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More than 70 individual VOCs were identified in the leachate plume of a closed municipal landfill. Concentrations were low when compared with data published for other landfills, and total VOCs accounted for less than 0.1% of the total dissolved organic carbon. The VOC concentrations in the core of the anoxic leachate plume are variable, but in all cases they were found to be near or below detection limits within 200 m of the landfall. In contrast to the VOCs, the distributions of chloride ion, a conservative tracer, and nonvolatile dissolved organic carbon, indicate little dilution over the same distance. Thus, natural attentuation processes are effectively limiting migration of the VOC plume. The distribution of...
Categories: Publication; Types: Citation; Tags: Groundwater
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Natural landscapes in the Southwestern United States are changing. In recent decades, rising temperatures and drought have led to drier conditions, contributed to large-scale ecological impacts, and affected many plant and animal species across the region. The current and future trajectory of climate change underscores the need for managers and conservation professionals to understand the impacts of these patterns on natural resources. In this regional assessment of the Southwest Climate Change Initiative, we evaluate changes in annual average temperatures from 1951–2006 across major habitats and large watersheds and compare these changes to the number of species of conservation concern that are found within these...
A two-dimensional finite element model was used to simulate the groundwater recovery process under various surface mining situations. The simulation results were used to predict the rate at which soil settlement takes place. It was found that the groundwater recovery process is very fast immediately after mine closure and cessation of dewatering programmes; a significant part of mine land settlement can be measured at such times. This paper presents a method for deriving the relationship between the re-establishment of the natural groundwater regime to its equilibrium position as existed prior to the commencement of mining operations and mine spoil settlement.
Summary A detailed local-scale monitoring network was used to assess CFC distribution in an unconfined sand aquifer in southwestern Ontario where the zone of 1–5-year-old groundwater was known with certainty because of prior use of a bromide tracer. Groundwater ⩽5 years old was confined to an aerobic zone at ⩽5 m depth and had CFC concentrations consistent with modern atmospheric mixing ratios at recharge temperatures of 7–11 °C, as was observed in the 3-m thick vadose zone at the site. At depths below 6 m, the groundwater became progressively more reducing, however, with a denitrifying horizon at 6–7 m depth, and a Mn and Fe reducing zone below 7 m depth. In the anaerobic zone, 3H/3He ratios indicated that groundwater-age...
We examined the chemical reactions influencing dissolved concentrations, speciation, and transport of naturally occurring arsenic (As) in a shallow, sand and gravel aquifer with distinct geochemical zones resulting from land disposal of dilute sewage effluent. The principal geochemical zones were: (1) the uncontaminated zone above the sewage plume [350 µM dissolved oxygen (DO), pH 5.9]; (2) the suboxic zone (5 µM DO, pH 6.2, elevated concentrations of sewage-derived phosphate and nitrate); and (3) the anoxic zone [dissolved iron(II) 100–300 µM, pH 6.5–6.9, elevated concentrations of sewage-derived phosphate]. Sediments are comprised of greater than 90% quartz but the surfaces of quartz and other mineral grains are...
This study proposes the use of several problems of unstable steady state convection with variable fluid density in a porous layer of infinite horizontal extent as two-dimensional (2-D) test cases for density-dependent groundwater flow and solute transport simulators. Unlike existing density-dependent model benchmarks, these problems have well-defined stability criteria that are determined analytically. These analytical stability indicators can be compared with numerical model results to test the ability of a code to accurately simulate buoyancy driven flow and diffusion. The basic analytical solution is for a horizontally infinite fluid-filled porous layer in which fluid density decreases with depth. The proposed...
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In this paper, we present a flexible approach for simulating one- and two-dimensional routing of surface water using a numerical surface water routing (SWR) code implicitly coupled to the groundwater-flow process in MODFLOW. Surface water routing in SWR can be simulated using a diffusive-wave approximation of the Saint-Venant equations and/or a simplified level-pool approach. SWR can account for surface water flow controlled by backwater conditions caused by small water-surface gradients or surface water control structures. A number of typical surface water control structures, such as culverts, weirs, and gates, can be represented, and it is possible to implement operational rules to manage surface water stages...
Categories: Publication; Types: Citation; Tags: Groundwater
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More than 10 billion gallons (38 × 106 m3) of acid industrial liquid waste has been injected in about 11 years under high pressure into a saline-water-filled part of a limestone aquifer of low transmissivity between 1,400 and 1,700 feet (430 and 520 m) below land surface near Pensacola, Florida. A similar waste disposal system is planned for the same zone at a site about 8.5 miles (13.7 km) to the east. The injection zone is the lower limestone of the Floridan aquifer. The lower limestone is overlain by a confining layer of plastic clay about 220 feet (67 m) thick at the active injection site and underlain by another confining layer of shale and clay. The upper confining layer is overlain by the upper limestone...
Categories: Publication; Types: Citation; Tags: Groundwater
The Conservation Reserve Program (CRP) is one of the largest programs of the U.S. Department of Agriculture (USDA) that encourages farmers and ranchers to establish resource-conserving vegetative covers to address soil, water and related resource issues on their lands. This research study examines the relationship between the CRP and the changes in the groundwater levels within Texas County in the Oklahoma Panhandle region. The region overlies the central portion of the High Plains Aquifer that has shown significant decline in groundwater levels, due largely to the development of irrigated agriculture. Using the calibrated SWAT (Soil and Water Assessment Tool) model and GIS-based analysis, a significant spatial...
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The collection of borehole geophysical logs and images and continuous water-level data was conducted by the U.S. Geological Survey South Atlantic Water Science Center in the vicinity of the GMH Electronics Superfund site near Roxboro, North Carolina, during December 2012 through July 2015. The study purpose was part of a continued effort to assist the U.S. Environmental Protection Agency in the development of a conceptual groundwater model for the assessment of current contaminant distribution and future migration of contaminants. Previous work by the U.S. Geological Survey South Atlantic Water Science Center at the site involved similar data collection, in addition to surface geologic mapping and passive diffusion...
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Regional finite-difference models tend to have large cell sizes, often on the order of 1–2 km on a side. Although the regional flow patterns in deeper formations may be adequately represented by such a model, the intricate surface water and groundwater interactions in the shallower layers are not. Several stream reaches and nearby wells may occur in a single cell, precluding any meaningful modeling of the surface water and groundwater interactions between the individual features. We propose to replace the upper MODFLOW layer or layers, in which the surface water and groundwater interactions occur, by an analytic element model (GFLOW) that does not employ a model grid; instead, it represents wells and surface waters...
Categories: Publication; Types: Citation; Tags: Groundwater
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Groundwater-quality data collected between 1993 and 2015 were compiled from the U.S. Geological Survey (USGS) National Water Information System (NWIS) database for 722 wells in the San Joaquin Valley (SJV). Groundwater-quality data retrieved included lab analyses of complete major ion data (calcium, magnesium, sodium, potassium, chloride, sulfate, nitrate, alkalinity, bicarbonate, carbonate, silica, and TDS) for 613 samples, and an additional 109 samples with measured values of specific conductance. Most of these wells were sampled as part of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project or the USGS National Water Quality Assessment (NAWQA) Program. In addition...
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Natural occurrences of ground water with moderate (10 to 50 micrograms per liter) to high (greater than 50 micrograms per liter) concentrations of arsenic are common throughout much of the Western United States. High concentrations of arsenic are generally associated with one of four geochemical environments: (1) basin-fill deposits of alluvial-lacustrine origin, particularly in semiarid areas, (2) volcanic deposits, (3) geothermal systems, and (4) uranium and gold-mining areas. These findings are based on an extensive literature review, compilation of unpublished reports and data, and the review of data bases containing more than 7,000 analyses of ground-water samples for arsenic. In the first two environments,...
Categories: Publication; Types: Citation; Tags: Groundwater
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This dataset includes the magnetotelluric (MT) sounding data collected in 2009 in and near the San Luis Basin, New Mexico. The U.S. Geological Survey conducted a series of multidisciplinary studies, including MT surveys, in the San Luis Basin to improve understanding of the hydrogeology of the Santa Fe Group and the nature of the sedimentary deposits comprising the principal groundwater aquifers of the Rio Grande rift. The shallow unconfined and the deeper confined Santa Fe Group aquifers in the San Luis Basin are the main sources of municipal water for the region. The population of the San Luis Basin region is growing rapidly and water shortfalls could have serious consequences. Future growth and land management...


map background search result map search result map Managing Changing Landscapes in the Southwestern United States Water level data during pumping for stressed HPFM measurements for selected boreholes near GMH Electronics Superfund site, Roxboro, NC (2012-2015) Modern groundwater-quality, depth, and well-construction data for selected wells in the San Joaquin Valley, California, 1993-2015 Magnetotelluric sounding data, station 1, Taos Plateau Volcanic Field, New Mexico, 2009 Water level data during pumping for stressed HPFM measurements for selected boreholes near GMH Electronics Superfund site, Roxboro, NC (2012-2015) Modern groundwater-quality, depth, and well-construction data for selected wells in the San Joaquin Valley, California, 1993-2015 Managing Changing Landscapes in the Southwestern United States