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At least 1,009 records · Page 56Linked to original sources
USGS1992

Simulation of regional ground-water flow in the Cambrian-Ordovician aquifer system in the northern Midwest, United States: in Regional aquifer-system analysis

A six-State area in the northern Midwest of the United States has become increasingly dependent on ground water from the Cambrian-Ordovician aquifer system, which consists of a sequence of sandstones, carbonate rocks, and shales. Ground-water withdrawals from the aquifer system began in the late 1800's and increased to approximately 684 million gallons per day (1,058 cubic feet per second) by 1980. This withdrawal has caused more than 900 feet of decline in the potentiometric surface of the aquifer system in parts of the Chicago, Ill., area. Pumping in Minneapolis-St. Paul, Minn., Milwaukee, Wis., and central Iowa has produced a few hundreds of feet of water-level decline. A quasi-three-dimensional ground-water flow model was developed to improve understanding of the regional ground-water flow system by simulating the aquifer system under the conditions that existed before and during ground-water development. The Cambrian-Ordovician aquifer system and the overlying rocks were incorporated in the conceptual model as five aquifer layers with four intervening confining layers. The aquifer layers, from top to bottom, are as follows: Quaternary deposits and Cretaceous rocks (aquifer layer 5); basal Devonian carbonate rocks and underlying Silurian carbonate rocks (aquifer layer 4); Middle Ordovician St. Peter Sandstone, Lower Ordovician Prairie du Chien Group, and Upper Cambrian Jordan Sandstone (aquifer layer 3); Upper Cambrian Ironton and Galesville Sandstones (aquifer layer 2); and Upper Cambrian Mount Simon Sandstone and Precambrian Hinckley Sandstone (aquifer layer 1). The effects on the flow system of ground water having variable density and the individual aquifer layer contribution of flow to wells open to several aquifer layers were simulated by incorporating appropriate terms in the ground-water flow equation and corresponding modifications in the ground-water flow model. Results of steady-state simulations are shown as maps of freshwater head and as flow-rate vectors. A comparison was made of available predevelopment head data and simulated predevelopment heads for the Mount Simon, St. Peter-Prairie du Chien-Jordan, and Silurian-Devonian aquifers. The root mean square of the differences between observed and simulated heads for these aquifers was 53, 36, and 44 feet, respectively. Steady-state model simulation indicates that regional recharge areas are located in northwestern Iowa, southeastern Minnesota, much of Wisconsin, northern Illinois, and central Missouri. Regional discharge areas are located near the Mississippi River and its tributaries, the Missouri River, Lake Michigan, and the Illinois basin. Results of a transient simulation of the period 1861 to 1980 are shown as maps of freshwater head and freshwater-head decline. The root mean square of the differences between observed and simulated heads for the St. Peter-Prairie du Chien-Jordan aquifer was 63 feet. In addition, hydrographs of simulated hydraulic head were compared with hydrographs of observed head in wells open to various combinations of aquifers. The numerous head measurements within a model node display a wide range in magnitude; however, their historical trend generally follows the trend of the simulated heads. The simulated recharge from the glacial drift to the immediately underlying bedrock aquifers averages 0.03, 0.06, 0.24, and 0.02 inch per year, respectively, to the Mount Simon, Ironton-Galesville, St. Peter- Prairie du Chien-Jordan, and Silurian-Devonian aquifers for predevelopment conditions and 0.03, 0.07, 0.45, and 0.07 inch per year, respectively, to the same aquifers for 1976-80. These recharge rates are less than 1.5 percent of average annual precipitation of about 30 inches per year. Most of the recharge from precipitation discharges to streams as base flow through local and intermediate ground-water flow systems. Only a small fraction of the precipitation recharges the deeper, regional flow system. The simulated predevelopment recharge of 571 cubic feet per second is balanced by an equivalent discharge. For the period 1976-80, simulated recharge increased to 1,398 cubic feet per second. Total discharge, including pumpage from the four bedrock aquifers, increased to 1,619 cubic feet per second. The difference in recharge and discharge during this period is from aquifer storage. Results of variable-density simulations indicate that the rate of ground-water movement is small in areas where ground water is highly mineralized. The rates and directions are controlled by the intrinsic permeability of the rock, freshwater head gradients, and gravitational force.

Iowa, Illinois, Indiana, Michigan, Minnesota, Miss↗
USGS2002

Simulation of Ground-Water Flow in the Middle Rio Grande Basin Between Cochiti and San Acacia, New Mexico

This report describes a three-dimensional, finite difference, ground-water-flow model of the Santa Fe Group aquifer system within the Middle Rio Grande Basin between Cochiti and San Acacia, New Mexico. The aquifer system is composed of the Santa Fe Group of middle Tertiary to Quaternary age and post-Santa Fe Group valley and basin-fill deposits of Quaternary age. Population increases in the basin since the 1940's have caused dramatic increases in ground-water withdrawals from the aquifer system, resulting in large ground-water-level declines. Because the Rio Grande is hydraulically connected to the aquifer system, these ground-water withdrawals have also decreased flow in the Rio Grande. Concern about water resources in the basin led to the development of a research plan for the basin focused on the hydrologic interaction of ground water and surface water (McAda, D.P., 1996, Plan of study to quantify the hydrologic relation between the Rio Grande and the Santa Fe Group aquifer system near Albuquerque, central New Mexico: U.S. Geological Survey Water-Resources Investigations Report 96-4006, 58 p.). A multiyear research effort followed, funded and conducted by the U.S. Geological Survey and other agencies (Bartolino, J.R., and Cole, J.C., 2002, Ground-water resources of the Middle Rio Grande Basin, New Mexico: U.S. Geological Survey Circular 1222, 132 p.). The modeling work described in this report incorporates the results of much of this work and is the culmination of this multiyear study. The purpose of the model is (1) to integrate the components of the ground-water-flow system, including the hydrologic interaction between the surface-water systems in the basin, to better understand the geohydrology of the basin and (2) to provide a tool to help water managers plan for and administer the use of basin water resources. The aquifer system is represented by nine model layers extending from the water table to the pre-Santa Fe Group basement rocks, as much as 9,000 feet below the NGVD 29. The horizontal grid contains 156 rows and 80 columns, each spaced 3,281 feet (1 kilometer) apart. The model simulates predevelopment steady-state conditions and historical transient conditions from 1900 to March 2000 in 1 steady-state and 52 historical stress periods. Average annual conditions are simulated prior to 1990, and seasonal (winter and irrigation season) conditions are simulated from 1990 to March 2000. The model simulates mountain-front, tributary, and subsurface recharge; canal, irrigation, and septic-field seepage; and ground-water withdrawal as specified-flow boundaries. The model simulates the Rio Grande, riverside drains, Jemez River, Jemez Canyon Reservoir, Cochiti Lake, riparian evapotranspiration, and interior drains as head-dependent flow boundaries. Hydrologic properties representing the Santa Fe Group aquifer system in the ground-water-flow model are horizontal hydraulic conductivity, vertical hydraulic conductivity, specific storage, and specific yield. Variable horizontal anisotropy is applied to the model so that hydraulic conductivity in the north-south direction (along model columns) is greater than hydraulic conductivity in the east-west direction (along model rows) over much of the model. This pattern of horizontal anisotropy was simulated to reflect the generally north-south orientation of faulting over much of the modeled area. With variable horizontal anisotropy, horizontal hydraulic conductivities in the model range from 0.05 to 60 feet per day. Vertical hydraulic conductivity is specified in the model as a horizontal to vertical anisotropy ratio (calculated to be 150:1 in the model) multiplied by the horizontal hydraulic conductivity along rows. Specific storage was estimated to be 2 x 10-6 per foot in the model. Specific yield was estimated to be 0.2 (dimensionless). A ground-water-flow model is a tool that can integrate the complex interactions of hydrologic boundary conditions, aquifer materials

Water-Resources Investigations Report↗
USGS1997

Numerical simulation of ground-water flow through glacial deposits and crystalline bedrock in the Mirror Lake area, Grafton County, New Hampshire

This report documents the development of a computer model to simulate steady-state (long-term average) flow of ground water in the vicinity of Mirror Lake, which lies at the eastern end of the Hubbard Brook valley in central New Hampshire. The 10-km2 study area includes Mirror Lake, the three streams that flow into Mirror Lake, Leeman's Brook, Paradise Brook, and parts of Hubbard Brook and the Pemigewasset River. The topography of the area is characterized by steep hillsides and relatively flat valleys. Major hydrogeologic units include glacial deposits, composed of till containing pockets of sand and gravel, and fractured crystalline bedrock, composed of schist intruded by granite, pegmatite, and lamprophyre. Ground water occurs in both the glacial deposits and bedrock. Precipitation and snowmelt infiltrate to the water table on the hillsides, flow downslope through the saturated glacial deposits and fractured bedrock, and discharge to streams and to Mirror Lake. The model domain includes the glacial deposits, the uppermost 150m of bedrock, Mirror Lake, the layer of organic sediments on the lake bottom, and streams and rivers within the study area. A streamflow routing package was included in the model to simulate baseflow in streams and interaction between streams and ground water. Recharge from precipitation is assumed to be areally uniform, and riparian evapotranspiration along stream banks is assumed negligible. The spatial distribution of hydraulic conductivity is represented by dividing the model domain into several zones, each having uniform hydraulic properties. Local variations in recharge and hydraulic conductivities are ignored; therefore, the simulation results characterize the general ground-water system, not local details of ground-water movement. The model was calibrated using a nonlinear regression method to match hydraulic heads measured in piezometers and wells, and baseflow in three inlet streams to Mirror Lake. Model calibration indicates that recharge from precipitation to the water table is 26 to 28 cm/year. Hydraulic conductivities are 1.7 x 10-6 to 2.7 x 10-6 m/s for glacial deposits, about 3 x 10-7 m/s for bedrock beneath lower hillsides and valleys, and about 6x10-8 m/s for bedrock beneath upper hillsides and hilltops. Analysis of parameter uncertainty indicates that the above values are well constrained, at least within the context of regression analysis. In the regression, several attributes of the ground-water flow model are assumed perfectly known. The hydraulic conductivity for bedrock beneath upper hillsides and hilltops was determined from few data, and additional data are needed to further confirm this result. Model fit was not improved by introducing a 10-to-1 ration of horizontal-to-vertical anisotropy in the hydraulic conductivity of the glacial deposits, or by varying hydraulic conductivity with depth in the modeled part (uppermost 150m) of the bedrock. The calibrated model was used to delineate the Mirror Lake ground-water basin, defined as the volumes of subsurface through which ground water flows from the water table to Mirror Lake or its inlet streams. Results indicate that Mirror Lake and its inlet streams drain an area of ground-water recharge that is about 1.5 times the area of the surface-water basin. The ground-water basin extends far up the hillside on the northwestern part of the study area. Ground water from this area flows at depth under Norris Brook to discharge into Mirror Lake or its inlet streams. As a result, the Mirror Lake ground-water basin extends beneath the adjacent ground-water basin that drains into Norris Brook. Model simulation indicates that approximately 300,000 m3/year of precipitation recharges the Mirror Lake ground-water basin. About half the recharge enters the basin in areas where the simulated water table lies in glacial deposits; the other half enters the basin in areas where the simulated water table lies in be

New Hampshire↗
USGS2003

Phosphorus in a ground-water contaminant plume discharging to Ashumet Pond, Cape Cod, Massachusetts, 1999

The discharge of a plume of sewagecontaminated ground water emanating from the Massachusetts Military Reservation to Ashumet Pond on Cape Cod, Massachusetts, has caused concern about excessive loading of nutrients, particularly phosphorus, to the pond. The U.S. Air Force is considering remedial actions to mitigate potentially adverse effects on the ecological characteristics of the pond from continued phosphorus loading. Concentrations as great as 3 milligrams per liter of dissolved phosphorus (as P) are in ground water near the pond's shoreline; concentrations greater than 5 milligrams per liter of phosphorus are in ground water farther upgradient. Temporary drive-point wells were used to collect water samples from 2 feet below the pond bottom to delineate concentration distributions in the pore waters of the pond-bottom sediments. Measurements in the field of specific conductance and colorimetrically determined orthophosphate concentrations provided real-time data to guide the sampling. The contaminant plume discharges to the Fishermans Cove area of Ashumet Pond as evidenced by elevated levels of specific conductance and boron, which are chemically conservative indicators of the sewage-contaminated ground water. Concentrations of nonconservative species, such as dissolved phosphorus, manganese, nitrate, and ammonium, also were elevated above background levels in ground water discharging to the pond, but in spatially complex distributions that reflect their distributions in ground water upgradient of the pond. Phosphorus concentrations exceeded background levels (greater than 0.10 milligram per liter) in the pond-bottom pore water along 875 feet of shoreline. Greatest concentrations (greater than 2 milligrams per liter) occurred within 30 feet of the shore in an area about 225 feet long. Calculations of phosphorus flux in the aquifer upgradient of Ashumet Pond, as determined from water-flux estimates from a steady-state ground-water-flow model and phosphorus concentrations (in 1999) from multilevel samplers about 75 feet upgradient of the pond, indicate that dissolved phosphorus moves towards the pond and discharges to it with the inflowing ground water at a rate as high as about 316 kilograms per year.

Massachusetts↗
USGS1997

Measurement of ground-water storage change and specific yield using the temporal-gravity method near Rillito Creek, Tucson, Arizona

The temporal-gravity method was used to estimate ground-water storage change and specific -yield values at wells near Rillito Creek, Tucson, Arizona, between early December 1992 and early January 1994. The method applies Newton's Law of Gravitation to measure changes in the local gravitational field of the Earth that are caused by changes in the mass and volume of ground water. Gravity at 50 stations in a 6-square-mile area was measured repeatedly relative to gravity at two bedrock stations. Ephemeral recharge through streamflow infiltration during the winter of 1992-93 resulted in water-level rises and gravity increases near Rillito Creek as the volume of ground water in storage increased. Water levels in wells rose as much as 30 feet, and gravity increased as much as 90 microgals. Water levels declined and gravity decreased near the stream after the last major winter flow but continued to rise and increase, respectively, in downgradient areas. Water levels and gravity relative to bedrock were measured at 10 wells. Good linear correlations between water levels and gravity values at five wells nearest the stream allowed for the estimation of specific-yield values for corresponding stratigraphic units assuming the mass change occurred in an infinite horizonal slab of uniform thickness. Specific-yield values for the stream-channel deposits at three wells ranged from 0.15 to 0.34, and correlation coefficients ranged from 0.81 to 0.99. Specific-yield values for the Fort Lowell Formation at three wells ranged from 0.07 to 0.18, and correlation coefficients ranged from 0.82 to 0.93. Specific-yield values were not calculated for the five wells farthest from the stream because of insufficient water-level and gravity change or poor correlations between water level and gravity. Poor correlations between water levels and gravity resulted from ground-water storage change in perched aquifers and in the unsaturated zone near ephemeral streams. Seasonal distributions of ground-water storage change since early December 1992 were evaluated from gravity change at all stations using Gauss's Law. Changes in the distribution of gravity are caused by the flow of water into or out of ground-water storage. Gravity along two profiles was measured frequently to evaluate spatial and temporal distributions of gravity change. Gravity variations indicated preferential ground-water flow to the south in the western part of the study area where the saturate thickness of the aquifer is greatest. Storage changes from December 1992 through early March 1993, mid-May 1993, late August 1993, and early January 1994 were calculated as increases of 7,900, 8,000, 6,300, and 3,700 acre-feet, respectively. Seasonal variations in storage were caused by ground-water withdrawlas, ground-water flow across the boundaries of the gravity-station network, and streamflow infiltration from December 1992 through late April 1993. Most of the estimated recharge of 10,900 acre-feet occurred before mid-May 1993.

Arizona↗
USGS1964

Use of ground-water reservoirs for storage of surface water in the San Joaquin Valley, California

The San Joaquin Valley includes roughly the southern two-thirds of the Central Valley of California, extending 250 miles from Stockton on the north to Grapevine at the foot of the Tehachapi Mountains. The valley floor ranges in width from 25 miles near Bakersfield to about 55 miles near Visalia; it has a surface area of about 10,000 square miles. More than one-quarter of all the ground water pumped for irrigation in the United States is used in this highly productive valley. Withdrawal of ground water from storage by heavy pumping not only provides a needed irrigation water supply, but it also lowers the ground-water level and makes storage space available in which to conserve excess water during periods of heavy runoff. A storage capacity estimated to be 93 million acre-feet to a depth of 200 feet is available in this ground-water reservoir. This is about nine times the combined capacity of the existing and proposed surface-water reservoirs in the San Joaquin Valley under the California Water Plan. The landforms of the San Joaquin Valley include dissected uplands, low plains and fans, river flood plains and channels, and overflow lands and lake bottoms. Below the land surface, unconsolidated sediments derived from the surrounding mountain highlands extend downward for hundreds of feet. These unconsolidated deposits, consisting chiefly of alluvial deposits, but including some widespread lacustrine sediments, are the principal source of ground water in the valley. Ground water occurs under confined and unconfined conditions in the San Joaquin Valley. In much of the western, central, and southeastern parts of the valley, three distinct ground-water reservoirs are present. In downward succession these are 1) a body of unconfined and semiconfined fresh water in alluvial deposits of Recent, Pleistocene, and possibly later Pliocene age, overlying the Corcoran clay member of the Tulare formation; 2) a body of fresh water confined beneath the Corcoran clay member, which occurs in alluvial and lacustrine deposits of late Pliocene age or older; and 3) a body of saline connate water contained in marine sediments of middle Pliocene or older age, which underlies the fresh-water body throughout the area. In much of the eastern part of the valley, especially in the areas of the major streams, the Corcoran clay member is not present and ground water occurs as one fresh-water body to considerable depth. The ground-water body is replenished by infiltration of rainfall, by infiltration from streams, canals, and ditches, by underflow entering the valley from tributary stream canyons, and by infiltration of excess irrigation water. In much of the valley, however, the annual rainfall is so low that little penetrates deeply, and soil-moisture deficiency is perennial. Infiltration from stream channels and canals and from irrigated fields are the principal sources of groundwater recharge. The ground-water storage capacity of the San Joaquin Valley has been estimated in an earlier report (Davis and others, 1959) as 93 million acre-feet. This is the quantity of water that would drain by gravity from the valley deposits if the regional water level were lowered from 10 to 200 feet below the land surface. Storage capacity was estimated for only the part of the valley considered to be potentially usable as a ground-water reservoir. In this study, a 200foot depth was selected as a practical valley-wide depth limit for unwatering under full utilization of the ground-water reservoir, even though in localized areas sections in excess of 350 feet in depth have already been dewatered. Some of the factors that locally limit the utilization of the ground-water reservoir are inferior water quality, relatively impermeable surface soils, and relatively impermeable subsurface deposits. On the basis of a detailed analysis of la peg model, the subsurface geology of the San Joaquin Valley was subdivided into predominantly permeable and impermeable zones in the 1

Water Supply Paper↗
USGS1990

Ground-water hydrology of Pahvant Valley and adjacent areas, Utah

The primary ground-water reservoir in Pahvant Valley and adjacent areas is in the unconsolidated basin fill and interbedded basalt. Recharge in 1959 was estimated to be about 70,000 acre-feet per year and was mostly by seepage from streams, canals, and unconsumed irrigation water and by infiltration of precipitation. Discharge in 1959 was estimated to be about 109,000 acre-feet and was mostly from springs, evapotranspiration, and wells. Water-level declines of more than 50 feet occurred in some areas between 1953 and 1980 because of less-than-normal precipitation and extensive pumping for irrigation. Water levels recovered most of these declines between 1983 and 1986 because of reduced withdrawals and record quantities of precipitation. The quality of ground water in the area west of Kanosh has deteriorated since large ground-water withdrawals began in about 1953. The cause of the deterioration probably is movement of poor quality water into the area from the southwest and possibly the west during periods of large ground-water withdrawals and recycling of irrigation water. The quality of water from some wells has improved since 1983, due to increased recharge and decreased withdrawals for irrigation. Water-level declines of m:>re than 80 feet in some parts of Pahvant Valley are projected if ground-water withdrawals continue for 20 years at the 1977 rate of about 96,000 acre-feet. Rises of as much as 58 feet and declines of as much as 47 feet are projected with withdrawals of 48,000 acre-feet per year for 20 years. The elimination of recharge from the Central Utah Canal is projected to cause water-level declines of up to 8 feet near the canal.

Utah↗
USGS2002

Quality of shallow ground water in areas of recent residential and commercial development, Wichita, Kansas, 2000

Water samples from 30 randomly distributed monitoring wells in areas of recent residential and commercial development (1960–96), Wichita, Kansas, were collected in 2000 as part of the High Plains Regional Ground-Water Study conducted by the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. The samples were analyzed for about 170 water-quality constituents that included chlorofluorocarbons, physical properties, dissolved solids and major ions, nutrients and dissolved organic carbon, trace elements, pesticide compounds, and volatile organic compounds. The purpose of this report is to provide an assessment of water quality in recharge to shallow ground water underlying areas of recent residential and commercial development and to determine the relation of ground-water quality to overlying urban land use. Analyses of water from the 30 monitoring wells for chlorofluorocarbons were used to estimate apparent dates of recharge. Water from 18 wells with nondegraded and uncontaminated chlorofluorocarbon concentrations had calculated apparent recharge dates that ranged from 1979 to 1990 with an average date of 1986. Water from 14 monitoring wells (47 percent) exceeded the 500-milligrams-per-liter Secondary Maximum Contaminant Level established by the U.S. Environmental Protection Agency for dissolved solids in drinking water. The Secondary Maximum Contaminant Levels of 250 milligrams per liter for chloride and sulfate were exceeded in water from one well. The source of the largest concentrations of dissolved solids and associated ions, such as chloride and sulfate, in shallow ground water in the study area probably is highly mineralized water moving out of the Arkansas River into the adjacent, unconsolidated deposits and mixing with the dominant calcium bicarbonate water in the deposits. Concentrations of most nutrients in water from the sampled wells were small, with the exception of nitrate. Although water from the sampled wells did not have nitrate concentrations larger than the 10-milligram-per-liter Maximum Contaminant Level for drinking water, water from 50 percent of the sampled wells showed nitrate enrichment (concentrations greater than 2.0 milligrams per liter). Most trace elements in water from the sampled wells were detected only in small concentrations, and few exceeded respective water-quality standards. Twenty percent of iron concentrations, 40 percent of manganese concentrations, 3 percent of arsenic concentrations, and 13 percent of uranium concentrations exceeded respective Maximum Contaminant Levels or Secondary Maximum Contaminant Levels. A total of 47 pesticide compounds were analyzed in ground-water samples during this study. Water from 73 percent of the wells sampled had detectable concentrations of one or more of 8 of these 47 compounds. The herbicide atrazine or its degradation product deethylatrazine were detected most frequently (in water from 70 percent of the sampled wells). Metolachlor was detected in water from 10 percent of the wells, and simazine was detected in water from 30 percent of the wells sampled. Other pesticides detected included dieldrin, pendimethalin, prometon, and tebuthiuron (each in water from 3 percent of the wells). All concentrations of these compounds were less than established Maximum Contaminant Levels. A total of 85 volatile organic compounds (VOCs) were analyzed in ground-water samples during this study. Water from 43 percent of the wells had a detectable concentration of one or more VOCs. Chloroform was the most frequently detected VOC (23 percent of the wells sampled).Seven other VOCs were detected in water at frequencies of 13 percent or less in the wells sampled. Concentrations of VOCs were less than respective Maximum Contaminant Levels, except one sample with a concentration of 9.0 micrograms per liter for tetrachloroethylene (Maximum Contaminant Level of 5.0 micrograms per liter). An analysis of hydraulic gradient, flow velocity, and residence time of the ground water indicated potential recharge areas that ranged from 0.8 to 2.8 miles upgradient of monitoring-well locations. Nineteen (63 percent) of these potential recharge areas were in agricultural areas or areas in transition from agricultural to residential and (or) commercial land use at the time water sampled from the monitoring wells was recharged to the shallow ground water. The occurrence of atrazine or deethylatrazine in water from 70 percent of the monitoring wells may indicate a historical agricultural land-use relation. This agricultural relation also may affect concentrations of other water-quality constituents of possible agricultural origin such as nitrate, which generally were in excess of background concentrations in shallow ground water.

Kansas↗
USGS2002

Hydrogeologic framework, ground-water geochemistry, and assessment of nitrogen yield from base flow in two agricultural watersheds, Kent County, Maryland

Hydrostratigraphic and geochemical data collected in two adjacent watersheds on the Delmarva Peninsula, in Kent County, Maryland, indicate that shallow subsurface stratigraphy is an important factor that affects the concentrations of nitrogen in ground water discharging as stream base flow. The flux of nitrogen from shallow aquifers can contribute substantially to the eutrophication of streams and estuaries, degrading water quality and aquatic habitats. The information presented in this report includes a hydrostratigraphic framework for the Locust Grove study area, analyses and interpretation of ground-water chemistry, and an analysis of nutrient yields from stream base flow. An understanding of the processes by which ground-water nitrogen discharges to streams is important for optimal management of nutrients in watersheds in which ground-water discharge is an appreciable percentage of total streamflow. The U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency (USEPA), collected and analyzed hydrostratigraphic and geochemical data in support of ground-water flow modeling by the USEPA. The adjacent watersheds of Morgan Creek and Chesterville Branch have similar topography and land use; however, reported nitrogen concentrations are generally 6 to 10 milligrams per liter in Chesterville Branch but only 2 to 4 milligrams per liter in Morgan Creek. Ground water in the surficial aquifer in the recharge areas of both streams has high concentrations of nitrate (greater than 10 milligrams per liter as N) and dissolved oxygen. One component of the ground water discharging to Morgan Creek typically is anoxic and contains virtually no dissolved nitrate; most of the ground water discharging to Chesterville Branch is oxygenated and contains moderately high concentrations of nitrate. The surficial aquifer in the study area is composed of the deeply weathered sands and gravels of the Pensauken Formation (the Columbia aquifer) and the underlying glauconitic sands of the upper Aquia Formation (the Aquia aquifer). The lower 6 to 9 meters of the Aquia Formation is a low-permeability silt-clay with abundant glauconite. The Aquia confining layer underlies the Columbia-Aquia surficial aquifer throughout the study area. The sediment redox transition, identified in cores, that occurs in the upper 0.5 to 1 meter of the Aquia confining layer is thought to be a site for subsurface denitrification of ground water. The first confined aquifer is composed of the glauconitic sands in the upper 9 to 11 meters of the Hornerstown Formation. The Hornerstown aquifer is underlain by 10 to 15 meters of glauconitic silt-clay at the base of the Hornerstown Formation (the Hornerstown confining layer), and 5 meters of low-permeability clay in the underlying Severn Formation. The Aquia and Hornerstown Formations dip and thicken to the southeast, and the Aquia confining layer subcrops shallowly (within 5 meters of the land surface) in a band that strikes southwest to northeast across the northern edge of the study area. The surficial aquifer is very thin (generally less than 5 meters) north of Morgan Creek, and the alluvial valley of Morgan Creek has incised into the top of the Aquia confining layer. In contrast, the Aquia confining layer lies 22 meters below Chesterville Branch, and the surficial aquifer approaches 30 meters in thickness (away from the creek). Chemically reduced iron sulfides and glauconite in the Aquia confining layer are likely substrates for denitrification of nitrate in ground water. Evidence from the dissolved concentrations of nitrate, sulfate, iron, argon, and nitrogen gas, and stable nitrogen isotopes support the interpretation that ground water flowing near the top of the Aquia confining layer, or through the confined Hornerstown aquifer, has undergone denitrification. This process appears to have the greatest effect on ground-water chemistry north of Morgan Creek, where the surficial aquifer is thin and a greater percentage of the ground water contacts the Aquia confining layer. The base-flow discharges of total nitrogen from the two watersheds are of similar magnitude, although Chesterville Branch has somewhat higher loads (29,000 kilograms of nitrogen per year) than Morgan Creek (20,000 kilograms of nitrogen per year), although Morgan Creek has a larger drainage area and a greater discharge of water. The base-flow yield of nitrogen (load per unit area) in Chesterville Branch (median of 0.058 grams per second per square kilometer at the outlet) is more than twice that of Morgan Creek (median of 0.022 grams per second per square kilometer at the outlet), reflecting the higher concentration of nitrate in ground water discharging to Chesterville Branch. Total nitrogen concentrations tend to decrease downstream in Chesterville Branch and increase downstream in Morgan Creek. The downstream trend in Chesterville Branch may be affected by instream nitrogen uptake and denitrification, and an increasing proportion of older, denitrified ground water in downstream discharge. The downstream trends in Morgan Creek may be affected by inflow from tributaries, downstream changes in the source of discharge water, and downstream changes in the riparian zone, which could affect the processes and degree of denitrification. Although these two watersheds appear to have landscape features (such as topography, land use, and soils) that would produce similar nitrogen discharges, a more detailed examination of landscape features indicates that Chesterville Branch has soils that are slightly better drained, tributary stream outlets at higher altitudes, and a slightly higher percentage of agricultural land. All of these factors have been related to higher nitrogen yields. Nonetheless, most of the data support the interpretation that hydrostratigraphy has the greatest effect in producing the difference in nitrogen yields between the two watersheds.

Maryland↗
USGS2009

Examining Submarine Ground-Water Discharge into Florida Bay by using 222Rn and Continuous Resistivity Profiling

Estimates of submarine ground-water discharge (SGD) into Florida Bay remain one of the least understood components of a regional water balance. To quantify the magnitude and seasonality of SGD into upper Florida Bay, research activities included the use of the natural geochemical tracer, 222Rn, to examine potential SGD hotspots (222Rn surveys) and to quantify the total (saline + fresh water component) SGD rates at select sites (222Rn time-series). To obtain a synoptic map of the 222Rn distribution within our study site in Florida Bay, we set up a flow-through system on a small boat that consisted of a Differential Global Positioning System, a calibrated YSI, Inc CTD sensor with a sampling rate of 0.5 min, and a submersible pump (z = 0.5 m) that continuously fed water into an air/water exchanger that was plumbed simultaneously into four RAD7 222Rn air monitors. To obtain local advective ground-water flux estimates, 222Rn time-series experiments were deployed at strategic positions across hydrologic and geologic gradients within our study site. These time-series stations consisted of a submersible pump, a Solinist DIVER (to record continuous CTD parameters) and two RAD7 222Rn air monitors plumbed into an air/water exchanger. Repeat time-series 222Rn measurements were conducted for 3-4 days across several tidal excursions. Radon was also measured in the air during each sampling campaign by a dedicated RAD7. We obtained ground-water discharge information by calculating a 222Rn mass balance that accounted for lateral and horizontal exchange, as well as an appropriate ground-water 222Rn end member activity. Another research component utilized marine continuous resistivity profiling (CRP) surveys to examine the subsurface salinity structure within Florida Bay sediments. This system consisted of an AGI SuperSting 8 channel receiver attached to a streamer cable that had two current (A,B) electrodes and nine potential electrodes that were spaced 10 m apart. A separate DGPS continuously sent position information to the SuperSting. Results indicate that the 222Rn maps provide a useful gauge of relative ground-water discharge into upper Florida Bay. The 222Rn time-series measurements provide a reasonable estimate of site- specific total (saline and fresh) ground-water discharge (mean = 12.5+-11.8 cm d-1), while the saline nature of the shallow ground-water at our study site, as evidenced by CPR results, indicates that most of this discharge must be recycled sea water. The CRP data show some interesting trends that appear to be consistent with subsurface geologic and hydrologic characterization. For example, some of the highest resistivity (electrical conductivity-1) values were recorded where one would expect a slight subsurface freshening (for example bayside Key Largo, or below the C111 canal).

Open-File Report↗
USGS2006

Estimating cost of ground‐water withdrawal for river basin planning

Comparative costs of ground water were needed for comprehensive planning of water resources development in the Susquehanna River basin in order to appraise the feasibility of alternative sources of water supply. Log‐normal plots on logarithmic‐probability paper that represented specific capacities adjusted to 180 days of pumping were used to estimate well yields and costs of obtaining the ground water from each of 65 potential aquifers. The 25, 50, and 75 percent probability of occurrence of the specific capacities of successful wells were used in the calculations. The estimated well yields at these probabilities of occurrence were obtained using hypothetical well designs and selected drawdowns. Ground‐water costs for the estimated or design yields were calculated using amortized costs of well construction, electrical power costs, and maintenance costs, all obtained from standard sources. The calculated well yields and costs for the 25 to 75 percent probability interval range from 15 to 9,000 gpm (gallons per minute) and from $0.004 to $0.11 per thousand gallons of design yield. The yields and costs group according to aquifer rock type. The calculated costs decrease with increasing well yield and the available yield depends upon the aquifer rock type available. Representative costs per thousand gallons of design yield for selected yields from aquifers composed of different rock types analyzed are: 50 gpm −$0.060 for shale and interbedded sandstone and shale, and $0.050 for metamorphic rock; 100 gpm ‐ $0.043 or shale and interbedded sandstone and shale, $0.037 for metamorphic rock, and $0.032 for carbonate rock; 500 gpm—$0.020 for sandstone, $0.015 for carbonate rock, and $0.012 for glacial sand and gravel; and 1,000 gpm —$0.009 for glacial sand and gravel. Differences in cost to obtain the same yield from different rock types are primarily due to differences in electrical power costs as determined by differences in pumping water levels. If used with caution, the generalized yield and cost estimates for aquifer rock types may have usefulness in estimating ground‐water costs and yields in similar humid areas. They are primarily useful for planning and comparative purposes, but not for the actual design of engineering projects.

Groundwater↗
USGS2009

Quality characteristics of ground water in the Ozark aquifer of northwestern Arkansas, southeastern Kansas, southwestern Missouri and northeastern Oklahoma, 2006-07

Because of water quantity and quality concerns within the Ozark aquifer, the State of Kansas in 2004 issued a moratorium on most new appropriations from the aquifer until results were made available from a cooperative study between the U.S. Geological Survey and the Kansas Water Office. The purposes of the study were to develop a regional ground-water flow model and a water-quality assessment of the Ozark aquifer in northwestern Arkansas, southeastern Kansas, southwestern Missouri, and northeastern Oklahoma (study area). In 2006 and 2007, water-quality samples were collected from 40 water-supply wells completed in the Ozark aquifer and spatially distributed throughout the study area. Samples were analyzed for physical properties, dissolved solids and major ions, nutrients, trace elements, and selected isotopes. This report presents the results of the water-quality assessment part of the cooperative study. Water-quality characteristics were evaluated relative to U.S. Environmental Protection Agency drinking-water standards. Secondary Drinking-Water Regulations were exceeded for dissolved solids (11 wells), sulfate and chloride (2 wells each), fluoride (3 wells), iron (4 wells), and manganese (2 wells). Maximum Contaminant Levels were exceeded for turbidity (3 wells) and fluoride (1 well). The Maximum Contaminant Level Goal for lead (0 milligrams per liter) was exceeded in water from 12 wells. Analyses of isotopes in water from wells along two 60-mile long ground-water flow paths indicated that water in the Ozark aquifer was at least 60 years old but the upper age limit is uncertain. The source of recharge water for the wells along the flow paths appeared to be of meteoric origin because of isotopic similarity to the established Global Meteoric Water Line and a global precipitation relation. Additionally, analysis of hydrogen-3 (3H) and carbon-14 (14C) indicated that there was possible leakage of younger ground water into the lower part of the Ozark aquifer. This may be caused by cracks or fissures in the confining unit that separates the upper and lower parts of the aquifer, poorly constructed or abandoned wells, or historic mining activities. Analyses of major ions in water from wells along the flow paths indicated a transition from freshwater in the east to saline water in the west. Generally, ground water along flow paths evolved from a calcium magnesium bicarbonate type to a sodium calcium bicarbonate or a sodium calcium chloride bicarbonate type as water moved from recharge areas in Missouri into Kansas. Much of this evolution occurred within the last 20 to 25 miles of the flow paths along a water-quality transition zone near the Kansas-Missouri State line and west. The water quality of the Kansas part of the Ozark aquifer is degraded compared to the Missouri part. Geophysical and well-bore flow information and depth-dependent water-quality samples were collected from a large-capacity (1,900-2,300 gallons per minute) municipal-supply well to evaluate vertical ground-water flow accretion and variability in water-quality characteristics at different levels. Although the 1,050-foot deep supply well had 500 feet of borehole open to the Ozark aquifer, 77 percent of ground-water flow entering the borehole came from two 20-foot thick rock layers above the 1,000-foot level. For the most part, water-quality characteristics changed little from the deepest sample to the well-head sample, and upwelling of saline water from deeper geologic formations below the well was not evident. However, more saline water may be present below the bottom of the well.

Arkansas, Kansas, Missouri, Oklahoma↗
USGS2000

Water-quality assessment of the Trinity River Basin, Texas— Ground-water quality of the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers, February-August 1994

Ground-water samples were collected from wells in the outcrops of the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers during February-August 1994 to determine the quality of ground water in the three major aquifers in the Trinity River Basin study unit, Texas. These samples were collected and analyzed for selected properties, nutrients, major inorganic constituents, trace elements, pesticides, dissolved organic carbon, total phenols, methylene blue active substances, and volatile organic compounds as part of the U.S. Geological Survey National Water-Quality Assessment Program. Quality-control practices included the collection and analysis of blank, duplicate, and spiked samples. Samples were collected from 12 shallow wells (150 feet or less) and from 12 deep wells (greater than 150 feet) in the Trinity aquifer, 11 shallow wells and 12 deep wells in the Carrizo-Wilcox aquifer, and 14 shallow wells and 10 deep wells in the Gulf Coast aquifer. The three aquifers had similar water chemistries-calcium was the dominant cation and bicarbonate the dominant anion. Statistical tests relating well depths to concentrations of nutrients and major inorganic constituents indicated correlations between well depth and concentrations of ammonia nitrogen, nitrite plus nitrate nitrogen, bicarbonate, sodium, and dissolved solids in the Carrizo-Wilcox aquifer and between well depth and concentrations of sulfate in the Gulf Coast aquifer. The tests indicated no significant correlations for the Trinity aquifer. Concentrations of dissolved solids were larger than the secondary maximum contaminant level of 500 milligrams per liter established for drinking water by the U.S. Environmental Protection Agency in 12 wells in the Trinity aquifer, 4 wells in the Carrizo-Wilcox aquifer, and 6 wells in the Gulf Coast aquifer. Iron concentrations were larger than the secondary maximum contaminant level of 300 micrograms per liter in at least 3 samples from each aquifer, and manganese concentrations were larger than the secondary maximum contaminant level of 50 micrograms per liter in at least 2 samples from each aquifer. The pesticides atrazine, deethylatrazine, and pp'-DDE were detected in at least one sample from each aquifer. Diazinon was detected in 11 Trinity aquifer samples and 4 Carrizo-Wilcox aquifer samples. Each aquifer had one detection of a volatile organic compound-benzene in the Trinity aquifer, trichlorofluoromethane in the Carrizo-Wilcox aquifer, and trichloromethane in the Gulf Coast aquifer.

Texas↗
USGS1999

Hydrogeology and simulation of ground-water flow in the Ohio River alluvial aquifer near Carrollton, Kentucky

The alluvial aquifer near Carrollton, Kentucky, lies in a valley eroded by glacial meltwater that was later part filled with outwash sand and gravel deposits. The aquifer is unconfined, and ground water flows from the adjacent bedrock-valley wall toward the Ohio River and ground-water withdrawal wells. Ground-water-level and Ohio River stage data indicate the alluvial aquifer was at or near steady-state condition in November 1995. A two-dimensional, steady-state ground-water-flow model was developed to estimate the hydraulic properties, the rate of recharge, and the contributing areas to discharge boundaries for the Ohio River alluvial aquifer at Carrollton and the surrounding area. Results from previous investigations, available hydrogeologic data, and observations of water levels from area ground-water wells were compiled to conceptualize the ground-water-flow system and construct the numerical model. Ground water enters the modeled area by induced infiltration from the Ohio River and smaller streams, flow from the bedrock-valley wall, and infiltration of precipitation. Ground water exits the modeled area primarily through withdrawal wells and flow to the Ohio River. A sensitivity analysis of the model indicates that it is most sensitive to changes in the stage of the Ohio River and conductance values for the riverbed material. A particle-tracking simulation was used to delineate recharge and discharge boundaries of the flow system and contributing areas for withdrawal wells, and to estimate time of travel through the flow system.

Water-Resources Investigations Report↗
USGS2002

Changes in ground-water quality in the Canal Creek Aquifer between 1995 and 2000-2001, West Branch Canal Creek area, Aberdeen Proving Ground, Maryland

Since 1917, Aberdeen Proving Ground, Maryland has been the primary chemical-warfare research and development center for the U.S. Army. Ground-water contamination has been documented in the Canal Creek aquifer because of past disposal of chemical and ordnance manufacturing waste. Comprehensive sampling for volatile organic compounds in ground water by the U.S. Geological Survey in the West Branch Canal Creek area was done in June?October 1995 and June?August 2000. The purpose of this report is (1) to compare volatile organic compound concentrations and determine changes in the ground-water contaminant plumes along two cross sections between 1995 and 2000, and (2) to incorporate data from new piezometers sampled in spring 2001 into the plume descriptions. Along the southern cross section, total concentrations of volatile organic compounds in 1995 were determined to be highest in the landfill area east of the wetland (5,200 micrograms per liter), and concentrations were next highest deep in the aquifer near the center of the wetland (3,300 micrograms per liter at 35 feet below land surface). When new piezometers were sampled in 2001, higher carbon tetrachloride and chloroform concentrations (2,000 and 2,900 micrograms per liter) were detected deep in the aquifer 38 feet below land surface, west of the 1995 sampling. A deep area in the aquifer close to the eastern edge of the wetland and a shallow area just east of the creek channel showed declines in total volatile organic compound concentrations of more than 25 percent, whereas between those two areas, con-centrations generally showed an increase of greater than 25 percent between 1995 and 2000. Along the northern cross section, total concentrations of volatile organic compounds in ground water in both 1995 and 2000 were determined to be highest (greater than 2,000 micrograms per liter) in piezometers located on the east side of the section, farthest from the creek channel, and concentrations were progressively lower at piezometer locations closer to the creek channel. Total volatile organic compound concentrations increased more than 25 percent in some areas in the middle depths of the aquifer; however, it could not be determined if a defined plume was moving farther downgradient along ground-water flow paths toward the creek channel, or vertically downward because of density differences within the aquifer.

Water-Resources Investigations Report↗
USGS1986

Limnological characteristics of selected lakes in the Nebraska sandhills, U.S.A., and their relation to chemical characteristics of adjacent ground water

Limnological characteristics of Crane, Hackberry, Island and Roundup Lakes, and chemical characteristics of shallow ground water, within the Crescent Lake National Wildlife Refuge, western Nebraska, were determined during a preliminary investigation of the interaction between lakes and ground water in this study area between 1980 and 1984. When ice cover was absent, the lakes were well-mixed vertically, regardless of season. Depth to which 1% of surface illumination penetrated was commonly less than 1m. Variability in light penetration, as measured by Secchidisk transparency, appeared to be unrelated to changes in algal biomass, even though algal biomass, measured as chlorophyll a, varied seasonally within a two-order-of-magnitude range. Blue-green algae were the most abundant phytoplankton; this condition occurred most often when the ratio of total nitrogen to total phosphorus in the lakes' water was less than 29. Although rotifers and copepod naupli commonly were the most abundant zooplankton in the lakes, cladocerans were dominant occasionally. Either sodium or calcium was the most abundant cation, and bicarbonate was the most abundant anion, in water from water-table wells and lakes sampled during the study. The second most abundant cation in the ground water was related to the location of the sampled well within the ground-water system. The lakes were a source of dissolved organic carbon seeping to ground water. Chemical and hydrologic data indicate there is interaction between lakes and ground water in the study area.

Nebraska↗
USGS2014

Ground‐water in Utah

In common with many of the arid and semiarid States, the prosperity of Utah probably is more dependent upon the amount of water available than upon any other natural resource. Although only about four per cent of the State is irrigated, a shortage of water for irrigation becomes a major calamity. A large part of the water‐supply for the State is derived from surface‐streams, but a most valuable supplement to this supply is the water available from underground sources. Ground‐water is used extensively for domestic, stock‐watering, and industrial purposes as well as for irrigation. The primary source of the municipal water‐supply for Salt Lake City is from streams entering the Jordan River Valley from the western slope of the Wasatch Mountains. However, since the drought‐year of 1931, a supplementary municipal supply has been obtained from ground‐water, and, among the 17 wells developed by the City during the extreme drought of 1934, one—yielding about ten cubic feet per second, or 4500 gallons a minute—is probably the largest in the State. Ogden, the second largest city in Utah, with a population of about 40,000, obtains the major part of its municipal water‐supply from a group of artesian wells in Ogden Valley about 12 miles east of the City. A considerable part of the water‐supply for the City of Brigham is obtained from wells. Springs constitute the source of most of the water‐supply for Logan, Provo, and many smaller towns and localities in the State. In nearly every developed area of the State ground‐water is used for some purpose, and in some areas the water‐supply is obtained almost entirely from wells.

Utah↗
USGS2006

Evaluation of the ground-water flow model for northern Utah Valley, Utah, updated to conditions through 2002

This report evaluates the performance of a numerical model of the ground-water system in northern Utah Valley, Utah, that originally simulated ground-water conditions during 1947-1980 and was updated to include conditions estimated for 1981-2002. Estimates of annual recharge to the ground-water system and discharge from wells in the area were added to the original ground-water flow model of the area. The files used in the original transient-state model of the ground-water flow system in northern Utah Valley were imported into MODFLOW-96, an updated version of MODFLOW. The main model input files modified as part of this effort were the well and recharge files. Discharge from pumping wells in northern Utah Valley was estimated on an annual basis for 1981-2002. Although the amount of average annual withdrawals from wells has not changed much since the previous study, there have been changes in the distribution of well discharge in the area. Discharge estimates for flowing wells during 1981-2002 were assumed to be the same as those used in the last stress period of the original model because of a lack of new data. Variations in annual recharge were assumed to be proportional to changes in total surface-water inflow to northern Utah Valley. Recharge specified in the model during the additional stress periods varied from 255,000 acre-feet in 1986 to 137,000 acre-feet in 1992. The ability of the updated transient-state model to match hydrologic conditions determined for 1981-2002 was evaluated by comparing water-level changes measured in wells to those computed by the model. Water-level measurements made in February, March, or April were available for 39 wells in the modeled area during all or part of 1981-2003. In most cases, the magnitude and direction of annual water-level change from 1981 to 2002 simulated by the updated model reasonably matched the measured change. The greater-than-normal precipitation that occurred during 1982-84 resulted in period-of-record high water levels measured in many of the observation wells in March 1984. The model-computed water levels at the end of 1982-84 also are among the highest for the period. Both measured and computed water levels decreased during the period representing ground-water conditions from 1999 to 2002. Precipitation was less than normal during 1999-2002. The ability of the model to adequately simulate climatic extremes such as the wetter-than-normal conditions of 1982-84 and the drier-than-normal conditions of 1999-2002 indicates that the annual variation of recharge to the ground-water system based on streamflow entering the valley, which in turn is primarily dependent upon precipitation, is appropriate but can be improved. The updated transient-state model of the ground-water system in northern Utah Valley can be improved by making revisions on the basis of currently available data and information.

Utah↗