bluuebunny/crossref_metadata_2025 huggingface dataset:
KYSPILL: A Practical Modeling System of Scale‐Dependent Dispersion after Chemical Spills
Authors: Serrano Sergio E.
Published: August 2005

Scale‐dependent dispersion is a phenomenon that manifests as an increase in the magnitude of the dispersion parameters with the distance of travel, or the time after the spill. This implies that contaminant plumes occupy a larger portion of the aquifer at later times than that predicted by the traditional convection‐dispersion models. Although it is an area of active research, scale‐dependent ground water pollution modeling is now available through the practical application of a new hydrologic theory of dispersion. The KYSPILL software was developed as an application of this theory. KYSPILL provides an easy way to simulate and graph the movement of contaminant plumes in heterogeneous soils and aquifers. It has self‐supported menus and windows that allow the selection of the type of spill, the input of hydrogeologic data, and the plotting of contours and breakthrough curves. It simulates biological or radioactive decay, adsorption, point or nonpoint sources in the unsaturated zone and subsequently in the saturated zone. An automatic self‐diagnosis system tests every input data, and an on‐line, context‐sensitive, help system aids the user in the input data and running phases. KYSPILL is a simple tool for those chemical spills with little or uncertain data. It may be used for preliminary forecasting, monitoring planning, or remedial actions.
Effects of Steady‐State Assumption on Hydraulic Conductivity and Recharge Estimates in a Surficial Aquifer System
Authors: Halford Keith J.
Published: August 2005

The ability of a calibrated flow model to predict the behavior of a surficial aquifer system is governed by the quality of the hydraulic conductivity and recharge estimates used. Reasonable lateral and vertical hydraulic conductivities can be estimated by steady‐state simulations driven by effective recharge rates that approximate the net effects of evapotranspiration, and water released from storage during periods of recession. Results from a hypothetical, transient, cross‐sectional model indicated that most of the water was contributed uniformly from storage from five to 25 days after a recharge event. Results also showed that a steady‐state, snapshot calibration approach can be used on aquifers in a humid climate with diffusivities between 20 and 500 m2/d. Most estimates of the lateral and vertical hydraulic conductivities of the hypothetical aquifer system were within 30% of the actual values. Estimates of hydraulic conductivity from the transient cases were similar to those from the snapshot calibration cases. The long‐term recharge rate could be identified by calibrating to multiple synoptic surveys that were sampled over the range of drier to wetter conditions. The effective recharge rates estimated for the driest and wettest conditions bracketed the long‐term recharge rate. Results suggested that the effective recharge rate estimated for the synoptic survey with the lowest water level root‐mean‐square (RMS) error was the best estimate of the long‐term recharge rate. A field application of the snapshot calibration approach simulated the surficial aquifer system beneath Cecil Field Naval Air Station well and provided reasonable estimates of the long‐term recharge rate (0.4 mm/d) relative to the range of recharge rates that were independently estimated by the chloride concentration ratio method (0.2 to 0.6 mm/d).
Effects of Velocity on the Transport of Two Bacteria Through Saturated Sand
Authors: Hendry M. J. , Lawrence J. R. , Maloszewski P.
Published: August 2005

Transport of the bacteria Klebsiella oxytoca and Burkholderia cepacia G4PR1 (G4PR1) was investigated in column experiments conducted under conditions that allowed us to quantify sorption under a range of ground water velocities. Column experiments (33 mm I.D. × 114 mm long columns) were conducted at four linear water velocities (0.5 to 14 cm.hr−1) through a medium to coarse grained silica sand. The peak C/Co concentrations for both bacteria were attenuated with respect to a conservative tracer (Cl−), and well‐defined tailing was observed. Breakthroughs of both bacteria were influenced by the water velocity. In the case of G4PR1, the attenuation of the peak C/Co concentrations increased as the velocity decreased while the peak C/Co concentrations for K. oxytoca were similar at velocities between 3 and 13 cmhr−1 but decreased at the lowest velocity tested (0.6 cm‐hr−1). The tailing reached constant C/Co values of between 2 × 10−3 and 5 × 10−3, and between 2 × 10−5 and 5 × 10−5 for K. oxytoca and G4PR1 after 2t0. A one‐dimensional mathematical model for advective‐dispersive transport that accounts for irreversible (kirr) and reversible (kf and kr) sorption was used to quantify the sorption process. Both irreversible and reversible sorption was required to obtain good fits to the measured K. oxytoca data. Results of this modeling suggested that kirr and kr are independent of velocity and an empirical relationship was developed relating kf to velocity. For G4PR1, the best fits were obtained using only reversible sorption. Results of the modeling suggested that kf was independent of velocity at all velocities tested and kr was independent of velocity at velocities between 3 and 13 cmhr−1. At the lowest velocity investigated (0.5 cmhr−1), the kf value decreased considerably. This study showed that sorption characteristics are bacteria specific, and are likely related to surface chemistry because G4PR1 is more hydrophobic than K. oxytoca. The study also showed that in order for bacterial transport experiments to be directly applicable to the subsurface, they should be conducted at velocities similar to those observed in the subsurface, or the relationship between the sorption parameter(s) and velocity should be known.
Degradation of Aromatic and Chlorinated Aliphatic Hydrocarbons in the Anaerobic Part of the Grindsted Landfill Leachate Plume: In Situ Microcosm and Laboratory Batch Experiments
Authors: Bjerg Poul L. , Riigge Kirsten , Cortsen Jesper , Nielsen Per H. , Christensen Thomas H.
Published: August 2005

The fate of seven aromatic and four chlorinated aliphatic compounds was studied using in situ microcosm (ISM) and laboratory batch (LB) experiments performed at six distances along a flow line in the anaerobic leachate plume downgradient of the Grindsted Landfill, Denmark. The redox conditions were dominated by iron reduction in this part of the plume (15 to 60 m downgradient of the landfill); however, methanogenesis and sulfate reduction also took place closer to the landfill (15 to 45 m). Generally, good accordance was found between the degradation of the compounds determined by the two experimental approaches, considering the limitations of the experimental periods (up to 220 days for the ISM and up to 537 days for the LB). Of the aromatic compounds, toluene, o‐ and m/p‐xylene were degraded, while benzene, ethylbenzene, and naphthalene were not degraded, neither in the ISM nor in the LB at any distance from the landfill. All the chlorinated aliphatic compounds, (TeCM, 1,1,1‐TCA, PCE, and TCE) were degrad‐able; however, the degradation potential for PCE and TCE depended on the distance from the landfill. For most compounds, both approaches gave results comparable to those of the natural gradient field injection experiment performed in the same plume. This suggests that laboratory batch experiments, which are easier to run than ISM experiments, may be a useful tool in determining the degradability of mono aromatic hydrocarbons and chlorinated aliphatic hydrocarbons under strongly anaerobic conditions in the investigation of natural attenuation in landfill leachate plumes.
Bioremediation of Petroleum Hydrocarbon‐Contaminated Ground Water: The Perspectives of History and Hydrology
Authors: Chapelle Francis H.
Published: August 2005

Bioremediation, the use of microbial degradation processes to detoxify environmental contamination, was first applied to petroleum hydrocarbon‐contaminated ground water systems in the early 1970s. Since that time, these technologies have evolved in some ways that were clearly anticipated by early investigators, and in other ways that were not foreseen. The expectation that adding oxidants and nutrients to contaminated aquifers would enhance biodegradation, for example, has been born out by subsequent experience. Many of the technologies now in common use such as air sparging, hydrogen peroxide addition, nitrate addition, and bioslurping, are conceptually similar to the first bioremediation systems put into operation. More unexpected, however, were the considerable technical problems associated with delivering oxidants and nutrients to heterogeneous ground water systems. Experience has shown that the success of engineered bioremediation systems depends largely on how effectively directions and rates of ground water flow can be controlled, and thus how efficiently oxidants and nutrients can be delivered to contaminated aquifer sediments.

The early expectation that injecting laboratory‐selected or genetically engineered cultures of hydrocarbon‐degrading bacteria into aquifers would be a useful bioremediation technology has not been born out by subsequent experience. Rather, it appears that petroleum hydrocarbon‐degrading bacteria are ubiquitous in ground water systems and that bacterial addition is usually unnecessary. Perhaps the technology that was least anticipated by early investigators was the development of intrinsic bioremediation. Experience has shown that natural attenuation mechanisms ‐ biodegradation, dilution, and sorption ‐ limit the migration of contaminants to some degree in all ground water systems. Intrinsic bioremediation is the deliberate use of natural attenuation processes to treat contaminated ground water to specified concentration levels at predetermined points in the aquifer. In current practice, intrinsic bioremediation of petroleum hydrocarbons requires a systematic assessment to show that ambient natural attenuation mechanisms are efficient enough to meet regulatory requirements and a monitoring program to verify that performance requirements are met in the future.
Field Data and Ground Water Modeling in a Layered Fractured Aquifer
Authors: Gburek W.J. , Folmar GJ. , Urban J.B.
Published: August 2005

Surface refraction seismic surveys were conducted within a 7.3 km2 east‐central Pennsylvania watershed to characterize the geometry of its shallow layered and fractured bedrock. These data were augmented with observations from 29 rock cores. Hydraulic conductivity (K) of the bedrock was determined by interval packer testing within the boreholes. Finally, the MODFLOW ground water model was applied to the layered aquifer geometry in a three‐dimensional format to determine watershed‐scale aquifer parameters by model calibration to observed watershed data. Seismic testing showed that the aquifer could be characterized by four distinct layers, each with its own characteristic seismic velocity. Hydraulic conductivity determined by field testing decreased with depth, ranging from greater than 1.0 m day−1 in the shallow, highly fractured layer to approximately 0.01 m day−1 in the regional aquifer. Its distribution with depth reflected the increase in seismic velocities and decrease in extent of fracturing observed in the cores. Aquifer geometry determined from seismic testing and rock cores was used to define model layer geometry, and K values from model calibration compared favorably to those determined by field testing. The ground water 00 model was also used in calibration mode to determine specific yields (S y) of the characteristic fracture layers. These were all low, ranging from 0.005 in the highly fractured layer to 0.0001 in the regional aquifer. When aquifer geometry determined from detailed seismic surveys is used as the basis for watershed‐scale ground water modeling in these shallow layered and fractured systems, hydraulic parameters derived by field testing compare well to those determined by model calibration.
Reef and Nonreef Aquifers—A Comparison of Hydrogeology and Geochemistry, Northwestern Indiana
Authors: Schnoebelen Douglas J. , Krothe Noel C.
Published: August 2005

The principal bedrock aquifer system across much of Indiana consists of carbonate rocks of Silurian and Devonian age. The Silurian‐Devonian aquifer system is used extensively for irrigation in northwestern Indiana and is approximately 170 m thick. Reef and nonreef carbonate aquifers in northwestern Indiana were assessed using hydrogeology (lithology, geophysical logs, aquifer tests) and geochemistry (major ions and stable isotopes).

The study showed differences in water quantity and quality between the reef and nonreef aquifers. The reef aquifer had few shales, abundant fossiliferous material (up to 100 m thick), and high porosities (10 to 15%). The nonreef aquifer had abundant shales, less fossiliferous material (a few meters thick), and low porosities. Total transmissivities at the reef sites were 697 m2/d, (meters squared per day) and 4831 m2/d, compared to 46 m2/d at the nonreef site. Flowpaths in the nonreef aquifer were associated with fractures and poorly connected moldic porosity with larger fractures and better connected vuggy porosity in the reef aquifer. Water chemistry data for the nonreef aquifer showed mean concentrations of sodium (235 mg/L [milligrams per liter]), sulfate (160 mg/L), sul‐fide (13 mg/L), fluoride (2.7 mg/L), and dissolved solids (635 mg/L) approximately two to five times larger when compared to mean concentrations in the reef aquifer. Ground water at the nonreef site was classified as a sodium‐bicarbonate type while that at the reef sites was calcium‐magnesium bicarbonate. The oxygen/deuterium isotope data indicates recharge from modern precipitation and not Pleistocene‐age recharge.
Cost Enectiveness of Well Site Selection Methods in a Fractured Aquifer
Authors: Taylor Kendrick C. , Minor Timothy B. , Chesley Matthew M. , Matanawi Korblaah
Published: August 2005

In regions where ground water flow is restricted to sparse, narrow fractures, productive and nonproductive drilling sites frequently are separated by only a few tens of meters. Drilling success rates are low in these areas because favorable drilling sites occur infrequently and are difficult to identify. The drilling success rate can be increased when imagery and surface geophysics are incorporated into the site selection method. We present a method to evaluate the economic benefit of various site selection methods and show that the use of surface geophysics and aerial photography can reduce drilling costs by approximately a factor of two in an area with a low drilling success rate that is characterized by narrow fracture zones covered with several meters of weathered clays and thick vegetation. The benefits are smaller and less certain when social considerations are a strong factor in site selection.
Rethinking Poisson‐Based Statistics for Ground Water Quality Monitoring
Authors: Loftis Jim C. , Iyer Hariharan K. , Baker Heather J.
Published: August 2005

Both the U.S. Environmental Protection Agency (EPA) and the American Society for Testing and Materials (ASTM) provide guidance for selecting statistical procedures for ground water detection monitoring at Resource Conservation and Recovery Act (RCRA) solid and hazardous waste facilities. The procedures recommended for dealing with large numbers of nondetects, as may often be found in data for volatile organic compounds (VOCs), include, but are not limited to, Poisson prediction limits (in both the EPA guidance and ASTM standard) and Poisson tolerance limits (EPA guidance only). However, many of the proposed applications of the Poisson model are inappropriate. The development and application of the Poisson‐based methods are explored for two types of data, counts of analytical hits and actual concentration measurements. Each of these two applications is explored along two lines of reasoning, a first‐principles argument and a simple empirical fit.

The application of Poisson‐based methods to counts of analytical hits, including simultaneous consideration of multiple VOCs, appears to have merit from both a first principles and an empirical standpoint. On the other hand, the Poisson distribution is not appropriate for modeling concentration data, primarily because the variance of the distribution does not scale appropriately with changing units of measurement. Tolerance and prediction limits based on the Poisson distribution are not scale invariant. By changing the units of observation in example problems drawn from EPA guidance, use of the Poisson‐based tolerance and prediction limits can result in significant errors. In short, neither the Poisson distribution nor associated tolerance or prediction limits should be used with concentration data. EPA guidance does present, however, other, more appropriate, methods for dealing with concentration data in which the number of nondetects is large. These include nonparametric tolerance and prediction limits and a test of proportions based on the binomial distribution.
Bicarbonate, Sulfate, and Chloride Water in a Shallow, Clastic‐Dominated Coastal Flow System, Argentina
Authors: Logan William S. , Auge Miguel P. , Panarello Héctor O.
Published: August 2005

Most of the cities southeast of Buenos Aires, Argentina, depend heavily on ground water for water supply. Whereas ground water quality is generally good in the region, economic development along the coastal plain has been constrained by high salinities.

Fifty‐four wells were sampled for major ions in zones of recharge, transport and discharge in an area near La Plata, 50 km southeast of Buenos Aires. The shallow, southwest to northeast coastal flow system is >30 km long but is only 50 to 80 m thick. It consists of Plio‐Pleistocene fluvial sand overlain by Pleistocene eolian and fluvial silt and Holocene estuarine silty clay.

Hydrochemical endmembers include HCO3, SO4, and Cl water. Bicarbonate‐type water includes high plain recharge water (Ca‐Na‐HCO3) that evolves through cation exchange and calcite dissolution to a high pH, pure Na‐HCO3 endmember at the southwest edge of the coastal plain. Similar Na‐HCO3 water is also found underlying recharge areas of the central coastal plain, and a lens of Ca‐HCO3 water is associated with a ridge of shell debris parallel to the coast.

Mixed cation‐Cl water near the coastline represents intruded sea water that has undergone cation exchange. Chemically similar water underlying the southwest coastal plain, however, can be shown isotopically to have formed from fairly dilute solutions concentrated many times by evapotranspiration.

In the central coastal plain, Na‐SO4‐Cl water (up to 17,000 mg/L SO4) underlies hummocks and, at depth, forms plumes in the subsurface. The chemical controls are dissolution of gypsum precipitated during pyrite oxidation, evapotranspiration, and calcite precipitation.

This extreme diversity of water chemistry in a shallow, clastic flow system is uncommon. It is made possible by (1) the presence of oxidized, originally pyritic, but slightly permeable sediments that have been exposed to evolving geochemical and hydro‐dynamic conditions, and (2) highly focused recharge that favors the development of fresh water bodies underlying recharge zones and stagnant, evaporated water underlying other areas.
Evaluation of Electromagnetic Induction as a Reconnaissance Technique to Characterize Unsaturated Flow in an Arid Setting
Authors: Scanlon Bridget R. , Paine Jeffrey G. , Goldsmith Richard S.
Published: August 2005

The use of apparent electrical conductivity (ECa) measured with electromagnetic (EM) induction was examined as a reconnaissance tool for characterizing unsaturated flow in a semiarid region in the Chihuahuan Desert of Texas. Aboveground conductivity meters (EM31 and EM38) were used to measure ECa along transects in various geomorphic settings. Eight boreholes were drilled at different locations along the transects, and a downhole conductivity meter (EM39) was used to measure ECa. Samples were collected for analysis of clay, water, and chloride content to evaluate factors affecting spatial variability in ECa. Variations in ECa measured with the aboveground EM31 meter were affected by variations in clay content in a playa/interplaya setting, water content in a fissure, and chloride content adjacent to a drainage system. These factors affecting ECa were confirmed by comparing ECa measured with the downhole EM39 meter and clay, water, and chloride content of soil samples from boreholes. The hydrologic significance of parameters controlling ECa was evaluated. Variations in clay content are not hydrologically significant in this basin. High correlations between ECa and water content are difficult to interpret because in some areas water content variations simply reflect variations in clay content, as in the playa/interplaya setting, whereas in other areas higher water contents reflect higher water flux, as in the fissure. In some areas water content was below threshold values; therefore, ECa did not respond to water content or salinity in these areas. Although EM induction alone cannot distinguish causes of ECa changes, it provides a valuable tool for delineating variations in ECa that can be used to guide borehole locations and to provide valuable information for interpolating and extrapolating from point estimates provided by borehole data.
Boulton's Delayed Yield: A Different Context
Authors: Narasimhan T.N.
Published: August 2005

In 1954, Boulton proposed a delayed yield idealization to account for the dynamic contribution of water from the zone of desaturation during a pumping test in an unconfined aquifer. During the 1970s, the reasonableness of this idealization was questioned by some on the grounds that the exponential function with a constant parameter, used by Boulton to quantify the drainage process, was too simplistic and that the parameter will, in actuality, vary in time and space. Rather than discussing the merit of the delayed yield idealization in regard to an unconfined aquifer, the present work explores a different physical situation of an aquifer in which Boulton's idealization is realistic. Laboratory evidence exists to suggest that the deformation behavior of some aquifer materials is time dependent (creep or strain accumulation). In turn, this time dependence of deformation leads to a time dependence of the compressibility of the aquifer material, and hence, a time dependence of the aquifer's specific storage. In situations where the specific storage of an aquifer may be characterized by such time dependence, and if such time dependence can be reasonably approximated by an exponential function, then the response of such an aquifer to a constant rate pumping test will be described accurately by Boulton's mathematical formulation.
Spatial and Temporal Variability of Hydraulic Conductivity in Active Reattachment Bars of the Colorado River, Grand Canyon
Authors: Springer Abraham E. , Petroutson William D. , Semmens Betsy A.
Published: August 2005

Ground water/surface water interaction in rivers is dependent on the hydraulic conductivity of sediments lining the streambed. This study was designed to determine the temporal and spatial variability of the hydraulic conductivity of active sedimentary deposits lining the streambed of the Colorado River in the Grand Canyon. These reattachment bars form aquifers and create return‐current channels that are critical for supporting terrestrial and aquatic ecosystems. Monitoring wells were placed in five separate reattachment bars over a 200 mile long reach of the Colorado River below Glen Canyon Dam. Hydraulic conductivity was measured in all wells with the pneumatic slug test method. There is no significant difference in hydraulic conductivity among the five reattachment bars in the Grand Canyon. Hydraulic conductivity is bimodally distributed within a reattachment bar because of differing sizes of sediments deposited under different eddy velocities. A major controlled release of water from Glen Canyon Dam in March 1996 redistributed the sediments in the reattachment bars and compressed sediments deposited during previous floods. Hydraulic conductivity was significantly lower in these sediments after the flood due to the increased effective stress from the newly deposited sediment. A year later, after the sediments had drained and some deflation had occurred, hydraulic conductivity of sand deposits returned to values similar to pre‐flood values, whereas fine‐grained sediments that compressed weren't able to elastically respond.
Characterization of a Ground Water Hydrochemical System Through Multivariate Analysis: Clustering into Ground Water Zones
Authors: Suk Heejun , Lee Kang‐Kun
Published: August 2005

Multivariate data analyses were performed with the hydrochemical data from a small area in Incheon, Korea. Previous studies based on hydrogeological and hydrochemical observations proposed that the ground water hydrochemical system of the site is governed by two distinct hydrochemical regimes. Each of the two regimes governs a ground water zone, zones A and B. The ground water in zone A is characterized by confined aquifer conditions and low values of dissolved oxygen (DO), NO3−, SO42+, Na+, Cl−, and Mg2+, without much seasonal fluctuation in chemical properties. On the other hand, the ground water in zone B is characterized by unconfined aquifer conditions, relatively higher DO and NO3−, and higher, but seasonally variable, Na+ and Cl−. The hydrochemical data used for the interpretation of the previous studies are employed for factor and cluster analysis. Major factors are interpreted as correlates of chemical processes. Factor scores are computed and the cluster analysis is performed using factor scores. The zones discretized from the cluster analysis have the same distribution pattern as the zones delineated in the previous studies. The factor scores and the cluster analysis results also imply seasonal variation of the ground water hydrochemical system.
Fluorescent Dye and Media Properties Affecting Sorption and Tracer Selection
Authors: Kasnavia Torez , Vu De , Sabatini David A.
Published: August 2005

This paper discusses the importance of fluorescent dye sorption when selecting dyes for tracer studies. The effect of dye and media properties on dye sorption was evaluated using four fluorescent dyes (fluorescein, rhodamine B, rhodamine WT, and sul‐forhodamine B), two oppositely charged mineral surfaces (alumina and silica), and n‐octanol (as a neutral organic phase). Fluorescein, which has only negative functional groups, sorbed least onto negatively charged silica but most onto positively charged alumina. The rhodamine dyes, with a permanent positive charge and negatively charged functional groups, sorbed onto both alumina and silica. Sulforhodamine B, with two strongly electronegative sulfonic groups, sorbed less onto negatively charged silica than did rhodamine WT, which has two carboxyl groups. Dye partitioning into n‐octanol was strongly pH dependent with fluorescein being the most hydrophobic, followed by rhodamine WT and sulforhodamine B. Since fluorescent dyes are subject to sorption, dye selection should be based on their chemical properties, media characteristics, and laboratory batch and column studies.
Transport and Attenuation of Carboxylate‐Modified Latex Microspheres in Fractured Rock Laboratory and Field Tracer Tests
Authors: Becker Matthew W. , Reimus Paul W. , Vilks Peter
Published: August 2005

Understanding colloid transport in ground water is essential to assessing the migration of colloid‐size contaminants, the facilitation of dissolved contaminant transport by colloids, in situ bioremediation, and the health risks of pathogen contamination in drinking water wells. Much has been learned through laboratory and field‐scale colloid tracer tests, but progress has been hampered by a lack of consistent tracer testing methodology at different scales and fluid velocities. This paper presents laboratory and field tracer tests in fractured rock that use the same type of colloid tracer over an almost three orders‐of‐magnitude range in scale and fluid velocity. Fluorescently‐dyed carboxylate‐modified latex (CML) microspheres (0.19 to 0.98 μm diameter) were used as tracers in (1) a naturally fractured tuff sample, (2) a large block of naturally fractured granite, (3) a fractured granite field site, and (4) another fractured granite/schist field site. In all cases, the mean transport time of the microspheres was shorter than the solutes, regardless of detection limit. In all but the smallest scale test, only a fraction of the injected microsphere mass was recovered, with the smaller microspheres being recovered to a greater extent than the larger microspheres. Using existing theory, we hypothesize that the observed microsphere early arrival was due to volume exclusion and attenuation was due to aggregation and/or settling during transport. In most tests, microspheres were detected using flow cytometry, which proved to be an excellent method of analysis. CML microspheres appear to be useful tracers for fractured rock in forced gradient and short‐term natural gradient tests, but longer residence times may result in small microsphere recoveries.
Hydrochemical Approach to the Alterations of the Recharge of a Karst Aquifer Consecutive to a Long Pumping Period: Example Taken from Pinchinade Graben (Mouans‐Sartoux, French Riviera)
Authors: Reynaud A. , Guglielmi Y. , Mudry J. , Mangan C.
Published: August 2005

The carbonate aquifer of the Pinchinade graben, which has a well‐delimited geometry, involves water with well‐defined chemical types from calcium sulfate to magnesium bicarbonate. Each ground water type corresponds to a well‐delimited area of the aquifer: the magnesium bicarbonate for the Liassic and Rhetian limestone water (with 10 to 30 mg L‐1 of sulfate) and calcium sulfate for the water of the relatively impermeable layer of the underlying Keuper (with 300 to 1500 mg L−1 of sulfate). A four‐year pumping test with a bimonthly to daily monitoring of water chemistry has allowed evaluation of the renewal of the exploitable water reserve. During the four‐year period, the survey shows that the average discharge is balanced by natural recharge (2.8 to 105 m3 y−1). A change in the chemical character of the water was observed from Rhetian to Keuper type (from 35 to 167 mg L−1 of sulfate). Such a change indicates a progressive exhaustion of the Rhetian reserves, which are the greater part of the exploitable reserve in the area. The same phenomenon is observed daily depending on the pumped discharge and the season. For pumping rates below 26 m3 h−1, the borehole drains the Rehetian inflows to a degree depending on high or low water levels. For pumping rates above 26 m3 h−1, whatever the period, the permeable Keuper layers are pumped and sulfate peaks ensue.
Development of a Comprehensive Watershed Model Applied to Study Stream Yield under Drought Conditions
Authors: Perkins Samuel P. , Sophocleous Marios
Published: August 2005

We developed a model code to simulate a watershed's hydrology and the hydraulic response of an interconnected stream‐aquifer system, and applied the model code to the Lower Republican River Basin in Kansas. The model code links two well‐known computer programs: MODFLOW (modular 3‐D flow model), which simulates ground water flow and stream‐aquifer interaction; and SWAT (soil water assessment tool), a soil water budget simulator for an agricultural watershed. SWAT represents a basin as a collection of subbasins in terms of soil, land use, and weather data, and simulates each subbasin on a daily basis to determine runoff, percolation, evaporation, irrigation, pond seepage, and crop growth. Because SWAT applies a lumped hydrologic model to each sub‐basin, spatial heterogeneities with respect to factors such as soil type and land use are not resolved geographically, but can instead be represented statistically. For the Republican River Basin model, each combination of six soil types and three land uses, referred to as a hydrologic response unit (HRU), was simulated with a separate execution of SWAT. A spatially weighted average was then taken over these results for each hydrologic flux and time step by a separate program, SWBAVG. We wrote a package for MODFLOW to associate each subbasin with a subset of aquifer grid cells and stream reaches, and to distribute the hydrologic fluxes given for each subbasin by SWAT and SWBAVG over MODFLOW's stream‐aquifer grid to represent tributary flow, surface and ground water diversions, ground water recharge, and evapotranspiration from ground water. The Lower Republican River Basin model was calibrated with respect to measured ground water levels, streamflow, and reported irrigation water use. The model was used to examine the relative contributions of stream yield components and the impact on stream yield and base flow of administrative measures to restrict irrigation water use during droughts. Model results indicate that tributary flow is the dominant component of stream yield and that reduction of irrigation water use produces a corresponding increase in base flow and stream yield. However, the increase in stream yield resulting from reduced water use does not appear to be of sufficient magnitude to restore minimum desirable streamflows.
Enhancements for Passive Vapor Extraction: The Hanford Study
Authors: Ellerd Michael G. , Massmann Joel W. , Schwaegler Daniel P. , Rohay Virginia J.
Published: August 2005

Passive vapor extraction involves wells that are screened in the unsaturated zone and open to the atmosphere. Gas will flow out of the subsurface through the open well during periods of low barometric pressure. Field and modeling studies have been completed to evaluate enhancements for a passive vapor extraction system at a site contaminated with carbon tetrachloride on the Hanford nuclear reservation near Richland, Washington. During a 38‐hour period of low barometric pressure, approximately 500 m3 of air were vented from the subsurface. Approximately 27 grams of carbon tetrachloride were removed from the subsurface during this same outflow event. On an annual basis, more than 15 kilograms of carbon tetrachloride have been removed from each of several passive extraction wells. Computer simulations based on the field data indicate that surface covers smaller than 30 m radius will result in relatively small enhancements of flow. However, with larger surface seals (i.e., up to 90 m radius), volumetric flow rates more than doubled. Simulations showed that check valves might increase the rate at which subsurface gases are extracted by a factor of nearly three. These estimates are sensitive to dispersion coefficients. If not properly designed, filters used to treat effluent gases from passive extraction systems can significantly reduce the effectiveness of these systems.
Spatial Estimation of Transmissivity Using Artificial Neural Network
Authors: Mukhopadhyay Amitabha
Published: August 2005

The spatial interpolation of transmissivity and other hydrogeological parameters, based on data measured or observed at well locations, is necessary for the numerical simulation of various ground water flow and transport problems. The application of artificial neural network technology for this purpose has been investigated for the transmissivity of the Dammam Formation Aquifer in Kuwait. It has been found that reasonable estimates of this parameter can be obtained with the help of a network that uses the location coordinates, altitude of the top of the Dammam Formation, and logarithm of the total dissolved solids content of the ground water of the aquifer as the input neurons, and the logarithm of the transmissivity value as the output neuron. A better estimate is obtained with a model that takes into account the information on the occurrence of circulation loss in the Dammam Formation. This information, however, can only be obtained at a site where a well has penetrated the Dammam Formation, and unlike the altitude of a stratigraphic horizon and total dissolved solids content, cannot be extrapolated with any certainty away from a well site. This model, therefore, has limited value in estimating the transmissivity of the Dammam Formation. The artificial neural network models are found to give better estimates of transmissivity of the Dammam Formation in Kuwait when compared with the more commonly used kriging model.
A Heuristic Model of Aerobic Biodegradation of Dissolved Hydrocarbons in Aquifers
Authors: Ma Yang , Kemblowski Marian W. , Urroz Gilberto E.
Published: August 2005

In this paper, we present a heuristic model of mixing and aerobic degradation based on a conceptual understanding of the mixing process in heterogeneous media, rather than on a rigorous derivation from the stochastic transport equations. The mean‐behavior, heuristic approach, with a uniform velocity field, was used to reproduce organic plume behavior from a previously published simulation for random pore water velocity fields. The heuristic model presented herein requires that the mixing coefficient be calibrated to explain field data; therefore, in that sense, the model is not predictive. The numerical model uses a modified form of a particle tracking model to account for multispecies transport. Transport simulation includes a random‐walk component, while biodegradation is simulated with Monod kinetics. Numerical simulations are presented for nonreactive transport in homogeneous media, and for reactive transport in heterogeneous media. A sensitivity analysis of the model is performed to determine the effect of the mixing coefficient in the model.
Mass‐Transfer Limitations for Macroscale Bioremediation Modeling and Implications on Aquifer Clogging
Authors: MacDonald Thomas R. , Kitanidis Peter K. , McCarty Perry L. , Roberts Paul V.
Published: August 2005

In engineered in situ bioremediation, substrates are injected into the subsurface to stimulate microbial metabolism and growth. Models are useful in the design and optimization of such systems, such as in devising strategies to prevent clogging of soil by large bacterial populations around wells. Such models are macroscale, i.e., they do not resolve pore‐scale variability; rather, substrate and biomass concentrations are bulk averages that vary from block to block. These models give unrealistic predictions, in that they predict monotonically increasing biomass growth everywhere except where the limiting substrate concentration is very small. This work examines the possibility of biofilm mass‐transfer limitations at the pore scale using both the traditional biofilm model as well as previously published results from an upscaling model. Results from the biofilm model suggest that limitations on biofilm growth due to mass‐transfer resistance could be significant in coarse‐grained soils with adequate substrate availability. The upscaling approach confirms this result. While these two approaches do not yield identical results, both do agree that coarser grain sizes tend to cause greater mass transfer resistance. These are the conditions most likely to occur near injection well screens of an enhanced bioremediation system, where clogging is most commonly observed. The upscaling approach also indicates that the degree of mass transfer resistance is reduced at higher ground water velocities, which are also most commonly observed near well screens. These results could be useful for improving macroscale bioremediation models to more accurately predict rates of biomass growth and aquifer clogging.
Effects of Shear Detachment on Biomass Growth and In Situ Bioremediation
Authors: MacDonald Thomas R. , Kitanidis Peter K. , McCarty Perry L. , Roberts Paul V.
Published: August 2005

The dispersed growth model incorporating Monod kinetics has often been applied to simulate enhanced in situ bioremediation of contaminants. The dispersed growth model might not adequately address the impacts of the growth of large bacterial populations that can often have the unwanted effect of clogging the porous media. Two mechanisms that could affect model predictions of biomass are biofouling and biomass detachment due to shear stress. A mathematical model was developed to evaluate the potential impact of shear detachment on biomass distribution and the prediction of contaminant biodegradation by comparing the impact of both shear detachment and biofouling together with that of biofouling alone. The results of this examination can aid in designing a system for in situ bioremediation using computer simulations and in evaluating a system's ability to meet remediation goals. The model simulations indicate that shear detachment of biomass can be an important process to include in model simulations used to predict the effectiveness of a bioremediation system and the time before significant clogging occurs.
Improved Piezometer Construction and Sampling Techniques to Determine Pore Water Chemistry in Aquitards
Authors: Wassenaar Leonard I. , Hendry M. Jim
Published: August 2005

Due to extremely slow water recovery rates in aquitards and high contamination potential from sealing materials, installation of piezometers in aquitards for geochemical studies requires specialized construction and careful sampling techniques. Few methods have been demonstrated for obtaining representative ground water samples for geochemical parameters from piezometers in aquitards. Here we implement and evaluate an aquitard piezometer installation and ground water chemistry sampling strategy and show that the use of an inert gas pocket in piezometer construction can be used to delay seal contamination for at least three years and avoid oxygenation and disturbance of downhole redox conditions. Major ion analyses did not change appreciably through the standing water columns in the aquitard piezometers over time; however, reliable measurements of typically unstable geochemical parameters (dissolved oxygen, pH, and oxidation‐reduction potential) were best obtained using downhole, in situ instrumentation, provided there was at least 2 to 10 m of standing water in the piezometer.
Impacts of Irrigated Vegetable Agriculture on a Humid North‐Central U.S. Sand Plain Aquifer
Authors: Kraft G J. , Stites W. , Mechenich D.J.
Published: August 2005

We determined the impacts of irrigated vegetable agriculture on ground water quality in a 29 km2 portion of the Wisconsin central sand plain (WCSP). Vegetable fields cover 22% of the study area and are used for growing potatoes, sweet corn, snap beans, peas, field corn, and soybeans. We found that contaminant plumes from fields underlay about 54% of the area. Plumes were 3 to >16 m thick and in places occupied the entire aquifer thickness. Impacted ground water retained the chemical signature observed under fields, and compared with unimpacted ground water, had elevated NO3‐N (median 13.7 mg L−1 impacted vs. 0.5 for unimpacted) and Cl (median 23 vs. 2.0 mg L−1) and 1.4 to 2.5 times the Ca, Mg, K, Na, and SO4. NO3‐N detections exceeded 10 mg L−1 in 58% of impacted monitoring wells compared with none of the unimpacted wells. Evidence of denitrification was observed, but rarely. Residues of the pesticides alachlor, atrazine, carbofuran, metolachlor, and metribuzin were detected, but usually at summed concentrations of <1 μg L−1 outside of fields. The maximum observed sum of pesticide residues was 8 μg L−1. Not all potential pesticide residues were detectable by the analytical method.

Agricultural impacts limit the aquifer's value as a source of potable water, because wells are unable to tap unimpacted ground water through much of the area. Results of this study are generally applicable to other humid sandy areas in the north‐central United States and elsewhere. Impacts might be more severe elsewhere because the agricultural land use is frequently denser and ground water flowpaths are longer.
Laboratory Investigation of Surfactant‐Enhanced Trichloroethene Solubilization Using Single‐Well, “Push‐Pull” Tests
Authors: Field J.A. , Istok J.D. , Schroth M.H. , Sawyer T.E. , Humphrey M.D.
Published: August 2005

The objective of this study was to evaluate the ability of the single‐well, “push‐pull” test to characterize the enhanced solubilization of trichloroethene (TCE) by a hexadecyl diphenyl oxide disulfonate (DOWFAX) surfactant. Batch solubilization experiments indicated a linear relationship between TCE solubility and DOWFAX concentration characterized by weight‐ and molar‐solubilization ratios of 0.26 and 1.25, respectively. Laboratory push‐pull tests were performed in wedge‐shaped physical aquifer models to simulate the alternating radially divergent/convergent flow field in the vicinity of an injection/extraction well. Experiments were conducted in a TCE‐free sediment pack and in a sediment pack initially containing liquid TCE with an initial saturation of ∼ 5% of the total pore volume. In an experiment conducted in the absence of DOWFAX, maximum TCE concentrations during the extraction phase were ∼ 0.6 g/L. In contrast, in an experiment conducted with 13.5 g/L active DOWFAX, TCE concentrations during the extraction phase increased to ∼ 3.2 g/L and TCE mass recovery increased by a factor of ∼ 3. Two additional experiments conducted with DOWFAX in the same sediment pack yielded smaller maximum TCE concentrations and mass recoveries. The increased density of injected DOWFAX solutions due to TCE solubilization resulted in significant sinking of injected solutions and an accumulation of DOWFAX and TCE at greater depths in the sediment pack; however, no mobilization or sinking of liquid TCE was observed. The results indicate that push‐pull tests can provide useful information on surfactant enhanced solubilization of nonaqueous phase liquids in the subsurface.
Laboratory and Field Investigation of Surfactant Sorption Using Single‐Well, “Push‐Pull” Tests
Authors: Istok J.D. , Field J.A. , Schroth M.H. , Sawyer T.E. , Humphrey M.D.
Published: August 2005

Sorption to aquifer sediments can limit the effectiveness of surfactants injected to solubilize residual nonaqueous phase liquid contaminants in the subsurface. The objective of this study was to evaluate the ability of the single‐well, push‐pull test to characterize sorption of linear alkylbenzene sulfonate (LAS) and hexadecyl diphenyl oxide disulfonate (DOWFAX) surfactants to natural aquifer sediment in situ. Batch sorption isotherms for both surfactants exhibited Langmuir‐type sorption behavior with larger apparent sorption maxima for LAS than for DOWFAX. However, numerical transport simulations based on batch sorption isotherms were unable to predict the retardation and chromatographic separation of LAS homologs and conservative transport of DOWFAX observed during laboratory and field push‐pull tests, indicating that the single‐well, push‐pull test method can more accurately describe in situ surfactant sorption and transport behavior than batch sorption isotherms.
Effect of Shallow Penetration and Streambed Sediments on Aquifer Response to Stream Stage Fluctuations (Analytical Model)
Authors: Zlotnik Vitaly A. , Huang Huihua
Published: August 2005

An analytical model of stream‐aquifer interaction is proposed that considers the effects from a small degree of aquifer penetration and low‐permeability sediments on the head response to an arbitrary stream‐stage hydrograph. Aquifer sections under the stream and beyond are considered in a single model. The model of ground water flow in the aquifer is based on the Dupuit assumptions corrected for leakage from the stream. The model can use stream‐stage hydrographs in both analytical and tabular forms. The nondimensional linear boundary value problem is solved for hydraulic head in the aquifer using numerical Laplace transforms and a convolution algorithm. The proposed solution is used to assess the impact of shallow penetration and low‐permeability streambed sediments on head responses by comparison with available solutions which neglect these factors.