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At least 793 records · Page 44Linked to original sources
USGS2023

Arsenic, chromium, uranium, and vanadium in rock, alluvium, and groundwater, Mojave River and Morongo Areas, western Mojave Desert, southern California

Trace elements within groundwater that originate from aquifer materials and pose potential public-health hazards if consumed are known as geogenic contaminants. The geogenic contaminants arsenic, chromium, and vanadium can form negatively charged ions with oxygen known as oxyanions. Uranium complexes with bicarbonate and carbonate to form negatively charged ions having aqueous chemistry similar to oxyanions. The concentrations of arsenic, chromium, uranium, and vanadium in groundwater result from the combined effects of (1) geologic abundance within aquifer materials; (2) the fraction of these elements that have weathered from and sorbed to the surfaces of mineral grains and are potentially available to groundwater; and (3) the aqueous chemistry of dissolved oxyanions in groundwater during different redox conditions and pH, both of which are affected by hydrogeology, including the length of time groundwater has been in contact with aquifer materials. Concentrations of arsenic, chromium, uranium, and vanadium were measured in samples of (1) rock, surficial alluvium, and drill cuttings using portable (handheld) X-ray fluorescence (pXRF); (2) operationally defined fractions extractable from these materials; and (3) water from wells sampled between 2000 and 2018 within the 3,500 square mile Mojave River area and Morongo area of the western Mojave Desert, southern California. Regionally, rock and surficial alluvium in the Mojave River and Morongo areas are high in arsenic, low in chromium and uranium, and near the average bulk continental crust concentration for vanadium. Locally, high chromium concentrations are present in mafic rock within the San Gabriel Mountains; high uranium concentrations are present in felsic rock within the San Bernardino Mountains; and high arsenic, uranium, and vanadium concentrations are present in extrusive (volcanic) felsic rock within uplands surrounding groundwater basins along the Mojave River downstream from Barstow, California. Elemental assemblages identified using principal component analyses (PCA) of pXRF data were used to characterize felsic, mafic, and felsic volcanic source terranes in rock, surficial alluvium, and in geologic material penetrated by selected monitoring wells drilled between 1994 and 2018. Highly felsic alluvium associated with recent deposition from the Mojave River was identified along the 90-mile length of the floodplain aquifer along the river. The thickness of these highly felsic alluvial deposits ranged from 200 feet (ft) near Victorville and near Barstow to a thin veneer about 30 ft thick downstream from Victorville and downstream portions of the floodplain aquifer within the Mojave Valley. Groundwater in the Mojave River and Morongo areas was generally oxic and alkaline (pH≥7.5). Maximum concentrations of arsenic, hexavalent chromium [Cr(VI)], uranium, and vanadium in water from as many as 498 wells sampled between 2000 and 2018 were 360, 140, 1,470, and 690 micrograms per liter (μg/L), respectively. Water from 22 percent of sampled wells exceeded the U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL) for arsenic of 10 μg/L, with arsenic concentrations commonly exceeding the MCL in water from wells east of Barstow, deep wells in the Victorville fan, and in suboxic or reduced groundwater within the floodplain aquifer. Water from about 1 percent of sampled wells had Cr(VI) concentrations greater than the California MCL for total chromium of 50 μg/L, whereas 13 percent of sampled wells had Cr(VI) concentrations greater than the former California MCL of 10 μg/L. Hexavalent chromium concentrations were highest in water from wells in the Sheep Creek alluvial fan, eroded from mafic rock in the San Gabriel Mountains, although Cr(VI) concentrations greater than the former California MCL also were present elsewhere in the study area where mafic materials or older groundwater were present. Water from about 9 percent of sampled wells exceeded the EPA MCL for uranium of 30 μg/L, with concentrations exceeding the MCL commonly associated with irrigation return from agricultural land overlying the floodplain aquifer. Water from about 7 percent of sampled wells had vanadium concentrations greater than the California notification level of 50 μg/L; most of these wells were in the Victorville fan within the Mojave River area. In general, arsenic concentrations were higher in suboxic or reduced water; chromium concentrations were higher in oxic, alkaline (pH≥7.5) water; uranium concentrations were higher in circumneutral to slightly alkaline water (pH≤7.4); and vanadium concentrations were higher in highly alkaline (pH≥8.0) water, independent of redox status. Concentrations within geologic source terranes are not the sole factor controlling the concentrations of geogenic elements in groundwater. Differences in mineral weathering, pH-dependent sorption to surface-exchange sites on mineral grains, and aqueous geochemistry (especially redox status and pH) affect geogenic element concentrations in groundwater. Consequently, the relative abundances of arsenic, Cr(VI), uranium, and vanadium in groundwater differ from their relative abundances in the average bulk continental crust and their regional abundances in rock and surficial alluvium within groundwater basins of the western Mojave Desert. Processes that control the concentrations of arsenic, chromium, uranium, and vanadium in groundwater operate at the mineral-grain and aquifer scale. At the mineral-grain scale, sequential chemical extraction data show arsenic and uranium are more available to groundwater (under specific geochemical conditions) than chromium or vanadium, which largely are unavailable within unweathered mineral grains. Additionally, chromium and vanadium form few aqueous complexes and bind tightly with iron minerals within surface coatings on mineral grains making them less available to groundwater, whereas complexation with other dissolved ions enhances the solubility of uranium and, to a lesser extent, arsenic. Complexation also increases the valence (less negative charge) and increases the size of dissolved oxyanions and uranium complexes with bicarbonate and carbonate making them less readily sorbed to aquifer materials. At the aquifer scale, hydrogeology (including isolation of water in aquifers from surface sources of recharge, older groundwater age, and long contact times between groundwater and aquifer materials) combined with geochemical processes (such as silicate weathering) to produce alkaline groundwater. Desorption from sorption sites on the surfaces of mineral grains with increasing pH increases arsenic, chromium, and vanadium concentrations in water from wells and increases Cr(VI) concentrations as long as water remains oxic. Aqueous geochemistry and concentrations of geogenic contaminants also are affected by anthropogenic activities including (1) discharge of treated municipal wastewater, which may change the redox status of groundwater; (2) return from irrigated agriculture, which may alter the chemistry of groundwater and increase the solubility of trace elements such as uranium; and (3) groundwater pumping and subsequent water-level declines, which may change the source of water yielded by wells. The quality of water imported from northern California and infiltrated from ponds for groundwater recharge may be altered by naturally present trace elements, especially uranium in areas of agricultural land use or chromium within mafic alluvium.

California↗
USGS2004

Hydrogeology and ground-water-flow simulation in the former airfield area of Naval Support Activity Mid-South, Millington, Tennessee

Naval Support Activity Mid-South is a Department of the Navy base located in Millington, Tennessee. The facility was home to the Naval Aviation Technical Training Center from 1943 until 1996. As part of the Base Closure and Realignment Act of 1990, the primary training mission of the facility was realigned and most of the northern part of the base, referred to as the Northside and consisting primarily of an airfield, was transferred to the city of Millington in January 2000. During environmental investigations at the base, plumes of dissolved chlorinated solvents resulting from past aircraft maintenance and training operations were identified in shallow ground water beneath the airfield area. The airfield area containing the plumes has been designated as Area of Concern (AOC) A. Chlorinated solvents, primarily trichloroethene (TCE), are the principal contaminants in ground water at AOC A, with TCE identified in concentrations as high as 4,400 micrograms per liter. The nature and extent of these plumes at AOC A were addressed during a Resource Conservation and Recovery Act Facility Investigation, and selected options for remediation currently are being implemented under a corrective action program. As part of these efforts, the U.S. Geological Survey (USGS) is working with the Navy and its consultants to study the hydrogeologic framework of the base and surrounding area, with a focus on AOC A. Since 1997, investigations at and near the facility have produced data prompting revisions and additions to information published that year in two USGS reports. The updates are presented in this report and consist primarily of (1) refinements to selected hydrogeologic maps presented in the 1997 reports, on the basis of data collected from new wells at on- and off-base locations, (2) additional hydraulic-conductivity data collected for the alluvial-fluvial deposits aquifer at AOC A, and (3) construction of a potentiometric-surface map of the shallow aquifer for the former part of the Naval Support Activity Mid-South Northside and adjacent off-base locations for February and March 2000 water-level conditions. Additionally, a numerical ground-water-flow model of AOC A was developed and calibrated to the February and March 2000 potentiometric-surface data, the results of which also are presented in this report. Particle-tracking simulations were used with the model to simulate ground-water-flow paths from two sites suspected of being contaminant source areas at AOC A. The flow paths indicated by the particle tracking simulations agree reasonably well with maps of the interpreted extents of TCE plumes. The time-of-travel plots show that advective travel times from the two suspected source areas to the model boundary are controlled by relative proximities of the source areas to a part of AOC A identified from investigations and simulated with the model as having the highest horizontal hydraulic conductivity.

Tennessee↗
USGS2005

Trends in surface-water quality at selected National Stream Quality Accounting Network (NASQAN) stations, in Michigan

To demonstrate the value of long-term, water-quality monitoring, the Michigan Department of Environmental Quality (MDEQ), in cooperation with the U.S. Geological Survey (USGS), initiated a study to evaluate potential trends in water-quality constituents for selected National Stream Quality Accounting Network (NASQAN) stations in Michigan. The goal of this study is to assist the MDEQ in evaluating the effectiveness of water-pollution control efforts and the identification of water-quality concerns. The study included a total of nine NASQAN stations in Michigan. Approximately 28 constituents were analyzed for trend tests. Station selection was based on data availability, land-use characteristics, and station priority for the MDEQ Water Chemistry Monitoring Project. Trend analyses were completed using the uncensored Seasonal Kendall Test in the computer program Estimate Trend (ESTREND), a software program for the detection of trends in water-quality data. The parameters chosen for the trend test had (1) at least a 5-year period of record (2) about 5 percent of the observations censored at a single reporting limit, and (3) 40 percent of the values within the beginning one-fifth and ending one-fifth of the selected period. In this study, a negative trend indicates a decrease in concentration of a particular constituent, which generally means an improvement in water quality; whereas a positive trend means an increase in concentration and possible degradation of water quality. The results of the study show an overall improvement in water quality at the Clinton River at Mount Clemens, Manistee River at Manistee, and Pigeon River near Caseville. The detected trend for these stations show decreases in concentrations of various constituents such as nitrogen compounds, conductance, sulfate, fecal coliform bacteria, and fecal streptococci bacteria. The negative trend may indicate an overall improvement in agricultural practices, municipal and industrial wastewater-treatment processes, and effective regulations. Phosphorus data for most of the study stations could not be analyzed because of the data limitations for trend tests. The only station with a significant negative trend in total phosphorus concentration is the Clinton River at Mount Clemens. However, scatter-plot analyses of phosphorus data indicate decreasing concentrations with time for most of the study stations. Positive trends in concentration of nitrogen compounds were detected at the Kalamazoo River near Saugatuck and Muskegon River near Bridgeton. Positive trends in both fecal coliform and total fecal coliform were detected at the Tahquamenon River near Paradise. Various different point and nonpoint sources could produce such positive trends, but most commonly the increase in concentrations of nitrogen compounds and fecal coliform bacteria are associated with agricultural practices and sewage-plant discharges. The constituent with the most numerous and geographically widespread significant trend is pH. The pH levels increased at six out of nine stations on all the major rivers in Michigan, with no negative trend at any station. The cause of pH increase is difficult to determine, as it could be related to a combination of anthropogenic activities and natural processes occurring simultaneously in the environment. Trends in concentration of major ions, such as calcium, sodium, magnesium, sulfate, fluoride, chloride, and potassium, were detected at eight out of nine stations. A negative trend was detected only in sulfate and fluoride concentrations; a positive trend was detected only in calcium concentration. The major ions with the most widespread significant trends are sodium and chloride; three positive and two negative trends were detected for sodium, and three negative and two positive trends were detected for chloride. The negative trends in chloride concentrations outnumbered the positive trends. This result indicates a slight improvement in surface-water quality because chloride as a point source in natural water comes from deicing salt, sewage effluents, industrial wastes, and oil fields. For other major ions, such as magnesium and potassium, both positive and negative trends were detected. These changes in trends indicate changes in surface-water quality caused by a variety of point and non-point sources throughout Michigan, as well as natural changes in the environment.

Michigan↗
USGS2017

Methods for estimating selected low-flow frequency statistics and mean annual flow for ungaged locations on streams in North Georgia

The U.S. Geological Survey, in cooperation with the Georgia Department of Natural Resources, Environmental Protection Division, developed regional regression equations for estimating selected low-flow frequency and mean annual flow statistics for ungaged streams in north Georgia that are not substantially affected by regulation, diversions, or urbanization. Selected low-flow frequency statistics and basin characteristics for 56 streamgage locations within north Georgia and 75 miles beyond the State’s borders in Alabama, Tennessee, North Carolina, and South Carolina were combined to form the final dataset used in the regional regression analysis. Because some of the streamgages in the study recorded zero flow, the final regression equations were developed using weighted left-censored regression analysis to analyze the flow data in an unbiased manner, with weights based on the number of years of record. The set of equations includes the annual minimum 1- and 7-day average streamflow with the 10-year recurrence interval (referred to as 1Q10 and 7Q10), monthly 7Q10, and mean annual flow. The final regional regression equations are functions of drainage area, mean annual precipitation, and relief ratio for the selected low-flow frequency statistics and drainage area and mean annual precipitation for mean annual flow. The average standard error of estimate was 13.7 percent for the mean annual flow regression equation and ranged from 26.1 to 91.6 percent for the selected low-flow frequency equations. The equations, which are based on data from streams with little to no flow alterations, can be used to provide estimates of the natural flows for selected ungaged stream locations in the area of Georgia north of the Fall Line. The regression equations are not to be used to estimate flows for streams that have been altered by the effects of major dams, surface-water withdrawals, groundwater withdrawals (pumping wells), diversions, or wastewater discharges. The regression equations should be used only for ungaged sites with drainage areas between 1.67 and 576 square miles, mean annual precipitation between 47.6 and 81.6 inches, and relief ratios between 0.146 and 0.607; these are the ranges of the explanatory variables used to develop the equations. An attempt was made to develop regional regression equations for the area of Georgia south of the Fall Line by using the same approach used during this study for north Georgia; however, the equations resulted with high average standard errors of estimates and poorly predicted flows below 0.5 cubic foot per second, which may be attributed to the karst topography common in that area. The final regression equations developed from this study are planned to be incorporated into the U.S. Geological Survey StreamStats program. StreamStats is a Web-based geographic information system that provides users with access to an assortment of analytical tools useful for water-resources planning and management, and for engineering design applications, such as the design of bridges. The StreamStats program provides streamflow statistics and basin characteristics for U.S. Geological Survey streamgage locations and ungaged sites of interest. StreamStats also can compute basin characteristics and provide estimates of streamflow statistics for ungaged sites when users select the location of a site along any stream in Georgia.

Georgia↗
USGS2008

Water Quality Conditions in Upper Klamath and Agency Lakes, Oregon, 2005

During June-October 2005, water quality data were collected from Upper Klamath and Agency Lakes in Oregon, and meteorological data were collected around and within Upper Klamath Lake. Data recorded at two continuous water quality monitors in Agency Lake showed similar temperature patterns throughout the field season, but data recorded at the northern site showed more day-to-day variability for dissolved oxygen concentration and saturation after late June and more day-to-day variability for pH and specific conductance values after mid-July. Data recorded from the northern and southern parts of Agency Lake showed more comparable day-to-day variability in dissolved oxygen concentrations and pH from September through the end of the monitoring period. For Upper Klamath Lake, seasonal (late July through early August) lows of dissolved oxygen concentrations and saturation were coincident with a seasonal low of pH values and seasonal highs of ammonia and orthophosphate concentrations, specific conductance values, and water temperatures. Patterns in these parameters, excluding water temperature, were associated with bloom dynamics of the cyanobacterium (blue-green alga) Aphanizomenon flos-aquae in Upper Klamath Lake. In Upper Klamath Lake, water temperature in excess of 28 degrees Celsius (a high stress threshold for Upper Klamath Lake suckers) was recorded only once at one site during the field season. Large areas of Upper Klamath Lake had periods of dissolved oxygen concentration of less than 4 milligrams per liter and pH value greater than 9.7, but these conditions were not persistent throughout days at most sites. Dissolved oxygen concentrations in Upper Klamath Lake on time scales of days and months appeared to be influenced, in part, by bathymetry and prevailing current flow patterns. Diel patterns of water column stratification were evident, even at the deepest sites. This diel pattern of stratification was attributable to diel wind speed patterns and the shallow nature of most of Upper Klamath Lake. Timing of the daily extreme values of dissolved oxygen concentration, pH, and water temperature was less distinct with increased water column depth. Chlorophyll a concentrations varied spatially and temporally throughout Upper Klamath Lake. Location greatly affected algal concentrations, in turn affecting nutrient and dissolved oxygen concentrations - some of the highest chlorophyll a concentrations were associated with the lowest dissolved oxygen concentrations and the highest un-ionized ammonia concentrations. The occurrence of the low dissolved oxygen and high un-ionized ammonia concentrations coincided with a decline in algae resulting from cell death, as measured by concentrations of chlorophyll a. Dissolved oxygen production rates in experiments were as high as 1.47 milligrams of oxygen per liter per hour, and consumption rates were as much as -0.73 milligrams of oxygen per liter per hour. Dissolved oxygen consumption rates measured in this study were comparable to those measured in a 2002 Upper Klamath Lake study, and a higher rate of dissolved oxygen consumption was recorded in dark bottles positioned higher in the water column. Data, though inconclusive, indicated that a decreasing trend of dissolved oxygen productivity through July could have contributed to the decreasing dissolved oxygen concentrations and percent saturation recorded in Upper Klamath Lake during this time. Phytoplankton self-shading was evident from a general inverse relation between depth of photic zone and chlorophyll a concentrations. This shading caused net dissolved oxygen consumption during daylight hours in lower parts of the water column that would otherwise have been in the photic zone. Meteorological data collected in and around Upper Klamath Lake showed that winds were likely to come from a broad range of westerly directions in the northern one-third of the lake, but tended to come from a narrow range of northwesterly directions

Scientific Investigations Report↗
USGS2013

Analysis and inundation mapping of the April-May 2011 flood at selected locations in northern and eastern Arkansas and southern Missouri

Precipitation that fell from April 19 through May 3, 2011, resulted in widespread flooding across northern and eastern Arkansas and southern Missouri. The first storm produced a total of approximately 16 inches of precipitation over an 8-day period, and the following storms produced as much as 12 inches of precipitation over a 2-day period. Moderate to major flooding occurred quickly along many streams within Arkansas and Missouri (including the Black, Cache, Illinois, St. Francis, and White Rivers) at levels that had not been seen since the historic 1927 floods. The 2011 flood claimed an estimated 21 lives in Arkansas and Missouri, and damage caused by the flooding resulted in a Federal Disaster Declaration for 59 Arkansas counties that received Federal or State assistance. To further the goal of documenting and understanding floods, the U.S. Geological Survey, in cooperation with the Federal Emergency Management Agency, the U.S. Army Corps of Engineers–Little Rock and Memphis Districts, and Arkansas Natural Resources Commission, conducted a study to summarize meteorological and hydrological conditions before the flood; computed flood-peak magnitudes for 39 streamgages; estimated annual exceedance probabilities for 37 of those streamgages; determined the joint probabilities for 11 streamgages paired to the Mississippi River at Helena, Arkansas, which refers to the probability that locations on two paired streams simultaneously experience floods of a magnitude greater than or equal to a given annual exceedance probability; collected high-water marks; constructed flood-peak inundation maps showing maximum flood extent and water depths; and summarized flood damages and effects. For the period of record used in this report, peak-of-record stage occurred at 24 of the 39 streamgages, and peak-of-record streamflow occurred at 13 of the 30 streamgages where streamflow was determined. Annual exceedance probabilities were estimated to be less than 0.5 percent at three streamgages. The joint probability values for streamgages paired with the Mississippi River at Helena, Ark., streamgage indicate a low probability of concurrent flooding with the paired streamgages. The inundation maps show the flood-peak extent and water depth of flooding for two stream reaches on the White River and two on the Black River; the vicinities of the communities of Holly Grove and Cotton Plant, Ark.; a reach of the White River that includes the crossing of Interstate 40 north of De Valls Bluff, Ark.; and the Tailwaters of Beaver Dam near Eureka Springs, Ark., Table Rock Dam near Branson, Mo., and Bull Shoals Dam near Flippin, Ark. The data and inundation maps can be used for flood response, recovery, and planning efforts by Federal, State, and local agencies.

Arkansas;Missouri↗
USGS2019

Capacity and area of Grand Lake O’ the Cherokees, northeastern Oklahoma, 2009

In February 2017, the Grand River Dam Authority filed to relicense the Pensacola Hydroelectric Project with the Federal Energy Regulatory Commission. The predominant feature of the Pensacola Hydroelectric Project is Pensacola Dam, which impounds Grand Lake O’ the Cherokees (locally called Grand Lake) in northeastern Oklahoma. Identification of information gaps and assessment of project effects on stakeholders are central aspects of the Federal Energy Regulatory Commission relicensing process. Due to the natural changes to the reservoir over time, new capacity and area tables are needed periodically. The most recent complete capacity and area table was produced in 1940. Capacity and area tables identify the relations between the elevation of the water surface and the volume of water that can be impounded at each water surface elevation. This report (1) presents an updated capacity and area table for Grand Lake O’ the Cherokees for 2009, (2) describes the methods used to calculate the updated capacity and area values presented in the table, and (3) compares the updated capacity table to historical capacity tables produced from a survey in 1940 and from a hydrographic survey of the lake by the Oklahoma Water Resources Board in 2009. The new capacity values computed for Grand Lake O’ the Cherokees indicate that capacity at conservation pool elevation has decreased about 157,000 acre-feet or 10 percent since 1940 and capacity at top of dam elevation has decreased about 200,000 acre-feet or 8 percent since 1940. This difference in the capacities could be attributed to the advancements of technologies; the techniques used for surveying lakes have changed from the 1940 survey to the 2009 survey. Another possible reason for loss in capacity could be as time progresses, lakes like Grand Lake O’ the Cherokees slowly impound sediment carried by the rivers that feed into the lakes, thus diminishing the amount of water that the lake holds. The most recent survey used measured water depths and Global Position System collected electronically, but the methods used to collect data in 1940 are unknown. Due to the advancement of technology, the 2009 survey is likely more precise than the 1940 survey.

Oklahoma↗
USGS2011

Assessing controls on perched saturated zones beneath the Idaho Nuclear Technology and Engineering Center, Idaho

Waste byproducts associated with operations at the Idaho Nuclear Technology and Engineering Center (INTEC) have the potential to contaminate the eastern Snake River Plain (ESRP) aquifer. Recharge to the ESRP aquifer is controlled largely by the alternating stratigraphy of fractured volcanic rocks and sedimentary interbeds within the overlying vadose zone and by the availability of water at the surface. Beneath the INTEC facilities, localized zones of saturation perched on the sedimentary interbeds are of particular concern because they may facilitate accelerated transport of contaminants. The sources and timing of natural and anthropogenic recharge to the perched zones are poorly understood. Simple approaches for quantitative characterization of this complex, variably saturated flow system are needed to assess potential scenarios for contaminant transport under alternative remediation strategies. During 2009-2011, the U.S. Geological Survey (USGS), in cooperation with the U.S. Department of Energy, employed data analysis and numerical simulations with a recently developed model of preferential flow to evaluate the sources and quantity of recharge to the perched zones. Piezometer, tensiometer, temperature, precipitation, and stream-discharge data were analyzed, with particular focus on the possibility of contributions to the perched zones from snowmelt and flow in the neighboring Big Lost River (BLR). Analysis of the timing and magnitude of subsurface dynamics indicate that streamflow provides local recharge to the shallow, intermediate, and deep perched saturated zones within 150 m of the BLR; at greater distances from the BLR the influence of streamflow on recharge is unclear. Perched water-level dynamics in most wells analyzed are consistent with findings from previous geochemical analyses, which suggest that a combination of annual snowmelt and anthropogenic sources (for example, leaky pipes and drainage ditches) contribute to recharge of shallow and intermediate perched zones throughout much of INTEC. The source-responsive fluxes model was parameterized to simulate recharge via preferential flow associated with intermittent episodes of streamflow in the BLR. The simulations correspond reasonably well to the observed hydrologic response within the shallow perched zone. Good model performance indicates that source-responsive flow through a limited number of connected fractures contributes substantially to the perched-zone dynamics. The agreement between simulated and observed perched-zone dynamics suggest that the source-responsive fluxes model can provide a valuable tool for quantifying rapid preferential flow processes that may result from different land management scenarios.

Scientific Investigations Report↗
USGS2005

Water-quality trend analysis and sampling design for streams in the Red River of the North Basin, Minnesota, North Dakota, and South Dakota, 1970-2001

The Bureau of Reclamation is considering several alternatives to meet the future municipal, rural, and industrial water-supply needs in the Red River of the North (Red River) Basin, and an environmental impact statement is being prepared to evaluate the potential effects of the various alternatives on the water quality and aquatic health in the basin in relation to the historical variability of streamflow and constituent concentration. Therefore, a water-quality trend analysis was needed to determine the amount of natural water-quality variability that can be expected to occur in the basin, to determine if significant water-quality changes have occurred as a result of human activities, to explore potential causal mechanisms for water-quality changes, and to establish a baseline from which to monitor future water-quality trends. This report presents the results of a study conducted by the U.S. Geological Survey, in cooperation with the Bureau of Reclamation, to analyze historical water-quality trends in two dissolved major ions, dissolved solids, three nutrients, and two dissolved trace metals for nine streamflow-gaging stations in the basin. Annual variability in streamflow in the Red River Basin was high during the trend-analysis period (1970-2001). The annual variability affects constituent concentrations in individual tributaries to the Red River and, in turn, affects constituent concentrations in the main stem of the Red River because of the relative streamflow contribution from the tributaries to the main stem. Therefore, an annual concentration anomaly, which is an estimate of the interannual variability in concentration that can be attributed to long-term variability in streamflow, was used to analyze annual streamflow-related variability in constituent concentrations. The concentration trend is an estimate of the long-term systematic changes in concentration that are unrelated to seasonal or long-term variability in streamflow. Concentrations that have both the seasonal and annual variability removed are called standardized concentrations. Numerous changes that could not be attributed to natural streamflow-related variability occurred in the standardized concentrations during the trend-analysis period. During various times from the late 1970's to the mid-1990's, significant increases occurred in standardized dissolved sulfate, dissolved chloride, and dissolved- solids concentrations for eight of the nine stations for which water-quality trends were analyzed. Significant increases also occurred from the early 1980's to the mid-1990's for standardized dissolved nitrite plus nitrate concentrations for the main-stem stations. The increasing concentrations for the main-stem stations indicate the upward trends may have been caused by human activities along the main stem of the Red River. Significant trends for standardized total ammonia plus organic nitrogen concentrations occurred for most stations. The fitted trends for standardized total phosphorus concentrations for one tributary station increased from the late 1970's to the early 1980's and decreased from the early 1980's to the mid-1990's. Small but insignificant increases occurred for two main-stem stations. No trends were detected for standardized dissolved iron or dissolved manganese concentrations. However, the combination of extreme high-frequency variability, few data, and the number of censored values may have disguised the streamflow-related variability for iron. The time-series model used to detect historical concentration trends also was used to evaluate sampling designs to monitor future water-quality trends. Various sampling designs were evaluated with regard to their sensitivity to detect both annual and seasonal trends during three 4-month seasons. A reasonable overall design for detecting trends for all stations and constituents consisted of eight samples per year, with monthly sampling from April to August and bimonthly sampling from October to February.

Scientific Investigations Report↗
USGS2018

Baseline water quality of an area undergoing shale-gas development in the Muskingum River watershed, Ohio, 2015–16

In 2015–16, the U.S. Geological Survey, in cooperation with the Muskingum Watershed Conservancy District, led a study to assess baseline (2015–16) surface-water quality in six lake drainage basins within the Muskingum River watershed that are in the early years of shale-gas development. In 2015, 9 of the 10 most active counties in Ohio for oil and gas development were wholly or partially within the Muskingum River watershed. In addition to shale gas development, the area has a history of conventional oil and gas development and coal mining. In all, 30 surface-water sites were sampled: 20 in tributaries flowing to the lakes, 4 in lakes themselves, and 6 downstream of the lakes. At each of the 30 sites, 6 samples were collected to characterize surface-water chemistry throughout a range of hydrologic conditions. The sampling generally occurred during low flows (periods of greater groundwater contribution) rather than during runoff events (periods of high stream stage). Trilinear diagrams of major ion chemistry revealed three main types of water in the study area―sulfate-dominated waters, bicarbonate-dominated waters, and waters with mixed bicarbonate and chloride anions. Most sites produced samples of bicarbonate-dominated water, and 11 sites produced samples with sulfate-type waters. Mixed bicarbonate and chloride waters were found in samples from two of the six lake drainage basins studied. The baseline (2015–16) assessment of surface-water quality in the study area indicated that few water-chemistry constituents and properties occurred at concentrations or levels that would adversely affect aquatic organisms. Chemical-specific, aquatic life use criteria were not met in only three instances: two were for total dissolved solids at sites likely impacted by coal mining in their drainage basins (hereafter referred to as “mine-impacted sites”), and one was for dissolved oxygen. Mine drainage from historical coal mining in the region likely affected the quality of about one-third of the streams sampled. To simplify interpretation of water-chemistry results, 11 sites with sulfate-type water were identified as mine-impacted sites based on water-quality criteria established by Ohio Department of Natural Resources, Division of Mineral Resources Management, and separated out for subsequent statistical analysis. Concentrations or levels of bicarbonate, boron, calcium, carbonate, total dissolved solids, fluoride, magnesium, lithium, pH, potassium, sodium, specific conductance, strontium, sulfate, and suspended sediment in water were higher (significance level of 0.05) at mine-impacted stream sites than at non-mine-impacted stream sites. An accidental release of oil- and gas-related brines could increase salinity (sodium and chloride), the concentration of total dissolved solids in shallow groundwater and streams, and specific conductance. For this study, chloride concentrations in the study area ranged from 2.12 to 76.1 milligrams per liter. Sources of chloride in water samples were evaluated using binary mixing curves and ratios of chloride to bromide. These ratios indicated that 13 samples from 3 sites in the drainage basin that contained the highest density of conventional oil and gas wells in the study, as well as 4 samples collected from other drainage basins, likely contained a component of brine. Concentrations or levels of barium, bromide, chloride, iron, lithium, manganese, and sodium were significantly higher (alpha = 0.05) in samples with a component of brine than in samples without a component of brine. Benzene, toluene, ethylbenzene and xylene (BTEX), compounds that occur naturally in crude oil, made up 24 of the 45 detections (53 percent) of volatile organic compounds in the study area. The BTEX detections were not associated with sites containing a component of brine. The only volatile organic compound detected in any of the 17 samples that contained a component of brine was acetone, detected in 3 (18 percent) of these samples and in 11 percent of samples not containing a component of brine. Considering that BTEX are gasoline hydrocarbons and that most of the detections occurred during warmer months in and around the lakes, the BTEX detections likely are associated with increases in outdoor activities such as automobile and boating traffic. Radium-226 and radium-228 were included in the list of analytes for this study because production water from shale-gas drilling can contain these naturally occurring radioactive materials. Concentrations of radium-226 exceeded background levels in only two surface-water samples. Concentrations of radium-228 exceeded background levels in one surface-water sample. A brine signature potentially indicative of oil and gas contamination was detected in samples collected at two sites that contained active or plugged waste injection wells, or both. Results from the study indicated significant differences in the median concentrations of bromide, chloride, lithium, manganese, sodium, and total dissolved nitrogen between sites with and without injection wells in their drainage areas. Median concentrations of bromide, chloride, lithium, and sodium, which are common oil- and gas-related contaminants, were higher at sites with injection wells in their drainage areas compared to sites without injection wells. Historical (1960s, 1970s, and 1980s) chloride concentrations and streamflow data at or near five of the six sampling sites downstream from each lake dam were compared to current (2015–16) values. An analysis of covariance was done to test the effects of streamflow, time (decade), and the combined effects (cross product) of streamflow and time on chloride concentrations. Those analyses indicated that streamflow was not significant in explaining the variation in chloride concentration, likely because streamflow in those locations is controlled by dam operations; therefore, association between runoff-generating events and streamflow is less direct than in unregulated streams. From the 1980s to the study period (2015–16), data for three of the five lakes indicated an increase in chloride concentrations. The comparison of historical and current (2015–16) study data from samples collected at another lake indicated that chloride concentrations increased from the 1960s to the 1970s, but concentrations in the 1970s and 2015–16 were similar even though 13 samples from this lake drainage basin were classified as having a component of brine. Median chloride concentrations for the fifth lake, however, seemed to decrease from the 1980s to 2015–16.

Ohio↗
USGS2024

Generalized potentiometric maps of the Fort Union, Hell Creek, and Fox Hills aquifers within the Standing Rock Reservation

Generalized potentiometric surfaces of the Fort Union, Hell Creek, and Fox Hills aquifers were constructed to assess the groundwater resources of the Standing Rock Reservation. Additionally, this information can provide water managers with tools and data to effectively manage water resources in the future. Previous studies that mapped the geology and hydrogeology of the area at differing scales were used to confirm in which aquifer the study wells were completed. Water-level data from wells are provided by the U.S. Geological Survey Groundwater System Inventory database, the South Dakota Department of Agriculture and Natural Resources, and the North Dakota Department of Water Resources. Hydrographs were constructed for five selected observation wells to evaluate historical water-level fluctuations and trends. Hydrographs for the Hell Creek aquifer showed a flat trend with a rise in 2020. Hydrographs for the deeper Fox Hills aquifer showed that water levels fluctuated in response to climatic conditions and demonstrated an increasing trend in water-level elevations starting in 2010. Hydrographs were not constructed for any wells completed in the Fort Union Formation because none of the wells had continuous long-term measurements. Generalized potentiometric surfaces, constructed from interpolating water-level elevations, gave insight into groundwater flow directions. Groundwater in the Fort Union aquifer likely flows radially outward from the northwest part of the study area to the northeast and south-southeast parts. Groundwater in the Hell Creek aquifer generally flows from higher elevations in the northwest towards lower areas, where surface-water tributaries have incised into the aquifer. Groundwater in the Fox Hills aquifer likely flows from higher elevations in the west, southwest, and central parts of the study area towards the valleys of the Grand River and Missouri River. Most wells used for constructing potentiometric maps had only one recorded water-level measurement from drillers at the time of well construction. These measurements are often subject to error because the well is still recovering and because of spatial limitations of data availability. Also, because single water-level measurements were recorded at different points in time, additional uncertainty is introduced by fluctuating climatic conditions effect on water levels. Potentiometric map interpretation limitations are a result of areas with sparse data. Limitations also arise from potentiometric surfaces generalizing a complex and dynamic hydrogeologic system; however, the generalized potentiometric surface maps can be used to assist water managers and can help prioritize locations for future monitoring in areas with high uncertainty from sparse existing data.

North Dakota, South Dakota↗
USGS2007

Bankfull Regional Curves for Streams in the Non-Urban, Non-Tidal Coastal Plain Physiographic Province, Virginia and Maryland

Natural-channel design involves constructing a stream channel with the dimensions, slope, and plan-view pattern that would be expected to transport water and sediment and yet maintain habitat and aesthetics consistent with unimpaired reaches. The adequate description of channel geometry in unimpaired reaches often is an important component of natural-channel design projects and can be facilitated through empirical regression relations, or regional curves, relating bankfull geometry to drainage area. One-variable, ordinary least-squares regressions relating bankfull discharge, bankfull cross-sectional area, bankfull width, and bankfull mean depth to drainage area were developed based on data collected at 20 streamflow-gaging stations in Virginia and Maryland. These regional curves can be used to estimate the bankfull discharge and bankfull channel geometry when the drainage area of a watershed is known. Field data collected at the site for each streamflow-gaging station included one longitudinal profile of bankfull features and channel-bed slope, two riffle cross-section surveys of channel geometry, cross-section pebble counts, and one site sketch with photographs of the channel and bankfull features. The top of the bank was the bankfull feature most indicative of bankfull geometry. Field data were analyzed to determine bankfull cross-sectional area, bankfull width, bankfull mean depth, and D50- and D84-particle sizes for the two riffles at each site. The bankfull geometry from the 8 sites surveyed during this study represents the average of two riffle cross sections for each site, and the bankfull geometry from the 12 Maryland sites represents one cross section for each site. Regional curves developed for the 20 sites had coefficient of determination (R2) values of 0.945, 0.890, 0.871, and 0.793 for bankfull cross-sectional area, width, mean depth, and discharge, respectively. The regional curves represent conditions for streams with defined channels and bankfull features in Virginia and Maryland with drainage areas ranging from 0.28 to 113 square miles. All sites included in the development of the regional curves were located on streams with U.S. Geological Survey streamflow-gaging stations. These curves can be used to verify bankfull features identified in the field and bankfull stage for ungaged streams in non-urban areas.

Scientific Investigations Report↗
USGS2010

Geology, geochemistry, and geophysics of the Fry Canyon uranium/copper project site, southeastern Utah: Indications of contaminant migration

The Fry Canyon uranium/copper project site in San Juan County, southeastern Utah, was affected by the historical (1957–68) processing of uranium and copper-uranium ores. Relict uranium tailings and related ponds, and a large copper heap-leach pile at the site represent point sources of uranium and copper to local soils, surface water, and groundwater. This study was designed to establish the nature, extent, and pathways of contaminant dispersion. The methods used in this study are applicable at other sites of uranium mining, milling, or processing. The uranium tailings and associated ponds sit on a bench that is as much as 4.25 meters above the level of the adjacent modern channel of Fry Creek. The copper heap leach pile sits on bedrock just south of this bench. Contaminated groundwater from the ponds and other nearby sites moves downvalley and enters the modern alluvium of adjacent Fry Creek, its surface water, and also a broader, deeper paleochannel that underlies the modern creek channel and adjacent benches and stream terraces. The northern extent of contaminated groundwater is uncertain from geochemical data beyond an area of monitoring wells about 300 meters north of the site. Contaminated surface water extends to the State highway bridge. Some uranium-contaminated groundwater may also enter underlying bedrock of the Permian Cedar Mesa Sandstone along fracture zones. Four dc-resistivity surveys perpendicular to the valley trend were run across the channel and its adjacent stream terraces north of the heap-leach pile and ponds. Two surveys were done in a small field of monitoring wells and two in areas untested by borings to the north of the well field. Bedrock intercepts, salt distribution, and lithologic information from the wells and surface observations in the well field aided interpretation of the geophysical profiles there and allowed interpretation of the two profiles not tested by wells. The geophysical data for the two profiles to the north of the well field suggest that the paleochannel persists at least 900 m to the north of the heap leach and pond sites. Contamination of groundwater beneath the stream terraces may extend at least that far. Fry Creek surface water (six samples), seeps and springs (six samples), and wells (eight samples) were collected during a dry period of April 16–19, 2007. The most uranium-rich (18.7 milligrams per liter) well water on the site displays distinctive Ca-Mg-SO 4 -dominant chemistry indicating the legacy of heap leaching copper-uranium ores with sulfuric acid. This same water has strongly negative δ 34 S of sulfate (–13.3 per mil) compared to most local waters of –2.4 to –5.4 per mil. Dissolved uranium species in all sampled waters are dominantly U(VI)-carbonate complexes. All waters are undersaturated with respect to U(VI) minerals. The average 234 U/ 238 U activity ratio (AR) in four well waters from the site (0.939±0.011) is different from that of seven upstream waters (1.235±0.069). This isotopic contrast permits quantitative estimates of mixing of site-derived uranium with natural uranium in waters collected downstream. At the time of sampling, uranium in downstream surface water was mostly (about 67 percent) site-derived and subject to further concentration by evaporation. Three monitoring wells located approximately 0.4 kilometer downstream contained dominantly (78–87 percent) site-derived uranium. Distinctive particles of chalcopyrite (CuFeS) and variably weathered pyrite (FeS 2 ) are present in tailings at the stream edge on the site and are identified in stream sediments 1.3 kilometers downstream, based on inspection of polished grain mounts of magnetic mineral separates.

Utah↗
USGS2004

Direction of ground-water flow in the surficial aquifer in the vicinity of impact areas G-10 and K-2, Camp Lejeune Marine Corps Base, North Carolina, 2004

Marine Corps Base Camp Lejeune is located in Onslow County in the North Carolina Coastal Plain. In support of North Carolina Department of Environment and Natural Resource requirements, Camp Lejeune is developing a site closure plan for two Resource Conservation and Recovery Act (RCRA) regulated open burn/open detonation (OB/OD) facilities located within Impact Area K-2 and Impact Area G-10, respectively. Both Impact Areas are used for training activities involving live artillery fire. The two OB/OD facilities are used to treat RCRA regulated waste munitions. To provide Base officials with information needed for assessing the quality of ground water at these sites, hydrologic data were used to characterize groundwater flow directions and hydraulic gradients in the surficial aquifer underlying the Impact Areas. Water-level data in the unconfined surficial aquifer and potentiometric head data in the underlying Castle Hayne aquifer were compiled from existing and newly drilled wells. Water-table contour maps were developed for Impact Areas K-2 and G-10 to examine the direction of ground-water flow in the surficial aquifer. The primary directions of ground-water flow beneath K-2 are southward and eastward toward discharge zones along the New River and its tributaries. Beneath interior areas of G-10, water in the surficial aquifer flows outward in all directions toward discharge zones along local streams that drain westward to the New River or to streams that drain southward and eastward to the Intracoastal Waterway and the Atlantic Ocean. Long-term water-level data for the period October 1994 through September 2004 at selected Camp Lejeune well sites were used to examine trends in ground-water levels and vertical hydraulic gradients between the surficial and Castle Hayne aquifers. Evaluation of water-level data for three wells in the surficial aquifer indicated no significant trends for this period of record. The apparent water-level declines in two of the three Castle Hayne wells examined are likely the result of local pumping of the Castle Hayne aquifer. Vertical hydraulic gradients determined for two well cluster sites indicate a downward flow of water from the surficial aquifer into the underlying Castle Hayne aquifer.

Scientific Investigations Report↗
USGS2012

Biodegradation of chloroethene compounds in groundwater at Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, 1999-2010

The U.S. Geological Survey evaluated the biodegradation of chloroethene compounds in groundwater beneath the former landfill at Operable Unit 1 (OU 1) of the U.S. Naval Undersea Warfare Center (NUWC), Division Keyport. The predominant contaminants in groundwater are the chloroethene compounds trichloroethene, cis -1,2-dichloroethene, and vinyl chloride. The remedy selected for groundwater contamination at OU 1 includes phytoremediation and natural attenuation. In 1999, the U.S. Navy planted two hybrid poplar plantations, referred to as the northern and southern plantations, over the most contaminated parts of the landfill. The U.S. Navy monitors tree health, groundwater levels, and contaminant concentrations to assess the effectiveness of phytoremediation. The U.S. Geological Survey began a cooperative effort with the U.S. Navy in 1995 to monitor the effectiveness of natural attenuation processes for removing and controlling the migration of chloroethenes and chloroethanes. Field and laboratory studies from 1996 through 2000 demonstrated that biodegradation of chloroethenes and chloroethanes in shallow groundwater at OU 1 was substantial. The U.S. Geological Survey monitored geochemical and contaminant concentrations in groundwater annually from 2001 through 2010. This report presents groundwater geochemical and contaminant data collected by the U.S. Geological Survey during June 2010 and evaluates evidence for continued biodegradation of chloroethenes in groundwater. Geochemical and contaminant concentration data through 2010 indicate that biodegradation of chloroethenes in groundwater continued beneath the landfill at OU 1. Contaminant concentrations in groundwater decreased beneath most of the 9-acre landfill between 1999 and 2010. The evidence indicating that biodegradation was a primary cause for the decreased concentrations included decreasing ratios of more highly chlorinated compounds to less chlorinated compounds over time, and widespread detections of non-chlorinated biodegradation end-products ethane and ethene. No widespread changes in groundwater reduction-oxidation (redox) conditions were observed that could result in either more or less efficient biodegradation. Even with continued biodegradation, dissolved-phase contaminant concentrations in the tens of milligrams per liter have persisted beneath part of the 0.7-acre southern plantation. The magnitude and persistence of those concentrations indicate that non-aqueous phase liquid chloroethenes likely are present beneath the southern plantation and are not substantially affected by biodegradation. During 2010, chloroethenes continued to be measured in shallow groundwater samples from the southern part of the adjacent marsh, although at the lowest concentrations ever measured. Flux calculations based on 2010 data indicate that 95 percent of dissolved-phase chloroethenes in the upper aquifer beneath the southern landfill were degraded before discharging to surface water. Overall, biodegradation of chloroethenes in groundwater throughout OU 1 continued through 2010, and it prevented most of the mass of dissolved-phase chloroethenes in the upper aquifer beneath the landfill from discharging to surface water.

Washington↗
USGS2007

Natural and diverted low-flow duration discharges for streams affected by the Waiahole Ditch System, windward O`ahu, Hawai`i

For nearly a century, the Waiahole Ditch System has diverted an average of approximately 27 million gallons per day of water from the wet, northeastern part of windward O`ahu, Hawai`i, to the dry, central part of the island to meet irrigation needs. The system intercepts large amounts of dike-impounded ground water at high altitudes (above approximately 700 to 800 ft) that previously discharged to Waiahole (and its tributaries Waianu and Uwao), Waikane, and Kahana Streams through seeps and springs. Diversion of this ground water has significantly diminished low flows in these streams. Estimates of natural and diverted flows are needed by water managers for (1) setting permanent instream flow standards to protect, enhance, and reestablish beneficial instream uses of water in the diverted streams and (2) allocating the diverted water for instream and offstream uses. Data collected before construction of the Waiahole Ditch System reflect natural (undiverted) flow conditions. Natural low-flow duration discharges for percentiles ranging from 50 to 99 percent were estimated for four sites at altitudes of 75 to 320 feet in Waiahole Stream (and its tributaries Waianu and Uwao Streams), for six sites at altitudes of 10 to 220 feet in Waikane Stream, and for three sites at altitudes of 30 to 80 feet in Kahana Stream. Among the available low-flow estimates along each affected stream, the highest natural Q50 (median) flows on Waiahole (altitude 250 ft), Waianu (altitude 75 ft), Waikane (altitude 75 ft), and Kahana Streams (altitude 30 ft) are 13, 7.0, 5.5, and 22 million gallons per day, respectively. Q50 (median) is just one of five duration percentiles presented in this report to quantify low-flow discharges. All flow-duration estimates were adjusted to a common period of 1960-2004 (called the base period). Natural flow-duration estimates compared favorably with limited pre-ditch streamflow data available for Waiahole and Kahana Streams. Data collected since construction of the ditch system reflect diverted flow conditions, which can be further divided into pre-release and post-release periods - several flow releases to Waiahole, Waianu, and Waikane Streams were initiated between December 1994 and October 2002. Comparison of pre-release to natural flows indicate that the effects of the Waiahole Ditch System diversion are consistently greater at lower low-flow conditions (Q99 to Q90) than at higher low-flow conditions (Q75 to Q50). Results also indicate that the effects of the diversion become less significant as the streams gain additional ground water at lower altitudes. For Waiahole Stream, pre-release flows range from 25 to 28 percent of natural flows at an altitude of 250 feet and from 19 to 20 percent at an altitude of 320 feet. For Waikane Stream, pre-release flows range from 30 to 46 percent of natural flows at an altitude of 10 feet and from 7 to 19 percent at an altitude of 220 feet. For Kahana Stream, pre-release flows range from 65 to 72 percent of natural flows at an altitude of 30 feet and from 58 to 71 percent at an altitude of 80 feet. Estimates of post-release flows were compared with estimates of natural flows to assess how closely current streamflows are to natural conditions. For Waianu Stream, post-release flows at an altitude of 75 feet are 41 to 46 percent lower than corresponding natural flows. For Waikane Stream, post-release flows at an altitude of 75 feet are within 12 percent of the corresponding natural flows. Comparisons of pre-release and post-release flows for Waikane Stream at altitudes of 10 to 220 feet were used to assess downstream changes in flow along the stream reach where flow releases were made. For a particular stream altitude, proportions of pre-release to post-release flows associated with median flows are consistently greater than proportions associated with lower low flows because the relative effect of the flow release is smaller at higher low flows. Similarly, for a particular f

Hawaii↗
USGS2026

Peak-, mean-, and low-streamflow regional-regression equations for natural streamflow in central and western Colorado, 2019

The U.S. Geological Survey (USGS), in cooperation with the Colorado Department of Transportation, developed peak-, mean-, and low-streamflow regional-regression equations for estimating various statistics for natural streamflow in hydrologic regions of central and western Colorado. The peak-streamflow regression equations were developed using data from 418 streamgages, consisting of 15,202 years of record and a mean of approximately 36 years of record per streamgage. The mean- and low-streamflow regional-regression equations were developed using data from 323 streamgages where daily streamflow data were collected year-round. The annual exceedance-probability discharges for each streamgage were computed using the USGS software program PeakFQ. Mean monthly and 7-day minimum and maximum streamflows were computed using the USGS software program SWToolbox. Streamflow-duration values were computed using an R script. The regional-regression equations were determined using data for the period of record for a given streamgage through water year 2019. Geographic information systems datasets were used to develop 55 basin and 42 climatic characteristics, which were evaluated as candidate explanatory variables in the regression analysis. For the peak-streamflow regional-regression equations, the study area was divided into four hydrologic regions based on mean basin elevation, including the Plateau (less than 8,014 feet), Mid-Elevation (8,015 feet to 9,492 feet), Sub-Alpine (9,493 feet to 10,490 feet), and Alpine (greater than 10,490 feet) regions. For the peak-streamflow equations, the selection of basin and climatic characteristics was based on the 1-percent annual exceedance-probability discharge for each hydrologic region. For the mean streamflow, streamflow-duration values, and 7-day minimum and maximum streamflows, the study area was divided into four hydrologic regions based on river basin, including the (1) Colorado-East Slope Headwaters, (2) Green River, (3) Rio Grande, and (4) San Juan-Dolores. For mean streamflows, basin and climatic characteristics were evaluated separately for the annual period and each month for each hydrologic region. Regional regression equations published in this report are available for use in the USGS web-based program StreamStats.

Colorado↗
USGS2008

Base of principal aquifer for the Elkhorn-Loup model area, North-Central Nebraska

In Nebraska, the water managers in the Natural Resources Districts and the Nebraska Department of Natural Resources are concerned with the effect of ground-water withdrawal on the availability of surface water and the long-term effects of ground-water withdrawal on ground- and surface-water resources. In north-central Nebraska, in the Elkhorn and Loup River Basins, ground water is used for irrigation, domestic supply, and public supply; surface water is used in this area for irrigation, recreation, and hydropower production. In recognition of these sometimes competing ground- and surface-water uses in the Elkhorn and Loup River Basins, the U.S. Geological Survey, the Lewis and Clark Natural Resources District, the Lower Elkhorn Natural Resources District, the Lower Loup Natural Resources District, the Lower Niobrara Natural Resources District, the Lower Platte North Natural Resources District, the Middle Niobrara Natural Resources District, the Upper Elkhorn Natural Resources District, and the Upper Loup Natural Resources District agreed to cooperatively study water resources in the Elkhorn and Loup River Basins. The goals of the overall study were to construct and calibrate a regional ground-water flow model of the area and to use that flow model as a tool to assess current and future effects of ground-water irrigation on stream base flow and to help develop long-term water-resource management strategies for this area, hereafter referred to as the Elkhorn-Loup model area. The Elkhorn-Loup model area covers approximately 30,800 square miles, and extends from the Niobrara River in the north to the Platte River in the south. The western boundary of the Elkhorn-Loup model area coincides with the western boundary of the Middle Niobrara, Twin Platte, and Upper Loup Natural Resources Districts; the eastern boundary coincides with the approximate location of the western extent of glacial till in eastern Nebraska. The principal aquifer in most of the Elkhorn-Loup model area is the High Plains aquifer; the principal aquifer in the remaining part of the Elkhorn-Loup model area is an unnamed alluvial aquifer. The upper surface of the geologic units that directly underlie the aquifer is called the 'base of aquifer' in this report. The geologic unit that forms the base of aquifer in the Elkhorn-Loup model area varies by location. The Tertiary-age Brule Formation generally is the base of aquifer in the west; the Cretaceous-age Pierre Shale generally is the base of aquifer in the east. The purpose of this report is to update the altitude and configuration of the base of the principal aquifer in the Elkhorn-Loup model area and a 2-mile buffer area around the Elkhorn-Loup model area, using base-of-aquifer data from test holes, registered water wells, and oil and gas wells within the Elkhorn-Loup model area and a 20-mile buffer area around the Elkhorn-Loup model area that have become available since the publication of earlier maps of the base of aquifer for this area. The base-of-aquifer map is important for the Elkhorn-Loup ground-water flow model because it defines the model's lower boundary. The accuracy of the Elkhorn-Loup ground-water flow model and the accuracy of the model's predictions about the effects of ground-water irrigation on stream base flow are directly related to the accuracy of the model's lower boundary.

Scientific Investigations Map↗