USGS Science⌕ Search

SEARCH · USGS Science

Results for “Water-Resources Report”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources
USGS2001

Simulation of ground-water flow and transport of chlorinated hydrocarbons at Graces Quarters, Aberdeen Proving Ground, Maryland

Military activity at Graces Quarters, a former open-air chemical-agent facility at Aberdeen Proving Ground, Maryland, has resulted in ground-water contamination by chlorinated hydrocarbons. As part of a ground-water remediation feasibility study, a three-dimensional model was constructed to simulate transport of four chlorinated hydrocarbons (1,1,2,2-tetrachloroethane, trichloroethene, carbon tetrachloride, and chloroform) that are components of a contaminant plume in the surficial and middle aquifers underlying the east-central part of Graces Quarters. The model was calibrated to steady-state hydraulic head at 58 observation wells and to the concentration of 1,1,2,2-tetrachloroethane in 58 observation wells and 101direct-push probe samples from the mid-1990s. Simulations using the same basic model with minor adjustments were then run for each of the other plume constituents. The error statistics between the simulated and measured concentrations of each of the constituents compared favorably to the error statisticst,1,2,2-tetrachloroethane calibration. Model simulations were used in conjunction with contaminant concentration data to examine the sources and degradation of the plume constituents. It was determined from this that mixed contaminant sources with no ambient degradation was the best approach for simulating multi-species solute transport at the site. Forward simulations were run to show potential solute transport 30 years and 100 years into the future with and without source removal. Although forward simulations are subject to uncertainty, they can be useful for illustrating various aspects of the conceptual model and its implementation. The forward simulation with no source removal indicates that contaminants would spread throughout various parts of the surficial and middle aquifers, with the100-year simulation showing potential discharge areas in either the marshes at the end of the Graces Quarters peninsula or just offshore in the estuaries. The simulation with source removal indicates that if the modeling assumptions are reasonable and ground-water cleanup within30 years is important, source removal alone is not a sufficient remedy, and cleanup might not even occur within 100 years.

Water-Resources Investigations Report↗
USGS2001

Hydrologic setting and geochemical characterization of free-phase hydrocarbons in the alluvial aquifer at Mandan, North Dakota, November 2000

Free-phase hydrocarbons are present in the alluvial aquifer at Mandan, North Dakota. A large contaminant body of the hydrocarbons [light nonaqueous phase liquid (LNAPL)] floats on the water table about 20 feet below land surface. The main LNAPL body is about 6 feet thick, and the areal extent is about 657,000 square feet. A study was conducted to describe the hydrologic setting and characterize the geochemical composition of the free-phase hydrocarbons in the alluvial aquifer. Most of the study area is underlain by alluvium of the Heart River Valley that ranges in thickness from about 25 to 109 feet. The alluvium can be divided into three stratigraphic units silty clay, silty sand, and sand and is underlain by shales and sandstones. Monitoring wells were installed prior to this study, to an average depth of about 29 feet. Regional ground-water flow in the Heart River aquifer generally may be from west-northwest to eastsoutheast and is influenced by hydraulic connections to the river. Hydraulic connections also are probable between the aquifer and the Missouri River. Ground-water flow across the north boundary of the aquifer is minimal because of adjacent shales and sandstones of relatively low permeability. Recharge occurs from infiltration of precipitation and is spatially variable depending on the thickness of overlying clays and silts. Although the general water-table gradient may be from west-northwest to east-southeast, the flow directions can vary depending on the river stage and recharge events. Any movement of the LNAPL is influenced by the gradients created by changes in water-level altitudes. LNAPL samples were collected from monitoring wells using dedicated bailers. The samples were transferred to glass containers, stored in the dark, and refrigerated before shipment for analysis by a variety of analytical techniques. For comparison purposes, reference-fuel samples provided by the refinery in Mandan also were analyzed. These reference-fuel samples included a current diesel fuel, a closely related but slightly broader refinery-cut fuel, a crude-oil composite, unleaded regular gasoline, and additives. Four principal analytical techniques were used for geochemical characterization: Purge-and-trap gas chromatography/mass spectrometry (volatile components); capillary gas chromatography/mass spectrometry (semivolatile components); isotope ratio mass spectrometry (carbon isotopes; whole oils); and liquid chromatography/mass spectrometry with electrospray ionization (additives and other organic components). Volatile analytes included solvents, disinfection byproducts, halogenated hydrocarbons, and alkylbenzenes, including benzene, toluene, ethylbenzene, and meta-, para-, and orf/zo-xylenes. Semivolatile analytes included rt-alkanes, isoprenoid alkanes, cycloalkanes, and polycyclic aromatic hydrocarbons and related compounds (naphthalenes, phenanthrenes, and dibenzothiophenes and their alkylated derivatives). Of the additives, only the diesel-fuel additive with the red dye marker was amenable to electrospray ionization. Results indicate the LNAPL consists of closely correlatable diesel fuel at various stages of degradation. All LNAPL samples contained the red dye marker for diesel fuel. None of the samples contained chlorinated solvents associated with industries such as drycleaning or automotive maintenance. Solvents such as acetone, dimethyl ether, and methylene chloride and the gasoline additives methyl-t-butyl ether (MTBE), ethyl-t-butyl ether (ETBE), and t-amyl-methyl ether (TAME) were not found. With one possible exception, no evidence of a different diesel or other hydrocarbon fuel contribution was identified. At one site near the north edge of the main LNAPL body, evidence exists for traces of possible gasoline components in addition to the diesel fuel. The geochemical analysis of the LNAPL and correlations with other fuel products and additives strongly suggest episodic releases of a single, local-source, diesel fuel into the aquifer over an extended period of time.

North Dakota↗
USGS2001

Water temperature of streams in the Cook Inlet basin, Alaska, and implications of climate change

Water-temperature data from 32 sites in the Cook Inlet Basin, south-central Alaska, indicate various trends that depend on watershed characteristics. Basins with 25 percent or more of their area consisting of glaciers have the coldest water temperatures during the open-water season, mid-May to mid-October. Streams and rivers that drain lowlands have the warmest water temperatures. A model that uses air temperature as input to predict water temperature as output was utilized to simulate future trends in water temperature based on increased air temperatures due to climate warming. Based on the Nash-Sutcliffe coefficient, the model produced acceptable results for 27 sites. For basins with more than 25 percent glacial coverage, the model was not as accurate. Results indicate that 15 sites had a predicted water-temperature change of 3 degrees Celsius or more, a magnitude of change that is considered significant for the incidence of disease in fish populations.

Water-Resources Investigations Report↗
USGS2001

Effects of ground-water withdrawals on flow in the Sauk River Valley Aquifer and on streamflow in the Cold Spring area, Minnesota

The U. S. Geological Survey, in cooperation with the city of Cold Spring, Minnesota conducted a study during 1998-99 to: (1) determine the contributing areas of groundwater flow to high-capacity wells, (2) delineate the 10-, 20-, and 30-year time-of-travel zones to high-capacity wells, and (3) determine changes in streamflow in the Sauk River due to ground-water withdrawals. Surficial aquifers underlie a portion of the uplands in the north-central part of the study area and the Sauk River Valley. The upland surficial aquifer is unconfined, with saturated thicknesses ranging from 6 to 37 feet. The Sauk River Valley aquifer consists of hydraulically connected sand and gravel units: (1) the generally continuous surficial unconfined unit underlying the Sauk River Valley and (2) buried confined units that are overlain by till or lake clays in the upland areas. Maximum saturated thickness of the Sauk River Valley aquifer is about 50 feet. Thicknesses of the buried units are generally 10 to 20 feet. Ground-water flow in the upland surficial aquifer is (1) to the south and southeast toward the margins of the aquifer and (2) toward an unnamed creek valley in the northwestern part of the study area. Ground-water flow in the Sauk River Valley aquifer is from upland areas toward the Sauk River and the connected chain of lakes. Based on hydrograph analysis, ground-water recharge rates to the aquifers during 1999 ranged from 5.3 to 8.6 inches per year, with an average value of 7.0 inches per year. Streamflow measurements indicated net gains of 44.8 and 25.8 cubic feet per second for the Sauk River from Cold Spring to Rockville during October 1998 and August 1999, respectively. In general, the Sauk River probably is a gaining stream in all reaches, except for the reach adjacent to the Gold'n Plump Poultry Processing Plant well field. Ground-water withdrawals from the well field induce infiltration of water from the Sauk River to the underlying aquifer. The measured gains in streamflow for Brewery Creek were 2.75 and 2.25 cubic feet per second during October 1998 and August 1999, respectively. A numerical ground-water-flow model was constructed and calibrated for steady-state conditions. Based on the calibrated model, areal recharge accounts for 51.5 percent of the sources of water to the aquifers in the Cold Spring area and inflow through constant-head boundaries contributes 45.8 percent. The largest discharges from the aquifers are leakage from the Sauk River Valley aquifer to the Sauk River and Brewery Creek (53.7 percent) and outflow through constant-head boundaries (33.1 percent). The simulated contributing areas for selected watersupply wells in the Cold Spring area generally extend to and possibly beyond the model boundaries to the north and to the southeast. The contributing areas for the Gold'n Plump Poultry Processing Plant supply wells extend: (1) to the Sauk River, (2) to the north to and possibly beyond to the northern model boundary, and (3) to the southeast to and possibly beyond the southeastern model boundary. The primary effects of projected increased ground-water withdrawals of 0.23 cubic feet per second (7.5 percent increase) were to: (1) decrease outflow from the Sauk River Valley aquifer through constant-head boundaries and (2) decrease leakage from the valley unit of the Sauk River Valley aquifer to the streams. No appreciable differences were discernible between the simulated steady-state contributing areas to wells with 1998 pumpage and those with the projected pumpage.

Minnesota↗
USGS2001

Simulations of flooding on the Tennessee River in the vicinity of U.S. Highway 231 near Huntsville, Alabama

A two-dimensional finite-element surface-water model was used to study the effects of proposed modifications to the U.S. Highway 231 corridor on water-surface elevations and flow distributions during flooding in the Tennessee River Basin south of Huntsville, Madison County, Alabama. Flooding was first simulated for the March 19, 1973, flood for the existing conditions in order to calibrate the model to measured data collected by the U.S. Geological Survey (USGS) and the Tennessee Valley Authority (TVA) during and after the flood. After model calibration, the effects of flooding were simulated for two scenarios---existing and proposed conditions----for the 100-year and 500-year recurrence intervals. The first scenario was to simulate the existing bridge and highway configuration for the U.S. Highway 231 crossing of the Tennessee River flood plain. The second scenario was to simulate the proposed modifications to this bridge and highway configuration. The simulation of floodflow for the Tennessee River flood of March 19, 1973, in the study reach compared closely to discharge measurement and flood profile data obtained during and after the flood. The flood of March 19, 1973, had an estimated peak discharge of 323,000 cubic feet per second and was estimated to be about 50-year flood event. Simulation of the 100-year floodflow for the Tennessee River for the existing conditions at U.S. Highway 231 indicates that of the peak flow, 92.1 percent (316,500 cubic feet per second) was conveyed by the main channel bridge, 4.0 percent (13,800 cubic feet per second) by the northernmost relief bridge, and 3.8 percent (13,200 cubic feet per second) by the southernmost relief bridge. The water-surface elevation predicted in the vicinity of the USGS gaging station was 576.91 feet. No overtopping of U.S. Highway 231 occurrec. For the 500-year flood, the simulation indicates that of the peak flow, 89.2 percent (359,000) cubic feet per second) was conveyed by the main channel bridge, 5.6 percent (22,600 cubic feet per second) by the northernmost relieft bridge, and 5.2 percent (20,900 cubic feet per second) by the southernmost relief bridge. The water-surface elevation predicted in the vicinity of the USGS gaging station was 580.91 feet. No overtopping of U.S. Highway 231 occurred; however, the girders of both relief bridges were partially submerged. Simulation of the 100-year floodflow for the Tennessee River for the proposed conditions indicates that of the peak flow, 93.2 percent (319,800 cubic feet per second) was conveyed by the proposed main channel bridge, 3.3 percent (11,400 cubic feet per second) by the proposed northernmost relief bridge, and 3.4 percent (11,800 cubic feet per second) by the proposed southernmost relief bridge. The water-surface elevation predicted in the vicinity of the USGS gaging station was 576.93 feet. No overtopping of U.S. Highway 231 occurred. For the 500-year flood, the simulation indicates that of the peak flow, 90.9 percent (365,400 cubic feet per second) was conveyed by the proposed main channel bridge, 4.3 percnet (17,300 cubic feet per second) by the proposed northernmost relief bridge, and 4.8 percent (19,400 cubic feet per second) by the proposed southernmost relief bridge. The water-surface elevation predicted in the vidinity of the USGS gaging station was 580.93 feet. No overtopping of U.S. Highway 231 occurred; however, the girders of both relief bridges were partially submerged.

Water-Resources Investigations Report↗
USGS2002

Estimated water withdrawals, water use, and water consumption in Illinois, Indiana, Iowa, Kentucky, Michigan, Missouri, and Wisconsin, 1950-95

From 1950 through 1995, the U.S. Geological Survey tabulated water withdrawals throughout the United States, including the northcentral States of Illinois, Indiana, Iowa, Kentucky, Michigan, Missouri, and Wisconsin. During this period, total water withdrawals increased in each of the north-central States by at least a factor of two. Illinois led the north-central States in total withdrawals, withdrawals from surface water and, typically, withdrawals from ground water. Per capita withdrawals were largest in Indiana or Illinois, however, the disparity in per capita withdrawals in the north-central States decreased from 1950 through 1995. Surface water was the source of 75 to 95 percent of all water withdrawals in the north-central States and consistently accounted for over 90 percent of total withdrawals in Illinois. From 1950 through 1995, the magnitude of increase in withdrawals from surface water was lower in Illinois than in most of the other north-central States, even though surface-water withdrawals in Illinois increased from about 9,000 to 19,000 million gallons per day. Total water withdrawals from ground water in Illinois have decreased by about 150 million gallons per day since 1975. From 1950 through 1995, from 68 to 86 percent of the total water withdrawals in Illinois were for generation of thermoelectric power; this percentage is higher than for the other north-central States and has increased since 1970. Approximately 12 percent of water withdrawals in Illinois are for municipal water supply, which was consistent with the other north-central States. Ten percent or less of the water withdrawn in the north-central States is estimated to have been consumed.

Water-Resources Investigations Report↗
USGS2001

Effects of land use on water quality and transport of selected constituents in streams in Mecklenburg County, North Carolina, 1994–98

Transport rates for total solids, total nitrogen, total phosphorus, biochemical oxygen demand, chromium, copper, lead, nickel, and zinc during 1994–98 were computed for six stormwater-monitoring sites in Mecklenburg County, North Carolina. These six stormwater-monitoring sites were operated by the Mecklenburg County Department of Environmental Protection, in cooperation with the City of Charlotte, and are located near the mouths of major streams. Constituent transport at the six study sites generally was dominated by nonpoint sources, except for nitrogen and phosphorus at two sites located downstream from the outfalls of major municipal wastewater-treatment plants. To relate land use to constituent transport, regression equations to predict constituent yield were developed by using water-quality data from a previous study of nine stormwater-monitoring sites on small streams in Mecklenburg County. The drainage basins of these nine stormwater sites have relatively homogeneous land-use characteristics compared to the six study sites. Mean annual construction activity, based on building permit files, was estimated for all stormwater-monitoring sites and included as an explanatory variable in the regression equations. These regression equations were used to predict constituent yield for the six study sites. Predicted yields generally were in agreement with computed yields. In addition, yields were predicted by using regression equations derived from a national urban water-quality database. Yields predicted from the regional regression equations generally were about an order of magnitude lower than computed yields. Regression analysis indicated that construction activity was a major contributor to transport of the constituents evaluated in this study except for total nitrogen and biochemical oxygen demand. Transport of total nitrogen and biochemical oxygen demand was dominated by point-source contributions. The two study basins that had the largest amounts of construction activity also had the highest total solids yields (1,300 and 1,500 tons per square mile per year). The highest total phosphorus yields (3.2 and 1.7 tons per square mile per year) attributable to nonpoint sources also occurred in these basins. Concentrations of chromium, copper, lead, nickel, and zinc were positively correlated with total solids concentrations at most of the study sites (Pearson product-moment correlation >0.50). The site having the highest median concentrations of chromium, copper, and nickel also was the site having the highest computed yield for total solids.

North Carolina↗
USGS2001

Hydrologic budgets for the Madison and Minnelusa aquifers, Black Hills of South Dakota and Wyoming, water years 1987-96

The Madison and Minnelusa aquifers are two of the most important aquifers in the Black Hills area of South Dakota and Wyoming. Quantification and evaluation of various hydrologic budget components are important for managing and understanding these aquifers. Hydrologic budgets are developed for two scenarios, including an overall budget for the entire study area and more detailed budgets for subareas. Budgets generally are combined for the Madison and Minnelusa aquifers because most budget components cannot be quantified individually for the aquifers. An average hydrologic budget for the entire study area is computed for water years 1987-96, for which change in storage is approximately equal to zero. Annual estimates of budget components are included in detailed budgets for nine subareas, which consider periods of decreasing storage (1987-92) and increasing storage (1993-96). Inflow components include recharge, leakage from adjacent aquifers, and ground-water inflows across the study area boundary. Outflows include springflow (headwater and artesian), well withdrawals, leakage to adjacent aquifers, and ground-water outflow across the study area boundary. Leakage, ground-water inflows, and ground-water outflows are difficult to quantify and cannot be distinguished from one another. Thus, net ground-water flow, which includes these components, is calculated as a residual, using estimates for the other budget components. For the overall budget for water years 1987-96, net ground-water outflow from the study area is computed as 100 ft3/s (cubic feet per second). Estimates of average combined budget components for the Madison and Minnelusa aquifers are: 395 ft3/s for recharge, 78 ft3/s for headwater springflow, 189 ft3/s for artesian springflow, and 28 ft3/s for well withdrawals. Hydrologic budgets also are quantified for nine subareas for periods of decreasing storage (1987-92) and increasing storage (1993-96), with changes in storage assumed equal but opposite. Common subareas are identified for the Madison and Minnelusa aquifers, and previous components from the overall budget generally are distributed over the subareas. Estimates of net ground-water flow for the two aquifers are computed, with net ground-water outflow exceeding inflow for most subareas. Outflows range from 5.9 ft3/s in the area east of Rapid City to 48.6 ft3/s along the southwestern flanks of the Black Hills. Net groundwater inflow exceeds outflow for two subareas where the discharge of large artesian springs exceeds estimated recharge within the subareas. More detailed subarea budgets also are developed, which include estimates of flow components for the individual aquifers at specific flow zones. The net outflows and inflows from the preliminary subarea budgets are used to estimate transmissivity of flow across specific flow zones based on Darcy?s Law. For estimation purposes, it is assumed that transmissivities of the Madison and Minnelusa aquifers are equal in any particular flow zone. The resulting transmissivity estimates range from 90 ft2/d to about 7,400 ft2/d, which is similar to values reported by previous investigators. The highest transmissivity estimates are for areas in the northern and southwestern parts of the study area, and the lowest transmissivity estimates are along the eastern study area boundary. Evaluation of subarea budgets provides confidence in budget components developed for the overall budget, especially regarding precipitation recharge, which is particularly difficult to estimate. Recharge estimates are consistently compatible with other budget components, including artesian springflow, which is a dominant component in many subareas. Calculated storage changes for subareas also are consistent with other budget components, specifically artesian springflow and net ground-water flow, and also are consistent with water-level fluctuations for observation wells. Ground-water budgets and flowpaths are especially complex i

Water-Resources Investigations Report↗
USGS2002

Monitoring and analysis of combined sewer overflows, Riverside and Evanston, Illinois, 1997-99

The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, collected and analyzed flow data in combined sewer systems in Riverside and Evanston, northeastern Illinois, from March 1997 to December 1999. Continuous 2- and 5-minute stage and velocity data were collected during surcharged and nonsurcharged conditions at 12 locations. Mass balances were calculated to determine the volume of water flowing through the tide-gate openings to the Des Plaines River and the North Shore Channel and to determine the volume of water flowing past the sluice gate to the deep tunnel. The sewer systems consist of circular pipes ranging in diameter from 0.83 feet to 10.0 feet, elliptical siphon pipes, ledges, and tide and sluice gates. Pipes were constructed of either brick and mortar or concrete, and ranged from having smooth surfaces to rough, pitted and crumbling surfaces. One pipe was noticeably affected by water infiltration from saturated ground. During data analysis, many assumptions were necessary because of the complexity of the flow data and sewer-system configurations. These assumptions included estimating the volume of water entering an interceptor sewer at the ''Gage Street pipe'' at Riverside, the effect of infiltration on the ''brick pipe'' at Riverside, and the minimum velocity required for the meter to make an accurate velocity determination. Other factors affecting the analysis of flow data included possible non-instrumented sources of inflow, and backwater conditions in some pipes, which could have caused error in the data analysis. Variations of these assumptions potentially could cause appreciable changes to the final massbalance calculations. Mass-balance analysis at Riverside indicated a total inflow volume into chamber 3 of approximately 721,000 cubic feet (ft3) during April 22-26, 1999. Outflow volume to the Des Plaines River at Riverside through the tide gate was approximately 132,000 ft3; outflow volume to the deep tunnel through the sluice gate was approximately 267,000 ft3. The mass-balance analysis at Evanston indicated a total inflow volume into chamber 3 of approximately 5,970,000 ft3 during April 21-26, 1999. The outflow volume to the North Shore Channel through the tide gates at Evanston was approximately 2,920,000 ft3; outflow volume to the deep tunnel through the sluice gates was approximately 3,050,000 ft3.

Water-Resources Investigations Report↗
USGS2001

Status of water levels and selected water-quality conditions in the Mississippi River valley alluvial aquifer in eastern Arkansas, 2000

During the spring of 2000, water levels were measured in 735 wells completed in the Mississippi River Valley Alluvial aquifer in eastern Arkansas. Water samples were collected during the summer of 2000 from 151 wells completed in the alluvial aquifer. All samples were measured for specific conductance, and samples from 104 wells were analyzed for dissolved chloride concentrations. The regional direction of ground-water flow is generally to the south and east except where affected by ground-water withdrawals. In 2000, the highest water-level altitude measured was 289 feet above sea level in northeastern Clay County. The lowest water-level altitude measured was 78 feet above sea level in southwestern Ashley County. A large depression in the potentiometric surface is located in Arkansas, Lonoke, and Prairie Counties. Two shallower depressions are located in Craighead, Cross, and Poinsett Counties and Lee, Monroe, St. Francis, and Woodruff Counties. Potentiometric depressions seem to be forming in four new areas in Ashley, Chicot, Desha, Greene, and Lincoln Counties. Comparisons of water-level changes in cones of depression from 1994 to 2000 show increases in depth and areal extent. Water-level data from 25 wells with 26 or more years of record indicate long-term water levels in the alluvial aquifer declined an average of about 0.6 foot per year from 1975 to 2000. Specific conductance measurements made on water samples collected during the study ranged from 190 microsiemens per centimeter at 25 degrees Celsius at a well in Drew County to 1,690 microsiemens per centimeter at 25 degrees Celsius at a well in Ashley County. Dissolved chloride concentrations ranged from 2.2 milligrams per liter at wells in Crittenden and St. Francis Counties to 550 milligrams per liter at a well in Chicot County. The areas of high chloride concentrations generally coincide with areas of high specific conductance.

Arkansas↗
USGS2002

Ground-water quality in the West Salt River Valley, Arizona, 1996–98 — Relations to hydrogeology, water use, and land use

The U.S. Geological Survey collected and analyzed ground-water samples in the West Salt River Valley from 64 existing wells selected by a stratified-random procedure. Samples from an areally distributed group of 35 of these wells were used to characterize overall ground-water quality in the basin-fill aquifer. Analytes included the principal inorganic constituents, trace constituents, pesticides, and volatile organic compounds. Additional analytes were tritium, radon, and stable isotopes of hydrogen and oxygen. Analyses of replicate samples and blank samples provided evidence that the analyses of the ground-water samples were adequate for interpretation. The median concentration of dissolved solids in samples from the 35 wells was 560 milligrams per liter, which exceeded the U.S. Environmental Protection Agency Secondary Maximum Contaminant Level for drinking water. Eleven of the 35 samples had a nitrate concentration (as nitrogen) that exceeded the U.S. Environmental Protection Agency Maximum Contaminant Level for drinking water of 10 milligrams per liter. Pesticides were detected in eight samples; concentrations were below the Maximum Contaminant Levels. Deethylatrazine was most commonly detected. The pesticides were detected in samples from wells in agricultural or urban areas that have been irrigated. Concentrations of all trace constituents, except arsenic, were less than the Maximum Contaminant Levels. The concentration of arsenic exceeded the Maximum Contaminant Level of 50 micrograms per liter in two samples. Nine monitoring wells were constructed in an area near Buckeye to assess the effects of agricultural land use on shallow ground water. The median concentration of dissolved solids was 3,340 milligrams per liter in samples collected from these wells in August 1997. The nitrate concentration (as nitrogen) exceeded the Maximum Contaminant Level (10 milligrams per liter) in samples from eight of the nine monitoring wells in August 1997 and again in February 1998. Analyses of all samples collected from the monitoring wells indicated low concentrations of pesticides and volatile organic compounds. The most frequently detected pesticides were deethylatrazine and atrazine. Trichloromethane (chloroform) and tetrachloroethene (PCE) were the most frequently detected volatile organic compounds in the monitoring wells. Two compounds [dieldrin and 1,1-dichloro-2,2-bis(p-dichlorodiphenyl)ethylene (DDE)], decomposition products of two banned pesticides, aldrin and dichlorodiphenylethylene (DDT), were detected at low concentrations in samples analyzed for the agricultural land-use study. In the West Salt River Valley, a high concentration of the heavier oxygen isotope?oxygen-18?in ground water generally indicates effects of evaporation on recharge water from irrigation. Wells in undeveloped areas and wells that have openings beneath a confining bed generally yield ground water that is free of the effects of irrigation seepage. Samples from these wells did not contain detectable concentrations of pesticides. The median concentrations of nitrate (as nitrogen) and dissolved solids in samples from wells in undeveloped areas were 1.7 milligrams per liter and 257 milligrams per liter, respectively. The median concentrations of nitrate (as nitrogen) and dissolved solids in samples from wells that yield water from below confining beds were 2.0 and 747 milligrams per liter, respectively.

Arizona↗
USGS2001

Evaluation of water-level recovery, 1996-97 to 1999-2000, and comparison of 1999-2000 and 1972-73 water levels in Goleta Central subbasin, Santa Barbara County, California

Ground-water levels were measured during January 1999-June 2000 to evaluate the rate of water-level recovery in the Goleta Central ground-water subbasin that has resulted from injection of about 2,225 acre-feet of surplus water for storage in the ground-water basin. Injection of surplus water was tabulated and compared with water-level rises since 1996 to evaluate the effectiveness of the recharge effort. Water levels have risen about 4 to 37 feet since 1996-97. A preliminary water budget was compiled to assess recharge and discharge in the basin, and it is estimated that total inflow exceeded total outflow during 1998-99 by about 2,844 to 7,518 acre-feet. In addition, water levels for 1999-2000 were compared with water levels for 1972-73 to determine if a 'drought buffer' exists. Water levels measured in two wells during January 1999-June 2000 exceeded January 1972-June 1973 levels. Water levels in the remaining wells measured during January 1999-June 2000 ranged from less than 1 foot to about 32 feet below 1972-73 water levels. In general, the largest water-level rise between 1996-97 and 1999-2000 was about 37 feet in the southeastern end of the basin; the rise was less than 4 feet in the western end of the basin and about 10 feet north of the Goleta Fault. Long-term hydrographs indicate that water levels have been recovering throughout the basin since the early 1990's.

California↗
USGS2001

Geochemistry of the Madison and Minnelusa aquifers in the Black Hills area, South Dakota

The Madison and Minnelusa aquifers are two of the most important aquifers in the Black Hills area because of utilization for water supplies and important influences on surface-water resources resulting from large springs and streamflow- loss zones. Examination of geochemical information provides a better understanding of the complex flow systems within these aquifers and interactions between the aquifers. Major-ion chemistry in both aquifers is dominated by calcium and bicarbonate near outcrop areas, with basinward evolution towards various other water types. The most notable differences in major-ion chemistry between the Madison and Minnelusa aquifers are in concentrations of sulfate within the Minnelusa aquifer. Sulfate concentrations increase dramatically near a transition zone where dissolution of anhydrite is actively occurring. Water chemistry for the Madison and Minnelusa aquifers is controlled by reactions among calcite, dolomite, and anhydrite. Saturation indices for gypsum, calcite, and dolomite for most samples in both the Madison and Minnelusa aquifers are indicative of the occurrence of dedolomitization. Because water in the Madison aquifer remains undersaturated with respect to gypsum, even at the highest sulfate concentrations, upward leakage into the overlying Minnelusa aquifer has potential to drive increased dissolution of anhydrite in the Minnelusa Formation. Isotopic information is used to evaluate ground-water flowpaths, ages, and mixing conditions for the Madison and Minnelusa aquifers. Distinctive patterns exist in the distribution of stable isotopes of oxygen and hydrogen in precipitation for the Black Hills area, with isotopically lighter precipitation generally occurring at higher elevations and latitudes. Distributions of 18O in ground water are consistent with spatial patterns in recharge areas, with isotopically lighter 18O values in the Madison aquifer resulting from generally higher elevation recharge sources, relative to the Minnelusa aquifer. Three conceptual models, which are simplifications of lumped-parameter models, are considered for evaluation of mixing conditions and general ground-water ages. For a simple slug-flow model, which assumes no mixing, measured tritium concentrations in ground water can be related through a first-order decay equation to estimated concentrations at the time of recharge. Two simplified mixing models that assume equal proportions of annual recharge over a range of years also are considered. An ?immediate-arrival? model is used to conceptually represent conditions in outcrop areas and a ?time-delay? model is used for locations removed from outcrops, where delay times for earliest arrival of ground water generally would be expected. Because of limitations associated with estimating tritium input and gross simplifying assumptions of equal annual recharge and thorough mixing conditions, the conceptual models are used only for general evaluation of mixing conditions and approximation of age ranges. Headwater springs, which are located in or near outcrop areas, have the highest tritium concentrations, which is consistent with the immediate-arrival mixing model. Tritium concentrations for many wells are very low, or nondetectable, indicating general applicability of the timedelay conceptual model for locations beyond outcrop areas, where artesian conditions generally occur. Concentrations for artesian springs generally are higher than for wells, which indicates generally shorter delay times resulting from preferential flowpaths that typically are associated with artesian springs. In the Rapid City area, a distinct division of isotopic values for the Madison aquifer corresponds with distinguishing 18O signatures for nearby streams, where large streamflow recharge occurs. Previous dye testing in this area documented rapid ground-water flow (timeframe of weeks) from a streamflow loss zone to sites located several miles away. These results are used to ill

Water-Resources Investigations Report↗
USGS2001

Nitrate concentrations, 1936-99, and pesticide concentrations, 1990-99, in the unconfined aquifer in the San Luis Valley, Colorado

The first documented analysis of nitrate concentrations for ground water in the unconfined aquifer was done in 1936. This valleywide investigation indicated that nitrate concentrations were 0.3 milligram per liter or less in water-quality samples from 38 wells completed in the unconfined aquifer. A valleywide study conducted in the late 1940's documented the first occurrences of nitrate concentrations greater than 3 mg/L. Up to this time, soil fertility was maintained primarily through the use of cattle and (or) sheep manure and crop rotation. Subsequent valleywide studies have documented several occurrences of elevated nitrate concentrations in the unconfined aquifer in a localized, intensively cultivated area north of the Rio Grande. The nitrate concentrations in water appear to have changed in response to increasing use of commercial inorganic fertilizers after the mid-1940's. A 1993 valleywide study evaluated the potential health risk associated with elevated nitrate concentrations in domestic water supplies. Water-quality samples from 14 percent of the wells sampled contained nitrate concentrations greater than 10 milligrams per liter. Most of the samples that contained concentrations greater than 10 milligrams per liter were collected from wells located in the intensively cultivated area north of the Rio Grande. During the 1990's, several local, small-scale, and field-scale investigations were conducted in the intensively cultivated area north of the Rio Grande. These studies identified spatial and temporal variations in nitrate concentration and evaluated the effectiveness of using shallow monitoring wells to determine nitrate leaching. Variations in nitrate concentration were attributed, in part, to seasonal recharge of the aquifer by surface water with low nitrate concentrations. Shallow monitoring wells were effective for determining the amount of nitrate leached, but because of the amount of residual nitrate in the soil from previous seasons, were ineffective in evaluating variations in the amount of nitrate leaching associated with differences in application rates. It was concluded that irrigation practices have the greatest effect on leaching of nitrate to the aquifer. Management tools, such as irrigation scheduling, center-pivot sprinkler systems, soil and ground-water nitrogen credits, and cultivation of cover and winter crops, are being used to help maintain crop quality and yields while minimizing the potential of leaching and reducing residual nitrogen left in the soil. Review of available data from previous studies indicates that most of the sampled wells with elevated nitrate concentrations are located in the intensively cultivated area north of the Rio Grande. This area represents about 10 percent of the San Luis Valley and approximately 35 percent of the crop and pasture land in the valley. The area where nitrate concentrations exceed the U.S. Environmental Protection Agency drinking water maximum contaminant level represents about 150 square miles or 5 percent of the valley. Aquifer vulnerability to and contamination by pesticides was not evaluated until the 1990's. Risk analyses indicated that selected pesticides can pose a contamination threat to an unconfined aquifer in areas consisting primarily of sandy loam soil; sandy loam soils are common in the San Luis Valley. Water-quality samples collected from some wells during 1990 and 1993 indicated trace- to low-level pesticide contamination. The occurrence of pesticides was infrequent and isolated.

Water-Resources Investigations Report↗