Daniel W. Elliott and Wei-xian Zhang, Lehigh University

Herein, we report the results from laboratory studies and a field pilot test in which nanoscale bimetallic particles were to remediate trichloroethene ("TCE") and other chlorinated hydrocarbons in soils and groundwater. To our knowledge, the pilot test represents the first field demonstration of the technology. The particles consist of colloidal zero-valent iron (0.1-0.2 m m) with a discontinuous coating of palladium. Our work demonstrates that the nanoparticles rapidly transform such chlorinated hydrocarbons as TCE, dichloroethenes ("DCEs"), and vinyl chloride ("VC") to innocuous end products, namely ethane, ethene, and chloride both in the laboratory and in the field. Approximately 1.7 kg of the particles were gravity-fed into TCE-contaminated groundwater in a well-characterized area of an active manufacturing site in NJ. Field parameters including pH, dissolved oxygen ("DO"), oxidation-reduction potential ("ORP"), and conductivity were systematically measured in the test area to monitor changes in groundwater chemistry. Routine sampling for volatile organic compounds ("VOC"), dissolved and total iron, and chloride, was also conducted. TCE reduction efficiencies of up to 96.5% were observed within the test area. Wide temporal and spatial variations were noted as reduction efficiencies generally declined with increasing distance from the point of injection. These variations are largely attributable to the mass transfer (i.e. advection and dispersion) of the injected BMP within the test area. Data from the field test were consistent with the laboratory results in that contaminant dechlorination was accompanied by a sharp decrease of ORP and an increase of pH. In most of the downgradient monitoring locations, the ORP and pH responses were observed to precede TCE reductions. These reactions also created conditions favorable for microbial-mediated natural attenuation of TCE. Based upon these results, the nanoparticle technology appears to be a very promising remediation technology for soils and groundwater contaminated by chlorinated hydrocarbons.

Ron Adams, P.E., EBSI, Inc., Dr. William Mahaffey, Pelorus, Inc., Dr. William Slack, FRx, Inc., Mark Vigneri, Environmental Business Solutions International, (EBSI) Inc., Richard Werner, CPG, Environmental Consulting, Inc.

In-situ chemical treatment of soil and groundwater at contaminated sites has become increasingly accepted as a feasible, cost-effective, and timely method of site remediation. Laboratory-scale testing has clearly demonstrated the effectiveness of a wide-range of common, often times food-grade, chemicals in transforming or enhancing the transformation of many contaminants. While lab results show success, field application is less predictable due to naturally occurring chemical interferences and site limitations due to the lithologic and hydrogeologic setting. The key difficulty in implementing site treatment to achieve cleanup goals has been the ability to cost-effectively deliver treatment chemicals such that treatment chemicals come in contact with site contaminants prior to degrading or participating in un-wanted side reactions. The On-Contact Remediation Process® overcomes this barrier by following a four stage site treatment model:

Physical Stage – Most EBSI soil or groundwater sites are treated using Propagations. Propagations are replacements for inefficient injection wells. Propagations are installed using a hydraulic fracturing like technology to create a thin (2 to 4 cm) disk-like structure of up to 11,000 sq. ft. in influence. Treatment chemicals are infiltrated through this structure creating a treatment interval ranging in 7 to 20 feet in thickness (3 to 10 feet above and below the propagation plane). Final structure of a propagation is mapped using transits, sonics and down hole probes.

The On-Contact® family also includes a tension application system for groundwater remediation in fractured rock, pump and treat augmentation, a percolation bin system for shallow soils, sediment access system and new experimental wide-area in-situ system to be commercially available in 2001.

Preparation Stage – In all On-Contact® designs, contaminated areas are prepared in the subsurface for a higher efficiency of contaminant conversion to base states or harmless compounds. To prevent rebound effects contaminants need to be removed from adhering to, or being encapsulated in, local geology. To accomplish this, very low concentration and volume mixtures of conditioning reagents are used to enhance the chemical remediation within the influence of the Propagations.

Conversion Stage – Using oxidizers, food grade acids, catalysts, and/or reducing agents specifically configured for the site conditions, on-site contaminants are converted to harmless states "on-contact" as treatment chemicals are infiltrated through the propagation structure.

Restoration Stage –When independent testing results conclude a project is completed a Restoration Stage is applied. This is to reset sub-surface conditions, such as, pH or dissolved oxygen back to near-background levels. This protects water and soil quality, restores biological conditions and gives the site an ability to resist low-level contamination in the future.

One of the major innovations of the On-Contact® family is the use of sub-surface electronics to monitor the condition and travel of remedial chemistry and the real-time survivability of the contaminants. Real-time monitoring allows for tuning of application stages, ending the unpredictability of batch in-situ application.

Stephen Johnson, MPH, Peter Richards, MS, and Patrick Hurley, BS, MA DEP

In April 2001 the Massachusetts DEP installed a permeable reactive barrier (PRB) to treat a groundwater plume of chlorinated solvents migrating from an electronics manufacturer in Needham, Massachusetts toward the Town of Wellesley’s Rosemary Valley wellfield. The Town of Wellesley operates four water-supply wells within the Rosemary Brook basin, which account for approximately 52 percent of the town’s total water supply. The permeable reactive barrier technology is defined by EPA as "a permeable zone containing or creating a reactive treatment area oriented to intercept and remediate a contaminant plume". PRBs may be used to treat groundwater contaminated by chlorinated ethanes and ethenes and dissolved metals; research is progressing towards their application to other contaminants. The primary contaminant of concern at this site is trichloroethene (TCE), which has a maximum average concentration of approximately 225 micrograms per liter in the vicinity of the PRB; the federal drinking water standard is 5 micrograms per liter. The PRB is composed of a mix of granular zero-valent iron filings and sand with a design pure-iron thickness which varies along its length from 0.6 to 1.7 feet. The PRB was designed to intercept the entire overburden plume; previous study had indicated that the contaminant flux in the bedrock was negligible. Accordingly, the PRB was designed to be installed to the bedrock surface, up to 60 feet below grade in some places, with a length of 550 feet across the width of the plume. Though PRBs are no longer considered an innovative technology, the installation of a PRB in a residential neighborhood within a busy street, receiving approximately 17,000 vehicles per day, presented some unique construction difficulties.

Stephen Koenigsberg and Craig Sandefur, Regenesis

xygen Release Compound (ORC^®) is proprietary formulation of intercalated magnesium peroxide that releases oxygen slowly and facilitates the aerobic degradation of a range of environmental contaminants including petroleum hydrocarbons, certain chlorinated hydrocarbons, ether oxygenates and nitroaromatics. The history of ORC’s introduction and acceptance represents a model for the evolution of an innovative technology. This statement comes by virtue of the fact that since 1994 ORC has been used on over 6,500 sites worldwide and has been the subject of an extensive body of literature. This technology, which can be further characterized as one that employs a "time release electron acceptor", has now been clearly established as a sensible strategy for engineering accelerated bioattenuation on sites where design, capital and management intensive options are either undesirable or contraindicated. ORC can be configured as a permeable reactive barrier, applied as a broader plume treatment and emplaced post-excavation as part of the backfill. Some guidelines for using ORC have also emerged. It is contraindicated at sites where the BOD/COD load, seasonal or otherwise, is excessive or poorly understood, i.e, the technology is best applied to dissolved phase plumes and moderate levels of residual NAPL once the majority of the source is removed by more mechanically intensive means. With regard to the range of compounds that can be addressed, ORC was first used for the remediation of BTEX and TPH groundwater contamination and other applications have since been made, with variable results, on an array of other aerobically degradable compounds such as VC, PCP, PAHs and MTBE. With respect to MTBE, as early as 1996 consultants using ORC noticed that MTBE concentrations decreased at a higher than expected rate. Working on this foundation, in concert with published evidence that ethers are aerobically biodegradable, additional field experiments demonstrated that oxygen can indeed enhance the remediation of MTBE; a concept that has since been verified in other quarters.

Carlos S. Pachon, US EPA Technology Innovation Office.

It recent years the trend in remedy decisions made in sites in the Superfund program appeared to indicate a trend toward greater use of containment over treatment. Recent data suggests that the decline in selection of treatment options has stopped, and a slight increase has been witnessed over the last 2 years. In 1999 treatment decisions accounted for 47% of all source control records of decision signed in Superfund, and nearly half of these were in-situ remedies. Soil vapor extraction and solidification or stabilization continue to be the most frequently selected technologies (25% and 24% respectively). Bioremediation and Air Sparging were the third and fourth most selected technologies at about 13% each. In recent years, Superfund has continued to adopt innovative treatment technologies for soil and groundwater as these move up the development pipeline, such as Phytoremediation (9 projects) and Permeable Reactive Barriers (8 projects). Information on the application of these technologies is made available through the Annual Status Report (http://cluin.org/asr) and EPA’s online technology database (www.epareachit.org) to assist other decision makers in their search for information on past performances of these solutions to the nation’s hazardous waste problems.

Andrew R. Vitolins, Bruce R. Nelson, Scott A. Underhill, Malcolm Pirnie, Inc., LeeAnn M.H. Thomas, Canadian Pacific Railway.

Canadian Pacific Railway retained Malcolm Pirnie, Inc. to evaluate and implement remedial alternatives to address soil containing diesel fuel compounds at a former engine house facility in upstate New York. Due to the presence of historic structures and on-site operations, soil excavation was not practical. Traditional in-situ approaches would not have achieved site closure within the client's timeframe. Based on these site constraints, in-situ chemical oxidation was chosen as the preferred remedial alternative. A targeted treatment program was used to remediate unsaturated and saturated soils. This program consisted of multiple injections at varying depths within each of 148 temporary Geoprobe* injection points during two, separate, 10-day treatment events. Approximately 22,000 gallons of a chemical oxidant/catalyst mixture was injected into the subsurface during the project. This was the first application of this technology in unsaturated soils in the Northeast and the first in New York State to utilize temporary injection points. The use of in-situ chemical oxidation at this site greatly reduced the time and cost required for treatment. In accordance with the client's objectives, the project was completed in less than one year. The actual treatment time was less than three months. The results of the post-treatment samples show that the concentrations of the petroleum constituents in the subsurface soils were significantly reduced from their pre-treatment levels. Concentrations of volatile and semi-volatile organic petroleum compounds were reduced by approximately 70 percent, while the total petroleum hydrocarbon concentration was reduced by nearly 50 percent. Based on these results, it is estimated that more than 11,500 pounds of petroleum hydrocarbons were destroyed during the treatment program. The project has shown that the use of this technology can be as effective as traditional in-situ treatment technologies used for treating unsaturated and saturated subsurface diesel fuel contamination.