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

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At least 577 records · Page 32Linked to original sources
USGS2005

Indoor radon risk potential of Hawaii

A comprehensive evaluation of radon risk potential in the State of Hawaii indicates that the potential for Hawaii is low. Using a combination of factors including geology, soils, source-rock type, soil-gas radon concentrations, and indoor measurements throughout the state, a general model was developed that permits prediction for various regions in Hawaii. For the nearly 3,100 counties in the coterminous U.S., National Uranium Resource Evaluation (NURE) aerorad data was the primary input factor. However, NURE aerorad data was not collected in Hawaii, therefore, this study used geology and soil type as the primary and secondary components of potential prediction. Although the radon potential of some Hawaiian soils suggests moderate risk, most houses are built above ground level and the radon soil potential is effectively decoupled from the house. Only underground facilities or those with closed or recirculating ventilation systems might have elevated radon potential. ?? 2005 Akade??miai Kiado??.

Journal of Radioanalytical and Nuclear Chemistry↗
USGS2010

Accuracy of gap analysis habitat models in predicting physical features for wildlife-habitat associations in the southwest U.S.

Despite widespread and long-standing efforts to model wildlife-habitat associations using remotely sensed and other spatially explicit data, there are relatively few evaluations of the performance of variables included in predictive models relative to actual features on the landscape. As part of the National Gap Analysis Program, we specifically examined physical site features at randomly selected sample locations in the Southwestern U.S. to assess degree of concordance with predicted features used in modeling vertebrate habitat distribution. Our analysis considered hypotheses about relative accuracy with respect to 30 vertebrate species selected to represent the spectrum of habitat generalist to specialist and categorization of site by relative degree of conservation emphasis accorded to the site. Overall comparison of 19 variables observed at 382 sample sites indicated ???60% concordance for 12 variables. Directly measured or observed variables (slope, soil composition, rock outcrop) generally displayed high concordance, while variables that required judgments regarding descriptive categories (aspect, ecological system, landform) were less concordant. There were no differences detected in concordance among taxa groups, degree of specialization or generalization of selected taxa, or land conservation categorization of sample sites with respect to all sites. We found no support for the hypothesis that accuracy of habitat models is inversely related to degree of taxa specialization when model features for a habitat specialist could be more difficult to represent spatially. Likewise, we did not find support for the hypothesis that physical features will be predicted with higher accuracy on lands with greater dedication to biodiversity conservation than on other lands because of relative differences regarding available information. Accuracy generally was similar (>60%) to that observed for land cover mapping at the ecological system level. These patterns demonstrate resilience of gap analysis deductive model processes to the type of remotely sensed or interpreted data used in habitat feature predictions. ?? 2010 Elsevier B.V.

Ecological Modelling↗
USGS2016

An overview of current applications, challenges, and future trends in distributed process-based models in hydrology

Process-based hydrological models have a long history dating back to the 1960s. Criticized by some as over-parameterized, overly complex, and difficult to use, a more nuanced view is that these tools are necessary in many situations and, in a certain class of problems, they are the most appropriate type of hydrological model. This is especially the case in situations where knowledge of flow paths or distributed state variables and/or preservation of physical constraints is important. Examples of this include: spatiotemporal variability of soil moisture, groundwater flow and runoff generation, sediment and contaminant transport, or when feedbacks among various Earth’s system processes or understanding the impacts of climate non-stationarity are of primary concern. These are situations where process-based models excel and other models are unverifiable. This article presents this pragmatic view in the context of existing literature to justify the approach where applicable and necessary. We review how improvements in data availability, computational resources and algorithms have made detailed hydrological simulations a reality. Avenues for the future of process-based hydrological models are presented suggesting their use as virtual laboratories, for design purposes, and with a powerful treatment of uncertainty.

Journal of Hydrology↗
USGS2006

Detection of water quality trends at high, median, and low flow in a Catskill Mountain stream, New York, through a new statistical method

The effects of changes in acid deposition rates resulting from the Clean Air Act Amendments of 1990 should first appear in stream waters during rainstorms and snowmelt, when the surface of the watershed is most hydrologically connected to the stream. Early detection of improved stream water quality is possible if trends at high flow could be separately determined. Trends in concentrations of sulfate (SO 4 2− ), nitrate (NO 3 − ), calcium plus magnesium (Ca 2+ +Mg 2+ ), and acid‐neutralizing capacity (ANC) in Biscuit Brook, Catskill Mountains, New York, were assessed through segmented regression analysis (SRA). The method uses annual concentration‐to‐discharge relations to predict concentrations for specific discharges, then compares those annual values to determine trends at specific discharge levels. Median‐flow trends using SRA were comparable to those predicted by the seasonal Kendall tau test and a multiple regression residual analysis. All of these methods show that stream water SO 4 2− concentrations have decreased significantly since 1983; Ca 2+ +Mg 2+ concentrations have decreased at a steady but slower rate than SO 4 2− ; and ANC shows no trend. The new SRA method, however, reveals trends that differ at specified flow levels. ANC has increased, and NO 3 − concentrations have decreased at high flows, but neither has changed as significantly at low flows. The general downward trend in SO 4 2− flattened at median flow and reversed at high flow between 1997 and 2002. The reversal of the high‐flow SO 4 2− trend is consistent with increases in SO 4 2− concentrations in both precipitation and soil solutions at Biscuit Brook. Separate calculation of high‐flow trends provides resource managers with an early detection system for assessing changes in water quality resulting from changes in acidic deposition.

Water Resources Research↗
USGS1997

The Phanerozoic impact cratering rate: Evidence from the farside of the Moon

The relatively recent (<1 b.y.) flux of asteroids and comets forming large craters on the Earth and Moon may be accurately recorded by craters with bright rays on the Moon's farside. Many previously unknown farside rayed craters are clearly distinguished in the low-phase-angle images returned by the Clementine spacecraft. Some large rayed craters on the lunar nearside are probably significantly older than 1 Ga; rays remain visible over the maria due to compositional contrasts long after soils have reached optical maturity. Most of the farside crust has a more homogeneous composition and only immature rays are visible. The size-frequency distribution of farside rayed craters is similar to that measured for Eratosthenian craters (up to 3.2 b.y.) at diameters larger than 15 km. The areal density of farside rayed craters matches that of a corrected tabulation of nearside Copernican craters. Hence the presence of bright rays due to immature soils around large craters provides a consistent time-stratigraphic basis for defining the base of the Copernican System. The density of large craters less than ∼3.2 b.y. old is ∼3.2 times higher than that of large farside rayed craters alone. This observation can be interpreted in two ways: (1) the average cratering rate has been constant over the past 3.2 b.y. and the base of the Copernican is ∼1 Ga, or (2) the cratering rate has increased in recent geologic time and the base of the Copernican is less than 1 Ga. We favor the latter interpretation because the rays of Copernicus (800–850 m.y. old) appear to be very close to optical maturity, suggesting that the average Copernican cratering rate was ∼35% higher than the average Eratosthenian rate. Other lines of evidence for an increase in the Phanerozoic (545 Ga) cratering rate are (1) the densities of small craters superimposed on Copernicus and Apollo landing sites, (2) the rates estimated from well-dated terrestrial craters (≤120 m.y.) and from present-day astronomical observations, and (3) the Proterozoic rate suggested by the crater record of Australia. The hypothesis most consistent with several key observations is that the cratering rate has increased by ∼2x during the past ∼300 m.y‥

Journal of Geophysical Research E: Planets↗
USGS2017

Is biotic resistance enhanced by natural variation in diversity?

Theories linking diversity to ecosystem function have been challenged by the widespread observation of more exotic species in more diverse native communities. Few studies have addressed the underlying processes by dissecting how biotic resistance to new invaders may be shaped by the same environmental influences that determine diversity and other community properties. In grasslands with heterogeneous soils, we added invaders and removed competitors to analyze the causes of invasion resistance. Abiotic resistance was measured using invader success in the absence of the resident community. Biotic resistance was measured as the reduction in invader success in the presence of the resident community. Invaders were most successful where biotic resistance was lowest and abiotic resistance was highest, confirming the dominant role of biotic resistance. Contrary to theory, though, biotic resistance was highest where both species richness and functional diversity were lowest. In the multivariate framework of a structural equation model, biotic resistance was independent of community diversity, and was highest where fertile soils led to high community biomass. Seed predation slightly augmented biotic resistance without qualitatively changing the results. Soil-related genotypic variation in the invader also did not affect the results. We conclude that in natural systems, diversity may be correlated with invasibility and yet have little effect on biotic resistance to invasion. More generally, the environmental causes of variation in diversity should be considered when examining the potential functional consequences of diversity.

Oikos↗
USGS1982

Preliminary evaluation of the potential for artificial ground-water recharge in eastern San Joaquin County, California

In response to increasing demand on water supplies and declining water levels in San Joaquin County, the U. S. Geological Survey, in cooperation with the San Joaquin County Flood Control and Water Conservation District, is evaluating the potential for artificially recharging the aquifer system in eastern San Joaquin County, California. Through a well canvass and analyses of existing data on geology, soils, and drillers logs, this study (phase one of three phases) resulted in identification of 20 sites for exploratory test drilling in areas potentially favorable for artificial recharge. Ten of the sites are in areas adjacent to the Mokelumne River, six are in areas adjacent to the Calaveras River and Mormon Slough, and four are north of Littlejohns Creek. (USGS)

Open-File Report↗
USGS1993

Effects of recharge on the transport of agricultural chemicals at the Princeton, Minn. Management Systems Evaluation Area (MSEA), 1991-92

Rates of water movement through the unsaturated zone greatly affect the amount and concentrations of agricultural chemicals that may reach the water table. For example, recharge can flush to the water table chemicals that have accumulated In the unsaturated zone during dry periods. A better understanding of how topography influences recharge and the movement of agricultural chemicals is needed. In 1991, the U.S. Geological Survey (USGS), with funding from the USGS Toxic Substances Hydrology Program, began studying the movement of water and agricultural chemicals to the water table at the Management Systems Evaluation Area (MSEA) near Princeton, Minnesota. Instruments were installed to measure the movement of moisture through the soil beneath a corn field. Samples of the recharge water were analyzed for concentrations of agricultural chemicals and tracers. Field recharge and tracer tests were simulated In the laboratory.

Minnesota↗
USGS1995

U.S. Geological Survey Subsidence Interest Group conference, Edwards Air Force Base, Antelope Valley, California, November 18-19, 1992; Abstracts and summary

Land subsidence, the loss of surface elevation as a result of the removal of subsurface support, affects every state in the United States. More than 17,000 mi 2 of land in the United States has been lowered by the various processes that produce land subsidence with annual costs from resulting flooding and structural damage that exceed $125 million. It is estimated that an additional $400 million is spent nationwide in attempts to control subsidence. Common causes of land subsidence include the removal of oil, gas, and water from underground reservoirs; dissolution of limestone aquifers (sinkholes); underground mining activities; drainage of organic soils; and hydrocompaction (the initial wetting of dry soils). Overdrafting of aquifers is the major cause of areally extensive land subsidence, and as ground-water pumping increases, land subsidence also will increase. Land subsidence and its effects on engineering structures have been recognized for centuries, but it was not until this century that the processes that produce land subsidence were identified and understood. In 1928, while working with field data from a test of the Dakota Sandstone aquifer, O.E. Meinzer of the U.S. Geological Survey recognized the compressibility of aquifers. Around the same time, Karl Terzaghi, a soil scientist working at Harvard University, developed the one-dimensional consolidation theory that provided a quantitative means of predicting soil compaction resulting from the drainage of compressible soils. Thus, with the recognition of the compressibility of aquifers (Meinzer), and the development of a quantitative means of predicting soil compaction as a consequence of the reduction of intergranular pore pressure (Terzaghi), the theory of aquifer-system compaction was formed. With the widespread availability of electric power in rural areas, and the advent of the deep turbine pump, ground-water withdrawals increased dramatically throughout the country in the 1940's and 1950's. Along with this unprecedented increase in pumpage, substantial amounts of land subsidence were observed in several areas of the United States, most notably in Arizona, California, and Texas. Beginning in 1955, under the direction of Joseph Poland, the Geological Survey began the "Mechanics of Aquifers Project," which focused largely on the processes that resulted in land subsidence due to the withdrawal of ground water. This research team gained international renown as they advanced the scientific understanding of aquifer mechanics and land-subsidence theory. The results of field studies by members of this research group not only verified the validity of the application of Terzaghi's consolidation theory to compressible aquifers, but they also provided definitions, methods of quantification, and confirmation of the interrelation among hydraulic head declines, aquifer-system compaction, and land subsidence. In addition to conducting pioneering research, this group also formed a "center of expertise," providing a focal point within the Geological Survey for the dissemination of technology and scientific understanding in aquifer mechanics. However, when the "Mechanics of Aquifers Project" was phased out in 1984, the focal point for technology transfer no longer existed. Interest among various state and local agencies in land subsidence has persisted, and the Geological Survey has continued to participate in a broad spectrum of cooperative and Federally funded projects in aquifer mechanics and land subsidence. These projects are designed to identify and monitor areas with the potential for land subsidence, to conduct basic research in the processes that control land subsidence and the development of earth fissures, as well as to develop new quantitative tools to predict aquifer-system deformation. In 1989 an ad hoc "Aquifer Mechanics and Subsidence Interest Group" (referred to herein as the "Subsidence Interest Group") was formed

California↗
USGS1995

Collection of short papers on Beaver Creek watershed studies in West Tennessee, 1989-94

In 1989, the U.S. Geological Survey began a scientific investigation to evaluate the effect of agricultural activities on water quality and the effectiveness of agricultural best management practices in the Beaver Creek watershed, West Tennessee. The project is being conducted jointly with other Federal, State, county agencies, the farming community, and academic institutions, in support of the U.S. Department of Agriculture's Hydrologic Unit Area program. The Beaver Creek project has evolved into a long-term watershed assessment and monitoring program. In 1991, a grant was received to develop and evaluate sampling strategies for higher order streams. During the summer of 1992, a reconnaissance of water-quality conditions for the shallow aquifers in Shelby, Tipton, Fayette, and Haywood Counties was conducted and included 89 domestic wells in the Beaver Creek watershed. Results from this effort lead to the development of a 1-year program to evaluate cause- and-effect relations that can explain the observed water-quality conditions for the shallow aquifers in the watershed. In 1992 the USGS, in cooperation with the Soil Conservation Service and the Shelby County Soil Conservation District, began an evaluation of in-stream processes and in-stream resource-management systems. In 1993, a biomonitoring program was established in the watershed. This collection of eight articles and abstracts was originally published in the American Water Resources Association National Symposium on Water Quality Proceedings for the national conference held in Chicago in 1994 and describes what has been learned in the study to date.

Tennessee↗
USGS2018

Water budget of the upper Chehalis River Basin, southwestern Washington

Groundwater and surface water collectively supply the domestic, agricultural, and industrial needs of the 895-square mile upper Chehalis River Basin upstream of Grand Mound, Washington, while providing streamflow for fish and other aquatic species in the Chehalis River and its tributaries. To support sustainable water management decision-making, a water budget (including precipitation, interception, groundwater recharge, surface runoff, and groundwater pumping) was developed for the upper Chehalis River Basin during October 2001–September 2015. Water-budget components were estimated from the U.S. Geological Survey Soil-Water-Balance (SWB) model except for groundwater pumping, which was estimated from public water purveyor records, annual system data from the Washington State Department of Health, census population data, and water-use estimates. Groundwater recharge estimated from the SWB model was compared to base flow, a proxy for groundwater recharge, independently estimated from separation of the hydrograph recorded by the U.S. Geological Survey streamgage at the outlet of the basin. Mean annual precipitation for the basin was estimated at 72.6 inches, of which 35 percent was lost to evapotranspiration, 30 percent was recharged to groundwater, 30 percent was surface runoff, and 5 percent was lost to interception. SWB model estimates of groundwater recharge were 17 percent less than estimates of base flow from hydrograph separation. Groundwater pumpage in the basin was estimated at 1 percent of groundwater recharge estimated by SWB and 0.8 percent of base flow estimated by hydrograph separation. These estimates form a baseline for understanding future changes to components of water use and may be used to inform numerical groundwater models to support sustainable management of water resources in the upper Chehalis River Basin.

Washington↗
USGS2022

Assessing private well contamination in Grant, Iowa, and Lafayette Counties, Wisconsin: The southwest Wisconsin groundwater and geology study

Rural residents of Grant, Iowa, and Lafayette Counties in Wisconsin rely on private wells for their water. Contaminants like nitrate and bacteria from septic systems, fertilizer, and manure can contaminate the groundwater that residents use. Groundwater is vulnerable to contamination where the soil layer is thin and the bedrock is fractured, which is the case for much of the study region. This study includes five objectives that were designed to assess and understand private well water contamination in the three counties.

Wisconsin↗
USGS2003

Sedimentation rates in the marshes of Sand Lake National Wildlife Refuge

Impoundments located within river systems in the Northern Great Plains are vulnerable to sediment inputs because intensive agriculture in watersheds has increased soil erosion and sediments in rivers. At the request of the U.S. Fish and Wildlife Service (FWS), we evaluated the vertical accretion of sediment in the Mud Lake impoundment of Sand Lake National Wildlife Refuge (NWR), Brown County, South Dakota. The Mud Lake impoundment was created in 1936 by constructing a low-head dam across the James River. We collected sediment cores from the Mud Lake impoundment during August 2000 for determination of vertical accretion rates. Accretion rates were estimated using cesium-13 7 and lead-210 isotopic dating techniques to estimate sediment accretion over the past 100 years. Accretion rates were greatest near the dam (1.3 cm yr-1) with less accretion (0.2 cm yr-1) occurring in the upper reaches of Mud Lake. As expected, accretion was highest near the dam where water velocities and greater water depth facilitates sediment deposition. Higher rates of sedimentation (accretion> 2.0 cm year-1) occurred during the 1990s when river flows were especially high. Since 1959, sediment accretion has reduced maximum pool depth of Mud Lake near the dam by 55 cm. Assuming that sediment accretion rates remain the same in the future, we project Mud Lake will have a maximum pool depth of 77 and 51 cm by 2020 and 2040, respectively. Over this same time frame, water depths in the upper reaches of Mud Lake would be reduced to< 2 cm. Projected future loss of water depth will severely limit the ability of managers to manipulate pool levels in Mud Lake to cycle vegetation and create interspersion of cover and water to meet current wildlife habitat management objectives. As predicted for major dams constructed on rivers throughout the world, Mud Lake will have a finite life span. Our data suggests that the functional life span of Mud Lake since construction will be < 100 years. We anticipate that over the next 20 years, sediments entering Mud Lake will reduce water depths to the point that current wildlife management objectives cannot be achieved through customary water-level manipulations. Sedimentation impacts are not unique to the Sand Lake NWR. It is widely accepted that impoundments trap sediments and shallow impoundments, such as those managed by the FWS, are especially vulnerable. Given the ecological impacts associated with loss of water depths, we recommend that managers begin evaluating the long-term wildlife management goals for the refuge relative to associated costs and feasibility of options available to enhance and maximize the life span of existing impoundments, including upper watershed management.

Report↗
USGS2000

Imaging and modeling new VETEM data

In previously reported work (Wright and others, 2000) we found that the very early time electromagnetic (VETEM) prototype system produced data from which high resolution images of a buried former foundry site at the Denver Federal Center were made. The soil covering the site is about 30 mS/m conductivity, and is thus relatively unfavorable for ground penetrating radar (GPR) imaging. We have surveyed portions of this site again with new electric field dipole antennas and a new receiver designed for these antennas. Comparisons of the images produced using the loop antennas to those produced using the electric field dipole antennas illustrate that for this application the loop antennas produced more useful images. The larger man-made structures can be seen more clearly because they are not masked by dispersion and/or smaller scale variations as with the electric field dipole antennas. The VETEM system now contains an array of antennas with appropriate transmitters and receivers and can be operated as a low frequency time domain GPR or as a high frequency time domain electromagnetic (EM) system with several possible antenna spacings and polarizations. We plan to examine additional configurations. Numerical modeling of the perpendicular loop antenna configuration has been done and depth estimates produced. We conclude that, as with other GPR and time domain EM systems, the best choice of operating parameters depends on the application and the environment, but the inherent flexibility of the VETEM system allows a wide range of options.

Conference Paper↗
USGS2003

Raster dataset showing the probability of elevated concentrations of nitrate in ground water in Colorado, hydrogeomorphic regions and fertilizer use estimates included

This dataset is one of eight datasets produced by this study. Four of the datasets predict the probability of detecting atrazine and(or) desethyl-atrazine (a breakdown product of atrazine) in ground water in Colorado; the other four predict the probability of detecting elevated concentrations of nitrate in ground water in Colorado. The four datasets that predict the probability of atrazine and(or) desethyl-atrazine (atrazine/DEA) are differentiated by whether or not they incorporated atrazine use and whether or not they incorporated hydrogeomorphic regions. The four datasets that predict the probability of elevated concentrations of nitrate are differentiated by whether or not they incorporated fertilizer use and whether or not they incorporated hydrogeomorphic regions. Each of the eight datasets has its own unique strengths and weaknesses. The user is cautioned to read Rupert (2003, Probability of detecting atrazine/desethyl-atrazine and elevated concentrations of nitrate in ground water in Colorado: U.S. Geological Survey Water-Resources Investigations Report 02-4269, 35 p., http://water.usgs.gov/pubs/wri/wri02-4269/) to determine if he(she) is using the most appropriate dataset for his(her) particular needs. This dataset specifically predicts the probability of detecting elevated concentrations of nitrate in ground water in Colorado with hydrogeomorphic regions and fertilizer use included. The following text was extracted from Rupert (2003). Draft Federal regulations may require that each State develop a State Pesticide Management Plan for the herbicides atrazine, alachlor, metolachlor, and simazine. Maps were developed that the State of Colorado could use to predict the probability of detecting atrazine/DEA in ground water in Colorado. These maps can be incorporated into the State Pesticide Management Plan and can help provide a sound hydrogeologic basis for atrazine management in Colorado. Maps showing the probability of detecting elevated nitrite plus nitrate as nitrogen (nitrate) concentrations in ground water in Colorado also were developed because nitrate is a contaminant of concern in many areas of Colorado. Maps showing the probability of detecting atrazine/DEA at or greater than concentrations of 0.1 microgram per liter and nitrate concentrations in ground water greater than 5 milligrams per liter were developed as follows: (1) Ground-water quality data were overlaid with anthropogenic and hydrogeologic data by using a geographic information system (GIS) to produce a dataset in which each well had corresponding data on atrazine use, fertilizer use, geology, hydrogeomorphic regions, land cover, precipitation, soils, and well construction. These data then were downloaded to a statistical software package for analysis by logistic regression. (2) Relations were observed between ground-water quality and the percentage of land-cover categories within circular regions (buffers) around wells. Several buffer sizes were evaluated; the buffer size that provided the strongest relation was selected for use in the logistic regression models. (3) Relations between concentrations of atrazine/DEA and nitrate in ground water and atrazine use, fertilizer use, geology, hydrogeomorphic regions, land cover, precipitation, soils, and well-construction data were evaluated, and several preliminary multivariate models with various combinations of independent variables were constructed. (4) The multivariate models that best predicted the presence of atrazine/DEA and elevated concentrations of nitrate in ground water were selected. (5) The accuracy of the multivariate models was confirmed by validating the models with an independent set of ground-water quality data. (6) The multivariate models were entered into a geographic information system and the probability GRIDS were constructed.

Open-File Report↗
USGS2003

Probability of detecting atrazine/desethyl-atrazine and elevated concentrations of nitrate in ground water in Colorado

Draft Federal regulations may require that each State develop a State Pesticide Management Plan for the herbicides atrazine, alachlor, metolachlor, and simazine. Maps were developed that the State of Colorado could use to predict the probability of detecting atrazine and desethyl-atrazine (a breakdown product of atrazine) in ground water in Colorado. These maps can be incorporated into the State Pesticide Management Plan and can help provide a sound hydrogeologic basis for atrazine management in Colorado. Maps showing the probability of detecting elevated nitrite plus nitrate as nitrogen (nitrate) concentrations in ground water in Colorado also were developed because nitrate is a contaminant of concern in many areas of Colorado. Maps showing the probability of detecting atrazine and(or) desethyl-atrazine (atrazine/DEA) at or greater than concentrations of 0.1 microgram per liter and nitrate concentrations in ground water greater than 5 milligrams per liter were developed as follows: (1) Ground-water quality data were overlaid with anthropogenic and hydrogeologic data using a geographic information system to produce a data set in which each well had corresponding data on atrazine use, fertilizer use, geology, hydrogeomorphic regions, land cover, precipitation, soils, and well construction. These data then were downloaded to a statistical software package for analysis by logistic regression. (2) Relations were observed between ground-water quality and the percentage of land-cover categories within circular regions (buffers) around wells. Several buffer sizes were evaluated; the buffer size that provided the strongest relation was selected for use in the logistic regression models. (3) Relations between concentrations of atrazine/DEA and nitrate in ground water and atrazine use, fertilizer use, geology, hydrogeomorphic regions, land cover, precipitation, soils, and well-construction data were evaluated, and several preliminary multivariate models with various combinations of independent variables were constructed. (4) The multivariate models that best predicted the presence of atrazine/DEA and elevated concentrations of nitrate in ground water were selected. (5) The accuracy of the multivariate models was confirmed by validating the models with an independent set of ground-water quality data. (6) The multivariate models were entered into a geographic information system and the probability maps were constructed.

Colorado↗
USGS2013

Iron mineralogy and bioaccessibility of dust generated from soils as determined by reflectance spectroscopy and magnetic and chemical properties--Nellis Dunes recreational area, Nevada

Atmospheric mineral dust exerts many important effects on the Earth system, such as atmospheric temperatures, marine productivity, and melting of snow and ice. Mineral dust also can have detrimental effects on human health through respiration of very small particles and the leaching of metals in various organs. These effects can be better understood through characterization of the physical and chemical properties of dust, including certain iron oxide minerals, for their extraordinary radiative properties and possible effects on lung inflammation. Studies of dust from the Nellis Dunes recreation area near Las Vegas, Nevada, focus on characteristics of radiative properties (capacity of dust to absorb solar radiation), iron oxide mineral type and size, chemistry, and bioaccessibility of metals in fluids that simulate human gastric, lung, and phagolysosomal fluids. In samples of dust from the Nellis Dunes recreation area with median grain sizes of 2.4, 3.1, and 4.3 micrometers, the ferric oxide minerals goethite and hematite, at least some of it nanosized, were identified. In one sample, in vitro bioaccessibility experiments revealed high bioaccessibility of arsenic in all three biofluids and higher leachate concentration and bioaccessibility for copper, uranium, and vanadium in the simulated lung fluid than in the phagolysosomal fluid. The combination of methods used here to characterize mineral dust at the Nellis Dunes recreation area can be applied to global dust and broad issues of public health.

Nevada↗
USGS2023

Multiresidue extraction of current-use pesticides from complex solid matrices using energized dispersive guided extraction with analysis by gas and liquid chromatography tandem mass spectroscopy

The development of sample processing techniques that recover a broad suite of pesticides from solid matrices, while mitigating coextracted matrix interferences, and reducing processing time is beneficial for high throughput analyses. The objective of this study was to evaluate the effectiveness of an automated extraction system for pesticide analyses in solid environmental samples. An Energized Dispersive Guided Extraction (EDGE) system was used to evaluate two different extraction solvents in optimizing the extraction of 210 pesticides and pesticide transformation products. A graphitized carbon cleanup step was implemented, and three elution solvents were evaluated separately for analyte recoveries. Recoveries between 70 and 130% were achieved for 167 compounds in a test soil using acetonitrile as an extraction solvent and carbon cleanup with acetonitrile and dichloromethane elutions. Nine field samples (soil, sediment, and biosolids) were extracted using the newly developed method and were compared with a previously validated pressurized liquid extraction (PLE) method using an Accelerated Solvent Extraction (ASE) system. Concentrations obtained from the two methods were comparable (linear R 2 > 0.999), suggesting similar performance between the EDGE and PLE extractions in complex matrices. The new method provided slightly better sensitivities in comparison to the PLE method, ranging from 0.09 to 2.56 ng g −1 . The method presented here significantly reduces extraction setup and runtimes while also minimizing the volume of carcinogenic solvents ( e.g. , dichloromethane) used in the laboratory and presents a sensitive multiresidue method for a wide range of pesticides in solid matrices.

Chemosphere↗