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At least 37 records · Page 2Linked to original sources
USGS1995

Quality of surface water and ground water in the proposed artificial-recharge project area, Rillito Creek basin, Tucson, Arizona, 1994

Controlled artificial recharge of surface runoff is being considered as a water-management technique to address the problem of ground-water overdraft. The planned use of recharge facilities in urban areas has caused concern about the quality of urban runoff to be recharged and the potential for ground-water contamination. The proposed recharge facility in Rillito Creek will utilize runoff entering a 1-mile reach of the Rillito Creek between Craycroft Road and Swan Road for infiltration and recharge purposes within the channel and excavated overbank areas. Physical and chemical data were collected from two surface-water and two ground-water sites in the study area in 1994. Analyses of surface-water samples were done to determine the occurrence and concentration of potential contaminants and to determine changes in quality since samples were collected during 1987-93. Analyses of ground-water samples were done to determine the variability of ground-water quality at the monitoring wells throughout the year and to determine changes in quality since samples were collected in 1989 and 1993. Surface-water samples were collected from Tanque Verde Creek at Sabino Canyon Road (streamflow-gaging station Tanque Verde Creek at Tucson, 09484500) and from Alamo Wash at Fort Lowell Road in September and May 1994, respectively. Ground-water samples were collected from monitoring wells (D- 13-14)26cbb2 and (D-13-14)26dcb2 in January, May, July, and October 1994. In surface water, calcium was the dominant cation, and bicarbonate was the dominant anion. In ground water, calcium and sodium were the dominant cations and bicarbonate was the dominant anion. Surface water in the area is soft, and ground water is moderately hard to hard. In surface water and ground water, nitrogen was found predominantly as nitrate. Concentrations of manganese in ground-water samples ranged from 60 to 230 micrograms per liter and exceeded the U.S. Environmental Protection Agency secondary maximum contaminant level for drinking water of 50 micrograms per liter. None of the constituents in surface-water and ground-water samples exceeded the U.S. Environmental Protection Agency primary maximum contaminant levels for drinking water or State of Arizona aquifer water-quality standards. Concentrations of major ions, nutrients, and trace elements in water from the monitoring wells did not vary significantly throughout the year and were not significantly different from concentrations in samples collected in March 1989 and January and September 1993. Priority pollutants were not found in surface-water samples or ground-water samples, and organochlorine pesticides were not found in ground-water samples. Dieldrin and biphenyl polychlor were the only pesticides found in surface water and were at the minimum reporting levels in one sample from Alamo Wash.

Water-Resources Investigations Report↗
USGS1997

Water-quality assessment of south-central Texas: Occurrence and distribution of volatile organic compounds in surface water and ground water, 1983-94, and implications for future monitoring

The study area of the South-Central Texas study unit of the National Water-Quality Assessment Program comprises the Edwards aquifer in the San Antonio region and its catchment area. The first phase of the assessment includes evaluation of existing water-quality data for surface water and ground water, including volatile organic compounds, to determine the scope of planned monitoring. Most analyses of volatile organic compounds in surface water are from the National Pollutant Discharge Elimination System sites in San Antonio, Texas. Nine volatile organic compounds were detected at the six sites. The three compounds with the most detections at National Pollutant Discharge Elimination System sites are 1,2,4-trimethylbenzene, toluene, and xylene. Analysis of volatile organic compounds in ground water was limited to Edwards aquifer wells. Twenty-eight volatile organic compounds were detected in samples from 89 wells. The five most commonly detected compounds in samples from wells, in descending order, are tetrachloroethene, trichloroethene, bromoform, chloroform, and dibromochloromethane. Detections of volatile organic compounds in surface water and ground water within the South-Central Texas study area are limited to site-specific sources associated with development; therefore, planned monitoring for possible detections of volatile organic compounds as part of the National Water-Quality Assessment Program will emphasize areas of expanding population and development. Monitoring of volatile organic compounds is planned at National Pollutant Discharge Elimination System sites, at basic fixed surface-water sites, and in the ground-water study-unit surveys.

Texas↗
USGS2005

Age of irrigation water in ground water from the Eastern Snake River Plain Aquifer, south-central Idaho

Stable isotope data ( 2 H and 18 O) were used in conjunction with chlorofluorocarbon (CFC) and tritium/helium-3 ( 3 H/ 3 He) data to determine the fraction and age of irrigation water in ground water mixtures from farmed parts of the Eastern Snake River Plain (ESRP) Aquifer in south-central Idaho. Two groups of waters were recognized: (1) regional background water, unaffected by irrigation and fertilizer application, and (2) mixtures of irrigation water from the Snake River with regional background water. New data are presented comparing CFC and 3 H/ 3 He dating of water recharged through deep fractured basalt, and dating of young fractions in ground water mixtures. The 3 H/ 3 He ages of irrigation water in most mixtures ranged from about zero to eight years. The CFC ages of irrigation water in mixtures ranged from values near those based on 3 H/ 3 He dating to values biased older than the 3 H/ 3 He ages by as much as eight to 10 years. Unsaturated zone air had CFC-12 and CFC-113 concentrations that were 60% to 95%, and 50% to 90%, respectively, of modern air concentrations and were consistently contaminated with CFC-11. Irrigation water diverted from the Snake River was contaminated with CFC-11 but near solubility equilibrium with CFC-12 and CFC-113. The dating indicates ground water velocities of 5 to 8 m/d for water along the top of the ESRP Aquifer near the southwestern boundary of the Idaho National Engineering and Environmental Laboratory (INEEL). Many of the regional background waters contain excess terrigenic helium with a 3 He/ 4 He isotope ratio of 7 x 10-6 to 11 x 10-6 (R/R a = 5 to 8) and could not be dated. Ratios of CFC data indicate that some rangeland water may contain as much as 5% to 30% young water (ages of less than or equal to two to 11.5 years) mixed with old regional background water. The relatively low residence times of ground water in irrigated parts of the ESRP Aquifer and the dilution with low-NO 3 irrigation water from the Snake River lower the potential for NO 3 contamination in agricultural areas.

Ground Water↗
USGS2002

Interactions between surface water and ground water and effects on mercury transport in the north-central Everglades

The hydrology of the north-central Everglades was altered substantially in the past century by canal dredging, land subsidence, ground-water pumping, and levee construction. Vast areas of seasonal and perennial wetlands were converted to uses for agriculture, light industry, and suburban development. As the catchment area for the Everglades decreased, so did the sources of water from local precipitation and runoff from surrounding uplands. Partly in response to those alterations, water-resources managers compartmentalized the remaining wetlands in the north-central Everglades into large retention basins, called Water Conservation Areas (WCAs). In spite of efforts to improve how water resources are managed, the result has been frequent periods of excessive drying out or flooding of the WCAs because the managed system does not have the same water-storage capacity as the pre-drainage Everglades. Linked to the hydrological modifications are ecological changes including large-scale invasions of cattail, loss of tree islands, and diminishing bird populations in the Everglades. Complex interactions among numerous physical, chemical, and biological factors are responsible for the long-term degradation of the ecological character of the Everglades.Over the past 15 years, a new set of smaller wetland basins, called Stormwater Treatment Areas (STAs), have been designed and constructed by water-resources engineers on the former wetlands adjacent to WCAs. The purpose of STAs is to remove excess nutrients from agricultural drainage water prior to its input to WCAs. STAs tend to be about one-tenth the size of a WCA, and they are located on former wetlands on the northwestern side of WCAs on sites that were managed as farmland for much of the twentieth century in an area referred to as the Everglades Agricultural Area, or EAA. The objective of the present investigation was to quantify interactions between surface water and ground water in the Everglades Nutrient Removal Project (ENR), a prototype project for the STAs that began operation in 1994. Determining the effect of ground water on the mercury balance of the ENR treatment wetland was an important additional objective. In order to broaden the relevance of conclusions to all parts of the north-central Everglades, interactions between surface water and ground water and mercury also were investigated in Water Conservation Area 2A (WCA-2A) and, to a lesser extent, in two other WCA basins, WCA-2B and WCA-3A.An important conclusion of this study is that creation of the WCA basins, and accompanying water-resources management, have appreciably increased both recharge and discharge in the north-central Everglades compared with pre-drainage conditions. Recharge and discharge are highest near the northern and northwestern edges of the Everglades, in the relatively small basins such as ENR and the STAs that share borders with both WCA-1 and the EAA. All basins experienced greater increases in recharge relative to discharge, because of the effects that land subsidence and ground-water pumping outside the Everglades had on hydraulic gradients. The highest basin-wide estimate of recharge was measured in ENR, where recharge averaged 0.9 centimeter per day (cm/d) over a 4-year study period. For perspective, that estimate of recharge is the equivalent of 30 percent of pumped surface-water inflows and 230 percent of average daily precipitation in ENR. Ground-water discharge was 10 times smaller than recharge at ENR. The present study estimated a basin-averaged recharge for WCA-2A (0.2 cm/d) that was a factor of 4 smaller than ENR. Although preliminary, that estimate of recharge is 5 times higher than previous estimates (approximately 0.04 cm/d), probably because the newer measurements were able to quantify recharge and discharge at finer spatial and temporal scales. Recharge at WCA-2A is smaller than ENR because WCA-2A has a smaller topographic gradient (3 x 10-5 and 2 x 10-4 in WCA-2A and ENR, respective

Florida↗
USGS1992

Seasonal changes in ground-water quality and ground-water levels and directions of ground-water movement in southern Elmore County, southwestern Idaho, including Mountain Home Air Force Base, 1990-91

The study area is located in southern Elmore County, southwestern Idaho, and includes the Mountain Home Air Force Base located approximately 10 mi southwest of the city of Mountain Home. Chemical analyzes have been made periodically since the late 1940's on water samples from supply wells on the Air Force Base. These analyses indicate increases in specific conductance and in concentrations of nitrogen compounds, chloride, and sulfate. The purposes of this report, which was prepared in cooperation with the Department of the Air Force, are to describe the seasonal changes in water quality and water levels and to depict the directions of ground-water movement in the regional aquifer system and perched-water zones. Although data presented in this report are from both the regional ground-water system and perched-water zones, the focus is on the regional system. A previous study by the U.S. Geological Survey (Parliman and Young, 1990) describes the areal changes in water quality and water levels during the fall of 1989. During March, July, and October 1990, 141 wells were inventoried and depth to water was measured. Continuous water-level recorders were installed on 5 of the wells and monthly measurements of depth to water were made in 17 of the wells during March 1990 through February 1991. Water samples from 33 wells and 1 spring were collected during the spring and fall of 1990 for chemical analyses. Samples also were collected monthly from 11 of those wells during April to September 1990 (table 1). Selected well-construction and water-use data and measurements of depth to water for 141 wells are given in table 2 (separated sheets in envelope). Directions of ground-water movement and selected hydrographs showing seasonal fluctuations of water levels in the regional ground-water system and perched-water zones are shown on sheet 2. Changes in water levels in the regional ground-water system during March to October 1990 are shown on sheet 2.

Idaho↗
USGS2000

Occurrence and quality of surface water and ground water within the Yavapai-Prescott Indian Reservation, central Arizona, 1994-98

The Yavapai-Prescott Indian Reservation encompasses about 1,395 acres in central Arizona adjacent to the city of Prescott. From October 1994 to September 1997, the annual average rainfall was 14.9 inches and the total annual streamflow leaving the reservation along Granite Creek was about 430 acre-feet more than the amount of streamflow entering the reservation. The channel-fill and valley-fill sediments within the flood plain of Granite Creek make up the principal aquifer. The only ground-water development is from spring discharge that is being contained for livestock and wildlife use. About 29 acre-feet of ground water leaves the reservation each year after discharging into Granite Creek. Water levels in wells throughout the reservation reflect seasonal variations in rainfall and snowmelt. Surface water and ground water on the reservation are calcium bicarbonate types. Specific-conductance field measurements ranged from 187 to 724 microsiemens per centimeter for surface water and 381 to 990 microsiemens per centimeter for ground water. Fecal streptococcal bacteria and fecal coliform bacteria in the surface water make the water unsuitable for domestic use. Some volatile and semivolatile organic compounds were detected in samples of surface water, ground water, and streambed sediment. The potential for contamination exists from point and nonpoint sources on and off the reservation.

Arizona↗
USGS2002

Use of isotopes to identify sources of ground water, estimate ground-water-flow rates, and assess aquifer vulnerability in the Calumet region of northwestern Indiana and northeastern Illinois

Isotope data collected in the Calumet Region of northwestern Indiana and northeastern Illinois, one of the most heavily industrialized regions of the United States, indicated that water in the surficial Calumet aquifer is well mixed. The Calumet aquifer is recharged areally by precipitation and locally may be recharged by surface water. The residence time of ground water in the Calumet aquifer is approximately 5 to 15 years. Ground-water-flow rates through the Calumet aquifer are estimated to be 400 to 2,300 feet per year. The permeable deposits, shallow water table, lack of an overlying confining unit, and proximity to numerous contaminant sources indicate that the Calumet aquifer is vulnerable to contamination. Isotopic data indicate that ground water in the confining unit underlying the Calumet aquifer is derived from a variety of sources that include Lake Michigan, modern precipitation, and discharge from the basal Silurian-Devonian bedrock aquifer. The source and apparent age of the water are variable and appear to be affected locally by various geologic and hydraulic factors. The vertical ground-water-flow rate through the unweathered part of the confining unit is about 0.20 feet per year and is about 6.3 feet per year through the weathered part. The data indicate the weathered part of the confining unit may be more vulnerable to contamination than the unweathered confining unit. Ground water in the basal Silurian-Devonian aquifer is derived from Lake Michigan, glacial-age water, and modern precipitation. Post-1952 recharge has occurred in the vicinity of Stony Island, Ill. Ground-water recharge of the Silurian-Devonian aquifer may be occurring near Calumet Harbor. The Silurian-Devonian aquifer is vulnerable to contamination where the confining unit is thin or absent or where the integrity of the confining unit has been compromised.

Illinois, Indiana↗
USGS2007

Surface-water, ground-water, and sediment geochemistry of epizonal and shear-hosted mineral deposits in the Tintina Gold Province--Arsenic and antimony distribution and mobility

Epigenetic mineral deposits in the Tintina Gold Province are generally characterized by high concentrations of arsenic and antimony in their mineral assemblage. A total of 347 samples (ground water, surface water, and stream sediment) were collected to investigate the distribution and mobility of arsenic and antimony in the environment near known mineral deposits. Samples were collected from east to west at Keno Hill and Brewery Creek, Yukon, Canada; and Cleary Hill, True North, Scrafford Mine, Fairbanks, Ryan Lode, Stampede Creek, Slate Creek, and Donlin Creek, all in Alaska. Surface- and ground-water samples are all slightly acidic to near-neutral in pH (5-8), have a wide range in specific conductance (surface water 17-2,980 microsiemens per centimeter and ground water 170-2,940 microsiemens per centimeter), and show elevated dissolved arsenic and antimony concentrations (arsenic in surface water is less than 1 to 380 micrograms per liter and in ground water is less than 1 micrograms per liter to 1.5 milligrams per liter; antimony in surface water is less than 2 to 660 micrograms per liter and in ground water is less than 2 to 60 micrograms per liter). Stream sediments downstream from these deposits have high concentrations of arsenic and antimony (arsenic median is 1,670 parts per million, maximum is 10,000 parts per million; antimony median is 192 parts per million, maximum is 7,200 parts per million). The mobility of arsenic and antimony is controlled by the local redox environment, with arsenic being less mobile in oxidized surface waters relative to antimony, and arsenic more mobile in reduced ground water. These factors suggest that both antimony and arsenic may be useful pathfinder elements in water and sediment for targeting similar style deposits elsewhere in the Tintina Gold Province.

Alaska, Yukon↗
USGS1987

Ground-water withdrawals and changes in ground-water levels, ground-water quality, and land-surface subsidence in the Houston district, Texas, 1980-84

During 1980-84, ground-water withdrawals from the Chicot and Evangeline aquifers in the Houston district decreased from 511 million gallons per day to 444 million gallons per day. This 13-percent decrease was due to the increased availability of surface water and a decreased demand for water. The largest decreases in ground-water withdrawals occurred in the Houston area. Ground-water pumpage was 219.2 million gallons per day during 1984 compared to 254.8 million gallons per day during 1980. Decreases in ground-water withdrawals from 1980 through 1984 occurred in most of the other areas in the Houston district (Pasadena, Katy, Baytown-LaPorte, and Texas City). Large decreases in ground-water withdrawals for rice irrigation in the Katy area were offset by increases in ground-water withdrawals for public supply. Hence, in the Katy area, the quantity of ground water withdrawn during 1984, 148.9 million gallons per day, was only slightly less than the 157.5 million gallons per day withdrawn during 1980. Water levels generally rose in the eastern part of the Houston district and declined in the western part from spring 1980 to spring 1985. The rise of water levels in wells in the Chicot and Evangeline aquifers was as much as 80 feet and 60 feet, respectively. The decline of water levels in wells in the Chicot and Evangeline aquifers was as much as 40 feet and 80 feet, respectively. Slight decreases in chloride concentrations in water from the Chicot aquifer occurred in the Alta Loma area between 1980 and 1984. In 1980, chloride concentrations in water from the Chicot aquifer ranged from 250 to 790 milligrams per liter, whereas in 1984, chloride concentrations ranged from 180 to 710 milligrams per liter. Water from one well in the Texas City area had an increase in chloride concentrations from 265 milligrams per liter in 1980 to 300 milligrams per liter in 1984. In water from another well in the Texas City area, chloride concentrations decreased from 760 milligrams per liter in 1980 to 710 milligrams per liter in 1984. The concentrations of chloride and dissolved solids in water from the Evangeline aquifer remained less than 100 milligrams per liter and 500 milligrams per liter during 1980-84. Land-surface subsidence is still evident in the Houston district. Subsidence rates between 1980 and early 1985 in the eastern and southeastern parts of the Houston district were less than during 1975-79. At the Seabrook site, where a monitor measures most of the subsidence, the average compaction rate during 1980 to early 1985 was 0.04 foot per year while during 1975-79, the rate was 0.14 foot per year. However, subsidence rates in the western, southwestern, and northern parts of the Houston district during 1980 to early 1985 increased from the 1975-79 rates. At the Addicks site, the land surface has subsided at a rate of about 0.17 foot per year from 1980 to early 1985. The subsidence rate from 1975 through 1979 at the site was 0.11 foot per year.

Texas↗
USGS1994

Stable isotopes of hydrogen and oxygen in surface water and ground water at selected sites on or near the Idaho National Engineering Laboratory, Idaho

Relative stable isotopic ratios for hydrogen and oxygen compared to standard mean ocean water are presented for water from 4 surface-water sites and 38 ground-water sites on or near the Idaho National Engineering Laboratory (INEL). The surface-water samples were collected monthly from March 1991 through April 1992 and after a storm event on June 18, 1992. The ground-water samples either were collected during 1991 or 1992. These data were collected as part of the U.S. Geological Survey's continuing hydrogeological investigations at the INEL. The relative isotopic ratios of hydrogen and oxygen are reported as delta H-2 and as delta 0-18, respectively. The values in water from the four surface-water sites ranged from -143.0 to -122 and from -18.75 to -15.55, respec- tively. The values in water from the 38 ground- water sites ranged from -141.0 to -120.0 and from -18.55 to -14.95, respectively.

Open-File Report↗
USGS2006

Monitoring of changes in quality of ground water

Ground water of acceptable quality is commonly interspersed with water of inferior quality. Water of inferior quality may be naturally occurring salty water commonly underlying fresh water, or it may be enclaves of contaminated water from wastes that lie in the fresh-water bodies. Disposal of wastes on and in the ground and pumping of water from wells cause a dispersion of contaminated water; migration of contaminated water toward wells may be spontaneously induced by the natural hydraulic gradient, or it may be induced artificially by the cone of depression about one or more wells. Economic methods of determining precisely the boundary zones between contaminated and uncontaminated water are not available. Much reliance is placed on monitoring wells. A prerequisite to monitoring is a synthetic hydrogeologic framework or model in which the behavior of the contaminated water is conceived. Such a conceptual model, using pertinent data that are available, helps to assess the need for monitoring and to guide a monitoring program for optimum results. Unplanned, indiscriminate monitoring of water from wells is expensive, inefficient, and fallible. The need for monitoring will increase in the future; yet, the proper objective is to improve the technology of determining the distribution of contaminated water so that monitoring can be minimized and conducted with optimum results.

Groundwater↗
USGS2000

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

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

Nevada↗
USGS1971

Tunnels and dikes of the Koolau Range, Oahu, Hawaii, and their effect on storage depletion and movement of ground water

Ground water impounded by dikes in the Koolau Range is a major source of water for the island of Oahu, Hawaii, and many tunnels have been bored into the range to develop it. All water-development tunnels, except Waihee tunnel, have depleted storage in the rocks they penetrate and are now discharging at rates that are but fractions of the rates possible at full storage. Rocks above the floor of the water-development part of Waihee tunnel have never been completely dewatered, and storage can be manipulated by regulating outflow. Thus, storage for this tunnel can be increased during periods of low demand and discharged at high rates during periods of high demand. A measure of the rate of drainage or depletion of storage is the recession constant b in the recession-curve equation Qt=Q0e-b t. The higher the value of b, the faster water can be drawn from storage or returned to storage through artificial recharge. Mathematical analysis of the flow-recession curve of Waihee tunnel shows that (1) its recession constant is 0.00401, (2) net storage (exclusive of recharge) is 2,200 million gallons (6,800 acre-feet), and (8) initial discharge from full storage would be about 19 million gallons per day. Analysis of flow-recession curves for Waiahole ditch tunnel (main bore) and Haiku tunnel shows that these tunnels have drainage characteristics that are similar to those of Waihee tunnel. The composite recession constant computed for the four tunnels north of Waiahole is about one-third as large as that computed for the Waiahole ditch tunnel (main bore) and the tunnels to the south. The difference is due to an abrupt change in spacing of dikes north of Waiahole. At and south of Waiahole Stream, dikes are spaced tens or hundreds of feet apart; north of Waiahole, they are spaced inches or a few feet apart. Storage could be restored by bulkheading at the controlling dike or dikes after an analysis is made of the flow-recession curve for each tunnel. Such analyses will show which tunnels are best for storage restoration. The reciprocal of the recession constant is the time, in days, it would take to drain about two-thirds of the storage. The shorter this time is the better storage may be manipulated to meet seasonal peak demands for water.

Water Supply Paper↗
USGS1998

Ground-water levels, predevelopment ground-water flow, and stream-aquifer relations in the vicinity of the Savannah River Site, Georgia and South Carolina

Ground-water levels, predevelopment ground-water flow, and stream-aquifer relations in the vicinity of the U.S. Department of Energy Savannah River Site, Georgia and South Carolina, were evaluated as part of a cooperative study between the U.S. Geological Survey, U.S. Department of Energy, and Georgia Department of Natural Resources. As part of this evaluation: (1) ground-water-level fluctuations and trends in three aquifer systems in sediment of Cretaceous and Tertiary age were described and related to patterns of ground-water use and precipitations; (2) a conceptual model ofthe stream-aquifer flow system was developed; (3) the predevelopment ground-water flow system, configuration of potentiometric surfaces, trans-river flow, and recharge-discharge relations were described; and (4) stream-aquifer relations and the influence of river incision on ground-water flow and stream-aquifer relations were described. The 5,147-square mile study area is located in the northern part of the Coastal Plain physiographic province of Georgia and South Carolina. Coastal Plain sediments comprise three aquifer systems consisting of seven aquifers that are separated hydraulically by confining units. The aquifer systems are, in descending order: (1) the Floridan aquifer system—consisting of the Upper Three Runs and Gordon aquifers in sediments of Eocene age; (2) the Dublin aquifer system—consisting of the Millers Pond, upper Dublin, and lower Dublin aquifers in sediments of Paleocene-Late Cretaceous age; and (3) the Midville aquifer system—consisting of the upper Midville and lower Midville aquifers in sediments of Late Cretaceous age. The Upper Three Runs aquifer is the shallowest aquifer and is unconfined to semi-confined throughout most of the study area. Ground-water levels in the Upper Three Runs aquifer respond to a local flow system and are affected mostly by topography and climate. Ground-water flow in the deeper, Gordon aquifer and Dublin and Midville aquifer systems is characterized by local flow near outcrop areas to the north, changing to intermediate flow and then regional flow downdip (southeastward) as the aquifers become more deeply buried. Water levels in these deeper aquifers show a pronounced response to topography and climate in the vicinity of outcrops, and diminish southeastward where the aquifer is more deeply buried. Stream stage and pumpage affect ground-water levels in these deeper aquifers to varying degrees throughout the study area. The geologic characteristics of the Savannah River alluvial valley substantially control the configuration of potentiometric surfaces, ground-water-flow directions, and stream-aquifer relations. Data from 18 shallow borings indicate incision into each aquifer by the paleo Savannah River channel and subsequent infill of permeable alluvium, allowing for direct hydraulic connection between aquifers and the Savannah River along parts of its reach. This hydraulic connection may be the cause of large ground-water discharge to the river near Jackson, S.C., where the Gordon aquifer is in contact with Savannah River alluvium, and also the cause of lows or depressions formed in the potentiometric surfaces of confined aquifers that are in contact with the alluvium. Ground water in these aquifers flows toward the depressions. The influence of the river is diminished downstream where the aquifers are deeply buried, and upstream and downstream ground-water flow is possibly separated by a water divide or "saddle". Water-level data indicate that saddle features probably exist in the Gordon aquifer and Dublin aquifer system, and also might be present in the Midville aquifer system. Ground-water levels respond seasonally or in long term to changes in precipitation, evapotranspiration, pumpage, and river stage. Continuous water-level data and water-levels measured in a network of 271 wells during the Spring (May) and Fall (October) in 1992, indicate that seasonal water-level changes generally are less than 4 feet, and that larger changes occur near supply wells. Long-term data (more than 10 years of record) from 283 wells indicate that water levels in most aquifers declined during some period prior to 1993. Although most declines were less than 15 feet and were limited to scattered areas influenced by supply wells, widespread declines of as much as 59 feet occurred in the lower Midville aquifer in Richmond County, Georgia. Water-level data at well-cluster sites indicate that in the vicinity of major ground-water divides, head decreases with depth; and in the vicinity of a regional drain, such as the Savannah River, head increases with depth. Although this vertical head distribution holds true over much of the study area, water-level data indicate that the Gordon, Millers Pond, and lower Dublin aquifers are apparent hydrologic "sinks" in parts of the study area, indicating a potential for vertical leakage from both above and below. Reasons for anomalously low heads in these three aquifers are unclear, but probably are related to: (1) subsurface pinchout of the aquifer, that influences flow patterns in the ground-water flow system, (2) hydraulic connection of the aquifer to river alluvium and associated large ground-water discharge, or (3) water-level declines as a result of pumpage. Estimated average ground-water discharge to the Savannah River based on data from 1941, 1942, and 1949, was 1,220 cubic feet per second; of which 46 percent was from the local flow system, 41 percent was from the intermediate flow system, and 13 percent was from the regional flow system. Estimated ground-water discharge during the 1954 and 1986 droughts indicates that the contribution from the intermediate flow system decreased in a downstream direction, and that most ground-water discharge was from the local flow system. The decreased contribution from the intermediate flow system in downstream reaches may be related to a downdip (downstream) thickening of confining units underlying the stream, that reduces upward leakage of water. Flow lines based on contours of the estimated predevelopment potentiometric surface of the confined Dublin and Midville aquifer systems, suggest ground-water flow beneath the floodplain of the Savannah River from one side of the river to the other side. This phenomenon, termed trans-river flow, is assumed to occur for a short distance into Georgia prior to discharge into the Savannah River alluvial valley. Trans-river flow is influenced by changes in hydraulic gradient (ground-water levels) near the river. Trans-river flow cannot be inferred from contours of the potentiometric surface of the Gordon or Upper Three Runs aquifers.

Georgia, South Carolina↗
USGS2005

Effects of decreased ground-water withdrawal on ground-water levels and chloride concentrations in Camden County, Georgia, and ground-water levels in Nassau County, Florida, from September 2001 to May 2003

During October 2002, the Durango Paper Company formerly Gillman Paper Company) in St. Marys, Georgia, shut down paper-mill operations; the shutdown resulted in decreased ground-water withdrawal in Camden County by 35.6 million gallons per day. The decrease in withdrawal resulted in water-level rise in wells completed in the Floridan aquifer system and the overlying surficial and Brunswick aquifer systems; many wells in the St. Marys area flowed for the first time since the mill began operations during 1941. Pumping at the mill resulted in the development of a cone of depression that coalesced with a larger adjacent cone of depression at Fernandina Beach, Florida. Since closure of the mill, the cone at St. Marys is no longer present, although the cone still exists at Fernandina Beach, Florida. Historical water-level data from the production wells at the mill indicate that the pumping water level ranged from 68 to 235 feet (ft) below North American Vertical Datum of 1988 (NAVD 88) and averaged about 114 ft when the mill was operating. Since the shutdown, it is estimated that water levels at the mill have risen about 140 ft and are now at about 30 ft above NAVD 88. The water-level rise in wells in outlying areas in Camden County was less pronounced and ranged from about 5 to 10 ft above NAVD 88. Because of the regional upward water-level trend in the Upper Floridan aquifer that started during 19992000 in most of the coastal area, combined with a steeper upward trend beginning during October 2002, it was not possible to determine if the 510 ft rise in water levels in wells away from St. Marys was due to the mill closure. In addition to water-level rise of 2226 ft in the Floridan aquifer system, water-level rises in the overlying surficial and Brunswick aquifer systems at St. Marys after the shutdown indicate upward leakage of water. Water levels had stabilized in the confined surficial and Upper and Lower Floridan aquifers by AprilMay 2003; however, the water level in the upper Brunswick aquifer was still rising as of May 2003. Chloride concentrations in the Upper Floridan aquifer in Camden County do not exceed the State and Federal drinking-water standard of 250 milligrams per liter (mg/L). With the exception of three wells located at St. Marys, all of the wells sampled during this study (from September 2002 to May 2003) had chloride concentrations ranging from 30 to 50 mg/L, which are considered within background levels for the Upper Floridan aquifer in this area. The three wellstwo at the Durango Paper Company and the other an old unused City of St. Marys wellhad chloride concentrations that ranged from 74 to 175 mg/L, which are above the background level, but were still below the 250-mg/L drinking-water standard. The source has not been determined for the elevated chloride concentration in these wells; the chloride concentration in one of the wells has decreased slightly since the paper-mill shutdown. Chloride concentrations throughout Camden County showed little change after the paper-mill shutdown.

Florida, Georgia↗
USGS1974

Seawater intrusion, ground-water pumpage, ground-water yield, and artificial recharge of the Pajaro Valley area, Santa Cruz and Monterey Counties, California

The Pajaro Valley area, California, covering about 120 square miles (310 km 2 ), extends from the southern part of Santa Cruz County to several miles south of the county line into Monterey County. It borders the Pacific Ocean on the west and the Santa Cruz Mountains on the east. The city of Watsonville is the largest center of population. Seawater intrusion is occurring in the Pajaro Valley area from several miles north to several miles south of the mouth of the Pajaro River and in a small area about 4 miles (6.5 km) north of the river. The intrusion extends inland about 1 mile (1.6 km). Two water-bearing zones are being intruded--the depth intervals 100-200 feet (30-60 m) and 300-600 feet (90-180 m). Ground-water pumpage averaged 49,100 acre-feet per year (60.6 hm 3 /yr) for the 9-year period 1963-71. The long-term ground-water yield of the Pajaro Valley is about 44,000 acre-feet per year (54.3 hm 3 /yr). Artificial recharge can be effected through modified streambeds at infiltration rates as high as 3 feet per day (0.9 m/d). Injection wells may have recharge capabilities of as much as 500 gallons per minute (1.9 m 3 /min).

California↗
USGS2006

Effects of Irrigation, Drought, and Ground-Water Withdrawals on Ground-Water Levels in the Southern Lihue Basin, Kauai, Hawaii

A numerical ground-water-flow model was used to investigate the effects of irrigation on ground-water levels in the southern Lihue Basin, Kauai, Hawaii, and the relation between declining ground-water levels observed in the basin in the 1990s and early 2000s and concurrent drought, irrigation reduction, and changes in ground-water withdrawal. Results of steady-state model simulations indicate that changing from pre-development to 1981 irrigation and ground-water-withdrawal conditions could, given enough time for steady state to be achieved, raise ground-water levels in some areas of the southern Lihue Basin by as much as 200 feet, and that changing from 1981 to 1998 irrigation and ground-water-withdrawal conditions could lower ground-water levels in some areas by as much as 100 feet. Transient simulations combining drought, irrigation reduction, and changes in ground-water withdrawal show trends that correspond with those observed in measured water levels. Results of this study indicate that irrigation reduction was the primary cause of the observed decline in ground-water-levels. In contrast, ground-water withdrawal had a long-duration but small-magnitude effect, and drought had a widespread, high-magnitude but short-duration effect. Inasmuch as irrigation in the future is unlikely to return to the same levels as during the period of peak sugarcane agriculture, the decline in ground-water levels resulting from the reduction and ultimate end of sugarcane irrigation can be considered permanent. Assuming that irrigation does not return to the southern Lihue Basin and that, on average, normal rainfall persists and ground-water withdrawal remains at 1998 rates, model projections indicate that average ground-water levels in the Kilohana-Puhi area will continue to recover from the drought of 1998-2002 and eventually rise to within about 4 feet of the pre-drought conditions. Long-term climate trends, increases in ground-water withdrawal, or other factors not simulated in the model could also affect ground-water levels in the southern Lihue Basin in the future.

Scientific Investigations Report↗