Life‐cycle assessment of in situ thermal remediation

A detailed cradle‐to‐grave life‐cycle assessment (LCA) of an in situ thermal treatment remedy for a chlorinated‐solvent‐contaminated site was performed using process LCA. The major materials and activities necessary to install, operate, monitor, and deconstruct the remedy were included in the analysis. The analysis was based on an actual site remedy design and implementation to determine the potential environmental impacts, pinpoint major contributors to impacts, and identify opportunities for improvements during future implementation. The Electro‐Thermal Dynamic Stripping Process (ET‐DSP?) in situ thermal technology coupled with a dual‐phase extraction and treatment system was evaluated for the remediation of 4,400 yd³ of tetrachloroethene‐ and trichloroethene‐impacted soil, groundwater, and bedrock. The analysis was based on an actual site with an estimated source mass of 2,200 lbs of chlorinated solvents. The remedy was separated into four stages: remedy installation, remedy operation, monitoring, and remedy deconstruction. Environmental impacts were assessed using Sima Pro software, the ecoinvent database, and the ReCiPe midpoint and endpoint methods. The operation stage of the remedy dominated the environmental impacts across all categories due to the large amount of electricity required by the thermal treatment technology. Alternate sources of electricity could significantly reduce the environmental impacts of the remedy across all impact categories. Other large impacts were observed in the installation stage resulting from the large amount of diesel fuel, steel, activated carbon, and asphalt materials required to implement the technology. These impacts suggest where opportunities for footprint reductions can be found through best management practices such as increased materials reuse, increased recycled‐content materials use, and clean fuels and emission control technologies. Smaller impacts were observed in the monitoring and deconstruction stages. Normalized results show the largest environmental burdens to fossil depletion, human toxicity, particulate matter formation, and climate‐change categories resulting from activities associated with mining of fossil fuels for use in electricity production. In situ thermal treatment can reliably remediate contaminated source areas with contaminants located in low‐permeability zones, providing complete destruction of contaminants in a short amount of time, quick return of the site to productive use, and minimized quantities of hazardous materials stored in landfills for future generations to remediate. However, this remediation strategy can also result in significant emissions over a short period of time. It is difficult to quantify the overall value of short‐term cleanups with intense treatment emissions against longer‐term cleanups with lower treatment emissions because of the environmental, social, and economic trade‐offs that need to be considered and understood. LCA is a robust, quantitative tool to help inform stakeholder discussions related to the remedy selection process, trade‐off considerations, and environmental footprint‐reduction opportunities, and to complement a broader toolbox for the evaluation of sustainable remediation strategies. © 2012 Wiley Periodicals, Inc.     

New advancements for in situ treatment using electrical resistance heating

Electrical resistance heating (ERH) is proving to be an effective technology to rapidly heat the subsurface and, in doing so, removing volatile organic compounds. Practitioners of this technology have observed that other processes (biodegradation, abiotic degradation, hydrolysis, and possibly others) occur to break down the chemicals of concern, and remediation is not solely accomplished through vaporization. Few sites treated using ERH have been monitored during and after treatment to identify and evaluate the processes occurring and assess the contribution of these other biological and chemical processes in the remediation effort so that they may be incorporated in the remediation design. At Fort Lewis, Washington, a landfill has been undergoing ERH treatment in three phases, where chlorinated volatile organic compounds represent the primary chemicals of concern in soil and groundwater. Other chemicals of concern include petroleum products, oils, and lubricants. The Fort Lewis remediation projects provided an opportunity to observe the reactions occurring in the subsurface during ERH and fine‐tune the study with each phase of operation. This study is still under way. However, the data gathered to date, which focuses on biodegradation, provides insights into the processes that have been observed. For the Fort Lewis site, biotic and abiotic degradation processes have been observed throughout the range of operating temperatures. At the lower temperature ranges (up to 70°C), biological processes appear to predominate. Above 70°C, abiotic processes become much more active. The goal of this work is to eventually optimize the use of these intrinsic processes in ERH remediation to reduce energy requirements and costs. © 2007 Wiley Periodicals, Inc.     

Sustained treatment: Implications for treatment timescales associated with source‐depletion technologies

Sustained treatment is an emerging concept used to describe enhancements in attenuation capacity after the conclusion of the active treatment period for a given source‐depletion technology. The term includes mechanisms that lead to contaminant transformation or destruction over extended periods of time, such as endogenous biomass decay, slow diffusion of remedial amendments from low‐permeability zones, and the formation of reactive mineral species. This “value‐added” treatment continues after the end of capital expenditures at a site, and it provides additional insight in determining if monitored natural attenuation is a viable long‐term option for a site. This article identifies several sustained treatment mechanisms, examines technology‐specific factors that contribute to sustained treatment, and explores the potential timescales of sustained treatment relative to active treatment. As demonstrated in post‐treatment site data obtained during a comprehensive source‐depletion technology performance survey, enhanced bioremediation is the most promising in promoting sustained treatment, and this beneficial effect can extend for several years due to factors such as slow biomass decay. There is little evidence that other commonly used technologies (thermal treatment, in situ chemical oxidation, surfactant‐enhanced remediation, or cosolvent flushing) result in any significant sustained treatment. An exception would be a cosolvent flushing project where large quantities of biodegradable cosolvent are left in the subsurface at the end of the project, which could result in sustained long‐term dechlorination activity. In the case of in situ chemical oxidation, factors that contribute to a higher incidence of concentration rebound mask any potential sustained treatment effects. © 2011 Wiley Periodicals, Inc.     

Challenges of soil mixing using catalyzed hydrogen peroxide with rotating dual axis blending technology

Although known to be one of the most effective oxidants for treatment of organic contaminants, catalyzed hydrogen peroxide (CHP) is typically not used for soil mixing applications because of health and safety concerns related to vapor generation and very rapid rates of reaction in open excavations. In likely the first large‐scale in situ CHP soil mixing application, an enhanced CHP, modified Fenton's reagent (MFR), was applied during soil mixing at the Kearsarge Metallurgical Superfund Site in New Hampshire. An innovative rotating dual‐axis blender (DAB) technology was used to safely mix the MFR into low‐plasticity silt and clay soils to remediate residual 1,1,1‐trichloroethane (111TCA); 1,1‐dichloroethene (11DCE); and 1,4‐dioxane (14D). It was expected that the aggressive treatment approach using relatively “greener” hydrogen peroxide (HP) chemistry would effectively treat Site contaminants without significant byproduct impacts to groundwater or the adjacent pond. The remediation program was designed to treat approximately 3,000 cubic yards of residual source area soil in situ by aggressively mixing MFR into the soils. The subsurface interval treated was from 7 to 15 feet below ground surface. To accurately track the soil mixing process and MFR addition, the Site was divided into 109 10‐foot square treatment cells that were precisely located, dosed, and mixed using the DAB equipped with an on‐board GPS system. The use of stabilizing agents along with careful calculation of the peroxide dose helped to ensure vapor‐free conditions in the vicinity of the soil mixing operation. Real‐time sampling and monitoring were critical in identifying any posttreatment exceedences of the cleanup goals. This allowed retreatment and supplemental testing to occur without impacting the soil mixing/in situ chemical oxidation (ISCO) schedule. Posttreatment 24‐hr soil samples were collected from 56 random locations after ensuring that the HP had been completely consumed. The posttreatment test results showed that 111TCA and 11DCE concentrations were reduced to nondetect (ND) or below the cleanup goals of 150 μg/kg for 111TCA and 60 μg/kg for 11DCE. Supplemental posttreatment soil samples, collected six months after treatment, showed 100 percent compliance with the soil treatment goals. Groundwater samples collected one year after the MFR soil mixing treatment program showed either ND or low concentrations for 111TCA, 11DCE, and 14D. Successful stabilization and site restoration was performed after overcoming considerable challenges associated with loss of soil structure, high liquid content, and reduced bearing capacity of the blended soils.     

In Situ Remediation of 1,4‐Dioxane Using Electrical Resistance Heating

Recent regulatory changes need more challenging treatment goals for 1,4‐dioxane. However, significant treatment limitations exist in part due to the high solubility and low Henry's law constant of 1,4‐dioxane. Two case studies are reported with substantial 1,4‐dioxane concentration reductions through in situ thermal remediation via electrical resistance heating (ERH). Concentration reductions greater than 99.8 percent of 1,4‐dioxane have been observed in the field using ERH. Concentrations of 1,4‐dioxane in air and steam extracted by an ERH vapor recovery system have also been evaluated. Laboratory studies were conducted to further understand the mechanisms that enable ERH remediation of 1,4‐dioxane. Vapor liquid equilibrium studies in water and soil were conducted and utilized to develop an ERH treatment cost model for 1,4‐dioxane. Existing field data were correlated to the 1,4‐dioxane treatment cost model. Field observations and laboratory testing indicate steam stripping that occurs through ERH remediation is an effective treatment method for 1,4‐dioxane. ©2015 Wiley Periodicals, Inc.     

In situ remediation of PCE at a site with clayey lithology and a significant smear zone

Groundwater at the former Serry's Dry Cleaning site in Corvallis, Oregon, was impacted by chlorinated volatile organic compounds (CVOCs). The primary CVOCs impacting the site include tetrachloroethene, trichloroethene, dichloroethene, and vinyl chloride, which were detected at concentrations up to 22,000, 1,700, 3,100, and 7 μg/L, respectively, prior to treatment. Large seasonal fluctuations in groundwater CVOC concentrations indicated that a significant fraction of the CVOC mass was present in the smear zone. Field‐scale pilot tests were performed for the Oregon Department of Environmental Quality's Dry Cleaner Program to evaluate the performance of EHC® in situ chemical reduction (ISCR) technology. The pilot study involved evaluating field performance and physical distribution into low‐permeability soil using basic Geoprobe® injection tooling. The testing results confirmed that bioremediation enhanced by ISCR supported long‐term treatment at the site. This article describes the implementation and results of the tests. Performance data are available from a three‐year period following the injections, allowing for a discussion about sustained performance and reagent longevity. © 2010 Wiley Periodicals, Inc.     

Vegetative remediation process offers advantages over traditional pump-and-treat technologies

The use of bioremediation technologies to clean up contaminated soil and groundwater is increasingly winning favor over more costly and often ineffective mechanical approaches. One new type of bioremediation process, known as TreeMediation^TM, uses trees and other vegetation to remediate soil by acting as a natural pump to extract and remediate contaminated groundwater in aquifers less than 30 feet deep. This article describes this innovative treatment method, shows its advantages over traditional pump and-treat techniques, and explains how TreeMediation is being used to extract nitrate and ammonium contamination from an aquifer in New Jersey.     

ART in‐well technology proves effective in treating 1,4‐dioxane contamination

A common industrial solvent additive is 1,4‐dioxane. Contamination of dissolved 1,4‐dioxane in groundwater has been found to be recalcitrant to removal by conventional, low‐cost remedial technologies. Only costly labor and energy‐intensive pump‐and‐treat remedial options have been shown to be effective remedies. However, the capital and extended operation and maintenance costs render pump‐and‐treat technologies economically unfeasible at many sites. Furthermore, pump‐and‐treat approaches at remediation sites have frequently been proven over time to merely achieve containment rather than site closure. A major manufacturer in North Carolina was faced with the challenge of cleaning up 1,4‐dioxane and volatile organic compound–impacted soil and groundwater at its site. Significant costs associated with the application of conventional approaches to treating 1,4‐dioxane in groundwater led to an alternative analysis of emerging technologies. As a result of the success of the Accelerated Remediation Technologies, LLC (ART) In‐Well Technology at other sites impacted with recalcitrant compounds such as methyl tertiarybutyl ether, and the demonstrated success of efficient mass removal, an ART pilot test was conducted. The ART Technology combines in situ air stripping, air sparging, soil vapor extraction, enhanced bioremediation/oxidation, and dynamic subsurface groundwater circulation. Monitoring results from the pilot test show that 1,4‐dioxane concentrations were reduced by up to 90 percent in monitoring wells within 90 days. The removal rate of chlorinated compounds from one ART well exceeded the removal achieved by the multipoint soil vapor extraction/air sparging system by more than 80 times. © 2005 Wiley Periodicals, Inc.     

Enhanced anaerobic bioremediation of a TCE source at the Tarheel Army Missile Plant using EOS

EOS, or emulsified oil substrate, was used to stimulate anaerobic biodegradation of trichloroethene (TCE) and tetrachloroethene (PCE) at a former Army‐owned manufacturing facility located in the Piedmont area of North Carolina. Previous use of chlorinated solvents at the facility resulted in soil and groundwater impacts. Ten years of active remediation utilizing soil vacuum extraction and air sparging (SVE/AS) were largely ineffective in reducing the TCE/PCE plume. In 2002, the Army authorized preparation of an amended Remedial Action Plan (RAP) to evaluate in situ bioremediation methods to remediate TCE in groundwater. The RAP evaluated eight groundwater remediation technologies and recommended EOS as the preferred bioremediation alternative for the site. Eight wells were drilled within the 100 × 100 feet area believed to be the primary source area for the TCE plume. In a first injection phase, dilute EOS emulsion was injected into half of the wells. Distribution of the carbon substrate through the treatment zone was enhanced by pumping the four wells that were not injected and recirculating the extracted water through the injection wells. The process was repeated in a second phase that reversed the injection/extraction well pairs. Overall, 18,480 pounds of EOS were injected and 163,000 gallons of water were recirculated through the source area. Anaerobic groundwater conditions were observed shortly after injection with a corresponding decrease in both PCE and TCE concentrations. Dissolved oxygen, oxidation‐reduction potential, and sulfate concentrations also decreased after injection, while TCE‐degradation products, ferrous iron, and methane concentrations increased. The reduction in TCE allowed the Army to meet the groundwater remediation goals for the site. Approximately 18 months after injection, eight wells were innoculated with a commercially prepared dechlorinating culture (KB‐1) in an attempt to address lingering cis‐1,2‐dichloroethene (cis‐DCE) and vinyl chloride (VC) that continued to be observed in some wells. Dehalococcoides populations increased slightly post‐bioaugmentation. Both cis‐DCE and VC continue to slowly decrease. © 2007 Wiley Periodicals, Inc.     

Successful unsaturated zone treatment of PCE with sodium permanganate

In situ chemical oxidation (ISCO) with permanganate has been widely used for soil and groundwater treatment in the saturated zone. Due to the challenges associated with achieving effective distribution and retention in the unsaturated zone, there is a great interest in developing alternative injection technologies that increase the success of vadose‐zone treatment. The subject site is an active dry cleaner located in Topeka, Kansas. A relatively small area of residual contamination adjacent to the active facility building has been identified as the source of a large sitewide groundwater contamination plume with off‐site receptors. The Kansas Department of Health and Environment (KDHE) currently manages site remedial efforts and chose to pilot‐test ISCO with permanganate for the reduction of perchloroethene (PCE) soil concentrations within the source area. KDHE subsequently contracted Burns & McDonnell to design and implement an ISCO pilot test. A treatability study was performed by Carus Corporation to determine permanganate‐soil‐oxidant‐demand (PSOD) and the required oxidant dosing for the site. The pilot‐test design included an ISCO injection approach that consisted of injecting aqueous sodium permanganate using direct‐push technology with a sealed borehole. During the pilot test, approximately 12,500 pounds of sodium permanganate were injected at a concentration of approximately 3 percent (by weight) using the methods described above. Confirmation soil sampling conducted after the injection event indicated PCE reductions ranging from approximately 79 to more than 99 percent. A follow‐up treatment, consisting of the injection of an additional 6,200 pounds of sodium permanganate, was implemented to address residual soil impacts remaining in the soil source zone. Confirmation soil sampling conducted after the treatment indicated a PCE reduction of greater than 90 percent at the most heavily impacted sample location and additional reductions in four of the six samples collected. © 2009 Wiley Periodicals, Inc.     

Constant Head Injection for Enhanced In Situ Chemical Oxidation

With the successful implementation of in situ chemical oxidation (ISCO) programs to remediate contaminated soil and groundwater aquifers worldwide, ISCO has become established as a traditional remediation technique. On the basis of historical success, expanded ISCO practices are now routinely applied to increasingly difficult geologic environments, including formerly problem locations such as those containing nonaqueous‐phase liquid, fractured bedrock, low‐conductivity media, and highly layered and/or heterogeneous aquifers. Effective delivery of amendment, however, remains the single most important aspect of successful remediation, particularly given the range of potentially applicable delivery methods and site complexities. Selecting the most appropriate technique for any specific site depends upon a clear understanding of the variety of site constraints, including factors such as site conditions, underlying geology, contaminant distribution, technology limitations, and other project‐specific factors. Because the injection program is often the largest cost associated with implementation of an ISCO project, it is critical to develop a cost‐effective injection method for each site. Constant head injection provides a cost‐effective alternative for sites with low‐conductivity lithology(ies). Constant head injection employs a continuous low‐pressure application method to deliver ISCO agents over a long period of time. This synergistic method complements the existing site conditions and heterogeneity, working with the natural conditions, rather than trying to overcome or destroy the site geology using highly aggressive delivery techniques. © 2014 Wiley Periodicals, Inc.     

Evolution of predictive tools for in situ bioremediation and natural attenuation evaluations

Proving the viability of in situ bioremediation technologies and gathering data for its full‐scale implementation typically involves collecting multiple rounds of data and often completing microcosm studies. Collecting these data is cumbersome, time‐consuming, costly, and typically difficult to scale. A new method of completing microcosm studies in situ using an amendable sampling device deployed and incubated in groundwater monitoring wells provides actionable data to expedite site cleanup. The device, referred to as a Bio‐Trap® sampler, is designed to collect actively colonizing microbes and dissolved organic compounds from groundwater for analysis using conventional analytical techniques and advanced diagnostic tools that can answer very specific design and viability questions relating to bioremediation. Key data that can be provided by in situ microcosm studies using Bio‐Trap® samplers include definitively demonstrating contaminant destruction by using compound‐specific isotope analysis and providing data on the mechanism of the degradation by identifying the responsible microbes. Three case studies are presented that demonstrate the combined flexibility of Bio‐Trap® samplers and advanced site diagnostics. The applications include demonstrating natural attenuation of dissolved chlorinated solvents, demonstrating natural attenuation of dissolved petroleum compounds, and using multiple Bio‐Trap® samplers to comparatively assess the viability of bioaugmentation at a chlorinated solvent release site. At each of these sites, the in situ microcosm studies quickly and cost‐effectively answered key design and viability questions, allowing for regulatory approval and successful full‐scale implementation. © 2010 Wiley Periodicals, Inc.     

Augmenting in-situ remediation by soil vapor extraction with six-phase soil heating

The use and performance of soil vapor extraction (SVE) as an in-situ remedial technology has been limited at numerous sites because of both geologic and chemical factors. SVE systems are not well suited to sites containing low permeability soils or sites contaminated with recalcitrant compounds. Six-phase soil heating (SPSH) has been developed by the Battelle Pacific Northwest Laboratories (Battelle) to enhance SVE systems. The technology utilizes resistive soil heating to increase the vapor pressure of subsurface contaminants and to generate an in-situ source of steam. The steam strips contaminants sorbed onto soil surfaces and acts as a carrier gas, providing an enhanced mechanism by which the contaminants can reach an extraction well. Full-scale applications of SPSH have been performed at the U.S. Department of Energy's Savannah River Site in Aiken, South Carolina; at a former fire training site in Niagara Falls, New York; and at Fort Richardson near Anchorage, Alaska. At each site, chlorinated solvents were present in low permeability soils and SPSH was applied in conjunction with SVE. The results of the three applications showed that SPSH is a cost-effective technology that can reduce the time required to remediate a site using only conventional SVE.     

1,4‐Dioxane Treatment Technologies

The chlorinated solvent stabilizer 1,4‐dioxane (DX) has become an unexpected and recalcitrant groundwater contaminant at many sites across the United States. Chemical characteristics of DX, such as miscibility and low sorption potential, enable it to migrate at least as far as the chlorinated solvent from which it often originates. This mobility and recalcitrance has challenged remediation professionals to redesign existing treatment systems and monitoring networks to accommodate widespread contamination. Furthermore, remediation technologies commonly applied to chlorinated solvent co‐contaminants, such as extraction and air stripping or in situ enhanced reductive dechlorination, are relatively ineffective on DX removal. These difficulties in treatment have required the industry to identify, develop, and demonstrate new and innovative technologies and approaches for both ex situ and in situ treatment of this emerging contaminant. Great strides have been made over the past decade in the development and testing of remediation technologies for removal or destruction of DX in groundwater. This article briefly summarizes the fate and transport characteristics of DX that make it difficult to treat, and presents technologies that have been demonstrated to be applicable to groundwater treatment at the field scale.  ©2016 Wiley Periodicals, Inc.     

In situ Remediation of Metals Comes of Age

Since the early 1970s, technologies for remediating organic contamination in soils and groundwater have evolved through three stages with primary emphasis on (1) gross removal processes, (2) active in situ treatment, and (3) risk-based closure and natural attentuation. Technologies for treating metals contamination are evolving through similar stages. In the late 1990s, metals remediation has arrived at the second stage in which a wide range of in situ technologies are available either to extract metals directly from the subsurface or to render them immobile and harmless. In situ geochemical fixation is an example of a commercial technology capable of addressing a wide range of metals contamination sites. Four case histories demonstrate the versatility of this approach. Other promising technologies for treating metals contamination are also emerging. These include geokinetics, biocatalytic precipitation processes, phytoremediation, and artificial wetlands. As our knowledge continues to grow, the most elegant solutions to metals contamination will rely more and more heavily on the soil's natural capacity to stabilize and immobilize metals over time.     

Sustainable soil remediation by refrigerated condensation at sites with “high‐concentration” recalcitrant compounds and NAPL: Two case studies

Remediation of recalcitrant compounds at sites with high concentrations of volatile organic compounds (VOCs) or nonaqueous‐phase liquids (NAPLs) can present significant technical and financial (long‐term) risk for stakeholders. Until recently, however, sustainability has not been included as a significant factor to be considered in the feasibility and risk evaluation for remediation technologies. The authors present a framework for which sustainability can be incorporated into the remediation selection criteria focusing specifically on off‐gas treatment selection for soil vapor extraction (SVE) remediation technology. SVE is generally considered an old and standard approach to in situ remediation of soils at a contaminated site. The focus on off‐gas treatment technology selection in this article allows for more in‐depth analysis of the feasibility evaluation process and how sustainable practices might influence the process. SVE is more commonly employed for recovery of VOCs from soils than other technologies and generally employs granular activated carbon (GAC), catalytic, or thermal oxidation, or an emerging alternative technology known as cryogenic‐compression and condensation combined with regenerative adsorption (C3–Technology). Of particular challenge to the off‐gas treatment selection process is the potential variety of chemical constituents and concentrations changing over time. Guidance is available regarding selection of off‐gas treatment technology (Air Force Center for Environmental Excellence, 1996; U.S. Environmental Protection Agency, 2006). However, there are common shortcomings of off‐gas treatment technology guidance and applications; practitioners have rarely considered sustainability and environmental impact of off‐gas treatment technology selection. This evaluation includes consideration of environmental sustainability in the selection of off‐gas treatment technologies and a region‐specific (Los Angeles, California) cost per pound and time of remediation comparisons between GAC, thermal oxidation, and C3–Technology. © 2008 Wiley Periodicals, Inc.     

In Situ solidification—A case study at a former manufactured gas plant in Macon,Georgia

In situ solidification (ISS) is a reliable, EPA‐recognized technology for the treatment of industrial and waste sites. ISS was employed at a former manufactured gas plant (MGP) site in Macon, Georgia, for the treatment of approximately 33,000 cubic yards of coal tar residues in the saturated zone soil. The site is regulated by the Georgia Environmental Protection Division (EPD) under the Hazardous Site Rehabilitation Act (HSRA) and is located approximately four blocks from downtown Macon. This article will review the technical and regulatory basis for the successful use of this technology, provide an overview of the treatability and pilot testing used to develop the design and implementation of the treatment process, and present the results of the application of ISS to an MGP site. The results of groundwater monitoring, pre and postremediation, will also be discussed. © 2004 Wiley Periodicals, Inc.     

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

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.     

Groundwater geochemistry diagnostics during in situ ERH remediation

In situ remediation represents a series of challenges in interpreting the monitoring data on remedial progress. Among these challenges are problems in determining the progress of the remediation and the mechanisms responsible, so that the process can be optimized. The release of organic pollutants to groundwater systems and in situ remediation technologies alter the groundwater chemistry, but outside of natural attenuation studies using inorganic chemical analyses as indicators of intrinsic biodegradation, typically little attention has been paid to the changes in inorganic groundwater chemistry. Smith (2008) noted that during an electrical resistance heating remediation that took place at a confidential site in Chicago, a two‐orders‐of‐magnitude increase in chloride concentrations occurred during the remediation. This increase in chloride resulted in a corresponding increase in calcium as a result of what is known as the common ion effect. Carbon dioxide is the gas found in highest concentrations in natural groundwater (Stumm & Morgan, 1981), and its fugacity (partial pressure) corresponds directly with calcium concentrations. Carbon dioxide at supersaturation in groundwater is capable of dissolving organic compounds, such as trichloroethene, facilitating removal of nonaqueous‐phase liquids at temperatures below the boiling point of water. One means of diagnosing these reactions is through the use of compound‐specific isotopic analysis, which is capable of distinguishing between evaporation, biodegradation, and differences in sources. The appropriate diagnosis has the potential to optimize the benefits from these reactions, lower energy costs for removal of nonaqueous‐phase liquids, and direct treatment where it is needed most. © 2010 Wiley Periodicals, Inc.     

Spatial Distribution of Geobacteraceae and Sulfate‐Reducing Bacteria During In Situ Bioremediation of Uranium‐Contaminated Groundwater

Analysis of the physiological status of subsurface microbial communities generally relies on the study of unattached microorganisms in the groundwater. These approaches have been employed in studies on bioremediation of uranium‐contaminated groundwater at a study site in Rifle, Colorado, in which Geobacter species typically account for over 90 percent of the microbial community in the groundwater during active uranium reduction. However, to develop efficient in situ bioremediation strategies it is necessary to know the status of sediment‐associated microorganisms as well. In order to evaluate the distribution of the natural community of Geobacter during bioremediation of uranium, subsurface sediments were packed into either passive flux meters (PFMs) or sediment columns deployed in groundwater monitoring wells prior to acetate injection during in situ biostimulation field trials. The trials were performed at the Department of Energy's (DOE's) Rifle Integrated Field Research Challenge site. Sediment samples were removed either during the peak of Fe(III) reduction or the peak of sulfate reduction over the course of two separate field experiments and preserved for microscopy. Direct cell counts using fluorescence in situ hybridization (FISH) probes targeting Geobacter species indicated that the majority of Geobacter cells were unattached during Fe(III) reduction, which typically tracks with elevated rates of uranium reduction. Similar measurements conducted during the sulfate‐reducing phase revealed the majority of Geobacter to be attached following exhaustion of more readily bioavailable forms of iron minerals. Laboratory sediment column studies confirmed observations made with sediment samples collected during field trials and indicated that during Fe(III) reduction, Geobacter species are primarily unattached (90 percent), whereas the majority of sulfate‐reducing bacteria and Geobacter species are attached to sediment surfaces when sulfate reduction is the predominant form of metabolism (75 percent and 77 percent, respectively). In addition, artificial sediment experiments showed that pure cultures of Geobacter uraniireducens, isolated from the Rifle site, were primarily unattached once Fe(III) became scarce. These results demonstrate that, although Geobacter species must directly contact Fe(III) oxides in order to reduce them, cells do not firmly attach to the sediments, which is likely an adaptive response to sparsely and heterogeneously dispersed Fe(III) minerals in the subsurface. © 2013 Wiley Periodicals, Inc.