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USGS2007

Hydrologic conditions in northwest Florida: 2006 water year

National data for streamflow, ground-water levels, and quality of water for the 2006 water year are accessible to the public on the U.S. Geological Survey's (USGS) Site Information Management System (SIMS) website http://web10capp.er.usgs.gov/adr06_lookup/search.jsp. This fact sheet describes data and hydrologic conditions throughout northwest Florida during the 2006 water year (fig. 1), when record-low monthly streamflow conditions were reported at several streamgage locations. Prior to 1960, these data were published in various USGS Water-Supply Papers and included water-related data collected by the USGS during the water year (October 1 to September 30). In 1961, a series of annual reports, 'Water Resources Data-Florida,' was introduced that published surface-water data. In 1964, a similar report was introduced for the purposes of publishing water-quality data. In 1975, the reports were merged to a single volume and were expanded to publish data for surface water, water quality, and ground-water levels. Formal publication of the annual report series was discontinued at the end of the 2005 water year, upon activation of the SIMS website database.

Florida↗

USGS1997

U.S. Geological Survey Subsidence Interest Group Conference; proceedings of the Technical Meeting, Las Vegas, Nevada, February 14-16, 1995

Introduction to Papers: This report is a compilation of short papers that are based on oral presentations summarizing the results of recent research that were given at the third meeting of the Subsidence Interest Group held in Las Vegas, Nevada, February 14-16, 1995. The report includes case studies of land subsidence and aquifer-system deformation resulting from fluid withdrawal, geothermal development, and mine collapse. Methods for monitoring land subsidence using Global Positioning System technology for the rapid and accurate measurement of changes in land-surface altitude also are described. The current status of numerical simulation of land subsidence in the USGS is summarized, and several of the short papers deal with the development and application of new numerical techniques for simulation and quantification of aquifer system deformation. Not all oral presentations made at the meeting are documented in this report. Several of the presentations were of ongoing research and as such, the findings were provisional in nature and were offered at the meeting to stimulate scientific discussion and debate among colleagues. The information presented in this report, although only a subset of the proceedings of the meeting in Las Vegas, should help expand the scientific basis for management decisions to mitigate or control the effects of land subsidence. The short papers describing the results of these studies provide a cross section of ongoing research in aquifer mechanics and land subsidence and also form an assessment of the current technology and 'state of the science.' The analytical and interpretive methods described in this report will be useful to scientists involved in studies of ground-water hydraulics and aquifer-system deformation.

Open-File Report↗

USGS2008

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

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

New Mexico↗

USGS1994

Deuterium content of water from wells and perennial springs, southeastern California

The areal distribution of the concentrations of the stable isotopes deuterium and oxygen-18 in ground water in southeastern California is depicted and evaluated in this report. The deuterium content of about 300 ground-water samples and the oxygen-18 content of 101 of these samples are presented. Thirty-two of the samples were collected by the U.S. Geological Survey in 1977–78 as part of a study to determine the mineral and brine potential of playa lakes in selected basins in southeastern California. Most of the remaining samples were collected during the winters and springs of 1981 and 1982 as part of the Climate Change Program of the Geological Survey. Selected additional samples were collected through 1986. Stable-isotope data from three previous studies also have been included. These data are for 19 samples from the Coso thermal area east of the southern Sierra Nevada (Fournier and Thompson, 1980, tables 1,2), 5 samples from areas in Nevada just east of Death Valley (Winograd and Friedman, 1972, table 1), and 9 samples from the Imperial Valley (Coplen, 1971, table 1). Also presented for comparison are weighted averages of deuterium content of recent precipitation collected for this report at 32 stations over the 7-year period from April 1982 to April 1989 (Irving Friedman and G.I. Smith, U.S. Geological Survey, written commun., 1989).

Hydrologic Atlas↗

USGS1990

Surface-water hydrology of Honey Lake Valley, Lassen County, California, and Washoe County, Nevada

Honey Lake Valley straddles the state line of California and Nevada, about 35 miles north of Reno; about three-fourths of the area is in California. In this report, Honey Lake Valley (also referred to as the "basin") includes the entire area within the hydrographic boundary (fig. 1). Susanville, Calif., in the northwest part of the basin, is the largest town. Population is increasing rapidly both in the Susanville area and in the Reno area of adjacent Washoe County, Nev. Both Lassen and Washoe Counties have identified water resources in Honey Lake Valley as a possible source to meet their needs for future development. An important component of an assessment of the availability of additional long-term supply is an appraisal of surface-water resources. The U.S. Geological Survey, in cooperation with the California Department of Water Resources and the Nevada Division of Water Resources, began a hydrologic assessment of the area in 1987. The study was primarily an appraisal of ground-water resources, but it also included an assessment of surface-water resources. The purpose of this map report is to present the results of the surface-water assessment, including (1) a broad overview of surface-water conditions in the basin, (2) an estimate of mean annual streamflow to the valley floor, and (3) an evaluation of the characteristics of Honey Lake. This report will be republished by the U.S. Geological Survey as a Hydrologic-Investigations Atlas. Results of this study related to ground-water resources of the basin are discussed in a separate report (Handman and others, 1990) and are summarized in a short "Water Fact Sheet" by Handman (1990).

California, Nevada↗

USGS2000

Regional ground-water evapotranspiration and ground-water budgets, Great Basin, Nevada

PART A: Ground-water evapotranspiration data from five sites in Nevada and seven sites in Owens Valley, California, were used to develop equations for estimating ground-water evapotranspiration as a function of phreatophyte plant cover or as a function of the depth to ground water. Equations are given for estimating mean daily seasonal and annual ground-water evapotranspiration. The equations that estimate ground-water evapotranspiration as a function of plant cover can be used to estimate regional-scale ground-water evapotranspiration using vegetation indices derived from satellite data for areas where the depth to ground water is poorly known. Equations that estimate ground-water evapotranspiration as a function of the depth to ground water can be used where the depth to ground water is known, but for which information on plant cover is lacking. PART B: Previous ground-water studies estimated groundwater evapotranspiration by phreatophytes and bare soil in Nevada on the basis of results of field studies published in 1912 and 1932. More recent studies of evapotranspiration by rangeland phreatophytes, using micrometeorological methods as discussed in Chapter A of this report, provide new data on which to base estimates of ground-water evapotranspiration. An approach correlating ground-water evapotranspiration with plant cover is used in conjunction with a modified soil-adjusted vegetation index derived from Landsat data to develop a method for estimating the magnitude and distribution of ground-water evapotranspiration at a regional scale. Large areas of phreatophytes near Duckwater and Lockes in Railroad Valley are believed to subsist on ground water discharged from nearby regional springs. Ground-water evapotranspiration by the Duckwater phreatophytes of about 11,500 acre-feet estimated by the method described in this report compares well with measured discharge of about 13,500 acre-feet from the springs near Duckwater. Measured discharge from springs near Lockes was about 2,400 acre-feet; estimated ground-water evapotranspiration using the proposed method was about 2,450 acre-feet. PART C: Previous estimates of ground-water budgets in Nevada were based on methods and data that now are more than 60 years old. Newer methods, data, and technologies were used in the present study to estimate ground-water recharge from precipitation and ground-water discharge by evapotranspiration by phreatophytes for 16 contiguous valleys in eastern Nevada. Annual ground-water recharge to these valleys was estimated to be about 855,000 acre-feet and annual ground-water evapotranspiration was estimated to be about 790,000 acrefeet; both are a little more than two times greater than previous estimates. The imbalance of recharge over evapotranspiration represents recharge that either (1) leaves the area as interbasin flow or (2) is derived from precipitation that falls on terrain within the topographic boundary of the study area but contributes to discharge from hydrologic systems that lie outside these topographic limits. A vegetation index derived from Landsat-satellite data was used to estimate phreatophyte plant cover on the floors of the 16 valleys. The estimated phreatophyte plant cover then was used to estimate annual ground-water evapotranspiration. Detailed estimates of summer, winter, and annual ground-water evapotranspiration for areas with different ranges of phreatophyte plant cover were prepared for each valley. The estimated ground-water discharge from 15 valleys, combined with independent estimates of interbasin ground-water flow into or from a valley, were used to calculate the percentage of recharge derived from precipitation within the topographic boundary of each valley. These percentages then were used to estimate ground-water recharge from precipitation within each valley. Ground-water budgets for all 16 valleys were based on the estimated recharge from precipitation and estimated evapotranspiration. Any imba

Nevada↗

USGS1996

Ground-water levels in intermontane basins of the northern Rocky Mountains, Montana and Idaho

The Regional Aquifer-System Analysis (RASA) program is a series of studies by the U.S. Geological Survey (USGS) to analyze regional ground-water systems that compose a major portion of the Nation's water supply (Sun, 1986). The Northern Rocky Mountains Intermontane Basins is one of the study regions in this national program. The main objectives of the RASA studies are to (1) describe the groundwater systems as they exist today, (2) analyze the known changes that have led to the systems present condition, (3) combine results of previous studies in a regional analysis, where possible, and (4) provide means by which effects of future ground-water development can be estimated. The purpose of this study, which began in 1990, was to increase understanding of the hydrogeology of the intermontane basins of the Northern Rocky Mountains area. This report is Chapter B of a three-part series and shows the general distribution of ground-water levels in basin-fill deposits in the study area. Chapter A (Tuck and others, 1996) describes the geologic history and generalized hydrogeologic units. Chapter C (Clark and Dutton, 1996) describes the quality of ground and surface waters in the study area. Ground-water levels shown in this report were measured primarily during summer 1991 and summer 1992; however, historical water levels were used for areas where more recent data could not be obtained. The information provided allows for the evaluation of general directions of ground-water flow, identification of recharge and discharge areas, and determination of hydraulic gradients within basin-fill deposits.

Hydrologic Atlas↗

USGS2006

Gravity and magnetic data in the vicinity of Virgin Valley, southern Nevada

This report contains 10 interpretive cross sections and an integrated text describing the geology of parts of the Colorado, White River, and Death Valley regional ground-water flow systems, Nevada, Utah, and Arizona. The primary purpose of the report is to provide geologic framework data for input into a numerical ground-water model. Therefore, the stratigraphic and structural summaries are written in a hydrogeologic context. The oldest rocks (basement) are Early Proterozoic metamorphic and intrusive crystalline rocks that are considered confining units because of their low permeability. Late Proterozoic to Lower Cambrian clastic units overlie the crystalline rocks and are also considered confining units within the regional flow systems. Above the clastic units are Middle Cambrian to Lower Permian carbonate rocks that are the primary aquifers in the flow systems. The Middle Cambrian to Lower Permian carbonate rocks are overlain by a sequence of mainly clastic rocks of late Paleozoic to Mesozoic age that are mostly considered confining units, but they may be permeable where faulted. Tertiary volcanic and plutonic rocks are exposed in the northern and southern parts of the study area. In the Clover and Delamar Mountains, these rocks are highly deformed by north- and northwest-striking normal and strike-slip faults that are probably important conduits in transmitting ground water from the basins in the northern Colorado and White River flow systems to basins in the southern part of the flow systems. The youngest rocks in the region are Tertiary to Quaternary basin-fill deposits. These rocks consist of middle to late Tertiary sediments consisting of limestone, conglomerate, sandstone, tuff, and gypsum, and younger Quaternary surficial units consisting of alluvium, colluvium, playa deposits, and eolian deposits. Basin-fill deposits are both aquifers and aquitards.

Open-File Report↗

USGS2003

Estimated Ground-Water Withdrawals from the Death Valley Regional Flow System, Nevada and California, 1913-98

Ground-water withdrawals from 1913 through 1998 from the Death Valley regional flow system have been compiled to support a regional, three-dimensional, transient ground-water flow model. Withdrawal locations and depths of production intervals were estimated and associated errors were reported for 9,300 wells. Withdrawals were grouped into three categories: mining, public-supply, and commercial water use; domestic water use; and irrigation water use. In this report, groupings were based on the method used to estimate pumpage. Cumulative ground-water withdrawals from 1913 through 1998 totaled 3 million acre-feet, most of which was used to irrigate alfalfa. Annual withdrawal for irrigation ranged from 80 to almost 100 percent of the total pumpage. About 75,000 acre-feet was withdrawn for irrigation in 1998. Annual irrigation withdrawals generally were estimated as the product of irrigated acreage and application rate. About 320 fields totaling 11,000 acres were identified in six hydrographic areas. Annual application rates for high water-use crops ranged from 5 feet in Penoyer Valley to 9 feet in Pahrump Valley. The uncertainty in the estimates of ground-water withdrawals was attributed primarily to the uncertainty of application rate estimates. Annual ground-water withdrawal was estimated at about 90,000 acre-feet in 1998 with an assigned uncertainty bounded by 60,000 to 130,000 acre-feet.

Water-Resources Investigations Report↗

USGS1994

Data on observation wells, ground-water levels, and ground-water quality for the stratified-drift aquifer in the northwestern basin of Country Pond, Kingston, New Hampshire

Observation-well, ground-water-level, and ground- water-quality data were collected for a study of ground-water contamination in stratified drift at Country Pond in Kingston, New Hampshire. The report includes drilling records for 30 wells installed at various depths in stratified drift beneath Country Pond. Ground-water levels are recorded for nine wells drilled under the direction of the U.S. Geological Survey in May 1991. Water-quality analyses are presented for 56 ground-water samples collected from 30 wells drilled during the investigation. Samples were analyzed in the laboratory for 40 volatile organic compounds. Ground-water contamination from volatile organic compounds was found in 23 of the 56 samples collected.

Open-File Report↗

USGS2000

MODFLOW-2000, The U.S. Geological Survey modular ground-water model: User guide to modularization concepts and the ground-water flow process

MODFLOW is a computer program that numerically solves the three-dimensional ground-water flow equation for a porous medium by using a finite-difference method. Although MODFLOW was designed to be easily enhanced, the design was oriented toward additions to the ground-water flow equation. Frequently there is a need to solve additional equations; for example, transport equations and equations for estimating parameter values that produce the closest match between model-calculated heads and flows and measured values. This report documents a new version of MODFLOW, called MODFLOW-2000, which is designed to accommodate the solution of equations in addition to the ground-water flow equation. This report is a user's manual. It contains an overview of the old and added design concepts, documents one new package, and contains input instructions for using the model to solve the ground-water flow equation.

Open-File Report↗

USGS1992

Data on water quality, lake sediment, and lake-level fluctuation, St. Croix Indian Reservation, Wisconsin, 1981-87

This report is a compilation of data on surface- and ground-water quality, lake sediment, and lake-level fluctuation collected by the U.S. Geological Survey (USGS) during 1981- 87 on or near the St. Croix Indian Reservation. The purpose of this report is to provide baseline data on selected aspects of the water resources of the St. Croix Indian Reservation as a referenceby which future hydrologic changes can be discerned. The tribal lands are adjacent to Bashaw, BigRound, Big Sand, Clam, Gaslyn, Rice, and Sand Lakes and the Danbury Settlement along the St. Croix River. Water samples from each of these lakes and Bear Lake, which is not adjacent to tribal land, were analyzed for water-quality indicators. Lakelevel fluctuations also were measured for each lake except Big Round Lake. Grain-size and chemical analyses were done on lake-sediment samples from Bashaw, Rice, Clam, Gaslyn, and Bear Lakes. Ground-water samples from wells on or near tribal land in Burnett County (27 wells) and Polk County (3 wells) were collected and analyzed for water quality.

Wisconsin↗

USGS1997

Availability of ground-water data for California, water year 1996

This Fact Sheet serves as an index to California ground-water data for 1996. The 2-page report contains a map of California showing the number of wells (by county) with available water-level and water- quality data for the current year and instructions for obtaining this and other ground-water information contained in the data bases of the Water Resources Division, California District.

Fact Sheet↗

USGS1994

Overview of environmental and hydrogeologic conditions at Dillingham, Alaska

The remote city of Dillingham is at the northern end of Bristol Bay in southwestern Alaska. The hydrology of the area is strongly affected by the mild maritime climate and local geologic conditions. Dillingham residents obtain drinking water from both deep and shallow aquifers composed of gravels and sands and separated by layers of clay underlying the community. Alternative sources of drinking water are limited to the development of new wells because surface-water sources are of inadequate quantity or quality or are located at too great a distance from the population. The Federal Aviation Administration owns or operates airway support facilities in Dillingham and wishes to consider the severity of contamination and the current environmental setting when they evaluate options for compliance with environmental regulations at their facilities. This report describes the climate. vegetation, geology, soils, ground-water and surface-water hydrology, and flood potential of the areas surrounding the Federal Aviation Administration facilities near Dillingham.

Open-File Report↗

USGS2008

Current (2004-07) conditions and changes in ground-water levels from predevelopment to 2007, Southern High Plains aquifer, east-central New Mexico: Curry County, Portales, and Causey Lingo underground water basins

The Southern High Plains aquifer is the principal aquifer in Curry and Roosevelt Counties, N. Mex., and primary source of water in southeastern New Mexico. Successful water-supply planning for New Mexico's Southern High Plains requires knowledge of the current aquifer conditions and a context to estimate future trends given current aquifer-management policy. This report provides a summary of the current (2007) water-level status of the Southern High Plains aquifer in New Mexico, including a basis for estimating future trends by comparison with historical conditions. This report includes estimates of the extent of ground-water level declines in the Curry County, Portales, and Causey-Lingo Ground-water Management Area parts of the High Plains Aquifer in eastern New Mexico since predevelopment. Maps representing 2007 water levels, water-level declines, aquifer saturated thickness, and depth to water accompanied by hydrographs from representative wells for the Southern High Plains aquifer in the Curry County, Portales, and Causey Lingo Underground Water Basins were prepared in cooperation with the New Mexico Office of the State Engineer. The results of this mapping show the water level declined as much as 175 feet in the study area at rates as high as 1.76 feet per year.

New Mexico↗

USGS2007

Nitrogen species in soil, sediment, and ground water at a former sewage-treatment wastewater lagoon: Naval Air Station Whidbey Island, Island County, Washington

The potential for contamination of ground water from remnant sewage sludge in re-graded sediments of a deconstructed sewage-treatment lagoon was evaluated. Ground-water levels were measured in temporary drive-point wells, and ground-water samples were collected and analyzed for nutrients and other water-quality characteristics. Composite soil and sediment samples were collected and analyzed for organic carbon and nitrogen species. Multiple lines of evidence, including lack of appreciable organic matter in sediments of the former lagoon, agronomic analysis of nitrogen, the sequestration of nitrogen in the developing soils at the former lagoon, and likely occurrence of peat deposits within the aquifer material, suggest that the potential for substantial additions of nitrogen to ground water beneath the former sewage lagoon resulting from remnant sewage sludge not removed from the former lagoon are small. Concentrations of nitrogen species measured in ground-water samples were small and did not exceed the established U.S. Environmental Protection Agency’s maximum contaminant levels for nitrate (10 milligrams per liter). Concentrations of nitrate in ground-water samples were less than the laboratory reporting limit of 0.06 milligram per liter. Seventy to 90 percent of the total nitrogen present in ground water was in the ammonia form with a maximum concentration of 7.67 milligrams per liter. Concentrations of total nitrogen in ground water beneath the site, which is the sum of all forms of nitrogen including nitrate, nitrite, ammonia, and organic nitrogen, ranged from 1.15 to 8.44 milligrams per liter. Thus, even if all forms of nitrogen measured in ground water were converted to nitrate, the combined mass would be less than the maximum contaminant level. Oxidation-reduction conditions in ground water beneath the former sewage lagoon were reducing. Given the abundant supply of ambient organic carbon in the subsurface and in ground water at the former lagoon, any nitrate that may leach from residual sludge and be transported to ground water with recharge is expected to be quickly denitrified or transformed to nitrite and ammonia under the strongly reducing geochemical conditions that are present. Concentrations of organic carbon, the primary constituent of sewage sludge, in sediments of the former sewage lagoon were less than 1 percent, indicating a near absence of organic matter. The amount of total nitrogen present in the sediments at the former sewage lagoon was only about 25 percent of the amount typically present in developed agricultural soils. The lack of substantial carbon and nitrogen in sediments of the former sewage lagoon indicates that surficial sediments of the former lagoon are essentially devoid of residual sewage sludge. The largest concentration of total nitrogen measured in soil samples from the former sewage lagoon (330 milligrams per kilogram) was used to calculate an estimate of the amount of nitrogen that might be leached from residual sewage sludge by recharge. During the first two years following deconstruction of the former sewage lagoon, the concentration of total nitrogen in recharge leachate might exceed 10 milligrams per liter but the recharge leachate would not likely result in substantial increases in the nitrate concentration in ground water to concentrations greater than the drinking-water maximum contaminant level of 10 milligrams per liter.

Washington↗

USGS2008

Effects of Land-Use Changes and Ground-Water Withdrawals on Stream Base Flow, Pocono Creek Watershed, Monroe County, Pennsylvania

The Pocono Creek watershed drains 46.5 square miles in eastern Monroe County, Pa. Between 2000 and 2020, the population of Monroe County is expected to increase by 70 percent, which will result in substantial changes in land-use patterns. An evaluation of the effect of reduced recharge from land-use changes and additional ground-water withdrawals on stream base flow was done by the U.S. Geological Survey (USGS) in cooperation with the U.S. Environmental Protection Agency (USEPA) and the Delaware River Basin Commission as part of the USEPA?s Framework for Sustainable Watershed Management Initiative. Two models were used. A Soil and Water Assessment Tool (SWAT) model developed by the USEPA provided areal recharge values for 2000 land use and projected full buildout land use. The USGS MODFLOW-2000 ground-water-flow model was used to estimate the effect of reduced recharge from changes in land use and additional ground-water withdrawals on stream base flow. This report describes the ground-water-flow-model simulations. The Pocono Creek watershed is underlain by sedimentary rock of Devonian age, which is overlain by a veneer of glacial deposits. All water-supply wells are cased into and derive water from the bedrock. In the ground-water-flow model, the surficial geologic units were grouped into six categories: (1) moraine deposits, (2) stratified drift, (3) lake deposits, (4) outwash, (5) swamp deposits, and (6) undifferentiated deposits. The unconsolidated surficial deposits are not used as a source of water. The ground-water and surface-water systems are well connected in the Pocono Creek watershed. Base flow measured on October 13, 2004, at 27 sites for model calibration showed that streams gained water between all sites measured except in the lower reach of Pocono Creek. The ground-water-flow model included the entire Pocono Creek watershed. Horizontally, the modeled area was divided into a 53 by 155 cell grid with 6,060 active cells. Vertically, the modeled area was discretized into four layers. Layers 1 and 2 represented the unconsolidated surficial deposits where they are present and bedrock where the surficial deposits are absent. Layer 3 represented shallow bedrock and was 200 ft (feet) thick. Layer 4 represented deep bedrock and was 300 ft thick. A total of 873 cells representing streams were assigned to layer 1. Recharge rates for model calibration were provided by the USEPA SWAT model for 2000 land-use conditions. Recharge rates for 2000 for the 29 subwatersheds in the SWAT model ranged from 6.11 to 22.66 inches per year. Because the ground-water-flow model was calibrated to base-flow data collected on October 13, 2004, the 2000 recharge rates were multiplied by 1.18 so the volume of recharge was equal to the volume of streamflow measured at the mouth of Pocono Creek. During model calibration, adjustments were made to aquifer hydraulic conductivity and streambed conductance. Simulated base flows and hydraulic heads were compared to measured base flows and hydraulic heads using the root mean squared error (RMSE) between measured and simulated values. The RMSE of the calibrated model for base flow was 4.7 cubic feet per second for 27 locations, and the RMSE for hydraulic heads for 15 locations was 35 ft. The USEPA SWAT model was used to provide areal recharge values for 2000 and full buildout land-use conditions. The change in recharge ranged from an increase of 37.8 percent to a decrease of 60.8 percent. The ground-water-flow model was used to simulate base flow for 2000 and full buildout land-use conditions using steady-state simulations. The decrease in simulated base flow ranged from 3.8 to 63 percent at the streamflow-measurement sites. Simulated base flow at streamflow-gaging station Pocono Creek above Wigwam Run near Stroudsburg, Pa. (01441495), decreased 25 percent. This is in general agreement with the SWAT model, which estimated a 30.6-percent loss in base flow at the streamflow-gaging station.

Scientific Investigations Report↗

USGS2003

Ground-Water Resources in the Black Hills Area, South Dakota

The availability of ground-water resources in the Black Hills area is influenced by many factors including location, local recharge and ground-water flow conditions, and structural features. Thus, the availability of ground water can be extremely variable throughout the Black Hills area, and even when water is available, it may not be suitable for various uses depending on the water quality. The major bedrock aquifers in the Black Hills area are the Deadwood, Madison, Minnelusa, Minnekahta, and Inyan Kara aquifers. Minor bedrock aquifers occur in other hydrogeologic units, including confining units, due to fracturing and interbedded permeable layers. Various information and maps are presented in this report that describe availability and quality of ground-water resources in the Black Hills area. However, there is no guarantee of obtaining usable water at any location due to the extreme potential variability in conditions that can affect the availability and quality of ground water in the area. Maps presented in this report include the distribution of hydrogeologic units; depth to the top of the five formations that contain major aquifers; thickness of the five formations that contain major aquifers; potentiometric maps for the five major aquifers; saturated thickness of the Madison and Minnelusa aquifers; water temperature in the Madison aquifer; specific conductance in the Madison, Minnelusa, and Inyan Kara aquifers; hardness in the Inyan Kara aquifer; sulfate concentrations in the Minnelusa aquifer; and radon concentrations in the Deadwood aquifer. Water quality of the major aquifers generally is very good in and near outcrop areas but deteriorates progressively with distance from the outcrops. In the Minnelusa aquifer, an abrupt increase in concentrations of dissolved sulfate occurs downgradient from outcrop areas, where a zone of active anhydrite dissolution occurs. Most limitations for the use of ground water are related to aesthetic qualities associated with hardness and high concentrations of chloride, sulfate, sodium, manganese, and iron. Very few health-related limitations exist for ground water; most limitations are for radionuclides, such as radon and uranium. In addition, high concentrations of arsenic have been measured in a few samples from the Minnelusa aquifer.

Water-Resources Investigations Report↗