Characterization and pilot‐scale studies for chemical oxidation remediation of fractured shale

The distribution of volatile organic compounds (VOCs) in fractured shale overlain by thin (< 10 feet) overburden at the Watervliet Arsenal near Albany, New York, was initially determined by sampling water from the fracture network using packer systems in boreholes and also using conventional monitoring wells. Furthermore, short‐term pumping and injection tests were conducted and the boreholes were logged using a variety of geophysical and hydrophysical tools. Tetrachloroethene is the dominant VOC in the groundwater, with lesser concentrations of trichloroethene and degradation products (cis‐1,2‐dichloroethene, trans‐1,2‐dichloroethene, and vinyl chloride). The vertical VOC distributions in the rock matrix were obtained from continuous‐cored holes from which small rock samples, collected at many depths between 18 and 150 feet below ground surface, were analyzed. The rock core VOC concentrations were determined by methanol extraction of crushed rock followed by direct methanol injection onto a gas chromatograph and subsequent estimation of rock porewater VOC concentrations. The rock core data support the concept that diffusion‐driven mass transfer has caused nearly all the VOC mass initially present in the fractures to now reside in the rock matrix, which has a porosity three or four orders of magnitude larger than the bulk fracture porosity. The results of the site characterization indicate that an effective site investigation strategy in fractured shale must include characterization of both the fracture and matrix contaminant distribution. These results also indicate that the most favorable remediation technologies for this fractured shale are those that will destroy VOCs in the rock matrix, particularly contaminants in the sorbed phase, and also destroy the VOC mass in the fractures including both dissolved and immiscible phases. The site characterization resulted in the selection of potassium permanganate for an in situ chemical oxidation pilot study. © 2004 Wiley Periodicals, Inc.     

The in situ treatment of TCE and PFAS in groundwater within a silty sand aquifer

Chlorinated ethenes such as trichloroethene (TCE), cis‐1,2‐dichloroethene (cis‐1,2‐DCE), and vinyl chloride along with per‐ and polyfluoroalkyl substances (PFAS) have been identified as chemicals of concern in groundwater; with many of the compounds being confirmed as being carcinogens or suspected carcinogens. While there are a variety of demonstrated in‐situ technologies for the treatment of chlorinated ethenes, there are limited technologies available to treat PFAS in groundwater. At a former industrial site shallow groundwater was impacted with TCE, cis‐1,2‐DCE, and vinyl chloride at concentrations up to 985, 258, and 54 µg/L, respectively. The groundwater also contained maximum concentrations of the following PFAS: 12,800 ng/L of perfluoropentanoic acid, 3,240 ng/L of perfluorohexanoic acid, 795 ng/L of perfluorobutanoic acid, 950 ng/L of perfluorooctanoic acid, and 2,140 ng/L of perfluorooctanesulfonic acid. Using a combination of adsorption, biotic, and abiotic degradation in situ remedial approaches, the chemicals of concern were targeted for removal from the groundwater with adsorption being utilized for PFAS whereas adsorption, chemical reduction, and anaerobic biodegradation were used for the chlorinated ethenes. Sampling of the groundwater over a 24‐month period indicated that the detected PFAS were treated to either their detection, or below the analytical detection limit over the monitoring period. Postinjection results for TCE, cis‐1,2‐DCE, and vinyl chloride indicated that the concentrations of the three compounds decreased by an order of magnitude within 4 months of injection, with TCE decreasing to below the analytical detection limit over the 24‐month monitoring period. Cis‐1,2‐DCE, and vinyl chloride concentrations decreased by over 99% within 8 months of injections, remaining at or below these concentrations during the 24‐month monitoring period. Analyses of Dehalococcoides, ethene, and acetylene over time suggest that microbiological and reductive dechlorination were occurring in conjunction with adsorption to attenuate the chlorinated ethenes and PFAS within the aquifer. Analysis of soil cores collected pre‐ and post‐injection, indicated that the distribution of the colloidal activated carbon was influenced by small scale heterogeneities within the aquifer. However, all aquifer samples collected within the targeted injection zone contained total organic carbon at concentrations at least one order of magnitude greater than the preinjection total organic carbon concentrations.     

Pilot‐scale evaluation of in situ cometabolic bioremediation of TCE in groundwater using PHOSter® technology

A study was conducted to evaluate the efficacy of PHOSter® technology for treating groundwater contaminated with trichloroethene (TCE) at Edwards Air Force Base, California. The technology consists of injecting a gaseous mixture of air, methane, and nutrients into groundwater with the objective of stimulating the growth of methanotrophs, a naturally occurring microbial group that is capable of catalyzing the aerobic degradation of chlorinated solvents into nontoxic products. Injection operations were performed at one well for a period of three months. Six monitoring wells were utilized for groundwater and wellhead vapor monitoring and for groundwater and microbial sampling. In the five monitoring wells located within 44 feet of the injection well, the following results were observed: dissolved oxygen concentrations increased to a range between 6 and 8 milligrams per liter (μg/L); the biomass of target microbial groups increased by one to five orders of magnitude; and TCE concentrations decreased by an average of 92 percent, and to below the California primary maximum contaminant level (MCL; 5 micrograms per liter [µg/L]) in the well closest to the injection well. © 2008 Wiley Periodicals, Inc. *

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

     

Bench‐ and pilot‐scale applications of electrochemical peroxidation: A new remedial concept

Electrochemical peroxidation (ECP) is a proprietary process that utilizes sacrificial iron electrodes and stochiometrically balanced applications of hydrogen peroxide to efficiently destroy aqueous phase contaminants. In laboratory trials it has been successful in reducing, often to non‐detectable levels, BTEX, fuel additives, chlorinated solvents, and polychlorinated biphenyls in ground waters. The process has also been found effective in reducing the chemical and biological oxygen demand of industrial waste water. Agency‐approved pilot tests will be conducted at two gasoline spill sites during 2000 where traditional pump and treat methods have proven ineffectual because of ground water chemistry or subsurface hydrologic conditions. The ECP process utilizes a tripartite treatment strategy consisting of 1) ex situ chemical oxidation; 2) in situ oxidation by reinjection of treated water with residual oxidants at the head of the plume; and 3) reestablishment of aerobic biodegradation by alteration of subsurface redox conditions. In contrast to other in situ oxidation treatment methods, dissolved iron is derived electrochemically, negating the need for ferrous salt addition. Dilute hydrogen peroxide (3 percent) is incrementally added to maximize oxidation efficiency and eliminate safety and environmental concerns accompanying the use of highly concentrated solutions. Results of laboratory trials and the geological and geochemical considerations of upcoming pilot‐scale applications are presented. Other potential applications currently under investigation include combination with other remedial processes (e.g. permeable barriers and hydrogen release compounds) to insure complete and rapid contaminant mineralization.     

Full‐scale in‐situ biobarrier demonstration for containment and treatment of MTBE

The Naval Facilities Engineering Service Center (NFESC), Arizona State University, and Equilon Enterprises LLC are partners in an innovative Environmental Security Technology Certification Program cleanup technology demonstration designed to contain dissolved MTBE groundwater plumes. This full‐scale demonstration is being performed to test the use of an oxygenated biobarrier at Naval Base Ventura County, in Port Hueneme, California. Surprisingly, few cost‐effective in‐situ remedies are known for the cleanup of MTBE‐impacted aquifers, and remediation by engineered in‐situ biodegradation was thought to be an unlikely candidate just a few years ago. This project demonstrates that MTBE‐impacted groundwater can be remediated in‐situ through engineered aerobic biodegradation under natural‐flow conditions. With respect to economics, the installation and operation costs associated with this innovative biobarrier system are at least 50 percent lower than those of a conventional pump and treat system. Furthermore, although it has been suggested that aerobic MTBE biodegradation will not occur in mixed MTBE‐BTEX dissolved plumes, this project demonstrates otherwise. The biobarrier system discussed in this article is the largest of its kind ever implemented, spanning a dissolved MTBE plume that is over 500 feet wide. This biobarrier system has achieved an in‐situ treatment efficiency of greater than 99.9 percent for dissolved MTBE and BTEX concentrations. Perhaps of greater importance is the fact that extensive performance data has been collected, which is being used to generate best‐practice design and cost information for this biobarrier technology. © 2001 John Wiley & Sons, Inc.     

Ex situ treatment of MTBE‐containing groundwater by a UV peroxide system

This article describes the design, implementation, and operating results for an ex situ ultraviolet/hydrogen peroxide (UVP) system to treat methyl tert‐butyl ether (MTBE) in extracted groundwater. The UVP modification was designed to reduce the operation and maintenance costs of an existing groundwater pump‐and‐treat treatment system that relied on air stripping and carbon adsorption. The UVP system is relatively inexpensive and can easily be scaled to cope with different groundwater extraction rates up to 80 gpm by adding UV lamps in series or in parallel at the higher groundwater extraction rates. The MTBE concentration in the effluent from the UVP system to the carbon vessels decreased from an average of 590 μg/L to approximately 2 μg/L on average over 33 months of operation of the UVP. Incorporation of this UVP modification as a second‐stage treatment to the groundwater pump‐and‐treat/soil vapor extraction system, after the air stripper and prior to the carbon vessels, significantly increased the usable life of the carbon (from two months previously to about two years after installation) and completely resolved the issue of frequent MTBE breakthroughs of the carbon that had plagued the remediation system since its inception. © 2006 Wiley Periodicals, Inc.     

Treatment of Sydney N.S. tar pond sludge in a pilot‐scale rotary kiln

Tar pond wastes from Sydney, Nova Scotia, containing 50 ppm or more of polychlorinated biphenyls (PCBs) were treated in a pilot‐scale rotary kiln. In order to use the existing feed system attached to the rotary kiln, the wastes were first oven‐dried. Stack gas sampling was conducted during the test, which included measurement of volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), semi‐volatile organic compounds (SVOCs), HCl, and metals. The purpose of this study was to determine emissions from treatment of the tar pond waste using rotary kiln technology. It was found that the dried sludge could sustain combustion in the kiln without any supporting fuel. The emissions of polychlorinated dibenzodioxins/furans (PCDD/Fs) were higher than the Canadian Council of Ministers of the Environment (CCME) air emissions guidelines, and the reasons for this are discussed. © 2008 Wiley Periodicals, Inc.     

Evaluating the longevity of a PFAS in situ colloidal activated carbon remedy

The remediation of per‐ and polyfluoroalkyl substances by injection of colloidal activated carbon (CAC) at a contaminated site in Central Canada was evaluated using various visualization and modeling methods. Radial diagrams were used to illustrate spatial and temporal trends in perfluoroalkyl acid (PFAA) concentrations, as well as various redox indicators. To assess the CAC adsorption capacity for perfluorooctane sulfonate (PFOS), laboratory Freundlich isotherms were derived for PFOS mixed with CAC in two solutions: (1) PFOS in a pH 7.5 synthetic water that was buffered by 1 millimolar NaHCO₃ (K_f = 142,800 mg^1‐a L^a/kg and a = 0.59); and (2) a groundwater sample (pH = 7.4) containing PFOS among other PFAS from a former fire‐training area in the United States (K_f = 4,900 mg^1‐a L^a/kg and a = 0.24). A mass balance approach was derived to facilitate the numerical modeling of mass redistribution after CAC injection, when mass transitions from a two‐phase system (aqueous and sorbed to organic matter) to a three‐phase system that also includes mass sorbed to CAC. An equilibrium mixing model of mass accumulation over time was developed using a finite‐difference solution and was verified by intermodel comparison for prediction of CAC longevity in the center of a source area. A three‐dimensional reactive transport model (ISR‐MT3DMS) was used to indicate that the CAC remedy implemented at the site is likely to be effective for PFOS remediation for decades. Model results are used to recommend remedial design and monitoring alternatives that account for the uncertainty in long‐term performance predictions.     

Pilot‐scale demonstration of in situ capping of PCB‐containing sediments in the lower Grasse River

A fish‐consumption advisory is currently in effect in a seven‐mile stretch of the Grasse River in Massena, New York, due to elevated levels of PCBs in fish tissue. One remedial approach that is being evaluated to reduce the PCB levels in fish from the river is in situ capping. An in‐river pilot study was conducted in the summer of 2001 to assess the feasibility of capping PCB‐containing sediments of the river. The study consisted of the construction of a subaqueous cap in a seven‐acre portion of the river using various combinations of capping materials and placement techniques. Optimal results were achieved with a 1:1 sand/topsoil mix released from a clamshell bucket either just above or several feet below the water surface. A longer‐term monitoring program of the capped area commenced in 2002. Results of this monitoring indicated: 1) the in‐place cap has remained intact since installation; 2) no evidence of PCB migration into and through the cap; 3) groundwater advection through the cap is not an important PCB transport mechanism; and 4) macroinvertebrate colonization of the in‐place cap is continuing. Additional follow‐up monitoring in the spring of 2003 indicated that a significant portion of the cap and, in some cases, the underlying sediments had been disturbed in the period following the conclusion of the 2002 monitoring work. An analysis of river conditions in the spring of 2003 indicated that a significant ice jam had formed in the river directly over the capping pilot study area, and that the resulting increase in river velocities and turbulence in the area resulted in the movement of both cap materials and the underlying sediments. The pilot cap was not designed to address ice jam–related forces on the cap, as the occurrence of ice jams in this section of the river had not been known prior to the observations conducted in the spring of 2003. These findings will preclude implementation of the longer‐term monitoring program that had been envisioned for the pilot study. The data collected immediately after cap construction in 2001 and through the first year of monitoring in 2002 serve as the basis for the conclusions presented in this article. It should be recognized that, based on the observation made in the spring of 2003, some of these conclusions are no longer valid for the pilot study area.The occurrence of ice jams in the lower Grasse River and their importance on sediments and PCBs within the system are currently under investigation. © 2003 Wiley Periodicals, Inc.     

The in situ treatment of synthetic musk fragrances in groundwater

Synthetic musk fragrances (SMFs) have been shown to be micropollutants in various aquatic and groundwater systems, often occurring at microgram per liter concentrations. Studies have shown that the most commonly detected SMFs in water are nitro musks and polycyclic musks. The SMFs are typically introduced into the environment in continuous streams such as from wastewater and land application of wastewater or sludge generated during wastewater treatment. Various studies for the treatment of SMFs have been undertaken for wastewater but studies for the treatment of SMFs in groundwater are limited, especially for in situ treatment. A pilot‐scale test was conducted to determine if the use of colloidal activated carbon (CAC) could effectively reduce dissolved concentrations of nitro and polycyclic synthetic musk compounds including musk xylene, musk ketone, galaxolide, and tonalide. The pilot test was carried out downgradient of a septic system in Central Canada where a series of nitrification and denitrification reactions are occurring in an unconfined aquifer. A 10‐weight percent CAC solution was injected into a series of temporary direct push injection points to target the synthetic musk plume. The plume contained galaxolide and tonalide concentrations up to 687 and 187 nanograms per liter (ng/L), respectively, while the concentrations of musk ketone and musk xylene were below the method detection limit (20 ng/L). A total of 13,950 liters of CAC solution was injected during one injection event. The pilot test results indicated that the CAC was effectively delivered to the target injection zone resulting in an increase in total organic carbon concentrations within the saturated soil greater than two orders of magnitude compared to the background concentrations. Analyses of the groundwater chemistry before and post‐injection indicated that the CAC had no detrimental impact on the groundwater quality while reducing the concentration of dissolved galaxolide and tonalide within the plume to below the method detection limits within 51 days of injection with the exception of two of the 14 wells monitored which had galaxolide and tonalide concentrations up to 78 and 35 ng/L. Within 6 months of application, the concentrations of galaxolide and tonalide had decreased to below the method detection limits. Subsequent monitoring of the groundwater quality over a one‐year period failed to detect galaxolide and tonalide, suggesting that the CAC was effective in attenuating the galaxolide and tonalide.     

A chemox treatment for urea‐ and ammonium‐contaminated groundwater

In a pilot project performed at a fertilizer manufacturing facility, a one‐step chemical oxidation technique successfully treated urea‐ and ammonium‐contaminated groundwater. The oxidation reaction occurred in an 1,100‐gallon batch reactor. The contaminated inflow was buffered by the metered addition of sodium bicarbonate solution and subsequently treated with sodium hypochlorite in an 8:1 weight ratio of Cl₂:N. In an instantaneous reaction, the urea and ammo‐nium‐N were completely oxidized to nitrogen gas that was vented to the atmosphere during mixing. The pH of the reactor discharge was ?6.5. Sodium sulfite was used to reduce residual hypochlorite in the reactor effluent to chloride to provide process water with characteristics suitable for discharge. Oxidation rates were similar with different strengths of hypochlorite; however, a 5 to 6 percent sodium hypochlorite (as Cl₂) solution was the most stable. © 2005 Wiley Periodicals, Inc.     

Solvent extraction and soil washing treatment of contaminated soils from wood preserving sites: Bench‐scale studies

Bench‐scale solvent extraction and soil washing studies were performed on soil samples obtained from three abandoned wood preserving sites included in the National Priority List. The soil samples from these sites were contaminated with high levels of polyaromatic hydrocarbons (PAHs), pentachlorophenol (PCP), dioxins, and heavy metals. The effectiveness of the solvent extraction process was assessed using liquefied propane or dimethyl ether as solvents over a range of operating conditions. These studies have demonstrated that a two‐stage solvent extraction process using dimethyl ether as a solvent at a ratio of 1.61 per kg of soil could decrease dioxin levels in the soil by 93.0 to 98.9 percent, and PCP levels by 95.1 percent. Reduction percentages for benzo(a)pyrene (BaP) potency estimate and total detected PAHs were 82.4 and 98.6 percent, respectively. Metals concentrations were not reduced by the solvent extraction treatment. These removal levels could be significantly improved using a multistage extraction system. Commercial scale solvent extraction using liquefied gases costs about $220 per ton of contaminated soil. However, field application of this technology at the United Creosote site, Conroe, Texas, failed to perform to the level observed at bench scale due to the excessive foaming and air emission problem. Soil washing using surfactant solution and wet screening treatability studies were also performed on the soil samples in order to assess remediation strategies for sites. Although aqueous phase solubility of contaminants seemed to be the most important factor affecting removal of contaminants from soil, surfactant solutions (3 percent by weight) having nonionic surfactants with hydrophile‐lipophile balance (HLB) of about 14 (Makon‐12 and Igepal CA 720) reduced the PAH levels by an average of 71 percent, compared to no measurable change when pure deionized water was used. Large fractioza of clay and silt (<0.06mm), high le!ezielsof orgaizic contami‐ nants and hzimic acid can makesoil washing less applicable.     

Identification of pyrene‐degradation pathways: Bench‐scale studies using Pseudomonas fluorescens 29L

This article summarizes the bench‐scale studies to identify pyrene‐degradation pathways using an environmental microbial isolate, Pseudomonas fluorescens 29L. Strain 29L was grown on 50 mg of pyrene per liter of mineral medium. At a pyrene biodegradation rate of 14.7 mg/L of medium/day, 82.38 percent of pyrene was degraded in six days. Naphthalene and phenanthrene accounted for 1.09 percent and 3.69 percent, respectively, of the carbon mass from pyrene in the late log phase. Substituted benzene compounds accounted for 26.10 percent of the carbon mass from pyrene in the late log phase. In the stationary phase, carboxylic acids accounted for 10.44 percent of the carbon mass from pyrene. Strain 29L mutants were used for enzyme assays. Pyrene is oxidized by monoxygenases and dioxygenases, and the oxidized ring is cleaved. These enzymes were induced in the presence of pyrene and their activities peaked in the late log phase. No gentisate 1,2‐dioxygenase activity was detected in Strain 29L wild type (WT), whereas mutant M15 did not show any catechol 2,3‐dioxygenase activity. This indicates the possibility of multiple branchings in the pyrene‐biodegradation pathways. In conclusion, multiple degradative pathways are operating concurrently in this strain. The study shows the versatility of Pseudomonas fluorescens Strain 29L for pyrene degradation. It also emphasizes the need to study pyrene‐degradation pathways in other microorganisms so as to enhance the bioremediation potential for the in situ treatment of pyrene‐contaminated sites. © 2008 Wiley Periodicals, Inc.     

Before‐after control‐impact paired modeling of groundwater bentazon treatment at a phytoremediation site

A Before‐ After Control‐ Impact Paired (BACIP) model was used to evaluate the effectiveness of phytoremediation treatment on reduction of bentazon concentrations in shallow groundwater at a study site in Louisiana. Two different statistical approaches were made to evaluate the impact to this test site from the remediation program through time. Data were evaluated by Bayesian analysis of variance test methods. Data sets were unique in that the control data used for impact evaluation, as compared to before and after data, were compiled from groundwater upgradient monitoring wells existing prior to remediation. The statistical model supports the hypothesis that the phytoremediation program has positively impacted groundwater at the study site. © 2006 Wiley Periodicals, Inc.     

The in situ treatment of BTEX,MTBE, and TBA in saline groundwater

A pilot‐scale test was conducted in a saline aquifer to determine if a petroleum hydrocarbon (PHC) plume containing benzene (B), toluene (T), ethylbenzene (E), xylenes (X), methyl tert‐butyl ether (MTBE), and tert‐butyl alcohol (TBA) could be treated effectively using a sequential treatment approach that employed in situ chemical oxidation (ISCO) and enhanced bioremediation (EBR). Chemical oxidants, such as persulfate, have been shown to be effective in reducing dissolved concentrations of BTEX (B + T + E + X) and additives such as MTBE and TBA in a variety of geochemical environments including saline aquifers. However, the lifespan of the oxidants in saline environments tends to be short‐lived (i.e., hours to days) with their effectiveness being limited by poor delivery, inefficient consumption by nontargeted species, and back‐diffusion processes. Similarly, the addition of electron acceptors has also been shown to be effective at reducing BTEX and associated additives in saline groundwater through EBR, however EBR can be limited by various factors similar to ISCO. To minimize the limitations of both approaches, a pilot test was carried out in a saline unconfined PHC‐impacted aquifer to evaluate the performance of an engineered, combined remedy that employed both approaches in a sequence. The PHC plume had total BTEX, MTBE, and TBA concentrations of up to 4,584; 55,182; and 1,880 μg/L, respectively. The pilot test involved injecting 13,826 L of unactivated persulfate solution (19.4 weight percent (wt.%) sodium persulfate (Na₂S₂O₈) solution into a series of injection wells installed within the PHC plume. Parameters monitored over a 700‐day period included BTEX, MTBE, TBA, sulfate, and sulfate isotope concentrations in the groundwater, and carbon and hydrogen isotopes in benzene and MTBE in the groundwater. The pilot test data indicated that the BTEX, MTBE, and TBA within the PHC plume were treated over time by both chemical oxidation and sulfate reduction. The injection of the unactivated persulfate resulted in short‐term decreases in the concentrations of the BTEX compounds, MTBE, and TBA. The mean total BTEX concentration from the three monitoring wells within the pilot‐test area decreased by up to 91%, whereas MTBE and TBA mean concentrations decreased by up to 39 and 58%, respectively, over the first 50 days postinjection in which detectable concentrations of persulfate remained in groundwater. Concentrations of the BTEX compounds, MTBE, and TBA rebounded at the Day 61 marker, which corresponded to no persulfate being detected in the groundwater. Subsequent monitoring of the groundwater revealed that the concentrations of BTEX continued to decrease with time suggesting that EBR was occurring within the plume. Between Days 51 and 487, BTEX concentrations decreased an additional 84% from the concentration measured on Day 61. Mean concentrations of MTBE showed a reduction during the EBR phase of remediation of 33% while the TBA concentration appeared to decrease initially but then increased as the sulfate concentration decreased as a result of MTBE degradation. Isotope analyses of dissolved sulfate (³⁴S and ¹⁸O), and compound‐specific isotope analysis (CSIA) of benzene and MTBE (¹³C and ²H) supported the conclusions that ISCO and EBR processes were occurring at different stages and locations within the plume over time.     

In Situ treatment of PFAS‐impacted groundwater using colloidal activated Carbon

Poly‐ and perfluoroalkyl substances (PFASs) have been identified by many regulatory agencies as contaminants of concern within the environment. In recent years, regulatory authorities have established a number of health‐based regulatory and evaluation criteria with groundwater PFAS concentrations typically being less than 50 nanograms per liter (ng/L). Subsurface studies suggest that PFAS compounds are recalcitrant and widespread in the environment. Traditionally, impacted groundwater is extracted and treated on the surface using media such as activated carbon and exchange resins. These treatment technologies are generally expensive, inefficient, and can take decades to reach treatment objectives. The application of in situ remedial technologies is common for a wide variety of contaminants of concern such as petroleum hydrocarbons and volatile organic compounds; however, for PFASs, the technology is currently emerging. This study involved the application of colloidal activated carbon at a site in Canada where the PFASs perfluorooctanoate (PFOA) and perfluorooctane sulfonic acid (PFOS) were detected in groundwater at concentrations up to 3,260 ng/L and 1,450 ng/L, respectively. The shallow silty‐sand aquifer was anaerobic with an average linear groundwater velocity of approximately 2.6 meters per day. The colloidal activated carbon was applied using direct‐push technology and PFOA and PFOS concentrations below 30 ng/L were subsequently measured in groundwater samples over an 18‐month period. With the exception of perfluoroundecanoic acid, which was detected at 20 ng/L and perfluorooctanesulfonate which was detected at 40 ng/L after 18 months, all PFASs were below their respective method detection limits in all postinjection samples. Colloidal activated carbon was successfully distributed within the target zone of the impacted aquifer with the activated carbon being measured in cores up to 5 meters from the injection point. This case study suggests that colloidal activated carbon can be successfully applied to address low to moderate concentrations of PFASs within similar shallow anaerobic aquifers.     

Pilot scale testing composite swellable organosilica nanoscale zero‐valent iron—Iron‐Osorb®—for in situ remediation of trichloroethylene

Iron‐Osorb^® is a solid composite material of swellable organosilica with embedded nanoscale zero‐valent iron that was formulated to extract and dechlorinate solvents in groundwater. The unique feature of the highly porous organosilica is its strong affinity for chlorinated solvents, such as trichloroethylene (TCE), while being impervious to dissolved solids. The swellable matrix is able to release ethane after dechlorination and return to the initial state. Iron‐Osorb^® was determined to be highly effective in reducing TCE concentrations in bench‐scale experiments. The material was tested in a series of three pilot scale tests for in situ remediation of TCE in conjunction with the Ohio Environmental Protection Agency at a site in central Ohio. Results of these tests indicate that TCE levels were reduced for a period of time after injection, then leveled out or bounced back, presumably due to depletion of zero‐valent iron. Use of tracer materials and soil corings indicate that Iron‐Osorb^® traveled distances of at least 20 feet from the injection point during soil augmentation. The material appears to remain in place once the injection fluid is diluted into the surrounding groundwater. Overall, the technology is promising as a remediation method to treat dilute plumes or create diffuse permeable reactive barriers. Keys to future implementation include developing injection mechanisms that optimize soil distribution of the material and making the system long‐lasting to allow for continual treatment of contaminants emanating from the soil matrix. © 2011 Wiley Periodicals, Inc.     

Field‐scale evaluation of a biobarrier for the treatment of a trichloroethene plume

In the 1960s, trichloroethene (TCE) was used at what is now designated as Installation Restoration Program Site 32 Cluster at Vandenberg Air Force Base to flush missile engines prior to launch and perhaps for other degreasing activities, resulting in releases of TCE to groundwater. The TCE plume extends approximately 1 kilometer from the previous launch facilities beyond the southwestern end of the site. To limit further migration of TCE and chlorinated degradation by‐products, an in situ, permeable, reactive bioremediation barrier (biobarrier) was designed as a cost‐effective treatment technology to address the TCE plume emanating from the source area. The biobarrier treatment would involve injecting carbon‐based substrate and microbes to achieve reductive dechlorination of volatile organic compounds, such as TCE. Under reducing conditions and in the presence of certain dechlorinating microorganisms, TCE degrades to nontoxic ethene in groundwater. To support the design of the full‐scale biobarrier, a pilot test was conducted to evaluate site conditions and collect pertinent design data. The pilot test results indicated possible substrate delivery difficulties and a smaller radius of influence than had been estimated, which would be used to determine the final biobarrier well spacing. Based on these results, the full‐scale biobarrier design was modified. In January 2010, the biobarrier was implemented at the toe of the source area by adding a fermentable substrate and a dechlorinating microbial culture to the subsurface via an injection well array that spanned the width of the TCE plume. After the injections, the groundwater pH in the injection wells continued to decrease to a level that could be detrimental to the population of Dehalococcoides in the SDC‐9^TM culture. In addition, 7 months postinjection, the injection wells could not be sampled due to fouling. Cleaning was required to restore their functions. Bioassay and polymerase chain reaction analyses were conducted, as well as titration tests, to assess the need for biobarrier amendments in response to the fouling issues and low pH. Additionally, slug tests were performed on three wells to evaluate possible localized differences in hydraulic conductivity within the biobarrier. Based on the test results, the biobarrier was amended with sodium carbonate and inoculated a second time with SDC‐9^TM. The aquifer pH was restored, and reductive dechlorination resumed in the treatment zone, evidenced by the reduction in TCE and the increase in degradation products, including ethene. © 2011 Wiley Periodicals, Inc.     

Microbial responses to in situ chemical oxidation,six‐phase heating,and steam injection remediation technologies in groundwater

The evaluation of microbial responses to three in situ source removal remedial technologies—permanganate‐based in situ chemical oxidation (ISCO), six‐phase heating (SPH), and steam injection (SI)—was performed at Cape Canaveral Air Station in Florida. The investigation stemmed from concerns that treatment processes could have a variety of effects on the indigenous biological activity, including reduced biodegradation rates and a long‐term disruption of community structure with respect to the stimulation of TCE (trichloroethylene) degraders. The investigation focused on the quantity of phospholipid fatty acids (PLFAs) and its distribution to determine the immediate effect of each remedial technology on microbial abundance and community structure, and to establish how rapidly the microbial communities recovered. Comprehensive spatial and temporal PLFA screening data suggested that the technology applications did not significantly alter the site's microbial community structure. The ISCO was the only technology found to stimulate microbial abundance; however, the biomass returned to predemonstration values shortly after treatment ended. In general, no significant change in the microbial community composition was observed in the SPH or SI treatment areas, and even small changes returned to near initial conditions after the demonstrations. © 2004 Wiley Periodicals, Inc.