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At least 235 records · Page 13Linked to original sources
USGS2010

Carbon and hydrogen isotopic evidence for the origin of combustible gases in water-supply wells in north-central Pennsylvania

The origin of the combustible gases in groundwater from glacial-outwash and fractured-bedrock aquifers was investigated in northern Tioga County, Pennsylvania. Thermogenic methane (CH 4 ) and ethane (C 2 H 6 ) and microbial CH 4 were found. Microbial CH 4 is from natural in situ processes in the shale bedrock and occurs chiefly in the bedrock aquifer. The δ 13 C values of CH 4 and C 2 H 6 for the majority of thermogenic gases from water wells either matched or were between values for the samples of non-native storage-field gas from injection wells and the samples of gas from storage-field observation wells. Traces of C 2 H 6 with microbial CH 4 and a range of C and H isotopic compositions of CH 4 indicate gases of different origins are mixing in sub-surface pathways; gas mixtures are present in groundwater. Pathways for gas migration and a specific source of the gases were not identified. Processes responsible for the presence of microbial gases in groundwater could be elucidated with further geochemical study.

Pennsylvania↗
USGS2011

Mercury capture by selected Bulgarian fly ashes: Influence of coal rank and fly ash carbon pore structure on capture efficiency

Mercury capture by fly ash C was investigated at five lignite- and subbituminous-coal-burning Bulgarian power plants (Republika, Bobov Dol, Maritza East 2, Maritza East 3, and Sliven). Although the C content of the ashes is low, never exceeding 1.6%, the Hg capture on a unit C basis demonstrates that the low-rank-coal-derived fly ash carbons are more efficient in capturing Hg than fly ash carbons from bituminous-fired power plants. While some low-C and low-Hg fly ashes do not reveal any trends of Hg versus C, the 2nd and, in particular, the 3rd electrostatic precipitator (ESP) rows at the Republika power plant do have sufficient fly ash C range and experience flue gas sufficiently cool to capture measurable amounts of Hg. The Republika 3rd ESP row exhibits an increase in Hg with increasing C, as observed in other power plants, for example, in Kentucky power plants burning Appalachian-sourced bituminous coals. Mercury/C decreases with an increase in fly ash C, suggesting that some of the C is isolated from the flue gas stream and does not contribute to Hg capture. Mercury capture increases with an increase in Brunauer-Emmett-Teller (BET) surface area and micropore surface area. The differences in Hg capture between the Bulgarian plants burning low-rank coal and high volatile bituminous-fed Kentucky power plants suggests that the variations in C forms resulting from the combustion of the different ranks also influence the efficiency of Hg capture. ?? 2010 Elsevier Ltd.

Applied Geochemistry↗
USGS2011

Diel variation of selenium and arsenic in a wetland of the Great Salt Lake, Utah

D iel (24-h) changes in Se and As concentrations in a freshwater wetland pond bordering the Great Salt Lake (GSL) were examined. Selenium concentrations (filtered and unfiltered) changed on a diel basis, i.e., were depleted during early morning and enriched during daytime over August 17–18. During the May 24–25, 2006 and September 29–30 diel studies, no significant 24-h trends were observed in Se concentrations compared to August, which showed daily maximums up to 59% greater than the daily minimum. Both filtered and unfiltered As concentrations also varied on a diel cycle, with increased concentrations during early morning and decreased concentrations during daytime. Filtered As concentrations increased 110% during the May 24–25, 2006 diel study. Selenium varied in phase with pH, dissolved O 2 (DO), and water temperature ( T w ) whereas As varied opposite to Se, pH, DO and T w . Changes in pH, DO and T w showed a direct linear correlation ( r = 0.74, 0.75, and 0.55, respectively) to filtered Se. Also pH, DO and T w were inversely correlated to filtered As concentration ( r = −0.88, −0.87, and −0.84, respectively). Equilibrium geochemical speciation and sorption models were used to examine the potential oxidation state changes in Se and As, and sorption and desorption reactions corresponding to the observed 24-h variations in pe and pH. In this wetland it was postulated that diel Se variation was driven by sorption and desorption due to photosynthesis-induced changes in pH and redox conditions. Diel variations of As were hypothesized to be linked to pH-driven sorption and desorption as well as co-precipitation and co-dissolution with mineral phases of Mn.

Utah↗
USGS2011

Ultramafic-derived arsenic in a fractured bedrock aquifer

In the fractured bedrock aquifer of northern Vermont, USA, As concentrations in groundwater range from <1 to 327??g/L (<13-4360nm/L) and these elevated occurrences have a general spatial association with ultramafic rock bodies. The ultramafic rocks in this region are comprised mainly of serpentinites and talc-magnesite rocks with average As concentration of 93ppm and a range from 1 to 1105ppm. By comparison, the other main lithologies in the study area are depleted in As relative to the ultramafics: the average As concentration in metabasaltic rocks is 4.1ppm with a range of <1-69ppm, and mean As concentration in meta-sedimentary phyllites and schists is 22ppm with a range of <1-190ppm. In the ultramafic rocks, As is correlated with Sb and light rare earth elements, indicating that As was introduced to the ultramafic rocks during metasomatism by fluids derived from the subducting slab. Evidence from sequential chemical extraction, X-ray diffraction (XRD) and stoichiometric analysis indicates that the majority of the As is located in antigorite and magnesite (MgCO3) with lesser amounts in magnetite (Fe3O4). Hydrochemistry of monitoring wells drilled into fractured ultramafic rock in a groundwater recharge area with no anthropogenic As source reveals above background As (2-9??g/L) and an Mg-HCO3 hydrochemical signature that reflects dissolution of antigorite and magnesite, confirming that As in groundwater can be derived from ultramafic rock dissolution. Arsenic mobility in groundwater affected by ultramafic rock dissolution may be enhanced by alkaline pH values and relatively high HCO3- concentrations. ?? 2011 Elsevier Ltd.

Applied Geochemistry↗
USGS2011

Particle-size dependence on metal(loid) distributions in mine wastes: Implications for water contamination and human exposure

The mining and processing of metal-bearing ores has resulted in contamination issues where waste materials from abandoned mines remain in piles of untreated and unconsolidated material, posing the potential for waterborne and airborne transport of toxic elements. This study presents a systematic method of particle size separation, mass distribution, and bulk chemical analysis for mine tailings and adjacent background soil samples from the Rand historic mining district, California, in order to assess particle size distribution and related trends in metal(loid) concentration as a function of particle size. Mine tailings produced through stamp milling and leaching processes were found to have both a narrower and finer particle size distribution than background samples, with significant fractions of particles available in a size range (???250 ??m) that could be incidentally ingested. In both tailings and background samples, the majority of trace metal(loid)s display an inverse relationship between concentration and particle size, resulting in higher proportions of As, Cr, Cu, Pb and Zn in finer-sized fractions which are more susceptible to both water- and wind-borne transport as well as ingestion and/or inhalation. Established regulatory screening levels for such elements may, therefore, significantly underestimate potential exposure risk if relying solely on bulk sample concentrations to guide remediation decisions. Correlations in elemental concentration trends (such as between As and Fe) indicate relationships between elements that may be relevant to their chemical speciation. ?? 2011 Elsevier Ltd.

Applied Geochemistry↗
USGS2011

Surface complexation modeling for predicting solid phase arsenic concentrations in the sediments of the Mississippi River Valley alluvial aquifer, Arkansas, USA

The potential health impact of As in drinking water supply systems in the Mississippi River Valley alluvial aquifer in the state of Arkansas, USA is significant. In this context it is important to understand the occurrence, distribution and mobilization of As in the Mississippi River Valley alluvial aquifer. Application of surface complexation models (SCMs) to predict the sorption behavior of As and hydrous Fe oxides (HFO) in the laboratory has increased in the last decade. However, the application of SCMs to predict the sorption of As in natural sediments has not often been reported, and such applications are greatly constrained by the lack of site-specific model parameters. Attempts have been made to use SCMs considering a component additivity (CA) approach which accounts for relative abundances of pure phases in natural sediments, followed by the addition of SCM parameters individually for each phase. Although few reliable and internally consistent sorption databases related to HFO exist, the use of SCMs using laboratory-derived sorption databases to predict the mobility of As in natural sediments has increased. This study is an attempt to evaluate the ability of the SCMs using the geochemical code PHREEQC to predict solid phase As in the sediments of the Mississippi River Valley alluvial aquifer in Arkansas. The SCM option of the double-layer model (DLM) was simulated using ferrihydrite and goethite as sorbents quantified from chemical extractions, calculated surface-site densities, published surface properties, and published laboratory-derived sorption constants for the sorbents. The model results are satisfactory for shallow wells (10.6 m below ground surface), where the redox condition is relatively oxic or mildly suboxic. However, for the deep alluvial aquifer (21–36.6 m below ground surface) where the redox condition is suboxic to anoxic, the model results are unsatisfactory.

Arkansas↗
USGS2011

Biogeochemical factors affecting the presence of 210 Po in groundwater

The discovery of natural 210 Po enrichment at levels exceeding 500 mBq/L in numerous domestic wells in northern Nevada, USA, led to a geochemical investigation of the processes responsible for its mobilization. 210 Po activities in 63 domestic and public-supply wells ranged from below 1 mBq/L to 6590 ± 590 mBq/L, among the highest reported levels in the USA. There is little spatial or depth variability in 210Pb activity in study-area sediments and mobilization of a few percent of the 210 Po in the sediments would account for all of the 210 Po in water. Stable-isotope measurements indicate SO 4 reduction has occurred in all 210 Po contaminated wells. Sulfide species are not accumulating in the groundwater in much of Lahontan Valley, probably because of S cycling involving microbial SO 4 reduction, abiotic oxidation of H 2 S to S 0 by Mn(IV), followed by microbial disproportionation of S 0 to H 2 S and SO 4 . The high pH, Ca depletion, MnCO3 saturation, and presence of S 0 in Lahontan Valley groundwater may be consequences of the anaerobic S cycling. Consistent with data from naturally-enriched wells in Florida, 210 Po activities begin to decrease when aqueous sulfide species begin to accumulate. This may be due to formation and precipitation of PoS, however, Eh–pH diagrams suggest PoS would not be stable in study-area groundwater. An alternative explanation for the study area is that H 2 S accumulation begins when anaerobic S cycling stops because Mn oxides are depleted and their reduction is no longer releasing 210 Po. Common features of 210 Po-enriched groundwater were identified by comparing the radiological and geochemical data from Nevada with data from naturally-enriched wells in Finland, and Florida and Maryland in the USA. Values of pH ranged from <5 in Florida wells to >9 in Nevada wells, indicating that pH is not critical in determining whether 210 Po is present. Where U is present in the sediments, the data suggest 210 Po levels may be elevated in aquifers with (1) SO 4 -reducing waters with low H 2 S concentrations, or (2) anoxic or oxic waters with extremely high Rn activities, particularly if the water is turbid.

Applied Geochemistry↗
USGS2011

Arsenic in sediments, groundwater, and streamwater of a glauconitic Coastal Plain terrain, New Jersey, USA-Chemical " fingerprints" for geogenic and anthropogenic sources

Glauconite-bearing deposits are found worldwide, but As levels have been determined for relatively few. The As content of glauconites in sediments of the Inner Coastal Plain of New Jersey can exceed 100 mg/kg, and total As concentrations (up to 5.95 μg/L) found historically and recently in streamwaters exceed the State standard. In a major watershed of the Inner Coastal Plain, chemical “fingerprints” were developed for streambed sediments and groundwater to identify contributions of As to the watershed from geologic and anthropogenic sources. The fingerprint for streambed sediments, which included Be, Cr, Fe and V, indicated that As was predominantly of geologic origin. High concentrations of dissolved organic C, nutrients (and Cl − ) in shallow groundwater indicated anthropogenic inputs that provided an environment where microbial activity released As from minerals to groundwater discharging to the stream. Particulates in streamwater during high flow constituted most of the As load; the chemical patterns for these particulates resembled the geologic fingerprint of the streambed sediments. The As/Cr ratio of these suspended particles likely indicates they derived not only from runoff, but from groundwater inputs, because As contributed by groundwater is sequestered on streambed sediments. Agricultural inputs of As were not clearly identified, although chemical characteristics of some sediments indicated vehicle-related inputs of metals. Sediment sampling during dry and wet years showed that, under differing hydrologic conditions, local anthropogenic fingerprints could be obscured but the geologic fingerprint, indicating glauconitic sediments as an As source, was robust.

New Jersey↗
USGS2011

A model for assessing, quantifying, and correcting for index element mobility in weathering studies

Evidence shows that high field strength (HFS) elements commonly used to index chemical weathering are variably mobile. This mobility may be linked to redistribution of suspended solids. A mass-balance model is presented that can quantify such redistribution without assuming immobility for any single element. Two tropical weathering profiles on quartz diorite and basalt are examined and redistribution of the HFS elements Zr and Ti is documented, along with potential corrections for the resulting changes in measured concentrations.

Applied Geochemistry↗
USGS2011

Investigating the complex interface where bedrock transforms to regolith

The interface where bedrock transforms to regolith is not planar but rather has a roughness that varies with the scale of observation. The complexity of this surface is manifested in both element-depth and fragment size-depth distributions and may sometimes be related to the longitudinal profiles of watershed streams. The fractal nature of the bedrock-regolith interface means that the interface has a “thickness” which is >20 m in two ridgetop examples from Pennsylvania and Puerto Rico. Such weathering thicknesses, modeled as a function of one-dimensional fluid flow, are affected by the balance between rates of weathering and erosion. One-dimensional models are consistent with weathering advance rates that vary with equilibrium solubility and porefluid velocities (and not reaction kinetics). However, fluid flow is not strictly downward and one-dimensional. Permeability of regolith changes as particle size and bulk density changes with depth. Thus, both downward and lateral flow occurs especially at reaction fronts where reactions change permeability. The rate of weathering advance is, therefore, affected by the 3-dimensional distribution of reaction zones that affect permeability across the watershed. Quantitative models of such phenomena over a range of spatial and temporal scales are needed.

Applied Geochemistry↗
USGS2011

The delicate balance between soil production and erosion, and its role on landscape evolution

The diversity in landscapes at the Earth’s surface is the result, amongst other things, of the balance (or imbalance) between soil production and erosion. While erosion rates are well constrained, it is only recently that we have been able to quantify rates of soil production. Uranium-series isotopes have been useful to provide such estimates independently of erosion rates. In this study, new U-series isotope are presented data from weathering profiles developed over andesitic parent rock in Puerto Rico, and granitic bedrock in southeastern Australia. The site in Australia is located on a highland plateau, neighbouring a retreating escarpment where soil production rates between 10 and 50 mm/kyr have been determined. The results show that production rates are invariant in these two regions of Australia with values between 15 and 25 mm/kyr for the new site. Andesitic soils show much faster rates, about 200 mm/kyr. Overall, soil production rates determined with U-series isotopes range between 10 and 200 mm/kyr. This is comparable to erosion rates in soil-mantled landscapes, but faster than erosion in cratonic areas and slower than in alpine regions and cultivated areas. This suggests that soil-mantled landscapes maintain soil because they can: there is a balance between production and erosion. Similarly, thick weathering profiles develop in cratonic areas because, despite slow erosion rates, soil production is still significant. Bare landscapes in Alpine regions are probably the result of the inability of soil production to catch up with fast erosion rates, although this needs testing by U-series isotope studies of these regions. Finally, the range of production rates is up to several orders of magnitude lower than erosion rates in cultivated areas, demonstrating quantitatively the fast depletion of soil resources with common agricultural practices.

Applied Geochemistry↗
USGS2011

Vadose zone controls on weathering intensity and depth: Observations from grussic saprolites

An investigation of vadose zone weathering processes has been undertaken on grussic saprolites developed on Californian granitoids. Preliminary results indicate strong climatic control, through infiltration, on the depth and intensity of weathering. At sites with higher infiltration, the vadose zone is comprehensively altered to grussic saprolite and saprock. Conversely, lower infiltration sites display only thin grussic saprolites, strongly influenced by rock texture. Both vadose zone and weathering depth appear to be governed by local base level, and vadose zone hydrology exerts a fundamental control on the effective operation and relative dominance of the key weathering reactions. In zones of matrix permeability, oxidation of biotite comprehensively disaggregates the rock but results in little mass loss and clay mineral formation. Conversely, the higher transient flow rates that characterize zones of fracture permeability result in plagioclase hydrolysis, significant mass losses and accompanying clay mineral formation. A variable hydrological regime may also contribute to high partial pressures of O 2 in vadose zone pore waters and pore spaces, thereby enhancing the oxidative environment and further predisposing grussic saprolite formation.

Applied Geochemistry↗
USGS2011

Carbon and nitrogen biogeochemistry of a Prairie Pothole Wetland, Stutsman County, North Dakota, USA

The concentration and form of dissolved organic C (DOC) and N species (NH 4 + and NO 3 - ) were investigated as part of a larger hydrogeochemical study of the Cottonwood Lake Study Area within the Prairie Potholes region. Groundwater, pore water and surface wetland water data were used to help characterize the relationships between surface and groundwater with respect to nutrient dynamics. Photosynthesis and subsequent decomposition of vegetation in these hydrologically dynamic wetlands generates a large amount of dissolved C and N, although the subsurface till, derived in part from organic matter rich Pierre Shale, is a likely secondary source of nutrients in deeper groundwater. While surface water DOC concentrations ranged from 2.2 to 4.6 mM, groundwater values were 0.15 mM to 3.7 mM. Greater specific UV absorbance (SUVA 254 ) in the wetland water column and in soil pore waters relative to groundwater indicate more reactive DOC in the surface to near-surface waters. Circumneutral wetlands had greater SUVA254, possibly because of variations in vegetation communities. The dominant inorganic nitrogen species was NH 4 + in both wetland water and most ground water samples. The exceptions were 3 wells with NO 3 - ranging from 38 to 115 μM. Shallow groundwater wells (Well 28 and Well 13S) with greater connection to wetland surface water had greater NH 4 + concentrations (1.1 mM and 120 μM) than other well samples (3–90 μM). Pore water nutrient chemistry was more similar to surface water than ground water. Nitrogen results suggest reducing conditions in both groundwater and surface water, possibly due to the microbial uptake of O 2 by decaying vegetation in the wetland water column, labile organic C available in shallow groundwater, or the oxidation of pyrite associated with the subsurface.

North Dakota↗
USGS2011

Using stable isotopes to understand hydrochemical processes in and around a Prairie Pothole wetland in the Northern Great Plains, USA

Millions of internally drained wetland systems in the Prairie Potholes region of the northern Great Plains (USA and Canada) provide indispensable habitat for waterfowl and a host of other ecosystem services. The hydrochemistry of these systems is complex and a crucial control on wetland function, flora and fauna. Wetland waters can have high concentrations of SO 2- 4 due to the oxidation of large amounts of pyrite in glacial till that is in part derived from the Pierre shale. Water chemistry including δ 18 O H2O , δ 2 H H2O , and δ 34 S SO4 values, was determined for groundwater, soil pore water, and wetland surface water in and around a discharge wetland in North Dakota. The isotopic data for the first time trace the interaction of processes that affect wetland chemistry, including open water evaporation, plant transpiration, and microbial SO 4 reduction.

Applied Geochemistry↗
USGS2011

Seasonal dynamics of CO2 profiles across a soil chronosequence, Santa Cruz, California

Concentrations of CO 2 in soil atmosphere and CO 2 efflux were measured across a marine terrace soil chronosequence near Santa Cruz, California. Soil development, specifically the formation of an argillic horizon, has created a two-tier soil gas profile in the older terrace soils. The soil above the argillic horizon has seasonal variations in soil CO 2 associated with plant respiration. The older soils with dense argillic horizons maintain a year round ∼1%CO 2 below the argillic horizon. The CO 2 efflux during the growing season is higher on the older terraces.

California↗
USGS2011

Methods for evaluating in-stream attenuation of trace organic compounds

Wastewater treatment plants are often the most substantial contributor of trace organic compounds including pharmaceuticals, steroidal hormones, and surfactants to surface waters. Studying stream reaches below wastewater treatment plants provide valuable information on the environmental persistence of these compounds. Three methods for conducting field investigations to evaluate in-stream attenuation of trace organic compounds are presented: (1) using intrinsic tracers in wastewater, (2) environmental sampling coupled with dye studies to assess travel times between sample locations, and (3) Lagrangian sampling. Advantages and limitations of each method are discussed, along with key findings from several investigations.

Applied Geochemistry↗
USGS2011

Composition, stability, and measurement of reduced uranium phases for groundwater bioremediation at Old Rifle, CO

Reductive biostimulation is currently being explored as a possible remediation strategy for U-contaminated groundwater, and is being investigated at a field site in Rifle, CO, USA. The long-term stability of the resulting U(IV) phases is a key component of the overall performance of the remediation approach and depends upon a variety of factors, including rate and mechanism of reduction, mineral associations in the subsurface, and propensity for oxidation. To address these factors, several approaches were used to evaluate the redox sensitivity of U: (1) measurement of the rate of oxidative dissolution of biogenic uraninite (UO 2(s) ) deployed in groundwater at Rifle, (2) characterization of a zone of natural bioreduction exhibiting relevant reduced mineral phases, and (3) laboratory studies of the oxidative capacity of Fe(III) and reductive capacity of Fe(II) with regard to U(IV) and U(VI), respectively.

Colorado↗
USGS2011

Responses of soil and water chemistry to mountain pine beetle induced tree mortality in Grand County, Colorado, USA

Pine forest in northern Colorado and southern Wyoming, USA, are experiencing the most severe mountain pine beetle epidemic in recorded history, and possible degradation of drinking-water quality is a major concern. The objective of this study was to investigate possible changes in soil and water chemistry in Grand County, Colorado in response to the epidemic, and to identify major controlling influences on stream-water nutrients and C in areas affected by the mountain pine beetle. Soil moisture and soil N increased in soils beneath trees killed by the mountain pine beetle, reflecting reduced evapotranspiration and litter accumulation and decay. No significant changes in stream-water NO 3 - "> NO 3 - or dissolved organic C were observed; however, total N and total P increased, possibly due to litter breakdown or increased productivity related to warming air temperatures. Multiple-regression analyses indicated that % of basin affected by mountain pine beetles had minimal influence on stream-water NO 3 - "> NO 3 - and dissolved organic C; instead, other basin characteristics, such as percent of the basin classified as forest, were much more important.

Colorado↗