Enhanced reductive dechlorination of PCE in unconsolidated soils

An Interstate Technology and Regulatory Council (ITRC) forum was recently held that focused on six case studies in which bioremediation of dense nonaqueous phase liquids (DNAPLs) was performed. The objective was to demonstrate that there is credible evidence for bioremediation as a viable environmental remediation technology. A discussion of the first case study from the ITRC forum was published in the previous issue of Remediation. This article presents a discussion of the second case study, which involves enhanced reductive dechlorination (ERD) of tetrachloroethene (PCE) in unconsolidated soils—primarily silts and clays with very low permeabilities. The project results indicate that complete reductive dechlorination was achieved and provide encouragement that large amounts of nonaqueous solvent can be brought into the reductive dechlorination treatment process by dissolution and desorption, giving support to the contention that the capacity to attack nonaqueous mass is a prerequisite for any effective treatment of DNAPL source zones. The site geology for this project was relatively unfavorable, and further work is needed to confirm that the ERD technology can economically reach a natural attenuation endpoint for this type of setting. © 2006 Wiley Periodicals, Inc.     

Enhanced anaerobic bioremediation in a DNAPL residual source zone: Test Area North case study

An Interstate Technology and Regulatory Council (ITRC) forum was recently held that focused on case studies in which bioremediation of dense nonaqueous‐phase liquids (DNAPLs) was performed. This first case study, the Test Area North (TAN) site of the Idaho National Engineering and Environmental Laboratory, involves a trichloroethene (TCE) residual source area in a deep, fractured basalt aquifer that has been undergoing enhanced bioremediation since January 1999. Complete dechlorination from TCE to ethene was documented within nine months of operation, and sodium lactate injections were shown to enhance TCE mass transfer from the residual source. Since that time, optimization of injection strategies has maintained efficient dechlorination while demonstrating accelerated cleanup at a lower cost by changing to a whey powder amendment that solubilizes DNAPL. © 2006 Wiley Periodicals, Inc.     

Successful ISCR‐enhanced bioremediation of a TCE DNAPL source utilizing EHC® and KB‐1®

Remediation of chlorinated solvent DNAPL sites often meets with mixed results. This can be attributed to the diametrically opposed nature of the impacts, where the disparate dissolved‐phase plume is more manageable than the localized, high‐concentration source area. A wide range of technologies are available for downgradient plume management, but the relative mass of contaminants in a DNAPL source area generally requires treatment for such technologies to be effective over the long term. In many cases, the characteristics of DNAPL source zones (e.g., depth, soil heterogeneity, structural limitations) limit the available options. The following describes the successful full‐scale implementation of in situ chemical reduction (ISCR) enhanced bioremediation of a TCE DNAPL source zone. In this demonstration, concentrations of TCE were rapidly reduced to below the maximum contaminant level (MCL) in less than six months following implementation. The results described herein suggest that ISCR‐enhanced bioremediation is a viable remedial alternative for chlorinated solvent source zones. © 2010 Wiley Periodicals, Inc.     

TCE plume remediation via ISCR‐enhanced bioremediation utilizing EHC® and KB‐1®

Groundwater below an operating manufacturing facility in Portland, Oregon, was impacted by chlorinated volatile organic compounds (CVOCs), with concentrations indicative of a dense, nonaqueous‐phase liquid (DNAPL) release. The downgradient plume stretched under the adjacent Willamette River, intersecting zones of legacy impacts from a former manufactured gas plant (MGP). An evaluation of source‐area and downgradient plume treatment remedies identified in situ bioremediation as most likely to be effective for the CVOC plume, while leaving the legacy impacts for other responsible parties. With multiple commercially available products to choose from, the team developed and implemented a bench test to identify the most appropriate technology, which was further evaluated in a field pilot study. The results of the testing demonstrated conclusively that bioremediation enhanced by in situ chemical reduction (ISCR) using EHC® and KB‐1® was most appropriate for this site, providing outstanding results. The following describes the implementation and results of the tests. © 2008 Wiley Periodicals, Inc.     

DNAPL Source Depletion: 1. Predicting Rates and Timeframes

Given the relatively rapid rate of dense nonaqueous‐phase liquid (DNAPL) ganglia depletion, source zones are generally dominated by horizontal layers of DNAPL after a release to the saturated zone. Estimating the time required to attain specific source strength reduction targets resulting from partial DNAPL source depletion is challenging due to a lack of available screening models, and because little has been done to synthesize available empirical data. Analytical and semi‐analytical models are used to study general DNAPL pool dissolution dynamics. The half‐life for the decline in DNAPL source strength (i.e., aqueous mass discharge) is demonstrated as proportional to the square root of the pool length, the thickness of the pool, and the solubility for single component DNAPLs. The through‐pool discharge is shown to be potentially significant for thin pools or in upper regions of thicker pools. An empirical analysis is used to evaluate average concentration decline rates for 13 in situ chemical oxidation (ISCO) and 16 enhanced in situ bioremediation (EISB) sites. Mean apparent decline rates, based on the time required to achieve the observed source strength reduction, are calculated for the ISCO and EISB sites (half‐lives of 0.39 year and 0.29 year, respectively). The empirical study sites are shown to have faster decline rates than for a large, complex study site where ISCO was implemented (half‐life of 2.5 years), and for a conceptual pool‐dominated trichloroethene source zone where EISB was simulated (half‐life of 2.5 years). Guidance is provided on using these findings in estimating timeframes for partial DNAPL depletion goals. © 2014 Wiley Periodicals, Inc.     

Integrated approach to PCE‐impacted site characterization,site management,and enhanced bioremediation

Tetrachloroethene (PCE)‐ and trichloroethene (TCE)‐impacted sites pose significant challenges even when site characterization activities indicate that biodegradation has occurred naturally. Although site‐specific, regulatory, and economic factors play roles in the remedy‐selection process, the application of molecular biological tools to the bioremediation field has streamlined the assessment of remedial alternatives and allowed for detailed evaluation of the chosen remedial technology. The case study described here was performed at a PCE‐impacted site at which reductive dechlorination of PCE and TCE had led to accumulation of cis‐dichlorethene (cis‐DCE) with concentrations ranging from approximately 10 to 100 mg/L. Bio‐Trap® samplers and quantitative polymerase chain reaction (qPCR) enumeration of Dehalococcoides spp. were used to evaluate three remedial options: monitored natural attenuation, biostimulation with HRC®, and biostimulation with HRC‐S®. Dehalococcoides populations in HRC‐S‐amended Bio‐Traps deployed in impacted wells were on the order of 10³ to 10⁴ cells/bead but were below detection limits in most unamended and HRC‐amended Bio‐Traps. Thus the in situ Bio‐Trap study identified biostimulation with HRC‐S as the recommended approach, which was further evaluated with a pilot study. After the pilot HRC‐S injection, Dehalococcoides populations increased to 10⁶ to 10⁷ cells/bead, and concentrations of cis‐DCE and vinyl chloride decreased with concurrent ethene production. Based on these results, a full‐scale HRC‐S injection was designed and implemented at the site. As with the pilot study, full‐scale HRC‐S injection promoted growth of Dehalococcoides spp. and stimulated reductive dechlorination of the daughter products cis‐DCE and vinyl chloride. © 2008 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.     

ERD of Residual TCE DNAPL Achieving Nondetect from a Single Injection of Food‐Grade Waste

Residual dense nonaqueous phase liquid (DNAPL) composed of trichloroethene (TCE) was identified in a deeper interval of an overburden groundwater system at a manufacturing facility located in northern New England. Site hydrostratigraphy is characterized by two laterally continuous and transmissive zones consisting of fully‐saturated fine sand with silt and clay. The primary DNAPL source was identified as a former dry well with secondary contributions from a proximal aboveground TCE storage tank. A single additive‐injection mobilization in 2001 utilizing a food‐grade injectate formulated with waste dairy product and inactive yeast enhanced residual TCE DNAPL destruction in situ by stimulating biotic reductive dechlorination. The baseline TCE concentration was detected up to 97,400 μg/L in the deeper interval of the overburden groundwater system, and enhanced reductive dechlorination (ERD) achieved >99 percent reduction in TCE concentrations in groundwater over nine years with no evidence of sustained rebound. TCE concentrations have remained nondetect below 2.0 μg/L for the last five consecutive sampling rounds between 2013 and 2015. ERD utilizing a food‐grade injectate is a green remediation technology that has destroyed residual DNAPL at the site and achieved similar results at other residual DNAPL sites during both pilot‐ and full‐scale applications. ©2016 Wiley Periodicals, Inc.     

DNAPL Source Depletion: 2. Attainable Goals and Cost–Benefit Analyses

It is difficult to quantify the range in source strength reduction (MdR) that may be attainable from in situ remediation of a dense nonaqueous‐phase liquid (DNAPL) site given that available studies typically report only the median MdR without providing insights into site complexity, which is often a governing factor. An empirical study of the performance of in situ remediation at a wide range of DNAPL‐contaminated sites determined MdRs for in situ bioremediation (EISB), in situ chemical oxidation (ISCO), and thermal treatment remedies. Median MdR, geometric mean MdR, and lower/upper 95 percent confidence interval for the mean were: 49x, 105x, 20x/556x, respectively, for EISB; 9x, 21x, and 4x/110x for ISCO; and 19x, 31x, and 6x/150x for thermal treatment. Lower MdR values were determined for large, complex sites and for sites with DNAPL pool‐dominated source zones. A feasibility analysis of partial DNAPL depletion is described for a pool‐dominated source zone. Back‐diffusion from low‐hydraulic conductivity units within a pool‐dominated source zone is shown to potentially sustain a secondary source for more than 1,000 years, indicating that aggressive source treatment may not reduce the remediation timeframe. Estimated plume response demonstrates there may be no reduction in cost associated with aggressive treatment, and little difference in risk reduction associated with the various alternatives. Monitored natural attenuation (MNA) for the source zone is shown to be a reasonable alternative for the pool‐dominated source zone considered in this example. It is demonstrated that pool‐dominated source zones with a large range in initial DNAPL mass (250 to 1,500 kg) may correspond to a narrow range in source strength (20 to 30 kg/year). This demonstrates that measured source strength is nonunique with respect to DNAPL mass in the subsurface and, thus, source strength should not be used as the sole basis for predicting how much DNAPL mass remains or must be removed to achieve a target goal. If aggressive source zone treatment is to be implemented due to regulatory requirements, strategic pump‐and‐treat is shown to be most cost effective. These remedial decisions are shown to be insensitive to a range of possible DNAPL pool conditions. At sites with an existing pump‐and‐treat system, a significant increase in mass removal and source strength reduction may be achieved for a low incremental cost by strategic placement of extraction wells and pumping rate selection. © 2014 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.     

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.     

Kinetic study of permanganate oxidation of tetrachloroethylene at a high pH under acidic conditions

Since carbon compounds are the main component of dense nonaqueous phase liquids (DNAPLs), the end products of all in situ chemical oxidation (ISCO) will include carbon dioxide. If the production rate of carbon dioxide exceeds the capacity of water to remove the carbon dioxide, degassing will occur. The uncontrolled carbon dioxide gas may change the flow patterns, remobilize the pooled DNAPL, transport DNAPL vapor, and reduce the relative permeability to the aqueous phase. Under high pH buffered conditions, most of the carbon dioxide will be dissolved in water. In this study, potassium permanganate oxidation of tetrachloroethylene (PCE) was conducted using a sodium carbonate buffered solution (1 g/L, pH = 10.6 ± 0.1) at three different temperatures (5, 10, and 20°C) and three potassium permanganate concentrations (0.2, 1, and 5 g/L). Extensive kinetic studies suggest that the overall oxidation is a second‐order reaction and pseudo‐first‐order with respect to PCE and potassium permanganate, respectively. The second‐order rate constant and the activation energy were 0.028 ± 0.001 M^?1s^?1 at 20°C and 43.9 ± 2.85 kJ/M, respectively. This study provides a base for further experimental and field studies on potassium permanganate oxidation of PCE under natural or artificial high pH buffered conditions. © 2004 Wiley Periodicals, Inc.     

Rapid Cleanup of Chlorinated Solvent Source Zones: Synergies Between Chemical and Biological Degradation

A chlorinated volatile organic compound (cVOC) source area approximately 25 by 100 ft in a heavily industrialized urban area was characterized with groundwater tetrachloroethene (PCE) concentrations up to 9,180 μg/L. This is approximately 6 percent of PCE's aqueous solubility, indicative of the presence of residual dense, nonaqueous phase liquid. The resulting dissolved‐phase plume migrated off‐site. Biotic and abiotic dechlorination using a combination of a food‐grade organic carbon‐based electron donor and zero‐valent iron suspended in a food‐grade emulsifying agent reduced the source area PCE concentrations by 98 percent within 27 weeks, with minimal downgradient migration of daughter products dichloroethene and vinyl chloride. Combining biological dechlorination with iron‐based chemical dechlorination is synergistic, enhancing treatment aggressiveness, balancing pH, and optimizing degradation of both DNAPL and dissolved‐phase cVOCs. © 2013 Wiley Periodicals, Inc.     

Enhanced dichloroethene biodegradation in fractured rock under biostimulated and bioaugmented conditions

Significant microbial reductive dechlorination of [1,2 ¹⁴C] cis‐dichloroethene (DCE) was observed in anoxic microcosms prepared with unamended, fractured rock aquifer materials, which were colonized in situ at multiple depths in two boreholes at the Naval Air Warfare Center (NAWC) in West Trenton, New Jersey. The lack of significant reductive dechlorination in corresponding water‐only treatments indicated that chlororespiration activity in unamended, fractured rock treatments was primarily associated with colonized core material. In these unamended fractured rock microcosms, activity was highest in the shallow zones and generally decreased with increasing depth. Electron‐donor amendment (biostimulation) enhanced chlororespiration in some but not all treatments. In contrast, combining electron‐donor amendment with KB1 amendment (bioaugmentation) enhanced chlororespiration in all treatments and substantially reduced the variability in chlororespiration activity both within and between treatments. These results indicate (1) that a potential for chlororespiration‐based bioremediation exists at NAWC Trenton but is limited under nonengineered conditions, (2) that the limitation on chlororespiration activity is not entirely due to electron‐donor availability, and (3) that a bioaugmentation approach can substantially enhance in situ bioremediation if the requisite amendments can be adequately distributed throughout the fractured rock matrix. © 2012 Wiley Periodicals, Inc.*     

Creosote DNAPL Recovery‐Well Design for Mass Removal

Sites with dense nonaqueous‐phase liquid (DNAPL) contamination present significant remediation challenges in terms of technical practicability and cost. Remedial approaches to DNAPL sites often follow a management approach rather than removal or eradication approaches, particularly due to the uncertainties associated with the benefits of partial source mass removal, as complete source removal is unlikely. Mass‐removal technologies should be evaluated for all DNAPL sites, although implementation of recovery technologies will be limited to a few sites based upon site‐specific factors. Sitewide remedial strategies that employ source reduction, where applicable, and incorporate associated risk‐reduction technologies, including monitored natural attenuation, are advised. Creosote DNAPL sites are particularly challenging, as they are predominantly composed of low‐solubility polycyclic aromatic hydrocarbons that form long‐term continuing sources. Additionally, the physical properties of creosote DNAPL, including high viscosity and relatively low density, result in significant migration potential and considerable dissolved‐phase groundwater impacts. An innovative creosote DNAPL source recovery well design was developed to achieve separate‐phase removal of pooled creosote DNAPL. The design presented herein employs modified circulation‐well technology to mobilize DNAPL to the engineered recovery well, where it is gravity‐settled into a sump to permit separate‐phase mass removal of the emplaced DNAPL source without groundwater production or treatment. A discharge mass flux protocol was developed to verify dissolved‐phase plume stability and the benefit of the source mass removal. © 2013 Wiley Periodicals, Inc.     

Optimal Treatment Zone Moves During Enhanced Reductive Dechlorination in Fractured Bedrock

An enhanced bioremediation pilot test was implemented to study the efficacy of enhancing in situ reductive dechlorination of tetrachloroethene (PCE) in shallow bedrock where some intrinsic degradation to cis‐1,2‐dichloroethene (cis‐1,2‐DCE) was observed without further degradation to vinyl chloride or nontoxic ethene. Limited Dehalococcoides spp. cell concentrations were present within the study area prior to the gravity‐fed injection of an injectate of fermentable carbon substrates in native anaerobic groundwater. Direct connectivity between the injection well screen and performance monitoring well was evidenced and resulted in the degradation of nearly all PCE to cis‐1,2‐DCE, significant decrease in pH, and apparent inhibited Dehalococcoides spp. growth in the study area groundwater in the first six months. After 24 months, nearly all cis‐1,2‐DCE had degraded to nontoxic ethene, pH rebounded to more optimal levels, and abundant growth of Dehalococcoides spp. (6.8E05 cells/mL) and its functional gene expressions responsible for complete dechlorination were evident. The observations indicated initial poor dechlorination within the injection zone did not preclude effective treatment, allowing sufficient monitoring time showed the effective treatment zone (or more‐optimal fringe) first moved outward from the injection zone beyond the monitoring point and then receded back toward the point of injection over a period of two years. ©2015 Wiley Periodicals, Inc.     

Successful full‐scale enhanced anaerobic dechlorination at a NAPL strength 1,1,1‐TCA source area

Bioremediation of 1,1,1‐trichloroethane (TCA) is more challenging than bioremediation of other chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE). TCA transformation often occurs under methanogenic and sulfate‐reducing conditions and is mediated by Dehalobacter. The source area at the project site contains moderately permeable medium sand with a low hydraulic gradient and is approximately 0.5 acre. TCA contamination generally extended to 35 feet, with the highest concentrations at approximately 20 feet. The concentrations then decreased with depth; several wells contained 300 to 600 mg/L of TCA prior to bioremediation. The area of treatment also contained 2 to 30 mg/L of TCE from an upgradient source. Initial site groundwater conditions indicated minimal biotic dechlorination and the presence of up to 20 mg/L of nitrate and 90 mg/L of sulfate. Microcosm testing indicated that TCA dechlorination was inhibited by the site's relatively low pH (5 to 5.5) and high TCA concentration. After the pH was adjusted and TCA concentrations were reduced to less than 35 mg/L (by dilution with site water), dechlorination proceeded rapidly using whey (or slower with sodium lactate) as an electron donor. Throughout the remediation program, increased resistance to TCA inhibition (from 35 to 200 mg/L) was observed as the microbes adapted to the elevated TCA concentrations. The article presents the results of a full‐scale enhanced anaerobic dechlorination recirculation system and the successful efforts to eliminate TCA‐ and pH‐related inhibition. © 2012 Wiley Periodicals, Inc.     

Enhanced bioremediation using whey powder for a trichloroethene plume in a high‐sulfate,fractured granitic aquifer

An in situ bioremediation (ISB) pilot study, using whey powder as an electron donor, is being performed at Site 19, Edwards Air Force Base, California, to treat groundwater contaminated with trichloroethene (TCE) via anaerobic reductive dechlorination. Challenging site features include a fractured granitic aquifer, complex geochemistry, and limited biological capacity for reductive dechlorination. ISB was conducted in two phases with Phase I including one‐and‐a‐half years of biostimulation only using whey powder and Phase II including biostimulation with buffered whey powder and bioaugmentation. Results of Phase I demonstrated effective distribution of whey during injections resulting in depletion of high concentrations of sulfate and methanogenesis, but acid production due to whey fermentation and limited buffering capacity of the aquifer resulted in undesirable impacts to pH. In addition, cis‐1,2‐dichloroethene (cis‐1,2‐DCE) stall was observed, which correlated to the unsuccessful growth of native Dehalococcoides populations. Therefore, Phase II included the successful buffering of whey powder using bicarbonate, which mitigated negative pH effects. In addition, bioaugmentation resulted in successful transport of Dehalococcoides populations to greater than 50 feet away from the injection point four months after inoculation. A concomitant depletion of accumulated cis‐1,2‐DCE was observed at all wells affected by bioaugmented Dehalococcoides. © 2008 Wiley Periodicals, Inc.     

In situ treatment of a dilute chlorinated solvent plume in an acidic aerobic aquifer

In situ bioremediation was selected in the Record of Decision (ROD) as the remedial technology for a 29‐acre dilute, acidic and aerobic, chlorinated solvent plume (principally trichloroethylene [TCE] and 1,1‐dichloroethylene) for a Superfund site located in central New Jersey. Implementation of the remedy at full‐scale began in late 2010, using reductive dechlorination and bioaugmentation, and treatment has continued steadily over the last 9 years. The amendments injected include electron donor and alkaline (bicarbonate) buffer solution and, once anaerobic aquifer conditions became established, a bioaugmentation culture. Amendment injections occurred in multilevel injection wells (IWs), to maintain control over the vertical interval of amendment delivery. The areal coverage of the plume has been reduced by 59% based on the 10 µg/L TCE isocontour and the contaminant mass has been reduced by 79% through the 9 years of treatment. Lessons learned from this project include the need for bioaugmentation in the acidic aquifer and an efficient and effective manner of well construction and amendment injection using multiscreen single casing IWs and packer systems. Additional lessons learned include differences in longevity of the electron donor amendment versus the bicarbonate neutralization additive, and the need for varied amendment delivery techniques (IWs, direct injection, horizontal well installation) in selected lower permeable zones to attain treatment.     

Optimization and validation of enhanced biological reduction of 1,2,3‐trichloropropane in groundwater

Laboratory and field demonstration studies were conducted to assess the efficacy of enhanced biological reduction of 1,2,3‐trichloropropane (TCP) in groundwater. Laboratory studies evaluated the effects of pH and initial TCP concentrations on TCP reduction and the activity of a microbial inoculum containing Dehalogenimonas (Dhg). Laboratory results showed successful reduction at a pH of 5 to 9 with optimal reduction at 7 to 9 and at initial TCP concentrations ranging from 10 to over 10,000 micrograms per liter (μg/L). Based on findings from the laboratory study, the effects of TCP concentration, geochemical conditions, and amendment concentration on bioremediation efficacy were investigated during a field demonstration at a site with relatively low initial concentrations of TCP (< 2 μg/L). The field demonstration included injection of emulsified vegetable oil (EVO) and lactate as a carbon substrate for biostimulation, followed by bioaugmentation using the microbial inoculum containing Dhg. Post‐injection performance monitoring demonstrated reduction of TCP to below laboratory detection limits (< 0.005 μg/L) after an initial lag period of approximately six months following injections. TCP reduction was accompanied by generation of the degradation byproduct propene. A marginal increase in TCP concentrations, potentially due to an influx of upgradient aerobic groundwater containing TCP, was observed eight months after injections thereby demonstrating the sensitivity of this bioaugmentation application to changes in geochemical parameters. Despite this marginal increase, performance monitoring results indicate continued TCP biodegradation 15 months after implementation of the injection program. This demonstration suggests that enhanced biodegradation of TCP by combining biostimulation and bioaugmentation may be a promising solution to the challenges associated with remediation of TCP, even when present at low part per billion concentrations in groundwater.