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USGS2023

Introduction to study area hydrogeology, chromium sources, site history, and purpose of study

Between 1952 and 1964, hexavalent chromium, Cr(VI), was released into groundwater from the Pacific Gas and Electric Company (PG&E) Hinkley compressor station in the Mojave Desert 80 miles (mi) northeast of Los Angeles, California. Remediation began in 1992, and in 2010, site cleanup was projected to require between 10 and 95 years and was expected to cost between $36 and $176 million. A 2007 PG&E study estimated the natural Cr(VI) background in groundwater in Hinkley Valley to be 3.1 micrograms per liter (μg/L). This concentration was used for interim regulatory purposes by the Lahontan Regional Water Quality Control Board (RWQCB). In the fourth quarter (October–December) 2015, the regulatory Cr(VI) plume extended about 3.0 mi downgradient from the release location within the Hinkley compressor station, while groundwater having Cr(VI) concentrations greater than 3.1 μg/L was present more than 8 mi downgradient. Although rocks and minerals in the area are naturally low in chromium, alluvium eroded from the San Gabriel Mountains and transported to Hinkley Valley by the Mojave River, and locally small exposures of mafic rock, including hornblende diorite and basalt, may contribute Cr(VI) to groundwater. In response to limitations of the PG&E 2007 Cr(VI) background study’s methodology, uncertainty in the natural Cr(VI) background concentration, and an increase in the mapped extent of groundwater having Cr(VI) concentrations greater than the interim regulatory background of 3.1 μg/L, the Lahontan RWQCB concluded that the 2007 PG&E background Cr(VI) study should be updated. The purpose of the updated study is to estimate background Cr(VI) concentrations in groundwater within the upper aquifer upgradient, downgradient, near the margins, and within the footprint of the PG&E Cr(VI) plume in Hinkley, California. The scope of the study included eight tasks; results from those tasks are presented in the chapters within this professional paper.

California↗

USGS2013

Hydrologic drought of water year 2011 compared to four major drought periods of the 20th century in Oklahoma

Water year 2011 (October 1, 2010, through September 30, 2011) was a year of hydrologic drought (based on streamflow) in Oklahoma and the second-driest year to date (based on precipitation) since 1925. Drought conditions worsened substantially in the summer, with the highest monthly average temperature record for all States being broken by Oklahoma in July (89.1 degrees Fahrenheit), June being the second hottest and August being the hottest on record for those months for the State since 1895. Drought conditions continued into the fall, with all of the State continuing to be in severe to exceptional drought through the end of September. In addition to effects on streamflow and reservoirs, the 2011 drought increased damage from wildfires, led to declarations of states of emergency, water-use restrictions, and outdoor burning bans; caused at least $2 billion of losses in the agricultural sector and higher prices for food and other agricultural products; caused losses of tourism and wildlife; reduced hydropower generation; and lowered groundwater levels in State aquifers. The U.S. Geological Survey, in cooperation with the Oklahoma Water Resources Board, conducted an investigation to compare the severity of the 2011 drought with four previous major hydrologic drought periods during the 20th century – water years 1929–41, 1952–56, 1961–72, and 1976–81. The period of water years 1925–2011 was selected as the period of record because few continuous record streamflow-gaging stations existed before 1925, and gaps in time existed where no streamflow-gaging stations were operated before 1925. In water year 2011, statewide annual precipitation was the 2d lowest, statewide annual streamflow was 16th lowest, and statewide annual runoff was 42d lowest of those 87 years of record. Annual area-averaged precipitation totals by the nine National Weather Service climate divisions from water year 2011 were compared to those during four previous major hydrologic drought periods to show how precipitation deficits in Oklahoma varied by region. The nine climate divisions in Oklahoma had precipitation in water year 2011 ranging from 43 to 76 percent of normal annual precipitation, with the Northeast Climate Division having the closest to normal precipitation and the Southwest Climate Division having the greatest percentage of annual deficit. Based on precipitation amounts, water year 2011 ranked as the second driest of the 1925–2011 period, being exceeded only in one year of the 1952 to 1956 drought period. Regional streamflow patterns for water year 2011 indicate that streamflow in the Arkansas-White-Red water resources region, which includes all of Oklahoma, was relatively large, being only the 26th lowest since 1930, primarily because of normal or above-normal streamflow in the northern part of the region. Twelve long-term streamflow-gaging stations with periods of record ranging from 67 to 83 years were selected to show how streamflow deficits varied by region in Oklahoma. Statewide, streamflow in water year 2011 was greater than streamflows measured in years during the drought periods of 1929–41, 1952–56, 1961–72, and 1976–81. The hydrologic drought worsened going from the northeast toward the southwest in Oklahoma, ranging from 140 percent (above normal streamflow) in the northeast, to 13 percent of normal streamflow in southwestern Oklahoma. The relatively low streamflow in 2011 resulted in 83.3 percent of the statewide conservation storage being available at the end of the water year in major reservoirs, similar to conservation storage in the preceding severe drought year of 2006. The ranking of streamflow as the 16th smallest for the 1925–2011 period, despite precipitation being ranked the 2d smallest, may have been caused, in part, by the relatively large streamflow in northeastern Oklahoma during water year 2011.

Oklahoma↗

USGS2013

Use of multi-node wells in the Groundwater-Management Process of MODFLOW-2005 (GWM-2005)

Many groundwater wells are open to multiple aquifers or to multiple intervals within a single aquifer. These types of wells can be represented in numerical simulations of groundwater flow by use of the Multi-Node Well (MNW) Packages developed for the U.S. Geological Survey’s MODFLOW model. However, previous versions of the Groundwater-Management (GWM) Process for MODFLOW did not allow the use of multi-node wells in groundwater-management formulations. This report describes modifications to the MODFLOW–2005 version of the GWM Process (GWM–2005) to provide for such use with the MNW2 Package. Multi-node wells can be incorporated into a management formulation as flow-rate decision variables for which optimal withdrawal or injection rates will be determined as part of the GWM–2005 solution process. In addition, the heads within multi-node wells can be used as head-type state variables, and, in that capacity, be included in the objective function or constraint set of a management formulation. Simple head bounds also can be defined to constrain water levels at multi-node wells. The report provides instructions for including multi-node wells in the GWM–2005 data-input files and a sample problem that demonstrates use of multi-node wells in a typical groundwater-management problem.

Techniques and Methods↗

USGS1985

Comparison of two methods for estimating ground-water recharge in 1978-80, Santa Maria Valley, California

Infiltration from the Santa Maria River and the lower part of the Sisquoc River constitutes most of the groundwater recharge to the aquifer system of Santa Maria Valley, California. The annual recharge volumes commonly are much greater or smaller than the long-term average annual recharge. A comparison of two methods of estimating annual recharge indicates that, in Santa Maria Valley, a seepage-loss method is comparable to a water-level-change method. Both methods indicate that recharge was about 600,000 acre-feet during 1978-80. By the seepage-loss method, annual recharges for 1978, 1979, and 1980 are estimated as 290,000, 130,000, and 190,000 acre-feet. Using the water-level-change method, annual recharges during 1978, 1979, and 1980 are estimated at 230,000, 190,000, and 160,000 acre-feet. A log-Pearson Type III probability distribution of annual flows gaged on the Sisquoc River indicates that average annual recurrence intervals of recharge events equal to those of 1978, 1979, and 1980 are 20, 4, and 10 years. (USGS)

Water-Resources Investigations Report↗

USGS1987

Water resources of the Rio Grande de Añasco-lower valley, Puerto Rico

A large amount of water suitable for most uses is available in the lower Rio Grande de Anasco Valley, the major source of which is the Rio Grande de Anasco which contributes about 95% of the surface water inflow to the lower valley. River flow at El Espino exceeds 100 cu ft/sec about 85% of the time and 200 cu ft/sec 50% of the time. Average daily flow for the driest months of the year (February, March, and April), is almost always <100 cu ft/sec. In contrast, the average daily flow for the wettest, months of the year (September, October, and November), is > 120 cu ft/sec. During the study period, flows of the Rio Canas averaged about 5 cu ft/sec. The lower valley is underlain by igneous rocks that have been eroded to depths of 350 ft or more below sea level. The valley is filled with 250 ft or more of limestone and clay, that in turn is overlain by as much as 100 ft of alluvium. The amount of groundwater available is unknown. There are large volumes of water in the saturated mostly fine-grained alluvium of Zone II, but as a whole the alluvium does not yield water readily to wells. Sand and gravel deposits associated with former river channels yield an estimated 100 to 150 gal/min to wells. The principal source of groundwater is the limestone of Zone III, that reportedly yields as much as 500 gal/min to wells. The quality of surface water especially that of Rio Grande de Anasco was very good. Specific conductance seldom exceeds 250 microsiemens/cm, even at low flows. Both salinity and sodium are low, falling in the Cl-S1 irrigation water classification. Water quality in the lower 5,000 ft or so of the river was affected by saltwater encroachment from the sea. The water quality of the other streams and canals in the lower valley was variable depending on susceptibility of saltwater encroachment, contamination from man-made sources, and concentration of minerals by evapotranspiration. Specific conductance however seldom exceeded 500 microsiemens/cm and the water usually falls in the C1-S2 classification. The quality of groundwater in the alluvial aquifer was about the same as that of the water of the Rio Grande de Anasco except where encroached by saltwater or contaminated. The water from the limestone was more mineralized than that of the alluvium (about 600 to 700 microsiemens/cm), and was somewhat similar to that of the smaller streams and canals in the valley.

Puerto Rico↗

USGS1990

Geochemistry of batch-extract waters derived from spoil material collected at the Cordero coal mine, Powder River basin, Wyoming

Batch-mixing experiments to evaluate postmining water quality at the Cordero Mine were conducted by the U.S. Geological Survey during 1984 to 1985. Contact of groundwater from the spoil aquifer with fresh spoil material caused only small changes in major-element concentrations and in pH, unless sulfide oxidation or contact with soluble salts, such as epsomite, occurred. In contrast, large changes in major-element concentration resulted when water from the coal aquifer contacted the spoil material. Only three of seven reaction models considered to explain the water quality changes during the batch-mixing experiments were consistent with the thermodynamic and mineralogical data. The three models used to account for the observed water quality changes derived potassium from potassium feldspar; magnesium from chlorite or epsomite or both; sodium from cation exchange and halite; chloride from halite; silica from potassium feldspar and chlorite; sulfate from gypsum, or epsomite or both, and carbon from carbon dioxide. In general, water quality samples obtained from the batch-mixing experiments using water from the coal aquifer had smaller major-ion concentrations than the actual water quality in the spoil aquifer. These differences can be explained by the limited amount of efflorescent salt dissolution and volume of water used in the experiments. Correction ratios calculated for these experiments may be applied to batch-mixing experiments at other mines in the area, to predict postmining water quality. (USGS)

Water-Resources Investigations Report↗

USGS2021

Rapid-response unsaturated zone hydrology: Small-scale data, small-scale theory, big problems

The unsaturated zone (UZ) extends across the Earth’s terrestrial surface and is central to many problems related to land and water resource management. Flow of water through the UZ is typically thought to be slow and diffusive, such that it could attenuate fluxes and dampen variability between atmospheric inputs and underlying aquifer systems. This would reduce water resource vulnerability to contaminants and water-related hazards. Reducing or negating that effect, however, spatially concentrated and rapid flow and transport through the unsaturated zone is surprisingly common and becoming more so with the increasing frequency and magnitude of extreme hydroclimatic events. Arising from the wide range in the rates and complex modes of nonlinear flow processes, these effects are among the most poorly characterized hydrologic phenomena. Issues of scale present additional difficulties. Equations representing unsaturated processes have been developed and tested on the basis of field and laboratory measurements typically made at scales from pore size to plot size. In contrast, related problems of significant interest to society, including floods, aquifer recharge, landslides, and groundwater contamination, range from watershed to regional scales. The disparity between the scale of our understanding and the scale of interest for societal problems has spurred application of these model equations at increasingly coarse resolutions over larger areas than can be justified by existing measurements or theory. This mismatch in scales requires an assumption that spatially averaging slow diffusive flow and rapid preferential flow can effectively represent the influence of both processes across vast areas. Given the currently inadequate recognition and quantitative characterization of focused and rapid processes in unsaturated flow, these phenomena are critically in need of expanded attention and effort.

Frontiers in Earth Science↗

USGS1985

RAPID REMOVAL OF A GROUNDWATER CONTAMINANT PLUME.

A groundwater management model is used to design an aquifer restoration system that removes a contaminant plume from a hypothetical aquifer in four years. The design model utilizes groundwater flow simulation and mathematical optimization. Optimal pumping and injection strategies achieve rapid restoration for a minimum total pumping cost. Rapid restoration is accomplished by maintaining specified groundwater velocities around the plume perimeter towards a group of pumping wells located near the plume center. The model does not account for hydrodynamic dispersion. Results show that pumping costs are particularly sensitive to injection capacity. An 8 percent decrease in the maximum allowable injection rate may lead to a 29 percent increase in total pumping costs.

Conference Paper↗

USGS2002

High-resolution characterization of chemical heterogeneity in an alluvial aquifer

The high-resolution capabilities of direct-push technology were exploited to develop new insights into the hydrochemistry at the margin of an alluvial aquifer. Hydrostratigraphic controls on groundwater flow and contaminant loading were revealed through the combined use of direct-push electrical conductivity (EC) logging and geochemical profiling. Vertical and lateral variations in groundwater chemistry were consistent with sedimentary features indicated by EC logs, and supported a conceptual model of recharge along the floodplain margin.

Acta Universitatis Carolinae, Geologica↗

USGS2002

High-resolution characterization of chemical heterogeneity in an alluvial aquifer

The high-resolution capabilities of direct push technology were exploited to develop new insights into the hydrochemistry at the margin of an alluvial aquifer. Hydrostratigraphic controls on groundwater flow and contaminant loading were revealed through the combined use of direct push electrical conductivity (EC) logging and geochemical profiling. Vertical and lateral variations in groundwater chemistry were consistent with sedimentary features indicated by EC logs, and were supported by a conceptual model of recharge along the flood plain margin.

IAHS-AISH Publication↗

USGS1978

Jordan aquifer of Iowa

Water demand for all uses in Iowa is increasing at an accelerated rate. Demand has increased from about 1,800 million gallons per day in 1955 to 3,500 million gallons per day in 1975 (MacKichan, 1957; Murray and Reeves, 1977). By the year 2020, water demand is expected to be eight times that in 1975 (Barnard and Dent, 1976). Historically, about 75 percent of the demand, excluding that required for power generation, has been met by withdrawals from the water-bearing zones (aquifers) in Iowa's ground-water reservoir. Because this percentage is expected to remain about the same, the anticipated future demands will require extensive withdrawals from the ground-water reservoir. The increasing stress on the ground-water system, which already is severely stressed in several places in the state, will create development and management problems that will require hydrologic information to solve. In order to provide this information, the lowa Geological Survey in cooperation with the U.S. Geological Survey has instituted a series of investigations to define, describe, and evaluate the major aquifers in Iowa's groundwater reservoir. Information from each investigation will be presented in atlas format.

Iowa↗

USGS2019

Hydrogeologic framework of the Virginia Eastern Shore

The Yorktown-Eastover aquifer system of the Virginia Eastern Shore consists of upper, middle, and lower confined aquifers overlain by correspondingly named confining units and underlain by the Saint Marys confining unit. Miocene- to Pliocene-age marine-shelf sediments observed in 205 boreholes include medium- to coarse-grained sand and shells that compose the aquifers and fine-grained sand, silt, and clay that compose the confining units. The upper confining unit also includes fine-grained and organic-rich back-barrier and estuarine sediments of Pleistocene age. An overlying surficial aquifer is composed mostly of Pleistocene-age nearshore sand and gravel with smaller amounts of cobbles and boulders. In addition, Pleistocene-age sediments that fill three buried paleochannels are for the first time explicitly delineated here as distinct hydrogeologic units. Two aquifers are composed of medium- to coarse-grained fluvial sand and gravel, and an intervening confining unit is composed of fine-grained estuarine sand, silt, clay, and organic material. Aquifer and confining-unit sediments are also mixed with reworked marine-shelf sediments eroded from the sides of the paleochannels. Hydrogeologic units of the Yorktown-Eastover aquifer system generally dip eastward, are as much as several tens of feet thick, and have an undulating configuration possibly resulting from the underlying Chesapeake Bay impact crater. Aquifers and confining units are incised by the three paleochannels along an upward-widening and eastward-lengthening series of structural “windows.” Hydrogeologic units within mainstems and branching tributaries of the paleochannels dip southeastward parallel to slopes of the paleochannels, are as much as several tens of feet thick, and laterally abut the Yorktown-Eastover aquifer system along paleochannel sidewalls. The Yorktown-Eastover aquifer system is thereby hydraulically breached by the paleochannels to alternately create barriers to or conduits for groundwater flow. Results of previously documented aquifer tests at 58 wells indicate that transmissivity is generally greatest in young, shallow, and coarse-grained nearshore and fluvial sediments of the surficial aquifer and paleochannels. Transmissivity progressively decreases with depth in older, deeper, and finer grained marine-shelf sediments of the Yorktown-Eastover aquifer system, probably because they have undergone compaction as a result of greater overburden pressure over longer periods of time. Compiled chloride concentrations in samples from 330 wells generally increase downward, with most of the samples collected at altitudes above −300 feet and with most concentrations less than 250 milligrams per liter. The saltwater-transition zone has a broad trough-like shape aligned with the peninsula, being relatively shallow along the coastline and deeper along the central “spine.” Because movement of the saltwater is slow, the configuration largely reflects groundwater flow prior to widespread groundwater withdrawals. Fresh groundwater has leaked downward along deep parts of the saltwater-transition zone and leaked upward along shallower parts to discharge at the coast. The saltwater-transition zone also exhibits an anomalous ridge across the center of the peninsula. Groundwater levels indicate that the saltwater ridge formed primarily by the Exmore paleochannel acting as a large lateral collector drain. Groundwater levels were lowered, and the position of saltwater-transition zone was elevated, by a flow conduit that intercepted groundwater that otherwise would have flowed toward and discharged along the coastline. Nearly all freshwater on the Virginia Eastern Shore is supplied by groundwater withdrawals, which have lowered water levels, altered hydraulic gradients, and created a concern for saltwater intrusion. Previous characterizations of groundwater conditions that are relied on to manage groundwater development have been limited by a lack of hydrogeologic information, particularly data on buried paleochannels that are critical to safeguarding the groundwater supply. Using recently available expanded information, the U.S. Geological Survey undertook a study in cooperation with the Virginia Department of Environmental Quality during 2016–19 to develop an improved description of the groundwater system called a “hydrogeologic framework.” The hydrogeologic framework can aid water-supply planning and development by providing information on broad trends in aquifer configurations, hydraulic properties, and proximity to saltwater to avoid chloride contamination. Digital models to evaluate effects of groundwater withdrawals can also be improved with expanded data and capabilities to evaluate paleochannel hydraulic connections and the potential for saltwater movement. The hydrogeologic framework is limited by the nonuniform distribution of boreholes and the subjective delineation of aquifers and confining units, including those within paleochannels that are regarded as preliminary. The configuration of the saltwater-transition zone is also regarded as preliminary because of the nonuniform distribution of groundwater samples. Low well-sampling frequency precludes characterizing movement of the saltwater-transition zone. A monitoring strategy of sampling and possibly electromagnetic-induction well logging could be used to detect saltwater movement.

Virginia↗

USGS2022

Documentation for the Skeletal Storage, Compaction, and Subsidence (CSUB) Package of MODFLOW 6

This report describes the skeletal storage, compaction and subsidence (CSUB) package of MODFLOW 6. The CSUB package simulates the vertical compaction of compressible sediments and land subsidence. The package simulates groundwater storage changes and elastic compaction in coarse-grained aquifer sediments. The CSUB package also simulates groundwater storage changes and elastic and inelastic compaction in fne-grained, compressible interbeds, or in extensive confning units. The package can account for effective stress-dependent changes in storage properties. The CSUB package can also explicitly account for the contribution of water compressibility to groundwater storage changes. Compaction of compressible sediments is formulated using Terzaghi’s elastoplastic model and assumes the total compaction is a small fraction of the total initial thickness of compressible sediments. Compaction is controlled by head or pore-pressure changes and overburden stress changes associated with water-table changes, and thus by effective stress changes within coarse-and fne-grained compressible sediments. If the stress in a compressible unit is less than the preconsolidation stress, compaction is elastic (recoverable). If the stress in a compressible sediment is greater than the preconsolidation stress, compaction is inelastic (irrecoverable) and permanent land subsidence occurs. The propagation of head changes within fne-grained, compressible interbeds is represented numerically using a transient, one-dimensional (vertical) groundwater fow equation. This equation accounts for delayed release of water from storage or uptake of water into storage in the interbeds. Vertical hydraulic conductivity, elastic and inelastic skeletal specifc storage, and interbed thickness control the timing of interbed storage changes. Interbeds that are thin, have a relatively large vertical hydraulic conductivity, or relatively small specifc-storage values equilibrate quickly with heads/pore pressures in surrounding coarse-grained sediments and can be represented as no-delay interbeds that use the simulated groundwater head in a cell to calculate interbed compaction and do not need to be solved numerically using a vertically discretized interbed and the vertical groundwater fow equation. In addition to the applicability to confned groundwater fow systems, several features of the CSUB package make it applicable to shallow, unconfned groundwater fow systems. Geostatic stress can be treated as a function of water-table elevation, and compaction is a function of computed changes in effective stress. The porosity, void ratio, and thickness of shallow and deep coarse-grained aquifer sediments, fne-grained interbeds, and extensive confning units can vary in time based on calculated strain.

Techniques and Methods↗

USGS2023

Chromium in minerals and selected aquifer materials

Between 1952 and 1964, hexavalent chromium, Cr(VI), was released into groundwater from a Pacific Gas and Electric Company (PG&E) compressor station in Hinkley, California, in the western Mojave Desert 80 miles northeast of Los Angeles, California. In 2015, the extent of anthropogenic Cr(VI) in groundwater in Hinkley and Water Valleys was uncertain, but some Cr(VI) in groundwater may be naturally occurring from rock and aquifer material. To evaluate potential sources of natural Cr(VI), chromium and other selected trace-element concentrations were measured by inductively coupled plasma-mass spectrometry (ICP-MS), with multi-acid digestion, on 34 samples of surficial alluvium and core material from Hinkley and Water Valleys, California, and on 2 samples of alluvium from the mafic Sheep Creek fan to the southwest. Chromium concentrations in Hinkley and Water Valleys ranged from 2 to 110 milligrams per kilogram (mg/kg), with a median concentration of 14 mg/kg; concentrations were highest in weathered mafic hornblende diorite associated with Iron Mountain. High chromium concentrations also were present within fine-textured materials and visually abundant iron- and manganese-oxide coatings on the surfaces of mineral grains. For comparison, chromium concentrations as high as 170 mg/kg were measured in mafic alluvium from the Sheep Creek fan. In contrast, chromium concentrations were lowest in Mojave-type deposits (Mojave River stream and lake margin deposits), with a median of 6 mg/kg. Chromium concentrations measured by ICP-MS compared favorably with concentrations measured by portable (handheld) X-ray fluorescence (pXRF; chapter B), on the basis of least-squares regression results and a coefficient of determination (R 2 ) of 0.97. Minerals in bulk samples and the heavy (dense) mineral fractions isolated from those samples were identified using optical techniques, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Quartz and feldspar were the most abundant minerals, especially within recent and older Mojave River deposits. Chromium concentrations were as high as 1,250 mg/kg in the heavy-mineral fraction, with specific gravity greater than 3.32. Chromium was not commonly detected in the light-mineral fraction, with specific gravity less than 2.85. Most chromium within the heavy-mineral fraction was substituted within magnetite mineral grains less than 100 micrometers (μm) in diameter, and almost no chromite was present within the heavy-mineral fraction. Although magnetite is resistive to weathering, weathering of magnetite to hematite was identified (1) in Miocene materials underlying unconsolidated deposits in the western subarea of Hinkley Valley and (2) in alluvium within Water Valley that contains weathered minerals eroded from Miocene rock. Less-dense, more easily weathered chromium-containing amphiboles, such as actinolite in older Mojave River alluvium and hornblende in locally derived alluvium from Iron Mountain, were identified optically. Magnetite was not identified in weathered hornblende diorite and was less abundant in locally derived materials and in Miocene materials than in Mojave-type deposits. A comparison of ICP-MS data and sequential extraction data shows that approximately 90 percent of chromium in aquifer material within Hinkley and Water Valleys was not extractable and was interpreted to reside within unweathered mineral grains. Most extractable chromium was within the strong acid extractable fraction. Chromium within the weakly sorbed, and specifically sorbed extractable fractions in oxide accumulations within the regulatory Cr(VI) plume is potentially mobile into groundwater with changes in ionic strength or pH. Although Hinkley and Water Valleys are regionally low in chromium, natural geologic sources of chromium may be present in aquifer materials penetrated by wells completed in (1) weathered hornblende diorite bedrock underlying the western subarea; (2) Miocene deposits underlying the western subarea and unconsolidated material in the northern subarea and Water Valley containing basalt or weathered minerals eroded from Miocene deposits; (3) unconsolidated material containing visually abundant iron- and manganese-oxide coatings on the surfaces of mineral grains that are present near the water table and near lithologic or geologic contacts; and (4) brown clay and mudflat/playa deposits in the northern subarea. Brown clay and mudflat/playa deposits in the eastern subarea near Mount General have a low-chromium, felsic mineralogy similar to Mojave River deposits and do not contain high concentrations of chromium; however, manganese(IV) oxides within these materials may facilitate oxidation of trivalent chromium, Cr(III), to Cr(VI).

California↗

USGS2018

Simulation of groundwater flow, 1895–2010, and effects of additional groundwater withdrawals on future stream base flow in the Elkhorn and Loup River Basins, central Nebraska—Phase three

The U.S. Geological Survey, in cooperation with the Lewis and Clark, Lower Elkhorn, Lower Loup, Lower Platte North, Lower Niobrara, Middle Niobrara, Upper Elkhorn, and the Upper Loup Natural Resources Districts, designed a study to refine the spatial and temporal discretization of a previously modeled area. This updated study focused on a 30,000-square-mile area of the High Plains aquifer and constructed regional groundwater-flow models to evaluate the effects of groundwater withdrawal on stream base flow in the Elkhorn and Loup River Basins, Nebraska. The model was calibrated to match groundwater-level and base-flow data from the stream-aquifer system from pre-1940 through 2010 (including predevelopment [pre-1895], early development [1895–1940], and historical development [1940 through 2010] conditions) using an automated parameter-estimation method. The calibrated model then was used to simulate hypothetical development conditions (2011 through 2060). Predicted changes to stream base flow based on simulated changes to groundwater withdrawal will aid in developing strategies for management of hydrologically connected water supplies. Additional wells were simulated throughout the model domain and pumped for 50 years to assess the effect of wells on aquifer depletions, including stream base flow. The percentage of withdrawal for each well after 50 years, which was compensated by aquifer reductions to stream base flow, storage, or evapotranspiration, was computed and mapped. These depletions are influenced by aquifer properties, time, and distance from the well. Stream base-flow depletion results showed that the closer the added well was to a stream, the greatest the effect on the stream base flow. Areas of stream base-flow depletion percentages greater than 80 percent were generally within 1 mile (mi) from the stream. The distance increased to 6 mi near the confluence of the Dismal and Middle Loup Rivers, and the North Loup and Calamus Rivers. The percentage of stream base-flow depletion decreased as the distance from the stream increased. Areas more than 10 mi from the stream generally had a stream base-flow depletion of 10 percent or less. Evapotranspiration depletion was largest in areas closest to streams, specifically in the Elkhorn River watershed. It was also larger in areas of interdunal wetlands within the Sand Hills. Evapotranspiration depletion was negligible in areas greater than 5 mi from a stream, with the exception of interdunal areas in Cherry, Grant, and Arthur Counties. The storage depletion percentage increased as the distance from a stream increased. Storage depletion was largest in areas between streams. Areas experiencing the smallest amount of storage depletion were adjacent to streams. Calibrated model outputs and streamflow depletion analysis are publicly available online. Accuracy of the simulations is affected by input data limitations, system simplifications, assumptions, and resources available at the time of the simulation construction and calibration. Most of the important limitations relate either to data used as simulation inputs or to data used to estimate simulation inputs. Development of the regional simulations focused on generalized hydrogeologic characteristics within the study area and did not attempt to describe variations important to local-scale conditions. These simulations are most appropriate for analyzing groundwater-management scenarios for large areas and during long periods and are not suitable for analysis of small areas or short periods.

Nebraska↗

USGS2019

Groundwater-level change for the periods 2002–8, 2008–12, and 2008–16 in the Santa Fe Group aquifer system in the Albuquerque area, central New Mexico

The U.S. Geological Survey, in cooperation with the Albuquerque Bernalillo County Water Utility Authority (ABCWUA), has developed a series of maps and associated reports, beginning in 2002, that document groundwater levels in the production zone of the Santa Fe Group aquifer system beneath a large area of the City of Albuquerque, New Mexico (hereafter called the study area). Herein, we document the construction of groundwater-level change maps for representative conditions during three periods: 2002–8, 2008–12, and 2008–16. Groundwater-elevation changes correspond to water use by the ABCWUA, with declines occurring prior to 2008 and accelerating recovery after 2008. Prior to 2008, the ABCWUA relied exclusively on groundwater from the Santa Fe Group aquifer system for municipal water supply. For the period 2002–8, near the end of the period of exclusive groundwater use, groundwater elevations in the production zone of the Santa Fe Group aquifer system declined as much as 20 to 30 feet. The largest 2002–8 groundwater-elevation declines were observed near the southeast corner of the study area and to the west of the Rio Grande. Since the ABCWUA implemented the San Juan-Chama Drinking Water Project in 2008, the proportion of municipal water supply sourced directly from surface water has increased to approximately two-thirds of the total water supply in 2016. Following initiation of this change in supply in 2008, groundwater elevations in the production zone of the Santa Fe Group aquifer system cumulatively rose as much as 20 to 30 feet by 2012 and 30 to 40 feet by 2016. The largest groundwater-elevation rises were observed near the northeast and southeast corners of the study area and to the west of the Rio Grande, whereas groundwater-elevation declines since 2008 were restricted to a localized area on the eastern margin of the study area. The area beneath the pre-flood-control-era (1971) flood plain of the Rio Grande underwent the least amount of groundwater-level change during any period, with minimal change prior to 2008 and small groundwater-elevation rises of less than 10 feet since 2008.

New Mexico↗

USGS2017

Land subsidence and recovery in the Albuquerque Basin, New Mexico, 1993–2014

The Albuquerque Bernalillo County Water Utility Authority (ABCWUA) drinking water supply was almost exclusively sourced from groundwater from within the Albuquerque Basin before 2008. In 2008, the San Juan-Chama Drinking Water Project (SJCDWP) provided surface-water resources to augment the groundwater supply, allowing for a reduction in groundwater pumping in the Albuquerque Basin. In 2013, the U.S. Geological Survey, in cooperation with the ABCWUA, began a study to measure and compare aquifer-system and land-surface elevation change before and after the SJCDWP in 2008. Three methods of data collection with different temporal and spatial resolutions were used for this study: (1) aquifer-system compaction data collected continuously at a single extensometer from 1994 to 2013; (2) land-surface elevation change from Global Positioning System (GPS) surveys of a network of monuments collected in 1994–95, 2005, and 2014; and (3) spatially distributed Interferometric Synthetic Aperture Radar (InSAR) satellite data from 1993 to 2010. Collection of extensometer data allows for direct and continuous measurement of aquifer-system compaction at the extensometer location. The GPS surveys of a network of monuments allow for periodic measurements of land-surface elevation change at monument locations. Interferograms are limited in time by lifespan of the satellite, orbital pattern, and data quality but allow for measurement of gridded land-surface elevation change over the study area. Each of these methods was employed to provide a better understanding of aquifer-system compaction and land-surface elevation change for the Albuquerque Basin. Results do not show large magnitudes of subsidence in the Albuquerque Basin. High temporal-resolution but low spatial-resolution data measurements of aquifer-system compaction at the Albuquerque extensometer show elastic aquifer-system response to recovering groundwater levels. Results from the GPS survey of the network of monuments show inconsistent land-surface elevation changes over the Albuquerque Basin, likely because of the lack of significant change and the complexity of subsurface stratigraphy in addition to the spatial and temporal heterogeneity of groundwater withdrawals over the study period. Results from the InSAR analysis show areas of land-surface elevation increase after 2008, which could be attributed to elastic recovery of the aquifer system. The spatial extent to which elastic recovery of the aquifer system has resulted in recovery of land-surface elevation is limited to the in-situ measurements at the extensometer. Examination of spatially distributed InSAR data relative to limited spatial extent of the complex heterogeneity subsurface stratigraphy may explain some of the heterogeneity of land-surface elevation changes over this study period.

New Mexico↗

USGS2024

Preparing for today's and tomorrow's water-resources challenges in eastern Long Island, New York

Freshwater is a vital natural resource. Although New York is a water-rich State, the wise and economical use of water resources is needed to ensure that there is enough water of adequate quality for both human and ecological needs—both for today and for tomorrow. Nowhere in New York is this more evident than in Nassau and Suffolk Counties on Long Island, where the public water supply is obtained from the sole-source aquifers located directly beneath the nearly 3 million people who live there. In 2023, in eastern Long Island’s Suffolk County, groundwater was pumped from these aquifers by more than 1,100 public water-supply wells to meet the needs of about 1.5 million people.

New York↗