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Groundwater & aquifers

Find USGS research on groundwater & aquifers. Use publication dates, geographic coverage, abstracts, and original report links to locate studies relevant to a particular place.

218 records · Page 2Linked to original sources

USGS2026

Scenarios to assess the future water availability in the Mississippi River Valley Alluvial Aquifer for the Cache River and Grand Prairie Regions of Arkansas

The U.S. Geological Survey, as part of the Arkansas Groundwater Initiative, developed forecast scenarios using previously calibrated MODFLOW 6 groundwater models that focused on the Cache and Grand Prairie Critical Groundwater Areas to assess the impact of future climate and water management strategies on the Mississippi River Valley alluvial aquifer. A Soil Water Balance model was used to forecast recharge and irrigation water use. The forecast scenario period was from January 1, 2019, through December 31, 2055, with monthly stress periods. Twenty scenarios were simulated and included seven alternate climate forecasts, five 13 general groundwater pumping reduction scenarios (round 1), and groundwater pumping reduction scenarios by crop type and for the Bayou Meto Water Management Project and Grand Prairie Area Demonstration Project (round 2). Declines in saturated thickness within the Cache Critical Groundwater Area were larger for 18 of the 20 scenarios as compared to outside of the Critical Groundwater Area. The largest average increase in saturated thickness inside the Critical Groundwater Area was 6.4 m which occurred for the round 1, 50 percent reduction scenario. Automatic reductions in groundwater pumping by MODFLOW 6 in the Cache simulation ranged from 0.02 to 13.1 percent of total groundwater pumping. For the Grand Prairie model domain, the average change in saturated thickness of the Mississippi River Valley alluvial aquifer inside the Critical Groundwater Area for the forecast period ranged between -6.6 to 1.7 m. The average saturated thickness of the Mississippi River Valley alluvial aquifer inside the Grand Prairie Critical Groundwater Area declined for 16 of the 20 scenarios. The average reduction in requested groundwater pumping for all scenarios inside the Grand Prairie Critical Groundwater Area was 25.1 percent, and the largest reduction was 46.5 percent.

ESS Open Archive↗

USGS2025

Potentiometric surface maps and groundwater-level hydrographs for confined aquifers of the New Jersey Coastal Plain, 2018

The U.S. Geological Survey, in cooperation with the New Jersey Department of Environmental Protection (NJDEP), prepared potentiometric surface maps for 10 confined aquifers of the New Jersey Coastal Plain physiographic province based on water-level measurements collected during late 2018 and early 2019 from 951 wells in New Jersey and parts of Pennsylvania and Delaware. Maps were prepared for the confined Cohansey aquifer, Rio Grande water-bearing zone, Atlantic City 800-foot sand, Piney Point aquifer, Vincentown aquifer, Wenonah-Mount Laurel aquifer, Englishtown aquifer system, and the upper, middle, and lower aquifers of the Potomac-Raritan-Magothy aquifer system. Potentiometric surface maps indicate regional cones of depression in the following aquifers and the counties in which they are centered: Atlantic City 800-foot sand in Atlantic County, the Piney Point aquifer in Cumberland County, the Wenonah-Mount Laurel aquifer and Englishtown aquifer system in Monmouth and Ocean Counties, the Wenonah-Mount Laurel aquifer in Camden and Gloucester County, the upper aquifer of the Potomac-Raritan-Magothy aquifer system in Ocean County, and the upper, middle, and lower aquifers of the Potomac-Raritan-Magothy aquifer system in Camden County. Cones of depression with smaller areal extents were in the confined Cohansey aquifer, the Rio Grande water-bearing zone, the Atlantic City 800-foot sand centered in Cape May County, the Piney Point aquifer centered in Ocean County, the Wenonah-Mount Laurel aquifer in Salem and Burlington Counties, the Englishtown aquifer system in Camden County, the upper aquifer of the Potomac-Raritan-Magothy aquifer system in Monmouth County, and the middle aquifer of the Potomac-Raritan-Magothy aquifer system in Monmouth, Ocean, and Salem Counties. No cone of depression was interpreted in the Vincentown aquifer. Long-term hydrographs are presented for 75 wells spanning each of the 10 confined aquifers, and contain a mix of discrete water-level measurements and daily mean water levels based on continuously recorded 15-minute data. Changes of water levels during 2014–19, as indicated by the hydrographs, were compared with those of previous periods to assess any departures from historical data. During 2014–19, water levels were stable and fluctuated within similar ranges as previous periods in the following aquifers and locations: all wells in the confined Cohansey aquifer, the Rio Grande water-bearing zone, the Vincentown aquifer, the Englishtown aquifer system, the Piney Point aquifer wells in Burlington and Ocean Counties, six of eight wells in the Wenonah-Mount Laurel aquifer, all wells in the upper and lower aquifers of the Potomac-Raritan-Magothy aquifer system outside NJDEP Critical Areas, and all wells in the middle aquifer of the Potomac-Raritan-Magothy aquifer system except those within NJDEP Critical Area II. Increasing water levels in 2014–19, ongoing since historical periods, were indicated in the following aquifers and locations: Atlantic County wells in the Piney Point aquifer, all wells in the upper and lower aquifers of the Potomac-Raritan-Magothy aquifer system outside NJDEP Critical Areas, and all wells in the middle aquifer of the Potomac-Raritan-Magothy aquifer system within NJDEP Critical Area II. Water levels in the Atlantic City 800-foot sand also increased during 2014–19 in wells in Atlantic County and northern Cape May County closer to the center of the cone of depression in that aquifer, which is a response unique to this period and absent from previous periods. During 2013–19, continued decreasing water levels, ongoing since previous periods, were indicated by hydrographs of Atlantic City 800-foot sand wells in southern Cape May County, Piney Point aquifer wells in Cumberland County where the regional cone of depression is located, and two wells in the Wenonah-Mount Laurel aquifer—070478, which in 2014–19 departed from previous periods, and 330020, which continued a gradual decrease throughout its period of record.

New Jersey↗

USGS2025

Altitude of the potentiometric surface and depth to water in the Mississippi River Valley alluvial aquifer, spring 2022

Potentiometric-surface and depth-to-water maps for spring 2022 were created for the Mississippi River Valley alluvial aquifer (MRVA) using groundwater-altitude data from 1,136 wells completed in the MRVA and from the altitude of the top of the water surface in area rivers from 160 streamgages. The potentiometric-surface and depth-to-water maps for 2022 were created to support investigations to characterize the MRVA as part of the U.S. Geological Survey Water Availability and Use Science Program. Sufficient data were available to map the potentiometric surface and depth to water of the MRVA for spring 2022 for about 83 percent of the aquifer area. The potentiometric contours ranged from 0 to 340 feet (ft) above the North American Vertical Datum of 1988. The regional direction of groundwater gradient was generally to the south-southwest, except in areas of groundwater-altitude depressions, where the groundwater gradient was into the depression, and near rivers, where the groundwater gradient can be from aquifer to the river or from the river into the aquifer. There are large depressions in the potentiometric-surface map in the lower one-half of the Cache region and in much of the Grand Prairie and Delta regions. Depth to water in the MRVA, spring 2022, by well ranged from 5.00 ft above land surface to 145.66 ft below land surface.

Mississippi River Valley alluvial aquifer↗

USGS2025

Aquifer storage change and storage properties, Rio Rancho, New Mexico, 2019–23

To better understand changes in groundwater storage and groundwater elevations, the U.S. Geological Survey, in cooperation with the City of Rio Rancho, New Mexico, carried out a multiyear groundwater monitoring project. Groundwater-level data were collected at 27 locations, including sites having multiple wells screened at different depths and those having long-term records. A repeat microgravity network of 20 stations was established, and surveys were carried out three times per year. The microgravity method provides a direct, quantitative measurement of mass change caused by aquifer filling or draining. Data collected during the 2019–23 study period indicate generally stable groundwater conditions, with small fluctuations in groundwater levels (increasing at some wells, declining at others), and small declines in groundwater storage over the period of record at most gravity locations (average = −0.33 foot of water per year). The discrepancy between the water-level and microgravity data may have been caused by a loss of soil moisture in the unsaturated zone, which is as much as 1,000 feet thick in some areas. At the Rio Rancho Advanced Water Treatment Facility, where the city recharges water through direct injection, there may be seasonal correlations in storage related to injection but no longer-term accumulation of recharged water in the immediate vicinity of the facility, indicating water is moving efficiently into the aquifer.

New Mexico↗

USGS2025

Groundwater response to managed aquifer recharge at the Southeast Houghton Artificial Recharge Project in Tucson, Arizona

Managed aquifer recharge is a widespread practice for storing water in the subsurface as groundwater. At a managed aquifer recharge facility in southern Arizona, groundwater-level and repeat microgravity data were collected to monitor aquifer response. These data were used to inform parameter identification for an unsaturated-zone flow model used to simulate the recharge process. The facility, the Southeast Houghton Artificial Recharge Project (SHARP), consists of 3 surface basins (about 27,600 square meters [6.8 acres] total surface area) where recycled water is distributed in recharge cycles lasting several months, with dry periods in between. During the study period, December 2020–December 2022, Tucson Water (the City of Tucson’s water utility) reported 6.56×10 6 cubic meters of water (5,320 acre-feet) recharged. Monitoring included groundwater-level observations at 3 monitoring wells and repeat microgravity measurements at as many as 22 locations (some stations were destroyed between surveys). Six gravity surveys were carried out using absolute- and relative-gravity meters. Large gravity increases, more than 250 microgals, were observed during the first repeat survey, 3.5 months after the start of recharge, but only in the immediate vicinity of the recharge basins. Data show that water moved downward to the water table, and storage changes in the unsaturated zone away from the facility were likely minimal. Gravity decreased at stations more than 1 kilometer from the facility, consistent with regional groundwater-level changes. Groundwater-level increases in wells adjacent to the recharge basins began 2 months after the second repeat gravity survey, and 5.5 months after recharge began. Unsaturated-zone flow modeling was carried out using software that simulates water movement and parameter estimation. Model calibration was carried out by minimizing an objective function calculated from the differences between simulated and observed groundwater levels, and between simulated and observed repeat microgravity data. Including repeat microgravity data in the objective function reduced the uncertainty in estimated parameter values for saturated hydraulic conductivity and saturated water content. Modeling indicated that the unsaturated zone between the recharge basins and the water table does not become saturated even after 685 days of simulated infiltration. This gradual wetting may account for increasing infiltration rates over time, as hydraulic conductivity increases with increasing water content. Unsaturated-zone water content decreased rapidly between recharge cycles. Model-simulated groundwater mounding extended about 1 kilometer from the center of SHARP after the 685-day period following the onset of recharge.

Arizona↗

USGS2025

Hydrogeologic framework and conceptual model of the Red River alluvial aquifer east of Lake Texoma, southeastern Oklahoma, 1980–2022

The 1973 Oklahoma Groundwater Law (Oklahoma Statutes §82-1020.5) requires that the Oklahoma Water Resources Board conduct hydrologic investigations of the State’s groundwater basins to support a determination of the maximum annual yield for each groundwater basin. At present (2025), the Oklahoma Water Resources Board has not established a maximum annual yield for the Red River alluvial aquifer east of Lake Texoma. To support the evaluation and determination of a maximum annual yield, a hydrogeologic framework and conceptual groundwater-flow model were developed to assess groundwater availability in the Red River alluvial aquifer east of Lake Texoma. The scope of this hydrologic investigation is the alluvium and terrace containing the Red River alluvial aquifer in Oklahoma between Lake Texoma, the Texas State line, and the Arkansas State line, an extent referred to in this report as “the eastern part of the Red River alluvial aquifer.” Parts of the alluvium and terrace extent in Arkansas and Texas are included in some analyses to address hydrologic influences from outside the aquifer’s boundaries in Oklahoma. The eastern part of the Red River alluvial aquifer in southeastern Oklahoma consists of approximately 401,280 acres of Quaternary alluvium and terrace deposits associated with the Red River and its major tributaries. Mean annual recharge to the aquifer for the 1980–2022 study period was estimated to be 8.62 inches per year, or 17.98 percent of the mean annual precipitation over the same period (47.94 inches). This mean annual recharge rate is equivalent to an inflow of approximately 288,250 acre-feet per year for the eastern part of the Red River alluvial aquifer. Recharge estimated using the Soil-Water-Balance code accounts for 98.7 percent of the conceptual-model inflows to the eastern part of the Red River alluvial aquifer. Saturated-zone evapotranspiration accounts for 11.9 percent and net streambed seepage accounts for 87.4 percent of the outflows in the conceptual model.

Arkansas, Oklahoma, Texas↗

USGS2025

Estimated hydrogeologic, spatial, and temporal distribution of self-supplied domestic groundwater withdrawals for aquifers of the Virginia Coastal Plain

Water use from private-domestic wells accounts for nearly 40 percent of total groundwater withdrawals in the Virginia Coastal Plain Physiographic Province (henceforth called the Virginia Coastal Plain). However, because self-supplied domestic water use generally falls below the Virginia Department of Environmental Quality (VDEQ) reporting and management threshold of 300,000 gallons per month, quantifying these withdrawals is challenging. This report builds upon the foundation of previous U.S. Geological Survey investigations by providing revised techniques to improve estimates of the aquifer source, spatial distribution, and monthly magnitude of these groundwater withdrawals. The aquifer sources of private-domestic wells in the Virginia Coastal Plain were estimated by cross-referencing 8,264 well records from the VDEQ and the Virginia Department of Health to a digital model of the Virginia Coastal Plain hydrogeologic framework. This analysis highlights the regional importance of the Yorktown-Eastover, Potomac, and surficial aquifers. Collectively, these three aquifers account for 80 percent of self-supplied domestic groundwater withdrawals. The population using self-supplied domestic water was estimated using census blocks, well-use ratios, building footprints, and land-use and land-cover data to produce a high-resolution, disaggregated, raster-based dataset. This approach improves upon previous models at the census-block or road-network scale by reducing the low-density spread of the self-supplied domestic population across undeveloped areas and concentrating the population and its corresponding water use in the areas where it is most likely to occur. Results show that an estimated 475,332 people comprise the 2020 self-supplied domestic population of the Virginia Coastal Plain, an increase of 5.7 percent since 2010, and the greatest concentrations of self-supplied domestic population surround large cities. Estimates could be further refined with the addition of current and complete spatial data on public water-system service areas. The quantity of water used by the self-supplied domestic population was estimated by modifying published state per-capita water-use coefficients with the corresponding monthly variability assessed from Virginia Coastal Plain public water-system withdrawal data. This analysis estimates an average increase of 12 percent from June through August and an average decrease of 8 percent from December through March from the baseline annual average of 80 gallons per day per capita, which generally matches similar studies in the eastern United States. The application of these revised methodologies for the estimation of private-domestic wells and the self-supplied domestic population improves understanding of domestic groundwater use in the Virginia Coastal Plain across hydrogeologic, spatial, and temporal scales. These revisions help better inform water-resource managers and decision makers and support higher resolution groundwater modeling. Furthermore, these methods are transferrable to other areas where self-supplied domestic water withdrawals are important to the overall water budget.

Virginia↗

USGS2025

Hydrogeology of unconsolidated and bedrock aquifers along the Salmon River, including Malone, Franklin County, New York

The U.S. Geological Survey, in cooperation with the New York State Department of Environmental Conservation, investigated the hydrogeology of the unconsolidated and bedrock aquifers along the Salmon River corridor in northern Franklin County, New York. The study area covers roughly 147 square miles and includes the village of Malone and parts of the Towns of Malone, Bellmont, Burke, Constable, Westville, Bangor, Duane, and Franklin, New York. Groundwater is the primary source for water supply within the study area. Eighty-three percent of all residents use public water supplied from two production wells that draw water from a thick, highly productive sand-and-gravel aquifer likely receiving induced infiltration from the Salmon River. Twenty-four percent of the 187 verified domestic wells in the study area outside of the production well service area boundary are screened in typically discontinuous deposits of stratified sand and sand and gravel. Seventy-six percent of the wells are completed in bedrock aquifers including the Potsdam Sandstone, metamorphic rocks, Theresa Formation, and unknown bedrock. Characterizing and understanding potential groundwater resources is critical for protecting the quality of the groundwater. The information in this report may be used to guide delineation of groundwater contributing areas, assess potential threats to aquifers from both point and nonpoint sources, respond to contamination from spills or leaks from underground storage facilities or other sources, and to support assessments for future development of municipal water supplies.

New York↗

USGS2026

Status and understanding of groundwater quality in the San Joaquin Valley Kern County subbasin domestic-supply aquifer study unit, 2022—California GAMA Priority Basin Project

The quality of water accessed by domestic wells (here referred to as domestic groundwater resources) in the San Joaquin Valley Kern County subbasin (basin number 5-022.14) was assessed as part of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project (GAMA-PBP), in cooperation with the California State Water Resources Control Board. Kern County is at the southern end of the San Joaquin Valley in California, and about 30,000 residents are estimated to use privately owned domestic wells for drinking water. Domestic wells typically draw from shallower parts of the aquifer system than public-supply wells and can be more vulnerable to effects from surface activities. Kern County is host to a highly productive agricultural industry, with Bakersfield as the main urban center. The Kern River runs through Bakersfield from the southern Sierra Nevada and intersects the Kern Water Bank, one of the largest groundwater banking operations in California, at the Kern River Intertie. The section of the Kern River running through the Kern Water Bank is dry most years. Kern County also encompasses some of the most productive oil and gas basins in California, with extensive underground and surface disposal of oil-field wastewater. This study was based on data collected from 33 sites sampled by the U.S. Geological Survey for the GAMA-PBP in 2022. To provide context for the water quality assessment, measured concentrations were compared to regulatory and non-regulatory health-based and aesthetic benchmarks. A grid-based method was used to estimate the proportions of the groundwater resources used for domestic-supply wells that have water-quality constituents below (low relative concentration), approaching (moderate relative concentration), or above (high relative concentration) benchmark concentrations. At least one measured constituent with a regulatory benchmark was categorized as having a high relative concentration in 72 percent of the aquifer area used for domestic groundwater resources. Inorganic constituents were detected at high concentrations in 45 percent of the domestic groundwater resources, and the constituents detected above regulatory benchmarks were arsenic, nitrate, and uranium. At least one organic constituent was detected at high concentrations in 41 percent of the domestic groundwater resources, and the constituents exceeding regulatory benchmarks were the fumigants 1,2,3-trichloropropane (1,2,3-TCP), 1,2-dibromo-3-chloropropane (dibromochloropropane [DBCP]), 1,2-dibromoethane (EDB), and the per-and polyfluoroalkyl substance (PFAS) perfluorooctanesulfonate. The disinfection by-product chloroform, the fumigant 1,2-dichloropropane, the herbicides atrazine and hexazinone, and the herbicide degradates 2-chloro-6-ethylamino-4-amino-s-triazine, 2-chloro-4,6-diamino-s-triazine, 4-hydroxychlorothalonil, and metolachlor sulfonic acid were detected in more than 10 percent of domestic groundwater resources, but concentrations did not exceed regulatory benchmarks. Land use, groundwater age (fraction of modern water and mean age), and geochemical environment (oxic or anoxic conditions, pH, alkalinity) were associated with the distribution of high relative concentrations of inorganic and organic constituents. Young, oxygenated water is recharged along the Kern River and adjacent recharge ponds, or as irrigation water in the agricultural areas. High concentrations of nitrate and volatile organic compounds occurred in the oxic water in urban and agricultural areas. The fumigants 1,2,3-TCP, DBCP, and EDB were reported throughout the agricultural areas, whereas chloroform, tetrachloroethene, and PFAS were associated with urban land use. High uranium concentrations were associated with young, modern groundwater in agricultural areas with low pH and high bicarbonate. Total dissolved solids increased with distance from the Kern River, as the contributions of fresh, oxic water decreased. High concentrations of arsenic were present in older anoxic or alkaline groundwater away from areas of recharge. Overall, groundwater age, redox conditions, and the source of recharge as a result of different land uses contribute to large aquifer-scale portions of domestic groundwater resources that exceed health-based benchmarks for nitrate, uranium, and fumigant concentrations.

California↗

USGS2023

Evaluation of models for estimating hydraulic conductivity in glacial aquifers from NMR logging

Nuclear magnetic resonance (NMR) logging is a promising method for estimating hydraulic conductivity ( K ). During the past ∼60 years, NMR logging has been used for petroleum applications, and different models have been developed for deriving estimates of permeability. These models involve calibration parameters whose values were determined through decades of research on sandstones and carbonates. We assessed the use of five models to derive estimates of K in glacial aquifers from NMR logging data acquired in two wells at each of two field sites in central Wisconsin, USA. Measurements of K , obtained with a direct push permeameter (DPP), K DPP , were used to obtain the calibration parameters in the Schlumberger-Doll Research, Seevers, Timur-Coates, Kozeny-Godefroy, and sum-of-echoes (SOE) models so as to predict K from the NMR data; and were also used to assess the ability of the models to predict K DPP . We obtained four well-scale calibration parameter values for each model using the NMR and DPP measurements in each well; and one study-scale parameter value for each model by using all data. The SOE model achieved an agreement with K DPP that matched or exceeded that of the other models. The Timur-Coates estimates of K were found to be substantially different from K DPP . Although the well-scale parameter values for the Schlumberger-Doll, Seevers, and SOE models were found to vary by less than a factor of 2, more research is needed to confirm their general applicability so that site-specific calibration is not required to obtain accurate estimates of K from NMR logging data.

Wisconsin↗

USGS2026

Hydrogeology, groundwater salinity distributions, and assessment of the effect of oil-production activities on groundwater in the Midway Valley area, western Kern County, San Joaquin Valley, California

This study seeks to determine the effects of oil field produced water disposal operations and well mechanical integrity issues on groundwater quality in oil fields in the southwest San Joaquin Valley, California. Whereas previous studies used groundwater wells to study shallow aquifers outside the oil fields, this study demonstrates that future approaches may use oil well geophysical logs to map groundwater head gradients, create salinity profiles and document changes in salinity over time in oil field areas with sparse groundwater well data and at depths greater than 330 m. We also incorporate an analysis of well histories to determine potential effects of compromised wellbore seals on changes in aquifer quality that cannot be explained by water disposal practices. Water quality in the aquifers is naturally brackish across most of the area, with better quality groundwater occurring in the eastern part. Geophysical logs are used to determine salinity variations within aquifers including the depth at which TDS exceeds 10,000 mg/L. This depth ranges from 366 m in the northwest to approximately 1,500 m in the southeast. Oil well porosity logs are used to determine water table elevations. These logs indicate the water table slopes south-southeast, showing the predominant groundwater flow direction is from oil field disposal areas toward better quality groundwater east of the oil fields. Geophysical logs show formation resistivity near some disposal facilities has decreased over time, indicating the salinity of the aquifer has increased due to disposal of saline produced water in injection wells and ponds. Oil well history analysis suggests that increased salinity over time in water-saturated sand intervals >1.5 km from disposal facilities may be caused by mechanical failures and/or incomplete borehole seals in poorly constructed or abandoned wellbores prevalent throughout the study area—particularly wells drilled prior to 1930.

California↗

USGS2025

Hydraulic conductivity and transmissivity estimates from slug tests in wells within the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020

During the spring and summer of 2020, the U.S. Geological Survey conducted single-well slug tests on selected observation wells within the Mississippi Alluvial Plain in Arkansas and Mississippi to estimate hydraulic conductivity and transmissivity values for the Mississippi River Valley alluvial and middle Claiborne aquifers. Well and aquifer data were collected from field measurements, well-construction reports, and published aquifer-thickness information. A total of 324 slug-in and slug-out tests were conducted on 48 wells by using mechanical slugs to displace the water column and submersible pressure transducers to record changes in water levels in the wells. Hydraulic conductivity of the aquifers in which the wells are screened was estimated by curve fitting the water-level-change data using aquifer test analysis software. Estimates of aquifer transmissivity were made by multiplying the estimated hydraulic conductivity value by the aquifer thickness at well locations. Mean hydraulic conductivity estimates for 44 observation wells screened in the Mississippi River Valley alluvial aquifer range from 3 to 401 feet per day, and mean transmissivity estimates range from 285 to 80,559 feet squared per day. Mean hydraulic conductivity estimates for four observation wells screened in units of the middle Claiborne aquifer range from 0.14 to 183 feet per day, and mean transmissivity estimates range from 55 to 67,913 feet squared per day. The results from these tests can be used to improve the understanding of water availability and groundwater migration, to refine groundwater models, and to ultimately provide stakeholders and decisionmakers better information for management of the groundwater resources within the Mississippi Alluvial Plain.

Arkansas, Mississippi↗

USGS2026

Top Elevation of Glacial Till and Thickness of the Big Sioux Aquifer Delineated From Electrical Resistivity Tomography Surveys Near Sioux Falls, South Dakota, 2022 and 2025

The City of Sioux Falls, South Dakota, requested the U.S. Geological Survey perform electrical resistivity surveys on three parcels of land north of the city. Electrical resistivity data were collected along a total of 22 transects during March 14–18, 2022, and November 17–21, 2025. Results from electrical resistivity surveys were used to delineate the top of glacial till deposits for the purpose of characterizing the Big Sioux aquifer near the city. Delineating geologic contacts provides important information on groundwater storage, flow dynamics, well design and placement, contaminant transport, groundwater–surface-water interactions, and regional water modeling. The top elevation of glacial till and the thickness of the Big Sioux aquifer varied among the three survey areas. The interpreted top elevation of glacial till in the North survey area decreases from east to west toward a slough, with elevations ranging from 1,403 to 1,418 feet (ft). The estimated thickness of the Big Sioux aquifer in the North survey area increased from east to west, with thicknesses ranging from 23 to 38 ft. The top elevation of glacial till in the Well 72 survey area generally decreases from northwest to southeast. Top elevations of the glacial till in the Well 72 survey area ranged from 1,400 to 1,409 ft along the southern end of transect W72_2. The estimated thickness of the Big Sioux aquifer in the Well 72 survey area was greatest along a southeast to northwest trending channel, with thicknesses ranging from 28 to 40 ft. The top elevation of glacial till in the Nose survey area generally decreases west toward the Big Sioux River. Top elevations of the glacial till in the Nose survey area ranged from 1,362 to 1,395 ft. The estimated thickness of the Big Sioux aquifer in the Nose survey area ranged from 33 to 70 ft.

South Dakota↗

USGS2025

Quantitative subsurface characterization illuminates the origin of the Quaternary Mississippi River Valley alluvial aquifer

The Mississippi River Valley alluvial aquifer (MRVA) is vital to U.S. food security and global agricultural supply. However, quantitative understanding of its Quaternary origin, architecture, and hydrologic function remains incomplete. Here we develop a three-dimensional hydrostratigraphic model to characterize the deposition of clay and silt, fine-medium sands, and graveliferous sands using lithologic data from 75,000 boreholes compiled across the Lower Mississippi Valley and a geostatistical method—interval kriging. We find that cyclic glacial entrenchments, evidenced by remnants of pre-Wisconsinan postglacial sediments, alongside geodynamic activities shaped the MRVA basal configuration. Stratal weakening from faulting and salt diapirism enhanced glacial incision and thereby produced abrupt aquifer thickening. We demarcate the top of graveliferous sands as the regional marker of the Pleistocene-Holocene transition. The MRVA hydrostratigraphy reveals hydrologic function and geologic controls on groundwater storage and quality, advancing the assessment of aquifer sustainability under a changing climate, with implications for alluvial aquifers globally.

Arkansas, Illinois, Kentucky, Louisiana, Mississip↗

USGS2025

Status of water-level altitudes and long-term and short-term water-level changes in the Chicot and Evangeline (undifferentiated) and Jasper aquifers, greater Houston area, Texas, 2024

Since the early 1900s, groundwater withdrawn from the primary aquifers that compose the Gulf Coast aquifer system—the Chicot, Evangeline, and Jasper aquifers—has been an important source of water in the greater Houston area, Texas. This report, prepared by the U.S. Geological Survey in cooperation with the Harris-Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, Lone Star Groundwater Conservation District, and Brazoria County Groundwater Conservation District, is one in an annual series of reports depicting the status of water-level altitudes and water-level changes in these aquifers in the greater Houston area. In this report, the Chicot and Evangeline aquifers are treated as a single aquifer for the purposes of providing annual assessments of regional-scale water-level altitudes and water-level changes over time. In 2024, shaded depictions of estimated water-level altitudes for the Chicot and Evangeline aquifers (undifferentiated) ranged from about 301 feet (ft) below the North American Vertical Datum of 1988 (NAVD 88) to about 184 ft above NAVD 88. The largest decline in water-level altitudes depicted by the 1977–2024 long-term water-level-change map was in south-central Montgomery County. In comparison, the 1990–2024 long-term water-level-change map depicts the largest declines in water-level altitudes in an area northwest of The Woodlands and in an area of northern Waller County. The largest rise in water-level altitudes for 1977–2024 is depicted in an area of east-central Harris County, whereas the largest rise in water-level altitudes for 1990–2024 is depicted in an area of central Harris County. The 5-year short-term water-level-change map depicts the largest declines in several parts of the study area, but these declines are concentrated primarily in northern Fort Bend County, southwestern Harris County, and south-central Montgomery County. The largest rise for 2019–24 is depicted at a well in northern Fort Bend County. The 1-year short-term water-level-change map depicts the largest declines at a well in northern Fort Bend County and a well in west-central Harris County. The largest rise for 2023–24 is depicted at a well in east-central Fort Bend County. In 2024, shaded depictions of estimated water-level altitudes for the Jasper aquifer ranged from about 255 ft below NAVD 88 to about 321 ft above NAVD 88. The 2000–24 long-term water-level-change map depicts the largest water-level decline in an area of central San Jacinto County; the largest rise is depicted in an area of central Grimes County. The 5-year short-term water-level-change map depicts the largest declines across parts of central and southern Montgomery County and at one well in north-central Harris County. The largest rise for 2019–24 is depicted at a well centered on the Montgomery-Grimes County line. The 1-year short-term water-level-change map depicts the largest declines at two wells in south-central Montgomery County and one well in northwestern Montgomery County on the west side of Lake Conroe. The largest rises during 2023–24 are depicted at one well in northwestern Montgomery County and one well in south-central Montgomery County.

Texas↗

USGS2026

Water-withdrawal and groundwater-level fluctuations, physical and infiltration characteristics of Ohio River sediment, and isotope-based estimates of water sources relative to a riverbank filtration system in an alluvial aquifer, Louisville, Kentucky, 2000–20

The U.S. Geological Survey and the Louisville Water Company, from 2000 to 2020, cooperatively investigated physical and hydrologic conditions in the Ohio River alluvial aquifer and adjacent riverbed sediments in the northeast part of Louisville, Kentucky, to increase knowledge of processes affecting water sources to collector wells during operation of a riverbank filtration system (RBF). The RBF, in 2020, included an initial collector well (CW1) completed in 1999 and a tunnel and collector well system (TCWS) composed of four collector wells (CW2–CW5) completed in late 2010 that were connected by a tunnel that routed water to a pumping station and a treatment plant. Daily mean water-withdrawal rates typically ranged from about 10.4 to 20.7 million gallons per day (Mgal/d) from 2005 to 2007, then were cyclic from 2008 to 2010 and ranged from as low as about 9 to 13 Mgal/d in winter-spring months up to about 19 to 20 Mgal/d in summer-autumn months. From 2011 through 2017, peak daily mean water-withdrawal rates from CW2–CW5 fluctuated between winter-spring lows of about 20–30 Mgal/d to summer-autumn peak rates of about 41.6 Mgal/d in 2013 to about 48.2 Mgal/d in 2012. From 2017 to 2020, TCWS peak daily mean water-withdrawal rates decreased from about 45.7 Mgal/d in 2017 to about 37.5 Mgal/d in 2020 and peak daily mean rates from CW1 ranged from about 20.7 Mgal/d in 2020 to about 21.6 Mgal/d in 2018. Periods in 2019–20 with tunnel pumping station daily mean water-withdrawal rates smaller than about 30 Mgal/d had generally stable water levels in CW2 and indicated the sustainable yield of the TCWS collector wells under the prevailing hydrologic conditions. Drawdown during July–August of 2008 and 2009 was associated with CW1, the sole operating collector well. Groundwater-flow directions outside the CW1 cone of depression during July–August of 2008 and 2009 were from areas near the alluvial valley margin toward the Ohio River and in 2009 toward Harrods Creek. Collector wells CW2 through CW5 derived water during 2011–19 surveys from surface-water infiltration, as indicated by drawdown that extended beneath the Ohio River and Harrods Creek. Increases in drawdown toward the alluvial valley margins in July–August of 2013 and 2015, compared with July 2011, indicated less available recharge from those flow directions and decreased yield of groundwater from the aquifer after progressively longer TCWS water withdrawals. Drawdown at CW2–CW5 and at observation wells between them lessened in October 2019 and indicated that onshore groundwater levels can recover when collector well withdrawals decrease. Overlapping cones of depression in 2011–15 potentiometric surfaces centered around CW2, CW3, CW4, and CW5, and drawdown along divides between those wells indicated well interference between collector wells. Well-interference effects increased during 2013 and 2015 survey periods, despite decreased water-withdrawal rates compared with July 2011, and expanded to include CW1 when its use resumed. Groundwater-level fluctuations in observation wells near the Ohio River were consistent with gradual depletion of groundwater yield during tunnel pumping station operation at river elevations of about 420 feet above the National Geodetic Vertical Datum of 1929 (NGVD 29) and enhanced recharge of the aquifer when river elevations were above flood stage of about 430 feet above NGVD 29. Groundwater-level declines in observation wells near the Ohio River were most apparent in summer and some autumn months between 2012 and 2017 during periods when tunnel pumping station mean daily water-withdrawal rates were about 35 Mgal/d or more. Periods of relatively stable groundwater levels during 2019–20 in observation wells between CW2–CW5, when tunnel pumping station water-withdrawal rates were about 30–33 Mgal/d or less, also indicated that the prevailing sustainable yield was about 30 Mgal/d or less. Wells associated with CW3 and CW4 had the largest increases in slopes of best-fit lines relating water-level difference to water-withdrawal rate between 2012 and 2020, an indication of decreased efficiencies of those wells to supply water or of changes in groundwater yield around the well. Increased slopes of best-fit lines relating water-level difference to water-withdrawal rate from 2019 to 2020, when groundwater levels were otherwise relatively stable, also indicated that the specific capacity of one or more TCWS collector wells may have declined during that period. Riverbed surface elevation, roughness, and hardness changes between hydroacoustic surveys indicated active accretion and erosion of bed sediment offshore from the riverbank filtration system in 2002–4. Riverbed hydraulic conductivity computed from 2013 to 2015 in tests at 11 sites ranged from 0.2 to 230 feet per day. Ten temporary piezometer sites with adjacent operating collector wells had drawdowns that ranged from about 4 to 11.7 feet and hammer blows greater than or equal to 49 counts, which indicated a relatively great density of alluvial sediments and the potential for diminished riverbed infiltration rates. Contributions of Ohio River infiltration to collector wells estimated from deuterium and oxygen-18 isotopic ratios in representative Ohio River and groundwater samples were considerably larger in warmer months than cooler months and ranged from 80–90 percent in CW1–CW5 in May 2020 to 100 percent in May 2019 at CW2, CW4, and CW5. Groundwater contributions to water withdrawals by collector wells increased in cooler autumn months and ranged from 40 percent at CW3 and CW5 in November 2020 to 70 percent at CW2, CW4, and CW5 in November–December 2019. November 2019 and November 2020 isotopic compositions of water from the collector wells had enriched deuterium and oxygen-18 isotopic ratios consistent with mixtures of evaporation-modified water from the Ohio River and meteoric-origin groundwater.

Indiana, Kentucky↗

USGS2025

Assessing nonpoint-source uranium pollution in an irrigated stream-aquifer system

Uranium (U) in rocks and soils of arid and semi-arid environments can be mobilized by irrigation and fertilization, posing environmental and health risks. Elevated U, along with selenium (Se) and nitrate (NO 3 ) co-constituents, necessitates careful monitoring and management. We developed a distributed-parameter numerical model to assess U pollution in an irrigated stream-aquifer system, applying it to a 552 km 2 region in Colorado's Lower Arkansas River Valley (LARV) over 14 years. A MODFLOW model, describing groundwater and stream flow, was coupled with an RT3D-OTIS model to portray reactive U transport. Calibration using the PESTPP-iES iterative ensemble smoother (iES) software indicated good agreement with observed U concentrations. The model revealed substantial and variable U levels across the LARV, highlighting potential hotspots and possible contributing factors, such as geological composition of the bedrock and near-surface shale and aquifer sediments derived from them, irrigation practices, and riparian landscape. U levels exceed the chronic standard (85th percentile = 30 μg/L, set by the US Environmental Protection Agency), which is the permissible regulatory threshold, in groundwater across 44 % of the region and along the river by an average factor of 2.9. Simulated average U concentrations in the non-riparian aquifer and river are 124 μg/L and 60 μg/L, respectively, compared with 112 μg/L and 62 μg/L for measured values. The average 85th percentile U concentration is 222 μg/L in the aquifer and 82 μg/L in the river. Average simulated U mass loading to the river is 0.17 kg/day per km, compared to an estimated 0.23 kg/day per km. Findings provide a baseline for comparing future simulated outcomes of alternative best management practices (BMPs) for U pollution mitigation and offer a methodology applicable to other irrigated regions.

Colorado↗

USGS2025

Modeling seawater intrusion along the Alabama coastline using physical and machine learning models to evaluate the effects of multiscale natural and anthropogenic stresses

Seawater intrusion threatens groundwater resources in coastal regions, including southern Baldwin County, Alabama, where the freshwater-saltwater interface dynamics remain poorly understood. To address this gap, this study uses combined physics-based and machine-learning models to quantify seawater intrusion caused by natural (storm surges) and anthropogenic (human activities) perturbations. The long short-term memory network and wavelet analysis were used to assess vertical aquifer vulnerabilities, revealing that the shallow part of the Coastal lowlands aquifer system (CL1) in the southern Baldwin County region is more susceptible to sea level rise and groundwater extraction than deeper aquifers. Based on these findings, a cross-sectional numerical model (physics approach) for the CL1 aquifer was developed to evaluate tidal and storm surge effects, using Tropical Storm Claudette (June 2021) as a case study. Results showed that tidal fluctuations had a minimal impact on the saltwater-freshwater interface location, whereas storm surges caused substantial inland movement, with effects lasting for nine months. The steady-state version of the three-dimensional (3D) physical model predicted seawater intrusion across the entire area, and convolutional neural network-based modeling further validated the model results. The 3D physical model was also applied to a smaller area to assess human impact on the saltwater interface due to two groundwater pumping scenarios (± 50% of the baseline pumping rate). Results revealed that a 50% increase in groundwater withdrawals caused seawater to advance ~ 320 m inland, whereas a 50% reduction led to a ~ 270-meter retreat. This study highlights the vulnerability of Alabama’s shallow coastal aquifers to seawater intrusion due to storm surges and human activities, and demonstrates that combining physics-based models with machine learning approaches can improve groundwater predictions, though its accuracy depends on the availability of site-specific data.

Alabama↗