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At least 1,657 records · Page 92Linked to original sources
USGS2000

Ground-water quality in the Appalachian Plateaus, Kanawha River basin, West Virginia

Water samples collected from 30 privately-owned and small public-supply wells in the Appalachian Plateaus of the Kanawha River Basin were analyzed for a wide range of constituents, including bacteria, major ions, nutrients, trace elements, radon, pesticides, and volatile organic compounds. Concentrations of most constituents from samples analyzed did not exceed U.S. Environmental Protection Agency (USEPA) standards. Constituents that exceeded drinking-water standards in at least one sample were total coliform bacteria, Escherichia coli (E. coli) , iron, manganese, and sulfate. Total coliform bacteria were present in samples from five sites, and E. coli were present at only one site. USEPA secondary maximum contaminant levels (SMCLs) were exceeded for three constituents -- sulfate exceeded the SMCL of 250 mg/L (milligrams per liter) in samples from 2 of 30 wells; iron exceeded the SMCL of 300 µg/L (micrograms per liter) in samples from 12 of the wells, and manganese exceeded the SMCL of 50 µg/L in samples from 17 of the wells sampled. None of the samples contained concentrations of nutrients that exceeded the USEPA maximum contaminant levels (MCLs) for these constituents. The maximum concentration of nitrate detected was only 4.1 mg/L, which is below the MCL of 10 mg/L. Concentrations of nitrate in precipitation and shallow ground water are similar, potentially indicating that precipitation may be a source of nitrate in shallow ground water in the study area. Radon concentrations exceeded the recently proposed maximum contaminant level of 300 pCi/L at 50 percent of the sites sampled. The median concentration of radon was only 290 pCi/L. Radon-222 is a naturally occurring, carcinogenic, radioactive decay product of uranium. Concentrations, however, did not exceed the alternate maximum contaminant level (AMCL) for radon of 4,000 pCi/L in any of the 30 samples. Arsenic concentrations exceeded the proposed MCL of 5µg/L at 4 of the 30 sites. No samples exceeded the current MCL of 50 µg/L. Neither pesticides nor volatile organic compounds (VOCs) were prevalent in the study area, and the concentrations of the compounds that were detected did not exceed any USEPA MCLs. Pesticides were detected in only two of the 30 wells sampled, but four pesticides -- atrazine, carbofuran, DCPA, and deethylatrazine -- were detected in one well; molinate was detected in the other well. All of the pesticides detected were at estimated concentrations of only 0.002 µg/L. Of the VOCs detected, trihalomethane compounds (THMs), which can result from chlorination of a well, were the most common. THMs were detected in 13 of the 30 wells sampled. Gasoline by-products, such as benzene, toluene, ethylbenzene and xylene (BTEX compounds) were detected in 10 of the 30 wells sampled. The maximum concentration of any of the VOCs detected in this study, however, was only 1.040 µg/L, for the THM dichlorofluoromethane. Water samples from 25 of the wells were analyzed for chlorofluorocarbons (CFCs) to estimate the apparent age of ground water. The analyses indicated that age of water ranged from 10 to greater than 57 years, and that the age of ground water could be correlated with the topographic setting of the wells sampled. Thus the apparent age of water in wells on hilltops was youngest (median of 13 years) and that of water in wells in valleys was oldest (median of 42 years). Water from wells on hillsides was intermediate in age (median of 29 years). These data can be used to define contributing areas to wells, corroborate or revise conceptual ground-water flow models, estimate contaminant travel times from spills to other sources such as nearby domestic or public supply wells, and to manage point and nonpoint source activities that may affect critical aquifers.

West Virginia↗
USGS2004

Status of sea otter populations in southcentral and southeast Alaska, 2002-2003

During the years 2002-2004 estimated sea otter population sizes were calculated for Southeast Alaska, Prince William Sound, and the Kenai Peninsula and Cook Inlet regions of Alaska. Aerial surveys were conducted by a single observer from a float-equipped Bellanca Scout fixed-wing aircraft flying at 91 m altitude and 65 mph. The surveys followed protocols written by Bodkin and Udevitz (1999). The survey design consisted of systematic sampling of 400 m wide transects that were uniformly placed throughout the survey area. Selection and sampling of transects was proportional to expected sea otter abundance, with most effort taking place in transects over waters 0-40 m in depth. Intensive searches were periodically conducted within transects to estimate the proportion of sea otters not detected on strips. To obtain an adjusted population size estimate, strip counts are adjusted for the area not surveyed and by a correction factor.

Alaska↗
USGS2005

Hydrology and simulation of ground-water flow in Cedar Valley, Iron County, Utah

Cedar Valley, located in the eastern part of Iron County in southwestern Utah, is experiencing rapid population growth. Cedar Valley traditionally has supported agriculture, but the growing population needs a larger share of the available water resources. Water withdrawn from the unconsolidated basin fill is the primary source for public supply and is a major source of water for irrigation. Water managers are concerned about increasing demands on the water supply and need hydrologic information to manage this limited water resource and minimize flow of water unsuitable for domestic use toward present and future public-supply sources. Surface water in the study area is derived primarily from snowmelt at higher altitudes east of the study area or from occasional large thunderstorms during the summer. Coal Creek, a perennial stream with an average annual discharge of 24,200 acre-feet per year, is the largest stream in Cedar Valley. Typically, all of the water in Coal Creek is diverted for irrigation during the summer months. All surface water is consumed within the basin by irrigated crops, evapotranspiration, or recharge to the ground-water system. Ground water in Cedar Valley generally moves from primary recharge areas along the eastern margin of the basin where Coal Creek enters, to areas of discharge or subsurface outflow. Recharge to the unconsolidated basin-fill aquifer is by seepage of unconsumed irrigation water, streams, direct precipitation on the unconsolidated basin fill, and subsurface inflow from consolidated rock and Parowan Valley and is estimated to be about 42,000 acre-feet per year. Stable-isotope data indicate that recharge is primarily from winter precipitation. The chloride mass-balance method indicates that recharge may be less than 42,000 acre-feet per year, but is considered a rough approximation because of limited chloride concentration data for precipitation and Coal Creek. Continued declining water levels indicate that recharge is not sufficient to meet demand. Water levels in many areas are at or close to historic lows. In 2000, withdrawal from wells was estimated to be 36,000 acre-feet per year. About 4,000 acre-feet per year are estimated to discharge to evapotranspiration or as subsurface outflow. Prior to large-scale ground-water development, ground-water discharge by evapotranspiration and discharge to springs was much larger. Ground water along the eastern margin of the valley between Cedar City and Enoch is unsuitable for domestic use because of high dissolved-solids and nitrate concentrations. The predominant ions of Ca and SO4 in this area indicate dissolution of gypsum in the Markagunt Plateau to the east. Data collected during this study were compared to historic data; there is no evidence to indicate deterioration in ground-water quality. The spatial distribution of ground water with high nitrate concentration does not appear to be migrating beyond its previously known extent. No single source can be identified as the cause for elevated nitrate concentrations in ground water. Low nitrogen-15 values north of Cedar City indicate a natural geologic source. Higher nitrogen-15 values toward the center of the basin and associated hydrologic data indicate probable recharge from waste-water effluent. Excess dissolved nitrogen gas and low nitrate concentrations in shallow ground water indicate that denitrification is occurring in some areas. A computer ground-water flow model was developed to simulate flow in the unconsolidated basin fill. The method of determining recharge from irrigation was changed during the calibration process to incorporate more areal and temporal variability. In general, the model accurately simulates water levels and water-level fluctuations and can be considered an adequate tool to help determine the valley-wide effects on water levels of additional ground-water withdrawals and changes in water use. The model was used to simulated water-level changes caused by projecting current withdrawal rates, increased withdrawal rates, and a 10-year drought. Water levels declined 20 to 275 feet in the southern and central parts of the valley and less than 20 feet north of Enoch

Utah↗
USGS2002

Simulated transport and biodegradation of chlorinated ethenes in a fractured dolomite aquifer near Niagara Falls, New York

Leakage of trichloroethene (TCE) from a neutralization pond at a former manufacturing facility near Niagara Falls, N.Y. during 1950-87 into the Guelph Formation of the Lockport Group, a fractured dolomite aquifer, created a plume of TCE and its metabolites that, by 1990, extended about 4,300 feet south of the facility. A smaller plume of dense, nonaqueous-phase liquids (DNAPL) probably serves as a continuing source of TCE. The presence of the TCE metabolites cis-1,2-dichloroethene (DCE), vinyl chloride (VC), and ethene in the plume, and the results of previous laboratory microcosm studies, indicate that the TCE is being degraded by naturally occurring microorganisms. Biodegradation rates of TCE and its metabolites were estimated through simulation with BIOMOC, a solute-transport model that represents multispecies reactions through Monod kinetics. A fracture zone in the Guelph Formation was represented as a porous medium containing an extensive, 3-foot thick layer with several interconnected fractures; this layer is bounded above and below by subhorizontal stratigraphic contacts. The Monod reaction constants were estimated through nonlinear regression to minimize the difference between computed concentrations of TCE and its metabolites, and the concentrations measured before and during 5 years of pump-and-treat remediation. Transport simulations indicated that, by April 1998, the chlorinated ethene plume had reached a dynamic equilibrium between the rate of TCE dissolution and the rate of removal through pumping and biodegradation. Biodegradation of chlorinated ethenes at the site can be simulated as first-order reactions because the concentrations are generally less than the half-saturation constants estimated for Monod kinetics (320 mg/L for TCE, 10 mg/L for DCE, and 1 mg/L for VC). Computed degradation rates are proportional to the estimated ground-water velocity, which could vary by more than an order magnitude at the site, as indicated by the estimated range of fracture porosity--3 to 0.3 percent. Half-lives corresponding to first-order rate constants estimated for the lower velocity (5 to 15 feet per day) ranged from 21 to 25 days for TCE, 170 to 230 days for DCE, and 18 to 23 days for VC. Chlorinated ethene concentrations of April 1998 were better reproduced when the TCE source was represented as a constant concentration than as a constant flux, because the latter predicted that the plume would dissipate after 5 years of pump-and-treat remediation. This result indicates that the rate of TCE dissolution is not limited by the mass of TCE in the DNAPL plume. Simulation of diffusion by the transport model MOC3D indicated that concentrations of these contaminants within the rock matrix surrounding the fracture zone were relatively unchanged after 5 years of pump-and-treat remediation. The principal sources of uncertainty in the prediction of biodegradation rates and of the fate of chlorinated ethenes at the site are the fracture porosity and DNAPL mass in the aquifer.

New York↗
USGS1997

Detection of underground voids in Ohio by use of geophysical methods

Geophysical methods are generally classified as electrical, potential field, and seismic methods. Each method type relies on contrasts of physical properties in the subsurface. Forward models based on the physical properties of air- and water-filled voids within common geologic materials indicate that several geophysical methods are technically feasible for detection of subsurface voids in Ohio, but ease of use and interpretation varies widely between the methods. Ground-penetrating radar is the most rapid and cost-effective method for collection of subsurface data in areas associated with voids under roadways. Electrical resistivity, gravity, or seismic reflection methods have applications for direct delineation of voids, but data-collection and analytical procedures are more time consuming. Electrical resistivity, electromagnetic, or magnetic methods may be useful in locating areas where conductive material, such as rail lines, are present in abandoned underground coal mines. Other electrical methods include spontaneous potential and very low frequency (VLF); these latter two methods are considered unlikely candidates for locating underground voids in Ohio. Results of ground-penetrating radar surveys at three highway sites indicate that subsurface penetration varies widely with geologic material type and amount of cultural interference. Two highway sites were chosen over abandoned underground coal mines in eastern Ohio. A third site in western Ohio was chosen in an area known to be underlain by naturally occurring voids in lime stone. Ground-penetrating radar surveys at Interstate 470, in Belmont County, Ohio, indicate subsurface penetration of less than 15 feet over a mined coal seam that was known to vary in depth from 0 to 40 feet. Although no direct observations of voids were made, anomalous areas that may be related to collapse structures above voids were indicated. Cultural interference dominated the radar records at Interstate 70, Guernsey County, Ohio, where coal was mined under the site at a depth of about 50 feet. Interference from overhead powerlines, the field vehicle, and guardrails complicated an interpretation of the radar records where the depth of penetration was estimated to be less than 5 feet. Along State Route 33, in Logan County, Ohio, bedding planes and structures possibly associated with dissolution of limestone were profiled with ground-penetrating radar. Depth of penetration was estimated to be greater than 50 feet.

Water-Resources Investigations Report↗
USGS1999

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

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

Ohio↗
USGS2025

Community estimate of global glacier mass changes from 2000 to 2023

Glaciers are indicators of ongoing anthropogenic climate change 1 . Their melting leads to increased local geohazards 2 , and impacts marine 3 and terrestrial 4 , 5 ecosystems, regional freshwater resources 6 , and both global water and energy cycles 7 , 8 . Together with the Greenland and Antarctic ice sheets, glaciers are essential drivers of present 9 , 10 and future 11 , 12 , 13 sea-level rise. Previous assessments of global glacier mass changes have been hampered by spatial and temporal limitations and the heterogeneity of existing data series 14 , 15 , 16 . Here we show in an intercomparison exercise that glaciers worldwide lost 273 ± 16 gigatonnes in mass annually from 2000 to 2023, with an increase of 36 ± 10% from the first (2000–2011) to the second (2012–2023) half of the period. Since 2000, glaciers have lost between 2% and 39% of their ice regionally and about 5% globally. Glacier mass loss is about 18% larger than the loss from the Greenland Ice Sheet and more than twice that from the Antarctic Ice Sheet 17 . Our results arise from a scientific community effort to collect, homogenize, combine and analyse glacier mass changes from in situ and remote-sensing observations. Although our estimates are in agreement with findings from previous assessments 14 , 15 , 16 at a global scale, we found some large regional deviations owing to systematic differences among observation methods. Our results provide a refined baseline for better understanding observational differences and for calibrating model ensembles 12 , 16 , 18 , which will help to narrow projection uncertainty for the twenty-first century 11 , 12 , 18 .

Nature↗
USGS2011

Hydrogeologic and geochemical characterization of groundwater resources in Rush Valley, Tooele County, Utah

The water resources of Rush Valley were assessed during 2008–2010 with an emphasis on refining the understanding of the groundwater-flow system and updating the groundwater budget. Surface-water resources within Rush Valley are limited and are generally used for agriculture. Groundwater is the principal water source for most other uses including supplementing irrigation. Most groundwater withdrawal in Rush Valley is from the unconsolidated basin-fill aquifer where conditions are generally unconfined near the mountain front and confined at lower altitudes near the valley center. Productive aquifers also occur in fractured bedrock along the valley margins and beneath the basin-fill deposits in some areas. Drillers’ logs and geophysical gravity data were compiled and used to delineate seven hydrogeologic units important to basin-wide groundwater movement. The principal basin-fill aquifer includes the unconsolidated Quaternary-age alluvial and lacustrine deposits of (1) the upper basin-fill aquifer unit (UBFAU) and the consolidated and semiconsolidated Tertiary-age lacustrine and alluvial deposits of (2) the lower basin-fill aquifer unit (LBFAU). Bedrock hydrogeologic units include (3) the Tertiary-age volcanic unit (VU), (4) the Pennsylvanian- to Permian-age upper carbonate aquifer unit (UCAU), (5) the upper Mississippian- to lower Pennsylvanian-age upper siliciclastic confining unit (USCU), (6) the Middle Cambrian- to Mississippian-age lower carbonate aquifer unit (LCAU), and (7) the Precambrian- to Lower Cambrian-age noncarbonate confining unit (NCCU). Most productive bedrock wells in the Rush Valley groundwater basin are in the UCAU. Average annual recharge to the Rush Valley groundwater basin is estimated to be about 39,000 acre-feet. Nearly all recharge occurs as direct infiltration of snowmelt and rainfall within the mountains with smaller amounts occurring as infiltration of streamflow and unconsumed irrigation water at or near the mountain front. Groundwater generally flows from the higher altitude recharge areas toward two distinct valley-bottom discharge areas: one in the vicinity of Rush Lake in northern Rush Valley and the other located west and north of Vernon. Average annual discharge from the Rush Valley groundwater basin is estimated to be about 43,000 acre-feet. Most discharge occurs as evapotranspiration in the valley lowlands, as discharge to springs and streams, and as withdrawal from wells. Subsurface discharge outflow to Tooele and Cedar Valleys makes up only a small fraction of natural discharge. Groundwater samples were collected from 25 sites (24 wells and one spring) for geochemical analysis. Dissolved-solids concentrations in water from these sites ranged from 181 to 1,590 milligrams per liter. Samples from seven wells contained arsenic concentrations that exceed the Environmental Protection Agency Maximum Contaminant Level of 10 micrograms per liter. The highest arsenic levels are found north of Vernon and in southeastern Rush Valley. Stable-isotope ratios of oxygen and deuterium, along with dissolved-gas recharge temperatures, indicate that nearly all modern groundwater is meteoric and derived from the infiltration of high altitude precipitation in the mountains. These data are consistent with recharge estimates made using a Basin Characterization Model of net infiltration that shows nearly all recharge occurring as infiltration of precipitation and snowmelt within the mountains surrounding Rush Valley. Tritium concentrations between 0.4 and 10 tritium units indicate the presence of modern (less than 60 years old) groundwater at 7 of the 25 sample sites. Apparent 3 H/ 3 He ages, calculated for six of these sites, range from 3 to 35 years. Adjusted minimum radiocarbon ages of premodern water samples range from about 1,600 to 42,000 years with samples from 11 of 13 sites being more than 11,000 years. These data help to identify areas where modern groundwater is circulating through the hydrologic system on time scales of decades or less and indicate that large parts of the principal basin-fill and the bedrock aquifers are much less active and receive little to no modern recharge.

Utah↗
USGS2012

Well network installation and hydrogeologic data collection, Assateague Island National Seashore, Worcester County, Maryland, 2010

The U.S. Geological Survey, as part of its Climate and Land Use Change Research and Development Program, is conducting a multi-year investigation to assess potential impacts on the natural resources of Assateague Island National Seashore, Maryland that may result from changes in the hydrologic system in response to projected sea-level rise. As part of this effort, 26 monitoring wells were installed in pairs along five east-west trending transects. Each of the five transects has between two and four pairs of wells, consisting of a shallow well and a deeper well. The shallow well typically was installed several feet below the water table—usually in freshwater about 10 feet below land surface (ft bls)—to measure water-level changes in the shallow groundwater system. The deeper well was installed below the anticipated depth to the freshwater-saltwater interface—usually in saltwater about 45 to 55 ft bls—for the purpose of borehole geophysical logging to characterize local differences in lithology and salinity and to monitor tidal influences on groundwater. Four of the 13 shallow wells and 5 of the 13 deeper wells were instrumented with water-level recorders that collected water-level data at 15-minute intervals from August 12 through September 28, 2010. Data collected from these instrumented wells were compared with tide data collected north of Assateague Island at the Ocean City Inlet tide gage, and precipitation data collected by National Park Service staff on Assateague Island. These data indicate that precipitation events coupled with changes in ambient sea level had the largest effect on groundwater levels in all monitoring wells near the Atlantic Ocean and Chincoteague and Sinepuxent Bays, whereas precipitation events alone had the greatest impact on shallow groundwater levels near the center of the island. Daily and bi-monthly tidal cycles appeared to have minimal influence on groundwater levels throughout the island and the water-level changes that were observed appeared to vary among well sites, indicating that changes in lithology and salinity also may affect the response of water levels in the shallow and deeper groundwater systems throughout the island. Borehole geophysical logs were collected at each of the 13 deeper wells along the 5 transects. Electromagnetic induction logs were collected to identify changes in lithology; determine the approximate location of the freshwater-saltwater interface; and characterize the distribution of fresh and brackish water in the shallow aquifer, and the geometry of the fresh groundwater lens beneath the island. Natural gamma logs were collected to provide information on the geologic framework of the island including the presence and thickness of finer-grained deposits found in the subsurface throughout the island during previous investigations. Results of this investigation show the need for collection of continuous water-level data in both the shallow and deeper parts of the flow system and electromagnetic induction and natural gamma geophysical logging data to better understand the response of this groundwater system to changes in precipitation and tidal forcing. Hydrologic data collected as part of this investigation will serve as the foundation for the development of numerical flow models to assess the potential effects of climate change on the coastal groundwater system of Assateague Island.

Maryl↗
USGS2024

Simulation of groundwater flow in the Long Island, New York regional aquifer system for pumping and recharge conditions from 1900 to 2019

The U.S. Geological Survey has developed a transient, groundwater-flow model that simulates hydrologic conditions in the Long Island aquifer system as part of an ongoing (since 2016) multiyear, cooperative investigation with the New York State Department of Environmental Conservation. The goals of this investigation are to assist stakeholders and resource managers to evaluate the response of the hydrologic system to changes in future hydraulic stresses. Responses in the hydrologic system include changes in water levels in the hydrogeologic units; discharge to streams, coastal waters, and subsurface infrastructure; and the extent of saline groundwater in the aquifers. Hydraulic stresses include future water-supply management and changes in land use and infrastructure. The numerical model synthesizes a diverse set of physiographic, geologic, climatic, land-use, and historical population, water use, and infrastructure data to physically represent the Long Island aquifer system from land surface to bedrock and to simulate annual hydrologic conditions between 1900 and 2019. A three-dimensional hydrogeologic framework was developed from existing and recently collected borehole geologic and geophysical data collected as part of a companion drilling program. Water-transmitting properties of the principal aquifer sediments were defined in three dimensions from new and existing lithologic logs. The distribution of recharge from precipitation was estimated from landscape characteristics and climate data. Anthropogenic recharge from wastewater, leaky infrastructure, and storm runoff were estimated from population, infrastructure, and pumping data. Water-use data, including well locations, depths, and pumping rates, were obtained from historical sources and records and used to estimate pumping stresses continuously in time and space, at an annual average time scale. The data were incorporated into a three-dimensional numerical model using the U.S. Geological Survey finite difference modeling code MODFLOW 6; the model encompassed all of Long Island and surrounding surface waters and simulated historical hydrologic conditions from 1900 to 2019. The calibration process involved trial and error adjustments using prior knowledge to improve general fit to observations followed by an inverse calibration to update and optimize input parameters, using an iterative ensemble smoother algorithm implemented in PEST++ version 5.0. This resulted in a model that generally was in good agreement with observed, dynamically varying hydrologic conditions from 1900 to 2019. The calibrated model was used to develop two base-case models for scenario testing of future, hypothetical conditions where one represented average-annual conditions, and one represented average-seasonal conditions from 2010 to 2019. The model representing average-annual conditions was modified further to represent an alternate sea-level position of 6 feet above the North American Vertical Datum of 1988, and the model representing average-seasonal conditions was modified to represent the average seasonal effects of a 5-year drought imposed upon current hydrologic conditions. Recharge is the sole source of water to the aquifer system; groundwater discharges to coastal water and streams and is withdrawn by pumped wells. Model-estimated annual recharge ranged from about 11 inches in 1965 to 41 inches in 1983. On average, from 2010 to 2019, about 23 percent of water was pumped from wells, and about 47 and 27 percent discharged to coastal waters and streams, respectively; the remaining 4 percent was water that moved into storage in the aquifer matrix. Water levels on Long Island vary naturally during time in response to changes in recharge; the amount of variation is largest in the interior of the island, in areas with highest water table altitudes near groundwater divides and lowest near streams and the coastal waters. The total range of water table altitudes on Long Island between 1900 and 2019 ranged from near 0 to more than 70 feet in western parts of Long Island. The largest range in altitudes is in New York City and is associated with areas of large historical withdrawals between the 1920s and the late 1980s. Water table altitudes generally varied by less than 10 feet in eastern Suffolk County, where the aquifer is under more natural conditions. Saltwater intrusion is of great concern on Long Island, particularly in western Long Island where both the unconfined and confined parts of the aquifer system have been intruded in response to large-scale groundwater withdrawals; however, the volume of freshwater in the islandwide aquifer system only has changed by about 5 percent between 1900 and 2019. The decadal change in the freshwater volume was largest during the early and mid-20th century, corresponding to the largest historical pumping, but that volume change did not exceed 1 percent. The negligible change in freshwater volume suggests that saltwater intrusion as of 2019 was limited at an islandwide scale but continues to occur in local areas of Queens and Nassau Counties, adversely affecting current water supplies and limiting future water supplies for affected communities. The regional groundwater model developed for this investigation is a tool that can be used to help determine the viability of current and future water supplies at a regional scale and can be used to support development of additional models at finer scale to support more focused assessments of groundwater sustainability.

New York↗
USGS2001

Assessment of water-quality conditions in the J.B. Converse Lake watershed, Mobile County, Alabama, 1990-98

J.B. Converse (Converse) Lake is a 3,600-acre, tributary-storage reservoir in Mobile County, southwestern Alabama. The lake serves as the primary drinking-water supply for the city of Mobile. The Converse Lake watershed lies within the Coastal Plain Physiographic Province. Semiconsolidated to unconsolidated sediments of sand, silt, gravel, and clay underlie the watershed, and are covered by acidic soils. Land use in the watershed is mainly forest (64 percent) and agriculture (31 percent). Residential and commercial development account for only 1 percent of the total land use in the watershed. Converse Lake receives inflow from seven major tributaries. The greatest inflows are from Big Creek, Crooked Creek, and Hamilton Creek that had mean annual streamflows of 72.2, 19.4, and 25.0 cubic feet per second, respectively, for the period 1990 to 1998, which represents about 72 percent of the total annual streamflow to the lake. The total mean annual inflow to the lake is estimated to be about 163 cubic feet per second. In general, water quality in Converse Lake and its tributaries meets the criteria established by the Alabama Department of Environmental Management (ADEM) for drinking-water supplies, whole-body contact, and aquatic life. The exceptions include acidic pH levels, iron and manganese levels above secondary or aesthetic criteria, and fecal bacterial levels in some tributaries above whole-body contact (swimmable) criteria. The pH levels throughout the watershed were commonly below the criteria level of 6.0, but this appears to have been a naturally occurring phenomenon caused by poorly buffered soil types, resistant sediments, and forested land use. Median iron and manganese levels were above aesthetic criteria levels of 300 and 50 micrograms per liter, respectively, in some tributaries. All tributary sites in the Converse Lake watershed had median and minimum dissolved-oxygen concentrations above the ADEM criteria level of 5 milligrams per liter except for Boggy Branch, which had a minimum dissolved-oxygen concentration of 3.7 milligrams per liter. The degree to which nutrient contributions from tributaries were causing nutrient enrichment and eutrophication in Converse Lake was assessed. Trend analysis detected little or no change in nutrient concentrations at the tributary and lake sites in the Converse Lake watershed from the 1991 to 1998 water years. Nutrient concentrations at most tributary sites exhibited a significant, positive relation with streamflow that indicated the dominant source of nutrient input to the watershed is from nonpoint contributions. From 1990 to 1998, computed mean annual loads of 75,400 kilograms of total nitrogen, 36,950 kilograms of total Kjeldahl nitrogen, 28,870 kilograms of total inorganic nitrogen, and 3,480 kilograms of total phosphorus were contributed to the lake by Big Creek, Hamilton Creek, and Crooked Creek combined. These mean annual loads of nutrients corresponded to borderline eutrophic/mesotrophic conditions in the lake. Of the combined loads, 62 percent of the total nitrogen, 70 percent of the total Kjeldahl nitrogen, 54 percent of the total inorganic nitrogen, and 47 percent of the total phosphorus originated from the forested subbasin of Big Creek. The more residential and agricultural subbasins of Crooked Creek and Hamilton Creek, however, yielded over twice the total phosphorus load per hectare of land use. Crooked and Hamilton Creek subbasins also had higher yields of the more bioavailable total inorganic nitrogen. A simplistic empirical model could not explain the relation between year-to-year nutrient contributions to Converse Lake from the tributaries and the lake's ability to assimilate those contributions. The potential presence of pathogens in the lake and its tributaries was assessed based on fecal bacterial concentrations. Fecal bacterial concentrations at some tributary sites were above existing criteria for swimmable uses. Contributions of fecal bacte

Water-Resources Investigations Report↗
USGS1980

Hydrology and model study of the proposed Prosperity Reservoir, Center Creek Basin, southwestern Missouri

A dam and reservoir have been proposed for construction on Center Creek, Jasper County, in southwestern Missouri. Ground-water levels in the hills adjacent to the reservoir will rise when the impoundment is completed. One of the problems is that the proposed site of Prosperity Reservoir is a few miles upstream from the lead-zinc mining area known as the Oronogo-Duenweg belt. In this belt transmissivities are variable but appear to be higher than they are in the immediate area of the reservoir. Grove Creek lies down-gradient from the reservoir area and separates it from the mining belt. A model study indicates that inflow from the proposed reservoir to the water table could cause water level rises varying from about 20 feet near the reservoir to 0.5 to 1.0 foot in the southern part of Grove Creek drainage basin. These rises will cause significant changes to the natural ground-water flow system. Increased ground-water elevations in the reservoir area could result in increased ground-water gradients and discharge to Grove and Center Creeks. The increase in ground-water discharge to Grove Creek, and in turn Center Creek, will have the beneficial effect of diluting mine-water discharge from the Oronogo-Duenweg belt during periods of low flow. However, if Grove Creek does not act as an effective drain and if conduits extend beneath Grove Creek to transfer the increased water available to the Oronogo-Duenweg belt, the flow regimen could change in the mining belt west of Grove Creek increasing mine-water discharge to Center Creek downstream from the reservoir. Bedrock in the area is Mississippian limestone, the deeply solutioned formation that contained the ore deposits. The limestone in the mining district was greatly altered by solution prior to ore deposition while the limestone in the area of the reservoir was altered less. The extent of the alteration is related to the aquifer characteristics in that high and low values of transmissivity and storage coefficient correspond to greatly altered brecciated rocks in the mining district and less altered, less brecciated rocks in the reservoir area, respectively. The authors suggest that an ancestral east-flowing White River drained the area about Joplin in Late Mississippian time. This is based on the configuration of the contact between Meramecian and Osagean rocks of Mississippian age. A high topographic area existed in the region about Joplin in which the water table stood 200 feet below the land surface when sinkholes and caverns of that depth were formed. The large number of Pennsylvanian-filled sinkholes in the Joplin area and the smaller number to the east suggest a higher land surface to the west than that to the east. The distribution of paleokarst sinkholes supports the conclusion based on the configuration of the Meramecian-Osagean contact.

Missouri↗
USGS2014

Simulated effects of increased groundwater withdrawals in the Cave Springs area, Hixson, Tennessee

Concern for future water supplies in Tennessee has grown in recent years as a result of increased awareness of competing needs, the impact of droughts, and the need for more water to support growing populations. The U.S. Geological Survey conducts investigations to improve the knowledge about interactions of geology, climate, humans, and ecosystems with the water cycle, which is critical to understanding and optimizing water availability. The Hixson Utility District in Hamilton County, Tennessee, uses groundwater resources in the Cave Springs area as a water supply, withdrawing water from two well fields located at Cave Springs and Walkers Corner. Historically, Hixson Utility District has withdrawn about 5 million gallons per day (Mgal/d) at the Cave Springs well field and between 2 and 3 Mgal/d at the Walkers Corner well field. To assess the capacity of the groundwater resources in the Cave Springs area to meet future demands, four different scenarios of increased groundwater withdrawals were analyzed using computer model simulations. In the study area, groundwater is present in both regolith and bedrock. Groundwater flow in the regolith occurs as diffuse flow as recharge from precipitation moves through the regolith to discharge to streams and springs or to the underlying bedrock. Most of the bedrock in the study area has low primary porosity and permeability; however, fracturing and dissolution have produced substantial secondary porosity and permeability. Groundwater flow through the bedrock occurs as both diffuse and conduit flow. Recharge to the aquifer is from two distinct sources: direct infiltration of precipitation and losing streams. A major source of recharge to the aquifer that supplies Cave Springs is surface water that is lost from North Chickamauga Creek as it flows from the Cumberland Plateau onto the Newman Limestone. Average annual streamflow loss (groundwater recharge) from this reach of North Chickamauga Creek for the period November 2000 through June 2006 is about 18 cubic feet per second (ft 3 /s). Groundwater leaves the aquifer as either discharge to North Chickamauga Creek, Poe Branch, and Lick Branch; discharge to Chickamauga Lake; spring flow to Cave Springs or Rogers Spring; or withdrawals at the Cave Springs or Walkers Corner well fields. Using computer model simulations, four scenarios of increased groundwater withdrawals were analyzed. Each of these four scenarios are compared to a base-case simulation that uses groundwater withdrawal rates from 2012 of 5.1 Mgal/d from the Cave Springs well field and 2.7 Mgal/d from the Walkers Corner well field. Under scenarios A and B, pumpage is increased at Cave Springs by 2 Mgal/d and 5 Mgal/d, respectively, while pumpage at Walkers Corner remains unchanged. Under scenarios C and D, pumpage is increased at Walkers Corner by 2.6 Mgal/d and 4.5 Mgal/d, respectively, while pumpage at Cave Springs remains unchanged. The effects of the increased withdrawals were analyzed by comparing water budget changes of the groundwater discharges to Chickamauga Lake, North Chickamauga Creek, Cave Springs, Poe Branch, and Lick Branch/Rogers Spring for each of the scenarios and evaluating changes in groundwater levels at the well fields. Under scenarios A and B, the largest change in the water budget occurs for flow to Cave Springs with decreases of 1.9 and 4.7 ft 3 /s, respectively. Similarly, groundwater discharge to North Chickamauga Creek decreases by 1.0 ft 3 /s and 2.6 ft 3 3/s, respectively. Under scenarios C and D, the largest change in the water budget occurs for flow to Chickamauga Lake with decreases of 1.3 ft 3 /s and 2.3 ft 3 /s, respectively. Similarly, groundwater discharge to North Chickamauga Creek decreases by 1.1 ft 3 /s and 2.1 ft 3 /s, respectively. Changes in groundwater levels at the well fields were also analyzed. At the Cave Springs well field, maximum declines in groundwater levels due to additional pumpage are less than 1 foot for all scenarios. Groundwater level changes at the Cave Springs well field are small due to the highly transmissive nature of the aquifer in this location. Maximum groundwater-level declines at Walkers Corner are less than 1 foot for scenarios A and B and about 52 feet and 82 feet for scenarios C and D, respectively. Under scenarios C and D, the regional potentiometric surface shows a large cone of depression centered on the Walkers Corner well field and elongated along geologic strike.

Tennessee↗
USGS2000

Estimating the probability of elevated nitrate (NO2+NO3-N) concentrations in ground water in the Columbia Basin Ground Water Management Area, Washington

Logistic regression was used to relate anthropogenic (man-made) and natural factors to the occurrence of elevated concentrations of nitrite plus nitrate as nitrogen in ground water in the Columbia Basin Ground Water Management Area, eastern Washington. Variables that were analyzed included well depth, depth of well casing, ground-water recharge rates, presence of canals, fertilizer application amounts, soils, surficial geology, and land-use types. The variables that best explain the occurrence of nitrate concentrations above 3 milligrams per liter in wells were the amount of fertilizer applied annually within a 2-kilometer radius of a well and the depth of the well casing; the variables that best explain the occurrence of nitrate above 10 milligrams per liter included the amount of fertilizer applied annually within a 3-kilometer radius of a well, the depth of the well casing, and the mean soil hydrologic group, which is a measure of soil infiltration rate. Based on the relations between these variables and elevated nitrate concentrations, models were developed using logistic regression that predict the probability that ground water will exceed a nitrate concentration of either 3 milligrams per liter or 10 milligrams per liter. Maps were produced that illustrate the predicted probability that ground-water nitrate concentrations will exceed 3 milligrams per liter or 10 milligrams per liter for wells cased to 78 feet below land surface (median casing depth) and the predicted depth to which wells would need to be cased in order to have an 80-percent probability of drawing water with a nitrate concentration below either 3 milligrams per liter or 10 milligrams per liter. Maps showing the predicted probability for the occurrence of elevated nitrate concentrations indicate that the irrigated agricultural regions are most at risk. The predicted depths to which wells need to be cased in order to have an 80-percent chance of obtaining low nitrate ground water exceed 600 feet in the irrigated agricultural regions, whereas wells in dryland agricultural areas generally need a casing in excess of 400 feet. The predicted depth to which wells need to be cased to have at least an 80-percent chance to draw water with a nitrate concentration less than 10 milligrams per liter generally did not exceed 800 feet, with a 200-foot casing depth typical of the majority of the area.

Washington↗
USGS2017

Sequence stratigraphy, seismic stratigraphy, and seismic structures of the lower intermediate confining unit and most of the Floridan aquifer system, Broward County, Florida

Deep well injection and disposal of treated wastewater into the highly transmissive saline Boulder Zone in the lower part of the Floridan aquifer system began in 1971. The zone of injection is a highly transmissive hydrogeologic unit, the Boulder Zone, in the lower part of the Floridan aquifer system. Since the 1990s, however, treated wastewater injection into the Boulder Zone in southeastern Florida has been detected at three treated wastewater injection utilities in the brackish upper part of the Floridan aquifer system designated for potential use as drinking water. At a time when usage of the Boulder Zone for treated wastewater disposal is increasing and the utilization of the upper part of the Floridan aquifer system for drinking water is intensifying, there is an urgency to understand the nature of cross-formational fluid flow and identify possible fluid pathways from the lower to upper zones of the Floridan aquifer system. To better understand the hydrogeologic controls on groundwater movement through the Floridan aquifer system in southeastern Florida, the U.S. Geological Survey and the Broward County Environmental Planning and Community Resilience Division conducted a 3.5-year cooperative study from July 2012 to December 2015. The study characterizes the sequence stratigraphy, seismic stratigraphy, and seismic structures of the lower part of the intermediate confining unit aquifer and most of the Floridan aquifer system. Data obtained to meet the study objective include 80 miles of high-resolution, two-dimensional (2D), seismic-reflection profiles acquired from canals in eastern Broward County. These profiles have been used to characterize the sequence stratigraphy, seismic stratigraphy, and seismic structures in a 425-square-mile study area. Horizon mapping of the seismic-reflection profiles and additional data collection from well logs and cores or cuttings from 44 wells were focused on construction of three-dimensional (3D) visualizations of eight sequence stratigraphic cycles that compose the Eocene to Miocene Oldsmar, Avon Park, and Arcadia Formations. The mapping of these seismic-reflection and well data has produced a refined Cenozoic sequence stratigraphic, seismic stratigraphic, and hydrogeologic framework of southeastern Florida. The upward transition from the Oldsmar Formation to the Avon Park Formation and the Arcadia Formation embodies the evolution from (1) a tropical to subtropical, shallow-marine, carbonate platform, represented by the Oldsmar and Avon Park Formations, to (2) a broad, temperate, mixed carbonate-siliciclastic shallow marine shelf, represented by the lower part of the Arcadia Formation, and to (3) a temperate, distally steepened carbonate ramp represented by the upper part of the Arcadia Formation. In the study area, the depositional sequences and seismic sequences have a direct correlation with hydrogeologic units. The approximate upper boundary of four principal permeable units of the Floridan aquifer system (Upper Floridan aquifer, Avon Park permeable zone, uppermost major permeable zone of the Lower Floridan aquifer, and Boulder Zone) have sequence stratigraphic and seismic-reflection signatures that were identified on cross sections, mapped, or both, and therefore the sequence stratigraphy and seismic stratigraphy were used to guide the development of a refined spatial representation of these hydrogeologic units. In all cases, the permeability of the four permeable units is related to stratiform megaporosity generated by ancient dissolution of carbonate rock associated with subaerial exposure and unconformities at the upper surfaces of carbonate depositional cycles of several hierarchical scales ranging from high-frequency cycles to depositional sequences. Additionally, interparticle porosity also contributes substantially to the stratiform permeability in much of the Upper Floridan aquifer. Information from seismic stratigraphy allowed 3D geomodeling of hydrogeologic units—an approach never before applied to this area. Notably, the 3D geomodeling provided 3D visualizations and geocellular models of the depositional sequences, hydrostratigraphy, and structural features. The geocellular data could be used to update the hydrogeologic structure inherent to groundwater flow simulations that are designed to address the sustainability of the water resources of the Floridan aquifer system. Two kinds of pathways that could enable upward cross-formational flow of injected treated wastewater from the Boulder Zone have been identified in the 80 miles of high-resolution seismic data collected for this study: a near-vertical reverse fault and karst collapse structures. The single reverse fault, inferred to be of tectonic origin, is in extreme northeastern Broward County and has an offset of about 19 feet at the level of the Arcadia Formation. Most of the 17 karst collapse structures identified manifest as columniform, vertically stacked sagging seismic reflections that span early Eocene to Miocene age rocks equivalent to much of the Floridan aquifer system and the lower part of the overlying intermediate confining unit. In some cases, the seismic-sag structures extend upward into strata of Pliocene age. The seismic-sag structures are interpreted to have a semicircular shape in plan view on the basis of comparison to (1) other seismic-sag structures in southeastern Florida mapped with two 2D seismic cross lines or 3D data, (2) comparison to these structures located in other carbonate provinces, and (3) plausible extensional ring faults detected with multi-attribute analysis. The seismic-sag structures in the study area have heights as great as 2,500 vertical feet, though importantly, one spans about 7,800 feet. Both multi-attribute analysis and visual detection of offset of seismic reflections within the seismic-sag structures indicate faults and fractures are associated with many of the structures. Multi-attribute analysis highlighting chimney fluid pathways also indicates that the seismic-sag structures have a high probability for potential vertical cross-formational fluid flow along the faulted and fractured structures. A collapse of the seismic-sag structures within a deep burial setting evokes an origin related to hypogenic karst processes by ascending flow of subsurface fluids. In addition, paleo-epigenic karst related to major regional subaerial unconformities within the Florida Platform generated collapse structures (paleo-sinkholes) that are much smaller in scale than the cross-formational seismic-sag structures.

Florida↗
USGS1999

Ground-water system, estimation of aquifer hydraulic properties, and effects of pumping on ground-water flow in Triassic sedimentary rocks in and near Lansdale, Pennsylvania

Ground water in Triassic-age sedimentary fractured-rock aquifers in the area of Lansdale, Pa., is used as drinking water and for industrial supply. In 1979, ground water in the Lansdale area was found to be contaminated with trichloroethylene, tetrachloroethylene, and other man-made organic compounds, and in 1989, the area was placed on the U.S. Environmental Protection Agency's (USEPA) National Priority List as the North Penn Area 6 site. To assist the USEPA in the hydrogeological assessment of the site, the U.S. Geological Survey began a study in 1995 to describe the ground-water system and to determine the effects of changes in the well pumping patterns on the direction of ground-water flow in the Lansdale area. This determination is based on hydrologic and geophysical data collected from 1995-98 and on results of the simulation of the regional ground-water-flow system by use of a numerical model. Correlation of natural-gamma logs indicate that the sedimentary rock beds strike generally northeast and dip at angles less than 30 degrees to the northwest. The ground-water system is confined or semi-confined, even at shallow depths; depth to bedrock commonly is less than 20 feet (6 meters); and depth to water commonly is about 15 to 60 feet (5 to 18 meters) below land surface. Single-well, aquifer-interval-isolation (packer) tests indicate that vertical permeability of the sedimentary rocks is low. Multiple-well aquifer tests indicate that the system is heterogeneous and that flow appears primarily in discrete zones parallel to bedding. Preferred horizontal flow along strike was not observed in the aquifer tests for wells open to the pumped interval. Water levels in wells that are open to the pumped interval, as projected along the dipping stratigraphy, are drawn down more than water levels in wells that do not intersect the pumped interval. A regional potentiometric map based on measured water levels indicates that ground water flows from Lansdale towards discharge areas in three drainages, the Wissahickon, Towamencin, and Neshaminy Creeks. Ground-water flow was simulated for different pumping patterns representing past and current conditions. The three-dimensional numerical flow model (MODFLOW) was automatically calibrated by use of a parameter estimation program (MODFLOWP). Steady-state conditions were assumed for the calibration period of 1996. Model calibration indicates that estimated recharge is 8.2 inches (208 millimeters) and the regional anisotropy ratio for the sedimentary-rock aquifer is about 11 to 1, with permeability greatest along strike. The regional anisotropy is caused by up- and down-dip termination of high-permeability bed-oriented features, which were not explicitly simulated in the regional-scale model. The calibrated flow model was used to compare flow directions and capture zones in Lansdale for conditions corresponding to relatively high pumping rates in 1994 and to lower pumping rates in 1997. Comparison of the 1994 and 1997 simulations indicates that wells pumped at the lower 1997 rates captured less ground water from known sites of contamination than wells pumped at the 1994 rates. Ground-water flow rates away from Lansdale increased as pumpage decreased in 1997. A preliminary evaluation of the relation between ground-water chemistry and conditions favorable for the degradation of chlorinated solvents was based on measurements of dissolved-oxygen concentration and other chemical constituents in water samples from 92 wells. About 18 percent of the samples contained less than or equal to 5 milligrams per liter dissolved oxygen, a concentration that indicates reducing conditions favorable for degradation of chlorinated solvents.

Water-Resources Investigations Report↗
USGS1985

Evaluation of the ground-water resources of the lower Susquehanna River basin, Pennsylvania and Maryland

Ground water in the 3,458-square-mile lower Susquehanna River basin occupies secondary openings in bedrock. The distribution of openings is a function of lithology, depth, and topography. Local flow systems account for most of the total ground-water flow. Average annual recharge for the lower basin is 1,857 million gallons per day, most of which discharges to streams. The water table is a subdued replica of land surface; its depth varies with topography, but is generally 20 to 70 feet below land surface. Ground water circulates to depths of 500 to 600 feet below the water table. A digital model of regional, unconfined ground-water flow was developed and used to evaluate the ground-water resources of the lower basin. On the basis of lithologic and hydrologic differences, the area was subdivided into 21 hydrogeologic units, each with different hydrologic characteristics. Each unit was divided into two layers to handle decreasing secondary permeability with depth. A finite-difference grid with square blocks approximately one mile on a side was used. The model was calibrated under steady-state and transient conditions. The model-generated results were compared to estimated water-table altitudes and estimated base flows in the steady-state calibration. In the transient calibration, the model-generated results were compared to observed changes in water-table altitude from November 1, 1980 through April 22, 1981. Hydraulic conductivity increases from hilltops to valley bottoms. The average hydraulic conductivity for carbonate units is about 21 feet per day, which is an order of magnitude greater than the corresponding averages for Paleozoic sedimentary, Triassic sedimentary, and crystalline units. The Cumberland Valley carbonate rocks have the greatest average hydraulic conductivity--about 174 feet per day in valley bottoms. The average gaining-stream leakage coefficient for all carbonate units is about 16 feet per day, which is two orders of magnitude greater than the corresponding averages for the other lithologies. The Cumberland Valley carbonate rocks have the greatest gaining-stream leakage coefficient--about 43 feet per day. The specific yields are 0.035, 0.020, 0.020 and 0.007 for the carbonate, Paleozoic sedimentary, crystalline, and Triassic sedimentary units, respectively. The calibrated model was used to simulate the effects of a ground-water withdrawal of 1 inch per year on water-table altitudes and average annual base flows in the modeled area. The overall effect is least for the carbonate units and greatest for the Triassic sedimentary units. The model also was used to simulate a standardized potential yield for each unit by assuming that the maximum acceptable consequence of a hypothetical withdrawal scheme is an ultimate 50-percent reduction in average annual base flow. Based on this, the potential yield for the modeled area is 891 million gallons per day. The Cumberland Valley carbonate rocks have the greatest potential yield--0.47 million gallons per day per square mile. The carbonate units have the greatest average potential yield, followed by the Paleozoic sedimentary, crystalline, and Triassic sedimentary units. About 90 percent of the eventual decline in water-table altitudes and the eventual reduction in average annual base flows occurs within five years of the implementation of the hypothetical withdrawal scheme. Nearly all of the ground water withdrawn is derived from reduced discharge to streams. The calibrated model can be used to provide estimates of the impacts of ground-water development schemes on regional ground-water levels and base flows of streams. It can not be used to simulate local cones of depression or local base-flow changes. The reliability of the model is a function of its approximation of the physical characteristics of the ground-water flow system, the two calibrations, various simplifying assumptions, and the lack of calibration under ground-water withdrawal conditions. It can be used in steady-state or transient mode to assess the effects of both natural and artificial stresses.

Maryland, Pennsylvania↗
USGS2021

Water-quality trends of urban streams in Independence, Missouri, 2005–18

The U.S. Geological Survey and the city of Independence, Missouri, Water Pollution Control Department has studied the water quality and ecological condition of urban streams within Independence since 2005. Selected physical properties, nutrients, chloride, fecal indicator bacteria (Escherichia coli and total coliform), total dissolved solids, and suspended-sediment concentration data for base-flow and stormflow samples were used to document temporal trends in concentrations and flow-weighted concentrations; and annual loads were computed and investigated for selected nutrients, chloride, and suspended sediment. The six study sites included in this report are located on five urban streams: Rock Creek, a tributary in the city that drains to the Missouri River; three tributaries of the Little Blue River within the city (East Fork Little Blue River, Adair Creek, and Spring Branch Creek); and two sites on the main stem of the Little Blue River (one upstream from the city and one downstream from the three tributaries). Many factors such as population, land use, and climate, and combinations of these factors contributed to the significant changes in the concentrations and transport of nutrients, chloride, fecal indicator bacteria, and suspended sediment in the urban streams within Independence. The population of Independence and the amount of developed land in the urban watersheds remained unchanged during the 2005–18 study. Differences were noted in precipitation and in streamflow during the study. Annual precipitation and streamflow were separated into two time periods within the study—period 1 (2006–10), having greater annual streamflow and precipitation, and period 2 (2011–18), having about 30 percent lower annual streamflow and less precipitation. Streamflow was an important factor in the transport of nitrogen, phosphorus, chloride, and suspended sediment from the urban watersheds. Changes in data collection methodology during the study period and improvements to the city stormwater and wastewater infrastructure also could have contributed to some of the trends. Between 2009 and 2015, more than 35 million dollars of improvements were made to stormwater and wastewater infrastructure within the city. These improvements, such as additional sewage overflow holding tanks, removal of septic tanks, and improved and expanded sanitary sewer lines and storm overflows, also could have affected the decreased nutrients and fecal indicator bacteria trends among the urban streams in the study area. Models were used for analyzing streamflow-related variability in constituent concentrations and loads to determine if the water quality changed significantly during the study period. Trends in concentration data at four sites were analyzed using a statistical package called R–QWTREND and trends in load data were analyzed at six sites using a statistical package called Weighted Regressions on Time, Discharge, and Season-Kalman filter (WRTDS–K); both developed by the U.S. Geological Survey and publicly available for use. Statistically significant trends in flow-weighted nutrient concentrations and loads generally were downward during the study period. The only nutrient compound with a statistically significant upward trend in flow-weighted concentration was dissolved orthophosphate as phosphorus at the Rock Creek site and the upstream site on the Little Blue River. A statistically significant downward trend in annual dissolved ammonia load was identified at the downstream Little Blue River site. A significant upward linear trend in annual orthophosphate as phosphorus load was identified on Adair Creek. A statistically significant upward trend in dissolved chloride concentrations was identified at the downstream Little Blue River site. Road salt application near the site during the winter could have resulted in higher concentrated runoff during wet weather conditions. Annual chloride loads significantly decreased in Adair Creek and Spring Branch Creek. The mean annual chloride load transported in the drier (2011–18) period 2 was significantly less than during the wetter (2006–10) period 1, indicating that trends in precipitation runoff are an important factor in trends in annual transport of chloride. Statistically significant downward trends in flow-weighted fecal indicator bacteria Escherichia coli (E. coli) population densities were noted for Rock Creek and the down-stream site on the Little Blue River. However, no trend was identified in E. coli population density at the upstream Little Blue River site. The downward trend in E. coli population density at the downstream site could be a result of decreased streamflow and precipitation over the study period, storage of fecal indicator bacteria in the Little Blue River streambed within the study area, die-off of fecal indicator bacteria during travel from upstream to downstream, changes in the sample collection methodology, improvements to the city’s storm-water and wastewater infrastructures, or a combination of these factors. The statistically significant downward trend in suspended-sediment concentration identified at the upstream Little Blue River site could be affected by the decreased streamflow and precipitation during the study period, by changes in sampling methods within the study period, and by the decrease in construction and urban land development upstream from the city. No statistically significant change was indicated in the annual suspended-sediment load transported from Independence to the Little Blue River during the study period. More than one-half the suspended sediment transported in the Little Blue River originated in the watershed upstream from Independence. The Little Blue River and many of its tributaries that drain Independence have been designated as recreational waters classified for whole-body contact class B and secondary contact recreation, and some have been listed as impaired for E. coli by the Missouri Department of Natural Resources from urban runoff and storm sewers. Observations were made among the available E. coli population density data for both Little Blue River sites to further understand water-quality conditions over the study period. Both Little Blue River sites had similar medians and geometric means for the recreational season (April through October) and during the full study period, both of which are greater than the regulatory population density for both recreational classes. The Little Blue River drainage area nearly doubles in size from the upstream to downstream site; therefore, the consistent geometric mean and median of E. coli population densities at the upstream and downstream Little Blue River sites could be primarily due to the larger volume of streamflow creating a dilution effect. Other possible factors could be storage of fecal indicator bacteria in stream bed sediments, die-off of fecal indicator bacteria during transport, improvements to the city’s wastewater and stormwater infrastructure, changes to sampling methodology, or a combination of these factors. Specific sources of the E. coli are currently (2019) unknown.

Missouri↗