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1.
In situ biogeochemical transformation involves biological formation of reactive minerals in an aquifer that can destroy chlorinated solvents such as trichloroethene (TCE) without accumulation of intermediates such as vinyl chloride. There is uncertainty regarding the materials and geochemical conditions that are required to promote biogeochemical transformation. The objective of this study was to identify amendments and biogeochemical conditions that promote in situ biogeochemical transformation. Laboratory columns constructed with plant mulch were supplemented with different amendments and were operated under varying conditions of water chemistry and hydraulic residence time. Four patterns of TCE removal were observed: (1) no removal, (2) biotic transformation of TCE to cis‐1,2‐dichloroethene (cis‐1,2‐DCE), (3) biogeochemical transformation of TCE without accumulation of reductive dechlorination products, and (4) mixed behavior where a combination of patterns was observed either simultaneously or over time. Principal coordinates analysis and analysis of variance (ANOVA) identified factors that promoted biogeochemical transformation: (1) high influent sulfate concentration, (2) relatively high hydraulic retention time, (3) supplementation of mulch with vegetable oil, and (4) addition of hematite or magnetite. The combination of the first three factors promoted complete sulfate reduction and a high volumetric sulfate consumption rate. The fourth factor provided a source of ferrous iron and/or a surface to which sulfide could react to form reactive iron sulfides. Many columns demonstrated either no TCE removal or a biotic TCE transformation pattern. Modification of column operation to include all four factors identified above promoted biogeochemical transformation in these columns. These results support the importance of the factors in biogeochemical transformation.  相似文献   

2.
Mass discharge across transect planes is increasingly used as a metric for performance assessment of in situ groundwater remediation systems. Mass discharge estimates using concentrations measured in multilevel transects are often made by assuming a uniform flow field, and uncertainty contributions from spatial concentration and flow field variability are often overlooked. We extend our recently developed geostatistical approach to estimate mass discharge using transect data of concentration and hydraulic conductivity, so accounting for the spatial variability of both datasets. The magnitude and uncertainty of mass discharge were quantified by conditional simulation. An important benefit of the approach is that uncertainty is quantified as an integral part of the mass discharge estimate. We use this approach for performance assessment of a bioremediation experiment of a trichloroethene (TCE) source zone. Analyses of dissolved parent and daughter compounds demonstrated that the engineered bioremediation has elevated the degradation rate of TCE, resulting in a two‐thirds reduction in the TCE mass discharge from the source zone. The biologically enhanced dissolution of TCE was not significant (～5%), and was less than expected. However, the discharges of the daughter products cis‐1,2, dichloroethene (cDCE) and vinyl chloride (VC) increased, probably because of the rapid transformation of TCE from the source zone to the measurement transect. This suggests that enhancing the biodegradation of cDCE and VC will be crucial to successful engineered bioremediation of TCE source zones.  相似文献   

3.
A substantial cost of granular iron permeable reactive barriers is that of the granular iron itself. Cutting the iron with sand can reduce costs, but several performance issues arise. In particular, reaction rates are expected to decline as the percentage of iron in the blend is diminished. This might occur simply as a function of iron content, or mass transfer effects may play a role in a much less predictable fashion. Column experiments were conducted to investigate the performance consequences of mixing Connelly granular iron with sand using the reduction kinetics of trichloroethylene (TCE) to quantify the changes. Five mixing ratios (i.e., 100%, 85%, 75%, 50%, and 25% of iron by weight) were studied. The experimental data showed that there is a noticeable decrease in the reaction rate when the content of sand is 25% by weight (iron mass to pore volume ratio, Fe/Vp = 3548 g/L) or greater. An analysis of the reaction kinetics, using the Langmuir-Hinshelwood rate equation, indicated that mass transfer became an apparent cause of rate loss when the iron content fell below 50% by weight (Fe/Vp = 2223 g/L). Paradoxically, there were tentative indications that TCE removal rates were higher in a 15% sand + 85% iron mixture (Fe/Vp = 4416 g/L) than they were in 100% iron (Fe/Vp = 4577 g/L). This subtle improvement in performance might be due to an increase of iron surface available for contact with TCE, due to grain packing in the sand-iron mixture.  相似文献   

4.
Elevated particulate concentrations in ground water samples can bias contaminant concentration data. This has been particularly problematic for metal analyses where artificially increased turbidity levels can affect metals concentrations and confound interpretation of the data. However, few studies have been conducted to determine the impact of particulates on trichloroethylene (TCE), cis-dichloroethylene (c-DCE), and vinyl chloride concentrations.
Laboratory batch studies and field investigations were conducted to evaluate the effects of suspended solids on VOC concentrations in ground water samples analyzed by purge-and-trap gas chromatography. Three different solids were used to assess the effects of suspended particulates. The solids were aquifer material from a field site in North Carolina and two reference clay minerals (kaolinite and Namontimorillonite). During the laboratory portion of this study, the solids were used to determine effects on TCE concentrations under controlled laboratory conditions.
The same solids were used in a field study to compare the laboratory results with field results. Solids were added to the sample vials prior it) sample collection to intentionally increase turbidity levels in the water samples. Results of the study indicate essentially no decrease in TCE, c-DCH, or vinyl chloride concentrations due to increased turbidity levels.  相似文献   

5.
This paper aims to reconcile discrepancies among reports of dechlorination performance in the presence of sulfate, by analyzing data from the literature, presenting results from laboratory experiments performed with mixed anaerobic microbial cultures, and synthesizing respective findings. A complete set of metrics for dechlorination progress was developed and used in the analysis of selected field and laboratory studies. When differences in site and experimental conditions are accounted for and definitions of dechlorination completeness are harmonized, the inverse relationship between dechlorination performance and sulfate concentration becomes clearer. This relationship was investigated in detail with laboratory experiments on mixed anaerobic microbial cultures enriched with the same concentration of trichloroethylene (TCE) and different sulfate concentrations, equal to near zero (considered as the baseline culture), 30, 400, and 1100 mg/L. In all experiments, sulfate reduction proceeded concurrently with dechlorination. The observed behavior was bimodal, indicating a transition in dechlorination performance between 30 and 400 mg/L. Under low donor to acceptor stoichiometry conditions, TCE dechlorination was incomplete in all experiments after 14 days, while the percentage of TCE moles reduced to vinyl chloride was lower by about 50% in the experiments with high sulfate concentrations. When donor was added in excess to stoichiometry needs for TCE reduction, TCE dechlorination was complete in the baseline culture, while only little ethene was detected in the high sulfate concentration cultures. When all studies are considered together, it appears that the presence of sulfate does not preclude complete dechlorination but rather delays it. Data analysis also suggests that the proposed upper limit of 500 mg/L for the range of initial sulfate concentration that is not problematic for dechlorination should be revised to a lower value.  相似文献   

6.
We have previously defined in situ biogeochemical transformation as the biogenic formation of reactive minerals that are capable of abiotically degrading chlorinated solvents such as trichloroethene without accumulation of degradation products such as vinyl chloride (AFCEE et al. 2008 ). This process has been implemented in biowalls used to intercept contaminated groundwater. Abiotic patterns of contaminant degradation were observed at Altus Air Force Base (AFB) and in an associated column study, but not at other sites including Dover AFB. These abiotic patterns were associated with biogenic formation of reactive iron sulfide minerals. Iron sulfides in the form of small individual grains, coatings on magnetite, and sulfur‐deficient pyrite framboids were observed in samples collected from the Altus AFB biowalls and one of the EPA columns. Larger iron sulfide grains coated with oxide layers were observed in samples collected from Dover AFB. Altus AFB and the EPA column differed from Dover AFB in that groundwater flow at Dover AFB was relatively slow and potentially reversing. High volumetric sulfate consumption rates, an abiotic pattern of trichloroethene (TCE) degradation, and the formation of small, high surface area iron sulfide particles were associated with relatively high rates of TCE removal via an abiotic pattern. Geochemical modeling demonstrated that iron monosulfides such as mackinawite were near saturation, and iron disulfides such as pyrite were supersaturated at all sites. This environmental condition can be supportive of nucleation of small particles rather than crystal growth leading to larger particles. When nucleation is dominant, small, high surface area, and reactive particles result. When crystal growth dominates the crystals are larger and have lower specific surface area and reactivity. These results taken together suggest that creation of a dynamic environment can promote biogeochemical transformation based on generation of reactive iron sulfides.  相似文献   

7.
Anaerobic microcosms containing sediment and water were amended to generate a range of mass loadings of FeS. Microcosms were then spiked with trichloroethylene (TCE) and the concentration of TCE and possible volatile reaction products monitored over time. The lowest yields of TCE, as well as the lowest yields of reaction products regulated under the Safe Drinking Water Act (i.e., dichloroethylene isomers and vinyl chloride), were observed at FeS mass loadings at or above 20 g/L. Sixty eight days after spiking with TCE, selected microcosms were amended with sulfate and lactate, or sulfate, Fe(II), and lactate, and the effect of these amendments on TCE transformation and yield of regulated products was compared to microcosms that did not receive any amendments. Addition of sulfate, Fe(II), and lactate led to the greatest improvement on TCE depletion rates and the lowest yields of regulated reaction products compared with addition of sulfate and lactate, or no amendments. Analysis of kinetic modeling suggests that microbial and abiotic processes acted in concert to promote TCE transformation to a relatively low yield of regulated products in microbially active microcosms that contained high mass loadings of FeS.  相似文献   

8.
Four samples of two commercially available iron brands used as substrate for iron permeable reactive barriers (PRBs) were tested for suitability for remediation of perchloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cDCE) and vinyl chloride (VC). Kinetic studies indicate that rates of reaction are enhanced for cDCE and VC on Connelly iron (2.8 x 10(-4) to 6.9 x 10(-4) L/m2/hr and 2.0 x 10(-4) to 9.0 x 10(-4) L/m2/hr, for cDCE and VC, respectively) vs. Peerless iron (3.1 x 10(-5) to 4.6 x 10(-5) L/m2/hr and 2.4 x 10(-5) to 4.1 x 10(-5) L/m2/hr, for cDCE and VC, respectively). Carbon isotopic analyses of the residual chlorinated ethylene (CE) during degradation indicate significant fractionation occurs during reductive dechlorination, with, for example, up to 70% enrichment in carbon isotopic values observed when VC is more than 99% degraded. Comparison of fractionation factors (epsilon) indicates significant differences in carbon isotopic fractionation for different iron types and for different CEs. For the lower CEs (cDCE and VC) in particular, both slower reaction rates and larger fractionation are observed for degradation on Peerless vs. Connelly iron. This is the first study to establish a correlation between the rate of abiotic degradation on Fe(0) and the extent of isotopic fractionation, and the first to confirm consistent differences in these two parameters as a function of iron type. The possibility that these differences in kinetics and carbon isotopic fractionation for cDCE and VC are related to differences in branching ratios between competing hydrogenolysis and beta-elimination reactions during reductive dechlorination on the iron surfaces is discussed.  相似文献   

9.
Contamination of groundwater with chlorinated ethenes is common and represents a threat to drinking water sources. Standard anaerobic bioremediation methods for the highly chlorinated ethenes PCE and TCE are not always effective in promoting complete degradation. In these cases, the target contaminants are degraded to the daughter products DCE and/or vinyl chloride. This creates an additional health risk, as vinyl chloride is even more toxic and carcinogenic than its precursors. New treatment modalities are needed to deal with this widespread environmental problem. We describe successful bioremediation of a large, migrating, dilute vinyl chloride plume in Massachusetts with an aerobic biostimulation treatment approach utilizing both oxygen and ethene. Initial microcosm studies showed that adding ethene under aerobic conditions stimulated the rapid degradation of VC in site groundwater. Deployment of a full‐scale treatment system resulted in plume migration cutoff and nearly complete elimination of above‐standard VC concentrations.  相似文献   

10.
Approximately 190 kg of 2 μm‐diameter zero‐valent iron (ZVI) particles were injected into a test zone in the top 2 m of an unconfined aquifer within a trichloroethene (TCE) source area. A shear‐thinning fluid was used to enhance ZVI delivery in the subsurface to a radial distance of up to 4 m from a single injection well. The ZVI particles were mixed in‐line with the injection water, shear‐thinning fluid, and a low concentration of surfactant. ZVI was observed at each of the seven monitoring wells within the targeted radius of influence during injection. Additionally, all wells within the targeted zone showed low TCE concentrations and primarily dechlorination products present 44 d after injection. These results suggest that ZVI can be directly injected into an aquifer with shear‐thinning fluids to induce dechlorination and extends the applicability of ZVI to situations where other emplacement methods may not be viable.  相似文献   

11.
Large laboratory columns (15.2 cm diameter, 183 cm long) were fed with groundwater containing trichloroethylene (TCE), were biostimulated and bioaugmented, and were monitored for over 7.5 years. The objective of the study was to observe how the selection of the carbon and energy source, i.e., whey, Newman Zone® standard surfactant emulsified oil and Newman Zone nonionic surfactant emulsified oil, affected the rate and extent of dechlorination. Column effluent was monitored for TCE and its degradation products, redox indicators (nitrate‐N, Fe(II), sulfate), and changes in iron mineralogy. Total bacteria and Dehalococcoides mccartyi strains were quantified using q‐PCR. Complete dechlorination was only observed in the whey treated columns, occurring 1 year after bioaugmentation with addition of a culture known to dechlorinate TCE to ethene, and 3 years later in the non‐bioaugmented column. The addition of the emulsified oils with or without bioaugmentation resulted in dechlorination only through cis‐DCE and vinyl chloride. While Dehalococcoides mccartyi strains are the only known bacteria that can fully dechlorinate TCE, their presence, either natural or augmented, was not the sole determiner of complete dechlorination. The establishment of a supporting microbial community and biogeochemistry that developed with continuous feeding of whey, in addition to the presence of D. mccartyi, were necessary to support complete reductive dechlorination. Results confirm that careful selection of a biostimulant is critical to the success of TCE dechlorination in complex soil environments.  相似文献   

12.
Groundwater contamination associated with two former industrial facilities in Denver, Colorado, has led to concerns about vapor intrusion into residences adjacent to the facilities. 1,1,1-Trichloroethane (1,1,1-TCA), 1,1-dichloroethene (1,1-DCE), and trichloroethene (TCE) are the main contaminants of concern in groundwater, with trace levels of 1,2-dichloroethane (1,2-DCA) present at one of the sites. Indoor air monitoring programs have been ongoing at these two sites since 1998 and recent results have suggested that background, indoor source, 1,2-DCA has been increasing in the frequency of detection, and median and maximum concentration over the past several years. A lines of evidence evaluation was undertaken for both sites in order to document the predominance of indoor sources of 1,2-DCA. Evidence utilized included spatial evaluation of 1,2-DCA in indoor air; comparison of 1,2-DCA concentrations in mitigated and unmitigated homes; a phone survey to evaluate the potential for smoking to contribute to indoor air 1,2-DCA levels; evaluation of mitigation system effluent data; and an evaluation of volatile organic compound (VOC) ratios in groundwater and indoor air. The results of this evaluation indicated that smoking had no demonstrable influence on measured indoor air concentrations. In addition, it appears that consumer products have had a markedly increased influence on indoor air concentrations since 2005. Data from one of the industrial facilities at one of the sites also indicated that polyvinyl chloride (PVC) and vinyl composite floor adhesive used in a building remodel in 2005 apparently generated elevated levels of indoor 1,2-DCA and vinyl chloride, which have been sustained up to the present time.  相似文献   

13.
A tracer test was conducted to characterize the flow of groundwater across a permeable reactive barrier constructed with plant mulch (a biowall) at the OU‐1 site on Altus Air Force Base, Oklahoma. This biowall is intended to intercept and treat groundwater contaminated by trichloroethylene (TCE) in a shallow aquifer. The biowall is 139‐m long, 7.3‐m deep, and 0.5‐m wide. Bromide was injected from an upgradient well into the groundwater as a conservative tracer, and was subsequently observed breaking through in monitoring wells within and downgradient of the biowall. The bromide breakthrough data demonstrate that groundwater entering the biowall migrated across it, following the slope of the local groundwater surface. The average seepage velocity of groundwater was approximately 0.06 m/d. On the basis of the Darcy velocity of groundwater and geometry of the biowall, the average residence time of groundwater in the biowall was estimated at 10 d. Assuming all TCE removal occurred in the biowall, the reduction in TCE concentrations in groundwater across the biowall corresponds to a first‐order attenuation rate constant in the range of 0.38 to 0.15 per d. As an independent estimate of the degradation rate constant, STANMOD software was used to fit curves through data on the breakthrough of bromide and TCE in selected wells downgradient of the injection wells. Best fits to the data required a first‐order degradation rate constant for TCE removal in the range of 0.13 to 0.17 per d. The approach used in this study provides an objective evaluation of the remedial performance of the biowall that can provide a basis for design of other biowalls that are intended to remediate TCE‐contaminated groundwater.  相似文献   

14.
Degradation of dissolved chlorinated solvents using granular iron is an established in situ technology. This paper reports on investigations into mixing iron and bentonite with contaminated soil for in situ containment and degradation of dense nonaqueous phase liquid source zones. In the laboratory, hypovials containing soil, water, bentonite, iron, and free-phase trichloroethene (TCE) were assembled. Periodic measurement of TCE, chloride, and degradation products showed progressive degradation of TCE to nondetectable levels. Subsequently, a demonstration was conducted at Canadian Forces Base Borden near Alliston, Ontario, Canada, where, in 1991, a portion of the surficial aquifer was isolated and free-phase tetrachloroethene (PCE) was introduced. Using a drill rig equipped with large-diameter mixing blades, three mixed zones were prepared containing 0%, 5%, and 10% granular iron by volume. The bentonite was added to serve as a lubricant to facilitate injection of the iron and to isolate the contaminated zone. Analysis of core samples showed reasonably uniform distributions of iron through the mixed zones. Monitoring over a 13-month period following installation showed, relative to the control, a decline in PCE concentrations to virtually nondetectable values. Reaction rates in the laboratory tests were similar to those reported in the literature, while the rate in the field test was substantially lower. The lower rate may be a consequence of mass transfer limitations under the static conditions of the field test. Results indicate that mixing iron and bentonite into source zones may be an effective means of source-zone remediation, with the particular advantage of being relatively immune to effects of geologic heterogeneity.  相似文献   

15.
Understanding basic controls on aquifer microbiology is essential to managing water resources and predicting impacts of future environmental change. Previous theoretical and laboratory studies indicate that pH can influence interactions between microorganisms that reduce ferric iron and sulfate. In this study, we test the environmental relevance of this relationship by examining broad‐scale geochemical data from anoxic zones of aquifers. We isolated data from the U.S. Geological Survey National Water Information System for 19 principal aquifer systems. We then removed samples with chemical compositions inconsistent with iron‐ and sulfate‐reducing environments and evaluated the relationships between pH and other geochemical parameters using Spearman's rho rank correlation tests. Overall, iron concentration and the iron‐sulfide concentration ratio of groundwater share a statistically significant negative correlation with pH (P < 0.0001). These relationships indicate that the significance of iron reduction relative to sulfate reduction tends to increase with decreasing pH. Moreover, thermodynamic calculations show that, as the pH of groundwater decreases, iron reduction becomes increasingly favorable relative to sulfate reduction. Hence, the relative significance of each microbial reaction may vary in response to thermodynamic controls on microbial activity. Our findings demonstrate that trends in groundwater geochemistry across different regional aquifer systems are consistent with pH as a control on interactions between microbial iron and sulfate reduction. Environmental changes that perturb groundwater pH can affect water quality by altering the balance between these microbial reactions.  相似文献   

16.
Abstract

An in situ microbial filter technology is being tested and developed for remediating migrating subsurface plumes contaminated with low concentrations of trichloroethylene (TCE). The current focus is the establishment of a replenishable bioactive zone (catalytic filter) along expanding plume boundaries by the injection of a representative methanotrophic bacterium, Methylosinus trichosporium OB3b. This microbial filter strategy has been successfully demonstrated using emplaced, attached resting cells (no methane additions) in a 1.1 m flow-through test bed loaded with water-saturated sand. Two separate 24 h pulses of TCE (109 ppb and 85 ppb), one week apart, were pumped through the system at a flow velocity of 15 mm h?1; no TCE (< 0.5 ppb) was detected on the downstream side of the microbial filter. Subsequent excavation of the wet sand confirmed the existence of a TCE-bioactive zone 21 days after it had been created. An enhanced longevity of the cellular, soluble-form methane monooxygenase produced by this methanotroph is a result of the laboratory bioreactor culturing conditions. Additional experiments with cells in sealed vials and emplaced in the 1.1 m test bed yielded a high resting-cell finite TCE biotransformation capacity of about 0.25 mg per mg of bacteria; this is suitable for a planned sand-filled trench field demonstration at a Lawrence Livermore National Laboratory site.  相似文献   

17.
Core samples taken from a zero-valent iron permeable reactive barrier (ZVI PRB) at Cornhusker Army Ammunition Plant, Nebraska, were analyzed for physical and chemical characteristics. Precipitates containing iron and sulfide were present at much higher concentrations in native aquifer materials just upgradient of the PRB than in the PRB itself. Sulfur mass balance on core solids coupled with trends in ground water sulfate concentrations indicates that the average ground water flow after 20 months of PRB operation was approximately twenty fold less than the regional ground water velocity. Transport and reaction modeling of the aquifer PRB interface suggests that, at the calculated velocity, both iron and hydrogen could diffuse upgradient against ground water flow and thereby contribute to precipitation in the native aquifer materials. The initial hydraulic conductivity ( K ) of the native materials is less than that of the PRB and, given the observed precipitation in the upgradient native materials, it is likely that K reduction occurred upgradient to rather than within the PRB. Although not directly implicated, guar gum used during installation of the PRB is believed to have played a role in the precipitation and flow reduction processes by enhancing microbial activity.  相似文献   

18.
Zhang Y  Gillham RW 《Ground water》2005,43(1):113-121
Long-term reactivity and permeability are critical factors in the performance of granular iron permeable reactive barriers (PRBs). Thus it is a topic of great practical importance, as well as scientific interest. In this study, four types of source solutions (distilled H2O, 10 mg/L TCE, 300 mg/L CaCO3, and 10 mg/L TCE + 300 mg/L CaCO3) were supplied to four columns containing a commercial granular iron material. In all four columns, gases accumulated to approximately 10% of the initial porosity and resulted in declines in permeability of approximately 50% to 80%. In the columns receiving CaCO3, carbonate precipitates accumulated to approximately 7% of the initial porosity, with no apparent decline in permeability. The data indicate that precipitates formed initially at the influent ends of the columns, reducing the reactivity of the iron in this region. As a consequence of the reduced reactivity, calcium and bicarbonate migrated further into the column, to precipitate in a region where the reactivity remained high. Thus precipitation occurred as a moving front through the columns. The results suggest improved methods for PRB design and rehabilitation, and also suggest improvements that are needed in the mathematical models developed for predicting long-term performance.  相似文献   

19.
A chemiresistor microchemical sensor has been developed to detect and monitor volatile organic compounds in unsaturated and saturated subsurface environments. A controlled study was conducted at the HAZMAT Spill Center at the Nevada Test Site, where the sensor was tested under a range of temperature, moisture, and trichloroethylene (TCE) concentrations. The sensor responded rapidly when exposed to TCE placed in sand, and it also responded to decreases in TCE vapor concentration when clean air was vented through the system. Variations in temperature and water vapor concentration impacted baseline chemiresistor signals, but at high TCE concentrations the sensor response was dominated by the TCE exposure. Test results showed that the detection limit of the chemiresistor to TCE vapor in the presence of fluctuating environmental variables (i.e., temperature and water vapor concentration) was on the order of 1000 parts per million by volume, which is about an order of magnitude higher than values obtained in controlled laboratory environments. Automated temperature control and preconcentration is recommended to improve the stability and sensitivity of the chemiresistor sensor.  相似文献   

20.
Toxic and carcinogenic effects of arsenic in drinking water continue to impact people throughout the world and arsenic remains common in groundwater at cleanup sites and in areas with natural sources. Advances in groundwater remediation are needed to attain the low concentrations that are protective of human health and the environment. In this article, we present the successful use of a permeable reactive barrier (PRB) utilizing sulfate reduction coupled with zero‐valent iron (ZVI) to remediate the leading edge of a dissolved arsenic plume in a wetland area near Tacoma, Washington. A commercially available product (EHC‐M®, Adventus Americas Inc., Freeport, Illinois) that contains ZVI, organic carbon substrate, and sulfate was injected into a reducing, low‐seepage‐velocity aquifer elevated in dissolved arsenic and iron from a nearby, slag‐containing landfill. Removal effectiveness was strongly correlated with sulfate concentration, and was coincident with temporary redox potential (Eh) reductions, consistent with arsenic removal by iron sulfide precipitation. The PRB demonstrates that induced sulfate reduction and ZVI are capable of attaining a regulatory limit of 5 µg/L total arsenic, capturing of 97% of the arsenic entering the PRB, and sustaining decreased arsenic concentrations for approximately 2 years, suggesting that the technology is appropriate for consideration at other sites with similar hydrogeochemical conditions. The results indicate the importance of delivery and longevity of minimum sulfate concentrations and of maintaining sufficient dissolved organic carbon and/or microscale ZVI to precipitate FeS, a precursor phase to arsenic‐bearing pyrite that may provide a stable, long‐term sink for arsenic.  相似文献   

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