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At least 1,495 records · Page 83Linked to original sources
USGS2012

Effects of groundwater pumping in the lower Apalachicola-Chattahoochee-Flint River basin

USGS developed a groundwater-flow model of the Upper Floridan aquifer in lower Apalachicola-Chattahoochee-Flint River basin in southwest Georgia and adjacent parts of Alabama and Florida to determine the effect of agricultural groundwater pumping on aquifer/stream flow within the basin. Aquifer/stream flow is the sum of groundwater outflow to and inflow from streams, and is an important consideration for water managers in the development of water-allocation and operating plans. Specifically, the model was used to evaluate how agricultural pumping relates to 7Q10 low streamflow, a statistical low flow indicative of drought conditions that would occur during seven consecutive days, on average, once every 10 years. Argus ONETM, a software package that combines a geographic information system (GIS) and numerical modeling in an Open Numerical Environment, facilitated the design of a detailed finite-element mesh to represent the complex geometry of the stream system in the lower basin as a groundwater-model boundary. To determine the effects on aquifer/stream flow of pumping at different locations within the model area, a pumping rate equivalent to a typical center-pivot irrigation system (50,000 ft3/d) was applied individually at each of the 18,951 model nodes in repeated steady-state simulations that were compared to a base case representing drought conditions during October 1999. Effects of nodal pumping on aquifer/stream flow and other boundary flows, as compared with the base-case simulation, were computed and stored in a response matrix. Queries to the response matrix were designed to determine the sensitivity of targeted stream reaches to agricultural pumping. Argus ONE enabled creation of contour plots of query results to illustrate the spatial variation across the model area of simulated aquifer/streamflow reductions, expressed as a percentage of the long-term 7Q10 low streamflow at key USGS gaging stations in the basin. These results would enable water managers to assess the relative impact of agricultural pumping and drought conditions on streamflow throughout the basin, and to develop mitigation strategies to conserve water resources and preserve aquatic habitat.

Alabama, Georgia, Florida↗
USGS2013

A preliminary assessment of streamflow gains and losses for selected stream reaches in the lower Guadalupe River Basin, Texas, 2010-12

The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers–Fort Worth District, the Texas Water Development Board, the Guadalupe-Blanco River Authority, and the Edwards Aquifer Authority, investigated streamflow gains and losses in the lower Guadalupe River Basin during four selected base-flow periods in March 2010, April 2011, August 2011, and, for a stream reach between Seguin, Tex., and Gonzales, Tex., in September 2012. Major sources of streamflow in this basin include releases from Canyon Lake, inflow from major springs (Comal Springs, San Marcos Springs, and Hueco Springs), and base flow (groundwater seeping to streams). Streamflow and spring-flow data were collected at 35 streamflow-gaging stations (including 6 deployed for this study) during the base-flow periods. This report describes streamflow in the lower Guadalupe River Basin, which consists of the Guadalupe River drainage basin downstream from Canyon Lake to the Guadalupe River near Tivoli, Tex. Streamflow conditions in the lower Guadalupe River Basin were analyzed by computing surface-water budgets for reaches of the lower Guadalupe River and tributary streams. Streamflow gains and losses were mapped for reaches where the computed gain or loss was greater than the uncertainty in the computed streamflow at the upstream and downstream ends of the reach. During the March 15–21, 2010, base-flow period, five reaches had gains greater than the uncertainty in the computed streamflow, including reach 1 on the Guadalupe River, which gained 130 cubic feet per second (ft 3 /s), and reach 3 on the Comal River, which gained 359 ft 3 /s. Streamflow gains during March 2010 primarily were derived from (1) inflow from the Edwards aquifer outcrop, including Hueco Springs and Comal Springs; (2) flow conveyed through the alluvium of the streambed; (3) inflows from the Carrizo-Wilcox aquifer and the Yegua Jackson aquifer; and (4) groundwater inflows from the Gulf Coast aquifer, which are enhanced by seepage losses from Coleto Creek Reservoir. During this base-flow period, none of the reaches had a loss greater in magnitude than the uncertainty in the computed streamflow. During the April 10–16, 2011, base-flow period, three reaches had gains greater than the uncertainty in the computed streamflow. Among these three reaches were reach 1 on the Guadalupe River, which gained 40.7 ft 3 /s, and reach 3 on the Comal River, which gained 271 ft 3 /s—reaches where streamflow gains were also measured in March 2010. Streamflow gains during April 2011 primarily were derived from (1) inflow from the Edwards aquifer outcrop, including Hueco Springs and Comal Springs; and (2) inflows from the Carrizo-Wilcox aquifer. During this base-flow period, three reaches had losses greater in magnitude than the uncertainty in the computed streamflow. A reach of the Blanco River near Kyle, Tex. (reach 10), lost 18.7 cubic feet per second (ft3/s). Much of this loss likely entered the groundwater system through the numerous faults that intersect the stream channel northwest of Kyle. The reach that included the confluence of the Guadalupe and San Marcos Rivers (reach 17) lost 155 ft 3 /s, likely as recharge to the Sparta and Queen City aquifers. During the August 19–25, 2011, base-flow period, three reaches had gains greater than the uncertainty in the computed streamflow, including reach 3 on the Comal River (168 ft 3 /s gain), which was one of the reaches where gains in streamflow also were measured in March 2010 and April 2011. Streamflow gains in August 2011 were primarily from (1) inflows from Comal Springs, (2) inflows from the Yegua Jackson aquifer, and (3) groundwater inflows from the Gulf Coast aquifer, which are enhanced by seepage losses from Coleto Creek Reservoir. During this base-flow period, five reaches had losses greater in magnitude than the uncertainty in the computed streamflow. The reach including the confluence of the Guadalupe and Comal Rivers lost 82.8 ft 3 /s. Much of that loss likely seeped into the local groundwater system. The reach of the Guadalupe River south of New Braunfels, Tex., to Seguin, Tex., lost 53.5 ft 3 /s. Part of that loss may have been from seepage through streambed alluvium. Reaches 9 and 10 of the Blanco River near Kyle lost 2.20 and 6.60 ft 3 /s, respectively, likely as infiltration through numerous faults intersecting the stream channel northwest of Kyle. Plum Creek between Lockhart, Tex., and Luling, Tex., lost 2.11 ft 3 /s, likely as recharge to the Carrizo-Wilcox aquifer. A base-flow period during September 22–28, 2012, was studied for the reach of the Guadalupe River between Seguin and Gonzalez, including flows from San Marcos River and Plum Creek. During this period, for the Guadalupe River reach between Seguin and Oak Forest, no computed gains or losses were greater in magnitude than the uncertainty in the computed streamflow.

Texas↗
USGS2022

Hydrologic modeling of a perennial firn aquifer in southeast Greenland

A conceptual model, based on field observations and assumed physics of a perennial firn aquifer near Helheim Glacier (southeast Greenland), is evaluated via steady-state 2-D simulation of liquid water flow and energy transport with phase change. The simulation approach allows natural representation of flow and energy advection and conduction that occur in vertical meltwater recharge through the unsaturated zone and in lateral flow within the saturated aquifer. Agreement between measured and simulated aquifer geometry, temperature, and recharge and discharge rates confirms that the conceptual field-data-based description of the aquifer is consistent with the primary physical processes of groundwater flow, energy transport and phase change. Factors that are found to control simulated aquifer configuration include surface temperature, meltwater recharge rate, residual total-water saturation and capillary fringe thickness. Simulation analyses indicate that the size of perennial firn aquifers depends primarily on recharge rates from surface snowmelt. Results also imply that the recent aquifer expansion, likely due to a warming climate, may eventually produce lakes on the ice-sheet surface that would affect the surface energy balance.

Journal of Glaciology↗
USGS2013

Sediment distribution and hydrologic conditions of the Potomac aquifer in Virginia and parts of Maryland and North Carolina

Sediments of the heavily used Potomac aquifer broadly contrast across major structural features of the Atlantic Coastal Plain Physiographic Province in eastern Virginia and adjacent parts of Maryland and North Carolina. Thicknesses and relative dominance of the highly interbedded fluvial sediments vary regionally. Vertical intervals in boreholes of coarse-grained sediment commonly targeted for completion of water-supply wells are thickest and most widespread across the central and southern parts of the Virginia Coastal Plain. Designated as the Norfolk arch depositional subarea, the entire sediment thickness here functions hydraulically as a single interconnected aquifer. By contrast, coarse-grained sediment intervals are thinner and less widespread across the northern part of the Virginia Coastal Plain and into southern Maryland, designated as the Salisbury embayment depositional subarea. Fine-grained intervals that are generally avoided for completion of water-supply wells are increasingly thick and widespread northward. Fine-grained intervals collectively as thick as several hundred feet comprise two continuous confining units that hydraulically separate three vertically spaced subaquifers. The subaquifers are continuous northward but merge southward into the single undivided Potomac aquifer. Lastly, far southeastern Virginia and northeastern North Carolina are designated as the Albemarle embayment depositional subarea, where both coarse- and fine-grained intervals are of only moderate thickness. The entire sediment thickness functions hydraulically as a single interconnected aquifer. A substantial hydrologic separation from overlying aquifers is imposed by the upper Cenomanian confining unit. Potomac aquifer sediments were deposited by a fluvial depositional complex spanning the Virginia Coastal Plain approximately 100 to 145 million years ago. Westward, persistently uplifted granite and gneiss source rocks sustained a supply of coarse-grained sand and gravel. Immature, high-gradient braided streams deposited longitudinal bars and channel fills across the Norfolk arch subarea. By contrast, across the Salisbury and Albemarle embayment subareas, mature, medium- to low-gradient meandering streams deposited medium- to coarse-grained channel fills and point bars segregated from fine-grained overbank deposits. The Virginia depositional complex merged northward across the Salisbury embayment subarea with another complex in Maryland. Here, additional sediments were received from schist source rocks that underwent three cycles of initial uplift and rapid erosion followed by crustal stability and erosional leveling. Because of the predominance of coarse-grained sediments, transmissivity, hydraulic conductivity, and regional velocities of lateral flow through the Potomac aquifer are greatest across the Norfolk arch depositional subarea, but decrease progressively northward with increasingly fine-grained sediments. Confining units hydraulically separate the Potomac aquifer from overlying aquifers, as indicated by large vertical hydraulic gradients. By contrast, most of the Potomac aquifer internally functions hydraulically as a single interconnected aquifer, as indicated by uniformly small vertical gradients. Most fine-grained sediments within the aquifer do not hydraulically separate overlying and underlying coarse-grained sediments. Across the Salisbury embayment depositional subarea, however, hydraulic separation among the vertically spaced subaquifers is imposed by the intervening confining units. The Potomac aquifer is the largest and most heavily used source of groundwater in the Virginia Coastal Plain. Water-level declines as great as 200 feet create the potential for saltwater intrusion. Conventional stratigraphic correlation has been generally ineffective at accurately characterizing complexly distributed fluvial sediments that compose the Potomac aquifer. Consequently, the aquifer’s internal hydraulic connectivity and overall hydrologic function have not been well understood. Water-supply planning and development efforts have been hampered, and interpretations of regulatory criteria for allowable water-level declines have been ambiguous. An investigation undertaken during 2010–11 by the U.S. Geological Survey, in cooperation with the Virginia Department of Environmental Quality, provides a comprehensive regional description of the spatial distribution of Potomac aquifer sediments and their relation to hydrologic conditions. Altitudes and thicknesses of 2,725 vertical sediment intervals represent the spatial distribution of Potomac aquifer sediments in the Virginia Coastal Plain and adjacent parts of Maryland and North Carolina. Sediment intervals are designated as either dominantly coarse or fine grained and were determined by interpretation of geophysical logs and ancillary information from 456 boreholes. Sediment-interval and borehole summary statistical data indicate regional trends in sediment lithology and stratigraphic continuity, upon which three structurally based and hydrologically distinct sediment depositional subareas are designated. Broad patterns of sediment deposition over time are inferred from published sediment pollen-age data. Discrepancies in previously drawn hydrostratigraphic relations between southeastern Virginia and northeastern North Carolina are partly resolved based on borehole geophysical logs and a recently documented geologic map and corehole. A conceptual model theorizes the depositional history of the sediments and geologically accounts for their distribution. Documented pumping tests of the Potomac aquifer at 197 locations produced 336 values of transmissivity and 127 values of storativity. Based on effective aquifer thicknesses, 296 values of sediment hydraulic conductivity and 113 values of sediment specific storage are calculated. Vertical hydraulic gradients are calculated from 9,479 pairs of water levels measured between November 17, 1953, and October 4, 2011, in 129 closely spaced pairs of wells. Borehole sediment-interval and related data provide a means to achieve high yielding production wells in the Potomac aquifer by site-specific targeting of drilling operations toward water-bearing coarse-grained sand and gravel. Advance knowledge of the potential of different parts of the aquifer also aids in planning optimal groundwater-development areas. Depositional subareas further provide a possible context for resource management. Current (2013) regulatory limits on water-level declines are relative to top surfaces of subdivided upper, middle, and lower Potomac aquifers across the entire Virginia Coastal Plain, but have the potential to exceed the same limit relative to a single undivided Potomac aquifer. By contrast, designation of the sediments as a single aquifer in the Norfolk arch and Albemarle embayment subareas—and as a series of vertically spaced subaquifers and intervening confining units in the Salisbury embayment subarea—best reflects understanding of the Potomac aquifer and can avoid the potential for excessive water-level declines. Simulation modeling to evaluate effects of groundwater withdrawals could be designed similarly, including vertical discretization and (or) zonation of the Potomac aquifer based on depositional subareas and a geostatistical distribution of aquifer properties derived from borehole sediment-interval data. Further resource-management information needs extend beyond the developed part of the Potomac aquifer, particularly across the Northern Neck and Middle Peninsula where only the shallowest part of the aquifer is known, and include structural aspects such as faults, basement bedrock, and the Chesapeake Bay impact crater.

Maryland, North Carolina, Virginia↗
USGS2020

Groundwater quality and groundwater levels in Dougherty County, Georgia, April 2019 through March 2020

The Upper Floridan aquifer is the uppermost, reliable aquifer in southwest Georgia. The aquifer lies on top of the Claiborne, Clayton, and Cretaceous aquifers, all of which exhibited water level declines in the 1960s and 1970s. The U.S. Geological Survey has been working cooperatively with Albany Utilities to monitor groundwater quality and availability in these aquifers since 1977. During January 2020, nine wells were sampled—six for anions, metals, and nitrate plus nitrite as nitrogen, and three for anions, metals, and pesticides. Nitrate plus nitrite as nitrogen concentrations ranged from 2.4 milligrams per liter (mg/L) to 10.4 mg/L, and no pesticides were detected. Nitrate plus nitrite as nitrogen concentrations in well 12L277, open to the Upper Floridan aquifer, have been above the U.S. Environmental Protection Agency Maximum Contaminant Level of 10 mg/L for nitrates in drinking water since 2014. Flow direction in the Upper Floridan aquifer is to the south and toward the Flint River. Water levels varied during the past year above and below period of record median values. Water levels in the Upper Floridan aquifer were primarily above median levels. Water levels in the Claiborne aquifer were above median levels, whereas water levels in the Clayton and Cretaceous aquifers were below median levels.

Georgia↗
USGS2023

Development of an integrated hydrologic flow model of the Rio San Jose Basin and surrounding areas, New Mexico

The Rio San Jose Integrated Hydrologic Model (RSJIHM) was developed to provide a tool for analyzing the hydrologic system response to historical water use and potential changes in water supplies and demands in the Rio San Jose Basin. The study area encompasses about 6,300 square miles in west-central New Mexico and includes the communities of Grants, Bluewater, and San Rafael and three Native American Tribal lands: the Acoma and Laguna Pueblos and the Navajo Nation. Perennial surface water features are sparse in the study area and most water resources consist of groundwater pumped from sedimentary and basalt aquifers. Calibration of the RSJIHM was performed using PEST++ (version 4.3.20) and BeoPEST (version 13.6). Model parameter values were adjusted during calibration to fit model simulated values to the measured or estimated values for several observation groups: (1) solar radiation, (2) potential evapotranspiration, (3) actual evapotranspiration, (4) precipitation and minimum and maximum air temperature, (5) snow water equivalent, (6) snow-covered area, (7) streamflow, (8) hydraulic head, (9) springflow at Ojo del Gallo, (10) springflow at Horace Springs, (11) surface-water releases from Bluewater Lake, and (12) surface-water diversions for irrigation within the Bluewater-Toltec Irrigation District. The simulated average annual hydrologic budget from 1950 through 2018 indicated that the majority (greater than 98 percent) of precipitation within the basin was consumed by evapotranspiration, leaving 1.2 percent to recharge the groundwater system, 0.47 percent to direct runoff to streams, and 0.20 percent to infiltrate the soil zone and interflow to streams. The average annual recharge to the groundwater system and runoff to streams simulated by the RSJIHM was about 28,000 and 11,000 acre-feet, respectively. The RSJIHM simulated about 590,000 acre-feet of cumulative aquifer storage depletion from 1950 through 2018. Additional work that could improve the simulation capability of the RSJIHM includes (1) further data collection (streamflow, head, springflow) in the southwestern subbasin that includes the El Malpais National Monument, (2) incorporating temporally variable vegetation parameters, (3) spatial downscaling of the hydrometeorological input datasets, (4) incorporating additional spatial variability to hydraulic property parameters on the basis of new data collection, and (5) using environmental tracers to verify and calibrate model parameters.

New Mexico↗
USGS2014

Baseline groundwater quality from 34 wells in Wayne County, Pennsylvania, 2011 and 2013

Wayne County, Pennsylvania, is underlain by the Marcellus Shale, which currently (2014) is being developed elsewhere in Pennsylvania for natural gas. All residents of largely rural Wayne County rely on groundwater for water supply, primarily from bedrock aquifers (shales and sandstones). This study, conducted by the U.S. Geological Survey in cooperation with the Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey (Pennsylvania Geological Survey), provides a groundwater-quality baseline for Wayne County prior to development of the natural gas resource in the Marcellus Shale. Selected wells completed in the Devonian-age Catskill Formation, undifferentiated; the Poplar Gap and Packerton Members of the Catskill Formation, undivided; and the Long Run and Walcksville Members of the Catskill Formation, undivided, were sampled. Water samples were collected once from 34 domestic wells during August 2011 and August and September 2013 and analyzed to characterize their physical and chemical quality. Samples were analyzed for 45 constituents and properties, including nutrients, major ions, metals and trace elements, radioactivity, and dissolved gases, including methane and radon-222. The quality of the sampled groundwater was generally within U.S. Environmental Protection Agency (USEPA) drinking-water standards, although in some samples, the concentrations of a few constituents exceeded USEPA drinking-water standards and health advisories. The pH of water samples ranged from 5.5 to 9.3 with a median of 7.0. The pH was outside the USEPA secondary maximum contaminant level (SMCL) range of 6.5 to 8.5 in water samples from 14 of the 34 wells (41 percent). Eleven samples had a pH less than 6.5, and three samples had a pH greater than 8.5. Dissolved oxygen concentrations ranged from 0.2 to 11.5 milligrams per liter (mg/L) with a median of 4.7 mg/L. The dissolved oxygen concentration was less than 1 mg/L in water samples from 6 wells; 5 of these 6 water samples had a pH greater than 7.7. Concentrations of dissolved methane ranged from less than 0.00006 to 3.3 mg/L. Methane was detectable in 22 of the 34 wells sampled (65 percent). Methane concentrations were greatest in the 5 samples with pH of 7.8 or higher, ranging from 0.040 to 3.3 mg/L. These samples also had among the lowest concentrations of dissolved oxygen. Three water samples, which had sufficient dissolved methane concentrations (greater than 0.9 mg/L), were analyzed for isotopes of carbon and hydrogen in the methane. The isotopic ratio values fell within (two samples) or close to (one sample) the range for a thermogenic natural gas source. The total dissolved solids concentration ranged from 33 to 346 mg/L; the median concentration was 126 mg/L. Sodium concentrations ranged from 1.07 to 116 mg/L; the median concentration was 9.42 mg/L. The sodium concentration exceeded the USEPA health advisory for sodium of 20 mg/L in water samples from 7 of the 34 wells (21 percent). Concentrations of dissolved arsenic ranged from less than 0.06 to 21.8 micrograms per liter (µg/L); the median concentration was 0.59 µg/L. Water samples from 2 of the 34 wells (6 percent) exceeded the USEPA maximum contaminant level (MCL) of 10 µg/L for arsenic. Concentrations of dissolved manganese ranged from less than 0.15 to 61.5 µg/L; the median concentration was 0.42 µg/L. A water sample from 1 of the 34 wells (3 percent) exceeded the USEPA SMCL of 50 µg/L for manganese; the concentration was less than the USEPA lifetime health advisory of 300 µg/L for manganese. Activities of radon-222 in water from the 34 sampled wells ranged from 110 to 7,180 picocuries per liter (pCi/L); the median activity was 2,105 pCi/L. Water samples from 33 of the 34 wells (97 percent) exceeded the proposed USEPA MCL of 300 pCi/L, and 4 water samples (12 percent) exceeded the USEPA proposed alternative MCL of 4,000 pCi/L for radon-222. Differences in groundwater chemistry were related to pH. Water with a pH greater than 7.6 generally had low dissolved oxygen concentrations, indicating reducing conditions in the aquifer. These high pH waters also had relatively elevated concentrations of methane, arsenic, boron, bromide, fluoride, lithium, and sodium but low concentrations of copper, nickel, and zinc. Water samples with a pH greater than 7.8 had methane concentrations equal to or greater than 0.04 mg/L.

Pennsylvania↗
USGS2015

Importance of the colmation layer in the transport and removal of cyanobacteria, viruses, and dissolved organic carbon during natural lake-bank filtration

This study focused on the importance of the colmation layer in the removal of cyanobacteria, viruses, and dissolved organic carbon (DOC) during natural bank filtration. Injection-and-recovery studies were performed at two shallow (0.5 m deep), sandy, near-shore sites at the southern end of Ashumet Pond, a waste-impacted, kettle pond on Cape Cod, MA, that is subject to periodic blooms of cyanobacteria and continuously recharges a sole-source drinking-water aquifer. The experiment involved assessing the transport behaviors of bromide (conservative tracer), Synechococcus sp. IU625 (cyanobacterium, 2.6 ± 0.2 µm), AS-1 (tailed cyanophage, 110 nm long), MS2 (coliphage, 26 nm diameter), and carboxylate-modified microspheres (1.7 µm diameter) introduced to the colmation layer using a bag-and-barrel (Lee-type) seepage meter. The injectate constituents were tracked as they were advected across the pond water–groundwater interface and through the underlying aquifer sediments under natural-gradient conditions past push-point samplers placed at ∼30-cm intervals along a 1.2-m-long, diagonally downward flow path. More than 99% of the microspheres, IU625, MS2, AS-1, and ∼44% of the pond DOC were removed in the colmation layer (upper 25 cm of poorly sorted bottom sediments) at two test locations characterized by dissimilar seepage rates (1.7 vs. 0.26 m d −1 ). Retention profiles in recovered core material indicated that >82% of the attached IU625 were in the top 3 cm of bottom sediments. The colmation layer was also responsible for rapid changes in the character of the DOC and was more effective (by three orders of magnitude) at removing microspheres than was the underlying 20-cm-thick segment of sediment.

Massachusetts↗
USGS1988

Ground-water geochemistry of the Albuquerque-Belen Basin, central New Mexico

The purpose of this study was to define the areal distribution of different water types, use the distribution to help define the groundwater flow system, and identify processes resulting in differences in groundwater quality in the Albuquerque-Belen Basin in central New Mexico. The chemistry of surface water inflow from adjacent areas, which infiltrates and recharges the aquifer along the basin margin, affects the groundwater quality in the eastern and southeastern areas of the basin. Groundwater in the eastern area generally has a specific conductance less than 400 microsiemens, and calcium and bicarbonate are the dominant ions. Mixing of recharge, groundwater inflow, and surface inflow from adjacent areas, which have different chemical compositions, is the major process affecting groundwater quality in the southwestern, western, and northern areas of the basin. In these areas, there is a large range in specific conductance and distribution of dissolved ions. Groundwater quality in the Rio Grande valley is affected by the infiltration of excess irrigation water. The excess irrigation water generally has a larger specific conductance than other groundwater in the valley, so mixing of these waters results in shallow groundwater generally having larger specific conductance than the deeper groundwater. (USGS)

New Mexico↗
USGS2011

Trace elements and radon in groundwater across the United States, 1992-2003

Trace-element concentrations in groundwater were evaluated for samples collected between 1992 and 2003 from aquifers across the United States as part of the U.S. Geological Survey National Water-Quality Assessment Program. This study describes the first comprehensive analysis of those data by assessing occurrence (concentrations above analytical reporting levels) and by comparing concentrations to human-health benchmarks (HHBs). Data from 5,183 monitoring and drinking-water wells representing more than 40 principal and other aquifers in humid and dry regions and in various land-use settings were used in the analysis. Trace elements measured include aluminum (Al), antimony (Sb), arsenic (As), barium (Ba), beryllium (Be), boron (B), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), lithium (Li), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se), silver (Ag), strontium (Sr), thallium (Tl), uranium (U), vanadium (V), and zinc (Zn). Radon (Rn) gas also was measured and is included in the data analysis. Climate influenced the occurrence and distribution of trace elements in groundwater whereby more trace elements occurred and were found at greater concentrations in wells in drier regions of the United States than in humid regions. In particular, the concentrations of As, Ba, B, Cr, Cu, Mo, Ni, Se, Sr, U, V, and Zn were greater in the drier regions, where processes such as chemical evolution, ion complexation, evaporative concentration, and redox (oxidation-reduction) controls act to varying degrees to mobilize these elements. Al, Co, Fe, Pb, and Mn concentrations in groundwater were greater in humid regions of the United States than in dry regions, partly in response to lower groundwater pH and (or) more frequent anoxic conditions. In groundwater from humid regions, concentrations of Cu, Pb, Rn, and Zn were significantly greater in drinking-water wells than in monitoring wells. Samples from drinking-water wells in dry regions had greater concentrations of As, Ba, Pb, Li, Sr, V, and Zn, than samples from monitoring wells. In humid regions, however, concentrations of most trace elements were greater in monitoring wells than in drinking-water wells; the exceptions were Cu, Pb, Zn, and Rn. Cu, Pb, and Zn are common trace elements in pumps and pipes used in the construction of drinking-water wells, and contamination from these sources may have contributed to their concentrations. Al, Sb, Ba, B, Cr, Co, Fe, Mn, Mo, Ni, Se, Sr, and U concentrations were all greater in monitoring wells than in drinking-water wells in humid regions. Groundwater from wells in agricultural settings had greater concentrations of As, Mo, and U than groundwater from wells in urban settings, possibly owing to greater pH in the agricultural wells. Significantly greater concentrations of B, Cr, Se, Ag, Sr, and V also were found in agricultural wells in dry regions. Groundwater from dry-region urban wells had greater concentrations of Co, Fe, Pb, Li, Mn, and specific conductance than groundwater from agricultural wells. The geologic composition of aquifers and aquifer geochemistry are among the major factors affecting trace-element occurrence. Trace-element concentrations in groundwater were characterized in aquifers from eight major groups based on geologic material, including (1) unconsolidated sand and gravel; (2) glacial unconsolidated sand and gravel; (3) semiconsolidated sand; (4) sandstone; (5) sandstone and carbonate rock; (6) carbonate rock; (7) basaltic and other volcanic rock; and (8) crystalline rock. The majority of groundwater samples and the largest percentages of exceedences of HHBs were in the glacial and nonglacial unconsolidated sand and gravel aquifers; in these aquifers, As, Mn, and U are the most common trace elements exceeding HHBs. Overall, 19 percent of wells (962 of 5,097) exceeded an HHB for at least one trace element. The trace elements with HHBs included in this summary were Sb, As, Ba, Be, B, Cd, Cr,

Scientific Investigations Report↗
USGS2010

Combined use of groundwater dating, chemical, and isotopic analyses to resolve the history and fate of nitrate contamination in two agricultural watersheds, Atlantic coastal plain, Maryland

The history and fate of groundwater nitrate (NO 3 − ) contamination were compared in 2 small adjacent agricultural watersheds in the Atlantic coastal plain by combined use of chronologic (CCl 2 F 2 , 3 H), chemical (dissolved solids, gases), and isotopic (δ 15 N,δ 13 C, δ 34 S) analyses of recharging groundwaters, discharging groundwaters, and surface waters. The results demonstrate the interactive effects of changing agricultural practices, groundwater residence times, and local geologic features on the transfer of NO 3 − through local flow systems. Recharge dates of groundwaters taken in 1990–1992 from the surficial aquifer in the Chesterville Branch and Morgan Creek watersheds near Locust Grove, Maryland, ranged from pre-1940 to the late 1980’s. When corrected for localized denitrification by use of dissolved gas concentrations, the dated waters provide a 40-year record of the recharge rate of NO 3 − , which increased in both watersheds by a factor of 3–6, most rapidly in the 1970's. The increase in groundwater NO 3 − over time was approximately proportional to the documented increase in regional N fertilizer use, and could be accounted for by oxidation and leaching of about 20–35% of the fertilizer N. Groundwaters discharging upward beneath streams in both watersheds had measured recharge dates from pre-1940 to 1975, while chemical data for second-order reaches of the streams indicated average groundwater residence times in the order of 20+ years. At the time of the study, NO 3 − discharge rates were less than NO 3 − recharge rates for at least two reasons: (1) discharge of relatively old waters with low initial NO 3 − concentrations, and (2) local denitrification. In the Chesterville Branch watershed, groundwaters remained oxic throughout much of the surficial aquifer and discharged relatively unaltered to the stream, which had a relatively high NO 3 − concentration (9–10 mg/L as N). In the Morgan Creek watershed, groundwaters were largely reduced and denitrified before discharging to the stream, which had a relatively low NO 3 − concentration (2–3 mg/L as N). Chemical and isotopic data indicate that quantitative denitrification occurred within buried calcareous glauconitic marine sediments that are present at relatively shallow depths beneath the Morgan Creek watershed. NO 3 − removal by forests, wetlands, and shallow organic-rich soils in near-stream environments was largely avoided by groundwaters that followed relatively deep flow paths before converging and discharging rapidly upward to the streams.

Maryland↗
USGS2020

Identifying areas of degrading and improving groundwater-quality conditions in the State of California, USA, 1974-2014

Areas of improving and degrading groundwater-quality conditions in the State of California were assessed using spatial weighting of a new metric for scoring wells based on constituent concentrations and the direction and magnitude of a trend slope (Sen). Individual well scores were aggregated across 2135 equal-area grid cells covering the entire groundwater resource used for public supply in the state. Spatial weighting allows results to be aggregated locally (well or grid cell), regionally (groundwater basin), provincially, or statewide. Results differentiate degrading (increasing concentration trends) areas with low to moderate concentrations (unimpaired) from degrading areas with moderate to high concentrations (impaired). Results also differentiate improving areas (decreasing concentration trends) in the same manner. Multi-year to decadal groundwater-quality trends were computed from periodic, inorganic water-quality data for 38 constituents collected between 1974 and 2014 for compliance monitoring of nearly 13,000 public-supply wells (PSWs) in the State of California. Mann-Kendall (MK) rank correlations and Sen’s slope estimator were used to detect statistically significant trends for the entire period of recorded data (long-term trend), for the period since 2000 (recent trend), for different pumping seasons (seasonal trend), and for reversals of trends. Statewide, the most frequently detected trends since 2000 were for nitrate (36%), gross alpha/uranium (10%), arsenic (14%), total dissolved solids (TDS) (23%), and the major ions that contribute to TDS (19–28%). The Transverse and Selected Peninsular Ranges (TSPR) and the San Joaquin Valley (SJV) hydrogeologic provinces had the largest percentage of areas with moderate to high nitrate concentrations and groundwater quality trends. Improving nitrate concentrations in parts of the TSPR is associated with long-term managed aquifer recharge that has replaced historical, agriculturally affected groundwater with low-nitrate recharge in parts of the TSPR. This example suggests that application of dilute, excess surface water to agricultural fields during the winter could improve groundwater-quality in the SJV over the long term.

California↗
USGS2016

Altitudes and thicknesses of hydrogeologic units of the Ozark Plateaus aquifer system in Arkansas, Kansas, Missouri, and Oklahoma

A hydrogeologic framework was constructed to represent the altitudes and thicknesses of hydrogeologic units within the Ozark Plateaus aquifer system as part of a regional groundwater-flow model supported by the U.S. Geological Survey Water Availability and Use Science Program. The Ozark Plateaus aquifer system study area is nearly 70,000 square miles and includes parts of Arkansas, Kansas, Missouri, and Oklahoma. Nine hydrogeologic units were selected for delineation within the aquifer system and include the Western Interior Plains confining system, the Springfield Plateau aquifer, the Ozark confining unit, the Ozark aquifer, which was divided into the upper, middle, and lower Ozark aquifers to better capture the spatial variation in the hydrologic properties, the St. Francois confining unit, the St. Francois aquifer, and the basement confining unit. Geophysical and well-cutting logs, along with lithologic descriptions by well drillers, were compiled and interpreted to create hydrologic altitudes for each unit. The final compiled dataset included more than 23,000 individual altitude points (excluding synthetic points) representing the nine hydrogeologic units within the Ozark Plateaus aquifer system.

Arkansas, Kansas, Missouri, Oklahoma↗
USGS1984

Water-quality data for aquifers in east-central New Jersey, 1981-82

Data are presented in tables for 238 wells representing nine aquifers underlying the New Jersey Coastal Plain. Approximately two-thirds of these wells are screened in the unconfined Kirkwood-Cohansey aquifer system, the principal source of groundwater in the study area. In addition, seven local streams were sampled in their headwaters under base flow conditions. Field measurements include water temperature, specific conductance, pH, and alkalinity; laboratory determinations include common inorganic ions, nutrients, trace metals, dissolved organic carbon, and volatile organic compounds. Other tables include lithology and hydrologic characteristics of geologic units, well-construction data, and median and extreme values of constituents in water of the Kirkwood-Cohansey aquifer system. A plate shows all sampling sites and presents three hydrogeologic sections delineating subsurface relationships. (USGS)

Open-File Report↗
USGS2021

Impacts of climate change on groundwater availability and spring flows: Observations from the highly productive Medicine Lake Highlands/Fall River Springs Aquifer System

Medicine Lake Highlands/Fall River Springs Aquifer System, located in northeastern California, is home to some of the largest first-order springs in the United States. This work assesses the likely effects of projected climate change on spring flow. Four anticipated climate futures (GFDL A2, GFDL B1, CCSM4 rcp 8.5, CNRM rcp 8.5) for California, which predict a range of conditions (generally warming and transitioning from snow to rain with variable amounts of total precipitation), are postulated to affect groundwater recharge primarily by changing evapotranspiration. The linkages between climate variables and spring flow are evaluated using a water balance model that represents the physics of evapotranspiration and recharge, the Basin Characterization Model. Three of the four climate scenarios (GFDL A2, GFDL B1, CCSM4 rcp 8.5) project that by the year 2100, groundwater recharge (and consequently decreased spring flow) will decrease by 27%, 21%, and 9%, respectively. The fourth scenario (CNRM rcp 8.5) showed an increase in recharge of 32% due to a significant increase in precipitation (27%). Evapotranspiration increases due to a shift in the type of precipitation and a longer growing season. While the likelihood of each scenario is outside the scope of this work, unless total precipitation increases dramatically in the future, increased temperatures and decreasing precipitation will likely result in reduced spring flows, along with warmer water temperatures in downstream habitats.

California↗
USGS2007

Geochemical interpretations of groundwater flow systems

Interest in the geochemistry of groundwater is increasing owing to the great number of current projects involving underground liquid waste storage, artificial recharge of potable water, accidental contamination of groundwater bodies, sanitary landfills, and pollution monitoring. Geochemical techniques used to facilitate the understanding of a groundwater system range from extremely simple to those requiring sophisticated theories, equipment, and procedures. An interpretation of the simple trilinear diagram for samples collected from the Yucatan Peninsula of Mexico provided evidence that the fresh-water body was only a few tens of meters thick and was underlain everywhere by an extensive body of salt water. A geochemical technique that has been used effectively to identify the source of salt water in coastal aquifers is measurement of the carbon-14 concentrations. Carbon-14 has been used in a regional carbonate aquifer to determine the velocity of groundwater movement, rates of chemical reactions, and distribution of hydraulic conductivity. The application of principles of irreversible thermodynamics to groundwater systems provides a basis for constructing models which permit prediction, over both time and space, of changes in head distribution and chemical character of the water resulting from imposed stresses on the system. In essence, proper application of irreversible thermodynamics combines the potential theory of Hubbert with principles of reversible chemical thermodynamics, such as solution of carbonate minerals, to describe and explain controlling chemical reactions and processes of groundwater systems.

Florida, South Carolina↗
USGS1980

Ground water in the Piedmont Upland of central Maryland

Aquifers in a 130-square-mile area of the central Maryland and Piedmont, are shown to be the sole or principal source of water. The study area is underlain chiefly by crystalline rocks and partly by unaltered sandstones and siltstones. The groundwater is derived from local precipitation and generally occurs under water-table conditions. Its movement is restricted by the lack of interconnected openings, and most groundwater occurs within 300 feet of the land surface. Hydrographs indicate no long-term change in groundwater storage. A few wells yield more than 100 gallons per minute, but about 70% of 286 inventoried wells yield 10 gallons per minute or less; most specific capacities are less than 1.0 gallon per minute per foot. The groundwater quality is generally satisfactory without treatment and there are no known widespread pollution problems. Estimated daily figures on groundwater use are as follows; 780,000 gallons for domestic purposes; 55,000 for commercial purposes; and 160,000 for public supply. Although part of the area is served by an existing surface-water supply and could be served by possible extension of those and other public-supply water mains, much of the rural population is dependent on the groundwater available from private wells tapping the single aquifer that underlies any given location. Neither the groundwater conditions nor this dependence on individual wells is unique to the study area, but, rather, applies to the entire Piedmont province. (USGS)

Maryland↗
USGS1983

Potentiometric surface of the Floridan Aquifer and its use in management of water resources, St. Johns River Water Management District, Florida

The Floridan aquifer supplies most of the fresh groundwater for municipal, industrial, and agricultural uses within the 12,400 sq mi St. Johns River Water Management District. Because of the growing demand for water and the variation in rainfall, resource managers need timely information on short-term and long-term changes in the availability of fresh water. The purpose of this report is to explain potentiometric surface maps and their value in assessing the resource, particularly during drought conditions. The Floridan aquifer is recharged by rainfall falling directly on the outcrop of the aquifer, and, where the aquifer is overlain by the surficial aquifer with the water table above the potentiometric surface of the Floridan, by water infiltrating downward from the overlying surficial aquifer. Water is discharged by pumping and free-flowing wells, springflow, and upward leakage into overlying formations, streams, and lakes or into the ocean. Fluctuations in the potentiometric surface reflect net gains (recharge) or losses (discharge) of water stored in the aquifer. Net gains occur during the wet season (June through September) when recharge exceeds discharge and causes the potentiometric surface to rise in most places. Net losses in storage, and declines in the potentiometric surface, follow during the dry season (October through May) when discharge exceeds recharge. Seasonal changes in the potentiometric surface, based on a 2-yr average of water level measurements during May and September 1977, and May and September 1978, are illustrated. Two of the greater long-term declines in the potentiometric surface have occurred in the growing metropolitan areas of Jacksonville and Orlando-Winter Park, the two largest public suppliers of water in the Water Management District. Municipal pumpage increased in Jacksonville from 37 million gallons per day (mgd) in 1961 to 56 mgd in 1980. The increased pumpage and a deficiency in rainfall of 15.8 inches contributed to a decline in the potentiometric surface of as much as 15 ft. Orlando-Winter Park municipal pumpage increasing from 27 mgd in 1961 to 62 mgd in 1980. The periodic preparation of maps showing changes in the potentiometric surface of the aquifer provide the best base information for both short-term and long-term management of the water resources in the St. Johns River Water Management District. (Lantz-PTT)

Water-Resources Investigations Report↗