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1

Electronic Resource

Numerical Simulation of Air Sparging for Remediation of NAPL Contamination (1997)

McCray, John E. ; Falta, Ronald W.

Oxford, UK : Blackwell Publishing Ltd

Ground water 35 (1997), S. 0

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ISSN: 1745-6584

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: A numerical simulation study of air sparging for the removal of nonaqueous phase liquids (NAPLs) from the subsurface is presented. These simulations were performed using the T2VOC integrated finite-difference, multiphase-flow, contaminant transport code. The code is used to model two-dimensional air sparging experiments from Ji et al. (1993) which include both homogeneous and heterogeneous permeability distributions. The model predicts the experimental gas plume shape and behavior very well. Field-scale simulations using a radially symmetric, cylindrical mesh are then used to model hypothetical DNAPL and LNAPL spills and air sparging remediation performance in various hydrogeologic settings. Both homogeneous and heterogeneous systems are considered. The results of the study indicate that the sparging-induced gas pressure increase, or “positive pressure,” measured at steady state below the water table, closely corresponds to both the subsurface gas distribution and the effective zone of contaminant reduction. Because this positive pressure is easily measured in the field with a simple monitoring device, it can be used to realistically define the sparging radius of influence.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6584.1997.tb00065.x

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2

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Cyclodextrin-Enhanced Solubilization of Organic Contaminants with Implications for Aquifer Remediation (2000)

McCray, John E. ; Boving, Thomas B. ; Brusseau, Mark L.

Oxford, UK : Blackwell Publishing Ltd

Ground water monitoring & remediation 20 (2000), S. 0

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ISSN: 1745-6592

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: Reagents that enhance the aqueous solubility of non-aqueous phase organic liquid (NAPL) contaminants are under investigation for use in enhanced subsurface remediation technologies. Cyclodextrin, a glucose-based molecule, is such a reagent. In this paper, laboratory experiments and numerical model simulations are used to evaluate and understand the potential remediation performance of cyclodextrin. Physical properties of cyclodextrin solutions such as density, viscosity, and NAPL-aqueous inter-facial tension are measured. Our analysis indicates that no serious obstacles exist related to fluid properties that would prevent the use of cyclodextrin solutions for subsurface NAPL remediation. Cyclodextrin-enhanced solubilization for a large suite of typical ground water contaminants is measured in the laboratory, and the results are related to the physicochemical properties of the organic compounds. The most-hydrophobic contaminants experience a larger relative solubility enhancement than the less-hydrophobic contaminants but have lower aqueous-phase apparent solubilities. Numerical model simulations of enhanced-solubilization flushing of NAPL-contaminated soil demonstrate that the more-hydrophilic compounds exhibit the greatest mass-removal rates due to their greater apparent solubilities, and thus are initially more effectively removed from soil by enhanced-solubilization-flushing reagents. However, the relatively more hydrophobic contaminants exhibit a greater improvement in contaminant mass-removal (compared with water flushing) than that exhibited for the relatively hydrophilic contaminants.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6592.2000.tb00256.x

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3

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A Subregional-Scale Method to Assess Aquifer Vulnerability to Pesticides (2002)

Schlosser, Stephanie A. ; McCray, John E. ; Murray, Kyle E. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Ground water 40 (2002), S. 0

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ISSN: 1745-6584

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: A method to predict aquifer vulnerability to pesticide contamination at the subregional scale was developed. The assessment method was designed to incorporate relevant hydrologic and pesticide-transport information and to use generally available data. The method assumes steady-state advection of pesticides in the vadose zone, including sorption and biological decay. The solution is presented as a vulnerability index (VI) that increases as the aquifer vulnerability increases. The hydrologic input data for the VI model are obtained from the soil survey geographic database. Pesticides were grouped into three leachability classes using a leachabiiity ratio (half-life divided by organic carbon partition coefficient). Pesticide transformation is assumed to occur in the surface layer. The influence of vertical transport in the remainder of the vadose zone has been incorporated by applying a multiplying factor to the VI that varies with depth to ground water. Hydraulic conductivity is used as a surrogate for soil-water velocity for practical purposes. The performance of the VI model is evaluated using ground water data from Weld County, Colorado. The model is demonstrated to be successful at predicting relative vulnerability, defined as the magnitude of pesticide concentration and percent of wells in a unit that exhibit a pesticide detection. Areas of low, medium, and high vulnerability are assigned. Results indicate that the vulnerability classifications are most dependent on the leachability ratio, hydraulic conductivity, and organic carbon content.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6584.2002.tb02514.x

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4

Electronic Resource

Polymer-Enhanced DNAPL Flushing from Low-Permeability Media: An Experimental Study (2003)

Darwish, Mohamed I.M. ; McCray, John E. ; Currie, Peter K. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Ground water monitoring & remediation 23 (2003), S. 0

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ISSN: 1745-6592

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: Remediation of dense nonaqueous phase liquids (DNAPLs) is recognized as one of the most difficult problems associated with ground water pollution. The pump-and-treat technique, usually consisting of a continuous operation of extraction-injection wells, is widely used for ground water remediation. In a stratified or otherwise heterogeneous aquifer, however, this technique suffers from tailing and rebound problems, which limit its cleanup efficiency and result in higher operation costs. The tailing and rebound is usually due to slow diffusion of contaminants out of lower- permeability heterogeneities into the flow regime of the higher-permeability zone. In this study, we conduct bench-scale experiments to investigate a novel polymer system and injection method to improve the pump-and-treat technique for DNAPL trapped in a layer of porous media that has a relatively low permeability compared to the surrounding media. This technique might be useful, for example, to remove DNAPL from these low-permeability zones after removal of DNAPL from the higher-permeability zones by a more traditional remediation method. The polymer system consists of a mixture of anionic and cationic polyacrylamides in solution and the injection method is based on flow-induced polymer adsorption, called bridging adsorption. The study includes single and parallel-column experiments. The measured polymer penetration depths were compared with values predicted from a numerical simulation, which was developed previously by the authors of this paper. The experiments and simulations show that the polymer injection leads to a modification of the permeability contrast that favors a more efficient pump-and-treat process. These results suggest that additional research to upscale the technology to pilot scales is warranted.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6592.2003.tb00675.x

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5

Electronic Resource

Model Parameters for Simulating Fate and Transport of On-Site Wastewater Nutrients (2005)

McCray, John E. ; Kirkland, Shiloh L. ; Siegrist, Robert L. ; [et al.]

Oxford, UK; Malden, USA : Blackwell Science Inc

Ground water 43 (2005), S. 0

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ISSN: 1745-6584

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: This paper presents a critical review of model-input parameters for transport of on-site wastewater treatment system (OWS) pollutants. Approximately 25% of the U.S. population relies on soil-based OWS for effective treatment and protection of public health and environmental quality. Mathematical models are useful tools for understanding and predicting the transport and fate of wastewater pollutants and for addressing water-budget issues related to wastewater reclamation from site to watershed scales. However, input parameters for models that simulate fate and transport of OWS pollutants are not readily obtained. The purpose of this analysis is to illustrate an objective, statistically supported method for choosing model-input parameters related to nitrogen (N) and phosphorus (P). Data were gathered from existing studies reported in the literature. Cumulative frequency distributions (CFDs) are provided for OWS effluent concentrations of N and P, nitrification and denitrification rates, and linear sorption isotherm constants for P. When CFDs are not presented, ranges and median values are provided. Median values for model-input parameters are as follows: total N concentration (44 mg/L), nitrate-N (0.2 mg/L), ammonium (60 mg/L), phosphate-P (9 mg/L), organic N (14 mg/L), zero-order nitrification rate (264 mg/L/d), first-order nitrification (2.9/d), first-order dentrification (0.025/d), maximum soil capacity for P uptake (237 mg/kg), linear sorption isotherm constant for P (15.1 L/kg), and OWS effluent flow rates (260 L/person/d).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6584.2005.0077.x

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6

Electronic Resource

NAPLANAL: A Tool for Analyzing NAPL Saturation and Composition (2003)

McCray, John E. ; Cohen, Robert M.

Oxford, UK : Blackwell Publishing Ltd

Ground water 41 (2003), S. 0

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ISSN: 1745-6584

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: Overall, NAPLANAL is excellent freeware. The software is useful for engineers and scientists to understand the spatial heterogeneities in NAPL distribution and composition at a site. This information can be useful for designing NAPL remediation schemes, and potentially for modeling contaminant transport from NAPL-mixture source zones if enough soil chemical and physical data were available. The program is also useful for university teaching because students can rapidly assess multiphase concentrations of NAPL mixtures while integrating physical and chemical information obtained from typical analyses performed on soil samples collected while drilling monitoring wells.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6584.2003.tb02597.x

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7

Electronic Resource

Partitioning Tracer Tests for Evaluating Remediation Performance (2000)

Cain, R. Brent ; Johnson, Gwynn R. ; McCray, John E. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Ground water 38 (2000), S. 0

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ISSN: 1745-6584

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: Partitioning tracer tests (PTTs) are being used in environmental systems for the detection and estimation of nonaqueous phase liquid (NAPL) saturations in contaminated aquifers. A series of such studies was recently conducted at Hill Air Force Base, Utah, in two hydraulically isolated test cells of an aquifer contaminated by light nonaqueous phase liquids (LNAPL). These experiments were performed before and after two remediation efforts, a complexing sugar flush (CSF) and a recirculating in-well aeration (IWA) system. The breakthrough curves obtained from monitoring tracer concentrations in the extraction wells indicated the presence of an immiscible phase, and the LNAPL saturation values determined from the pre- and post-PTTs allowed the estimation of remediation efficiencies for both test cells. These remediation efficiencies, a removal of 43% of the LNAPL for the CSF and an increase of 32% for the IWA system, are consistent with data obtained from cores collected from within the experiment zones. The apparent increase in contamination for the IWA cell is likely due to a significant change in the LNAPL distribution caused by the flow system associated with the IWA technology. Several factors influenced the interpretation of the PTT data. Physical heterogeneities at the site caused significant tailing of the tracer concentrations and required the use of a simple extrapolation technique to account for the concentrations below analytical quantification limits. Degradation affected selected nonreactive and reactive tracers, causing the overestimation and underestimation of LNAPL saturations, respectively.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb02711.x

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8

Electronic Resource

Numerical Modeling of Unsaturated Flow in Wastewater Soil Absorption Systems (2003)

Beach, Deborah N. Huntzinger ; McCray, John E.

Oxford, UK : Blackwell Publishing Ltd

Ground water monitoring & remediation 23 (2003), S. 0

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ISSN: 1745-6592

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences

Notes: It is common practice in the United States to use wastewater soil absorption systems (WSAS) to treat domestic wastewater. WSAS are expected to provide efficient, long-term removal of wastewater contaminants prior to ground water recharge. Soil clogging at the infiltrative surface of WSAS occurs due to the accumulation of suspended solids, organic matter, and chemical precipitates during continued wastewater infiltration. This clogging zone (CZ) creates an impedance to flow, restricting the hydraulic conductivity and rate of infiltration. A certain degree of clogging may improve the treatment of wastewater by enhancing purification processes, in part because unsaturated flow is induced and residence times are significantly increased. However, if clogging becomes excessive, the wastewater pond height at the infiltrative surface can rise to a level where system failure occurs. The numerical model HYDRUS-2D is used to simulate unsaturated flow within WSAS to better understand the effect of CZs on unsaturated flow behavior and hydraulic retention times in sandy and silty soil. The simulations indicate that sand-based WSAS with mature CZs are characterized by a more widely distributed flow regime and longer hydraulic retention times. The impact of clogging on water flow within the silt is not as substantial. For sand, increasing the hydraulic resistance of the CZ by a factor of three to four requires an increase in the pond height by as much as a factor of five to achieve the same wastewater loading. Because the degree of CZ resistance directly influences the pond height within a system, understanding the influence of the CZ on flow regimes in WSAS is critical in optimizing system design to achieve the desired pollutant-treatment efficiency and to prolong system life.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1745-6592.2003.tb00672.x

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