APPENDIX B

Checklist #1 Air Sparging Pilot Tests and Detailed Evaluation of Air Sparging Applicability

Checklist #2 Administrative Checklist for Air Sparging Design Report

MINIMUM DESIGN REQUIREMENTS AND COMMON
ACCEPTED ENGINEERING PRACTICES:
AIR SPARGING SYSTEMS

INTRODUCTION

Traditionally, soil and groundwater contamination has been remedied by excavating the contaminated soil and pumping and treating the groundwater. Soil excavation is frequently impractical and cost prohibitive to implement as the primary corrective action. On the other hand, pump and treat technologies, while effective at containing contaminant migration, can be extremely slow in achieving remediation due to the physical and chemical limitations inherent in the process. Therefore, significant quantities of contaminated soils can potentially remain in the vadose (unsaturated) zone and beneath the water table. These soils may act as a lingering source of contamination to groundwater.

Air sparging is an innovative technology developed to address contamination present below the water table. Air sparging can be divided into two distinct technologies, in well aeration and in situ air sparging (IAS). In-well aeration is the process of injecting air into a well, producing groundwater circulation which strips the volatile fraction of contamination present. In-situ air sparging (IAS) involves injecting air directly into water saturated soils in order to remove contaminants through a combination of volatilization and aerobic biodegradation. Typically, IAS is used in conjunction with soil vapor extraction (SVE) to eliminate the off-site migration of vapors while simultaneously treating unsaturated zone soils.

This document is intended to assist property owners, industry, businesses and consultants by outlining requirements for approval of a WQD Permit to Construct. Brief overviews of both in-well aeration and IAS are included along with common and accepted engineering practices with respect to IAS systems presented in the form of recommendations. Recommendations are not given for in-well aeration since it has not been widely implemented and is not considered a full-scale technology. This document is intended to be used in conjunction with Guideline #2, "Applying for a Permit to Construct for a Corrective Action System," and Guideline #5, "Soil Vapor Extraction and Bioventing Systems." Due to the possible complex nature and variable characteristics of sites amenable to air sparging systems, information presented herein should not be viewed as a design manual or issuance of formal policy, but merely as a general reference guide for all parties involved. However, the design report and operation and monitoring recommendations are generally considered to be the minimum content required by the Groundwater Pollution Control (GPC) program to evaluate an application for a Permit to Construct. The application should include rationale describing how the remediation design meets the common and accepted engineering practices described within this guideline. If the design deviates from these practices, the application materials must contain justifications for the deviations. The justifications should include the information outlined in the WQD Rules and Regulations Chapter XI, Section 5, as described in Guideline #2, "Applying for a Permit to Construct for a Corrective Action System."

REGULATORY REQUIREMENTS

The approval of a 'Permit to Construct' application is required of all corrective action systems intended for sites regulated under the Groundwater Pollution Control (GPC) program. A subsurface investigation (SSI) is required prior to the selection and design of a corrective action system. A SSI Work plan must be submitted to the GPC program prior to conducting field investigation work. For a detailed explanation of the application and review process, including information to be collected during the SSI phase, the reader is referred to Guideline #2. It is highly recommended that this document be reviewed prior to the information presented below. Guideline #5, "Soil Vapor Extraction and Bioventing Systems," should also be reviewed since installation of an SVE system will likely be required when IAS is used.

Although not covered specifically in this guidance, IAS systems may require the installation of off-gas treatment. The Air Quality Division may require a permit for all air emissions associated with IAS/SVE systems. For more information, contact the Air Quality Division at (307) 777-7391. Disposal or treatment of contaminated soils in conjunction with the construction, installation or modification of an IAS system must meet the Solid and Hazardous Waste Division requirements. For more information, contact the Solid and Hazardous Waste office at (307) 777-7752. If subsurface injection of water generated during the construction, installation, modification or operation of an IAS system is planned, a separate Underground Injection Control (UIC) Permit is required. For more information, contact the UIC Program at (307) 777-7095. Whenever a discharge to surface water is proposed, the applicant must obtain a National Pollution Discharge Elimination System (NPDES) Permit. Contact the NPDES Program Manager at (307) 777-7082 for more information.

IN-WELL AERATION PROCESS DESCRIPTION

In-well aeration involves injecting air into the bottom of a well or trench screened in the saturated zone. As the injected air travels upward through the water column, bubbles form which remove volatile and semi-volatile organic compounds present. The upward movement of air also produces an airlift pump effect, as groundwater is pulled into the well from deeper screened portions and out of the well from shallower screened portions. Contaminant concentrations are reduced as groundwater circulates through the well, eliminating the need for pumping and treating the water at the surface.

Although in-well aeration may sometimes prove to be more efficient than conventional pump and treat, many of the same limitations apply to both processes. The low solubility of many contaminants and the inhibitory effect of slow mass transfer within heterogeneous geological conditions may retard the remediation process.

IN SITU AIR SPARGING (IAS) PROCESS DESCRIPTION

In situ air sparging (IAS) is the process of injecting air directly into contaminated areas of the saturated zone. IAS technology is commonly used in conjunction with soil vapor extraction (SVE) systems, allowing for treatment of vadose zone soils, saturated zone soils and groundwater in the saturated zone. Implementing an IAS system without SVE can potentially create a net positive pressure in the subsurface, inducing contaminant migration into previously uncontaminated areas. In some cases it may be argued that vapor recovery systems are not necessary (i.e., in remote locations where total potential emission rates are below acceptable levels, etc.). The discussion presented below is limited to the IAS portion only; the reader is referred to Guideline #5, "Soil Vapor Extraction and Bioventing Systems," for information regarding SVE recommendations and requirements.

The three primary mechanisms responsible for contaminant removal during the operation of IAS systems are believed to be: 1) in situ stripping of dissolved volatile organic compounds (VOC's), 2) volatilization of dissolved and adsorbed contaminants found beneath the water table and in the capillary fringe, and 3) aerobic biodegradation of both dissolved and adsorbed contamination as a consequence of additional oxygen supplied by the injected air. When an IAS system is optimized for stimulating biodegradation it is sometimes referred to as biosparging. Typically biosparging systems are initially operated for volatilization and stripping; the system is then fine-tuned for biodegradation. Detailed recommendations for biosparging are beyond the scope of this guidance since the process depends greatly on site specific characteristics. Although, general monitoring recommendation to measure biodegradation potential and performance are provided.

A typical IAS system has one or more subsurface air injection points or designated wells screened only below the water table (see Figure 1 in Appendix A). The injected air then travels vertically and horizontally through the soil and is greatly influenced by the degree of heterogeneity. Significant channeling can result from relatively small or subtle permeability changes. Channeling which leads to an increase in the secondary permeability of the soil potentially reduces the effectiveness of the IAS system due to mass transfer (e.g. diffusion) limitations. Therefore, IAS is applicable primarily at sites where homogeneous subsurface conditions prevail. Under these conditions, IAS technology has proven to be effective for removal of volatile organic compounds, semi volatile organic compounds and aerobically biodegradable compounds including petroleum hydrocarbons and some chlorinated solvents. Variations of combined IAS/SVE systems include the use of horizontal wells or trenches instead of traditional vertical well systems. The use of a line of vertical sparge wells can be effective for intercepting a migrating plume.

The mass transfer phenomenon which occur during IAS are a consequence of complex interactions between chemical, physical and microbial processes. Currently many of these interactions are not well understood. It is also difficult to predict the flow path taken by the air between the injection point and vadose zone soils. For these reasons, design of IAS systems is somewhat dependent on empirical knowledge. IAS is considered to be a rapidly evolving technology with need for continuous refinement.

DATA NEEDS

Since many of the driving mechanisms behind IAS systems are not fully understood, the importance of the subsurface investigation phase cannot be overemphasized. The specific data that should be collected and evaluated in order to assess the feasibility of in situ air sparging can be found in Guideline #2. Site specific criteria, contaminant characterization, soil related criteria, and groundwater related criteria are outlined as requirements of the subsurface investigation (SSI) phase. In particular, the horizontal and vertical permeability of the saturated zone and the vapor/dissolved phase partitioning of the contaminants must be evaluated to determine the possible effectiveness of an IAS system. Dissolved iron concentrations must also be measured when determining groundwater characteristics during the SSI phase. Iron may precipitate during the sparging operation and could cause aquifer clogging, potentially reducing porosity and permeability.

If the following conditions are detected during the SSI phase, in situ air sparging will not be approved as a remedial technology:

• If a measurable quantity of free product is present (i.e. greater than a floating sheen or film), an IAS system cannot be implemented without first recovering the free product. Air sparging can create groundwater mounding which could potentially cause free product to migrate.
• IAS cannot be used to treat groundwater in a confined aquifer because the injected air would be trapped by the confining layer and could not escape to the unsaturated zone. The trapped air would cause an increase in the downgradient movement of dissolved phase contamination.

It is also important to re-emphasize that the presence of fine grained materials or other geologic heterogeneities which may limit the migration of air to the water table surface, will adversely effect the efficiency of an air sparging system and may even promote dissolved and vapor phase contaminant migration. Semi-confined aquifer conditions or overlying low permeability zones will require the need for an adequate number of soil vapor extraction wells to relieve the positive pressures caused by the IAS system. If heterogeneous conditions prevail, the applicant must obtain significant data during the SSI phase in order to substantiate the appropriateness of air sparging as the remedial alternative and to have an effective remedial design.

PILOT SCALE TESTING FOR IN SITU AIR SPARGING

In order to implement an efficient IAS system, it is necessary to understand the pattern of air flow that will occur in the subsurface. This is generally accomplished by conducting short term pilot studies, consisting of three sequential tests over a period of at least 24 hours. For sites with significant subsurface heterogeneities, prolonged testing may be warranted. Typically, SVE systems must be installed in conjunction with air sparging systems to enhance VOC removal, treat unsaturated zone soils, and/or prevent off-site migration. Approval from the WQD must be obtained prior to proposing an IAS system without an SVE system. These tests are required of all proposed in situ air sparging systems and should be executed in the following order:

1) Air permeability test for SVE portion of system: must be implemented, when required, as described in Guideline #5, "Soil Vapor Extraction and Bioventing Systems," See the referenced document for test recommendations and requirements.

2) Air sparging test with SVE turned off: this portion must be conducted for a period of at least 4 hours.

3) Combined sparge/vent test with SVE and IAS operating concurrently: final portion with both SVE and IAS activated for no less than 12 hours.

Effective implementation of these tests should:

• Determine the SVE zone of influence.
• Estimate the areal influence of the air sparging system to determine number and placement of sparging wells.
• Define the vacuum and pressure requirements for effective treatment and capture of volatilized contamination.
• Determine if hydraulic controls will be necessary to contain possible plume migration.

Guidelines regarding standard practices for the design and implementation of IAS testing and combined IAS/SVE testing are presented below. Adherence to these guidelines should improve the overall quality of test data obtained. However, it is important to note that deviations may be necessary due to widely varying site conditions.

Construction Recommendations for Pilot Test Components:

Air Injection Wells: Existing groundwater monitoring wells are typically not used as air injection wells since injection wells must be screened exclusively in the saturated zone. The following standards apply (also refer to GPC Guideline, "Minimum Content Requirements: Sub-Surface Investigation (SSI) Work plans," for additional minimum standards and conditions for monitoring wells):

• The air injection well(s) should generally be located in an area of significant groundwater contamination. Although, if the air injection wells are placed in a curtain to intercept a contaminant plume, the wells would be located on the downgradient end of the plume.
• The injection well(s) should not be placed in the vicinity of man-made air flow conduits, such as sewer or utility lines.

• The top of the screened interval must be placed significantly below the seasonally low water table to ensure that screen will not be exposed under any circumstance.

• Depth of the screened interval is also contingent on contamination depth. The top of the screened interval must be placed sufficiently below the contaminant plume or area to be targeted (generally from 5 to 15 feet below deepest contamination under low water table conditions). However, the depth should not be greater than 30 to 40 feet below the ground surface or greater than 20 feet below the water table.
• Screen length is typically 2 to 5 feet; increased screened intervals generally do not improve system efficiency since air tends to exit at the top of the screen.
• The filter pack should not extend more than 1 or 2 feet above the top of the screened interval. Filter pack material should be selected based on the average grain size of soils below the water table.
• Heat generated during air compression should be taken into account when selecting well and piping materials.
• Well construction should ensure that short-circuiting of air is unlikely to occur across the seal and surface grout.
• Air injection wells constructed specifically for injection are preferred, although a piezometer(s) might be adequate for pilot testing if placed or driven sufficiently under the water table.

Monitoring Components: It is apparent that current monitoring practices are inadequate in terms of establishing a quantitative evaluation of the IAS process. Recent research has indicated that current monitoring practices overestimate the extent of saturated zone air flow by a factor of at least 2 to 8 when compared with results of cross borehole electrical resistance tomography. Other innovative monitoring technologies still in the development phase include neutron probe logging and capacitance probe logging. Until these techniques are adopted as common practice for IAS monitoring, conventional monitoring will be considered adequate for establishing the IAS zone of influence. Therefore, an adequate number of monitoring points should be installed in the vadose and saturated zones in order to estimate the zone of influence of the SVE and IAS systems.

• Vadose zone monitoring: vacuum/pressure monitoring wells (or probes) are required for the SVE and combined IAS/SVE portions of the pilot test. See Guideline #5, "Soil Vapor Extraction and Bioventing Systems" for recommendations regarding construction.
• Monitoring below water table: groundwater monitoring wells are required for the IAS and combined IAS/SVE portions of the pilot test. Refer to GPC Guideline "Minimum Content Requirements: Sub-Surface Investigation (SSI) Work plans," for additional minimum standards and conditions for monitoring well.

Miscellaneous Pilot Testing Components:

• Air extraction wells are required for the SVE and combined IAS/SVE portions of the pilot test. See Guideline #5, "Soil Vapor Extraction and Bioventing Systems" for recommendations regarding construction.
• Oil free compressors or a standard compressors equipped with downstream coalescing and particulate filters must be used to ensure that injected air is free of contaminants.
• Check valves should be installed between the injection well and the compressor to prevent potential line fouling. Pressure in the saturated zone may force air and water up the well when the system is turned off.
• Heat exchanger may be recommended if heat generated during air compression is a concern.
• Mufflers may be required during testing, depending on the size of compressor used and the potential for generating public nuisance conditions.

SVE Portion of Pilot Test:

Standard procedures and monitoring requirements of the SVE portion of the pilot test can be found in Guideline #5, "Soil Vapor Extraction and Bioventing Systems." This portion of the test can be terminated only after the vacuum response conditions reach equilibrium.

IAS Portion of Pilot Test:

Standard Procedures:

• At least two different injection pressures must be applied, holding pressure constant for a minimum of two hours at each step. Typical pressures range from 2 psig up to 60 psig, depending on the soil characteristics. Injection pressure must overcome the hydraulic pressure, frictional losses in system, and capillary resistance.
• The injection pressure should not exceed 3 times the static hydraulic pressure calculated at the top of the injection well screened interval. It is believed that turbulent flow occurs at higher pressures, potentially producing increased contaminant dissolution and plume migration.
• The injection pressure should not exceed 80% of the total pressure exerted by the weight of the soil and water above the top of the screen. It is believed that higher pressures may produce fracturing in the sparging well annular seal or along weak joints in the soil, resulting in a loss of system efficiency.
• Typical air flow rates range from 2 scfm to 25 scfm.
• Although not required, the use of an inert tracer gas (typically helium) can provide direct evidence of the pattern of sparged air breakthrough to the vadose zone.

Monitoring Requirements:

• Pressure readings (in vadose zone) and flow rate readings (at the injection point) should be taken several times at each valve setting.
• Groundwater mounding should be measured periodically at the injection point and in multiple monitoring wells.
• Measure subsurface gas phase contaminant (VOC's) concentration changes in vadose zone wells/probes and water table wells.
• Measure changes in dissolved oxygen (DO) in groundwater monitoring wells.
• Measure concentration of tracer gas (when used) in vadose zone.

Combined IAS/SVE Portion of Pilot Test:

Standard Procedures:

• The soil vapor extraction well(s) and air sparge injection well(s) must be operated concurrently for a period of at least 12 hours.
• The SVE extraction rate must exceed the air sparge injection rate to ensure that a net negative pressure is maintained in the subsurface and vapor migration is prevented. Typically, the air sparging rate varies between 20 percent and 80 percent of the soil vapor extraction flow rate.

Monitoring Requirements:

• Measure SVE vacuum and flow rates and sparging pressure and flow rates periodically.
• Monitor pressure in the vadose zone.
• Groundwater mounding should be measured periodically at the injection point and in multiple monitoring wells.
• Measure subsurface gas phase contaminant (VOC's) concentration changes in vadose zone wells/probes and water table wells.
• Measure changes in dissolved oxygen (DO) in groundwater monitoring wells.
• If biodegradation potential is to be evaluated for future system optimization, measure CO₂ gas in vadose zone wells and dissolved in groundwater. The DO should be measured over a 24 hour period at the following intervals: 2, 4, 8, and 24 hours following start-up. It is also recommended that oxidation reduction potential, pH, and conductivity and temperature is measured and recorded.

Reporting Pilot Scale Test Results:

• A site map drawn to scale indicating:

Locations of air extraction well(s) and vacuum measuring points. Locations of air injection points and groundwater monitoring wells. Paved areas, buildings, and structures that may act as surface seals or infiltration barriers. Buried utility trenches or other subsurface structures that may act as zones of increased permeability.

• Descriptions of field equipment and procedures used during testing.
• Sampling methods and procedures.
• Boring logs and 'as-built' construction diagrams for air extraction well(s), vacuum monitoring wells/points, air injection well(s) and groundwater monitoring wells.

For SVE portion:

• Table of operating flow rates at different vacuum steps, vacuum measured at monitoring points and duration of each vacuum step applied. Barometric pressure readings should also be tabulated. Times of readings should be included.
• Plot of soil vapor vacuum vs. horizontal distance from the extraction well. Graph should be plotted on semi-log paper with vacuum as the log scale (y-axis). A linear regression analysis should be performed on the data.
• Table of VOC levels in extracted vapors (measured prior to any off-gas treatment system), temperature of extracted vapor and time readings were taken. Average VOC mass removal rates for the test must be calculated from extraction concentrations and flow rates for each vacuum step.

For IAS portion:

• Table of operating flow rates, pressures and duration of each injection step, including time readings taken.
• Table of monitoring well/vapor probe VOC measurements taken with FID/PID, including time of reading.
• Table of water level measurements, including time measurement taken.
• Table of DO readings at monitoring wells (with time of reading noted).
• Plot of soil pressure in vadose zone vs. distance from sparge well.
• Plot of soil gas measurements (VOC's and O₂, CO₂ and He when measured) vs. time.

For combined SVE/IAS portion:

• Table of operating flow rates, vacuums, pressures and time measurements taken.
• Table of VOC levels in extracted vapors (measured prior to any off-gas treatment system), temperature of extracted vapor and time readings were taken. Extraction concentrations must be converted to average VOC removal rates for the test.
• Table of water level measurements, including time measurement taken.
• Table of DO readings at monitoring wells (with time of reading noted).
• Plot of changes in water table elevation vs. time for different observation wells at various distances from sparge well.
• Plot of soil gas measurements (VOC's and O₂, CO₂ when measured) vs. time.
• Plot of DO measured in groundwater wells vs. distance from sparging well.

FULL SCALE IAS DESIGN

Pilot scale test results are usually submitted with the detailed full-scale system design. The field data obtained from the pilot scale tests should be carefully evaluated to determine the following:

1) The intrinsic permeability of the site (both air and hydraulic permeability), including the relationship between horizontal and vertical permeability in the vadose and saturated zone.

2) The number and location of extraction (vent) wells and injection points needed to:

a) achieve the required air flow distribution in the subsurface and

b) ensure that vapors in vadose zone are captured by the SVE system.

3) The appropriate blower/vacuum pump.

4) If required, the appropriate air treatment control technology (approved by AQD).

Design considerations and recommendations, along with system installation and operation suggestions, are presented below. The discussion is limited to the IAS portion of system design only. The reader is referred to Guideline #5, "Soil Vapor Extraction and Bioventing Systems." It is also important to note that all of the information previously presented regarding the implementation of a pilot scale test is also relevant to full scale systems.

General Design Considerations/Recommendations:

When evaluating the pilot scale results the following should be taken into consideration:

• In a heterogeneous, mixed lithology site the zone of influence of an air sparging well might appear to be large due to the lateral dispersion of air that occurs when low permeability layers are encountered.
• The presence of air bubbles in groundwater monitoring wells should not be viewed as concrete evidence of thorough permeation of the injected air through the aquifer.
• Due to constraints in current monitoring practices, estimating the zone of influence of an injection well should be limited to approximating the area influenced. This can be done by averaging the radial distances measured for positive pressure in the vadose zone, DO in the saturated zone and increases in vadose zone VOC concentrations during the IAS portion of testing.
• Designers have also used one to two times the air injection depth as an approximation of zone of influence for an air sparging point. Research has demonstrated that this may be a valid assumption for homogeneous media.
• The results from pilot scale tests should not be the only criteria evaluated when estimating the design zone of influence of an air injection point. The zone of influence of the air injection point depends primarily on the hydraulic conductivity of the aquifer material in which sparging is taking place. Soil heterogeneities and differences between lateral and vertical permeabilities are also important.
• It should not be assumed that contaminants within the chosen zone of influence for a sparging point will be remediated at the same rate.

System Configuration and Components:

Injection Well Placement and Construction:

• Due to the obscure nature of current design practices for IAS systems, an injection well configuration employing highly overlapping zones of influence is favorable. However, the use of multiple sparge points to obtain an apparent overlap does not necessarily assure that all of the volume of water will be reached by the air with equal efficiency.
• When a line of injection wells are intended to act as a sparging wall or permeable barrier, the design must address the potential for the dissolved contaminant plume to bypass treatment (e.g., flow around wall). This condition might arise due to the change in hydraulic conductivity produced by adding air into saturated zone.
• Systems which are in remote locations and systems which will not have personnel on site 24 hours a day, will be required to have an automatic control panel to ensure that when the air extraction wells are not operational, the air sparging system will also be turned off.

Manifold Piping:

• Slope the manifold piping towards the extraction wells so that condensate or entrained groundwater will drain toward the well.
• If the system is to be operated on a long term basis and during winter months, winterization provisions are required (e.g., bury manifold below frost line among others).
• PVC pipe should not be connected directly to the compressor because of the high temperature of the air at the compressor outlet.

Blower:

• A discharge muffler is required in situations where public nuisance conditions might arise.
• Blowers must be protected from suction of water and particulates by using in-line filters and moisture knockouts. Accumulated water may require treatment prior to disposal.

IAS Instrumentation/Flow Measuring Equipment:

• Horizontal injection wells: used when shallow water table conditions exist, when the zone of contamination exists within a specific stratigraphic unit, or when the system is to placed underneath a facility. Horizontal wells must be designed and installed properly to ensure that air exits along the entire length of the screen.
• Pulse sparging: operating the sparge system on an intermittent basis may provide a benefit in some cases by inducing agitation and mixing of groundwater, potentially alleviating the inherent diffusion and mass transport limitations. In the case of an interception or barrier system, cycling/pulsing could allow groundwater flow to resume and bring new contaminated water into the sparging wall. The benefit of pulsed operation should be evaluated using site specific criteria.

DESIGN REPORT FOR COMBINED IAS/SVE SYSTEM

General Requirements:

• Discussion, justification, and rationale for system design with a description of the systems' capabilities for remediating the soil and groundwater (including the smear zone). If any stratification is present at the site, the discussion must address how heterogeneities affect subsurface air flow patterns.
• Engineering calculations for determining extraction and injection well spacing, including zone of influence estimates for both the SVE and IAS wells. Clearly state all assumptions. Legible, hand written calculations are acceptable. Include references for formulas and methodology used.
• If free product is present, designers must include a description of free product removal method(s) to be performed prior to implementing IAS/SVE system.
• Discuss the ratio of extracted air to injected air for sites where SVE is required.
• If any computer modeling is used, include model assumptions and results.
• If a water trap or groundwater pumping is proposed, discuss the need for treating extracted water. If treatment is required, describe technology to be used. See WQD Rules and Regulations Chapter XI, Sections 6 and 7, for more information regarding wastewater treatment final design report requirements.
• Brief description of off gas treatment proposed (when treatment is required by AQD).
• Submit winterization provisions (Continuous year-round operation may likely be required).
• Design drawings must be scaled to show sufficient detail.

Plan View:

Scaled site map(s) illustrating and identifying:

• Contaminated area to be remediated (dissolved iso-concentration contours and free product thickness contours).

Note: Product thicknesses may be difficult to contour in very low permeability (fine grained) or fractured consolidated subsurface conditions. Please indicate product thickness at monitoring well locations.
• Potentiometric surface.
• Location of proposed and existing extraction/injection wells and monitoring points/wells.
• Zone of influence of extraction wells and injection wells.
• Location of manifold, blower and other equipment.
• Subsurface structures present (i.e., underground utilities, etc.).
• Paved areas, buildings and surface structures present. Include residential areas and locations where basements may be present.

Process and Instrumentation Schematic:

• Process flow diagram indicating all components and direction of air/water flow through system components (i.e., below ground and above ground equipment).

Profile Views and Cross Sections:

• Typical monitoring well/point cross section: one cross section is sufficient for all wells constructed in the same manner; depths of screened interval must be identified on plan view for all wells.
• Representative hydrogeologic cross sections: profile view of highest contamination zone illustrating and identifying elevations of ground surface, boundaries between differing lithologies and/or permeabilities, water table, screened interval of extraction/injection wells lying in cross section, and analytical soil sampling results at respective depths.

Specifications:

• Size and type of blower/vacuum pump including range of operating flow rates, manufacturers performance curves, and vacuum levels.
• Piping specifications including sizing and compatibility of piping materials with contaminants.
• Maximum flow ratings for activated carbon units, oil-water separators, or other treatment units proposed.
• Specifications of measuring instruments including vacuum and flow gauges.

OPERATION AND MONITORING

Operation and Maintenance Manual:

The efficiency and reliability of air sparging is largely dependant on system design; however, adequate maintenance becomes the critical factor once a system is operational. For this reason an Operation and Maintenance (O&M) Manual must be submitted for review. A general outline representing the minimum information required in an O&M manual can be found in Appendix C of GPC Guideline #2. In addition to the outline, the O&M manual shall contain the following:

• The remediation systems may need to be operated nearly continuously to achieve containment and/or recovery purposes; therefore, the following issues must also be described in detail within the O&M manual:

1) A description of systems' capabilities to operate during routine or emergency maintenance, power outages, or other unforeseen circumstance is required. The discussion must specify details such as availability of the owner or operator during the emergency situation, among others.

2) An analysis of length of time the remediation system can safely be off-line during emergency or maintenance situations is also required. Factors such as potential receptors, groundwater velocity, type and amount of contamination should be included in the discussion. Measures must be implemented to ensure that the system will not be out of operation longer than safely feasible. Examples of such measures include parallel or redundant equipment, adequate availability of equipment parts, operator response time and availability, etc.

• The requirements of the Division of Occupational Health and Safety (OSHA) must be met during construction, installation, and operation of the remediation system. For more information call (307) 777-7786.
• A Health and Safety Plan (HASP) and/or a Spill Prevention, Control, and Countermeasures (SPCC) Plan may need to be submitted to meet federal requirements.

As-Builts:

The 'as-built' construction information is due along with the first monitoring report (see performance monitoring below) approximately 60 days after system startup. The 'as-built' submittal should include the following:

• Any deviations from the plans and specifications in the design report.
• Complete 'as-built' construction drawings and specifications.

Performance Monitoring Plan:

A Performance Monitoring Plan (PMP) must be submitted prior to issuance of the Permit to Construct. Following WQD's approval of the PMP, it should be included in the O&M manual. The PMP should include at a minimum:

• SVE: Proposed monitoring frequency for air flow rates, vacuum and VOC concentrations.
• IAS: Proposed monitoring frequency for flow, pressure, VOC, O₂ and CO₂.
• Descriptions of analytical methods and sampling procedures.
• Proposed frequency of reporting.

IAS/SVE System Monitoring Recommendations:

Note: These recommendations are general guidelines only and significant variations may be warranted or required depending on site specific characteristics.

Vacuum, Pressure and Air Flow Monitoring Recommendations:

• Daily monitoring for first week, weekly for first month, and at least monthly after start up.
• Measurements should be taken at each injection wellhead, extraction wellhead, manifold branch, at blower and at stack.
• Measurements should be taken at surrounding monitoring wells/probes with the same frequency as pilot test during initial startup of full scale system to verify zone of influence estimates. Groundwater levels should be measured daily for first week and as needed thereafter to monitor for groundwater mounding.

Note: Air flow rates should be measured directly with a dedicated device, not estimated from blower performance curves.

Contaminant Concentration Monitoring Recommendations:

• Daily monitoring of VOC concentrations in system effluent (prior to any off-gas treatment) performed with a portable meter, preferably with an FID, for first week, and weekly for the first month. VOC monitoring of system effluent should be performed at least monthly after startup, concurrently with air flow measurements.
• Off-gas VOC composition sampling performed by analytical laboratory (BTEX, TPH analysis and/or other applicable parameters) shall occur at start-up, and at an acceptable frequency following start-up (at least at the minimum frequency required by WDEQ/AQD if applicable).
• Monthly VOC field screening at individual wellheads following start-up.

Monitoring for Biosparging Performance:

• CO₂ and O₂ should be monitored in vadose zone and below water table when system's biodegradation performance is to be measured and evaluated. Measurements should be taken at least bi-weekly initially and quarterly to annually after optimization.

REFERENCES

Ahfield, D.P., A. Dahmani and W. Ji, 1994. " A Conceptual Model of Field Behavior of Air Sparging and Its Implications for Application." Groundwater Monitoring and Remediation, Fall.

Boulding, J.R., 1995. Practical Handbook of Soil, Vadose Zone, and Ground-Water Contamination: Assessment, Prevention and Remediation. CRC Press, Inc., Boca Raton, Florida.

Cookson, J.T., 1995. Bioremediation Engineering: Design and Application. McGraw-Hill, Inc., New York, New York.

Fetter, C.W., 1993. Contaminant Hydrogeology. Macmillan Publishing Company, New York, New York.

Freeze, R.A. and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Inc., Englewood Cliffs, New Jersey.

Hinchee, R.E., editor, 1994. Air Sparging for Site Remediation. Lewis Publishers, Ann Arbor, Michigan.

Johnson, R.L. et. al., 1993. "An Overview of In Situ Air Sparging." Ground Water Monitoring Review. Vol. 13, No. 4, Fall.

Marley, M.C. and C.J. Bruell, 1995. In Situ Air Sparging: Evaluation of Petroleum Industry Sites and Considerations for Applicability, Design and Operation. American Petroleum Institute Publication 4609.

Marley, M.C., D.J. Hazebrouck and M.T. Walsh, 1992. "The Application of In Situ Air Sparging as an Innovative Soils and Groundwater Remediation Technology." Ground Water Monitoring Review. Vol. 12, No. 2, Spring.

Marley, M.C. et. al., 1994. "The Design of an In Situ Sparging Trench." The Proceedings of the 1994 Petroleum Hydrocarbons and Organic Chemicals in Groundwater: Prevention, Detection and Remediation Conference, November 2-4, 1994, Houston, Texas. National Groundwater Association.

U.S. EPA, 1992. "A Technology Assessment of Soil Vapor Extraction and Air Sparging." EPA/600/R-92/173.

U.S. EPA, 1994. "How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers." EPA/510/B-94/003.

Wi, J., et. al., 1993. "Laboratory Study of Air Sparging: Air Flow Visualization." Groundwater Monitoring and Remediation, Fall.

APPENDIX A

APPENDIX B

GPC GUIDELINE #6 - Checklist #1: Air Sparging Pilot Tests and Detailed Evaluation of Air Sparging Applicability

This checklist is intended to aid in reviewing proposals for conducting detailed pilot tests of air sparging systems. The list also incorporates criteria to be reviewed after performing the pilot test in order to further evaluate the potential effectiveness of using air sparging at a site. If the answer to several questions is no, modifications to the proposed testing procedures may be warranted or additional information should be requested.