bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased Thermal‐Pulse Flowmeter Resolution by Adding a Packer and Computer
Authors: Lyles Brad F.
Published: February 2007

Measurement accuracy was increased by nearly one order of magnitude by outfitting the thermal‐pulse flowmeter (TFM) with an inflatable packer. To accurately measure slow water velocities in boreholes greater than 15 cm diameter, it is necessary to divert borehole fluids through the TFM by inflating a packer. During calibration it was noted that the TFM's accuracy decreased as the borehole diameter increased. With Lhe packer inflated the TFM has a useful flow measurement range of 0.08 to 15 L/min (with flow velocities of 0.24 ± 0.012 cm/inin to 45.7 ± 0.61 cm/min, respectively, in 20‐cm‐diameter pipe), compared to 0.8 to 57 L/min for a packcrless TFM. A computer interlace was added to the TFM to provide a real‐time graphical display of the differential voltage output from the TFM, a running mean and standard deviation of the pulse‐response time, and a mean flow rate and velocity based on calibration curve fits.
Analytical Solutions for Determination of Non‐Steady‐ State and Steady‐State Capture Zones
Authors: Yang Y. Jeffrey , Spencer Richard D. , Gates Todd M.
Published: February 2007

This paper presents analytical solutions for determining non‐steady‐state capture zones produced by a single recovery well and steady‐state capture zones produced by multiple recovery wells. Analysis of non‐steady‐slate capture zones is based on the lime‐dependent location of caplure zone stagnation points and the geometric similarity between steady‐slate and non‐steady‐state capture zones. The analytical solution of steady‐state capture zones is obtained from spatial variations of discharge potential across the capture zone boundary. Both capture zone analyses are based on the assumptions of uniform flow field with a constant hydraulic conductivity, the Dupuit assumption of insignificant vertical flow, a negligible delayed yield, and a fully penetrating well with a constant pumping rate. For a ground water pump‐and‐trcat remediation program, the pumping rate and well location design variables can be adjusted to ensure containment of the ground water contaminant plume.
Overexploitation and Deterioration of Aquifers in Venezuela
Authors: Jegat H. , Alvarado J. , Loaiciga H.A.
Published: February 2007

Approximately 50 percent of the potable, industrial, and agricultural water supply in Venezuela comes from ground water, mined through some 40,000 wells scattered around the country. The majority of the productive aquifers consist of quaternary deposits in mountain valleys and coastal lowlands, all of which are situated in areas with limited or low precipitation. Intensive exploitation of several of these aquifers for the last 30 years has resulted in overdraft conditions and ground water contamination, causing serious socio‐economic consequences in various regions of Venezuela. This paper reviews the quality and quantity aspects of overdrafted aquifers in Venezuela, which can he classified into three major categories: (1) aquifers in the coastal lowlands in the stales of Falcon and Zulia of northern Venezuela: (2) the intermontane Carora and Quibor Valley Aquifers: and (3) aquifers in the Lake Valencia Watershed. If current trends of aquifer overexploitation continue, further water deficits and irreversible environmental damage are predicted.
Vadose Zone Monitoring: Experiences and Trends in the United States
Authors: Cullen Stephen J.
Published: February 2007

The vadose zone is the portion of the geologic profile above a perennial aquifer. Inclusion of mandatory vadose zone monitoring techniques as an approach to aquifer protect ion was first proposed under the Resource Conservation and Recovery Act in the United States in 1978 and has since received increasing acceptance at federal and stale levels. The goals of a vadose zone characterization and monitoring effort are to establish background conditions, identify contaminant transport pathways, identify the extent and degree of existing contamination, establish the basis for monitoring network design, measure the parameters needed in a risk assessment, and provide detection of contaminant migration toward ground water resources. The benefits of vadose zone monitoring include early warning of contaminant migration, potential reduction of ground water monitoring efforts, reduction of contaminant spreading and volume, and reduced time and cost of remediation once a contaminant release occurs. Vadose zone characterization and monitoring techniques should be considered as critical hydrologic tools in the prevention of ground water resource degradation.
Radium in Coastal Sarasota County Ground Water
Authors: Walters Michael O.
Published: February 2007

Sarasota County is one of 10 generalized areas of the continental United States known to haw high concentrations of naturally occurring radium in fresh ground water (Chandler 1989). Various authors have conducted investigations to examine the distribution of radium in ground water, rivers, and estuaries. They concluded that ground water was the source of radium, but rivers were also enriched with radium as a result of the interaction with ground water. The Glulf of Mexico also has areas with radium enrichment resulting from geothermal springs with concentrations as high as 51 picocuries per liter. During 1986 and 1987. the Health and Rehabilitative Services of the state of Florida collected ground water data for radium analysis of private drinking water wells. These data were used to develop a contour map of radium‐226 concentrations for coastal Sarasota County.
Design of a Multi‐Level Monitoring Well for Continuous Sample Collection
Authors: Ayers Jerry F. , Gosselin David C.
Published: February 2007

As part of a study of the flow dynamics and sampling environment around a high‐capacity irrigation well, it was necessary to design and install a multi‐level monitoring well network close to the production well. A requirement of the monitoring well network was the capability of continuous pumping over periods typical of those used during water sample collection. This was accomplished through the use of a control valve and air manifold system connected 10 a common gasoline engine‐operated air compressor. The system provided adequate air pressure to operate 24 half‐size bladder pumps to depths between 21 feet (6.4 m) and 56 feet (17.1 m) below the surface. Preliminary data collected from the monitoring well network indicate that the system will meet the requirements of the high‐capacity well study.
DNAPL Flow Behavior in a Contaminated Aquifer: Evaluation of Field Data
Authors: Oolman T. , Godard S. T. , Pope G.A. , Jin M. , Kirchner K.
Published: February 2007

A pool of dense nonaqueous phase liquid (DNAPI.) containing TCE and other chlorinated solvents has been removed from the subsurface at Hill Air Force Base, Uthah. as part of an interim remedial action. The removal of the DNAPI. pool means that future off‐site migration of dissolved contaminants in the ground water is minimized, and costs for final remedial actions are reduced. A pump‐and‐treat system recovered more than 23.000) gallons of DNAPI. and one million gallons of contaminated ground water from the aquifer. The efficiency of this remedial action was evaluated on the basis of extensive field and laboratory data. The behavior of DNAPI. flow in the aquifer sands was characterized by collecting core samples from two borings in the DNAPL pool and measuring relative permeabilities and DMAPI. saturation. Core Hooding results show that approximately one‐third of the DNAPI. originally in the pool is not recovered by water displacement, but remains as a residual saturation held in place by capillary pressure. However, subsequent Hooding with two pore volumes of surfactant solution reduced the residual DNAPI. saturation in the sand by one order of magnitude. Analytical and numerical models for the DNAPI flow behavior at the site were developed. This is the first time that such models have been developed and applied to an actual DNAPI. pumping lest conducted in the field. Because measured permeabilities and residual saturations were used lo calibrate the models. the model predictions could be used lo provide valuable insights into the controlling mechanisms for DNAPL recovery. The data collection and modeling procedures outlined in this paper can be used lo enhance the efficiency and minimize the cost 10 clean up this and other DNAPI.‐contaminated sites.
Estimation of Leakage Rates Through Flexible Membrane Liners
Authors: Murray Gordon B. , McBean Edward A. , Sykes Jonathan F.
Published: February 2007

Leakage rate calculations for both low‐ permeability soil liners and composite liners using flexible membrane liners (FMLs) overlying low‐permeability soil are developed. Latin‐Hypercube simulations with uncertainly assigned to the soil liner hydraulic conductivity value and the spatial frequency of FML holes are used to examine the variability in the liner leakage rates. The low‐permeability soil hydraulic conductivity is the parameter with the greatest effect on landfill liner leakages rates. Composite liners have a significant impact on reducing leakage rates through the landfill liner.
Comparability of Large‐Scale Studies of Agricultural Chemical Contamination of Rural Private Wells
Authors: Ray Chittaranjan , Schock Susan C.
Published: February 2007

Detection of agricultural chemicals in ground water has prompted numerous studies. Federal, state, and regional studies were conducted in the last 10 years in order to assess the occurrence of agricultural chemicals in ground water. The results of the studies present the number or percentage of samples with agricultural chemicals above the drinking water standard or health advisory levels as well as samples with detections of one or more compounds. Data comparison from one state or region to another are frequently referred to by regulatory and agency personnel involved in water quality and agriculture issues. Unless the history of pesticide use, method of chemical analyses, detection limits, statistical design of the sampling plan, well type, well depth, geology of the formation material, and typical land use around the wellhead are known, such comparisons can be misleading. Reporting the limitations or presenting a disclaimer should be a key element for a study so that “apples and oranges” are not compared.
The Use of Invertebrates in Ground Water Monitoring: A Rising Research Field
Authors: Malard Florian , Plenet Sandrine , Gibert Janine
Published: February 2007

The use of invertebrates as biomonitors of ground water quality is a relatively new approach that has come of age with the development of ground water ecology. The benefits of such an approach are illustrated by four examples of field biomonitoring from several sites in various hydrogeological settings. Contamination of the interstitial zone by heavy metals in some sectors of the Rhóne River (France) was shown by the scarcity of insect species; sewage pollution in the saturated zone of a karstic aquifer was indicated by the low relative abundances of stygobites as compared with those of stygophiles and stygoxenes; and enrichment with organic matter of an underflow was clearly demonstrated by the extremely high density of ground water invertebrates such as oligochaetes, ostracods, and isopods. Examination of the spatial changes in the composition and abundance of invertebrate assemblages was also useful in determining the direction and intensity of water fluxes between a river and its underflow, as well as in delineating the reduced or oxidized zones in a manganese‐polluted aquifer. Finally, the selected case studies emphasized the variety of methodological approaches that could be developed in ground water contamination biomonitoring, as well as the complementary and sometimes new information provided by this innovative method in comparison with that obtained by conventional pollution monitoring techniques.
Multimedia Risk‐Based Soil Cleanup at a Gasoline‐Contaminated Site Using Vapor Extraction
Authors: Mills William B. , Johnson Kay M. , Liu Sally , Loh John Y. , Lew Christine S.
Published: February 2007

At a utility service center, gasoline from an underground storage tank had leaked into subsurface vadose zone soils for several years. To remediate the site, a soil vapor extraction (SVE) system was installed and operated. At the completion of the SVE operation, gasoline‐containing residues in several confirmation soil borings exceeded agency‐mandated cleanup levels. Rather than continue with SVE, a risk‐based approach was developed to evaluate what levels of gasoline‐containing residues could be left in the soil and still protect human health. The risk‐based approach consisted of simulating the fate of chemical residues through the vadose zone and then into both the ground water and atmosphere. Receptor point concentrations were predicted, and health risks were assessed. The risk assessment concluded that ingestion of contaminated ground water and inhalation of air while showering were the largest potential contributors to risk, and that risks associated with inhalation of vapor‐containing ambient air are small. However, all predicted risks are below the acceptable risk levels of 10−6 individual cancer risk probability and 1.0 hazard index. Therefore, the lead agency accepted the recommendation that the site requires no further remediation. The service center continues normal operations today.
Temporal Changes in VOC Discharge to Surface Water from a Fractured Rock Aquifer During Well Installation and Operation, Greenville, South Carolina
Authors: Vroblesky D. A. , Robertson J. F.
Published: February 2007

Analysis of the vapor in passive vapor samplers retrieved from a streambed in fractured rock terrain implied that volatile organic carbon (VOC) discharge from ground water to surface water substantially increased following installation of a contaminant recovery well using air rotary drilling. The air rotary technique forced air into the aquifer near the stream. The injection produced an upward hydraulic gradient that appears to have transported water and contaminants from deeper parts of the aquifer through fractures into shallow parts of the aquifer. Once in the shallow flow regime, the contamination was transported to the stream, where it discharged during the next several weeks following well installation. After the recovery well was activated and began continuously pumping contaminated ground water to a treatment facility, the VOC concentrations in the stream bottom passive vapor samplers decreased to below detectable concentrations, suggesting that the withdrawal had captured the contaminated ground water that previously had discharged to the stream.
Evaluation of Subsurface Oxygen Sensors for Remediation Monitoring
Authors: Li Dong X. , Lundegard Paul D.
Published: February 2007

Continuous remediation monitoring using sensors is potentially a more effective and inexpensive alternative to current methods of sample collection and analysis. Gaseous components of a system are the most mobile and easiest to monitor. Continuous monitoring of soil gases such as oxygen, carbon dioxide, and contaminant vapors can provide important quantitative information regarding the progress of bioremediation efforts and the area of influence of air sparging or soil venting. Laboratory and field tests of a commercially available oxygen sensor show that the subsurface oxygen sensor provides rapid and accurate data on vapor phase oxygen concentrations. The sensor is well suited for monitoring gas flow and oxygen consumption in the vadose zone during air sparging and bioventing. The sensor performs well in permeable, unsaturated soil environments and recovers completely after being submerged during temporary saturated conditions. Calibrations of the in situ oxygen sensors were found to be stable after one year of continuous subsurface operation. However, application of the sensor in saturated soil conditions is limited. The three major advantages of this sensor for in situ monitoring arc as follows: (1) it allows data acquisition at any specified time interval; (2) it provides potentially more accurate data by minimizing disturbance of subsurface conditions; and (3) it minimizes the cost of field and laboratory procedures involved in sample retrieval and analysis.
Ground Water Contamination from Creosote Sites
Authors: Kiilerich Ole , Arvin Erik
Published: February 2007

Field data from 44 waste sites contaminated with creosote have been compiled in a database. The data from each site included geological and hydrogeological parameters and the concentrations of creosote compounds in the ground water at various distances from the pollution sources. The creosote compounds that were measured included mononuclear aromatic hydrocarbons and polynuclear aromatic hydrocarbons (PAH) and phenols. Already 50 m down‐gradient of the creosote waste sites, 90 percent of the concentrations were from three to 50 times lower than at the source, and most of the median concentrations were below detection limit (0.1 to 0.5 μg/L). The maximum concentrations of benzene, toluene, and xylenes (BTX) and phenols were much lower under aerobic than under anaerobic conditions. Among the phenols, the xylenols (dimethylphenols) appear in higher concentrations under aerobic conditions than phenol and the cresols do. The highest concentrations found were of the same order of magnitude as the calculated solubilities found in the literature, except the chrysene and benz(a)pyrene concentrations, which were one to two orders of magnitude higher than the solubilities.
Arrays of Unpumped Wells for Plume Migration Control by Semi‐Passive In Situ Remediation
Authors: Wilson Ryan D. , Mackay Douglas M. , Cherry John A.
Published: February 2007

Arrays of unpumped wells can be used as discontinuous permeable walls in which each well serves both as a means to focus ground water flow into the well for treatment and as a container either for permeable reactive media which directly destroy dissolved ground water contaminants or for devices or materials which release amendments that support in situ degradation of contaminants within the aquifer downgradient of the wells. This paper addresses the use of wells for amendment delivery, recognizing the potential utility of amendments such as electron acceptors (e.g., oxygen nitrate), electron donors (primary substrates), and microbial nutrients for stimulating bioremediation, and the potential utility of oxidizers, reducers, etc., for controlled abiotic degradation. Depending on its rate and constraints, the remedial reaction may occur within the well and/or downgradient. For complete remediation of ground water passing through the well array, the total flux of amendment released must meet or exceed the total flux demand imposed by the plume. When there are constraints on the released concentration of amendment (relative to the demand), close spacing of the wells may be required. If the flux balance allows wider spacing, it is likely that limited downgradient spreading of the released amendment will then be the primary constraint on interwell spacing. Divergent flow from the wells, roughly two times the well diameter, provides the bulk of downgradient spreading and constrains maximum well spacing in the absence of significant lateral dispersion. Stronger lateral dispersion enhances the spreading of amendment, thereby increasing the lateral impact of each well, which allows for wider well spacing.
Use of Aerobic and Anaerobic Microcosms to Assess BTEX Biodegradation in Aquifers
Authors: Salanitro J.P. , Wisniewski H.L. , Byers D.L. , Neaville C.C. , Schroder R.A.
Published: February 2007

The natural attenuation of soluble aromatic hydrocarbons (BTEX) in aquifer plumes is controlled by several factors, including the concentration of BTEX and dissolved oxygen (DO) or other electron acceptors (EA), hydrogeological factors (dispersion, dilution, aquifer reaeration rate), and the presence of BTEX‐degrading microbes. We have investigated three laboratory soil and/or well water systems (aerobic, anaerobic, and chronic low DO) which may represent field plume conditions. Microcosm prepared with sufficient DO always degraded hydrocarbons ( 10,000 ppb) at high rates ( 0.10/d) with no lag phase. Experimental simulations of chronic low DO were performed in a pressure transducer‐controlled respirometer in which O2 was maintained at constant low levels (e.g., 0.2 to 2 mg/L). BTX also biodegraded rapidly (0.3 to 0.7/d) at all DO levels. These results suggest that plumes which appear to have low DO but continuous O2 infiltration significantly bioattenuate hydrocarbons. The anaerobic biodegradation potential of BTEX was determined in microcosms prepared with subsoil or well water samples amended with NO3‐, Fe‐3, SO4‐2, or no added EA. Well water from the “aerobic” or “anaerobic” portions of one site plume showed losses in BTEX, but there was no correlation between the presence of reduced EA and degradation. Anaerobic slurries prepared from subsoil of another site showed a significant decrease (0.02 to 0.25/d) in BTEX with lag times of 0 to 40 days. Reduced gases (CH4, H2S, H2) were not produced, but high concentrations of soil‐bound Fe+2 formed, suggesting that Fe+3 may have been a predominant anaerobic EA. These data indicate that the presumed consumption/reduction of anaerobic EA may not always be coupled to BTEX losses in ground water plumes.
Horizontal and Vertical Well Comparison for In Situ Air Sparging
Authors: Plummer Charles R. , Nelson James D. , Zumwalt Gary S.
Published: February 2007

A laboratory study was conducted to determine the effectiveness ol vertical and horizontal well configurations for ground water remediation using in situ air sparging. A lexan lank was designed and constructed to allow both the visualization of air flow and quantitative measurement of the distribution of air flow. Two media, sand and glass beads. were tested with both Vertical and horizontal air sources. In each case, most of the air traveled through preferential channels as continuous flow rather than as discrete bubbles as reported in other studies. Liven though glass beads were selected to have the same grain‐size distribution as the sand, air flow was quite different through the two media. Results show that glass beads are not a suitable material for modeling air flow through natural sediments. In this study, the horizontal well proved to be more effective than the vertical well by impacting more of the media with a uniform distribution of air throughout the media. The vertical well resulted in a nonuniform distribution of air flow with most of the air concentrated directly above the well.
Byproduct Formation During the Reduction of TCE by Zero‐Valence Iron and Palladized Iron
Authors: Liang Liyuan , Korte Nic , Goodlaxson J.D. , Clausen Jay , Fernando Quintus , Muftikian Rosy
Published: February 2007

Trichloroethene (TCE) was reduced with zero‐valence iron and palladized iron in zero‐head‐space extractors. Progress of the reaction in these batch studies was monitored with purge‐and‐trap gas chromatography and a flame ionization detector. When a 5 ppm initial concentration of TCF. reacts with zero‐valence iron, approximately 140 ppb of vinyl chloride persists for as long as 73 days. The concentration of vinyl chloride (approximately If) ppb) remaining with palladized iron is approximately an order of magnitude less than when zero‐valence iron is the reductant. These data suggest that volatile byproducts may be under‐represented in oilier published data regarding reduction with zero‐valence metals. These results also demonstrate that the reduction of TCE with palladized iron (0.05 percent palladium) is more than an order of magnitude faster than with zero‐valence iron. Wilh a 5:1 solution‐to‐solid ratio the TCE half‐life with zero‐valence iron is 7.41 hours. but is only 0.59 hours with the palladized iron.
Fate of MTBE Relative to Benzene in a Gasoline‐Contaminated Aquifer (1993–98)
Authors: Landmeyer James E. , Chapelle Francis H. , Bradley Paul M. , Pankow James F. , Church Clinton D. , Tratnyek Paul G.
Published: February 2007

Methyl tert‐butyl ether (MTBE) and benzene have been measured since 1993 in a shallow, sandy aquifer contaminated by a mid‐1980s release of gasoline containing fuel oxygenates. In wells downgradient of the release area, MTBK was detected before benzene, reflecting a chromatographic‐like separation of these compounds in the direction of ground water flow. Higher concentrations of MTBE and benzene were measured in the deeper sampling ports of multilevel sampling wells located near the release area, and also up to 10 feet (3 m) below the water table surface in nested wells located farther from the release area. This distribution of higher concentrations at depth is caused by recharge events that deflect originally horizontal ground water flowlines. In the laboratory, microcosms containing aquifer material incubated with uniformly labeled 14C‐MTBE under aerobic and anaerobic. Fe(III)‐reducing conditions indicated a low but measurable biodegradation potential (<3%14C‐MTBW as 14CO2) after a seven‐month incubation period, Tert‐butyl alcohol (TBA), a proposed microbial‐MTBE transformation intermediate, was detected in MTBE‐contaminated wells, but TBA was also measured in unsaturated release area sediments. This suggests that TBA may have been present in the original fuel spilled and does not necessarily reflect microbial degradation of MTBE. Combined, these data suggest that milligram per liter to microgram per liter decreases in MTBE concentrations relative to benzene are caused by the natural attenuation processes of dilution and dispersion with less‐contaminated ground water in the direction of flow rather than biodegradation at this point source gasoline release site.
A Method for Installing Piezometers in Large Cobble Bed Rivers
Authors: Geist David R. , Joy Mark C. , Lee David R. , Gonser Tom
Published: February 2007

An impact drive point method is described for emplacing piezometers in a cobble river bottom where this has previously been difficult without the use of drilling rigs. To force the drive point piezometers through coble, the vibrational impact of an air‐powered hammer was carried directly to the drive point by the use of an internal drive rod. After insertion to depth, the drive rod was removed from the lower portion of the piezometer and a standpipe was added to extend the piezometer above the river level. Piezometers installed in this way have permitted water quality analysis and dynamic measurement of vertical potentials in cobble sediments ranging in size from 2.5 to >30 cm and the method has been successfully used in the Columbia River, USA, and Töss River, Switzerland. This innovative method provides information on the hydrodynamics of pore water in highly permeable, cobble deposits that are common in high‐energy river and lake bottoms. Piezometers installed using the internal drive rod method facilitate the assessment of the temporal and spatial dynamics of recharge and discharge at the ground water/surface water interface and analyses of the ecological connectivity between the hyporheic zone and surface water of rivers and streams. This information will lead to improved management decisions related to our nation's ground water and surface water supplies.
Enhancement of In Situ Bioremediation of BTEX‐Contaminated Ground Water by Oxygen Diffusion from Silicone Tubing
Authors: Gibson Thomas L. , Abdul Abdul S. , Chalmer Paul D.
Published: February 2007

A field study of oxygen‐enhanced biodegradation was carried out in a sandy iron‐rich ground water system contaminated with gasoline hydrocarbons. Prior to the oxygen study, intrinsic microbial biodegradation in the contaminant plume had depleted dissolved oxygen and created anaerobic conditions. An oxygen diffusion system made of silicone polymer tubing was installed in an injection well within an oxygen delivery zone containing coarse highly permeable sand. During the study, this system delivered high dissolved oxygen (DO) levels (39 mg/L) to the ground water within a part of the plume. The ground water was sampled at a series of monitors in the test zone downgradient of the delivery well to determine the effect of oxygen on dissolved BTEX, ground water geochemistry, and microbially mediated biodegradation processes. The DO levels and Eh increased markedly at distances up to 2.3 m (7.5 feet) downgradient. Potential biofouling and iron precipitation effects did not clog the well screens or porous medium. The increased dissolved oxygen enhanced the population of aerobes while the activity of anaerobic sulfate‐reducing bacteria and methanogens decreased. Based on concentration changes, the estimated total rate of BTEX biodegradation rose from 872 mg/day before enhancement to 2530 mg/day after 60 days of oxygen delivery. Increased oxygen flux to the test area could account for aerobic biodegradation of 1835 mg/day of the BTEX. The estimated rates of anaerobic biodegradation processes decreased based on the flux of sulfate, iron (II), and methane. Two contaminants in the plume, benzene and ethylbenzene, are not biodegraded as readily as toluene or xylenes under anaerobic conditions. Following oxygen enhancement, however, the benzene and ethylbenzene concentrations decreased about 98%, as did toluene and total xylenes.
Modeling Multispecies Reactive Transport in Ground Water
Authors: Clement T.P. , Sun Y. , Hooker B.S. , Petersen J.N.
Published: February 2007

In this paper, the details of RT3D, a general purpose, multispecies, reactive transport code, are presented. The code uses MODFLOW to simulate flow and several MT3D sub‐programs to simulate advection and dispersion. A set of reaction modules were developed and incorporated into RT3D to simulate various types of multispecies reactive transport. This new computer model can be used for analyzing different types of subsurface contaminant reactions, microbial metabolisms, and microbial transport kinetics. Details of the model and numerical solution procedure are presented. The numerical formulation of the code is general enough to allow description of any type of reaction with any number of mobile/immobile species. Several example problems are presented to test the performance of the code, and to illustrate its features. The presented numerical model is shown to be a useful tool for analyzing different types of subsurface bioremediation systems. Prediction based on this model can be used for screening remediation alternatives including natural attenuation and/or for forecasting contaminant exposure levels and environmental risks at sensitive, downgradient receptors.
A Study of Long‐Term MTBE Attenuation in the Borden Aquifer, Ontario, Canada
Authors: Schirmer Mario , Barker James F.
Published: February 2007

In 1988 and 1989, a natural gradient tracer test was performed in the shallow, aerobic and aquifer at Canadian Forces Base (CFB) Borden. A mixture of ground water containing dissolved oxygenated gasoline was injected below the water table along with chloride (Cl‐) as a conservative tracer. The migration of BTEX, MTBE, and Cl was monitored in detail for 16 moths. The mass of BTEX compounds in the plume diminished significantly with time due to intrinsic aerobic biodegradation, while MTBE showed only a small decrease in mass over the 16‐month period. In 1995/96, a comprehensive ground water sampling program was undertaken to define the mass of MTBE still present in the aquifer. Since the plume had migrated into an unmonitored section of the Borden Aquifer, numerical modeling and geostatistical methods were applied to define an optimal sampling grid and to improve the level of confidence in the results. A drive point profiling system was used to obtain ground water samples. Numerical modeling with no consideration of degradation pedicted maximum concentrations in excess of 3000 μg/L; field sampling found maximum concentrations of less than 200 μg/L. A mass balance for the remaining MTBE mass in the aquifer eight years after injection showed that only 3% of the original mass remained. Sorption, volatilization, a biotic degradation, and plant uptake are not considered significant attenuation processes for the field conditions. Therefore, we suggest that biodegradation may have played a major role in the attenuation of MTBE within the Borden Aquifer.
LNAPL Volume Calculation: Parameter Estimation by Nonlinear Regression of Saturation Profiles
Authors: Lundegard Paul D. , Mudford Brett S.
Published: February 2007

An estimation of the volume of light nonaqueous phase liquids (LNAPL) is often required during site assessment, remedial design, or litigation. LNAPL volume can be estimated by a strictly empirical approach whereby core samples, distributed throughout the vertical and lateral extent of LNAPL, are analyzed for LNAPL content, and these data are then integrated to compute a volume. Alternatively, if the LNAPL has obtained vertical equilibrium, the thickness of LNAPL in monitoring wells can be used to calculate of LNAPL in monitoring wells can be used to calculate LNAPL volume at the well locations if appropriate soil and LNAPL properties can be estimated.

A method is described for estimating key soil and LNAPL properties by nonlinear regression of vertical profiles of LNAPL saturation. The methods is relatively fast, cost effective, and amenable to quantitative analysis of uncertainty. Optionally, the method allows statistical determination of best‐fit values for the Van Genuchten capillary parameters (n, αoil‐water and αoil‐air), residual water saturation and ANAPL density. The sensitivity of the method was investigated by fitting field LNAPL saturation profiles and then determining the variation in misfit (mean square residual) as a function of parameter value for each parameter. Using field data from a sandy aquifer, the fitting statistics were found to be highly sensitive to LNAPL density, αoil‐water and αoil‐air moderately sensitive to the Van Genuchten n value, and weakly sensitive to residual water saturation. The regression analysis also provides information that can be used to estimate uncertainty in the estimated parameters, which can then be used to estimate uncertainty in calculated values of specific volume.
Diisopropanolamine Biodegradation Potential at Sour Gas Plants
Authors: Gieg Lisa M. , Greene E. Anne , Coy Debora L. , Fedorak Phillip M.
Published: February 2007

The potential for aerobic and anaerobic biodegradation of a sour gas treatment chemical, diisopropanolamine (DIPA), was studied using contaminated aquifer materials from three sour gas treatment sites in western Canada. DIPA was found to be readily consumed under aerobic conditions at 8°C and 28°C in shake flask cultures incubated with aquifer material from each of the sites, and this removal was characterized by first‐order kinetics. In addition, DIPA biodegradation was found to occur under nitrate‐, Min(IV)., and Fe(III)‐reducing conditions at 28°C, and in some cases at 8°C, in laboratory microcosms, DIPA loss corresponded to consumption of nitrate, and production of Mn(II) and Fe(II) in viable microcosms compared to corresponding sterile controls. A threshold DIPA concentration near 40 mg/L was observed in the anaerobic microcosms. This report provides the first evidence that DIPA is biodegraded under anaerobic conditions, and our data suggest that biodegradation may contribute to DIPA attenuation under aerobic and anaerobic conditions in aquifers contaminated with this sour gas treatment chemical.
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

Water 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

Site 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

Two 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

Use 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

Accurate 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

Characterizing 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

Remediation 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

An 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.