Remedial Process Optimization and Ozone Sparging for Petroleum Hydrocarbon‐Impacted Groundwater

A former natural gas processing station is impacted with total petroleum hydrocarbons (TPH) and benzene. Remedial process optimization (RPO) was conducted to evaluate the effectiveness of the historical air sparging/soil vapor extraction (AS/SVE) system and the current groundwater extraction and treatment system. The RPO indicated that both remedial activities offered no further benefit in meeting remediation goals. Instead, an in situ chemical oxidation (ISCO) system was recommended. Ozone was selected, and the results of a bench test indicated that the ozone demand was 8 to 12 mg ozone/mg TPH and that secondary by‐products would include hexavalent chromium and bromate. A capture zone analysis was conducted through groundwater flow modeling (MODFLOW) to ensure containment of the injected oxidant using the existing groundwater extraction system. Results of a pilot study indicated that the optimum frequency of ozone sparging is 60 minutes in order to reach a maximum radius of influence of 20 feet. TPH concentrations within the treatment zone decreased by 97 percent over two months of ozone sparging. Concentrations of hexavalent chromium and bromate increased from nondetect to 44 and 110 mg/L, respectively, during the ozone sparging but attenuated to nondetectable concentrations within three months of system shut down. ©2016 Wiley Periodicals, Inc.     

Matrix Diffusion Modeling Applied to Long‐Term Pump‐and‐Treat Data: 2. Results From Three Sites

The data mining/groundwater modeling methodology developed in McDade et al. (2013) was performed to determine if matrix diffusion is a plausible explanation for the lower‐concentration but persistent chlorinated solvent plumes in the groundwater‐bearing units at three different pump‐and‐treat systems. Capture‐zone maps were evaluated, and eight wells were identified that did not draw water from any of the historical source areas but captured water from the sides of the plume. Two groundwater models were applied to study the persistence of the plumes in the absence of contributions from the historical source zones. In the wells modeled, the observed mass discharge generally decreased by about one order of magnitude or less over 4 to 10 years of pumping, and 1.8 to 17 pore volumes were extracted. In five of the eight wells, the matrix diffusion model fit the data much better than the advection dispersion retardation model, indicating that matrix diffusion better explains the persistent plume. In the three other wells, confounding factors, such as a changing capture zone over time (caused by changes in pumping rates in adjacent extraction wells); potential interference from a high‐concentration unremediated source zone; and limited number of pore volumes removed made it difficult to confirm that matrix diffusion processes were active in these areas. Overall, the results from the five wells indicate that mass discharge rates from the pumping wells will continue to show a characteristic “long tail'' of mass removal from zones affected by active matrix diffusion processes. Future site management activities should include matrix diffusion processes in the conceptual site models for these three sites. © 2013 Wiley Periodicals, Inc.     

Using uncertainty analysis to reduce costs at a pump-and-treat site

The former Nebraska Ordnance Plant site in east-central Nebraska was included on the National Priorities List because of explosives and trichloroethene contamination. The preferred groundwater remedy includes hydraulic containment of the contaminated groundwater and focused extraction of the more highly contaminated groundwater as components of the remedial action. The purpose of hydraulic containment is to stop the spread of contamination, while the more aggressive focused extraction will be used to speed up the remediation and reduce total cleanup costs. This case study illustrates how straightforward groundwater models were combined with uncertainty analysis to select a precise definition of the focused extraction areas. The purpose of the analysis was to reduce ultimate remediation costs, given the significant uncertainty associated with the estimated remediation times. The selected definition provides a basis for more sophisticated groundwater modeling, the goal of which was to locate extraction wells and define their flow rates. The batch flushing model provided the governing equations, and Monte Carlo analysis was used for the uncertainty analysis. All of the analysis was performed on a personal computer using commercially available software.     

The Stochastic Approach in Groundwater Modeling for the Optimization of Hydraulic Barriers

A three‐dimensional stochastic groundwater flow and contaminant transport model has been developed to optimize groundwater containment at an industrial site in Italy and to define likely future contaminant distribution under different confinement or remediation scenarios. The transport model was first calibrated using a deterministic approach to simulate the hydrochemical conditions prior to the optimization of groundwater extraction, then a probabilistic simulation was conducted to predict future contaminant concentrations. The stochastic approach allowed introducing an estimate of the uncertainty of the hydrogeological and chemical parameters into the model, simulating the probability density function of the contaminant concentrations after the application of the optimized barrier wells pumping rates. This allowed the calculation of the time required for the concentrations of each modeled parameter to decrease to under the regulatory limit at the compliance point, and associating the related uncertainty into the model. Quantifying the model prediction uncertainty facilitated a better understanding of the site environmental conditions, providing the site owners additional information for managing the site and allocating related economic resources. ©2016 Wiley Periodicals, Inc.     

Field Performance of Point Velocity Probes at a Tidally Influenced Site

Conventional methods to estimate groundwater velocity that rely on Darcy's Law and average hydrogeologic parameter values are insensitive to local‐scale heterogeneities and anisotropy that control advective flow velocity and direction. Furthermore, at sites that are tidally influenced or have extraction wells with variable pumping schedules, infrequent water‐level measurements may not adequately characterize the range and significance of transient hydraulic conditions. The point velocity probe (PVP) is a recently developed instrument capable of directly measuring local‐scale groundwater flow velocity and direction. In particular, PVPs may offer distinct advantages for sites with complex groundwater–surface water interactions and/or with spatially and temporally variable groundwater flow conditions. The PVP utilizes a small volume of saline tracer and inexpensive sensors to directly measure groundwater flow direction and velocity in situ at the centimeter‐scale and discrete times. The probes are installed in conventional direct‐push borings, rather than in wells, thus minimizing the changes and biases in the local flow field caused by well installation and construction. Six PVPs were installed at a tidally influenced site in North Carolina to evaluate their implementability, performance, and potential value as a new site characterization tool. For this study, a new PVP prototype was developed using a rapid prototyping machine (i.e., a “three‐dimensional printer'') and included both horizontally and vertically oriented tracer detectors. A site‐specific testing protocol was developed to account for the spatially and temporally variable hydraulic conditions and groundwater salinity. The PVPs were tested multiple times, and the results were compared to the results of several different groundwater flux and velocity estimation tools and methods, including a heat‐pulse flowmeter, passive flux meters, single‐well tracer tests, and high‐resolution hydraulic gradient analysis. Overall, the results confirmed that the PVP concept is valid and demonstrated that reliable estimates of groundwater velocity and direction can be obtained in simple settings. Also, PVPs can be successfully installed by conventional methods at sites where the formation consists primarily of noncohesive soils and the water table is relatively shallow. Although some PVP tests yielded consistent and reliable results, several tests did not. This is likely due to the highly transient flow conditions and limitations associated with the PVP design and testing procedures. PVPs offer particular advantages over, and can effectively complement, other groundwater flow characterization techniques for certain conditions, and objectives may be useful for characterizing complex flow patterns under steady conditions; however, this study suggests that PVPs are best suited for conditions where the flow hydraulics are not highly transient. For sites where the hydraulic conditions are highly transient, the most reliable approach for understanding groundwater flow behavior and groundwater–surface water interactions would generally involve both a high‐resolution hydraulic gradient analysis and another local‐scale method, such as tracer testing. This study also highlighted some aspects of the current PVP design and testing protocol that can be improved upon, including a more robust connection between the PVP and injection line and further assessment of tracer solution density effects on vertical flow. © 2013 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.     

Constant Head Injection for Enhanced In Situ Chemical Oxidation

With the successful implementation of in situ chemical oxidation (ISCO) programs to remediate contaminated soil and groundwater aquifers worldwide, ISCO has become established as a traditional remediation technique. On the basis of historical success, expanded ISCO practices are now routinely applied to increasingly difficult geologic environments, including formerly problem locations such as those containing nonaqueous‐phase liquid, fractured bedrock, low‐conductivity media, and highly layered and/or heterogeneous aquifers. Effective delivery of amendment, however, remains the single most important aspect of successful remediation, particularly given the range of potentially applicable delivery methods and site complexities. Selecting the most appropriate technique for any specific site depends upon a clear understanding of the variety of site constraints, including factors such as site conditions, underlying geology, contaminant distribution, technology limitations, and other project‐specific factors. Because the injection program is often the largest cost associated with implementation of an ISCO project, it is critical to develop a cost‐effective injection method for each site. Constant head injection provides a cost‐effective alternative for sites with low‐conductivity lithology(ies). Constant head injection employs a continuous low‐pressure application method to deliver ISCO agents over a long period of time. This synergistic method complements the existing site conditions and heterogeneity, working with the natural conditions, rather than trying to overcome or destroy the site geology using highly aggressive delivery techniques. © 2014 Wiley Periodicals, Inc.     

Performance assessment of hanging funnel‐and‐gate structures designed by reverse particle tracking for capturing polluted groundwater

The objective of this study was to evaluate the capability of partially penetrating (hanging) funnel‐and‐gate structures, designed using reverse flow trajectories, for capturing plumes of contaminated groundwater. Linear capture structures, comprised of two slurry cutoff walls on either side of a permeable gate, were positioned perpendicular to regional groundwater flow in a hypothetical unconfined aquifer. A four‐step approach was used for each of two simulated settings: (1) a numerical mass transport model generated a contaminant plume originating from a source area; (2) a particle‐tracking model projected groundwater flow paths upstream from a treatment gate; (3) the structure was widened and deepened until bounding path lines contained the plume; and (4) mass transport simulation tested the ability of the structure to capture the plume. Results of this study suggest that designing funnel‐and‐gate structures using reverse particle tracking may result in too small a structure to capture a contaminant plume. This practice generally ignores effects of hydrodynamic dispersion, which may enlarge plumes such that contaminants move beneath or around a capture structure. This bypassing effect may be considerable even for low values of dispersivity. Particle‐tracking approaches may also underestimate the amount of time required to reduce contaminant concentrations to acceptable levels. © 2007 Wiley Periodicals, Inc.     

Re‐evaluation of treatment approach for a site contaminated with Freon‐113 and 1,1,1‐trichloroethane

This study demonstrates a remedial approach for completing the remediation of an aquifer contaminated with 1,1,2‐trichlorotrifluoroethane (Freon‐113) and 1,1,1‐trichloroethane (TCA). In 1987, approximately 13,000 pounds of Freon‐113 were spilled from a tank at an industrial facility located in the state of New York. The groundwater remediation program consisted of an extraction system coupled with airstripping followed by natural attenuation of residual contaminants. In the first phase, five recovery wells and an airstripping tower were operational from April 1993 to August 1999. During this time period over 10,000 pounds of CFC‐13 and 200 pounds of TCA were removed from the groundwater and the contaminant concentrations decreased by several orders of magnitude. However, the efficiency of the remediation system to recover residual Freon and/or TCA reduced significantly. This was evidenced by: (1) low levels (< 10 ppb) of Freon and TCA captured in the extraction wells and (2) a slight increase of Freon and/or TCA in off‐site monitoring wells. A detailed study was conducted to evaluate the alternative for the second‐phase remediation. Results of a two‐year groundwater monitoring program indicated the contaminant plume to be stable with no significant increase or decrease in contaminant concentrations. Monitored geochemical parameters suggest that biodegradation does not influence the fate and transport of these contaminants, but other mechanisms of natural attenuation (primarily sorption and dilution) appear to control the fate and transport of these contaminants. The contaminants appear to be bound to the soil matrix (silty and clay units) with limited desorption as indicated by the solid phase analyses of contaminant concentrations. Results of fate and transport modeling indicated that contaminant concentrations would not exceed the action levels in the wells that showed a slight increase in contaminant concentrations and in the downgradient wells (sentinel) during the modeled timeframe of 30 years. This feasibility study for natural attenuation led to the termination of the extraction system and a transaction of the property, resulting in a significant financial benefit for the original site owner. © 2003 Wiley Periodicals, Inc.     

Insufficient source area remediation results in the rebound of TCE breakdown products in groundwater

In the early 1990s, a soil removal action was completed at a former disposal pit site located in southern Michigan. This action removed waste oil, cutting oil, and chlorinated solvents from the unsaturated zone. To contain groundwater contaminant migration at the site, a groundwater pump‐and‐treat system comprised of two extraction wells operating at a combined flow of 50 gallons per minute, carbon treatment, and a permitted effluent discharge was designed, installed, and operated for over 10 years. Groundwater monitoring for natural attenuation parameters and contaminant attenuation modeling demonstrated natural attenuation of the contaminant plume was adequate to attain site closure. As a result of incomplete contaminant source removal, a rebound of contaminants above the levels established in the remedial action plan (RAP) has occurred in the years following system shutdown and site closure. Groundwater concentrations have raised concerns regarding potential indoor air quality at adjacent residential properties constructed in the past 9 to 10 years. The only remedial option available in the original RAP is to resume groundwater pump‐and‐treat. To remediate the source area, an alternate remediation strategy using an ozone sparge system was developed. The ozone sparge remediation strategy addresses the residual saturated zone contaminants beneath the former disposal pit and reestablishes site closure requirements without resumption of the pump‐and‐treat system. A pilot study was completed successfully; and the final system design was subsequently approved by the Michigan Department of Environmental Quality. The system was installed and began operations in July 2010. As of the January 2011 monitoring event, the system has shown dramatic improvement in site contaminant concentrations. The system will continue to operate until monitoring results indicate that complete treatment has been obtained. The site will have achieved the RAP objectives when the system has been shut down and meets groundwater residential criteria for four consecutive quarters. © 2011 Wiley Periodicals, Inc.     

ART in‐well technology proves effective in treating 1,4‐dioxane contamination

A common industrial solvent additive is 1,4‐dioxane. Contamination of dissolved 1,4‐dioxane in groundwater has been found to be recalcitrant to removal by conventional, low‐cost remedial technologies. Only costly labor and energy‐intensive pump‐and‐treat remedial options have been shown to be effective remedies. However, the capital and extended operation and maintenance costs render pump‐and‐treat technologies economically unfeasible at many sites. Furthermore, pump‐and‐treat approaches at remediation sites have frequently been proven over time to merely achieve containment rather than site closure. A major manufacturer in North Carolina was faced with the challenge of cleaning up 1,4‐dioxane and volatile organic compound–impacted soil and groundwater at its site. Significant costs associated with the application of conventional approaches to treating 1,4‐dioxane in groundwater led to an alternative analysis of emerging technologies. As a result of the success of the Accelerated Remediation Technologies, LLC (ART) In‐Well Technology at other sites impacted with recalcitrant compounds such as methyl tertiarybutyl ether, and the demonstrated success of efficient mass removal, an ART pilot test was conducted. The ART Technology combines in situ air stripping, air sparging, soil vapor extraction, enhanced bioremediation/oxidation, and dynamic subsurface groundwater circulation. Monitoring results from the pilot test show that 1,4‐dioxane concentrations were reduced by up to 90 percent in monitoring wells within 90 days. The removal rate of chlorinated compounds from one ART well exceeded the removal achieved by the multipoint soil vapor extraction/air sparging system by more than 80 times. © 2005 Wiley Periodicals, Inc.     

A practical approach to steam‐enhanced dual‐phase extraction: A case study

This article presents the results of a pilot test that was conducted to determine the effectiveness of using steam‐enhanced dual‐phase extraction (DPE) at a former industrial site in New York. The pilot test proved that steam‐enhanced DPE was very effective at removing significant contaminant mass from the subsurface in a relatively short time period. Concentrations of volatile organic compounds and semivolatile organic compounds in the vapor stream and groundwater were successfully reduced, in some cases by orders of magnitude. Based on the results of the steam‐enhanced DPE pilot test, the final remedy for the site includes implementing this technology at selected areas as an alternative to DPE alone or other remedial alternatives, such as excavation or groundwater pump and treat. © 2003 Wiley Periodicals, Inc.     

Successful combination of remediation techniques at a former silver factory

A residential area that was formerly part of a silver factory site severely contaminated with chlorinated solvents was remediated using an in situ electro‐bioreclamation technique. Electro‐bioreclamation is a method for heating soil and groundwater combined with soil vapor and low‐yield groundwater extraction and enhanced reductive dechlorination (ERD). During the first two years of remediation in the source area (the intensive phase), a total of 80 kg of volatile organic compounds (VOCs) was removed by heating combined with ERD. After another two years of ERD in the source and plume areas (the attenuation phase), the VOC concentrations were reduced to a level below 100 μg/L in groundwater. Given these satisfying results, electro‐reclamation in combination with ERD turned out to be a successful in situ remediation technique for removing VOCs. © 2006Wiley Periodicals, Inc.     

Breakthrough in 2D‐CSIA Technology for 1,4‐Dioxane

A dual isotope technology based on compound‐specific stable isotope analysis of carbon and hydrogen (2D‐CSIA) was recently developed to help identify sources and monitor in situ degradation of the contaminant 1,4‐dioxane (1,4‐D) in groundwater. Site investigation and optimized remediation have been the focus of thousands of CSIA applications completed for volatile organic contaminants (VOCs) worldwide. CSIA for the water miscible 1,4‐D, however, has been technically challenging. The most commercially available sample preparation settings “Purge and Trap” for VOC could not efficiently extract 1,4‐D out of water for a reliable CSIA measurement, especially when the concentration is below 100 μg/L. Such a high reporting limit has prevented CSIA from being used for effective site investigation and remediation monitoring at most 1,4‐D contaminated sites, where 1,4‐D is often present at very low ppb levels. This article outlines the recent breakthrough in 2D‐CSIA technology for 1,4‐D in water, reported down to ～1 μg/L for carbon, and ～10 μg/L to 20 μg/L for hydrogen using solid‐phase extraction based on EPA Method 522, and its benefit is highlighted through a case study at a 1,4‐D contaminated site. ©2016 Wiley Periodicals, Inc.     

Matrix Diffusion Modeling Applied to Long‐Term Pump‐and‐Treat Data: 1. Method Development

Despite the installation in the 1980s and 1990s of hydraulic containment systems around known source zones (four slurry walls and ten pump‐and‐treat systems), trichloroethene (TCE) plumes persist in the three uppermost groundwater‐bearing units at the Middlefield‐Ellis‐Whisman (MEW) Superfund Study Area in Mountain View, California. In analyzing TCE data from 15 recovery wells, the observed TCE mass discharge decreased less than an order of magnitude over a 10‐year period despite the removal of an average of 11 pore volumes of affected groundwater. Two groundwater models were applied to long‐term groundwater pump‐and‐treat data from 15 recovery wells to determine if matrix diffusion could explain the long‐term persistence of a TCE plume. The first model assumed that TCE concentrations in the plume are controlled only by advection, dispersion, and retardation (ADR model). The second model used a one‐dimensional diffusion equation in contact with two low‐permeability zones (i.e., upper and lower aquitard) to estimate the potential effects of matrix diffusion of TCE into and out of low‐permeability media in the plume. In all 15 wells, the matrix diffusion model fit the data much better than the ADR model (normalized root mean square error of 0.17 vs. 0.29; r² of 0.99 vs. 0.19), indicating that matrix diffusion is a likely contributing factor to the persistence of the TCE plume in the non‐source‐capture zones of the MEW Study Area's groundwater‐extraction wells. © 2013 Wiley Periodicals, Inc.     

Soil Vapor Extraction and Chemical Oxidation to Remediate Chlorinated Solvents in Fractured Crystalline Bedrock: Pilot Study Results and Lessons Learned

A pilot study was completed at a fractured crystalline bedrock site using a combination of soil vapor extraction (SVE) and in‐situ chemical oxidation (ISCO) with Fenton's Reagent. This system was designed to destroy 1,1,1‐trichloroethane (TCA) and its daughter products, 1,1‐dichloroethene (DCE) and 1,1‐dichloroethane (DCA). Approximately 150 pounds of volatile organic compounds (VOCs) were oxidized in‐situ or removed from the aquifer as vapor during the pilot study. Largely as a result of chemical oxidation, TCA concentrations in groundwater located within a local groundwater mound decreased by 69 to 95 percent. No significant rebound in VOC concentration was observed in these wells. Wells located outside of the groundwater mound showed less dramatic decreases in VOC concentration, and the data show that vapor stripping and short‐term groundwater migration following the oxidant injection were the key processes at these wells. Although the porosity of the aquifer at the site is on the order of 2 percent or less, the pilot study showed that SVE could be an effective remedial process in fractured crystalline rock. © 2002 Wiley Periodicals, Inc.     

Migration of VOC Plume in the Subsurface Domain at the Y‐12 National Security Site

During the production of thermonuclear fusion weapons at the Y‐12 National Security Complex (Y‐12 NSC) in Oak Ridge, Tennessee, between 1950 and 1963, the regional environment was extensively contaminated by volatile organic compounds (VOCs). Old Salvage Yard (OSY) on the western side of the site has been characterized as the major source of VOCs. In order to analyze the long‐term fate and transport of chlorinated VOC sources, an integrated surface and subsurface flow and transport model was developed for the Y‐12 NSC using the hydrodynamic and transport numerical package MIKE‐SHE. The model was developed considering the recent hydrogeological investigations on preferential flow and transport pathways at the site. The model was calibrated using the recorded groundwater flow and water‐quality data. The modeling simulated migration of the VOC plume for the next 100 years. Considering a range of hydrogeological and transport parameters, uncertainty of the results is discussed. The modeling predicted that tetrachloroethene, trichloroethene, and 1,2‐dichloroethene may exceed human health–related risk levels for the next 10 to 20 years. However, the contamination is unlikely to migrate to surface water under the current hydrogeological conditions and will decay below acceptable risk levels within approximately 20 years. © 2013 Wiley Periodicals, Inc.     

Effectiveness of Capture Zones Generated by Intermittent Pumping of a PV‐Powered Pump‐and‐Treat System Without Energy Storage

A common technology to remediate and/or contain contaminated groundwater is pump‐and‐treat remediation (P&T). Traditionally, P&T systems have been designed to operate continuously to achieve steady‐state capture zones, for which large amounts of energy are required. Green and sustainable remediation (GSR) is emerging as a viable method to minimize the adverse effects of remediation on the environment. One of the challenges associated with photovoltaic‐ (PV‐) powered P&T systems is the assessment of their performance given the intermittent nature of the power availability. This article characterizes the hydraulic containment effectiveness of a PV‐powered P&T system without energy storage using data collected at two different remediation sites, a Dry‐Cleaning Environmental Response Trust Fund site in Rolla, Missouri, and the Former Nebraska Ordnance Plant near Mead, Nebraska. Additionally, a method to estimate the effectiveness of the hydraulic containment as a function of the total volume of groundwater expected to be extracted is being proposed. Two transient and a continuously pumped capture zones were modeled using Visual MODFLOW^® 2012.1 along with MODPATH and compared. The study shows that smaller capture zones will be generated from intermittent pumping when compared to continuous pumping. © 2013 Wiley Periodicals, Inc.     

Using pneumatic fracturing extraction to achieve regulatory compliance and enhance voc removal from low-permeability formations

The New Jersey Department of Environmental Protection and Energy (NJDEPE) has been developing cleanup regulations that focus on remediation, rather than extended delineation, and on integrating regulatory requirements with technological developments. To this end, the NJDEPE, under the regulatory aegis of the Environmental Cleanup and Responsibility Act (ECRA), is monitoring an innovative treatment technology pilot test at a TCE-contaminated ECRA site in Hillsborough, New Jersey. The purpose of the study is to determine the applicability of pneumatic fracturing extraction (PFE) as a source-removal technique for extracting volatile organic compounds (VOCs) trapped informations with low permeability. The technology being pilot tested is pneumatic fracturing extraction, a process for enhancing permeability to promote in-situ removal and treatment of VOCs. The patented process uses high-pressure air injected into an isolated subsurface zone at controlled rates and pressures. At a critical point, the geologic material ruptures, and fractures are created that radiate outward from the fracture location. At the pilot test site, formation air flow was increased from 400 percent to 700 percent. PFE is a key component of the overall remediation strategy at the Hillsborough site. Consistent with proposed NJDEPE regulations, a ground-water pump-and-treat system will be installed for plume migration control. Once the pump-and-treat system has been established and shown to be effective, a more aggressive source removal program will be implemented using PFE. This program will include construction of a vadose zone PFE system and evaluation of the use of pneumatic fracturing to remove saturated zone residual dense nonaqueous phase liquids (DNAPL). Preliminary calculations suggest that if source zone concentrations can be reduced to 10 ppm of TCE, then TCE groundwater concentrations may be reduced to background levels at the property boundary compliance points.     

The horizontal reactive media treatment well (HRX Well®) for passive in situ remediation: Design,implementation, and sustainability considerations

A new in situ remediation concept termed a Horizontal Reactive Media Treatment Well (HRX Well^®) is presented that utilizes a horizontal well filled with reactive media to passively treat contaminated groundwater in situ. The approach involves the use of a large‐diameter directionally drilled horizontal well filled with solid reactive media installed parallel to the direction of groundwater flow. The engineered contrast in hydraulic conductivity between the high in‐well reactive media and the ambient aquifer hydraulic conductivity results in the passive capture, treatment, and discharge back to the aquifer of proportionally large volumes of groundwater. Capture and treatment widths of up to tens of feet can be achieved for many aquifer settings, and reductions in downgradient concentrations and contaminant mass flux are nearly immediate. Many different types of solid‐phase reactive treatment media are already available (zero valent iron, granular activated carbon, biodegradable particulate organic matter, slow‐release oxidants, ion exchange resins, zeolite, apatite, etc.). Therefore, this concept could be used to address a wide range of contaminants. Laboratory and pilot‐scale test results and numerical flow and transport model simulations are presented that validate the concept. The HRX Well can access contaminants not accessible by conventional vertical drilling and requires no aboveground treatment or footprint and requires limited ongoing maintenance. A focused feasibility evaluation and alternatives analysis highlights the potential cost and sustainability advantages of the HRX Well compared to groundwater extraction and treatment systems or funnel and gate permeable reactive barrier technologies for long‐term plume treatment. This paper also presents considerations for design and implementation for a planned upcoming field installation.