bluuebunny/crossref_metadata_2025_split huggingface dataset:
Decision Analysis for Leachate Control at a Fractured Rock Landfill
Authors: Lepage Nicolas , Hamel Pascal , Lefebvre René , Therrien René , Blais Chantale 
Published: February 2007

AbstractThe municipal landfill at the Complexe Environnemental de Saint‐Michel (CESM) in Montreal, which is the third largest in North America, is located in a former quarry in fractured limestone. Impressive measures are taken to monitor and control biogas and leachate generated at the site. Leachate containment is presently performed with a pumping well completed within the waste. The efficiency of the well in controlling off‐site leachate migration is questioned because field observations strongly suggest that the nearby former Francon quarry is diverting local ground water flow. To address this issue, four additional hydraulic control options are considered: (1) increased pumping at the existing waste well; (2) new pumping wells in the rock on the eastern limit of the site; (3) new injection wells in the rock on the eastern limit; and (4) combination of new injection wells at the same location and new water supply wells upgradient of the landfill. We evaluated the four hydraulic control options at the CESM using two coupled models: (1) a decision model based on an objective function weighting the risk, costs, and benefits of each option translated into dollar units; and (2) a numerical ground water flow model to represent the effect of operational conditions and ascertain success. Decision analysis offers a quantitative unbiased tool to evaluate the potential and relative cost of each option, but qualitative considerations and judgment still must be used for a complete evaluation. Our analysis confirms that scenario 4, which was the intuitively favored option, represents the best containment strategy.
An Evaluation of Horizontal Recirculation Using Single‐Well Tests, Pumping Tests, Tracer Tests, and the Colloidal Borescope
Authors: Korte Nic , Kearl Peter M. , Siegrist Robert L. , Muck Maureen T. , Schlosser Robert M. 
Published: February 2007

AbstractExtensive hydrodynamic testing was performed as part of a program to evaluate horizontal recirculation as a means of removing contaminants from thin, interbedded aquifers. Two test sites, each containing a pair of horizontal recirculation wells, were evaluated using various hydraulic tests. Results of these evaluations showed that ground water was intercepted more than 100 feet beyond the wells, and that the hydraulic gradient increased by more than two orders of magnitude. Aquifer heterogeneity, however, controlled the efficiency and uniformity of ground water flow. Heterogeneity was assessed with a variety of techniques. Bromide tracer tests and the colloidal borescope provided the most useful data. For example, at an uncontaminated site, the leading edge of the bromide tracer traversed the 100 feet between the injection and extraction wells in 21 hours, and the peak bromide concentration was observed in 2.6 days, compared with the four days predicted by a pumping test. The resulting maximum velocity calculation was consistent with measurements made with the borescope in preferential flow zones. Data obtained from a highly contaminated location indicated that assessments of aquifer heterogeniety are further complicated by the presence of DNAPL. Very low flow occurred in a highly contaminated zone, despite the fact that lithologic descriptions indicated that this region contained permeable sand and gravel.
A County‐Level Assessment of Ground Water Contamination by Pesticides
Authors: Shukla Sanjay , Mostaghimi Saied , Shanholt Vernon O. , Collins Michael C. , Ross Burton B. 
Published: February 2007

AbstractA pesticide screening model was integrated with a geographic information system (GIS) for evaluating the ground water vulnerability to pesticide contamination in Albemarle County, Virginia. The attenuation factor (AF). an index of pesticide mass emission from the vadose zone, was used to evaluate the relative contamination potential of 70 pesticides used in the county. Results for only three pesticides—atrazine, dicamba, and lindane—are discussed in this paper. Spatial (land use, soils, and hydrogeology) and relational (soil and pesticide properties) data layers were combined with the AF model within the GIS environment for spatial computation of AF for actual and 2 m ground water depths. For each pesticide, a ground water vulnerability map with five contamination potential categories (high, medium, low, very low, and unlikely) was generated, based on the spatial distribution of AF for each cell size of 0.27 acre (0.11 ha). To consider the variability in pesticide transport, model simulations were performed for “maximum,”“average,” and “minimum” scenarios of pesticide leaching. Under the average leaching scenario (2 m depth), the three pesticides were found to have very low to low levels of contamination potential in some areas. For maximum leaching scenario (2 m depth), contamination potential of these three pesticides increased to low to medium levels. When actual ground water depth was used, no significant contamination potential was indicated by any of the three pesticides. The modeling approach was evaluated using the data from a limited monitoring study in Albemarle County. Although agreement between the model prediction and actual pesticide detection was observed, extent of the data was not sufficient enough to draw firm conclusions about the model's success in predicting contamination potential. A sensitivity analysis of the methodology revealed that significant uncertainty can be involved in predicting the county‐scale contamination potential. To make better use of this study, it is recommended that a comprehensive pesticide monitoring be undertaken in Albemarle County.
Free‐Product Recovery of Petroleum Hydrocarbon Liquids
Authors: Charbeneau Randall J. , Johns Russell T. , Lake Larry W. , McAdams Michael J. 
Published: February 2007

AbstractRecovery wells remain the principle technology for removal of free‐product hydrocarbon liquids from the subsurface. This paper presents simple models for estimating hydrocarbon recovery rates using wells and vacuum‐enhanced systems. Use of LNAPL volume balance between LNAPL recovery rate and formation free‐product volume leads to development of algebraic equations that can be used to estimate recovery times. Selection of model parameters is discussed, model comparisons are made, and applications are presented for design and analysis of recovery systems using wells. Model validation is also discussed.
Oxidation of Binary DNAPL Mixtures Using Potassium Permanganate with a Phase Transfer Catalyst
Authors: Seol Yongkoo , Schwartz Franklin W. , Lee Sangsuk 
Published: February 2007

AbstractPhase transfer catalysts (PTCs) can enhance the oxidation of pure DNAPLs using potassium permanganate by facilitating reactions in the organic phase. This study examined the influence of pentyltriphenylphosphonium bromide (PTPP) as a PTC on the rate of permanganate (MnO4‐) oxidation of DNAPLs in pure phases and mixtures. Kinetic batch experiments with trichloroethylene (TCE), 1,1,2‐trichloroethane (TCA), tetrachloroethylene (PCE), 1,1,2,2‐tetrachloroethane (TECA), and their mixtures, (1:1, v/v) were performed in test tubes to assess reaction rates. The disappearance of MnO4‐ was quantified by capturing digital images pf the tubes. This rapid photographic monitoring approach was validated by comparison with an UV‐Vis spectrometer method. The PCE/TCA mixture was selected to examine the impact of relative contents of a component in the binary mixture on the MnO4‐ disappearance. The comparative rates of MnO4‐ consumption for pure phases were TCE > TECA > PCE > TCA. PTPP increased MnO4‐ consumption rates, especially for TCE and TECA as pure, phases. The consumption rates of mixtures without PTPP were lower than those including the pure phases. However, due to their high extraction capability for PTPP‐MnO4‐ ion pairs, TCA and TECA appeared to increase the MnO4‐ consumption significantly when they were mixed with TCE or PCE, The increase in consumption rates with PTPP was most remarkable with the mixture of PCE and TCA. Chloride concentration showed faster increases for the mixtures with relative PCE contents ranging about 5 % to 90%, maximum at about 50% PCE, than for pure phases of PCE and TCA when the PTC assisted the reactions. The PTC appears to be promising in its ability to increase oxidation rates of DNAPL mixtures.
DNAPL Characterization Methods and Approaches, Part 1: Performance Comparisons
Authors: Kram Mark L. , Keller Arturo A. , Rossabi Joseph , Everett Lorne G. 
Published: February 2007

AbstractContamination from the use of chlorinated solvents, often classified as dense nonaqueous phase liquids (DNAPLs) when in an undissolved state, represents an environmental challenge with global implications. Mass‐transfer limitations due to rate‐limited dissolution can lead to long‐term aquifer persistence for even small volumetric fractions. The identification of DNAPL source zones located beneath the water table is critical to ultimately achieve site remediation and aquifer restoration. This paper provides a comparison of the advantages and disadvantages of many of the methods being used for detecting and delineating DNAPL contaminant source zones. The objective is to determine which options are best to pursue based on site characteristics, method performance, and method costs. DNAPL characterization methods are grouped into approaches, which include site preparation, characterization, and data‐processing activities necessary to design an effective remediation system. We compare the different approaches based on the level of chemical and hydrogeologic resolution, and the need for additional data requirements. Our findings can be used to assist with selection of appropriate site remediation management options.
Diffusive Oxygen Emitters for Enhancement of Aerobic In Situ Treatment
Authors: Wilson Ryan D. , Mackay Douglas M. 
Published: February 2007

AbstractAerobic biodegradation can be enhanced within contaminant plumes by elevating typically low dissolved oxygen (D.O.) levels using materials or devices that passively release oxygen. We have developed passive devices that provide a uniform, steady, long‐term source of oxygen by diffusion from pressurized polymeric tubing and report test results under lab and field conditions. Lab flow‐through reactor tests were conducted to determine the diffusion coefficient (D) of oxygen through four readily available tubing materials. Oxygen diffusion was greatest through Tygon® 3350 platinum‐cured silicone (D = 6.67 ± 10‐7 cm2/sec), followed by 2075 Ultra Chemical Resistant Tygon (1.59 ± 10‐7 cm2/sec), 2275 High Purity Tygon (5.11 ± 10‐8 cm2/sec), and low‐density polyethylene (LDPE; 1.73 ± 10‐8 cm2/sec). Variable‐pressure release tests with LDPE resulted in very close estimates of D, which confirmed that mass transfer is controlled by diffusion and that the concentration gradient is a valid approximation of the chemical potential driving diffusion. LDPE emitter devices were designed and installed in seven 8‐inch‐diameter well screens across a portion of a gasoline plume at a former service station. With the devices pressurized to 620.5 kPag (kilopascals gauge) late in the test, steady‐state D.O. concentrations reached as high as 25 mg/L, comparing favorably to the value predicted using the mass‐transfer coefficient estimated from the lab test (26.3 mg/L). The method can also be used to release other gases for other reasons: gaseous tracers (i.e., sulphur hexafluoride, helium, and argon), hydrogen (for reductive dechlorination), or light alkanes (for cometabolic biodegradation of methyl tertiary butyl ether [MTBE] or chlorinated solvents).
Numerical Modeling of Unsaturated Flow in Wastewater Soil Absorption Systems
Authors: Beach Deborah N. Huntzinger , McCray John E. 
Published: February 2007

AbstractIt 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.
Extent of Benzene Biodegradation in Saturated Soil Column During Air Sparging
Authors: Adams Jeffrey A. , Ready Krishna R. 
Published: February 2007

AbstractIn situ air sparging has emerged as a popular remedial alternative to traditional pump‐and‐treat for the remediation of volatile organic contaminants in saturated soils and ground water. During air sparging, a gas, usually air, is injected into the subsurface below the lowest known point of contamination. The air induces partitioning of dissolved‐phase and free‐phase contamination into the vapor phase. Additionally, the injected air increases subsurface dissolved oxygen concentrations, potentially stimulating aerobic biodegradation. To take advantage of the ability of subsurface microbial populations to degrade organic compounds, air sparging may be implemented in a manner different from a traditional air sparging application; a technique often referred to as biosparging. This paper presents the results of a laboratory study performed to demonstrate the potential contribution of aerobic biodegradation to the attenuation of VOCs during the use of air sparging. This study included a series of controlled laboratory column tests using a soil profile subjected to biomass infiltration and a range of dissolved‐phase benzene concentrations. The test results demonstrated that, although the partitioning of NAPL‐ and aqueous‐phase benzene into the vapor phase through volatilization was the dominant removal mechanism, biodegradation could account for a substantial portion of the benzene removal during the application of air sparging. In order for considerable aerobic biodegradation to occur, however, sufficient amounts of dissolved oxygen must exist within the subsurface to serve as an electron acceptor. The presence of a soil matrix reduced the rates of biodegradation within the column tests when compared to batch reactor tests due to the discontinuous contact of the biomass, aqueous‐phase benzene, nutrients, and dissolved oxygen. Additionally, the rates of biodegradation that were observed during testing were independent of the initial aqueous‐phase benzene concentrations and the biomass concentrations selected for this study. Finally, the dissolved‐oxygen concentration was observed to be the rate‐limiting factor for biodegradation.
An Improved Method for Estimation of Biodegradation Rate with Field Data
Authors: Zhang You‐Kuan , Heathcote Richard C. 
Published: February 2007

AbstractThe method of Buscheck and Alcantar (1995) is shown to be valid for the concentration data observed in wells along the centerline and near a source of relatively large area as compared with the lateral dispersion of the plume. When such a condition is not satisfied, the method of Buscheck and Alcantar (1995) overestimates the biodegradation rate due to its usage of a solution to a one‐dimensional advection‐dispersion equation that does not consider lateral dispersion and finite source size. It is also shown that the concentration of a two‐ or three‐dimensional plume does not always decrease exponentially with the distance from the source along a plume centerline. An improved method based on multidimensional solutions of Domenico (1987) is proposed. In using the improved method, observed concentrations are normalized by the error functions embedded in the solutions to two‐ or three‐dimensional advection‐dispersion equations for a continuous source of finite size. With the normalized concentrations and following the procedure of Buscheck and Alcantar (1995), one may estimate the biodegradation rate, which is usually smaller than that obtained with the original data. It is demonstrated with the field data presented by Buscheck and Alcantar (1995) at the Fairfax Terminal that the method of Buscheck and Alcantar (1995) indeed overestimates the biodegradation rate by 21% and 65% for a two‐dimensional plume and for a three‐dimensional plume, respectively.
Field Evaluation of the Effectiveness of Surfactant Modified Zeolite and Iron‐Oxide‐Coated Sand for Removing Viruses and Bacteria from Ground Water
Authors: Schulze‐Makuch Dirk , Bowman Robert S. , Pillai Suresh D. , Guan Huade 
Published: February 2007

AbstractField experiments were conducted to evaluate the efficiency of iron‐oxide‐coated sand (ICS) and surfactant modified zeolite (SMZ) to remove viruses and bacteria from ground water. The reactive media were employed as filter packs of a pumping well that withdrew sewage effluent from a constructed wetland at a rate of 0.72 L/min. The contact time of the pumped water with the filter pack (10 cm thick) was about two minutes. Upgradient of the pumping well, the sewage effluent was spiked with MS‐2 bacteriophage and E. coli. While the employed ICS filter pack failed to remove viruses and bacteria to a significant degree, the SMZ filter pack removed more than 99% of the viruses and 100% of E. coli from the ground water while fresh. In an additional field experiment using the same configuration but leaving the filter pack in place for more than five months, the SMZ filter pack was still removing 100% of E. coli, but failed to reduce virus numbers to a significant degree.
A Modified Radial Diagram Approach for Evaluating Natural Attenuation Trends for Chlorinated Solvents and Inorganic Redox Indicators
Authors: Carey Grant R. , Van Geel Paul J. , Wiedemeier Todd H. , McBean Edward A. 
Published: February 2007

AbstractSelection of monitored natural attenuation as a ground water remedy requires that sound scientific documentation clearly illustrating the effectiveness of this remedial alternative be presented to regulatory agencies and concerned citizens. An innovative radial diagram approach is applied to illustrate natural attenuation trends for total benzene, toluene, ethylbenzene, and xylenes (BTEX) and chlorinated ethenes at a former fire training area at Pittsburgh Air Force Base, New York. A BTEX‐CAH (chlorinated aliphatic hydrocarbons) radial diagram map shows that concentrations of site contaminants are generally decreasing along the primary flowpath downgradient from the source area. This radial diagram map also suggests that there is a spatial correlation between decreasing CAH parent compound concentrations and increasing or stable daughter product concentrations. This provides secondary evidence of intrinsic biodegradation of TCE downgradient from the source area. A SEQUENCE‐Redox™ map suggests that there is a spatial correlation between trends in electron acceptor and metabolic byproduct concentrations, and the decline in total BTEX concentrations downgradient from the source area. This correlation provides secondary evidence for the intrinsic biodegradation of total BTEX in the aquifer. This study demonstrates that radial diagram visual aids can provide a clear and efficient approach for documenting natural attenuation lines of evidence, as an alternative or a complement to using multiple contour maps, tabulated data, or log‐linear plots.
Monitoring Partitioning Tracer Testing and Surfactant Flooding by In‐Line Gas Chromatography Techniques
Authors: Suva Jeff A. K. , Mariner Paul E. , Meinardus Hans W. , Ginn Jon S. 
Published: February 2007

AbstractAn automated in‐line analytical system has been developed to provide near real‐time results for partitioning interwell tracer testing (PITT) and surfactant enhanced aquifer remediation (SEAR). The analytical methodology is based on gas chromatography (GC) with flame ionization detection and direct aqueous injection. The system was constructed from both commercially available and custom‐manufactured components that are linked electronically to facilitate autonomous operation. For the field trials presented herein, the in‐line GC method provided superior or comparable PITT and SEAR data compared to conventional sample collection followed by shipment and analysis at a commercial analytical laboratory. Analytical precolumns were shown to effectively safeguard the integrity of the analytical column, despite the consecutive analysis of more than 1000 samples per PITT or SEAR. Additionally, the use of the in‐line GC resulted in an 85% and 74% reduction in analytical costs per PITT and SEAR, respectively.
Analytical Solutions for Free‐Hydrocarbon Recovery Using Skimmer and Dual‐Pump wells
Authors: Johns Russell T. , Lake Larry W. , Obigbesan Abimbola B. , Bermudez Leonardo , Hassan M.R. , Charbeneau Randall J. 
Published: February 2007

AbstractAccidental release of petroleum hydrocarbons to the subsurface may occur through spills around refineries, leaking pipelines, storage tanks, or other sources. If the spill is large, the hydrocarbon liquids may eventually reach a water table and spread laterally in a pancake‐like lens. Hydrocarbons that exist as a separate phase are termed light nonaqueous phase liquids (LNAPLs). The portion of the LNAPL that is mobile, not entrapped as residual saturation, is termed “free product.”This paper presents new analytical solutions for the design of long‐term free‐product recovery from aquifers with skimmer, single‐ and dual‐pump wells. The solutions are for steady‐state flow, based on the assumption of vertical equilibrium, and include the effect of coning of LNAPL, air, and water on flow. The solutions are valid for soils of large hydraulic conductivity where the effect of capillary pressure on coning is small.The results show how to estimate the maximum rate of inflow of LNAPL for skimmer wells, i.e., wells in which LNAPL is recovered with little or no water production. The paper also shows how to calculate the increase in LNAPL recovery when water is pumped by single‐ or dual‐pump wells. A simple equation is given that can be used to adjust the water rate to avoid smearing of the LNAPL below the water table.