Title: Introduction Text: Chemical oxidation has been used for decades in the municipal and industrial wastewater industries for the ex situ treatment of organic contaminants. This industry has proven that a variety of toxic organics are amenable to destruction or at least partial degradation through chemical oxidation processes. Subsequently, research was initiated in applying this technology to groundwater in situ, using a variety of oxidants such as potassium permanganate and Fenton's reagent. These studies began with a focus on the removal of petroleum compounds, but later research encompassed chlorinated solvents. The use of chemical oxidation for the treatment of chlorinated solvents, including dense nonaqueous-phase liquid (DNAPL), is advancing through bench- and pilot-scale studies and subsequent field demonstrations. This tool presents the most recent advances in the understanding of the application of in situ chemical oxidation. Visual Direction: Photo of overhead shot of buildings at a remediation site and photo of equipment at an in situ chemical oxidation plot.

Title: Background on Chemical Oxidation (1 of 2) Text: Subsurface toxic contamination is a widespread problem and organic chemicals are often the primary contaminants of concern (COC). In-situ chemical oxidation (ISCO) is the application of a strong oxidizing agent into the groundwater to destroy or degrade organic chemicals. The migration of the oxidant can be controlled hydraulically using arrays of injection and/or extraction wells. The oxidants degrade contaminants by converting them to benign compounds, ideally CO2, H2O, and mineral salts. However, intermediate byproducts may also be formed. ISCO can be used to treat DNAPL as well as dissolved-phase contaminants. Contaminants potentially amenable to treatment by ISCO include benzene, toluene, ethylbenzene, and xylenes (BTEX); tetrachloroethylene (PCE); trichloroethylene (TCE); dichloroethylenes; polycyclic aromatic hydrocarbon (PAH) compounds, and many other organic contaminants. Visual Direction: Figure illustrating the in situ chemical oxidation process including injection wells and the formation of free radicals in the subsurface from hydrogen peroxide injection.

Title: Background on Chemical Oxidation (2 of 2) Text: The goal of ISCO is to oxidize a target compound, transforming it to a non-toxic or less-toxic product. Oxidation potential is a measure of the oxidative power of an oxidant. The higher the oxidation potential, the greater the oxidative power. Complete mineralization is the desired endpoint of an ISCO process. Because of their easy availability, relatively low cost, and other favorable characteristics, potassium permanganate and Fenton's reagent (hydroxyl radical) are the two most common oxidants that have been used for in situ treatment. Fenton's reagent involves the combination of [hydrogen peroxide (H2O2) and ferrous iron (Fe²+)] to form a hydroxyl-free radical. Ozone is another potential oxidant used in the field, but it exhibits oxidation rates that are several orders of magnitude lower than the hydroxyl-free radical. Visual Direction: Table with the oxidation potential of select oxidants including fluorine, hydroxyl radical, ozone, hydrogen peroxide, and others.

Title: Oxidant Definition Text: An oxidant is an electron-deficient chemical that oxidizes another chemical by accepting electrons; it has the tendency to accept electrons from other chemicals (preferably target contaminants in groundwater and soil). Visual Direction: No Graphic.

Title: DNAPL Text: A dense nonaqueous-phase liquid (DNAPL) is a liquid that is denser than water and does not dissolve or mix easily in water (it is sparingly soluble). In the presence of water it forms a separate phase from the water. Many chlorinated solvents, such as TCE, exist as DNAPL in the subsurface. Visual Direction: No Graphic.

Title: Factors Affecting ISCO Application Text: Several factors can influence the effectiveness of an ISCO application. Click on the factors listed on the left for more information. Visual Direction: List of Solid Oxidant Demand; Oxidant Dosage; Potential for Mobilization of Metals; Effects on Soil Permeability; Post ISCO Rebound; Oxidant Distribution

Title: Natural Soil Oxidation Demand (SOD) Text: The natural SOD often exceeds the oxidant demand of the COC by 2 or 3 orders of magnitude. Aquifer species contributing to SOD include reduced solid species (e.g., sulfides), natural organic matter, and reduced aqueous species (e.g., dissolved iron). These native reduced species often consume much of the oxidant injected into an aquifer. This natural oxidation demand needs to be accounted for in dosing. Visual Direction: No Graphic.

Title: Oxidant Dosage Text: During ISCO, complex organic matter breaks down to simpler carbon compounds that are more bioavailable. As a result, total organic carbon (TOC), chemical oxygen demand (COD), and biological oxygen demand (BOD) have been found to increase in groundwater at some sites. Completely oxidizing these native reduced species may be undesirable. If the site is overdosed with oxidant, then the entire redox buffering capacity of the treatment zone could be destroyed. This makes it difficult for anaerobic microbial populations to re-establish. At the same time, too low an oxidant dosage can reduce the effectiveness of the application. A bench-scale treatability test is useful in determining the oxidant dosage based on site-specific variables. Visual Direction: No Graphic.

Title: Potential for Mobilization of Metals Text: Redox-sensitive metals (e.g., Cr, As, Se, Hg) naturally present in most soil can be mobilized during ISCO application. Often, the metals that are mobilized during ISCO are attenuated in or near the treatment zone and may not migrate very far in the aquifer. Metals that are mobilized are attenuated by adsorption onto natural organic matter, soil minerals, and on the MnO2 itself (produced from the consumption of KMnO4 in permanganate applications). Visual Direction: No Graphic.

Title: Effects on Soil Permeability Text: In some aquifers, the addition of oxidants reduces permeability. For permanganate applications, MnO2 solids formation and accumulation can reduce permeability and is based on the injected KMnO4 concentration, injection rate, and natural geochemical variables. Also, the formation of CO2 gas reduces soil permeability. This phenomenon depends on the carbonate composition of the aquifer and geology. Contrary to expectations, in many aquifers, permeability may actually increase. Factors contributing to increases in soil permeability include relatively high levels of oxidizable matter, such as total organic carbon, DNAPL, and reduced mineral species. In many cases, the net effect of these changes is that permeability in the treatment zone remains relatively the same. Visual Direction: No Graphic.

Title: Post ISCO Rebound Text: Post-ISCO COC concentrations may decrease and then increase again, even though considerable DNAPL mass has been destroyed. Increased permeability following ISCO may lead to increased advection and diffusion of COCs from the pores into the bulk flow. Oxidation of soil organic matter may cause more COCs to be released from the sorbed to the dissolved phase. The implication of this phenomenon is that a second injection (or multiple injections) may be desirable after a new equilibrium is reached. Visual Direction: No Graphic.

Title: Oxidant Application Method Text: The performance can also depend on the oxidant delivery method as follows: The recirculation approach involves both injection and extraction. This approach allows for better hydraulic control, better distribution of the oxidant, and less chance of contaminant migration. However, reinjection may be subject to stricter guidelines in some states. Also, more elaborate aboveground equipment is required to filter out MnO2 (during permanganate application), replenish oxidant, and remove trace metals from the recirculating water. The injection-only approach is viewed as 'easy' and is currently practiced more often. For this approach, injection wells are either arranged to make use of the natural gradient to distribute the oxidant or multiple temporary injection points are used to reach the entire target treatment zone. Higher injection pressures may also be required in tighter soils. This increases the possibility of spreading the contaminants, Mn (during permanganate application), and trace metals downgradient under these pressures. In general, it is advisable to inject the oxidant into the target treatment zone from the outside-in. This minimizes the potential for spreading of the target contamination to surrounding regions of the aquifer. If injections are started from within the treatment zone, there may be potential for spreading the contamination that desorbs or is mobilized due to the oxidation, under the influence of the outward hydraulic gradient (created by the injection pressure). Visual Direction: No Graphic.

Title: Advantages of ISCO Text: Contaminants can potentially be destroyed in situ, unlike thermal or surfactant flushing technologies, which mobilize and extract contaminants from the subsurface for aboveground treatment Reagents involved are relatively inexpensive (e.g., potassium permanganate at $1.00 to $1.50/lb) Potentially effective with many different types of organic contaminants in sorbed and DNAPL states Cost effective treatment for contaminant source zones or "hot spots" Visual Direction: No Graphic.

Title: Limitations of ISCO Text: Some handling hazard (e.g., 30% to 50% hydrogen peroxide solutions can cause severe burns; also, compound is unstable, and a potential for fire and explosions exists) As with any in situ technology, reagent delivery to the target regions may be challenging Strong oxidants may oxidize other (naturally occurring) reduced species in the subsurface An injection permit is required May not be cost effective for treating very dispersed and/or dilute plumes Visual Direction: No Graphic.

Title: Permanganate Process Overview (1 of 2) Text: Permanganate has been shown to oxidize a wide variety of organic and inorganic compounds in water. It is applied as a 1% to 5% solution prepared from potassium permanganate crystals that are delivered in bulk to the site. Permanganate has a unique affinity for oxidizing organic compounds containing carbon-carbon double bonds, aldehyde groups, or hydroxyl groups. Certain nitro-aromatic compounds are oxidized as well. Visual Direction: A permanganate oxidation equation for a chlorinated compound. It transforms the compound primarily to carbon dioxide and chloride.

Title: Permanganate Process Overview (2 of 2) Text: The chemical structure of the COC affects oxidation. The addition of chlorine atoms (which themselves have a strong oxidative potential) to a COC molecule reduce its reactivity. For example, it is easier to oxidize 1,2-DCE than TCE. Also, double bonds and the presence of hydroxyl and nitroso groups make the contaminant more susceptible to oxidation. Permanganate has been shown to oxidize chloroethenes, PAHs, chlorinated pesticides (e.g., aldrin and dieldrin), high explosives, and some chlorophenols. Permanganate is ineffective with chlorinated alkanes (e.g., dichloroethane) and aromatic hydrocarbons (e.g., benzene and chlorobenzene). Methyl tert-butyl ether (MTBE) will oxidize to tert-butyl alcohol (TBA); however, the functional group is oxidized, but not the parent structure. Visual Direction: The permanganate oxidation equations for PCE and TCE. These compounds are transformed primarily to carbon dioxide and chloride.

Title: Reaction Rate Text: The rate of reaction depends on both the aqueous concentration of KMnO4 and the COC. This is known as a second order reaction. An increase in the concentration of injected KMnO4 increases the rate of oxidation of the COC. This is shown in the table by a decrease in TCE and 1,2-DCE half-life with an increase in the consumption of KMnO4. The rate of MnO2 (solid) formation around the injection point may increase with higher KMnO4 levels. MnO2 solids may initially be colloidal or transportable. However, the colloids may eventually coagulate and deposit in the pores, especially if a lot of solids are generated in a short time period. Therefore, using very high KMnO4 concentrations may not be desirable if loss of porosity around the injection points is a concern. A bench scale treatability test is the best means of optimizing the KMnO4 concentration based on such site-specific factors. Visual Direction: Table of half lives of for TCE and 1,2-DCE based on KMnO4 concentrations ranging from 5 to 1000 mg/L.

Title: Second Order Kinetics Text: A second order reaction is a reaction whose rate depends on the concentration of one reactant raised to the second power or on the concentrations of two different reactants, each raised to the first power. Visual Direction: No Graphic.

Title: Factors Affecting Permanganate Application Text: Several factors can influence the effectiveness of permanganate application as noted below: Industrial-grade KMnO4 (and to some extent NaMnO4) contains Cr as a trace impurity. An increase in Cr in groundwater at ISCO sites has typically been attributed to the injected oxidant. Industrial KMnO4 also contains nickel, which has been found at elevated levels at some sites. At most sites, migration of these trace metals from the treatment zone can be attenuated by adsorption on various aquifer constituents. Precautions should be taken when handling permanganate, but safety hazards are not as great as for H2O2. Treatability testing should be done on a site-specific basis to determine optimum oxidant dosage and injection point spacing. In general, a lower permanganate dosage between 0.1% to 3% is recommended. A lower dosage minimizes MnO2 solids deposition around injection points. Overdosing leads to depletion of natural organic carbon and other natural reductants in the aquifer that are important for subsequent microbial regrowth. Pilot injection using a single well or drive point can be useful. Many vendors do a tracer test to determine radius of influence and well spacing required at the site. In general, 5-foot, 10-foot, or up to 15-foot injection spacing is required. Visual Direction: No Graphic.

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Title: Interagency DNAPL Consortium (IDC) Project Text: A performance evaluation of permanganate injection was conducted at Launch Complex 34 (LC34) at Cape Canaveral Air Station in Florida. The objective of this study was to evaluate the cost and performance of ISCO in destroying TCE present as a DNAPL within the saturated zone. The project was sponsored by the Interagency DNAPL Consortium (IDC). Visual Direction: Site view of Cape Canaveral Air Force Station Launch Complex 34.

Title: IDC Text: The IDC is comprised of the following government agencies: United States Air Force Naval Facilities Engineering Command United Stated Department of Energy United States Environmental Protection Agency National Aeronautics and Space Administration Visual Direction: No Graphic.

Title: Site Characterization Text: Site characterization indicated DNAPL was concentrated near two low-permeability zones in the surficial aquifer (see yellow and red regions on Figure 1). A confined aquifer was present underneath a fairly thin confining unit (see Figure 2). The ISCO plot was estimated to contain a total of 6,122 kg of TCE with 5,039 kg present as free-phase DNAPL. Visual Direction: Figure of DNAPL concentration in a surficial aquifer. Figure showing a cross-section of soil layers.

Title: ISCO Equipment Layout Text: Permanganate injection was used for chemical oxidation at LC34. An automated portable bulk feed system was used to prepare the KMnO4 for injection. Solid KMnO4 was fed into a heated flash mixer where it was dissolved in tap water. Potassium permanganate has a solubility of 64 mg/L at 20 degrees Celsius and can easily be made into a 2% or less solution in water. The solution at 1.7% KMnO4 was filtered to remove any particulates and injected into the surficial aquifer. Additional system elements included: Eight injection points used to deliver the permanganate solution to the subsurface. Three central groundwater recovery wells to provide hydraulic containment and to improve in situ mixing. Several multiport sampling wells to track technology performance. Visual Direction: Diagram of ISCO equipment layout including bulk feed trailer, transfer blower, KMnO4 hopper, bulk solids feeder, mix tank, injection pumps, duplex filters, and the injection manifold.

Title: ISCO Equipment at LC34 Text: Visual Direction: A picture of ISCO equipment at LC34 including a dry KMnO4 hopper, control module and liquid mixing tank, sand filter tank, and the oxidant injection manifold.

Title: Validation of Performance Text: A performance assessment was conducted to answer the following questions: Is DNAPL migrating to surrounding regions? Are COCs being destroyed or recovered? What is the state of test plot after treatment? Visual Direction: Pictures of drilling equipment for site monitoring.

Title: Are COCs being destroyed or recovered? Text: Soil sampling was used as the main tool for determining TCE/DNAPL mass removal. Approximately 82% of the total TCE mass and 84% of the DNAPL mass was removed due to the chemical oxidation application. Much of this removal can be attributed to destruction of TCE by oxidation, as indicated by the chloride buildup in the plot. The sharp increase in carbon dioxide and related alkalinity levels in the groundwater is another sign of considerable oxidation occurring in the aquifer. Visual Direction: Two 3-D cross sections showing TCE concentrations in soil both before and after oxidant treatment.

Title: TCE Mass Removal Estimate Text: Approximately 82% of the total TCE mass and 84% of the DNPAL mass were removed due to ISCO. Visual Direction: Table showing values for mass removal of TCE and DNAPL calculations.

Title: Is DNAPL migrating to surrounding regions? Text: Some DNAPL appeared in monitoring wells located between two test plots where chemical oxidation and six-phase heating technologies were being applied concurrently. It is difficult to attribute the DNAPL migration to one of the two technologies. The strong hydraulic gradient generated by the oxidant injection is unlikely to cause DNAPL migration, unless some DNAPL is already present in mobile form. Visual Direction: Picture showing location of monitoring wells with DNAPL at the site.

Title: What is the state of test plot after treatment? Text: Several parameters were monitored for 6 to 9 months after the project to asses the state of the test plot. The anomalous behavior of some the parameters indicates that the ISCO reactions are very complex and may result in a wider variety of byproducts. The results were as follows: Groundwater pH and dissolved oxygen levels remained stable. Oxidation reduction potential (ORP), chloride, alkalinity, and total dissolved solids (TDS) levels rose. Dissolved iron levels remained constant and sulfate levels increased. Three trace metals (Cr, Ni, and Tl) showed a short-term increase above state standards. The presence of these metals in the permanganate may have contributed to the elevated levels and they are expected to subside over time. Click through Figures 2 to 4 to view the results of the chloride, aerobic microbe, and anaerobic microbe monitoring efforts. Visual Direction: Tables with results of test plot assessment for three ISCO plots (upper sand, middle fine-grained, and lower sand units).

Title: Text: Chloride Levels Chloride concentrations were elevated post-demonstration and during extended 6-month monitoring. Concentrations during post-demonstration were double those of pre-demonstration levels. Concentrations remained elevated during extended monitoring, but had decreased slightly in the upper sand and middle fine-grained units. Concentrations appeared to continue to increase in the lower sand unit. Visual Direction: Table showing chloride levels at site (pre and post demonstration) and results of extended monitoring.

Title: Aerobic Microbial Counts Analysis Text: Aerobic Microbes Aerobic microbial counts increased significantly from pre-demonstration levels. Levels were elevated up to 6 months after the demonstration and continued to increase as shown in the extended monitoring up to 9 months later. Visual Direction: Table showing aerobic microbial counts at site (pre and post demonstration) and results of extended monitoring.

Title: Anaerobic Microbial Counts Text: Anaerobic Microbes Anaerobic microbial counts were also elevated during the post-demonstration period 6 to 9 months following application. Visual Direction: Table showing anaerobic microbial counts at site (pre and post demonstration) and results of extended monitoring.

Title: Key Points: Permanganate Text: The following are some key points and lessons learned from past ISCO applications using permanganate: Trace metals may exceed groundwater standards temporarily. Industrial grade NaMnO4 has a lower trace metals content than KMnO4 and may be more suitable from a regulatory perspective. Permanganate is less expensive when purchased as a solid. SOD may ultimately drive oxidant dosage, permanganate concentration, injection time, and well spacing. Permanganate persists in the environment for a much longer time than Fenton's reagent. Therefore, the lag time between injection events may be longer for efficient use. The best indicator of how much DNAPL mass has been oxidized is the increase in chloride, not the decrease in COC levels. Visual Direction: No Graphic.

Title: Fenton's Reagent Process Overview Text: In a classic Fenton's reaction, hydrogen peroxide and ferrous iron combine to generate hydroxyl free radicals, which are a highly reactive species. Fenton's reagent is produced on site by adding an iron catalyst to a hydrogen peroxide solution. A 50% solution of peroxide is common for this application. This reaction progresses best under relatively low pH conditions (3 to 5) and in many aquifers, an acid (e.g., sulfuric acid) has to be added to the treatment zone to create these low pH conditions. The hydroxyl free radical cleaves chemical bonds and oxidizes organic compounds nonselectively which result in the formation of successively smaller chained hydrocarbon compounds. The intermediate compounds formed are generally mono- and di-carboxyl acids, which are nonhazardous, naturally occurring substances. These are oxidized to carbon dioxide and water (a complete mineralization) during subsequent sequential reactions. Visual Direction: An equation showing Fenton's reaction, which involves hydrogen peroxide and iron forming a hydroxyl free radical.

Title: Reaction Rate Text: Fenton's reagent also produces a second order reaction. The principal active component is the hydroxyl free radical, which is produced by catalytic chemical reaction between hydrogen peroxide and ferrous iron under optimum pH conditions (pH=3 to 5). Visual Direction: Table of compounds including benzene, toluene, PCBs, and others and their corresponding reaction rate with Fenton's reagent.

Title: Mineralization Definition Text: The complete conversion of an organic compound to inorganic products (principally water and carbon dioxide). Visual Direction: No Graphic.

Title: Role of Other Reactive Species (1 of 2) Text: When relatively high concentrations of hydrogen peroxide (2% - 12% H2O2) are used, other reactive species such as superoxide anion (O2-) and hydroperoxide anion (HO2-) are generated. These reactive ions facilitate the effectiveness of the treatment. Roll over the highlighted free radicals for more information. Visual Direction: Equations showing the formation of other reactive species such as the superoxide anion and the hydroperoxide anion.

Title: Role of Other Reactive Species (2 of 2) Text: The other reactive species (e.g., superoxide anion, hydroperoxide anion) may facilitate the destruction of sorbed contaminants as shown in the figure. These reactive species, which are reductants, facilitate the desorption of sorbed contaminants and make them more amenable to destruction by the hydroxyl free radical. Optimum peroxide concentrations are usually 0.5% to 12% and are highly specific. Lower concentrations (0.5% to 1%) are most effective when contaminants are not sorbed and DNAPLS are not present. Higher concentrations (2% to 12%) are usually required to treat sorbed and DNAPL contaminants. Visual Direction: Figure showing desorption by reductants of sorbed contaminants.

Title: Superoxide Anion Text: The superoxide anion is: A reductant A nucleophile Relatively long-lived in water Very long-lived in organic solvents The compounds which are reduced by the superoxide anion include: Carbon tetrachloride Hexachloroethane PCE TCE Visual Direction: No Graphic.

Title: Hydroperoxide Anion Text: The hydroperoxide anion is: A conjugate base of H2O2 (pKa = 11.75) A reductant A strong nucleophile Relatively short-lived: recombines with H+ Compounds treated by the hydroperoxide anion include: 1,3,5-trinitrobenzene Esters Amides Organophosphorus esters Carbomates Visual Direction: No Graphic.

Title: Other Catalysts for Fenton's Reactions Text: Fenton's reaction is not limited to ferrous iron [Iron (II)] as the only catalyst; a range of different catalysts may be involved: Iron (III) instead of Iron (II) Iron Chelates Other Natural Minerals The type of catalyst selected should be based on site-specific treatability testing to account for the complexity of oxidation chemistry. Visual Direction: No Graphic.

Title: Catalysis by Iron (III) Text: Iron(II) is most effective at low (mg/L) hydrogen peroxide concentrations. Iron(III) is most effective at high (% level) hydrogen peroxide concentrations. Conditions required for iron-catalyzed Fenton's reactions to generate oxygen transient species include: Hydroxyl radicals: >0.01 mg/L hydrogen peroxide Superoxide: >500 mg/L hydrogen peroxide Hydroperoxide: >1-2% hydrogen peroxide. Therefore, selecting the right concentration of hydrogen peroxide at a given site for a given contaminant is important. Visual Direction: No Graphic.

Title: Catalysis by Iron Chelates Text: Iron chelates include: Iron-EDTA (Ethylenediaminetetraacetic Acid) Iron-NTA (Nitrolotriacetic Acid) Iron-Citrate The advantage is that iron chelates promote Fenton's reactions at neutral pH. The disadvantage is the there is a high potential for metals mobility after the chelate is oxidized. Also, the chelate itself may consume much of the hydrogen peroxide injected. Visual Direction: No Graphic.

Title: Catalysis by Other Natural Minerals Text: At many sites, there may be no need to add ferrous compounds. Natural soil minerals can catalyze the reaction and form reactive radicals. A pH of 3-4 is required for these catalysis reactions to occur (which may require acid addition). The pH rebounds after treatment and may release carbonates as CO2. This provides the highest degree of H2O2 stability and addition of an iron catalyst is not required. Different minerals may favor the generation of different radicals. For example: Pyrolusite (manganese ore) generates O2- and Illmenite (titanium ore) generates OH-, O2-, HO2-. Visual Direction: No Graphic.

Title: Factors Affecting Fenton's Reagent Application Text: The nature of the COC determines the optimum peroxide (H2O2) concentration and the efficiency of the reactions. The various reactive species formed during Fenton's reactions promote desorption of sorbed COCs (Figure A). The more hydrophobic the contaminant (as indicated by the octanol-water coefficient, KOW), the greater the amount of H2O2 required for its destruction (Figure B). Destruction of DNAPL by Fenton's reagent has been documented in the field and laboratory. Research results show that DNAPL destruction by Fenton's reagent occurs more rapidly than any other treatment process (Figure C). These processes likely involve the superoxide radical. Even when dissolved COC concentrations do not show a significant decrease, considerable DNAPL mass may have been oxidized. This is caused by the exothermic reaction promoting higher desorption of DNAPL or improved advective flow and higher dissolved concentrations. Visual Direction: Three figures: nature of COC's in the aquifer (Figure A), nature of the COC determines the H2O2 requirements (Figure B), and laboratory test results of the destruction of carbon tetrachloride DNAPL (Figure C).

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Title: Case Study 2: MW-13 Area (Marvin et al., 2002) Text: The site is in an industrial and undeveloped area 3 miles from the San Francisco Bay. From 1972 to 1993, a solvent recovery and distribution operation occupied the site. Currently, the site houses a chemical storage and distribution facility, owned by an independent corporation. The investigation and remediation activities were conducted from 1995 to 1999. An interim remedial action was implemented in 1999 to 2002. The final remedial action plan was written in 2002. Visual Direction: Photograph of ISCO application equipment including personnel, drill rig, and drums.

Title: Hydrogeology Text: Pavement or fill is present from the surface to 2 ft below ground surface (bgs). Silty clay exists from the base of the overlying fill material to approximately 12 ft bgs. The static water table is about 4 to 6 ft bgs, within the silty clay. The shallow groundwater zone (SGZ) runs from approximately 12 ft bgs to 18 to 30 ft bgs. From 18 to 30 ft bgs to 43 to 49 ft bgs is basal clay. Groundwater flow velocity in the SGZ varies from 41 ft/yr on site to 288 ft/yr downgradient. Visual Direction: Figure of groundwater plume at site.

Title: RI/FS Text: During site investigation activities, four hot spots were identified where total volatile organic compound (VOC) concentrations exceeded 100 mg/kg in soil. In June 1999, a dual phase extraction system was implemented as an interim remedial action at the four hot spots. Remedial action objectives of 90% concentration reduction were achieved at three of the hot spot areas by December 2000. An increasing trend of elevated VOC concentrations in MW-13 led to the discovery of a 5th hot spot area in April of 2000. ISCO was implemented in January 2001 at the 5th hot spot area. In May of the same year, source remediation (dual phase extraction and ISCO) and ground-water plume monitored natural attenuation (MNA) was recommended as the final remedy in the Remedial Action Plan. Current activities at the site include dual phase extraction at one hot spot, groundwater sampling and analysis, and ISCO post-treatment evaluations. Visual Direction: Three figures: groundwater plume at site, soil sampling locations, and pre-treatment soil sampling.

Title: Remedial Action Objective (RAOs) Text: RAOs at the 5th hot spot include the removal of at least 80% of the COC mass and/or residual DNAPLs in the saturated and unsaturated zones and the mitigation of the observed trend of increasing COC concentrations in the downgradient monitoring well (MW-13). The impact on reductive dechlorination and other natural attenuation mechanisms were to be minimized. Visual Direction: No Graphic.

Title: Performance Text: After a short 2-week field treatment, it was estimated that Fenton's Reagent injection achieved greater than 85% VOC mass removal and concentration reduction. This estimate was based on pre- and post-treatment direct push sampling of soil and groundwater. Chlorinated volatile organic compounds (CVOCs) showed an immediate decrease in the downgradient well (MW-13) and then leveled off. Long-term data do not suggest significant CVOC rebound or any adverse impact to aquifer chemistry. A complete RI with details on hydrogeology and aquifer chemistry was crucial to the successful implementation of the ISCO technology at this site. Results of the study suggest that ISCO can contribute to overall site cleanup as a source remediation technique to increase effectiveness of downgradient plume remediation. Visual Direction: Bar charts of the short-term results of soil and groundwater CVOC concentrations and long-term results of dissolved oxygen data and groundwater CVOC concentrations.

Title: Fenton's Reagent Advantages Text: Hydroxyl free radical is much more reactive than permanganate and can therefore oxidize many more COCs Although the hydroxyl free radical is the best known reactive species generated through Fenton's reactions, other reactive species are also generated in smaller amounts enabling the reagent to destroy nearly all organic contaminants and treat strongly sorbed and DNAPL contaminants Chemicals involved do not appear to contain trace impurities of concern Color of the reagents is not a concern There is no significant generation of solids that could clog the aquifer Visual Direction: No Graphic.

Title: Fenton's Reagent Limitations Text: Peroxide and hydroxyl free radicals are extremely short-lived and this could limit distribution (reaction rate is diffusion controlled). Other reactive species generated are more long-lived. Safety issues with hydrogen peroxide include chemical fires, explosions, and chemical burns Reaction is highly exothermic and higher peroxide concentrations can cause steaming and volatilization of COCs Requires optimal pH conditions (between 3 and 5) Visual Direction: No Graphic.

Title: Key Points: Fenton's Reagent Text: The following are some key points and lessons learned from past ISCO applications using Fenton's reagent: There are several advantages and limitations associated with the use of Fenton's reagent compared to permanganate. Depending upon the COC type and the presence of DNAPLs, hydrogen peroxide doses typically range from 0.5% to 12%. Process conditions that should be evaluated during pilot-scale studies include catalysts, pH, and peroxide concentration. The primary design consideration for injection well spacing is hydrogen peroxide stability. The stability of hydrogen peroxide is highly variable and controls the radius of influence of injection. It is often necessary for well spacing to be closer than required for permanganate. In addition to the hydroxyl free radical, Fenton's reagent also generates other radicals such as the superoxide anion and hydroperoxide anion that facilitate contaminant destruction and broaden the range of applicable contaminants. More than one treatment phase is usually required for effective cleanup. Visual Direction: No Graphic.

Title: Conclusions Text: This tool presented recent advances and lessons learned related to the application of ISCO for groundwater remediation. Based on the above information, it is evident that a successful application of ISCO is dependent on several factors. These include adequate site characterization, treatability testing, injection implementation, and post-treatment monitoring. Good site characterization and identification of the COC source zone is crucial to the successful implementation of ISCO. Treatability tests are also necessary at all sites to determine oxidant dosage, need for catalysts, well spacing, and other design variables. It should be noted that multiple injections may be desirable at many sites to optimize oxidant distribution and contaminant mass removal. Multiple injections may allow additional oxidation of residual contaminant mass. Multiple injections may also mitigate the tendency for dissolved contaminant levels to rebound after ISCO. It is also important to note that ISCO causes significant changes in the aquifer that could influence subsequent MNA or enhanced bioremediation of contaminant residuals. For this reason, post-treatment monitoring of water quality parameters and microbial populations are desirable after ISCO application. Visual Direction: No Graphic.

Title: Contact Information Text: For more information about in situ chemical oxidation, please contact: NFESC POC (805) 982-1656 PRTH_NFESCT2@navy.mil Visual Direction: No Graphic.

Title: References Text: Books and Reports Battelle, 2002. Demonstration of ISCO Treatment of a DNAPL Source Zone at Launch Complex 34 in Cape Canaveral Air Station. Final Innovative Technology Evaluation Report. Prepared for the Interagency DNAPL Consortium by Battelle, Columbus, Ohio. Siegrist, R., M. Urynowicz, O. West, M. Crimi, and K. Lowe. 2001. Principles and Practices of In-Situ Chemical Oxidation Using Permanganate. Battelle Press, Columbus, Ohio. ISBN 1-57477-102-7. Journal Papers and Conference Publications DeHghi, B., A. Hodges, and T. Feng. 2002. Post-treatment evaluation of Fenton’s Reagent in-situ chemical oxidation. In Remediation of Chlorinated and Recalcitrant compounds – 2002. Proceedings of the Third International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 2002. Battelle Press, Columbus, Ohio. ISBN 1-57477-132-9. Marvin, B., J. Chambers, A. Leavitt, and C. Schreier. 2002. Chemical and engineering challenges to in-situ permanganate remediation. In Remediation of Chlorinated and Recalcitrant compounds – 2002. Proceedings of the Third International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 2002. Battelle Press, Columbus, Ohio. ISBN 1-57477-132-9. Pignatello, J.J., and Baehr, 1994. Waste management: ferric complexes as catalysts for "Fenton" degradation of 2,4-D and metalochlor in soil. J. Environ. Qual. 23:365-369 Web Sites Fenton's Reagent: Subsurface Contaminants Focus Area (DOE/EM-0484). Visual Direction: No Graphic.