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Groundwater resources in Cape Verde provide water for agriculture, industry, and human consumption. These resources are limited and susceptible to contamination. Additional groundwater resources are needed for continued agricultural development, particularly during times of drought, but increased use and (or) climatic change may have adverse effects on the quantity and quality of freshwater available. In volcanic island aquifers such as those of Cape Verde, a lens of fresh groundwater typically ?floats? upon a layer of brackish water at the freshwater/saltwater boundary, and increased pumping may cause salt water intrusion or other contamination. A recent U.S. Geological Survey study assessed baseline groundwater...
Categories: Publication; Types: Citation
One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciation and sorption reactions on the ground-water transport of Np and Pu, two redox-sensitive elements. Earlier 1D simulations (Reardon, 1981) considered the kinetically limited dissolution of calcite and its effect on ion-exchange reactions (involving 90Sr, Ca, Na, Mg and K), and documented the spatial variation of a 90Sr partition coefficient under both transient and steady-state chemical conditions. In contrast, the simulations presented here assume local equilibrium for all reactions, and consider sorption on constant potential, rather than constant charge, surfaces. Reardon's (1981) seminal findings on the spatial...
Chemical and isotopic data for groundwater from throughout the Middle Rio Grande Basin, central New Mexico, USA, were used to identify and map groundwater flow from 12 sources of water to the basin, evaluate radiocarbon ages, and refine the conceptual model of the Santa Fe Group aquifer system. Hydrochemical zones, representing groundwater flow over thousands to tens of thousands of years, can be traced over large distances through the primarily siliciclastic aquifer system. The locations of the hydrochemical zones mostly reflect the “modern” predevelopment hydraulic-head distribution, but are inconsistent with a trough in predevelopment water levels in the west-central part of the basin, indicating that this trough...
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...
Geochemistry has contributed significantly to the understanding of ground-water systems over the last 50 years. Historic advances include development of the hydrochemical facies concept, application of equilibrium theory, investigation of redox processes, and radiocarbon dating. Other hydrochemical concepts, tools, and techniques have helped elucidate mechanisms of flow and transport in ground-water systems, and have helped unlock an archive of paleoenvironmental information. Hydrochemical and isotopic information can be used to interpret the origin and mode of ground-water recharge, refine estimates of time scales of recharge and ground-water flow, decipher reactive processes, provide paleohydrological information,...
Halite brine (saturation ranging from 45 to 80%) lies within glacial sediments that fill the Onondaga Trough, a bedrock valley deepened by Pleistocene glaciation near Syracuse, New York State, USA. The most concentrated brine occupies the northern end of the trough, about 10 km downgradient of the northern limit of halite beds in the Silurian Salina Group, the assumed source of salt. The chemical composition of the brine and its radiocarbon age suggest that the brine originally formed about 16,700 years ago through dissolution of halite by glacial melt water and later mixed with saline bedrock water. Two hypotheses regarding the formation of the brine pool were tested through variable-density flow simulations using...
NETPATH-WIN is an interactive user version of NETPATH, an inverse geochemical modeling code used to find mass-balance reaction models that are consistent with the observed chemical and isotopic composition of waters from aquatic systems. NETPATH-WIN was constructed to migrate NETPATH applications into the Microsoft WINDOWS® environment. The new version facilitates model utilization by eliminating difficulties in data preparation and results analysis of the DOS version of NETPATH, while preserving all of the capabilities of the original version. Through example applications, the note describes some of the features of NETPATH-WIN as applied to adjustment of radiocarbon data for geochemical reactions in groundwater...
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One of the major water-quality problems in the Chesapeake Bay is an overabundance of nutrients from the streams and rivers that discharge to the Bay. Some of these nutrients are from nonpoint sources such as atmospheric deposition, agricultural manure and fertilizer, and septic systems. The effects of efforts to control nonpoint sources, however, can be difficult to quantify because of the lag time between changes at the land surface and the response in the base-flow (ground water) component of streams. To help resource managers understand the lag time between implementation of management practices and subsequent response in the nutrient concentrations in the base-flow component of streamflow, a study of ground-water...
Categories: Publication; Types: Citation
This raster data set delineates the predicted probability of elevated volatile organic compound (VOC) concentrations in groundwater in the Eagle River watershed valley-fill aquifer, Eagle County, North-Central Colorado, 2006-2007. This data set was developed by a cooperative project between the U.S. Geological Survey, Eagle County, the Eagle River Water and Sanitation District, the Town of Eagle, the Town of Gypsum, and the Upper Eagle Regional Water Authority. This project was designed to evaluate potential land-development effects on groundwater and surface-water resources so that informed land-use and water management decisions can be made. This groundwater probability map and its associated probability maps...
Categories: Publication; Types: Citation
Groundwater resources in Cape Verde provide water for agriculture, industry, and human consumption. These resources are limited and susceptible to contamination. Additional groundwater resources are needed for continued agricultural development, particularly during times of drought, but increased use and (or) climatic change may have adverse effects on the quantity and quality of freshwater available. In volcanic island aquifers such as those of Cape Verde, a lens of fresh groundwater typically ?floats? upon a layer of brackish water at the freshwater/saltwater boundary, and increased pumping may cause salt water intrusion or other contamination. A recent U.S. Geological Survey study assessed baseline groundwater...
Categories: Publication; Types: Citation
Chemical and isotopic data were obtained from ground water and surface water throughout the Middle Rio Grande Basin (MRGB), New Mexico, and supplemented with selected data from the U.S. Geological Survey (USGS) National Water Information System (NWIS) and City of Albuquerque water-quality database in an effort to refine the conceptual model of ground-water flow in the basin. The ground-water data collected as part of this study include major- and minor-element chemistry (30 elements), oxygen-18 and deuterium content of water, carbon-13 content and carbon-14 activity of dissolved inorganic carbon, sulfur-34 content of dissolved sulfate, tritium, and dissolved atmospheric gases including nitrogen, argon, helium, chlorofluorocarbons,...
Categories: Publication; Types: Citation