Dense Nonaqueous Phase Liquids (DNAPLs)

Treatment Technologies

In Situ Oxidation

This page identifies general resources that contain detailed information on ISCO design and implementation. Information on applications of the technology specific to a chemical class can be found in the class subsections listed to the right. More resources on this technology for a wide range of contaminants can be found in the In Situ Oxidation pages of Technology Focus.

ISCO is an aggressive remediation technology that has been applied both to DNAPL source zones and to the dissolved-phase chemicals emanating from the source zones. Chemical oxidation typically involves reduction/oxidation (redox) reactions that chemically convert hazardous contaminants to nonhazardous or less toxic compounds that are more stable, less mobile, or inert. Redox reactions involve the transfer of electrons from one chemical to another. Specifically, one reactant is oxidized (loses electrons) and one is reduced (gains electrons). There are several oxidants capable of degrading contaminants. Commonly used oxidants include potassium or sodium permanganate, Fenton's catalyzed hydrogen peroxide, hydrogen peroxide, ozone, and sodium persulfate. Each oxidant has advantages and limitations, and while applicable to soil contamination and some source zone contamination, they have been applied primarily toward remediating groundwater.

The selection of an oxidant for site cleanup involves the following key concepts:

Is the oxidant capable of degrading the contaminant of concern? Is a catalyst or other additive required to increase effectiveness?
What is the soil oxidant demand (SOD)? SOD is a measure of how the naturally occurring materials in soil will affect the performance of some of the oxidants. For non-selective oxidants, high SOD will increase the cost of cleanup, as more oxidant will be required.
What is the naturally occurring pH of the soil/groundwater system? Some oxidants require an acidic environment to work. If the soil is basic, an acid needs to be applied in addition to the oxidant.
How will the decomposition rate of the oxidant affect application strategies? Some unreacted oxidants may remain in the subsurface for weeks to months, while others naturally decompose within hours of injection.

The type of delivery system selected depends upon the depth of the contaminants, the physical state of the oxidant (gas, liquid, solid), and its decomposition rate. Backhoes, trenchers, and augers have been used to work liquid and solid oxidants into contaminated soil and sludge. Liquids can be delivered either by gravity through wells and trenches or by injection. For vadose zones, gravity has the drawback of a relatively small area of influence. Pressurized injection of liquids or gases, either through the screen of a well or the probe of a direct-push (DP) rig, will force the oxidant into the formation. The DP rig offers a cost-effective way of delivering the oxidant, and if needed, the hole can be completed as a small-diameter well for later injections. Potassium permanganate and other solid-phase chemical oxidants have also been added by hydraulic or pneumatic fracturing.

The site stratigraphy plays an important role in the distribution of oxidants. Fine-grained units redirect oxidants to more permeable areas and are difficult to penetrate; hence, they can be the source of rebound later on as contaminants diffuse out. Long-lived oxidants (e.g., permanganate) have the potential to remain active as this diffusion occurs, and they can mitigate some of the potential rebound.

Chemical oxidation usually requires multiple applications. The table provides a qualitative list of oxidant reactivities with common site contaminants.

Reactivity of Oxidants with Commonly Found Contaminants

Oxidant	High	Moderate	Low
Ozone	PCE, TCE, DCE, VC, MTBE, CB, PAHs Phenols, Explosives, PCBs, Pesticides	BTEX, CH₂Cl₂	CT, CHCl₃,
Hydrogen Peroxide¹	PCE, TCE, DCE, VC, CB, BTEX, MTBE, Phenols	DCA, CH₂Cl₂, PAHs, Explosives	TCA, CT, CHCl₃, PCBs, Pesticides
Calcium Peroxide	PCE, TCE, DCE, VC, CB	DCA, CH₂Cl₂	CT, CHCl₃
Fenton's Reagent	PCE, TCE, DCE, VC, CB, BTEX, MTBE, Phenols	DCA, CH₂Cl₂, PAHs, Explosives	TCA, CT, CHCl₃, PCBs, Pesticides
Potassium/Sodium Permanganate	PCE, TCE, DCE, VC, TEX, PAHs, Phenols, Explosives	Pesticides	B, DCA, CH₂Cl₂, TCA, CT, CB, CHCl₃, PCBs
Sodium Persulfate (Iron)	PCE, TCE, DCE, VC, CB, BTEX, Phenols	DCA, CH₂Cl₂, CHCl₃, PAHs, Explosives, Pesticides	TCA, CT, PCBs
Sodium Persulfate (Heat and Base pH 12)	All CVOCs, BTEX, MTBE, PAHs, Phenols, Explosives, PCBs, Pesticides, TPH

Source: ITRC 2005, Brown 2003, Watts 2011, and Root et al 2005
¹ Peroxide without a catalyst must be applied at higher concentrations, which are inherently hazardous, and the reactions are more difficult to predict and control.

In the special case of NAPLs, oxidants that are in a water-based solution will be able to react only with the dissolved phase of the contaminant, since the two will not mix. This property limits their activity to the oxidant solution/NAPL interface. Cost estimates depend on the heterogeneity of the site subsurface, soil oxidation demand, stability of the oxidant, and type and concentration of the contaminant. Care should be taken when comparing different technologies on a cubic yard basis without considering these site attributes. Cost data can be found in ITRC (2005) and Brown (2003). In situ chemical oxidation has been used at dozens of sites, and oxidizing compounds are available from a variety of vendors.

Sodium or Potassium Permanganate. Permanganate is a non-specific oxidizer of contaminants with low standard oxidation potential and high SOD. It can be used over a wide range of pH values and does not require a catalyst. Permanganate tends to remain in the subsurface for a long time, allowing for more contaminant contact and the potential of reducing rebound. As permanganate oxidizes organic materials, manganese oxide forms as a dark brown to black precipitate. During the treatment of large bodies of NAPL with high concentrations of permanganate, this precipitate may form a coating that reduces contact between oxidant and NAPL. The extent to which this reduction negatively affects contaminant oxidation has not been quantified. Potassium permanganate has a much lower solubility than sodium permanganate and generally is applied at lower concentrations. Commercial-grade permanganates may contain elevated concentrations of heavy metals, and they may lower the pH of the treated zone (U.S. EPA 2004). If bioremediation is planned as a polishing step, permanganate will have an adverse effect on microbial activity and may cause a change in microbe distribution. This effect is generally transitory. Also, there is some evidence that permanganates may be inhibitory to Dehalococcoides ethenogenes, the microbial species that completely dechlorinates PCE and TCE (Hrapovic et al. 2005).

Fenton's Catalyzed Hydrogen Peroxide. Fenton's reagent uses hydrogen peroxide in the presence of ferrous sulfate to generate hydroxyl radicals that are powerful oxidants. The reaction is fast, releases oxygen and heat, and can be difficult to control. Because of the fast reaction, the area of influence around the injection point is small. In conventional application, the reaction needs to take place in an acidified environment, which generally requires the injection of an acid to lower the treatment zone pH to between three and five. The reaction oxidizes the ferrous iron to ferric iron and causes it to precipitate, which can result in a loss of permeability in the soil near the injection point. Over time, the depletion of the ferrous ion can be rate limiting for the process. Chelated iron can be used to preserve the iron in its ferrous state at neutral pH, thus eliminating the acid requirement. The byproducts of the reaction are relatively benign, and the heat of the reaction may cause favorable desorption or dissolution of contaminants and their subsequent destruction. It also may cause the movement of contaminants away from the treatment zone or allow them to escape to the atmosphere. There are safety concerns with handling Fenton's reagent on the surface, and the potential exists for violent reactions in the subsurface. In many cases, there may be sufficient iron or other transition metals in the subsurface to eliminate the need to add ferrous sulfate.

Hydrogen Peroxide. While catalysts can be added to increase oxidation potential, hydrogen peroxide can be used alone to oxidize contaminants. Peroxide oxidation is an exothermic reaction that can generate sufficient heat to boil water. The generation of heat can assist in making contaminants more available for degradation, as well as allowing them to escape to the surface. With its high reaction and decomposition rates, hydrogen peroxide is not likely to address contaminants found in low permeability soil. Solid peroxides (e.g., calcium peroxide) in slurry form moderate the rate of dissolution and peroxide generation, thereby allowing a more uniform distribution.

Ozone. One of the stronger oxidants, ozone can be applied as a gas or dissolved in water. As a gas, ozone can degrade a number of chemicals directly in both the dissolved and pure forms, and it provides an oxygen-rich environment for contaminants that degrade under aerobic conditions. It also degrades in water to form radical species that are highly reactive and non-specific. Ozone may require longer injection times than other oxidants, and vapor control equipment may be needed at the surface. Because of its reactivity, ozone may not be appropriate for slow diffusion into low-permeability soil.

Sodium Persulfate. Persulfate is a strong oxidant with a higher oxidation potential than hydrogen peroxide and a potentially lower SOD than permanganate or peroxide. Persulfate reaction is slow unless placed in the presence of a catalyst, such as ferrous iron, or heated to produce sulfate free radicals that are highly reactive and capable of degrading many organic compounds. At temperatures above 40�C, persulfate becomes especially reactive and can degrade most organics (Block et al. 2004). Like Fenton's reagent, the ferrous iron catalyst (when used) will degrade with time and precipitate (U.S. EPA 2006). Persulfate also can be activated in the presence of base conditions (pH 12). The aquifer can be made basic by the addition of a strong alkali hydroxide such as potassium or sodium hydroxide. Persulfate activation decreases as the pH falls (from 12) but does not stop even at a pH of 8 (Miraglio 2009).

Technology Advantages

Contaminant mass can be destroyed in situ.
Rapid destruction/degradation of contaminants (measurable reductions in weeks or months).
Produces no significant wastes (VOC offgas is minimal), except Fenton's.
Reduced mobilization, operation, and monitoring costs due to rapid results.
Compatible with post-treatment monitored natural attenuation.
Has potential to enhance aerobic and anaerobic biodegradation of residual hydrocarbons.
Likely to cause minimal disturbance to site operations.

Technology Limitations

Potentially higher initial and overall costs relative to other source area solutions.
Contamination in low permeability soils may not be readily contacted and destroyed by chemical oxidants (persulfate and permanganate can have longer activities in the subsurface and may be useful for destruction of back diffusing chemicals and direct diffusion into low permeability soils).
Fenton's reagent can produce a significant quantity of explosive offgas. Special precautions (i.e., an SVE system) are required for appropriate implementation of remedial action involving Fenton's chemistry.
Dissolved contaminant concentrations may rebound weeks or months following chemical oxidation treatment.
Dissolved contaminant plume configuration may be altered by chemical oxidation application.
Significant health and safety concerns are associated with applying oxidants.
May not be able to reduce contaminants to background or very low concentrations due to limitations of technology or cost.
Significant losses of chemical oxidants may occur as they react with soil/bedrock material rather than contaminants.
Permanganate may significantly alter aquifer geochemistry, which can cause clogging of the aquifer through precipitation of minerals in pore spaces. Other oxidants that use ferrous iron as an activation agent can cause the precipitation of ferric iron, which can reduce the permeability of the soil around the injection point.

ISCO performance at any given site is dependent upon the contact achieved between the oxidant and the contaminants, which in turn is controlled by the DNAPL architecture and other site-specific conditions. Oxidation technologies have the potential for achieving significant mass destruction of organics in the subsurface; however, the results of field and laboratory work indicate that complete removal of contaminants may not be achieved with these technologies even under optimal conditions (NRC 2004). Innovators are combining the benefits of ISCO implementation with compatible technologies, such as solvent flushing and bioremediation, to maximize remediation potential.

Block, P., R. Brown, and D. Robinson. 2004. Novel activation technologies for sodium persulfate in situ chemical oxidation. Proceedings of the Fourth International Conference on the Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA.

Brown, R. 2003. In situ chemical oxidation: performance, practice, and pitfalls. 2003 AFCEE Technology Transfer Workshop, February 25, 2003, San Antonio, TX.

Hrapovic, L. et al. 2005. Laboratory study of treatment of trichloroethene by chemical oxidation followed by bioremediation. Environmental Science & Technology, Vol 39 No 8, p 2888-2897.

ITRC. 2005. Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, 2nd Edition.

Miraglio, M.A. 2009. Base-Activated Persulfate Treatment of Contaminated Soils with pH Drift from Alkaline to Circumneutral. Master's thesis, Washington State University.

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

Root, D.K. et al. 2005. Investigation of Chlorinated Methanes Treatability Using Activated Sodium Persulfate. Proceedings of the First International Conference on Environmental Science and Technology.

U.S. EPA. 2004. How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers, EPA 510/R-04/002. Office of Underground Storage Tanks.

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

Watts, R.J. 2011. Enhanced Reactant-Contaminant Contact through the Use of Persulfate In Situ Chemical Oxidation (ISCO). SERDP Project ER-1489, 290 pp, 2011

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General Resources | Performance Monitoring for In Situ Oxidation

General Resources

Base-Activated Persulfate Treatment of Contaminated Soils with pH Drift from Alkaline to Circumneutral
Miraglio, M.A., Washington State University Master's Thesis, 38 pp, 2009

Experiments on persulfate activity when pH drifts below 12 that show some activity remains.

Chemical Oxidation
Chapter XIII in How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers
U.S. EPA, Office of Underground Storage Tanks
EPA 510-R-04-002, 52 pp, 2004

Concurrent treatment of source area saturated and unsaturated zones with chemical oxidation usually requires its integration of with other remedial technologies that target unsaturated zone contamination (e.g., SVE). SVE is likely to be included as a component of ISCO solutions even if there is no specific need to treat unsaturated soils in the source area because it can help alleviate safety issues associated with controlling and recovering offgas.

Chemical Oxidation Site Profiles

U.S. EPA has developed a searchable database of case studies in which information about completed and ongoing full-scale applications of in situ chemical oxidation to address a variety of contaminants is summarized.

Development of a Design Tool for Planning Aqueous Amendment Injection Systems: ESTCP Cost and Performance Report
ESTCP Project ER-200626, 41 pp, 2012

This project focused on the development and application of tools for the design of in situ anaerobic bioremediation using soluble substrates (SS) and emulsified vegetable oil (EVO), and ISCO systems using permanganate. Results from 3-D numerical simulations in heterogeneous aquifers were used to develop relationships between reagent distribution and amount of fluid/reagent injected and then to develop simple, spreadsheet-based design tools to assist in planning EVO, SS, and permanganate injection systems for in situ aquifer treatment. These design tools are strictly focused on improving reagent distribution. Additional documentation is available on the SERDP-ESTCP website at the bottom of the page for Project ER-200626.

Engineering Issue Paper: In Situ Chemical Oxidation
EPA 600-R-06-072, 60 pp, 2006

This issue paper provides an overview of ISCO remediation technology and fundamentals based on peer-reviewed literature, EPA reports, web sources, current research, conference proceedings, and other pertinent information.

Enhanced Reactant-Contaminant Contact through the Use of Persulfate In Situ Chemical Oxidation (ISCO)
Watts, R.J.
SERDP Project ER-1489, 290 pp, 2011

This report describes the results of an investigation of the activation and persistence of persulfate in the subsurface to evaluate the potential for contact between the oxidant source and contaminants. Results showed that most minerals do not activate persulfate, particularly in the concentrations commonly found in the subsurface. Iron chelate-activated persulfate and base-activated persulfate generate hydroxyl radical, sulfate radical, and reductants, and provide the basis for widespread treatment of different classes of contaminants in the subsurface. Many organic compounds activate persulfate, including phenoxides and ketones. Because soil organic matter contains phenolic and ketonic moieties, it is a potent activator of persulfate. Depending on the acidity of the soil organic matter, it could activate persulfate with minimal addition of base. Persulfate has minimal effects on the mineralogy of the subsurface, with the exception of aging ferrihydrite. It can increase the permeability of some subsurface materials. Activated persulfate is a highly reactive remediation system that has sufficient longevity and transport characteristics to treat contaminants in low permeability regions of the subsurface.

Field Demonstration, Optimization, and Rigorous Validation of Peroxygen-Based ISCO for the Remediation of Contaminated Groundwater: CHP Stabilization Protocol
Watts, R., A. Teel, R. Brown, and T. Pac.
ESTCP Project ER-200632, 99 pp, 2014

Although catalyzed hydrogen peroxide propagations (CHP) is the ISCO process with the most robust chemistry and potential for contaminant destruction, peroxide is unstable in the subsurface. Recent advances, however, show that the addition of sodium citrate, sodium malonate, and sodium phytate potentially can slow peroxide decomposition rates up to 50-fold. The optimal implementation of these stabilizers for use in CHP field applications is detailed in this guide and illustrated with two case histories.

Ground Water Sample Preservation at In-Situ Chemical Oxidation Sites: Recommended Guidelines
Ko, S., S.G. Huling, and B. Pivetz.
EPA 600-R-12-049, 16 pp, 2012

This issue paper provides background information and general guidelines for methods and procedures that can be used to detect whether an oxidant (permanganate or persulfate) is present in groundwater, to approximate the oxidant concentration, and to estimate and deliver the volume or mass of preservative (ascorbic acid) required to preserve the binary mixture groundwater sample. An appendix provides specific details regarding preservation procedures.

Improved Monitoring Methods for Performance Assessment During Remediation of DNAPL Source Zones
R. Siegrist, 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.

Improved Understanding of Fenton-Like Reactions for the In Situ Remediation of Contaminated Groundwater, Including Treatment of Sorbed Contaminants and Destruction of DNAPLs
R.J. Watts, F.J. Loge, and A.L. Teel.
Strategic Environmental Research and Development Program (SERDP), 276 pp, 2006

Investigation of the processes and mechanisms associated with the use of catalyzed hydrogen peroxide propagations (CHP, or modified Fenton's reagent) for ISCO shows that superoxide has a major role in the degradation of highly oxidized contaminants, the destruction of DNAPLs, and the enhanced desorption of hydrophobic contaminants from soils and subsurface solids. The suite of reactive oxygen species generated in CHP reactions, including hydroxyl radical, superoxide, and the strong nucleophile hydroperoxide, provide a near-universal treatment matrix for chemical contaminants. This report discusses the applicability of modified Fenton's to the destruction of carbon tetrachloride, chloroform, benzo[a]pyrene, hexadecane, 1,1,1-TCA, 1,2-DCA, PCE, and TCE.

In Situ Chemical Oxidation Multimedia Training Tool
U.S. Navy, Naval Facilities Engineering Command, Environmental Restoration Technology Transfer, Multimedia Training Tools website, 23 pp.

A variety of toxic organics, including DNAPLs, are amenable to destruction or at least partial degradation through chemical oxidation processes initiated by the application of compounds such as potassium permanganate or Fenton's reagent. The most recent advances in the understanding of the application of ISCO for groundwater remediation are presented through this multimedia training tool.

In Situ Chemical Treatment: Technology Evaluation Report
Yujun Yin and Herbert E. Allen.
Ground-Water Remediation Technologies Center (GWRTAC). TE-99-01, 82 pp, 1999

In situ chemical treatment techniques are useful for treatment of source areas to reduce the mass of contaminants and intercept plumes to remove mobile organics and metals. Chemical injection treatment mechanisms can be oxidative, reductive/precipitative, or desorptive/dissolvable, depending upon the chemical/contaminant interaction. Chemicals can be delivered to the subsurface via well injection techniques, deep soil mixing and hydraulic fracturing, or installation of permeable chemical treatment walls. The main chemical injection in situ treatments discussed are oxidation, flushing, and reduction and immobilization. Treatment wall reactions include immobilization of inorganics and organics via sorption, immobilization of inorganics via precipitation, and degradation of inorganic anions and organics. This report discusses the chemistry and the engineering aspects of available in situ chemical treatment technologies and provides information on costs, lessons learned, and regulatory issues.

Investigation of Chlorinated Methanes Treatability Using Activated Sodium Persulfate
Root, D.K, E.M. Lay, P.A. Block, and W.G. Cutler.
Proceedings of the First International Conference on Environmental Science and Technology, 6 pp, 2005

This paper examines the reactivity of persulfate with chlorinated methanes using various activation mechanisms.

Optimizing Injection-Based Remediation in Bedrock: Lessons from DNAPL Remediation by Chemical Oxidation
Dombrowski, P. | DCHWS 2021 Design and Construction at Hazardous Waste Sites Virtual Symposium, 29-30 March and 1 April, Virtual, 19 slides, 2021

Presentation describes an application of ISCO to treat bedrock groundwater contamination. It looks at the lessons learned over four injections of sodium persulfate to treat bedrock contaminated with PCE DNAPL.

Principles and Practices of In Situ Chemical Oxidation Using Permanganate
R.L. Siegrist, M.A. Urynowicz, O.R. West, M.L. Crimi, and K.S. Lowe.
Battelle Press, Columbus, OH, ISBN:1-57477-102-7, 336 pp, 2001

Provides guidance on the evaluation and design of in situ chemical oxidation systems with a focus on the use of potassium and sodium permanganate for remediation of organically contaminated sites.

Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, 2nd Edition
Interstate Technology & Regulatory Council (ITRC). ISCO-2, 172 pp, 2005

In addition to technical and regulatory guidance, includes 14 case studies of ISCO implementation, 4 of them at sites (dry cleaners and a wood treatment facility) affected by DNAPL contaminants.

Technical Report: Subsurface Injection of In Situ Remedial Reagents (ISRRs) within the Los Angeles Regional Water Quality Control Board Jurisdiction
Wilson, S., D. Clexton, C. Sandefur, et al.
In Situ Remediation Reagents Injection Working Group, 46 pp, 2009

This compilation of general tools and best practices provides a reference manual for the planning, design, and field implementation phases of ISCO projects, with a strong emphasis on safety considerations. Specific attention is given to avoiding the visible surfacing of injected ISRR materials, minimizing impact to landscaping, and ensuring no surface pathway for potential ISRR runoff.

Technology Status Review: In Situ Oxidation
Environmental Security Technology Certification Program (ESTCP), Arlington, VA. 50 pp, 1999

Following a survey of several government sites where ISCO was used, this report was prepared to help establish the basis for selecting and designing the technology, to assess the costs and performance of the technology at specific sites, to assess the reasons for success or failure of ISCO, and to provide guidance on the use of the technology.

Performance Monitoring for In Situ Oxidation

The comprehensive table below provides recommendations for performance monitoring parameters at ISCO sites. Performance monitoring parameters are site specific and should be chosen through the data quality objectives process.

ISCO (in situ chemical oxidation) is an aggressive remediation technology that has been applied both to DNAPL source zones and to dissolved-phase chemicals emanating from source zones. Chemical oxidation typically involves reduction/oxidation (redox) reactions that chemically convert hazardous contaminants to nonhazardous or less toxic compounds, which are more stable, less mobile, or inert. The oxidants commonly used for these reactions are potassium or sodium permanganate, Fenton's reagent (catalyzed hydrogen peroxide), hydrogen peroxide, ozone, and sodium persulfate. These redox reactions are considered non-specific because they involve not only the target oxidant and organic compounds but also some inorganic substances and naturally occurring organic matter.

The major objectives for monitoring ISCO performance are measurements of contaminant mass reduction and oxidant dispersion. Secondary objectives are detection of potential heavy metal mobilization and physical/chemical changes in the aquifer.

Contaminant mass reduction can be determined directly by measuring the reduction in groundwater contaminant concentrations and soil core concentrations, or indirectly with surrogates or tracers. Surrogates, such as chloride from the destruction of chlorinated aliphatics and benzenes, carbon dioxide, and carbon isotopes, can be used to measure mass reduction. The partitioning interwell tracer technique and other tracer methods can be used to estimate DNAPL mass before and after an oxidation injection. Contaminant flux changes also can be useful in determining remediation success; however, depending on the DNAPL architecture, a reduction in contaminant mass is not always followed by a reduction in flux.

Oxidant dispersion is measured directly in perimeter and selected target zone wells by testing for unreacted oxidant. Groundwater surrogates that show the presence of oxidant reactions include sulfate (Fenton's reagent and persulfate); dissolved oxygen (ozone, peroxide, and Fenton's reagent); pH, especially when ferrous sulfate (Fenton's reagent and persulfate) is the catalyst; redox; and specific conductance. Geophysical techniques, such as cross-borehole radar and electrical resistivity (see abstracts below), can be used to provide a three-dimensional image of oxidant movement in the subsurface. These techniques can identify areas where the oxidant did not penetrate or areas that were bypassed entirely by the oxidant (ITRC 2005).

Changes in redox or pH conditions have the potential to mobilize naturally occurring metals. While these metals generally do not remain soluble as they move downgradient of the treatment area, they should be monitored. Also, commercial grade permanganate can contain heavy metals, such as chromium, at concentrations that could be of concern (EPA 2006).

Major cations can be used to track changes in mineral composition due to oxidant treatment and in some cases to identify where oxidants, such as potassium and sodium in permanganate and persulfate solutions, have been.

Additional information for non-specific performance monitoring techniques is available in Detection and Site Characterization.

Table 1. Performance Monitoring Parameters for In Situ Oxidation

Performance Parameter¹	Method	Data Use	Performance Expectation	Recommended Frequency of Analysis²
Contaminants of Concern (COCs) in groundwater	VOCs, EPA SW-846: 8260B SVOCs, SW-846: 8270D Depending upon the detection limits desired, chemical class-specific testing methods might be used (e.g., SW-846: 8310 for PAHs).	Regulatory compliance levels for COCs are the values by which success of the remediation system will be measured.	Contaminant values typically decline to less than regulatory compliance levels within the treatment zone after oxidant injection.	Pre- and post-injection (ITRC 2004). For permanganate and persulfate, ITRC 2005 recommends monthly for three months following injection. For Fenton's, ITRC 2005 recommends screening for VOCs daily at start and close.
COCs in soil (ITRC 2004 and 2005)	VOCs, EPA SW-846: 8260B SVOCs, SW-846: 8270D Depending upon the detection limits desired, chemical class-specific testing methods might be used (e.g., SW-846: 8310 for PAHs).	Regulatory compliance levels for COCs are the values by which success of the remediation system will be measured. This will also allow an estimate of contaminant destruction if not complete.	General decline in contaminant mass.	Baseline and at the end of the reaction period (persulfate and permanganate can remain active for some time after injection).
Oxidant (Fenton's Reagent, Hydrogen Peroxide, Ozone, Potassium/Sodium Permanganate, Sodium Persulfate)	Colorimetric	Determine radius of distribution, and measure persistence (ITRC 2005 and ITRC 2004).	Evidence of oxidant should be found throughout target zone.	During or shortly after injection episodes. If extraction wells are used, they should be tested during the injection period (ITRC 2004).
Metals (primary concern: Arsenic, Barium, Cadmium, Chromium, Copper, Iron, Lead, and Selenium) (ITRC 2005); Aluminum (ITRC 2004)	EPA SW-846: 6010C	Verify that redox- sensitive metals have not mobilized to hazardous levels. Verify that potentially lower pH levels have not mobilized metals to hazardous levels.	Some metals can become more soluble in an oxidized state; commercial grade permanganate can contain trace levels of heavy metals (e.g., chromium); some persulfate and Fenton's applications can lower pH and potentially mobilize metals.	Pre-, during, and post-injection (ITRC 2004). For permanganate and persulfate ITRC 2005 recommends monthly for three months following injection.
Major Cations (Ca, Fe, K, Mg, Na, Mn)	EPA SW-846: 6010C Ion-selective electrode (ISE)⁴ for field measurement of K, Ca, Na, and Mg	Measure changes in aquifer geochemistry. Determine if sufficient iron is available in the reaction zone to catalyze hydrogen peroxide and persulfate.	Reduced mineral species in the target zone can be oxidized and made soluble; a change in pH can increase solubility.	Pre-, during, and post-injection (ITRC 2004). For Fenton's, ITRC 2005 recommends daily start and close monitoring for iron..
Total Dissolved Solids	EPA Method 160.1	Measure changes in aquifer geochemistry.	Oxidant application typically changes the amount of suspended solids in aquifer treatment zone.	Pre-, during, and post-injection (ITRC 2004).
Chloride, Nitrate, Sulfate, Fluoride	EPA Method 300.1 EPA SW-846: 9056A Ion Chromatography ISE for field measurement of chloride, nitrate, and fluoride	Track changes in mineral composition due to oxidant treatment (ITRC 2005).	Provide line of evidence for distribution radius (sulfate); provide line of evidence for chlorinated hydrocarbon destruction (chloride); support bioremediation decision making if appropriate (nitrate).	Pre-, during, and post-injection (ITRC 2004).
Bromide	EPA Method 300.1 or EPA SW-846: 9056A Ion Chromatography ISE for field measurement	Injection fluid tracer.	Conservative ion that should move with the injection fluid.	Pre-, during, and post-injection (ITRC 2004)
Alkalinity as CaCO₃	APHA et al. 1992: 2320 B ISE for field measurement	Determine buffering capacity of aquifer to anticipate acid requirements for pH modification.³ If source area is acidic, will give indication of whether manganese ion (sodium and potassium permanganate) formed from the reductant reaction will persist (ITRC 2005).	Alkalinity affects the ability to adjust the aquifer pH if needed.	Pre-, during, and post-injection (ITRC 2004).
Dissolved Oxygen	Flow-through electrode cell downhole probe	Indicator of organic pollutant load and oxidant movement.	Increases in dissolved oxygen concentrations reflect oxidizing conditions and generally coincide with the oxidant movement (ITRC 2005).	Pre-, during, and post-injection (ITRC 2004 and 2005). For Fenton's, ITRC 2005 recommends daily start and close.
Dissolved Carbon Dioxide	APHA et al. 1992: 4500-CO₂ C (titrimetric) or 4500-CO₂ D (calculation requiring known values for total alkalinity and pH) ISE for field measurement	Indicator of oxidant activity.	Carbon dioxide is a by-product of the oxidation process and can be an indication of the rate and extent of oxidation (ITRC 2005).	Pre-, during, and post-injection (ITRC 2005) For Fenton's, ITRC 2005 recommends daily start and close.
Oxidation Reduction Potential (ORP)	Flow-through electrode cell downhole probe	Water quality parameter and oxidation pathway indicator.	Application of ISCO should result in increased ORP in the reaction area (ITRC 2005).	Pre-, during, and post-injection (ITRC 2004 and 2005). For Fenton's, ITRC 2005 recommends daily start and close.
pH	Flow-through electrode cell downhole probe	Water quality parameter. Determine if pH is appropriate for desired oxidant reaction and adjust if necessary.	Most ISCO chemicals react differently under different pH conditions; adjusting pH can lead to the most favorable reaction conditions (ITRC 2005). Oxidation of VOCs with persulfate tends to lower pH into a fairly acidic range that can mobilize heavy metals in the soil matrix.	Pre-, during, and post-injection (ITRC 2004 and 2005). For Fenton's, beginning and daily (ITRC 2005).
Temperature	Flow-through cell in situ temperature gauge (e.g., thermocouple) downhole probe	Water quality parameter and for Fenton's reagent and hydrogen peroxide a safety parameter.	Fenton's reagent and hydrogen peroxide reactions with organic matter are highly exothermic. Reaction of sodium permanganate in the presence of high concentrations of reductant also can be exothermic (ITRC 2005).	Pre-, during, and post-injection (ITRC 2004 and 2005). For Fenton's ITRC 2005 recommends constant monitoring during injection.
Specific Conductance	Flow-through electrode cell downhole probe	Water quality parameter. Additional line of evidence for oxidant dispersion (ITRC 2005).	Slight increases in conductivity are frequently observed following oxidant injections (ITRC 2005).	Pre-, during, and post-injection (ITRC 2004 and 2005). For Fenton's ITRC 2005 recommends daily start and close.
Groundwater Elevations	Water Interface Sensor Instrument	Determine groundwater gradient (flow direction and speed).	Injection rate should not greatly change gradient to ensure contaminants are not forced out of treatment zone.	During injection (ITRC 2004).

¹ Parameters are those suggested in ITRC 2005 and supplemented by ITRC 2004 and EPA 2006

² ITRC 2005 recommends that comprehensive post-injection sampling should be completed at least three months after the last injection.

³ EPA 2006

⁴ ISE . Consult manufacturers for further information. A site-specific interference could limit use of ISE.

References

Engineering Issue Paper: In Situ Chemical Oxidation
EPA 600-R-06-072, 60 pp, 2006

Standard Methods for the Examination of Water and Wastewater, 18th Edition
American Public Health Association (APHA), American Water Works Association, and Water Environment Federation, 1992 Standard Methods commercial Web site

Strategies for Monitoring the Performance of DNAPL Source Zone Remedies
Interstate Technology & Regulatory Council, 205 pp, 2004

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

Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, 2nd Edition
Interstate Technology & Regulatory Council (ITRC). ISCO-2, 172 pp, 2005

Abstracts

Automated Geophysical Monitoring of In Situ Engineered Treatments