR REDUCTION IN TARGET CONSTITUENTS IN SOIL HORIZONS IN THE VADOSE ZONE AT THE ELECTRO VOICE INC DEMONSTRATION SITE Critical VOC Concentration mgkg Pretreatment Posttreatment Treatment Horizonquot Sampling Sampling Percent Reduction Upper horizon 32177 074 9977 Sludge layer 166103 30769 8148 Lower horizon A1 9642 098 9899 Lower horizon A2 3768 042 9899 Lower horizon B 1357 030 9779 ource Modi ed from L S Environmental Protection Agency 1995 Notes a Sum of benzene toluene ethylbenzene xylenes 11dichloroethene trichloroethene and tetrachloroethene b The hot zone was delineated into horizons based on lithology and contaminant levels VOC Volatile organic compound mgkg milligrams per kilogram TABLE 3 5 PERFORMANCE OF SUBSURFACE VOLATILIZATION VENTILATION SYSTEM FOR REDUCTION IN INDIVIDUAL TARGET CON STITUENTS IN THE VADOSE ZONE AT ELECTRO VOICE INC DEMONSTRATION SITE Sum of the Weighted Mean Concentration mgkg Pretreatment Posttreatment Target Constituents Sampling Sampling Percent Reduction Benzene 001 000 NC Toluene 9284 1442 8447 Ethylbenzene 3741 606 8381 Xylenes 20550 4528 7797 11Dichloroethene 001 000 NC Trichloroethene 036 000 NC Tetrachloroethene 537 044 9181 Source Modified from US Environmental Protection Agency 1 95 Notes mgkg Milligrams per kilogram NC Not calculated a meaningful percent reduction cannot be provided because of low pretreatment concentrations TABLE 3 6 SUMMARY OF COST DATA FOR IN SI TU BIOREMEDIATION AS WELL AS PUMP AND TREAT WITH SOIL VAPOR EXTRACTION Costs Site Cost 7 32000 and Mobile Well Installation 183000 50690 Other Fixed 73 2 Mobilization Cost 13 Total and Mobilization Costs 45 2407 341468 Cost Pound of Contaminant 21 and Maintenance Consumable Cost Demobilization Costs Notes ISB In situ bioremediation includes vacuum extraction see Section 34 l PTSVE Pumpandtreat system combined with soil vapor extraction 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 amp Preparation 32500 7 7 Building Enclosure 1039 by 1539 10000 7 7 Utility Connections 5000 7 7 System Installation 15000 7 7 Total Costs 62500 7 i 2 Permitting amp Regulatory Requirements 10000 7 i 3 Capital Equipment amortized over 10 years Vacuum Pump 450 450 450 Blower 450 450 450 Plumbing 3333 3333 3334 Building Heater 333 333 334 Total Costs 4566 4566 4568 4 Startup 7957 7 i 5 Consumables Health and Safety Gear 1000 1000 1000 6 Labor 6300 6300 6300 7 Utilities Electricity Blower and Pump 3900 3900 3900 Electricity Heater 660 660 660 Total Costs 4560 4560 4560 8 Ef uent Treatment and Disposal Costs NA NA NA 9 Residuals and Waste Shipping and Handling Contaminated Drill Cuttings 12500 7 6000 Contaminated Personal Protective Equipment 6000 1000 3000 Total Costs 18500 1000 9000 1 Analytical Services 20000 20000 20000 1 Maintenance and Modi cations NA NA NA 12 Demobilization i 7 2500 TOTAL ANNUAL COSTS 135383 37426 47928 TOTAL REMEDIATION COSTS 220737 ource Modified from Department of Energy 1996 Notes NA Not available 7 Not applicable 338 TABLE 3 8 VENDORS OF AIR SPARGIN G TECHNOLOGIESSI Name of Vendor Address and Phone Number Point of Contact Billings and Associates Inc 3816 Academy Parkway N NE Albuquerque New Mexico 87109 505 3451116 Rick Billings Terra Vac Inc 1555 Williams Drive Suite 102 Marietta Georgia 300666282 770 4218008 Charles Pineo Envirogen Inc 480 Neponset Street Canton Massachusetts 02021 617 8215560 Alla Werner IT Corporation 2925 Briar Park Houston Texas 77042 713 7842800 John Mastroianni Quaternary Investigations Inc 300 West Olive Street Suite A Colton California 923 24 800 4230740 Tony Morgon Horizontal Technologies Inc 2309 Hancock Bridge Parkway 33990 PO Box 150820 Cape Coral Florida 339150820 Donald Justice Groundwater Control Inc 754 Harrison Avenue Jacksonville Florida 32220 800 8436133 Jeff Haluch KVA Analytical Systems 281 Main Street Box 574 Falmouth Massachusetts 02541 508 5400561 Steve Leffert H2 Oil PO Box 9028 Bend Oregon 977089028 541 3827070 Troy York Note a This list is not inclusive of all vendors capable of providing air sparging technologies This list re ects vendors contacted during the preparation of this report 339 CHAPTER 40 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 freephase product contamination DPE is often referred to as multiphase extraction MPE or total uids 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 fullscale systems outline strengths and limitations of DPE technology and provide recommendations for using DPE Cited gures and tables appear at the end of the chapter 41 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 sernisaturated 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 Droptube entrainment extraction Extraction of total uids 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 gasliquid separator and treated Wellscreen 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 41 stream at the well screen transported to the treatment system in a common pipe manifold separated in a gasliquid separator and treated Downholepump 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 sitespeci c remediation goals Relative costs for the different types are also largely determined by these factors 42 APPLICABILITY DPE is applicable to sites with the following characteristics VOC contamination Soil groundwater and freeproduct contaminant phases Low to moderate hydraulic conductivity soils The following subsections address contaminant properties and phases as well as soil characteristics for which DPE is most effective 421 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 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 signi cant role in remediation of petroleum hydrocarbons at sites employing DPE Roth and others 1995 422 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 porespace moisture and adsorbed to soil particles DPE also effectively removes dissolved and free phase both light and dense NAPL LNAPL and DNAPL contamination in groundwater Remediation capabilities of DPE in the vadose zone are similar to those of SVE Because it uses inwell 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 lled 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 ow induced by the extraction well 43 vacuum to desiccate previously saturated and partially saturated soils in the capillary fringe and smear zone As a result of exposure to soil vapor ow 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 affmity 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 freephase 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 freephase product that would not otherwise be extractable Baker and Bierschenk 1995 423 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 ow 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 43 ENGINEERING DESCRIPTION Implementation of DPE involves construction of extraction wells or modi cation of existing monitoring wells and installation of extraction and treatment equipment Figure 41 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 Speci c design factors related to the method of DPE employed ultimately determine the physical as well as operating characteristics of the system and in uence its ability to achieve sitespeci c remediation goals The following subsections discuss general DPE system design and describe characteristics of the three types of DPE systems 431 Dual Phase Extraction System Design DPE system design considerations include extraction well construction anticipated vapor and water ow rates vaporliquid 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 4311 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 ow characteristics and vadose zone of in uence DPE pilot testing is then conducted to determine both step and steadystate characteristics of the extraction system Parameters that may be monitored during testing include the following Induced vacuum versus distance Water drawdown versus distance Wellhead vacuum Vapor extraction rates Groundwater extraction rates Vapor hydrocarbon content Extracted groundwater quality Following the pilot test additional monitoring may be conducted to assess the rate at which system characteristics return to equilibrium Analysis of vapor extraction data obtained during pilot testing is similar to that for SVE pilot testing Parameters related to groundwater extraction such as extraction ow 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 fullscale 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 fullscale 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 4312 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 lter pack are generally sized using guidelines for groundwater extraction WDNR 1993 to prevent entrainment of nes into the extraction system Well diameter is based on sitespeci c design factors similar to those for SVE and on requirements of the type of DPE employed39 the diameter must be large enough to accommodate any downhole apparatus associated with extraction system requirements Existing monitoring wells with suf cient diameter and adequate design characteristics appropriatelysized screen slots can be converted for use as extraction wells Downhole pump systems generally require larger diameter wells than either wellscreen or droptube entrainment systems Fullscale DPE systems have been installed to approximately 100 feet below ground surface bgs Speci c 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 dissolvedphase contamination well spacing is largely based on the groundwater capture radius or the distance from a well where drawdown is sulfrcient 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 in uence Tetra Tech 1996b or the distance from the well where the slope of the free water surface approaches zero LNAPL will theoretically not ow 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 in uence The SVE design zone of in uence is generally more conservative than the actual zone of in uence 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 ow 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 4313 Extraction Equipment Design Typical components of the extraction system include an extraction blower vaporliquid 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 I r r 439 and J u 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 47 frequently determined by multiplying the vapor extraction rate for a single well as determined through pilot testing or so ware 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 ow 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 in uence 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 ow rate and achievable vacuum and desired ef ciency 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 wellscreen entrainment and drop tube entrainment Vaporliquid 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 uid if generated in sufficient quantities Use of extracted water for seal uid generally requires close monitoring 48 to prevent overheating and failure of the vacuum pump Placement of the airwater separator upstream of the vacuum pump prevents carryover of silts or sediments into the pump For sites with oating product an oilwater 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 andor 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 4314 System Monitoring Parameters monitored during fullscale 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 432 Dual Phase Extraction System Characteristics This subsection discusses design and operating features of each type of DPE and the unique bene ts and drawbacks of each type of system 4321 Drop Tu be Entrainment Extraction Droptube 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 49 extraction manifold piping system to an airwater 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 droptube entrainment extraction well is presented in Figure 42 During startup of an extraction system incorporating drop tubes it may be necessary to prime the extraction well with air to induce vapor ow 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 airlifting effect Selfpriming droptube designs have been developed to enable automatic priming of the system upon startup One patented droptube design incorporates single or multiple perforations which enable vapor ow to reduce uid 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 airbleed 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 designtube extraction depth As the extraction area is dewatered during operation of a droptube type system increases in saturated zone thickness and soil vapor ow are accompanied by a decrease in manifold vacuum at the vaporliquid separator As a result unbalanced conditions may occur in which vacuum at some extraction wells drops below that required to entrain water Water colunm buildup in these wells may cut off vapor ow and result in short circuiting Rebalancing of system vacuums may be necessary to restore vapor ow to all extraction wells Liquid and vapor removal in droptube 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 droptube 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 ow rates and the inner diameter of the drop tube Stenning and Martin 1968 Droptube type systems are generally inefficient for high ow 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 410 range of approximately 5 to 20 gpm use of entrainment extraction may be appropriate based on sitespeci c factors and design goals At higher water extraction rates vacuum pump energy requirements increase and downholepump 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 vaporliquid ratio and turbulence in the suction tube and extraction piping manifold This quotstrippingquot action results in reduced extracted groundwater contaminant concentrations and enables more efficient vaporphase treatment of the contaminants Groundwater treatment requirements may be reduced or potentially eliminated Reported stripping efficiencies of approximately 90 percent are 00111111011 Use of a droptube 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 droptube type wells Removal of free product using a droptube entrainment extraction system may be complicated by poor water quality or high hardness content Emulsi cation of free product and water can occur in the airwater 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 droptube 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 4322 Well Screen Entrainment In wellscreen entrainment DPE systems vacuum is applied to a well screened in the vadose and saturated zones Vapor ow 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 4inch well screens can be used Tetra Tech 1996c 411 For systems in which well depth exceeds applied vacuum expressed in feet of water priming may be necessary to induce vapor ow on startup Priming is achieved by inserting a tube into the extraction well below the water surface to introduce air ow into the well Reduced uid column density resulting from introduction of air enables twophase ow 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 ow 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 twophase ow System hydraulics may facilitate the use of ambient air for priming or may dictate the use of an air compressor to initiate air ow 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 Wellscreen entrainment systems bene t from the stripping action of highextraction vacuum and turbulence in the extraction well and manifold piping Similar to droptube 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 Extractionwell 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 extractionwell 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 nes from collection points primarily the airwater separator Patents apply to various aspects of well screen entrainment extraction Patent holders include Xerox Corporation and Dames amp Moore Incorporated 4323 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 Dualpipe manifolds are constructed for vapor and water removal A schematic of a downholepump 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 Variablespeed 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 variablespeed drive pumps and associated controls instrumentation are higher than for singlespeed pumps Use of downhole pumps is more efficient than entrainment extraction for removal of groundwater Brown and others 1994 Generally downholepump 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 downholepump system or one of the types of entrainment extraction is used Downholepump extraction may be more effective than entrainment extraction for systems requiring deep well installation Downholepump systems do not bene t from the stripping action associated with entrainment extraction systems Groundwater treatment requirements are therefore similar to those expected from conventional pump and treat systems 44 PERFORMANCE AND COST ANALYSIS The following subsections discuss the performance and cost of ve example DPE systems 441 Performance DPE has been implemented at a variety of sites contaminated with gasolinerange petroleum hydrocarbons and VOCs The following case studies describe the design and performance of ve fullscale DPE systems Three of the case studies involve droptube entrainment type systems one involves wellscreen entrainment and one involves downholepump extraction 4411 Underground Storage Tank Release from a Gasoline Station in Houston Texas Vacuum enhanced pumping VEP a form of droptube 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 selfpriming 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 concem consisted of a groundwater benzene toluene ethylbenzene and xylene BTEX plume and an associated freeproduct plume The aerial extent of the groundwater plume was approximately 50000 square feet BTEX concentrations in a majority of the plume exceeded 30 milligrams per liter mgL 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 After 7000 hours approximately 290 days of operation two small BTEX plumes with concentrations below 2 and 5 mgL remained Free product had been completely removed Cumulative contaminant mass removed from the site was approximately 36000 pounds approximately 5400 gallons Approximately 162 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 mgL TPH 1 mgL total BTEX and 05 mgL benzene 4412 Underground Storage Tank Release from a Former Car Rental Lot in Los Angeles California A droptube 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 ow of 1000 scfm at an inlet vacuum of 15 inches of mercury Water from the separator was treated using liquidphase GAC Photographs 41 42 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 Gasolinerange 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 1400 mgkg with an average concentration of 100 mgkg Monitoring wells at the site contained up to 3 feet of oating product Extraction wells were typically screened from approximately 20 to 35 feet bgs although some screens extended up to 10 feet bgs and others extended down to 50 feet bgs Well spacing was approximately 40 feet with closer spacings used in areas with higher contaminant concentrations An average of 20 scfm was obtained from each well at a wellhead vacuum of 10 inches of mercury After 10 weeks of operation measured groundwater levels were an average of 5 feet lower than before operations began During the 28 weeks of system operation more than 17000 pounds of contaminant was removed 2600 gallons of gasoline equivalent and 89000 gallons of groundwater had been extracted and treated Seventy ve percent of soil samples collected contained nondetectable levels of benzene and detections in the remaining samples were approximately 017 mgkg Con rmatory groundwater samples collected from three wells contained nondetectable levels of BTEX and total volatile hydrocarbons Site closure was obtained in 1991 4413 Release From An Electronics Manufacturing Facility In Texas A droptube 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 aircooled rotary lobe blower a liquidvapor 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 11 followed by a 10 to 12 foot layer of sandy silty stiff laminated clay Unit 111 Beneath the upper three layers is a fossiliferous silty shale Groundwater in the vicinity of the site occurs within the silty layer Unit 11 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 61 x 10395 cmsec At the start of system operation the affected groundwater plume ranged in depth from 15 to 22 feet and extended over an approximate area of 205000 square feet The plume contained a maximum concentration of 225 mgL of chlorinated solvents Contaminants of concern included phenol 583 mgL 12dichloroethane 118 mgL methylene chloride 88 mgL trichloroethylene 844 mgL and BTEX 0074 mgL benzene 0305 mgL toluene 0018 mgL ethylbenzene and 295 mgL xylene respectively Operation of the system is ongoing performance information is not available at this time Remediation goals include lt0001 mgL phenol 0003 mgL l2 dichloroethane lt0005 mgL methylene chloride toluene ethyl benzene and xylene and 0005 mgL trichloroethylene and benzene 4414 Underground Storage Tank Release from a Gasoline Station in Indiana Twophase vacuum extraction a form of wellscreen 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 vaporliquid 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 signi cant portion of site soils contained VOCs at concentrations exceeding 1000 mgkg and two areas contained concentrations exceeding 10000 mgkg Two groundwater BTEX plumes were associated with the soil contamination one with maximum BTEX concentrations exceeding l000 ugL and one with maximum BTEX concentrations exceeding 16000 ugL 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 ef ciencies 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 ugL benzene and 1000 ugL total BTEX for 4 17 on site wells and 150 and 500 ugL for benzene and total BTEX respectively for offsite wells Approximately 2500 pounds of contaminant 334 gallons as gasoline and 1051700 gallons of groundwater were removed and treated Water discharged from the system vaporliquid separator contained total BTEX concentrations ranging from 7 to 1300 ugL Discharge criteria to a publicly owned treatment works was 3000 ugL 4415 Release from a Gasoline Underground Storage Tank for a Vehicle Fueling Station at a Hospital in Madison Wisconsin A downholepump 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 6inch diameter vertical extraction well screened from 5 to 30 feet bgs with a 3foot 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 ow rate of 10 gallons per minute gpm and treated by an air stripper before discharge to an onsite storm sewer Site soils consisted of sandy ll from ground surface to 10 to 19 feet bgs The ll was underlain by a 3 to 4foot layer of organic silt and peat Depth to groundwater was approximately 13 to 20 feet The system began operation in June 1994 Approximately 8500000 gallons of groundwater and 120 pounds of contaminant were removed during the first 15 years of operation Groundwater benzene concentrations dropped from 276 ugL to 8 ugL after 6 months of operation and to 2 ugL after 15 years of operation The system was shut down in January 1996 Benzene concentrations at the extraction well were found to uctuate around the cleanup standard of 5 ugL and had risen to 8 ugL 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 442 Cost Analysis Costs for implementing a DPE system are highly variable and depend on sitespeci c 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 removedtreated for Case Study 1 45 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 selfpriming 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 identi ed patent holders who were contacted during preparation of this report 46 STRENGTHS AND LIMITATIONS The following list outlines the primary strengths of DPE for remediation of sites contaminated with VOCs Increases water extraction rates in low permeability settings Increases the vapor extraction zone of influence Addresses smear zone and saturated soil contamination Enhances removal of freephase and residual NAPL Potentially reduces ex situ groundwater treatment by inwell stripping in entrainment extraction wells Potentially eliminates the need for downhole pumps and associated controls and instrumentation through the use of entrainment extraction The following list outlines the primary limitations of DPE for remediation of sites contaminated with VOCs Less costeffective for permeable soil types Operating costs may be high depending upon blower 39 l and 39 treatment requirements Shortcircuiting of air ow from the surface may limit effectiveness 47 RECOMNIENDATION S DPE capitalizes on synergistic effects produced by simultaneous lowering of the groundwater table and increasing extraction well vacuum Use of DPE for remediation of contaminated sites is most advantageous for sites contaminated with volatile compounds and with moderate to low hydraulic conductivity soils The presence of existing monitoring wells in strategic locations may provide an opportunity for minimizing system capital costs through conversion of the wells for extraction DPE can be a cost effective method of rapidly remediating both soil and groundwater contaminated with VOCs This technology provides for the remediation of the vadose zone capillary fringe smear zone and existing water table by extracting both water and air through the same borehole Before a DPE system is implemented efforts should be undertaken to assess groundwater and soil characteristics and project objectives to determine which type of DPE is appropriate for the site Any patents that may apply to the technology should be thoroughly researched and if necessary the appropriate licensing and fees should be assessed and included in the project cost estimate 4 20 48 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 VacuumEnhanced Recovery of Water and NAPL Concept and Field Test Journal of Soil Contamination 415776 Brown Richard A RJ Falotico and DM 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 TN J J Mastroianni CE Blanchard J G Morse 1993 Analysis Methods and Design of Vacuum Enhanced Pumping Systems to Optimize Accelerated Site Cleanup Kr39useman GP and NA de Ridder 1991 Analysis and Evaluation of Pumping Test Data ILRI Wageningen The Netherlands 1991 Second Edition Lindhult Eric C JM Tarsavage and KA Foukaris 1995 Remediation in Clay using TwoPhase 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 Cleanup Using Vacuum Enhanced Pumping Miller Anthony W and D R Gan 1995 Soil and Groundwater Remediation Using DualPhase 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 DualPhase Extraction and Bioventing Superfund 16 Conference and Exhibition Proceedings Stenning AH and CB Martin 1968 An Analytical and Experimental Study of AirLift Pump Performance Transactions of the ASME Journal of Engineering for Power April Pages 106110 421 Trowbridge Bretton E and DE Ott 1991 The Use of InSitu Dual Extraction for Remediation of Soil and Groundwater National Groundwater Association and National Water Well Association US Environmental Protection Agency EPA 1994 Vendor Information System for Innovative Treatment Technologies VISITT Version 40 Database Prepared by Of ce of Solid Waste and Emergency Response Technology Innovation Of ce Cincinnati Ohio Wisconsin Department of Natural Resources 1993 Guidance for Design Installation and Operation of Soil Venting Systems PUBLSW18593 July 422 FIGURE 41 SCHEMATIC OF A DUALPHASE EXTRACTION SYSTEM Discharge Extracted Vapor Vacuum and Groundwater Blower Va or Vapor p Liquid From Other Separator Vapor Dual Phase Treatment Extraction Wells MK 4 V M H A AA A gt gt ZltltV MM 4 M A lt ampltm 1zzxx mampw gt g 3 U C 3 O t 0 water Discharge Treatment 2 z YE Dual Phase Extraction Well Well Screen Entrainment Type SOURCE MODIFIED FROM MCCOY AND ASSOCIATES INC 1992 SCHEMATIC OF A DUALPHASE EXTRACTION SYSTEM FlGURE 41 FIGURE 42 DROPTUBE ENTRAINMENT EXTRACTION WELL Residual VOC SOURCE MODIFIED FROM KOERNER AND LONG 1994 Contamination Extracted Soil Vapor and Groundwater to 3 Extraction Pump and AirWater Separator 5 V39Srsoi39l39 yq pr g 39 Sou Vdp and 39 I Entrained Groundwater DROPTUBE ENTRAINMENT EXTRACTION WELL 42 4 24 FIGURE 43 DOWNHOLEPUMP EXTRACTION WELL Extracted Groundwater to Groundwater Treatment Extracted Soil Vapor to Vapor Treatment w A kWVKW ltgt lt 397 397 quot Residual VOC Z Contamination 39 SOII VOP0r SOURCE MODIFIED FROM KOERNER AND LONG 1994 DOWNHOLEPUMP EXTRACTION WELL FIGURE 43 425 FIGURE 44 EXTRACTION SYSTEM PERFORMANCE Average Cost per Pound LiQ CLd A Cost per Pound 1800 40000 1700 35000 1600 A A m 30000 01500 g 39D 25000 11gt 1400 5 E 8 1300 20000 01 0 0 1200 E 15000 3 11 00 E quot 3 E 10000 E II 1000 W o 5000 900 3800 Mass Removed O l I l I I r I l I I I 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5 500 6000 6500 7000 Hours of System Operation EXTRACTION SYSTEM PERFORMANCE FIGURE 44 TABLE 4 1 COST DATA FOR DUAL PHASE EXTRACTION TECHNOLOGIES Cost per pound Case Total Cost Capital of contaminant Cost per gallon of Study VendorConsultant Cost removed groundwater 1 IT Corporation 380000 7 10 023 2 Terra Vac 600000 7 40 700 3 Groundwater Services 7 7 7 7 Inc 4 Dames amp Moore 331600 60000 130 031 5 Eder Associates Inc 7 58000 7 7 Note 7 Information is not available 427 TABLE 4 2 VENDORS OF DUAL PHASE EXTRACTION TECHNOLOGIES Name of Vendor Address and Phone Number Point of Contact Dames amp Moore 2325 Maryland Road Willow Grove PA 19090 215 6577134 Joseph Tarsavage Eder Associates Inc 8025 Excelsior Drive Anthony Miller Madison WI 53717 608 8361500 First Environment Inc 90 Riverdale Road Rick Dorrler Riverdale NJ 07457 201 6169700 Fluor Daniels GTI Inc 100 River Ridge Drive Norwood MA 02062 800 6350053 David Peterson Groundwater Services Inc 2211 Norfolk Suite 1600 John Connor Houston TX 77098 713 5226300 International Technologies 2925 Briar Park John Mastroianni Corporation IT Houston TX 77042 713 7842800 Radian International 2455 Horsepen Road Suite 250 Christopher Herndon VA 20171 Koerner 703 7136493 Smith Environmental One Plymouth Meeting Dan Guest Technologies Corporation Plymouth Meeting PA 19462 610 8253800 Terra Vac Incorporated 1555 Williams Drive Suite 102 Marietta GA 300666282 404 4218008 Charles Pineo Wayne Perry Inc 8281 Commonwealth Avenue Buena Park CA 90621 714 8260352 Don Pinkerton Note This list is not inclusive of all vendors capable of providing dualphase extraction technologies This list re ects those vendors contacted during the preparation of this report CHAPTER 50 DIRECTIONAL DRILLING This chapter focuses on the application of directionallydrilled horizontal wells to enhance SVE bioventingbiosparging 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 gures and tables follow references at the end of the chapter 51 TECHNOLOGY OVERVIEW The first directionally drilled horizontal wells for environmental remediation were installed in 1988 as part of horizontal extraction and injection remediation systems at the DOE Savannah River Site SRS Integrated Site Technology Demonstration Seven wells were installed at the SRS to demonstrate innovative in situ remediation technologies Between 1988 and 1993 the DOE s Office of Science and Technology supported the development and deployment of directional drilling technology for environmental applications at the SRS The DOE also funded the development and demonstration of directional drilling technologies at the Sandia National Laboratory in Albuquerque New Mexico between 1991 and 1995 Kaback and others 1996 Today the use of horizontal wells for SVE and air sparging has moved into the private sector Horizontal directional drilling is considered an acceptable technology in appropriate geologic environments and for appropriate contaminants it can result in better performance and lower overall cost than vertical wells Horizontal wells can be used to access areas generally not accessible using vertical well drilling technologies such as under buildings and airport tarmacs Figure 51 illustrates a hypothetical horizontal well network installed beneath a building to access contaminated soil and groundwater Two recent largescale applications of this technology occurred at the John F Kennedy IF K Airport Tetra Tech 1996a where more than 50 horizontal wells totaling more than 20000 feet in length were installed to rernediate 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 US 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 uids 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 uids 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 52 illustrates a blind borehole completion 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 Figure 53 illustrates a continuous well completion An overview of a horizontal well installation is as follows Advance a pilot hole Enlarge the hole using a reaming drill bit by pushing or pulling the bit through the pilot hole In a continuous borehole the reaming drill bit tool is inserted into the borehole at the exit point and pulled back to the drill rig Install the well by pushing or pulling the well casings into the borehole In continuous boreholes well installation generally occurs during the reaming phase second bullet Figure 54 illustrates advancing a pilot hole and Figure 55 illustrates backreaming and well casing installation 52 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 bene ts to using horizontal wells These include Horizontal wells can have as much as a 50 percent larger zone of influence than vertical wells because they can provide a linear constant and uniform air delivery or vacuum to the formation Horizontal wells can increase the performance of remedial systems such as SVE bioventing and air sparging because horizontal wells conform closer to the distribution of the contaminant than vertical wells In air sparging systems horizontal wells can be oriented perpendicular to the groundwater ow direction In this manner groundwater can be exposed to a curtain of oxygen as the groundwater ows by the sparge well Horizontal wells can reduce the limitations of anisotropic hydraulic conductivities common in most strati ed 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 IF K approximately 36 horizontal air sparging and 18 SVE wells have been installed to rernediate 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 5414 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 521 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 dif cult because of the reduction of the speci c 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 dif culty for example in cobble and coarse gravels 522 Distances Achieved Horizontal boreholes as long as 2600 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 53 ENGINEERING DESCRIPTION Directional drilling methodologies were rst developed and used by the utility industry for the installation of buried utility conduits sewer pipes power lines etc Large rivercrossing 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 uids guidance system well construction materials and design considerations for directional drilling as well as the common problems encountered during directional drilling projects 531 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 51 through 54 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 uids 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 suf cient pulling force to retract the casing into the completed borehole Horizoan 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 pullback The drill rig must also provide torque to the drill strings Most drilling methods require that the drill string be rotated while it is advanced into the borehole to reduce drag friction on the drill string Drill rigs are available in a range of sizes They are classi ed 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 51 through 53 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 54 shows a maxi rig Mini drill rigs are mounted on a trailer a truck or a selfpropelled tracked vehicle The drilling uid system is limited water or a dilute bentonite based uid are commonly used A mini drill rig s maximum thrust force is less than 40000 pounds Their use is limited to small diameter 4inch range pipe installations at depths of less than 30 feet in semiconsolidated sediments Midi drill rigs are mounted on a trailer or a selfpropelled tracked vehicle These rigs have a maximum thrust force of less than 80000 pounds They are used to drill continuous or blind boreholes and install pipes up to 8 inches in diameter The drilling uid systems are larger and can accommodate all types of drilling uids Maxi drill rigs are mounted on trailers These rigs have a maximum thrust force of up to 800000 pounds Maxi rigs can accommodate any type of drilling uid have been used to drill up to 60inch 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 532 Drilling Assembly The drilling assembly used during horizontal drilling consists of a drilling tool a bent subassernbly and a guidance system The drilling tool is preferentially oriented in the borehole by the bent subassernbly 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 tricone type drilling tool hydraulically assisted jobstyle drilling tool and compaction tools These drilling tools are described below 5321 Tri Cone Type Drilling Tools A tricone type drilling tool uses a downhole mud motor tricone 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 56 shows typical drilling assembly for the different drilling phases Downhole mud motors or tricone type drill bits are powered by drilling uid that is pumped down the drill pipe The drilling uid either a bentonite or organic polymerbased drilling uid facilitates the turning of the drill bit The drilling uid is removed by development and using sodium hypochlorite Downhole mud motors and water are the most commonly used tools in the environmental drilling industry 5322 Hydraulically Assisted Jet Style Drilling Tools Hydraulically assisted jetstyle slant head uidassisted drill bit drilling tools are the most commonly used drill tools today Hydraulically assisted jetstyle drilling tools use hydraulic pressure to cut the geologic formation The hydraulic jet is directed from a bent housing or from a drilling uid port on a drill bit attached to a bent subassembly To drill the curved section the bent subassemny 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 5323 Compaction Tools Compaction tools work on the same principle as wood chisels Compaction tools are wedgeshaped 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 533 Drilling Fluids Drilling uids 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 uids to the formation 57 Drilling uids are either bentonite clay based or synthetic or natural polymer based Selection of the proper drilling uid is essential for a successful drilling project Recent advances in drilling uid formulations have resulted in mixed metal hydroxide bentonite uids and xantham polymer systems that have a high gel strength to carry drill cuttings and ltration control to seal the borehole Special well development uids are used to remove the drilling uids from the well for example mixed metal hydroxide drilling uids require well development using sodium acid polyphosphate to occulate the bentonite and clean the well Xantham polymerbased drilling uid breaks down and is easily removed using sodium hypochlorite during well development Xantham polymerbased drilling uid also breaks down over time This type of drilling uid 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 uids It can also lower well installation costs by reducing well development time 534 Guidance Systems The guidance system allows the driller to control the orientation pitch and depth of the drilling tool It is located in the downhole assembly behind the drilling tool and the bent subassembly There are three common types of guidance systems as follows Radio beaconreceiver systems Magnetometeraccelerometer systems Inertial gyroscopic systems Each system provides location and depth data The radio beacon method uses a surface tool to walk along the ground surface while following the drilling tool during drilling It is limited to depths of up to 25 feet The magnetometeraccelerometer system orients using a surface imposed magnetic eld 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 535 Directionally Drilled Well Installation Directionally drilled well materials screens casing and installation steps are described in the following subsections 5351 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 exibility 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 berglassepoxy resin are well suited to short radius boreholes because of their exibility 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 exibility necessary Mast and Koerner 1996 5352 Well Screens Traditional prepacked dual well screens single well screens enveloped in a geotextile lter 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 wirewrapped screens geotextile fabric wrapping and louvered stainless steel multilayered stainless steel and sintered HDPE and stainless steel have been used Wirewrapped screens are only available in PVC and steel Wirewrapped 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 speci cally 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 5353 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 5354 Well Installation The steps of installation of directionally drilled horizontal wells are as follows Installation of the pilot hole and exit trenches The pilot holes are generally drilled with an approach angle of less than 25 degrees Wilson 1995b Figure 54 illustrates the installation of the pilot hole Continuous Boreholes switch drill bits at the exit point and enlarge the borehole using a reaming tool A carrier casing is generally pulled into the borehole with the reaming drill bit Blind Boreholes washover pipe equipped with a reaming bit is advanced over the pilot hole drill string This step helps clean the borehole wall and enlarges the hole to allow casing installation The pilot hole drill string is removed and the washover casing remains to be used to install the well materials Figure 55 illustrates the backreaming and casing installation process The screen and riser are installed in the carrier casing or washover pipe The casing is removed and the well material is left in the formation The well is developed with water and special drilling mud removal solutions Install SVE and air sparging system components 536 Design Considerations The important design considerations for directional drilling are described below 510 5361 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 l996d The design process must consider space availability drill rig capabilities well materials and cost to arrive at the approach angle and radius of curvature 5362 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 air ow 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 blowerend 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 ow Designing the well screen to correct for nonuniform air ow 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 care ll screen design resulted in uniform air ow patterns These investigators estimated air ow rates for a well in the design phase using the model TETRAD Vinsome and Shook 1993 Lundegard and Andersen 1996 Using the derived ow 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 537 Common Problems Common problems in directional drilling projects result primarily from poor planning by the engineering contractor and a lack of experience and preparation by the drilling contractor Historical problems have occurred for various reasons as follows Wilson 1995b Not fully characterizing the horizontal well site geology and geochemistry Not fully researching the credentials of the drilling company Not planning and researching the drilling uid and screen materials and design carefully Not developing the well adequately Not evaluating carefully the potential for pressure drops due to slope geology or well loss Not using a contractor experienced in planning procuring and implementing a horizontal well installation program Not retaining a driller who understands the intricacies of drilling in the speci c geologic environment Not providing close oversight to the drilling contractor Drilling contractors providing undersized and undermaintained equipment for the job Drilling contractors drilling the pilot hole too quickly and not creating a smooth uniform curvature to the borehole Not maintaining a consistent pressure along the length of the horizontal well Two solutions to the problem of inconsistent pressure are to reduce the diameter of the well screen toward the exhaust end of the screen or to use a sintered HDPE screen that can be custom made to have varying pore size while maintaining the same open area along its length 54 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 IF K The IF K case study presents the most ambitious and upto date information regarding the use of horizontal wells for SVE and air sparging 512 541 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 con dential 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 eld was conducted as part of this analysis These individuals are listed in Section 582 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 biover1ting 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 strati ed sediments by being oriented in the direction of the higher horizontal hydraulic conductivity tensor 5411 US 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 22 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 230000 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 ASSVE strategy involved the installation of two parallel horizontal wells These wells were aligned with the orientation of the process sewer line The two horizontal wells were installed in 1989 using technology borrowed from the petroleum industry One 300footlong air sparging well was installed below the water table at a depth of 150 to 175 feet The 200footlong SVE well was installed to a depth of 75 feet A 20week 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 ow 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 16000 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 1600 and 1800 ugL to 200 and 300 ugL 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 5412 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 275footlong well with a 190footlong screen installed at depths ranging from 6 to 13 feet bgs in a silty sand to sandy silt soil Air ow 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 ow data for use in the model Air permeabilities were back calculated The model was then used to calculate the theoretical zone of influence of the vertical and horizontal wells The modeling results showed that the zone of in uence of the vertical and horizontal wells at a vacuum pressure of 25 Pascal were 47 and 123 meters respectively indicating that one 60meter horizontal well could provide the same areal coverage as 22 vertical wells A cost evaluation indicated that based on well installation costs alone a 60meterlong 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 5413 Hastings East Industrial Park Wade and others 1996 under direction of the US Army Corps of Engineers conducted a 1year 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 US 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 16000 ugL in groundwater A fullscale remedial system incorporating air sparging using both horizontal and vertical wells was designed installed and extensively tested over a period of 1 year Figure 57 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 10392 cms and at l X 10397 cms respectively This system was designed as an integrated approach using the horizontal well as both a method of containment and a device for contaminant mass removal by installing it perpendicular to the groundwater gradient across the width of the contaminant plume With this orientation a vertical curtain of sparged air aligned perpendicular to the groundwater ow direction was created so the air can strip the TCE from the groundwater as it ows by the horizontal well The horizontal well was placed approximately 370 feet downgradient from the source of the plume The borehole for the well was drilled with a 600footradius of curvature considered to be a large radius No information regarding drill rig type or other speci cs of the drilling phase was available The horizontal well has a 6inch diameter and a 200footlong 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 bentonitebased drilling mud The well was then videotaped to con rm 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 4inch diameter and a 5footlong continuously wound stainless steel S creen 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 ve 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 ow 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 ow 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 ow rates of 160 to 320 scfm and the vertical well operated at ow 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 516 zone of in uence 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 ow 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 58 and 59 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 lSfootthick aquifer showed much less TCE reduction39 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 signi cant 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 ef ciencies 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 5414 John F Kennedy Airport The Port Authority of New York and New Jersey has installed the most ambitious ASSVE 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 510 and 511 illustrate the layout of the system The system uses approximately 13000 feet of horizontal SVE wells and 7000 feet of horizontal air sparging wells The design of the 517 horizontal SVE and horizontal air sparging wells was based on a pilot study and was followed by a fullscale 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 andor 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 concem 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 148000 mgkg and nondetected to 584000 mgkg respectively The concentration of BTEX and SVOCs in groundwater ranged from nondetected to 6000 ugL and nondetected to 4000 ugL respectively Roth and Pressly 1996 The geology at JFK includes hydraulic ll consisting of ne to medium sand with trace silt to depths of 10 to 16 feet bgs The ll is underlain by a thin low permeability clayeypeat 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 eld 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 260foot long horizontal SVE well constructed with 3inch diameter HDPE The horizontal SVE well was installed about 35 feet bgs and has a varying slot size of 160 feet of 001 inch and 100 feet of 0020 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 ow rates and distribution of air ow rates Figures 512 and 513 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 ow and the resulting geometric distribution of pressure vacuum as measured by pressure and vacuum monitoring points around the wells Horizontal SVE air ow versus vacuum data were plotted and linearly regressed to solve for ow per foot of screen interval as a function of vacuum at the center of the screen Vacuum line loss versus ow were also plotted and linearly regressed to solve for the change in vacuum as a function of ow These evaluations were used to design the screen slot size and 518 distance between the horizontal SVE and horizontal air sparging wells in the fullscale pilot test and remediation system The objective for the fullscale test was to affect a l50foot 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 50foot zone of in uence with a 04 to 08 scfm per foot of well screen having a pressure of 389 psi at the well end A fullscale pilot test was conducted to verify the ndings of the pilot test and collect additional data for the design of the remediation system The horizontal SVE well used in the fullscale test was installed to a depth of 35 feet with a total length of 660 feet and a 530foot long well screen The screen used a 025inch slotted well screen with the distance between slots varying from 025 to 0875 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 in uence Figures 512 and 513 illustrate the soil vacuum and sparge pressure at the maximum blower rates Results of the fullscale pilot test showed that the maximum zone of in uence 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 ow rate from the horizontal SVE well ranged from 220 to 720 cfm The SVE air ow per foot of screen length ratio was 042 to 137 cubic feet per minute per foot cfmft The goal of 1 l3 cfmft along the entire length of screen was not realized The investigators determined the air ow rate per section of screen using the streamline and equipotential distribution of vacuum and pressure for each test The zone of in uence 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 in uence observed was 52 30 and 10 feet at the beginning middle and end of the screen respectively The air sparging ow rate ranged from 60 to 480 cfm and air ow per foot of screen length ratio was 013 to 101 cfmft The goal for zone of in uence of the air sparging well was 40 feet with an air ow per foot of screen length ration of 09 The ow rate in the screen portion of the well closest to the SVE blower was 3 times greater than the ow rate further from the blower This information was used to design the screen for the remediation system The goal of the nal design was to have even air ow along the length of the horizontal SVE and horizontal air sparging well To compensate for this air ow variation along the screen section the screens for the fullscale 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 signi cant 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 3month 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 2month reconnaissance and scheduling effort was undertaken just to locate the borehole paths Fifteen horizontal SVE wells were installed to screen depths of about 35 to 5 feet bgs Twenty seven horizontal air sparging wells were installed with screen depths at about 12 feet bgs More than 3700 feet of interconnecting subsurface manifolds and piping was installed to connect the well elds 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 rst 2 months of operation show that the systems have extracted about 18600 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 ow per foot of screen rates within the design speci cations However several wells are operating with air ow per foot of screen rates below design speci cation In addition many wells have pressure and air ow drops from the blower to the ends of the screen lengths It is anticipated that these rates will increase as the residual drilling uid in the wells biodegrade and pore water in the vadose zone evaporates 542 Cost Analysis Obtaining cost data from vendors was difficult In general they would not release speci c information on their cost structure Cost information based on interview responses obtained from the vendors and experts 520 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 ef cientfrom 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 55 VENDORS Table 51 presents a list of vendors that were identi ed 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 con dence that the drilling contractor will install the well to meet the project speci cations 56 STRENGTHS AND LIMITATIONS The following list outlines some of the strengths of using horizontal well technology for environmental remediation Boreholes can follow the geometric trend of the contaminant plume since the boreholes can be guided in the horizontal plane One horizontal well can rernediate a surface area many times that of a single vertical well because contaminant plumes are generally vertically thin and horizontally 521 extensive This is because horizontal hydraulic conductivities are generally several times those of vertical hydraulic conductivities Horizontal wells can access contaminated areas that cannot be reached by conventional remedial methods Horizontal wells cause minimal impact to activities at the ground surface such as vehicle traffic plant operations and ight lines Horizontal wells technology is nondestructive in that it does not damage existing land improvements Horizontal wells can be completed in most geologic environments by the use of alternative drilling mud uids 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 The vertical capture zone of a horizontal well is limited by the vertical hydraulic conductivity of the formation If the contamination is distributed across several geologic strata the effectiveness of horizontal wells may be reduced Areas with highly uctuating water tables can cause problems with SVE systems if the water table variability is not fully understood Drilling uids can disturb and alter the borehole surface and reduce the effective permeability of the geologic formation limiting the zone of influence of the well Installation of horizontal wells is several times more expensive than installation of vertical wells A careful cost analysis must be conducted to determine the feasibility of a horizontal well drilling program Installation of horizontal wells requires knowledge of all potential subsurface obstacles along its path Detailed mapping along the borehole path may be required 522 Others limitations and considerations include impacts of drilling uids on SVE well ef ciency dif culties in well development uniform air deliveryrecovery drilling uid breakout and potential drainage to surface features invasion 57 RECOMIVIENDATION S 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 linearellipsoid 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 ne 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 58 REFERENCES This section includes a list of references cited in Chapter 5 Subsection 581 and a table presenting professional contacts Subsection 582 A comprehensive bibliography is provided in Appendix B 581 Cited References Armstrong JE CA Mendoza BJ Moore and PE Hardisty 1995 A Comparison of Horizontal Versus Vertical Wells for Soil Vapour Extraction Presented at Solutions 95 International Association of Hydrogeolo gist Congress XXVI Edmonton Alberta June 4 10 Bardsley DS l995 Horizontal Well Materials World Wide Web Home Page httpwwwhorizontalwellcom Environmental Consultants LLC Downs CE 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 237243 May 1315 Kaback DD BB Looney CA Eddy and TC Hazen 1991 Innovative Ground Water and Soil Remediation In Situ Air Stripping Using Horizontal Wells Westinghouse Savannah River Company 523 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 DD 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 2970180 April Knaebel KS 1981 Simpli ed Sparger Design Chemical Engineering March 9 Pages 116117 Looney BB T Hazen D Kaback and C Eddy 1991 FullScale Field Test of the In Situ Air Stripping Process at the Savannah River Integrated Demonstration Test Site WSRCRD9122 Aiken South Carolina Westinghouse Savannah River Company July 29 Lundegard PD and G Anderson 1996 MultiPhase Numerical Simulation of Air Sparging Performance Groundwater Volume 343 Pages 451460 Lundegard PD 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 VA and CE Koerner 1996 Environmental Horizontal Directional Drilling Technology NoDig Engineering Volume 3 Number 2 Pages 1721 March and April May DW 1994 The Use of Horizontal Wells for Subsurface Soil and Aquifer Restoration Drilling Technology In JP Vozniak ed American Society of Mechanical Engineers New York New York PDVolume 56 Pages 227239 Mendoza CA 1992 VapourT Users Guide Department of Geology University of Alberta Edmonton Perry RH and CH Chilton ed 1975 Chemical Engineers Handbook Fifth Edition McGraw Hill New York Tetra Tech EM Inc Tetra Tech 1996a Personal Communication between Paul Frankel Hydro geolo gist 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 RJ and NC Pressly 1996 Remediation of JetFuelContaminated 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 US Department of Energy 1995 In Situ Biorernediation Using Horizontal Wells Innovative Technology Summary Report Prepared by Colorado Center for Environmental Management Denver CO US Environmental Protection Agency 1994 Alternative Methods for Fluid Delivery and Recovery EPA625R94003 Vinsome PDW and GM Shook 1993 MultiPurpose Simulation Journal of Petroleum Science and Engineering Volume 9 Pages 2938 Wade A GW Wallace SF Siegwald WA Lee and KC McKinney 1996 Performance Comparison Between a Horizontal and a Vertical Air Sparging Well A FullScale OneYear Pilot Study In Proceedings of the Tenth National Outdoor Action Conference and Exposition Las Vegas Nevada National Ground Water Association Pages 189206 May 1315 Wilson D D 1995a Introduction to 1995 NGWA Environmental Horizontal Well Seminar World Wide Web Home Page http wwwhorizontalwellcom October Wilson DD 1995b Environmental Horizontal Well Drilling and Installation Methods World Wide Web Home Page httpwwwhorizontalwellcom by Environmental Consultants LLC 582 Professional Contacts Name Af liation Armstrong James 403 2470200 KomeX International Ltd Birdwell Dale 405 2353371 Genesis Environmental COX Bob 510 2271105 X420 OHIVI Inc Downs Charlie PhD 303 9364002 Private Consultant Pollution Prevention Associates Fournier Louis B 610 5582121 STAR Environmental Kaback Dawn 303 2970180 X111 Colorado Center for Environmental Management Kirshner Marv Ph 212 4358255 FX 212 4358276 Alt Ph 201 9616600 X8255 Port Authority of New York and New Jersey Layne Roger 18006546481 Ditch Witch Inc The Charles Machine Works Inc Meyer Eric 504 9224450 Radian Corporation Baton Rouge Pressly Nick 516 2865890 Pressly amp Associates Inc Wilson David D 303 4221302 Horizontal Well and Environmental Consultants Inc INFORMATION CENTERS Organiz ation Contact Name Services National Ground Water Mark Shepherd Provide database search for issues related to Association X 594 groundwater 18005517379 Remedial Action Program Mary Bales Information Center 423 2413098 Collect documentation on issues related to decontamination decommissioning and remediation of sites 527 FIGURE 5 1 HORIZONTAL WELL NETWORK INSTALLED BENEATH A BUILDING TO REMEDIATE SOIL AND GROUNDWATER SOURCE MODIFIED FRDM WEMPLE AND OTHERS vast HORIZONTAL WELL NETWORK INSTALLED BENEATH A BUILDING TO REMEDIATE SOIL AND GROUNDWATER FIGURE 51 FIGURE 5 2 BLIND BOREHOLE COMPLETION Packer III III lllll ll Illll l IIIII Illll II quotIII III IIIII II III quotIII Illll III III SOURCE MODIFIED FROM DIRECTED TELHNULOEIES DRILUNG NC was BLIND BOREHOLE COMPLETION FIGURE 52 FIGURE 5 3 CONTINUOUS WELL COMPLETION Launch Exit PM H NIH IN I U IHI Hm IIIH Hm 1 i quot 39 quot 39 239 um I I N NIH Um HM Hm gt SOURCE MODIFIED FROM DIRECYED TECHNOLOGIES DR LLING INC 1996 CONTINUOUS WELL COMPLETION FIGURE 53 FIGURE 5 4 PILOT HOLE ADVANCEMENT Dilectiurmi Dririing Unit A gt M V Launch Pit Wm Driil D rili String Exii PR SOURCE MODiFIED FROM DiRECTED TECHNOLOGiES DRiLLiNG NC 1995 PILOT HOLE ADVANCEMENT FIGURE 54 FIGURE 5 5 BACK REAMING AND WELL CASING INSTALLATION WeII Screen and Casing Directional DrilIing Unit 4 gt Drllllng String 1 X Buckreoming Tool SOURCE MODIFIED FROM DIRECTED TECHNOLOGIES DRILLING INQ 996 BACKREAMING AND WELL CASING INSTALLATION FIGL RE 55 FIGURE 5 6 TYPICAL DOWNHOLE HARDWARE FOR DIFFERENT DRILLING PHASES Steerlnq Tool Hausa Flex Sub l I Drill BllJ ls39 to 2039 Nonmugnetic Drill Rods Drilling Assembly Reamer Drill Rod Drill Rod Entrance PorIdI Exit Portal FIeaming Assembly Fl 39bl Reamer swivel E k e PSIIlnq Assembly tug Fiberglass Drill Rod casing Reaming and Casing Pullback Assembly SOURCE MODIFIED FROM WEMPLE AND OTHERS 1994 TYPICAL DOWNHOLE HARDWARE FOR DIFFERENT DRILLING PHASES FIGURE 56 FIGURE 5 7 HASTINGS EAST INDUSTRIAL PARK SITE PLAN SHOWING HORIZONTAL AND VERTICAL WELL AIR SPARGINGSOIL VAPOR EXTRACTION SYSTEM G VemcaI Sparging WeII ASW I Son Gas Plume mm X 1 Centerhne uI Screened k A Portion of Honzontor X Sparginq We Aswvz 9 A AMW ISIE 0 5500 AMWV39HQH A A 14000 A raw ma g 7 460 7 MWAMB E o Mw 126 I I g 0 A chler irf TE39W WS MWVHSB Contaminamn Plume VESI OZPW AND v A Y 0 A M 3953 w Msa 9 E 1 ooowgL 550 Groundwater Plume Luann I Soil Vapor ExtracUon Wall gt Groundwate39 Flow Di39ett cn A M 39 39 H Gmndwme39 mm M meowL Conlour of TCE Concentr ion in IXI Soil Ga Mnnimring Wequot Groundwater Befm PIla may Begun IDOuAgL r t TEE c I 39 39 L I A I 1 w H Ann law 0 Annual man In Pr quot0 quot quot 66 quot E Soil Gas Before Pilot Study Began Grount wnter Sampling Ioca an and TCF m 50 0 50 m Concentration pg L in Groundwater at Mamme containm a g contammated sou sludge and was was 2700 The VIP 5 5 FG JW39E SWP B PM the suspected souvce oI V035 in the vcldose zone cmd nvesllgutlon May Io duIy 993 grommet SOURCE MODIFIED FROM WADE AND OTHERS I995 HASTINGS EAST INDUSTRIAL PARK SITE PLAN SHOWING HORIZONTAL AND VERTICAL WELL AIR SPARGINGSOIL VAPOR EXTRACTIONS SYSTEM FIGURE
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