Use of iron-based technologies in contaminated land and groundwater remediation: a review

Remediation of PAH-contaminated sediments by chemical oxidation.

Quantitation of hydroxyl radical during Fenton oxidation following a single addition of iron and peroxide

: The U.S. Environmental Protection Agency (EPA) Engineering Issue Papers are a series of technology transfer documents that summarize the latest available information on specific technical issues, including fate and transport, specific contaminants, selected treatment and site remediation technologies, and related other issues. This Engineering Issue Paper is intended to provide remedial project managers (RPMs), on-scene coordinators (OSCs), contractors, and other state, industry, or private remediation managers with information to assist in the evaluation and possible selection of appropriate in-situ chemical oxidation (ISCO) remedial alternatives. This Engineering Issue Paper provides an up-to-date overview of ISCO remediation technology and fundamentals, and is developed based on peer-reviewed literature, EPA reports, web sources, current research, conference proceedings, and other pertinent information.

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In-Situ Chemical Oxidation

Hydrogen peroxide decomposition in model subsurface systems.

A method of treating contaminants in soil and/or groundwater comprising adding a source of an oxidizing agent and an aqueous solution of a metal catalyst having a pH of from about 5 to 8 to the in situ environment in amounts capable of producing reactive species sufficient to oxidize at least one of the contaminants.

Soil and/or groundwater remediation process

Fenton's reagent in its conventional form, although effective for contaminant treatment, is impractical from an in-situ field application perspective due to low pH requirements (i.e., pH 3-4), and limited reagent mobility when introduced into the subsurface. Modified Fenton's processes that use chelated-iron catalysts and stabilized hydrogen peroxide have been developed with the goal of promoting effective in-situ field application under native pH conditions (i.e., pH 5-7), while extending the longevity of hydrogen peroxide. Laboratory experiments conducted in soil columns packed with organic soil to compare modified Fenton's catalysts with conventional catalysts (acidified iron [II]) indicated superior mobility and sorption characteristics for modified Fenton's catalysts. Furthermore, the acidic pH of a conventional catalyst was buffered to the native soil range, leading to increased iron precipitation/adsorption following permeation through the soil column. The chelates present within the modified Fenton's catalyst showed greater affinity toward iron compared with the native soil and, hence, minimized iron loss through adsorption during the permeation process even at pH 5-7.



Field effectiveness of the modified Fenton's process was demonstrated at a former dry-cleaning facility located in northeast Florida. Preliminary laboratory-scale experiments were conducted on soil-slurry and groundwater samples to test the process efficacy for remediation of chlorinated solvents. Based on successful experimental results that indicated a 94 percent (soil slurry) to 99 percent (groundwater) reduction of cis-1,2-DCE, PCE, and TCE, a field-scale treatment program was initiated utilizing a plurality of dual-zone direct push injection points installed in a grid fashion throughout the site. Results of treatment indicated a 72 percent reduction in total chlorinated contamination detected in the site groundwater following the first injection event; the reduction increased to 90 percent following the second injection event. © 2002 Wiley Periodicals Inc.

Modified Fenton's processes for effective in-situ chemical oxidation—Laboratory and field evaluation

Laboratory, pilot, and full-scale experiments were used to evaluate and optimize the ISOTECSM remedial process at a warehousing facility in Union, New Jersey. Based on modified Fenton's oxidative chemistry, the ISOTECSM process uses a proprietary catalytic agent that delays formation of reactive hydroxyl radicals. This allows adequate dispersion of the hydroxyl radicals, which is an oxidizing agent, throughout a contaminant plume. Ground-water at the site was contaminated with high levels of gasoline and waste oil constituents, principally BTEX and MTBE. Bench scale microcosm studies were used to evaluate the appropriate site-specific stoichiometric relationships between catalyst, stabilizers, and oxidizers; the effect of contaminant type and concentration; and the pH optima. Based on results of the laboratory studies, a pilot-scale study was performed at the site. One injection point for catalyst, stabilizers, and oxidant was installed in the contaminated zone at the site, with one hydraulically connected downgradient well used for monitoring. A single treatment of the reagents in the optimal stoichiometry determined from the laboratory study was injected in-situ over a period of three days. A 98.5 percent reduction in volatile organics was observed in the area treated, with the radial extent of treatment estimated to be approximately 20 feet, based on the presence of hydroxyl radicals detected in hydraulically connected areas and at the surface. The full-scale process employed six injection points and three treatment cycles over a three-month period. Subsequent to treatment, contaminant levels were either nondetectable or were reduced to below applicable New Jersey groundwater standards, with regulatory closure on the site achieved in less than one year.

In-Situ Fenton-Like Oxidation of Volatile Organics: Laboratory, Pilot, and Full-Scale Demonstrations

Laboratory, pilot, and full-scale experiments were used to evaluate and optimize the ISOTECSM remedial process at a warehousing facility in Union, N. J. Based on modified Fenton’s oxidative chemistry, the ISOTEC SM process uses a proprietary catalytic agent which delays formation of reactive hydroxyl radicals. This allows adequate dispersion of the hydroxyl radicals, which is an oxidizing agent, throughout a contaminant plume. Groundwater at the site was contaminated with high levels of gasoline and waste oil constituents, principallybenzene, toluene, ethylebenzene, xylenes (BTEX) andmethyl-t-butylether (MTBE). Bench scale microcosm studies were used to evaluate the appropriate site-specific stoichiometric relationships between catalyst, stabilizers, and oxidizers; the effect of contaminant type and concentration; and the pH optima. Based on results of the laboratory studies, a pilot-scale study was performed at the site. One injection point for catalyst, stabilizers, and oxidant was installed in the contaminated zone at the site, with one hydraulically connected downgradient well used for monitoring. A single treatment of the reagents in the optimal stoichiometry determined from the laboratory study was injected in situ over a period of three days. A 98.5% reduction in volatile organics was observed in the area treated, with the radial extent of treatment estimated to be approximately 20 feet, based on the presence of hydroxyl radicals detected in hydraulically connected areas and at the surface. The full-scale process employed six injection points and three treatment cycles over a three month period. Subsequent to treatment, contaminant levels were either non-detectable or were reduced to below applicable New site. ISOTEC’s treatment activities were completed over several days within a six month period, with the case closed in under a year from start to finish.

In Situ Fenton-like Oxidation of Volatile Organics

The Red Rock Hydroelectric Project converted the existing Red Rock Dam near Pella, Iowa, from a non-powered dam into a multi-purpose dam. The existing flood control dam was constructed by the U.S. Army Corps of Engineers (USACE) in the 1960s on the Des Moines River near Pella, Iowa. The hydroelectric project was developed by Western Minnesota Municipal Power Agency and generates up to 55 MW with an average annual energy output of 178 gigawatt-hours. The new intake, penstock and powerhouse are located immediately adjacent to the spillway. Construction required large excavations into the upstream and downstream sides of the existing embankment dam and two penetrations through the existing gravity dam monoliths. Extensive water and earth-retention systems, prescriptive construction staging, and a robust dam safety surveillance program were designed to maintain and monitor the integrity of the existing dam throughout construction and avoid impacts to active USACE flood control operations. Construction was completed in 2020. This paper provides an overview of the unique challenges involved with the design and construction of a new hydroelectric project at an existing and active flood control dam.

Thomas Andrews

Papers

Soil and/or groundwater remediation process

Modified Fenton's processes for effective in-situ chemical oxidation—Laboratory and field evaluation

In-Situ Fenton-Like Oxidation of Volatile Organics: Laboratory, Pilot, and Full-Scale Demonstrations

In Situ Fenton-like Oxidation of Volatile Organics

Red Rock Hydroelectric Project – New hydro development at an existing flood control dam