U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

For more information on Surfactant or Cosolvent Flushing, please contact:

Jim Cummings
Technology Assessment Branch

PH: (703) 603-7197 | Email: cummings.james@epa.gov



In Situ Flushing

Guidance

Guidance on in situ flushing technology practices—conceptual design processes, applicability to various contaminants and site conditions, and implementation and performance monitoring—is readily available. This page provides basic information on flushing agents and identifies additional resources for planning and designing flushing remedies, monitoring system performance, and understanding the regulatory context of implementing in situ flushing technology.


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Technology Planning and Design | Technical Resources | Review Articles | Performance Monitoring for In Situ Flushing | Performance Monitoring Resources | Regulation

Technology Planning and Design

The techniques employed the most in soil flushing are surfactant and cosolvent flooding for fuels and chlorinated solvents. There are many types of surfactants (cationic, anionic, nonionic), and while adjustments can be made in the fluid composition, anionic or nonionic surfactants are generally used. This is because their negative or neutral charge reduces the possibility of their sorption to negatively charged clay particles. They also are generally less toxic than cationic surfactants (EPA 2006).

Surfactants are commonly constructed with hydrophobic and hydrophilic chemical components, meaning that one end of the molecule is attracted to oil (or organic compounds) and the other to water. Surfactants chosen primarily to increase the contaminant (generally a NAPL) solubility are used in a solubilization flood. Surfactants chosen to produce ultra-low interfacial tensions are employed in a mobilization flood (Kueper et al. 1997). Mobilization flooding is an option only when there is a high degree of certainty that the solution can be recovered, such as with a competent bedrock or capillary barrier underlying the treatment zone (EPA 2006).

Surfactant flooding involves the preparation of low-viscosity surfactant solutions that are pumped through the contaminated zone by introduction at injection points and removal from extraction points. Polymer amendments that will increase the viscosity of the surfactant solution might be required for higher viscosity contaminants (e.g., creosote) when temperature augmentation for viscosity reduction is not feasible. The surfactant flooding wellfield generally will be composed of dedicated surfactant injection and extraction points, and water injection points for hydraulic control (NFESC 2003).

Electrolytes and cosolvents are other additives that a typical surfactant solution might contain. In addition to being effective with the target contaminant, the surfactant solution is tailored to be compatible with the site-specific geologic conditions, soil, soil pore water, and groundwater (if applicable). For example, a flushing solution that is compatible with a site's soil chemistry will not adhere to the soil and reduce its effective porosity and permeability. A cosolvent, such as isopropanol, can be used to improve the surfactant solubility in solution and provide the surfactant and contaminant solution with an acceptable viscosity. Chemicals added to the surfactant solution might require treatment along with the contaminant at the recovery end (NAVFAC 2002). Surfactants often can be recycled.

Cosolvents, usually alcohols, are chemicals that dissolve in both water and NAPL. In an alcohol flood, the alcohol may partition into both the NAPL and water phases. Partitioning affects the viscosity, density, solubility, and interfacial tension of the NAPL (Kueper et al. 1997). The physical properties of the co-dissolved NAPL vary with the amount of alcohol available for interaction, and whether the alcohol preferentially dissolves into the NAPL or into the water. Where contact is made between NAPL and cosolvent, complete miscibility is achievable and results in a pumpable solution. Depending upon the density of the NAPL and the proportions of alcohol and water, the solution may be more or less dense than water (EPA 2006). Cosolvents that microbes can use as substrates have the added advantage of promoting bioremediation if they are used at nontoxic levels (Adamson et al. 2011).

Nonvolatile metals are among the classes of chemical compounds treated successfully by in situ flushing (Roote 1997, Lestan et al. 2008, Hashim et al. 2011). The particular reagent necessary is dependent not only on the metal, but its chemical form or species. The pH (buffering capacity) of the soil can affect the amount of flushing solution needed, especially when acids and bases are used. Acidic solutions are applicable for removal of metals and basic organic contaminants; dilute acid solutions also can be used for flushing some inorganic-metal salts, such as carbonates of nickel, zinc, and copper. Metals might also require reducing agents or chelating or complexing agents, although Hashim et al. (2011) cautions that chelate flushing tends to destroy the soil profile because it strips major cations important for plant nutrition and maintenance of soil structure along with the metals. Reductants and oxidants can convert heavy metals to more soluble compounds, and basic solutions might be used to treat phenols and metals bound to the soil organic fraction (Roote 1997, Hashim et al. 2011).

Many site-specific factors can affect the selection, design, and effectiveness of a flushing technology:

  • The impact of lateral heterogeneity, such as the presence of discontinuous silt lenses.
  • Preferential pathways for water movement caused by either discontinuities in subsurface properties or features such as clastic dikes, which can limit flushing effectiveness if contaminated zones are bypassed.
  • Slope to layers or inherent layer anisotropy that could impose lateral flow.
  • Surface features that cause ponding of water rather than infiltration. These types of uncertainties are considered in the design of a soil flushing system, including design of a groundwater capture system in terms of the necessary capture zone. Quantification of surface infiltration rates for a site also has significance when evaluating the applicability of soil flushing (Truex et al. 2010).

Before implementing surfactant and/or cosolvent flushing, performance of bench-scale treatability testing is recommended to ensure the selection of the agents best suited to the type of contamination and the site-specific soil and geochemical conditions. Modeling of subsurface conditions is commonly done to identify the best delivery system (NAVFAC 2002). Soil flushing tends to work best at sites that have spaces in the soil that permit the movement of the flushing solution through it, such as sands and gravels. The permeability of the strata can be measured as hydraulic conductivity, with favorable values in the range of 1.0 x10-4 cm/sec or higher (ITRC 2003), and limiting factors in the range of <1.0 x 10-5 cm/sec. Heterogeneous soil reduces the efficiency of the flood sweep and may prevent optimum contact between the agent(s) and the target contaminant. Flushing of relatively homogeneous but lower permeability (between 10-4 and 10-5 cm/sec) units is possible, but it requires a high induced gradient to move the agent, while greatly increasing the remediation time. Other soil factors that can adversely affect efficiency are high cation exchange capacity, high buffering capacity, high organic soil content, and pH (NAVFAC 2002).

Costs are dependent on whether flushing is used as a long-term source removal technique or as a temporary pathway management solution in conjunction with other technologies (CL:AIRE 2011). The U.S. Army Corps of Engineers explored cost driver information and cost analysis for soil flushing using the 2006 version of the Remedial Action Cost Engineering and Requirements (RACER) software. The RACER analysis identified soil permeability as the primary cost driver. Soils with lower permeability are more recalcitrant to flushing and thus can increase remediation time significantly, which increases costs. Depth to groundwater is the secondary cost driver—a deeper water table increases the cost to complete (FRTR 2007). Other factors to consider include the waste type and the quantity to be treated, as well as design and engineering, which can be a considerable expense. Purchase of surfactants can be a significant component of the total cost, especially if surfactant concentrations of 4 to 8 wt% are used; however, as surfactant concentrations are lowered toward 1 wt% or lower, and as surfactant recovery and reuse are implemented, costs become more economical (NRC 2004).

The Water Science and Technology Board of the National Research Council pointed out in 2004 that additional research is needed to advance good sweep efficiency during flushing, to optimize the implementation of surfactant/cosolvent technologies in karst and fractured bedrock formations, to evaluate the combination of flushing technologies with other source zone and/or plume remedial technologies, and to evaluate the long-term impact of contaminant mass removal on post-flushing water flooding and natural attenuation (NRC 2004). Research continues in these areas.

References:

Adamson, D.T., T.M. McGuire, C.J. Newell, and H. Stroo. 2011. Sustained treatment: Implications for treatment timescales associated with source-depletion technologies. Remediation Journal 21(2):27-50.

Contaminated Land: Applications in Real Environments (CL:AIRE). 2011. Contaminated Land Remediation: Final Report. Environment Agency, Defra Research Project SP1001, London, UK.

Federal Remediation Technologies Roundtable (FRTR). 2007. 4.7: Soil Flushing. Remediation Technologies Screening Matrix, Version 4.0.

Hashim, M.A., S. Mukhopadhyay, J.N. Sahu, and B. Sengupta. 2011. Remediation technologies for heavy metal contaminated groundwater. Journal of Environmental Management 92(10):2355-2388.

ITRC. 2003. Technical and Regulatory Guidance for Surfactant/Cosolvent Flushing of DNAPL Source Zones.

Kueper, B. et al. 1997. Technology Practices Manual for Surfactants and Cosolvents (TR-97-2). Advanced Applied Technology Demonstration Facility Program, Rice University.

Lestan, D., C.-L. Luo, and X.-D. Li. 2008. The use of chelating agents in the remediation of metal-contaminated soils: a review. Environmental Pollution 153(1):3-13.

National Research Council (NRC). 2004. Contaminants in the Subsurface: Source Zone Assessment and Remediation. National Academies Press, Washington, DC.

NAVFAC. 2002. Adobe PDF LogoSurfactant-Enhanced Aquifer Remediation (SEAR) Design Manual, NFESC Technical Report TR-2206-ENV.

Roote, D.S. 1997. Adobe PDF LogoIn Situ Flushing: Technology Overview Report. Ground-Water Remediation Technologies Analysis Center, TO-97-02.

Truex, M.J. et al. 2010. Adobe PDF LogoEvaluation of Soil Flushing for Application to the Deep Vadose Zone in the Hanford Central Plateau. PNNL-19938.

U.S. EPA. 2006. Adobe PDF LogoIn Situ Treatment Technologies for Contaminated Soil: Engineering Forum Issue Paper. EPA 542-F-06-013.

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Technical Resources

Chelating Agents for Land Decontamination Technologies
Tsang, D.C.W., I.M.C. Lo Rao, and Y. Surampalli (eds.).
American Society of Civil Engineers, Reston, VA. ISBN: 978-0-7844-1218-3, 294 pp, 2012

Chelating agents (or chelants) refer to ligands that can occupy multiple positions in the inner coordination sphere of the central metal ion, leading to the formation of multidentate metal-chelant complexes (or chelates). Chelating agents are able to enhance metal extraction from contaminated soil or sediment and facilitate metal mobility in the subsurface. This book focuses on the engineering applications of chelating agents for soil washing, soil flushing, phytoremediation, and electrokinetic remediation.

Contaminants in the Subsurface: Source Zone Assessment and Remediation
National Research Council, Committee on Source Removal of Contaminants in the Subsurface. National Academies Press, Washington, DC. ISBN: 030909447X, 383 pp, 2004

After discussing the definition of 'source zone' and the characterization thereof, this report reviews the suite of technologies available for source remediation and their ability to reach a variety of cleanup goals, from meeting regulatory standards for ground water to reducing costs. The report proposes elements of a protocol for accomplishing source remediation that should enable project managers to decide whether and how to pursue source remediation at their sites.

Contaminated Land Remediation: Final Report
Contaminated Land: Applications in Real Environments (CL:AIRE). Environment Agency, Defra Research Project SP1001, London, UK. 120 pp, 2011

This report summarizes the current understanding and use of 21 cleanup technologies in the UK, identifies current and likely future factors influencing their selection, and sets out the relative economic, environmental, and social costs and benefits (i.e., the sustainability) of each technique. For each technology (including in situ flushing), the report gives a brief description; information concerning the effectiveness of each method in addressing different contaminants; circumstances (e.g., geology, hydrogeology, contaminant form) that might affect technology implementation; advantages and disadvantages; and barriers to use.

Delivery and Mixing in the Subsurface: Processes and Design Principles for In Situ Remediation
Kitanidis, P.K. and P.L. McCarty (eds.).
Springer, New York. ISBN: 978-1-4614-2238-9. SERDP-ESTCP Environmental Remediation Technology, Vol. 4, 325 pp, 2012

This technology monograph describes the principles of chemical delivery and mixing systems and their design and implementation for effective in situ remediation. In situ technologies discussed include chemical oxidation, surfactant/cosolvent flushing, subsurface reactors, recirculation systems, PRBs, gas delivery via sparging, and intrinsic remediation in natural-gradient systems. Numerous case studies are provided. Table of contents and abstracts.

Adobe PDF LogoEvaluating LNAPL Remedial Technologies for Achieving Project Goals
Interstate Technology & Regulatory Council (ITRC) LNAPLs Team. LNAPL-2, 144 pp, 2009

This guidance provides a framework to help stakeholders select the best-suited remedial technology for an LNAPL site and outlines which technologies apply in different site situations. Coverage includes water flooding and flushing with surfactants or cosolvents.

INDOT Guidance Document for In-Situ Soil Flushing
Lee, L.S., X. Zhai, and J. Lee, Purdue Univ., West Lafayette, IN.
SPR-2335; FHWA/IN/JTRP-2006/28, 49 pp, 2007

Contains information ranging from the basic chemistry and mechanisms of cosolvent and surfactant flushing to the key factors that need to be considered during the selection, design, and implementation of this technology. Also provides information on several categories of contaminants subject to in situ flushing. This text was written to provide general guidance rather than as a design manual. Additional information: Lab Testing and Field Implementation of Soil Flushing

Adobe PDF LogoIn-Situ Flushing Technologies: Combined Remedies
Pennell, K.D.
NIEHS/EPA Combined Remedies Workshop, June 27-28, 2006, Tufts University, Medford, MA. 14 slides, 2006

This presentation addresses steps to reduce actual and perceived flushing costs, incomplete mass removal, surfactant compatibility with bioremediation, and minimizing or countering downward mobilization of contaminants, with references to more detailed sources of information.

Adobe PDF LogoInnovative Site Remediation Technology, Vol. 3: Soil Washing/Soil Flushing
Anderson, W.C. (ed.). American Academy of Environmental Engineers, Annapolis, MD. 174 pp, 1995

Remediation Hydraulics
Payne, F.C., J.A. Quinnan, and S.T. Potter.
CRC Press, Boca Raton, FL. ISBN: 9780849372490, 432 pp, 2008

This text addresses the need to predict and control fluid movement in the subsurface. It discusses how to conduct realistic assessments of contaminant plume structure and achieve contact between injected reagents and target compounds; offers instruction for the design and application of reagent delivery systems that support in situ chemical and biological treatment strategies for groundwater cleanup; and introduces tracer design and interpretation methods for cost-effective design of large-scale injection systems.

Adobe PDF LogoSelecting and Assessing Strategies for Remediating LNAPL in Soils and Aquifers
Johnston, C.D.
CRC for Contamination Assessment and Remediation of the Environment, Adelaide, Australia: CRC CARE Technical Report 18, 194 pp, 2010

This report provides guidance in selecting and matching the performance of remediation technologies to a range of subsurface settings, risk reduction targets, and concerns. Surfactant, cosolvent, and natural flushing are discussed. The emphasis is on LNAPL that has infiltrated the water table. One of the aims is to identify the gaps in the current understanding of remediation process and performance in the various subsurface settings.

Adobe PDF LogoSurfactant Selection for Enhanced Contaminant Extraction
Sabatini, D., R. Knox, and J. Harwell.
Groundwater Quality: Remediation and Protection. International Association of Hydrological Sciences, IAHS Publication No 250:361-366(1998)

This paper discusses surfactant-enhanced solubilization versus mobilization for a variety of contaminants. Solubilization increases the density of the contaminant-loaded surfactant solution by only several wt% compared to mobilization, which involves a much more dense, moving front of DNAPL. It is important to identify from the outset whether solubilization or mobilization of DNAPL is desired because not all surfactants can accomplish the low interfacial tension necessary to conduct a mobilization flood. Unit processes for contaminant-surfactant separation and surfactant re-use are summarized and illustrated by examples from field demonstrations.

Adobe PDF LogoSurfactant-Enhanced Aquifer Remediation (SEAR) Design Manual
Naval Facilities Engineering Service Center. NFESC Technical Report TR-2206-ENV, 110 pp, 2002

Adobe PDF LogoSurfactant-Enhanced Aquifer Remediation (SEAR) Implementation Manual
Londergan, J. and L. Yeh. Naval Facilities Engineering Service Center. NFESC Technical Report TR-2219-ENV54, 54 pp, 2003

Adobe PDF LogoSurfactant-Enhanced DNAPL Remediation: Surfactant Selection, Hydraulic Efficiency, and Economic Factors
Sabatini, D.A., R.C. Knox, and J.H. Harwell.
EPA 600-S-96-002, 15 pp, 1996

Surfactants and Cosolvents for NAPL Remediation: a Technology Practices Manual
Lowe, D.F.; C.L. Oubre; C.H. Ward (eds.). Lewis Publications, Boca Raton, FL. ISBN: 0-8493-4117-5. 448 pp, 1999. Additional information: The Table of Contents is available at the publisher's website.

Surfactants and Interfacial Phenomena, 4th Edition
Rosen, M.J. and J.T. Kunjappu.
John Wiley & Sons, ISBN-10: 0-470-54194-6; ISBN-13: 978-0-470-54194-4, 616 pp, 2012

Using a minimum of mathematics, the text describes the properties and applications of surfactants. It explains the mechanisms by which these materials operate in interfacial processes such as foaming, wetting, emulsion formation, and detergency, and shows the correlations between a surfactant's chemical structure and its action. This update features coverage of relevant new literature appearing after the third edition.

Adobe PDF LogoSurfactants/Cosolvents: Technology Evaluation Report
Jafvert, C.T.
Ground-Water Remediation Technologies Analysis Center, TE-96-02, 50 pp, 1996

A DNAPL source zone was established within a sheet-pile isolated cell through a controlled release of PCE to evaluate DNAPL remediation by in situ cosolvent flushing. Ethanol was used as the cosolvent, and the main remedial mechanism was enhanced dissolution based on the phase behavior of the water/ethanol/PCE system. Over a 40-day period, 64% of an initial mass of 83 L of PCE was removed by flushing the cell with a solution of 70% ethanol and 30% water; however, tracer results suggest that some PCE was inaccessible to the ethanol solution, which led to the inefficient PCE removal rates observed.

Adobe PDF LogoTechnical and Regulatory Guidance for Surfactant/Cosolvent Flushing of DNAPL Source Zones
Interstate Technology & Regulatory Council, Dense Nonaqueous Phase Liquids Team, Washington, DC. DNAPLs-3, 151 pp, 2003

Adobe PDF LogoTechnologies for Dense Nonaqueous Phase Liquid Source Zone Remediation: Technology Evaluation Report
Fountain, J.C. TE-98-02. 1998

Technology Practices Manual for Surfactants and Cosolvents
Kueper, B., et al. Advanced Applied Technology Demonstration Facility (AATDF) Program, Rice University. TR-97-2, 1997.

This manual is intended to assist decision makers with the evaluation and potential application of surfactant/cosolvent flushing for the remediation of subsurface contamination. The report provides a basic understanding of the technologies, their applicability and limitations, and an understanding of the factors to be considered when implementing projects.

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Review Articles

Coupling Surfactants/Cosolvents with Oxidants for Enhanced DNAPL Removal: A Review
Dugan, P.J., R.L. Siegrist, and M.L. Crimi.
Remediation Journal 20(3):27-49(2010)
Additional information: Slide presentationAdobe PDF Logo; Abstract

Remediation Technologies for Heavy Metal Contaminated Groundwater
Hashim, M.A., S. Mukhopadhyay, J.N. Sahu, and B. Sengupta.
Journal of Environmental Management 92(10):2355-2388(2011)
Abstract

Soil Flushing : A Review of the Origin of Efficiency Variability
Atteia, O., E. Del Campo Estrada, and H. Bertin.
Reviews in Environmental Science and Biotechnology 12(4):379-389(2013)

Although surfactant alone gives efficiencies of 80-85% in lab experiments, the amounts of product required for field injection may not be economically sustainable. The literature indicates that soil flushing efficiency can vary from 0% to almost 100% in the field, which illuminates the importance of knowledge concerning the site characteristics and contaminant location, amount, and behavior as well as other factors. For initial saturations lower than 1%, soil flushing may be an inefficient technique. This paper provides an overview of recent lab, pilot, and field studies of soil and groundwater remediation, with a focus on chlorinated solvents.

Adobe PDF LogoSurfactant-Enhanced Remediation of Contaminated Soil: A Review
Mulligan, C.N., R.N. Yong, and B.F. Gibbs.
Engineering Geology 60(1-4):371-380(2001)

Adobe PDF LogoThe Use of Chelating Agents in the Remediation of Metal-Contaminated Soils: A Review
Lestan, D., C.-L. Luo, and X.-D. Li.
Environmental Pollution 153(1):3-13(2008)

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Performance Monitoring for In Situ Flushing

The performance of an in situ soil flushing system depends largely upon the amount of contact achieved between the flushing solution and the contaminants, and the effectiveness of recovery. The appropriateness of the flushing solution, the soil adsorption coefficients of the contaminants, and the permeability of the soil are also key factors (EPA 1997).

For inorganic contaminants that might be flushed with plain water, the increase in groundwater concentrations of the target contaminant as flushing begins indicates its transfer from the vadose zone to the saturated zone, where it can be captured by extraction wells. At perchlorate-contaminated Site 285, Edwards Air Force Base, neutron logging was used to monitor wetting front migration down to groundwater, and a potassium bromide tracer released as a slug at the start of soil flushing provided confirmation that the introduced water had reached the aquifer. A perchlorate spike was detected in the groundwater after ~20 weeks of flushing (Battey et al. 2006). With continued flushing of treated water through the vadose and saturated zones, contaminant groundwater concentrations are expected to decline at Site 285. The effectiveness of the treatment for contaminated soil can be documented via confirmation soil boreholes after groundwater contaminant concentrations return to their pre-soil flushing levels (Battey et al. 2007).

The applications most often employed in soil flushing are surfactant and cosolvent flooding for fuels and chlorinated solvents (EPA 2006). The table below provides a list of performance monitoring parameters for surfactant and cosolvent flushing. Most of the table addresses surfactant flushing, which requires a greater amount of monitoring compared with cosolvent flushing alone because of its greater capacity to mobilize NAPL. The type and amount of data needed is site specific and will be affected by the site hydrogeology and size and architecture of the source area.

Discussions of the different sampling and analysis methods appropriate for surfactant/cosolvent flushing can be found in NFESC 2003 and ITRC 2003.

For assessing the performance of a chemical flood, the most direct method would be to measure the amount of DNAPL mass removed, but this approach is complicated by the uncertainty associated with estimating the initial amount of DNAPL mass present at a site. This uncertainty also affects estimating (1) the final average NAPL saturation (i.e., the volume percent of the pore space that still contains NAPL) and (2) the percentage of the initial contaminant mass removed. The performance of a surfactant/cosolvent flushing system generally is measured by the following metrics: the source strength or mass flux of contaminants emanating from the source; the percentage of the injected chemicals recovered (a measure of the efficiency of hydraulic control); and the risk associated with any NAPL remaining after treatment, as well as the risk reduction accomplished with the NAPL removal action (ITRC 2003).

Several indirect techniques can be used to measure the success of a surfactant flood: tracers, such as the partitioning interwell tracer test, where the measurement is performed before and after the flood; contaminant flux measurements, also performed before and after the flood; and geophysical techniques, such as electrical resistivity tomography, performed during the flood. Descriptions of other general techniques that might be useful can be found in Remediation Measurement Tools.

Performance Monitoring Parameters for In Situ Flushing of NAPLs

Sampling Location

Performance Parameter

Method

Data Use

Recommended Frequency of Analysis

Fresh Surfactant Tank Batches

Surfactant

Potentiometric Titration, High Performance Liquid Chromatography, Evaporative Light Scattering, and UV or Fluorescence (NFESC 2003).




Determine if concentrations of the flush are within specifications for all three components. Note that for some cases small fluctuations in electrolyte concentrations can have profound effects on the phase performance of the injectant (ITRC 2004).

Before injection from tank begins. In batch mixing, samples to be taken from top and bottom of tank to verify uniform mixing (NFESC 2003).

Electrolyte1

Specific conductance by surrogate (hand-held meter), SW-846: 6010C for confirmation of Ca+2 or Na+1 concentrations (NFESC 2003).

Ion Selective Electrode (ISE)3 for field measurement of Ca+2 or Na+1

Cosolvent, if present2

If Alcohol, SW-846: 8015C (GC) or SW-846: 8260B (preferably field for either).

Overall Quality

Phase behavior test (NFESC 2003).

To determine if injectant mixing with site NAPL will yield phase results comparable to the laboratory phase behavior standards.

Temperature, pH, Specific Conductance

Hand-held meter

Provide baseline indicator parameters.

Injection Wells

Water Levels

Manual water/air interface meter, Pressure transducer

Provides warning of potential plugging of soil pore space

Baseline and frequently during injection. Note that NFESC 2003 recommends the pressure transducer as it can provide near-continuous readings.

Source Area Monitoring Wells

Free-phase NAPL levels

Oil/water interface probe.

Identify mobilization of free phase NAPL. Note that NFESC 2003 recommends to the extent possible that identified free phase NAPL be removed from a site before surfactant flushing begins.

Periodically during injection. Exact number of times is site specific (ITRC 2003).

Dissolved Contaminants of Concern (COCs) and degradation products2

Non-halogenated VOCs, EPA SW-846: 8015C (GC)

Aromatic and halogenated VOCs, 8021B (GC), or

VOCs, 8260B (GC/MS)(preferably field)

SVOCs,  8270D (GC/MS) (preferably field). Note that for some less common NAPLs, there might be specific tests for them that yield better detection limits, if needed.

Monitors cleanup progress at that sampling point. Note that NFESC 2003 recommends multi-level sampling wells instead of single-screen wells to determine if uniform cleanup is occurring.

Baseline, periodically during injection process, and after flush is over. Exact number of times is site specific (ITRC 2003).

Injectant Concentrations:

     Surfactant

Potentiometric Titration, High Performance Liquid Chromatography, Evaporative Light Scattering, and Ultraviolet or Fluorescence (NFESC  2003)

ISE for field measurement

Provides information on whether flushing fluid is reaching the sampling point (fluid dispersion). After complete flushing is over, including final water flush, provides information on whether any surfactants are left.

Periodically during injection process, and after flush is over. Exact number of times is site specific (ITRC 2003).

     Electrolyte1

Specific conductance by surrogate (hand held meter), SW-846: 6010C for confirmation of Ca+2 or Na+1 concentrations (NFESC 2003)

ISEs for field measurement of Ca+2, Na+1.

     Cosolvent, if present2

If Alcohol, SW-846: 8015C (GC) or SW-846: 8260B (preferably field for either). Note for GC or GC/MS methods NFESC 2003 recommends using a packed column rather than the capillary column usually deployed with these methods because of potential clogging issues.

Temperature, pH, Specific Conductance

Hand held probes, in-line cells.

Provides information on potential changes in subsurface and injectant chemistry (NFESC 2003).

Groundwater Levels

Water/air interface probes, pressure transducers.

Provides information on whether hydraulic control is being maintained. Provides information in conjunction with the injection well water levels on whether there may be a loss in permeability due to the injection NFESC 2003).

Perimeter Monitoring Wells

Dissolved COCs and degradation products

Non-halogenated VOCs, SW-846: 8015C (GC)

Aromatic and halogenated VOCs, 8021B (GC), or VOCs, 8260B (GC/MS) (preferably field)

SVOCs, SW-846: 8270D (GC/MS) (preferably field). Note that there might be specific tests for less common NAPLs that yield better detection limits, if needed.

Used to verify hydraulic control. A steep rise in concentrations would mean it is not in control (NFESC 2003).

Frequency is site specific (NFESC 2003, ITRC 2004).

Injectant Concentrations1

     Surfactant

Potentiometric Titration, High Performance Liquid Chromatography, Evaporative Light Scattering, and Ultraviolet or Fluorescence (NFESC 2003)

ISE for field measurement

Used to verify hydraulic control. There should not be any injectant materials in these wells during the flushing operation (NFESC 2003).

     Electrolyte1

Specific conductance by surrogate (hand held meter), SW-846: 6010C for confirmation of Ca+2 or Na+1 concentrations (NFESC 2003).

ISEs for field measurement of Ca+2, Na+1.

     Cosolvent, if present

If Alcohol, SW-846: 8015C (GC) or SW-846: 8260B (preferably field for either).

Temperature, pH, Specific Conductance

Hand-held probe, in-line cell.

Provides information on potential changes in subsurface and injectant chemistry (NFESC 2003).

Groundwater Levels

Water/air interface probes, pressure transducers.

Used to verify hydraulic control (NFESC 2003).

Extraction Well Effluents

Dissolved COCs and degradation products2

Non-halogenated VOCs, SW-846: 8015C (GC)

Aromatic and halogenated VOCs, 8021B (GC), or VOCs, SW-846: 8260B (GC/MS) VOCs (preferably field)

SVOCs, 8270D (GC/MS) (preferably field). There might be specific tests for the less common NAPLs that yield better detection limits, if needed.

Used to measure cleanup progress. Also used to calculate the amount of contaminants removed (NFESC  2003 and ITRC 2003).

Site specific; however, to ensure an adequate amount of certainty in the contaminant removal mass, estimating at least 20 to 30 samples from each extraction well is recommended (NFESC 2003 and ITRC 2003). NFESC 2003 also suggests considering in-line auto sampling and GC analysis for COC recovery calculations.

Injectant Concentrations:

     Surfactant

Potentiometric Titration, High Performance Liquid Chromatography, Evaporative Light Scattering, and UV or Fluorescence (NFESC 2003). ISE for field measurement.

Used to determine injectant recovery rates (NFESC 2003).

Site specific (ITRC 2003).

     Electrolyte1

Specific conductance by surrogate (hand held meter), SW-846 6010C for confirmation of Ca+2 or Na+1 concentrations (NFESC 2003).

ISEs for field measurement of Ca+2, Na+1.

     Cosolvent, if present2

If Alcohol, SW-846: 8015C (GC) or SW-846: 8260B (preferably field for either).

Temperature, pH, Specific Conductance

Hand-held probe, in-line cell.

Provides information on potential changes in subsurface and injectant chemistry (NFESC 2003).

As needed for process monitoring. Taken at the same rate as COC sampling is done (NFESC 2003).

Flow Rates

Flow meters, bucket tests (NFESC 2003).

For performance monitoring the flow rate is associated with the COC contaminant concentration to develop a contaminant mass removal rate.

Oil-Water Separator Tank

NAPL

Volumetric.

Determines NAPL mass removal for use in calculating total mass removal.

Site specific (NFESC 2003).

Statistically Determined, Random Soil Cores in the Source Zone Area

COCs, degradation products, and NAPL

Non-halogenated VOCs, SW-846: 8015C (GC)

Aromatic and halogenated VOCs, 8021B (GC), or VOCs, 8260B (GC/MS) (preferably field)

SVOCs, 8270D (GC/MS) (preferably field). There might be specific tests for the less common NAPLs that yield better detection limits, if needed.

For DNAPL, visual observation or indicator dye, such as Sudan IV or Red Oil O (Kram et al. 2001).

Used to estimate cleanup success.

At the end of the final water flush (NFESC 2003).

1 Note: Some commercial-grade salts (NaCl, CaCl2) can contain low levels of metal/metalloid contaminants of concern. For example, at the Camp Lejeune surfactant demonstration (ESTCP 2001), arsenic was monitored

2 Note: For GC or GC/MS methods, NFESC 2003 recommends using a packed column rather than the capillary column usually deployed with these methods because of potential clogging issues. Also, for COC effluent measurements in source area wells and extraction wells the sample may have to be diluted to keep the concentration within the linear range of the instrument.

3 Note: ISE methods can be used for field measurements of Ca+2, Na+1, and surfactant. The instrument manufacturer should be consulted to determine whether a site-specific condition might affect use.

Performance parameters and locations are those suggested in NFESC 2003 and ITRC 2004.

References:

Battey, T.F. et al. 2007. Soil Flushing through a Thick Vadose Zone: Perchlorate Removal Documented at Edwards AFB, California. American Geophysical Union, Fall Meeting 2007, Abstract H33E-1685.

Battey, T.F. et al. 2006. Adobe PDF LogoSoil Flushing to Remove Perchlorate from a Thick Vadose Zone in the Arid Southwest. Perchlorate 2006: Progress toward Understanding and Cleanup. Groundwater Resources Association of California.

ESTCP. 2001. Adobe PDF LogoTechnical Report for Surfactant-Enhanced DNAPL Removal at Site 88, Marine Corps Base Camp Lejeune, North Carolina. Environmental Security Technology Certification Program.

ITRC. 2003. Adobe PDF LogoTechnical and Regulatory Guidance for Surfactant/Cosolvent Flushing of DNAPL Source Zones. Interstate Technology & Regulatory Council. DNAPLs-3.

ITRC. 2004. Adobe PDF LogoStrategies for Monitoring the Performance of DNAPL Source Zone Remedies. Interstate Technology & Regulatory Council. DNAPLs-5.

Jafvert, C.T. 1996. Adobe PDF LogoSurfactants/Cosolvents: Technology Evaluation Report. Ground Water Remediation Technologies Analysis Center (GWRTAC). TE-96-02.

Kram, M., A.A. Keller, J. Rossabi, and L.G. Everett. 2001. DNAPL Characterization Methods and Approaches, Part 1: Performance Comparisons. Ground Water Monitoring and Remediation 21(1):67-76.

NFESC. 2003. Adobe PDF LogoSurfactant-Enhanced Aquifer Remediation (SEAR) Implementation Manual Naval Facilities Engineering Service Center. TR-2219-ENV54.

SW-846 On-Line: Test Methods for Evaluating Solid Waste, Physical/Chemical Methods. U.S. EPA, Office of Resource Conservation and Recovery.

U.S. EPA. 2006. Adobe PDF LogoIn Situ Treatment Technologies for Contaminated Soil: Engineering Forum Issue Paper. EPA 542-F-06-013.

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Performance Monitoring Resources

Controlled Release, Blind Test of DNAPL Remediation by Ethanol Flushing
Brooks, M.C., M.D. Annable, P.S.C. Rao, K. Hatfield, J.W. Jawitz, W.R. Wise, A.L. Wood, and C.G. Enfield.
Journal of Contaminant Hydrology 69:281-297(2004)

A DNAPL source zone was established within a sheet-pile isolated cell through a controlled release of PCE to evaluate DNAPL remediation by in situ cosolvent flushing. Ethanol was used as the cosolvent, and the main remedial mechanism was enhanced dissolution based on the phase behavior of the water/ethanol/PCE system. Over a 40-day period, 64% of an initial mass of 83 L of PCE was removed by flushing the cell with a solution of 70% ethanol and 30% water; however, tracer results suggest that some PCE was inaccessible to the ethanol solution, which led to the inefficient PCE removal rates observed. Longer abstract

Adobe PDF LogoCost and Performance Report for LNAPL Characterization and Remediation: Partition Interwell Tracer Testing (PITT) and Rapid Optical Screening Tool (ROSTTM) Characterization and Evaluation of the Feasibility of Surfactant Enhanced Aquifer Remediation (SEAR) at the Chevron Cincinnati Facility, Hooven, OH
EPA 542-R-05-017, 2005

DNAPL Characterization Methods and Approaches
Kram, M., A.A. Keller, J. Rossabi, and L.G. Everett.
Ground Water Monitoring and Remediation 21(1):67-76(2001) & 22(1):46-61(2002)

Adobe PDF LogoDevelopment of Assessment Tools for Evaluation of the Benefits of DNAPL Source Zone Treatment
Abriola, L.M., P. Goovaerts, K.D. Pennell, and F.E. Loeffler.
SERDP Project ER-1293, 173 pp, 2008

This report details the results of work that has enhanced the understanding of significant mechanisms controlling DNAPL source zone behavior and describes lessons learned that can provide improved DNAPL site management strategies. It discusses 4 important concepts: (1) partial source-zone mass removal (mainly through in situ flushing technologies in this study) can result in substantial local concentration and mass flux reductions; (2) potential remediation efficiency is closely linked to source-zone architecture (ganglia-to-pool ratios); (3) biostimulation and bioaugmentation approaches are feasible for treatment of DNAPL source zones; and (4) the uncertainty in mass discharge estimates can be quantified through application of geostatistical methods to field measurements.

Adobe PDF LogoEvaluation of In-Situ DNAPL Remediation and Innovative Site Characterization Techniques
Sillan, R.K., M.D. Annable, and P.S.C. Rao.
Florida Center for Solid and Hazardous Waste Management, Gainesville. 69 pp, 1999

This study reports the evaluation of the field-scale performance of in situ cosolvent flushing and innovative tracer techniques for site characterization of the former Sages Dry Cleaner site.

Adobe PDF LogoImpacts of DNAPL Source Treatment: Experimental and Modeling Assessment of the Benefits of Partial DNAPL Source Removal
Wood, A.L., M.D. Annable, J.W. Jawitz, R.W. Falta, M.C. Brooks, C.G. Enfield, P.S.C. Rao, and M.N. Goltz.
EPA 600-R-09-096, SERDP Project ER-1295, 172 pp, Sep 2009

For 2002 surfactant flushing at Hill AFB, a transect of passive flux meters (PFMs) used to measure TCE mass flux before and after the surfactant flood indicated a reduction in TCE flux of ~90%. With the integral pumping test method, water was subsequently extracted from the same series of wells, and a contaminant concentration/time series was measured in each pumping well effluent. These two methods were compared to mass flux calculated using water quality data from the transect of fully screened wells (10 monitoring wells on 10-ft centers downgradient from the DNAPL source zone). The three independent measurement techniques provided comparable results. For the Sages Dry Cleaner site 1998 pilot-scale ethanol flush, the performance estimate was supported by soil core results and a post-remedial partitioning tracer test. A second ethanol flood conducted in 2004 to remove additional PCE provided the opportunity to evaluate the impact of source depletion on contaminant mass flux.

Adobe PDF LogoImproved Monitoring Methods for Performance Assessment During Remediation of DNAPL Source Zones
Siegrist, R., R. Oesterreich, L. Woods, and M. Crimi.
Strategic Environmental Research and Development Program (SERDP), Project ER-1490, 116 pp, 2010

Investigators evaluated (1) the effects that sampling methods can have on the accuracy of measurements made for chlorinated solvents in samples of porous media collected from intact cores, and (2) the effects that remediation agents can have on the ability to infer CVOC mass levels in the subsurface based on groundwater concentration data. The accuracy of VOC measurements was investigated using an experimental apparatus packed with sandy porous media and contaminated with known levels of VOCs (PCE, TCE, TCA) sampled using different methods under variable, but controlled, conditions. Five sampling methods were examined representing different degrees of porous media disaggregation and duration of atmospheric exposure that can occur during sample acquisition and preservation in the field. CVOCs were studied at dissolved, sorbed, and nonaqueous phases. Five porous media temperatures were examined ranging from 5 to 80 degrees C to represent ambient or thermal remediation conditions, and two water saturation levels were used to mimic vadose zone and groundwater zone conditions. Results show that sampling method attributes can impact the accuracy of VOC measurements in porous media by causing negative bias in VOC concentration data ranging from near 0 to 90% or more. In situ remediation technologies, such as thermal treatment, ISCO, and flushing, have the potential to alter subsurface properties, which can affect the behavior of CVOCs, including DNAPLs.

Site-Specific Verification of Surfactant-Cosolvent Flushing
Vane, L., and S.L. Yeh.
NATO/CCMS Pilot Study. Evaluation of demonstrated and emerging technologies for the treatment of contaminated land and groundwater (Phase III). 2001 Special Session: Performance verification of in situ remediation technologies. EPA 542-R-02-002, p 59-78, 2002

This paper describes the use of soil core analysis and partitioning interwell tracer tests to assess technology performance during a field demonstration of surfactant-based soil flushing of PCE at MCB Camp Lejeune. Although the pre-flush PITT results provided useful information, the post-flush PITT results were unusable because an impurity in the surfactant solution sorbed to the aquifer soils, which caused an unanticipated change in the partitioning behavior of the tracers.

Adobe PDF LogoStrategies for Monitoring the Performance of DNAPL Source Zone Remedies
Interstate Technology and Regulatory Council (ITRC) Dense Nonaqueous-Phase Liquids Team. DNAPLs-5, 206 pp., Aug 2004.

Performance monitoring parameters for surfactant/cosolvent flushing include measuring DNAPL volume and dissolved contaminant concentration in extraction wells and monitoring points to assess remedial progress, as well as monitoring fluid chemistry (e.g., temperature, pH, specific conductance, and electrolyte concentrations); injection system pressure; injection and recovery flow rates; and changes in water level and level of free-phase DNAPL.

Adobe PDF LogoTracer Techniques for DNAPL Source Delineation and In-Situ Flushing Techniques for Enhanced Source Removal: Pilot Scale Demonstrations at the Dover National Test Site
Brooks, M.C., M.D. Annable, and S.C. Rao.
AFRL-ML-TY-TR-2003-4512, 293 pp, 2001

A study was performed to evaluate the performance of innovative tracer techniques for DNAPL characterization and in situ cosolvent and surfactant flushing for DNAPL removal at the Dover National Test Site, Dover AFB, DE. The project involved controlled releases of up to 100L of perchloroethene (PCE) into test cells for each remedial technology. After the PCE release, two partitioning tracer tests were conducted: one before and another after the remedial test. The first remedial demonstration involved cosolvent flushing and the second, surfactant flushing. This report focuses on the four partitioning tracer tests and the cosolvent flushing demonstration.

Adobe PDF LogoUsing Multilevel Samplers to Assess Ethanol Flushing and Enhanced Bioremediation at Former Sages Drycleaners
Brown, Gordon Hitchings, Master's thesis, University of Florida, 98 pp, 2006

A network of multilevel sampling wells (MLS) was installed in the Sages site source area to collect liquid samples before, during, and for 6 years after the 1998 pilot test to determine the initial and post-remedial PCE architecture at the site. Remedial performance was evaluated through comparison of pre- and post-remedial groundwater samples and partitioning tracer tests. The ethanol flushing test was effective at removing significant levels of subsurface PCE and favorably reduced the contaminant flux at most MLS locations. The use of ethanol as the remedial fluid also fostered microbial reductive dechlorination of residual PCE.

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Regulation

Some regulatory concerns are associated with the implementation of surfactant/cosolvent flushing because these technologies involve the introduction of chemical reagents into the subsurface, typically through injection wells, and because the technologies are designed to mobilize contaminants (although the intent is to control their migration and capture them). Use of injection technologies can be restricted or prohibited by regulatory or procedural barriers that vary from state to state (ITRC 2003). Land disposal restrictions and underground injection control regulations, for example, can limit selection of the flushing solution. At a former drycleaner, ethanol was substituted for isopropanol because of regulatory concern about the toxicity and persistence of isopropanol. The applicable federal and state regulatory agencies specify injection permit requirements. When applying for a permit, all chemicals involved, including unreacted compounds and impurities (e.g., benzene used as a drying agent in absolute alcohol), must be listed (NAVFAC 2002).

For CERCLA sites, the remedial alternatives must satisfy Applicable or Relevant and Appropriate Requirements (ARARs). Non-CERCLA sites (RCRA sites, private sites, state Superfund sites, and federal facilities) also can have potentially applicable regulations at the state and federal level (ITRC 2003).

Federal EPA initiatives to reduce regulatory (and legislative) barriers to the use of innovative in situ remediation technologies have been implemented as follows:

  • Since 1992, EPA has been granting states the authority to implement the Treatability Exclusion Rule; the Research, Development, and Demonstration Permit Program; and the Subpart X Permit Program. Those authorities are granted to states to simplify the approval process for technologies and to allow flexibility in testing and demonstrating innovative treatment technologies (ITTs).
  • To further promote the use of innovative technologies, in 1994 EPA revised its Treatability Study Sample Exclusion Rule (59 FR 8362) to allow treatability studies on up to 10,000 kg of media contaminated with nonacute hazardous waste without the requirement for permitting and manifesting.
  • In addition, EPA encouraged streamlining RCRA permits and orders for ITT development and use and encouraged state adoption and streamlining of EPA authorization to administer the treatment study sample exclusion rule.
  • In 1993, EPA issued the Superfund Response Action Contractor Indemnification Rule (58 FR 5972), designed to help contractors who use ITTs obtain lower deductibles on liability insurance.
  • EPA's 1996 area of contamination (AOC) policy allows soils to be excavated, moved, treated, and redeposited within the AOC without triggering RCRA regulatory requirements (ITRC 2005).
  • In December 2000, EPA issued a memorandum, Applicability of RCRA Section 3020 to In-Situ Treatment of Ground Water, which clarifies that reinjection of treated groundwater to promote in situ treatment is allowed under section 3020(b), as long as certain conditions are met. Specifically, the groundwater must be treated prior to reinjection; the treatment must be intended to substantially reduce hazardous constituents in the ground water—either before or after reinjection; the cleanup must be protective of human health and the environment; and the injection must be part of a response action under CERCLA section 104 or 106 or a RCRA corrective action intended to clean up the contamination.
  • EPA's Underground Injection Control (UIC) Program is responsible for regulating the construction, operation, permitting, and closure of injection wells that place fluids underground for storage or disposal. The UIC website offers guidance to inform state regulators and owners and operators of injection wells on how to operate injection wells safely to prevent contamination of underground drinking water resources.

Individual state regulations may be more restrictive than EPA requirements; hence, review of individual state regulations is important.

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