Exploratory drilling for water and use of ground water for irrigation in Steptoe Valley, Nevada
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Water Supply Paper↗
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Records of precipitation, water levels, and ground-water recharge to the Edwards and associated limestones, San Antonio area, Texas, 1970
No abstract available.
Edwards Underground Water District Bulletin↗
Records of precipitation, water levels, and ground-water recharge to the Edwards and associated limestones, San Antonio area, Texas, 1971
No abstract available.
Edwards Underground Water District Bulletin↗
Records of precipitation, water levels, and ground-water recharge to the Edwards and associated limestones, San Antonio area, Texas, 1972-73
No abstract available.
Edwards Underground Water District Bulletin↗
Ground-water contamination near a uranium tailings disposal site in Colorado
Contaminants from uranium tailings disposed of at an active mill in Colorado have seeped into the shallow ground water onsite. This ground water discharges into the Arkansas River Valley through a superposed stream channel cut in the resistant sandstone ridge at the edge of a synclinal basin. In the river valley, seasonal surface-water irrigation has a significant impact on hydrodynamics. Water levels in residential wells fluctuate up to 20 ft and concentrations of uranium, molybdenum, and other contaminants also vary seasonally, with highest concentrations in the Spring, prior to irrigation, and lowest concentrations in the Fall. Results of a simple transient mixing cell model support the hypothesis that lateral ground-water inflow, and not irrigation recharge, is the source of ground-water contamination.
Colorado↗
Simulation of ground-water flow and evaluation of water-management alternatives in the Assabet River Basin, Eastern Massachusetts
Water-supply withdrawals and wastewater disposal in the Assabet River Basin in eastern Massachusetts alter the flow and water quality in the basin. Wastewater discharges and stream-flow depletion from ground-water withdrawals adversely affect water quality in the Assabet River, especially during low-flow months (late summer) and in headwater areas. Streamflow depletion also contributes to loss of aquatic habitat in tributaries to the river. In 19972001, water-supply withdrawals averaged 9.9 million gallons per day (Mgal/d). Wastewater discharges to the Assabet River averaged 11 Mgal/d and included about 5.4 Mgal/d that originated from sources outside of the basin. The effects of current (2004) and future withdrawals and discharges on water resources in the basin were investigated in this study. Steady-state and transient ground-water-flow models were developed, by using MODFLOW-2000, to simulate flow in the surficial glacial deposits and underlying crystalline bedrock in the basin. The transient model simulated the average annual cycle at dynamic equilibrium in monthly intervals. The models were calibrated to 19972001 conditions of water withdrawals, wastewater discharges, water levels, and nonstorm streamflow (base flow plus wastewater discharges). Total flow through the simulated hydrologic system averaged 195 Mgal/d annually. Recharge from precipitation and ground-water discharge to streams were the dominant inflow and outflow, respectively. Evapotranspiration of ground water from wetlands and non-wetland areas also were important losses from the hydrologic system. Water-supply withdrawals and infiltration to sewers averaged 5 and 1.3 percent, respectively, of total annual out-flows and were larger components (12 percent in September) of the hydrologic system during low-flow months. Water budgets for individual tributary and main stem subbasins identified areas, such as the Fort Meadow Brook and the Assabet Main Stem Upper subbasins, where flows resulting from anthropo-genic activities were relatively large percentages, compared to other subbasins, (more than 20 percent in September) of total out-flows. Wastewater flows in the Assabet River accounted for 55, 32, and 20 percent of total nonstorm streamflow (base flow plus wastewater discharge) out of the Assabet Main Stem Upper, Middle, and Lower subbasins, respectively, in an average September. The ground-water-flow models were used to evaluate water-management alternatives by simulating hypothetical scenarios of altered withdrawals and discharges. A scenario that included no water management quantified nonstorm stream-flows that would result without withdrawals, discharges, septic-system return flow, or consumptive use. Tributary flows in this scenario increased in most subbasins by 2 to 44 percent relative to 19972001 conditions. The increases resulted mostly from variable combinations of decreased withdrawals and decreased infiltration to sewers. Average annual nonstorm streamflow in the Assabet River decreased slightly in this scenario, by 2 to 3 percent annually, because gains in ground-water discharge were offset by the elimination of wastewater discharges. A second scenario quantified the effects of increasing withdrawals and discharges to currently permitted levels. In this simulation, average annual tributary flows decreased in most subbasins, by less than 1 to 10 percent relative to 19972001 conditions. In the Assabet River, flows increased slightly, 1 to 5 percent annually, and the percentage of wastewater in the river increased to 69, 42, and 27 percent of total nonstorm streamflow out of the Assabet Main Stem Upper, Middle, and Lower subbasins, respectively, in an average September. A third set of scenarios quantified the effects of ground-water discharge of wastewater at four hypothetical sites, while maintaining 19972000 wastewater discharges to the Assabet River. Wastewater, discharged at a constant rate that varied among sites from 0.3 to 1
Scientific Investigations Report↗
Hydrogeology and ground-water quality, Chippewa Township, Isabella County, Michigan, 2002-05
The ground-water resource potential of Chippewa Township, Isabella County, Mich. was characterized on the basis of existing hydrogeologic data, water-level records, analyses of water samples, and interpretation of geophysical survey data. Eight ground-water samples were collected and analyzed for major ions, nutrients, and trace-metal composition. In addition, 10 direct current-resistivity soundings were collected throughout Chippewa and Coe Townships to identify potential freshwater in the aquifer system. The aquifer system includes complexly interbedded glaciofluvial, glaciolacustrine, and basal-lodgment tills, which overlie Jurassic or Pennsylvanian sedimentary rocks. In parts of the township, freshwater is present in all geologic units, but in most areas saline water is encountered near the base of Pleistocene glacial deposits and in the Jurassic or Pennsylvanian bedrock. A near-surface sheet of relatively dense basal-lodgment till likely prevents, or substantially retards, significant direct recharge of ground water to glacial and bedrock aquifers in Chippewa and adjacent townships. Glacial sands and gravels form the principal aquifer for domestic wells (97.5 percent of wells in the township). The single community water supply in the township has wells screened in glacial deposits near the base of the glacial drift. Increased withdrawals of ground water in response to increasing demand has led to a slight decline in water quality from this supply. This water-quality decline is related primarily to an increase of dissolved sulfate, which is probably a function of well depth and dissolution of gypsum, a common mineral constituent in the Jurassic “red beds” , which form the uppermost bedrock unit throughout most of the township. One explanation for the increase in sulfate is upconing of saline water from bedrock sources, which may contain saline water.
Michigan↗
Optimization of ground-water withdrawal in the lower Fox River communities, Wisconsin
Pumping from closely spaced wells in the Central Brown County area and the Fox Cities area near the north shore of Lake Winnebago has resulted in the formation of deep cones of depression in the vicinity of the two pumping centers. Water-level measurements indicate there has been a steady decline in water levels in the vicinity of these two pumping centers for the past 50 years. This report describes the use of ground-water optimization modeling to efficiently allocate the ground-water resources in the Lower Fox River Valley. A 3-dimensional ground-water flow model was used along with optimization techniques to determine the optimal withdrawal rates for a variety of management alternatives. The simulations were conducted separately for the Central Brown County area and the Fox Cities area. For all simulations, the objective of the optimization was to maximize total ground-water withdrawals. The results indicate that ground water can supply nearly all of the projected 2030 demand for Central Brown County municipalities if all of the wells are managed (including the city of Green Bay), 8 new wells are installed, and the water-levels are allowed to decline to 100 ft below the bottom of the confining unit. Ground water can supply nearly all of the projected 2030 demand for the Fox Cities if the municipalities in Central Brown County convert to surface water; if Central Brown County municipalities follow the optimized strategy described above, there will be a considerable shortfall of available ground water for the Fox Cities communities. Relaxing the water-level constraint in a few wells, however, would likely result in increased availability of water. In all cases examined, optimization alternatives result in a rebound of the steady-state water levels due to projected 2030 withdrawal rates to levels at or near the bottom of the confining unit, resulting in increased well capacity. Because the simulations are steady-state, if all of the conditions of the model remain the same these withdrawal rates would be sustainable in perpetuity.
Wisconsin↗
Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System Underlying Northern Preble County, Ohio
The U.S. Geological Survey (USGS), in cooperation with the Miami Conservancy District, collected and analyzed samples of the aquifer materials and ground water from multiple depths at two sites in northern Preble County, Ohio. The aquifer materials included glacial deposits and Silurian carbonate bedrock. In the study area, elevated arsenic concentrations have been detected in ground water from both types of aquifers. The aquifer materials were described in terms of the stratigraphy and the bulk elemental composition of 70 samples. In addition, six water-producing horizons were selected for more detailed study; ground-water quality was analyzed, microanalytical techniques were used to examine thin sections of the aquifer materials, and simplified geochemical modeling was done to identify plausible reactions between the ground water and aquifer materials. At both study sites, the highest solid-phase arsenic concentrations were from a roughly similar stratigraphic position - a transition zone that extends from just above the Wisconsinan/Illinoian contact to just below the Pleistocene/Silurian contact. For carbonate bedrock, the solid-phase arsenic concentrations were generally low (<1 to 4 mg/kg (milligrams per kilogram)). The one notable exception was a thin horizon about 10 feet below the top of bedrock, which had an arsenic concentration of 42 mg/kg. This horizon showed some textural and compositional evidence of alteration by geothermal fluids. Additional study might be warranted to investigate whether arsenic concentrations in ground water from carbonate bedrock could be decreased by excluding discrete horizons from the open intervals of wells. For glacial deposits, solid-phase arsenic concentrations were slightly higher in fine-grained deposits (2 to 20 mg/kg) than in coarse-grained deposits (2 to 9 mg/kg). In ground water, arsenic concentrations ranged from <1 to 51 ug/L (micrograms per liter); samples from two horizons had concentrations greater than the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) of 10 ug/L. Dissolved arsenic concentrations appear to be more closely related to redox conditions of the ground water than to the arsenic content of the aquifer materials. Geochemical modeling and thin-section analysis were generally consistent with the idea that arsenic was released to water from iron oxides under iron-reducing conditions. In addition, there was some evidence in support of the idea that arsenic can be removed from ground water by precipitation of sulfide minerals, which occurs under sulfate-reducing conditions. At one site, the dissolved arsenic concentrations in two water-bearing horizons increased from <1 to 51 ug/L over a depth of 15 feet. The large increase might be due to a shift from sulfate-reducing to methanogenic conditions; in the absence of sulfate reduction, arsenic is not sequestered in sulfide minerals and may accumulate in the ground water.
Scientific Investigations Report↗
Water-quality assessment of part of the Upper Mississippi River Basin, Minnesota and Wisconsin - Ground-water quality in an agricultural area of Sherburne County, Minnesota, 1998
The quality of shallow ground water in a 75-mi 2 agricultural area of the Anoka Sand Plain aquifer in central Minnesota is described as part of the National Water Quality Assessment (NAWQA) Program - a national-scale assessment of the quality of water resources within large study units in various hydrologic settings. Data were collected during 1998 from 29 wells completed in the aquifer, which predominantly consists of surficial glacial sand and gravel sediments. The depth below land surface to the water table ranged from 3.3 to 44 ft (median of 15.5 ft). Ground water was of the calciummagnesium bicarbonate type. Ionic constituents also included sodium, sulfate, and chloride. Iron and manganese concentrations generally were not greater than their U.S. Environmental Protection Agency (USEPA) Secondary Maximum Contaminant Levels (300 and 50 ug/L, respectively). About 38 percent of 29 samples had nitrate-N (nitrogen) concentrations greater than the USEPA Maximum Contaminant Level (MCL) of 10 mg/L. About 72 percent of the samples had nitrate-N concentrations greater than the presumed natural background level of 3 mg/L. The maximum nitrate-N concentration was 47 mg/L. The median nitrate-N concentration of 7.1 mg/L, although not greater than the MCL, exceeded the natural background level. Nitrogen isotope ratios indicate that the sources of nitrate were commercial fertilizer and soil organic matter. Concentrations of total dissolved phosphorus and orthophosphate were generally less than 1 mg/L. About 86 percent of 29 samples had detectable concentrations of at least 1 of 13 pesticide compounds. The samples were analyzed for 83 pesticide compounds. Frequencies of detection of these compounds were: deethylatrazine-79 percent; atrazine-76 percent; metolachlor-41 percent; metribuzin and bentazon-21 percent; prometon-10 percent; tebuthiuron-7 percent; and alachlor, 2,6-diethylaniline, dicamba, dinoseb, malathion, and simazine-3 percent. The detected pesticide compounds had concentrations less than 1 ug/L. Detected compounds with USEPA MCLs (atrazine, bentazon, alachlor, dinoseb, and simazine) had concentrations less than their respective MCLs. About 50 percent of 20 samples analyzed for 86 volatile organic compounds (VOCs) had detectable concentrations of at least 1 of 7 VOCs. Frequencies of detection of these 7 VOCs were: 1,2,3,4-tetramethylbenzene-40 percent; and trichlorofluoromethane, styrene, chloromethane, benzene, methylbenzene, and trichloromethane-5 percent. The detected VOCs had concentrations less than 0.120 ug/L. Detected VOCs with USEPA MCLs - styrene, benzene, methylbenzene, and trichloromethane - were present at concentrations 2-4 orders of magnitude less than their respective MCLs. Tritium concentrations had a range of from 7.5 to 18.8 tritium units (TUs) and a median of 12.5 TUs. These concentrations indicate that the ground water predominantly recharged after testing of thermonuclear weapons during the early 1950's.
Minnesota↗
Ground-water, surface-water, and water-chemistry data, Black Mesa area, northeastern Arizona— 2006-07
The N aquifer is the major source of water in the 5,400 square-mile Black Mesa area in northeastern Arizona. Availability of water is an important issue in northeastern Arizona because of continued water requirements for industrial and municipal use and the needs of a growing population. Precipitation in the Black Mesa area is typically about 6 to 14 inches per year. The water-monitoring program in the Black Mesa area began in 1971 and is designed to provide information about the long-term effects of ground-water withdrawals from the N aquifer for industrial and municipal uses. This report presents results of data collected for the monitoring program in the Black Mesa area from January 2006 to September 2007. The monitoring program includes measurements of (1) ground-water withdrawals, (2) ground-water levels, (3) spring discharge, (4) surface-water discharge, and (5) ground-water chemistry. Periodic testing of ground-water withdrawal meters is completed every 4 to 5 years. The Navajo Tribal Utility Authority (NTUA) yearly totals for the ground-water metered withdrawal data were unavailable in 2006 due to an up-grade within the NTUA computer network. Because NTUA data is often combined with Bureau of Indian Affairs data for the total withdrawals in a well system, withdrawals will not be published in this year's annual report. From 2006 to 2007, annually measured water levels in the Black Mesa area declined in 3 of 11 wells measured in the unconfined areas of the N aquifer, and the median change was 0.0 feet. Measurements indicated that water levels declined in 8 of 17 wells measured in the confined area of the aquifer. The median change for the confined area of the aquifer was 0.2 feet. From the prestress period (prior to 1965) to 2007, the median water-level change for 30 wells was -11.1 feet. Median water-level changes were 2.9 feet for 11 wells measured in the unconfined areas and -40.2 feet for 19 wells measured in the confined area. Spring flow was measured once in 2006 and once in 2007 at Moenkopi School Spring. Flow decreased by 18.9 percent at Moenkopi School Spring. During the period of record, flow fluctuated, and a decreasing trend was apparent. Continuous records of surface-water discharge in the Black Mesa area have been collected from streamflow gages at the following sites: Moenkopi Wash at Moenkopi (1976 to 2006), Dinnebito Wash near Sand Springs (1993 to 2006), Polacca Wash near Second Mesa (1994 to 2006), and Pasture Canyon Springs (August 2004 to December 2006). Median flows during November, December, January, and February of each water year were used as an index of the amount of ground-water discharge to the above named sites. For the period of record at each streamflow-gaging station, the median winter flows have generally remained even, showing neither a significant increase nor decrease in flows. There is not a long enough period of record for Pasture Canyon Spring for a trend to be apparent. In 2007, water samples were collected from 1 well and 1 spring in the Black Mesa area and were analyzed for selected chemical constituents. Concentrations of dissolved solids, chloride, and sulfate have varied at Peabody well 5 for the period of record, and there is an apparent increasing trend. Dissolved-solids, chloride, and sulfate concentrations increased at Moenkopi School Spring during the more than 12 years of record.
Arizona↗
The effects of channel excavation on water-quality characteristics of the Black River and on ground-water levels near Dunn, North Carolina
During 1976-81 data were collected at three sites on the Black River near Dunn, N.C., to define the effects of channel excavation on stream quality and on ground-water levels in nearby areas. One of the data sites was located upstream from the five-mile long excavated reach and served as a background station. Changes in various characteristics of this Coastal Plain stream were determined by comparing data collected before, during, and after the construction period. After deepening of the channel by more than 2 feet, ground-water levels within 100 feet of the stream declined a proportionate amount; however, levels in a well 500 feet from the stream were unchanged. Flow velocities during channel deepening were 100 percent higher than velocities prior to construction. An average increase in water temperatures of about one degree Celsius was observed following removal of trees and brush that provided shading to the stream. After construction, concentrations of dissolved oxygen also increased. The percent of saturation increased 20 to 25 percent in the lower values. Maximum concentrations of suspended sediment increased from about 75 mg/L prior to construction to over 2000 mg/L during construction. Within a year after construction, levels of suspended sediment during stormflow had decreased but remained 5 to 10 times greater than preconstruction levels. Little or no change occurred in pH, total-dissolved solids, nitrogen, phosphorus, and bacteria.
North Carolina↗
Analysis of nitrate and volatile organic compound data for ground water in the Great Salt Lake Basins, Utah, Idaho, and Wyoming, 1980-98
In 1995, ground water was the source of drinking water to about 52 percent of the population served by public drinking water systems in the Great Salt Lake Basins study unit, which includes parts of Utah, Idaho, and Wyoming. Existing nitrate and volatile organic compound data for ground water collected in the study unit were compiled and summarized as part of the National Water-Quality Assessment Program’s objective to describe water-quality conditions in the Nation’s aquifers. Prerequisites for the inclusion of nitrate and volatile organic compound data into this retrospective analysis are that the data set is available in electronic form, the data were collected during 1980-98, the data set is somewhat regional in coverage, and the locations of the sampled sites are known. Ground-water data stored in the U.S. Geological Survey’s National Water Information System and the Idaho and Utah Public Drinking Water Systems databases were reviewed. Only the most recent analysis was included in the data sets if more than one analysis was available for a site. The National Water Information System data set contained nitrate analyses for water from 480 wells. The median concentration of nitrate was 1.30 milligrams per liter for the 388 values above minimum reporting limits. The maximum contaminant level for nitrate as established by the U.S. Environmental Protection Agency was exceeded in water from 10 of the 200 wells less than or equal to 150 feet deep and in water from 3 of 280 wells greater than 150 feet deep. The Public Drinking Water Systems data set contained nitrate analyses for water from 587 wells. The median concentration of nitrate was 1.12 milligrams per liter for the 548 values above minimum reporting limits. The maximum contaminant level for nitrate was exceeded at 1 site and 22 sites had concentrations equal to or greater than 5 milligrams per liter. The types of land use surrounding a well and the well depth were related to measured nitrate concentrations in the sampled ground water. Overall, water sampled from wells in rangeland areas had a lower median measured nitrate concentration (0.76 milligrams per liter) than water from areas with an agricultural or urban/residential land use (1.41 and 1.20 milligrams per liter, respectively). In the National Water Information System data set, the median measured nitrate concentration in water from urban/residential areas varied from 1.00 milligrams per liter for wells greater than 150 feet deep to 1.84 milligrams per liter for wells less than or equal to 150 feet deep. The Public Drinking Water Systems and the National Water Information System data sets contained analyses for most of the State and Federally regulated volatile organic compounds in water from about 368 and 74 wells, respectively. Fifteen different volatile organic compounds were detected at least once in ground water sampled from the Great Salt Lake Basins study unit. Water from 21 wells contained at least 1 volatile organic compound at detectable concentrations. About 68 percent of the volatile organic compounds detected were in water sampled from wells in Salt Lake County, Utah. Tetrachloroethylene was the most commonly detected volatile organic compound in ground water sampled from the study unit, present in 8 out of 442 samples. Maximum contaminant levels for tetrachloroethylene and 1,1-dichloroethylene as established by the U.S. Environmental Protection Agency were exceeded in water from one well each.
Idaho,Utah, Wyoming↗
Hydrogeology and analysis of the ground-water-flow system of the eastern shore, Virginia
Ground water is the sole freshwater supply for the Eastern Shore Peninsula in Virginia. The fresh ground-water-flow system consists of a water-table aquifer underlain by three confined aquifers separated by intervening confining units. Results of simulations using a sharp-interface, ground-water-flow model indicate that current levels of withdrawal have not caused noticeable saltwater intrusion and that lateral movement of the boundary between saltwater and freshwater is slow and takes place over long periods of time.
Water Supply Paper↗
Simulation of Hydrologic-System Responses to Ground-Water Withdrawals in the Hunt-Annaquatucket-Pettaquamscutt Stream-Aquifer System, Rhode Island
A numerical-modeling study was done to better understand hydrologic-system responses to ground-water withdrawals in the Hunt-Annaquatucket-Pettaquamscutt (HAP) stream-aquifer system of Rhode Island. System responses were determined by use of steady-state and transient numerical ground-water-flow models. These models were initially developed in the late 1990s as part of a larger study of the stream-aquifer system. The models were modified to incorporate new data made available since the original study and to meet the objectives of this study. Changes made to the models did not result in substantial changes to simulated ground-water levels, hydrologic budgets, or streamflows compared to those calculated by the original steady-state and transient models. Responses of the hydrologic system are described primarily by changes in simulated streamflows and ground-water levels throughout the basin and by changes to flow conditions in the aquifer in three wetland areas immediately east of the Lafayette State Fish Hatchery, which lies within the Annaquatucket River Basin in the town of North Kingstown. Ground water is withdrawn from the HAP aquifer at 14 large-capacity production wells, at an industrial well, and at 3 wells operated by the Rhode Island Department of Environmental Management at the fish hatchery. A fourth well has been proposed for the hatchery and an additional production well is under development by the town of North Kingstown. The primary streams of interest in the study area are the Hunt, Annaquatucket, and Pettaquamscutt Rivers and Queens Fort Brook. Total model-calculated streamflow depletions in these rivers and brook resulting from withdrawals at the production, industrial, and fish-hatchery wells pumping at average annual 2003 rates are about 4.8 cubic feet per second (ft3/s) for the Hunt River, 3.3 ft3/s for the Annaquatucket River, 0.5 ft3/s for the Pettaquamscutt River, and 0.5 ft3/s for Queens Fort Brook. The actual amount of streamflow reduction in the Annaquatucket River caused by pumping actually is less, 1.1 ft3/s, because ground water that is pumped at the fish-hatchery wells (2.2 ft3/s) is returned to the Annaquatucket River after use at the hatchery. One of the primary goals of the study was to evaluate the response of the hydrologic system to simulated withdrawals at the proposed well at the fish hatchery. Withdrawal rates at the proposed well would range from zero during April through September of each year to a maximum of 260 gallons per minute [about 0.4 million gallons per day (Mgal/d)] in March of each year. The average annual withdrawal rate at the fish hatchery resulting from the addition of the proposed well would increase by only 0.13 ft3/s, or about 5 percent of the 2003 withdrawal rate. The increased pumping rate at the hatchery would further reduce the average annual flow in Queens Fort Brook by less than 0.05 ft3/s and in the Annaquatucket River by about 0.1 ft3/s (which includes some model error). A new production well in the Annaquatucket River Basin is under development by the town of North Kingstown. A simulated pumping rate of 1.0 Mgal/d (1.6 ft3/s) at this new well resulted in additional streamflow depletions, compared to those calculated for the 2003 withdrawal conditions, of 0.8 and 0.2 ft3/s in the Annaquatucket and Pettaquamscutt Rivers, respectively. The source of water for about 30 percent of the well's pumping rate, or about 0.5 ft3/s, is derived from ground-water inflow from the Chipuxet River Basin across a natural ground-water drainage divide that separates the Annaquatucket and Chipuxet River Basins; the remaining 0.1 ft3/s of simulated pumping consists of reduced evapotranspiration from the water table. Model-calculated changes in water levels in the aquifer for the various withdrawal conditions simulated in this study indicate that ground-water-level declines caused by pumping are generally less than 5 feet (ft). However, ground-water-level declines of as
Open-File Report↗
Atlas of ground-water resources in Puerto Rico and the U.S. Virgin Islands
This atlas presents an overview of the ground-water resources of the main island of Puerto Rico; two of its larger offshore islands, Isla de Culebra and Isla de Vieques; and the three principal islands of the U.S. Virgin Islands, St. Thomas, St. John, and St. Croix. The atlas presents the most important ground-water information available for these islands, and is written for water managers and the general public. It describes, through the use of maps, graphs, and hydrogeologic sections, the most important aspects of the geohydrology, ground-water flow system, and groundwater withdrawals for the principal aquifers in these islands. Most of the information presented in the atlas is from published reports, although unpublished data from ongoing studies by the U.S. Geological Survey were used to prepare parts of the atlas. This report provides a useful compilation of information concerning major aquifers in Puerto Rico and the U.S. Virgin Islands and provides a first step in gaining a general knowledge of these aquifers. More detailed information is available from the primary sources referenced in the report. The atlas contains an introductory section and 15 sections describing the ground-water resources of 12 regions within the 7 ground-water areas of the main island of Puerto Rico, Isla de Culebra and Isla de Vieques (described in a single section of the atlas), and the U.S. Virgin Islands (St. Thomas and St. John are described in one section of the atlas and St. Croix in another), and a concluding section describing present and potential problems related to the development of ground-water resources. Information presented in each of 15 descriptive sections of the atlas include the (1) location and major geographic features of the area covered by that section, (2) population and estimated (4) hydrogeology of the area, (5) ground-water levels and movements, and (6) a description of soil permeabilities.
Water-Resources Investigations Report↗
Ground water in the Eugene-Springfield area, southern Willamette Valley, Oregon
The cities of Eugene and Springfield and their outlying suburban and rural districts constitute an area of rapid population growth where progressively greater volumes of ground water are being required for irrigation and industrial and public supplies. The area is also one of diverse geologic and hydrologic conditions. As used in this report, the Eugene-Springfield area covers about 450 square miles and includes a part of the lower foothills of the Coast and Cascade Ranges and a strip of the main valley plain of the southern Willamette Valley. Volcanic and sedimentary rock units exposed in the foothills range in age from Eocene to Miocene. In the main valley plain the older units are overlain by Pleistocene and Holocene alluvial deposits. Marine-deposited sandstone, siltstone, shale, and mudstone of the older sedimentary units are fine grained and poorly permeable and yield water slowly to wells. The volcanic rocks, primarily of dacitic and andesitic composition, yield small quantities of water that are generally adequate only for domestic use. The alluvial deposits (sand and gravel) of the valley plain (central lowland) contain the most productive aquifers in the area and are considered to be the only ground-water reservoir for which large-scale development of ground-water supplies is feasible. Aquifers in the area are recharged principally by direct infiltration of precipitation. Most of the precipitation, which averages about 4C inches per year, occurs during late autumn and winter. Minimum recharge by infiltration of precipitation to the alluvial aquifers beneath the valley plain is estimated to be about 100,000 acre-feet. Ground water is discharged naturally from the central lowland by seepage and spring flow to small streams, by subsurface outflow to adjacent areas, and by evapotranspiration. Storage capacity of the central lowland in the Eugene-Springfield area is estimated to be about 2.1 million acre-feet in the zone 10-150 feet below land surface. The quantity of ground water available annually from this area is far greater than the 23,000 acre-feet pumped for all uses in 1968. This pumpage was about 23 percent of the perennial yield (100,000 acre-ft), and about 77,000 acre-feet of water was left available for additional withdrawal. If annual withdrawals of water were increased to 100,000 acre-feet per year, the levels in the ground-water reservoir would be lowered. Once new equilibriums are established, increased withdrawals could be accommodated without progressive losses in aquifer storage or excessive losses in flow of the larger streams. Ground water from the alluvial deposits of the valley plain is chemically suitable for irrigation and other uses, as is most of the water obtained from perched-water bodies in the sedimentary and volcanic rocks. However, the mineral content of water from the older sedimentary rocks, particularly from deeper producing zones, is greater than the mineral content of water from the alluvial deposits. Locally, some of the water from the older rocks is too saline for most uses. Increased use of ground water may result in certain problems pertaining to waste-disposal practices, local overdraft of aquifers, well interference, and well construction. Present data are adequate to evaluate some of the factors relating to foreseeable problems but allow only tentative conclusions to be drawn about other factors, which include local direction of flow, rate of ground-water movement, and areas of possible ground-water contamination. Additional information obtained through systematic study will be needed to deal with these problems.
Oregon↗
Geochemistry of Surface and Ground Water in Cement Creek from Gladstone to Georgia Gulch and in Prospect Gulch, San Juan County, Colorado
In San Juan County, Colo., the effects of historical mining continue to contribute metals to ground water and surface water. Previous research by the U.S. Geological Survey identified ground-water discharge as a significant pathway for the loading of metals to surface water in the upper Animas River watershed from both acid-mine drainage and acid-rock drainage. In support of this ground-water research effort, Prospect Gulch was selected for further study and the geochemistry of surface and ground water in the area was analyzed as part of four sampling plans: (1) ten streamflow and geochemistry measurements at five stream locations (four locations along Cement Creek plus the mouth of Prospect Gulch from July 2004 through August 2005), (2) detailed stream tracer dilution studies in Prospect Gulch and in Cement Creek from Gladstone to Georgia Gulch in early October 2004, (3) geochemistry of ground water through sampling of monitoring wells, piezometers, mine shafts, and springs, and (4) samples for noble gases and tritium/helium for recharge temperatures (recharge elevation) and ground-water age dating. This report summarizes all of the surface and ground-water data that was collected and includes: (1) all sample collection locations, (2) streamflow and geochemistry, (3) ground-water geochemistry, and (4) noble gas and tritium/helium data.
Colorado↗