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At least 649 records · Page 36Linked to original sources

USGS2009

Design and Installation of a Groundwater Monitoring-Well Network in the High Plains Aquifer, Colorado

The High Plains aquifer is an important water source for irrigated agriculture and domestic supplies in northeastern Colorado. To address the needs of Colorado's Groundwater Protection Program, the U.S. Geological Survey designed and installed a groundwater monitoring-well network in cooperation with the Colorado Department of Agriculture in 2008 to characterize water quality in the High Plains aquifer underlying areas of irrigated agriculture in eastern Colorado. A 30-well network was designed to provide for statistical representation of water-quality conditions by using a computerized technique to generate randomly distributed potential groundwater sampling sites based on aquifer extent, extent of irrigated agricultural land, depth to water from land surface, and saturated thickness. Twenty of the 30 sites were selected for well installation, and wells were drilled and installed during the period June-September 2008. Lithologic logs and well-construction reports were prepared for each well, and wells were developed after drilling to remove mud and foreign material to provide for good hydraulic connection between the well and aquifer. Documentation of the well-network design, site selection, lithologic logs, well-construction diagrams, and well-development records is presented in this report.

Data Series↗

USGS2022

Improving gas-derived parameterization of groundwater using free phase gas measurements

Dissolved atmogenic gasses in groundwater provide significant information about recharge conditions, flowpath, and age. Free phase gas in aquifers is largely ignored in these analyses and there is a lack of quantitative analysis for gas flux mechanisms. Many related fields encountering multiphase flow acknowledge that the presence of bubbles allows for the rapid exsolution of dissolved gasses and volatile compounds through diffusive and polar forces. By measuring the mass flow of the exsolved gas at a spring, coupled with compositional analysis in the free and dissolved phases, we show that not incorporating the effects of the free gas phase of bubbling springs introduces error in the estimation of total gas quantities, particularly light noble gasses. This can significantly affect the corresponding estimation of noble gas temperature (NGT) and apparent age. We examine the transport of free and dissolved gas from the recharge zone, using water level variation data, to the discharge location where the gases are measured. This technique of using the free gas phase for assessing aquifer dynamics will improve groundwater conceptual models, particularly in karstic aquifers where rapid fluctuations in the water table facilitate the development of excess air, generating multiphase spring discharge.

Environmental Science: Water Research & Technology↗

USGS2014

Simulation of water-table aquifers using specified saturated thickness

Simulating groundwater flow in a water-table (unconfined) aquifer can be difficult because the saturated thickness available for flow depends on model-calculated hydraulic heads. It is often possible to realize substantial time savings and still obtain accurate head and flow solutions by specifying an approximate saturated thickness a priori, thus linearizing this aspect of the model. This specified-thickness approximation often relies on the use of the “confined” option in numerical models, which has led to confusion and criticism of the method. This article reviews the theoretical basis for the specified-thickness approximation, derives an error analysis for relatively ideal problems, and illustrates the utility of the approximation with a complex test problem. In the transient version of our complex test problem, the specified-thickness approximation produced maximum errors in computed drawdown of about 4% of initial aquifer saturated thickness even when maximum drawdowns were nearly 20% of initial saturated thickness. In the final steady-state version, the approximation produced maximum errors in computed drawdown of about 20% of initial aquifer saturated thickness (mean errors of about 5%) when maximum drawdowns were about 35% of initial saturated thickness. In early phases of model development, such as during initial model calibration efforts, the specified-thickness approximation can be a very effective tool to facilitate convergence. The reduced execution time and increased stability obtained through the approximation can be especially useful when many model runs are required, such as during inverse model calibration, sensitivity and uncertainty analyses, multimodel analysis, and development of optimal resource management scenarios.

Ground Water↗

USGS2014

Status and understanding of groundwater quality in the Sierra Nevada Regional study unit, 2008: California GAMA Priority Basin Project

Groundwater quality in the Sierra Nevada Regional (SNR) study unit was investigated as part of the California State Water Resources Control Board’s Groundwater Ambient Monitoring and Assessment Program Priority Basin Project. The study was designed to provide statistically unbiased assessments of the quality of untreated groundwater within the primary aquifer system of the Sierra Nevada. The primary aquifer system for the SNR study unit was delineated by the depth intervals over which wells in the State of California’s database of public drinking-water supply wells are open or screened. Two types of assessments were made: (1) a status assessment that described the current quality of the groundwater resource, and (2) an evaluation of relations between groundwater quality and potential explanatory factors that represent characteristics of the primary aquifer system. The assessments characterize untreated groundwater quality, rather than the quality of treated drinking water delivered to consumers by water distributors. The status assessment was based on water-quality data collected by the U.S. Geological Survey from 83 wells in the SNR study unit in 2008 and from 117 wells in 3 small study units within the SNR study unit in 2006–07 and on water-quality data compiled in the State’s database for 1,066 wells sampled in 2006–08. To provide some context for the results, water-quality data were converted to relative-concentrations (RCs), which are the sample concentrations divided by the concentrations of Federal or California regulatory and non-regulatory benchmarks for drinking-water quality. RCs for inorganic constituents (major ions, trace elements, nutrients, and radioactive constituents) were classified as “high” (RC > 1.0, indicating that concentration is above the benchmark), “moderate” (1.0 ≥ RC > 0.5), or “low” (RC ≤ 0.5). For organic constituents (volatile organic compounds and pesticides) and special-interest constituents (perchlorate and N -nitrosodimethylamine [NDMA]), the boundary between moderate and low RCs was set at 0.1. All benchmarks used for organic constituents were health-based, whereas health-based and aesthetic-based benchmarks were used for inorganic constituents. The primary metric used for quantifying regional-scale groundwater quality was “aquifer-scale proportion.” Aquifer-scale proportions were calculated as the areal percentages of the primary aquifer system having high, moderate, and low RCs for a given constituent or class of constituents. The SNR study unit area was classified into four aquifer lithologic types—granitic rocks, metamorphic rocks, sedimentary deposits, and volcanic rocks—and aquifer-scale proportions were calculated on an area-weighted basis for each of the four aquifer lithologies and for the study unit as a whole (aggregated system). The results of the status assessment indicated that inorganic constituents were present at high and moderate RCs in greater proportions in the SNR study unit aggregated primary aquifer system than were organic constituents and that there were significant differences (p < 0.05) between the four aquifer lithologies. One or more inorganic constituents with health-based benchmarks were present at high RCs in 16 percent of the aggregated primary aquifer system and at moderate RCs in 21 percent. Arsenic (9.7 percent), uranium (2.9 percent), boron (2.0 percent), fluoride (1.8 percent), and nitrate (1.4 percent) were the constituents most commonly present at high RCs. For inorganic constituents with aesthetic-based benchmarks, 18 percent of the aggregated primary aquifer system had high RCs of one or more constituent, and 6.8 percent had moderate RCs. Iron (15.8 percent), manganese (15.1 percent), and total dissolved solids (1.3 percent) were the constituents most commonly present at high RCs. Organic constituents were not detected in 72 percent of the primary aquifer system. One or more organic constituents had high RCs in 0.1 percent of the primary aquifer system, moderate RCs in 3.0 percent, and low RCs in 25 percent. Proportions of the four lithologic primary aquifer systems with high or moderate concentrations of organic constituents were not significantly different. Three organic constituents had area-weighted detection frequencies greater than 10 percent in the primary aquifer system as a whole or at least one of the four lithologic primary aquifer systems: the gasoline oxygenate methyl tert -butyl ether, the trihalomethane chloroform, and the herbicide simazine. The special-interest constituent perchlorate was detected at high RCs in 0.01 percent of the primary aquifer system and at moderate RCs in 1.0 percent, and detection frequencies could be accounted for by the distribution of perchlorate under natural conditions. Statistical tests were used to evaluate relations between constituent concentrations and potential explanatory factors descriptive of land use, geography, depth, geochemical conditions, and groundwater age. Higher concentrations of trace elements, radioactive constituents, and constituents with aesthetic-based benchmarks generally were associated with anoxic conditions, higher pH, and location within a particular compositional band in the Sierra Nevada batholith corresponding to the southwestern part of the study unit. High concentrations of organic constituents generally were associated with greater proportions of urban land use. No significant relations were observed between the concentrations of organic constituents and measures of well depth or groundwater age, perhaps because of the high proportions of springs and modern groundwater in the dataset.

California↗

USGS2020

Evaluating the effects of downscaled climate projections on groundwater storage and simulated base-flow contribution to the North Fork Red River and Lake Altus, southwest Oklahoma (USA)

Potential effects of projected climate variability on base flow and groundwater storage in the North Fork Red River aquifer, Oklahoma (USA), were estimated using downscaled climate model data coupled with a numerical groundwater-flow model. The North Fork Red River aquifer discharges groundwater to the North Fork Red River, which provides inflow to Lake Altus. To approximate future conditions, Coupled Model Intercomparison Project Phase 5 climate data were downscaled to the watershed and a time-series of scaling factors were developed and interpolated for three climate scenarios (central tendency, warmer and drier, and less warm and wetter) representing future climate conditions for the period 2045–2074. These scaling factors were then applied to a soil-water-balance model to produce groundwater recharge and evapotranspiration estimates. A MODFLOW groundwater-flow model of the North Fork Red River aquifer used the scaled recharge and evapotranspiration data to estimate changes in base flow and water-surface elevation of Lake Altus. Compared to a baseline scenario, the mean percent change in annual base flow during 2045–2074 was −10.8 and −15.9% for the central tendency and warmer/drier scenarios, respectively; the mean percent change in annual base flow for the less-warm/wetter scenario was +15.7%. The mean annual percent change in groundwater storage for the central tendency, warmer/drier, and less-warm/wetter climate scenarios and the baseline are −2.7, −3.2, and +3.0%, respectively. The range of outcomes from the climate scenarios may be influenced by variability in the downscaled climate data for precipitation more than for temperature.

Oklahoma↗

USGS2014

Status and understanding of groundwater quality in the South Coast Interior groundwater basins, 2008: California GAMA Priority Basin Project

Groundwater quality in the approximately 653-square-mile (1,691-square-kilometer) South Coast Interior Basins (SCI) study unit was investigated as part of the Priority Basin Project of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The South Coast Interior Basins study unit contains eight priority groundwater basins grouped into three study areas, Livermore, Gilroy, and Cuyama, in the Southern Coast Ranges hydrogeologic province. The GAMA Priority Basin Project is being conducted by the California State Water Resources Control Board in collaboration with the U.S. Geological Survey (USGS) and the Lawrence Livermore National Laboratory. The GAMA South Coast Interior Basins study was designed to provide a spatially unbiased assessment of untreated (raw) groundwater quality within the primary aquifer system, as well as a statistically consistent basis for comparing water quality between basins. The assessment was based on water-quality and ancillary data collected by the USGS from 50 wells in 2008 and on water-quality data from the California Department of Public Health (CDPH) database. The primary aquifer system was defined by the depth intervals of the wells listed in the CDPH database for the SCI study unit. The quality of groundwater in the primary aquifer system may be different from that in the shallower or deeper water-bearing zones; shallow groundwater may be more vulnerable to surficial contamination. The first component of this study, the status of the current quality of the groundwater resource, was assessed by using data from samples analyzed for volatile organic compounds (VOCs), pesticides, and naturally occurring inorganic constituents, such as trace elements and minor ions. This status assessment is intended to characterize the quality of groundwater resources within the primary aquifer system of the SCI study unit, not the treated drinking water delivered to consumers by water purveyors. Relative-concentrations (sample concentration divided by the health- or aesthetic-based benchmark concentration) were used for evaluating groundwater quality for those constituents that have Federal or California regulatory or non-regulatory benchmarks for drinking-water quality. A relative-concentration greater than 1.0 indicates a concentration greater than a benchmark, and a relative-concentration less than or equal to 1.0 indicates a concentration equal to or less than a benchmark. Relative-concentrations of organic constituents and special-interest constituents were classified as “high” (relative-concentration greater than 1.0), “moderate” (relative-concentration greater than 0.1 and less than or equal to 1.0), or “low” (relative-concentration less than or equal to 0.1). Relative-concentrations of inorganic constituents were classified as “high” (relative-concentration greater than 1.0), “moderate” (relative-concentration greater than 0.5 and less than or equal to 1.0), or “low” (relative-concentration less than or equal to 0.5). Aquifer-scale proportion was used as the primary metric in the status assessment for evaluating regional-scale groundwater quality. High aquifer-scale proportion is defined as the percentage of the area of the primary aquifer system with a relative-concentration greater than 1.0 for a particular constituent or class of constituents; percentage is based on an areal rather than a volumetric basis. Moderate and low aquifer-scale proportions were defined as the areal percentage of the primary aquifer system with moderate and low relative-concentrations, respectively. Two statistical approaches—grid-based and spatially weighted—were used to evaluate aquifer-scale proportions for individual constituents and classes of constituents. Grid-based and spatially weighted estimates were comparable in the SCI study unit (within 90-percent confidence intervals). Inorganic constituents (one or more) with health-based benchmarks were detected at high relative-concentrations in 29 percent of the primary aquifer system, at moderate relative-concentrations in 37 percent, and at low relative-concentrations in 34 percent. High aquifer-scale proportions of inorganic constituents primarily reflected high aquifer-scale proportions of nitrate (14 percent), boron (8.6 percent), molybdenum (8.6 percent), and arsenic (5.7 percent). In contrast, the relative-concentrations of organic constituents (one or more) were high in 1.6 percent, moderate in 2.0 percent, and low or not detected in 96 percent of the primary aquifer system. Of the 207 organic and special-interest constituents analyzed for, 15 constituents were detected. Perchlorate was found at moderate relative-concentrations in 34 percent of the aquifer. Two organic constituents were frequently detected (in greater than 10 percent of samples): the trihalomethane chloroform and the herbicide simazine. The second component of this study, the understanding assessment, identified natural and human factors that may have affected groundwater quality by evaluating land use, physical characteristics of the wells, and geochemical conditions of the aquifer. This evaluation was done by using statistical tests of correlations between these potential explanatory factors and water-quality data. Concentrations of arsenic, molybdenum, and manganese were generally greater in anoxic and pre-modern groundwater than other groundwater. In contrast, concentrations of nitrate and perchlorate were significantly higher in oxic and modern groundwater. Concentrations of simazine were greater in modern than pre-modern groundwater. Chloroform detections were positively correlated with greater urban land use. Boron concentrations and chloroform detections were higher in the Livermore study area than in the other study areas of the SCI; total dissolved solids and sulfate concentrations were greater in the Cuyama study area.

California↗

USGS2013

California Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project--shallow aquifer assessment

The California State Water Resources Control Board’s (SWRCB) GAMA Program is a comprehensive assessment of statewide groundwater quality in California. From 2004 to 2012, the GAMA Program’s Priority Basin Project focused on assessing groundwater resources used for public drinking-water supplies. More than 2,000 public-supply wells were sampled by U.S. Geological Survey (USGS) for this effort. Starting in 2012, the GAMA Priority Basin Project began an assessment of water resources in shallow aquifers in California. These shallow aquifers provide water for domestic and small community-supply wells, which are often drilled to shallower depths in the groundwater system than public-supply wells. Shallow aquifers are of interest because shallow groundwater may respond more quickly and be more susceptible to contamination from human activities at the land surface, than the deeper aquifers. The SWRCB’s GAMA Program was developed in response to the Groundwater Quality Monitoring Act of 2001 (Water Code sections 10780-10782.3): a public mandate to assess and monitor the quality of groundwater resources used for drinking-water supplies, and to increase the availability of information about groundwater quality to the public. The U.S. Geological Survey is the technical lead of the Priority Basin Project. Stewardship of California’s groundwater resources is a responsibility shared between well owners, communities, and the State. Participants and collaborators in the GAMA Program include Regional Water Quality Control Boards, Department of Water Resources, Department of Public Health, local and regional groundwater management entities, county and local water agencies, community groups, and private citizens. Well-owner participation in the GAMA Program is entirely voluntary.

California↗

USGS2021

Update of the groundwater flow model for the Great Miami buried-valley aquifer in the vicinity of Wright-Patterson Air Force Base near Dayton, Ohio

A previously constructed numerical model simulating the regional groundwater flow system in the vicinity of the Wright-Patterson Air Force Base near Dayton, Ohio, was updated to incorporate current hydrologic stresses and conditions and improve the usefulness of the model for water-supply planning and protection. The original model, which simulated conditions from 1997 to 2001, was reconstructed with the most recently available U.S. Geological Survey groundwater modeling software and recalibrated to represent average groundwater flow conditions for the period of October 2018. The steady-state, three-dimensional, three-layer MODFLOW model of the aquifer encompasses about 241 square miles in Montgomery, Greene, and Clark Counties. The Great Miami buried-valley aquifer consists of glacial sands and gravels in a buried bedrock valley. The shale bedrock in the area is poorly permeable, but the glacial deposits can yield as much as 2,000 gallons per minute to wells. As groundwater is the primary source of drinking water in the heavily populated study area, groundwater pumping from the buried-valley aquifer represents the largest time-varying stress in the groundwater flow model. The model simulated 228 pumped wells. Hydraulic conductivities in the model ranged from less than 1 foot per day to 450 feet per day. Simulated recharge rates ranged from 6 inches per year to 12.2 inches per year. Boundary conditions and aquifer properties were unchanged from the previous model. Model grid spacing and orientation also were not modified from the previous model. Parameter estimation software was used to optimize model input parameters by matching simulated values to observed (estimated or measured) values. Calibrated parameters included horizontal hydraulic conductivity, vertical hydraulic conductivity, riverbed conductance, and recharge. Model calibration used measured water levels (hydraulic heads) from 124 observation wells, and streamflow gain/loss measurements from select reaches of the Mad River and its tributaries were compared with simulated streamflow gain/loss. Performance of the updated model is similar to previous studies. Eighty-one percent of simulated hydraulic heads were within 10 feet of the measured hydraulic heads, but comparison of the simulated streamflow gain/loss with the measured gain/loss indicates that streamflow gain/loss is not well represented by the updated model. The particle tracking program MODPATH was used to calculate groundwater flow paths from recharge areas to selected existing and proposed groundwater withdrawal sites that service Wright-Patterson Air Force Base. Areas contributing groundwater to withdrawal sites were delineated based on 1-, 5-, and 10-year groundwater travel times. In addition, groundwater flow paths were calculated to simulate a groundwater release at eight sites near Wright-Patterson Air Force Base.

Scientific Investigations Report↗

USGS1981

Hydrology and model of North Fork Solomon River Valley, Kirwin Dam to Waconda Lake, north-central Kansas

The alluvial valley of the North Fork Solomon River is an important agricultural area. Reservoir releases diverted below Kirwin Dam are the principal source of irrigation water. During the 1970'S, severe water shortages occurred in Kirwin Reservoir and other nearby reservoirs as a result of an extended drought. Some evidence indicates that surface-water shortages may have been the result of a change in the rainfall-runoff relationship. Examination of the rainfall-runoff relationship shows no apparent trend from 1951 to 1968, but annual records from 1969 to 1976 indicate that deficient rainfall occurred during 6 of the 8 years. Ground water from the alluvial aquifer underlying the river valley also is used extensively for irrigation. Utilization of ground water for irrigation greatly increased from about 200 acre-feet in 1955 to about 12,300 acre-feet in 1976. Part of the surface water diverted for irrigation has percolated downward into the aquifer raising the ground-water level. Ground-water storage in the aquifer increased from 230,000 acre-feet in 1946 to 275,000 acre-feet in 1976-77. A digital model was used to simulate the steady-state conditions in the aquifer prior to closure of Kirwin Dam. Model results indicated that precipitation was the major source of recharge to the aquifer. The effective recharge, or gain from precipitation minus evapotranspiration, was about 11,700 acre-feet per year. The major element of discharge from the aquifer was leakage to the river. The simulated net leakage (leakage to the river minus leakage from the river) was about 11,500 acre-feet per year. The simulated value is consistent with the estimated gain in base flow of the river within the area modeled. Measurements of seepage used to determine gain and loss to the stream were made twice during 1976. Based on these measurements and on base-flow periods identified from hydrographs, it was estimated that the ground-water discharge to the stream has increased about 4,000 acre-feet per year from 1946 to 1976. During the same period, ground water withdrawn from the aquifer increased 12,100 acre-feet per year. Hydrographs of water levels in wells indicate some withdrawal from aquifer storage during 1976, possibly as a combined result of below-normal rainfall and greatly increased pumpage. The analysis of data is inconclusive as to whether the aquifer can sustain increased groundwater development. However, the analysis does indicate that the aquifer could sustain withdrawals at the 1976 rate for several consecutive years of drought similar to the 1976 conditions.

Kansas↗

USGS2009

Simulation of the Groundwater-Flow System in Pierce, Polk, and St. Croix Counties, Wisconsin

Groundwater is the sole source of residential water supply in Pierce, Polk, and St. Croix Counties, Wisconsin. A regional three-dimensional groundwater-flow model and three associated demonstration inset models were developed to simulate the groundwater-flow systems in the three-county area. The models were developed by the U.S. Geological Survey in cooperation with the three county governments. The objectives of the regional model of Pierce, Polk, and St. Croix Counties were to improve understanding of the groundwaterflow system and to develop a tool suitable for evaluating the effects of potential water-management programs. The regional groundwater-flow model described in this report simulates the major hydrogeologic features of the modeled area, including bedrock and surficial aquifers, groundwater/surface-water interactions, and groundwater withdrawals from high-capacity wells. Results from the regional model indicate that about 82 percent of groundwater in the three counties is from recharge within the counties; 15 percent is from surface-water sources, consisting primarily of recirculated groundwater seepage in areas with abrupt surface-water-level changes, such as near waterfalls, dams, and the downgradient side of reservoirs and lakes; and 4 percent is from inflow across the county boundaries. Groundwater flow out of the counties is to streams (85 percent), outflow across county boundaries (14 percent), and pumping wells (1 percent). These results demonstrate that the primary source of groundwater withdrawn by pumping wells is water that recharges within the counties and would otherwise discharge to local streams and lakes. Under current conditions, the St. Croix and Mississippi Rivers are groundwater discharge locations (gaining reaches) and appear to function as 'fully penetrating' hydraulic boundaries such that groundwater does not cross between Wisconsin and Minnesota beneath them. Being hydraulic boundaries, however, they can change in response to water withdrawals. Tributary rivers act as 'partially penetrating' hydraulic boundaries such that groundwater can flow underneath them through the deep sandstone aquifers. The model also demonstrates the effects of development on groundwater in the study area. Water-level declines since predevelopment (no withdrawal wells) are most pronounced where pumping is greatest and flow between layered aquifers is impeded by confining units or faults. The maximum simulated water-level decline is about 40 feet in the deep Mount Simon aquifer below the city of Hudson, Wisconsin. Three inset models were extracted from the regional model to demonstrate the process and additional capabilities of the U.S. Geological Survey MODFLOW code. Although the inset models were designed to provide information about the groundwater-flow system, results from the inset models are presented for demonstration purposes only and are not sufficiently detailed or calibrated to be used for decisionmaking purposes without refinement. Simulation of groundwater/lake-water interaction around Twin Lakes near Roberts, in St. Croix County, Wisconsin, showed that groundwater represents approximately 5 to 20 percent of the overall lake-water budget. Groundwater-contributing areas to streams in western Pierce County are generally similar in size to the surface-water-contributing areas but do not necessarily correspond to the same land area. Transient streamflow simulations of Osceola Creek in Polk County demonstrate how stream base flow can be influenced not only by seasonal precipitation and recharge variability but also by systematic changes to the system, such as groundwater withdrawal from wells.

Scientific Investigations Report↗

USGS2022

Mapping areas of groundwater susceptible to transient contamination events from rapid infiltration into shallow fractured-rock aquifers in agricultural regions of the conterminous United States

Current time-invariant groundwater vulnerability assessments may not capture intermittent contamination events in landscape areas that experience rapid infiltration following precipitation or snowmelt. Occurrences of rapid infiltration and intermittent degradation of groundwater quality are frequently reported in fractured-rock aquifers. This investigation identifies landscape areas underlain by fractured rock within the conterminous United States (CONUS) that may be susceptible to rapid infiltration and where groundwater is a principal source of water supply to the population. Our analysis shows that approximately 27 percent of the CONUS, corresponding to a population of approximately 150 million people, is both underlain by fractured rock and denoted as an area of significant groundwater use. The results of this survey identified shallow fractured-rock aquifers underlying glacial sediments in the upper Midwest and northeastern United States as areas that may be subject to rapid infiltration events. Additionally, aquifers associated with the early Mesozoic basins located in the northeastern and mid-Atlantic United States and bands of carbonate aquifers in the southeastern United States show high susceptibility to rapid infiltration. Index values used in this investigation indicate isolated areas in the western half of the United States also show high susceptibility to rapid infiltration. The isolated areas in Oklahoma, Texas, Arkansas, and southwestern Missouri correspond to karst regions of carbonate aquifers. The isolated areas showing high susceptibility to rapid infiltration and contamination from agricultural sources are locations where more detailed investigations of transient contamination events are warranted. This survey also addresses the potential for contaminant longevity in fractured-rock aquifers stemming from intermittent contamination events. Contaminants that can dissolve into the groundwater following infiltration may be introduced into fractures, and the dissolved constituents can diffuse from fractures into the porosity of the adjacent rock matrix. These constituents can then diffuse back into permeable fractures and adversely affect groundwater quality at downgradient locations over an extended time frame. Rock types with larger matrix porosities have the capacity to retain and then release larger quantities of dissolved constituents, resulting in longer residence times for dissolved groundwater contaminants. The magnitude of the dissolved contaminant concentration infiltrating to the water table will also dictate whether the contaminant concentration in the groundwater exceeds limits for human consumption over the duration of a contamination event. In general, sedimentary- and carbonate-rock aquifers have larger matrix porosities in comparison to igneous- and metamorphic-rock aquifers, and thus, they are more susceptible to longer contaminant residence times. Aquifers composed of sedimentary or carbonate rock constitute approximately 51 percent of the CONUS, and 19 percent of the CONUS is associated with sedimentary- or carbonate-rock aquifers that are of significance for groundwater use. Depending on the contaminants of concern and the concentration of the contaminants introduced into the groundwater from infiltrating water, it would be beneficial for investigations of susceptibility to rapid infiltration to also consider the potential for contaminant longevity. This investigation identifies areas of rapid infiltration into fractured rock using index values applied to the attributes (1) depth to the water table, (2) depth to bedrock, and (3) percentage of sand in soil, where larger index values indicate a greater susceptibility to rapid infiltration. These attributes are selected as the most likely factors that affect rapid infiltration to the water table. The combination of depth to water table and depth to bedrock highlight those aquifer settings that are characterized as shallow fractured-rock aquifers, where the water table may reside either in the bedrock or in overlying unconsolidated geologic materials. In addition, we consider the percentage of agricultural use as a land-use attribute when formulating an index of susceptibility to rapid infiltration and contamination. Agricultural areas are well recognized as nonpoint sources of contaminants that can affect groundwater quality because of seasonal amendments applied to the land surface. Rural agricultural areas are also characterized by septic tanks and leach fields for onsite treatment of wastewater, which may also be a source of contamination that may be introduced into the groundwater following precipitation or snowmelt events.

Conterminous United States↗

USGS2022

Status of water-level altitudes and long-term water-level changes in the Chicot and Evangeline (undifferentiated) and Jasper aquifers, greater Houston area, Texas, 2021

Since the early 1900s, groundwater withdrawn from the primary aquifers that compose the Gulf Coast aquifer system—the Chicot and Evangeline (undifferentiated) and Jasper aquifers—has been the primary 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 aquifers in the greater Houston area. In contrast to previous reports, the Chicot and Evangeline aquifers are treated as a single hydrogeologic unit in this report. In 2021, shaded depictions of water-level altitudes for the Chicot and Evangeline aquifers (undifferentiated) ranged from 300 feet (ft) below the North American Vertical Datum of 1988 (NAVD 88) to 300 ft above NAVD 88. The largest decline in water-level altitudes indicated by the 1977–2021 long-term water-level-change map for the Chicot and Evangeline aquifers (undifferentiated) was in the north-central part of The Woodlands, Tex., whereas the 1990–2021 long-term water-level-change map for the Chicot and Evangeline aquifers (undifferentiated) depicts a large area of decline in water-level altitudes in northwestern Harris County, northwest of Jersey Village, Tex. The largest rise in water-level altitudes in the Chicot and Evangeline aquifers (undifferentiated) was observed in a relatively large area in southeastern Harris County for 1977–2021, whereas the largest rise in water-level altitudes for 1990–2021 was in a relatively large area in central Harris County. In 2021, shaded depictions of water-level altitudes for the Jasper aquifer ranged from 250 ft below NAVD 88 to 300 ft above NAVD 88. The 2000–21 long-term water-level-change map for the Jasper aquifer depicts water-level declines throughout most of the study area where water-level-altitude data from the Jasper aquifer were collected, with the largest decline in northern Harris County southwest of The Woodlands.

Texas↗

USGS2024

Groundwater sustainability and land subsidence in California’s Central Valley

The Central Valley of California is one of the most prolific agricultural regions in the world. Agriculture is reliant on the conjunctive use of surface-water and groundwater. The lack of available surface-water and land-use changes have led to pumping-induced groundwater-level and storage declines, land subsidence, changes to streamflow and the environment, and the degradation of water quality. As a result, in part, the Sustainable Groundwater Management Act (SGMA) was developed. An examination of the components of SGMA and contextualizing regional model applications within the SGMA framework was undertaken to better understand and quantify many of the components of SGMA. Specifically, the U.S. Geological Survey (USGS) updated the Central Valley Hydrologic Model (CVHM) to assess hydrologic system responses to climatic variation, surface-water availability, land-use changes, and groundwater pumping. MODFLOW-OWHM has been enhanced to simulate the timing of land subsidence and attribute its inelastic and elastic portions. In addition to extending CVHM through 2019, the new version, CVHM2, includes several enhancements as follows: managed aquifer recharge (MAR), pumping with multi-aquifer wells, inflows from ungauged watersheds, and more detailed water-balance subregions, streamflow network, diversions, tile drains, land use, aquifer properties, and groundwater level and land subsidence observations. Combined with historical approximations, CVHM2 estimates approximately 158 km 3 of storage loss in the Central Valley from pre-development to 2019. About 15% of the total storage loss is permanent loss of storage from subsidence that has caused damage to infrastructure. Climate extremes will likely complicate the efforts of water managers to store more water in the ground. CVHM2 can provide data in the form of aggregated input datasets, simulate climatic variations and changes, land-use changes or water management scenarios, and resulting changes in groundwater levels, storage, and land subsidence to assist decision-makers in the conjunctive management of water supplies.

California↗

USGS1988

Solute geochemistry of the Snake River plain regional aquifer system, Idaho and eastern Oregon

Four geochemical approaches were used to determine chemical reactions controlling solute concentrations in the Snake River Plain regional aquifer system: (1) calculation of a solute balance within the aquifer, (2) identification of weathered products in the aquifer frame- work, (3) comparison of thermodynamic mineral saturation indices with plausible solute reactions, and (4) comparison of stable-isotope ratios of the solutes with those in the aquifer framework. Solutes in the geo- thermal groundwater system underlying the main aquifer were examined by calculating thermodynamic mineral saturation indices, stable-isotope ratios, geothermometry, and radiocarbon dating. Water budgets, hydrologic arguments, and isotopic analyses for the eastern Snake River Plain aquifer system demonstrate that most, if not all, water is of local meteoric and not juvenile or formation origin. Thus, the solutes must also originate within the basin. Solute balance, isotopic, mineralogic, and thermodynamic arguments suggest that about 20 per- cent of the solutes leaving the basin are derived from reactions with rocks forming the aquifer framework. Most of the remaining solutes are introduced from tributary drainage basins. Mass-balance calculations, thermodynamic arguments, and petro- graphic observations indicate that calcite and silica are precipitated in the aquifer. Petrographic evidence and thermodynamic arguments sug- gest that olivine, pyroxene, plagioclase, pyrite, and anhydrite are being weathered from the aquifer framework. Large amounts of sodium, chloride, and sulfate, relative to their concentration in the igneous rock, are being removed from the aquifer. Release of fluids from inclusions in the igneous rocks and initial flushing of grain boundaries and pores of detrital marine sediments in interbeds are believed to be a major source of these solutes. Identification and quantification of reactions controlling solute concentrations in ground water in the eastern plain indicate that the aquifer is not a large mixing vessel that simply stores and transmits water and solutes but is undergoing diagenesis and is both a source and a sink for solutes. Evaluation of solute concentrations and stable-isotope ratios of hydrogen, oxygen, carbon, and sulfur along groundwater flowpaths that transect irrigated areas suggests that irrigation water may have altered solute concentrations and isotope ratios in the eastern Snake River Plain aquifer system. The changes, however, have been small because of the similarity of solute concentrations and ratios in applied irrigation water and in native ground water, and because of rapid movement and large dispersivity of the aquifer. Reactions controlling solutes in the western Snake River basin are believed to be similar to those in the eastern basin but, because of dif- ferent hydrologic conditions, a definitive analysis could not be made. The regional geothermal system that underlies the Snake River Plain contains total dissolved solids similar to those in the overlying Snake River Plain aquifer system but contains higher concentrations of sodium, bicarbonate, silica, fluoride, sulfate, chloride, arsenic, boron, and lithium, and lower concentrations of calcium, magnesium, and hydrogen. These solutes are believed to be derived from reactions similar to those in the Snake River Plain aquifer system, except that ion exchange and hydrol- ysis play a role in controlling solute concentrations in the geothermal system. Geothermometry calculations of selected ground-water samples from known geothermal areas throughout the basin suggest that the geother- mal system is large in areal extent but has relatively low temperatures. Approximately half of the silica-quartz calculated water temperatures are greater than 90 °C. Radiocarbon dating of geothermal water in the Salmon Falls and Bruneau-Grand View areas in the south central part of the Snake River basin suggests that residence time of the geother- mal water is about 17,700 years.

Idaho;Oregon↗

USGS2023

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, 2022

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 hydrogeologic unit for the purposes of providing annual assessments of regional-scale water-level altitudes and changes over time. In 2022, shaded depictions of water-level altitudes for the Chicot and Evangeline aquifers (undifferentiated) ranged from about 270 feet (ft) below the North American Vertical Datum of 1988 (NAVD 88) to about 195 ft above NAVD 88. The largest decline in water-level altitudes indicated by the 1977–2022 long-term water-level-change map was southeast of The Woodlands. In comparison, the 1990–2022 long-term water-level-change map depicts declines in water-level altitudes in localized areas at or near certain wells in parts of northwestern Harris County and southern Montgomery County. The largest rise in water-level altitudes for 1977–2022 was observed in a relatively large area in southeastern Harris County, whereas the largest rise in water-level altitudes for 1990–2022 was observed in a relatively small area in central Harris County. The 5-year short-term water-level-change map depicts the largest declines at three wells in northern Fort Bend County and the largest rises at five wells in southwestern and central Harris County. The 1-year short-term water-level-change map depicts the largest decline at a well in north-central Harris County and the largest rises at a well in north-central Fort Bend County and a well in southwestern Harris County. In 2022, shaded depictions of water-level altitudes for the Jasper aquifer ranged from about 213 ft below NAVD 88 to about 285 ft above NAVD 88. The 2000–22 long-term water-level-change map depicts water-level declines throughout most of the study area where water-level-measurement data from the aquifer were collected, with the largest decline in north-central Harris County and south-central Montgomery County south of The Woodlands. The 5-year short-term water-level-change map depicts the largest decline at a well in Conroe and the largest rise at a well in south-central Montgomery County. The 1-year short-term water-level-change map depicts the largest decline at a well in south-central Montgomery County east of The Woodlands and the largest rise at a well in Conroe.

Texas↗

USGS2024

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, 2023

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 2023, shaded depictions of water-level altitudes for the Chicot and Evangeline aquifers (undifferentiated) ranged from about 286 feet (ft) below the North American Vertical Datum of 1988 (NAVD 88) to about 169 ft above NAVD 88. The largest decline in water-level altitudes indicated by the 1977–2023 long-term water-level-change map was in south-central Montgomery County southeast of The Woodlands. In comparison, the 1990–2023 long-term water-level-change map depicts the largest declines in water-level altitudes in localized areas at or near certain wells in parts of northwestern Harris County and south-central Montgomery County. The largest rise in water-level altitudes for 1977–2023 is depicted in a relatively large area in southeastern Harris County, whereas the largest rise in water-level altitudes for 1990–2023 is depicted in a relatively large area in central Harris County. The 5-year short-term water-level-change map depicts the largest declines at three wells in northern Fort Bend County, one well in western Harris County, and three wells in south-central Montgomery County and the largest rise at one well in central Harris County. The 1-year short-term water-level-change map depicts the largest declines at one well in northern Fort Bend County and two wells in southwestern Harris County and the largest rises at one well in northern Brazoria County and one well in south-central Montgomery County. In 2023, shaded depictions of water-level altitudes for the Jasper aquifer ranged from about 242 ft below NAVD 88 to about 218 ft above NAVD 88. The 2000–23 long-term water-level-change map depicts water-level declines throughout the study area where water-level-measurement data from the aquifer were collected, with the largest declines in north-central Harris County and south-central Montgomery County south of The Woodlands. The 5-year short-term water-level-change map depicts the largest declines at two wells in central Montgomery County near Conroe and two wells in south-central Montgomery County southeast of The Woodlands and the largest rise at one well in western Montgomery County. The 1-year short-term water-level-change map depicts the largest declines at four wells in south-central Montgomery County southeast of The Woodlands and one well in central Montgomery County near Conroe and the largest rises at two wells in western Montgomery County.

Texas↗

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↗

USGS2009

Hydrogeology and Simulation of Groundwater Flow in the Plymouth-Carver-Kingston-Duxbury Aquifer System, Southeastern Massachusetts

The glacial sediments that underlie the Plymouth-Carver-Kingston-Duxbury area of southeastern Massachusetts compose an important aquifer system that is the primary source of water for a region undergoing rapid development. Population increases and land-use changes in this area has led to two primary environmental effects that relate directly to groundwater resources: (1) increases in pumping that can adversely affect environmentally sensitive groundwater-fed surface waters, such as ponds, streams, and wetlands; and (2) adverse effects of land use on the quality of water in the aquifer. In response to these concerns, the U.S. Geological Survey, in cooperation with the Massachusetts Department of Environmental Protection, began an investigation in 2005 to improve the understanding of the hydrogeology in the area and to assess the effects of changing pumping and recharge conditions on groundwater flow in the Plymouth-Carver-Kingston-Duxbury aquifer system. A numerical flow model was developed based on the USGS computer program MODFLOW-2000 to assist in the analysis of groundwater flow. Model simulations were used to determine water budgets, flow directions, and the sources of water to pumping wells, ponds, streams, and coastal areas. Model-calculated water budgets indicate that approximately 298 million gallons per day (Mgal/d) of water recharges the Plymouth-Carver-Kingston-Duxbury aquifer system. Most of this water (about 70 percent) moves through the aquifer, discharges to streams, and then reaches the coast as surface-water discharge. Of the remaining 30 percent of flow, about 25 percent of the water that enters the aquifer as recharge discharges directly to coastal areas and 5 percent discharges to pumping wells. Groundwater withdrawals are anticipated to increase from the current (2005) rate of about 14 Mgal/d to about 21 Mgal/d by 2030. Pumping from large-capacity production wells decreases water levels and increases the potential for effects on surface-water bodies, which are affected by pumping and wastewater disposal locations and rates. Pumping wells that are upgradient of surface-water bodies potentially capture water that would otherwise discharge to these surface-water bodies, thereby reducing streamflow and pond levels. The areas most affected by proposed increases in groundwater withdrawals are in the Towns of Plymouth and Wareham where more than half of the proposed increase in pumping will occur. In response to an increase of about 7 Mgal/d of pumping, groundwater discharge to streams is reduced by about 6 cubic feet per second (ft3/s) (about 4 Mgal/d) from a total of about 325 ft3/s. Reduction in streamflow is moderated by an increase of artificial recharge from wastewater returned to the aquifer by onsite domestic septic systems and centralized wastewater treatment facilities. It is anticipated that about 3 Mgal/d of the 7 Mgal/d of increase in pumped water will be returned to the aquifer as wastewater by 2030. Currently (2005) about 3 percent of groundwater discharge to streams is from wastewater return flow to the aquifer during average conditions. During drought conditions, the component of streamflow augmented by wastewater return flow doubles as wastewater recharge remains constant and aquifer recharge rates decrease. Wastewater return flow, whether as direct groundwater discharge to streams or as an additional source of aquifer recharge, increases the height of the water table near streams, thereby moderating the effects of increased groundwater withdrawals on streamflow. An analysis of a simulated drought similar to the 1960s drought of record indicates that the presence of streams moderates the effects on water levels of reduced aquifer recharge. The area where water-table altitudes were least affected by drought was in the Weweantic River watershed in the Town of Carver. Water levels decreased by less than 2 feet from current average conditions compared to decreases of greater than 5

Scientific Investigations Report↗