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Groundwater & aquifers

Find USGS groundwater and aquifer publications. Search an aquifer name or place, compare source-supplied dates and open reports for hydrogeology, recharge and water-level studies.

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USGS1985

A description of aquifer units in eastern Oregon

Geologic formations in Oregon, east of the crest of the Cascade Range, have been grouped according to similarities in their hydrogeologic and geologic properties into six major aquifer units. Two of the units, the Mesozoic-Paleozoic and the John Day-Clarno aquifers, are low-permeability aquifers, have hydraulic conductivities generally less than 1 ft/d (feet per day), and are generally capable of yielding only a few gallons per minute to wells. These are important aquifer units, nevertheless, because they are the only economical source of domestic water present in east-central Oregon where they outcrop. Four of the aquifer units contain beds or zones of high permeability materials with hydraulic conductivities that commonly range between 5 and 50 ft/d. In many localities where these units are present, they are capable of yielding 200 gallons/min or more to wells. These productive aquifer units are the Columbia River Basalt, the Cenozoic volcanic and sedimentary , Cenozoic sedimentary, and the Quaternary sediment aquifers, respectively. North of the Blue Mountains, the Columbia River Basalt aquifer is a major aquifer of regional extent and, in that area, heavy withdrawals, chiefly for irrigation, have resulted in regional groundwater level declines. South of the Blue Mountains, the basalt underlies rugged terrane, is not developed, and little is known about its hydraulic properties. Other major aquifer units are heavily developed in localized areas or in basins throughout eastern Oregon. (USGS)

Water-Resources Investigations Report↗

USGS1989

Geohydrology and susceptibility of major aquifers to surface contamination in Alabama; area 11

This report delineates and describes the geohydrology and susceptibility of major aquifers to contamination in Butler, Conecuh, Covington, Crenshaw, Escambia, and Monroe Counties, Alabama. The major aquifers are the Pliocene-Miocene, Upper Floridan, Lisbon, Nanafalia-Clayton, and Providence-Ripley. The largest pumping centers in the area are Andalusia and Monroeville, where groundwater use is about 5 and 4 million gal/day, respectively. Estimated maximum withdrawal in 1987 for all uses in the area was about 44 million gal/day. Depressions have developed in the potentiometric surfaces of the Lisbon aquifer near Andalusia and Opp, the Nanafalia-Clayton aquifer near Luverne, Andalusia, Beatrice, and Monroeville, and the Providence-Ripley aquifer at Greenville. Significant declines in the potentiometric surfaces of the other major aquifers are not apparent. Recharge areas for all major aquifers are susceptible to contamination, but the probability of contamination of the Lisbon, Nanafalia-Clayton, and Providence-Ripley aquifers is low because the recharge areas are remote from areas of the withdrawal. The depressions in the recharge area for the Upper Floridan aquifer and the area where the Pliocene-Miocene aquifer is overlain by the gravelly sands of the Citronelle Formation are highly susceptible to contamination from the surface. (USGS)

Water-Resources Investigations Report↗

USGS1990

A digital simulation of the glacial-aquifer system in the northern three-fourths of Brown County, South Dakota

A digital model was developed to simulate groundwater flow in a complex glacial-aquifer system that includes the Elm, Middle James, and Deep James aquifers in South Dakota. The average thickness of the aquifers ranges from 16 to 32 ft and the average hydraulic conductivity ranges from 240 to 300 ft/day. The maximum steady-state recharge to the aquifer system was estimated to be 7.0 in./yr, and the maximum potential steady- state evapotranspiration was estimated to be 35.4 in/yr. Maximum monthly recharge for 1985 ranged from zero in the winter to 2.5 in in May. The potential monthly evapotranspiration for 1985 ranged from zero in the winter to 7.0 in in July. The average difference between the simulated and observed water levels from steady-state conditions (pre-1983) was 0. 78 ft and the average absolute difference was 4.59 ft for aquifer layer 1 (the Elm aquifer) from 22 observation wells and 3.49 ft and 5.10 ft, respectively, for aquifer layer 2 (the Middle James aquifer) from 13 observation wells. The average difference between the simulated and observed water levels from simulated monthly potentiometric heads for 1985 in aquifer layer 1 ranged from -2.54 ft in July to 0.59 ft in May and in aquifer layer 2 ranged from -1.22 ft in April to 4.98 ft in November. Sensitivity analysis of the steady-state model indicates that it is most sensitive to changes in recharge and least sensitive to changes in hydraulic conductivity. (USGS)

Water-Resources Investigations Report↗

USGS1990

Hydrogeology of aquifers in Cretaceous and younger rocks in the vicinity of Onslow and southern Jones counties, North Carolina

Unconsolidated sediments in Onslow and Jones Counties, North Carolina overlie crystalline basement rocks and range in thickness from about 700 ft to more than 1,800 ft, thickening toward the east. This material is composed of permeable sand and limestone interlayered with relatively impermeable clay and silt beds. Sediments are divided into two groups: aquifers in Quaternary-, and Tertiary-aged rocks and aquifers in Cretaceous-aged rocks. Aquifers in the Cretaceous rocks provide most of the groundwater for public supplies and are the focus of this report. The aquifers in Cretaceous rocks are the Peedee, Black Creek, upper Cape Fear, and lower Cape Fear aquifers, which are composed of beds or groups of beds of sand and gravel. Each aquifer is overlain by a clay and silt bed, that impedes the flow of water between aquifers. The thickness of Cretaceous hydrogeologic units ranges from about 700 ft to more than 1, 300 ft. Hydrogeologic units are correlated using 60 geophysical logs and accompanying drillers ' logs along with water level and water quality data. Three hydrogeologic sections demonstrate the continuity of the aquifers and confining units, show water levels and chloride concentration in water from test intervals, and delineate where chloride concentration in water exceeds 250 mg/L within each aquifer. Maps of each aquifer in Cretaceous rocks show altitude of its top, thickness, sand percentage, and the transition from freshwater to saltwater. Maps of the confining units show thickness and sand percentage of each.

North Carolina↗

USGS2013

Prediction, time variance, and classification of hydraulic response to recharge in two karst aquifers

Many karst aquifers are rapidly filled and depleted and therefore are likely to be susceptible to changes in short-term climate variability. Here we explore methods that could be applied to model site-specific hydraulic responses, with the intent of simulating these responses to different climate scenarios from high-resolution climate models. We compare hydraulic responses (spring flow, groundwater level, stream base flow, and cave drip) at several sites in two karst aquifers: the Edwards aquifer (Texas, USA) and the Madison aquifer (South Dakota, USA). A lumped-parameter model simulates nonlinear soil moisture changes for estimation of recharge, and a time-variant convolution model simulates the aquifer response to this recharge. Model fit to data is 2.4% better for calibration periods than for validation periods according to the Nash–Sutcliffe coefficient of efficiency, which ranges from 0.53 to 0.94 for validation periods. We use metrics that describe the shapes of the impulse-response functions (IRFs) obtained from convolution modeling to make comparisons in the distribution of response times among sites and between aquifers. Time-variant IRFs were applied to 62% of the sites. Principal component analysis (PCA) of metrics describing the shapes of the IRFs indicates three principal components that together account for 84% of the variability in IRF shape: the first is related to IRF skewness and temporal spread and accounts for 51% of the variability; the second and third largely are related to time-variant properties and together account for 33% of the variability. Sites with IRFs that dominantly comprise exponential curves are separated geographically from those dominantly comprising lognormal curves in both aquifers as a result of spatial heterogeneity. The use of multiple IRF metrics in PCA is a novel method to characterize, compare, and classify the way in which different sites and aquifers respond to recharge. As convolution models are developed for additional aquifers, they could contribute to an IRF database and a general classification system for karst aquifers.

South Dakota, Texas↗

USGS2016

Geology, selected geophysics, and hydrogeology of the White River and parts of the Great Salt Lake Desert regional groundwater flow systems, Utah and Nevada

The east-central Great Basin near the Utah-Nevada border contains two great groundwater flow systems. The first, the White River regional groundwater flow system, consists of a string of hydraulically connected hydrographic basins in Nevada spanning about 270 miles from north to south. The northernmost basin is Long Valley and the southernmost basin is the Black Mountain area, a valley bordering the Colorado River. The general regional groundwater flow direction is north to south. The second flow system, the Great Salt Lake Desert regional groundwater flow system, consists of hydrographic basins that straddle the Utah-Nevada border, with a length of about 150 miles from north to south. The general regional groundwater flow direction is from south to north towards the Great Salt Lake Desert. For 15 years with support from the Southern Nevada Water Authority (SNWA), hydrologists, geologists, and geophysicists studied the basin connections and the groundwater resources in these and adjacent flow systems over an area of about 25,000 square miles. A major first part of the SNWA study was constructing a 3-dimensional digital hydrogeologic framework based on geologic maps and cross sections at 1:250,000 scale. This framework documents the presence of three major aquifers: (1) Paleozoic carbonate rocks, (2) Eocene to Miocene volcanic rocks, and (3) Miocene to Holocene basin-fill sediments, as well as confining units that constrain flow. We interpret that movement of most groundwater through and across basins is by fracture-dominated flow along faults/fractures, yet in most places flow is prevented or retarded across faults, so mapping structures gives a first approximation to conduits and barriers to flow. The most important structures by far are high-angle normal faults of the basin-range episode of east-west extensional deformation. This event began at about 20 Ma, although most deformation and the formation of the present topography took place between 10 Ma and present. This topography consists of north-trending basins (mostly grabens) that alternate with north- trending ranges (mostly horsts); erosion of the ranges filled the basins with clastic alluvial basin-fill deposits. Geophysics provides data on the third dimension (cross sections) of the hydrogeologic framework. Audiomagnetotelluric profiles and gravity inversion located faults and enabled us to estimate thicknesses of basin-fill deposits. To this framework, hydrologic studies addressed precipitation, surface water, and springs, as well as groundwater levels, volumes, geochemistry, water budgets, and monitoring. At nearly the same time as our study, the Utah Geological Survey (UGS) and U.S. Geological Survey (USGS) addressed the same issues in many of the same areas, and publication of the efforts by all three agencies reveals a surprising similarity of conclusions, with some critical exceptions, which therefore demonstrates the great value of many scientists independently studying the same complex scientific problem. The differences in conclusions include directions and volumes of some ground- water flow paths, such as one proposed by the USGS of unlikely groundwater flow from Steptoe Valley to southern Snake Valley, and another proposed by the UGS of unlikely significant groundwater recharge flow from the Snake Range to the Fish Springs complex.

Utah↗

USGS2014

Pesticides in groundwater of the United States: decadal-scale changes, 1993-2011

The national occurrence of 83 pesticide compounds in groundwater of the United States and decadal-scale changes in concentrations for 35 compounds were assessed for the 20-year period from 1993–2011. Samples were collected from 1271 wells in 58 nationally distributed well networks. Networks consisted of shallow (mostly monitoring) wells in agricultural and urban land-use areas and deeper (mostly domestic and public supply) wells in major aquifers in mixed land-use areas. Wells were sampled once during 1993–2001 and once during 2002–2011. Pesticides were frequently detected (53% of all samples), but concentrations seldom exceeded human-health benchmarks (1.8% of all samples). The five most frequently detected pesticide compounds—atrazine, deethylatrazine, simazine, metolachlor, and prometon—each had statistically significant (p < 0.1) changes in concentrations between decades in one or more categories of well networks nationally aggregated by land use. For agricultural networks, concentrations of atrazine, metolachlor, and prometon decreased from the first decade to the second decade. For urban networks, deethylatrazine concentrations increased and prometon concentrations decreased. For major aquifers, concentrations of deethylatrazine and simazine increased. The directions of concentration changes for individual well networks generally were consistent with changes determined from nationally aggregated data. Altogether, 36 of the 58 individual well networks had statistically significant changes in concentrations of one or more pesticides between decades, with the majority of changes attributed to the five most frequently detected pesticide compounds. The magnitudes of median decadal-scale concentration changes were small—ranging from −0.09 to 0.03 µg/L—and were 35- to 230,000-fold less than human-health benchmarks.

Groundwater↗

USGS2000

Geochemistry of the Springfield Plateau aquifer of the Ozark Plateaus Province in Arkansas, Kansas, Missouri and Oklahoma, USA

Geochemical data indicate that the Springfield Plateau aquifer, a carbonate aquifer of the Ozark Plateaus Province in central USA, has two distinct hydrochemical zones. Within each hydrochemical zone, water from springs is geochemically and isotopically different than water from wells. Geochemical data indicate that spring water generally interacts less with the surrounding rock and has a shorter residence time, probably as a result of flowing along discrete fractures and solution openings, than water from wells. Water type throughout most of the aquifer was calcium bicarbonate, indicating that carbonate-rock dissolution is the primary geochemical process occurring in the aquifer. Concentrations of calcium, bicarbonate, dissolved oxygen and tritium indicate that most ground water in the aquifer recharged rapidly and is relatively young (less than 40 years). In general, field-measured properties, concentrations of many chemical constituents, and calcite saturation indices were greater in samples from the northern part of the aquifer (hydrochemical zone A) than in samples from the southern part of the aquifer (hydrochemical zone B). Factors affecting differences in the geochemical composition of ground water between the two zones are difficult to identify, but could be related to differences in chert content and possibly primary porosity, solubility of the limestone, and amount and type of cementation between zone A than in zone B. In addition, specific conductance, pH, alkalinity, concentrations of many chemical constituents and calcite saturation indices were greater in samples from wells than in samples from springs in each hydrochemical zone. In contrast, concentrations of dissolved oxygen, nitrite plus nitrate, and chloride generally were greater in samples from springs than in samples from wells. Water from springs generally flows rapidly through large conduits with minimum water-rock interactions. Water from wells flow through small fractures, which restrict flow and increase water-rock interactions. As a result, springs tend to be more susceptible to surface contamination than wells. The results of this study have important implications for the geochemical and hydrogeological processes of similar carbonate aquifers in other geographical locations. Copyright (C) 2000 John Wiley and Sons, Ltd.Geochemical data indicate that the Springfield Plateau carbonate aquifer has two distinct hydrochemical zones. With each hydrochemical zone, water from springs is geochemically and isotopically different from the water from wells. Spring water generally interacts less with the surrounding rock and has a shorter residence time, probably as a result of flowing along discrete fractures and solution openings, than water from wells. Factors affecting the differences in the geochemical composition of groundwater between the two zones are difficult to identify, but could be related to differences in chert content and possibly primary porosity, solubility of the limestone, and amount and type of cementation between zones.

Hydrological Processes↗

USGS2009

Biogeochemistry at a wetland sediment-alluvial aquifer interface in a landfill leachate plume

The biogeochemistry at the interface between sediments in a seasonally ponded wetland (slough) and an alluvial aquifer contaminated with landfill leachate was investigated to evaluate factors that can effect natural attenuation of landfill leachate contaminants in areas of groundwater/surface-water interaction. The biogeochemistry at the wetland-alluvial aquifer interface differed greatly between dry and wet conditions. During dry conditions (low water table), vertically upward discharge was focused at the center of the slough from the fringe of a landfill-derived ammonium plume in the underlying aquifer, resulting in transport of relatively low concentrations of ammonium to the slough sediments with dilution and dispersion as the primary attenuation mechanism. In contrast, during wet conditions (high water table), leachate-contaminated groundwater discharged upward near the upgradient slough bank, where ammonium concentrations in the aquifer where high. Relatively high concentrations of ammonium and other leachate constituents also were transported laterally through the slough porewater to the downgradient bank in wet conditions. Concentrations of the leachate-associated constituents chloride, ammonium, non-volatile dissolved organic carbon, alkalinity, and ferrous iron more than doubled in the slough porewater on the upgradient bank during wet conditions. Chloride, non-volatile dissolved organic carbon (DOC), and bicarbonate acted conservatively during lateral transport in the aquifer and slough porewater, whereas ammonium and potassium were strongly attenuated. Nitrogen isotope variations in ammonium and the distribution of ammonium compared to other cations indicated that sorption was the primary attenuation mechanism for ammonium during lateral transport in the aquifer and the slough porewater. Ammonium attenuation was less efficient, however, in the slough porewater than in the aquifer and possibly occurred by a different sorption mechanism. A stoichiometrically balanced increase in magnesium concentration with decreasing ammonium and potassium concentrations indicated that cation exchange was the sorption mechanism in the slough porewater. Only a partial mass balance could be determined for cations exchanged for ammonium and potassium in the aquifer, indicating that some irreversible sorption may be occurring. Although wetlands commonly are expected to decrease fluxes of contaminants in riparian environments, enhanced attenuation of the leachate contaminants in the slough sediment porewater compared to the aquifer was not observed in this study. The lack of enhanced attenuation can be attributed to the fact that the anoxic plume, comprised largely of recalcitrant DOC and reduced inorganic constituents, interacted with anoxic slough sediments and porewaters, rather than encountering a change in redox conditions that could cause transformation reactions. Nevertheless, the attenuation processes in the narrow zone of groundwater/surface-water interaction were effective in reducing ammonium concentrations by a factor of about 3 during lateral transport across the slough and by a factor of 2 to 10 before release to the surface water. Slough porewater geochemistry also indicated that the slough could be a source of sulfate in dry conditions, potentially providing a terminal electron acceptor for natural attenuation of organic compounds in the leachate plume.

Journal of Contaminant Hydrology↗

USGS2011

Groundwater chemistry near an impoundment for produced water, Powder River Basin, Wyoming, USA

The Powder River Basin is one of the largest producers of coal-bed natural gas (CBNG) in the United States. An important environmental concern in the Basin is the fate of the large amounts of groundwater extracted during CBNG production. Most of this produced water is disposed of in unlined surface impoundments. A 6-year study of groundwater flow and water chemistry at one impoundment, Skewed Reservoir, has produced the most detailed data set for any impoundment in the Basin. Data were collected from a network of 21 observation wells and three suction lysimeters. A groundwater mound formed atop bedrock within initially unsaturated, unconsolidated deposits underlying the reservoir. Heterogeneity in physical and chemical properties of sediments resulted in complex groundwater flow paths and highly variable groundwater chemistry. Sulfate, bicarbonate, sodium, and magnesium were the dominant ions in all areas, but substantial variability existed in relative concentrations; pH varied from less than 3 to more than 9, and total dissolved solids concentrations ranged from less than 5000 to greater than 100,000 mg/L. Selenium was a useful tracer of reservoir water; selenium concentrations exceeded 300 μg/L in samples obtained from 18 of the 24 sampling points. Groundwater travel time from the reservoir to a nearby alluvial aquifer (a linear distance of 177 m) was calculated at 474 days on the basis of selenium concentrations. The produced water is not the primary source of solutes in the groundwater. Naturally occurring salts and minerals within the unsaturated zone, dissolved and mobilized by infiltrating impoundment water, account for most of the solute mass in groundwater. Gypsum dissolution, cation-exchange, and pyrite oxidation appear to be important reactions. The complex geochemistry and groundwater flow paths at the study site underscore the difficulty in assessing effects of surface impoundments on water resources within the Powder River Basin.

Wyoming↗

USGS2005

An evaluation of effects of groundwater exchange on nearshore habitats and water quality of western Lake Erie

Historically, the high potentiometric surface of groundwater in the Silurian/Devonian carbonate aquifer in Monroe County, MI resulted in discharge of highly mineralized, SO 4 -rich groundwater to the Lake Erie shoreline near both Erie State Game Area (ESGA) and Pointe Mouillee State Game Area (PMSGA). Recently, regional groundwater levels near PMSGA have been drawn down as much as 45 m below lake level in apparent response to quarry dewatering. From August to November of 2003, we conducted preliminary studies of groundwater flow dynamics and chemistry, shallow lake water chemistry, and fish and invertebrate communities at both sites. Consistent with regional observations, groundwater flow direction in the nearshore at ESGA was upward, or toward Lake Erie, and shallow nearshore groundwater chemistry was influenced by regional groundwater chemistry. In contrast, at PMSGA, the groundwater flow potential was downward and lake water, influenced by quarry discharge seeping downward into nearshore sediments, produced a different lake and shallow groundwater chemistry than at ESGA. Although the invertebrate and young fish community was similar at the two sites, taxonomic groups tolerant of degraded water quality were more prevalent at PMSGA. Sensitive taxa were more prevalent at ESGA. We propose a conceptual model, based on well-described models of groundwater/seawater interaction along coastal margins, to describe the interconnection among geologic, hydrologic, chemical, and biological processes in the different nearshore habitats of Lake Erie, and we identify processes that warrant further detailed study in the Great Lakes.

Lake Erie↗

USGS1991

Microbial production of organic acids in aquitard sediments and its role in aquifer geochemistry

Microbial activity in aquifers plays an important part in the chemical evolution of ground water 1–5 . The most important terminal electron-accepting microbial processes in deeply buried anaerobic aquifers are iron reduction, sulphate reduction and methanogenesis 5–8 , each of which requires simple organic compounds or hydrogen (H 2 ) as electron donors. Until now, the source of these compounds was unknown because the concentrations of dissolved organic carbon and sedimentary organic carbon in aquifers are extremely low 9–11 . Here we show that rates of microbial fermentation exceed rates of respiration in organic-rich aquitards (low-permeability sediments stratigraphically adjacent to higher-permeability aquifer sediments), resulting in a net accumulation of simple organic acids in pore waters. In aquifers, however, respiration outpaces fermentation, resulting in a net consumption of organic acids. The concentration gradient that develops in response to these two processes drives a net diffusive flux of organic acids from aquitards to aquifers. Diffusion calculations demonstrate that rates of organic acid transport are sufficient to account for observed rates of microbial respiration in aquifers. This overall process effectively links the large pool of sedimentary organic carbon in aquitards to microbial respiration in aquifers, and is a principal mechanism driving groundwater chemistry changes in aquifers.

Nature↗

USGS1990

Rates of microbial metabolism in deep coastal plain aquifers

Rates of microbial metabolism in deep anaerobic aquifers of the Atlantic coastal plain of South Carolina were investigated by both microbiological and geochemical techniques. Rates of [2- 14 C]acetate and [U- 14 C]glucose oxidation as well as geochemical evidence indicated that metabolic rates were faster in the sandy sediments composing the aquifers than in the clayey sediments of the confining layers. In the sandy aquifer sediments, estimates of the rates of CO 2 production (millimoles of CO 2 per liter per year) based on the oxidation of [2- 14 C] acetate were 9.4 × 10 −3 to 2.4 × 10 −1 for the Black Creek aquifer, 1.1 × 10 −2 for the Middendorf aquifer, and <7 × 10 −5 for the Cape Fear aquifer. These estimates were at least 2 orders of magnitude lower than previously published estimates that were based on the accumulation of CO 2 in laboratory incubations of similar deep subsurface sediments. In contrast, geochemical modeling of groundwater chemistry changes along aquifer flowpaths gave rate estimates that ranged from 10 −4 to 10 −6 mmol of CO 2 per liter per year. The age of these sediments (ca. 80 million years) and their organic carbon content suggest that average rates of CO 2 production could have been no more than 10 −4 mmol per liter per year. Thus, laboratory incubations may greatly overestimate the in situ rates of microbial metabolism in deep subsurface environments. This has important implications for the use of laboratory incubations in attempts to estimate biorestoration capacities of deep aquifers. The rate estimates from geochemical modeling indicate that deep aquifers are among the most oligotrophic aquatic environments in which there is ongoing microbial metabolism.

South Carolina↗

USGS1986

Hydrogeologic data for the Dakota aquifer system in Nebraska

Data utilized in preparing an interpretive hydrogeologic report on the Dakota aquifer system in Nebraska are summarized. The study area is a 370,000 sq mi area that includes all of Kansas and Nebraska and parts of Arkansas, Colorado, Missouri, New Mexico, Oklahoma, and Texas. The broad objective for each Regional Aquifer-System analysis (RASA) study is to assemble geologic, hydrologic, and geochemical information; to analyze and develop an understanding of the hydrogeologic system; and to develop predictive capabilities that will contribute to effective management of groundwater resources. The Central Midwest RASA project includes the study of the major regional aquifers that occur in the stratigraphic interval between the Precambrian surface and the top of the Great Plains aquifer system. The Dakota aquifer system in Nebraska, which is the equivalent of the Great Plains aquifer system, can best be defined as those sandstones and shales occurring in the stratigraphic interval between the base of the Cretaceous system and the top of the first major sandstone bed below the Cretaceous Greenhorn Limestone. This aquifer systems underlies approximately 94 percent of the State. Distribution of data sites is not uniform across the State. Although the aquifer systems underlies all or parts of 88 of Nebraska 's 93 counties, hydrogeologic data on the Dakota are available only for 83 counties. Individual data sites were selected on the basis of the completeness and representativeness of data for the site and to provide an adequate areal distribution of data needed to describe the hydrogeology of the aquifer system. Four tables are used to summarize hydrogeologic data. (USGS)

Open-File Report↗

USGS1989

Subsurface storage of liquids in the Floridan aquifer system in south Florida

The Floridan aquifer system in south Florida is composed chiefly of carbonate rocks that range in age from early Miocene to Paleocene. The top of the Floridian aquifer system generally occurs at depths ranging from 500 to 1,000 ft, and the average thickness is about 3,000 ft. It is divided into three general hydrogeologic units that include Upper Floridan aquifer, the middle confining unit, and the Lower Floridan aquifer. Groundwater movement in the Upper Floridan aquifer is generally from the area of highest head in central Florida, eastward to the Straits of Florida, westward to the Gulf of Mexico, and, to a much lesser extent, southward. Injection of nontoxic liquid wastes into deep, saline parts of the Floridan aquifer system as a pollution-control measure began in 1943 with injection of oilfield brine in southwest Florida. Since then, the practice has quickly expanded, and many high capacity municipal and industrial injection wells are now in operation in southeast Florida. The principal use of the Floridan aquifer system in south Florida is for subsurface storage of liquid waste. The Boulder Zone of the Lower Floridan aquifer is extensively used as a receptacle for injected treated municipal wastewater, oilfield brine and, to a lesser extent, industrial wastewater. Pilot studies indicate a potential for cyclic storage of freshwater in the Upper Floridan aquifer in south Florida. (USGS)

Open-File Report↗

USGS2016

Water-level changes in the High Plains aquifer, Republican River Basin in Colorado, Kansas, and Nebraska, 2002 to 2015

The High Plains aquifer underlies 111.8 million acres (about 175,000 square miles) in parts of eight States—Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. More than 95 percent of the water withdrawn from the High Plains aquifer is used for irrigation. Water-level declines began in parts of the High Plains aquifer soon after the beginning of substantial irrigation with groundwater in the aquifer area (about 1950). The Republican River Basin is 15.9 million acres (about 25,000 square miles) and is located in northeast Colorado, northern Kansas, and southwest Nebraska. The Republican River Basin overlies the High Plains aquifer for 87 percent of the basin area. Water-level declines had begun in parts of the High Plains aquifer within the Republican River Basin by 1964. In 2002, management practices were enacted in the Middle Republican Natural Resources District in Nebraska to comply with the Republican River Compact Final Settlement. The U.S. Geological Survey, in cooperation with the Middle Republican Natural Resources District, completed a study of water-level changes in the High Plains aquifer within the Republican River Basin from 2002 to 2015 to enable the Middle Republican Natural Resources District to assess the effect of the management practices, which were specified by the Republican River Compact Final Settlement. Water-level changes determined from this study are presented in this report. Water-level changes from 2002 to 2015 in the High Plains aquifer within the Republican River Basin, by well, ranged from a rise of 9.4 feet to a decline of 43.2 feet. The area-weighted, average water-level change from 2002 to 2015 in this part of the aquifer was a decline of 4.5 feet.

Colorado, Kansas, Nebraska↗

USGS2008

Questa baseline and pre-mining ground-water quality investigation. 17. Geomorphology of the Red River Valley, Taos County, New Mexico, and influence on ground-water flow in the shallow alluvial aquifer

In April 2001, the U.S. Geological Survey (USGS) and the New Mexico Environment Department (NMED) began a cooperative study to infer the pre-mining ground-water chemistry at the Molycorp molybdenum mine site in the Red River Valley of north-central New Mexico. This report is one in a series of reports that can be used to determine pre-mining ground-water conditions at the mine site. Molycorp’s Questa molybdenum mine in the Red River Valley, northern New Mexico, is located near the margin of the Questa caldera in a highly mineralized region. The bedrock of the Taos Range surrounding the Red River is composed of Proterozoic rocks of various types, which are intruded and overlain by Oligocene volcanic rocks associated with the Questa caldera. Locally, these rocks were altered by hydrothermal activity. The alteration zones that contain sulfide minerals are particularly important because they constitute the commercial ore bodies of the region and, where exposed to weathering, form sites of rapid erosion referred to as alteration scars. Over the past thousand years, if not over the entire Holocene, erosion rates were spatially variable. Forested hillslopes eroded at about 0.04 millimeter per year, whereas alteration scars eroded at about 2.7 millimeters per year. The erosion rate of the alteration scars is unusually rapid for naturally occurring sites that have not been disturbed by humans. Watersheds containing large alteration scars delivered more sediment to the Red River Valley than the Red River could remove. Consequently, large debris fans, as much as 80 meters thick, developed within the valley. The geomorphology of the Red River Valley has had several large influences on the hydrology of the shallow alluvial aquifer, and those influences were in effect before the onset of mining within the watershed. Several reaches where alluvial ground water emerges to become Red River streamflow were observed by a tracer dilution study conducted in 2001. The aquifer narrows where erosion-resistant bedrock, which tends to form vertical cliffs, restricts the width of the valley bottom. Although the presence of a shallow bedrock sill, overlain by shallow alluvium, is a plausible cause of ground-water emergence, this cause was not demonstrated in the study area. The water-table gradient can locally decrease in the downstream direction because of changes in the hydraulic properties of the alluvium, and this may be a contributing cause of ground-water emergence. However, at one site (near Cabin Springs), ground-water emergence could not be explained by spatial changes in geometric or hydraulic properties of the aquifer. Furthermore, the available evidence demonstrates that ground water flowing through bedrock fractures or colluvium entered the north side of the alluvial aquifer, and is the cause of ground-water emergence. At that location the alluvial aquifer was already flowing full, causing the excess water to emerge into the stream. An indirect consequence of altered rock in the tributary watersheds is the rapid erosion rate of alteration scars combined with the hydraulic properties of sediments shed from those scars. Where alteration scars are large the debris fans at the mouths of the tributary watersheds substantially encroach into the Red River Valley. At such locations debris-fan materials dominate the width and thickness of the alluvium in the valley and reduce the rate of flow of ground water within the Red River alluvial aquifer. Most sites of groundwater emergence are located immediately upstream from or along the margins of debris fans. A substantial fraction of the ground water approaching a debris fan can emerge to become streamflow. This last observation has three implications. First, very little water can flow the entire length of the study area entirely within the alluvial aquifer because the ground water repeatedly contacts debris-fan sediments over that length. Second, it follows that emerging water containing unique elemental constituents must have entered the alluvial aquifer at a relatively short distance upstream. Third, a gravel aquifer downstream from a large debris fan can transmit more ground water than flows into it through the debris fan. This observation explains how the water table can be naturally, and permanently, located well beneath the level of the bed of a perennial stream.

New Mexico↗

USGS2010

Land-Use Analysis and Simulated Effects of Land-Use Change and Aggregate Mining on Groundwater Flow in the South Platte River Valley, Brighton to Fort Lupton, Colorado

Land use in the South Platte River valley between the cities of Brighton and Fort Lupton, Colo., is undergoing change as urban areas expand, and the extent of aggregate mining in the Brighton-Fort Lupton area is increasing as the demand for aggregate grows in response to urban development. To improve understanding of land-use change and the potential effects of land-use change and aggregate mining on groundwater flow, the U.S. Geological Survey, in cooperation with the cities of Brighton and Fort Lupton, analyzed socioeconomic and land-use trends and constructed a numerical groundwater flow model of the South Platte alluvial aquifer in the Brighton-Fort Lupton area. The numerical groundwater flow model was used to simulate (1) steady-state hydrologic effects of predicted land-use conditions in 2020 and 2040, (2) transient cumulative hydrologic effects of the potential extent of reclaimed aggregate pits in 2020 and 2040, (3) transient hydrologic effects of actively dewatered aggregate pits, and (4) effects of different hypothetical pit spacings and configurations on groundwater levels. The SLEUTH (Slope, Land cover, Exclusion, Urbanization, Transportation, and Hillshade) urban-growth modeling program was used to predict the extent of urban area in 2020 and 2040. Wetlands in the Brighton-Fort Lupton area were mapped as part of the study, and mapped wetland locations and areas of riparian herbaceous vegetation previously mapped by the Colorado Division of Wildlife were compared to simulation results to indicate areas where wetlands or riparian herbaceous vegetation might be affected by groundwater-level changes resulting from land-use change or aggregate mining. Analysis of land-use conditions in 1957, 1977, and 2000 indicated that the general distribution of irrigated land and non-irrigated land remained similar from 1957 to 2000, but both land uses decreased as urban area increased. Urban area increased about 165 percent from 1957 to 1977 and about 56 percent from 1977 to 2000 with most urban growth occurring east of Brighton and Fort Lupton and along major transportation corridors. Land-use conditions in 2020 and 2040 predicted by the SLEUTH modeling program indicated urban growth will continue to develop primarily east of Brighton and Fort Lupton and along major transportation routes, but substantial urban growth also is predicted south and west of Brighton. Steady-state simulations of the hydrologic effects of predicted land-use conditions in 2020 and 2040 indicated groundwater levels declined less than 2 feet relative to simulated groundwater levels in 2000. Groundwater levels declined most where irrigated land was converted to urban area and least where non-irrigated land was converted to urban area. Simulated groundwater-level declines resulting from land-use conditions in 2020 and 2040 are not predicted to substantially affect wetlands or riparian herbaceous vegetation in the study area because the declines are small and wetlands and riparian herbaceous vegetation generally are not located where simulated declines occur. See Report PDF for unabridged abstract.

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