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At least 1,063 records · Page 59Linked to original sources
USGS2004

Simulation of ground-water flow in the Potomac-Raritan-Magothy aquifer system, Pennsauken Township and vicinity, New Jersey

The Potomac-Raritan-Magothy aquifer system is one of the primary sources of potable water in the Coastal Plain of New Jersey, particularly in heavily developed areas along the Delaware River. In Pennsauken Township, Camden County, local drinking-water supplies from this aquifer system have been contaminated by hexavalent chromium at concentrations that exceed the New Jersey maximum contaminant level. In particular, ground water at the Puchack well field has been adversely affected to the point where, since 1984, water is no longer withdrawn from this well field for public supply. The area that contains the Puchack well field was added to the National Priorities List in 1998 as a Superfund site. The U.S. Geological Survey (USGS) conducted a reconnaissance study from 1996 to 1998 during which hydrogeologic and water-quality data were collected and a ground-water-flow model was developed to describe the conditions in the aquifer system in the Pennsauken Township area. The current investigation by the USGS, in cooperation with the U.S. Environmental Protection Agency (USEPA), is an extension of the previous study. Results of the current study can be applied to a Remedial Investigation and Feasibility Study conducted at the Puchack well field Superfund site. The USGS study collected additional data on the hydrogeology and water-quality in the area. These data were incorporated into a refined model of the ground-water-flow system in the Potomac-Raritan-Magothy aquifer system. A finite-difference model was developed to simulate ground-water flow and the advective transport of chromium-contaminated ground water in the aquifers of the Potomac-Raritan-Magothy aquifer system in the Pennsauken Township area. An 11-layer model was used to represent the complex hydrogeologic framework. The model was calibrated using steady-state water-level data from March 1998, April 1998, and April 2001. Water-level recovery during the shutdown of Puchack 1 during March to April 1998 was simulated to evaluate model performance in relation to changing stresses. The Delaware River contributes appreciable-flow to the ground-water system from areas where the Middle and Lower aquifers crop out beneath the river. A transient simulation of an aquifer test near the Delaware River was run to help characterize the hydraulic conductivity of the riverbed sediments represented in the model. Vertical flow across confining units between the aquifers is highly variable and is important in the movement of water and associated contaminants through the flow system. The model was imbedded within a regional model of the Potomac-Raritan-Magothy aquifer system in Camden County. In general, a simulation of baseline conditions, which can provide a representation on which simulations of various alternatives can be based for the feasibility study, incorporated average conditions from 1998 to 2000. Ground-water withdrawals within the model area during this period averaged about 14 Mgal/d. Regional ground-water flow is from recharge areas and from the Delaware River to downgradient pumped wells located just east of the model area in central Camden County. Simulation results show an important connection between the Intermediate sand and the Lower aquifer of the Potomac-Raritan-Magothy aquifer system in the vicinity of the chromium-contaminated area. The Delaware River contributes nearly 10 Mgal/d to the flow system, whereas recharge contributes about 6 Mgal/d. Ground-water withdrawals within the model area account for nearly 14 Mgal/d (mostly from the Lower aquifer of the Potomac-Raritan-Magothy aquifer system).

Scientific Investigations Report↗
USGS2007

Effects of Agricultural Land-Use Changes and Rainfall on Ground-Water Recharge in Central and West Maui, Hawai`i, 1926-2004

Concern surrounding declines in ground-water levels and an increase in the chloride concentration of water pumped from wells in the Iao aquifer system on the Island of Maui has prompted an investigation into the long-term sustainability of current (2006) and future ground-water withdrawals. As part of this investigation, a water budget for central and west Maui was calculated from which (1) ground-water recharge was estimated for the period 1926-2004 and (2) the effects of agricultural land-use changes and drought were analyzed. Estimated mean ground-water recharge decreased 44 percent from 1979 to 2004 in central and west Maui. Reduction in agricultural irrigation, resulting from more efficient irrigation methods and a reduction in the acreage used for agriculture, is largely responsible for the declining recharge. Recently, periods of lower-than-average rainfall have further reduced recharge. During the period 1926-79, ground-water recharge averaged 693 Mgal/d, irrigation averaged 437 Mgal/d, and rainfall averaged 897 Mgal/d. During the period 2000-04, ground-water recharge averaged 391 Mgal/d, irrigation averaged 237 Mgal/d, and rainfall averaged 796 Mgal/d. Simulations of hypothetical future conditions indicate that a cessation of agriculture in central and west Maui would reduce mean ground-water recharge by 18 percent in comparison with current conditions, assuming that current climatic conditions are the same as the long-term-average conditions during the period 1926-2004. A period of drought identical to that of 1998-2002 would reduce mean recharge by 27 percent. Mean recharge would decrease by 46 percent if this drought were to occur after a cessation of agriculture in central and western Maui. Whereas droughts are transient phenomena, a reduction in agricultural irrigation is likely a permanent condition.

Scientific Investigations Report↗
USGS1998

Ground water and surface water: A single resource

The importance of considering ground water and surface water as a single resource has become increasingly evident. Issues related to water supply, water quality, and degradation of aquatic environments are reported on frequently. The interaction of ground water and surface water has been shown to be a significant concern in many of these issues. Contaminated aquifers that discharge to streams can result in long-term contamination of surface water; conversely, streams can be a major source of contamination to aquifers. Surface water commonly is hydraulically connected to ground water, but the interactions are difficult to observe and measure. The purpose of this report is to present our current understanding of these processes and activities as well as limitations in our knowledge and ability to characterize them.

Circular↗
USGS1997

Simulation of ground-water flow in the Coastal Plain aquifer system of North Carolina

A three-dimensional finite-difference digital model was used to simulate ground-water flow in the 25,000-square-mile aquifer system of the North Carolina Coastal Plain. The model was developed from a hydrogeologic framework that is based on an alternating sequence of 10 aquifers and 9 confining units, which make up a seaward-thickening wedge of sediments that form the Coastal Plain aquifer system in the State of North Carolina. The model was calibrated by comparing observed and simulated water levels. The model calibration was achieved by adjusting model parameters, primarily leakance of confining units and transmissivity of aquifers, until differences between observed and simulated water levels were within acceptable limits, generally within 15 feet. The maximum transmissivity of an individual aquifer in the calibrated model is 200,000 feet squared per day in a part of the Castle Hayne aquifer, which consists predominantly of limestone. The maximum value for simulated vertical hydraulic conductivity in a confining unit was 2.5 feet per day, in a part of the confining unit overlying the upper Cape Fear aquifer. The minimum value was 4.1x10-6 feet per day, in part of the confining unit overlying the lower Cape Fear aquifer. Analysis indicated the model is highly sensitive to changes in transmissivity and leakance near pumping centers; away from pumping centers, the model is only slightly sensitive to changes in transmissivity but is moderately sensitive to changes in leakance. Recharge from precipitation to the surficial aquifer ranges from about 12 inches per year in areas having clay at the surface to about 20 inches per year in areas having sand at the surface. Most of this recharge moves laterally to streams, and only about 1 inch per year moves downward to the confined parts of the aquifer system. Under predevelopment conditions, the confined aquifers were generally recharged in updip interstream areas and discharged through streambeds and in downdip coastward areas. Hydrologic analysis of the flow system using the calibrated model indicated that, because of ground-water withdrawals, areas of ground-water recharge have expanded and encroached upon some major stream valleys and into coastal area. Simulations of pumping conditions indicate that by 1980 large parts of the former coastal discharge areas had become areas of potential or actual recharge. Declines of ground-water level, which are the result of water taken from storage, are extensive in some areas and minimal in others. Hydraulic head declines of more than 135 feet have occurred in the northern Coastal Plain since 1940 primarily due to withdrawals in the Franklin area in Virginia. Declines of ground-water levels greater than 110 feet have occurred in aquifers in the central Coastal Plain due to combined effects of pumpage for public and industrial water supplies. Water-level declines exceeding 100 feet have occurred in the Beaufort County area because of withdrawals for a mining operation and water supplies for a chemical plant. Head declines have been less than 10 feet in the shallow surficial and Yorktown aquifers and in the updip parts of the major confined aquifers distant from areas of major withdrawals. In 1980, contribution from aquifer storage was 14 cubic feet per second, which is about 4.8 percent of pumpage and about 0.05 percent of ground-water recharge. A water-budget analysis using the model simulations indicates that much of the water removed from the ground-water system by pumping ultimately is made up by a reduction in water leaving the aquifer system, which discharges to streams as base flow. The reduction in stream base flow was 294 cubic feet per second in 1980 and represents about 1.1 percent of the ground-water recharge. The net reduction to streamflow is not large, however, because most pumped ground water is eventually discharged to streams. In places, such as at rock quarries in Onslow and Craven Counties, water is lost from st

North Carolina↗
USGS1992

Simulation of regional ground-water flow in the Cambrian-Ordovician aquifer system in the northern Midwest, United States: in Regional aquifer-system analysis

A six-State area in the northern Midwest of the United States has become increasingly dependent on ground water from the Cambrian-Ordovician aquifer system, which consists of a sequence of sandstones, carbonate rocks, and shales. Ground-water withdrawals from the aquifer system began in the late 1800's and increased to approximately 684 million gallons per day (1,058 cubic feet per second) by 1980. This withdrawal has caused more than 900 feet of decline in the potentiometric surface of the aquifer system in parts of the Chicago, Ill., area. Pumping in Minneapolis-St. Paul, Minn., Milwaukee, Wis., and central Iowa has produced a few hundreds of feet of water-level decline. A quasi-three-dimensional ground-water flow model was developed to improve understanding of the regional ground-water flow system by simulating the aquifer system under the conditions that existed before and during ground-water development. The Cambrian-Ordovician aquifer system and the overlying rocks were incorporated in the conceptual model as five aquifer layers with four intervening confining layers. The aquifer layers, from top to bottom, are as follows: Quaternary deposits and Cretaceous rocks (aquifer layer 5); basal Devonian carbonate rocks and underlying Silurian carbonate rocks (aquifer layer 4); Middle Ordovician St. Peter Sandstone, Lower Ordovician Prairie du Chien Group, and Upper Cambrian Jordan Sandstone (aquifer layer 3); Upper Cambrian Ironton and Galesville Sandstones (aquifer layer 2); and Upper Cambrian Mount Simon Sandstone and Precambrian Hinckley Sandstone (aquifer layer 1). The effects on the flow system of ground water having variable density and the individual aquifer layer contribution of flow to wells open to several aquifer layers were simulated by incorporating appropriate terms in the ground-water flow equation and corresponding modifications in the ground-water flow model. Results of steady-state simulations are shown as maps of freshwater head and as flow-rate vectors. A comparison was made of available predevelopment head data and simulated predevelopment heads for the Mount Simon, St. Peter-Prairie du Chien-Jordan, and Silurian-Devonian aquifers. The root mean square of the differences between observed and simulated heads for these aquifers was 53, 36, and 44 feet, respectively. Steady-state model simulation indicates that regional recharge areas are located in northwestern Iowa, southeastern Minnesota, much of Wisconsin, northern Illinois, and central Missouri. Regional discharge areas are located near the Mississippi River and its tributaries, the Missouri River, Lake Michigan, and the Illinois basin. Results of a transient simulation of the period 1861 to 1980 are shown as maps of freshwater head and freshwater-head decline. The root mean square of the differences between observed and simulated heads for the St. Peter-Prairie du Chien-Jordan aquifer was 63 feet. In addition, hydrographs of simulated hydraulic head were compared with hydrographs of observed head in wells open to various combinations of aquifers. The numerous head measurements within a model node display a wide range in magnitude; however, their historical trend generally follows the trend of the simulated heads. The simulated recharge from the glacial drift to the immediately underlying bedrock aquifers averages 0.03, 0.06, 0.24, and 0.02 inch per year, respectively, to the Mount Simon, Ironton-Galesville, St. Peter- Prairie du Chien-Jordan, and Silurian-Devonian aquifers for predevelopment conditions and 0.03, 0.07, 0.45, and 0.07 inch per year, respectively, to the same aquifers for 1976-80. These recharge rates are less than 1.5 percent of average annual precipitation of about 30 inches per year. Most of the recharge from precipitation discharges to streams as base flow through local and intermediate ground-water flow systems. Only a small fraction of the precipitation recharges the deeper, regional flow system. The simulated predevelopment recharge of 571 cubic feet per second is balanced by an equivalent discharge. For the period 1976-80, simulated recharge increased to 1,398 cubic feet per second. Total discharge, including pumpage from the four bedrock aquifers, increased to 1,619 cubic feet per second. The difference in recharge and discharge during this period is from aquifer storage. Results of variable-density simulations indicate that the rate of ground-water movement is small in areas where ground water is highly mineralized. The rates and directions are controlled by the intrinsic permeability of the rock, freshwater head gradients, and gravitational force.

Iowa, Illinois, Indiana, Michigan, Minnesota, Miss↗
USGS2001

Trichloroethylene and 1,1-dichloroethylene concentrations in ground water after temporary shutdown of the reclamation well field at Air Force Plant 44, Tucson, Arizona, 1999

Industrial activities beginning in the early 1940s resulted in extensive contamination of ground water near the Tucson International Airport, Tucson, Arizona, including an area around Air Force Plant 44, an industrial facility located on land owned by the U.S. Air Force and operated by a defense contractor. Principal ground-water contaminants are volatile organic compounds, primarily trichloroethylene (also called trichloroethene) and 1,1-dichloroethylene (also called 1,1-dichloroethene). A ground- water reclamation system was put into operation in 1987 to extract and treat contaminated ground water at Air Force Plant 44 and the downgradient area that is south of Los Reales Road. The ground- water reclamation system consists of 25 extraction wells, 22 recharge wells, and a water-treatment facility. Soil-vapor extraction techniques are being used to remove volatile organic compounds from the unsaturated zone. More than 120,000 pounds of volatile organic compounds have been removed from the regional aquifer and overlying unsaturated zone at Air Force Plant 44 and adjacent downgradient areas south of Los Reales Road. Air Force Plant 44 and adjacent areas being remediated by the ground-water reclamation system are about 7 square miles. To assess ground-water cleanup progress at Air Force Plant 44 and surrounding areas south of Los Reales Road, and possibly to identify areas that are resistant to cleanup attempts, ground-water samples were collected and analyzed after water levels had returned to near-equilibrium conditions following a 3-week shutdown of extraction and recharge wells. Modifications of the standard ground-water sampling procedures used at the site also were tested. The modifications included tests of a reduced-flow purging and sampling method in six monitoring wells and vertical- profile sampling in five extraction wells at the reclamation well field. The water treatment facility and all extraction and recharge wells at the reclamation well field were shut down on April 15, 1999, and water levels were allowed to recover for about 3 weeks before samples of ground water were obtained from 102 wells at Air Force Plant 44 and surrounding areas. Concentrations of trichloroethylene and 1,1-dichloroethylene were determined for samples obtained during the sitewide sampling effort. Data for 101 wells sampled in February 1999 before shutdown were compared with data obtained for wells sampled in May 1999 after shutdown. Concentrations of trichloroethylene increased in 36 wells, remained the same in 32 wells, and decreased in 33 wells. Increases in concentrations of trichloroethylene of as much as 1,476 micrograms per liter and decreases of as much as 2,292 micrograms per liter were reported after shutdown. Concentrations of trichloroethylene remained the same for the two sampling periods in wells that had concentrations that were at, or close to, the lower reporting limit (0.5 micrograms per liter) before shutdown. Net change in concentrations of trichloroethylene after shutdown on a percentage basis ranged from an increase of 1,300 percent to a decrease of 100 percent. Increases in concentrations of 1,1-dichloroethylene after shutdown of the reclamation well field of as much as 66 micrograms per liter and decreases of as much as 411.6 micro- grams per liter were reported. Concentrations of 1,1-dichloroethylene remained the same for the two sampling periods in wells that had concentrations that were at, or close to, the lower reporting limit (0.5 micrograms per liter) before shutdown. Net change in concentrations of 1,1-dichloroethylene after shutdown on a percentage basis ranged from an increase of 660 percent to a decrease of 100 percent. Data obtained from the water samples indicate that the largest changes in concentrations of trichloroethylene and 1,1-dichloroethylene occurred in samples collected from wells completed in the upper zone of the regional aquifer, along the axis of the contaminant plume, in close proximity to previously identified historical disposal areas. Changes in contaminant concentrations observed after shutdown of the well field probably were the result of changes in ground-water flow directions under nonpumping conditions compared with those present when the extraction and recharge wells were operating. Minimal changes occurred at the perimeter of the plume, which suggests that operation of the reclamation well field has been successful at containing the spread of the plume. New contaminant-source areas were not identified within the perimeter of the plume. A modification of the standard sampling technique used at Air Force Plant 44 was tested in six wells. In these wells, greatly reduced flow rates were used for well purging and sampling. Results indicate no distinct pattern of change of contaminant concentrations compared with concentrations in samples subsequently obtained using the standard technique, and no advantage was evident for using this method in routine sampling of the monitoring wells at Air Force Plant 44. Temperature profiles obtained before vertical-profile sampling of selected wells indicate little temperature variation with depth. The temperature-profile information suggests that under nonpumping conditions, most of the water enters these wells near the top of the screened interval and moves downward in response to a hydraulic gradient in the regional aquifer. Samples at depths below the top of the screened interval probably do not accurately represent water from the adjacent sediments. Vertical-profile samples were obtained in five wells and analyzed for concentrations of trichloroethylene. None of the wells showed large enough variation of contaminant concentrations with depth to indicate that a major improvement in extraction efficiency could be obtained by pumping selectively from a restricted interval. The largest variation in concentrations of trichloroethylene with depth that was observed ranged from 62 micrograms per liter near the top of the screened interval to 42 micrograms per liter near the bottom of the screened interval of one of the wells. The lack of large variation is probably the result of downward water flow in the casing of these wells.

Arizona↗
USGS2002

Simulation of Ground-Water Flow in the Middle Rio Grande Basin Between Cochiti and San Acacia, New Mexico

This report describes a three-dimensional, finite difference, ground-water-flow model of the Santa Fe Group aquifer system within the Middle Rio Grande Basin between Cochiti and San Acacia, New Mexico. The aquifer system is composed of the Santa Fe Group of middle Tertiary to Quaternary age and post-Santa Fe Group valley and basin-fill deposits of Quaternary age. Population increases in the basin since the 1940's have caused dramatic increases in ground-water withdrawals from the aquifer system, resulting in large ground-water-level declines. Because the Rio Grande is hydraulically connected to the aquifer system, these ground-water withdrawals have also decreased flow in the Rio Grande. Concern about water resources in the basin led to the development of a research plan for the basin focused on the hydrologic interaction of ground water and surface water (McAda, D.P., 1996, Plan of study to quantify the hydrologic relation between the Rio Grande and the Santa Fe Group aquifer system near Albuquerque, central New Mexico: U.S. Geological Survey Water-Resources Investigations Report 96-4006, 58 p.). A multiyear research effort followed, funded and conducted by the U.S. Geological Survey and other agencies (Bartolino, J.R., and Cole, J.C., 2002, Ground-water resources of the Middle Rio Grande Basin, New Mexico: U.S. Geological Survey Circular 1222, 132 p.). The modeling work described in this report incorporates the results of much of this work and is the culmination of this multiyear study. The purpose of the model is (1) to integrate the components of the ground-water-flow system, including the hydrologic interaction between the surface-water systems in the basin, to better understand the geohydrology of the basin and (2) to provide a tool to help water managers plan for and administer the use of basin water resources. The aquifer system is represented by nine model layers extending from the water table to the pre-Santa Fe Group basement rocks, as much as 9,000 feet below the NGVD 29. The horizontal grid contains 156 rows and 80 columns, each spaced 3,281 feet (1 kilometer) apart. The model simulates predevelopment steady-state conditions and historical transient conditions from 1900 to March 2000 in 1 steady-state and 52 historical stress periods. Average annual conditions are simulated prior to 1990, and seasonal (winter and irrigation season) conditions are simulated from 1990 to March 2000. The model simulates mountain-front, tributary, and subsurface recharge; canal, irrigation, and septic-field seepage; and ground-water withdrawal as specified-flow boundaries. The model simulates the Rio Grande, riverside drains, Jemez River, Jemez Canyon Reservoir, Cochiti Lake, riparian evapotranspiration, and interior drains as head-dependent flow boundaries. Hydrologic properties representing the Santa Fe Group aquifer system in the ground-water-flow model are horizontal hydraulic conductivity, vertical hydraulic conductivity, specific storage, and specific yield. Variable horizontal anisotropy is applied to the model so that hydraulic conductivity in the north-south direction (along model columns) is greater than hydraulic conductivity in the east-west direction (along model rows) over much of the model. This pattern of horizontal anisotropy was simulated to reflect the generally north-south orientation of faulting over much of the modeled area. With variable horizontal anisotropy, horizontal hydraulic conductivities in the model range from 0.05 to 60 feet per day. Vertical hydraulic conductivity is specified in the model as a horizontal to vertical anisotropy ratio (calculated to be 150:1 in the model) multiplied by the horizontal hydraulic conductivity along rows. Specific storage was estimated to be 2 x 10-6 per foot in the model. Specific yield was estimated to be 0.2 (dimensionless). A ground-water-flow model is a tool that can integrate the complex interactions of hydrologic boundary conditions, aquifer materials

Water-Resources Investigations Report↗
USGS1997

Numerical simulation of ground-water flow through glacial deposits and crystalline bedrock in the Mirror Lake area, Grafton County, New Hampshire

This report documents the development of a computer model to simulate steady-state (long-term average) flow of ground water in the vicinity of Mirror Lake, which lies at the eastern end of the Hubbard Brook valley in central New Hampshire. The 10-km2 study area includes Mirror Lake, the three streams that flow into Mirror Lake, Leeman's Brook, Paradise Brook, and parts of Hubbard Brook and the Pemigewasset River. The topography of the area is characterized by steep hillsides and relatively flat valleys. Major hydrogeologic units include glacial deposits, composed of till containing pockets of sand and gravel, and fractured crystalline bedrock, composed of schist intruded by granite, pegmatite, and lamprophyre. Ground water occurs in both the glacial deposits and bedrock. Precipitation and snowmelt infiltrate to the water table on the hillsides, flow downslope through the saturated glacial deposits and fractured bedrock, and discharge to streams and to Mirror Lake. The model domain includes the glacial deposits, the uppermost 150m of bedrock, Mirror Lake, the layer of organic sediments on the lake bottom, and streams and rivers within the study area. A streamflow routing package was included in the model to simulate baseflow in streams and interaction between streams and ground water. Recharge from precipitation is assumed to be areally uniform, and riparian evapotranspiration along stream banks is assumed negligible. The spatial distribution of hydraulic conductivity is represented by dividing the model domain into several zones, each having uniform hydraulic properties. Local variations in recharge and hydraulic conductivities are ignored; therefore, the simulation results characterize the general ground-water system, not local details of ground-water movement. The model was calibrated using a nonlinear regression method to match hydraulic heads measured in piezometers and wells, and baseflow in three inlet streams to Mirror Lake. Model calibration indicates that recharge from precipitation to the water table is 26 to 28 cm/year. Hydraulic conductivities are 1.7 x 10-6 to 2.7 x 10-6 m/s for glacial deposits, about 3 x 10-7 m/s for bedrock beneath lower hillsides and valleys, and about 6x10-8 m/s for bedrock beneath upper hillsides and hilltops. Analysis of parameter uncertainty indicates that the above values are well constrained, at least within the context of regression analysis. In the regression, several attributes of the ground-water flow model are assumed perfectly known. The hydraulic conductivity for bedrock beneath upper hillsides and hilltops was determined from few data, and additional data are needed to further confirm this result. Model fit was not improved by introducing a 10-to-1 ration of horizontal-to-vertical anisotropy in the hydraulic conductivity of the glacial deposits, or by varying hydraulic conductivity with depth in the modeled part (uppermost 150m) of the bedrock. The calibrated model was used to delineate the Mirror Lake ground-water basin, defined as the volumes of subsurface through which ground water flows from the water table to Mirror Lake or its inlet streams. Results indicate that Mirror Lake and its inlet streams drain an area of ground-water recharge that is about 1.5 times the area of the surface-water basin. The ground-water basin extends far up the hillside on the northwestern part of the study area. Ground water from this area flows at depth under Norris Brook to discharge into Mirror Lake or its inlet streams. As a result, the Mirror Lake ground-water basin extends beneath the adjacent ground-water basin that drains into Norris Brook. Model simulation indicates that approximately 300,000 m3/year of precipitation recharges the Mirror Lake ground-water basin. About half the recharge enters the basin in areas where the simulated water table lies in glacial deposits; the other half enters the basin in areas where the simulated water table lies in be

New Hampshire↗
USGS2003

Phosphorus in a ground-water contaminant plume discharging to Ashumet Pond, Cape Cod, Massachusetts, 1999

The discharge of a plume of sewagecontaminated ground water emanating from the Massachusetts Military Reservation to Ashumet Pond on Cape Cod, Massachusetts, has caused concern about excessive loading of nutrients, particularly phosphorus, to the pond. The U.S. Air Force is considering remedial actions to mitigate potentially adverse effects on the ecological characteristics of the pond from continued phosphorus loading. Concentrations as great as 3 milligrams per liter of dissolved phosphorus (as P) are in ground water near the pond's shoreline; concentrations greater than 5 milligrams per liter of phosphorus are in ground water farther upgradient. Temporary drive-point wells were used to collect water samples from 2 feet below the pond bottom to delineate concentration distributions in the pore waters of the pond-bottom sediments. Measurements in the field of specific conductance and colorimetrically determined orthophosphate concentrations provided real-time data to guide the sampling. The contaminant plume discharges to the Fishermans Cove area of Ashumet Pond as evidenced by elevated levels of specific conductance and boron, which are chemically conservative indicators of the sewage-contaminated ground water. Concentrations of nonconservative species, such as dissolved phosphorus, manganese, nitrate, and ammonium, also were elevated above background levels in ground water discharging to the pond, but in spatially complex distributions that reflect their distributions in ground water upgradient of the pond. Phosphorus concentrations exceeded background levels (greater than 0.10 milligram per liter) in the pond-bottom pore water along 875 feet of shoreline. Greatest concentrations (greater than 2 milligrams per liter) occurred within 30 feet of the shore in an area about 225 feet long. Calculations of phosphorus flux in the aquifer upgradient of Ashumet Pond, as determined from water-flux estimates from a steady-state ground-water-flow model and phosphorus concentrations (in 1999) from multilevel samplers about 75 feet upgradient of the pond, indicate that dissolved phosphorus moves towards the pond and discharges to it with the inflowing ground water at a rate as high as about 316 kilograms per year.

Massachusetts↗
USGS1997

Measurement of ground-water storage change and specific yield using the temporal-gravity method near Rillito Creek, Tucson, Arizona

The temporal-gravity method was used to estimate ground-water storage change and specific -yield values at wells near Rillito Creek, Tucson, Arizona, between early December 1992 and early January 1994. The method applies Newton's Law of Gravitation to measure changes in the local gravitational field of the Earth that are caused by changes in the mass and volume of ground water. Gravity at 50 stations in a 6-square-mile area was measured repeatedly relative to gravity at two bedrock stations. Ephemeral recharge through streamflow infiltration during the winter of 1992-93 resulted in water-level rises and gravity increases near Rillito Creek as the volume of ground water in storage increased. Water levels in wells rose as much as 30 feet, and gravity increased as much as 90 microgals. Water levels declined and gravity decreased near the stream after the last major winter flow but continued to rise and increase, respectively, in downgradient areas. Water levels and gravity relative to bedrock were measured at 10 wells. Good linear correlations between water levels and gravity values at five wells nearest the stream allowed for the estimation of specific-yield values for corresponding stratigraphic units assuming the mass change occurred in an infinite horizonal slab of uniform thickness. Specific-yield values for the stream-channel deposits at three wells ranged from 0.15 to 0.34, and correlation coefficients ranged from 0.81 to 0.99. Specific-yield values for the Fort Lowell Formation at three wells ranged from 0.07 to 0.18, and correlation coefficients ranged from 0.82 to 0.93. Specific-yield values were not calculated for the five wells farthest from the stream because of insufficient water-level and gravity change or poor correlations between water level and gravity. Poor correlations between water levels and gravity resulted from ground-water storage change in perched aquifers and in the unsaturated zone near ephemeral streams. Seasonal distributions of ground-water storage change since early December 1992 were evaluated from gravity change at all stations using Gauss's Law. Changes in the distribution of gravity are caused by the flow of water into or out of ground-water storage. Gravity along two profiles was measured frequently to evaluate spatial and temporal distributions of gravity change. Gravity variations indicated preferential ground-water flow to the south in the western part of the study area where the saturate thickness of the aquifer is greatest. Storage changes from December 1992 through early March 1993, mid-May 1993, late August 1993, and early January 1994 were calculated as increases of 7,900, 8,000, 6,300, and 3,700 acre-feet, respectively. Seasonal variations in storage were caused by ground-water withdrawlas, ground-water flow across the boundaries of the gravity-station network, and streamflow infiltration from December 1992 through late April 1993. Most of the estimated recharge of 10,900 acre-feet occurred before mid-May 1993.

Arizona↗
USGS1964

Use of ground-water reservoirs for storage of surface water in the San Joaquin Valley, California

The San Joaquin Valley includes roughly the southern two-thirds of the Central Valley of California, extending 250 miles from Stockton on the north to Grapevine at the foot of the Tehachapi Mountains. The valley floor ranges in width from 25 miles near Bakersfield to about 55 miles near Visalia; it has a surface area of about 10,000 square miles. More than one-quarter of all the ground water pumped for irrigation in the United States is used in this highly productive valley. Withdrawal of ground water from storage by heavy pumping not only provides a needed irrigation water supply, but it also lowers the ground-water level and makes storage space available in which to conserve excess water during periods of heavy runoff. A storage capacity estimated to be 93 million acre-feet to a depth of 200 feet is available in this ground-water reservoir. This is about nine times the combined capacity of the existing and proposed surface-water reservoirs in the San Joaquin Valley under the California Water Plan. The landforms of the San Joaquin Valley include dissected uplands, low plains and fans, river flood plains and channels, and overflow lands and lake bottoms. Below the land surface, unconsolidated sediments derived from the surrounding mountain highlands extend downward for hundreds of feet. These unconsolidated deposits, consisting chiefly of alluvial deposits, but including some widespread lacustrine sediments, are the principal source of ground water in the valley. Ground water occurs under confined and unconfined conditions in the San Joaquin Valley. In much of the western, central, and southeastern parts of the valley, three distinct ground-water reservoirs are present. In downward succession these are 1) a body of unconfined and semiconfined fresh water in alluvial deposits of Recent, Pleistocene, and possibly later Pliocene age, overlying the Corcoran clay member of the Tulare formation; 2) a body of fresh water confined beneath the Corcoran clay member, which occurs in alluvial and lacustrine deposits of late Pliocene age or older; and 3) a body of saline connate water contained in marine sediments of middle Pliocene or older age, which underlies the fresh-water body throughout the area. In much of the eastern part of the valley, especially in the areas of the major streams, the Corcoran clay member is not present and ground water occurs as one fresh-water body to considerable depth. The ground-water body is replenished by infiltration of rainfall, by infiltration from streams, canals, and ditches, by underflow entering the valley from tributary stream canyons, and by infiltration of excess irrigation water. In much of the valley, however, the annual rainfall is so low that little penetrates deeply, and soil-moisture deficiency is perennial. Infiltration from stream channels and canals and from irrigated fields are the principal sources of groundwater recharge. The ground-water storage capacity of the San Joaquin Valley has been estimated in an earlier report (Davis and others, 1959) as 93 million acre-feet. This is the quantity of water that would drain by gravity from the valley deposits if the regional water level were lowered from 10 to 200 feet below the land surface. Storage capacity was estimated for only the part of the valley considered to be potentially usable as a ground-water reservoir. In this study, a 200foot depth was selected as a practical valley-wide depth limit for unwatering under full utilization of the ground-water reservoir, even though in localized areas sections in excess of 350 feet in depth have already been dewatered. Some of the factors that locally limit the utilization of the ground-water reservoir are inferior water quality, relatively impermeable surface soils, and relatively impermeable subsurface deposits. On the basis of a detailed analysis of la peg model, the subsurface geology of the San Joaquin Valley was subdivided into predominantly permeable and impermeable zones in the 1

Water Supply Paper↗
USGS1990

Ground-water hydrology of Pahvant Valley and adjacent areas, Utah

The primary ground-water reservoir in Pahvant Valley and adjacent areas is in the unconsolidated basin fill and interbedded basalt. Recharge in 1959 was estimated to be about 70,000 acre-feet per year and was mostly by seepage from streams, canals, and unconsumed irrigation water and by infiltration of precipitation. Discharge in 1959 was estimated to be about 109,000 acre-feet and was mostly from springs, evapotranspiration, and wells. Water-level declines of more than 50 feet occurred in some areas between 1953 and 1980 because of less-than-normal precipitation and extensive pumping for irrigation. Water levels recovered most of these declines between 1983 and 1986 because of reduced withdrawals and record quantities of precipitation. The quality of ground water in the area west of Kanosh has deteriorated since large ground-water withdrawals began in about 1953. The cause of the deterioration probably is movement of poor quality water into the area from the southwest and possibly the west during periods of large ground-water withdrawals and recycling of irrigation water. The quality of water from some wells has improved since 1983, due to increased recharge and decreased withdrawals for irrigation. Water-level declines of m:>re than 80 feet in some parts of Pahvant Valley are projected if ground-water withdrawals continue for 20 years at the 1977 rate of about 96,000 acre-feet. Rises of as much as 58 feet and declines of as much as 47 feet are projected with withdrawals of 48,000 acre-feet per year for 20 years. The elimination of recharge from the Central Utah Canal is projected to cause water-level declines of up to 8 feet near the canal.

Utah↗
USGS2002

Quality of shallow ground water in areas of recent residential and commercial development, Wichita, Kansas, 2000

Water samples from 30 randomly distributed monitoring wells in areas of recent residential and commercial development (1960–96), Wichita, Kansas, were collected in 2000 as part of the High Plains Regional Ground-Water Study conducted by the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. The samples were analyzed for about 170 water-quality constituents that included chlorofluorocarbons, physical properties, dissolved solids and major ions, nutrients and dissolved organic carbon, trace elements, pesticide compounds, and volatile organic compounds. The purpose of this report is to provide an assessment of water quality in recharge to shallow ground water underlying areas of recent residential and commercial development and to determine the relation of ground-water quality to overlying urban land use. Analyses of water from the 30 monitoring wells for chlorofluorocarbons were used to estimate apparent dates of recharge. Water from 18 wells with nondegraded and uncontaminated chlorofluorocarbon concentrations had calculated apparent recharge dates that ranged from 1979 to 1990 with an average date of 1986. Water from 14 monitoring wells (47 percent) exceeded the 500-milligrams-per-liter Secondary Maximum Contaminant Level established by the U.S. Environmental Protection Agency for dissolved solids in drinking water. The Secondary Maximum Contaminant Levels of 250 milligrams per liter for chloride and sulfate were exceeded in water from one well. The source of the largest concentrations of dissolved solids and associated ions, such as chloride and sulfate, in shallow ground water in the study area probably is highly mineralized water moving out of the Arkansas River into the adjacent, unconsolidated deposits and mixing with the dominant calcium bicarbonate water in the deposits. Concentrations of most nutrients in water from the sampled wells were small, with the exception of nitrate. Although water from the sampled wells did not have nitrate concentrations larger than the 10-milligram-per-liter Maximum Contaminant Level for drinking water, water from 50 percent of the sampled wells showed nitrate enrichment (concentrations greater than 2.0 milligrams per liter). Most trace elements in water from the sampled wells were detected only in small concentrations, and few exceeded respective water-quality standards. Twenty percent of iron concentrations, 40 percent of manganese concentrations, 3 percent of arsenic concentrations, and 13 percent of uranium concentrations exceeded respective Maximum Contaminant Levels or Secondary Maximum Contaminant Levels. A total of 47 pesticide compounds were analyzed in ground-water samples during this study. Water from 73 percent of the wells sampled had detectable concentrations of one or more of 8 of these 47 compounds. The herbicide atrazine or its degradation product deethylatrazine were detected most frequently (in water from 70 percent of the sampled wells). Metolachlor was detected in water from 10 percent of the wells, and simazine was detected in water from 30 percent of the wells sampled. Other pesticides detected included dieldrin, pendimethalin, prometon, and tebuthiuron (each in water from 3 percent of the wells). All concentrations of these compounds were less than established Maximum Contaminant Levels. A total of 85 volatile organic compounds (VOCs) were analyzed in ground-water samples during this study. Water from 43 percent of the wells had a detectable concentration of one or more VOCs. Chloroform was the most frequently detected VOC (23 percent of the wells sampled).Seven other VOCs were detected in water at frequencies of 13 percent or less in the wells sampled. Concentrations of VOCs were less than respective Maximum Contaminant Levels, except one sample with a concentration of 9.0 micrograms per liter for tetrachloroethylene (Maximum Contaminant Level of 5.0 micrograms per liter). An analysis of hydraulic gradient, flow velocity, and residence time of the ground water indicated potential recharge areas that ranged from 0.8 to 2.8 miles upgradient of monitoring-well locations. Nineteen (63 percent) of these potential recharge areas were in agricultural areas or areas in transition from agricultural to residential and (or) commercial land use at the time water sampled from the monitoring wells was recharged to the shallow ground water. The occurrence of atrazine or deethylatrazine in water from 70 percent of the monitoring wells may indicate a historical agricultural land-use relation. This agricultural relation also may affect concentrations of other water-quality constituents of possible agricultural origin such as nitrate, which generally were in excess of background concentrations in shallow ground water.

Kansas↗
USGS2002

Hydrogeologic framework, ground-water geochemistry, and assessment of nitrogen yield from base flow in two agricultural watersheds, Kent County, Maryland

Hydrostratigraphic and geochemical data collected in two adjacent watersheds on the Delmarva Peninsula, in Kent County, Maryland, indicate that shallow subsurface stratigraphy is an important factor that affects the concentrations of nitrogen in ground water discharging as stream base flow. The flux of nitrogen from shallow aquifers can contribute substantially to the eutrophication of streams and estuaries, degrading water quality and aquatic habitats. The information presented in this report includes a hydrostratigraphic framework for the Locust Grove study area, analyses and interpretation of ground-water chemistry, and an analysis of nutrient yields from stream base flow. An understanding of the processes by which ground-water nitrogen discharges to streams is important for optimal management of nutrients in watersheds in which ground-water discharge is an appreciable percentage of total streamflow. The U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency (USEPA), collected and analyzed hydrostratigraphic and geochemical data in support of ground-water flow modeling by the USEPA. The adjacent watersheds of Morgan Creek and Chesterville Branch have similar topography and land use; however, reported nitrogen concentrations are generally 6 to 10 milligrams per liter in Chesterville Branch but only 2 to 4 milligrams per liter in Morgan Creek. Ground water in the surficial aquifer in the recharge areas of both streams has high concentrations of nitrate (greater than 10 milligrams per liter as N) and dissolved oxygen. One component of the ground water discharging to Morgan Creek typically is anoxic and contains virtually no dissolved nitrate; most of the ground water discharging to Chesterville Branch is oxygenated and contains moderately high concentrations of nitrate. The surficial aquifer in the study area is composed of the deeply weathered sands and gravels of the Pensauken Formation (the Columbia aquifer) and the underlying glauconitic sands of the upper Aquia Formation (the Aquia aquifer). The lower 6 to 9 meters of the Aquia Formation is a low-permeability silt-clay with abundant glauconite. The Aquia confining layer underlies the Columbia-Aquia surficial aquifer throughout the study area. The sediment redox transition, identified in cores, that occurs in the upper 0.5 to 1 meter of the Aquia confining layer is thought to be a site for subsurface denitrification of ground water. The first confined aquifer is composed of the glauconitic sands in the upper 9 to 11 meters of the Hornerstown Formation. The Hornerstown aquifer is underlain by 10 to 15 meters of glauconitic silt-clay at the base of the Hornerstown Formation (the Hornerstown confining layer), and 5 meters of low-permeability clay in the underlying Severn Formation. The Aquia and Hornerstown Formations dip and thicken to the southeast, and the Aquia confining layer subcrops shallowly (within 5 meters of the land surface) in a band that strikes southwest to northeast across the northern edge of the study area. The surficial aquifer is very thin (generally less than 5 meters) north of Morgan Creek, and the alluvial valley of Morgan Creek has incised into the top of the Aquia confining layer. In contrast, the Aquia confining layer lies 22 meters below Chesterville Branch, and the surficial aquifer approaches 30 meters in thickness (away from the creek). Chemically reduced iron sulfides and glauconite in the Aquia confining layer are likely substrates for denitrification of nitrate in ground water. Evidence from the dissolved concentrations of nitrate, sulfate, iron, argon, and nitrogen gas, and stable nitrogen isotopes support the interpretation that ground water flowing near the top of the Aquia confining layer, or through the confined Hornerstown aquifer, has undergone denitrification. This process appears to have the greatest effect on ground-water chemistry north of Morgan Creek, where the surficial aquifer is thin and a greater percentage of the ground water contacts the Aquia confining layer. The base-flow discharges of total nitrogen from the two watersheds are of similar magnitude, although Chesterville Branch has somewhat higher loads (29,000 kilograms of nitrogen per year) than Morgan Creek (20,000 kilograms of nitrogen per year), although Morgan Creek has a larger drainage area and a greater discharge of water. The base-flow yield of nitrogen (load per unit area) in Chesterville Branch (median of 0.058 grams per second per square kilometer at the outlet) is more than twice that of Morgan Creek (median of 0.022 grams per second per square kilometer at the outlet), reflecting the higher concentration of nitrate in ground water discharging to Chesterville Branch. Total nitrogen concentrations tend to decrease downstream in Chesterville Branch and increase downstream in Morgan Creek. The downstream trend in Chesterville Branch may be affected by instream nitrogen uptake and denitrification, and an increasing proportion of older, denitrified ground water in downstream discharge. The downstream trends in Morgan Creek may be affected by inflow from tributaries, downstream changes in the source of discharge water, and downstream changes in the riparian zone, which could affect the processes and degree of denitrification. Although these two watersheds appear to have landscape features (such as topography, land use, and soils) that would produce similar nitrogen discharges, a more detailed examination of landscape features indicates that Chesterville Branch has soils that are slightly better drained, tributary stream outlets at higher altitudes, and a slightly higher percentage of agricultural land. All of these factors have been related to higher nitrogen yields. Nonetheless, most of the data support the interpretation that hydrostratigraphy has the greatest effect in producing the difference in nitrogen yields between the two watersheds.

Maryland↗
USGS2009

Examining Submarine Ground-Water Discharge into Florida Bay by using 222Rn and Continuous Resistivity Profiling

Estimates of submarine ground-water discharge (SGD) into Florida Bay remain one of the least understood components of a regional water balance. To quantify the magnitude and seasonality of SGD into upper Florida Bay, research activities included the use of the natural geochemical tracer, 222Rn, to examine potential SGD hotspots (222Rn surveys) and to quantify the total (saline + fresh water component) SGD rates at select sites (222Rn time-series). To obtain a synoptic map of the 222Rn distribution within our study site in Florida Bay, we set up a flow-through system on a small boat that consisted of a Differential Global Positioning System, a calibrated YSI, Inc CTD sensor with a sampling rate of 0.5 min, and a submersible pump (z = 0.5 m) that continuously fed water into an air/water exchanger that was plumbed simultaneously into four RAD7 222Rn air monitors. To obtain local advective ground-water flux estimates, 222Rn time-series experiments were deployed at strategic positions across hydrologic and geologic gradients within our study site. These time-series stations consisted of a submersible pump, a Solinist DIVER (to record continuous CTD parameters) and two RAD7 222Rn air monitors plumbed into an air/water exchanger. Repeat time-series 222Rn measurements were conducted for 3-4 days across several tidal excursions. Radon was also measured in the air during each sampling campaign by a dedicated RAD7. We obtained ground-water discharge information by calculating a 222Rn mass balance that accounted for lateral and horizontal exchange, as well as an appropriate ground-water 222Rn end member activity. Another research component utilized marine continuous resistivity profiling (CRP) surveys to examine the subsurface salinity structure within Florida Bay sediments. This system consisted of an AGI SuperSting 8 channel receiver attached to a streamer cable that had two current (A,B) electrodes and nine potential electrodes that were spaced 10 m apart. A separate DGPS continuously sent position information to the SuperSting. Results indicate that the 222Rn maps provide a useful gauge of relative ground-water discharge into upper Florida Bay. The 222Rn time-series measurements provide a reasonable estimate of site- specific total (saline and fresh) ground-water discharge (mean = 12.5+-11.8 cm d-1), while the saline nature of the shallow ground-water at our study site, as evidenced by CPR results, indicates that most of this discharge must be recycled sea water. The CRP data show some interesting trends that appear to be consistent with subsurface geologic and hydrologic characterization. For example, some of the highest resistivity (electrical conductivity-1) values were recorded where one would expect a slight subsurface freshening (for example bayside Key Largo, or below the C111 canal).

Open-File Report↗
USGS2006

Estimating cost of ground‐water withdrawal for river basin planning

Comparative costs of ground water were needed for comprehensive planning of water resources development in the Susquehanna River basin in order to appraise the feasibility of alternative sources of water supply. Log‐normal plots on logarithmic‐probability paper that represented specific capacities adjusted to 180 days of pumping were used to estimate well yields and costs of obtaining the ground water from each of 65 potential aquifers. The 25, 50, and 75 percent probability of occurrence of the specific capacities of successful wells were used in the calculations. The estimated well yields at these probabilities of occurrence were obtained using hypothetical well designs and selected drawdowns. Ground‐water costs for the estimated or design yields were calculated using amortized costs of well construction, electrical power costs, and maintenance costs, all obtained from standard sources. The calculated well yields and costs for the 25 to 75 percent probability interval range from 15 to 9,000 gpm (gallons per minute) and from $0.004 to $0.11 per thousand gallons of design yield. The yields and costs group according to aquifer rock type. The calculated costs decrease with increasing well yield and the available yield depends upon the aquifer rock type available. Representative costs per thousand gallons of design yield for selected yields from aquifers composed of different rock types analyzed are: 50 gpm −$0.060 for shale and interbedded sandstone and shale, and $0.050 for metamorphic rock; 100 gpm ‐ $0.043 or shale and interbedded sandstone and shale, $0.037 for metamorphic rock, and $0.032 for carbonate rock; 500 gpm—$0.020 for sandstone, $0.015 for carbonate rock, and $0.012 for glacial sand and gravel; and 1,000 gpm —$0.009 for glacial sand and gravel. Differences in cost to obtain the same yield from different rock types are primarily due to differences in electrical power costs as determined by differences in pumping water levels. If used with caution, the generalized yield and cost estimates for aquifer rock types may have usefulness in estimating ground‐water costs and yields in similar humid areas. They are primarily useful for planning and comparative purposes, but not for the actual design of engineering projects.

Groundwater↗
USGS2009

Quality characteristics of ground water in the Ozark aquifer of northwestern Arkansas, southeastern Kansas, southwestern Missouri and northeastern Oklahoma, 2006-07

Because of water quantity and quality concerns within the Ozark aquifer, the State of Kansas in 2004 issued a moratorium on most new appropriations from the aquifer until results were made available from a cooperative study between the U.S. Geological Survey and the Kansas Water Office. The purposes of the study were to develop a regional ground-water flow model and a water-quality assessment of the Ozark aquifer in northwestern Arkansas, southeastern Kansas, southwestern Missouri, and northeastern Oklahoma (study area). In 2006 and 2007, water-quality samples were collected from 40 water-supply wells completed in the Ozark aquifer and spatially distributed throughout the study area. Samples were analyzed for physical properties, dissolved solids and major ions, nutrients, trace elements, and selected isotopes. This report presents the results of the water-quality assessment part of the cooperative study. Water-quality characteristics were evaluated relative to U.S. Environmental Protection Agency drinking-water standards. Secondary Drinking-Water Regulations were exceeded for dissolved solids (11 wells), sulfate and chloride (2 wells each), fluoride (3 wells), iron (4 wells), and manganese (2 wells). Maximum Contaminant Levels were exceeded for turbidity (3 wells) and fluoride (1 well). The Maximum Contaminant Level Goal for lead (0 milligrams per liter) was exceeded in water from 12 wells. Analyses of isotopes in water from wells along two 60-mile long ground-water flow paths indicated that water in the Ozark aquifer was at least 60 years old but the upper age limit is uncertain. The source of recharge water for the wells along the flow paths appeared to be of meteoric origin because of isotopic similarity to the established Global Meteoric Water Line and a global precipitation relation. Additionally, analysis of hydrogen-3 (3H) and carbon-14 (14C) indicated that there was possible leakage of younger ground water into the lower part of the Ozark aquifer. This may be caused by cracks or fissures in the confining unit that separates the upper and lower parts of the aquifer, poorly constructed or abandoned wells, or historic mining activities. Analyses of major ions in water from wells along the flow paths indicated a transition from freshwater in the east to saline water in the west. Generally, ground water along flow paths evolved from a calcium magnesium bicarbonate type to a sodium calcium bicarbonate or a sodium calcium chloride bicarbonate type as water moved from recharge areas in Missouri into Kansas. Much of this evolution occurred within the last 20 to 25 miles of the flow paths along a water-quality transition zone near the Kansas-Missouri State line and west. The water quality of the Kansas part of the Ozark aquifer is degraded compared to the Missouri part. Geophysical and well-bore flow information and depth-dependent water-quality samples were collected from a large-capacity (1,900-2,300 gallons per minute) municipal-supply well to evaluate vertical ground-water flow accretion and variability in water-quality characteristics at different levels. Although the 1,050-foot deep supply well had 500 feet of borehole open to the Ozark aquifer, 77 percent of ground-water flow entering the borehole came from two 20-foot thick rock layers above the 1,000-foot level. For the most part, water-quality characteristics changed little from the deepest sample to the well-head sample, and upwelling of saline water from deeper geologic formations below the well was not evident. However, more saline water may be present below the bottom of the well.

Arkansas, Kansas, Missouri, Oklahoma↗
USGS2000

Water-quality assessment of the Trinity River Basin, Texas— Ground-water quality of the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers, February-August 1994

Ground-water samples were collected from wells in the outcrops of the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers during February-August 1994 to determine the quality of ground water in the three major aquifers in the Trinity River Basin study unit, Texas. These samples were collected and analyzed for selected properties, nutrients, major inorganic constituents, trace elements, pesticides, dissolved organic carbon, total phenols, methylene blue active substances, and volatile organic compounds as part of the U.S. Geological Survey National Water-Quality Assessment Program. Quality-control practices included the collection and analysis of blank, duplicate, and spiked samples. Samples were collected from 12 shallow wells (150 feet or less) and from 12 deep wells (greater than 150 feet) in the Trinity aquifer, 11 shallow wells and 12 deep wells in the Carrizo-Wilcox aquifer, and 14 shallow wells and 10 deep wells in the Gulf Coast aquifer. The three aquifers had similar water chemistries-calcium was the dominant cation and bicarbonate the dominant anion. Statistical tests relating well depths to concentrations of nutrients and major inorganic constituents indicated correlations between well depth and concentrations of ammonia nitrogen, nitrite plus nitrate nitrogen, bicarbonate, sodium, and dissolved solids in the Carrizo-Wilcox aquifer and between well depth and concentrations of sulfate in the Gulf Coast aquifer. The tests indicated no significant correlations for the Trinity aquifer. Concentrations of dissolved solids were larger than the secondary maximum contaminant level of 500 milligrams per liter established for drinking water by the U.S. Environmental Protection Agency in 12 wells in the Trinity aquifer, 4 wells in the Carrizo-Wilcox aquifer, and 6 wells in the Gulf Coast aquifer. Iron concentrations were larger than the secondary maximum contaminant level of 300 micrograms per liter in at least 3 samples from each aquifer, and manganese concentrations were larger than the secondary maximum contaminant level of 50 micrograms per liter in at least 2 samples from each aquifer. The pesticides atrazine, deethylatrazine, and pp'-DDE were detected in at least one sample from each aquifer. Diazinon was detected in 11 Trinity aquifer samples and 4 Carrizo-Wilcox aquifer samples. Each aquifer had one detection of a volatile organic compound-benzene in the Trinity aquifer, trichlorofluoromethane in the Carrizo-Wilcox aquifer, and trichloromethane in the Gulf Coast aquifer.

Texas↗