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USGS1999

Lithostratigraphy, geophysics, biostratigraphy, and strontium-isotope stratigraphy of the surficial aquifer system of eastern Collier County and northern Monroe County, Florida

In 1997, ten cores were drilled in eastern Collier County and northern Monroe County, within the limits of the Big Cypress National Preserve. These cores represent a continuation of the study of seven cores in western Collier County begun in 1996 and reported in Weedman and others (1997) and Edwards and others (1998). This joint U.S. Geological Survey and Florida Geological Survey project is designed to acquire subsurface geologic and hydrologic data in southwest Florida to extend current ground-water models, thereby expanding the utility of these models for land and water management. In this report we describe the lithostratigraphy, geophysical logging, sedimentological analysis, dinocyst biostratigraphy, and strontium-isotope stratigraphy of these ten cores. The three geophysical logs (natural gamma-ray, induction conductivity, and neutron porosity) assumed to be related to formation lithology and water quality show that a number of clay-rich zones are present in all of the boreholes, and that pore-water conductivity increases with depth. The clay-rich zones are confirmed by visual examination of core material and sedimentological analysis. The relative transmissivity calculated at 10-foot-thick intervals shows that in six of the boreholes, high values are associated with the shallow aquifer in the 0-40 ft interval. Two of the boreholes (the most northerly and the most easterly) showed relatively higher values of transmissivity in permeable zones at or somewhat below 100 ft in depth. Core geology and logs indicate that the deeper aquifers are not more permeable than similar deeper zones in the other boreholes, but rather that the shallow aquifer appears to be less permeable in these two coreholes. The Arcadia (?) Formation was only penetrated in the deepest core where it is late Miocene in age. The Peace River Formation was penetrated in all but the two westernmost cores. It yields a late Miocene age, based on both dinocysts and strontium-isotope stratigraphy. The top is an irregular surface. Age and stratigraphic relations suggest that the upper part of the Peace River and lower part of the unnamed formation are at least partially equivalent laterally. The unnamed formation was recovered in every core. It is thinnest in the northernmost core and thickest to the west. Ages calculated from strontium isotopes range from 6.9 to 4.6 million years ago (late Miocene to early Pliocene). The top of the unnamed formation is deepest to the north and it becomes shallower to the southwest. The Tamiami Formation also was recovered in every core and consistently yields early Pliocene ages; it yields late Pliocene ages near the top in two cores. The age and lateral relations strongly suggest that the lower part of the Tamiami Formation and the upper part of the unnamed formation are lateral facies of each other. The Fort Thompson (?) Formation, Miami Limestone, and undifferentiated siliciclastic sediments and limestone at the very top of the cores were not dated.

Florida↗

USGS2021

Using regional watershed data to assess water-quality impairment in the Pacific Drainages of the United States

Two datasets containing the first complete estimates of reach-scale nutrient, water use, dissolved oxygen, and pH conditions for the Pacific drainages of the United States were created to help inform water-quality management decisions in that region. The datasets were developed using easily obtainable watershed data, most of which have not been available until recently, and the techniques that were used provide a framework for integrating watershed data to assess water-quality impairment across other large hydrologic regions in the United States. These datasets were used to summarize regional nutrient and water-use conditions within impaired water bodies and to summarize regional dissolved oxygen concentrations and pH conditions for free-flowing stream reaches. Two examples are also presented that show how the datasets can be applied to specific water-quality management issues: (1) nutrient conditions in water bodies that have recently experienced problems with harmful algal blooms; and (2) dissolved oxygen and pH conditions in stream reaches likely to be populated by steelhead trout ( Oncorhynchus mykiss irideus ) during their summer run. The nutrient and water-use estimates could help inform actions aimed at managing water-quality conditions in impaired water bodies while the dissolved oxygen and pH predictions could be useful as screening tools to identify water bodies experiencing potential impairment.

California, Idaho, Montana, Nevada, Oregon, Utah, ↗

USGS1994

Water resources of the Menominee Indian Reservation of Wisconsin

Water resources of the Menominee Indian Reservation, Wisconsin, were investigated during the period October 1981 through September 1987. The report presents baseline data and some interpretation of ground- and surface-water hydrology and quality of the Reservation. The area stratigraphy consists of basal Precambrian crystalline bedrock and overlying till and sand and gravel deposits. In the Reservation, the glacial deposits range in thickness from zero to 180 feet. The bedrock aquifer is composed of fractured and weathered Precambrian bedrock within about 20 feet of the upper bedrock surface. The sand and gravel aquifer is composed of saturated, permeable sand and gravel that occurs as layers, lenses, terrace deposits, and valley fillings. The glacial material has a saturated thickness ranging from approximately 150 feet to zero feet in areas where the Precambrian bedrock crops out. Water-table conditions commonly occur in both aquifers. Horizontal hydraulic conductivity of the sand and gravel and bedrock aquifers is estimated to be 5 and 0.3 feet per day, respectively. The Wolf River and its tributaries drain the Reservation except for the eastern quarter, which is drained by the South Branch of the Oconto River. The average discharge of the Wolf River, monitored continuously during 1907-85 at Keshena Falls near Keshena, was 762 ft 3/s (cubic feet per second). Maximum instantaneous discharge was 5,200 ft3/s recorded on March 15, 1973, and the minimum was 91 ft3/s recorded on December 22,1939. Low flow and flood-frequency characteristics for the Wolf River were estimated using mean-daily discharge for the period of record at Keshena Falls. Ground water from the sand and gravel and bedrock aquifers is a calcium magnesium bicarbonate type. The composition of waters from the two aquifers is similar because water recharging the bedrock aquifer is from the overlying sand and gravel aquifer. Iron or manganese concentrations exceeding secondary maximum contaminant levels were found in water samples from approximately one-quarter to one-half of the wells sampled. Approximately three-quarters of the groundwater sampled during the study is moderately hard to very hard, with a median hardness equal to 171 mg/L (milligrams per liter) (as calcium carbonate)for the sand and gravel aquifer and 165mg/L (as calcium carbonate) for the bedrock aquifer. Alkalinity of the ground water ranged from26 to 211 mg/L, with a median value of 182 mg/L(as calcium carbonate) for the sand and gravel aquifer and ranged from 72 to 250 mg/L, with a median value of 170 mg/L (as calcium carbonate)for the bedrock aquifer. Water samples collected from Reservation streams and lakes were similar to ground water (calcium magnesium bicarbonate type), reflecting the strong surface-water/ground-water interaction in the study area. The chemical composition of water from lakes having inlets or outlets indicate that they are not influenced by precipitation as much as lakes that do not have inlets or outlets.

Wisconsin↗

USGS1999

Simulated effects of water exchanges on streamflow and specific conductance in the Arkansas River upstream from Avondale, Colorado

The potential effects of future water-exchange scenarios on streamflow and specific conductance in the Arkansas River were simulated with two accounting models. The major processes in the models simulated the historical exchange potential in the Arkansas River and the operation of a native and a nonnative Arkansas River water exchange. The potential effects of future exchange conditions were simulated using streamflow and specific-conductance data from the 1986-93 water-year study period. Hydrologic conditions during the study period were considered about average, compared to the long-term 1966-96 conditions. Therefore, the simulation results were indicative of the potential effects of future exchange conditions on streamflow and specific conductance during periods of average hydrologic conditions.

Colorado↗

USGS1968

Selected hydrologic data, San Pitch River drainage basin, Utah

The u.s. Geological Survey investigated the ground-water resources of the San Pitch River drainage basin during the period 1964- 67. The investigation was a cooperative project, financed equally by the Utah Department of Natural Resources, Division of Water Rights, and the Federal Government, and was a part of an investigation of the groundwater resources of the entire Sevier River drainage system. This report is intended to serve two purposes: (1) To make available to the public basic water-resources data useful in planning and studying development of water resources and (2) to supplement an interpretive report that will be published later. Included in the release are data collected by the Geological Survey since 1930.

Utah↗

USGS2000

Interaction between ground water and surface water in the northern Everglades and relation to water budget and mercury cycling; study methods and appendixes

The data presented in this report are products of an investigation that quantified interactions between ground water and surface water at several study sites in the northern Everglades. Goals included identifying the major geologic controls and human alterations that affect interactions between ground water and surface water, and determining how those interactions affect mercury contamination. The primary study area was the 3,815-acre Everglades Nutrient Removal (ENR), a wetland constructed in the early 1990s as a prototype Stormwater Treatment Area (STA), to determine the effectiveness in removing excess nutrients from agricultural drainage. In order to ensure that results from ENR are broadly informative, work was also conducted in Water Conservation Area-2A (WCA-2A), a 105,000-acre basin surrounded by levees. In the past 50 years, WCA-2A has experienced extensive re- engineering of water flow, alterations in the pattern of water-level fluctuations and timing of fire frequency, as well as substantial ecological changes. The most visible ecological alteration is the change in dominance over the past 30 years from a sawgrass wetland to cattail wetland in the northeastern part of WCA-2A. The drastic change in vegetation in WCA-2A resulted at least in part from inputs of excess phosphorus from agricultural drainage. Substantial data collection programs were already in progress in both ENR and WCA- 2A when the present work began. The South Florida Water Management District (SFWMD) constructed the ENR project in 1994 to determine the effectiveness of constructed wetlands for water treatment. Measurements of surface water flow and water quality were made frequently in ENR between 1994 and 1998. Fewer ground water data were collected at ENR, and almost all of it was collected from shallow wells emplaced on perimeter levees. In contrast to the short-term nature of data collection in ENR, hydrologic and chemical data were collected over a much longer period in WCA-2A (since at least the mid- 1970s), but the number of sites and data- collection frequency is much less. Very little prior ground water data were available in WCA-2A. Given the availability of prior information, the present study emphasized the collection of ground water field data, particularly in the interior wetland areas of ENR and WCA- 2A. New wells were emplaced to permit the geologic, hydraulic, and chemical sampling that was needed to characterize interactions between surface water and ground water. In particular, lithology and hydraulic properties of the Surficial aquifer were determined, ground water flow paths and velocities were delineated, hydrologic fluxes between surface water and ground water were measured, and water budgets and surface- subsurface fluxes of mercury were determined. The purpose of this report is to compile under one cover all of the data collected in this investigation. In addition, the report contains a detailed description of the study methods and information about study sites, borehole drilling, well construction, seepage meter installation, and hydraulic and geochemical chemical sampling. Data interpretations are the subject of a companion report.

Florida↗

USGS1986

Ground-water availability and water quality at Southbury and Woodbury, Connecticut

Increases in population and commercial and industrial development during the past 20 years have increased the demand for water in the Towns of Southbury and Woodbury, Connecticut. The stratified-drift aquifer, underlying much of the Pomperaug River valley, is the most practical source for additional large supplies. The yield of the aquifer was evaluated with a two-dimensional, digital flow model. The model was constructed with hydrologic data from previous studies, and test boring logs , seismic profiles, water-level measurements, and other information collected during the present study. Simulations made with the calibrated model indicate that, with no pumpage, groundwater levels in the aquifer will fall about 4.6 ft below average during low-recharge (least-favorable) periods, and rise about 0.6 ft above average during high-recharge (most-favorable) periods. Simulated withdrawals from 10 wells indicate that from 5.0 to 8.8 million gallons/day are available as total recharge rates range from 21.4 to 36.1 inches/year. If these pumpages were consumed or exported from the basin, estimated average flow reductions of the Pomperaug River would range from 7.7 to 12.9 cu ft/sec. The quality of the water from the stratified-drift aquifer is generally excellent in most areas and meets State drinking-water standards. Chemical analyses of groundwater from 11 wells in the Middle Quarter area of Woodbury indicate that organohalide compounds are present. A maximum trichloroethane concentration of 260 micrograms/L has been reported and groundwater in the area is presently being monitored for organohalides. The water meets standards established by the State. Surface water samples collected at 7 sites in the study area meet the Connecticut drinking water standards for all constituents except coliform bacteria. Complete conventional treatment of surface water from some wells will be required to meet State drinking water standards relative to coliforms. (USGS)

Water-Resources Investigations Report↗

USGS2009

Summary of Hydrologic Conditions in Georgia, 2008

The United States Geological Survey (USGS) Georgia Water Science Center (WSC) maintains a long-term hydrologic monitoring network of more than 290 real-time streamgages, more than 170 groundwater wells, and 10 lake and reservoir monitoring stations. One of the many benefits of data collected from this monitoring network is that analysis of the data provides an overview of the hydrologic conditions of rivers, creeks, reservoirs, and aquifers in Georgia. Hydrologic conditions are determined by statistical analysis of data collected during the current water year (WY) and comparison of the results to historical data collected at long-term stations. During the drought that persisted through 2008, the USGS succeeded in verifying and documenting numerous historic low-flow statistics at many streamgages and current water levels in aquifers, lakes, and reservoirs in Georgia. Streamflow data from the 2008 WY indicate that this drought is one of the most severe on record when compared to drought periods of 1950-1957, 1985-1989, and 1999-2002.

Fact Sheet↗

USGS1998

Probability of detecting atrazine/desethyl-atrazine and elevated concentrations of nitrate (NO2+NO3-N) in ground water in the Idaho part of the upper Snake River basin

Draft Federal regulations may require that each State develop a State Pesticide Management Plan for the herbicides atrazine, alachlor, cyanazine, metolachlor, and simazine. This study developed maps that the Idaho State Department of Agriculture might use to predict the probability of detecting atrazine and desethyl-atrazine (a breakdown product of atrazine) in ground water in the Idaho part of the upper Snake River Basin. These maps can be incorporated in the State Pesticide Management Plan and help provide a sound hydrogeologic basis for atrazine management in the study area. Maps showing the probability of detecting atrazine/desethyl-atrazine in ground water were developed as follows: (1) Ground-water monitoring data were overlaid with hydrogeologic and anthropogenic data using a geographic information system to produce a data set in which each well had corresponding data on atrazine use, depth to ground water, geology, land use, precipitation, soils, and well depth. These data then were downloaded to a statistical software package for analysis by logistic regression. (2) Individual (univariate) relations between atrazine/desethyl-atrazine in ground water and atrazine use, depth to ground water, geology, land use, precipitation, soils, and well depth data were evaluated to identify those independent variables significantly related to atrazine/ desethyl-atrazine detections. (3) Several preliminary multivariate models with various combinations of independent variables were constructed. (4) The multivariate models which best predicted the presence of atrazine/desethyl-atrazine in ground water were selected. (5) The multivariate models were entered into the geographic information system and the probability maps were constructed. Two models which best predicted the presence of atrazine/desethyl-atrazine in ground water were selected; one with and one without atrazine use. Correlations of the predicted probabilities of atrazine/desethyl-atrazine in ground water with the percent of actual detections were good; r-squared values were 0.91 and 0.96, respectively. Models were verified using a second set of groundwater quality data. Verification showed that wells with water containing atrazine/desethyl-atrazine had significantly higher probability ratings than wells with water containing no atrazine/desethylatrazine (p <0.002). Logistic regression also was used to develop a preliminary model to predict the probability of nitrite plus nitrate as nitrogen concentrations greater than background levels of 2 milligrams per liter. A direct comparison between the atrazine/ desethyl-atrazine and nitrite plus nitrate as nitrogen probability maps was possible because the same ground-water monitoring, hydrogeologic, and anthropogenic data were used to develop both maps. Land use, precipitation, soil hydrologic group, and well depth were significantly related with atrazine/desethyl-atrazine detections. Depth to water, land use, and soil drainage were signifi- cantly related with elevated nitrite plus nitrate as nitrogen concentrations. The differences between atrazine/desethyl-atrazine and nitrite plus nitrate as nitrogen relations were attributed to differences in chemical behavior of these compounds in the environment and possibly to differences in the extent of use and rates of their application.

Idaho↗

USGS1986

Water resources activities in Kentucky, 1986

The U.S. Geological Survey, Water Resources Division, conducts three major types of activities in Kentucky in order to provide hydrologic information and understanding needed for the best management of Kentucky 's and the Nation 's water resources. These activities are: (1) Data collection and dissemination; (2) Water-resources appraisals (interpretive studies); and (3) Research. Activities described in some detail following: (1) collection of surface - and groundwater data; (2) operation of stations to collect data on water quality, atmospheric deposition, and sedimentation; (3) flood investigations; (4) water use; (5) small area flood hydrology; (6) feasibility of disposal of radioactive disposal in deep crystalline rocks; (7) development of a groundwater model for the Louisville area; (8) travel times for streams in the Kentucky River Basin; (9) the impact of sinkholes and streams on groundwater flow in a carbonate aquifer system; (10) sedimentation and erosion rates at the Maxey Flats Radioactive Waste Burial site; and (11) evaluation of techniques for evaluating the cumulative impacts of mining as applied to coal fields in Kentucky. (Lantz-PTT)

Open-File Report↗

USGS1976

Water resources data for Connecticut, water year 1975

Water resources data for the 1975 water year for Connecticut consist of records of stage, discharge, and water quality of streams; contents and water quality of lakes and reservoirs; and water levels and water quality of ground water. This report contains discharge records for 56 gaging stations; tidal volume for 1 gaging station; stage only records for 3 tidal-gaging stations; contents for 36 lakes and reservoirs; water quality for 16 gaging stations, 39 partial-record flow stations, 3 lakes, 2 tidal stations, and 4 wells; and water levels for 27 observation wells. Also included are data for 65 crest-stage partial-record stations and 55 low-flow partial-record stations. Additional water data were collected at various sites, not part of the systematic data collection program, and are published as miscellaneous measurements. Locations of hydrologic stations are shown on figures 1 and 2. These data represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating State and Federal agencies in Connecticut.

Connecticut↗

USGS1977

Water resources data for Connecticut, water year 1976

Water resources data for the 1976 water year for Connecticut consist of records of stage, discharge, and water quality of streams; contents and water quality of lakes and reservoirs; and water levels and water quality of ground water. This report contains discharge records for 59 gaging stations; tidal volume for 1 gaging station; stage only records for 3 tidal-gaging stations; contents for 36 lakes and reservoirs; water quality for 72 gaging stations, 3 lakes, 13 tidal stations, and 3 wells; and water levels for 24 observation wells. Also included are 59 crest-stage partial-record stations and 45 low-flow partial-record stations. Additional water data were collected at various sites, not involved in the systematic data collection program, and are published as miscellaneous measurements. Locations of hydrologic stations are shown on figures 1 and 2. These data represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating State and Federal agencies in Connecticut.

Connecticut↗

USGS2006

Kendall-Theil Robust Line (KTRLine--version 1.0)-A Visual Basic Program for Calculating and Graphing Robust Nonparametric Estimates of Linear-Regression Coefficients Between Two Continuous Variables

The Kendall-Theil Robust Line software (KTRLine-version 1.0) is a Visual Basic program that may be used with the Microsoft Windows operating system to calculate parameters for robust, nonparametric estimates of linear-regression coefficients between two continuous variables. The KTRLine software was developed by the U.S. Geological Survey, in cooperation with the Federal Highway Administration, for use in stochastic data modeling with local, regional, and national hydrologic data sets to develop planning-level estimates of potential effects of highway runoff on the quality of receiving waters. The Kendall-Theil robust line was selected because this robust nonparametric method is resistant to the effects of outliers and nonnormality in residuals that commonly characterize hydrologic data sets. The slope of the line is calculated as the median of all possible pairwise slopes between points. The intercept is calculated so that the line will run through the median of input data. A single-line model or a multisegment model may be specified. The program was developed to provide regression equations with an error component for stochastic data generation because nonparametric multisegment regression tools are not available with the software that is commonly used to develop regression models. The Kendall-Theil robust line is a median line and, therefore, may underestimate total mass, volume, or loads unless the error component or a bias correction factor is incorporated into the estimate. Regression statistics such as the median error, the median absolute deviation, the prediction error sum of squares, the root mean square error, the confidence interval for the slope, and the bias correction factor for median estimates are calculated by use of nonparametric methods. These statistics, however, may be used to formulate estimates of mass, volume, or total loads. The program is used to read a two- or three-column tab-delimited input file with variable names in the first row and data in subsequent rows. The user may choose the columns that contain the independent (X) and dependent (Y) variable. A third column, if present, may contain metadata such as the sample-collection location and date. The program screens the input files and plots the data. The KTRLine software is a graphical tool that facilitates development of regression models by use of graphs of the regression line with data, the regression residuals (with X or Y), and percentile plots of the cumulative frequency of the X variable, Y variable, and the regression residuals. The user may individually transform the independent and dependent variables to reduce heteroscedasticity and to linearize data. The program plots the data and the regression line. The program also prints model specifications and regression statistics to the screen. The user may save and print the regression results. The program can accept data sets that contain up to about 15,000 XY data points, but because the program must sort the array of all pairwise slopes, the program may be perceptibly slow with data sets that contain more than about 1,000 points.

Techniques and Methods↗

USGS2005

Water resources data for Massachusetts and Rhode Island, water year 2004

This report includes records of stage, discharge, and water quality of streams; contents and elevation of lakes and ponds; and water levels of ground-water wells. This volume contains discharge records for 112 gaging stations; stage records for 2 gaging stations; stage records for 2 ponds; month-end contents of 1 reservoir; precipitation totals at 6 gaging stations; water quality for 21 gaging stations; air temperature at 2 climatological stations; and water levels for 131 observation wells. Locations of these sites are shown in figures 1 and 2. Hydrologic data were collected at many sites that were not involved in the systematic data-collection program; these data are published as miscellaneous discharge measurements, miscellaneous surface-water-quality, and miscellaneous ground-water-quality data. The data in this report represent that part of the National Water Information System (NWIS) operated by the U.S. Geological Survey and cooperating State and Federal agencies in Massachusetts and Rhode Island.

Water Data Report↗

USGS1995

Hydrology of Laguna Joyuda, Puerto Rico

A study was conducted by the U.S. Geological Survey to define the hydraulic and hydrologic characteristics of the Laguna Joyuda system (in southwestern Puerto Rico) and to determine the water budget of the lagoon. This shallow-water lagoon is connected to the sea by a single canal. Rainfall and evaporation, surface-water, groundwater, and tidal-flow data were collected from December 1, 1985, to April 30, 1988. A conceptual hydrologic model of the lagoon was developed and discharge measurements and modeling were undertaken to quantify the different flow components. The water balance during the 29-month study period was determined by measuring and estimating the different hydrologic components: 4.14 million cubic meters rainfall; 5.38 million cubic meters evaporation; 1.1 8 million cubic meters surface water; and 0.34 million cubic meters ground water. A total of 18.9 million cubic meters ebb flow (tidal outflow) was discharged from the lagoon and 14.4 million cubic meters flood flow (tidal inflow) entered through the canal during the study. Seawater inflow accounted for 71 percent of the water into the lagoon. The storage volume of the lagoon was about 1.55 million cubic meters. The lagoon's hydrologic-budget residual was 4.22 million cubic meters, whereas the sum of the estimated errors for the different hydrologic components amounted to 4.51 million cubic meters. Average flushing rate for the lagoon was estimated at 72 days. During the study, the specific conductance of the lagoon water ranged from 32,000 to 52,000 microsiemens per centimeter at 25 degrees Celsius, whereas the specific conductance of local seawater is about 45,000 to 55,000 microsiemens.

Water-Resources Investigations Report↗

USGS2026

Streamflow and surface-water presence data availability across the conterminous United States: A review for headwater systems

Water is essential for life on Earth, supporting ecosystems, human health, and economic activities. Hydrology relies on observational data, and this paper discusses regional and national datasets for the conterminous United States (CONUS) publicly available as of 2023, focusing on headwaters, defined as first- and second-order streams at 1:24000 scale. It identifies 72 primary and secondary datasets and 11 repositories and argues how better integration and accessibility of hydrological data can improve research. The paper distinguishes between datasets where streamflow was the primary data collection objective and those where it was secondary. This distinction highlights opportunities to consider data from efforts peripheral to hydrology but is still useful for understanding hydrologic conditions. The analysis reveals that out of about 118 000 active and inactive stream observation sites, about 6.6% and 25% are located on first- and second-order streams, respectively. This indicates a substantial data gap for headwater systems, which account for over 77% of stream length in CONUS. Federal agencies manage 72% of hydrologic monitoring sites across all stream orders, but only 34% of these are in headwater systems. Academic institutions operate about 2% of sites, with almost half (48%) in headwater systems, focusing on ecosystem research. State agencies also operate about 2% of sites, primarily on larger systems, with 19% on headwaters. Additionally, 23% of sites are managed by multiple agencies. Spatial patterns further reveal pronounced disparities among physiographic regions. Eastern and coastal provinces show relatively dense monitoring, while central and western regions show sparse coverage. These gaps reflect historical priorities, logistical constraints, funding limitations, and the high cost of continuous instrumentation. To address biases in monitoring networks, data collection could be enhanced with low-cost monitoring, community science, and remote sensing technologies. This study also notes the benefits of long-term monitoring and prioritizing retention of streamgages with longer records.

conterminous United States↗

USGS2000

Hydrogeology and simulation of ground-water flow at the Gettysburg Elevator Plant Superfund Site, Adams County, Pennsylvania

Ground water in Triassic-age sedimentary fractured-rock aquifers in the area of Gettysburg, Pa., is used as drinking water and for industrial and commercial supply. In 1983, ground water at the Gettysburg Elevator Plant was found by the Pennsylvania Department of Environmental Resources to be contaminated with trichloroethene, 1,1,1-trichloroethane, and other synthetic organic compounds. As part of the U.S. Environmental Protection Agency?s Comprehensive Environmental Response, Compensation, and Liability Act, 1980 process, a Remedial Investigation was completed in July 1991, a method of site remediation was issued in the Record of Decision dated June 1992, and a Final Design Report was completed in May 1997. In cooperation with the U.S. Environmental Protection Agency in the hydrogeologic assessment of the site remediation, the U.S. Geological Survey began a study in 1997 to determine the effects of the onsite and offsite extraction wells on ground-water flow and contaminant migration from the Gettysburg Elevator Plant. This determination is based on hydrologic and geophysical data collected from 1991 to 1998 and on results of numerical model simulations of the local ground-water flow-system. The Gettysburg Elevator Site is underlain by red, green, gray, and black shales of the Heidlersburg Member of the Gettysburg Formation. Correlation of natural-gamma logs indicates the sedimentary rock strike about N. 23 degrees E. and dip about 23 degrees NW. Depth to bedrock onsite commonly is about 6 feet but offsite may be as deep as 40 feet. The ground-water system consists of two zones?a thin, shallow zone composed of soil, clay, and highly weathered bedrock and a thicker, nonweathered or fractured bedrock zone. The shallow zone overlies the bedrock zone and truncates the dipping beds parallel to land surface. Diabase dikes are barriers to ground-water flow in the bedrock zone. The ground-water system is generally confined or semi-confined, even at shallow depths. Depth to water can range from flowing at land surface to more than 71 feet below land surface. Potentiometric maps based on measured water levels at the Gettysburg Elevator Plant indicate ground water flows from west to east, towards Rock Creek. Multiple-well aquifer tests indicate the system is heterogeneous and flow is primarily in dipping beds that contain discrete secondary openings separated by less permeable beds. Water levels in wells open to the pumped bed, as projected along the dipping stratigraphy, are drawn down more than water levels in wells not open to the pumped bed. Ground-water flow was simulated for steady-state conditions prior to pumping and long-term average pumping conditions. The three-dimensional numerical flow model (MODFLOW) was calibrated by use of a parameter estimation program (MODFLOWP). Steady-state conditions were assumed for the calibration period of 1996. An effective areal recharge rate of 7 inches was used in model calibration. The calibrated flow model was used to evaluate the effectiveness of the current onsite and offsite extraction well system. The simulation results generally indicate that the extraction system effectively captures much of the ground-water recharge at the Gettysburg Elevator Plant and, hence, contaminated ground-water migrating from the site. Some of the extraction wells pump at low rates and have very small contributing areas. Results indicate some areal recharge onsite will move to offsite extraction wells.

Pennsylvania↗

USGS1995

Water-quality characteristics of streams in the Treyburn Development area of Falls Lake watershed, North Carolina, 1988-93

Treyburn is a 5,400 acre planned, mixed-use community located in the Falls Lake watershed in the upper Neuse River Basin of North Carolina. From February 1988 through 1993, hydrologic-data were collected at 17 study sites in or near the Treyburn development to compare the effects of varying types of land-use development on the water-quality of streams flowing in or near the development. The collected hydrologic data included measurements of streamflow and concentrations of major dissolved constituents, nutrients, minor elements, and organic compounds. Streamflow in the study basin was approximately 40 percent lower in 1992 and 40 percent higher in 1993 than the long-term annual mean of the long-term discharge records at Flat River in Bahama. Calcium and bicarbonate were the predominant cation and anion at all study sites except one. Mean total nitrogen and phosphorus concentrations at sites in the Treyburn development ranged from 0.5 to 0.8 and 0.03 to 0.10 milligrams per liter, respectively. Total aluminum, iron, and manganese were the metals most frequently detected in the 200 organic compunds analyzed. Dichloro- difluoromethane and methylene chloride were detected most often.

North Carolina↗