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Groundwater & aquifers

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At least 721 records · Page 40Linked to original sources

USGS2010

Evaluation of Methods for Delineating Zones of Transport for Production Wells in Karst and Fractured-Rock Aquifers of Minnesota

Assessment of groundwater-flow conditions in the vicinity of production wells in karst and fractured-rock settings commonly is difficult due in part to the lack of detailed hydrogeologic information and the resources needed to collect it. To address this concern and to better understand the hydrogeology and aquifer properties of karst and fractured-rock aquifers in Minnesota, the U.S. Geological Survey, in cooperation with the Minnesota Department of Health, conducted a study to evaluate methods for delineating zones of transport for 24 production wells in karst and fractured-rock aquifers in Minnesota. Two empirical methods for delineating zones of transport around wells were applied to the 24 production wells that extract groundwater from karst and fractured-rock aquifers in nine Minnesota communities. These methods were the truncated-parabola and modified-ellipse methods, and both methods assume porous-media flow conditions. The 24 wells extracted water from a karst aquifer (Prairie du Chien-Jordan aquifer), porous aquifers interspersed with solution-enhanced fractures (Jordan and Hinckley aquifers), or fractured-bedrock aquifers (Biwabik Iron-Formation and Sioux Quartzite aquifers). Zones of transport delineated using these two empirical methods were compared with zones of transport previously delineated by Minnesota Department of Health hydrologists for the wells using the calculated-fixed-radius method and groundwater-flow models. Large differences were seen in the size and shapes of most zones of transport delineated using the truncated-parabola and modified-ellipse methods compared with the zones of transport delineated by the Minnesota Department of Health. In general, the zones of transport delineated using the truncated-parabola and modified-ellipse methods were smaller in area than those delineated by the Minnesota Department of Health and included only small parts of the Minnesota Department of Health zones of transport. About two-thirds(67 percent) of the individual or composite truncated parabolas and modified ellipses covered less than 50 percent of the area included in zones of transport delineated by the Minnesota Department of Health. The shapes of some of the truncated parabola and modified ellipses did not closely match the zones of transport delineated by the Minnesota Department of Health using the calculated-fixed-radius method and groundwater-flow models. Differences between the zones of transport delineated by the truncated-parabola and modified-ellipse methods and those delineated by the Minnesota Department of Health can be explained by variations inherent to the methods and by the amount of complexity taken into account by different groundwater-flow models. Additional field hydrogeologic studies would be needed at specific sites to support the use of these zone-of-transport delineation methods. Application of the truncated-parabola and modified-ellipse methods to sites for which existing hydrogeologic information is limited can produce questionable results in karst and fractured-rock settings, particularly in areas where many high-capacity wells or active mining operations are nearby.

Scientific Investigations Report↗

USGS2012

Hydrogeology of the stratified-drift aquifers in the Cayuta Creek and Catatonk Creek valleys in parts of Tompkins, Schuyler, Chemung, and Tioga Counties, New York

The surficial deposits, areal extent of aquifers, and the water-table configurations of the stratified-drift aquifer systems in the Cayuta Creek and Catatonk Creek valleys and their large tributary valleys in Tompkins, Schuyler, Chemung, and Tioga Counties, New York were mapped in 2009, in cooperation with the New York State Department of Environmental Conservation. Well and test-boring records, surficial deposit maps, Light Detection and Ranging (LIDAR) data, soils maps, and horizontal-to-vertical ambient-noise seismic surveys were used to map the extent of the aquifers, construct geologic sections, and determine the depth to bedrock (thickness of valley-fill deposits) at selected locations. Geologic materials in the study area include sedimentary bedrock, unstratified drift (till), stratified drift (glaciolacustrine and glaciofluvial deposits), and recent alluvium. Stratified drift consisting of glaciofluvial sand and gravel is the major component of the valley fill in this study area. The deposits are present in sufficient amounts in most places to form extensive unconfined aquifers throughout the study area and, in some places, confined aquifers. Stratified drift consisting of glaciolacustrine fine sand, silt, and clay are present locally in valleys underlying the surficial sand and gravel deposits in the southern part of the Catatonk Creek valley. These unconfined and confined aquifers are the source of water for most residents, farms, and businesses in the valleys. A generalized depiction of the water table in the unconfined aquifer was constructed using water-level measurements made from the 1950s through 2010, as well as LIDAR data that were used to determine the altitudes of perennial streams at 10-foot contour intervals and water surfaces of ponds and wetlands that are hydraulically connected to the unconfined aquifer. The configuration of the water-table contours indicate that the general direction of groundwater flow within Cayuta Creek and Catatonk Creek stratified-drift aquifers is predominantly from the valley walls toward the main streams in the valleys. The groundwater discharges from the aquifer system to the main-stem streams in the valleys. Locally, the direction of groundwater flow is radially away from groundwater mounds that have formed beneath upland tributaries that typically lose water where they flow on alluvial fans in the valleys. In some places, groundwater that would normally flow toward streams is intercepted by pumping wells.

New York↗

USGS1987

Hydrogeology, degradation of ground-water quality, and simulation of infiltration from the Delaware River into the Potomac aquifers, northern Delaware

Brackish water is infiltrating from the Delaware River into the underlying Potomac aquifers in the Cretaceous Potomac Formation in northern Delaware. Evidence that infiltration at the river is actually occurring includes chloride concentrations in the aquifers that are above ambient levels and chemical characteristics of groundwater and river water that are similar. Water quality within the Potomac aquifers has been degraded by the infiltration of river water and by leachate from waste disposal sites. The ambient groundwater has chloride concentrations from 10 to 21 mg/L. Chemical analyses indicate that the ambient groundwater is a sodium magnesium calcium-chloride sulfate bicarbonate type. Areas of the Potomac aquifers that have been degraded have chloride concentrations from 40 to 8,600 m/L, with specific conductances of 200 to 27 ,200 microsiemens/cm at 25 C. Chemical analyses indicate the groundwater in these areas is a sodium-chlorate type. Two wells in the lower Potomac aquifer near the Wilmington Marine Terminal also have been affected by the infiltration of river water. Leachate from waste disposal sites has caused localized groundwater degradation in all three Potomac aquifers, especially north of the Delaware Memorial Bridge and at sites near Army Creek and Red Lion Creek. Chloride concentrations up to 8,600 mg/L have resulted from waste disposal leachate. Simulated infiltration of river water into the Potomac aquifers accounts for approximately 6 to 12% of the total aquifer recharge in the area of influence of the pumping. There is a direct correlation between the rate of infiltration of river water and the total well-field pumpage. The rate of infiltration of river water for the pumping scenarios ranged from 0.31 to 0.62 million gal/day. Simulations of freshwater injection demonstrated that 12 barriers wells, each injecting 300 gal/min, would be needed to create a barrier against the infiltration of river water in the upper Potomac aquifer, whereas the middle Potomac aquifer would require 7 wells in injecting 200 gal/min. (Author 's abstract)

Water-Resources Investigations Report↗

USGS2023

Where the past meets the present: Connecting nitrogen from watersheds to streams through groundwater flowpaths

Groundwater discharge to streams is a nonpoint source of nitrogen (N) that confounds N mitigation efforts and represents a significant portion of the annual N loading to watersheds. However, we lack an understanding of where and how much groundwater N enters streams and watersheds. Nitrogen concentrations at the end of groundwater flowpaths are the culmination of biogeochemical and physical processes from the contributing land area where groundwater recharges, within the aquifer system, and in the near-stream riparian area where groundwater discharges to streams. Our research objectives were to quantify the spatial distribution of N concentrations at groundwater discharges throughout a mixed land-use watershed and to evaluate how relationships among contributing and riparian land cover, modeled aquifer characteristics, and groundwater discharge biogeochemistry explain the spatial variation in groundwater discharge N concentrations. We accomplished this by integrating high-resolution thermal infrared surveys to locate groundwater discharge, biogeochemical sampling of groundwater, and a particle tracking model that links groundwater discharge locations to their contributing area land cover. Groundwater N loading from groundwater discharges within the watershed varied substantially between and within streambank groundwater discharge features. Groundwater nitrate concentrations were spatially heterogeneous ranging from below 0.03–11.45 mg-N/L, varying up to 20-fold within meters. When combined with the particle tracking model results and land cover metrics, we found that groundwater discharge nitrate concentrations were best predicted by a linear mixed-effect model that explained over 60% of the variation in nitrate concentrations, including aquifer chemistry (dissolved oxygen, Cl − , SO 4 2− ), riparian area forested land cover, and modeled physical aquifer characteristics (discharge, Euclidean distance). Our work highlights the significant spatial variability in groundwater discharge nitrate concentrations within mixed land-use watersheds and the need to understand groundwater N processing across the many spatiotemporal scales within groundwater cycling.

Connecticut↗

USGS2017

Groundwater flow model for the Little Plover River basin in Wisconsin’s Central Sands

The Little Plover River is a groundwater-fed stream in the sand plains region of central Wisconsin. In this region, sandy sediment deposited during or soon after the last glaciation forms an important unconfined sand and gravel aquifer. This aquifer supplies water for numerous high-capacity irrigation, municipal, and industrial wells that support a thriving agricultural industry. In recent years the addition of many new wells, combined with observed diminished flows in the Little Plover and other nearby rivers, has raised concerns about the impacts of the wells on groundwater levels and on water levels and flows in nearby lakes, streams, and wetlands. Diverse stakeholder groups, including well operators, Growers, environmentalists, local land owners, and regulatory and government officials have sought a better understanding of the local groundwater-surface water system and have a shared desire to balance the water needs of the he liagricultural, industrial, and urban users with the maintenance and protection of groundwater-dependent natural resources. To help address these issues, the Wisconsin Department of Natural Resources requested that the Wisconsin Geological and Natural History Survey and U.S. Geological Survey cooperatively develop a groundwater flow model that could be used to demonstrate the relationships among groundwater, surface water, and well withdrawals and also be a tool for testing and evaluating alternative water management strategies for the central sands region. Because of an abundance of previous studies, data availability, local interest, and existing regulatory constraints the model focuses on the Little Plover River watershed, but the modeling methodology developed during this study can apply to much of the larger central sands of Wisconsin. The Little Plover River groundwater flow model simulates three-dimensional groundwater movement in and around the Little Plover River basin under steady-state and transient conditions. This model explicitly includes all high-capacity wells in the model domain and simulates seasonal variations in recharge and well pumping. The model represents the Little Plover River, and other significant streams and drainage ditches in the model domain, as fully connected to the groundwater system, computes stream base flow resulting from groundwater discharge, and routes the flow along the stream channel. A separate soil-water-balance (SWB) model was used to develop groundwater recharge arrays as input for the groundwater flow model. The SWB model uses topography, soils, land use, and climatic data to estimate recharge as deep drainage from the soil zone. The SWB model explicitly includes recharge originating as irrigation water, and computes irrigation using techniques similar to those used by local irrigation operators. The groundwater flow model uses the U.S. Geological Survey’s MODFLOW modeling code which is freely available, widely accepted, and commonly used by the groundwater community. The groundwater flow model and the SWB model use identical high-resolution numerical grids having model cells 100 feet on a side, with physical properties assigned to each grid cell. This grid allows accurate geographic placement of wells, streams, and other model features. The 3-dimensional grid has three layers; layers 1 and 2 represent the sand and gravel aquifer and layer 3 represents the underlying sandstone. The distribution of material properties in the model (hydraulic conductivity, aquifer thickness, etc.) comes from previous published geologic studies of the region, updated by calibration to recent streamflow and groundwater level data. The SWB model operates on a daily time step. The groundwater flow model was calibrated to monthly stress periods with time steps ranging from 1 to 16 days. More detailed time discretization is possible. The groundwater model was calibrated to water-level and streamflow data collected during 2013 and 2014 by adjusting model parameters (primarily hydraulic conductivity, storage, and recharge) until the model produced a conditionally optimal fit between field observations and model output, subject to consistency with previously published geologic studies. Calibration was performed under both steady and transient conditions, and used a sophisticated parameter-estimation procedure (PEST) for the calibration process and to identify important model parameters. For the Little Plover River, the two most important parameters are the global recharge multiplier and the hydraulic conductivity of the stream bed. The calibrated model produces water-level and mass-balance results that are consistent with field observations and previous studies of the area. The completed model is a powerful tool for testing and demonstrating alternative water-management scenarios. Example model applications described in this report include simulating how the cumulative impacts of pumping and land-use change have affected average baseflow in the Little Plover River. Depletion-potential mapping represents a method for predicting which wells and well locations have the greatest impact on nearby surface-water resources. The completed model is publicly available, along with a companion user’s guide to assist with its operation, at http://wgnhs.org/littleplover- river-groundwater-model.

Wisconsin↗

USGS2011

Review: Regional land subsidence accompanying groundwater extraction

The extraction of groundwater can generate land subsidence by causing the compaction of susceptible aquifer systems, typically unconsolidated alluvial or basin-fill aquifer systems comprising aquifers and aquitards. Various ground-based and remotely sensed methods are used to measure and map subsidence. Many areas of subsidence caused by groundwater pumping have been identified and monitored, and corrective measures to slow or halt subsidence have been devised. Two principal means are used to mitigate subsidence caused by groundwater withdrawal—reduction of groundwater withdrawal, and artificial recharge. Analysis and simulation of aquifer-system compaction follow from the basic relations between head, stress, compressibility, and groundwater flow and are addressed primarily using two approaches—one based on conventional groundwater flow theory and one based on linear poroelasticity theory. Research and development to improve the assessment and analysis of aquifer-system compaction, the accompanying subsidence and potential ground ruptures are needed in the topic areas of the hydromechanical behavior of aquitards, the role of horizontal deformation, the application of differential synthetic aperture radar interferometry, and the regional-scale simulation of coupled groundwater flow and aquifer-system deformation to support resource management and hazard mitigation measures.

Hydrogeology Journal↗

USGS2023

Determining seasonal recharge, storage changes, and specific yield using repeat microgravity and water-level measurements in the Mesilla Basin alluvial aquifer, New Mexico, 2016–2018

Increasing water demand and multi-year drought conditions within the Mesilla/Conejos-Médanos Basin near the New Mexico-Texas- Chihuahua border have resulted in diminished surface-water supplies and increased groundwater withdrawals. To better understand recharge to the shallow aquifer, the spatial and temporal groundwater storage changes, and the variability of specific yield (Sy) in the aquifer, seasonal groundwater elevation and repeat microgravity measurements were made during the irrigation release and non-release seasons of 2016, 2017, and 2018 at a network of locations near Las Cruces, New Mexico. The data collected during this investigation were able to capture seasonal change in groundwater elevations and storage from various sources of recharge at multiple sites in the shallow aquifer. Seasonal recharge in the study area was attributed to streamflow, the application and conveyance of irrigation water, and large or sustained precipitation events. However, increasing groundwater gradients in recent decades between piezometers close to the river and those more than a kilometer from the river suggests that recharge from river seepage has become localized at the seasonal scale. Overall, there was a net increase in storage of almost 8.4 cubic hectometers in the study reach between the start and end of the study, largely following the increased surface-water availability and above average precipitation in 2017. Specific yield, estimated by comparing the groundwater-level changes and storage changes at six sites in the study area, ranged from 0.14 (+/− 0.05) to 0.30 (+/− 0.06), which is slightly greater than previously reported estimates (0.10 to 0.25), but still within the error of the estimates. Most of the variability in the estimated storage change, that was not well-correlated with groundwater elevation change, is thought to be from soil moisture in the unsaturated zone. This investigation demonstrates the value of adding repeat microgravity measurements to conventional groundwater monitoring to better understand the sources and extent of recharge as well as the variability of Sy in the aquifer. Continued monitoring, under a variety of available surface water and meteorological conditions, could provide a more comprehensive understanding of the water budget and reduce the specific yield estimation uncertainty. Evaluating water-levels and storage conditions prior to, and following, local recharge events may help managers identify threshold conditions for aquifer storage depletions and recoveries.

New Mexico↗

USGS2018

Shallow bedrock limits groundwater seepage-based headwater climate refugia

Groundwater/surface-water exchanges in streams are inexorably linked to adjacent aquifer dynamics. As surface-water temperatures continue to increase with climate warming, refugia created by groundwater connectivity is expected to enable cold water fish species to survive. The shallow alluvial aquifers that source groundwater seepage to headwater streams, however, may also be sensitive to seasonal and long-term air temperature dynamics. Depth to bedrock can directly influence shallow aquifer flow and thermal sensitivity, but is typically ill-defined along the stream corridor in steep mountain catchments. We employ rapid, cost-effective passive seismic measurements to evaluate the variable thickness of the shallow colluvial and alluvial aquifer sediments along a headwater stream supporting cold water-dependent brook trout ( Salvelinus fontinalis ) in Shenandoah National Park, VA, USA. Using a mean depth to bedrock of 2.6 m, numerical models predicted strong sensitivity of shallow aquifer temperature to the downward propagation of surface heat. The annual temperature dynamics (annual signal amplitude attenuation and phase shift) of potential seepage sourced from the shallow modeled aquifer were compared to several years of paired observed stream and air temperature records. Annual stream water temperature patterns were found to lag local air temperature by ∼8–19 d along the stream corridor, indicating that thermal exchange between the stream and shallow groundwater is spatially variable. Locations with greater annual signal phase lag were also associated with locally increased amplitude attenuation, further suggestion of year-round buffering of channel water temperature by groundwater seepage. Numerical models of shallow groundwater temperature that incorporate regional expected climate warming trends indicate that the summer cooling capacity of this groundwater seepage will be reduced over time, and lower-elevation stream sections may no longer serve as larger-scale climate refugia for cold water fish species, even with strong groundwater discharge.

Limnologica - Ecology and Management of Inland Wat↗

USGS2006

Impacts of the 2004 tsunami on groundwater resources in Sri Lanka

The 26 December 2004 tsunami caused widespread destruction and contamination of coastal aquifers across southern Asia. Seawater filled domestic open dug wells and also entered the aquifers via direct infiltration during the first flooding waves and later as ponded seawater infiltrated through the permeable sands that are typical of coastal aquifers. In Sri Lanka alone, it is estimated that over 40,000 drinking water wells were either destroyed or contaminated. From February through September 2005, a team of United States, Sri Lankan, and Danish water resource scientists and engineers surveyed the coastal groundwater resources of Sri Lanka to develop an understanding of the impacts of the tsunami and to provide recommendations for the future of coastal water resources in south Asia. In the tsunami‐affected areas, seawater was found to have infiltrated and mixed with fresh groundwater lenses as indicated by the elevated groundwater salinity levels. Seawater infiltrated through the shallow vadose zone as well as entered aquifers directly through flooded open wells. Our preliminary transport analysis demonstrates that the intruded seawater has vertically mixed in the aquifers because of both forced and free convection. Widespread pumping of wells to remove seawater was effective in some areas, but overpumping has led to upconing of the saltwater interface and rising salinity. We estimate that groundwater recharge from several monsoon seasons will reduce salinity of many sandy Sri Lankan coastal aquifers. However, the continued sustainability of these small and fragile aquifers for potable water will be difficult because of the rapid growth of human activities that results in more intensive groundwater pumping and increased pollution. Long‐term sustainability of coastal aquifers is also impacted by the decrease in sand replenishment of the beaches due to sand mining and erosion.

Water Resources Research↗

USGS2009

Characteristics of Southern California coastal aquifer systems

Most groundwater produced within coastal Southern California occurs within three main types of siliciclastic basins: (1) deep (>600 m), elongate basins of the Transverse Ranges Physiographic Province, where basin axes and related fluvial systems strike parallel to tectonic structure, (2) deep (>6000 m), broad basins of the Los Angeles and Orange County coastal plains in the northern part of the Peninsular Ranges Physiographic Province, where fluvial systems cut across tectonic structure at high angles, and (3) shallow (75-350 m), relatively narrow fluvial valleys of the generally mountainous southern part of the Peninsular Ranges Physiographic Province in San Diego County. Groundwater pumped for agricultural, industrial, municipal, and private use from coastal aquifers within these basins increased with population growth since the mid-1850s. Despite a significant influx of imported water into the region in recent times, groundwater, although reduced as a component of total consumption, still constitutes a significant component of water supply. Historically, overdraft from the aquifers has caused land surface subsidence, flow between water basins with related migration of groundwater contaminants, as well as seawater intrusion into many shallow coastal aquifers. Although these effects have impacted water quality, most basins, particularly those with deeper aquifer systems, meet or exceed state and national primary and secondary drinking water standards. Municipalities, academicians, and local water and governmental agencies have studied the stratigraphy of these basins intensely since the early 1900s with the goals of understanding and better managing the important groundwater resource. Lack of a coordinated effort, due in part to jurisdictional issues, combined with the application of lithostratigraphic correlation techniques (based primarily on well cuttings coupled with limited borehole geophysics) have produced an often confusing, and occasionally conflicting, litany of names for the various formations, lithofacies, and aquifer systems identified within these basins. Despite these nomenclatural problems, available data show that most basins contain similar sequences of deposits and share similar geologic histories dominated by glacio-eustatic sea-level fluctuations, and overprinted by syndepositional and postdepositional tectonic deformation. Impermeable, indurated mid-Tertiary units typically form the base of each siliciclastic groundwater basin. These units are overlain by stacked sequences of Pliocene to Holocene interbedded marine, paralic, fluvial, and alluvial sediment (weakly indurated, folded, and fractured) that commonly contain the historically named "80-foot sand," "200-foot sand," and "400-foot gravel" in the upper part of the section. An unconformity, cut during the latest Pleistocene lowstand (?? 18 O stage 2; ca. 18 ka), forms a major sequence boundary that separates these units from the overlying Holocene fluvial sands and gravels. Unconfined aquifers occur in amalgamated coarse facies near the bounding mountains (forebay area). These units are inferred to become lithologically more complex toward the center of the basins and coast line, where interbedded permeable and low-permeability alluvial, fluvial, paralic, and marine facies contain confined aquifers (pressure area). Coastal bounding faults limit intrabasin and/or interbasin flow in parts of many basins. ?? 2009 Geological Society of America.

Special Paper of the Geological Society of America↗

USGS2016

Hydrologic conditions, recharge, and baseline water quality of the surficial aquifer system at Jekyll Island, Georgia, 2012-13

An increase of groundwater withdrawals from the surficial aquifer system on Jekyll Island, Georgia, prompted an investigation of hydrologic conditions and water quality by the U.S. Geological Survey during October 2012 through December 2013. The study demonstrated the importance of rainfall as the island’s main source of recharge to maintain freshwater resources by replenishing the water table from the effects of hydrologic stresses, primarily evapotranspiration and pumping. Groundwater-flow directions, recharge, and water quality of the water-table zone on the island were investigated by installing 26 shallow wells and three pond staff gages to monitor groundwater levels and water quality in the water-table zone. Climatic data from Brunswick, Georgia, were used to calculate potential maximum recharge to the water-table zone on Jekyll Island. A weather station located on the island provided only precipitation data. Additional meteorological data from the island would enhance potential evapotranspiration estimates for recharge calculations. Groundwater levels and specific-conductance measurements showed the dependence of freshwater resources on rainfall to recharge the water-table zone of the surficial aquifer system and to influence groundwater flow on Jekyll Island. The unseasonably dry conditions during November 2012 to April 2013 induced saline water infiltration to the water-table zone from the marshland separating the Jekyll River from the island. A strong correlation (R 2 = 0.97) of specific conductance to chloride concentration in water samples from wells installed in the water-table zone provided support for the determination of seasonal directions of groundwater flow by confirming salinity changes in the water-table zone. Unseasonably wet conditions during the late spring to August caused groundwater-flow reversals in some areas. The high dependence of the water-table zone in the surficial aquifer system on precipitation to replenish the aquifer with freshwater underscored the importance of monitoring groundwater levels, water quality, and water use to identify aquifer-discharge conditions that have the potential to promote seawater encroachment and degrade freshwater resources on Jekyll Island.

Georgia↗

USGS2018

Groundwater, surface-water, and water-chemistry data, Black Mesa area, northeastern Arizona—2015–2016

The Navajo (N) aquifer is an extensive aquifer and the primary source of groundwater in the 5,400-square-mile Black Mesa area in northeastern Arizona. Availability of water is an important issue in the Black Mesa area because of continued water requirements for industrial and municipal use by a growing population and because of the arid climate. Precipitation in the area typically ranges from less than 6 to more than 16 inches per year depending on location. The U.S. Geological Survey water-monitoring program in the Black Mesa area began in 1971 and provides information about the long-term effects of groundwater withdrawals from the N aquifer for industrial and municipal uses. This report presents results of data collected as part of the monitoring program in the Black Mesa area from November 2015 to December 2016. The monitoring program includes measurements of (1) groundwater withdrawals (pumping), (2) groundwater levels, (3) spring discharge, (4) surface-water discharge, and (5) groundwater chemistry. In calendar year 2016, total groundwater withdrawals were 3,540 acre-ft, industrial withdrawals were 1,090 acre-ft, and municipal withdrawals were 2,450 acre-ft. Total withdrawals during 2016 were about 52 percent less than total withdrawals in 2005 because of Peabody Western Coal Company’s discontinued use of water to transport coal in a coal slurry pipeline. From 2015 to 2016, annually measured water levels available for comparison in wells completed in the unconfined areas of the N aquifer within the Black Mesa area declined in 9 of 16 wells, and the median change was –0.1 feet. Water levels also declined in 8 of 16 wells measured in the confined area of the aquifer. The median change for the confined area of the aquifer was 0.0 feet. From the prestress period (prior to 1965) to 2016, the median water-level change for all 32 wells in both the confined and unconfined areas was –10.2 feet; the median water-level changes were –1.6 feet for the 16 wells measured in the unconfined areas and –36.1 feet for the 16 wells measured in the confined area. Spring flow was measured at four springs in 2016. Flow fluctuated during the period of record for Burro Spring and Pasture Canyon Spring, but a decreasing trend was statistically significant (p<0.05) at Moenkopi School Spring and Unnamed Spring near Dennehotso. Discharge at Burro Spring has remained relatively constant since it was first measured in the 1980s and discharge at Pasture Canyon Spring has fluctuated for the period of record. Continuous records of surface-water discharge in the Black Mesa area were collected from streamflow-gaging stations at the following sites: Moenkopi Wash at Moenkopi 09401260 (1976 to 2016), Dinnebito Wash near Sand Springs 09401110 (1993 to 2016), Polacca Wash near Second Mesa 09400568 (1994 to 2016), and Pasture Canyon Springs 09401265 (2004 to 2016). Median winter flows (November through February) of each water year were used as an index of the amount of groundwater discharge at the above-named sites. For the period of record, the median winter flows have generally remained constant at Dinnebito Wash and Polacca Wash, whereas a decreasing trend was indicated at Moenkopi Wash and Pasture Canyon Springs. In 2016, water samples collected from three wells and four springs in the Black Mesa area were analyzed for selected chemical constituents, and the results were compared with previous analyses from the same wells and springs. Concentrations of dissolved solids, chloride, and sulfate have varied at all three wells for the period of record, but neither increasing nor decreasing trends over time were found. Dissolved solids, chloride, and sulfate concentrations increased at Moenkopi School Spring during the more than 25 years of record at that site. Concentrations of dissolved solids, chloride, and sulfate at Pasture Canyon Spring have not varied significantly (p>0.05) since the early 1980s, and there is no increasing or decreasing trend in those data. Concentrations of dissolved solids, chloride, and sulfate at Burro Spring and Unnamed Spring near Dennehotso have varied for the period of record, but there is no statistical trend in the data.

Arizona↗

USGS2022

Groundwater, surface-water, and water-chemistry data, Black Mesa area, northeastern Arizona—2018–2019

The Navajo (N) aquifer is an extensive aquifer and the primary source of groundwater in the 5,400-square-mile Black Mesa area in northeastern Arizona. Water availability is an important issue in the Black Mesa area because of the arid climate, past industrial water use, and continued water requirements for municipal use by a growing population. Precipitation in the area typically ranges from less than 6 to more than 16 inches per year depending on location. The U.S. Geological Survey water-monitoring program in the Black Mesa area began in 1971 and provides information about the long-term effects of groundwater withdrawals from the N aquifer for industrial and municipal uses. This report presents results of data collected as part of the monitoring program in the Black Mesa area from calendar year 2019, and additionally uses streamflow statistics from November and December 2018. The monitoring program includes measurements of (1) groundwater withdrawals (pumping), (2) groundwater levels, (3) spring discharge, (4) surface-water discharge, and (5) groundwater chemistry. In calendar year 2019, total groundwater withdrawals were estimated to be 3,070 acre-feet (acre-ft), industrial withdrawals were 670 acre-ft, and municipal withdrawals were estimated to be 2,400 acre-ft. Total withdrawals during 2019 were about 58 percent less than total withdrawals in 2005 because of Peabody Western Coal Company’s discontinued use of water to transport coal in a coal slurry pipeline after 2005 and cessation of mining operations in 2019. Water levels measured in 2019 from wells completed in the unconfined areas of the N aquifer within the Black Mesa area showed a decline in 10 of 16 wells when compared with water levels from the prestress period (prior to 1965). The changes in water levels across all 16 wells ranged from +8.2 feet (ft) to −40.0 ft, and the median change was −1.7 ft. Water levels also showed decline in 16 of 18 wells measured in the confined area of the aquifer when compared to the prestress period. The median change for the confined area of the aquifer was −38.8 ft, with changes across all 18 wells ranging from +12.9 ft to −185.0 ft. Spring flow was measured at four springs in 2019. Flow fluctuated during the period of record for Burro Spring and Pasture Canyon Spring, but a decreasing trend was statistically significant (p<0.05) at Moenkopi School Spring and Unnamed Spring near Dennehotso. Discharge at Burro Spring has remained relatively constant since it was first measured in the 1980s and discharge at Pasture Canyon Spring has fluctuated for the period of record. Continuous records of surface-water discharge in the Black Mesa area were collected from streamflow-gaging stations at the following sites: Moenkopi Wash at Moenkopi 09401260 (1976 to 2019), Dinnebito Wash near Sand Springs 09401110 (1993 to 2019), Polacca Wash near Second Mesa 09400568 (1994 to 2019), and Pasture Canyon Springs 09401265 (2004 to 2019). Median winter flows (November through February) of each winter were used as an estimate of the amount of groundwater discharge at the above-named sites. For the period of record, the median winter flows have generally remained constant at Polacca Wash and Pasture Canyon Springs, whereas a decreasing trend was indicated at Moenkopi Wash and Dinnebito Wash. In 2019, water samples collected from four springs and three wells in the Black Mesa area were analyzed for selected chemical constituents. Results from the four springs were compared with previous analyses from the same springs. Concentrations of dissolved solids, chloride, and sulfate increased at Moenkopi School Spring during the more than 30 years of record at that site. Concentrations of dissolved solids, chloride, and sulfate at Pasture Canyon Spring have not varied significantly (p>0.05) since the early 1980s, and there is no increasing or decreasing trend in those data. Concentrations of dissolved solids, chloride, and sulfate at Unnamed Spring near Dennehotso have varied for the period of record, but there is no statistical trend in the data. Concentrations of dissolved solids and chloride at Burro Spring have varied for the period of record, but there is no statistical trend in the data; however, concentrations of sulfate from Burro Spring now show a trend towards lower concentrations. No statistical trend tests were performed for the three wells sampled in 2019 since less historical water-quality data were available for comparison.

Arizona↗

USGS2024

Groundwater, surface-water, and water-chemistry data, Black Mesa area, northeastern Arizona—2019–2021

The Navajo (N) aquifer is an extensive aquifer and the primary source of groundwater in the 5,400-square-mile Black Mesa area in northeastern Arizona. Water availability is an important issue in the Black Mesa area because of the arid climate, past industrial water use, and continued water requirements for municipal use by a growing population. Precipitation in the area typically ranges from less than 6 to more than 16 inches per year, depending on location. The U.S. Geological Survey water-monitoring program in the Black Mesa area began in 1971 and provides information about the long-term effects of groundwater withdrawals from the N aquifer for industrial and municipal uses. This report presents the results of data collected as part of the monitoring program in the Black Mesa area from calendar years 2020–2021 and, additionally, uses streamflow statistics from November and December 2019. The monitoring program includes measurements of (1) groundwater withdrawals (pumping), (2) groundwater levels, (3) spring discharge, (4) surface-water discharge, and (5) groundwater chemistry. In calendar year 2020, total groundwater withdrawals were estimated to be 2,680 acre-feet (acre-ft), and, in 2021, total withdrawals were estimated to be 2,570 acre-ft. Total withdrawals during 2021 were about 65 percent less than total withdrawals in 2005 because the Peabody Western Coal Company discontinued its use of water to transport coal in a coal slurry pipeline after 2005 and ceased mining operations in 2019. Owing to Navajo Nation and Hopi Reservation access restrictions during the Coronavirus pandemic, water levels were not collected from municipal wells in 2020 or 2021. Water levels measured in 2021 from wells completed in the unconfined areas of the N aquifer within the Black Mesa area showed a decline in 7 of 13 wells when compared with water levels from the prestress period (prior to 1965). The changes in water levels across all 13 wells ranged from +8.4 feet (ft) to −42.4 ft, and the median change was −0.4 ft. Water levels also showed decline in 11 of 12 wells measured in the confined area of the aquifer when compared to the prestress period. The median change for the confined area of the aquifer was −25.9 ft, with changes across all 12 wells ranging from +17.3 ft to −133.7 ft. Spring flow was measured at four springs between 2020 and 2021. Flow fluctuated during the period of record for Burro Spring and Pasture Canyon Spring, but a decreasing trend was statistically significant (p<0.05) at Moenkopi School Spring and Unnamed Spring near Dennehotso, Arizona. Discharge at Burro Spring has remained relatively constant since it was first measured in the 1980s, and discharge at Pasture Canyon Spring has fluctuated for the period of record. Continuous records of surface-water discharge in the Black Mesa area were collected from streamflow-gaging stations at the following sites: Moenkopi Wash at Moenkopi 09401260 (1976–2021), Dinnebito Wash near Sand Springs 09401110 (1993–2020), Polacca Wash near Second Mesa 09400568 (1994–2020), and Pasture Canyon Springs 09401265 (2004–2021). Median winter flows (November through February) of each winter were used as an estimate of the amount of groundwater discharge at the above-named sites. For the period of record, the median winter flows have generally remained constant at Polacca Wash and Pasture Canyon Springs, whereas a decreasing trend was observed at Moenkopi Wash and Dinnebito Wash. In 2020 and 2021, water samples were collected from a total of four springs in the Black Mesa area and analyzed for selected chemical constituents. Results from the four springs were compared with previous analyses from the same springs. Dissolved solids, chloride, and sulfate concentrations increased at Moenkopi School Spring during the more than 30 years of record at that site. Concentrations of dissolved solids and sulfate at Pasture Canyon Spring have not varied significantly (p>0.05) since the early 1980s, and there is no increasing or decreasing trend in those data. However, concentrations of chloride from Pasture Canyon Spring show a diminishing trend. Concentrations of dissolved solids, chloride, and sulfate at Unnamed Spring near Dennehotso have varied for the period of record, but there is no statistical trend in the data. Concentrations of dissolved solids at Burro Spring have varied for the period of record, but there is no statistical trend in the data. However, concentrations of chloride and sulfate from Burro Spring show a trend towards lower concentrations.

Arizona↗

USGS2009

Aquifer chemistry and transport processes in the zone of contribution to a public-supply well in Woodbury, Connecticut, 2002-06

A glacial aquifer system in Woodbury, Connecticut, was studied to identify factors that affect the groundwater quality in the zone of contribution to a community public-supply well. Water samples were collected during 2002-06 from the public-supply well and from 35 monitoring wells in glacial stratified deposits, glacial till, and fractured bedrock. The glacial aquifer is vulnerable to contamination from a variety of sources due to the short groundwater residence times and the urban land use in the contributing recharge area to the public-supply well. The distribution and concentrations of pH, major and trace elements, stable isotope ratios, recharge temperatures, dissolved organic carbon (DOC), and volatile organic compounds (VOCs), and the oxidation-reduction (redox) conditions, were used to identify recharge source areas, aquifer source material, anthropogenic sources, chemical processes, and groundwater-flow paths from recharge areas to the public-supply well, PSW-1. The major chemical sources to groundwater and the tracers or conditions used to identify them and their processes throughout the aquifer system include (1) bedrock and glacial stratified deposits and till, characterized by high pH and concentrations of sulfate (SO42-), bicarbonate, uranium (U), radon-222, and arsenic (As) relative to those of other wells, reducing redox conditions, enriched delta sulfur-34 (d34S) and delta carbon-13 (d13C) values, depleted delta oxygen-18 (d18O) and delta deuterium (dD) values, calcite near saturation, low recharge temperatures, and groundwater ages of more than about 9 years; (2) natural organic matter, either in sediments or in an upgradient riparian zone, characterized by high concentrations of DOC or manganese (Mn), low concentrations of dissolved oxygen (DO) and nitrate (NO3-), enriched d34S values, and depleted d18O and dD values; (3) road salt (halite), characterized by high concentrations of sodium (Na), chloride (Cl-), and calcium (Ca), and indicative chloride/bromide (Cl:Br) mass concentration ratios; (4) septic-system leachate, characterized by high concentrations of NO3-, DOC, Na, Cl-, Ca, and boron (B), delta nitrogen-15 (d15N) and d18O values, and indicative Cl:Br ratios; (5) organic solvent spills, characterized by detections of perchloroethene (PCE), trichloroethene (TCE), and 1,1-dichloroethene (1,1-DCE); (6) gasoline station spills, characterized by detections of fuel oxygenates and occasionally benzene; and (7) surface-water leakage, characterized by enriched d18O and dD values and sometimes high DOC and Mn-reducing conditions. Evaluation of Cl- concentrations and Cl:Br ratios indicates that most samples were composed of mixtures of groundwater and some component of road salt or septic-system leachate. Leachate from septic-tank drainfields can cause locally anoxic conditions with NO3- concentrations of as much as 19 milligrams per liter (mg/L as N) and may provide up to 15 percent of the nitrogen in water from well PSW-1, based on mixing calculations with d15N of NO3-. Most of the water that contributes to PSW-1 is young (less than 7 years) and derived from the glacial stratified deposits. Typically, groundwater is oxic, but localized reducing zones that result from abundances of organic matter can affect the mobilization of trace elements and the degradation of VOCs. Groundwater from fractured bedrock beneath the valley bottom, which is old (more than 50 years), and reflects a Mn-reducing to methanic redox environment, constitutes as much as 6 percent of water samples collected from monitoring wells screened at the bottom of the glacial aquifer. Dissolved As and U concentrations generally are near the minimum reporting level (MRL) (0.2 micrograms per liter or ?g/L and 0.04 ?g/L, respectively), but water from a few wells screened in glacial deposits, likely derived from underlying organic-rich Mesozoic rocks, contain As concentrations up to 7 ?g/L. At one location, concentrations of As and U were high

Scientific Investigations Report↗

USGS2022

Characterization of and temporal changes in groundwater quality of the Upper Black Squirrel Creek Basin, El Paso County, Colorado, 2018–20

In 2018–20, the U.S. Geological Survey, in cooperation with Upper Black Squirrel Creek Ground Water Management District, sampled 48 wells for Phase III of a multiphase plan investigating groundwater quality in the alluvial aquifer of the Upper Black Squirrel Creek Basin (UBSB), El Paso County, Colorado. Results for samples collected from October to December each year were used to assess spatial and temporal changes in groundwater quality and to differentiate sources of nitrate. Groundwater was predominantly classified as mixed-cation and mixed-anion water type in the aquifer, with variable chemistry along the periphery. Concentrations of constituents in groundwater were generally less than regulatory standards, except for nitrate in four wells. Isotopes of nitrogen and oxygen in nitrate identified four different potential sources or processes affecting nitrate in the alluvial aquifer: naturally occurring nitrate from soils, nitrate from animal and (or) human waste, and an unknown source, along with evidence of denitrification. Pharmaceutical compounds and personal-care products were detected in seven wells, with three wells having multiple detections. Stable isotopes of water indicated variability in seasonality of recharge throughout the UBSB alluvial aquifer. Nitrate concentrations from the 1984 study and the 1996 study were compared to the more recent concentrations in the 2013 study and the 2018–20 study. The northern one-third of the UBSB alluvial aquifer had a statistically significant increase in nitrate concentration from the 2013 study to the 2018–20 study, but no change was shown from the 1984 study to the 1996 study. The opposite was found true for the southern two-thirds of the UBSB alluvial aquifer with no statistically significant difference in nitrate concentration from the 2013 study to the 2018–20 study. Analysis of temporal changes indicated an increase in median and maximum nitrate concentrations from the 2013 study to the 2018–20 study throughout the UBSB alluvial aquifer. Continued sampling of wells in the UBSB would be beneficial to better determine temporal changes in groundwater quality, characterize human effects on water quality, and understand characteristics of the alluvial aquifer pertaining to sustainability of the resource.

Colorado↗

USGS1988

Preliminary appraisal of the effects of land use on water quality in stratified-drift aquifers in Connecticut

The stratified-drift aquifers that underlie 7.9 sq mi of the Potatuck and 12.7 sq mi of the Pomperaug River valley, CT, consist primarily of sand and gravel deposits up to 150 ft thick. Average horizontal hydraulic conductivity of the stratified drift ranges from 20 to 170 ft/day, and groundwater flows through the aquifers at an average rate of 2 to 3 ft/day. Land use in the study areas is changing from primarily undeveloped or agricultural lands to expanding residential, commercial, and light-industrial uses. Water quality data for 1923-82, that include 127 partial chemical analyses of groundwater samples from 38 wells in the two aquifers, were augmented by sampling during 1985 from 21 new stainless-steel wells for selected major inorganic constituents, trace elements, and organic chemicals. Nonparametric statistical procedures were used to compare the water quality data from four land use areas, for the two sampling periods, and between the two aquifers. Human activities associated with agricultural, residential, and industrial/commercial land uses have affected the quality of water in the stratified-drift aquifers underlying these land use areas. Statistical comparisons of water quality data between land use areas show significant differences, with the apparent relations between land use and groundwater being: (1) Median concentrations of most groundwater constituents are smallest in undeveloped areas; (2) Groundwater in agricultural areas has the largest median sulfate and total ammonia plus organic nitrogen concentrations. Agricultural areas are also characterized by groundwater with significantly greater median specific conductance, noncarbonate hardness, carbon dioxide, and magnesium concentrations relative to undeveloped areas; (3) Median concentrations of most major inorganic constituents, excluding potassium, sulfate, and total ammonia plus organic nitrogen, are greater in groundwater in residential areas than in undeveloped and agricultural areas. (4) Groundwater in industrial/commercial areas has the greatest median specific conductance, pH, carbon dioxide, calcium, magnesium, chloride bicarbonate, dissolved solids, boron, and strontium concentrations. (Author 's abstract)

Connecticut↗

USGS2010

Groundwater-quality data for the Sierra Nevada study unit, 2008: Results from the California GAMA program

Groundwater quality in the approximately 25,500-square-mile Sierra Nevada study unit was investigated in June through October 2008, as part of the Priority Basin Project of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The GAMA Priority Basin Project is being conducted by the U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board (SWRCB). The Sierra Nevada study was designed to provide statistically robust assessments of untreated groundwater quality within the primary aquifer systems in the study unit, and to facilitate statistically consistent comparisons of groundwater quality throughout California. The primary aquifer systems (hereinafter, primary aquifers) are defined by the depth of the screened or open intervals of the wells listed in the California Department of Public Health (CDPH) database of wells used for public and community drinking-water supplies. The quality of groundwater in shallower or deeper water-bearing zones may differ from that in the primary aquifers; shallow groundwater may be more vulnerable to contamination from the surface. In the Sierra Nevada study unit, groundwater samples were collected from 84 wells (and springs) in Lassen, Plumas, Butte, Sierra, Yuba, Nevada, Placer, El Dorado, Amador, Alpine, Calaveras, Tuolumne, Madera, Mariposa, Fresno, Inyo, Tulare, and Kern Counties. The wells were selected on two overlapping networks by using a spatially-distributed, randomized, grid-based approach. The primary grid-well network consisted of 30 wells, one well per grid cell in the study unit, and was designed to provide statistical representation of groundwater quality throughout the entire study unit. The lithologic grid-well network is a secondary grid that consisted of the wells in the primary grid-well network plus 53 additional wells and was designed to provide statistical representation of groundwater quality in each of the four major lithologic units in the Sierra Nevada study unit: granitic, metamorphic, sedimentary, and volcanic rocks. One natural spring that is not used for drinking water was sampled for comparison with a nearby primary grid well in the same cell. Groundwater samples were analyzed for organic constituents (volatile organic compounds [VOC], pesticides and pesticide degradates, and pharmaceutical compounds), constituents of special interest (N-nitrosodimethylamine [NDMA] and perchlorate), naturally occurring inorganic constituents (nutrients, major ions, total dissolved solids, and trace elements), and radioactive constituents (radium isotopes, radon-222, gross alpha and gross beta particle activities, and uranium isotopes). Naturally occurring isotopes and geochemical tracers (stable isotopes of hydrogen and oxygen in water, stable isotopes of carbon, carbon-14, strontium isotopes, and tritium), and dissolved noble gases also were measured to help identify the sources and ages of the sampled groundwater. Three types of quality-control samples (blanks, replicates, and samples for matrix spikes) each were collected at approximately 10 percent of the wells sampled for each analysis, and the results for these samples were used to evaluate the quality of the data for the groundwater samples. Field blanks rarely contained detectable concentrations of any constituent, suggesting that contamination from sample collection, handling, and analytical procedures was not a significant source of bias in the data for the groundwater samples. Differences between replicate samples were within acceptable ranges, with few exceptions. Matrix-spike recoveries were within acceptable ranges for most compounds. This study did not attempt to evaluate the quality of water delivered to consumers; after withdrawal from the ground, groundwater typically is treated, disinfected, or blended with other waters to maintain water quality. Regulatory benchmarks apply to finished drinking water that is served to the consumer, not to untreated groundwater. However, to provide some context for the results, concentrations of constituents measured in the groundwater were compared with regulatory and nonregulatory health-based benchmarks established by the U.S. Environmental Protection Agency (USEPA) and CDPH and with nonregulatory aesthetic and technical benchmarks established by CDPH. Comparisons between data collected for this study and drinking-water benchmarks are for illustrative purposes only and do not indicate compliance or noncompliance with regulatory benchmarks. All organic constituents and most inorganic constituents that were detected in groundwater samples from the 30 primary grid wells in the Sierra Nevada study unit were detected at concentrations less than drinking-water benchmarks. Of the 150 organic and special-interest constituents analyzed, 21 were detected in groundwater samples; all concentrations were less than regulatory and nonregulatory health-based benchmarks, and most were less than 1/10th of benchmark levels. One or more organic constituents were detected in 37 percent of the primary grid wells, and perchlorate was detected in 27 percent of the primary grid wells. Most samples analyzed for inorganic and radioactive constituents had concentrations or activities less than regulatory and nonregulatory health-based benchmarks. Nutrients were not detected at concentrations greater than health-based benchmarks. Six of the 30 primary grid wells (20 percent) and 7 of the 53 lithologic grid wells had concentrations of or activities for one or two constituents that were greater than the benchmarks. Constituents present in one or more samples at concentrations or activities greater than health-based benchmarks were arsenic (5 wells, MCL-US), gross alpha particle activity (4 wells, MCL-US), boron (2 wells, NL-CA), fluoride (1 well, MCL-CA), and selenium (1 well, MCL-US). Two of the wells that had high gross alpha particle activities had uranium concentrations (MCL-CA) and uranium activities (MCL-CA) greater than the benchmark levels. Four of the 29 samples analyzed had activities of radon-222 greater than the proposed alternative MCL-US. Most samples analyzed for inorganic constituents that had nonregulatory, aesthetic-based benchmarks (SMCLs) had concentrations less than these benchmarks. Total dissolved solids concentrations were less than the upper SMCL-CA in all 83 primary and lithologic grid well samples, and TDS concentrations were less than the recommended SMCL-CA in 79 of these samples. Manganese concentrations were greater than the SMCL-CA in 2 of the 30 primary grid wells (7 percent) and in 6 of the 53 lithologic grid wells, and iron concentrations were greater than the SMCL-CA in the same 2 primary grid wells and in 5 of the same lithologic grid wells.

California↗