bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preserving Ground Water Samples With Hydrochloric Acid Does Not Result in the Formation of Chloroform
Authors: Squillace Paul J. , Pankow James F. , Barbash Jack E. , Price Curtis V. , Zogorski John S. 
Published: February 2007

AbstractWater samples collected for the determination of volatile organic compounds (VOCs) are often preserved with hydrochloric acid (HCl) to inhibit the biotransformation of the analytes of interest until the chemical analyses can he performed. However, it is theoretically possible that residual free chlorine in the HCl can react with dissolved organic carbon (DOC) to form chloroform via the haloform reaction. Analyses of 1501 ground water samples preserved with HCl from the U.S. Geological Survey's National Water‐Quality Assessment Program indicate that chloroform was the most commonly detected VOC among 60 VOCs monitored. The DOC concentrations were not significantly larger in samples with detectable chloroform than in those with no delectable chloroform, nor was there any correlation between the concentrations of chloroform and DOC. Furthermore, chloroform was detected more frequently in shallow ground water in urban areas (28.5% of the wells sampled) than in agricultural areas (1.6% of the wells sampled), which indicates that its detection was more related to urban land‐use activities than to sample acidification. These data provide strong evidence that acidification with HCl does not lead to the production of significant amounts of chloroform in ground water samples. To verify these results, an acidification study was designed to measure the concentrations of all trihalomethanes (THMs) that can form as a result of HCl preservation in ground water samples and to determine if ascorbic acid (C6H8O6) could inhibit this reaction if it did occur. This study showed that no THMs were formed as a result of HCl acidification, and that ascorbic acid had no discernible effect on the concentrations of THMs measured.
Evaluation of Mass Flux to and from Ground Water Using a Vertical Flux Model (VFLUX): Application to the Soil Vacuum Extraction Closure Problem
Authors: DiGiulio Dominic C. , Ravi Varadhan , Brusseau Mark L. 
Published: February 2007

AbstractSite closure for soil vacuum extraction (SVE) application typically requires attainment or specified soil concentration standards based on the premise that mass flux from the vadose zone to ground water not result in levels exceeding maximum contaminant levels (MCLs). Unfortunately, realization of MCLs in ground water may not be attainable at many sites. This results in soil remediation efforts that may be in excess of what is necessary for future protection of ground water and soil remediation goals which often cannot be achieved within a reasonable time period. Soil venting practitioners have attempted to circumvent these problems by basing closure on some predefined percent total mass removal, or an approach to a vapor concentration asymptote. These approaches, however, are subjective and influenced by venting design. We propose an alternative strategy based on evaluation of five components: (1) site characterization, (2) design. (3) performance monitoring, (4) rule‐limited vapor transport, and (5) mass flux to and from ground water. Demonstration of closure is dependent on satisfactory assessment of all five components. The focus of this paper is to support mass flux evaluation. We present a plan based on monitoring of three subsurface zones and develop an analytical one‐dimensional vertical flux model we term VFLUX. VFLUX is a significant improvement over the well‐known numerical one‐dimensional model. VLEACH, which is often used for estimation of mass flux to ground water, because it allows for the presence of nonaqueous phase liquids (NAPLs) in soil, degradation, and a lime‐dependent boundary condition at the water table inter‐face. The time‐dependent boundary condition is the center‐piece of our mass flux approach because it dynamically links performance of ground water remediation lo SVE closure. Progress or lack of progress in ground water remediation results in either increasingly or decreasingly stringent closure requirements, respectively.
Fundamental Changes in In Situ Air Sparging How Patterns
Authors: Brooks Michael C. , Wise William R. , Annable Michael D. 
Published: February 2007

AbstractTwo types of gas‐phase flow patterns have been discussed and observed in the in situ air sparging (ISAS) literature: bubble flow and air channels. A critical factor affecting the flow pattern at a given location is the grain size of the porous medium. Visualization experiments reported in the literature indicate that a change in the flow pattern occurs around 1 to 2 mm grain diameters, with air channels occurring below the transition size and bubbles above. Analysis of capillary and buoyancy forces suggests that for a given gas‐liquid‐solid system, there is a critical size that dictates the dominant force, and the dominant force will in turn dictate the flow pattern. The dominant forces, and consequently the two‐phase flow patterns, were characterized using a Bond number modified with the porous media aspect ratio (pore throat to pore body ratio). Laboratory experiments were conducted to observe flow patterns as a function of porous media size and air flow rate. The experimental results and the modified Bond number analysis support the relationship of flow patterns to grain size reported in the literature.
Field Demonstrations Using the Waterloo Ground Water Profiler
Authors: Pitkin Seth E. , Cherry John A. , Ingleton Robert A. , Broholm Mette 
Published: February 2007

AbstractUse of direct‐push sampling tools fur rapid investigations of contaminated sites has proliferated in the past several years. A direct‐push device, referred to as a ground water sampling profiler, was recently developed at the University of Waterloo. This tool differs from oilier direct‐push tools in that point samples are collected at multiple depths in the same hole without retrieving, decontaminating, and re‐driving the tool alter each sampling event. The collection of point samples, rather than samples from a longer screened interval, allows an exceptional level of detail to be generated about the vertical distribution of contamination from each hole. The benefits of acquiring this level of detail arc contingent on minimization of vertical cross contamination of samples caused by drag down from high concentration zones into underlying low concentration zones. In a detailed study of chlorinated solvent plumes in sandy aquifers, we found that drag down using the profiler is minimal or non‐detectable even when the tool is driven through high concentration zones of dissolved chlorinated solvent contamination. Chlorinated solvent concentrations, primarily PCE and TCE at or below a detection limit of 1 μg/L, were obtained directly beneath plumes with maximum concentrations up to thousands of μg/L. Minimal drag down, on the order of a few μg/L to 20 μg/L, may have been observed below chlorinated solvent concentrations of several tens of thousands to hundreds of thousands of μg/L. Drag down through DNAPL zones was not evaluated.
Predicting Soil‐Water and Soil‐Air Transport Properties and Their Effects on Soil‐Vapor Extraction Efficiency
Authors: Poulsen Tjalfe G. , Moldrup Per , Yamaguchi Toshiko , Schjønning Per , Hansen Jens Aage 
Published: February 2007

AbstractAccurate prediction of water and air Iran sport parameters in variably saturated soil is necessary for modeling of soil‐vapor extraction (SVE) at soil sites contaminated with volatile organic chemicals (VOCs). An expression for predicting saturated water permeability (kl,s) in undisturbed soils from the soil total porosity and the field capacity soil‐water content was developed by fitting a tortuous‐tube fluid flow model to measured water permeability and gas diffusivity data. The new kl,s expression gave accurate predictions when tested against independent kl,s data. The kl,s expression was implemented in the Campbell relative water permeability model to yield a predictive model for water permeability in variably saturated, undisturbed soil. The water permeability model, together with recently developed predictive equations for gas permeability and gas diffusivity, was used in a two‐dimensional numerical SVE model that also included non‐equilibrium mass transfer of VOC from a separate phase (nonaqueous phase liquid [NAPL]) to the air phase. SVE: calculations showed that gas permeability is likely the most important factor controlling VOC migration and vapor extraction efficiency. Water permeability and gas diffusivity effects became significant at water contents near and above field capacity. The NAPL‐air mass transfer coefficient also had large impacts on simulated vapor extraction efficiency. The calculations suggest that realistic SVE models need to include predictive expressions for both conveciive, diffusive. and phase‐partitioning processes in natural, undisturbed soils.
Air Channel Formation, Size, Spacing, and Tortuosity During Air Sparging
Authors: Elder Carl R. , Benson Craig H. 
Published: February 2007

AbstractCharacterizing mass transfer during in situ air sparging requires knowledge of the size, shape, and interfacial area of air channels. These characteristics were determined by analysis of digital images of air channels passing through submerged glass beads having particle size in the sand range. Pore‐scale channeling occurred in all cases. The analysis showed that the air channels were narrower, more tortuous, more closely spaced, and moved nearly vertically through the coarser media. In the finer media, air channels had larger diameter, were spaced further apart, and passed nearly horizontally through the media. The mean diameter of the channels varied between 2.8 and 8.1 mm, and the mean spacing varied between 8.3 and 19.4 mm. Estimates of the area of the air‐water interface per unit volume of soil (a0), computed using data from the digital images and an assumed arrangement of channels, ranged from 0.02 to 0.2 mm2/mm3. Larger a0 were obtained for coarser media and uniformly graded media. These estimates of a0 compare well with published values for common packed‐column materials and for unsaturated soils.
Natural Attenuation: A Feasible Approach to Remediation of Ground Water Pollution at Landfills?
Authors: Christensen Thomas H. , Bjerg Paul L. , Kjeldsen Peter 
Published: February 2007

AbstractRemediation of ground water pollution at old landfills with no engineered leachate collection system is a demanding and costly operation. It requires control of the landfill body, since the majority of the pollutants are still present in the landfilled waste for decades after the site has been closed. However removing the source is an attractive approach to managing leachate plumes. Natural attenuation has been implemented for petroleum hydrocarbon plumes and chorinated solvent plumes, primarily in the United States. Natural attenuation has not yet gained a foothold with respect to leachate plumes, however. Based on the experience gained from 10 years of research on two Danish landfills, it is suggested that natural attenuation is a feasible approach but is more complicated and demanding than in the case of petroleum hydrocarbons and chlorinated solvent.
Location and Characterization of Subsurface Anomalies Using a Soil Conductivity Probe
Authors: Beck Frank P. , Clark Patrick J. , Puls Robert W. 
Published: February 2007

AbstractAn electrical conductivity probe, designed for use with “direct push” technology, has been successfully used to locate buried drums, contaminant plumes, and to precisely locate and characterize a previously installed permeable reactive iron wall. The conductivity probe was designed to characterize various soil and sediment types as it was driven through the dry and saturated soil matrix; however, its ability to locate and characterize subsurface anomalies may also prove to be a valuable asset. The probe uses an electrical field that works like and mimics the results from an oilfield engineering tool called the Wenner array. This electrical field array penetrates into the soil matrix to measure the electrical conductivity of the soil matrix surrounding the probe to a radius of about two to four inches. This tool has allowed operating personnel to verify the location of manmade or natural subsurface anomalies with precision.
Comparison of Hydraulic Conductivity Values Obtained from Aquifer Pumping Tests and Conservative Tracer Tests
Authors: Niemann William L. , Rovey Charles W. 
Published: February 2007

AbstractAfield site was established in an area of glacial outwash near Des Moines, Iowa. Hydraulic conductivity (K) of the outwash was measured in various ways including six pumping tests and two natural‐gradient Cl‐ tracer tests. The velocity of the conservative tracer was converted to K using measured gradients and effective porosity determined from two radial‐convergent Cl‐ tracer tests.K values measured from the conservative tracer tests are approximately one‐tenth to one‐twentieth the average pumping‐test value. Thus the K relevant to solute transport does not reflect the K measured by pumping tests. This discrepancy may be caused by the different scale and dimensionality of the two test types. Dispersion may prevent solutes from flowing exclusively within smaller high‐conductivity paths which strongly affect the K measured by pumping tests.
Decision Analysis for Pump‐and‐Treat Design
Authors: Russell Kevin T. , Rabideau Alan. J. 
Published: February 2007

AbstractThe use of decision analysis (DA) has been proposed as a technique for selecting from among alternative designs for subsurface remediation. To assess the ability of DA to generate consistent decisions for the widely practiced pump‐and‐treat (PAT) strategy, 27 candidate PAT designs were compared for a case study site. The sensitivity of the alternative selection to various modeling assumptions was examined, including the complexity of the site‐specific numerical models, the assumed degree of aquifer heterogeneity, the manner of defining failure, and the assumed cost of failure. The initial net‐present‐worth analysis resulted in the selection of one of two designs that included injection wells for effluent disposal and hydraulic control. However, when the injection wells were excluded from consideration, the selection from a diverse set of alternative PAT designs was highly sensitive to the particular modeling assumptions. In general, the practical usefulness of the DA approach is dependent on the ability to characterize the nature and probability of system failure.
Field Tests of a DNAPL Characterization System Using Cone Penetrometer‐Based Raman Spectroscopy
Authors: Rossabi J. , Riha B.D. , III J.W. Hass , Eddy‐Dilek C.A. , Lustin A.G. , Carrabba M. , Hyde W.K. , Bello J. 
Published: February 2007

AbstractCone penctrometer test (CPT) based Raman spectroscopy was used to identify separate phase tetrachloroethylene (PCE) and trichlorocthylene (TCE) contamination in the subsurface at two locations during field tests conducted at the U.S. Department of Energy's (DOE) Savannah River site. Clear characteristic Raman spectral peaks for PCE and TCE were observed at two sites and several depths during CPT deployment. Because of the uniqueness of a Raman spectrum for a given compound, these data are compelling evidence of the presence of the two compounds. The Raman spectral results correlated with high PCE and TCE concentrations in soil samples collected from the same subsurface zones, confirming that the method is a viable dense nonaqueous phase liquid (DNAPL) characterization technique. The Raman spectroscopic identification of PCE and TCE in these tests represents the first time that DNAPLs have been unequivocally located in the subsurface by an in situ technique.The detection limit of the Raman spectroscopy is related to the probability of contaminant droplets appearing on the optical window in the path of the probe light. Based on data from this fieldwork the Raman technique may require a threshold quantity of DNAPL to provide an adequate optical cross section for spectroscopic response. The low aqueous solubility of PCE and TCE and relatively weak optical intensity of the Raman signal precludes the detection of aqueous phase contaminants by this method, making it selective for DNAPL contaminants only.
Occurrence of MTBE in Heating Oil and Diesel Fuel in Connecticut
Authors: Robbins Gary A. , Henebry Brent J. , Cummins Timothy M. , Goad Christopher R. , Gilbert Edward J. 
Published: February 2007

AbstractThe objective of this study was to confirm if MTBE, which is not intentionally added to fuels other than gasoline, is a contaminant in heating oil and diesel fuel. The study entailed conducting a statewide sampling program of heating oil and diesel fuel in Connecticut. An analytical method was developed to conduct analyses of heating oil and diesel fuel for MTBE in the milligram per liter (mg/L) range. The method involved equilibrating product with water to extract MTBE followed by static head‐space analysis on aliquots of the water. Analyses were conducted using a gas chromatograph with a MTBE specific column. The statewide sampling program confirmed the widespread occurrence of MTBE in heating oil and diesel fuel. MTBE was detected in all samples collected during our sampling program at concentrations ranging from 9.7 to 906 mg/L in heating oil (26 samples), and from 74 to 120 mg/L in diesel fuel (five samples). Based on these ranges. MTBE concentrations in ground water in the vicinity of heating oil and diesel fuel releases could exceed thousands of micrograms per liter. Our analysis would suggest that the levels of heating oil and diesel fuel contamination observed could result from the commingling of only a few parts gasoline with thousands of parts of these fuels. The extent to which MTBE occurs in heating oil and diesel fuel nationwide is not known, but our data suggests that it may be widespread.
Laboratory and Numerical Investigations of Air Sparging Using MTBE as a Tracer
Authors: Mortensen Annette Pia , Jensen Karsten Høgh , Sonnenborg Torben Obel , Arvin Erik 
Published: February 2007

AbstractAir sparging experiments were conducted in a laboratory column to investigate air flow and mass transfer behavior in different types of sand at different air injection rates. Methyl tertiary butyl ether (MTBE) was applied as a tracer, and by measuring the volatilization and the mean air content during the experiments, the air flow pattern and its influence on mass transfer were assessed. The experimental results showed large differences among the sand types. In fine sand, the mean air content was high and the volatilization of MTBE was rapid with total recovery after a few hours. In coarse sand, the mean air content was low and the volatilization of MTBE was limited. The results indicate two different air flow distributions. In fine‐grained materials, a uniform air distribution can be expected compared to coarse‐grained materials where isolated air channels will limit the mass transfer. Afterwards, the experiments were simulated using the numerical multiphase flow code T2VOC, and the results compared to those obtained in the laboratory. The experiments with fine sand were simulated well, while for coarser sand types the volatilization was highly overestimated. The differences between model and laboratory results were mainly attributed to the nonuniformity of the air saturation and the neglection of kinetics in the mass transfer formulation.
Efficient Quantification of Total Petroleum Hydrocarbons and Applications at Two Contaminated Sites
Authors: Xie Guibo , Barcelona Michael J. 
Published: February 2007

AbstractCharacterization and remediation of petroleum contamination are complicated issues due to variable product compositions and site conditions. Generic group analytical methods such as total petroleum hydrocarbon (TPH) methods have played important field screening and regulatory functions for site characterization and cleanup. This study evaluated the application of three TPH methods (a GC/MS method, a spectrometric method EPA 418.1, and a rapid field method PetroFLAG). The results showed that quantification of TPH could be attained efficiently by a combination of rapid field methods (i.e., PetroFLAG) and more sophisticated fraction‐specific and target‐compound methods. TPH distributions suggested different source release information for two sites with different contaminant mixtures and climate conditions. TPH was also found to correlate with reductive redox capacity (RDC), an important parameter for the design of oxidative remediation schemes. The results indicated that good site specific correlations could be established to better estimate costs of the injection of chemical oxidants if necessary. RDC values varied broadly for both background (83 ˜ 569 meq/kg) and contaminated source (523 ˜ 6044 meq/kg) samples collected from actual sites.
Monitored Natural Attenuation of Contaminants in the Subsurface: Processes
Authors: Azadpour‐Keeley Ann , Keeley Jack W. , Russell Hugh H. , Sewell Guy W. 
Published: February 2007

AbstractAmong the alternatives considered for the remediation of soil and ground water at hazardous wastes sites are the use of natural processes to reduce or remove the contaminants of concern, Under favorable conditions, the use of natural attenuation can result in significant cost savings and compensate for uncertainties encountered in complex subsurface settings. In order to demonstrate that natural processes are effective in reaching established goals it is necessary to determine that transformation processes are taking place at a rate which is protective of human health and the environment, and that these processes will continue for an acceptable period of time.While chemical transformation, dispersion, dilution, sorption, and volatilization are discussed, aerobic and anaerobic degradation comprise the major processes for the reduction of contaminant mass in the subsurface. In discussing the mechanisms of natural attenuation, chlorinated aliphatics and petroleum hydrocarbons are used as examples because of their significant impact on subsurface contamination and the effect of their physiochemical properties on attenuation processes.
Effective Air Delivery from a Horizontal Sparging Well
Authors: Lundegard Paul D. , Chaffee Brent , LaBrecque Doug 
Published: February 2007

AbstractHorizontal air sparging (HASP) wells offer several potential advantages compared to linear arrays of vertical air sparging wells. For some of these advantages to be realized, however, HASP wells must be able to deliver air uniformly along the length of the well. HASP wells can fail to deliver air uniformly for either engineering or geological reasons.A 58 m (190‐foot) long HASP well, with a 15 m (50‐foot) long screen interval, was designed, installed, and tested in eolian dune sand. The relative uniformity of the geologic medium allowed specific evaluation of the impact of the well design on air delivery. A variety of monitoring approaches were used during a six‐day pilot test. Pressure drop within the sparge well was found to be negligible through the screen interval of the well. Soil gas pressure and ground water mounding responses were very similar at both ends of the well screen, suggesting relatively uniform air delivery throughout. Electrical resistance tomography results confirmed that airflow in the formation was similar at both ends of the screen interval and that the principal region of airflow was within 1.5 m (5 feet) of the axis of the well. Increased dissolved oxygen was primarily limited to a region within 2.3 m (7.5 feet) of the well and occurred throughout the length of the screen interval. These monitoring results show that HASP wells, properly constructed and installed, can supply air in a generally uniform manner along their length.