Corrective Action

The first step in developing a CAP is to identify the specific contaminant concerns associated with the release. There are four distinct contaminant phases that need to must be evaluated:

• Sorbed phase
• LNAPL (free phase)
• Dissolved phase
• Vapor phase

Each contaminant phase has potential concerns that must be reviewed and identified for a release. Specific contaminant concerns are identified in the table in the following section.

Remedial goals and associated objectives should be clearly defined based on the identified contaminant concern. Remediation goals are the desired condition to be achieved by the remedial strategy or action that constitutes the end of management for a specific concern. A remediation objective describes how the remediation goal will be accomplished and is established in order to select the technology(ies).

The table below identifies potential contaminant concerns for each phase with appropriate remedial objectives for each concern. A particular release event requiring active remediation will likely have multiple contaminant concerns and associated remedial objectives.

Combined with performance metrics and a remedial endpoint, the remedial objective becomes a SMART Objective (specific, measurable, agreed-upon, realistic, and time-based). A SMART Objective should be developed for each identified remediation goal. SMART is an acronym that is used to guide your goal setting. As it relates to remediation, each SMART objective should include the following components:

• Specific - The targeted treatment area and technology-specific endpoints are clearly stated.
• Measurable - Performance metrics that demonstrate progress toward the endpoint are clearly stated. Typically, multiple performance metrics are identified to reflect the multi-phase distribution of contaminants.
• Agreed Upon - The concerns, goals, objectives, targeted treatment areas, performance metrics, and endpoints are understood by all interested parties.
• Realistic - The selected technology has a demonstrated ability to achieve the SMART objective and the basis of technology selection is presented.
• Time-Based - The target date for when the technology-specific endpoint is projected to be achieved is clearly stated. Performance milestone, when appropriate, are identified.

It is important to understand that technology-specific endpoints do not necessarily eliminate the environmental concerns derived from the CSM. Technology specific endpoints appropriately account for the expectations of the technology. Combined remedy or treatment train approaches are discussed in subsequent sections of this CAP Preparation guidance.

Targeted treatment areas represent the area where the contaminant concern exists. Targeted treatment areas must be identified and depicted in a map and cross-sectional view for every remedial objective identified. Accessible and inaccessible areas should be clearly identified and appropriately described. As the figure below depicts, there are likely multiple, distinct targeted treatment areas for the identified site contaminant concerns.

This section describes a process for systematically evaluating, screening and selecting the most technically efficient and economically feasible remedial technologies to address identified contaminant concerns. This process establishes a clear basis of technology selection and should be followed when developing a CAP. Not all concerns will be addressed in a single CAP, as discussed below in the Treatment Train section of this guidance. An overview of selected remedial technologies is provided in the CAP Technologies section. The screening tools presented within the stepped process reflect OPS' collective experience in remediating petroleum release sites. Responsible Parties may recommend technologies that do not strictly adhere to the process or technologies that were not included in the OPS reviewed technologies; however, the basis of technology selection in those situations must be clearly supported.

Step 1 - Screen Technologies Based on the Contaminant Concern and Remedial Objective

Technologies are first screened based on their demonstrated ability to achieve a particular remedial objective. This initial step will eliminate many technologies from future consideration. The table below should be utilized when completing this step. Technologies that are not eliminated from consideration should be retained for additional screening.

Key

AS - Air Sparge	MNA - Monitored Natural Attenuation	PVI - Petroleum Vapor Intrusion
EFR - Enhanced Fluid Recovery	NSZD - Natural Source Zone Depletion	RBSLs - Risk Based Screening Levels
ISCO ‚Äì In Situ Chemical Oxidation	O2 - Oxygen	SESR - Surfactant-Enhanced Subsurface Remediation
LNAPL -  Light Non-Aqueous Phase Liquid	O3 - Ozone	SSTLs - Site-Specific Target Levels
MEP - Maximum Extent Practicable	POE - Point of Exposure	SVE- Soil Vapor Extraction
MPE - Multi-Phase Extraction

Step 2 - Screen Technologies Based on the Site Geologic Factors

Technologies should then be screened based on the geologic factors associated with the particular contaminant concern. This screening step eliminates technologies that rely on certain geologic conditions that are not present within the targeted treatment area. It is important to consider the contaminant mass storage and transport zones when completing this step. Lithologic applicability is included in the Technologies Overview table in the CAP Technologies section below.

Step 3 - Prioritize Additional Evaluation Factors and Perform a Comparative Analysis

A few viable remedial technologies may remain after performing the first two screening steps. The next step is to perform a comparative analysis of relevant additional evaluation factors that are present for a particular release. Evaluation factors to consider include:

• Cost - Estimates of upfront capital and life-cycle costs should be compared for each technology.
• Site restrictions - Physical (e.g., buildings and utilities), logistical (e.g., limited area to house a remediation shed or stockpile materials) or legal (e.g., offsite property access) site restrictions.
• Remediation time frame - A release may have specific time restrictions so the estimated time frame to achieve the remedial objective should be considered (e.g., very short for excavation to very long for monitored natural attenuation).
• Safety - Safety concerns should be evaluated (e.g., construction, operation and maintenance).
• Community concerns - Potential or real community concerns should be evaluated (e.g., traffic, noise, odors, dust).
• Carbon footprint/energy requirements - Compare energy consumption and greenhouse gas emissions.
• Waste stream management - Evaluate waste generation and management.
• Other - A project-specific evaluation factor can be incorporated into this screening step.

Cost is most typically a relevant evaluation factor to consider. A few other factors should be identified with stakeholder input, and a quantitative or semi-quantitative analysis should be performed to screen and rank the remaining remedial technologies. The advantages and limitations of each technology are discussed in the CAP Technologies section below and can be used to aid in this step. Ideally, a remedial approach will be selected at the completion of this step to proceed with a more site-specific evaluation of the technology.

Step 4 - Identify Critical Data Needs

The steps completed up to this point have largely been a desktop evaluation of existing data and experience. Critical field data needs should be identified and appropriately addressed prior to technology selection for full-scale application. Identification of critical data needs aid in supporting the following:

• Remedial selection - Will the selected technology effectively perform in the targeted treatment area?
• Efficacy of design - What information should be gathered to maximize the effectiveness of the technology?
• Performance monitoring - What baseline data are needed prior to implementation?

Pilot testing is an example of a critical data need and should be considered at all sites and in the context of how it aids remedial selection, the efficacy of design or performance monitoring. Critical data needs vary from technology to technology. Example Critical Data Needs are included for each technology in the CAP Technologies section.

Step 5 - Select the Technology(ies) to Address the Concern(s)

Completion of the above process lays the foundation for a good basis of selection for a remedial technology. The last step of the evaluation process is to select the technology to address the contaminant concern and achieve the remedial objective. Incorporation of Green and Sustainable Remediation practices is recommended once a remedial approach has been selected. This does not necessarily represent the end of the technology selection process as there are likely multiple contaminant concerns for a given release. As such, this process should be repeated as necessary to identify appropriate technologies to address contaminant concerns and achieve remediation goals. This process can be utilized to address multiple concerns within the same targeted area. Certain technologies may be able to address multiple remedial objectives and may offer the greatest utility for a release event. As described in the Define Remedial Goals and Objectives section above, a SMART objective should be developed for each remediation goal. This includes the identification of technology-specific performance metrics and remedial endpoints. Technology specific remedial endpoints may not necessarily result in the elimination of the contaminant concern. For that reason, the identification of a potential treatment train strategy may be appropriate to achieve site closure.

Formerly, a single remedial technology was typically selected with the expectation that the technology would achieve closure conditions for a release event. Experience has shown that this approach often did not achieve closure conditions and that another technology needed to be implemented after years of ineffective and costly assessment of the situation. The use of multiple technologies should be thoughtful and deliberate, rather than a reaction to a failed technology. A more practical and cost-effective approach may be to sequence or combine technologies based on the specific contaminant concerns and associated remedial goals.

A treatment train is a sequence of multiple remedial technologies, beginning with a primary remedy that will effectively treat the highest mass or concentrations of contamination that is followed by a secondary treatment technology to address remaining mass and, if necessary, a tertiary polishing step to achieve site closure. A combined remedy approach is similar to a treatment train, except that the methods are employed concurrently.

Performance metrics are measurable characteristics that relate to the remedial progress of technology in achieving the remedial objective and abating the contaminant concern. Technologies function differently (e.g., excavation versus MNA) and therefore the performance metrics used to demonstrate remedial progress depend on the technology used.

Some examples of performance metrics include the collection of the following:

• Air emission samples to evaluate contaminant mass reductions (common for mechanical systems).
• Specific indicators to evaluate the distribution and efficacy of an in-situ application.
• Geochemical parameters to aid in the understanding of the CSM, natural processes, and chemical specific decay rates (common for MNA).
• Groundwater samples to evaluate progress toward the remedial objective (common for dissolved phase contaminant concerns).
• Interim or final soil confirmation samples to evaluate the reduction of contaminant mass (common for sorbed phase contaminant concerns).

Performance metric collection frequency or occurrence should be related to remedial milestones. Examples of remedial milestones may include:

• Periodic collection of air emission samples to evaluate progress toward the remedial goal or system limitations (e.g., asymptotic levels as an endpoint).
• 50% mass reduction achieved based on an initial contaminant mass estimate.
• Groundwater BTEX concentrations remediated to 25%, 50% or 75% of either the SSTL or RBSL.

Ideally, each performance metric has a predetermined value that describes when the technology has reached the limits of beneficial application. That is the endpoint metric for the technology chosen and the associated remedial objective. As previously stated, technology-specific endpoints do not necessarily eliminate the environmental concerns derived from the CSM. Technology specific endpoints should however appropriately account for the expectations of the technology.

Identification of relevant performance metrics, their sample collection frequency or occurrence, and the technology-specific remedial endpoints should be clearly presented in the CAP for each and all remedial objectives.

As it relates to identified contaminant concerns, a groundwater monitoring network should largely coincide with the targeted treatment areas where the dissolved phase concern exists. Further, a groundwater monitoring network should adequately represent the understanding of the contaminant plume area, stability and migration potential. It is important to consider that a monitoring well network is designed to be representative of an area. It may be entirely appropriate to collect spatially relevant groundwater samples at locations other than the established monitoring well network to evaluate abatement of the contaminant concern within the targeted area. Tools are available to help establish a statistically significance monitoring schedule.

Sampling frequency should coincide with the milestones identified to evaluate progress toward the established remedial endpoint (i.e., RBSLs or SSTLs). At most sites, sampling frequency may vary from well to well based on the following:

• Intended purpose of the well (point of compliance versus source area)
• Historic understanding of the well
• Anticipated remedial change within the well

In general, monitoring wells should be sampled when it is expected that the data will be evaluated in a meaningful way (e.g., progress toward closure or confirmation of the CSM).

Monitoring and Remediation Reports (MRRs) should be submitted on a frequency that generally coincides with evaluation of the identified performance milestones and within the time frame identified to evaluate the remedial objective. Expectations associated with report evaluations are presented in the CAP Implementation section.

An acceptable CAP submittal will include all of the above components for every contaminant concern identified to be addressed within the CAP. As discussed, treatment train approaches may benefit the time and money spent on the release in the long run and should be considered. It may be appropriate to identify that a contaminant concern will not be specifically addressed within the initial corrective action phases so long as it is presented that the the concern will be aided by the proposed plan and/or that the concern will be addressed in a subsequent phased approach.

Excavation is the fastest and most effective remedial technology for surficial, vadose zone, and smear zone soil impacts. Removed contaminated material can either be disposed offsite, land farmed, or treated onsite (e.g., soil shredding, ex-situ thermal desorption) or offsite. In addition to removing soil impacts, excavation can also be used to expose the water table to enable direct treatment of contaminated groundwater (e.g., ISCO, activated carbon). Excavation can be the sole remedial technology and is commonly utilized as the primary remedy in a treatment train. However, excavation is not always possible due to access restrictions and there are a number of factors to consider when evaluating this option as described below.

Critical Data Needs

Although pilot testing is typically not required for excavation, additional data may be necessary to better define the area(s) to be excavated. A grid pattern of direct push borings is an effective manner of delineating the targeted excavation area and depth. During excavation, field screening should be conducted to provide real time data to aid in decision making such as horizontal and vertical excavation limits and confirmation soil sample locations.

A Materials Management Plan should be prepared to address the following questions:

• How much soil will need to be disposed or treated, and can the impacted soil be treated onsite and reused, or transported to a landfill or landfarm?
• What are landfill or landfarm requirements?
• Is clean overburden in the excavation zone, and can it be segregated and reused?
• Are Green and Sustainable Remediation principles being used?
• Have soil expansion factors (tons versus yards) been considered for transportation?
• Can surface cover be recycled?
• Will groundwater be encountered?
• What is the infiltration rate and will dewatering be necessary?
• Should a vapor barrier be added during backfill?
• Should infiltration piping be installed in the excavation prior to backfilling to facilitate future applications of ISCO, activated carbon, or nutrients?

Advantages

• Expedient removal of source area contaminant mass.
• Assurance that complete removal of accessible, targeted treatment area occurs.
• Ability to apply ISCO, activated carbon, or nutrients, directly to the exposed water table for groundwater remediation.
• Ability to install infiltration piping system in the excavation prior to backfilling to facilitate the application of future ISCO, activated carbon, or nutrient applications to the dissolved phase plume, if necessary.

Limitations

• Access restrictions posed by subsurface utilities, tank system components, onsite structures, and overhead restrictions such as dispenser canopies.
• Safety issues such as petroleum vapors, vapor monitoring and control, exclusion zone fencing, pedestrian concerns, and traffic control measures.
• Soil type(s) and hydrologic conditions may be a limiting factor for sloping or shoring, which may present OSHA restrictions.
• Carbon footprint should be considered.
• State and/or local regulations may require specific permits for groundwater dewatering, treatment or disposal, and stormwater management.
• Potential high-cost option based on quantity and available disposal/treatment options.

Performance Metrics

Excavation performance metrics must include adequate sidewall and floor soil confirmation samples. Documentation of the completed excavation must be entered into monitoring report tables and figures, and soil disposal manifests and/or data of treated mass must be provided. A photographic record of the excavation process is strongly recommended. Models such as REMFUEL can be used to evaluate the effectiveness of excavation on reducing the project lifetime and determine if and when the next step in the treatment train should be implemented.

Air sparge (AS) and soil vapor extraction (SVE) are common in-situ remedial methods for volatile fuel contamination. AS injects ambient air below the saturated zone to aerate the fuel contamination. SVE then induces a vacuum that volatilizes and removes fuel contamination in the vadose zone. Under applicable conditions, AS/SVE is capable of addressing moderate to high contaminant concentrations in the vadose, smear, and saturated zones. AS/SVE is often combined with excavation as part of a treatment train. AS/SVE designs should address targeted treatment areas identified during site characterization and subsequent data collection and CSM refinement. AS/SVE systems can be designed to also operate as biosparging/bioventing remediation systems, which are described below.

Critical Data Needs

Pilot testing should be conducted to evaluate AS/SVE technical feasibility and proper system design. The goal of the pilot test(s) is to measure and predict the effects of full-scale AS/SVE system operation, either separately or combined. Therefore, pilot test wells should be designed and constructed similar to the proposed full-scale design. Pilot testing must provide data on sustainable air flow rates, contaminant vapor removal rates, subsurface air flow vectors, effective radius-of-influence (ROI), and the number of AS/SVE wells needed to address the targeted treatment area(s). Pilot testing is also an opportunity to collect additional soil, groundwater, and vapor data to refine the CSM and optimize the CAP. If AS or SVE will be implemented individually as a stand-alone technology, pilot testing should be conducted as a step test using a minimum of three air flow rate steps. If AS will be used in conjunction with SVE, it is important to conduct step tests separately and in conjunction. A minimum of three monitoring points, at varying directions and distances (i.e., 10 feet, 20 feet, 30 feet, etc.) from the test point(s), is typical to observe the effect of pilot testing. Existing groundwater monitoring wells may be appropriate to act as pilot test monitoring points.

Advantages

• Proven technology with numerous case studies to document feasibility.
• Ability to treat moderate to high contaminant concentrations over a large treatment area.
• Relatively shorter timeframe to achieve remedial objectives.
• May also be implemented actively or passively, or mobile systems may be utilized if remedial timeframes or treatment areas are small.
• SVE can provide significant fugitive vapor control for prevention of PVI issues.

Limitations

• Limited effectiveness in low-permeability, fine-grained soil.
• Permitting requirements vary by city and county.
• Carbon footprint should be considered.
• Vapor emissions should be considered, and APEN permit may be required from CDPHE.
• Community concerns such as noise should be considered.

Performance Metrics

Performance metrics for AS/SVE remediation will generally include measuring the rate of extraction in the SVE effluent, and evaluation of the reduction in contaminant plume size and concentrations relative to calculated SSTLs. Mass removal calculations should be performed and tracked relative to initial contaminant mass estimates. Remediation progress of vadose and/or smear zone contamination will can be demonstrated through confirmation soil sampling, and by groundwater monitoring for the dissolved phase plume. ROI measurements should be performed to verify system performance, in addition to system optimization which can provide greater remedial effort to areas with remaining impacts. Sustained asymptotic levels after system optimization may be indicative of an effective endpoint for the AS/SVE system.

References

Design Criteria and Reporting Requirements (Vapor Extraction, Air Sparging) Guidance Document #17, Minnesota Pollution Control Agency Voluntary Investigation and Cleanup

Clu-In Air Sparging Guidance Document, Battelle, 2001

Guidance on Soil Vapor Extraction Optimization, Prepared For Air Force Center for Environmental Excellence, Brooks AFB, Texas

A biosparging system is similar to an AS system, except lower flow rates of air, or oxygen, are used to enhance bioremediation (the primary mechanism of biosparging) in the saturated zone, while minimizing volatilization (the primary mechanism of AS). Therefore, biosparging is a mechanical system near the biological end of the treatment train and is generally employed to address moderate to low contaminant concentrations. Bioventing is similar to SVE however air is injected, rather than extracted, at lower flows and volumes into the vadose zone to promote biodegradation. Biosparging and bioventing may be used alone or in conjunction with other technologies.

Critical Data Needs

Field pilot testing provides data on sustainable air flow rates, air pressures, subsurface air flow vectors, effective ROI, and the number of sparge or injection points needed. Pilot testing is also an opportunity to collect additional soil, groundwater, or vapor samples to refine the CSM and optimize the remediation plan. Similar to AS/SVE pilot testing, a minimum of three monitoring points, at varying directions and distances from the test point(s), is typical to observe the effect of pilot testing. Step tests will provide better data for optimal design. Existing groundwater monitoring wells may be useful as pilot test monitoring points.

Advantages

• Because air is injected at low flow rates, biosparging/bioventing can be effective in fine-grained lithology where AS/SVE is generally not technically feasible.
• PVI can be avoided by biosparging and bioventing at low flow rates, which eliminates the necessity for vapor capture or control by an SVE system.
• Liquid nutrients (see biodegradation) may also be added to the air stream to increase nutrient content and soil moisture if they are known to be limiting factors to bioremediation.
• Ability to convert an AS/SVE system to a biosparging or bioventing system when asymptotic limits of the AS/SVE system have been reached. This enables another step in a treatment train, which is a technically-efficient and cost-effective benefit.

Limitations

• Generally medium to longer timeframes to achieve remedial objectives.
• Ineffective for large mass, high contaminant concentrations.
• Performance Metrics

Performance metrics include measuring airflow and pressure at each point, changes in groundwater DO and ORP, and monitoring oxygen and CO2 in soil vapor samples. Remedial progress for vadose and/or smear zone contamination will generally be demonstrated by confirmation soil sampling, and by groundwater monitoring of the dissolved phase plume.

References

How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites, A Guide for Corrective Action Plan Reviewers (Chapters 3 and 8) EPA 510-R-04-002 May 2004

Biosparging Pilot Test Guidance, (Florida DEQ)

Bioventing

Procedures for Conducting Bioventing Pilot Tests and Long-Term Monitoring of Bioventing Systems, AFCEE 2004

Bioventing Degradation Rates of Petroleum Hydrocarbons and Determination of Scale-up Factors, A.A. Khan PhD Thesis, 2013

MPE involves the removal of LNAPL, groundwater, and vapor from the subsurface. There are multiple configurations of wells and equipment for MPE including:

• Using a submersible (electric) pump.
• Using a total fluids (pneumatic) pump.
• Adding well-bore vacuum extraction to either of these techniques which improves liquid recovery and also ventilates the vadose zone.
• Using a ‚Äúdrop tube‚Äù to entrain liquid in an (extracted) air stream, commonly known as Dual-Phase Extraction (DPE) or MPE.

Typically, sites with groundwater recovery rates greater than two (2) gallons per minute employ submersible pumps, and as hydraulic conductivity decreases, system designs move downward through the list to MPE. If minor LNAPL is present, total fluids pumps minimize emulsion with water, making LNAPL separation during treatment feasible.

MPE is applicable when contaminant concentrations are moderate to high, and depending on how the system is designed, it can be successful in a wide variety of situations. Most often MPE is used for LNAPL control/recovery, plume and vapor control (prevention of impact to a receptor), or, as one of the primary remedial technologies in a treatment train.

Critical Data Needs

Field pilot testing provides data on sustainable liquid recovery rates, air flows, drawdown, and the number of extraction points needed. Pilot testing is also an opportunity to collect additional soil/groundwater/vapor samples to refine the CSM and optimize the remediation plan. Pilot testing may take several days to allow static conditions to develop in the aquifer. Similar to AS/SVE and biosparging, a minimum of three monitoring points, at varying directions and distances from the test point(s), is typical to observe the effect of pilot testing. Existing groundwater monitoring wells may be used during testing. Pilot test wells should have similar construction to the intended final design so that testing data is directly applicable.

Advantages

• Multiple contaminant phases recovered simultaneously with a single technology.
• Provides hydraulic control.
• Provides vapor control.
• Effective for large and small treatment areas.

Limitations

• Moderate timeframe to achieve remedial objectives.
• MPE is relatively complicated and involves site construction, business interference, and permitting requirements.
• Significant troubleshooting issues associated with operation and maintenance.
• Moderate capital and operation and maintenance costs.
• If reinjection is considered, water conditioning and filtration will be necessary to avoid plugging the reinjection gallery prematurely, and a UIC permit will be required.
• Weather-proofing for winter operation is critical.
• Frequent maintenance to remove mineralization or biogrowth from treatment equipment.

Performance Metrics

System performance metrics will generally include measuring fluid flows, drawdown, vacuum ROI, and vapor emissions. Mass removal and LNAPL removal calculations should be performed and tracked relative to initial contaminant mass estimates. Performance metrics in vadose and/or smear zone contamination will generally be demonstrated through confirmatory soil sampling, and by groundwater monitoring for the dissolved phase plume.

References

Basics of Pump-and-Treat Ground-Water Remediation Technology, USEPA, 1990. EPA-600/8-90/003

Options for Discharging Treated Water from Pump and Treat Systems, USEPA, 2007. EPA 542-R-07-006

How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites, A Guide for Corrective Action Plan Reviewers (Chapter 11) EPA EPA 510-B-16-005 November 2016

Multi-Phase Extraction Engineering and Design, US Army Corps. Engrs. 1999. EM 1110-1-4010

Multi-Phase Extraction: State-of-the-Practice USEPA, 1999. EPA 542-R-99-004

ISCO reagents serve as oxidants that react with dissolved petroleum hydrocarbons (and other organic materials) causing rapid conversion of hydrocarbons to innocuous products such as carbon dioxide and water. ISCO reagents can also reduce sorbed phase saturated mass either through direct contact or phase partitioning from the sorbed phase to the dissolved phase. ISCO applications are appropriate for high to moderate dissolved phase concentrations and can be effective as a primary, secondary, or tertiary polishing step in a treatment train, depending on the identified contaminant concerns.

ISCO reagents are most typically introduced into the subsurface via pressurized injections using dedicated injection equipment. Other applications include French drain (or gravity feed) systems, and direct application to an open excavation. Common ISCO reagents include hydrogen peroxide, Fenton‚ Reagent (hydrogen peroxide catalyzed with iron), sodium persulfate, oxygen, and ozone (gas).

Critical Data Needs

Successful remediation using ISCO is dependent on a thorough understanding of subsurface conditions including, but not limited to, hydrogeology, contaminant distribution, mass storage and mass flux areas, and geochemical setting. Accurate contaminant mass estimates along with native soil oxidant demand estimates are needed within the identified targeted treatment area to establish a stoichiometric basis of optimal reagent dose. Critical data necessary for successful ozone gas injections include a determination of bacterial biomass, total organic carbon (TOC), iron (Fe), manganese (Mn), hydrogen sulfide (H2SO4), and carbonate levels.

Pilot testing should be considered to confirm the formations ability to accept the ISCO reagent. Additionally, pilot testing activities should aid in providing a basis for full-scale implementation. Baseline performance monitoring data should also be considered.

Advantages

• Rapid contaminant conversion (short timeframe).
• Relatively easy to work around physical and business restrictions within a targeted treatment area for pressurized injection application.
• Pressurized injection applications do not have capital or high infrastructure costs.
• High solubility of ozone.

Limitations

• Difficult to ensure contact between the ISCO reagent and targeted contaminant mass.
• Short reagent longevity. Dispersion cannot be relied on to facilitate contact.
• Can be cost prohibitive based on mass and soil oxidant demand estimates.
• Potential corrosive damage to tank systems and utilities, and surfacing of ISCO injectate in nearby basements, water wells, or surface water features.
• If present, common soil matrix (i.e., TOC, Fe, carbonates, etc.) can consume ozone prior to reaction with contaminants and limit effectiveness.
• Residual high pH is counterproductive to biodegradation so post-injection effort should be made to adjust pH to <8.

Performance Metrics

The primary performance metrics for ISCO applications are reductions in dissolved phase and sorbed phase concentrations within the targeted treatment area(s). Groundwater monitoring well data may be used to assess dissolved phase concentrations but other assessment locations within the targeted treatment area should also be considered. Secondary geochemical parameters specific to the oxidant and reaction may also be used to evaluate performance, distribution, and effect.

Carbon-based reagents are applied to targeted treatment areas where the activated carbon serves as a adsorption substrate for biodegradation of petroleum hydrocarbons under aerobic and anaerobic conditions. Activated carbon reagents are comprised of activated carbon that may be mixed with oxidants, bacteria, and nutrients. Activated carbon is most typically introduced into the subsurface via pressurized injections using dedicated injection equipment. Direct placement into an open excavation is another application method. Activated carbon applications are appropriate for moderate to low contaminant concentrations and as a secondary or tertiary polishing step in a treatment train.

Critical Data Needs

Successful remediation using carbon-based reagents is dependent on a thorough understanding of subsurface conditions including, but not limited to, hydrogeology, contaminant distribution, mass storage, mass flux areas, and geochemical setting. Contaminant mass estimates are needed within targeted treatment areas to establish a basis of optimal reagent amount.

Pilot testing should be considered to confirm the formations ability to accept material. Additionally, pilot testing activities should aid in providing a basis for full-scale implementation. Baseline performance monitoring data should also be considered.

Advantages

• Contaminant adsorption allows for sustained longevity of the bioremediation process.
• Carbon sequesters dissolved phase contaminants and reduces transport and flux.
• Relatively easy to work around physical and business restrictions within a targeted. treatment area for pressurized injection applications.

Limitations

• Difficult to ensure contact between with the targeted contaminant mass.
• Can be costly based on mass.
• Carbon can impact monitoring wells and compromise the ability of the well to be representative of the subsurface conditions.

Performance Metrics

The primary performance metrics for carbon-based reagent applications are reductions in dissolved phase and sorbed phase concentrations within the targeted treatment area(s). Groundwater monitoring well data may be used to assess dissolved phase concentrations unless there is evidence that a monitoring well has been impacted by carbon, but other assessment locations within the targeted treatment area should also be considered. Secondary geochemical parameters specific to the added amendments may also be used to evaluate performance, distribution, and effect.

SESR involves the injection of surfactants into the subsurface to desorb and mobilize LNAPL for subsequent mass recovery via extraction wells. Also referred to as surfactant flushing or soil washing, surfactant injections can be effective at treating the source of a dissolved phase plume to expedite site closure. SESR should be considered when persistent dissolved phase concentrations are observed because of residual quantities of LNAPL within the targeted pore spaces or to accelerate recovery of mobile LNAPL.

Critical Data Needs

Critical data needs for SESR includes the delineation of LNAPL targeted treatment zones to effectively design surfactant injections, LNAPL transmissivity values and gauged LNAPL in-well thicknesses are important data needs prior to implementation. LNAPL volume estimates and recovery estimates should also be considered.

Advantages

• Can effectively achieve LNAPL recovery.
• Short to very short time frame.

Limitations

• Potential access restrictions due to the presence of utilities and tank system components.
• Lithologic heterogeneity of targeted treatment areas.
• Costs and logistics associated with fluid treatment and disposal.

Performance Metrics

Performance metrics include reductions in LNAPL transmissivity, LNAPL recovery volumes, gauged in-well thicknesses, and dissolved phase contaminant concentrations over time.

Enhanced biodegradation is appropriate for relatively low contaminant concentrations or as a secondary or tertiary polishing step in a treatment train. Nutrients, such as nitrate and sulfate, are introduced into targeted treatment areas of the smear zone and saturated zone to enhance the biodegradation of petroleum hydrocarbons (biostimulation). The addition of bacteria (bioaugmentation) can also enhance the biodegradation of petroleum hydrocarbons.

Amendments are most typically introduced into the subsurface via pressurized injections using dedicated injection equipment. Other applications include French drain (or gravity feed) systems, and direct application to an open excavation.

Critical Data Needs

Successful remediation using enhanced biodegradation is dependent on a thorough understanding of subsurface conditions including, but not limited to, hydrogeology, contaminant distribution, mass storage and mass flux areas, and geochemical setting. Bench testing and or analytical data should be considered to identify the limiting factors prohibiting degradation processes to determine an optimal nutrient or bacteria addition. The collection of pre-introduction baseline data is important for petroleum contaminants of concern, nutrients, and geochemical parameters to enable comparison with post-introduction data.

Advantages

• Low cost.
• Applicable for low concentrations.
• Can be used in conjunction with biosparging to expedite remedial time frame

Limitations

• Potential access restrictions for injections (e.g., utilities and tank system components).
• Limiting factors may be difficult to determine and must be well understood prior to implementation.
• Potential long timeframe to achieve objectives.

Performance Metrics

Performance metrics for enhanced biodegradation include groundwater monitoring for primary and secondary parameters to track the effect of the nutrient addition on the targeted treatment area and overall subsurface environment. Primary parameters include petroleum contaminants of concern, and secondary parameters include nutrients (e.g., nitrogen, phosphorus, sulfate) and key geochemical parameters such as DO, pH, and ORP.

TD is a physical separation process that uses heat exchange to volatilize organic contaminants from a solid matrix. Air, combustion gas, or an inert gas is then used as a transfer medium to collect and treat the vaporized contaminants. All TD technologies consist of two steps: (1) heating the contaminated solids to volatilize the organic contaminants, and (2) treating the exhaust vapor stream to prevent emissions of the volatilized contaminants to the atmosphere. To be effective, TD systems must have adequate residence time, temperature, and mixing during the TD process. TD can be achieved by either in-situ or ex-situ treatment systems.

Critical Data Needs

Critical data needs for TD include characterizing the contaminants of concern, soil lithology, soil moisture content, and hydraulic conductivity. Depending on the contaminants of concern, soil is typically heated to temperatures ranging from 300 to 1,000 °F. For ex-situ TD, coarse-grained unconsolidated lithology such as sands and fine gravels are more readily treated because more surface area is exposed to the heating medium; clays may cause poor ex-situ TD performance by caking and inhibited heat transfer. Soil moisture content between 10% and 20% is optimal to mitigate dust problems during material-handling operations. Bench or pilot-scale treatability studies can be performed to assess the suitability of TD and for predicting the costs of full-scale operations.

Advantages

• Applicable for a wide range of volatile organic compounds, semivolatile organic compounds, and higher-boiling-point chlorinated compounds.
• Complete removal of contaminants.
• Fast to very fast remedial time frames.
• In-situ TD is essentially a ‚Äúclosed loop‚Äù system without the negative issues of noise, dust, fumes, and soil sorting posed by ex-situ TD.
• In-situ TD processes have very long residence times, which favor removal mechanisms that may be time dependent.
• In-situ TD increases soil permeability to enable effective treatment of clays and silts.
• Ex-situ TD remediated soils can be used as backfill.

Limitations

• High capital costs.
• High energy costs for the heat source.
• Availability of adequate onsite utilities (fuel or electricity).
• Noise, dust, fumes, odors, and soil sorting for ex-situ TD.
• Sufficient space for ex-situ TD system, soil preparation, and treated soil staging area.
• Moisture content above 20% can increase operating costs for ex-situ TD.
• Carbon footprint should be considered.

Performance Metrics

TD system performance is measured by comparing analytical results of untreated soil samples with analytical results of processed soils.

References

Thermal Conduction Heating for In-Situ Thermal Desorption of Soils, George L. Stegemeier (GSL Engineering, Inc.) and Harold J. Vinegar (Shell E&P Technology Applications and Research Co.), 2001

Thermal Desorption Ex Situ Soil Remediation Technology, Remediation Technologies Screening Matrix and Reference Guide, Version 4.0, Federal Remediation Technologies Roundtable.

Application Guide for Thermal Desorption Systems, Foster Wheeler Environmental Corporation and Battelle Corporation, Naval Facilities Engineering Service Center, April 1998.

EFR uses vacuum-enhanced recovery for mass removal of LNAPL from the saturated zone and perched LNAPL zones. LNAPL is primarily removed as a liquid but when used in conjunction with an induced vacuum, vapors are also extracted from the capillary fringe and vadose zone. Mass removal via EFR is most effective within a short time from when the release occurred (e.g., known catastrophic release).

Critical Data Needs

Critical data needs include delineation of LNAPL zones, and the measurement of LNAPL transmissivity from LNAPL baildown tests. LNAPL volume estimates and recovery estimates should also be developed.

Advantages

• Expedient recovery of migrating LNAPL.
• Effective in high-transmissivity coarse-grained lithology (sands and gravels).
• May be applied in heterogeneous soils where the EFR-induced vacuum can extract LNAPL from preferential pathways where LNAPL typically migrates and resides.

Limitations

• Not as effective in fine-grained low-permeability lithology such as silts and clays.
• Not effective as a dissolved-phase recovery technology.
• Waste management costs associated with fluid treatment and disposal.
• Long to very long remedial time frames for low-permeability soils.

Performance Metrics

Performance metrics for LNAPL recovery via EFR include decreasing LNAPL transmissivity (Tn) over time, and the quantity of LNAPL recovered as a percentage of the initial LNAPL volume estimate.

Petroleum contamination resides in the subsurface in four distinct phases: free (LNAPL), sorbed, dissolved, or vapor. Under favorable conditions, the combination of natural physical, chemical or biological processes will degrade chemicals of concern and reduce the risk associated with the release. In the context of petroleum releases, MNA refers to the attenuation of petroleum constituents in the dissolved phase, while NSZD focuses on the depletion of mass within the source zone. These natural remediation methods are typically considered as a tertiary step in a treatment train and should only be considered when contaminant conditions are stable and the release sources have been removed, repaired or replaced.

Critical Data Needs

Estimating and confirming the rate at which these natural processes degrade or deplete contaminants of concern is a critical data need for these technologies. In addition, a thorough understanding is needed of subsurface conditions including, but not limited to, hydrogeology, contaminant distribution, and geochemical setting. OPS‚Äô MNA tool or fate and transport modeling may be used as a line of evidence to support MNA. The MNA tool is available in the MNA Feasibility tab in the Corrective Action Plan Report format.

Advantages

• No capital or infrastructure costs.
• Minimal physical and/or business restrictions.

Limitations

• Long to very long time frame.
• A lot of analytical data may need to be collected to support the degradation rates and/or understand the MNA and NSZD processes.

Performance Metrics

MNA performance metrics for dissolved phase contamination include groundwater monitoring to track reductions in COC concentrations and plume size. Secondary groundwater parameters such as nitrate, sulfate, iron, temperature, and pH, should be monitored to track geochemical conditions. NSZD performance metrics include measuring the vertical distribution of soil gas constituents (O2, CO2, methane, and vapor phase petroleum hydrocarbons) over space and time, and estimating petroleum hydrocarbon mass loss rates and quantities through volatilization and biodegradation processes.

References

ASTM E1943: Standard Guide for Remediation of Groundwater by Natural Attenuation at Petroleum Release Sites

Evaluating Natural Source Zone Depletion at Sites with LNAPL ITRC, April 2009

System installation of the selected remedial technology should include obtaining all required access agreements, permitting requirements, equipment procurement, contractor bids (if necessary) and an anticipated installation schedule and time frame (which should include post-remediation monitoring).

Perform start-up activities and utilize optimization activities to identify any system limitations that may not have been evident or observed during pilot testing activities (i.e., critical data collection). Examples include blower/compressor size limitations, vacuum influence and flow rate irregularities.

Detail O&M activities related to remediation system in the number (or frequency) of O&M visits, tasks to be completed, data to be collected during O&M visits and, if warranted, additional optimization efforts to maximize remediation efficiency.  Perform careful monitoring of the performance metrics defined in the CAP Submittal section during the O&M phase.  This monitoring will allow OPS to evaluate the remediation progress and determine when a remedial technology has been applied to the maximum extent practicable. 

Remedial milestones, as defined above, are logical points to evaluate remedial performance data during the O&M phase and can also be used to demonstrate that the specific remedial technology has been applied to the maximum extent practicable. For example, submitting a monitoring and remediation report could be an appropriate juncture to provide the status and efficacy of the remedial technology being implemented.

Evaluate the performance metric data identified in the development phase to assess the progress of the remedial approach and to measure progress toward the remediation milestones, end points, and objectives.

Remediation milestones are junctures when decisions need to be made, such as moving to the next step/phase in a treatment train strategy, verifying that performance metrics have been met or requesting NFA and site closure. Evaluate the remediation milestones throughout CAP implementation.

After a full-scale remedial technology has reached a remedial milestone, evaluate the long-term effectiveness of the technology for meeting remedial objectives.

Below are some data evaluation examples.

• Collecting interim soil confirmation samples to determine whether the system has also reduced subsurface soil concentrations to SSTLs or RBSLs when off-gas readings associated with an SVE system have reached asymptotic levels
• Collecting groundwater plume data after introducing in-situ amendments that may indicate whether SSTLs or RBSLs have been achieved
• Drilling intra-plume confirmation soil borings/monitoring wells to ensure that smear zone soils and the dissolved phase groundwater plume have been reduced to SSTLs or RBSLs

Continue to evaluate performance metrics after achieving a remedial milestone to monitor the progress and efficacy of remediation. Examples include:

• Estimating the mass reduction achieved by the remedial technology and the mass remaining in a completed exposure pathway (i.e., subsurface vadose soil leaching to groundwater) based on the original SCR mass estimates
• Estimating the decrease in LNAPL mass recoverability, mobility and migration
• Estimating the reduction in the mass flux migrating downgradient within the dissolved phase groundwater plume as a direct result of mass reduction that occurred within the source area

Based on the results of the remedial performance evaluation, the remedial system may require optimization adjustments, or you may implement the next remedial sequence in the treatment train.

After the remedial performance data evaluation has been completed, answer the following questions to determine if the remedial objectives have been met.

• Are POEs protected?
• Has mass reduction been achieved?
• Was LNAPL recovery achieved?
• Have subsurface vadose soils been remediated to SSTLs or RBSLs?
• Has the smear zone been adequately treated to prevent further leaching to the dissolved phase groundwater plume?
• Has the dissolved phase plume been remediated to SSTLs or RBSLs?
• Has the downgradient or off-site mass flux been reduced?

If the answers to any of these questions indicate that the remedial objectives have not been met, identify, address and incorporate data gaps into the CSM to move the CAP implementation forward. This may require moving to the next sequence, or phase, in the treatment train strategy to progress the event to closure.

When all exposure pathways have been eliminated, request an NFA for the release event.

Leaking Underground Storage Tanks Corrective Action Resources

ITRC In Situ Chemical Oxidation

ITRC Mass Flux and Mass Discharge

ITRC MTBE and Other Oxigenates

ITRC Passive Samplers

ITRC Remediation Process Optimization

ITRC Remediation Risk Managements