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USGS1966

The changing pattern of ground-water development on Long Island, New York

Ground-water development on Long Island has followed a pattern that has reflected changing population trends, attendant changes in the use and disposal of water, and the response of the hydrologic system to these changes. The historic pattern of development has ranged from individually owned shallow wells tapping glacial deposits to large-capacity public-supply wells tapping deep artesian aquifers. Sewage disposal has ranged from privately owned cesspools to modern large-capacity sewage-treatment plants discharging more than 70 mgd of water to the sea. At present (1965), different parts of long Island are characterized by different stages of ground-water development. In parts of Suffolk County in eastern long Island, development is similar to the earliest historical stages. Westward toward New York City, ground-water development becomes more intensive and complex, and the attendant problems become more acute. The alleviation of present problems and those that arise in the future will require management decisions based on the soundest possible knowledge of the hydrologic system, including an understanding of the factors involved in the changing pattern of ground-water development on the island.

Circular↗

USGS1963

Ground-water contamination and legal controls in Michigan

The great importance of the fresh ground-water resources of Michigan is evident because 90 percent of the rural and about 70 percent of the total population of the State exclusive of the Detroit metropolitan area are supplied from underground sources. The water-supply and public-health problems that have been caused by some cases of ground-water contamination in the State illustrate the necessity of protecting this vital resource. Manmade and natural contaminants, including many types of chemical and organic matter, have entered many of the numerous aquifers of the State. Aquifers have been contaminated by waste-laden liquids percolating from the surface or from the zone of aeration and by direct injection to the aquifer itself. Industrial and domestic wastes, septic tanks, leaking sewers, flood waters or other poor quality surface waters, mine waters, solids stored or spread at the surface, and even airborne wastes all have been sources of ground-water contamination in Michigan. In addition, naturally occurring saline waters have been induced into other aquifers by overpumping or unrestricted flow from artesian wells, possibly by dewatering operations, and by the deepening of surface stream channels. Vertical migration of saline waters through open holes from formations underlying various important aquifers also has spoiled some of the fresh ground waters in the State. In spite of the contamination that has occurred, however, the total amount of ground water that has been spoiled is only a small part of the total resource. Neither is the contamination so widespread as that of the surface streams of Michigan. Overall legal authority to control most types of ground-water contamination in the State has been assigned by the Michigan Legislature to the Water Resources Commission, although the Department of Conservation and the Health Department also exercise important water-pollution control functions. The Michigan Supreme Court, in an important case upholding the power of the Water Resources Commission to control pollution of ground water, in effect has introduced the doctrine of reasonable use into the law of the State. Excluding controls administered by the Department of Conservation on activities of the oil and gas industry, however, legal controls have not been used abate intrusion of natural saline waters into fresh-water aquifers in response to pumping and other manmade changes in the hydrologic regimen.

Michigan↗

USGS1981

Effects of irrigation pumping on the ground-water system in Newton and Jasper Counties, Indiana

Flow in the ground-water system in Newton and Jasper Counties, Indiana, was simulated in a quasi-three-dimensional model in a study of irrigation use of ground water in the two counties. The ground-water system consists of three aquifers: (1) a surficial coarse sand aquifer known as the Kankakee aquifer, (2) a limestone and dolomite bedrock aquifer, and (3) a sand and gravel bedrock valley aquifer. Irrigation pumping, derived primarily from the bedrock, was estimated to be 34.8 million gallons per day during peak irrigation in 1977. Acreage irrigated with ground water is estimated to be 6,200 acres. A series of model experiments was used to estimate the effects of irrigation pumping on ground-water levels and streamflow. Model analysis indicates that a major factor controlling drawdown due to pumping in the bedrock aquifer are the variations in thickness and in vertical hydraulic conductivity in a semiconfining unit overlying the bedrock. Streamflow was not significantly reduced by hypothetical withdrawals of 12.6 million gallons per day from the bedrock aquifer and 10.3 million gallons per day in the Kankakee aquifer. Simulation of water-level recovery after irrigation pumping indicated that a 5-year period of alternating between increasing pumping and recovery will not cause serious problems of residual drawdown or ground-water mining.

Indiana↗

USGS2009

Evaluation of the effects of precipitation on ground-water levels from wells in selected alluvial aquifers in Utah and Arizona, 1936-2005

Increased withdrawals from alluvial aquifers of the southwestern United States during the last half-century have intensified the effects of drought on ground-water levels in valleys where withdrawal for irrigation is greatest. Furthermore, during wet periods, reduced withdrawals coupled with increased natural recharge cause rising ground-water levels. In order to manage water resources more effectively, analysis of ground-water levels under the influence of natural and anthropogenic stresses is useful. This report evaluates the effects of precipitation patterns on ground-water levels in areas of Utah and Arizona that have experienced different amounts of ground-water withdrawal. This includes a comparison of water-level records from basins that are hydrogeologically and climatologically similar but have contrasting levels of ground-water development. Hydrologic data, including records of ground-water levels, basin-wide annual ground-water withdrawals, and precipitation were examined from two basins in Utah (Milford and central Sevier) and three in Arizona (Aravaipa Canyon, Willcox, and Douglas). Most water-level records examined in this study from basins experiencing substantial ground-water development (Milford, Douglas, and Willcox) showed strong trends of declining water levels. Other water-level records, generally from the less-developed basins (central Sevier and Aravaipa Canyon) exhibited trends of increasing water levels. These trends are likely the result of accumulating infiltration of unconsumed irrigation water. Water-level records that had significant trends were detrended by subtraction of a low-order polynomial in an attempt to eliminate the variation in the water-level records that resulted from ground-water withdrawal or the application of water for irrigation. After detrending, water-level residuals were correlated with 2- to 10-year moving averages of annual precipitation from representative stations for the individual basins. The water-level residual time series for each well was matched with the 2- to 10-year moving average of annual precipitation with which it was best correlated and the results were compared across basins and hydrologic settings. Analysis of water-level residuals and moving averages of annual precipitation indicate that ground-water levels in the Utah basins respond more slowly to precipitation patterns than those from the Arizona basins. This is attributed to the dominant mechanism of recharge that most directly influences the respective valley aquifers. Substantial recharge in the Utah basins likely originates as infiltrating snowmelt in the mountain block far from the valley aquifer, whereas mountain-front recharge and streambed infiltration of runoff are the dominant recharge mechanisms operating in the Arizona basins. It was determined that the fraction of water-level variation caused by local precipitation patterns becomes more difficult to resolve with increasing effects of ground-water pumping, especially from incomplete records. As the demand for ground water increases in the southwestern United States, long-term records of ground-water levels have the potential to provide valuable information about the precipitation-driven variation in water levels, which has implications to water management related to water availability.

Arizona, Utah↗

USGS1964

Geology and ground-water resources of southeastern New Hampshire

The continued growth and development of southeastern New Hampshire, an area of about 390 square miles adjacent to the Atlantic Ocean, will depend partly on effectively satisfying the demand for water, which has increased rapidly since World War II. The report identifies and describes the principal geologic units with respect to the occurrence of ground water. These units include bedrock and the various unconsolidated deposits that mantle the bedrock surface discontinuously throughout the area. The bedrock formations, consisting of igneous and metamorphic rocks, chiefly of Paleozoic age, form a single water-bearing unit. Ground water is in joints and fractures. The fractures are small and scattered and therefore impart only a low permeability to the rocks. Wells in the bedrock commonly produce small but reliable supplies of ground water at depths of less than 150 feet. The yields of about 80 wells inventoried for this report ranged from 1? to 100 gpm (gallons per minute) and the median was 912 gpm. Depths ranged from 45 to 600 feet. The unconsolidated deposits consist of glacial drift of Pleistocene age; swamp deposits, alluvium, and beach deposits of Recent age; and eolian deposits of Pleistocene -and Recent age. For this report the glacial drift is divided into till, ice-contact deposits, marine deposits, and outwash and shore deposits. Glacial till forms a discontinuous blanket, commonly less than 15 but in some hills (drumlins) as much as about 200 feet thick. It has a low permeability but, because of its widespread outcrop area, it has been utilized as a source of water for numerous domestic supplies. Because most wells in till are shallow, many fail to meet modern demands during dry summers. Ice-contact deposits locally form kames, kame terraces, kame plains, and ice-channel fillings throughout the area. They overlie bedrock and till and range in thickness from less than 1 foot to as much as 190 feet. In general, the ice-contact deposits are coarse textured and permeable, but variations in- the physical and hydrologic properties of a single deposit and from deposit to deposit are common. Ice-contact deposits are the source of the larger ground-water supplies in southeastern New Hampshire. Marine deposits underlie lowlands and valleys to a distance of about 20 miles inland from the present coastline. They commonly overlie bedrock and till and at places overlie or are interbedded with ice-contact deposits. Marine deposits range in thickness from less than 1 foot to possibly 75 feet. They are fine textured and impermeable; they do not yield water to wells in southeastern New Hampshire but generally act as a barrier to ground-water movement. Outwash and shore deposits form broad sand plains or gently sloping terraces of small extent. At most places the outwash and shore deposits, which range in thickness from less than 1 foot to about 50 feet, overlie marine deposits, but at some places they overlie bedrock, till, or ice-contact deposits. The outwash and shore deposits are fine textured and moderately permeable. They commonly yield enough ground water to meet the needs of farms, homes, and small industries. Alluvium underlies the flood plains and channels of the principal streams and overlies bedrock and older unconsolidated deposits wherever streams cross the older units. The alluvium generally is not tapped by wells. Beach deposits occupy areas along the Atlantic Ocean between promontories of bedrock or till. In general beach deposits are permeable and are a source of water supplies for domestic use. Yields of wells are limited, however, by the danger of drawing in salty water. Recharge in southeastern New Hampshire is derived principally from precipitation on outcrop areas of ice-contact deposits and outwash and shore deposits during the nongrowing season. Ground water is discharged naturally by springs, by effluent seepage to streams and other bodies of surface water, and by evapotranspiration. It

Water Supply Paper↗

USGS1999

Use of environmental tracers to evaluate ground-water age and water-quality trends in a buried-valley aquifer, Dayton area, southwestern Ohio

Chlorofluorocarbons (CFC method) and tritium and helium isotopes (3H-3He method) were used as environmental tracers to estimate ground-water age in conjunction with efforts to develop a regional ground-water flow model of the buried-valley aquifer in the Dayton area, southwestern Ohio. This report describes results of CFC and water-quality sampling, summarizes relevant aspects of previously published work, and describes the use of 3H-3He ages to characterize temporal trends in ground-water quality of the buried-valley aquifer near Dayton, Ohio. Results of CFC sampling indicate that approximately 25 percent of the 137 sampled wells were contaminated with excess CFC's that rendered the ground water unsuitable for age dating. Evaluation of CFC ages obtained for the remaining samples indicated that the CFC compounds used for dating were being affected by microbial degradation. The degradation occurred under anoxic conditions that are found in most parts of the buried-valley aquifer. As a result, ground-water ages derived by the CFC method were too old and were inconsistent with measured tritium concentrations and independently derived 3H-3He ages. Limited data indicate that dissolved methane may play an important role in the degradation of the CFC's. In contrast, the 3H-3He technique was found to yield ground-water ages that were chemically and hydrologically reasonable. Ground-water ages derived by the 3H-3He technique were compared to values for selected water- quality characteristics to evaluate temporal trends in ground-water quality in the buried- valley aquifer. Distinct temporal trends were not identified for pH, alkalinity, or calcium and magnesium because of rapid equilibration of ground-water with calcite and dolomite in aquifer sediments. Temporal trends in which the amount of scatter and the number of outlier concentrations increased as ground-water age decreased were noted for sodium, potassium, boron, bromide, chloride, ammonia, nitrate, phosphate, sulfate, and organic carbon. Elevated concentrations of these constituents in shallow ground water are probably related to human activities. Temporal trends in which concentrations declined as ground-water age increased may reflect natural processes that reduce constituent concentrations to low levels. For example, the absence of nitrate detections in ground water recharged before 1980 may indicate natural removal of nitrate by bacterially mediated denitrification. Temporal trends observed for dissolved oxygen, iron, nitrate and silica indicate that these constituents may help identify recently (post-1990) recharged ground water.

Ohio↗

USGS1997

Ground-water resources of the Tallapoosa River basin in Georgia and Alabama - Subarea 5 of the Apalachicola-Chattahoochee-Flint and Alabama-Coosa-Tallapoosa river basins

Drought conditions in the 1980's focused attention on the multiple uses of the surface- and ground-water resources in the Apalachicola-Chattahoochee-Flint (ACT) and Alabama-Coosa-Tallapoosa (ACT) River basins in Georgia, Alabama, and Florida. State and Federal agencies also have proposed projects that would require additional water resources and revise operating practices within the river basins. The existing and proposed water projects create conflicting demands for water by the States and emphasize the problem of water-resource allocation. This study was initiated to describe ground-water availability in the Tallapoosa River basin of Georgia and Alabama, Subarea 5 of the ACF and ACT River basins, and to estimate the possible effects of increased ground-water use within the basin. Subarea 5 encompasses about 4,675 square miles (mi2) in Georgia and Alabama and contains parts of the Piedmont and Coastal Plain physiographic provinces. The Piedmont Province is underlain by a two-component aquifer system that is composed of a fractured, crystalline-rock aquifer and the overlying porous-media regolith aquifer. The Coastal Plain is underlain by a porous-media aquifer formed from the poorly consolidated deposits of sand, gravel, and clay. The conceptual model described for this study qualitatively subdivides the ground-water flow system into local (shallow), intermediate, and regional (deep) flow regimes. Ground-water discharge to tributaries mainly is from local and intermediate flow regimes and varies seasonally. The regional flow regime probably approximates steady-state conditions and discharges chiefly to major drains such as the Tallapoosa River, and in upstream areas, also to the Little Tallapoosa River and the Tallapoosa River. Ground-water discharge to major drains originates from all flow regimes. Mean-annual ground-water discharge to steams (baseflow) is considered to approximate the long-term, average recharge to ground water. The mean-annual baseflow was estimated using an automated hydrograph- separation method, and represents discharge from the local, intermediate, and regional flow regimes of the ground- water flow system. Mean-annual baseflow in Georgia was estimated to be 534 cubic feet per second (from the headwaters to the Georgia-Alabama State line), 3,250 ft3/s in Alabama, and 3,780 ft3/s for all of Subarea 5 (at the Subarea 5-Subarea 8 boundary). Stream discharge for selected sites on the Tallapoosa River and its tributaries were compiled for the years 1941, 1954, and 1986, during which sustained droughts occurred throughout most of the ACF-ACT area. Stream discharges were assumed to be sustained entirely by baseflow during the latter periods of these droughts. Estimated stream discharges near the end of the 1941, 1954, and 1986 drought years were 48, 15, and 85 ft3/s, respectively, at the Georgia-Alabama State line; and 481 , 126, and 448 ft3/s, respectively, at the mouth of the Tallapoosa River. Estimated baseflow near the end of the individual drought years was about 9 percent of the estimated mean-annual baseflow in Subarea 5. The potential exists for the development of ground-water resources on a regional scale throughout Subarea 5. Estimated ground-water use in 1990 was less than 1 percent of the estimated mean-annual baseflow, and about 6 percent of baseflow during the droughts of 1941, 1954, and 1986. Because ground-water use in Subarea 5 represents a relatively minor percentage of ground-water recharge, even a large increase in ground-water use in Subarea 5 in one State is likely to have little effect on ground-water and surface-water occurrence in the other. Indications of long-term ground-water levels declines were not observed; however, the number and distribution of observation wells for which long-term water-level measurements are available in Subarea 5 are insufficient to draw conclusions.

Alabama, Georgia↗

USGS1995

Similar agricultural areas, different ground-water quality, Red River of the North Basin, 1993-95

The U.S. Geological Survey has studied the ground-water quality within two areas of the Red River of the North Basin in southeastern North Dakota and west-central Minnesota. Although both areas are underlain by sandy surficial aquifers over which intensive irrigated agriculture dominates the land use, their ground-water quality differs. Ground water from the eastern study area has significantly higher concentrations of nitrate and agricultural herbicides than does ground water from the western area. Major differences in rainfall and minor differences in soils, depth to ground water, and agricultural practices between these two areas can account for the differences measured in ground-water quality. These same factors may indicate changes in ground-water quality from agricultural land uses in other surficial aquifers in the Red River of the North Basin.

Minnesota, North Dakota, South Dakota↗

USGS2002

Comparison of vapor concentrations of volatile organic compounds with ground-water concentrations of selected contaminants in sediments beneath the Sudbury River, Ashland, Massachusetts, 2000

A mixed plume of contaminants in ground water, including volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and metals, near the former Nyanza property in Ashland, Massachusetts, discharges to the Sudbury River upstream and downstream of Mill Pond and a former mill raceway. Polyethylene-membrane vapor-diffusion (PVD) samplers were installed in river-bottom sediments to determine if PVD samplers provide an alternative to ground-water sampling from well points for identifying areas of detectable concentrations of contaminants in sediment pore water near the ground-water and surface-water interface. In August and September 2000, the PVD samplers were installed near well points at depths of 8 to 12 inches in both fine and coarse sediments, whereas the well points were installed at depths of 1 to 5 feet in coarse sediments only. Comparison between vapor and water samples at 29 locations upstream from Mill Pond show that VOC vapor concentrations from PVD samplers in coarse river-bottom sediments are more likely to correspond to ground-water concentrations from well points than PVD samplers installed in fine sediments. Significant correlations based on Kendall's Tau were shown between vapor and ground-water concentrations for trichloroethylene and chlorobenzene for PVD samplers installed in coarse sediments where the fine organic layer that separated the two sampling depths was 1 foot or less in thickness. VOC concentrations from vapor samples also were compared to VOC, SVOC, and metals concentrations from ground-water samples at 10 well points installed upstream and downstream from Mill Pond, and in the former mill raceway. Chlorobenzene vapor concentrations correlated significantly with ground-water concentrations for 5 VOCs, 2 SVOCs, and 10 metals. Trichloroethylene vapor concentrations did not correlate with any of the other ground-water constituents analyzed at the 10 well points. Chlorobenzene detected by use of PVD samplers appears to be a strong indicator of the presence of VOCs, SVOCs, and metals in ground water sampled from well points at this site. Results from PVD samplers indicate that contaminant concentrations in water from well points installed 1 to 5 ft below fine sediments may not reflect concentrations in pore water less than 1 foot below the river bottom. There is insufficient information available to determine if VOC concentrations detected in PVD samplers are useful for identifying detectable aqueous concentrations of SVOCs and metals in sediment pore water at this site. Samples of pore water from a similar depth as PVD samplers are needed for confirmation of this objective.

Open-File Report↗

USGS2003

Natural remediation potential of arsenic-contaminated ground water

Migration of leachate from a municipal landfill in Saco, Maine has resulted in arsenic concentrations in ground water as high as 647 μg/L . Laboratory experimental data indicate the primary source of arsenic to be reductive dissolution of arsenic-enriched iron oxyhydroxides in the aquifer by organic carbon in landfill leachate. A core from an uncontaminated part of the aquifer yielded no dissolved iron or arsenic when leached with oxic ground water. Eluent ground water spiked with organic carbon in order to create reducing conditions mobilized both ferrous iron and arsenite from this core. The landfill was capped in early 1998 to eliminate the source of leachate. Cores from the contaminated portion of the aquifer were collected and leached with uncontaminated ground water in the laboratory to simulate natural remediation conditions. Data from these experiments show that significant concentrations of labile organic carbon have accumulated on aquifer solids, causing significant biological oxygen demand. In laboratory leaching experiments of the most contaminated core, the organic carbon caused complete consumption of the influent dissolved oxygen (6 mg/L) for 220 pore volumes. Arsenic leaching from contaminated cores rapidly decreased in concentration initially in response to flushing with uncontaminated ground water. Subsequent leaching produced more gradual decreases in dissolved arsenic concentrations, controlled by a combination of reductive dissolution of arsenic-enriched iron oxyhydroxides and adsorption/desorption. In leachate from the most contaminatedcore, arsenic concentrations exceeded the new United States Environmental Protection Agency drinking-water standard of 10 μg/L for more than 200 pore volumes. A geochemical model simulated the concentration of selected constituents as uncontaminated ground water eluted through contaminated aquifer solids. Concentrations of dissolved oxygen, arsenic, and iron, in leachate from one core were used to calibrate the model. This model was validated by successfully simulating constituent concentrations in leachate from cores collected from other contaminated areas of this aquifer.

Saco↗

USGS1992

Ground water chemistry and geochemical modeling of water-rock interactions at the Osamu Utsumi mine and the Morro do Ferro analogue study sites, Poços de Caldas, Minas Gerais, Brazil

Surface and ground waters, collected over a period of three years from the Osamu Utsumi uranium mine and the Morro do Ferro thorium/rare-earth element (Th/REE) deposits, were analyzed and interpreted to identify the major hydrogeochemical processes. These results provided information on the current geochemical evolution of ground waters for two study sites within the Poços de Caldas Natural Analogue Project. The ground waters are a K–Fe–SO 4 –F type, a highly unusual composition related to intense weathering of a hydrothermally altered and mineralized complex of phonolites. Tritium and stable isotope data indicate that ground waters are of meteoric origin and are not affected significantly by evaporation or water–rock interactions. Recharging ground waters at both study sites demonstrate water of less than about 35 years in age, whereas deeper, more evolved ground waters are below 1 TU but still contain in most cases detectable tritium. These deeper ground waters may be interpreted as being of 35 to 60 or more years in age, resulting mainly from an admixture of younger with older ground waters and/or indicating the influence of subsurface produced tritium. Geochemical processes involving water–rock–gas interactions have been modeled using ground water compositions, mineralogic data, ion plots and computations of speciation, non-thermodynamic mass balance and thermodynamic mass transfer. The geochemical reaction models can reproduce the water chemistry and mineral occurrences and they were validated by comparing the results of thermodynamic mass transfer calculations (using the PHREEQE program, Parkhurst et al., 1980). The results from the geochemical reaction models reveal that the dominant processes are production of CO 2 in the soil zone through aerobic decay of organic matter, dissolution of fluorite, calcite, K-feldspar, albite, chlorite and manganese oxides, oxidation of pyrite and sphalerite, and precipitation of ferric oxides, silica and kaolinite. Gibbsite precipitation can be modeled for the shallow (recharge) water chemistry at Morro do Ferro, consistent with known mineralogy. Recharge waters are undersaturated with respect to barite and discharging waters and deeper ground waters are saturated to supersaturated with respect to barite demonstrating a strong solubility control. Strontium isotope data demonstrate that sources other than calcium-bearing minerals are required to account for the dissolved strontium in the ground waters. These may include K-feldspar, smectite–chlorite mixed-layer clays and goyazite [SrAl 3 (PO 4 ) 2 (OH) 5 • H 2 O]. 1992.

Journal of Geochemical Exploration↗

USGS1997

Hydrogeology and ground-water flow in the Edwards-Trinity aquifer-system, west-central, Texas

Two finite-element ground-water flow models were developed for the Edwards–Trinity aquifer system, west-central Texas, to gain a better understanding of the flow system; one ground-water flow model was developed at a large scale to simulate the regional system and contiguous, hydraulically connected units, and one model was constructed at a smaller more detailed scale to simulate the most active areas of the system. The study area is divided into four geographic subareas: the Trans-Pecos (9,750 square miles), the Edwards Plateau (23,750 square miles), the Hill Country (5,500 square miles), and the Balcones fault zone (3,000 square miles). The major aquifers within the study area are the Edwards–Trinity aquifer underlying the Trans-Pecos and Edwards Plateau, the Trinity aquifer underlying the Hill Country, and the Edwards aquifer in the Balcones fault zone. Hydraulically connected aquifers include the High Plains aquifer north of the Edwards Plateau, and the Cenozoic Pecos alluvium aquifer adjacent to both the Trans-Pecos and the Edwards Plateau along the Pecos River. Minor contiguous aquifers include the Dockum, Ellenburger– San Saba, Marble Falls, Hickory, and Lipan, which is adjacent to the Colorado River in Tom Green and Concho Counties, Texas. The ground-water flow equations solved by the finite-element method are based on conservation of mass and energy. The equation for ground-water flow assumes laminar flow through a porous media. In places, the Edwards–Trinity aquifer system is a fractured karst system in which ground water flows through caverns and other features of secondary porosity development. The regional and subregional models were constructed to synthesize the known hydrologic boundaries and geologic structures into a heterogeneous continuum model of the karst ground-water flow system, rather than simulate the flow through specific fractures and caverns. A heterogeneous continuum or equivalent porous media approach uses an effective transmissivity and anisotropy for each element of the models. The models are calibrated both on water levels (representing potential energy) and estimates of recharge and discharge (for a realistic mass balance). A two-dimensional one-layer large-scale model (55,600 square miles) was developed for the Edwards–Trinity aquifer system and contiguous, hydraulically connected units, in westcentral Texas. A quasi-three-dimensional, multilayer more detailed scale ground-water flow model (12,300 square miles) was applied to the major aquifers of the Edwards–Trinity aquifer system in the Hill Country and the Balcones fault zone, and in part of the Edwards Plateau. The ground-water flow system in most of the study area within the Trans-Pecos and Edwards Plateau can be approximated with a one-layer regional model under steady-state conditions. Regionally, the Edwards–Trinity aquifer system in the Trans-Pecos and Edwards Plateau has been relatively static. Potentiometric maps from predevelopment and postdevelopment (winter 1974–75) indicate small differences in water levels. In local areas in the Trans-Pecos (in Pecos and Reeves Counties), ground-water withdrawals have exceeded recharge resulting in more than 300 feet of drawdown. Measurable differences between the 1974 and predevelopment potentiometric surfaces have been observed in small areas in the Trans-Pecos and in the northwestern part of the Edwards Plateau. The largest water-level declines in the Trans-Pecos have been observed in Pecos and Reeves Counties, and declines greater than 300 feet have been measured in Reeves County. Comparison of pre- and postdevelopment water budgets for the regional model indicates that the increase in groundwater withdrawals has captured 20 percent of the water that would have naturally discharged to streams, and 30 percent of the natural discharge to springs after ground-water development. Induced recharge from streams to the ground-water system increased by 12 percent in the postdevelopment simulation compared to the predevelopment simulation.

Texas↗

USGS1964

Ground-water resources of Waupaca County, Wisconsin

Waupaca County is in east-central Wisconsin. No serious ground-water problems existed in 1960 except in a few localities where crystalline rock is near land surface or is covered by nearly impermeable till. The use of ground water for irrigation has not appreciably affected ground-water levels. The county is covered by Pleistocene till, glaciolacustrine (lake), glaciofluvial (stream), and eolian (wind) deposits. In the northern three-quarters of the county these deposits overlie Precambrian crystalline rocks; in the remainder, they overlie sandstone of Cambrian age and, to a minor extent, dolomite of the Prairie du Chien Group of Ordovician age. The deposits of Pleistocene age, particularly outwash, are the principal sources of ground water except in those areas where the saturated thickness is slight or the permeability low. The sandstone of Cambrian age is an important aquifer in the southeastern part of the county. The crystalline rocks of Precambrian age yield little water except from fractures, joints, and weathered zones, and they are a source of water only in areas where better aquifers are absent. Ground water in Waupaca County occurs under both water-table and artesian conditions. The source of this ground water is precipitation that falls on the county and percolates downward to the zone of saturation. Regional movement of ground water is to the Wolf River. In most of the county the direction of movement is eastward or southeastward, except in the southeastern corner of the county, where the movement is westward. Water-level fluctuations reflect the variations of ground-water storage or artesian pressure in response to variations in recharge and discharge. Declining water levels from 1956 to 1959 reflect a period of below-normal precipitation, and rising water levels in late 1959 and 1960 reflect above-normal precipitation. Average precipitation, runoff, and evapotranspiration in 1959 are estimated to be 1,000, 400, and 600 mgd (million gallons per day) respectively. Pumpage in the county was estimated to be about 4 mgd in 1959, and about half of this amount was used for public supplies. A pumping test of a well in outwash deposits near Waupaca indicated that at that point the coefficient of transmissibility is about 100,000 gpd (gallons per day) per ft, the permeability is about 1,000 gpd per sq ft, the coefficient of storage is about 0.2, and the specific capacity is 41 gpm (gallons per minute) per ft of drawdown. These hydraulic characteristics are probably in the same order of magnitude as the characteristics of outwash deposits in the county in general. The water from wells in Waupaca County, although hard and generally containing iron, is good for most purposes.

Wisconsin↗

USGS2006

Hydrogeology and simulation of ground-water flow in the Silurian-Devonian aquifer system, Johnson County, Iowa

Bedrock of Silurian and Devonian age (termed the “Silurian-Devonian aquifer system”) is the primary source of ground water for Johnson County in east-central Iowa. Population growth within municipal and suburban areas of the county has resulted in increased amounts of water withdrawn from this aquifer and water-level declines in some areas. A 3-year study of the hydrogeology of the Silurian-Devonian aquifer system in Johnson County was undertaken to provide a quantitative assessment of ground water resources and to construct a ground-water flow model that can be used by local governmental agencies as a management tool. Johnson County is underlain by unconsolidated deposits of Quaternary age and Paleozoic-age bedrock units. The bulk of the Quaternary deposits consists of weathered and unweathered glacial till; however, shallow alluvium and buried sand and gravel deposits also are present. Six bedrock hydrogeologic units are present in Johnson County (oldest to youngest): Maquoketa confining unit, Silurian aquifer, Wapsipinicon Group (aquifer and confining unit), Cedar Valley aquifer, Upper Devonian shale confining unit, and Cherokee confining unit. Although separate aquifers and confining units are described, the Silurian- and Devonian-age units are considered as a single aquifer system. The top of the Silurian-Devonian aquifer system is considered as the top of the Cedar Valley aquifer, where present, and the base of the aquifer system is considered as the top of the Maquoketa confining unit. The hydraulic properties of the rocks that comprise the Silurian-Devonian aquifer system are highly variable as a result of the variable composition of the rocks and the presence of solution features in some of the carbonate-rock units. For the combined Silurian-Devonian aquifer system, specific capacity averages 2.1 gallons per minute per foot of drawdown, transmissivity averages about 580 feet squared per day, and hydraulic conductivity averages 8.3 feet per day. Recharge to the Silurian-Devonian aquifer system in Johnson County is predominantly from infiltration of precipitation to the bedrock. Discharge from the aquifer is primarily to municipal, industrial, and private-development wells. Reliable measurements of the amount of recharge to or discharge from the ground-water system in Johnson County, however, are not available. Altitude of the 1996 potentiometric surface ranged from more than 750 feet above the North American Vertical Datum of 1988 (NAVD88) in northern Johnson County to less than 575 feet above NAVD88 in the central part of the county. A large cone of depression within the potentiometric surface is present in the central part of the county, between Coralville and Iowa City. A large limestone quarry is located near the center of this cone of depression. Ground water generally flows from the northern and western parts of Johnson County either toward the cone of depression in the center of the county or south out of the county. Ground water also flows toward the Cedar River in the northeastern part of the county. A ground-water divide in the northeastern part of the county roughly approximates the surface-water divide between the Iowa River and Cedar River drainages. A numerical ground-water-flow model of the Silurian-Devonian aquifer system in Johnson County was used to test concepts of ground-water flow, to assess the need for additional data, and to evaluate the potential effects of anticipated increased ground-water development and drought. The 1-layer model was calibrated to average 1996 ground-water conditions, which were assumed to approximate steady-state flow conditions. The model also was used to simulate steady-state conditions for 2004, steady-state conditions using anticipated pumping rates for 2025, and potential future drought conditions. The simulated potentiometric surface generally replicated the potentiometric surface for 1996 and 2004 conditions. The calculated root mean squared error values for the 1996 and 2004 simulations were 13.6 and 18.6 feet, respectively. The mean absolute differences between measured and simulated water levels for the 1996 and 2004 simulations were about 11 and 14 feet, respectively. Total model-calculated inflow to the ground-water system for the 1996 simulation was 19.6 million gallons per day (Mgal/d), and the largest model-calculated inflow component was areal recharge (15.1 Mgal/d). Total model-calculated outflow from the ground-water system was 19.7 Mgal/d, and the largest outflow component was discharge to wells (10.5 Mgal/d). Model-calculated water-budget components for the 2004 simulation were similar to the 1996 components. Potential future steady-state conditions were simulated using anticipated 2025 pumping rates. Pumpage both for existing wells and for assumed new wells, based on anticipated population growth in the northern part of the county and for the nearby municipalities, was included in the model. Simulated 2025 pumpage was about 1.5 Mgal/d greater than simulated 2004 pumpage. Simulated steady-state ground-water levels, using anticipated 2025 pumping rates, were lower than 2004 simulated levels throughout the county, and simulated water-level declines ranged from less than 1 foot near the county boundaries to about 11 feet. Potential future drought conditions were simulated by assuming that recharge to the Silurian-Devonian aquifer system is reduced by a factor of 0.75 and that water-supply pumpage is increased by a factor of 1.25 over the anticipated 2025 pumping rates. Overall, simulated water levels for future drought conditions were greater than 5 feet lower than simulated 2004 conditions and were a maximum of about 30 feet lower in the northeastern part of the county. The greatest limitation to the model is the lack of measured or estimated water-budget components for comparison to simulated water-budget components. Because the model is only calibrated to measured water levels, and not to water-budget components, the model results are nonunique. Other model limitations include the relatively coarse grid scale, lack of detailed information on pumpage from the quarry and from private developments and domestic wells, and the lack of separate water-level data for the Silurian- and Devonian-age rocks.

Iowa↗

USGS2008

Regional nitrate and pesticide trends in ground water in the eastern San Joaquin Valley, California

Protection of ground water for present and future use requires monitoring and understanding of the mechanisms controlling long-term quality of ground water. In this study, spatial and temporal trends in concentrations of nitrate and pesticides in ground water in the eastern San Joaquin Valley, California, were evaluated to determine the long-term effects of agricultural and urban development on regional ground-water quality. Trends in concentrations of nitrate, the nematocide 1,2-dibromo-3-chloropropane, and the herbicide simazine during the last two decades are generally consistent with known nitrogen fertilizer and pesticide use and with the position of the well networks in the regional ground-water flow system. Concentrations of nitrate and pesticides are higher in the shallow part of the aquifer system where domestic wells are typically screened, whereas concentrations are lower in the deep part of the aquifer system where public-supply wells are typically screened. Attenuation processes do not seem to significantly affect concentrations. Historical data indicate that concentrations of nitrate have increased since the 1950s in the shallow and deep parts of the aquifer system. Concentrations of nitrate and detection of pesticides in the deep part of the aquifer system will likely increase as the proportion of highly affected water contributed to these wells increases with time. Because of the time of travel between the water table and the deep part of the aquifer system, current concentrations in public-supply wells likely reflect the effects of 40- to 50-yr-old management practices. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Conference Paper↗

USGS1973

Cost analysis of ground-water supplies in the North Atlantic region, 1970

The cost of municipal and industrial ground water (or, more specifically, large supplies of ground water) at the wellhead in the North Atlantic Region in 1970 generally ranged from 1.5 to 5 cents per thousand gallons. Water from crystalline rocks and shale is relatively expensive. Water from sandstone is less so. Costs of water from sands and gravels in glaciated areas and from Coastal Plain sediments range from moderate to very low. In carbonate rocks costs range from low to fairly high. The cost of ground water at the wellhead is low in areas of productive aquifers, but owing to the cost of connecting pipe, costs increase significantly in multiple-well fields. In the North Atlantic Region, development of small to moderate supplies of ground water may offer favorable cost alternatives to planners, but large supplies of ground water for delivery to one point cannot generally be developed inexpensively. Well fields in the less productive aquifers may be limited by costs to 1 or 2 million gallons a day, but in the more favorable aquifers development of several tens of millions of gallons a day may be practicable and inexpensive. Cost evaluations presented cannot be applied to any one specific well or specific site because yields of wells in any one place will depend on the local geologic and hydrologic conditions; however, with such cost adjustments as may be necessary, the methodology presented should have wide applicability. Data given show the cost of water at the wellhead based on the average yield of several wells. The cost of water delivered by a well field includes costs of connecting pipe and of wells that have the yields and spacings specified. Cost of transport of water from the well field to point of consumption and possible cost of treatment are not evaluated. In the methodology employed, costs of drilling and testing, pumping equipment, engineering for the well field, amortization at 5% percent interest, maintenance, and cost of power are considered. The report includes an analysis of test drilling costs leading to a production well field. The discussion shows that test drilling is a relatively low cost item and that more than a minimum of test holes in a previously unexplored area is, above all, simple insurance in keeping down costs and may easily result in final lower costs for the system. Use of the jet drill for testing is considered short sighted and may result in higher total costs and possibly failure to discover good aquifers. Economic development of ground water supplies will depend on obtaining qualified hydrologic and engineering advice, on carrying out adequate test drilling, and on utilizing high-quality (at times, more costly) material.

Water Supply Paper↗

USGS2002

Ground-water quality beneath an urban residential and commercial area, Montgomery, Alabama, 1999-2000

The Black Warrior River aquifer, which is composed of the Coker, Gordo, and Eutaw Formations, supplies more than 50 percent of the ground water used for public water supply in the Mobile River Basin. The city of Montgomery, Alabama, is partially built upon a recharge area for the Black Warrior River aquifer, and is one of many major population centers that depend on the Black Warrior River aquifer for public water supply. To represent the baseline ground-water quality in the Black Warrior River aquifer, water samples were collected from 30 wells located in a low-density residential or rural setting; 9 wells were completed in the Coker Formation, 9 wells in the Gordo Formation, and 12 wells in the Eutaw Formation. To describe the ground-water quality beneath Montgomery, Alabama, water samples also were collected from 30 wells located in residential and commercial areas of Montgomery, Alabama; 16 wells were completed in the Eutaw Formation, 8 wells in alluvial deposits, and 6 wells in terrace deposits. The alluvial and terrace deposits directly overlie the Eutaw Formation with little or no hydraulic separation. Ground-water samples collected from both the rural and urban wells were analyzed for physical properties, major ions, nutrients, metals, volatile organic compounds, and pesticides. Samples from the urban wells also were analyzed for bacteria, chlorofluorocarbons, dissolved gases, and sulfur hexafluoride. Ground-water quality beneath the urban area was compared to baseline water quality in the Black Warrior River aquifer.Compared to the rural wells, ground-water samples from urban wells contained greater concentrations or more frequent detections of chloride and nitrate, and the trace metals aluminium, chromium, cobalt, copper, nickel, and zinc. Pesticides and volatile organic compounds were detected more frequently and in greater concentrations in ground-water samples collected from urban wells than in ground-water samples from rural wells.The Spearman rho test was used to check for statistically significant covariance among urban ground-water quality and land-use type. The number of pesticides and volatile organic compounds detected and concentrations of nickel increased as the percentage of residential land use increased. Greater nickel concentrations also were associated with a greater number of volatile organic compounds detected. As the percentage of commercial land use increased, the numbers of pesticides and volatile organic compounds detected decreased. The number of pesticides detected in the urban ground-water samples increased as concentrations of nitrite plus nitrate increased; the number of pesticides detected and the concentrations of nitrite plus nitrate decreased as the age of the ground water increased. These correlations may indicate that, with time, pesticides and nitrate are removed from the ground-water system by physical, chemical, or biological processes.The effects of surficial geology on the occurrence of pesticides and volatile organic compounds was investigated by calculating frequencies of detection. The detection frequency for pesticides was greater for urban samples collected from wells where the surficial geology is sand than for urban samples collected from wells where the surficial geology is clay. The frequency of detection of volatile organic compounds did not show this relation.

Water-Resources Investigations Report↗

USGS2006

Characterization of surface-water resources in the Great Basin National Park area and their susceptibility to ground-water withdrawals in adjacent valleys, White Pine County, Nevada

Eight drainage basins and one spring within the Great Basin National Park area were monitored continually from October 2002 to September 2004 to quantify stream discharge and assess the natural variability in flow. Mean annual discharge for the stream drainages ranged from 0 cubic feet per second at Decathon Canyon to 9.08 cubic feet per second at Baker Creek. Seasonal variability in streamflow generally was uniform throughout the network. Minimum and maximum mean monthly discharges occurred in February and June, respectively, at all but one of the perennial streamflow sites. Synoptic-discharge, specific-conductance, and water- and air-temperature measurements were collected during the spring, summer, and autumn of 2003 along selected reaches of Strawberry, Shingle, Lehman, Baker, and Snake Creeks, and Big Wash to determine areas where surface-water resources would be susceptible to ground-water withdrawals in adjacent valleys. Comparison of streamflow and water-property data to the geology along each stream indicated areas where surface-water resources likely or potentially would be susceptible to ground-water withdrawals. These areas consist of reaches where streams (1) are in contact with permeable rocks or sediments, or (2) receive water from either spring discharge or ground-water inflow.

Scientific Investigations Report↗