Field Trial of Biosparging with Oxygen for Bioremediation of Volatile Organic Compounds

Xpert Design & Diagnostics, LLC (XDD), & Conestoga‐Rovers and Associates (CRA) conducted a biosparging field trial at a Superfund site in New Jersey. The biosparging field trial proved that biosparging with oxygen was very effective in promoting the biological destruction of benzene. The approximately 265‐day period of oxygen injection successfully reduced benzene concentrations by several orders of magnitude, or even to non‐detect values, at least 40 feet from the point of injection. Through co‐precipitation of arsenic with oxidized iron, biosparging also effectively reduced total concentrations of arsenic and iron in groundwater. Based on the results of the biosparging field trial, the final remedy for the site has been amended to include the use of biosparging technology as an alternative to groundwater pumping and aboveground treatment in select locations. © 2001 John Wiley & Sons,Inc.     

Microbially Mediated In Situ Desorption Accelerates Remediation of Large Gasoline Product Plume

Remediation of a large separate‐phase hydrocarbon product and associated dissolved‐phase gasoline plume was accelerated by coupling multiphase extraction with in situ microbial stimulation. At the beginning of remediation activities, the separate‐phase hydrocarbon plume extended an estimated seven acres with product thickness measuring up to 2.1 feet thick. Within 18 months after beginning extraction, reduction of gasoline constituents in groundwater became asymptotic and measureable product disappeared from the upgradient source area. At that time, the remediation team initiated a program of limited in situ anaerobic bioremediation with the goal of stimulating production of natural surfactants from native microbes to release petroleum from the soil matrix. Groundwater concentrations of gasoline constituents increased gradually over the next three years, improving recovery without biofouling the pump‐and‐treat infrastructure. Using this approach, the groundwater component of the remedy was completed in less than five years, substantially less than the 10 years to 15 years predicted by modeling. This strategy demonstrated a more sustainable approach to remediation, reducing electrical usage by an estimated 800 megawatt hours, reducing infrastructure requirements, and preserving an estimated 150 million gallons of groundwater for this arid agricultural area. © 2014 Wiley Periodicals, Inc.     

Solar‐powered in situ soil washing with surfactant to collect LNAPL

This article presents the findings of a sustainable, surfactant‐enhanced, product recovery pilot‐scale study (PSS) completed between January 2010 and May 2010 at the Hydrocarbon Burn Facility located at the John F. Kennedy Space Center in Florida. The goal of this study was to implement a unique, simple, and sustainable light nonaqueous‐phase liquid (LNAPL) recovery process and evaluate site‐specific volumes and rates of LNAPL that could be collected and the degree of soil and groundwater cleanup that could be achieved. The recovery process was a combination of groundwater recirculation at a rate of approximately 2.9 gallons per minute (11.0 liters per minute), soil washing via LNAPL mobilization, and collection of LNAPL via a hydrophobic LNAPL skimmer. A biodegradable surfactant, ECOSURF^TM SA‐15, was added to the recirculation line to lower the interfacial tension and facilitate LNAPL recovery via mobilization. All equipment (submersible pump, LNAPL skimmer, surfactant feed pump, controls, and various other equipment) used was powered by a solar panel array. Approximately 60 gallons (227 liters) or 429 pounds (195 kilograms) of LNAPL were collected at the recirculation site over approximately three months during the PSS. The data suggest that surfactant amendments greatly enhanced free product collection. The maximum rate of free product collection was approximately 1 gallon (3.8 liters) per day. © 2012 Wiley Periodicals, Inc.     

The Use of Natural Systems to Remediate Groundwater: Department of Energy Experience at the Savannah River Site

Natural remediation is moving toward the forefront as engineers clean groundwater at the Savannah River Site (SRS), a major Department of Energy (DOE) installation near Aiken, South Carolina. This article reviews two successful, innovative remediation methods currently being deployed: biosparging to treat chlorinated solvents and phytoremediation to address tritium in groundwater. The biosparging system reintroduces oxygen into the groundwater and injects nutrient compounds for in‐situ remediation. The system has greatly reduced the concentrations of trichloroethylene (TCE) and vinyl chloride in wells downgradient from a sanitary landfill (SLF). Phytoremediation is an emerging technology that promises effective and inexpensive cleanup of certain hazardous wastes. Using natural processes, plants can break down, trap and hold, or transpire contaminants. This article discusses the use of phytoremediation to reduce the discharge of tritium to an on‐site stream at SRS. © 2002 Wiley Periodicals Inc. *     

Phytoremediation of a Petroleum‐Hydrocarbon Contaminated Shallow Aquifer in Elizabeth City,North Carolina,USA

A former bulk fuel terminal in North Carolina is a groundwater phytoremediation demonstration site where 3,250 hybrid poplars, willows, and pine trees were planted from 2006 to 2008 over approximately 579,000 L of residual gasoline, diesel, and jet fuel. Since 2011, the groundwater altitude is lower in the area with trees than outside the planted area. Soil‐gas analyses showed a 95 percent mass loss for total petroleum hydrocarbons (TPH) and a 99 percent mass loss for benzene, toluene, ethylbenzene, and xylenes (BTEX). BTEX and methyl tert‐butyl ether concentrations have decreased in groundwater. Interpolations of free‐phase, fuel product gauging data show reduced thicknesses across the site and pooling of fuel product where poplar biomass is greatest. Isolated clusters of tree mortalities have persisted in areas with high TPH and BTEX mass. Toxicity assays showed impaired water use for willows and poplars exposed to the site's fuel product, but Populus survival was higher than the willows or pines on‐site, even in a noncontaminated control area. All four Populus clones survived well at the site. © 2014 Wiley Periodicals, Inc.*     

Remediation of a Diffuse Trichloroethene Plume in an Urban Setting

During an environmental assessment of a former fleet vehicle maintenance facility located in Jacksonville, Florida, dissolved trichloroethene (TCE) concentrations exceeding the Florida groundwater standard (3 micrograms per liter) were detected at a depth of 40 feet (12 meters) below land surface (bls). A plume was delineated that measured approximately 600 feet (183 meters) by 150 feet (46 meters), extending across a major road and onto adjacent properties. Shaw Environmental, Inc., which was acquired by CB&I in February 2012, performed pilot tests with in situ oxygen curtain (iSOC), and the injection of Anaerobic Biochem Plus (ABC+), a mixture of lactates, a phosphate buffer, fatty acids, and zero‐valent iron. Based on the pilot‐test results, ABC+ appeared the more effective of the two methods and was selected for full‐scale implementation. In February 2011, Shaw Environmental, Inc. and a subcontractor used direct‐push technology to inject ABC+ in 120 borings. By September 2011, the treatment succeeded in lowering the concentrations of TCE to below the Florida standard in all impacted wells. Subsequent sampling events indicate that TCE concentrations have remained below the standard, but sampling continues for iron, which is decreasing but remains slightly elevated. © 2013 Wiley Periodicals, Inc.     

Pilot Scale Demonstration of the Electrochemical Peroxidation Process at a Petroleum Spill Site

In a pilot test experiment involving approximately 200,000 gallons of groundwater, Electrochemical Peroxidation (ECP) was used to degrade aqueous phase volatile organic compounds (VOCs) including benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and methyl tertbutyl ether (MTBE) from a petroleum spill. ECP involves a form of the Fenton's Reagent reaction, which uses electrochemically generated iron and dilute hydrogen peroxide (<30 mg/L) to break down organic molecules through oxidation to carbon dioxide and water. This article discusses a pilot scale demonstration of the ECP technology and its application to aqueous phase organic contaminants. The remedial approach used at the pilot test site involves three phases: (1) ex‐situ chemical oxidation, (2) in‐situ oxidation by reinjection of treated effluent near the plume origin, and (3) reestablishment of aerobic biodegradation as the residual hydrogen peroxide discharged to a series of upgradient wells degrades to oxygen. Analytical results of the pilot demonstration indicate that the ex‐situ chemical oxidation reduced total BTEX concentrations in groundwater from over 1,000 ppb to undetectable concentrations (<1 ppb). © 2000 John Wiley & Sons, Inc.     

Directionally drilled horizontal wells offer cost savings and technical advantages over alternative soil and groundwater remediation systems

Directionally drilled horizontal wells offer the opportunity for significant cost savings and technical advantages over alternative trenched well and vertical well soil and groundwater remediation systems in many cases. The magnitude of the cost savings is a function of the remediation technology deployed and the values placed on the reduction of site impacts, dramatic reduction in the time required to achieve site remediation goals and requirements, the ability of horizontal well remediation to easily treat normally recalcitrant contaminants such as MTBE, and the ability to drill under paved areas, operating plants, residential areas, landfills, lagoons, waterways, ponds, basins, and other areas that are normally difficult or impossible to access with conventional drilling or trenching methods. In addition to improvements in site access capabilities, horizontal wells have been found capable of addressing contaminants that vertical wells do not readily treat, even with the same remediation technology deployed, especially if air‐based remediation technologies are deployed. With biosparging, for example, greater treatment capabilities of horizontal wells over vertical wells are attributed to greater oxygen flux over a broader area, a larger treatment zone, and extremely prolonged residence of groundwater contaminants in the aerobic treatment area, typically months or years. This article describes the use of directionally drilled horizontal wells for application of a variety of treatment technologies and includes costs of various options with a detailed comparison of biosparging options. © 2002 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.     

Sustainable wind‐driven bioventing at a petroleum hydrocarbon–impacted site

Bioventing—the injection of air into the vadose zone to increase microbial activity—is a commonly used, proven technology for remediating volatile organic compounds present in the vadose zone. Passive systems driven by wind or solar power are both more cost‐effective and sustainable than conventional systems. Such a passive system is being applied successfully to remediate a site impacted with total petroleum hydrocarbons (TPH) and benzene, toluene, ethylbenzene, and xylenes (BTEX) in soil. Bioventing technology was approved by the regulatory agency as an interim remedial action to remove chemicals of concern (COCs) in the vadose zone. A bioventing pilot study was conducted to evaluate the effectiveness of COC removal and collect parameters for full‐scale design and implementation. To evaluate the potential to use wind‐driven bioventing technology, two mobile weather stations were installed at the site and monitored for one month for a wind speed study. Based on the pilot‐test data and wind speed research, 12‐inch diameter funnel/vane 360‐degree wind collectors were designed as passive wind‐driven air‐injection devices and connected to existing monitoring wells. The measured air velocity ranged from 20 to 110 feet per minute during the start‐up and the first three months of operation and maintenance. Monitoring indicated a 20 percent oxygen delivery and greater than 90 percent reduction in COC concentrations, demonstrating a successful sustainable remediation with no power requirement and minimal operation and maintenance. © 2012 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.     

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.     

柴油低温临界吸收法回收装车挥发油气

研究了采用柴油低温临界吸收法回收装车挥发油气的效果。实验结果表明：按装车挥发油气中的总烃体积分数为20.88%、装车挥发油气流量为280 m³/h、年运行时间为2 668 h计,装置年回收油气量为291 t,装置年最大运行功率为206.770 MW,装置投资回收期为3 a;处理后净化气中的总烃体积分数为1.24%,排放质量浓度低于25 g/m³,油气回收率达95%。处理后净化气满足GB 20950—2007《储油库大气污染物排放标准》,取得了较好的环保效益和经济效益。     

Introduction to Therm Net Technology

The Introduction to Therm Net technology is an overview of how radio frequency (RF) beating can be implemented to enhance conventional remediation technologies. Included in the article is a case study of a project conducted in March 1996 at a gasoline release site. The project consisted of a “hot spot” application to reduce BETX concentrations to achieve site closure. The application consisted of RF heating, soil vapor extraction, and groundwater ventilation. A bench scale study was also conducted to measure the effects that RF heating and vapor extraction had on the removal of PAH constitutents from a coal tar sludge. Up to 100 percent reductions were observed for some of the constituents in the study. Also included is a graphical representation of temperature versus vapor pressure for contaminants typically encountered at remediation sites, illustrating that as temperature increases, the removal rate increases.     

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.     

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.     

从聚醚残渣中回收聚醚和磷酸二氢钾

采用热水萃取分离技术回收聚醚残渣中J的聚醚和膦酸二氰钾,考察了萃取温度、结晶温度、水洗条件等因素对产品回收情况的影响。工业试验结果表明：聚醚回收率大于75%,磷酸二氢钾的平均回收率为70%.工业化试生产得到磷酸二氢钾和聚醚的产品质量分别达到HG2321-92工业品一级标准和该厂制定的GEP560S企业标准。该技术具有聚醚和磷酸二氢钾回收率高、工艺简单等特点,且经济效益、环境效益和社会效益显著。     

Remediation of chlorinated ethenes,ethanes, and methanes in groundwater using carbon‐ and iron‐based electron donor

Field‐scale pilot tests were performed to evaluate enhanced reductive dechlorination (ERD) of dissolved chlorinated solvents at a former manufacturing facility located in western North Carolina (the site). Results of the site assessment indicated the presence of two separate chlorinated solvent–contaminated groundwater plumes, located in the northern and southern portions of the site. The key chlorinated solvents found at the site include 1,1,2,2‐tetrachloroethane, trichloroethene, and chloroform. A special form of EHC^® manufactured by Adventus Americas was used as an electron donor at this site. In this case, EHC is a pH‐buffering electron donor containing controlled release carbon and ZV Iron MicroSphere 200, a micronscale zero‐valent iron (ZVI) manufactured by BASF. Approximately 3,000 pounds of EHC were injected in two Geoprobe^® boreholes in the saprolite zone (southern plume), and 3,500 pounds of EHC were injected at two locations in the partially weathered rock (PWR) zone (northern plume) using hydraulic fracturing techniques. Strong reducing conditions were established immediately after the EHC injection in nearby monitoring wells likely due to the reducing effects of ZV Microsphere 200. After approximately 26 months, the key chlorinated VOCs were reduced over 98 percent in one PWR well. Similarly, the key chlorinated solvent concentrations in the saprolite monitoring wells decreased 86 to 99 percent after initial increases in concentrations of the parent chlorinated solvents. The total organic carbon and metabolic acid concentrations indicated that the electron donor lasted over 26 months after injection in the saprolite aquifer. © 2009 Wiley Periodicals, Inc.     

Stable Isotope Probing to Confirm Field‐Scale Co‐Metabolic Biodegradation of 1,4‐Dioxane

1,4‐Dioxane, a common co‐contaminant with chlorinated solvents, is present in groundwater at Site 24 at Vandenberg Air Force Base in California. Historical use of chlorinated solvents resulted in concentrations of 1,4‐dioxane in groundwater up to approximately 2,000 μg/L. Starting in 2013, an in situ propane biosparge system operation demonstrated reductions in 1,4‐dioxane concentrations in groundwater. The work detailed herein extends the efforts of the first field demonstration to a second phase and confirms the biodegradation mechanism via use of stable isotope probing (SIP). After two months of operation, 1,4‐dioxane concentrations decreased approximately 45 to 83 percent at monitoring locations in the test area. The results of the SIP confirmed ¹³C‐enriched 1,4‐dioxane was transformed into dissolved inorganic carbon (suggesting mineralization to carbon dioxide) and incorporated into microbial biomass (likely attributed to metabolic uptake of biotransformation intermediates or of carbon dioxide).  ©2016 Wiley Periodicals, Inc.     

Long‐term evaluation of an EHC injection permeable reactive barrier in a sulfate‐rich,high‐flow aquifer

Permeable reactive barriers (PRBs) have traditionally been constructed via trenching backfilled with granular, long‐lasting materials. Over the last decade, direct push injection PRBs with fine‐grained injectable reagents have gained popularity as a more cost‐efficient and less‐invasive approach compared to trenching. A direct push injection PRB was installed in 2005 to intercept a 2,500 feet (760 meter) long carbon tetrachloride (CT) groundwater plume at a site in Kansas. The PRB was constructed by injecting EHC^® in situ chemical reduction reagent slurry into a line of direct push injection points. EHC is composed of slow‐release plant‐derived organic carbon plus microscale zero‐valent iron (ZVI) particles, specifically formulated for injection applications. This project was the first full‐scale application of EHC into a flow‐through reactive zone and provided valuable information about substrate longevity and PRB performance over time. Groundwater velocity at the site is high (1.8 feet per day) and sulfate‐rich (~120 milligrams per liter), potentially affecting the rate of substrate consumption and the PRB reactive life. CT removal rates peaked 16 months after PRB installation with >99% removal observed. Two years post‐installation removal rates decreased to approximately 95% and have since stabilized at that level for the 12 years of monitoring data available after injection. Geochemical data indicate that the organic carbon component of EHC was mostly consumed after 2 years; however, reducing conditions and a high degree of chloromethane treatment were maintained for several years after total organic carbon concentrations returned to background. Redox conditions are slowly reverting and have returned close to background conditions after 12 years, indicating that the PRB may be nearing the end of its reactive life. Direct measurements of iron have not been performed, but stoichiometric demand calculations suggest that the ZVI component of EHC may, in theory, last for up to 33 years. However, the ZVI component by itself would not be expected to support the level of treatment observed after the organic carbon substrate had been depleted. A longevity of up to 5 years was originally estimated for the EHC PRB based on the maximum expected longevity of the organic carbon substrate. While the organic carbon was consumed faster than expected, the PRB has continued to support a high degree of chloromethane treatment for a significantly longer time period of over 12 years. Recycling of biomass and the contribution from a reduced iron sulfide mineral zone are discussed as possible explanations for the sustained reducing conditions and continued chloromethane treatment.