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Although depletion of storage in low-permeability confining layers is the source of much of the groundwater produced from many confined aquifer systems, it is all too frequently overlooked or ignored. This makes effective management of groundwater resources difficult by masking how much water has been derived from storage and, in some cases, the total amount of water that has been extracted from an aquifer system. Analyzing confining layer storage is viewed as troublesome because of the additional computational burden and because the hydraulic properties of confining layers are poorly known. In this paper we propose a simplified method for computing estimates of confining layer depletion, as well as procedures for...
18O is an ideal tracer for characterizing hydrological processes because it can be reliably measured in several watershed hydrological compartments. Here, we present multiyear isotopic data, i.e. 18O variations (δ18O), for precipitation inputs, surface water and groundwater in the Shingobee River Headwaters Area (SRHA), a well-instrumented research catchment in north-central Minnesota. SRHA surface waters exhibit δ18O seasonal variations similar to those of groundwaters, and seasonal δ18O variations plotted versus time fit seasonal sine functions. These seasonal δ18O variations were interpreted to estimate surface water and groundwater mean residence times (MRTs) at sampling locations near topographically closed-basin...
1. Riparian vegetation in dry regions is influenced by low-flow and high-flow components of the surface and groundwater flow regimes. The duration of no-flow periods in the surface stream controls vegetation structure along the low-flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape...
Summary Carroll et al. (2009) state that the United States Geological Survey (USGS) Death Valley Regional Flow System (DVRFS) model, which is based on MODFLOW, is “conceptually inaccurate in that it models an unconfined aquifer as a confined system and does not simulate unconfined drawdown in transient pumping simulations.” Carroll et al. (2009) claim that “more realistic estimates of water availability” can be produced by a SURFACT-based model of the DVRFS that simulates unconfined groundwater flow and limits withdrawals from wells to avoid excessive drawdown. Differences in results from the original MODFLOW-based model and the SURFACT-based model stem primarily from application by Carroll et al. (2009) of head...
A field experiment involving the release of carbon dioxide (CO2) into a shallow aquifer was conducted near Bozeman, Montana, during the summer of 2008, to investigate the potential groundwater quality impacts in the case of leakage of CO2 from deep geological storage. As an essential part of the Montana State University Zero Emission Research and Technology (MSU-ZERT) field program, food-grade CO2 was injected over a 30 day period into a horizontal perforated pipe a few feet below the water table of a shallow aquifer. The impact of elevated CO2 concentrations on groundwater quality was investigated by analyzing water samples taken before, during, and following CO2 injection, from observation wells located in the...
Groundwater more saline than seawater has been discovered in the tsunami breccia of the Chesapeake Bay Impact Crater. One hypothesis for the origin of this brine is that it may be a liquid residual following steam separation in a hydrothermal system that evolved following the impact. Initial scoping calculations have demonstrated that it is feasible such a residual brine could have remained in the crater for the 35 million years since impact. Numerical simulations have been conducted using the code HYDROTHERM to test whether or not conditions were suitable in the millennia following the impact for the development of a steam phase in the hydrothermal system. Hydraulic and thermal parameters were estimated for the...
Federally owned and managed public lands occupy approximately 30 percent of the land area of the United States, and anywhere from 50 percent to more than 80 percent of the land area of many of the western states. Determining the appropriate use of these lands involves balancing objectives related to economic, recreational, and conservation interests. This paper examines established and emerging conflicts within and across these objectives through both a narrative discussion of specific topics and a series of case studies. The authors find that new challenges, including pressures to devote portions of public lands to renewable energy project development and the multifaceted threats presented by climate change, will...
PRD1, an icosahedra-shaped, 62 nm (diameter), double-stranded DNA bacteriophage with an internal membrane, has emerged as an important model virus for studying the manner in which microorganisms are transported through a variety of groundwater environments. The popularity of this phage for use in transport studies involving geologic media is due, in part, to its relative stability over a range of temperatures and low degree of attachment in aquifer sediments. Laboratory and field investigations employing PRD1 are leading to a better understanding of viral attachment and transport behaviors in saturated geologic media and to improved methods for describing mathematically subsurface microbial transport at environmentally...
Abstract: We used a numerical model to investigate how a barrier island groundwater system responds to increases of up to 60 cm in sea level. We found that a sea-level rise of 20 cm leads to substantial changes in the depth of the water table and the extent and depth of saltwater intrusion, which are key determinants in the establishment, distribution and succession of vegetation assemblages and habitat suitability in barrier islands ecosystems. In our simulations, increases in water-table height in areas with a shallow depth to water (or thin vadose zone) resulted in extensive groundwater inundation of land surface and a thinning of the underlying freshwater lens. We demonstrated the interdependence of the groundwater...
We discuss that whilst energy conservation and energy efficiency both ultimately have the same goal they attempt to achieve this via very different approaches. We then discuss how both options face significant barriers to ultimately successfully reduce electricity consumption.
Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field-scale (apparent) estimated reaction rates and isotopic fractionations and local-scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O2 threshold for denitrification, and stable N isotope...
The effects of a dilute (ionic strength = 5 × 10−3 M) plume of treated sewage, with elevated levels (3.9 mg/L) of dissolved organic carbon (DOC), upon the pH-dependency and magnitude of bacterial transport through an iron-laden, quartz sand aquifer (Cape Cod, MA) were evaluated using sets of replicate, static minicolumns. Compared with uncontaminated groundwater, the plume chemistry diminished bacterial attachment under mildly acidic (pH 5.0–6.5) in-situ conditions, in spite of the 5-fold increase in ionic strength and substantively enhanced attachment under more alkaline conditions. The effects of the hydrophobic neutral and total fractions of the plume DOC; modest concentrations of fulvic and humic acids (1.5...
Coupled intragrain diffusional mass transfer and nonlinear surface complexation processes play an important role in the transport behavior of U(VI) in contaminated aquifers. Two alternative model approaches for simulating these coupled processes were analyzed and compared: (1) the physical nonequilibrium approach that explicitly accounts for aqueous speciation and instantaneous surface complexation reactions in the intragrain regions and approximates the diffusive mass exchange between the immobile intragrain pore water and the advective pore water as multirate first-order mass transfer and (2) the chemical nonequilibrium approach that approximates the diffusion-limited intragrain surface complexation reactions...
Groundwater nitrification is a poorly characterized process affecting the speciation and transport of nitrogen. Cores from two sites in a plume of contamination were examined using culture-based and molecular techniques targeting nitrification processes. The first site, located beneath a sewage effluent infiltration bed, received treated effluent containing O2 (> 300 µM) and NH4+ (51–800 µM). The second site was 2.5 km down-gradient near the leading edge of the ammonium zone within the contaminant plume and featured vertical gradients of O2, NH4+, and NO3− (0–300, 0–500, and 100–200 µM with depth, respectively). Ammonia- and nitrite-oxidizers enumerated by the culture-based MPN method were low in abundance at both...
In northern peatlands, subsurface ice formation is an important process that can control heat transport, groundwater flow, and biological activity. Temperature was measured over one and a half years in a vertical profile in the Red Lake Bog, Minnesota. To successfully simulate the transport of heat within the peat profile, the U.S. Geological Survey’s SUTRA computer code was modified. The modified code simulates fully saturated, coupled porewater-energy transport, with freezing and melting porewater, and includes proportional heat capacity and thermal conductivity of water and ice, decreasing matrix permeability due to ice formation, and latent heat. The model is verified by correctly simulating the Lunardini analytical...
Substantial questions remain about the time required for groundwater nitrate to be reduced below 10 mg L− 1 following establishment of vegetated riparian buffers. The objective of this study was to document changes in groundwater nitrate–nitrogen (NO3–N) concentrations that occurred within a few years of planting a riparian buffer. In 2000 and 2001 a buffer was planted adjacent to a first-order stream in the deep loess region of western Iowa with strips of walnut and cottonwood trees, alfalfa and brome grass, and switch grass. Non-parametric statistics showed significant declines in NO3–N concentrations in shallow groundwater following buffer establishment, especially mid 2003 and later. The dissolved oxygen generally...
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The U.S. Geological Survey (USGS) is providing an online map of water-table altitude contours in the upper glacial and Magothy aquifers on Long Island, New York, April-May 2013. USGS serves this map and geospatial data as a REST Open Map Service (as well as HTTP, JSON, KML, and shapefile), so end-users can use the map and data on mobile and web clients. A companion report, U.S. Geological Survey Scientific Investigations Map 3326 (Como and others, 2015; http://dx.doi.org/10.3133/sim3326) further describes data collection and map preparation and presents 68x22 in. PDF versions, 4 sheets, scale 1:125,000. This polyline shapefile consists of digital contours that represent the water table altitude in the upper...
The process whereby hydrogeologists interpret the available information to produce a justifiable set of simplifying assumptions to describe a groundwater system is called conceptual modelling. Although this process is inherent in all hydrogeological assessments and can therefore be regarded as synonymous with hydrogeological practice there are no standard specifications for it. A framework for conceptual modelling has been designed to both assist in the planning and process of the work and to provide an audit trail to facilitate independent scrutiny. The application of this framework is illustrated by two case histories, one of a small-scale investigation for a proposed cemetery and the other of an investigation...
Removal of water from terrestrial subsurface storage is a natural consequence of groundwater withdrawals, but global depletion is not well characterized. Cumulative groundwater depletion represents a transfer of mass from land to the oceans that contributes to sea-level rise. Depletion is directly calculated using calibrated groundwater models, analytical approaches, or volumetric budget analyses for multiple aquifer systems. Estimated global groundwater depletion during 1900–2008 totals ∼4,500 km3, equivalent to a sea-level rise of 12.6 mm (>6% of the total). Furthermore, the rate of groundwater depletion has increased markedly since about 1950, with maximum rates occurring during the most recent period (2000–2008),...
Development of coal-bed natural gas (CBNG) in the Powder River Basin, Wyoming, has increased substantially in recent years. Among environmental concerns associated with this development is the fate of groundwater removed with the gas. A preferred water-management option is storage in surface impoundments. As of January 2007, permits for more than 4000 impoundments had been issued within Wyoming. A study was conducted on changes in water and sediment chemistry as water from an impoundment infiltrated the subsurface. Sediment cores were collected prior to operation of the impoundment and after its closure and reclamation. Suction lysimeters were used to collect water samples from beneath the impoundment. Large amounts...
map background search result map search result map Contours of Water Table Altitudes in the Upper Glacial and Magothy Aquifers, April-May 2013 Contours of Water Table Altitudes in the Upper Glacial and Magothy Aquifers, April-May 2013