Background/Objectives.
Currently there are far fewer technologies available for treating metals impacts in groundwater in-situ than there are for treating organic contaminants. This relates to the fact that unlike organics, metals cannot be biologically degraded or be easily driven into a vapor phase to enhance their recovery. Effective in-situ treatment methods for arsenic stabilization offer a number of benefits over removal/recovery-based methods, but require careful consideration of mechanisms and longevity.
A patent-pending method for the in-situ removal of arsenic from groundwater will be introduced. The method facilitates the delivery and distribution of iron in a fully soluble form, followed by the formation of ferric iron oxyhydroxide precipitates that can remove arsenic from groundwater and retain it via co-precipitation. Thus far, distribution of iron has been limited due to iron particle size, solubility, and/or transport in the groundwater. Success has been achieved relying on shallow trenches for emplacement of reactive iron materials, but limited solutions have been developed for deep aquifers. The treatment approach provides a means to solve the historic challenge of effectively delivering and distributing iron in the subsurface. The end result is the creation of beneficial minerals that will not only retain the arsenic but remain stable in naturally aerobic and neutral aquifers, lending permanence and sustainability to the outcome. The approach can be tailored to site specific geochemical conditions, and may be designed to yield excess sorptive capacity/remediation potential to provide passive treatment of residual contaminant mass beyond the initial treatment event.
Approach/Activities.
Data will be presented from both a field site in Alaska, and laboratory testing completed to refine the approach. Results from the laboratory trials will include both jar and column tests to prove the reaction mechanism concepts and the ability to distribute iron without compromising permeability. Jar tests conducted in soil/groundwater slurries show removal of arsenic with addition of iron, acid, chelant and oxidant. Columns were prepared with site soil and groundwater, adding groundwater impacted with 1400 ug/L of arsenic. An injection test at a site in Alaska was also conducted, showing removal of more than 400 ug/L from monitoring wells within the influence of the injection.
Results/Lessons Learned.
Using this method, treatability studies have shown removal of over 1400 ug/L of arsenic is feasible. Injections at a field site in Alaska have demonstrated removal of 400 ug/L Arsenic impacts without loss of permeability in the aquifer. The results of bench and pilot scale-proof of concept studies will be presented in order to explain the theory driving this method and illustrate how this treatment method can be developed and applied at sites where elevated arsenic concentrations are observed. Additional laboratory trials conducted in the winter of 2013 will be available. Results from a planned for the winter of 2014 field trial may also be available.
The local municipality has conceptual redevelopment plans for a former manufactured gas plant (MGP) which have accelerated plans for full-scale cleanup. Located along a river used for shipping goods, the site is impacted with MGP DNAPL and LNAPL over approximately 0.80 acres within a sandy (dune) aquifer. The DNAPL exists between approximately 35 to 40 feet below grade and is present in river sediment. An air sparging fence is currently in operation to prevent exceedances of petroleum compounds associated with the LNAPL from entering the river.
ARCADIS and Savron are piloting the Self-Sustaining Treatment for Active Remediation (STAR) technology for remediation of both the LNAPL and DNAPL in November 2014. This is the first site where STAR will be applied to both LNAPL and DNAPL in the same unconfined aquifer. In situ stabilization/solidification (ISS) and in situ smoldering combustion technology are being evaluated for full-scale remedy, the latter of which has the potential to save the client approximately $1.5 million in remedial costs. The required design criteria and cost range are fairly well understood for the ISS remedy; however, the STAR technology has not yet been implemented full-scale at an MGP Site. Therefore, the STAR pilot test is being conducted to provide treatment verification and to provide critical design data such as radius of influence (ROI) and propagation rate which are the primary cost drivers for full-scale implementation, providing additional confidence to the full-scale cost comparison between ISS and STAR.
The expected data set will include operational parameters (temperature profiles in the subsurface at multiple radial distances and depths, VOC and CO/CO2 content of the vapor discharge, perimeter air monitoring results), as well as pre- and post-pilot test soil samples for TPH analysis. A discussion on best practices for ROI consideration and cost implications/ranges will be provided.
Soil pollution by hydrocarbons is a worldwide environmental concern. Among this class of pollutants, 37% of the French sites are contaminated by total petroleum hydrocarbons (TPH). Their impact on human health and environment is well known because of their hydrophobic characteristics permitting them to reach and accumulate in the food chain. They are indeed likely to cause toxic effects to human and environmental receptors. Furthermore this toxicity is closely related to their structures. Their physical and chemical properties such as solubility and Kow favour their accumulation in organic matter and human bodies via food chain. Furthermore, soil as well as groundwater quality are endangered by the accumulation of TPH.
Biological, physical and chemical in situ treatment methods are often used but these techniques are very often time-consuming and require high engineering costs. Besides, before implementing an in situ soil treatment technique at full-scale, laboratory tests should be performed in order to adapt the technique to the field conditions. As a consequence, ex situ techniques such as soil washing are getting more and more interest despite that soil excavation is necessary. Since 2007, French policy on polluted sites is strongly oriented towards the use and operation of in situ treatment methods. In situ treatment of TPH contaminated soils could be achieved by soil flushing. However, this remediation approach is still being developed by companies as it does not require soils excavation, allowing this technique still to be more cost-effective than ex situ processes. Surfactants are chemical compounds frequently used for the extraction of hydrocarbons from soil.
Although this washing technique is generally efficient to clean soil, the major concern remains in the treatment of the leachates containing both TPH and surfactants. Such solutions contain a significant amount of hard COD, which require an advanced oxidation treatment to be degraded. Electrochemical Advanced Oxidation Processes (EAOPs) have shown promising results to treat many poorly biodegradable organic compounds in solutions .
In order to improve the efficiency of soil washing treatment of hydrocarbon contaminated soils, an innovative combination of this soil treatment technique with an electrochemical advanced oxidation process (i.e. electro-Fenton (EF)) has been proposed.
An ex situ soil column washing experiment was performed on a genuinely diesel-contaminated soil. The washing solution was enriched with Tween® 80 at different concentrations, higher than the critical micellar concentration (CMC). The impact of soil washing was evaluated on the hydrocarbons concentration in the leachates collected at the bottom of the soil columns. These eluates were then studied for their degradation potential by EF treatment.
Results showed that a concentration of 5% of Tween® 80 was required to enhance hydrocarbons extraction from the soil. With this Tween® 80 concentration, the efficiency of the treatment was only about 1% after 24 h of washing. Electrochemical treatments performed thereafter with EF on the collected eluates revealed that the quasi-complete mineralization (> 99.5%) of the hydrocarbons was achieved within 32 h according to a linear kinetic trend. Toxicity was higher than in the initial solution and reached 95% of inhibition of Vibrio fischeri bacteria measured by Microtox® method, demonstrating the presence of remaining toxic compounds even after the complete degradation. Finally, the biodegradability (BOD5/COD ratio) reached a maximum of 20% after 20 h of EF treatment, which is not enough to implement a combination with a biological treatment process.
This work showed that Tween® 80 was able to extract the heaviest hydrocarbons fractions from a highly contaminated soil. Moreover, great biodegradability enhancement is observed by using EF treatment even if toxic compounds still remain in the eluates.
Perflourooctane sulfonate (PFOS) and perflouroctanoic acid (PFOA) are emerging as contaminats of concern in many countries and authorities around the world have recently establised regulatory limits for groundwater. However, there are many other perfluorinated compounds (PFCs) and precursors of PFOS and PFOA found in aqueous film forming foam (AFFF) which is often comprises the source of the PFCs. Therefore, there are analytical challenges to overcome when considering how to assess soil and groundwater contaminated with PFCs as there are multiple analytes which can biotransfrom slowly to form PFOS and PFOA. Methods to overcome this analytical chaenge will be discussed and analytical site data presented to demonstrate how the analytical challenged can be best adressed.
This presentation will review the fate and transport charecteristics of PFOS, consider recent toxiclogical data.
Perflurourinted compounds are difficult to remediate in soil and groundwater systems due to their recalcitrant nature (i.e. are not amenable to icrbial biodegradation) and lack of volatility, therefore in situ remedial options are limited. Activated persulfate chemistry has been used effectively to treat soil and groundwater contaminated by a wide range of pollutants of concern.
Recent laboratory work has demonstrated that activated persulfate is capable of oxidizing perfluorinated compounds in groundwater but only when a specific activation method is employed, as with the smart combined oxidation and reduction (ScisoR®) technology. Laboratory data will show how this technology can deflourinated and hence mineralise both PFOS and PFOA. However, using ther methods of oxidation, such as Fenton’s reagent, to oxidise PFC from a site soil, an increased mass of PFOS ad PFOA is observed as the precursors are transformed to the dead end products of this oxidation reaction.
Laboratory results indicate that the ScisoR® technology capable of destroying PFCs derived from sote soil and groundwater and hurdles to be overcome before the next steps, which invove field implementation of an in situ project, are described. Remedial technologies, such as directed groundwater recirculation (DGR) to address the very long plumes of low concentrations of PFC’s will be discussed, with examples of how ARCADIS has successfuly remediated long plumes over short timeframes.
Background/Objectives. The presence of pesticides in soil and groundwater can pose a threat to human health and the environment. Pesticide contamination can occur as a result of accidental releases or intentional dumping at formulation and retail sites, misuse during application, or even through normal use. For example, in 1987, over 20 different pesticides were found in the groundwater of 24 states. In situ chemical oxidation (ISCO) has not been used extensively to treat these compounds because the nature of pesticide use commonly involves large, low-level aerial applications for which ISCO is not typically well-suited. However, where such compounds have been released to the environment as point sources or in areas where high concentrations are targeted for remediation, ISCO may be appropriate to consider as a remedial technology. The objectives of this presentation are to discuss the treatability of common pesticides using ISCO and to present data from laboratory evaluations of the treatability of pesticides such as lindane, chlordane, heptachlor, and chlorobenzenes using oxidants such as activated persulfate, catalyzed hydrogen peroxide (CHP), and ozone.
Approach. A review of the use of advanced oxidative processes for the treatment of pesticides will be presented. Substantial work has been conducted in the water/wastewater treatment industries (i.e. ex situ) to evaluate pesticides treatability using oxidants. This work has guided the limited work that has been done in assessing pesticides treatability in soil and groundwater using oxidants, either ex situ or in situ. Results of four treatability studies will be presented, where different oxidants (CHP, activated persulfate, or ozone) were applied to pesticide-contaminated field soils. The presentation will focus on the site-specific and design factors that influence the success of oxidative treatment of the pesticides lindane, chlordane, heptachlor, and chlorobenzenes. Although limited, intermediate and byproduct data for these studies will be presented as well.
Lessons Learned. Common pesticides are amenable to degradation using oxidants. The extent of degradation depends on site-specific characteristics, such as the degree of sorption onto soils, and the ability to maintain oxidative conditions (i.e., oxidant persistence). Intermediates and byproducts of pesticide oxidation have been observed and should be monitored during and after application of oxidants. While it is evident that pesticides can be degraded by oxidants, the viability of ISCO for treating pesticides sites will depend on the nature of the contamination – the mass distribution; the soil characteristics including particle size, total organic content, and groundwater geochemistry; the site’s hydrogeology; and, specifically, the aerial extent and depth of contamination.
Transport and deposition of colloidal particles in saturated porous media are of great importance in many fields of science and engineering. A thorough understanding of particle filtration processes is essential for predicting the transport and fate of colloidal particles in the subsurface environment. Particles migrating through a porous medium can remain in suspension and be transported due to advection and dispersion phenomena, or be retained due to filtration and deposition onto the porous matrix. In particular, in the framework of the FP7 project Nanorem (G.A. Nr. 309517), the application of nanoparticles for groundwater remediation is the key research question. Colloid transport is a peculiar multi-scale problem, and pore-scale processes have an important impact on the transport at the larger scale. In this study, colloid transport modelling was carried out at different scales, from the pore scale (applying pore-network models) up to the full field scale. Assessing the mechanisms that control the mobility of reactive nanoparticles is of pivotal importance in the design, implementation, and performance evaluation of field applications. While numerical models for the simulation of dissolved contaminants transport are widely available, field scale models of nanoparticles with proven predictive ability are yet to be developed. This is mainly because the fundamental controlling mechanisms for the transport of nanoparticles in the subsurface at the field scale are not well understood.
Using pore network modelling we simulate fluid flow and transport of colloids within a network of interconnected pores (Raoof et al., 2013). Colloidal processes such as deposition and aggregation are implemented at the scale of individual pores. Averaging over the network domain composed of several pores, we derive macro-scale parameters to be used within field scale models (Raoof et al., 2010).
Transport of concentrated nanoparticle suspensions in porous media is affected by the rheological properties of the dispersing fluid (shear thinning) and by particle deposition and filtration in the porous matrix, which result in porous medium clogging (i.e. reduction of porosity and permeability). Moreover, the kinetics of particle retention is strongly influenced by the ionic strength of the pore water. Up to date, modelling of colloid transport in the presence of such complex interaction phenomena has been mainly faced in one-dimensional Cartesian coordinates for the simulation of laboratory column tests (Tosco et al., 2009; Tosco and Sethi, 2010), or at larger scales in simplified radial domains (Tosco et al., 2014), as implemented in MNMs (www.polito.it/groundwater/software/MNMs.php). In this work, a modelling tool for the simulation of colloid injection and transport under transients in ionic strength in more complex scenarios is developed and validated. To this aim colloid transport equations were implemented in the well-known transport model RT3D (Clement et al., 1998). The tool can be used for multi-dimensional simulations, and the approach is validated through comparison of results from MNMs and RT3D for a one-dimensional domain.
References
Clement, T.P., Sun, Y., Hooker, B.S., Petersen, J.N., 1998. Ground Water Monitoring and Remediation 18, 79-92.
Raoof, A., Hassanizadeh, S. M., & Leijnse, A. (2010). Upscaling transport of adsorbing solutes in porous media: Pore-network modeling. VZJ 9(3), 624-636.
Raoof, A., Nick, H. M., Hassanizadeh, S. M., & Spiers, C. J. (2013). PoreFlow: A complex pore-network model for simulation of reactive transport in variably saturated porous media. Computers & Geosciences, 61, 160-174.
Tosco, T.; Sethi, R. Environmental Science and Technology 2010, 44(23), 9062-9068.
Tosco, T.; Tiraferri, A.; Sethi, R. Environmental Science & Technology 2009, 43(12), 4425-4431.
Tosco, T.; Gastone, F.; Sethi, R. Journal of Contaminant Hydrology 2014, 166(0), 34-51.
Background/Objectives. Dissolved-phase 1,1,1-trichloroethane (TCA) is particularly
susceptible to hydrolysis and dehydrohalogenation reactions at elevated temperatures. For
example, laboratory-derived degradation rate constants for TCA increased from 0.068 day-1 at 50 Celsius (ºC) to more than 0.3 day-1 as temperatures approached 70ºC. A hot-water
injection/recirculation remediation system was designed, constructed and operated for 18 months to establish in situ treatment of TCA in groundwater. This work follows a previous work where bench-scale testing, thermal modeling, and field-scale pilot studies to evaluate the feasibility of using injection/recirculation of hot water to remediate dissolved and separate-phase TCA in groundwater at the Site. Remedial objectives included elimination of separate-phase TCA in the source area and decrease of dissolved phase TCA concentrations to below the groundwater standard of 200 micrograms per liter (ug/L).
Approach/Activities. The results from a field pilot study performed in 2007 and 2008 were used to develop a three-dimensional, numerical groundwater flow and thermal transport model for the surficial aquifer. A capture zone analysis was also performed to design an injection/recovery well network to propagate heated water throughout the desired treatment zone, as well as contain the source area and prevent downgradient migration of the dissolved constituents. In 2008, a fullscale remedial system was designed, which consisted of an automated hot water injection/recirculation system that used three downgradient recovery wells, a 108 kilowatt tankless water heater to heat the recovered groundwater to approximately 80ºC, and two injection wells near the suspected source area. This system was operated for an 18-month period (October 2008 to March 2010).
Results/Lessons Learned. TCA concentrations in the main source area were reduced from an
initial value of 8,200 ug/Lin August 2008 to <1.0 ug/L in March 2010, at which point the
remedial system operations were terminated. 1,1-Dichloroethene (DCE), generated via abiotic hydrolysis and dehydrohalogenation of TCA, increased from approximately 12 ug/L to 82 ug/L during the November 2008 to April 2010 monitoring period. 1,1-Dichloroethane (DCA) also was produced, likely from biotic reductive dechlorination of TCA, increasing from 25 ug/L to 150 ug/L. Follow-on hydraulic and thermal transport numerical modeling were performed to improve the model’s predictive ability by comparing simulated results to actual field results.
Model setup, calibration, and results from these evaluations also will be discussed in the paper. Future activities include long-term monitoring to document the declining DCE and DCA trends
Human industrial activities have resulted in a great number of contaminated land areas in Europe and the rest of the world. Management of those areas has to prevent any unexpected risk to humans or the environment. In order to ensure sustainable re-development of contaminated areas, there is need for innovative solutions to prevent and mitigate unacceptable risks to human health or the environment; particularly where problems seem intractable or the impacts of current treatments seem severe.
The use of nanoparticles in remediation has been advocated as offering a step-change in remediation technology performance and in extending the range of treatable problems. Yet this transition has not gained full momentum so far as was anticipated some years ago. Can nanoremediation really be the answer? What are the most important factors governing the overall market opportunity for, and sustainability of, nanoremediation projects?
Laboratory scale work implies nanotechnologies could offer a step-change in remediation capabilities: treating persistent contaminants, avoiding process intermediates and increasing the speed at which degradation or stabilisation can take place. In 2007 the European Commission Joint Research Centre forecast that the 2010 world market for environmental nanotechnologies would rapidly expand to be around $6 billion, with nanoremediation accounting for a substantial proportion of this. However, in practice, adoption of nanoremediation has been slow. While some projects may have gone unreported in the technical literature, the FP7 NanoRem project identified only around 70 examples of field scale applications of nZVI worldwide as of early 2014 (Nano-scale zero-valent iron – nZVI – is the most commonly used nanoremediation material). Only 17 of these were in Europe (cases in the Czech Republic, Germany and Italy), although bench-scale nanoremediation research is widespread across the EU. The majority of 70+ applications in the field noted by NanoRem were in situ injections of modified nZVI. From a commercial and practical standpoint therefore, nanoremediation has been largely as a niche technology for treating chlorinated solvents, competing with a range of alternatives.
The NanoRem project has set itself the goal of achieving a step change in the development and use of nanoremediation technology in Europe. To reach this goal does not only depend on the creation of new research information, but also on the transmission to remediation practitioners and encouraging their use of that information. As part of this process it has been engaging with a large number of stakeholders to investigate the principal drivers perceived as having an important effect on both the sustainability of the technology and its market opportunities.
This work has included discussion with the European stakeholder networks, NICOLE and COMMON FORUM, face to face discussions with remediation practitioners at workshops (including a dedicated workshop in Oslo in December 2014); via focus groups and questionnaires.
Regarding the sustainability, a wide range of stakeholders have been brought together to discuss their hopes and fears related to nanoremediation technology at two events. These debated environmental, economic and social concerns, which would likely influence the sustainability of a nanoremediation project. The most important factors, which would block or facilitate nanoremediation, were identified from the point of view of these cross-sectorial practitioners. Regarding the possible opportunities for nanoremediation market placement and penetration, push and pull factors have been systematically collected to inform sound scenarios for the market development in the EU by 2025.
This presentation will review the main findings of this process at the midpoint of the NanoRem project, “hot of the press” of the NanoRem deliverable on “Exploitation Strategy and Consultation” due April 2015.
Overview. Multiple areas of 1,1,1-trichloroethane (TCA) contamination were encountered
during investigations at a former manufacturing plant. In one area, leaks from a former degreaser pit resulted in TCA concentrations exceeding 1% of its aqueous solubility (13.3 milligrams per liter). Dense non-aqueous phase liquid (DNAPL) was also present in the source zone. The objective of the remedial effort was to reduce contaminant concentrations in the source zone to below the 1% TCA solubility value. After extensive laboratory treatability testing, the selected remedy for the site included heating of the saturated zone in the source area to enhance TCA removal via hydrolysis, followed by the injection of sodium persulfate to oxidize any remaining TCA and hydrolysis byproducts. Remedial investigations were conducted to develop the remedial design basis for the project and help achieve the site remedial objectives, understand hydrolysis reaction rates and byproduct formation, identify oxidation rates at varying temperatures, and estimate the remedial time frame.
Approach/Activities. Bench-scale laboratory analyses and thermal modeling were conducted
prior to implementation of the remedy. Bench-scale analyses evaluated the oxidation of TCA
using alkaline-activated sodium persulfate. A second phase of laboratory testing included
comparison of multiple activation methods, including heat (45oC), chelated iron (using citric
acid, ferrous sulfate, and ferric citrate), and hydrogen peroxide. In situ heating was accomplished by recirculating recovered groundwater through a tank-less hot water heater prior to reinjection into the source area, resulted in a maximum temperature rise of 70oC. At this temperature, TCA should autodecompose at a half life <1 day according to the Arrhenius equation. 1,1- Dichloroethene (DCE) and acetic acid are TCA hydrolysis byproducts; which are relatively easy targets for oxidation using sodium persulfate. The remedial approach included groundwater recirculation for a 6-month period, followed by a single injection of sodium persulfate as a polishing step.
Results/Lessons Learned. Treatability study results documented a nearly 50% reduction in TCA concentration by heat alone (due to hydrolysis) over a 13-day test period. Heat and hydrogen peroxide activation both resulted in a 100% reduction of TCA; however, volatilization was responsible for the removal of TCA mass in the hydrogen peroxide activated sample. The results of the treatability study indicated that heat-activated persulfate was highly effective for degrading TCA, and ferrous iron activated persulfate using high oxidant strength was also moderately successful. Heat alone offered moderate success over the 13 day test and it was predicted that a sustained heat application at higher temperature would enhance effectiveness as well as promote dissolution of DNAPL. The prolonged enhanced hydrolysis produced by heating the formation followed by persulfate injection utilizing the residual heat as an activator was completed in May 2011. Initial results 2 months after the injection of persulfate resulted in >97% reduction of TCA in the source area and destruction of >90% of the DCE byproduct.
Background/Objectives. Approximately 8 million litres of petroleum light non-aqueous phase liquid (LNAPL) reside in the subsurface at the former automotive facility.
Several petroleum types, ranging from gasoline to hydraulic oil, are present in 15 distinct
LNAPL plumes. Bench-scale treatability testing was used to compare the technical and fiscal
viability of five remediation technologies to address recoverable and residual LNAPL present at the site. The bench-tested remediation technologies included hydraulic recovery, surfactantenhanced recovery (SER), thermal-enhanced recovery, in-situ chemical oxidation (ISCO), and surfactant-enhanced in-situ chemical oxidation.
Approach/Activities. Undisturbed soil samples were used to support hydraulic recovery, SER,
and thermal-enhanced recovery. Water drive testing was performed on undisturbed soil cores to evaluate the fraction of LNAPL that could be recovered using hydraulic pumping. Sequential tests were performed following water drive testing to measure the incremental increase in LNAPL recovery using a surfactant solution and hot-water flood. The surfactant and solution strength was determined based on interfacial tension testing of site LNAPL and groundwater amended with various surfactants at a range of concentrations. Site LNAPL and groundwater were used to support ISCO and surfactant-enhanced ISCO testing. Site LNAPL was added to groundwater amended with sodium persulfate or Fenton’s reagent
(along with multiple activation methods) to determine if direct oxidation of the LNAPL was
feasible. Surfactant-enhanced ISCO was also evaluated on LNAPL-groundwater mixtures using surfactant and sodium persulfate. Broad total petroleum hydrocarbon (TPH) analysis was used to evaluate the performance of in-situ thermal destruction (ISTD), ISCO and surfactant-enhanced ISCO on preferential removal of low molecular weight constituents from the LNAPL.
Results/Lessons Learned. This broad bench-scale testing program was unique and provides
insight into commonly-held beliefs of the capabilities and cost effectiveness of common
remediation technologies to address LNAPL contamination. The testing results provided a direct comparison of the capacity of remedial technologies to recover/destroy LNAPL, as well as a basis for a cost benefit analysis of each remedial approach.
Background. The property is a former lumber mill that was developed in 1912 as a manufacturing plant for woodworking machines, and was sold and converted in 1919 to manufacture truck and automobile axles. Lubricants, cutting oils, and metal stock are currently utilized at the 600,000-square foot facility.
Subsurface investigations identified surficial anthropogenic fill material, underlain by a 3-inch to 6-foot thick layer of sawdust and wood fragments, underlain by native silt and clayey silt. The largest mass of wood matter was a 4- to 6-foot thick deposit beneath a parking lot near a river bordering the property.
The thickness of the wood matter decreased between the parking lot and the river, with the native soil transitioning to riverine sand deposits. Environmental investigations identified 18 Recognized
Environmental Conditions (RECs). In addition to RECs consistent with axle manufacturing operations, one unusual REC was identified; a dissolved barium (Ba+2) groundwater plume was found beneath the parking lot. Dissolved barium concentrations ranged up to 25 milligrams per liter (mg/L), well above the 2.0 mg/L state cleanup standard. This was the only area where groundwater standards were exceeded.
Approach. The investigation data were reviewed to evaluate the origin and distribution of barium. Plant operations did not use products with high barium content, suggesting the barium was naturally occurring. Results from 166 soil samples collected from 99 borings did not identify a barium source area. Groundwater data indicated the Ba+2 groundwater exceedances were limited to the parking lot. Fill material samples from the parking lot did not contain elevated concentrations of barium, however the presence of the fill material within the plume indicated a connection. A conceptual site model established
a correlation between the dissolved Ba+2 plume, groundwater depth, and thickness of organic fill deposits.
Barium solubility is influenced by geochemical conditions. A groundwater geochemical study was undertaken using a network of 39 monitoring wells. Groundwater samples were analyzed for 13 geochemical parameters. Results indicated groundwater in the dissolved Ba+2 plume contained elevated levels of chloride, ferrous iron, methane, and total dissolved solids; little to no sulfate or nitrate; negative oxidation reduction potential (ORP); and low dissolved oxygen (DO). The results were indicative of strongly anaerobic conditions. The organic fill material was promoting microbial activity that depleted DO concentrations. This reducing environment promoted the disassociation of stable, insoluble Ba+2 complexes with concurrent reduction of anions (e.g., sulfate to sulfide), making Ba+2 soluble in groundwater beneath the parking lot. The geochemical investigation showed DO concentrations rebounding from 0.15 mg/L to 1.3 mg/L approximately 10 feet downgradient of the fill material and within the native riverine sand deposits. These downgradient conditions allowed barium complexes with lower solubility to precipitate; dissolved Ba+2 concentrations decreased from 19 mg/L to 0.96 mg/L.
Results. Since the parking lot was the only area where groundwater constituents exceeded regulatory standards, active remedial measures such as excavating the organic fill or treating groundwater with Ba+2 binding agents were initially considered. The geochemical study demonstrated the Ba+2 plume was a localized phenomenon created by interactions among the fill material, microbial community, and groundwater. The study also found downgradient Ba+2 concentrations decreased under naturally occurring conditions as DO concentration increased through surface water infiltration and the confluence of groundwater with the river. The final recommendation was to address the Ba+2 plume through natural attenuation. The regulatory agency agreed, and the project received a No Further Action determination.
Background/Objectives. Enhanced reductive dechlorination (ERD) applications rely on
injection of organic carbon substrates over time to establish reducing conditions, foster microbial growth, and drive biodegradation of chlorinated volatile organic compounds (VOCs). Common organic carbon substrates include soluble compounds such as ethanol, lactate, molasses, and cheese whey, while slow-release compounds include emulsified vegetable oils (EVO) and other propriety amendments. Reported half-lives for these soluble compounds range from 10 to 60 days, suggesting these amendments may last several months or longer depending on the microbial ecology and dosing strength, while slow-release compounds may last several years. Typical remedial strategies involve the use of fate and transport modeling to develop preliminary remedial goals (PRGs) with active injections proceeding until PRGs are met, followed by a transition to monitored natural attenuation (MNA) as a polishing step. MNA transition strategies are typically based on general assumptions about TOC longevity and redox recovery following the active carbon injection period. The primary objective of this study is to gather empirical data to refine these assumptions based on a broad assessment of ERD sites that have transitioned to
MNA. This information is intended to help practitioners fine-tune injection and MNA transition
strategies.
Approach/Activities. Data from multiple ERD sites that have completed active carbon
injections and are currently undergoing post-injection monitoring will be evaluated to determine
(1) the duration of elevated TOC (above background) and (2) the timeframe for groundwater to recover to ambient redox conditions. Sites will be grouped based on common climatic and hydrogeologic factors (aquifer type, depositional environment, groundwater velocity, etc). This study will discuss one large full-scale case study to demonstrate the analytical approach and then summarize the results from the remaining sites.
Results/Lessons Learned. Preliminary post-injection results indicate that low, but elevated TOC concentrations often linger longer than predicted where soluble carbon substrates were injected at sites with lower groundwater velocities. Thus, low-level TOC concentrations can extend ERD treatment for up to two years after the last carbon injection, but can also delay the timeframe for groundwater to recover to ambient redox conditions. This may have implications for sites where treatment train remedies are being considered for other contaminants (e.g. chemical oxidation of 1,4-dioxane). At sites with high groundwater velocities, TOC concentrations dropped fairly rapidly following active injection period suggesting that was carbon washing out prior to complete degradation. Overall, the preliminary results suggest the both the substrate type and hydrogeologic setting influence TOC longevity and redox recovery. Thus, remedial strategies should be fine-tuned based on site-specific performance monitoring results.
Background/Objectives. The ability to perform both short and long-term operation of injectionbased in situ remedies is dependent on the aquifer matrix, which acts as a physical regulator during the injection events. Because an aquifer has a finite capacity for (1) fluid accommodation, and (2) the dissipation/assimilation of by-products stemming from reactions (e.g. precipitation, gas generation, biofouling) associated with the injected fluid, injection flow rates and pressures will shift both during injection events and over the lifetime of an injection-based remedy. The ability to “tune” the implementation of a remedy to optimize its performance, and ultimately reduce the lifecycle costs of the remedy, relies on anticipation of the above constraints.
Approach/Activities. Three field examples will be presented to demonstrate the theory and
science behind “Aquifer Tuning”, focusing on how aquifer structure (e.g. lithology, porosity,
permeability) and groundwater geochemistry (e.g. salinity) can have profound effects on short and long-term operation of injection-based systems. These examples will demonstrate how (and to what extent) aquifer constraints reduced remedy effectiveness, increased costs, and/or contributed to the risk of remedy failure. In addition, how these constraints were overcome to optimize the performance of the remedy and ultimately reduce the overall cost of remedy implementation will be discussed.
Results/Lessons Learned. The first field example is an injection site where a physical constraint (a semi-confining layer overlying the targeted injection interval) affected injection flow rates and inhibited reagent distribution.. After the realized affects (greater than anticipated) of the physical constraint, the injection approach was tuned to more effectively distribute the injection solution in a cost effective manner.
The second field example demonstrates how carbon loading must be considered to minimize
both short and long-term aquifer permeability reductions resulting from biogenic gas formation.
An instance of excess TOC loading resulted in immediate reduction of aquifer permeability
which was tuned by monitoring the dissipation of generated biogenic gases, re-establishment of baseline injection capacity and greater control on TOC loading of subsequent injection events The last field study demonstrates the importance of injection solution composition when delivering fluid into a saline environment. to prevent clay particle dispersion, which can result in an unrecoverable reduction in injection capacity. An adapted injection solution, designed to a compatible salinity of the aquifer, resulted in recovery of injection capacity and the continuation of the injection-based remedy.
Contamination of groundwater by industrial organic and inorganic pollutants is a global widespread problem. In recent years, the use of Iron nanoparticles is gaining a special attention as a promising technology for in situ remediation of contaminated aquifers. Injection of nano iron particles into contaminated groundwater is already applied nowadays. Yet, there are still obstacles for efficient and economically viable application of this technology. In particular, due to their high surface area, nano-size and high density nano iron particles in general and nano zero valent iron (nZVI) specifically, are inclined to agglomerate and attachment to subsurface solid matrix. Potential solutions for this problem include surface modifications of the particles to increase their stability and fracturing of the porous medium increasing its permeability and subsequently the particles mobility in the contaminated subsurface. Nevertheless, the knowledge about transport potential of nano iron particles in fractured media is still in its scarcity. Based on previous studies with colloidal particles, fractures are likely to be favorable carriers for nano iron particles and could facilitate their transport and the efficient application of nano iron particles at the field.
In this study we explored and quantified the mobility of several types of nano iron particles in fractured media. Stability tests and transport experiments were carried out in both low-salinity artificial rain water and in much more saline solutions, representing realistic groundwater composition. Some of the particles tested were also stabilized using carboxymethyl cellulose (CMC). The mobility of the particles was tested by transport experiments carried out in the laboratory. These experiments were carried out in a naturally fractured chalk core excavated from the field site in the northern Negev Desert, Israel. The highest particles recovery received in these experiments was of CMC stabilized Carbo-Iron® particles. Carbo-Iron® particles are consisting of activated carbon colloids and anchored deposits of nZVI clusters. The activated carbon acts as a spacer preventing agglomeration of the deposited nZVI structures. Additionally Carbo-Iron® particles have a more negative surface charge than pure nZVI that comes from the properties of the activated carbon colloids. These particles showed higher stability in our stability tests as well.
The next step in this research is therefore injecting CMC stabilized Carbo-Iron® particles in a natural fracture network in the field and analyze the particles recovery under natural conditions in larger scale (tens of meters). Preliminary tracer tests are being done nowadays to accurately define the fracture properties using soluble tracer experiments.
Sometimes it is immediately obvious that a site is complicated because of characteristics such as size, infrastructure, subsurface heterogeneity, or mix of contaminants. In other cases, a site’s complicated nature is realized only after the fact, when remedial actions fail to achieve remedial action objectives. Matrix diffusion is a reasonably well-known phenomenon whereby contamination migrates over time into low(er)-permeability strata and evades treatment, only to back-diffuse after remedial intervention, hampering or precluding short(er)-term achievement of drinking water type groundwater resource restoration goals.
The focus of this panel will be the underlying causes of and possible responses to this prevalent problem, popularly known as “rebound.” The panelists are leading researchers and practitioners working to understand the nature of the problem and evaluating and employing remedial strategies and tools. An important component of this panel will be upfront efforts to reach out to a wider group of researchers and consultants to identify scientific and engineering insights and issues, which will be incorporated into the discussion. Discussion topics will include:
• Is back diffusion really a problem? There are a number of possible explanations for
rebound. Before concluding that back diffusion is the problem, other possible
explanations and contributing sources must be ruled out.
• If rebound is occurring at a particular site, how serious is the problem and what are the
most important attributes? Current approaches to plume delineation may not be
producing accurate conceptual models of plume geometry and volume. A side effect is
inaccuracy in the matrix volume subject to diffusion and storage. Are emerging “highresolution” tools and strategies useful?
• What is/are the most appropriate and feasible response(s)? Possible responses are not
mutually exclusive, and they range from no action through passive to active remediation
over various temporal and spatial scales. Recent field results suggest that the matrix may
not be entirely “defenseless.” Not all sites that have low-permeability zones are
experiencing rebound, suggesting that attenuation processes may be at work.
The discussion will evaluate whether there have been developments in remedial technologies and scientific understanding of requisite persistence and/or matrix penetration attributes.
Background/Objectives. A new passive and sustainable remediation concept termed horizontal treatment (HRx) wells is presented that utilizes horizontal wells filled with reactive media to passively treat contaminated groundwater in-situ. The approach involves the use of directionally drilled horizontal wells filled with granular reactive media generally installed parallel to the direction of groundwater flow. The design leverages natural “flow-focusing” behavior induced by the high in-well hydraulic conductivity of the reactive media relative to the aquifer hydraulic conductivity to passively capture and passively treat proportionally large volumes of groundwater within the well. Clean groundwater then exits the horizontal well along its downgradient sections. Many different types of reactive media could be used (zero valent iron, activated carbon, IX resins, zeolite, phosphate, chitin, etc.); therefore, this concept could be used to address a wide range of contaminants. In contrast to many other in-situ remedial technologies, this technique may be appropriate and successful for low-permeability aquifers. Furthermore, the approach requires no above-ground treatment or footprint, limited ongoing maintenance, and allows the use of a wide range of reactive media that can readily be removed/recharged.
Approach/Activities. A series of quantitative three-dimensional flow and transport simulations
were completed utilizing MODFLOW and MT3D and interpreted with three-dimensional
visualization tools (EVS) to assess the general hydraulic performance, capture zones, residence times, effects of aquifer heterogeneity, and treatment effectiveness of the concept. To confirm the basic hydraulic and treatment concept and verify the model results, a three-dimensional physical model (sand tank) was constructed with zero valent iron (ZVI) used as the reactive media to treat a suite of contaminants.
Results/Lessons Learned. The modeling results demonstrate that capture widths greater than 50 feet can be achieved, and that near-immediate reductions in down-gradient concentrations and contaminant mass flux can be achieved. Compared to other remedial alternatives, the HRx system has several green and sustainable attributes that contribute to the triple bottom line (environmental, social and economic benefits). The approach greatly reduces carbon footprint and recurring and cumulative energy demands. Because the system does not require groundwater extraction, life-cycle water consumption is negligible, and the above-ground infrastructure is minimal. From an economic perspective, the annual and life-cycle costs are substantially lower than most conventional alternative remedial strategies, particularly if remedial performance goals are focused on reducing risk through eliminating contaminant mass discharge.
Background/Objectives. Site contractual obligations required remediation of a 3 mile long
trichloroethene (TCE) plume, to maximum contaminant
levels (MCLs) within 10 years. This presentation addresses the implementation of an adaptive approach to design and operation of the remedy to achieve site closure within the required time period. Upon ARCADIS taking control of the site, the plume dimensions were defined by reinterpreting all available site data. The initial delineation of the TCE plume had been based on approximately 20% of all the wells installed, and as a result, the plume was depicted as a 3 mile long contiguous mass. Due to the limited understanding of high permeability flow paths, pumpand- treat wells were installed where access was available - in many cases away from the main body of the TCE plume – rather than at strategic locations within the plume. This resulted in artificial widening of the plume that further obscured an accurate understanding of its geometry.
Approach/Activities. The plume was divided into five individual treatment areas, each with its
own conceptual site model (CSM) based on plume size, plume age, period of performance, and site conditions. Enhanced Reductive Dechlorination (ERD) was the primary remedial strategy in two areas, while pump-and-treat followed by re-injection was the focus in the remaining three areas. ERD was largely successful in areas where reagent distribution was achieved; however, well fouling, aquifer heterogeneities, and an insufficient well network lead to the cessation of ERD. For these reasons and the fact that significant mass reduction could be achieved, full scale implementation of pump-and-treat followed by re-injection was pursued. Sitewide MCLs were achieved by installing dual purpose extraction/injection wells over time, in an organized sequence after careful review of operational data and surrounding well data. High permeability zones were identified and remedial efforts were focused on the areas that would impact the greatest mass while still maintaining plume capture. Operation of strategically placed wells, optimization of remedial systems, and an adaptive design have combined to reduce the plume size by more than 95% in the last 4 years and allowed for greater operational flexibility and subsequently, greater efficiency.
Results/Lessons Learned. Regulatory collaboration was a critical component in developing and understanding accurate CSMs and in achieving site closure. A collaborative environment grew and facilitated better communication and site management. Full site closure will be achieved after regulatory-assigned compliance wells meet MCLs for three consecutive annual samples.
The 3 year pre-closure monitoring phase is scheduled to begin in 2012 and is expected to be
complete in 2014.
Background/Objectives. Karst terranes present unique challenges to geologists and engineers tasked with remediating groundwater where chlorinated or recalcitrant compounds have been released. Groundwater movement and chemical transport in karst aquifers is often complicated by extreme heterogeneity and anisotropy, turbulent flow, and transport pathways that are impracticable to characterize precisely. However, karst aquifers are not uncommon. These aquifers are present on all continents and crop on more than 20 percent of the earth’s land surface; at least 20 percent of the world’s population is partly or entirely dependent on water derived from them. Given this knowledge, it is important to understand how karst sites are currently being remediated. The work depicted here represents results from the first part of a two-part study designed to (1) examine current
remedial actions selected for sites located in karst terranes, and (2) evaluate their appropriateness and effectiveness.
Approach/Activities. Drawing on review of 73 remedial action plans from sites where groundwater remediation in karst terrane is mandated, as well as the authors’ experience
at over 15 karst sites throughout the United States, the following aspects of karst aquifer remediation were examined: addressing source zones, implementing engineering controls to eliminate exposure pathways, the use of institutional controls and groundwater management strategies, and performance monitoring strategies.
Results/Lessons Learned. Remedial approaches applied at karst sites are usually the same as those applied at non-karst sites. For example, source zones have most commonly been addressed by excavating unconsolidated material, and the most-common groundwater management strategy selected in the remedial action plans evaluated is monitored natural attenuation. However, karst-specific characteristics are often not considered when applying these technologies. In the case of source removal, the benefits of removal via excavation need to be evaluated against the potential for mobilizing contaminated soils into the karst aquifer, where they can act as long-term secondary sources of contamination to groundwater. The monitoring component of monitored natural attenuation is frequently accomplished using water-quality data obtained from wells that have not been demonstrated by tracer testing to be monitoring groundwater that is in transit and connected to the source zone. Springs that discharge the groundwater-of-interest are arguably the best places to monitor for attenuation, yet such monitoring is rarely required to be performed.
A number of remedial approaches that may be specific to karst are underused. For example, the interconnected, variably saturated epikarst present at many karst sites has been shown to be an excellent means of collecting and containing volatile vapors, but is rarely exploited in this fashion.
Performance monitoring of groundwater remedies in karst terranes requires special techniques. For remedies that involve moving groundwater (e.g., containment) tracer tests must be included to assess performance. The best places to monitor remedial performance are springs, surface streams, and groundwater-abstraction points. Reliance on monitoring well networks to assess performance has often been shown to be inappropriate. Despite this, the most-common form of groundwater monitoring required in karst-site RODs is the traditional, monitoring-well-based approach.