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At least 1,351 records · Page 75Linked to original sources
USGS2026

Evaluation of water quality in the Langford Valley–Irwin Groundwater Subbasin, Fort Irwin National Training Center, California, 1993–2019

The U.S. Army Fort Irwin National Training Center (NTC), 120 miles northeast of Los Angeles in the Mojave Desert of California, obtains its potable water supply from the Bicycle Valley and Langford Valley groundwater basins; Langford Valley groundwater basin is further subdivided into the Langford Well Lake and Irwin groundwater subbasins. The Irwin groundwater subbasin contains younger, unconsolidated deposits that have a saturated thickness of as much as 200 feet (ft) and a lower aquifer within older unconsolidated deposits as thick as 650 ft. Groundwater recharge under predevelopment conditions (before 1941) occurred primarily from infiltration of intermittent streamflow in small washes that cross the Irwin groundwater subbasin. Since that time, groundwater recharge has increased because of growth of the NTC in recent years and as a result of other processes, including (1) infiltration of treated wastewater into the aquifer through ponds near the NTC wastewater treatment facility (WWTF) and (2) infiltration of imported water and treated wastewater used for landscape irrigation at base housing and athletic fields. Water samples were collected from 17 wells and analyzed for field parameters, chemical constituents, and isotope composition in the Irwin groundwater subbasin between 2014 and 2019. These data were supplemented with water-chemistry data collected during 1993–95 and at other times if available. Between 1993–95 and 2015–19, median dissolved solids and nitrate concentrations in water from wells in the Irwin groundwater subbasin increased from 620 to 1,030 milligrams per liter (mg/L) and from 2.8 to 4.5 mg/L as nitrogen, respectively. After 2014, dissolved solids and nitrate concentrations in water from wells near the NTC WWTF decreased as a result of changes in source water quality attributable to reverse osmosis of treated drinking water delivered within the Irwin groundwater subbasin and to increased levels of treatment at the NTC WWTF. Based on delta oxygen-18 and delta deuterium isotope data, increases in dissolved solids concentrations in water from most wells were consistent with evaporation prior to recharge and mobilization of soluble salts from the unsaturated zone. Arsenic and fluoride concentrations in water from wells decreased between 1993–95 and 2015–19 as the basin filled with treated wastewater, but 2015–19 concentrations generally exceeded the California State Water Resources Control Board maximum contaminant levels of 10 micrograms per liter for arsenic and 2 mg/L for fluoride. Most groundwater in the Irwin groundwater subbasin has unadjusted carbon-14 ages ranging from 18,400 to 12,350 years before present. However, water from well 10E3, located along the wash near the subbasin outflow in the southeastern part of the Irwin groundwater subbasin, contained measurable tritium, which is consistent with infiltration of intermittent streamflow and groundwater recharge from the wash after 1952. Chemical and isotopic data indicate that treated wastewater is present in water from most wells in the upper aquifer that underlies the Irwin groundwater subbasin. Wells were not sampled to adequately determine the extent of treated wastewater and changes in water quality within the lower aquifer that underlies the Irwin groundwater subbasin.

California↗
USGS2021

Middle Holocene hydrologic changes catalyzed by river avulsion in Big Soda Lake, Nevada, USA

Big Soda Lake is a 63 m deep, 1.6 km 2 maar lake in the Great Basin of Nevada, USA. Water level in the lake is controlled by groundwater inputs from the surrounding aquifer and the only surface water input is rainfall, which is negligible. A core taken in 2010 records an 8.75 m depositional history of the lake. A radiocarbon date on fossil pollen from 8.4 m below the sediment water interface (BSWI) of 14,740 (+1120/−825) cal yr BP suggests that the core may cover the latest Pleistocene and Holocene depositional history of the lake. Stable isotope values of oxygen and carbon (δ 18 O and δ 13 C) on authigenic calcite, diatom assemblages, and sedimentary structures all show consistent hydrological change from initially saline water at the bottom of the core to fresh/brackish water at about 6 m BWSI, back to saline water at 4.3 m. At 4.3 m depth, the bedding and color of the core change abruptly, and the stable- isotope and diatom assemblages indicate a consistently hypersaline lake until near the top of the core, when fresh water entered the lake due to irrigation and canal building in the twentieth century. The stable isotopes of the calcite abruptly change from inversely varying isotopic compositions below 4.3 m depth to covarying above. This break between relatively fresh and saline conditions in the lake occurs during the middle Holocene, although the exact timing of the transition is unknown due to variability in the 14 C age determinations. The cause for such an abrupt change is difficult to explain through climate shifts, as evidence suggests climate in the Great Basin was different from what the Big Soda Lake record indicates in the Early Holocene. It is hypothesized that the Walker River flowed to the Carson River basin before 5600 cal yr BP, with water either flowing directly into the lake or raising the groundwater table sufficiently to freshen Big Soda Lake. The initial increase in salinity likely was caused by decreased flow of the Walker River due to Middle Holocene aridity. The lake level lowered slowly, and more saline conditions prevailed until 4.3 m depth when water from the Walker River stopped flowing into the Carson River basin. Above 4.3 m depth, diatom and isotopic evidence indicates that the lake became consistently saline. The isotopic and diatom assemblage transitions observed in Big Soda Lake sediment are not consistent with climate reconstructions and demonstrate that hydrologic shifts in a basin can be an important driver of change regardless of climatic conditions. However, climate shifts may also play a role in the hydrologic changes by supplying more or less water to river courses that may induce river avulsion.

Nevada↗
USGS1984

The ground-water resources in the Ross Barnett Reservoir area, Mississippi

The Ross Barnett Reservoir area occupies about 78 sq mi of a 490 sq mi study area northeast of the City of Jackson, MS. For several years, water use in the area has increased and during 1983 about 0.57 mil gal/day were obtained from groundwater sources. Virtually all groundwater in the area is used for public supplies. The principal aquifers currently used in the area are in the Sparta Sand and Cockfield Formations. The Sparta Sand is the most intensively developed and generally the highest yielding aquifer in the study area. Water level declines have averaged 2 to 3 ft/yr since 1940. The principal source of groundwater recharge to the aquifers is precipitation on outcrops of permeable strata northeast of the area. The base of freshwater is at the base of the Meridian-upper Wilcox aquifer except in the extreme northeast part of the area where the lower Wilcox aquifer contains freshwater. Water from the aquifers is suitable for public supply use without treatment except in a few places where iron concentrations are high, at from 0.10 to 9.3 mg/L. Excessive color is also a problem in the water from some wells in the area. Color was 20 units or greater in 8 of 25 wells sampled. (Author 's abstract)

Water-Resources Investigations Report↗
USGS2022

Assessment of well yield, dominant fractures, and groundwater recharge in Wake County, North Carolina

A cooperative study led by the U.S. Geological Survey and Wake County Environmental Services was initiated to characterize the fractured-rock aquifer system and assess the sustainability of groundwater resources in and around Wake County. This report contributes to the development of a comprehensive groundwater budget for the study area, thereby helping to enable resource managers to make sound and sustainable water-supply and water-use decisions. Construction information was used to analyze the well depth, casing depth, and reported well yield of more than 7,500 inventoried wells. The median well depth and casing depth were 265 feet (ft) below land surface (bls) and 68 ft bls, respectively, and the median well yield was 10 gallons per minute. Generally, well yield increased with depth to around 200 ft bls and then began to decrease with depth within the fractured-rock aquifer. Borehole geophysical logging methods were used to characterize the fractured-rock aquifer by mapping the orientation of geologic structures within the subsurface. Structure measurements were made on resulting log data and mapped to observed general spatial trends within the regional groundwater system and more distinct hydrogeologic units. Many of the fractures observed within the borehole logs are steeply dipping across Wake County, although open fractures with shallow dip angles were also observed in most rock classes. Regional geologic structural trends were observed in proximity to the Jonesboro Fault. Potential groundwater recharge in the study area was estimated using a Soil-Water-Balance (SWB) model, as well as using base flow hydrograph separation. The SWB model calculated net infiltration below the root zone for 1981 through 2019 for a 5,402-square-mile area that extends to the counties surrounding Wake County. The mean annual net infiltration rate for the 39-year period was about 8.6 inches per year for the study area. The mean annual net infiltration results from the SWB model were comparable to annual base flow estimates using the PART hydrograph-separation method at six U.S. Geological Survey streamgages within the study area. Mean annual base flow for all six drainage basins was near 7.5 inches per year and estimates ranged from 2.9 to 8.9 inches. Comparisons of mean annual potential recharge from the SWB model and base flow estimates were generally within 2 inches, except during high flows for most of the drainage basins in the study area.

North Carolina↗
USGS2013

Relation between organic-wastewater compounds, groundwater geochemistry, and well characteristics for selected wells in Lansing, Michigan

In 2010, groundwater from 20 Lansing Board of Water and Light (BWL) production wells was tested for 69 organic-wastewater compounds (OWCs). The OWCs detected in one-half of the sampled wells are widely used in industrial and environmental applications and commonly occur in many wastes and stormwater. To identify factors that contribute to the occurrence of these constituents in BWL wells, the U.S. Geological Survey (USGS) interpreted the results of these analyses and related detections of OWCs to local characteristics and groundwater geochemistry. Analysis of groundwater-chemistry data collected by the BWL during routine monitoring from 1969 to 2011 indicates that the geochemistry of the BWL wells has changed over time, with the major difference being an increase in sodium and chloride. The concentrations of sodium and chloride were positively correlated to frequency of OWC detections. The BWL wells studied are all completed in the Saginaw aquifer, which consists of water-bearing sandstones of Pennsylvanian age. The Saginaw aquifer is underlain by the Parma-Bayport aquifer, and overlain by the Glacial aquifer. Two possible sources of sodium and chloride were evaluated: basin brines by way of the Parma-Bayport aquifer, and surficial sources by way of the Glacial aquifer. To determine if water from the underlying aquifer had influenced well-water geochemistry over time, the total dissolved solids concentration and changes in major ion concentrations were examined with respect to well depth, age, and pumping rate. To address a possible surficial source of sodium and chloride, 25 well, aquifer, or hydrologic characteristics, and 2 groundwater geochemistry variables that might influence whether, or the rate at which, water from the land surface could reach each well were compared to OWC detections and well chemistry. The statistical tests performed during this study, using available variables, indicated that reduced time of travel of water from the land surface to the well opening was significantly correlated with detections of OWCs. No specific well or aquifer characteristic was correlated with OWC detections; however, wells with detections tended to have less modeled confining material thickness (as simulated in the regional groundwater flow model), which is an estimate of the amount of clay or shale between the Glacial and Saginaw aquifers. Additional analyses and collection of other data would be required to more conclusively identify the source and to determine the potential vulnerability of other wells because each BWL well may have a somewhat unique set of characteristics that governs its response to pumping. Therefore, it is possible that a relevant explanatory variable was not included in this analysis. The current patterns of geochemistry, and the relation between these patterns and volume of pumpage for the BWL wells, indicates other wells may be susceptible to OWCs in the future.

Michigan↗
USGS2015

Assessment of aquifer properties, evapotranspiration, and the effects of ditching in the Stoney Brook watershed, Fond du Lac Reservation, Minnesota, 2006-9

The U.S. Geological Survey, in cooperation with the Fond du Lac Band of Lake Superior Chippewa, assessed hydraulic properties of geologic material, recharge, and evapotranspiration, and the effects of ditching on the groundwater resources in the Stoney Brook watershed in the Fond du Lac Reservation. Geologic, groundwater, and surface-water data were collected during 2006–9 to estimate hydrologic properties in the watershed. Streamflow and groundwater levels in the shallow glacial deposits in the Stoney Brook watershed were analyzed to estimate groundwater-flow directions, groundwater recharge, and evapotranspiration within the watershed and to assess the effect of ditches on surrounding groundwater resources. Groundwater, streamflow, and precipitation data collected during the study (2006–9) can be used to update the U.S. Department of Agriculture’s Natural Resource Conservation Service and Fond du Lac Resource Management Division surface-water models, which are used to evaluate the effect of proposed adjustments to the ditching system on streamflow on wild rice production and aquatic habitats. Specific yields calculated from the well water levels ranged from 0.11 to 0.40, and hydraulic conductivities determined from water levels measured during well slug tests ranged from 1 to 7 feet per day. The values for specific yields were similar to values obtained in other studies done in glacial materials of similar composition in Minnesota. The higher hydraulic conductivity estimate (7 feet per day) was similar to lower hydraulic conductivities estimated in another hydrologic study conducted in Carlton County, Minnesota. The installation of drainage ditches in the Stoney Brook watershed has reduced water levels in lakes connected to the ditch system, and has locally reduced groundwater levels in shallow groundwater adjacent to the ditches and lakes. Differences in near-ditch groundwater hydrographs relative to far-ditch groundwater hydrographs indicate that the effect of the ditches on groundwater is only localized to near-ditch areas. These hydrograph differences resulted in large differences between recharge estimated at wells near and far from ditches. In this study, recharge estimated at wells within 50 feet of a ditch was influenced by ditch-water levels. Annual groundwater recharge estimates from water levels and streamflows during 2006–9 ranged from 0.36 to 34.8 inches, and varied with climate, geology, and well location relative to ditches. The higher recharge estimates were determined from analysis of groundwater levels in wells near the ditches because the shallow groundwater in these wells received both infiltration from ditches and areal groundwater recharge from precipitation. The water-table fluctuation method using a manual groundwater recession approach for wells far from ditches provided the best estimates of areal groundwater recharge to the shallow glacial aquifer because water levels in these wells were not affected by water infiltrating from ditches (bank storage). For wells more than 400 feet from ditches, mean annual areal groundwater recharge estimates using the manual groundwater recession approach for wells screened mostly in outwash sands during 2007, 2008, and 2009 ranged from 4.47 to 18.6 inches (wells 5, 7, 13, 14 and 15), and ranged from 0.43 to 2.85 inches for wells screened mostly in clayey sand or sandy clay (wells 9 and 16). Recharge estimates at wells far from ditches were similar to basinwide recharge estimates from streamflow. Daily fluctuations in water levels in two wells indicated that the evapotranspiration extinction depth in the Stoney Brook watershed is approximately 4.6 to 6 feet below the land surface. A polynomial regression fit of the daily evapotranspiration rates during 2006–9 for well 1 produced a total evapotranspiration estimate of 16.1 inches from June 26 to October 6 for every year. Evapotranspiration estimated from daily water-level fluctuations in wells near ditches is relatively high. The ditch-water surface allowed for relatively high evaporation compared to the land surface, which, with a good hydraulic connection to surrounding groundwater, resulted in relatively high fluctuations in daily groundwater levels near ditches, resulting in high evapotranspiration estimates.

Minnesota↗
USGS2004

Sources of nitrate contamination and age of water in large karstic springs of Florida

In response to concerns about the steady increase in nitrate concentrations over the past several decades in many of Florida's first magnitude spring waters (discharge ???2.8 m3/s), multiple isotopic and other chemical tracers were analyzed in water samples from 12 large springs to assess sources and timescales of nitrate contamination. Nitrate-N concentrations in spring waters ranged from 0.50 to 4.2 mg/L, and ??15N values of nitrate in spring waters ranged from 2.6 to 7.9 per mil. Most ??15N values were below 6 per mil indicating that inorganic fertilizers were the dominant source of nitrogen in these waters. Apparent ages of groundwater discharging from springs ranged from 5 to about 35 years, based on multi-tracer analyses (CFC-12, CFC-113, SF6, 3H/3He) and a piston flow assumption; however, apparent tracer ages generally were not concordant. The most reliable spring-water ages appear to be based on tritium and 3He data, because concentrations of CFCs and SF6 in several spring waters were much higher than would be expected from equilibration with modern atmospheric concentrations. Data for all tracers were most consistent with output curves for exponential and binary mixing models that represent mixtures of water in the Upper Floridan aquifer recharged since the early 1960s. Given that groundwater transit times are on the order of decades and are related to the prolonged input of nitrogen from multiple sources to the aquifer, nitrate could persist in groundwater that flows toward springs for several decades due to slow transport of solutes through the aquifer matrix.

Environmental Geology↗
USGS2010

Analysis of the Shallow Groundwater Flow System at Fire Island National Seashore, Suffolk County, New York

Fire Island National Seashore (FIIS) occupies 42 kilometers of the barrier island for which it is named that lies off the southern shore of Suffolk County, N.Y. Freshwater in the highly permeable, sandy aquifer underlying Fire Island is bounded laterally by marine surface waters and at depth by saline groundwater. Interspersed throughout FIIS are 17 pre-existing residential communities that in summer months greatly increase in population through the arrival of summer residents and vacationers; in addition, the National Park Service (NPS) has established several facilities on the island to accommodate visitors to FIIS. The 2.2 million people estimated by the NPS to visit Fire Island annually impact groundwater quality through the release of waste-derived contaminants, such as nutrients, pathogens, and organic compounds, into the environment. Waste-contaminated groundwater can move through the aquifer and threaten the ecological health of the adjacent back-barrier estuaries to which much of the groundwater ultimately discharges. In 2004, the U.S. Geological Survey (USGS), in cooperation with the NPS, began a 3-year investigation to (1) collect groundwater levels and water-quality (nutrient) samples, (2) develop a three-dimensional model of the shallow (water-table) aquifer system and adjacent marine surface waters, and (3) calculate nitrogen loads in simulated groundwater discharges from the aquifer to back-barrier estuaries and the ocean. The hydrogeology of the shallow aquifer system was characterized from the results of exploratory drilling, geophysical surveying, water-level monitoring, and water-quality sampling. The investigation focused on four areas-the communities of Kismet and Robbins Rest, the NPS Visitor Center at Watch Hill, and the undeveloped Otis Pike Fire Island High Dune Wilderness. Thirty-five observation wells were installed within FIIS to characterize subsurface hydrogeology and establish a water-table monitoring network in the four study areas. A variable-density model of the shallow aquifer system and adjacent marine surface waters was developed to simulate groundwater flow patterns and rates. Nitrogen loads from the shallow aquifer system were calculated from representative total nitrogen (TN) concentrations and simulated groundwater discharges to back-barrier estuaries and the ocean. The model simulates groundwater directions, velocities, and discharge rates under 2005 mean annual conditions. Groundwater budgets were developed for recharge areas of similar land use that contribute freshwater to back-barrier estuaries, the ocean, and subsea-discharge zones. Total freshwater discharge from the shallow aquifer system is about 43,500 cubic meters per day (m3/d) (79.8 percent) to back-barrier estuaries and about 10,200 m3/d (18.7 percent) to the ocean; about 836 m3/d (1.5 percent) may exit the system as subsea underflow. The total contribution of fresh groundwater to shoreline discharge zones amounts to about 53,700 m3/d (98.5 percent). The median age of freshwater discharged to back-barrier estuaries and the ocean was 3.4 years, and the 95th-percentile age was 20 years. The TN concentrations and loads under 2005 mean annual conditions for areas that contribute fresh groundwater to back-barrier estuaries and the ocean were calculated for the principal land uses on Fire Island. The overall TN load from the shallow aquifer system to shoreline discharge zones is about 16,200 kilograms per year (kg/yr) (82.2 percent) to back-barrier estuaries and about 3,500 kg/yr (17.8 percent) to the ocean. The overall TN load to marine surface waters amounts to about 19,700 kg/yr-roughly 6 percent of the annual TN load from shallow groundwater entering the South Shore Estuary Reserve (SSER) from the Suffolk County mainland, which is about 345,000 kg/yr. In contrast to the TN load from shallow groundwater for the SSER watershed, which annually yields about 353 kilograms per square kilometer (kg/km2), the overall TN loa

Scientific Investigations Report↗
USGS2022

Areas contributing recharge to priority wells in valley-fill aquifers in the Neversink River and Rondout Creek drainage basins, New York

In southeastern New York, the villages of Ellenville, Wurtsboro, Woodridge, the hamlet of Mountain Dale, and surrounding communities in the Neversink River and Rondout Creek drainage basins rely on wells that pump groundwater from valley-fill glacial aquifers for public water supply. Glacial aquifers are vulnerable to contamination because they are highly permeable and have a shallow depth to water table. To protect the quality of these water resources, water managers need accurate information about the areas that contribute recharge to production wells that pump from these aquifers. The New York State Department of Environmental Conservation and the New York State Department of Health designated eight priority wells in this region for which water supply protection is of primary concern. The U.S. Geological Survey, in cooperation with the New York State Department of Environmental Conservation and the New York State Department of Health, began an investigation in 2019 with the general objectives of (1) improving understanding of regional groundwater-flow system, (2) delineating areas contributing recharge to eight priority production wells, and (3) quantifying the uncertainty of these contributing areas in a probabilistic way that can be used to inform decision-making related to priority well source-water protection. To complete these objectives, a MODFLOW 6 groundwater model was created encompassing the eight priority wells and the surrounding flow system, which includes parts of the Neversink River and Rondout Creek Basins in Sullivan County and Ulster County, New York. The model was built using Python tools (such as flopy , modflow-setup , and sfrmaker ) that facilitate transparent and repeatable model development using existing datasets. The model parameters were estimated with a stepwise approach using an iterative ensemble smoother implementation of the Parameter ESTimation software PEST++ (version 5.0.0). We evaluated initial “best guess” parameter bounds with a prior Monte Carlo analysis. Results of the first prior Monte Carlo analysis were used to make informed adjustments to model parameter bounds (typically resulting in expanded bounds), and a second prior Monte Carlo analysis was run to identify improved ranges for model parameters during history matching. The history matching effort produced an ensemble of parameter values for the groundwater-flow model that spans the range of values within prior uncertainty bounds. The ensemble is informed by the historical observation data, within a reasonable range of uncertainty on those observations. This history-matched ensemble was used in a particle tracking Monte Carlo analysis to delineate the areas contributing recharge to priority wells. The groundwater-flow and particle tracking (MODPATH7) models were run once for each ensemble member. Deterministic contributing areas computed for each ensemble member were aggregated to produce maps showing the probability that a location contributes recharge to priority wells. Finally, the particle tracking Monte Carlo analysis was repeated for six pumping scenarios, representing a wide range of possible pumping levels, to incorporate uncertainty in future pumping rates related to population growth or other management decisions. Increasing pumping rates generally led to larger contributing recharge areas and larger areas of high probability that a location contributes recharge to priority wells. These maps show the overall uncertainty of the areas contributing recharge to priority wells in the study area and provide a tool for risk-based decision making for protection of well source water.

New York↗
USGS2004

The influence of groundwater chemistry on arsenic concentrations and speciation in a quartz sand and gravel aquifer

We examined the chemical reactions influencing dissolved concentrations, speciation, and transport of naturally occurring arsenic (As) in a shallow, sand and gravel aquifer with distinct geochemical zones resulting from land disposal of dilute sewage effluent. The principal geochemical zones were: (1) the uncontaminated zone above the sewage plume [350 μ M dissolved oxygen (DO), p H 5.9]; (2) the suboxic zone (5 μ M DO, p H 6.2, elevated concentrations of sewage-derived phosphate and nitrate); and (3) the anoxic zone [dissolved iron(II) 100–300 μ M, p H 6.5–6.9, elevated concentrations of sewage-derived phosphate]. Sediments are comprised of greater than 90% quartz but the surfaces of quartz and other mineral grains are coated with nanometer-size iron (Fe) and aluminum (Al) oxides and/or silicates, which control the adsorption properties of the sediments. Uncontaminated groundwater with added phosphate (620 μ M) was pumped into the uncontaminated zone while samples were collected 0.3 m above the injection point. Concentrations of As(V) increased from below detection (0.005 μ M) to a maximum of 0.07 μ M during breakthrough of phosphate at the sampling port; As(III) concentrations remained below detection. These results are consistent with the hypothesis that naturally occurring As(V) adsorbed to constituents of the coatings on grain surfaces was desorbed by phosphate in the injected groundwater. Also consistent with this hypothesis, vertical profiles of groundwater chemistry measured prior to the tracer test showed that dissolved As(V) concentrations increased along with dissolved phosphate from below detection in the uncontaminated zone to approximately 0.07 and 70 μ M, respectively, in the suboxic zone. Concentrations of As(III) were below detection in both zones. The anoxic zone had approximately 0.07 μ M As(V) but also had As(III) concentrations of 0.07–0.14 μ M, suggesting that release of As bound to sediment grains occurred by desorption by phosphate, reductive dissolution of Fe oxides, and reduction of As(V) to As(III), which adsorbs only weakly to the Fe-oxide-depleted material in the coatings. Results of reductive extractions of the sediments suggest that As associated with the coatings was relatively uniformly distributed at approximately 1 nmol/g of sediment (equivalent to 0.075 ppm As) and comprised 20%-50% of the total As in the sediments, determined from oxidative extractions. Quartz sand aquifers provide high-quality drinking water but can become contaminated when naturally occurring arsenic bound to Fe and Al oxides or silicates on sediment surfaces is released by desorption and dissolution of Fe oxides in response to changing chemical conditions.

Geochemical Transactions↗
USGS1988

Appraisal of the water resources of the Big Sioux Aquifer, Moody County, South Dakota

The Big Sioux aquifer in Moody County is a 55 sq mi, water table aquifer hydraulically connected to the Big Sioux River. The average thickness is 22 ft and the maximum thickness is 54 ft. A digital model was developed to simulate groundwater flow in the Big Sioux aquifer in Moody County. The model was calibrated for steady-state conditions using average hydrologic conditions from 1970 through 1979. Steady-state simulated water levels from 11 wells averaged 0.4 ft higher than measured water levels. The model was calibrated for transient conditions using 1983 water levels. The average monthly difference in 27 observation wells between simulated and measured water levels was 2.63 ft. Sensitivity analyses showed that recharge rate and evapotranspiration extinction depth had the largest effect on simulated water levels. A 4-inch/year increase in the recharge rate caused simulated water levels to rise 1.7 ft. A 2.5-ft increase in the extinction depth caused simulated water levels to decline 0.8 ft. The calibrated model was used to simulate the effects of three hypothetical hydrologic situations. The first situation simulated the transient effects of 1983 pumpage under severe drought conditions. The second hypothetical situation simulated the steady-state effects of increased pumping at a rate of 5,200 acre-ft/year under average hydrologic conditions. The third hypothetical situation simulated the transient effects of pumping 5,200 acre-ft/year under severe drought conditions. Stored water was not depleted in any nodes after these simulations. (USGS)

Water-Resources Investigations Report↗
USGS1986

Water levels in major artesian aquifers of the New Jersey Coastal Plain, 1983

Water levels and changes in water levels in the major aquifers of the New Jersey Coastal Plain are documented. Water levels in 1,071 wells were measured in 1983, and are compared with 827 water level measurements made in the same wells in 1978. Increased groundwater withdrawals from the major artesian aquifers that underlie the New Jersey Coastal Plain have caused large cones of depression in the artesian heads. These cones are delineated on detailed potentiometric surface maps based on water level data collected in the fall of 1983. Hydrographs from observation wells show trends of water levels for the 6-year period of 1978 through 1983. The Potomac-Raritan-Magothy aquifer system is divided into the lower, middle, and upper aquifers. The potentiometric surfaces in these aquifers form large cones of depression centered in the Camden and Middlesex-Monmouth County areas. Measured water levels declined as much as 23 ft in these areas for the period of study. The lowest levels are 96 ft below sea level in Camden County and 91 ft below sea level in the Middlesex-Monmouth County area. Deep cones of depression in coastal Monmouth and Ocean counties in both the Englishtown aquifer system and Wenonah-Mount Laurel aquifer are similar in location and shape. This is because of an effective hydraulic connection between these aquifers. Measured water levels declined as much as 29 ft in the Englishtown aquifer system and 21 ft in the Wenonah-Mount Laurel aquifer during the period of study. The lowest levels are 249 ft below sea level in the Englishtown aquifer system and 196 ft below sea level in the Wenonah-Mount Laurel aquifer. Water levels in the Piney Point aquifer are as low as 75 ft below sea level at Seaside Park, Ocean County and 35 ft below sea level in southern Cumberland County. Water levels in Cumberland County are affected by large withdrawals of groundwater in Kent County, Delaware. Water levels in the Atlantic City 800 ft sand of the Kirkwood Formation define an extensive elongated cone of depression. Water levels are as low as 76 ft below sea level near Margate and Ventnor, Atlantic County. Measured water levels declined as much as 9 ft in the coastal region between Cape May County and Ocean County for the period of study. (Author 's abstract)

Water-Resources Investigations Report↗
USGS2010

Occurrence of phosphorus in groundwater and surface water of northwestern Mississippi

Previous localized studies of groundwater samples from the Mississippi River Valley alluvial (MRVA) aquifer have demonstrated that dissolved phosphorus concentrations in the aquifer are much higher than the national background concentration of 0.03 milligram per liter (mg/L) found in 400 shallow wells across the country. Forty-six wells screened in the MRVA aquifer in northwestern Mississippi were sampled from June to October 2010 to characterize the occurrence of phosphorus in the aquifer, as well as the factors that might contribute to high dissolved phosphorus concentrations in groundwater. Dissolved phosphorus concentrations ranged from 0.12 to 1.2 mg/L with a median concentration of 0.62 mg/L. The predominant subunit of the MRVA aquifer in northwestern Mississippi is the Holocene alluvium in which median dissolved phosphorus concentrations were higher than the Pleistocene valley trains deposits subunit. Highest phosphorus concentrations occurred in water from wells located along the Mississippi River. A general association between elevated phosphorus concentrations and dissolved iron concentrations suggests that reducing conditions that mobilize iron in the MRVA aquifer also might facilitate transport of phosphorus. Using baseflow separation to estimate the contribution of baseflow to total streamflow, the estimated contribution to the total phosphorus load associated with baseflow at the Tensas River at Tendal, LA, and at the Bogue Phalia near Leland, MS, was 23 percent and 8 percent, respectively. This analysis indicates that elevated concentrations of dissolved phosphorus in the MRVA aquifer could be a possible source of phosphorus to streams during baseflow conditions. However, the fate of phosphorus in groundwater discharge and irrigation return flow to streams is not well understood.

Mississippi↗
USGS1986

Gulf Coast Regional Aquifer-System Analysis — A Mississippi perspective

The Gulf Coast Regional Aquifer-System Analysis is a study of regional aquifers in sediments of mostly Cenozoic age in an area of about 230,000 sq mi in the Central Plain of Alabama, Arkansas , Florida, Illinois, Kentucky, Louisiana, Mississippi, Missouri, Tennessee, and Texas, and an additional 60,000 sq mi offshore. Three aquifer systems have been identified: the Mississippi embayment aquifer system, the Texas coastal uplands aquifer system, and the coastal lowlands aquifer system. These aquifer systems thicken from < 100 ft near their updip limit to thousands of ft gulfward toward their downdip limits. The Mississippi embayment aquifer system exceeds 5,000 ft in thickness in central Louisiana and in southwestern Mississippi. The thickest area in southwestern Mississippi underlies most of the six Mississippi counties, centered around Jefferson County. The greatest thickness of the coastal lowlands aquifer system in Mississippi occurs in southern Hancock County where the system is composed of several individual aquifers and confining units. There are seven aquifers and three confining units in the Mississippi embayment aquifer system, five aquifers and two confining units in the Texas coastal uplands aquifer system, and five aquifers and two confining units in the coastal lowlands aquifer system. Most of the thicker parts of each aquifer system contain moderately saline to very saline water. Water in the Mississippi embayment aquifer system is moderately saline to very saline in most of a seven county area in southwestern Mississippi. About 9,600 million gal/day (gpd) of ground water was pumped from the aquifers in the study area during 1980. About 15% of that pumpage (or about 1,400 million gpd was in Mississippi, mostly from the Mississippi River Valley alluvial aquifer of the Mississippi embayment aquifer system. About 10% of the Mississippi pumpage, or 140 million gpd, was from the coastal lowlands aquifer system. Preliminary results from simulation of groundwater flow indicates that parts of Mississippi are major regional recharge areas for both the Mississippi embayment aquifer system and the coastal lowlands aquifer system.

Mississippi↗
USGS1989

Simulation of steady-state ground water and spring flow in the upper Floridan aquifer of coastal Citrus and Hernando Counties, Florida

A digital groundwater flow model was developed to approximate steady-state predevelopment flow conditions in the Upper Floridan aquifer of coastal west-central Florida. The aquifer is the major source of water and natural spring flow in the area. The aquifer was simulated as a one-layer system with constant vertical recharge and discharge rates. Calibrated transmissivities ranged from 8,640 sq ft/day in the northern part of the area to nearly 13,000,000 sq ft/day near large springs. Calibrated inflows were about 2,708 cu ft/sec; of this, about 2,565 cu ft/sec discharged as natural spring flow and 137 cu ft/sec discharged as upward leakage along the coast. The model was used to show how the system might respond to large manmade stresses. Withdrawal of 116 cu ft/sec from a hypothetical regional well field resulted in potentiometric-surface drawdowns ranging from 0.1 to 1.7 ft and declines of generally less than 0.2 ft along the coast. Total spring flow decreased 5%, and the effect on individual springs varied from 0.1 to 8.0%. Withdrawal of 62 cu ft/sec from the 4-sq-mi node at each spring resulted in six of seven springs to the south of the Chassahowitzka River contributing 50% of their flow to pumpage. Springs located north of the Chassahowitzka River contributed as much as 18% of their flow to pumpage. (USGS)

Water-Resources Investigations Report↗
USGS1987

Geohydrology and simulated effects of withdrawals on the Miocene aquifer system in the Mississippi Gulf Coast area

Intense development of the Miocene aquifer system for water supplies along the Mississippi Gulf Coast has resulted in large water level declines that have altered the groundwater flow pattern in the area. Water levels in some Miocene aquifers have declined about 2 ft/year since 1940; declines exceed 100 ft (80 ft sea level) in large areas along the coast. Water levels in the surficial aquifer system, generally less than 20 ft below land surface, have not declined. The Miocene and younger interbedded and lenticular sands and clays crop out in southern Mississippi and dip to the south and southwest. These sediments have large vertical variations in head and locally respond to stresses as separate aquifers. Freshwater recharge to the Miocene aquifer system primarily is from rainfall on the surficial aquifers. The water generally moves to the south and southeast along the bedding planes toward the Mississippi Gulf Coast where the water is either withdrawn by wells, discharges to the ocean, or gradually percolates upward into overlying aquifers. Drawdowns caused by large groundwater withdrawals along the coast probably have resulted in the gradual movement of the saltwater toward the pumping centers. In parts of the Miocene aquifer system commonly used for water supplies, the water generally is a sodium bicarbonate type. Increasing chloride concentrations in a few wells indicate that saline water is migrating into parts of all layers in the Pascagoula area. A quasi three-dimensional numerical model of the groundwater flow system was constructed and calibrated on the basis of the both pre- and post-development conditions. The effects of an expected 1.5% annual increase in groundwater withdrawals during the period 1985-2005 were evaluated by the flow model. Additional water level declines expected by the year 2005 in response to estimated pumpage are as follows: Gulfport, 135 ft in layer 4; Biloxi-Gulfport area, 100 ft in layer 5 and 50 ft in layer 3; Pascagoula area, 40 ft in layer 6 and 30 ft in layer 4. The most serious threats of saltwater encroachment occur in layers 4, 5, and 6 (the 800-, 600- and 400-ft sands) in the Pascagoula area where contamination of the southern edges of the production areas is expected to occur in less than 10 years. (Author 's abstract)

Water-Resources Investigations Report↗
USGS2011

Field verification of stable perched groundwater in layered bedrock uplands

Data substantiating perched conditions in layered bedrock uplands are rare and have not been widely reported. Field observations in layered sedimentary bedrock in southwestern Wisconsin, USA, provide evidence of a stable, laterally extensive perched aquifer. Data from a densely instrumented field site show a perched aquifer in shallow dolomite, underlain by a shale‐and‐dolomite aquitard approximately 25 m thick, which is in turn underlain by sandstone containing a 30‐m‐thick unsaturated zone above a regional aquifer. Heads in water supply wells indicate that perched conditions extend at least several kilometers into hillsides, which is consistent with published modeling studies. Observations of unsaturated conditions in the sandstone over a 4‐year period, historical development of the perched aquifer, and perennial flow from upland springs emanating from the shallow dolomite suggest that perched groundwater is a stable hydrogeologic feature under current climate conditions. Water‐table hydrographs exhibit apparent differences in the amount and timing of recharge to the perched and regional flow systems; steep hydraulic gradients and tritium and chloride concentrations suggest there is limited hydraulic connection between the two. Recognition and characterization of perched flow systems have practical importance because their groundwater flow and transport pathways may differ significantly from those in underlying flow systems. Construction of multi‐aquifer wells and groundwater withdrawal in perched systems can further alter such pathways.

Wisconsin↗
USGS2026

Assessing future hydrologic extremes using an integrated hydrology and river operations model in the Russian River watershed

Study region The Russian River watershed, situated in coastal, northern California, experiences hydrologic extremes, including periodic droughts and flooding. Water managers are working to maintain sustainable water supplies and environmental flows, while mitigating flood risks. Study focus This paper introduces an integrated hydrology and river operations model for the Russian River watershed. This model is distinct from models in previous studies because it represents surface-groundwater interactions and uses climate forcings to estimate dynamic water use demands that are superimposed onto both reservoir operations and water supply constraints. The model was used to examine three historical (1990–2015) and eight future (2016–2099) water use and climate change scenarios. New hydrological insights for the region The direct connection between streams and aquifers facilitated both annual aquifer replenishment by high winter streamflows and streamflow depletion by groundwater wells (19 % of pumped groundwater in alluvial aquifers from stream leakage) during critical low flow periods. Simulated streamflow changes included 59 % longer and 54 % more severe streamflow droughts, 26 % lower seasonal low streamflows, and up to 125 % higher peak streamflows, averaged over future climate and water use scenarios, suggesting increased future flood and water availability risks. Results showed the importance of reservoir operations for mitigating the impacts of increased hydroclimatic volatility, despite a decrease in reservoir reliability at Lake Mendocino, suggesting that reservoir management may be used to decrease future risks.

California↗