USGS Science⌕ Search

SEARCH · USGS Science

Results for “Journal of Solution Chemistry”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
USGS2010

Geochemical heterogeneity in a small, stratigraphically complex moraine aquifer system (Ontario, Canada): Interpretation of flow and recharge using multiple geochemical parameters

The Waterloo Moraine is a stratigraphically complex system and is the major water supply to the cities of Kitchener and Waterloo in Ontario, Canada. Despite over 30 years of investigation, no attempt has been made to unify existing geochemical data into a single database. A composite view of the moraine geochemistry has been created using the available geochemical information, and a framework created for geochemical data synthesis of other similar flow systems. Regionally, fluid chemistry is highly heterogeneous, with large variations in both water type and total dissolved solids content. Locally, upper aquifer units are affected by nitrate and chloride from fertilizer and road salt. Typical upper-aquifer fluid chemistry is dominated by calcium, magnesium, and bicarbonate, a result of calcite and dolomite dissolution. Evidence also suggests that ion exchange and diffusion from tills and bedrock units accounts for some elevated sodium concentrations. Locally, hydraulic “windows” cross connect upper and lower aquifer units, which are typically separated by a clay till. Lower aquifer units are also affected by dedolomitization, mixing with bedrock water, and locally, upward diffusion of solutes from the bedrock aquifers. A map of areas where aquifer units are geochemically similar was constructed to highlight areas with potential hydraulic windows.

Hydrogeology Journal↗
USGS2012

Rapid runoff via shallow throughflow and deeper preferential flow in a boreal catchment underlain by frozen silt (Alaska, USA)

In high-latitude catchments where permafrost is present, runoff dynamics are complicated by seasonal active-layer thaw, which may cause a change in the dominant flowpaths as water increasingly contacts mineral soils of low hydraulic conductivity. A 2-year study, conducted in an upland catchment in Alaska (USA) underlain by frozen, well-sorted eolian silt, examined changes in infiltration and runoff with thaw. It was hypothesized that rapid runoff would be maintained by flow through shallow soils during the early summer and deeper preferential flow later in the summer. Seasonal changes in soil moisture, infiltration, and runoff magnitude, location, and chemistry suggest that transport is rapid, even when soils are thawed to their maximum extent. Between June and September, a shift occurred in the location of runoff, consistent with subsurface preferential flow in steep and wet areas. Uranium isotopes suggest that late summer runoff erodes permafrost, indicating that substantial rapid flow may occur along the frozen boundary. Together, throughflow and deep preferential flow may limit upland boreal catchment water and solute storage, and subsequently biogeochemical cycling on seasonal to annual timescales. Deep preferential flow may be important for stream incision, network drainage development, and the release of ancient carbon to ecosystems

Alaska↗
USGS2021

Storm-scale and seasonal dynamics of carbon export from a nested subarctic watershed underlain by permafrost

Subarctic catchments underlain by permafrost sequester a major stock of frozen organic carbon (C), which may be mobilized as the Arctic warms. Warming can impact C export from thawing soils by altering the depth and timing of runoff related to changing storm and fire regimes and altered soil thaw depths. We investigated C export in a first order headwater stream (West Twin Creek) and its receiving third order river (Beaver Creek) in interior Alaska using discrete sampling of dissolved organic and inorganic C (DOC and DIC) and 15-min collection of specific conductance (SC), fluorescent dissolved organic matter (fDOM) and water discharge (Q). Storm SC-Q relationships displayed negative slopes, indicating solute limitation and limited influence of seasonal soil thaw on storm runoff chemistry. Concurrently, fDOM-Q displayed positive slopes that decreased over the summer, indicating flushing of a limited fDOM pool. Baseflow DIC increased over the season concurrent with soil thaw, with higher DIC at the larger scale indicating greater influence of deeper, mineral-rich flow paths. Storm and seasonal trends were generally similar at both scales. The biggest difference was in fDOM, which displayed higher concentrations and slower depletion in the first order stream. Improved process understanding from this study can be used to better predict carbon export and cycling by stream networks as northern forests and arctic regions continue to warm.

Alaska↗
USGS2021

Machine learning predictions of mean ages of shallow well samples in the Great Lakes Basin, USA

The travel time or “age” of groundwater affects catchment responses to hydrologic changes , geochemical reactions, and time lags between management actions and responses at down-gradient streams and wells. Use of atmospheric tracers has facilitated the characterization of groundwater ages, but most wells lack such measurements. This study applied machine learning to predict ages in wells across a large region around the Great Lakes Basin using well, chemistry, and landscape characteristics. For a dataset of age tracers in 961 samples, the travel time from the land surface to the sample location was estimated for each sample using parametric functions. The mean travel times were then modeled using a gradient boosting machine (GBM) algorithm with cross validation tuning of model metaparameters. The GBM approach was able to closely match estimated ages for the training data (RMSE = 0.26 natural-log scale years) and provided a reasonable match to testing data (RMSE = 0.84). Of the variables tested, well characteristics (e.g. depth), land use, hydrologic indicators (e.g. topographic wetness index), and water chemistry (e.g. nitrate, fluoride, and pH), substantially affected the predictions of age. GBM prediction was applied to 14,335 groundwater samples with median sample depth of 5.4 m, indicating for the Great Lakes Basin a broad distribution of ages among wells with a median of 32.9 years. Lag times of decades are likely for these wells to respond to changing solute fluxes near land surface. While depth variables most strongly affected predicted mean ages, chemical constituents exhibited smooth trends with age, consistent with prevailing conceptual models of evolving sources and geochemistry flowpaths. The results provide proof of concept for use of readily available variables of well, landscape, and chemical characteristics to improve groundwater age estimates across large regions.

Great Lakes basin↗
USGS2012

Chemistry of hydrothermal solutions from the southern Juan de Fuca Ridge

Fluids from three vent fields on the southern Juan de Fuca Ridge were sampled in September 1984 using the DSRV Alvin. The fluids are uniquely high in both chloride, which ranges up to twice the seawater value, and in metal content. Simple vapor-liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids. The cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes: (1) subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and (2) dissolution of a chloride-rich phase combined with a possible small loss of gas during sampling procedures. Although measured temperatures were all less than 300°C, quartz geothermometry suggests that the fluids have equilibrated at greater than 340°C. Quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber.

Journal of Geophysical Research B: Solid Earth↗
USGS2009

Low-btu gas in the US Midcontinent: A challenge for geologists and engineers

Several low-btu gas plays can be defined by mapping gas quality by geological horizon in the Midcontinent. Some of the more inviting plays include Permian strata west of the Central Kansas uplift and on the eastern flank of Hugoton field and Mississippi chat and other pays that subcrop beneath (and directly overlie) the basal Pennsylvanian angular unconformity at the southern end of the Central Kansas uplift. Successful development of these plays will require the cooperation of reservoir geologists and process engineers so that the gas can be economically upgraded and sold at a nominal pipeline quality of 950 btu/scf or greater. Nitrogen is the major noncombustible contaminant in these gas fields, and various processes can be utilized to separate it from the hydrocarbon gases. Helium, which is usually found in percentages corresponding to nitrogen, is a possible ancillary sales product in this region. Its separation from the nitrogen, of course, requires additional processing. The engineering solution for low-btu gas depends on the rates, volumes, and chemistry of the gas needing upgrading. Cryogenic methods of nitrogen removal are classically used for larger feed volumes, but smaller feed volumes characteristic of isolated, low-pressure gas fields can now be handled by available small-scale PSA technologies. Operations of these PSA plants are now downscaled for upgrading stripper well gas production. Any nitrogen separation process should be sized, within reason, to match the anticipated flow rate. If the reservoir rock surprises to the upside, the modularity of the upgrading units is critical, for they can be stacked to meet higher volumes. If a reservoir disappoints (and some will), modularity allows the asset to be moved to another site without breaking the bank.

Oil & Gas Journal↗
USGS2006

Investigating the role of gas bubble formation and entrapment in contaminated aquifers: Reactive transport modelling

In many natural and contaminated aquifers, geochemical processes result in the production or consumption of dissolved gases. In cases where methanogenesis or denitrification occurs, the production of gases may result in the formation and growth of gas bubbles below the water table. Near the water table, entrapment of atmospheric gases during water table rise may provide a significant source of O 2 to waters otherwise depleted in O 2 . Furthermore, the presence of bubbles will affect the hydraulic conductivity of an aquifer, resulting in changes to the groundwater flow regime. The interactions between physical transport, biogeochemical processes, and gas bubble formation, entrapment and release is complex and requires suitable analysis tools. The objective of the present work is the development of a numerical model capable of quantitatively assessing these processes. The multicomponent reactive transport code MIN3P has been enhanced to simulate bubble growth and contraction due to in-situ gas production or consumption, bubble entrapment due to water table rise and subsequent re-equilibration of the bubble with ambient groundwater, and permeability changes due to trapped gas phase saturation. The resulting formulation allows for the investigation of complex geochemical systems where microbially mediated redox reactions both produce and consume gases as well as affect solution chemistry, alkalinity, and pH. The enhanced model has been used to simulate processes in a petroleum hydrocarbon contaminated aquifer where methanogenesis is an important redox process. The simulations are constrained by data from a crude oil spill site near Bemidji, MN. Our results suggest that permeability reduction in the methanogenic zone due to in-situ formation of gas bubbles, and dissolution of entrapped atmospheric bubbles near the water table, both work to attenuate the dissolved gas plume emanating from the source zone. Furthermore, the simulations demonstrate that under the given conditions more than 50% of all produced CH 4 partitions to the gas phase or is aerobically oxidised near the water table, suggesting that these processes should be accounted for when assessing the rate and extent of methanogenic degradation of hydrocarbons.

Journal of Contaminant Hydrology↗
USGS1967

The ternary system K2SO4 MgSO4 CaSO4

Melting and subsolidus relations in the system K 2 SO 4 MgSO 4 CaSO 4 were studied using heating-cooling curves, differential thermal analysis, optics, X-ray diffraction at room and high temperatures and by quenching techniques. Previous investigators were unable to study the binary MgSO 4 CaSO 4 system and the adjacent area in the ternary system because of the decomposition of MgSO 4 and CaSO 4 at high temperatures. This problem was partly overcome by a novel sealed-tube quenching method, by hydrothermal synthesis, and by long-time heating in the solidus. As a result of this study, we found: (1) a new compound, CaSO 4 ·3MgSO 4 (m.p. 1201°C) with a field extending into the ternary system; (2) a high temperature form of MgSO 4 with a sluggishly reversible inversion. An X-ray diffraction pattern for this polymorphic form is given; (3) the inversion of β-CaSO 4 (anhydrite) to α-CaSO 4 at 1195°C, in agreement with grahmann ; (1) (4) the melting point of MgSO 4 is 1136°C and that of CaSO 4 is 1462°C (using sealed tube methods to prevent decomposition of the sulphates); (5) calcium langbeinite (K 2 SO 4 ·2CaSO 4 ) is the only compound in the K 2 SO 4 CaSO 4 binary system. This resolved discrepancies in the results of previous investigators; (6) a continuous solid solution series between congruently melting K 2 SOP 4 ·2MgSO 4 (langbeinite) and incongruently melting K 2 SO 4 ·2CaSO 4 (calcium langbeinite); (7) the liquidus in the ternary system consists of primary phase fields of K 2 SO 4 , MgSO 4 , CaSO 4 , langbeinite-calcium langbeinite solid solution, and CaSO 4 ·3MgSO 4 . The CaSO 4 field extends over a large portion of the system. Previously reported fields for the compounds (K 2 SO 4 ·MgSO 4 ·nCaSO 4 ), K 2 SO 4 ·3CaSO 4 and K 2 SO 4 ·CaSO 4 were not found; (8) a minimum in the ternary system at: 740°C, 25% MgSO 4 , 6% CaSO 4 , 69% K 2 SO 4 ; and ternary eutectics at 882°C, 49% MgSO 4 , 19% CaSO 4 , 32% K 2 SO 4 ; and 880°, 67·5% MgSO 4 , 5% CaSO 4 , 27·5% K 2 SO 4 .

Journal of Inorganic and Nuclear Chemistry↗
USGS2013

Chemical controls on fault behavior: weakening of serpentinite sheared against quartz-bearing rocks and its significance for fault creep in the San Andreas system

The serpentinized ultramafic rocks found in many plate-tectonic settings commonly are juxtaposed against crustal rocks along faults, and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults. To investigate this possibility, we conducted triaxial experiments under hydrothermal conditions (200-350°C), shearing serpentinite gouge between forcing blocks of granite or quartzite. In an ultramafic chemical environment, the coefficient of friction, µ, of lizardite and antigorite serpentinite is 0.5-0.6, and µ increases with increasing temperature over the tested range. However, when either lizardite or antigorite serpentinite is sheared against granite or quartzite, strength is reduced to µ ~ 0.3, with the greatest strength reductions at the highest temperatures (temperature weakening) and slowest shearing rates (velocity strengthening). The weakening is attributed to a solution-transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks. The operation of this process will promote aseismic slip (creep) along serpentinite-bearing crustal faults at otherwise seismogenic depths. During short-term experiments serpentine minerals reprecipitate in low-stress areas, whereas in longer experiments new Mg-rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite-crustal rock contact. Long-term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages, which may include extremely weak minerals such as saponite or talc, to play an increasingly important role in the mechanical behavior of the fault. Our results may explain the distribution of creep on faults in the San Andreas system.

California↗
USGS1990

Pattern of solute movement from snow into an upper Michigan stream

Precipitation, snowpack, snowmelt, and streamwater samples were collected in a small gauged watershed draining into Lake Superior during winter 1987–88 to assess the importance of snowmelt pattern and meltwater pathways in the occurrence of solute pulses in streamwater. The snowpack along the south shore of Lake Superior can contain 50% of annual precipitation inputs and 38% of annual ionic inputs including moderate levels of strong acids. Throughout winter, thawed surface soils and small but steady snowpack moisture release promoted movement of snowpack solutes to surface mineral soils. Preferential elution of K + , NH4 + , and H + from the snowpack occurred with the initial thaw. Most ions exhibited pulses in snowmelt. Transport of snowpack solutes to the stream during snowmelt was through near-surface soil macropores and overland flow. For those ions with concentrations higher in the snowpack than in the premelt streamwater, K + , NH 4 + , and H + , the earliest snowmelt pulses had the greatest influence on streamwater chemistry. Unlike other portions of the region with resistant bedrock, the widespread presence of alkaline glacial till provides excess stream acid neutralization capacity (ANC) to buffer acidic inputs. Peak winter streamwater ANC reduction was caused principally by spring melt dilution of base cations and associated alkalinity, constant high SO 4 2- levels, and an increase in NO 3 - . The maximum reduction in stream ANC was concurrent with overland flow. Relative to its snowmelt concentration, NO 3 - was highest in streamwater with some stream input likely the result of nitrification and N mineralization.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1988

Experimental studies in stream-aquifer interaction along the Arkansas River in Central Kansas - Field testing and analysis

During the last several years, streamflows of a number of Kansas streams have been reduced as a result of groundwater declines. In order to better understand and quantify stream-aquifer interrelationships, an eight-day comprehensive stream-aquifer pumping test, followed by recovery monitoring, was conducted along the Arkansas River near Great Bend, Kansas. In addition to water level monitoring in numerous observation wells, streamflow data, streambed hydraulic gradients, neutron probe-based water content of dewatered sediments, water chemistry and other data were collected. The alluvial aquifer is shown to be highly transmissive ( T = 1803 m 2 d −1 ) with the pumping stress (9538 m 3 d −1 ) having a radius of influence larger than 1.77 km, impacting both the aquifer levels and the streamflow in the nearby Arkansas River. Drawdown and recharge boundary effects were observed in all observation wells, including those on the opposite side of the river. The alluvial aquifer did not exhibit a water table behavior and responded as a leaky confined aquifer. A semiconfining clay layer less than 3 m thick and an additional recharge source from a nearby stream-alluvial system were the probable causes of the observed phenomena. Actual streamflow depletion is shown to be appreciably less than the computed depletion based on analytical solutions.

Kansas↗
USGS2005

Ongoing hydrothermal heat loss from the 1912 ash-flow sheet, Valley of Ten Thousand Smokes, Alaska

The June 1912 eruption of Novarupta filled nearby glacial valleys on the Alaska Peninsula with ash-flow tuff (ignimbrite), and post-eruption observations of thousands of steaming fumaroles led to the name ‘Valley of Ten Thousand Smokes’ (VTTS). By the late 1980s most fumarolic activity had ceased, but the discovery of thermal springs in mid-valley in 1987 suggested continued cooling of the ash-flow sheet. Data collected at the mid-valley springs between 1987 and 2001 show a statistically significant correlation between maximum observed chloride (Cl) concentration and temperature. These data also show a statistically significant decline in the maximum Cl concentration. The observed variation in stream chemistry across the sheet strongly implies that most solutes, including Cl, originate within the area of the VTTS occupied by the 1912 deposits. Numerous measurements of Cl flux in the Ukak River just below the ash-flow sheet suggest an ongoing heat loss of ∼250 MW. This represents one of the largest hydrothermal heat discharges in North America. Other hydrothermal discharges of comparable magnitude are related to heat obtained from silicic magma bodies at depth, and are quasi-steady on a multidecadal time scale. However, the VTTS hydrothermal flux is not obviously related to a magma body and is clearly declining. Available data provide reasonable boundary and initial conditions for simple transient modeling. Both an analytical, conduction-only model and a numerical model predict large rates of heat loss from the sheet 90 years after deposition.

Alaska↗
USGS2014

Evaluation of the importance of clay confining units on groundwaterflow in alluvial basins using solute and isotope tracers: the case of Middle San Pedro Basin in southeastern Arizona (USA)

As groundwater becomes an increasingly important water resource worldwide, it is essential to understand how local geology affects groundwater quality, flowpaths and residence times. This study utilized multiple tracers to improve conceptual and numerical models of groundwater flow in the Middle San Pedro Basin in southeastern Arizona (USA) by determining recharge areas, compartmentalization of water sources, flowpaths and residence times. Ninety-five groundwater and surface-water samples were analyzed for major ion chemistry (water type and Ca/Sr ratios) and stable ( 18 O, 2 H, 13 C) and radiogenic ( 3 H, 14 C) isotopes, and resulting data were used in conjunction with hydrogeologic information (e.g. hydraulic head and hydrostratigraphy). Results show that recent recharge (<60 years) has occurred within mountain systems along the basin margins and in shallow floodplain aquifers adjacent to the San Pedro River. Groundwater in the lower basin fill aquifer (semi confined) was recharged at high elevation in the fractured bedrock and has been extensively modified by water-rock reactions (increasing F and Sr, decreasing 14 C) over long timescales (up to 35,000 years BP ). Distinct solute and isotope geochemistries between the lower and upper basin fill aquifers show the importance of a clay confining unit on groundwater flow in the basin, which minimizes vertical groundwater movement.

Arizona↗
USGS2000

Mineralogic and compositional properties of Martian soil and dust: results from Mars Pathfinder

Mars Pathfinder obtained multispectral, elemental, magnetic, and physical measurements of soil and dust at the Sagan Memorial Station during the course of its 83 sol mission. We describe initial results from these measurements, concentrating on multispectral and elemental data, and use these data, along with previous Viking, SNC meteorite, and telescopic results, to help constrain the origin and evolution of Martian soil and dust. We find that soils and dust can be divided into at least eight distinct spectral units, based on parameterization of Imager for Mars Pathfinder (IMP) 400 to 1000 nm multispectral images. The most distinctive spectral parameters for soils and dust are the reflectivity in the red, the red/blue reflectivity ratio, the near-IR spectral slope, and the strength of the 800 to 1000 nm absorption feature. Most of the Pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide(s), sometimes mixed with small but varying degrees of well-crystalline ferric and ferrous phases. Darker soil units appear to be coarser-grained, compacted, and/or mixed with a larger amount of dark ferrous materials relative to bright soils. Nanophase goethite, akaganeite, schwertmannite, and maghemite are leading candidates for the origin of the absorption centered near 900 nm in IMP spectra. The ferrous component in the soil cannot be well-constrained based on IMP data. Alpha proton X-ray spectrometer (APXS) measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average Viking-derived soil elemental composition. Differences exist between Viking and Pathfinder soils, however, including significantly higher S and Cl abundances and lower Si abundances in Viking soils and the lack of a correlation between Ti and Fe in Pathfinder soils. No significant linear correlations were observed between IMP spectral properties and APXS elemental chemistry. Attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions. We attempted to use the Pathfinder results to constrain a number of putative soil and dust formation scenarios, including palagonitization and acid-fog weathering. While the Pathfinder soils cannot be chemically linked to the Pathfinder rocks by palagonitization, this study and McSween et al. [1999] suggest that palagonitic alteration of a Martian basaltic rock, plus mixture with a minor component of locally derived andesitic rock fragments, could be consistent with the observed soil APXS and IMP properties.

Journal of Geophysical Research E: Planets↗
USGS1991

Rock chemistry and fluid inclusion studies as exploration tools for ore deposits in the Sila batholith, southern Italy

The Sila batholith is the focus of an extensive petrogenetic research program, which includes an assessment of its potential to host granite-related ore deposits. Univariate and multivariate statistical techniques were applied to major- and minor-element rock geochemical data. The analysis indicates that the highest potential for mineralization occurs in corundum-normative, peraluminous, unfoliated, relatively late-stage plutons. The plutons are enriched in Rb, Nb, Ta and U, but depleted in Fe, Mg and Sr. The K/Rb, Ba/Rb, Rb/Sr and Rb 3 /Ba·Sr·K indices and high R -factor scores of Si-K-Rb are typical of mineralized granitic rocks. A reconnaissance fluid inclusion study indicates that the sub-solidus rock was infiltrated by solutions of widely different temperatures (50–416°C) and variable salinities (0 to ∼26 wt.% NaCl equivalent). The higher-temperature solutions probably represent granite or magmatic-related Hercynian fluids, whereas the lower-temperature fluids may be either Hercynian or Alpine in age. Fluids with characteristics typical of mineralized “porphyry” systems have not been recognized.

Journal of Geochemical Exploration↗
USGS2011

Groundwater chemistry near an impoundment for produced water, Powder River Basin, Wyoming, USA

The Powder River Basin is one of the largest producers of coal-bed natural gas (CBNG) in the United States. An important environmental concern in the Basin is the fate of the large amounts of groundwater extracted during CBNG production. Most of this produced water is disposed of in unlined surface impoundments. A 6-year study of groundwater flow and water chemistry at one impoundment, Skewed Reservoir, has produced the most detailed data set for any impoundment in the Basin. Data were collected from a network of 21 observation wells and three suction lysimeters. A groundwater mound formed atop bedrock within initially unsaturated, unconsolidated deposits underlying the reservoir. Heterogeneity in physical and chemical properties of sediments resulted in complex groundwater flow paths and highly variable groundwater chemistry. Sulfate, bicarbonate, sodium, and magnesium were the dominant ions in all areas, but substantial variability existed in relative concentrations; pH varied from less than 3 to more than 9, and total dissolved solids concentrations ranged from less than 5000 to greater than 100,000 mg/L. Selenium was a useful tracer of reservoir water; selenium concentrations exceeded 300 μg/L in samples obtained from 18 of the 24 sampling points. Groundwater travel time from the reservoir to a nearby alluvial aquifer (a linear distance of 177 m) was calculated at 474 days on the basis of selenium concentrations. The produced water is not the primary source of solutes in the groundwater. Naturally occurring salts and minerals within the unsaturated zone, dissolved and mobilized by infiltrating impoundment water, account for most of the solute mass in groundwater. Gypsum dissolution, cation-exchange, and pyrite oxidation appear to be important reactions. The complex geochemistry and groundwater flow paths at the study site underscore the difficulty in assessing effects of surface impoundments on water resources within the Powder River Basin.

Wyoming↗
USGS2019

2D micromodel study of clogging behavior of fine-grained particles associated with gas hydrate production in NGHP-02 gas hydrate reservoir sediments

Fine-grained particles (fines) commonly coexist with coarse-grained sediments that host gas hydrate. These fines can be mobilized by liquid and gas flow during gas hydrate production. Once mobilized, fines can clog pore throats and reduce reservoir permeability. Even where particle sizes are smaller than pore-throat sizes, clogs can form due to clusters of fines. For certain types of fines, particularly swelling clays, cluster sizes depend on pore-fluid chemistry, which changes as pore-fluid freshens during gas hydrate dissociation. Fines can also be concentrated by a moving gas/liquid interface, increasing the chances of pore-throat clogging regardless of fines type. To test the relative significance of these clogging mechanisms, 2D micromodel experiments have been conducted with different pore-throat widths (20, 40, 60 and 100 m), single-phase pore-fluids (deionized water and 2M-sodium-chloride solution), and moving gas/liquid interfaces on specimens from Sites NGHP-02-09 and NGHP-02-16 (NGHP-02: National Gas Hydrate Program Expedition 02) as well as a selection of pure fines (silica silt, mica, calcium carbonate, diatoms, kaolin, and bentonite). Clogging depended on the ratio of particle-to-pore throat size, and also on pore-fluid chemistry because the pore-fluid chemistry changes effectively increased or decreased the fines cluster size relative to the pore-throat width. These interactions can be predicted based on the fines electrical sensitivity (defined by Jang and Santamarina, 2016). The fine-grained sediment component (grain size < 75 m) from the primary gas hydrate reservoir layers at Sites NGHP-02-09 and -16 show clogging via blocking or size exclusion (sieving) due to the large particles. Clogs also formed due to bridging or blocking by clusters of the smaller particles. Clogging generally occurred for pore-water sediment concentrations so low (0.2% by mass or less), that it was difficult to resolve the enhanced clogging in the presence of the gas/liquid meniscus.

Bay of Bengal↗
USGS2005

Laboratory determination of the carbon kinetic isotope effects (KIEs) for reactions of methyl halides with various nucleophiles in solution

Large carbon kinetic isotope effects (KIEs) were measured for reactions of methyl bromide (MeBr), methyl chloride (MeCl), and methyl iodide (MeI) with various nucleophiles at 287 and 306 K in aqueous solutions. Rates of reaction of MeBr and MeI with H 2 O (neutral hydrolysis) or Cl − (halide substitution) were consistent with previous measurements. Hydrolysis rates increased with increasing temperature or pH (base hydrolysis). KIEs for hydrolysis were 51 ± 6% 0 for MeBr and 38 ± 8% 0 for MeI. Rates of halide substitution increased with increasing temperature and greater reactivity of the attacking nucleophile, with the fastest reaction being that of MeI with Br − . KIEs for halide substitution were independent of temperature but varied with the reactant methyl halide and the attacking nucleophile. KIEs were similar for MeBr substitution with Cl − and MeCl substitution with Br − (57 ± 5 and 60 ± 9% 0 , respectively). The KIE for halide exchange of MeI was lower overall (33 ± 8% 0 ) and was greater for substitution with Br − (46 ± 6% 0 ) than with Cl − (29 ± 6% 0 ).

Journal of Atmospheric Chemistry↗