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At least 865 records · Page 48Linked to original sources
USGS2003

Conjunctive-use optimization model of the Mississippi River Valley alluvial aquifer of Southeastern Arkansas

The Mississippi River Valley alluvial aquifer is a water-bearing assemblage of gravels and sands that underlies about 32,000 square miles of Missouri, Kentucky, Tennessee, Mississippi, Louisiana, and Arkansas. Because of the heavy demands placed on the aquifer, several large cones of depression have formed in the potentiometric surface, resulting in lower well yields and degraded water quality in some areas. A ground-water flow model of the alluvial aquifer was previously developed for an area covering 3,826 square miles, extending south from the Arkansas River into the southeastern corner of Arkansas, parts of northeastern Louisiana, and western Mississippi. The flow-model results indicated that continued ground-water withdrawals at rates commensurate with those of 1997 could not be sustained indefinitely without causing water levels to decline below half the original saturated thickness of the aquifer. Conjunctive-use optimization modeling was applied to the flow model of the alluvial aquifer to develop withdrawal rates that could be sustained relative to the constraints of critical ground-water area designation. These withdrawal rates form the basis for estimates of sustainable yield from the alluvial aquifer and from rivers specified within the alluvial aquifer model. A management problem was formulated as one of maximizing the sustainable yield from all ground-water and surface-water withdrawal cells within limits imposed by plausible withdrawal rates, and within specified constraints involving hydraulic head and streamflow. Steady-state conditions were selected because the maximized withdrawals are intended to represent sustainable yield of the system (a rate that can be maintained indefinitely).One point along the Arkansas River and one point along Bayou Bartholomew were specified for obtaining surface-water sustainable-yield estimates within the optimization model. Streamflow constraints were specified at two river cells based on average 7-day low flows with 10-year recurrence intervals. Sustainable-yield estimates were affected by the allowable upper limit on withdrawals from wells specified in the optimization model. Withdrawal rates were allowed to increase to 200 percent of the withdrawal rate in 1997. As the overall upper limit is increased, the sustainable yield generally increases. Tests with the optimization model show that without limits on pumping, wells adjacent to sources of water, such as large rivers, would have optimal withdrawal rates that were orders of magnitude larger than rates corresponding to those of 1997. Specifying an upper withdrawal limit of 100 percent of the 1997 withdrawal rate, the sustainable yield from ground water for the entire study area is 70.3 million cubic feet per day, which is about 96 percent of the amount withdrawn in 1997 (73.5 million cubic feet per day). If the upper withdrawal limit is increased to 150 percent of the 1997 withdrawal rate, the sustainable yield from ground water for the entire study area is 80.6 million cubic feet per day, which is about 110 percent of the amount withdrawn in 1997. If the upper withdrawal limit is increased to 200 percent of the 1997 withdrawal rate, the sustainable yield from ground water for the entire study area is 110.2 million cubic feet per day, which is about 150 percent of the amount withdrawn in 1997. Total sustainable yield from the Arkansas River and Bayou Bartholomew is about 4,900 million cubic feet per day, or about 6,700 percent of the amount of ground-water withdrawn in 1997. The large, sustainable yields from surface water represent a potential source of water that could supplement ground water and meet the total water demand. Unmet demand (defined as the difference between the optimized withdrawal rate or sustainable yield, and the anticipated demand) was calculated using different demand rates based on multiples of the 1997-withdrawal rate. Assuming that demand is the 1997 withdrawal rate, and that sustainable-

Water-Resources Investigations Report↗
USGS2004

Evaluation of the Feasibility of Freshwater Injection Wells in Mitigating Ground-Water Quality Degradation at Selected Well Fields in Duval County, Florida

The Fernandina permeable zone contains brackish water in parts of Duval County, Florida. Upward flow from the Fernandina permeable zone to the upper zone of the Lower Floridan aquifer increases chloride concentrations in ground water in parts of Duval County. Numerical models of the ground-water flow system in parts of Duval, St. Johns, and Clay Counties, Florida, were used to (1) estimate the vertical flows between the low-quality water of the Fernandina permeable zone and the high-quality water of the upper zone of the Lower Floridan aquifer in the vicinity of Deerwood 3 and Brierwood well fields, based on 2000 ground-water withdrawal rates; (2) determine how such vertical flows change as several scenarios of injection, withdrawal, and intervening rest periods are simulated in the two well fields; and (3) evaluate the effects of changes in less certain hydraulic parameters on the vertical flows between the Fernandina permeable zone and the upper zone of the Lower Floridan aquifer. The ground-water flow system was simulated with a four-layer model using MODFLOW-2000, which was developed by the U.S. Geological Survey. The first layer consists of specified-head cells simulating the surficial aquifer system with prescribed water levels. The second layer simulates the Upper Floridan aquifer. The third and fourth layers simulate the upper zone of the Lower Floridan aquifer and the Fernandina permeable zone, respectively. Average flow conditions in 2000 were approximated with a steady-state simulation. The changes in upward flow from the Fernandina permeable zone due to periods of injections and withdrawals were analyzed with transient simulations. The grid used for the ground-water flow model was uniform and composed of square 250-foot cells, with 400 columns and 400 rows. The active model area encompasses about 360 square miles in parts of Duval, St. Johns, and Clay Counties, Florida. Ground-water flow simulation was limited vertically to the bottom of the Fernandina permeable zone. The steady-state ground-water flow model was calibrated using time-averaged 2000 heads at 20 control points. Environmental-water heads in the Fernandina permeable zone were calculated for wells with variable water density. Transmissivity of the Upper Floridan aquifer, the upper zone of the Lower Floridan aquifer, and the Fernandina permeable zone, and the leakance of the intermediate confining unit, the middle semiconfining unit, and the semiconfining unit were obtained from regional ground-water flow models and adjusted until a reasonable fit between simulated and computed heads was obtained. The calibrated hydraulic properties from the steady-state ground-water flow model, and the calibrated storage coefficient from the transient model, were used to simulate hypothetical transient scenarios of injection, withdrawal, and intervening rest periods to assess changes in flow between the Fernandina permeable zone and the upper zone of the Lower Floridan aquifer. Based on the simulated flows between the Fernandina permeable zone and the upper zone of the Lower Floridan aquifer and the 18 million gallons per day of water available for injection, the reversal of the prevailing upward flow from the Fernandina permeable zone was not achieved. However, steady-state and transient simulations indicate that the upward flow of water from the Fernandina permeable zone could be reduced by as much as 64 percent, from 0.11 to 0.04 cubic foot per second, if only injection periods are simulated.

Water-Resources Investigations Report↗
USGS1974

Limnological study of Lake Shastina, Siskiyou County, California

Lake Shastina provides water for irrigation in Shasta Valley, as well as recreation. Presently, its shoreline is being developed for summer homes. Surface water constituted more than 90 percent of the approximately 50,000 acre-foot (62-cubic hectometre) inflow to Lake Shastina in the 1972 water year. Controlled outflow is via the Montague Main Canal; however, leakage from the lake through volcanic rocks to the northwest was estimated to be greater than the measured outflow. Appreciable annual changes in the quantity of water in storage in the lake are related mainly to variations in annual inflow. From June through August the lake was thermally stratified. In the spring and summer the epilimnion was often supersaturated with oxygen, while at the same time the hypolimnion was undersaturated and 'often devoid of dissolved oxygen. Vertical stratification of carbon dioxide, carbonate, bicarbonate, hydrogen ion, nitrogen, and phosphorus was also recorded during the spring and summer. Orthophosphate, total phosphorus, and total nitrogen concentrations (organic, ammonium, and nitrate) were highest in the hypolimnion during the period of thermal stratification. Ten-inch (25-centimetre) core samples from the reservoir bottom were chemically analyzed at 0.8-inch (2-centimetre) intervals. The concentrations ranged from 6.3 to 28.9 milligrams per gram of iron, 0.07 to 0.43 milligrams per gram of manganese, 0.4 to 2.7 milligrams per gram of organic nitrogen plus ammonium, and 0.06 to 1.3 milligrams per gram of total phosphorus. Organic matter in the cores ranged from 4 to 14 percent. Green algae and diatoms were the dominant algal types, reaching maximum concentrations of about 7 and 30 million cells per litre, respectively. These phytoplankton occurred near the surface during thermally stratified periods, but were distributed at greater depths during nonthermally stratified periods. Blue-green algae were present only in the spring samples, and reached a maximum concentration of about 5 million cells per litre. Zooplankton numbers were greatest in March, July, and September, with lesser concentrations in June. Three major zooplankton groups, Cladocera, Copepoda, and Rotifera, were present. The major groups of benthic organisms were Oligochaeta, Chironomidae, and Chaoborus, with numbers ranging from 3350, 890, and 8450 per square metre, respectively. A discussion on algal control is included.

California↗
USGS1980

The effects of using ground water to maintain water levels of Cedar Lake, Wisconsin

Cedar Lake, a kettle lake with no surface inlet or outlet, was studied to evaluate the feasibility of maintaining water levels of lakes in the glaciated kettle moraine area of eastern Wisconsin by pumping ground water into them. The general hydrogeology of the area around the lake was defined and the hydrology of the lake was studied in detail. There are two aquifer systems in the Cedar Lake area, and in general, throughout eastern Wisconsin. The shallow aquifer system is composed of unconsolidated glacial drift of Quaternary age and consolidated bedrock of Silurian age. Cedar Lake is located in a local recharge area within this system. The saturated thicknesses of the glacial drift and Silurian dolomite beneath the lake are approximately 100 feet and 500 feet, respectively. This aquifer system is separated from an underlying aquifer system by a layer of shale approximately '200 feet thick that forms an effective barrier to water movement. The deep aquifer system is composed of dolomites and sandstones of Ordovician and Cambrian age whose composite thickness is 600 to 650 feet. A water budget was prepared to quantify the components of the hydrologic system of Cedar Lake. Inflow to the lake averaged approximately ^5 inches per water year for the 2-year period October 197^ through September 1976. Inflow consisted of precipitation on the lake surface (28 inches), groundwater seepage to the lake (2 inches), and overland flow (15 inches) to the lake. Outflow averaged approximately U9 inches per year for the same 2- year period. Outflow consisted of evaporation (31 inches) from the lake surface and ground-water seepage from the lake (18 inches). A volume of water equivalent to that needed to raise the lake level 1*7 inches was pumped from the shallow aquifer system into Cedar Lake between February 1 and September 30, 1977. The water budget for the lake during this period indicated that approximately 90 percent of pumped water was either recycled from the lake to the well or otherwise lost as seepage from the lake. Selected physical and chemical characteristics of the lake water were measured periodically between October 197^ and September 1977- The water temperature ranged between 26°C in August to approximately 2°C in December during each year of the study. The dissolved-oxygen concentration of the water ranged from 13 milligrams per liter at the time ice cover first developed in December to h milligrams per liter at the time ice cover broke up the following April. The total nitrogen concentration of the water varied from 1.0 milligrams per liter during winter to 0.5 milligrams per liter during summer. The total phosphorus concentration of the water was fairly uniform throughout the year, averaging 0.01 milligrams per liter. The phytoplankton population was sampled periodically. The total phytoplankton count was small during winter, generally less than 250 cells per milliliter. These phytoplankton were composed of euglenoids, diatoms, green algae, and blue-green algae. The count increased to 50,000 to 100,000 cells per milliliter during summer. One or two species of blue-green algae dominated during these times. There were no identifiable changes in measured physical and chemical characteristics of lake water during sustained pumping of ground water into the lake, nor were there identifiable changes in the number or makeup of the phytoplankton community. Differences in physical and chemical characteristics of lake water and ground water added to the lake probably were not great enough to cause changes within the lake.

Wisconsin↗
USGS1982

Algal conditions in the Caloosahatchee River (1975-79), Lake Okeechobee to Franklin Lock, Florida

Maximum numbers of suspended algae occurred in late spring and early summer, in each of the years 1975-79, in the Caloosahatchee River. Numbers exceeded 100,000 cells per milliliter at all stations sometime during the study. Concentrations decreased during late summer and autumn and were low during winter, except in January 1979 when numbers at most sites exceeded 100,000 cells per milliliter. The January 1979 bloom coincided with large discharges from Lake Okeechobee. During previous winters, discharges and algal numbers were lower. During other seasons, algal blooms occurred most frequently under low-flow or stagnant conditions. The upstream site at Moore Haven, which had the least discharge and was most stagnant, had consistently higher algal concentrations than downstream sites. Blue-green algae were dominant in the river during the summer at the upstream site throughout the year. The percentage of blue-green algae decreased downstream. Concentrations of nitrite plus nitrate nitrogen were inversely correlated with concentrations of algae and decreased to near zero during algal blooms. The low concentrations of these forms of inorganic nitrogen relative to other major nutrients probably favor blue-green algae and limit growth of other algae. Contributions by the basin tributaries to the nutritive condition of the river were small because concentrations of nutrients, algal growth potential, and algae in the tributaries were generally less than those in the river. (USGS)

Florida↗
USGS1985

Ground-water flow in the Prairie du Chien-Jordan aquifer related to contamination by coal-tar derivatives, St. Louis Park, Minnesota

A three-dimensional, ground-water-flow model of the Prairie du Chien-Jordan aquifer and associated hydrogeologic units was developed to evaluate the movement of coal-tar derivatives from a coal-tar distillation and wood-preserving plant in St. Louis Park, Minnesota. A finite-difference grid was superimposed on the modeled area, which includes most of eastern Hennepin County. The individual cells are 400-foot squares in the center of the grid (St. Louis Park area); the cells increase in dimension toward the outside limits of the grid. Five geologic units are represented by four layers in the model. These units include the Jordan Sandstone, the Prairie du Chien Group (dolomite and sandy dolomite), the basal confining unit of the St. Peter Sandstone (silty and sandy shale), the St. Peter Sandstone, and glacial deposits in bedrock valleys. The model was calibrated for steady-state conditions for a period before significant ground-water development (1885-1930) and for a period of significant pumping stress (winter conditions, 1970 fs). A transient calibration was accomplished by simulation of a period during which seasonal changes in potentiometric head in the Prairie du Chien-Jordan aquifer were significant (1977-80). Sensitivity testing indicated that leakage to the upper model layer and the vertical hydraulic conductivity of the basal confining unit of the St. Peter Sandstone were the model hydrologic properties which, when changed, resulted in the greatest changes in model-calculated water levels. The calibrated model generally calculates water levels that are within 10 feet of measured values. Model simulations indicate that the potentiometric surface of the Prairie du Chien-Jordan aquifer would be raised by as much as 3 feet in the area of the plant site by water introduced into the aquifer through wells open to more than one aquifer system. The cones of impression created at these wells could have a significant impact on the transport of contaminants in the Prairie du Chien-Jordan. The presence of coal-tar derivatives in the aquifer has been difficult to explain in wells located upgradient from the plant site to the north, west, and southwest. Simulations suggest that, during periods of heavy withdrawal from certain of these wells (SLP10, SLP15, and SLP5), local hydraulic gradients may have been altered, resulting in the potential for the movement of contaminants from the area of the plant site to the wells. Cones of impression at multiaquifer wells near the plant site contributed to the alteration of local gradients. Simulation of a proposed gradient-control plan, in which lateral homogeneity and isotropy of individual hydro geologic units was assumed, indicates that the actions would be effective in limiting expansion of the contaminated volume in the Prairie du Chien-Jordan aquifer. The plan includes the control of withdrawal from five wells. The simulations also show, however, that modelcalculated potentiometric surfaces are sensitive to changes in withdrawal rates at wells not intended to be under the control of the plan. Management of discharge from these wells also will be important to overall effectiveness of the remedial-action plan.

Minnesota↗
USGS1990

Computerized stratified random site-selection approaches for design of a ground-water-quality sampling network

Computer software was written to randomly select sites for a ground-water-quality sampling network. The software uses digital cartographic techniques and subroutines from a proprietary geographic information system. The report presents the approaches, computer software, and sample applications. It is often desirable to collect ground-water-quality samples from various areas in a study region that have different values of a spatial characteristic, such as land-use or hydrogeologic setting. A stratified network can be used for testing hypotheses about relations between spatial characteristics and water quality, or for calculating statistical descriptions of water-quality data that account for variations that correspond to the spatial characteristic. In the software described, a study region is subdivided into areal subsets that have a common spatial characteristic to stratify the population into several categories from which sampling sites are selected. Different numbers of sites may be selected from each category of areal subsets. A population of potential sampling sites may be defined by either specifying a fixed population of existing sites, or by preparing an equally spaced population of potential sites. In either case, each site is identified with a single category, depending on the value of the spatial characteristic of the areal subset in which the site is located. Sites are selected from one category at a time. One of two approaches may be used to select sites. Sites may be selected randomly, or the areal subsets in the category can be grouped into cells and sites selected randomly from each cell.

Water-Resources Investigations Report↗
USGS1990

A method to estimate canal leakage to the Biscayne Aquifer, Dade County, Florida

The leakage characteristics of channels that partially penetrate the Biscayne aquifer and have reduced bed permeability were studied. Leakage characteristics were described in terms of a reach transmissivity-defined as the volume flow rate out of the channel per unit length of the channel per unit drawdown, where drawdown is defined as the difference in altitude between the water surface in the canal and the water table in the adjacent aquifer. A theoretical expression was developed to relate the reach transmissivity to the transmissivity of the formation, mean channel width, distance of drawdown measurement from the channel centerline, ratio of drawdowns on both sides of the channel, and local reach transmissivity associated with reduced bed permeability. This theoretical expression was verified using a fine-scale numerical model, which gave accurate results when drawdowns were measured beyond 10 aquifer depths from the side of the channel. Using the theoretical formulation, it is shown that the reach transmissivity employed in regional ground-water models, which are based on average drawdowns within a cell, depends on the size of the cell as well as the transmissivity of the formation, channel width, and local reach transmissivity due to reduced bed permeability. The theoretical reach transmissivity function was compared with field measurements at L-31N Canal and Snapper Creek Extension Canal in Dade County, Florida. Analyses of the data for both canals showed good agreement between the estimated and measured reach transmissivities. At L- 31N Canal, field measurements indicated that the local reach transmissivity was relatively uniform over a 2-mile reach of the channel (averaging 630 cubic feet per second per mile per foot), and the formation transmissivity was 1.8 x106 feet squared per day. At Snapper Creek Extension Canal, an approximate analysis was necessary due to the inability of the acoustic velocity meter to measure very low water velocities in the channel. Assuming an aquifer transmissivity of 1 x 106 feet squared per day, drawdown measurements indicated that the local reach transmissivity was about 400 cubic feet per second per mile per foot. The theoretical relation, combined with the local reach transmissivity and formation transmissivity, was sufficient to predict the leakage out of L-31N Canal and Snapper Creek Extension Canal for any drawdown scenario.

Florida↗
USGS1993

Hydrology and water quality of Wind Lake in southeastern Wisconsin

The hydrology and water quality of Wind Lake-a recreational lake in a densely populated area of southeastern Wisconsin was studied from October 1, 1987 through September 30,1989. A drought in 1988 affected the hydrologic budget of Wind Lake in water years 1988-89. Precipitation was 5.9 inches less than normal in water year 1988 but was 2.3 inches greater than normal in water year 1989. Streamflows were near normal in water year 1988 and 25 percent less than normal in water year 1989 as indicated by data from a nearby streamflow-gaging station. Surface runoff was the dominant source of water to the lake in water year 1988 and 75 percent of the inflow was from Big Muskego Lake. The water level in Big Muskego Lake was 1.1 feet below the dam crest at the start of the 1989 water year because of the 1988 drought. About 2,510 acre-feet of water had to fill Big Muskego Lake before water could discharge to Wind Lake. In water year 1989, surface runoff was still the dominant source of water to the lake, but Big Muskego Lake only contributed 52 percent of the water inflow. Streamflow dominated the outflow budget for both years. In water year 1988, 88 percent of the outflow budget left by way of Wind Lake outlet and 12 percent evaporated from the lake surface. In water year 1989, 81 percent of the outflow budget left by way of Wind Lake outlet and 19 percent evaporated from the lake surface. On the basis of outflow from Wind Lake for water year 1988, the hydraulic residence time was 0.46 year; in water year 1989 it was 1.05 years. The total phosphorus input to Wind Lake from external sources was the same for both years, 3,160 pounds. The largest percentage of the phosphorus load came from Big Muskego Lake-- 70 percent in water year 1988 and 65 percent in water year 1989. Analysis of data by use of Vollenweider's model indicates that the phosphorus loadings for each year would cause eutrophic conditions. Data from a nearby gaging station indicate that phosphorus loading to Wind Lake was less than normal. Phosphorus retention in the lake is small and averages 14 percent of the incoming load for both years. Oxygen depletion occurs in the bottom waters during winter and summer months. A maximum anoxic zone was reached on July 18, 1988, when depths greater than 15 feet (about 21 percent of the lake bottom area) were anoxic. Total phosphorus concentrations at the lake surface for both years ranged from 11 to 78 micrograms per liter. Mean total phosphorus concentrations in June, July, and August that had averaged 49 micrograms per liter in 1985 through 1987 declined to 20 micrograms per liter in water year 1988 and 22 micrograms per liter in water year 1989. This reduction was related to the drought and reduced phosphorus loadings. Phosphorus concentrations 1.5 feet above the lake bottom increase during summer anoxic periods. The phosphorus concentration increased at a rate of 5.2 and 4.8 micrograms per liter per day for total and dissolved orthophosphate phosphorus. A maximum concentration of 760 micrograms per liter of total phosphorus and 650 micrograms per liter of dissolved orthophosphate phosphorus occurred on September 21, 1988, just before autumn turnover. Internal loading of phosphorus for the period October 15, 1987 through October 14, 1988, was estimated to be 2,890 pounds. This represents 48 percent of the combined internal and external total-phosphorus input of 5,960 pounds. Algal populations in water year 1988 ranged from 28,200 to 1,610,000 cells per milliliter. A total of 143 species were identified. Blue-green algae dominated the algal population and ranged from 56 percent (February 16, 1988) to 99 percent (five other sampling dates). Aphanocapsa delicatissima caused the largest algal bloom, which reached a maximum concentration of 934,000 cells per milliliter (September 7, 1988). Zooplankton populations in water year 1988 ranged from 52.5 to 686 organisms per liter. Eighteen species were identified. The cladoceran, Daphnia, dominated 12 of the 18 samples.

Wisconsin↗
USGS1994

Identification of potential public water-supply areas of the Cape Cod aquifer, Massachusetts, using a geographic information system

Potential public water-supply areas of the Cape Cod aquifer, Massachusetts, were identified using a geographic information system (GIS) to aid regional and local ground-water resource management efforts. Criteria were selected to identify potential areas on the basis of data restrictions in addition to State requirements for siting new public water- supply wells, Federal or local restrictions on land use, and general hydrogeologic or water-quality concerns. Data layers were created for each criterion and overliad to eliminate areas from consideration as potential public water supplies. Remaining areas, those not included within the applied criteria, are the primary areas to consider for potential public water supplies. The areas identified in this analysis as potential public water supplies range from 0.5 to 7.9 percent of the individual flow cells, or 5.6 percent of the total flow cell area. The criteria were ranked so that criteria more limiting to potential public water supplies were given a higher rank than other criteria. The ranking scheme allows for the inclusion of areas with lower ranked criteria as potential public water supplies. Results can be viewed on a plat in this report, or accessed using the map-based, menu-driven GIS application, which provides interactive display and query of investigation results.

Water-Resources Investigations Report↗
USGS1996

Hydrologic and chemical interaction of the Arkansas River and the Equus Beds aquifer between Hutchinson and Wichita, south-central Kansas

Large chloride concentrations in Arkansas River water have the potential to degrade water quality in the adjacent Equus beds aquifer between Hutchinson and Wichita, Kansas. The aquifer is an important source of water for municipal, industrial, agricultural, and domestic uses. A three-dimensional, finite-difference, ground-water flow-model program (MODFLOW) was used with data from past studies and data collected during 1988-91 to simulate aquifer and stream conditions during the late 1930's, during 1940-89, and during 1990-2019. Results of ground-water flow-model simulations indicated that declining water levels in the Equus beds aquifer since the 1940's have caused base flow in the Arkansas and Little Arkansas Rivers to decrease. In 1940, the Arkansas and Little Arkansas Rivers had simulated net base-flow gains within the model area of about 21 and about 67 ft 3 /s (cubic feet per second), respectively. By the end of 1989, the Arkansas River had a simulated net base-flow loss of about 52 ft 3 /s, and the Little Arkansas River had a net base-flow gain of about 27 ft 3 /s. Simulations for 1990-2019 showed that the water-level changes in a selected model cell located in the central part of the Wichita well field could range from -0.2 to -78 feet. Waterlevel changes in a selected model cell located near the Arkansas River could range from +1.3 to -1.2 feet. In model simulations where only pumpage varied, net base-flow loss from the Arkansas River to the aquifer ranged from about 59 ft 3 /s (no increase in pumpage since 1989) to 117 ft 3 /s (a 3-percent per year increase in pumpage since 1989) by 2019. Assuming a chloride concentration of 630 milligrams per liter, the median concentration in Arkansas River water collected during 1988-91, the quantity of chloride discharged from the Arkansas River to the aquifer was estimated to have increased from about 21 tons per day in 1940 to about 100 tons per day in 1989. By 2019, chloride discharge was indicated to range from about 110 tons per day (associated with no increase in pumpage since 1989) to 200 tons per day (associated with a 3-percent per year increase in pumpage since 1989). A particle-tracking program (MODPATH), which used the results from the flow model, was used to simulate the distribution in the aquifer of chloride from the river during the same time periods. Particle-tracking simulations show that, during 1940-89, the simulated distribution of particles representing chloride from the Arkansas River expanded from relatively narrow bands near the river to a wider distribution within the aquifer and the Wichita well field. Particle-tracking simulations indicate that chloride discharge from the Arkansas River may have reached the edge of the Wichita well field as early as 1963.

Kansas↗
USGS2001

Benthic algae of benchmark streams in agricultural areas of eastern Wisconsin

Benthic algae were collected from 20 streams in the Western Lake Michigan Drainages by the U.S. Geological Survey in May and June of 1993 as part of the National Water-Quality Assessment program. These streams were selected to represent "benchmark" streams that were minimally affected by human activities, especially agriculture, for comparison to other streams in similar environmental settings. Streams were chosen from four relatively homogeneous units (RHU's) in agricultural areas with differing texture of surficial deposits and bedrock type. Blue-green algae were the dominant algal cells at all but 5 of the 20 stream sites, and the most abundant species at these sites was Calothrix parietina, a nitrogen-fixer typically found in pristine streams. Most of the taxa at all sites were diatoms. The dominant diatom guilds observed were the Achnanthes spp., erect forms, and Navicula spp. Except for three streams thought to have low productivity, the Shannon-Wiener diversity index for diatoms was high at all benchmark streams and indicated either minor stress or no stress on the diatom community. With regard to water quality, additional diatom indexes for 17 of 20 benchmark streams indicated no pollution effects and no significant siltation. All benchmark streams had good to excellent biological integrity and either minor or no impairment of aquatic life with regard to diatoms. A variety of algal metrics and relative abundances of diatom morphological guilds correlated with basin-, segment-and reach-level habitat characteristics, including drainage area, basin drainage density, basin soil permeability, Q/Q2 (instantaneous discharge measured at time of sampling divided by the estimated 2-year flood discharge), stream length, and average width of natural riparian vegetation. Algal taxa richness decreased with higher percentages of agricultural land and lower percentages of forested land. The relative abundance of pollution-tolerant diatoms was higher in streams where the basin land was primarily agricultural as compared to forested. The Shannon- Wiener diversity index for diatoms, the percentage of diatom taxa, and the percent relative abundances of diatom cells, pollution tolerant diatoms, Achnanthes spp., erect diatom forms, nitrogen-fixing algae, and blue-green algae differed significantly among either RHU's or ecoregions. Higher abundances of pollution-sensitive diatoms and a higher pollution index indicate that water quality in sampled streams in the North Central Hardwood Forests ecoregion may be less degraded than in streams in the Southeastern Wisconsin Till Plains ecoregion. Algal taxa richness decreased as specific conductance, dissolved nitrate plus nitrite, and suspended sediment increased. This relation may indicate a negative effect of agricultural activities on the algal taxa richness of the stream. Pollution-tolerant diatoms and the pollution index increased as these and additional factors correlated with agriculture increased. Multivariate analyses indicated multiple scales of environmental factors affect algae. Although two-way indicator species analysis (TWINSPAN), detrended correspondence analysis (DCA), and canonical correspondence analysis (CCA) generally separated sites according to RHU, only DCA ordination indicated a separation of sites according to ecoregion. Environmental variables con-elated with DCA axes 1 and 2 and therefore indicated as important explanatory factors for algal distribution and abundance were factors related to stream size, basin land use/cover, geomorphology, hydrogeology, and riparian disturbance. CCA analyses with a more limited set of environmental variables indicated that pH, average width of natural riparian vegetation (segment scale), basin land use/cover and Q/Q2 were the most important variables affecting the distribution and relative abundance of benthic algae at the 20 benchmark streams,

Wisconsin↗
USGS1996

Estimation of the recharge areas contributing water to the South Well Field, Columbus, Ohio

The city of Columbus, Ohio, operates four radial collector wells, designed to yield 42 Mgal/d (million gallons per day), in southern Franklin County, Ohio, as part of their municipal supply of water. The collector wells are adjacent to, and designed to induce infiltration from, Big Walnut Creek and Scioto River. A previously constructed, three-dimensional, steady-state and transient ground-water-flow model of this river-aquifer system was used to estimate contributing recharge areas (CRA's) and calculate particle flowpaths in southern Franklin County. The simulations were of two steady-state periods (October 1979 and March 1986) and one 5-year transient period (March 1986---June 1991). The first simulation (1979) was of conditions before construction of the collector wells. The second simulation (1986) was of conditions when the collector wells were producing 8 Mgal/d. During the 5 years covered in the transient simulation, production at the well field averaged 18.5 Mgal/d. Under the 1979 conditions, the largest ground-water contributing areas were of the quarries and Scioto River (41 and 47 percent of the study area, respectively). During 1986, when 8 Mgal/d was withdrawn, the primary contributing areas were of the quarries (40 percent), collector wells (34 percent), and rivers (8 percent). Travel times associated with simulated particles of water tracked from cells along Big Walnut Creek to their discharge points in cells along Scioto River were about 5 to 60 years in the 1979 simulation and about 7 to 41 years in the 1986 simulation. The endpoints of these particles varied as simulated pumping rates were increased to 22 Mgal/d. The 1986, 10-year CRA's of the collector wells under 8 Mgal/d-conditions totalled about 4.5 mi2. As the pumping rate was increased to 22 Mgal/d in a predictive simulation, 10-year CRA's of the collector wells increased to 6.7mi2. Because the transient simulation encompassed only 5 years, the 10-year CRA's could not be estimated from the transient simulation. However, the size of the 1- to 5-year CRA's for the transient simulation was similar to the size of the 1- to 5-year CRA's for a steady-state predictive simulation if well-field production were 16 Mgal/d. The transient simulations predicted discontinuous CRA's, especially adjacent to the rivers, due to changes in hydrologic stresses. Analyses of the steady-state and transient models showed that sizes of CRA's were most sensitive to changes in porosity, pumping rate, riverbed conductance, and horizontal hydraulic conductivity.

Ohio↗
USGS1997

Digital simulation of ground-water flow in the Warwick Aquifer, Fort Totten Indian Reservation, North Dakota

The demand for water from the Warwick aquifer, which underlies the Fort Totten Indian Reservation in northeastern North Dakota, has been increasing during recent years. Therefore, the Spirit Lake Sioux Nation is interested in resolving questions about the quantity and quality of water in the aquifer and in developing a water-management plan for future water use. A study was conducted to evaluate the surface-water and ground-water resources of the Fort Totten Indian Reservation and, in particular, the ground-water resources in the area of the Warwick aquifer. A major component of the study, addressed by this report, was to define the ground-water flow system of the aquifer. The Warwick aquifer consists of outwash deposits of the Warwick outwash plain that are as much as 30 feet thick and buried-valley deposits beneath the outwash plain that are as much as 200 feet thick. The aquifer is bounded on the north and west by end-moraine deposits and Devils Lake, on the south by the Sheyenne River Valley, and on the east by outwash deposits and ravines. The aquifer is underlain by Pierre Shale or by glacial till, clay, or silt. Ground-water gradients generally are small and rarely are more than 3 or 4 feet per mile. From 1982 to 1993, withdrawals from the Devils Lake well field averaged 1.5 cubic feet per second, and withdrawals from irrigation wells averaged 1.29 cubic feet per second. The combined discharge from springs may be about 3 cubic feet per second. During the early 1990s, the Warwick aquifer probably was in a steady-state condition with regard to storage change in the aquifer. A finite-difference, three-dimensional, ground-water flow model provided a reasonable simulation of ground-water flow in the Warwick aquifer. The aquifer was divided vertically into two layers and horizontally into a grid of 83 by 109 cells, each measuring 656 feet (200 meters) per side. The steady-state simulation was conducted using 1992 pumpage rates and October 1992 water levels. The mean absolute difference between simulated and derived water-level altitudes during final calibration of the model was 1.52 feet. The two transient simulations were conducted for 20 time intervals of 1 year each using both the small and large storage estimates, doubled 1992 pumpage from the Devils Lake well field, 1992 irrigation pumpage, and initial water-level altitudes simulated by the October 1992 steady-state simulation. In the simulation using the small storage estimate and doubled pumpage, model cells in the area of the well field went dry after 13 years. Assumptions made in the design of the model generally are supported by the digital simulation. Except in the area of Warwick Springs and smaller springs, lateral and basal boundaries of the aquifer are impermeable. The flow system is dominated by recharge and evapotranspiration. Recharge rates obtained during the calibration process were lower in topographically high areas than in topographically low areas. Hydraulic conductivity in the area of the Devils Lake well field was larger than that in the rest of the aquifer.

Water-Resources Investigations Report↗
USGS1997

Mesocosm experiments to assess factors affecting phosphorus retention and release in an extended Wisconsin wetland

Phosphorus retention by wetland sediments and vegetation was investigated in Jackson Creek wetland, an extension of an existing prairie marsh in southeastern Wisconsin. The extended wetland construction was undertaken in 1992-93 to help reduce the phosphorus loading to a downstream eutrophic lake. Two approaches were used to study potential and actual phosphorus retention in the system. Mesocosm experiments of 20-40 days duration indicated that retention of total and dissolved reactive phosphorus in mesocosm cells containing macrophytes and/or sediments was reduced by factors of 2-20 relative to cells containing only water or a copper algicide to suppress metabolic activity. In contrast to the nutrient trapping function, these results show a potential for net phosphorus release that can be associated with increased biological richness. Measurements of water flow and nutrient loads at the wetland's inflow and outflow points demonstrated 9-39% net uptake of phosphorus on an annual scale but frequent occurrences of net phosphorus release over shorter (one-month) time scales. These episodes of release are most likely during the summer months. Thus, the wetland role in phosphorus cycling is not one of a true source or sink, although the annual budget data alone suggest substantial net retention. Effective management of the wetland for its nutrient trapping potential can be hindered by this oversimplification. The system is instead subject to relatively short-term alternation between net import and export. The periodic phosphorus export, although representing a small fraction of net annual import, could be critical for growth of macrophyte and algal communities downstream.

Wisconsin↗
USGS1998

Hydrogeology and simulation of ground-water flow in the Paluxy aquifer in the vicinity of Landfills 1 and 3, U.S. Air Force Plant 4, Fort Worth, Texas

Ground-water contamination of the surficial terrace alluvial aquifer has occurred at U.S. Air Force Plant 4, a government-owned, contractor-operated facility, northwest of Fort Worth, Texas. A poorly constructed monitoring well, P–22M, open to the underlying middle zone of the Paluxy aquifer was installed at landfill 3, October 1987, allowing leakage of contaminated ground water to reach the Paluxy aquifer. This well was plugged and abandoned in November 1995. Additionally, volatile organic compounds have been detected in fractures in the Goodland-Walnut confining unit, the hydrogeologic unit separating the terrace alluvial aquifer from the underlying Paluxy aquifer, beneath the western part of landfill 1. Volatile organic compounds in concentrations near the analytical detection limit were detected in the upper Paluxy prior to the drilling of well P–22M. The ground-water-flow simulation model described in this report was developed to examine the best logistically feasible location to install recovery wells to capture the low concentration (less than 100 micrograms per liter) trichloroethylene plume beneath landfills 1 and 3 (west Paluxy plume). Once the recovery wells were installed (1996), the simulation model was recalibrated with new data. This report documents the capture area of the installed recovery wells. Four geologic units are pertinent to this site-specific model. From oldest to youngest, these are the Glen Rose Formation, Paluxy Formation, Walnut Formation, and Goodland Limestone. The Glen Rose Formation is relatively impermeable in the study area and forms the confining unit underlying the Paluxy Formation. The Paluxy Formation forms the Paluxy aquifer, which is a public drinking water supply for the City of White Settlement. The Walnut Formation and Goodland Limestone form the Goodland-Walnut confining unit overlying the Paluxy aquifer. Near landfill 3, gamma-ray logs indicate three distinct zones of the Paluxy Formation; upper, middle, and lower. The formation is about 170-feet thick near landfill 3, and each zone is about 57-feet thick. Two steady-state simulations using the computer program MODFLOW were analyzed using the particle-tracking computer program, MODPATH. One simulation is the calibration simulation using Paluxy aquifer water-level data for May 1993. The second simulation includes the installed recovery wells. A variably spaced grid was designed for the model. The smallest grid cells, 25 by 25 feet, are in the vicinity of landfills 1 and 3. The largest cells, 4,864.5 by 1,441.5 feet, are at the northwestern corner of the model grid near the Parker-Tarrant County line. The modeling was accomplished with three layers representing the upper, middle, and lower zones of the Paluxy aquifer. Particles, which represent contaminant molecules moving in solution with the ground water, were tracked from well P–22M and an area below landfill 1, at the top of the upper zone of the Paluxy aquifer, for 9 years (forward tracking). The forward tracking estimates where contaminants might move by advection from 1987 to 1996. Analysis of backward tracking from the new recovery wells indicates that the simulated contributing area to the recovery wells intercepts the contaminant plume, minimizing off-site migration of the west Paluxy plume. To determine the effectiveness of the recovery wells, monitoring wells southeast of Building 14 have been installed (1996–97) for sampling.

Texas↗
USGS2000

Methods of rating unsaturated zone and watershed characteristics of public water supplies in North Carolina

Overlay and index methods were derived for rating the unsaturated zone and watershed characteristics for use by the State of North Carolina in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes. The rating of the unsaturated zone and watershed characteristics represents a practical and effective means of assessing part of the inherent vulnerability of water supplies to potential contamination. Factors that influence the inherent vulnerability of the drinking water supply to potential contamination were selected and assigned ratings (on a scale of 1 to 10) to cover the possible range of values in North Carolina. These factors were assigned weights of 1, 2, or 3 to reflect their relative influence on the inherent vulnerability of the drinking water supply. The factor values were obtained from Geographic Information System data layers, and were transformed into grids having 60-meter by 60-meter cells, with each cell being assigned a value. Identification of factors, the development of ratings for each, and assignment of weights were based on (1) a literature search, which included examination of potential factors and their effects on the drinking water; and (2) consultation with experts in the science and engineering of hydrology, geology, forestry, agriculture, and water management. Factors selected for rating the inherent vulnerability of the unsaturated zone are vertical hydraulic conductance, land-surface slope, land cover, and land use. Vertical hydraulic conductance is a measure of the capacity of unsaturated material to transmit water. Land-surface slope influences whether precipitation runs off land surfaces or infiltrates into the subsurface. Land cover, the physical overlay of the land surface, influences the amount of precipitation that becomes overland flow or infiltrates into the subsurface. Land use describes activities that occur on the land surface and influence the potential generation of nonpoint-source contamination. Factors selected for rating the watershed characteristics upstream from surface-water intakes are average annual precipitation, land-surface slope, land cover, land use, and ground-water contribution. The average annual precipitation represents the mass of water that becomes available for transport in a watershed. Land-surface slope, land cover, and land use have similar influences in watersheds as those identified for the unsaturated zone. Ground-water contribution represents the part of streamflow that is derived from ground-water discharge.

North Carolina↗
USGS1969

Factors initiating phytoplankton blooms and resulting effects on dissolved oxygen in Duwamish River estuary, Seattle, Washington

Phytoplankton productivity, standing stock, and related environmental factors were studied during 1964-66 in the Duwamish River estuary, at Seattle, Wash., to ascertain the factors that affect phytoplankton growth in the estuary; a knowledge of these factors in turn permits the detection and evaluation of the influence that effluent nutrients have on phytoplankton production. The factors that control the concentration of dissolved oxygen were also evaluated because of the importance of dissolved oxygen to the salmonid populations that migrate through the estuary. Phytoplankton blooms, primarily of diatoms, occurred in the lower estuary during August 1965 and 1966. No bloom occurred during 1964, but the presence of oxygen-supersaturated surface water in August 1963 indicates that a bloom did occur then. Nutrients probably were not the primary factor controlling the timing of phytoplankton blooms. Ammonia ,and phosphate concentrations increased significantly downstream from the Municipality of Metropolitan Seattle's Renton Treatment Plant outfall after the plant began operation in June 1965, and concentrations of nitrogen and phosphorus were relatively high before operation of the Renton Treatment Plant and during nonbloom periods. The consistent coincidence of blooms with minimum fresh-water discharge and tidal exchange during August throughout the study period indicates that bloom timing probably was controlled mostly by hydrographic factors that determine retention time and stability of the surface-water layer. This control was demonstrated in part by a highly significant correlation of gross productivity with retention time (as indicated by fresh-water discharge) and vertical stability (as indicated by the difference between mean surface and mean bottom temperatures). The failure of a bloom to develop in 1964 is related to a minimum fresh-water discharge that was much greater than normal during that summer. Hydrographic factors are apparently important because, as shown by studies of other estuarine environments by other workers, phytoplankton production increases when the zone of vertical turbulent mixing is not markedly deeper than the compensation depth. Phytoplankton cells produced in the surface waters sink, thereby contributing oxidizable organic matter to the bottom saline-water wedge. The maximum BOD (biochemical oxygen demand) in this bottom wedge occurs in the same section of the estuary and ,at the same time as the maximum phytoplankton biomass (as indicated by chlorophyll a) and minimum DO (dissolved oxygen). Other sources of BOD occur in the estuary, and conditions of minimum discharge and tidal exchange assist in reducing DO. Nonetheless, the highly significant correlation of chlorophyll a with BOD throughout the summer indicates that respiration and decomposition of phytoplankton cells is dearly an important contributor of BOD. Increases in the biomass and resultant B0D of blooms because of increased effluent nutrients presumably would further decrease the concentration of DO. This possible effect of effluent nutrients was evaluated by laboratory .bioassays and by a comparison of mean annual biomasses in the estuary. A green algal population in vitro did increase in response to added effluent nutrients; however, the available field data suggest that a 46-percent increase in effluent discharge between 1965 and 1966 did not increase the estuary's phytoplankton biomass significantly.

Water Supply Paper↗