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When it comes to water resources management, it is critical to understand the factors that affect baseflow processes. Declines in baseflow due to increased use of the groundwater from unconfined aquifers is well documented, but that is not the case for confined aquifers. Furthermore, since the groundwater basin size and shape can be different than the surface water basin, the use of the surface basin to determine well withdrawal rates can affect baseflow and be problematic. This study used the variables determined to be related to baseflow variability (precipitation, temperature, drainage class, available storage, land use, and slope) and the withdrawal rates of wells located within the study basins to create regression models for the state of Wisconsin, United States. We find that: (1) precipitation and temperature variable are significant in explaining the temporal variability of baseflow, whereas land cover variables are important when the temporal variability is not considered; (2) evaporation and soil drainage are important in basins over unconfined aquifers, whereas precipitation the most significant over confined aquifers; (3) whether to use surface water or groundwater divides to delineate basins matters in particular conditions, and (4) groundwater withdrawal rates do not significantly affect baseflow when using statistical analysis. Therefore, analyzing baseflow should be supplemented by a process‐based model for the effects of groundwater withdrawals. [ABSTRACT FROM AUTHOR]

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Hydraulic Fracturing, known like Fracking, is being considered around the world as a potential method in the hydrocarbons extraction given the increase of production in USA and Canada during the last years with its implementation. The most criticized feature of the technique of hydraulic fracturing is the contamination of underground waters by fluids connected through the generated and/or pre-existing fractures. This work evaluates the viability of hydraulic fracturing in Colombian territory based in the study of the analogue models, considering the elastic properties of the reservoir rocks using gelatin, sand and clay that apply scaled pressure (lithostatic pressure to scale). The gelatin is used to simulate the source and reservoir zone, the clay will simulate one seal and the sand will simulate reservoir rocks of underground water. As a result seven different models were generated. There were simulated as 1) the anisotropy presence, 2) the rock seal presence, and 3) the injection groove of fluids in the pipeline. The completed models show that the required distance between the unconventional reservoir and underground waters to avoid contamination by fluids is ~200 m, also between the hydraulic fracturing point and the faults that connect with the shallows area is ~350 m, and it is suggested to study in detail the permeability of both: nearby faults and the rock seal. Two Colombian basins (Middle Magdalena Valley and Llanos) were taken as the main base to analyze the assessment of hydraulic fracturing according to the previously mentioned results, concluding that it is viable particularly in areas like Llanos Basin and with some precautions in similar zones to Middle Magdalena Valley Basin. [ABSTRACT FROM AUTHOR]

Similar to fracking, the development of tar sand mining in the U.S. has moved faster than understanding of potential water quality impacts. Potential water quality impacts of tar sand mining, processing, and disposal to springs in canyons incised approximately 200 m into the Tavaputs Plateau, at the Uinta Basin southern rim, Utah, USA, were evaluated by hydrogeochemical sampling to determine potential sources of recharge, and chemical thermodynamic estimations to determine potential changes in transfer of bitumen compounds to water. Because the ridgetops in an area of the Tavaputs Plateau named PR Spring are starting to be developed for their tar sand resource, there is concern for potential hydrologic connection between these ridgetops and perennial springs in adjacent canyons on which depend ranching families, livestock, wildlife and recreationalists. Samples were collected from perennial springs to examine possible progression with elevation of parameters such as temperature, specific conductance, pH, dissolved oxygen, isotopic tracers of phase change, water-rock interaction, and age since recharge. The groundwater age dates indicate that the springs are recharged locally. The progression of hydrogeochemical parameters with elevation, in combination with the relatively short groundwater residence times, indicate that the recharge zone for these springs includes the surrounding ridges, and thereby suggests a hydrologic connection between the mining, processing, disposal area and the springs. Estimations based on chemical thermodynamic approaches indicate that bitumen compounds will have greatly enhanced solubility in water that comes into contact with the residual bitumen–solvent mixture in disposed tailings relative to water that currently comes into contact with natural tar. [ABSTRACT FROM AUTHOR]

Transboundary aquifers found along the 2,000 mile-long border between Mexico and the United States are not governed by any treaty. Yet, these aquifers are the primary source of water for many of the twelve million people who live in this parched region. The region's groundwater, however, is being overexploited and contaminated, which is threatening the very life that it currently sustains. As populations continue to expand and current rates of haphazard development persist, the absence of an agreement for the management and allocation of this critical resource could lead to bi-national economic, social and environmental tragedies. This study reviews groundwater resources along the Mexico-United States border and considers the obstacles to the development of an international agreement. It also looks at existing sources of law at the local, regional, national, and international levels of governance. The article offers recommendations that may lead to an amicable arrangement between the two nations. [ABSTRACT FROM AUTHOR]

Ocean surges onto coastal lowlands caused by tropical and extra tropical storms, tsunamis, and sea level rise affect all coastal lowlands and present a threat to drinking water resources of many coastal residents. In 2005, two such storms, Hurricanes Katrina and Rita struck the Gulf Coast of the US. Since September 2005, water samples have been collected from water wells impacted by the hurricanes’ storm surges along the north shore of Lake Pontchartrain in southeastern Louisiana. The private and public water wells tested were submerged by 0.6–4.5 m of surging saltwater for several hours. The wells’ casing and/or the associated plumbing were severely damaged. Water samples were collected to determine if storm surge water inundated the well casing and, if so, its effect on water quality within the shallow aquifers of the Southern Hills Aquifer System. In addition, the samples were used to determine if the impact on water quality may have long-term implication for public health. Laboratory testing for several indicator parameters (Ca/Mg, Cl/Si, chloride, boron, specific conductance and bacteria) indicates that surge water entered water wells’ casing and the screened aquifer. Analysis of the groundwater shows a decrease in the Ca/Mg ratio right after the storm and then a return toward pre-Katrina values. Chloride concentrations were elevated right after Katrina and Rita, and then decreased downward toward pre-Katrina values. From September 2005 to June 2006, the wells showed improvement in all the saltwater intrusion indicators. [ABSTRACT FROM AUTHOR]

This is the second article in a three-part series (all published in this volume) describing the framework used to quantitatively allocate mass loading of metals to the Pinal Creek alluvial aquifer among multiple sources. This contribution describes the formation of, and zonations within, the 20 km plume, which consists of a Peripheral Margin (pH > 5.5), the Intermediate Zone (pH 4.2-5.5), and an Acidic Core (pH < 4.2), where metal-bearing iron oxyhydroxides and acid-bearing minerals (jarosite, Al[OH]SO 4 , and FeSO 4 cements) have precipitated. While source remediation has improved groundwater quality, temporal reductions in solute concentrations at downgradient wells exhibit asymptotic behavior due to ongoing dissolution of acid-bearing precipitates, demonstrating that the total mass of metals released to the system over the last 75 years will dictate the ultimate remedial duration and cost. Column experiments, geochemical modeling, and analysis of empirical data indicate a minimum range of remedial time frames from about 20 years in the Peripheral Margin to more than 140 years in the Acidic Core. This analysis comprises a hitherto neglected element of cost allocation by causatively linking historical releases to the current and future environmental degradation that will incur response costs. [ABSTRACT FROM AUTHOR]

Denitrification of 40 mg L-1 NO3-N groundwaterin the vicinity of Central City, NE was stimulated with ethanol in in situ microcosms that were vibrated into the aquifer sediment and, thus, filled with a relatively undisturbed, saturated sand and gravel matrix. In microcosms receiving the 1.25 C/N ratio, nitrate disappeared within 40 h; however, NO2-N accumulated and persisted after NO3-N was depleted. Nitrite has been documented in groundwater redoxclines and is expected to be reported more frequently with increased use of ion chromatography and dense sampling networks.Dissolved oxygen was consumed to < 2.0 mg L-1 within 15 h, and stoichiometric production of HCO3- occurred. Average denitrification rate decreased from 28.5 to 19.3 and to 16 mg N L-1 d- 1 for C/N ratios of 1.25, 2.5, and 5.0 mg L- 1. Kinetic N-isotope effects resulted in the delta15N enrichment of residual nitrate as denitrification progressed, thus, causing the initial delta15N value of ~ + 6% to increase to > + 20%. The data support measuring additional parameters to prevent misinterpretations when using delta15Nvalues in NO3- source identification investigations. Apparent isotope-enrichment factors, epsilon value, were derived from delta15N increases vs. NO3- and NO3- plus NO2- reduction. They ranged from -11 to -16%. for delta15N vs. residual NO3- plus NO2- and from -2.5 to -9% for delta15N vs. NO3- alone. Since NO3- could not be resolved from NO2- in the delta15N analysis, a delta15N depleted NO2- phase was not identified. Nevertheless, isotopically light enrichment factors are consiste [ABSTRACT FROM AUTHOR]

The purpose of this study was to compile, map, and evaluate regionalpatterns of fluoride concentrations in Texas groundwater. County-median fluoride levels were calculated from nearly 7,000 wells distributed among 237 Texas counties. Four regions having high fluoride levelswere identified. These regions occupy parts of west, southwest, north-central, and south Texas. At least 50 percent of the fluoride observations in each of five Texas counties exceeded the primary drinking water standard of 4.0 mg/L. All of those counties are located in northwest Texas. Statewide, 25 counties had a median fluoride level abovethe secondary standard of 2.0 mg/L. Several factors contribute to elevated fluoride levels in Texas aquifers, including seepage from nearby saline formations, sparse recharge and dilution, and native mineral constituents of the aquifers. Results of this study suggest that: (1) regional geology influences fluoride concentrations in Texas, (2) statewide, the pattern is not random, (3) fluoride levels are generally higher in the western part of the state, and (4) regions which warrant further monitoring include west-central and north-central Texas. [ABSTRACT FROM AUTHOR]