Surfactant‐Oxidant Co‐Application for Soil and Groundwater Remediation

In situ chemical oxidation (ISCO) typically delivers oxidant solutions into the subsurface for contaminant destruction. Contaminants available to the oxidants, however, are limited by the mass transfer of hydrophobic contaminants into the aqueous phase. ISCO treatments therefore often leave sites with temporarily clean groundwater which is subject to contaminant rebound when sorbed and free phase contaminants leach back into the aqueous phase. Surfactant Enhanced In situ Chemical Oxidation (S‐ISCO^®) uses a combined oxidant‐surfactant solution to provide optimized contaminant delivery to the oxidants for destruction via desorption and emulsification of the contaminants by the surfactants. This article provides an overview of S‐ISCO technology, followed by an implementation case study at a coal tar contaminated site in Queens, New York. Included are data points from the site which demonstrate how S‐ISCO delivers desorbed contaminants without uncontrolled contaminant mobilization, as desorbed and emulsified contaminants are immediately available to the simultaneously injected oxidant for reaction. ©2016 Wiley Periodicals, Inc.     

Remediation of Trapped Free‐Phase LNAPL

Free‐phase light nonaqueous phase liquids (LNAPLs) may be trapped in certain stratigraphic and structural features near or at contaminated sites due to seasonal or other variations in the water table elevation. The purpose of this article is to point out particular subsurface conditions that are conducive to trapping of free‐phase LNAPLs and to suggest approaches to remediating LNAPL‐contaminated sites exhibiting similar subsurface geometry and stratigraphy. To trap free‐phase LNAPL, a structure must have, in addition to closed contours, an upper boundary with pores small enough so that the LNAPL will not enter them. This boundary usually consists of clay‐rich sediments. The Lower Mississippi River Valley contains thousands of these potential traps associated with the geomorphic surfaces mapped as outwash or braided stream terraces, which are covered with thin layers of backswamp clays. These traps may have closure heights ranging from about 1 to 7.5 meters or more and have variable lateral extents. Based on surface geomorphic analysis, the potential LNAPL traps in the Lower Mississippi River Valley range in size from about 0.06 by 0.02 km to 4.19 by 0.69 km. The apparent best remediation strategy for LNAPL sites located on these geomorphic surfaces, which contain these trapping structures, is to first determine if free‐phase is present. If it is present, and is contained in one of the stratigraphic traps, the free‐phase can be removed through an extraction well or wells located at the trap apex. Geomorphic analysis and geophysical surveys may be necessary to accurately locate the trap apex. The remaining residual hydrocarbons might best be remediated using an air sparging system, although it may be necessary to install air vents through the clay cap by backfilling augured holes with washed sand. If it is determined that, due to geometry, the dissolved LNAPL plume cannot be adequately remediated using an air sparging system, then groundwater circulation wells or monitored natural attenuation may be alternative technologies. © 2002 Wiley Periodicals, Inc.     

Practical Perspectives of 1,4‐Dioxane Investigation and Remediation

1,4‐Dioxane (dioxane) is a contaminant of emerging concern that is classified by the U.S. Environmental Protection Agency as a likely human carcinogen. Dioxane has been used as a minor or major ingredient in many applications, and is also generated as an unwanted by‐product of industrial processes associated with the manufacturing of polyethylene, nonionic surfactants, and many consumer products (cosmetics, laundry detergents, shampoos, etc.). Dioxane is also a known stabilizer of chlorinated solvents, particularly 1,1,1‐trichloroethane, and has been commonly found comingled with chlorinated solvent plumes. Dioxane plumes at chlorinated solvent sites can complicate site closure strategies, which to date have not typically focused on dioxane. Aggressive treatment technologies have greatly advanced and are clearly capable of achieving lower parts per billion cleanup criteria using ex situ advanced oxidation processes and sorption media. In situ chemical oxidation has also been demonstrated to effectively remediate dioxane and chlorinated solvents. Other in situ remedies, such as enhanced bioremediation, phytoremediation, and monitored natural attenuation, have been studied; however, their ability to achieve cleanup levels is still somewhat questionable and is limited by co‐occurring contaminants. This article summarizes and provides practical perspectives on dioxane analysis, plume stability relative to other contaminants, and the development of investigation tools and treatment technologies.     

Remediation of PCB‐Contaminated Soil Using Extraction and Destruction: Bench‐Scale Test

Polychlorinated biphenyls (PCBs) are a persistent environmental issue worldwide. This study summarizes the results obtained from a bench‐scale test of remediating PCB‐impacted soil. The research aimed to evaluate the effectiveness of extracting the PCB Aroclor 1260 from soil, transferring it to a liquid matrix, and then treating the PCB‐containing liquid using an Activated Metal Treatment System, a technology developed by NASA based on zero valent magnesium (ZVMg). The soil was from a former electrical plant area impacted by PCBs. The initial concentration of untreated soil contained an average of 4.7 ± 0.15 mg/kg of Aroclor 1260. The results showed that the mass transfer phenomena is possible using ethanol as a liquid matrix, reaching transfer results up to 93 percent. The ZVMg enabled the destruction of the Aroclor 1260, which reached 20 percent without any buildup of undesirable by‐products, such as less chlorinated PCBs.  ©2016 Wiley Periodicals, Inc.     

Integrating Remediation and Reuse to Achieve Whole‐System Sustainability Benefits

This perspective article was prepared by members of the Sustainable Remediation Forum (SURF), a professional nonprofit organization seeking to advance the state of sustainable remediation within the broader context of sustainable site reuse. SURF recognizes that remediation and site reuse, including redevelopment activities, are intrinsically linked—even when remediation is subordinate to or sometimes a precursor of reuse. Although the end of the remediation life cycle has traditionally served as the beginning of the site's next life cycle, a disconnect between these two processes remains. SURF recommends a holistic approach that brings together remediation and reuse on a collaborative parallel path and seeks to achieve whole‐system sustainability benefits. This article explores the value of integrating remediation into the reuse process to fully exploit synergies and minimize the costs and environmental impacts associated with bringing land back into beneficial use. © 2013 Wiley Periodicals, Inc.     

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.     

In Situ Remediation of 1,4‐Dioxane Using Electrical Resistance Heating

Recent regulatory changes need more challenging treatment goals for 1,4‐dioxane. However, significant treatment limitations exist in part due to the high solubility and low Henry's law constant of 1,4‐dioxane. Two case studies are reported with substantial 1,4‐dioxane concentration reductions through in situ thermal remediation via electrical resistance heating (ERH). Concentration reductions greater than 99.8 percent of 1,4‐dioxane have been observed in the field using ERH. Concentrations of 1,4‐dioxane in air and steam extracted by an ERH vapor recovery system have also been evaluated. Laboratory studies were conducted to further understand the mechanisms that enable ERH remediation of 1,4‐dioxane. Vapor liquid equilibrium studies in water and soil were conducted and utilized to develop an ERH treatment cost model for 1,4‐dioxane. Existing field data were correlated to the 1,4‐dioxane treatment cost model. Field observations and laboratory testing indicate steam stripping that occurs through ERH remediation is an effective treatment method for 1,4‐dioxane. ©2015 Wiley Periodicals, Inc.     

Sustainable Remediation Considerations for Treatment of 1,4‐Dioxane in Groundwater

1,4‐Dioxane remediation is challenging due to its physiochemical properties and low target treatment levels. As such, applications of traditional remediation technologies have proven ineffective. There are a number of promising remediation technologies that could potentially be scaled for successful application to groundwater restoration. Sustainable remediation is an important consideration in the evaluation of remediation technologies. It is critically important to consider sustainability when new technologies are being applied or new contaminants are being treated with traditional technologies. There are a number of social, economic, and environmental drivers that should be considered when implementing 1,4‐dioxane treatment technologies. This includes evaluating sustainability externalities by considering the cradle‐to‐grave impacts of the chemicals, energy, processes, transportation, and materials used in groundwater treatment. It is not possible to rate technologies as more or less sustainable because each application is context specific. However, by including sustainability thinking into technology evaluations and implementation plans, decisions makers can be more informed and the results of remediation are likely to be more effective and beneficial. There are a number sustainable remediation frameworks, guidance documents, footprint assessment tools, life cycle assessment tools, and best management practices that can be utilized for these purposes. This paper includes an overview describing the importance of sustainability in technology selection, identifies sustainability impacts related to technologies that can be used to treat 1,4‐dioxane, provides an approximating approach to assess sustainability impacts, and summarizes potential sustainability impacts related to promising treatment technologies. ©2016 Wiley Periodicals, Inc.     

Remediation of acid mine drainage leachate by a physicochemical and biological treatment‐train approach

Biological and physicochemical approaches were utilized in a treatment train for acid mine dis charge (AMD) waters. Anaerobic bioreactors, chemical precipitation reactors, and biopolymer chelation reactors, operated in static, semicontinuous, and continuous flow modes, removed significant quantities of metals and sulfates associated with AMD water. Static tests indicated accept able copper removal via precipitation by generation of hydrogen sulfide in anaerobic reactors. However, low pH affected the biopolymer coating in the chelation reactor, resulting in loss of bed surface. Corrections of AMD to pH > 7 resulted in some metal precipitationprior to biopolymer treatment. A series of static semicontinuous tests at pH 5.0 provided improved metal and sulfate removal. Copper (Cu⁺) was reduced to trace concentrations, while manganese (Mn⁺), although reduced, proved to be the most recalcitrant of the metals. © 2006 Wiley Periodicals, Inc.     

Remediation of DDT‐contaminated soil using optimized mixtures of surfactants and a mixing system

Soil contaminated with persistent pesticides, such as DDT, poses a serious risk to humans and to wildlife. A surfactant‐aided soil‐washing technique was studied as an alternative method for remediation of DDT‐contaminated soil. An ex situ soil washing method was investigated using nonionic and anionic surfactants due to the clayey structure of the contaminated soil. A mixture of 1 percent nonionic surfactant (Brij 35) and 1 percent anionic surfactant (SDBS) removed more than 50 percent of DDT from soil in a flow‐through system, whereas individual surfactants or other combinations of the surfactants had a lower removal efficiency. The soil‐washing technique was improved using a mixing system. The mixture of surfactants was optimized in the mixing system, and the combination of 2 percent Brij 35 and 0.1 percent SDBS was found to be optimum, removing 70 to 80 percent of DDT. Prewashing of the soil with tap water decreased the adsorption of surfactants to soil particles by 30 to 40 percent, and postwashing recovered 90 percent of the surfactants. © 2010 Wiley Periodicals, Inc.     

Combined MODFLOW‐FRACTRAN Application to Assess Chlorinated Solvent Transport and Remediation in Fractured Sedimentary Rock

Detailed field investigations and numerical modeling were conducted to evaluate transport and fate of chlorinated solvent contamination in a fractured sedimentary bedrock aquifer (sandstone/siltstone/mudstone) at a Superfund site in central New Jersey. Field investigations provided information on the fractured rock system hydrogeology, including hydraulic gradients, bulk hydraulic conductivity, fracture network, and rock matrix, and on depth discrete contaminant distribution in fractures (via groundwater sampling) and matrix (via detailed subsampling of continuous cores). The numerical modeling endeavor involved application of both an equivalent porous media (EPM) model for flow and a discrete fracture network (DFN) model for transport. This combination of complementary models, informed by appropriate field data, allowed a quantitative representation of the conceptual site model (CSM) to assess relative importance of various processes, and to examine efficacy of remedial alternatives. Modeling progressed in two stages: first a large‐scale (20 km x 25 km domain) 3‐D EPM flow model (MODFLOW) was used to evaluate the bulk groundwater flow system and contaminant transport pathways under historic and current aquifer stress conditions and current stresses. Then, results of the flow model informed a 2‐D DFN transport model (FRACTRAN) to evaluate transport along a 1,000‐m flowpath from the source represented as a 2‐D vertical cross‐section. The combined model results were used to interpret and estimate the current and potential future extent of rock matrix and aqueous‐phase contaminant conditions and evaluate remedial strategies. Results of this study show strong effects of matrix diffusion and other processes on attenuating the plume such that future impacts on downgradient well fields under the hydraulic stresses modeled should be negligible. Results also showed futility of source remediation efforts in the fractured rock, and supported a technical impracticability (TI) waiver for the site. © 2013 Wiley Periodicals, Inc.     

Integrating the Social Dimension in Remediation Decision‐Making: State of the Practice and Way Forward

Sustainable remediation guidance, frameworks, and case studies have been published at an international level illustrating established sustainability assessment methodologies and successful implementation. Though the terminology and indicators evaluated may differ, one common theme among international organizations and regulatory bodies is more comprehensive and transparent methods are needed to evaluate the social sphere of sustainable remediation. Based on a literature review and stakeholder input, this paper focused on three main areas: (1) status quo of how the social element of sustainable remediation is assessed among various countries and organizations; (2) methodologies to quantitatively and qualitatively evaluate societal impacts; and (3) findings from this research, including challenges, obstacles, and a path forward. In conclusion, several existing social impact assessment techniques are readily available for use by the remediation community, including rating and scoring system evaluations, enhanced cost benefit analysis, surveys/interviews, social network analysis, and multicriteria decision analysis. In addition, a list of 10 main social indicator categories were developed: health and safety, economic stimulation, stakeholder collaboration, benefits community at large, alleviate undesirable community impacts, equality issues, value of ecosystem services and natural resources, risk‐based land management and remedial solutions, regional and global societal impacts, and contributions to other policies. Evaluation of the social element of remedial activities is not without challenges and knowledge gaps. Identification of obstacles and gaps during the project planning process is essential to defining sustainability objectives and choosing the appropriate tool and methodology to conduct an assessment. Challenges identified include meaningful stakeholder engagement, risk perception of stakeholders, and trade‐offs among the various triple bottom line dimensions. ©2015 Wiley Periodicals, Inc.     

Use of Large‐Scale Electrokinetic and ZVI Treatment for Chlorinated Solvent Remediation at an Active Industrial Facility

The combination of electrokinetic and zero‐valent iron (ZVI) treatments were used to treat soils contaminated with chlorinated solvents, including dense nonaqueous phase liquid (DNAPL), at an active industrial site in Ohio. The remediation systems were installed in tight clay soils under truck lots and entrances to loading docks without interruption to facility production. The electrokinetic system, called Lasagna^TM, uses a direct current electrical field to mobilize contaminant via electroosmosis and soil heating. The contaminants are intercepted and reduced in situ using treatment zones containing ZVI. In moderately contaminated soils around the Lasagna^TM‐treated source areas, a grid of ZVI filled boreholes were emplaced to passively treat residual contamination in decades instead of centuries. The remediation systems were installed below grade and did not interfere with truck traffic during the installation and three years of operation. The Lasagna^TM systems removed 80 percent of the trichloroethylene (TCE) mass while the passive ZVI borings system has reduced the TCE by 40 percent. The remediation goals have been met and the site is now in monitoring‐only mode as natural attenuation takes over. © 2014 Wiley Periodicals, Inc.     

Hydrogen Release Compound: A Cost‐Effective Alternative to PCE Remediation at Dry Cleaning Facilities

Tetrachloroethylene, also known as perchloroethylene or PCE, is one of the most difficult to treat chlorinated solvents when present in groundwater. Unfortunately, this elusive and recalcitrant compound is also the most commonly used dry cleaning solvent. As a result, releases of PCE at dry cleaning sites are somewhat common. Regenesis Bioremediation Products, of San Clemente, California, has developed Hydrogen Release Compound (HRC), which has been successfully used to promote bioremediation of PCE in groundwater. This product is directly injected into contaminated groundwater to speed up the natural attenuation of PCE through an anaerobic, natural process known as reductive dechlorination. A key benefit of HRC is its ability to slowly release hydrogen over extended periods of time. Reductive dechlorination relies on a steady source and readily available supply of electron donors as part of the degradation process. Hydrogen is one of the best electron donors available, and thus, the application of HRC significantly enhances the rate of PCE degradation. For dry cleaners, this technology can substantially reduce major design, capital, and operating costs, allowing the implementation of a low‐impact application and remediation solution. This article discusses the use of the HRC to remediate PCE contamination and presents the results of two specific HRC‐treated dry cleaner sites. © 2002 Wiley Periodicals, Inc.     

Spreadsheet‐Based Design Tool for In Situ Anaerobic Bioremediation Using Soluble Substrate

A Microsoft Excel spreadsheet‐based design tool has been developed to assist remediation professionals in the design of injection systems for distributing soluble substrate (SS) to enhance in situ anaerobic bioremediation. The user provides site data, design parameters, and unit‐cost information to generate estimates of remediation‐system cost and steady‐state contact efficiency (CE_SS) for various designs. CE_SS is estimated from a nonlinear regression equation that includes terms for the SS injection concentration (C_I), minimum substrate concentration (C_MIN), groundwater travel time between rows of injection wells (T_T), SS half‐life (T_H), substrate reinjection time interval (T_R), and pore volumes of substrate solution injected (PV). With this tool, users can quickly compare the relative costs and performance of different injection alternatives and identify the best design for their specific site conditions. The design process embodied in the tool includes: (1) entering injection‐well configuration and unit costs for well installation, injection, and substrate; (2) determining treatment‐zone dimension; (3) selecting trial injection‐well spacing, time period between substrate reinjection, and injection pore volume; and (4) estimating contact efficiency and capital and life‐cycle costs. This process is then repeated until a final design is selected. In most cases, injection costs increase with increasing CE_SS. However, the best (highest) ratio of CE_SS to injection cost typically occurs for CE_SS in the range of 70 to 80 percent. © 2013 Wiley Periodicals, Inc.     

California's Low‐Threat LUFT Site Closure Policy: Looking Forward

California's regulatory agencies have historically been at the forefront of national efforts to address environmental concerns. In 2012, California's agency for addressing leaking underground fuel tanks (LUFTs) adopted a policy that identifies low‐threat conditions warranting closure of an LUFT case. That development clearly fulfills the role of risk management in the risk assessment–risk management paradigm inherent in environmental remediation. It also encourages identification of additional categories of sites and other circumstances that are “low threat” to develop similar guidance on closure to apply to those sites. ©2015 Wiley Periodicals, Inc.