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  • Articles  (1,172)
  • Blackwell Publishing Ltd  (1,172)
  • 2020-2022
  • 2000-2004  (1,172)
  • Energy, Environment Protection, Nuclear Power Engineering  (1,172)
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  • Articles  (1,172)
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  • 1
    Electronic Resource
    Electronic Resource
    Studying Ground Water Under Delmarva Coastal Bays Using Electrical Resistivity (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Fresh ground water is widely distributed in subsurface sediments below the coastal bays of the Delmarva Peninsula (Delaware, Maryland, and Virginia). These conditions were revealed by nearly 300 km of streamer resistivity surveys, utilizing a towed multichannel cable system. Zones of high resistivity displayed by inversion modeling were confirmed by vibradrilling investigations to correspond to fresh ground water occurrences. Fresh water lenses extended from a few hundred meters up to 2 km from shore. Along the western margins of coastal bays in areas associated with fine-grained surficial sediments, high-resistivity layers were widespread and were especially pronounced near tidal creeks. Fresh ground water layers were less common along the eastern barrier-bar margins of the bays, where sediments were typically sandy. Mid-bay areas in Chincoteague Bay, Maryland, did not show evidence of fresh water. Indian River Bay, Delaware, showed complex subsurface salinity relationships, including an area with possible hypersaline brines. The new streamer resistivity system paired with vibradrilling in these investigations provides a powerful approach to recovering information required for extension of hydrologic modeling of shallow coastal aquifer systems into offshore areas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02643.x
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  • 2
    Electronic Resource
    Electronic Resource
    Ground Water Recharge and Discharge in the Central Everglades (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Rates of ground water recharge and discharge are not well known in the central Everglades. Here we report estimates of ground water recharge and discharge at 15 sites in the Everglades Nutrient Removal Project and in Water Conservation Area 2A (WCA-2A), along with measurements of hydraulic properties of peat at 11 sites. A simple hydrogeologic simulation was used to assess how specific factors have influenced recharge and discharge. Simulations and measurements agreed that the highest values of recharge and discharge occur within 600 m of levees, the result of ground water flow beneath levees. There was disagreement in the interior wetlands of WCA-2A (located 〉 1000 m from levees) where measurements of recharge and discharge were substantially higher than simulated fluxes. A five-year time series (1997 to 2002) of measured fluxes indicated that recharge and discharge underwent reversals in direction on weekly, monthly, and annual timescales at interior sites in WCA-2A. Ground water discharge tended to occur during average to moderately dry conditions when local surface water levels were decreasing. Recharge tended to occur during moderately wet periods or during very dry periods just as water levels began to increase following precipitation or in response to a pulse of surface water released from water-control structures by water managers. Discharge also tended to occur at sites in the wetland interior for ∼1 week preceding the arrival of the surface water pulse. We conclude that ground water recharge and discharge vary cyclically in the interior wetlands of the central Everglades, driven by the differential responses of surface water and ground water to annual, seasonal, and weekly trends in precipitation and operation of water-control structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02646.x
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  • 3
    Electronic Resource
    Electronic Resource
    What's New with CUASHI? (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02716.x
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  • 4
    Electronic Resource
    Electronic Resource
    Can the Desert Bloom? Lessons Learned from the Israeli Case (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Despite the central management of Israel's water resources and the highly planned strategy for a sustainable water supply, Israel has twice faced an acute water crisis during the past decade. Although the visible problem is related to a lack of additional quantities of water, the deterioration of water quality appears to be endangering the future use of available water quantities as well. A long-term policy of ground water mining (translated to salt water encroachments), and irrigation with relatively saline water and recycled waste water, among other damage, account for this deterioration. Enhanced flushing of the salt and contaminant load from the aquifers (using various techniques) is proposed as a solution to the problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02719.x
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  • 5
    Electronic Resource
    Electronic Resource
    A Method for Evaluating Horizontal Well Pumping Tests (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Predicting the future performance of horizontal wells under varying pumping conditions requires estimates of basic aquifer parameters, notably transmissivity and storativity. For vertical wells, there are well-established methods for estimating these parameters, typically based on either the recovery from induced head changes in a well or from the head response in observation wells to pumping in a test well. Comparable aquifer parameter estimation methods for horizontal wells have not been presented in the ground water literature. Formation parameter estimation methods based on measurements of pressure in horizontal wells have been presented in the petroleum industry literature, but these methods have limited applicability for ground water evaluation and are based on pressure measurements in only the horizontal well borehole, rather than in observation wells. This paper presents a simple and versatile method by which pumping test procedures developed for vertical wells can be applied to horizontal well pumping tests. The method presented here uses the principle of superposition to represent the horizontal well as a series of partially penetrating vertical wells. This concept is used to estimate a distance from an observation well at which a vertical well that has the same total pumping rate as the horizontal well will produce the same drawdown as the horizontal well. This equivalent distance may then be associated with an observation well for use in pumping test algorithms and type curves developed for vertical wells. The method is shown to produce good results for confined aquifers and unconfined aquifers in the absence of delayed yield response. For unconfined aquifers, the presence of delayed yield response increases the method error.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02723.x
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  • 6
    Electronic Resource
    Electronic Resource
    A Practical Model for Mobile, Residual, and Entrapped NAPL in Water-Wet Porous Media (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Flow of nonvolatile nonaqueous phase liquid (NAPL) and aqueous phases that account for mobile, entrapped, and residual NAPL in variably saturated water-wet porous media is modeled and compared against results from detailed laboratory experiments. Residual saturation formation in the vadose zone is a process that is often ignored in multifluid flow simulators, which might cause an overestimation of the volume of NAPL that reaches the ground water. Mobile NAPL is defined as being continuous in the pore space and flows under a pressure gradient or gravitational body force. Entrapped NAPL is defined as being occluded by the aqueous phase, occurring as immobile ganglia surrounded by aqueous phase in the pore space and formed when NAPL is replaced by the aqueous phase. Residual NAPL is defined as immobile, nonwater entrapped NAPL that does not drain from the pore spaces and is conceptualized as being either continuous or discontinuous. Free NAPL comprises mobile and residual NAPL. The numerical model is formulated on mass conservation equations for oil and water, transported via NAPL and aqueous phases through variably saturated porous media. To account for phase transitions, a primary variable switching scheme is implemented for the oil-mass conservation equation over three phase conditions: (1) aqueous or aqueous-gas with dissolved oil, (2) aqueous or aqueous-gas with entrapped NAPL, and (3) aqueous or aqueous gas with free NAPL. Two laboratory-scale column experiments are modeled to verify the numerical model. Comparisons between the numerical simulations and experiments demonstrate the necessity to include the residual NAPL formation process in multifluid flow simulators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02727.x
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  • 7
    Electronic Resource
    Electronic Resource
    Discussion of Papers (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02733.x
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  • 8
    Electronic Resource
    Electronic Resource
    More Data Required (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02612.x
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  • 9
    Electronic Resource
    Electronic Resource
    Special Section on Ground Water Research in China Featured in This Issue of Ground Water (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02616.x
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  • 10
    Electronic Resource
    Electronic Resource
    Surface Flow Boundary Conditions in Modeling Land Subsidence Due to Fluid Withdrawal (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Land subsidence due to subsurface fluid (water, gas, oil) withdrawal is often predicted by either finite element or finite difference numerical models based on coupled poroelastic theory, where the soil is represented as a semi-infinite medium bounded by the traction-free (ground) surface. One of the variables playing a most important role on the final outcome is the flow condition used on the traction-free boundary, which may be assumed as either permeable or impermeable. Although occasionally justified, the assumption of no-flow surface seems to be in general rather unrealistic. A permeable boundary where the fluid pressure is fixed to the external atmospheric pressure appears to be more appropriate. This paper addresses the response, in terms of land subsidence, obtained with a coupled poroelastic finite element model that simulates a distributed pumping from a horizontal aquifer confined between two relatively impervious layers, and takes either a permeable boundary surface, i.e., constant hydraulic potential, or an impermeable boundary, i.e., a zero Neumann flow condition. The analysis reveals that land subsidence is rather sensitive to the flow condition implemented on the traction-free boundary. In general, the no-flow condition leads to an overestimate of the predicted ground surface settlement, which could even be 1 order of magnitude larger than that obtained with the permeable boundary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02620.x
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  • 11
    Electronic Resource
    Electronic Resource
    Anaerobic Biodegradation of TCE in Laboratory Columns of Fractured Saprolite (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: An experiment was conducted to determine if biodegradation of trichloroethylene (TCE) can occur in previously uncontaminated ground water in saturated fractured saprolite (highly weathered material derived from sedimentary rocks). Two undisturbed columns (0.23 m diameter by 0.25 m long) of fractured saprolite were collected from ∼2 m depth at an uncontaminated site on the Oak Ridge Reservation, Oak Ridge, Tennessee. Natural, uncontaminated ground water from the site, which was degassed and spiked with dissolved phase TCE, was continuously pumped through one column containing the natural microbial communities (the biotic column). In a second column, the microorganisms were inhibited and the dissolved phase TCE was added under aerobic conditions (dissolved oxygen conditions 〉 2 ppm). In effluent from the biotic column, reducing conditions rapidly developed and evidence of anaerobic biodegradation of TCE, by the production of cDCE, first appeared ∼31 days after addition of TCE. Reductive dechlorination of TCE occurred after iron-reducing conditions were established and about the same time that sulfate reduction began. There was no evidence of methanogenesis. Analyses using polymerase chain reaction with specific primers sets detected the bacteria Geothrix, Geobacter, and Desulfococcus-Desulfonema-Desulfosarcina in the effluent of the biotic column, but no methanogens. The presence of these bacteria is consistent with iron- and sulfate-reducing conditions. In the inhibited column, there were no indicators of TCE degradation. Natural organic matter that occurs in the saprolite and ground water at the site is the most likely primary electron donor for supporting reductive dechlorination of TCE. The relatively rapid appearance of indicators of TCE dechlorination suggests that these processes may occur even in settings where low oxygen conditions occur seasonally due to changes in the water table.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02622.x
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  • 12
    Electronic Resource
    Electronic Resource
    Modeling Multiscale Heterogeneity and Aquifer Interconnectivity (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A number of methods involving indicator geostatistics were combined in a methodology for characterizing and modeling multiscale heterogeneity. The methodology circumvents sources of bias common in data from borehole logs. We applied this methodology to the complex heterogeneity within a regional system of buried valley aquifers, which occurs in the western glaciated plains of North America and includes the Spiritwood Aquifer. The region is conceptualized as having a hierarchical organization with three facies assemblage types (large-scale heterogeneity) and two facies types within each assemblage (small-scale heterogeneity). We statistically characterized the sedimentary architecture at both scales, formulated indicator correlation models from those characterizations, and used the models to simulate the architecture in a multiscale realization. We focused on the interconnectivity of units creating higher-permeability pathways. Higher-permeability pathways span the realization even though the proportion of higher-permeability facies is less than the percolation threshold. Thus, geologic structures as represented in the indicator correlation models create interconnectivity above that which would occur if the higher-permeability facies were randomly placed. This amount of interconnection among higher-permeability facies within the multiscale realization is consistent with that suggested in prior hydraulic and geochemical studies of the regional system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02720.x
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  • 13
    Electronic Resource
    Electronic Resource
    Ground Water Flow Parameterization of an Appalachian Coal Mine Complex (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: We examined a large (240 km2) northern Appalachian bituminous coal basin (Irwin Syncline, Westmoreland County, Pennsylvania) comprising 27 mine complexes with nine major (〉 2.5 × 103 L/min) discharges. The synclinal basin was divided into seven subbasins based on equilibrium hydraulic relationships established during the past 25 years. Recharge rates, mine pool velocity, and residence times respond to hydraulic changes in the overburden induced by mine subsidence. The estimated maximum depth for subsidence fractures is 60 m (30 times mined thickness) with recharge rates decreasing significantly in subbasins with thicker overburden (〉 75 m). Calculated subbasin recharge rates range from 2 to 6 × 10−4 L/min/m2 and are significantly lower than the previously used rate for the basin. Residence time of ground water in the Irwin subbasins calculated using average linear velocity ranged from one to five years and were more consistent with field observations than estimates obtained using discharge and basin volume area. A positive correlation (r2= 0.80) exists between net alkalinity of the mine water-impacted discharges and residence time in the mine pools. Our results for the Irwin coal basin suggest that use of a subbasin approach incorporating overburden depth, mining methodology, and the extent of postmining inundation will lead to improved determination of ground water flow parameters in mined watersheds in northern Appalachia and elsewhere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02724.x
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  • 14
    Electronic Resource
    Electronic Resource
    Analytical and Numerical Models to Explain Steady Rates of Spring Flow (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Flow from some springs in former glacial lakebeds of the Upper Midwest is extremely steady throughout the year and does not increase significantly after precipitation events or seasonal recharge. Analytical and simplified numerical models of spring systems were used to determine whether preferential ground water flow through high-permeability features in shallow sandstone aquifers could produce typical values of spring discharge and the unusually steady rates of spring flow. The analytical model is based on a one-dimensional solution for periodic ground water flow. Solutions to this model suggest that it is unlikely that a periodic forcing due to seasonal variations in areal recharge would propagate to springs in a setting where high-permeability features exist. The analytical model shows that the effective length of the aquifer, or the length of flowpaths to a spring, and the total transmissivity of the aquifer have the greatest potential to impact the nature of spring flow in this setting. The numerical models show that high-permeability features can influence the magnitude of spring flow and the results demonstrate that the lengths of ground water flowpaths increase when high-permeability features are explicitly modeled, thus decreasing the likelihood for temporal variations in spring flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02728.x
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  • 15
    Electronic Resource
    Electronic Resource
    A Tracer Dilution Method for Fracture Characterization in Bedrock Wells (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This investigation was undertaken to develop an integrated method of downhole fracture characterization using a tracer. The method presented can be used to locate water-bearing fractures that intersect the well, to determine the ambient fracture flow rate and hydraulic head, and to calculate fracture transmissivity. The method was tested in two fractured crystalline bedrock wells located at the University of Connecticut in Storrs. The method entails injecting a tracer (uranine dye) into the well, while at the same time water is pumped out of the well. After steady-state conditions are reached, a borehole tracer concentration profile is developed. The dilution of the tracer is used to locate the inflowing fractures and to determine their flow rate. The fracture flow rate, plus the drawdown in the well, is then used to determine the fracture hydraulic head, transmissivity, and ambient flow rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02731.x
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  • 16
    Electronic Resource
    Electronic Resource
    Geochemical Processes During Five Years of Aquifer Storage Recovery (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A key factor in the long-term viability of aquifer storage recovery (ASR) is the extent of mineral solution interaction between two dissimilar water types and consequent impact on water quality and aquifer stability. We collected geochemical and isotopic data from three observation wells located 25, 65, and 325 m from an injection well at an experimental ASR site located in a karstic, confined carbonate aquifer in South Australia. The experiment involved five major injection cycles of a total of 2.5 × 105 m3 of storm water (total dissolved solids [TDS] ∼ 150 mg/L) into the brackish (TDS ∼2400 mg/L) aquifer. ∼60% of the mixture was pumped out during the fifth year of the experiment. The major effect on water quality within a 25 m radius of the injection well following injection of storm water was carbonate dissolution (35 ± 6 g of CaCO3 dissolved/m3 of aquifer) and sulfide mineral oxidation (50 ± 10 g as FeS2/m3 after one injection). 〈 0.005% of the total aquifer carbonate matrix was dissolved during each injection event, and ∼0.2% of the total reduced sulfur. Increasing amounts of ambient ground water was entrained into the injected mixture during each of the storage periods. High 14CDIC activities and slightly more negative δ13CDIC values measured immediately after injection events show that substantial CO2(aq) is produced by oxidation of organic matter associated with injectant. There were no detectable geochemical reactions while pumping during the recovery phase in the fifth year of the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02691.x
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  • 17
    Electronic Resource
    Electronic Resource
    Discussion of Papers (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02693.x
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  • 18
    Electronic Resource
    Electronic Resource
    NGWA Interest Group Report from Orlando (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02663.x
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  • 19
    Electronic Resource
    Electronic Resource
    Ground Water Whirls (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Numerical experiments with steady-state ground water flow models show that spiraling flow lines occur in layered aquifers that have different anisotropic horizontal hydraulic conductivities in adjacent layers. Bundles of such flow lines turning in the same direction can be referred to as ground water whirls. An anisotropic layered block in a field of uniform horizontal flow results in one or more whirls with their axes in the uniform flow direction. The number of whirls depends on the number of interfaces between layers with different anisotropic properties. For flow to a well in an aquifer consisting of two anisotropic layers, with perpendicular major principal directions, whirls are found to occur in quadrants that are bounded by the principal directions of the hydraulic conductivity. The combined effect of flow to a well and a layered anisotropy implies that a single well in a system with a single anisotropic layer within an otherwise isotropic aquifer causes eight whirls. All adjacent whirls rotate in opposite directions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02670.x
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  • 20
    Electronic Resource
    Electronic Resource
    Author's Reply (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02631.x
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  • 21
    Electronic Resource
    Electronic Resource
    A Program for Evaluating Dual-Equilibrium Desorption Effects on Remediation (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Desorption is one of the most critical processes affecting the effectiveness of soil and ground water remediation. None of the currently adopted desorption models can accurately quantify desorption of low-hydrophobicity organic chemicals, and thus could potentially mislead remediation design and decision-making. A recently developed dual-equilibrium desorption (DED) model was found to be much more accurate in quantifying desorption. A screening-level transport model, DED-Transport, was developed to simulate the DED effect on behaviors of organic contaminant plumes during remediation. DED-Transport requires only simple parameters, but is applicable to many remediation scenarios. DED-Transport can be used as a decision-support tool in site remediation to more precisely predict the time required for cleanup.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02632.x
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  • 22
    Electronic Resource
    Electronic Resource
    Estrogen in a Karstic Aquifer (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Adverse impacts on the health of some fish populations, such as skewed sex distributions, have been noted in surface waters and in laboratory experiments with relatively low concentrations (above 25 ng/L) of natural estrogen (17 β-estradiol—E2). Sources of E2 to surface and ground waters can include avian, human, and mammalian waste products. The Ozark Plateau Aquifer (OPA) is a karstic basin that receives a significant portion of its water through losing reaches of rivers. Thus, there is a direct connection between surface water and ground water. The OPA was targeted for an E2 study to assess the potential for adverse health effects to aquatic organisms living in the system. Eight springs, which drain the aquifer, were sampled quarterly. The concentrations of E2 in the OPA ranged from 13 to 80 ng/L. For any one sampling event, the concentrations of E2 at the spring waters were statistically similar; however, the concentrations of E2 at all springs varied throughout the year. At Maramec Spring, one of the larger springs, the E2 concentration, was correlated with discharge. Based on the correlation between discharge and E2 concentration, aquatic organisms living in the plateau or in its discharged waters, including the threatened southern cavefish T. subterraneus, are exposed to concentration of E2 above 25 ng/L ∼60% of the time. This implies that organisms living in karst basins throughout the OPA are likely exposed to E2 concentrations that may adversely impact their reproductive success for a significant portion of each year.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02686.x
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    Field Evaluation of Emergency Well Disinfection for Contamination Events (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02444.x
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  • 24
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    Use of Temperature Profiles and Stable Isotopes to Trace Flow Lines: Nagaoka Area, Japan (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: In this study, we use borehole temperature data and stable isotopes to delineate the flow system and estimate the effect of urbanization in the Nagaoka area of Japan. Temperature profiles were measured four times in observation wells during the period 2000–2001 and compared with those measured in the same wells during the period 1977–1983 (Taniguchi 1986). Water was sampled in both observation and pumping wells during the same period. The temporal and spatial variability in temperature indicate clearly the effect of urban warming and heavy pumping on the ground water system. Urban warming caused higher temperatures recently as compared to the older values, and pumping caused induced recharge from the river to the ground water. The stable isotope data show the ground water flow system is divided into shallow, intermediate, and deep systems, and that land use and infiltration rate are affecting the shallow flow system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02453.x
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  • 25
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    Small-Scale Electrical Resistivity Tomography of Wet Fractured Rocks (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper describes a series of experiments that tested the ability of the electrical resistivity tomography (ERT) method to locate correctly wet and dry fractures in a meso-scale model. The goal was to develop a method of monitoring the flow of water through a fractured rock matrix.The model was a four by six array of limestone blocks equipped with 28 stainless steel electrodes. Dry fractures were created by placing pieces of vinyl between one or more blocks. Wet fractures were created by injecting tap water into a joint between blocks. In electrical terms, the dry fractures are resistive and the wet fractures are conductive. The quantities measured by the ERT system are current and voltage around the outside edge of the model. The raw ERT data were translated to resistivity values inside the model using a three-dimensional Occam's inversion routine. This routine was one of the key components of ERT being tested.The model presented several challenges. First, the resistivity of both the blocks and the joints was highly variable. Second, the resistive targets introduced extreme changes the software could not precisely quantify. Third, the abrupt changes inherent in a fracture system were contrary to the smoothly varying changes expected by the Occam's inversion routine. Fourth, the response of the conductive fractures was small compared to the background variability.In general, ERT was able to locate correctly resistive fractures. Problems occurred, however, when the resistive fracture was near the edges of the model or when multiple fractures were close together. In particular, ERT tended to position the fracture closer to the model center than its true location. Conductive fractures yielded much smaller responses than the resistive case. A difference-inversion method was able to correctly locate these targets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02456.x
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    “Methods to Determine Storativity of Infinite Confined Aquifers from a Recovery Test,” by Djaouida Chenaf and Robert P. Chapuis, July-August 2002 issue, v. 40, no. 4: 385–389. (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02459.x
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    “Implications of Observed and Simulated Ambient Flow in Monitoring Wells,” by Alper Elci, Fred J. Molz III, and W. R. Waldrop, November-December 2001 issue, v. 39, no. 6: 853–862. (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02461.x
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  • 28
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    Delineating and Quantifying Ground Water Discharge Zones Using Streambed Temperatures (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Streambed temperature mapping, hydraulic testing using minipiezometers, and geochemical analyses of interstitial water of the streambed were used to delineate the pattern of ground water discharge in a sandy streambed and to develop a flux-based conceptual model for ground water/surface water interactions. A new and simple empirical method was used to relate fluxes obtained from minipiezometer data to streambed temperatures. The relationship allowed flux to be calculated at locations where only streambed temperature measurements were made. Slug testing and potentiomanometer measurements at 34 piezometers indicated ground water discharge ranged from 0.03 to 446 L/m2/day (and possibly as high as 7060 L/m2/day) along a 60 m long by 11 to 14 m wide reach of river. Complex but similar plan-view patterns of flux were calculated for both summer and winter using hundreds of streambed temperatures measured on a 1 by 2 m grid. The reach was dominated by ground water discharge and 5% to 7% of the area accounted for ∼20% to 24% of the total discharge. 〈 12% of the total area consisted of recharge zones or no-discharge zones. A conceptual model for ground water/surface water interactions consisting of five different behaviors was developed based on the magnitude and direction of flux across the surface of the streambed. The behaviors include short-circuit discharge (e.g., high-flow springs), high discharge (e.g., preferential flowpaths), low to moderate discharge, no discharge (e.g., horizontal hyporheic or ground water flow), and recharge. Geological variations at depth played a key role in determining which type of flow behavior occurred in the streambed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02671.x
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  • 29
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    Validation of Numerical Ground Water Models Used to Guide Decision Making (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Many sites of ground water contamination rely heavily on complex numerical models of flow and transport to develop closure plans. This complexity has created a need for tools and approaches that can build confidence in model predictions and provide evidence that these predictions are sufficient for decision making. Confidence building is a long-term, iterative process and the author believes that this process should be termed model validation. Model validation is a process, not an end result. That is, the process of model validation cannot ensure acceptable prediction or quality of the model. Rather, it provides an important safeguard against faulty models or inadequately developed and tested models. If model results become the basis for decision making, then the validation process provides evidence that the model is valid for making decisions (not necessarily a true representation of reality). Validation, verification, and confirmation are concepts associated with ground water numerical models that not only do not represent established and generally accepted practices, but there is not even widespread agreement on the meaning of the terms as applied to models. This paper presents a review of model validation studies that pertain to ground water flow and transport modeling. Definitions, literature debates, previously proposed validation strategies, and conferences and symposia that focused on subsurface model validation are reviewed and discussed. The review is general and focuses on site-specific, predictive ground water models used for making decisions regarding remediation activities and site closure. The aim is to provide a reasonable starting point for hydrogeologists facing model validation for ground water systems, thus saving a significant amount of time, effort, and cost. This review is also aimed at reviving the issue of model validation in the hydrogeologic community and stimulating the thinking of researchers and practitioners to develop practical and efficient tools for evaluating and refining ground water predictive models.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02674.x
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    Interactive Models for Ground Water Flow and Solute Transport (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02445.x
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  • 31
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    Multiple-Aquifer Characterization from Single Borehole Extensometer Records (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Measurement and analysis of aquifer-system compaction have been used to characterize aquifer and confining unit properties when other techniques such as flow modeling have been ineffective at adequately quantifying storage properties or matching historical water levels in environments experiencing land subsidence. In the southeastern coastal plain of Virginia, high-sensitivity borehole pipe extensometers were used to measure 24.2 mm of total compaction at Franklin from 1979 through 1995 (1.5 mm/year) and 50.2 mm of total compaction at Suffolk from 1982 through 1995 (3.7 mm/year). Analysis of the extensometer data reveals that the small rates of aquifer-system compaction appear to be correlated with withdrawals of water from confined aquifers. One-dimensional vertical compaction modeling indicates measured compaction is the result of nonrecoverable hydrodynamic consolidation of the fine-grained confining units and interbeds, as well as recoverable compaction and expansion of coarse-grained aquifer units. The calibrated modeling results indicate that nonrecoverable specific storage values decrease with depth and range from 1.5 × 10−5/m for aquifer units to 1.5 × 10−4/m for confining units and interbeds. The aquifer and Potomac system recoverable specific storage values were all estimated to be 4.5 × 10−6/m, while the confining units and interbeds had values of 6.0 × 10−6/m. The calibrated vertical hydraulic conductivity values of the confining units and interbeds ranged from 6.6 × 10−4m/year to 2.0 × 10−3 m/year. These parameter values will be useful in future management and modeling of ground water in the Virginia Coastal Plain.
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    Modeling the Buildup of Iron Oxide Encrustations in Wells (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Ferric iron encrustations are a common problem that seriously affects the performance of wells and drains. Their formation is induced by the mixing of reduced ground water containing ferrous iron with oxic shallow ground water and exposure to air. The process of ferrous iron oxidation is a kinetically controlled reaction. The reaction rate has a quadratic dependency on pH. The precipitating oxides have an autocatalytic effect that further enhances reaction progress. This paper describes the application of kinetic models to the problem of encrustation formation. Influences of pH, residence time, and autocatalysis were modeled. The overall influence of the autocatalytic reaction path is particularly strong when initial amounts of iron oxides are present. Autocatalysis provides a good explanation on the development of well yield commonly measured in the field. Encrustation precipitation is slow at first, but speeds up after a sufficient amount of iron oxide has built up. An incomplete removal of iron oxide encrustations during rehabilitation leads to a renewed increase in catalytic efficiency and encrustation precipitation.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02452.x
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    Predictability of Surface Mine Spoil Hydrologic Properties in the Appalachian Plateau (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Prevention of acid mine drainage at surface coal mines in the Appalachian region relies to an extent on minimizing ground water contact with acid-forming materials, and maximizing ground water contact with alkalinity-yielding materials. Acid-forming materials are often selectively handled to minimize or prevent contact with ground water. Controlling ground water contact with acidic or alkaline materials depends on forecasting the level and range of fluctuation of the postmining water table within the mine backfill. Physical measurements and aquifer testing of more than 120 wells from 18 reclaimed mines in Kentucky, Ohio, Pennsylvania, and West Virginia have led to improved forecasting of the postmining ground water system. Factors that influence the ground water regime include spoil lithology and particle size, age of reclamation, spoil thickness, distance from the final highwall, and pit floor dip angle and direction. Spoil hydraulic conductivity (K) exhibits a 95% confidence interval range of six orders of magnitude about a mean K of 1.7 × 10−5 m/sec. Spoil aquifer saturated thickness is related to the overall thickness of the spoil, the lithology of the spoil, dip of the pit floor, and distance to the highwall. Saturated spoil thickness has a 95% confidence interval of 2.2 to 3.6 m about the mean of 2.9 m. The predicted saturated zone averages 19% of the total spoil thickness.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02457.x
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    Authors' Reply (2004)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2004.tb02460.x
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    Lithium Isotope Geochemistry and Origin of Canadian Shield Brines (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Hypersaline calcium/chloride shield brines are ubiquitous in Canada and areas of northern Europe. The major questions relating to these fluids are the origin of the solutes and the concentration mechanism that led to their extreme salinity. Many chemical and isotopic tracers are used to solve these questions. For example, lithium isotope systematics have been used recently to support a marine origin for the Yellowknife shield brine (Northwest Territories). While having important chemical similarities to the Yellowknife brine, shield brines from the Sudbury/Elliot Lake (Ontario) and Thompson/Snow Lake (Manitoba) regions, which are the focus of this study, exhibit contrasting lithium behavior.Brine from the Sudbury Victor mine has lithium concentrations that closely follow the sea water lithium-bromine concentration trajectory, as well as δ6Li values of approximately—28 %o. This indicates that the lithium in this brine is predominantly marine in origin with a relatively minor component of crustal lithium leached from the host rocks. In contrast, the Thompson/Snow Lake brine has anomalously low lithium concentrations, indicating that it has largely been removed from solution by alteration minerals. Furthermore, brine and nonbrine mine waters at the Thompson mine have large δ6Li variations of ∼30 %o, which primarily reflects mixing between deep brine with δ6Li of—35 ± 2‰ and near surface mine water that has derived higher δ6Li values through interactions with their host rocks. The contrary behavior of lithium in these two brines shows that, in systems where it has behaved conservatively, lithium isotopes can distinguish brines derived from marine sources.
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    From Models to Performance Assessment: The Conceptualization Problem (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Today, models are ubiquitous tools for ground water analyses. The intent of this paper is to explore philosophically the role of the conceptual model in analysis. Selection of the appropriate conceptual model is an a priori decision by the analyst. Calibration is an integral part of the modeling process. Unfortunately a wrong or incomplete conceptual model can often be adequately calibrated; good calibration of a model does not ensure a correct conceptual model. Petroleum engineers have another term for calibration; they refer to it as history matching. A caveat to the idea of history matching is that we can make a prediction with some confidence equal to the period of the history match. In other words, if we have matched a 10-year history, we can predict for 10 years with reasonable confidence; beyond 10 years the confidence in the prediction diminishes rapidly. The same rule of thumb applies to ground water model analyses. Nuclear waste disposal poses a difficult problem because the time horizon, 1000 years or longer, is well beyond the possibility of the history match (or period of calibration) in the traditional analysis. Nonetheless, numerical models appear to be the tool of choice for analyzing the safety of waste facilities. Models have a well-recognized inherent uncertainty. Performance assessment, the technique for assessing the safety of nuclear waste facilities, involves an ensemble of cascading models. Performance assessment with its ensemble of models multiplies the inherent uncertainty of the single model. The closer we can approach the idea of a long history with which to match the models, even models of nuclear waste facilities, the more confidence we will have in the analysis (and the models, including performance assessment). This thesis argues for prolonged periods of observation (perhaps as long as 300 to 1000 years) before a nuclear waste facility is finally closed.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2003.tb02395.x
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    Ground Water/Surface Water Interaction in a Fractured Rock Aquifer (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: In a recent field study of ground water/surface water interaction between a bedrock stream and an underlying fractured rock aquifer, it was determined that the majority of ground water discharge occurred through sparsely located vertical fractures. In this paper, the dominant mechanisms governing ground water/surface water exchange in such an environment are investigated using a numerical model. The study was conducted using several conceptual models based on the field study results. Although the field results provided the motivation for the modeling study, it was not intended to match modeling and field results directly. In addition, the extent of capture zones for discharging or recharging fractures was explored. The results of this study are intended to provide a better understanding of contaminant migration in the vicinity of bedrock streams. Based on the numerical results, the rate of ground water discharge (or recharge) was found to depend on the aperture size of the discharging feature, and on the distribution of hydraulic head with depth within the fracture network. It was determined that the extent of both the capture zone and reverse capture zone for an individual fracture can be extremely large, and will be determined by the height of the stream stage, the fracture apertures of the network, and the hydraulic-head distribution within the network. Because both the stream stage and the hydraulic-head distribution are transient, the size of the capture zone and/or the reverse capture zone for an individual fracture may change significantly over time. As a result, the migration path for contaminants within the fracture network and between the surface and subsurface will also vary significantly with time.
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    A Creative Solution to the NIMBY Problem (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2003.tb02371.x
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    Applications of a Total Dissolved Gas Pressure Probe in Ground Water Studies (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Measurements of dissolved gases have numerous applications in ground water hydrology, and it is now possible to measure the total dissolved gas pressure in situ using a probe. Dissolved gas pressure is measured by submerging a headspace volume with a gas-permeable membrane, allowing dissolved gases in the water to equilibrate with gases in the headspace, then measuring the pressure in the headspace with a pressure transducer. Total dissolved gas pressure (TGP) probes have many potential uses in ground water studies employing dissolved gases, including: (1) determining approximate excess air levels, which may provide information about the time and location of recharge; (2) screening wells for air contamination, which can compromise the accuracy of dissolved gas tracer techniques: (3) detecting a trapped gas phase, which can significantly reduce hydraulic conductivity and impede the transport of dissolved solutes and gases; (4) enabling the use of gas-filled passive diffusion samplers for determining accurate dissolved gas concentrations; and (5) determining relative concentrations of CH4 and CO2 when they are known to be highly abundant. Although TGP probes designed for surface water have been available for several years, TGP probes suitable for ground water applications have only recently become available. Herein we present what are, to our knowledge, the first reported ground water dissolved gas data collected using a TGP probe. We also explain the basic operating principles of these probes and discuss the potential applications listed.
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    Geochemical Effects on Metals Following Permanganate Oxidation of DNAPLs (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The application of in situ chemical oxidation for dense, nonaqueous phase liquid (DNAPL) remediation requires delivery of substantial levels of oxidant chemicals into the subsurface to degrade target DNAPLs and to satisfy natural oxidant demand. This practice can raise questions regarding changes in subsurface conditions, yet information regarding potential effects, especially at the field scale, has been lacking. This paper describes an evaluation of the effects on metals associated with in situ chemical oxidation using potassium permanganate at Launch Complex 34 (LC34), Cape Canaveral Air Station, Florida. At LC34, high concentrations of permanganate (1 to 2 wt%) were injected into the subsurface as part of a demonstration of DNAPL remediation technologies. In a companion experimental effort at the Colorado School of Mines, field samples were characterized and laboratory batch and mini-column studies were completed to assess effects of permanganate oxidation on metals in the subsurface one year after completion of the field demonstration. Results indicated there was potential for long-term immobilization of a portion of introduced manganese and no treatment-induced loss in subsurface permeability due to deposition of manganese oxides particles, which are a product of the oxidation reactions. Permanganate treatment did cause elevated manganese, chromium, and nickel concentrations in site ground water within the treated region. Some of these metals effects can be attenuated during downgradient flow through uncontaminated and untreated aquifer sediments.
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  • 41
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    Regional Estimation of Base Recharge to Ground Water Using Water Balance and a Base-Flow Index (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Naturally occurring long-term mean annual base recharge to ground water in Nebraska was estimated with the help of a water-balance approach and an objective automated technique for base-flow separation involving minimal parameter-optimization requirements. Base recharge is equal to total recharge minus the amount of evapotranspiration coming directly from ground water. The estimation of evapotranspiration in the water-balance equation avoids the need to specify a contributing drainage area for ground water, which in certain cases may be considerably different from the drainage area for surface runoff. Evapotranspiration was calculated by the WREVAP model at the Solar and Meteorological Surface Observation Network (SAMSON) sites. Long-term mean annual base recharge was derived by determining the product of estimated long-term mean annual runoff (the difference between precipitation and evapotranspiration) and the base-flow index (BFI). The BFI was calculated from discharge data obtained from the U.S. Geological Survey's gauging stations in Nebraska. Mapping was achieved by using geographic information systems (GIS) and geostatistics. This approach is best suited for regional-scale applications. It does not require complex hydrogeologic modeling nor detailed knowledge of soil characteristics, vegetation cover, or land-use practices. Long-term mean annual base recharge rates in excess of 110 mm/year resulted in the extreme eastern part of Nebraska. The western portion of the state expressed rates of only 15 to 20 mm annually, while the Sandhills region of north-central Nebraska was estimated to receive twice as much base recharge (40 to 50 mm/year) as areas south of it.
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    Autobiographical Sketch of Otto D.L Strack (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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    Response (2003)
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
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    A Digital Procedure for Ground Water Recharge and Discharge Pattern Recognition and Rate Estimation (2003)
    Oxford, UK : Blackwell Publishing Ltd
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A digital procedure to estimate recharge/discharge rates that requires relatively short preparation time and uses readily available data was applied to a setting in central Wisconsin. The method requires only measurements of the water table, fluxes such as stream baseflows, bottom of the system, and hydraulic conductivity to delineate approximate recharge/discharge zones and to estimate rates. The method uses interpolation of the water table surface, recharge/discharge mapping, pattern recognition, and a parameter estimation model. The surface interpolator used is based on the theory of radial basis functions with thin-plate splines. The recharge/discharge mapping is based on a mass-balance calculation performed using MODFLOW. The results of the recharge/discharge mapping are critically dependent on the accuracy of the water table interpolation and the accuracy and number of water table measurements. The recharge pattern recognition is performed with the help of a graphical user interface (GUI) program based on several algorithms used in image processing. Pattern recognition is needed to identify the recharge/discharge zonations and zone the results of the mapping method. The parameter estimation program UCODE calculates the parameter values that provide a best fit between simulated heads and flows and calibration head-and-flow targets. A model of the Buena Vista Ground Water Basin in the Central Sand Plains of Wisconsin is used to demonstrate the procedure.
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    Flow Dimension as an Indicator of Hydraulic Behavior in Site Characterization of Fractured Rock (2003)
    Oxford, UK : Blackwell Publishing Ltd
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: We examine the possibility of using the flow dimension identified from constant pressure injection tests as a tool for characterizing the hydraulic conditions of fractured media. The data comes from a low-conductivity crystalline rock site, from depths of up to 450 m, and is obtained with 2 m and 10 m measurement scales. In the analysis, the general solution for n-dimensional flow by Barker (1988) is applied. The results show that the most prominent characteristics of the medium can be identified; that is, linear and sublinear flow dimensions as distinguished from dimensions higher than two. In many cases, however, there is significant difficulty in distinguishing the dimensions n = 2, 2.5, and 3 from each other. This is usually because of the experimental difficulties in achieving the ideal conditions required by the theory during the early part of the experiment. In such cases, a full flow curve is not available for the type-curve fitting. In the nonunique cases the higher dimensions typically correspond to higher, sometimes unrealis-tically high, values of specific storage and to the less reliable and less representative early part of the experiment. Therefore, most of the dimensions in categories n= 3 can be excluded, thus leaving the majority observations in the categories of n= 2 and n = 2–2.5. The dominance of dimension n = 2 is more pronounced for data related to fracture zones in comparison to that related to “average” rock, in particular in the 2 m scale data. The proportion of low (n 〈 1.5) flow dimensions is small, but for the 10 m scale data it is relatively higher at greater depths and corresponds to lower conductivities. For the smaller 2 m scale data, the low dimensions are not linked to greater depths or systematically smaller conductivities, giving preliminary indication of different flow dimension behavior for the two different scales.
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    “Stream-Aquifer Interactions: Evaluation of Depletion Volume and Residual Effects from Ground Water Pumping,” by Xunhong Chen and Longcang Shu, May-June 2002 issue, v. 40, no. 3: 284–290. (2003)
    Oxford, UK : Blackwell Publishing Ltd
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    AUTHORS REPLY (2003)
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    Vadose Zone Flow Model Uncertainty as Conditioned on Geophysical Data (2003)
    Oxford, UK : Blackwell Publishing Ltd
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: An approach to estimating the uncertainty in model descriptions based on a landscape space to model space mapping concept is described. The approach is illustrated by an application making use of plot scale geophysical estimates of changes in water content profiles to condition a model of recharge to the Sherwood Sandstone Aquifer in the United Kingdom. It is demonstrated that the mapping is highly uncertain and that many different parameter sets give acceptable simulations of the observations. Multiple profile measurements over time offer only limited additional constraints on the mapping. The resulting mapping weights may be used to evaluate uncertainty in the predictions of vadose zone flow dynamics for the site.
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    Simulating Ground Water-Lake Interactions: Approaches and Insights (2003)
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Approaches for modeling lake-ground water interactions have evolved significantly from early simulations that used fixed lake stages specified as constant head to sophisticated LAK packages for MODFLOW. Although model input can be complex, the LAK package capabilities and output are superior to methods that rely on a fixed lake stage and compare well to other simple methods where lake stage can be calculated. Regardless of the approach, guidelines presented here for model grid size, location of three-dimensional flow, and extent of vertical capture can facilitate the construction of appropriately detailed models that simulate important lake-ground water interactions without adding unnecessary complexity. In addition to MODFLOW approaches, lake simulation has been formulated in terms of analytic elements. The analytic element lake package had acceptable agreement with a published LAK1 problem, even though there were differences in the total lake conductance and number of layers used in the two models. The grid size used in the original LAK1 problem, however, violated a grid size guideline presented in this paper. Grid sensitivity analyses demonstrated that an appreciable discrepancy in the distribution of stream and lake flux was related to the large grid size used in the original LAK1 problem. This artifact is expected regardless of MODFLOW LAK package used. When the grid size was reduced, a finite-difference formulation approached the analytic element results. These insights and guidelines can help ensure that the proper lake simulation tool is being selected and applied.
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    A Finite World, Earth Sciences, and Public Trust (2003)
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The beginning of the 21st century has coincided with our recognition that life-sustaining earth cycles are remarkably fine-tuned, and that humans have developed technological abilities to perturb these cycles. Also, inspired by the gifts of freedom and democracy, humans have given themselves laws to exploit nature for profit. The upshot is that nature's balance, governed by immutable physical laws, is being confronted by social laws driven by human aspirations. This conflict and its implications to the human relevance of the earth sciences are explored in the context of an extraordinary tradition of European culture known as public trust.
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    Influence of Aquifer Properties on Phytoremediation Effectiveness (2003)
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Recent research has shown that planting deep-rooted trees, such as poplar, can take up and degrade important ground water pollutants such as trichloroethylene (TCE) as they transpire water from the capillary fringe of shallow contaminated aquifers. The effect of hydrogeologic factors on the minimum plantation area needed to prevent downgradient migration of contaminated ground water is not well known. Accordingly, the objective of this research was to identify the hydrogeologic parameters that control phytoremediation effectiveness. We used a numerical ground water flow model to evaluate the effect that natural variations in hydrogeologic parameters and growing season duration have on the minimum plantation area required for capture. We found that the plantation area that was needed to completely capture a ground water contamination plume was directly proportional to aquifer horizontal hydraulic conductivity, saturated thickness, and ground water gradient. The plantation area needed for capture increased non-linearly with increasing plume width, aquifer anisotropy, and decreasing growing season duration. The plantation area needed for capture was generally insensitive to aquifer-specific yield and storativity. Steady-state simulations can be used to predict the plantation area needed for capture in many applications. A particularly important finding of this work is that evapotranspiration fluxes through plantations appropriately sized to contain the plume substantially exceeded the ground water flux through the plume itself.
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    The Journal of ‘Ground Water’: In the Beginning (2003)
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    Perspectives on Mexican Ground Water Resources (2002)
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    Injection-Extraction Treatment Well Pairs: An Alternative to Permeable Reactive Barriers (2002)
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Two of the biggest drawbacks of using permeable reactive barriers (PRBs) to treat contaminated ground water are the high capital cost of installation, particularly when the contaminated ground water is deep below ground surface, and the uncertainty of whether or not PRBs remain effective for the long time scales (e.g., decades) needed for many contaminant plumes. The use of an injection-extraction treatment well pair (IETWP) for capture and treatment of contaminated ground water can circumvent these difficulties, while still providing many of the same advantages offered by PRBs. In this paper, the hydraulics of IETWPs and PRBs are compared, focusing primarily on the width of the captured plume. It is demonstrated that IETWPs act as hydraulic barriers in a manner similar to PRBs, and that IETWPs provide excellent plume capture. A mathematical expression is presented for the plume capture width of an IETWP oriented perpendicular to the ground water flow direction in a homogeneous aquifer. Also discussed are other practical considerations that might determine whether an IETWP is better suited than a PRB for a particular contaminated site; these considerations include operating and maintenance costs, and the conditions under which an IETWP system can be used for in situ remediation.
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    Spatial and Temporal Variability of Ground Water Recharge in Central Australia: A Tracer Approach (2002)
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Two environmental tracer methods are applied to the Ti-Tree Basin in central Australia to shed light on the importance of recharge from floodouts of ephemeral rivers in this arid environment. Ground water carbon-14 concentrations from boreholes are used to estimate the average recharge rate over the interval between where the ground water sample first entered the saturated zone and the bore. Environmental chloride concentrations in ground water samples provide estimates of the recharge rate at the exact point in the landscape where the sample entered the saturated zone. The results of the two tracer approaches indicate that recharge rates around one of the rivers and an extensive flood-plain are generally higher than rates of diffuse recharge that occurs in areas of lower topographic relief. Ground water 2H/1H and 18O/16O compositions are all depleted in the heavier isotopes (δ2H = -67%0 to -50%0; 518O = -9.2%0 to -5.7%0) compared with the long-term, amount-weighted mean isotopic composition of rainfall in the area (δ2H = -33.8%0; δ18O = -6.3%0). This indicates that recharge throughout the basin occurs only after intense rainfall events of at least 150 to 200 mm/month. Finally, a recharge map is developed to highlight the spatial extent of the two recharge mechanisms. Floodout recharge to the freshest ground water (TDS 〈1000 mg/L) is ∼1.9 mm/year compared with a mean recharge rate of ∼0.2 mm/year to the remainder of the basin. These findings have important implications for management of the ground water resource.
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    GFLOW 2000: An Analytical Element Ground Water Flow Modeling System (2002)
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    Delineation of Three-Dimensional Well Capture Zones for Complex Multi-Aquifer Systems (2002)
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The delineation of well capture zones is a basic component of ground water protection. The conventional methodology for capture zone delineation is backward advective particle tracking, often applied under the assumption of a two-dimensional aquifer. The suitability of the conventional approach for complex heterogeneous multi-aquifer systems was investigated, using the Waterloo Moraine aquifer system as an example. It was found that the conventional approach produces irregular particle tracks that require judgment to interpret in a meaningful way, and it can raise questions that may affect the credibility of the capture zone delineation. As an alternative, the potentially powerful but little-used backward-in-time advective-dispersive transport approach was investigated. A key advantage of this approach is its capability to represent local heterogeneities through the dispersion term. The dispersion process has a natural smoothing effect that results in unambiguous capture zones without the need for interpretation, thus enhancing credibility. The question of capture zone validation is also addressed. The meaning of a three-dimensional capture zone is considered, and it is shown that a fully three-dimensional representation of the system is crucial for valid results. The distinction between the maximum extent capture zone and the surface capture zone is also explained. In the case of complex heterogeneous systems, advective particle tracking can be used as an initial screening tool, whereas the more realistic backward-transport modeling approach can be used for final capture-zone delineation.
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    Hydrogeology: Time for a New Beginning? (2002)
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    New Combined Log and Tracer Test Interpretation Method for Identifying Transfers in Fissured Aquifers (2002)
    Oxford, UK : Blackwell Publishing Ltd
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Tracer tests represent the most appropriate approach for assessing hydrodispersive parameters such as transversal and longitudinal dispersivities or kinematic porosity on an aquifer scale. They are generally carried out by injecting a tracer in a borehole and measuring its concentration over time in neighboring boreholes by extracted volume sampling or downhole measurements. Logging is one of the most suitable methods for evaluating fissured reservoirs. But short circuits between fractures with different hydraulic potential through boreholes induce mixing phenomena that cannot be avoided without packers. This mixing can shift the breakthrough curves deduced from the logs for each producing fracture and distort determination of their location.The method proposed in this paper aims at measuring the flow rate and the solute breakthrough for hydraulically active fractures, in open boreholes. It involves estimating a velocity profile along the borehole column by the analysis of two successive logs: a shift function according to depth is thus determined by comparison between log portions on each successive one. The velocity gradients reflect the inward or outward flow rates produced by each fracture. On the basis of these flow rates, it is possible to determine the mixing effects inside the borehole and then to plot unbiased breakthrough curves for each producing fracture.This method was applied at a granitic site in the eastern Pyrenees. In spite of some questionable limitations, the results showed that the method seems adapted to situations with many fractures. The precise hydraulic pattern which is obtained at the borehole scale is discussed in terms of a dual porosity model. Furthermore, interpretation of the breakthrough curves for fractures corrected for mixing effects revealed that Peclet numbers are strongly underestimated if this phenomenon is not considered.
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    Retardation of Organic Contaminants in Natural Fractures in Chalk (2002)
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Transport of a conservative compound and two sorbing compounds through fractured chalk was studied using flow-through columns consisting of chalk cores with a single subvertical fracture. Two types of chalk matrix were compared, an oxidized white chalk with low organic carbon content (0.2%), and a gray chalk with a higher organic carbon content (1.3%). Initial rapid breakthrough followed by a delayed approach to a relative concentration of unity for the conservative compound (2,6–difluorobenzoic acid [DFBA]) was clear evidence for diffusion into the porous chalk matrix. Matrix diffusion of DFBA was apparently much greater in the gray chalk columns than in the white chalk columns. Breakthrough curves (BTCs) of the sorbing compounds (2,4,6–tri-bromophenol [TBP] and ametryn [AME]) were retarded in all cases as compared to the conservative compound. Sorption retardation was far greater in the gray chalk as compared with the white chalk, in good agreement with results from batch sorption experiments. BTCs for the conservative compound were relatively nonhysteretic for both white and gray chalk columns. In contrast, BTCs for the sorbing compounds were hysteretic in all cases, demonstrating that sorption was not at equilibrium before desorp-tion began. These experiments suggest that on a field scale, transport of contaminants through fractures in chalk and other fractured porous media will be attenuated by diffusion and sorption into the matrix.
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    “Hydrogeological Research: Beginning of the End or End of the Beginning?” by F.W. Schwartz, and M. Ibaraki. 2001. Ground Water 39, no. 4: 492–498. (2002)
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    Ground Water Flow Analysis of a Mid-Atlantic Outer Coastal Plain Watershed, Virginia, U.S.A. (2002)
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Models for ground water flow (MODFLOW) and particle tracking (MODPATH) were used to determine ground water flow patterns, principal ground water discharge and recharge zones, and estimates of ground water travel times in an unconfined ground water system of an outer coastal plain watershed on the Delmarva Peninsula, Virginia. By coupling recharge and discharge zones within the watershed, flowpath analysis can provide a method to locate and implement specific management strategies within a watershed to reduce ground water nitrogen loading to surface water. A monitoring well network was installed in Eyreville Creek watershed, a first-order creek, to determine hydraulic conductivities and spatial and temporal variations in hydraulic heads for use in model calibration. Ground water flow patterns indicated the convergence of flow along the four surface water features of the watershed; primary discharge areas were in the noontide portions of the watershed. Ground water recharge zones corresponded to the surface water features with minimal development of a regional ground water system. Predicted ground water velocities varied between 〈 0.01 to 0.24 m/day, with elevated values associated with discharge areas and areas of convergence along surface water features. Some ground water residence times exceeded 100 years, although average residence times ranged between 16 and 21 years; approximately 95% of the ground water resource would reflect land use activities within the last 50 years.
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    Using Direct Current Resistivity Sounding and Geostatistics to Aid in Hydrogeological Studies in the Choshuichi Alluvial Fan, Taiwan (2002)
    Oxford, UK : Blackwell Publishing Ltd
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Ground water reservoirs in the Choshuichi alluvial fan, central western Taiwan, were investigated using direct-current (DC) resistivity soundings at 190 locations, combined with hydrogeological measurements from 37 wells. In addition, attempts were made to calculate aquifer transmissivity from both surface DC resistivity measurements and geostatistically derived predictions of aquifer properties.DC resistivity sounding data are highly correlated to the hydraulic parameters in the Choshuichi alluvial fan. By estimating the spatial distribution of hydraulic conductivity from the kriged well data and the cokriged thickness of the correlative aquifer from both resistivity sounding data and well information, the transmissivity of the aquifer at each location can be obtained from the product of kriged hydraulic conductivity and computed thickness of the geoelectric layer. Thus, the spatial variation of the transmissivities in the study area is obtained.Our work is more comparable to Ahmed et al. (1988) than to the work of Niwas and Singhal (1981). The first “constraint” from Niwas and Singhal's work is a result of their use of linear regression. The geostatistical approach taken here (and by Ahmed et al. [1988]) is a natural improvement on the linear regression approach.
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    Tie History of Hydrology at Stanford University (2002)
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    Natural Attenuation Reactions at a Uranium Mill Tailings Site, Western U.S.A. (2002)
    Oxford, UK : Blackwell Publishing Ltd
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper presents a modeling analysis of the geochemical evolution of a contaminated sandy aquifer at a uranium mill tailings site in the western United States. The tailings pond contains fluids having a pH of 1.5 to 3.5 and high levels of As, Be, Cd, Cr, Pb, Mo, Ni, Se, 226Ra, 228Ra, 230Th, 238U, and 234U. Seepage of tailings fluids into the aquifer has formed a low-pH ground water plume. The reclamation plan is to install a low-permeability cover on the tailings pond to stop the seepage and allow the plume to be attenuated by reactions with the aquifer matrix and flushed by uncontaminated upgradient ground water. To evaluate this reclamation scenario, ground water and sediment core samples were analyzed along one flowpath. Speciation-solubility and mass-transfer modeling revealed two sets of chemical reactions for acid seepage and flushing, respectively. The current concentrations and distribution of ground water constituents can be interpreted as being controlled by stepwise pH-buffer reactions with calcite, amorphous aluminum hydroxide, and amorphous iron hydroxides. These buffer reactions divide the aquifer into zones of near-constant pH, separated by interface zones. For the flushing stage, it is predicted that reactions with surface-bound species will dominate the reaction paths, and more pore volumes are required to neutralize the plume than predicted by models that do not consider surface reactions. Direct mineralogical and surface analysis is needed to substantiate this assertion.
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    Redox Patterns and Trace-Element Behavior in the East Midlands Triassic Sandstone Aquifer, U.K. (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 40 (2002), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Redox conditions exercise important controls on water chemistry in the red-bed Sherwood Sandstone Aquifer of the English East Midlands. A distinct redox boundary exists some 3 to 5 km downgradient of the onset of confined conditions, defined by a 300 mV drop in Eh and complete reaction of dissolved oxygen. The aerobic aquifer contains polluted water with high nitrate concentrations and organic carbon significantly above background concentrations (〉 0.2 mg/L). Concentrations of Fe, Mn, and Mo are highest in reducing ground water. As, Sb, Se, and U show a residence-time-dependent increase in aerobic ground water, but are much lower under reducing conditions. Iron oxides are believed to play a key role in determining the spatial patterns in many of these trace elements as a result of Eh- and pH-controlled sorption/desorption reactions, as well as some reductive dissolution in the confined aquifer. Fresh ground water persists in the confined aquifer to approximately 30 km downgradient of the redox boundary. However, SO4 concentrations increase progressively along the flowline as a result of the dissolution of gypsum or anhydrite. Concentrations of available organic carbon are low in ground water (1 mg/L or less) and are also likely to be limited in the sediments; conditions are insufficiently reducing for significant sulphate reduction to have taken place. Only in the extreme down-gradient (eastern) part of the aquifer do conditions become sufficiently reducing with some evidence of sulphate reduction. In this part of the aquifer, ground water is more saline (TDS values up to 10 g/L) and is believed to be composed substantially of older formation water. This has distinctive concentrations of several redox-influenced trace elements, with relatively high Fe, Mn, As, and Sb, occasional high Cr, and low Mo relative to the confined fresh ground water upgradient.
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    AUTHORS' REPLY (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2001.tb02468.x
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    Fate of the Herbicides 2,4,5-T, Atrazine, and DNOC in a Shallow, Anaerobic Aquifer Investigated by In Situ Passive Diffusive Emitters and Laboratory Batch Experiments (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The fate of the three herbicides 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), atrazine (6-chloro-N-ethyl-N′-[l-methyl-ethyl]-l,3,5-triazine-2,4-diamine), and DNOC (4,6-dinitro-2-methylphenol) in an anaerobic sandy aquifer was investigated. In the field, each of the herbicides was released simultaneously with tritiated water (HTO) as tracer in the depth interval 3 to 4 mbs (meters below surface) by use of passive diffusive emitters. Atrazine and 2,4,5-T were persistent during the approximately 18 days residence time in the aquifer. In contrast, DNOC was rapidly removed from the water phase following first-order kinetics. The removal mechanism was likely an abiotic reduction. At day 25, the first-order rate constant was 1.47 d−1, but it decreased with time and seemed to stabilize at 0.35 d−1 after 150 to 200 days.In the laboratory, batch experiments were conducted with sediments from 3 to 4 mbs and from 8 to 9 mbs. In these incubations, formation of Fe2+ and depletion of sulfate showed iron and sulfate reduction in sediment from 3 to 3.5 mbs and sulfate reduction in 3.5 to 4 mbs sediment. In sediment from 8 to 9 mbs, the dominant redox process was methane formation. In sediment from 3 to 3.5 mbs, only 27% to 52% of the 2,4,5-T remained after 196 days. 2,4,5-trichlorophenol was identified as the major metabolite. A lag period of at least 50 days was observed, and no degradation occurred in HgCl2 amended controls, verifying that the process was microbially mediated. In the other 2,4,5-T incubations and all the atrazine incubations, concentrations decreased linearly, but less than 25 % was removed within 200 to 250 days. No degradation products could be detected, and slow sorption was the likely explanation. In all the laboratory incubations DNOC was degraded, following first-order kinetics, and when normalized to the sediment/water-ratio, the field and laboratory derived rate constants compared well. The DNOC degradation in the methanogenic incubations (8 to 9 mbs) was up to 50 times faster than in the sediments from 3 to 4 mbs, likely due to the low redox potential.
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    Improved Calculations for Dewatered Cells in MODFLOW (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Use of the United States Geological Survey ground water flow model MODFLOW is often hampered by the occurrence of “dry cells.” While MODFLOW allows such cells to “rewet” in the course of a simulation, stability of the heads solution process is often problematical with rewetting functionality operative. In many cases of practical interest (particularly in mining applications), MOD-FLOW simply fails to converge. However by making a number of adjustments to the MODFLOW Block-Centered Flow package, it is possible to overcome this problem in many instances of MODFLOW deployment. These adjustments are such as to allow a layer to transmit water, albeit with a vastly reduced transmissivity, even if the water level in that layer is below its base. With these alterations MODFLOW cells can remain active even if they lie within the unsaturated zone.Testing of the code has demonstrated its ability to perform well in situations where performance of the unmodified MODFLOW is degraded by the necessity to dry and rewet cells. Comparison of heads calculated using the modified MODFLOW with those calculated using MODFLOW-SURFACT (a MODFLOW-based code developed by HydroGeoLogic Inc. that prevents the occurrence of dry cells through use of pseudo soil functions) reveals near-identical results between the two codes. Comparison with analytical solutions of water table location also reveals near coincidence. An example of one such application is presented herein.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2001.tb02474.x
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    Determination of Specific Yield for the Biscayne Aquifer with a Canal-Drawdown Test (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Data from a large-scale canal-drawdown test were used to estimate the specific yield (s) of the Biscayne Aquifer, an uncon-fined limestone aquifer in southeast Florida. The drawdown test involved dropping the water level in a canal by about 30 cm and monitoring the response of hydraulic head in the surrounding aquifer. Specific yield was determined by analyzing data from the unsteady portion of the drawdown test using an analytical stream-aquifer interaction model (Zlotnik and Huang 1999). Specific yield values computed from drawdown at individual piezometers ranged from 0.050 to 0.57, most likely indicating heterogeneity of specific yield within the aquifer (small-scale variation in hydraulic conductivity may also have contributed to the differences in sy among piezometers). A value of 0.15 (our best estimate) was computed based on all drawdown data from all piezometers.We incorporated our best estimate of specific yield into a large-scale two-dimensional numerical MODFLOW-based ground water flow model and made predictions of head during a 183–day period at four wells located 337 to 2546 m from the canal. We found good agreement between observed and predicted heads, indicating our estimate of specific yield is representative of the large portion of the Biscayne Aquifer studied here. This work represents a practical and novel approach to the determination of a key hydrogeological parameter (the storage parameter needed for simulation and calculation of transient unconfined ground water flow), at a large spatial scale (a common scale for water resource modeling), for a highly transmissive limestone aquifer (in which execution of a traditional pump test would be impractical and would likely yield ambiguous results). Accurate estimates of specific yield and other hydrogeological parameters are critical for management of water supply, Everglades environmental restoration, flood control, and other issues related to the ground water hydrology of the Biscayne Aquifer.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2001.tb02368.x
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    Hydrogeological Research: Beginning of the End or End of the Beginning? (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper uses citation data to assess whether articles published in key ground water journals such as Ground Water (GW) and Water Resources Research (WRR) are impacting research. Citation information was obtained from SCI Journal Citation Reports and The Web of Science—databases maintained by the Institute for Scientific Information (ISI). Information extracted from The Web of Science was processed further to remove corrections to papers, discussion/replies, and book reviews. Generally, there are many ground water papers published, but citations of these papers are limited. Approximately 10% to 15% of WRR articles, and 2% to 3% of GW articles attract more than 50 citations in their lifetimes. In both GW and WRR, the top 10% of papers eventually will contribute nearly half of the total yearly citations. Another emerging trend is a diminishing emphasis on citations to new work as compared to work more than 10 years in age. When articles in Ground Water or Journal of Hydrology cite papers in Water Resources Research, those papers cite work 10 or more years old half of the time. If one believes that citations are a measure of science impact, then there is cause for concern. Research is inefficient with much produced for little gain. On a typical industrial life-cycle curve, ground water research is likely ranked as mature and close to aging. At this stage, much work will have been completed and the number of truly impactful problems will have dwindled to just a few.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2001.tb02337.x
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    Ground Water/Surface Water Interactions in Lake Naivasha, Kenya, Using δ18O, δD, and 3H/3He Age-Dating (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: We have analyzed a series of ground water samples from the Lake Naivasha region, Kenya, for their helium isotopic composition. Lake Naivasha is unique among the East Africa Rift Valley lakes in that it is fresh. It has long been thought that the low salinity of this lake is due, in part, to rapid water loss from the lake into the local ground water system. Our results show that the Olkaria geothermal waters, south of the lake, are devoid of tritium and, thus, are more than 50 years old. An important implication of these results is that even if Olkaria geothermal reservoir water originated from Lake Naivasha, it has been underground for a long time, (〉50 years) and is not derived from present-day Lake Naivasha water. This flow time is of the same order of magnitude as conservative major solutes, such as chloride, as determined through residence time calculations. On the north side of Lake Naivasha, deep wells (91 m) have water ∼ 20 years old. Water from these wells has stable isotopic values resembling those of nearby rivers, and high-elevation eastern Rift water. This indicates that this water recharges from rains from high eastern Rift Valley escarpments. Many of the shallow wells on the south side of the lake have 3H/3He ages between four and 17 years. The young ages and the δ18 O-enriched signature of the water from these wells indicate that they are recharged by a mixture of water from the lake, Rift flanks, and water from deep pumping wells that is recharged during irrigation. Water mixing ratio calculations using δ18O and δD isotopes show that about 50% to 70% of the southern ground water system is derived from the lake, while the Olkaria geothermal reservoir water shows that 40% to 50% of this water is originally lake water. Calculated mean recharge rates range from 0.10 to 1.59 m/yr with a mean of 0.52±0.40 m/yr. Estimated horizontal velocity from 3H/3He age dating between Lake Naivasha and a well about 3 km to the south is 75 m/yr, giving average horizontal hydraulic conductivity of 6 m/day.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2001.tb02341.x
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    Exploitation of High-Yields in Hard-Rock Aquifers: Downscaling Methodology Combining GIS and Multicriteria Analysis to Delineate Field Prospecting Zones (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Based on research work in the Truyàre River catchment of the Massif Central (Lozàre Department, France), a methodology has been developed for delineating favorable prospecting zones of a few square kilometers within basement areas of several hundred, if not thousand, square kilometers for the purpose of siting high-yield water wells. The methodology adopts a functional approach to hard-rock aquifers using a conceptual model of the aquifer structure and of the functioning of the main aquifer compartments: the alterites (weathered and decayed rock), the underlying weathered-fissured zone, and the fractured bedrock. It involves an economically feasible method of mapping the thickness and spatial distribution of the alterites and the weathered-fissured zone, on which the long-term exploitation of the water resource chiefly depends. This method is used for the first time in hydrogeology.The potential ground water resources were mapped by GIS multicriteria analysis using parameters characterizing the structure and functioning of the aquifer, i.e., lithology and hydrogeological properties of the substratum, nature and thickness of the alterites and weathered-fissured zone, depth of the water table, slope, fracture networks and present-day tectonic stresses, and forecasted ground water quality.The methodology involves a coherent process of downscaling that, through applying methods that are increasingly precise but also increasingly costly, enables the selection of sites with diminishing surface areas as the work advances. The resulting documents are used for ground water exploration, although they can also be applied to the broader domain of land-use management.
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    Evaluation of Recharge in a Small Temperate Catchment Using Natural and Applied δ18O Profiles in the Unsaturated Zone (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A water balance study was used for determining recharge rate and mechanisms in the Enler Catchment, Northern Ireland. Here spatially limited data for the water balance resulted in varied calculation of the annual and monthly net infiltration rate. This paper outlines a method whereby high-resolution soil profiles (1 to 2 cm) were obtained from field cores in the upper 2 m of the unsaturated zone using δ18O of water. These profiles show changes in isotopic composition that range from individual rainfall events to annually integrated cycles of rainfall. Recharge rates were calculated from stable isotope profiles for each of the four main soil types in the study catchment and summed over each area resulting in an average recharge in the range 55 to 70 mm/a, which is comparable with previous findings. Applied isotopic tracer tests were also conducted to evaluate the extent of preferential flow through the two main soil types in the catchment. Rates of water movement found from these experiments show good agreement with natural isotopic profiles; however, evidence suggests that preferential flow is not the dominant process controlling water movement in this catchment. This type of data provides valuable information about recharge rates and mechanisms and may facilitate better prediction of contaminant transport pathways in the vadose zone.
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    In Situ Determination of Subsurface Microbial Enzyme Kinetics (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The single-well, push-pull test has been used in previous field studies to measure in situ zero- and first-order rates for aerobic and anaerobic microbial respiration in the saturated zone. In this paper we demonstrate that the test can also be used to obtain more generalized descriptions of the kinetics of microbially mediated enzymatic reactions. Laboratory and field tests were performed with the model enzyme substrate p-nitrophenyl-β-D-glucopyranoside (PNG). During a push-pull test, injected PNG is hydrolyzed in situ to p-nitrophenol (PNP); the rate of PNP production is taken as a measure of the β-glucosidase activity expressed by indigenous microorganisms. Laboratory tests were performed in physical aquifer models packed with natural aquifer sediment; field tests were performed in a shallow unconfined alluvial aquifer at a petroleum contaminated site. The laboratory and field tests demonstrate that it is possible to compute the in situ rate of PNP production as a function of PNG concentration using only data from a single push-pull test. These data can then be used to estimate the Michaelis-Menton kinetic parameters Vmax and Km for the hydrolysis reaction. This approach potentially extends the range of applicability of the push-pull test approach for use in determining kinetic parameters for a wide range of microbial processes in situ. These could include the broad class of substituted nitrophenyl substrates used to assay other enzyme systems, as well as microbially mediated redox reactions that occur during contaminant transformations.
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    Analytical Procedure for Simultaneous Use of Seven Fluorobenzoates in Multitracer Tests (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: An analytical procedure allowing simultaneous use of seven fluorobenzoate (FBA) isomers was developed and examined through column and field tracer experiments. The analytical method, based on high performance liquid chromatography (HPLC), included a reverse-phase separation method. This method was found to be very efficient for the FBA analysis, allowing accurate determination of seven FBAs in a single HPLC run, while avoiding analytical interference of other natural water constituents or pollutants. Consequently, this separation method allows the simultaneous use of seven isomers in multitracer tests in highly saline or contaminated environments. The mobility properties of the FBAs were examined in percolation experiments through a column filled with a mixture of crushed chalk and common fracture filling and coating material. The FBAs behaved conservatively as compared to bromid. All seven FBA isomers were successfully used in a multitracer test in a field percolation experiment designed to identify flowpath along a fracture plane.
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    A Modification to the Bouwer and Rice Method of Slug-Test Analysis for Large-Diameter, Hand-Dug Wells (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 39 (2001), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The Bouwer and Rice method of estimating the saturated hydraulic conductivity (Ks) from slug-test data was evaluated for geometries typical of hand-dug wells. A two-dimensional, radially symmetric and variably saturated, ground water transport model was used to simulate well recovery given a range of well and aquifer geometries and unsaturated soil properties, the latter in terms of the van Genuchten parameters. The standard Bouwer and Rice method, when applied to the modeled recharge rates, underestimated Ks by factors ranging from 1.3 to 5.6, depending on the well geometry and the soil type. The Bouwer and Rice analytical solution was modified to better explain the recovery rates as predicted by the numerical model, which revealed a significant dependence on the unsaturated soil for the shallow and wide geometries that are typical of traditional wells. The modification introduces a new parameter to the Bouwer and Rice analysis that is a measure of soil capillarity which improves the accuracy of Ks estimates by tenfold for the geometries tested.
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    On the Estimation of Stream Flow Depletion Parameters by Drawdown Analysis (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Hunt (1999) derived a model for computation of stream flow depletion caused by pumping from a well near a stream that does not fully penetrate the aquifer. The model input includes the transmissivity (T) and the storativity (S) of the aquifer and the conductance of the stream bed (λ). We study the experimental and hydrogeological conditions for which drawdown analysis can be expected to produce T, S, and λ estimates that can be used in the model of Hunt (1999) to predict depletion with a specified accuracy. The study is conducted by using a combination of sensitivity analysis and uncertainty analysis. The analysis shows that it is always important to have an accurate estimate of λ in order to accurately predict depletion. Recommendations for the design of a pumping test near a stream are given to achieve this. The pumping well should be located close to the stream. Accurate drawdown measurements should be made both near the pumping well and near the stream, and the measurements should be used simultaneously to estimate T, S, and λ. The duration of the pumping test should be relatively long in order to obtain an accurate estimate of λ. A methodology is proposed in which a desired accuracy of either the estimates of T, S, and λ, or the stream flow predicted from these estimates, is used to estimate the duration of the pumping test. Some examples indicate that in many cases the duration of the test should be from an hour to one or two months. However, if S is large (∼10−1) and λ is small (10-7 m/s) then the duration should be from several months to years. This would be expensive and not practical, so other methods should be used to estimate λ in this situation.
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    Recharge and Preservation of Laurentide Glacial Melt Water in the Canadian Shield (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Ground water inflows to drifts ranging from 700 to 1615 m below ground surface at the Con Mine, Yellowknife, Northwest Territories, Canada, were used to study deep hydrogeological flow regimes in Shield terrain. Salinity trends are due to mixing between low-TDS ground water and deep Ca(Na)-C1 brines (〉290 g/L) likely derived from Devonian sea water. C1-−δ18O relationships demonstrate that all inflows are a mixture of three distinct components: modern meteoric ground water (δ18O ∼−18.9 ± 0.1%o), brine (δ18O ∼−10%o), and an isotopically depleted water (δ18O ∼−28%o). The origin of this third endmember is attributed to glacial melt water injected into the subsurface during ablation of the Laurentide Ice Sheet at ca. 10 ka. A mechanism is proposed where high hydrostatic pressure in the ablation zone imposes strong downward gradients beneath the ice sheet margin. Numerical simulation with the SWIFT II finite-difference code recreates the observed salinity gradients within a modeled 50-year interval, corresponding with the rate of retreat of the ice sheet across the landscape at this time. The persistence of this melt water in the subsurface for some 10,000 years following retreat of the ice and decay of the steep hydraulic gradients highlights the importance of gradient, in addition to permeability, as a major control on ground water flow and transport in deep crystalline settings.
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    Partitioning Tracer Tests for Evaluating Remediation Performance (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Partitioning tracer tests (PTTs) are being used in environmental systems for the detection and estimation of nonaqueous phase liquid (NAPL) saturations in contaminated aquifers. A series of such studies was recently conducted at Hill Air Force Base, Utah, in two hydraulically isolated test cells of an aquifer contaminated by light nonaqueous phase liquids (LNAPL). These experiments were performed before and after two remediation efforts, a complexing sugar flush (CSF) and a recirculating in-well aeration (IWA) system. The breakthrough curves obtained from monitoring tracer concentrations in the extraction wells indicated the presence of an immiscible phase, and the LNAPL saturation values determined from the pre- and post-PTTs allowed the estimation of remediation efficiencies for both test cells. These remediation efficiencies, a removal of 43% of the LNAPL for the CSF and an increase of 32% for the IWA system, are consistent with data obtained from cores collected from within the experiment zones. The apparent increase in contamination for the IWA cell is likely due to a significant change in the LNAPL distribution caused by the flow system associated with the IWA technology. Several factors influenced the interpretation of the PTT data. Physical heterogeneities at the site caused significant tailing of the tracer concentrations and required the use of a simple extrapolation technique to account for the concentrations below analytical quantification limits. Degradation affected selected nonreactive and reactive tracers, causing the overestimation and underestimation of LNAPL saturations, respectively.
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    Risk-Based Drinking Water Standards: A Challenge for the Hydrologie Community (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb00234.x
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    Author’ Reply (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb00238.x
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    A Field Technique for Estimating Aquifer Parameters Using Flow Log Data (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A numerical model is used to predict flow along intervals between producing zones in open boreholes for comparison with measurements of borehole flow. The model gives flow under quasi-steady conditions as a function of the transmissivity and hydraulic head in an arbitrary number of zones communicating with each other along open boreholes. The theory shows that the amount of inflow to or outflow from the borehole under any one flow condition may not indicate relative zone transmissivity. A unique inversion for both hydraulic-head and transmissivity values is possible if flow is measured under two different conditions such as ambient and quasi-steady pumping, and if the difference in open-borehole water level between the two flow conditions is measured. The technique is shown to give useful estimates of water levels and transmissivities of two or more water-producing zones intersecting a single interval of open borehole under typical field conditions. Although the modeling technique involves some approximation, the principle limit on the accuracy of the method under field conditions is the measurement error in the flow log data. Flow measurements and pumping conditions are usually adjusted so that transmissivity estimates are most accurate for the most transmissive zones, and relative measurement error is proportionately larger for less transmissive zones. The most effective general application of the borehole-flow model results when the data are fit to models that systematically include more production zones of progressively smaller transmissivity values until model results show that all accuracy in the data set is exhausted.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb00243.x
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    Type-Curve Interpretation of Multirate Single-Hole Pneumatic Injection Tests in Unsaturated Fractured Rock (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: More than 270 multirate single-hole pneumatic injection tests were conducted by Guzman et al. (1996) within six shallow vertical and inclined boreholes in unsaturated fractured tuff at the Apache Leap Research Site (ALRS) near Superor, Arizona. The authors used steady-state formulae to obtain air permeability values for the rock based solely on late pressure data from each test. We developed pressure and pressure-derivative type-curves for the interpretation of transient data from these tests, which account for storage in the test interval due to air compressibility and skin effect due to damage to the surrounding rock. We applied our type-curves to pressure data from more than 40 of the tests to obtain information about air permeability, skin factor, phenomenology, and dimensionality of the flow regime on a nominal scale of 1 m in the immediate vicinity of each test interval. Our air permeabilities agreed well with those determined previously by means of steady- state formulae but correlated poorly with fracture density data. Nonlinear effects due to air compressibility were pronounced, but skin effect was generally small or nonexistent. Nonlinear two-phase flow and inertia were evident but did not have a significant impact on type-curve interpretation of the test data. Most of these data fit a continuum model of spherical airflow around the test interval, but a few fit a continuum model of radial flow or suggest the dominance of a single fracture. We take this to imply that fractures at the site are pneumatically well connected and can, for the most part, be treated as a porous continuum when analyzing airflow on scales of 1 m or more. This is supported by the finding that 1 m scale air permeability data from single-hole tests at the ALRS are amenable to geostatistical analysis (Chen et al. 2000), which views them as a sample from a random field defined over a continuum. That the same holds true on larger scale is indicated by our ability to interpret cross-hole pneumatic injection tests at the site by means of type-curves and inverse methods (Illman et al. 1998), which treat the entire rock mass as a porous continuum.
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    Evaluation of Ground-Penetrating Radar to Detect Free-Phase Hydrocarbons in Fractured Rocks—Results of Numerical Modeling and Physical Experiments (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: The suitability of common-offset ground-penetrating radar (GPR) to detect free-phase hydrocarbons in bedrock fractures was evaluated using numerical modeling and physical experiments. The results of one- and two-dimensional numerical modeling at 100 megahertz indicate that GPR reflection amplitudes are relatively insensitive to fracture apertures ranging from 1 to 4 mm. The numerical modeling and physical experiments indicate that differences in the fluids that fill fractures significantly affect the amplitude and the polarity of electromagnetic waves reflected by subhorizontal fractures. Air-filled and hydrocarbon-filled fractures generate low-amplitude reflections that are in-phase with the transmitted pulse. Water-filled fractures create reflections with greater amplitude and opposite polarity than those reflections created by air-filled or hydrocarbon-filled fractures.The results from the numerical modeling and physical experiments demonstrate it is possible to distinguish water-filled fracture reflections from air- or hydrocarbon-filled fracture reflections, nevertheless subsurface heterogeneity, antenna coupling changes, and other sources of noise will likely make it difficult to observe these changes in GPR field data. This indicates that the routine application of common-offset GPR reflection methods for detection of hydrocarbon-filled fractures will be problematic. Ideal cases will require appropriately processed, high-quality GPR data, ground-truth information, and detailed knowledge of subsurface physical properties.Conversely, the sensitivity of GPR methods to changes in subsurface physical properties as demonstrated by the numerical and experimental results suggests the potential of using GPR methods as a monitoring tool. GPR methods may be suited for monitoring pumping and tracer tests, changes in site hydrologic conditions, and remediation activities.
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    Letter to the Editor (2000)
    Oxford, UK : Blackwell Publishing Ltd
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb02698.x
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    Embedded Sidewall Samplers and Sensors to Monitor the Subsurface (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Subsurface properties such as moisture content, hydraulic head, or chemical composition may vary markedly over short vertical distances in soil and ground water systems, but conventional samplers and sensors placed in vertical boreholes are often unable to resolve these variations. To improve the resolution of subsurface monitoring, we have developed a method for accessing the side-wall of a vertical or angled borehole at many discrete intervals along the entire length of the borehole. The method uses an access device that embeds sensors or sediment samplers laterally through the borehole sidewall into the undisturbed formation to distances slightly less than the diameter of the borehole. The access device can also obtain a core sample up to 15 cm long and 4 cm in diameter, and then insert a permeable sleeve for extracting fluid samples (water, gas, nonaqueous phase liquids). The system has been used under field conditions in the United States and Denmark to place electrodes capable of measuring water content (using time domain reflectometry [TDR] waveguides), Eh (using platinum electrodes), or electrical resistivity (using a four-conductor electrode). At one site, as many as 22 water samplers and 19 resistivity electrodes were installed in a single borehole at vertical spacings as close as 7 cm. This approach was used to install horizontally oriented TDR waveguides at depths greater than 10 m, thereby extending the TDR technique to the study of deep vadose zones. Other applications include measurement of in situ Eh at a site where strong chemical oxidants were injected to remediate sediments contaminated by organic chemicals.
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    Long-Term Performance of In Situ Reactive Barriers for Nitrate Remediation (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Nitrate is now recognized as a widespread ground water contaminant, which has led to increased efforts to control and mitigate its impacts. This study reports on the long-term performance of four pilot-scale field trials in which reactive porous barriers were used to provide passive in situ treatment of nitrate in ground water. At two of the sites (Killarney and Borden), the reactive barriers were installed as horizontal layers underneath septic system infiltration beds; at a third site (Long Point), a barrier was installed as a vertical wall intercepting a horizontally migrating septic system plume; and at the fourth site (North Campus), a barrier was installed as a containerized subsurface reactor treating farm field drainage water. The reactive media consisted of 15% to 100% by volume of waste cellulose solids (wood mulch, sawdust, leaf compost), which provided a carbon source for heterotrophic denitrification. The field trials have been in semicontinuous operation for six to seven years at hydraulic loading rates ranging from six to 2000 L/day. Trials have been successful in attenuating influent NO3- (or NO3-+ NH4+ at Borden) concentrations averaging from 4.8 mg/L N at North Campus to 57 mg/L N at Killarney, by amounts averaging 80% at Killarney, 74% at Borden, 91 % at Long Point, and 58% at North Campus. Nitrate consumption rates were temperature dependent and ranged from 0.7 to 32 mg L N/day, but did not deteriorate over the monitoring period. Furthermore, mass-balance calculations indicate that carbon consumption by heterotrophic denitrification has so far used only about 2% to 3% of the initial carbon mass in each case. Results suggest that such barriers should be capable of providing NO3- treatment for at least a decade or longer without carbon replenishment.Reactive barriers have now been used to treat nitrate contamination from a variety of sources including septic systems, agricultural runoff, landfill leachate, and industrial operations. This demonstration of successful long-term operation should allow this technology to become more widely considered for nitrate remediation, particularly at sites where passive treatment requiring a minimum of maintenance is desired.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb02704.x
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    Integrating Borehole Logs and Aquifer Tests in Aquifer Characterization (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Integration of lithologic logs, geophysical logs, and hydraulic tests is critical in characterizing heterogeneous aquifers. Typically only a limited number of aquifer tests can be performed, and these need to be designed to provide hydraulic properties for the principle aquifers in the system. This study describes the integration of logs and aquifer tests in the development of a hydrostratigraphic model for the surficial aquifer system in and around Big Cypress National Preserve in eastern Collier County, Florida. Borehole flowmeter tests provide qualitative permeability profiles in most of 26 boreholes drilled in the study area. Flow logs indicate the depth of transmissive units, which are correlated across the study area. Comparison to published studies in adjacent areas indicates that the main limestone aquifer of the Tamiami Formation in the study area corresponds with the gray limestone aquifer in western Dade County and the water table and lower Tamiami Aquifer in western Collier County. Four strategically located, multiwell aquifer tests are used to quantify the qualitative permeability profiles provided by the flowmeter log analysis. The hydrostratigraphic model based on these results defines the main aquifer in the central part of the study area as unconfined to semiconfined with a transmissivity as high as 30,000 m2/day. The aquifer decreases in transmissivity to less than 10,000 m2/day in some parts of western Collier County, and becomes confined to the east and northeast of the study area, where transmissivity decreases to below 5000 m2/day.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb02707.x
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    Pesticides in Ground Water of the United States, 1992–1996 (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: During the first cycle of the National Water Quality Assessment (1992–1996), ground water in 20 of the nation's major hydro-logic basins was analyzed for 90 pesticide compounds (pesticides and degradates). One or more of the pesticide compounds examined were detected at 48.4% of the 2485 ground water sites sampled. However, approximately 70% of the sites where pesticides were detected, two or more pesticide compounds analyzed were present–documenting the prevalence of pesticide mixtures in ground water. The pesticide concentrations encountered were generally low, with the median total concentration (summation of concentrations for the 90 pesticide compounds) being 0.046 μg/L. Pesticides were commonly detected in shallow ground water beneath both agricultural (60.4%) and urban (48.5%) areas. This is an important finding because, although agricultural activities have long been associated with pesticide contamination, urban areas have only recently been recognized as a potential source of these types of compounds. Pesticides with higher frequencies of detection were generally those with more extensive use, greater environmental persistence, and greater mobility in ground water (lower soil-water partition coefficients).
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb00684.x
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    Reducing the Influence of Skin Effects on Hydraulic Conductivity Determinations in Multilevel Samplers Installed with Direct Push Methods (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Field tests were conducted to investigate skin effects in multilevel ground water samplers installed with direct push methods. Tests consisted of determining hydraulic conductivity values using slug tests in five multilevel samplers before, during, and after development. Development was conducted using a minisurge block tool designed for this study. Post-development hydraulic conductivity values were found to be 3.2 to 9.6 times greater than predevelopment values. The largest differences were observed in multilevel samplers positioned in low permeable materials that were installed in preprobed holes advanced by hydraulic hammering and pushing as opposed to probes situated in higher permeable materials that were installed in cored holes. The presence and magnitude of the skin effects, as well as the reduction of these effects by rigorous development, were confirmed through comparisons with steady-state pumping tests conducted in multilevel samplers and previously conducted slug tests in conventional monitoring wells. These results indicate the need for rigorous development prior to hydraulic conductivity testing in ground water samplers installed with direct push methods.
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    Struggling with the Meaning(s) and Measures of “Success” (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb02696.x
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    Software Spotlight (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb02699.x
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    Utility of Simple Models for Capture Zone Delineation in Heterogeneous Unconfined Aquifers (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Monte Carlo simulation is used to examine the utility of simple (homogeneous/isotropic) models for the delineation of wellhead protection areas (WHPAs) in heterogeneous, statistically anisotropic, unconfined aquifers. Capture zone geometry is investigated under two hydrologic conditions: regional gradient negligible compared to pumping and significant regional gradient compared to the local gradient due to pumping. Variability of capture zone geometry is quantified in terms of simple measurements (maximum transport distance and maximum width of the capture zone) and the probability of inclusion in the capture zone of a series of hypothetical contaminant source locations. These results indicate that substantial uncertainty exists in the delineation of a wellhead capture zone. This uncertainty is related, principally, to flow that occurs along preferential pathways associated with zones of high hydraulic conductivity. It is suggested that these uncertainties can be accommodated in one of three fashions depending on the value of land, the benefit of wellhead protection, and the availability of funds to perform more thorough field assessment. The first option is to modify the estimated capture zone by a factor of safety. In the absence of significant regional flow, a factor of safety of approximately three applied to the calculated fixed radius estimate of the capture zone appears to be sufficient for the conditions simulated in this project. In the case of a capture zone within a significant regional gradient, uncertainty in the location of the real capture zone will require safety factors on the width of the estimated capture zone on the order of 30, with a safety factor of approximately three in the longitudinal direction. The second option reduces these factors of safety by increasing the risk that the estimated capture zone will not cover the entire area of the real capture zone. Work available in the literature provides insight into the trade-off between the size of the estimated capture zone and the risk endured. The third option is to reduce uncertainty in the vicinity of a wellhead through additional expenditure to allow the application of classic hydrologic techniques involving conditioning or inverse modeling.
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    Effects of Heterogeneity in Aquifer Permeability and Biomass on Biodegradation Rate Calculations—Results from Numerical Simulations (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Numerical simulations were used to examine the effects of heterogeneity in hydraulic conductivity (K) and intrinsic biodegradation rate on the accuracy of contaminant plume-scale biodegradation rates obtained from field data. The simulations were based on a steady-state BTEX contaminant plume undergoing biodegradation under sulfate-reducing conditions, with the electron acceptor in excess. Biomass was either uniform or correlated with K to model spatially variable intrinsic biodegradation rates. A hydraulic conductivity data set from an alluvial aquifer was used to generate three sets of 10 realizations with different degrees of heterogeneity, and contaminant transport with biodegradation was simulated with BIOMOC. Biodegradation rates were calculated from the steady-state contaminant plumes using decrease in concentration with distance downgradient and a single flow velocity estimate, as is commonly done in site characterization to support the interpretation of natural attenuation. The observed rates were found to underestimate the actual rate specified in the heterogeneous model in all cases. The discrepancy between the observed rate and the “true” rate depended on the ground water flow velocity estimate, and increased with increasing heterogeneity in the aquifer. For a lognormal K distribution with variance of 0.46, the estimate was no more than a factor of 1.4 slower than the true rate. For an aquifer with 20% silt/clay lenses, the rate estimate was as much as nine times slower than the true rate. Homogeneous-permeability, uniform-degradation rate simulations were used to generate predictions of remediation time with the rates estimated from the heterogeneous models. The homogeneous models generally overestimated the extent of remediation or underestimated remediation time, due to delayed degradation of contaminants in the low-K areas. Results suggest that aquifer characterization for natural attenuation at contaminated sites should include assessment of the presence and extent of, and contaminant concentrations in, low-permeability areas of an aquifer.
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    Hydraulic Conductivities of Low Permeability Sediments Inferred from a Triple Pumping Test and Observed Vertical Gradients (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Knowing vertical conductivities of thick aquitards is important for simulating regional or local ground water flow. These hydraulic parameters are best determined by calibration of these models. Collection of reliable data from heavily pumped ground water reservoirs can be problematic. Another way to infer these hydraulic parameters is the simultaneous interpretation of different parts of a multiple pumping test using an inverse numerical model. Here, the drawdowns observed in the indirectly pumped aquifers allow us to deduce the vertical conductivities of the aquitards with an equivalent accuracy as the horizontal conductivities of the aquifers. When the hydraulic resistances of the aquitards are too large, it becomes impossible to induce observable drawdowns in the indirectly pumped aquifers, and the inverse model loses valuable input data. Observing vertical gradients in and over the aquitards in case of important vertical flow can make up for this loss. These data allow us to estimate the specific discharges through the successive parts of the aquitard and hence their hydraulic resistances. This useful information allows us to consider all these hydraulic resistances in one group of hydraulic parameters during the simultaneous interpretation of the multiple pumping test using an inverse numerical model. As this procedure reduces the number of identified parameter groups, it enhances their reliability. In this paper it is demonstrated how this reliability can be deduced from a number of statistical parameters that can also be used in the collinear diagnosis. The proposed interpretation procedure is demonstrated on a triple pumping test performed in and around the most important aquitard in Flanders, Belgium. The obtained results should first be integrated in a local ground water flow model. By the performance of a number of such integrated hydrogeological studies, the lateral change in the hydraulic properties of this aquitard can be evaluated.
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    Impacts of Unsaturated Zone Properties on Oxygen Transport and Aquifer Reaeration (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This study investigated the unsaturated zone properties that affect ground water reaeration (i.e., the diffusive flux of oxygen through the unsaturated zone and into an aquifer system). Laboratory column experiments were undertaken to quantify oxygen flux into anaerobic ground water as a function of soil type, soil water content, soil oxygen demand, and unsaturated zone thickness. Soils used in these studies included coarse sand, sand, loamy fine sand, fine sandy loam, silt, silty clay loam, bentonite, kaolin, and peat. The results showed that reaeration flux rates ranging from 11,000 to 12,000 mg/m2-day were possible under conditions typical of the natural environment. Soil water content provided the greatest resistance to oxygen transport in the unsaturated zone while the remaining factors of soil type, soil oxygen demand, and unsaturated zone thickness did not significantly inhibit reaeration flux into ground water. An unsaturated zone transport model based on Fick's second law and gas-liquid interfacial mass transport was developed and showed good agreement with the experimental results derived from the column studies. The results of this study suggest that unsaturated zone reaeration of anaerobic ground water may be a contributing factor in controlling the steady–state size and shape of hydrocarbon plumes and incorporating reaeration into ground water models—based on unsaturated zone properties—may allow for a more accurate representation of bioattenuation reactions taking place in subsurface environments.
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    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb02714.x
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    Book Reviews (2000)
    Oxford, UK : Blackwell Publishing Ltd
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Book reviewed in this article:“Natural Attenuation of Fuels and Chlorinated Solvents in the Subsurface” by Todd H. Wiedemeier, Hanadi S. Rifai, Charles J. Newell, and John T. Wilson Reviewed by Eric Nichols.
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    Ownership of Mine-Tunnel Discharge (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Water discharging from numerous tunnels constructed during mining in the Wasatch Mountains near Salt Lake City, Utah, flows into nearby creeks. Disputes over ownership of water feeding the creeks have resulted in extensive litigation. In the course of a legal dispute over ownership of outflow from the Kentucky-Utah (K-U) Tunnel we evaluated the patterns and rates of ground water flow using an integrated study of the geology, chemistry, isotopes, and chlorofluorohydrocarbon (CFC) composition of the water. A sequence of sedimentary rocks with a range of hydraulic conductivity values has been folded, faulted, intruded by igneous rocks, and then eroded to create the rough topography of the Wasatch Mountains. The similarity of composition among tunnel discharge, springs, and base flow in the creek indicates that the creek is fed by ground water circulating in local, shallow flow systems. Results of numerical simulations of ground water flow indicate that the K-U Tunnel likely intercepts ground water that, in the absence of the tunnel, would ultimately flow in the subsurface to Big Cottonwood Creek. CFC and tritium contents of the water indicate flow weighted average ground water travel times range from four to 23 years and support our conclusion that water discharging from the tunnel is moving within a shallow ground water flow system. Despite sparse data, the scientific understanding was deemed sufficient for the judge to rule that owners of the surface water also own the tunnel discharge because, in the absence of the tunnel, this water would supply the stream.
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    A Tracer Method to Determine Hydraulic Conductivity and Effective Porosity of Saturated Clays Under Low Gradients (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
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    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Based on the column tracer test, we developed a research method to determine the hydraulic conductivity and effective porosity of saturated clays under low hydraulic gradients or small flow rates. Derived from Darcy's law and the solute transport equation, this method evaluates the hydraulic conductivity through measuring solute concentrations rather than by measuring flow rates. And the effective porosity is determined by applying an analytical solution of the one-dimensional uniform flow equation.Two types of experimental data drawn from a review of the literature and four sorts of accuracy test data carried out in the laboratory are used to examine the proposed method. The reproducibilities of accuracy tests for hydraulic conductivity determination indicate a consistency within a 5.5% error margin. The experimental results further indicate that hydraulic conductivities determined using the tracer method are more precise than those from the conventional flowmeter method. In addition, with the assistance of the proposed tracer method, we argue that the effective porosities may be overestimated as shown in the drawn example cases due to mistaking total pore volumes as the effective pores. The results of the accuracy tests further indicate that the effective porosities of saturated clay specimens are significantly smaller than the total porosities, at least when the samples are allowed to swell freely.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2000.tb00244.x
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