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At least 433 records · Page 24Linked to original sources
USGS2013

Geology and oil and gas assessment of the Fruitland Total Petroleum System, San Juan Basin, New Mexico and Colorado: Chapter 6 in Geology and Oil and Gas Assessment of the Fruitland Total Petroleum System, San Juan Basin, New Mexico and Colorado

The Fruitland Total Petroleum System (TPS) of the San Juan Basin Province includes all genetically related hydrocarbons generated from coal beds and organic-rich shales in the Cretaceous Fruitland Formation. Coal beds are considered to be the primary source of the hydrocarbons. Potential reservoir rocks in the Fruitland TPS consist of the Upper Cretaceous Pictured Cliffs Sandstone, Fruitland Formation (both sandstone and coal beds), and the Farmington Sandstone Member of the Kirtland Formation, and the Tertiary Ojo Alamo Sandstone, and Animas, Nacimiento, and San Jose Formations. Analysis of the geochemistry of Fruitland coal-bed gas and co-produced water suggests that hydrocarbons in Fruitland coal beds began to form early in the depositional history of the Fruitland Formation with the generation of early microbial gas. Source rocks in the Fruitland entered the oil generation zone in the late Eocene and continued to generate minor oil and large quantities of thermogenic gas into middle Miocene time. Near the end of the Miocene, thermogenic hydrocarbon generation and subsidence in the San Juan Basin ceased, and the basin was uplifted and differentially eroded. Late-stage (secondary) microbial gas has been documented in Fruitland coal-bed reservoirs and was formed by microbial reduction of carbon dioxide during introduction of groundwater in the late Pliocene and Pleistocene. Most of this late-stage microbial gas is found just downdip from the northern, western, and southern Fruitland outcrops. The northern part of the Fruitland Formation is overpressured as a result of artesian conditions established in the Pliocene or Pleistocene. South and east of the overpressured area, the Fruitland is either normally pressured or underpressured. Four assessment units (AU) were defined in the Fruitland TPS. Of the four AUs, one consists of conventional gas accumulations and the other three are continuous-type gas accumulations: Tertiary Conventional Gas AU, Pictured Cliffs Continuous Gas AU, Basin Fruitland Coalbed Gas (CBG) AU, and Fruitland Fairway CBG AU. No oil resources that have the potential for additions to reserves in the next 30 years were estimated for this TPS. Gas resources that have the potential for additions to reserves in the next 30 years are estimated at a mean of 29.3 trillion cubic feet of gas (TCFG). Of this amount, 23.58 TCFG will come from coal-bed gas accumulations and 83.1 percent of this total is estimated to come from the Basin Fruitland CBG AU. The remaining 5.72 TCFG is allocated to continuous-type gas accumulations (5.64 TCFG) and conventional gas accumulations (0.08 TCFG). Although the Fruitland Fairway CBG AU has produced the most significant amount of coal-bed gas to date, the area of the AU is limited. New potentially productive wells will come from infill drilling, and the number of these wells will be limited by effective drainage area. Total natural gas liquids (NGL) that have the potential for additions to reserves in the next 30 years are estimated at a mean of 17.76 million barrels. Of this amount, 16.92 million barrels will come from the Pictured Cliffs Continuous Gas AU and the remainder from the Tertiary Conventional Gas AU.

Colorado;New Mexico↗
USGS1955

Geochemistry and mineralogy of a uraniferous lignite [South Dakota]

Detailed studies have been carried out on a uraniferous lignite from the Mendenhall strip mine, Harding County, S. Dak. By means of heavy-liquid separations, a mineral-free concentrate of the lignite was obtained that contained 13.8 percent ash and 0.31 percent uranium in the ash. The minerals (gypsum 69 percent, jarosite 10 percent, quartz 2 percent, kaolinite and clay minerals 19 percent, and calcite trace) contain only 7 percent of the uranium in the original coal, indicating an association of the uranium with the organic components of the lignite.Batch extractions show that 88.5 percent of the uranium can be extracted from the lignite by two consecutive treatments with boiling 1 N hydrochloric acid. Continuous extraction with hot 6 N hydrochloric acid removes 98.6 percent of the uranium.Columns of coal were treated with water, 1 N hydrochloric acid, 6 N hydrochloric acid, and a solution of lanthanum nitrate. The experiment with lanthanum nitrate indicated that only 1.2 percent of the uranium in the coal is held by ion exchange. The elutriation experiments showed that the uranium is held in the coal as an organo-uranium compound or complex that is soluble at a pH of less than 2.18.A geochemical mechanism by which the uranium may have been introduced into and retained by the lignite is discussed.

South Dakota↗
USGS2010

Episodes of low dissolved oxygen indicated by ostracodes and sediment geochemistry at Crystal Lake, Illinois, USA

Low dissolved oxygen during the summer and early fall controls profundal continental ostracode distribution in Crystal Lake (McHenry County), Illinois, favoring Cypria ophthalmica and Physocypria globula at water depths from 6 to 13 m. These species also thrived in the lake's profundal zone from 14,165 to 9600 calendar year before present (cal yr b.p.) during the late Boiling, Allerod, and Younger Dryas chronozones, and early Holocene. Characterized by sand, cemented tubules, large aquatic gastropod shells, and littoral ostracode valves, thin (1-6 cm) tempestite deposits punctuate thicker deposits of organic gyttja from 16,080 to 11,900 cal yr b.p. The succeeding 2300 yr (11,900-9600 cal yr b.p.) lack tempestites, and reconstructed water depths were at their maximum. Deposition of marl under relatively well-oxygenated conditions occurred during the remainder of the Holocene until the arrival of Europeans, when the lake returned to a pattern of seasonally low dissolved oxygen. Such conditions are also indicated in the lake sediment by the speciation of phosphorus, high concentrations of organic carbon, and abundant iron and manganese occluded to mineral grains. Initial low dissolved oxygen was probably caused by the delivery of dissolved P and Fe in shallow groundwater, the chemistry of which was influenced by Spodosol pedogenesis under a spruce forest. The triggering may have been regionally warm and wet conditions associated with retreat of the Lake Michigan lobe (south-central Laurentide Ice Sheet). ?? 2010, by the American Society of Limnology and Oceanography Inc.

Limnology and Oceanography↗
USGS2006

Possible linkages between lignite aquifers, pathogenic microbes, and renal pelvic cancer in northwestern Louisiana, USA

In May and September, 2002, 14 private residential drinking water wells, one dewatering well at a lignite mine, eight surface water sites, and lignite from an active coal mine were sampled in five Parishes of northwestern Louisiana, USA. Using a geographic information system (GIS), wells were selected that were likely to draw water that had been in contact with lignite; control wells were located in areas devoid of lignite deposits. Well water samples were analyzed for pH, conductivity, organic compounds, and nutrient and anion concentrations. All samples were further tested for presence of fungi (cultures maintained for up to 28 days and colonies counted and identified microscopically) and for metal and trace element concentration by inductively-coupled plasma mass spectrometry and atomic emission spectrometry. Surface water samples were tested for dissolved oxygen and presence of pathogenic leptospiral bacteria. The Spearman correlation method was used to assess the association between the endpoints for these field/laboratory analyses and incidence of cancer of the renal pelvis (RPC) based on data obtained from the Louisiana Tumor Registry for the five Parishes included in the study. Significant associations were revealed between the cancer rate and the presence in drinking water of organic compounds, the fungi Zygomycetes, the nutrients PO4 and NH3, and 13 chemical elements. Presence of human pathogenic leptospires was detected in four out of eight (50%) of the surface water sites sampled. The present study of a stable rural population examined possible linkages between aquifers containing chemically reactive lignite deposits, hydrologic conditions favorable to the leaching and transport of toxic organic compounds from the lignite into the groundwater, possible microbial contamination, and RPC risk. ?? Springer Science+Business Media B.V. 2006.

Environmental Geochemistry and Health↗
USGS1993

Physical properties, mineralogy, and geochemistry of Holocene varved sediments from Elk Lake, Minnesota

Elk Lake in northwestern Minnesota is situated close to a climatically sensitive ecotone, the forest-prairie border, that migrated back and forth over the drainage basin of the lake during the Holocene. The entire postglacial (Holocene) sediment record in the deepest part of Elk Lake is composed of annual layers (varves) that record the seasonal pulses of many sediment components, and, most important, provide high-resolution (seasonal) time calibration of rates and timing of environmental change. These varved sediments contain many allochthonous and autochthonous components that are sensitive to changing environmental conditions in the drainage basin and the lake. The mineral components of Elk Lake sediments consist mainly of authigenic calcium, magnesium, and manganese carbonate minerals (low-Mg calcite, high-Mg calcite, dolomite, and rhodochrosite), opaline silica (from diatoms), X-ray amorphous iron and manganese oxyhydroxides, and an iron phosphate mineral tentatively identified as rock-bridgeite [(Fe, Mn)Fe 4 (PO 4 ) 3 (OH) 5 ], plus minor contributions from fine-grained detrital quartz, feldspar, illite, and kaolinite. The most notable characteristic of the sediments in Elk Lake is that most of the components were formed in the lake. Q-mode factor analysis of sediment geochemistry reduced 23 observed compositional variables, expressed as percent or parts per million of elements, to three composite variables (factor loadings) whose “concentrations” are expressed on a scale of −1.0 to 1.0. Factor 1 expresses the composition of the inorganic clastic fraction based on concentrations of Mg, Na, Al, Cr, V, Y, Sc, Ni, Sr, Co, and Cu. Factor 2 expresses the similarities in variations of Fe, Mn, P, organic carbon, and Mo. Factor 3 loadings are a synthesis of concentrations of Mn, S, Ca, La, and Ba. Geochemical characteristics define three distinct chemical stages in the development of Elk lake: (1) a carbonate-, manganese-, iron-, sulfur-rich early-lake stage that lasted from 10,400 to 8200 varve yr; (2) a clastic- and diatom-rich mid-Holocene prairie-lake stage that lasted from 8200 to 4000 varve yr; and (3) a final iron-, manganese-, phosphate-, and organic-rich modern-lake stage that developed over the past 4000 yr. The chemical characteristics of the sediments deposited during these three lake phases can be represented by the average compositions of three groups of samples: (1) the average composition of sediments deposited over the past 2000 yr, representing the modern-lake stage; (2) the composition of a 50 varve sample centered on 5700 varve yr that represents the maximum clastic influx into the lake during the prairie period; and (3) the average composition of sediments deposited over the initial 2000 yr of the lake’s existence (10,400 to 8400 varve yr). The amplitudes of climatic oscillations, as reflected by changes in concentration of many climatically sensitive elements, were greatest during the prairie period, pronounced cycles having periodicities of several hundred years. The extremes of these oscillations occurred within several centuries or less, which suggests that significant changes in climate may occur abruptly and rapidly. Most notably, the end of the mid-Holocene prairie period, marked by a sudden decrease in the influx of detrital clastic material, occurred within a few decades.

Minnesota↗
USGS2010

Selected water-quality data from the Cedar River and Cedar Rapids well fields, Cedar Rapids, Iowa, 1999–2005

The Cedar River alluvial aquifer is the primary source of municipal water in the Cedar Rapids, Iowa area. Municipal wells are completed in the alluvial aquifer at approximately 40 to 80 feet deep. The City of Cedar Rapids and the U.S. Geological Survey have been conducting a cooperative study of the groundwater-flow system and water quality near the well fields since 1992. Previous cooperative studies between the City of Cedar Rapids and the U.S. Geological Survey have documented hydrologic and water-quality data, geochemistry, and groundwater models. Water-quality samples were collected for studies involving well field monitoring, trends, source-water protection, groundwater geochemistry, evaluation of surface and ground-water interaction, assessment of pesticides in groundwater and surface water, and to evaluate water quality near a wetland area in the Seminole well field. Typical water-quality analyses included major ions (boron, bromide, calcium, chloride, fluoride, iron, magnesium, manganese, potassium, silica, sodium, and sulfate), nutrients (ammonia as nitrogen, nitrite as nitrogen, nitrite plus nitrate as nitrogen, and orthophosphate as phosphorus), dissolved organic carbon, and selected pesticides including two degradates of the herbicide atrazine. In addition, two synoptic samplings included analyses of additional pesticide degradates in water samples. Physical field parameters (alkalinity, dissolved oxygen, pH, specific conductance and water temperature) were recorded with each water sample collected. This report presents the results of water quality data-collection activities from January 1999 through December 2005. Methods of data collection, quality-assurance samples, water-quality analyses, and statistical summaries are presented. Data include the results of water-quality analyses from quarterly and synoptic sampling from monitoring wells, municipal wells, and the Cedar River.

iowa↗
USGS2019

Authigenic mineral texture in submarine 1979 basalt drill core, Surtsey volcano, Iceland

Micrometer-scale maps of authigenic microstructures in submarine basaltic tuff specimens from a 1979 Surtsey volcano, Iceland, drill core acquired 15 years after eruptions terminated provide fresh perspectives for deciphering the initial alteration of oceanic basalt in a low temperature hydrothermal system. A novel investigative approach integrates synchrotron source X-ray microdiffraction (µXRD), X-ray microfluoresence (µXRF), micro-computed tomography (µCT), and scanning transmission electron microscopy (S/TEM) coupled with Raman spectroscopy to create finely resolved spatial frameworks that record a continuum of alteration in glass and olivine. Micro-analytical maps of vesicular and fractured lapilli in specimens from 157.1, 137.9, and 102.6 m depth, and borehole temperatures of 83, 93.9 and 141.3 °C measured in 1980, respectively, record the production of nanocrystalline clay mineral, zeolites, and Al-tobermorite in diverse microenvironments. Nanocrystalline clay mineral (nontronite) and zeolite (amicite) texture in linear microstructures have concentrically-oriented crystallographic preferred orientation. Raman spectra indicating degraded organic carbonaceous matter are associated with nanocrystalline clay mineral in 10–25 nm, sub-circular nanoscale cavities in altered glass at 137.9 m depth and in a concentrically-layered, crystallographically-oriented linear microstructure in altered olivine at 102.6 m. These features have little resemblance to previously described alteration features in basalt. Irregular alteration fronts between fresh and altered glass at 157.1 depth, however, show a resemblance to microchannels in older basalts. The integrated analyses describe the complex organization of previously unrecognized mineral textures in very young basalt and provide a foundational mineralogical reference for longitudinal, time-lapse characterizations of palagonitized basalt in oceanic environments.

Geochemistry, Geophysics, Geosystems↗
USGS1991

Large-scale distribution of metal contamination in the fine-grained sediments of the Clark Fork River, Montana, U.S.A.

Historic discharges from the mining and smelting complex at the head-waters of the Clark Fork River have resulted in elevated Ag, Cd, Cu, Pb and Zn concentrations in the <60 μm fraction of both bed and flood-plain sediments of the river. Processes affecting the trends in longitudinal distributions of these metals were investigated by repeated sampling over a 380 km river reach between August 1986 and July 1989. At the most upstream site, bed-sediment metal concentrations were enriched 18–115 times above least enriched tributaries, depending on the metal. All metals decreased exponentially with distance downstream away from mining. The exponential model predicts that elevated metal concentrations should occur over 550 km downstream, in Lake Pend Oreille. Longitudinal trends, obvious on a scale of hundreds of kilometers, were obscured by small-scale spatial variability when shorter stretches of the river were considered. Longitudinal dispersion appeared to be controlled largely by physical dilution with less-contaminated sediments. Evidence suggests that erosion of contaminated flood-plains contributes to metal contamination in the bed sediments. Tributary input appeared to have little influence on the large-scale, downstream distribution of metals; however, it did contribute to local variability in bed-sediment metal concentrations. Association of metals with specific mineral grains, as well as variability in total organic C and Fe concentration, appeared also to contribute to variability. Some year-to-year variability in bed-sediment metal concentrations was observed, however, trends in longitudinal dispersion were not significantly different between at least two of the years sampled.

Montana↗
USGS2007

Oil and gas geochemistry and petroleum systems of the Fort Worth Basin

Detailed biomarker and light hydrocarbon geochemistry confirm that the marine Mississippian Barnett Shale is the primary source rock for petroleum in the Fort Worth Basin, north-central Texas, although contributions from other sources are possible. Biomarker data indicate that the main oil-generating Barnett Shale facies is marine and was deposited under dysoxic, strong upwelling, normal salinity conditions. The analysis of two outcrop samples and cuttings from seven wells indicates variability in the Barnett Shale organic facies and a possibility of other oil subfamilies being present. Light hydrocarbon analyses reveal significant terrigenous-sourced condensate input to some reservoirs, resulting in terrigenous and mixed marine-terrigenous light hydrocarbon signatures for many oils. The light hydrocarbon data suggest a secondary, condensate-generating source facies containing terrigenous or mixed terrigenous-marine organic matter. This indication of a secondary source rock that is not revealed by biomarker analysis emphasizes the importance of integrating biomarker and light hydrocarbon data to define petroleum source rocks. Gases in the Fort Worth Basin are thermogenic in origin and appear to be cogenerated with oil from the Barnett Shale, although some gas may also originate by oil cracking. Isotope data indicate minor contribution of biogenic gas. Except for reservoirs in the Pennsylvanian Bend Group, which contain gases spanning the complete range of observed maturities, the gases appear to be stratigraphically segregated, younger reservoirs contain less mature gas, and older reservoirs contain more mature gas. We cannot rule out the possibility that other source units within the Fort Worth Basin, such as the Smithwick Shale, are locally important petroleum sources. Copyright ?? 2007. The American Association of Petroleum Geologists. All rights reserved.

American Association of Petroleum Geologists Bulle↗
USGS1993

Distribution and mode of occurrence of selenium in US coals

Selenium excess and deficiency have been established as the cause of various health problems in man and animals. Combustion of fossil fuels, especially coal, may be a major source of the anthropogenic introduction of selenium in the environment. Coal is enriched in selenium relative to selenium's concentration in most other rocks and relative to selenium in the Earth's crust. Data from almost 9,000 coal samples have been used to determine the concentration and distribution of selenium in US coals. The geometric mean concentration of selenium in US coal is 1.7 ppm. The highest mean selenium value (geometric mean 4.7 ppm) is in the Texas Region. Atlantic Coast (Virginia and North Carolina) and Alaska coals have the lowest geometric means (0.2 and 0.42 ppm, respectively). All western coal regions have mean selenium concentrations of less than 2.0 ppm. In contrast, all coal basins east of the Rocky Mountains (except for several small basins in Rhode Island, Virginia, and North Carolina) have mean selenium values of 1.9 or greater. Generally, variations in selenium concentration do not correlate with variations in ash yield, pyritic sulphur, or organic sulphur concentrations. This may be the result of multiple sources of selenium; however, in some non-marine basins with restricted sources of selenium, selenium has positive correlations with other coal quality parameters. Selenium occurs in several forms in coal but appears to be chiefly associated with the organic fraction, probably substituting for organic sulphur. Other important forms of selenium in coal are selenium-bearing pyrite, selenium-bearing galena, and lead selenide (clausthalite). Water-soluble and ion-exchangeable selenium also have been reported. ?? 1993 Copyright Science and Technology Letters.

Environmental Geochemistry and Health↗
USGS1999

Selected hydrologic data from the Cedar Rapids area, Linn County, Iowa, April 1996 through March 1999

The City of Cedar Rapids, Iowa obtains its municipal water supply from four well fields along the Cedar River. The wells are completed at depths of about 60 to 80 feet in a shallow alluvial aquifer adjacent to the Cedar River. The City of Cedar Rapids and the U.S. Geological Survey have conducted a cooperative study of the groundwater flow system and water quality near the well fields since 1992. The purpose of this report is to document selected hydrologic data collected from April 1996 through March 1999. Data include the results of water-quality analyses, ground-waterlevels continuously measured with pressure transducers and data recorders, and physical properties continuously monitored using multiprobe instruments. Water-quality samples were collected from selected wells and the Cedar River to conduct periodic monitoring, to evaluate ground-water geochemistry, to assess the occurrence of pesticides and herbicide degradates in the alluvial aquifer, and to characterize water quality in shallow ground water near a wetland area in the Seminole Well Field. Types of water-quality analyses included common ions (calcium, chloride, iron, magnesium, manganese, potassium, silica, sodium, and sulfate), trace elements (boron, bromide, and fluoride), nutrients (ammonia as nitrogen, nitrite as nitrogen, nitrite plus nitrate as nitrogen, and orthophosphate as phosphorus), dissolved organic carbon, and selected pesticides and herbicide degradates. Ground-water levels in selected observation wells were continuously measured to assess temporal trends in groundwater levels in the alluvial aquifer and bedrock aquifer, to help calibrate a ground-water flow model being constructed to simulate local groundwater flow under transient conditions near the well fields, and to assess hydrologic conditions near a wetland area in the Seminole Well Field. Physical properties (specific conductance, pH, dissolved oxygen, and water temperature) were continuously monitored to assess temporal variation and to help evaluate the interaction between the Cedar River and ground water in the alluvial aquifer.

Iowa↗
USGS1994

Geochemistry and solid-phase association of chromium in sediment from the Calcasieu River and estuary, Louisiana, U.S.A.

Sediment samples were collected from the lower Calcasieu River and estuary, Louisiana, in a study of the release of metals from sediments to the overlying water column. Whole samples were characterized by analyses that included: (1) determination of total sediment ammonium concentrations; (2) determination of total sediment Cr, Mn and Fe concentrations; (3) extraction of sediment with hydrogen peroxide followed by dilute hydrochloric acid to obtain recoverable metals, including oxides; and (4) extraction of sediment with hydrogen peroxide plus pyrophosphate at a pH of 7-8 to recover organically-bound Cr but not metal oxides. Concentrations of Cr, Mn and Fe in sediment interstitial water were determined. The concentrations of Cr in interstitial water could not be predicted from total sediment concentrations of Cr. Degradation of organic matter appeared to be the mechanism that caused elevated Cr concentrations in the interstitial water. Concentrations of Cr in interstitial water were positively correlated with total concentrations of ammonium in sediment. Concentrations of Cr in interstitial water that exceeded water-column concentrations of Cr were found when the total concentrations of ammonium in sediment exceeded 1 ??mol per gram wet weight. Concentrations of metals in interstitial water that are larger than metal concentrations in the water column create a potential for diffusive flux and metal enrichment of the overlying water column. ?? 1994.

Chemical Geology↗
USGS2007

Centimeter-scale characterization of biogeochemical gradients at a wetland-aquifer interface using capillary electrophoresis

Steep biogeochemical gradients were measured at mixing interfaces in a wetland-aquifer system impacted by landfill leachate in Norman, Oklahoma. The system lies within a reworked alluvial plain and is characterized by layered low hydraulic conductivity wetland sediments interbedded with sandy aquifer material. Using cm-scale passive diffusion samplers, "peepers", water samples were collected in a depth profile to span interfaces between surface water and a sequence of deeper sedimentary layers. Geochemical indicators including electron acceptors, low-molecular-weight organic acids, base cations, and NH4+ were analyzed by capillary electrophoresis (CE) and field techniques to maximize the small sample volumes available from the centimeter-scale peepers. Steep concentration gradients of biogeochemical indicators were observed at various interfaces including those created at sedimentary boundaries and boundaries created by heterogeneities in organic C and available electron acceptors. At the sediment-water interface, chemical profiles with depth suggest that SO42 - and Fe reduction dominate driven by inputs of organic C from the wetland and availability of electron acceptors. Deeper in the sediments (not associated with a lithologic boundary), a steep gradient of organic acids (acetate maximum 8.8 mM) and NH4+ (maximum 36 mM) is observed due to a localized source of organic matter coupled with the lack of electron acceptor inputs. These findings highlight the importance of quantifying the redox reactions occurring in small interface zones and assessing their role on biogeochemical cycling at the system scale.

Oklahoma↗
USGS1999

Copper, lead, mercury and zinc in periphyton from the south Florida ecosystem

Periphyton samples from the Big Cypress National Preserve were analyzed for concentrations of copper, lead, zinc, mercury, and methylmercury. Concentrations of organic carbon, inorganic carbon, nitrogen, and phosphorus in periphyton samples also were determined. The samples were extracted with sodium acetate solution at a pH of 5.5 to determine exchangeable and carbonate phase metal concentrations in periphyton. Total metal concentrations in the periphyton were directly related to the degree of calcite saturation in the water column. Exchangeable and carbonate phase metal concentrations were directly related to the percent inorganic carbon in the samples. A connection between the geochemistry of trace metals and calcite precipitation and dissolution is suggested.

Toxicological and Environmental Chemistry↗
USGS2014

Stratigraphic controls on fluid and solute fluxes across the sediment-water interface of an estuary

Shallow stratigraphic features, such as infilled paleovalleys, modify fresh groundwater discharge to coastal waters and fluxes of saltwater and nutrients across the sediment–water interface. We quantify the spatial distribution of shallow surface water–groundwater exchange and nitrogen fluxes near a paleovalley in Indian River Bay, Delaware, using a hand resistivity probe, conventional seepage meters, and pore-water samples. In the interfluve (region outside the paleovalley) most nitrate-rich fresh groundwater discharges rapidly near the coast with little mixing of saline pore water, and nitrogen transport is largely conservative. In the peat-filled paleovalley, fresh groundwater discharge is negligible, and saltwater exchange is deep (∼1 m). Long pore-water residence times and abundant sulfate and organic matter promote sulfate reduction and ammonium production in shallow sediment. Reducing, iron-rich fresh groundwater beneath paleovalley peat discharges diffusely around paleovalley margins offshore. In this zone of diffuse fresh groundwater discharge, saltwater exchange and dispersion are enhanced, ammonium is produced in shallow sediments, and fluxes of ammonium to surface water are large. By modifying patterns of groundwater discharge and the nature of saltwater exchange in shallow sediments, paleovalleys and other stratigraphic features influence the geochemistry of discharging groundwater. Redox reactions near the sediment–water interface affect rates and patterns of geochemical fluxes to coastal surface waters. For example, at this site, more than 99% of the groundwater-borne nitrate flux to the Delaware Inland Bays occurs within the interfluve portion of the coastline, and more than 50% of the ammonium flux occurs at the paleovalley margin.

Delaware↗
USGS2015

Arsenic and antimony geochemistry of mine wastes, associated waters and sediments at the Giant Mine, Yellowknife, Northwest Territories, Canada

Elevated levels of arsenic (As) and antimony (Sb) in water and sediments are legacy residues found downstream from gold-mining activities at the Giant Mine in Yellowknife, Northwest Territories (NWT), Canada. To track the transport and fate of As and Sb, samples of mine-waste from the mill, and surface water, sediment, pore-water, and vegetation downstream of the mine were collected. Mine waste, pore-water, and sediment samples were analyzed for bulk chemistry, and aqueous and solid-state speciation. Sediment and vegetation chemistry were evaluated using scanning electron microscope imaging, synchrotron-based element mapping and electron microprobe analysis. The distributions of As and Sb in sediments were similar, yet their distributions in the corresponding pore-waters were mostly dissimilar, and the mobility of As was greater than that of Sb. Competition for sorption sites is the most likely cause of elevated Sb concentrations in relatively oxidized pore-water and surface water. The aqueous and solid-state speciation of As and Sb also differed. In pore-water, As(V) dominated in oxidizing environments and As(III) in reducing environments. In contrast, the Sb(V) species dominated in all but one pore-water sample, even under reducing conditions. Antimony(III) appears to preferentially precipitate or adsorb onto sulfides as evidenced by the prevalence of an Sb(III)-S secondary solid-phase and the lack of Sb(III)(aq) in the deeper zones. The As(V)–O solid phase became depleted with depth below the sediment–water interface, and the Sb(V)–O phase persisted under relatively reducing conditions. In the surficial zone at a site populated by Equisetum fluviatile (common horsetail), As and Sb were associated with organic material and appeared mobile in the root zone. In the zone below active plant growth, As and Sb were associated primarily with inorganic phases suggesting a release and reprecipitation of these elements upon plant death. The co-existence of reduced and oxidized As and Sb species, instability of some phases under changing redox conditions, and plant uptake and release pose challenges for remediation efforts at the mine.

Northwest Territories↗
USGS2005

Questa baseline and pre-mining ground-water quality investigation. 14. Interpretation of ground-water geochemistry in catchments other than the Straight Creek catchment, Red River Valley, Taos County, New Mexico, 2002-2003

The U.S. Geological Survey, in cooperation with the New Mexico Environment Department, is investigating the pre-mining ground-water chemistry at the Molycorp molybdenum mine in the Red River Valley, New Mexico. The primary approach is to determine the processes controlling ground-water chemistry at an unmined, off-site but proximal analog. The Straight Creek catchment, chosen for this purpose, consists of the same Tertiary-age quartz-sericite-pyrite altered andesite and rhyolitic volcanics as the mine site. Straight Creek is about 5 kilometers east of the eastern boundary of the mine site. Both Straight Creek and the mine site are at approximately the same altitude, face south, and have the same climatic conditions. Thirteen wells in the proximal analog drainage catchment were sampled for ground-water chemistry. Eleven wells were installed for this study and two existing wells at the Advanced Waste-Water Treatment (AWWT) facility were included in this study. Eight wells were sampled outside the Straight Creek catchment: one each in the Hansen, Hottentot, and La Bobita debris fans, four in a well cluster in upper Capulin Canyon (three in alluvial deposits and one in bedrock), and an existing well at the U.S. Forest Service Questa Ranger Station in Red River alluvial deposits. Two surface waters from the Hansen Creek catchment and two from the Hottentot drainage catchment also were sampled for comparison to ground-water compositions. In this report, these samples are evaluated to determine if the geochemical interpretations from the Straight Creek ground-water geochemistry could be extended to other ground waters in the Red River Valley , including the mine site. Total-recoverable major cations and trace metals and dissolved major cations, selected trace metals, anions, alkalinity; and iron-redox species were determined for all surface- and ground-water samples. Rare-earth elements and low-level As, Bi, Mo, Rb, Re, Sb, Se, Te, Th, U, Tl, V, W, Y, and Zr were determined on selected samples. Dissolved organic carbon (DOC), mercury, sulfate stable isotope composition (δ 34 S and δ 18 O of sulfate), stable isotope composition of water (δ 2 H and δ 18 O of water) were measured for selected samples. Chlorofluorocarbons (CFC) and 3 He and 3 H were measured for age dating on selected samples. Linear regressions from the Straight Creek ground-water data were used to compare ground-water chemistry trends in non-Straight Creek ground waters with Straight Creek alluvial ground-water chemistry dilution trends. Most of the solute trends for the ground waters are similar to those for Straight Creek but there are some notable exceptions. In lithologies that contain substantial pyrite mineralization, acid waters form with similar chemistries to those in Straight Creek and all the waters tend to be calcium-sulfate type. Hottentot ground waters contain substantially lower calcium concentrations relative to those in Straight Creek. This anomaly results from the exposure of rhyolite porphyry in the Hottentot scar and weathering zone. The rhyolite contains less calcium than the altered andesites and tuffs in the Straight Creek catchment and probably does not have the abundant gypsum and calcite. The Hansen ground waters have reached gypsum saturation and have similar calcium, magnesium, and beryllium concentrations as Straight Creek ground waters but have lower concentrations of fluoride, manganese, zinc, cobalt, nickel, copper, and lithium. Lower concentrations of elements related to mineralization at Hansen likely reflect the more distal location of Hansen with respect to intrusive centers that provided the heat source for hydrothermal alteration. The other ground water with water chemistry trends that are outside the Straight Creek trends was from an alluvial well from Capulin Canyon (CC2A). Although it had pH values near 6.0 and most major ions similar to the other Capulin Canyon ground waters, it contained high concentrations of fluoride, manganese, aluminum, iron, beryllium, and zinc similar to a mineralized zone and had low alkalinity. Saturation indices indicate that solubility constraints continue to provide upper limits on some solute concentrations. Siderite, ferrihydrite, calcite, gypsum, rhodochrosite, and barite provide limits for concentrations of Fe(II), Fe(III), Ca, Mn, and Ba, respectively. Beryllium concentrations may be subject to an upper concentration limit by the solubility of Be(OH) 2 but these concentrations probably are not reached in the ground waters. Ground-water isotopic data were consistent with the meteoric water line estimated for precipitation in the Red River Valley, indicating that all the ground waters examined in this study were meteoric, recent in origin, and showed no substantial indication of evaporation. Tritium-helium-3 and chlorofluorocarbon (CFC) age dating were partially successful. Generally, dates were consistent with location and depth of wells. Two samples had good agreement between CFC dates and tritium-helium dates, whereas a third reflected either substantial mixing with younger or older waters or complications arising from excess helium-4. The well at La Bobita appeared to contain a large component of modern water, most likely as a result of mixing with water from Red River alluvial deposits.

New Mexico↗
USGS2008

Natural and Human Influences on Water Quality in a Shallow Regional Unconsolidated Aquifer, Northern Atlantic Coastal Plain

Data collected from more than 400 wells in the surficial unconfined aquifer in the Northern Atlantic Coastal Plain (New York through North Carolina) were compiled and analyzed to improve understanding of multiple natural and human influences on water quality in such shallow regional aquifers. Geochemical patterns were identified and described through principal components analysis on major ions, and correlation and logistic regression were used to relate observed concentrations of nitrate and selected pesticide compounds (atrazine, metolachlor, simazine, and deethylatrazine, an atrazine degradate) and volatile organic compounds (chloroform, 1,1,1-trichloroethane, tetrachlorethene, and methyl tert-butyl ether) to likely influences, such as observed geochemical patterns, land use, hydrogeology, and soils. Variability in major-ion concentrations is primarily related to ionic strength and redox condition. Concentrations of nitrate, pesticides, and volatile organic compounds are related to natural conditions, as well as the distribution of likely sources reflected in land use. Nitrate is most common in aerobic ground water and in relatively well-drained areas, for example; concentrations greater than 0.4 milligrams per liter may result from a variety of human activities, although concentrations greater than 3 milligrams per liter are more likely in agricultural areas. Atrazine, deethylatrazine, and metolachlor also are related to geochemical patterns, likely because ground-water geochemistry reflects hydrogeologic and soil conditions affecting pesticide transport to the water table. Results demonstrate the value of geochemical information along with the distribution of sources and other influences to understanding the regional occurrence of selected compounds in ground water. Such influences are not unique to the Northern Atlantic Coastal Plain, and thus observations and interpretations are relevant to broader areas.

Scientific Investigations Report↗