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 1,513 records · Page 84Linked to original sources
USGS2003

Ground-water quality beneath irrigated agriculture in the central High Plains aquifer, 1999-2000

In 1999 and 2000, 30 water-quality monitoring wells were installed in the central High Plains aquifer to evaluate the quality of recently recharged ground water in areas of irrigated agriculture and to identify the factors affecting ground-water quality. Wells were installed adjacent to irrigated agricultural fields with 10- or 20-foot screened intervals placed near the water table. Each well was sampled once for about 100 waterquality constituents associated with agricultural practices. Water samples from 70 percent of the wells (21 of 30 sites) contained nitrate concentrations larger than expected background concentrations (about 3 mg/L as N) and detectable pesticides. Atrazine or its metabolite, deethylatrazine, were detected with greater frequency than other pesticides and were present in all 21 samples where pesticides were detected. The 21 samples with detectable pesticides also contained tritium concentrations large enough to indicate that at least some part of the water sample had been recharged within about the last 50 years. These 21 ground-water samples are considered to show water-quality effects related to irrigated agriculture. The remaining 9 groundwater samples contained no pesticides, small tritium concentrations, and nitrate concentrations less than 3.45 milligrams per liter as nitrogen. These samples are considered unaffected by the irrigated agricultural land-use setting. Nitrogen isotope ratios indicate that commercial fertilizer was the dominant source of nitrate in 13 of the 21 samples affected by irrigated agriculture. Nitrogen isotope ratios for 4 of these 21 samples were indicative of an animal waste source. Dissolved-solids concentrations were larger in samples affected by irrigated agriculture, with large sulfate concentrations having strong correlation with large dissolved solids concentrations in these samples. A strong statistical correlation is shown between samples affected by irrigated agriculture and sites with large rates of pesticide and nitrogen applications and shallow depths to ground water.

Water-Resources Investigations Report↗
USGS2003

Hydrology and water quality of Elkhead Creek and Elkhead Reservoir near Craig, Colorado, July 1995–September 2001

The U.S. Geological Survey, in cooperation with the Colorado River Water Conservation District, collected and analyzed baseline streamflow and water-quality information for Elkhead Creek and water-quality and trophic-state information for Elkhead Reservoir from July 1995 through September 2001. In the study area, Elkhead Creek is a meandering, alluvial stream dominated by snowmelt in mountainous headwaters that produces most of the annual discharge volume and discharge peaks during late spring and early summer. During most of water year 1996 (a typical year), daily mean discharge at station 09246400 (downstream from the reservoir) was similar to daily mean discharge at station 09246200 (upstream from the reservoir). Flow-duration curves for stations 09246200 and 09246400 were nearly identical, except for discharges less than about 10 cubic feet per second. Specific conductance generally had an inverse relation to discharge in Elkhead Creek. During late fall and winter when discharge was small and derived mostly from ground water, specific conductance was high, whereas during spring and early summer, when discharge was large and derived mostly from snowmelt, specific conductance was low. Water temperatures in Elkhead Creek were smallest during winter, about 0.0 degrees Celsius ( o C), and largest during summer, about 20–25 o C. Concentrations of major ions, nutrients, trace elements, organic carbon, and suspended sediment in Elkhead Creek indicated no substantial within-year variability and no substantial differences in variability from one year to the next. A seasonal pattern in the concentration data was evident for most constituents. The seasonal concentration pattern for most of the dissolved constituents followed the seasonal pattern of specific conductance, whereas some nutrients, some trace elements, and suspended sediment followed the seasonal pattern of discharge. Statistical differences between station 09246200 (upstream from the reservoir) and station 09246400 (downstream from the reservoir) were indicated for specific conductance, dissolved calcium, magnesium, sodium, and sulfate, acid-neutralizing capacity, and dissolved solids. Trend analysis indicated upward temporal trends for pH, dissolved ammonia plus organic nitrogen, total nitrogen, and total phosphorus at station 09246200; upward temporal trends for dissolved and total ammonia plus organic nitrogen, total nitrogen, and total phosphorus were indicated at station 09246400. No downward trends were indicated for any constituents. Annual loads for dissolved constituents during water years 1996–2001 were consistently larger at station 09246400 than at station 09246200, except for silica and sulfate. Mean monthly loads for dissolved constituents followed the seasonal pattern of discharge, indicating that most of the annual loads were transported during March–June. Annual dissolved nutrient loads at stations 09246400 and 09246200 were not substantially different, except for total phosphorus and total nitrogen loads, which were smaller at the downstream station than at the upstream station, most likely due to biological uptake and settling in the reservoir. Mean annual suspended-sediment load during water years 1996–2001 was about 87-percent smaller at the downstream station than at the upstream station. Temperature in Elkhead Reservoir varied seasonally, from about 0 o C during winter when ice develops on the reservoir to about 20 o C during summer. Specific conductance varied from minimums of 138 to 169 microsiemens per centimeter at 25 o C (µS/cm) during snowmelt inflow to maximums of 424 to 610 µS/cm during early spring low flow (April). Median pH in the reservoir ranged from 7.2 to 8.0 at all sites near the surface. Median dissolved oxygen ranged from 7.1 to 7.2 milligrams per liter (mg/L) in near-surface samples and from 4.8 to 5.6 mg/L in near-bottom samples. During reservoir stratification, specific conductance generally was largest in the epilimnion, resulting from warm and relatively concentrated water from Elkhead Creek that was routed through the reservoir in the relatively warm epilimnion. The pH in the epilimnion generally increased from May to September, probably a result of algal productivity. In the hypolimnion, pH decreased slightly with depth in the July and September, probably a result of biomass decay processes and a lack of circulation during stratification. Concentrations of nutrients in both near-surface and near-bottom samples from Elkhead Reservoir were highest during snowmelt inflow (April–May). Total phosphorus concentrations in near-surface samples generally were largest during runoff, whereas total phosphorus concentrations in near-bottom samples generally were largest during July or September. Concentrations of nitrite plus nitrate in near-surface samples were substantially depleted by biological uptake during July, September, and October, compared to near-bottom samples. Variations in concentration of chlorophyll- a in near-surface samples were large during the growing season with peak seasonal concentrations during runoff or late summer and fall. Trophic state for Elkhead reservoir ranged from oligotrophic to eutrophic.

Colorado↗
USGS2003

Hydrogeology and Simulated Effects of Ground-Water Withdrawals in the Big River Area, Rhode Island

The Rhode Island Water Resources Board is considering expanded use of ground-water resources from the Big River area because increasing water demands in Rhode Island may exceed the capacity of current sources. This report describes the hydrology of the area and numerical simulation models that were used to examine effects of ground-water withdrawals during 1964?98 and to describe potential effects of different withdrawal scenarios in the area. The Big River study area covers 35.7 square miles (mi2) and includes three primary surface-water drainage basins?the Mishnock River Basin above Route 3, the Big River Basin, and the Carr River Basin, which is a tributary to the Big River. The principal aquifer (referred to as the surficial aquifer) in the study area, which is defined as the area of stratified deposits with a saturated thickness estimated to be 10 feet or greater, covers an area of 10.9 mi2. On average, an estimated 75 cubic feet per second (ft3/s) of water flows through the study area and about 70 ft3/s flows out of the area as streamflow in either the Big River (about 63 ft3/s) or the Mishnock River (about 7 ft3/s). Numerical simulation models are used to describe the hydrology of the area under simulated predevelopment conditions, conditions during 1964?98, and conditions that might occur in 14 hypothetical ground-water withdrawal scenarios with total ground-water withdrawal rates in the area that range from 2 to 11 million gallons per day. Streamflow depletion caused by these hypothetical ground-water withdrawals is calculated by comparison with simulated flows for the predevelopment conditions, which are identical to simulated conditions during the 1964?98 period but without withdrawals at public-supply wells and wastewater recharge. Interpretation of numerical simulation results indicates that the three basins in the study area are in fact a single ground-water resource. For example, the Carr River Basin above Capwell Mill Pond is naturally losing water to the Mishnock River Basin. Withdrawals in the Carr River Basin can deplete streamflows in the Mishnock River Basin. Withdrawals in the Mishnock River Basin deplete streamflows in the Big River Basin and can intercept water flowing to the Flat River Reservoir North of Hill Farm Road in Coventry, Rhode Island. Withdrawals in the Big River Basin can deplete streamflows in the western unnamed tributary to the Carr River, but do not deplete streamflows in the Mishnock River Basin or in the Carr River upstream of Capwell Mill Pond. Because withdrawals deplete streamflows in the study area, the total amount of ground water that may be withdrawn for public supply depends on the minimum allowable streamflow criterion that is applied for each basin.

Water-Resources Investigations Report↗
USGS2003

Reconnaissance of mercury and methylmercury in the St. Croix River and selected tributaries, Minnesota and Wisconsin, July 2000 through October 2001

A reconnaissance-level assessment to characterize total mercury and methylmercury concentrations during summer lowflow conditions was conducted in the St. Croix River Basin during July 2000 through October 2001. Samples were collected at 6 main stem and 16 tributary sites. Loads of total mercury and methylmercury increased in the St. Croix River main stem between Nevers Dam and Franconia. Total mercury and methylmercury concentrations were greatest during July in the Namekagon River. Methylmercury yields in the Namekagon River and Rush Creek were greater than the yield for other tributary streams. Methylmercury concentrations and yields were greater in tributaries draining wetland/forest watersheds than in tributaries draining agricultural/forest watersheds.

Minnesota, Wisconsin↗
USGS2004

Effects of flow modification on a cattail wetland at the mouth of Irondequoit Creek near Rochester, New York: Water levels, wetland biota, sediment, and water quality

An 11-year (1990-2001) study of the Ellison Park wetland, a 423-acre, predominantly cattail (Typha glauca) wetland at the mouth of Irondequoit Creek, was conducted to document the effects that flow modifications, including installation of a flow-control structure (FCS) in 1997 and increased diversion of stormflows to the backwater areas of the wetland, would have on the wetland's ability to decrease chemical loads transported by Irondequoit Creek into Irondequoit Bay on Lake Ontario. The FCS was designed to raise the water-surface elevation and thereby increase the dispersal and detention of stormflows in the upstream half of the wetland; this was expected to promote sedimentation and microbial utilization of nutrients, and thereby decrease the loads of certain constituents, primarily phosphorus, that would otherwise be carried into Irondequoit Bay. An ecological monitoring program was established to document changes in the wetland's water levels, biota, sedimentation rates, and chemical quality of water and sediment that might be attributable to the flow modifications. Water-level increases during storms were mostly confined to the wetland area, within about 5,000 ft upstream from the FCS. Backwater at a point of local concern, about 13,000 ft upstream, was due to local debris jams or constriction of flow by bridges and was not attributable to the FCS. Plant surveys documented species richness, concentrations of nutrients and metals in cattail tissues, and cattail productivity. Results indicated that observed differences among survey periods and between the areas upstream and downstream from the FCS were due to seasonal changes in water levels—either during the current year or at the end of the previous year's growing season—that reflected the water-surface elevation of Lake Ontario, rather than water-level control by the FCS. Results showed no adverse effects from the naturally high water levels that prevail annually during the spring and summer in the wetland, nor from the short-duration increases in water levels that result from FCS operation. Fish surveys documented the use of the wetland by 44 species, of which 25 to 29 species were found in any given year. Community composition was relatively consistent during the study, but seasonal and year-to-year variations in dominant resident and nonresident species were noted, and probably reflected natural or regional population patterns in Lake Ontario and Irondequoit Bay. The FCS allowed fish passage at all water levels and had no discernible adverse effect on the fish community. Bird surveys documented the use of the wetland by more than 90 species for breeding, feeding, and migration. Ground-nesting birds were unaffected by the FCS. Seasonally high water levels, rather than short-duration increases caused by the FCS, might have caused the scarcity or absence of certain wetland species by limiting the extent of breeding habitat for some species and the exposure of mud flats that attracted other species. Some noticeably scarce or absent species also were rare or absent elsewhere along the south-central shore of Lake Ontario. Benthic-macroinvertebrate studies were of minimal use for evaluating the effect of the FCS because no surveys were conducted after FCS installation. The precontrol results allowed assessment of the ecological quality of the wetland on the basis of biotic indices, and generally indicated moderately to severely impaired conditions. Differences between the macroinvertebrate communities in the southern part of the wetland and those in the northern part were attributed to habitat differences, such as substrate composition, water depth, and density of submerged aquatic vegetation. Sedimentation rates in the areas upstream and downstream from the FCS increased after the flow modifications, more in the area upstream from the FCS than in the downstream area. The concurrent downstream increase and the dynamic patterns of deposition and scour indicated that although the FCS and the other flow modifications undoubtedly were major factors in the postcontrol upstream increase in sedimentation rates, other factors, such as the magnitude, frequency, and the timing (season) of peak flows, might also have contributed. Periodic analyses of sediment samples from three longterm depositional sites in the wetland documented the concentrations of major and trace elements, polycyclic aromatic hydrocarbons, and organochlorine and organophosphate compounds. The concentrations of most constituents showed no substantial fluctuation or consistent upward or downward trend during the years sampled, nor did they identify any change after FCS installation. Comparison of the measured concentrations with sediment-quality guidelines that are used to assess the ecological quality of substrate environments indicated that the wetland was moderately to severely impaired—an assessment consistent with the benthic-macroinvertebrate biotic indices. During the precontrol period (1990–96), the wetland was a sink for particulate constituents (removal efficiencies for total phosphorus and total suspended solids were 28 and 47 percent, respectively), but had little effect on conservative constituents (chloride and sulfate). The wetland was a source of orthophosphate and ammonia (removal efficiencies were -38 and -84 percent, respectively). During the postcontrol period (1997–2001), the wetland continued to be a sink for particulate constituents (removal efficiencies for total phosphorus and total suspended solids were 45 and 52 percent, respectively); the exportation of orthophosphate by the wetland decreased (by 7 percent), whereas that of ammonia increased (by about 70 percent). The outflow loads of orthophosphate and ammonia represented about 15 and 2.3 percent of total phosphorus and total nitrogen loads, respectively. Changes in the loads of conservative constituents were negligible, and the overall removal efficiencies for other constituents during the precontrol period differed from those of the postcontrol period by no more than 5.4 percent. Statistical analyses of monthly inflow and outflow loads indicated significant differences between inflow and outflow loads of most constituents during the pre- and postcontrol periods. Load data were adjusted to remove the effects of dissimilar hydrologic conditions that prevailed during the pre- and postcontrol periods, and to isolate the water-quality-improvement effect that could be attributed solely to the FCS. Results indicated that the FCS contributed significantly to the decrease in total phosphorus loads, and slightly to a decrease in ammonia-plus-organic nitrogen loads, but had little or no significant effect on loads of other constituents.

New York↗
USGS2003

August median streamflow on ungaged streams in eastern Aroostook County, Maine

Methods for estimating August median streamflow were developed for ungaged, unregulated streams in the eastern part of Aroostook County, Maine, with drainage areas from 0.38 to 43 square miles and mean basin elevations from 437 to 1,024 feet. Few long-term, continuous-record streamflow-gaging stations with small drainage areas were available from which to develop the equations; therefore, 24 partial-record gaging stations were established in this investigation. A mathematical technique for estimating a standard low-flow statistic, August median streamflow, at partial-record stations was applied by relating base-flow measurements at these stations to concurrent daily flows at nearby long-term, continuous-record streamflow- gaging stations (index stations). Generalized least-squares regression analysis (GLS) was used to relate estimates of August median streamflow at gaging stations to basin characteristics at these same stations to develop equations that can be applied to estimate August median streamflow on ungaged streams. GLS accounts for varying periods of record at the gaging stations and the cross correlation of concurrent streamflows among gaging stations. Twenty-three partial-record stations and one continuous-record station were used for the final regression equations. The basin characteristics of drainage area and mean basin elevation are used in the calculated regression equation for ungaged streams to estimate August median flow. The equation has an average standard error of prediction from -38 to 62 percent. A one-variable equation uses only drainage area to estimate August median streamflow when less accuracy is acceptable. This equation has an average standard error of prediction from -40 to 67 percent. Model error is larger than sampling error for both equations, indicating that additional basin characteristics could be important to improved estimates of low-flow statistics. Weighted estimates of August median streamflow, which can be used when making estimates at partial-record or continuous-record gaging stations, range from 0.03 to 11.7 cubic feet per second or from 0.1 to 0.4 cubic feet per second per square mile. Estimates of August median streamflow on ungaged streams in the eastern part of Aroostook County, within the range of acceptable explanatory variables, range from 0.03 to 30 cubic feet per second or 0.1 to 0.7 cubic feet per second per square mile. Estimates of August median streamflow per square mile of drainage area generally increase as mean elevation and drainage area increase.

Maine↗
USGS2004

Herbicides and their transformation products in source-water aquifers tapped by public-supply wells in Illinois, 2001-02

During 2001-02, ground-water samples were collected from 117 public-supply wells distributed throughout Illinois to evaluate the occurrence of herbicides and their transformation products in the State?s source-water aquifers. Wells were selected using a stratified-random method to ensure representation of the major types of source-water aquifers in the State. Samples were analyzed for 18 herbicides and 18 transformation products, including 3 triazine and 14 chloroacetanilide products. Herbicide compounds (field-applied parent herbicides and their transformation products) were detected in 34 percent of samples. A subset of samples was collected unfiltered to determine if analytical results for herbicides in unfiltered samples are similar to those in paired filtered samples and, thus, can be considered equally representative of herbicide concentrations in ground water supplied to the public. The study by the U.S. Geological Survey was done in cooperation with the Illinois Environmental Protection Agency. Parent herbicides were detected in only 4 percent of all samples. The six most frequently detected herbicide compounds (from 5 to 28 percent of samples) were chloroacetanilide transformation products. The frequent occurrence of transformation products and their higher concentrations relative to those of most parent herbicides confirm the importance of obtaining information on transformation products to understand the mobility and fate of herbicides in ground-water systems. No sample concentrations determined during this study exceeded current (2003) Federal or State drinking-water standards; however, standards are established for only seven parent herbicides. Factors related to the occurrence of herbicide compounds in the State?s source-water aquifers include unconsolidated and unconfined conditions, various hydrogeologic characteristics and well-construction aspects at shallow depths, and proximity to streams. Generally, the closer an aquifer (or well location) is to a recharge area and (or) the stronger the hydraulic connection between an aquifer and a recharge area, the younger the ground water and the more vulnerable the aquifer will be to contamination by herbicide compounds. The weak relation between current (2001) statewide application rates of herbicides and current (2001-02) occurrence of herbicide compounds in source-water aquifers indicates that additional factors must be considered when relating herbicide-application rates to occurrence. These factors include historical application rates and the mobility and persistence of the various herbicide compounds in ground-water systems. Frequency of detection and concentrations of herbicides compounds in the State?s source-water aquifers are indicated to be highest during the spring, when crops are planted and herbicides primarily are applied. Excess nitrate (concentrations of nitrate, as nitrogen, higher than 3 milligrams per liter) in ground water strongly indicates the co-occurrence of herbicide compounds. However, nitrate concentrations are not a reliable indicator of herbicide-compound concentrations. The inverse relation found between current use of land for corn and soybean production and current occurrence of herbicide compounds in underlying aquifers indicates that various factors, along with current agricultural land use, contribute to herbicide occurrence. These factors include, among others, land-use history, ground-water age, ground-water-flow patterns, geology, soil microbiology, and chemistry and persistence of the herbicide compounds. Detection of agriculture-specific herbicide compounds in 71 percent of samples from urban areas with no current or recent agricultural land use near the sampled wells indicates that recharge to certain high-capacity supply wells may originate at considerable distances (up to about 10 miles) from the wells. Essentially no difference was found between the analytical results for herbicides in paired unfiltered and filtered samples,

Water-Resources Investigations Report↗
USGS2003

Ground-water use, locations of production wells, and areas irrigated using ground water in 1998, middle Humboldt River basin, north-central Nevada

In 1998, ground water was being pumped from about 420 production wells in the middle Humboldt River Basin for a variety of uses. Principal uses were for agriculture, industry, mining, municipal, and power plant purposes. This report presents a compilation of the number and types of production wells, areas irrigated by ground water, and ground-water use in 14 hydrographic areas of the middle Humboldt River Basin in 1998. Annual pumping records for production wells usually are reported to the Nevada Division of Water Resources. However, operators of irrigation wells are not consistently required to report annual pumpage. Daily power-consumption and pump-discharge rates measured at 20 wells during the 1998 irrigation season and total power use at each well were used to estimate the amount of water, in feet of depth, applied to 20 alfalfa fields. These fields include about 10 percent of the total area, 36,700 acres, irrigated with ground water in the middle Humboldt River Basin. In 1998 an average of 2.0 feet of water was applied to 14 fields irrigated using center-pivot sprinkler systems, and an average of 2.6 feet of water was applied to 6 fields irrigated using wheel-line sprinkler systems. A similar approach was used to estimate the amount of water pumped at three wells using pumps powered by diesel engines. The two fields served by these three wells received 3.9 feet of water by flood irrigation during the 1998 irrigation season. The amount of water applied to the fields irrigated by center-pivot and wheel-line irrigation systems during the 1998 irrigation season was less than what would have been applied during a typical irrigation season because late winter and spring precipitation exceeded long-term monthly averages by as much as four times. As a result, the health of crops was affected by over-saturated soils, and most irrigation wells were only used sporadically in the first part of the irrigation season. Power consumption at 19 of the 20 wells in the 1994-97 irrigation seasons was 110 to 235 percent of the power consumption in the 1998 irrigation season. If the amount of water applied to fields during the 1998 irrigation season were adjusted to account for these differences in power consumption, the average amount of water applied to a field during a typical season using center-pivot and wheel-line sprinkler systems would be 3.1 feet and 3.7 feet, respectively. Total ground water pumped in the middle Humboldt River Basin during 1998 was about 298,000 acre-feet. This pumpage was distributed as follows: 78 percent for mining, 19 percent for irrigation, and 3 percent for industrial, municipal, and power plants combined. Mining pumpage is by far the largest source of ground-water use because several large gold mines have extended below local ground-water levels and the area around each mine must be dewatered in order to maintain a dry and workable mine. Total mining pumpage in 1998 was 233,000 acre-feet, of this total, 23,600 acre-feet was for consumptive use and 209,000 acre-feet was for dewatering eight mines. Excess water from the mines being dewatered was distributed as follows: 74,500 acre-feet was returned to aquifers by infiltration; 33,100 acre-feet was used for irrigation and for consumptive use at two mines and a power plant; 96,700 acre-feet was released to the Humboldt River or one of its tributaries; and 5,260 acre-feet was lost to evaporation.

Water-Resources Investigations Report↗
USGS2003

Arsenic in midwestern glacial deposits — Occurrence and relation to selected hydrogeologic and geochemical factors

Ground-water-quality data collected as part of 12 U.S. Geological Survey National Water-Quality Assessment studies during 1996-2001 were analyzed to (1) document arsenic occurrence in four types of gla-cial deposits that occur in large areas of the Midwest, (2) identify hydrogeologic or geochemical factors asso-ciated with elevated arsenic concentrations, and (3) search for clues as to arsenic source(s) or mechanism(s) of mobilization that could be useful for designing future studies. Arsenic and other water-quality constituents were sampled in 342 monitor and domestic wells in parts of Illinois Indiana Ohio Michigan and Wisconsin. Arsenic was detected (at a concentration >1 ?g/L) in one-third of the samples. The maximum concentration was 84 ?g/L, and the median was less than 1 ?g/L. Eight percent of samples had arsenic concentrations that exceeded the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) of 10?g/L. Samples were from four aquifer types?confined valley fill, unconfined valley fill, outwash plain, and till with sand lenses. Highest arsenic concentrations were found in reducing waters from valley-fill depos-its. In confined valley fill, all waters were reducing and old (recharged before 1953), and almost half of sam-ples had arsenic concentrations greater than the MCL. In unconfined valley fill, redox conditions and ages were varied, and elevated arsenic concentrations were sporadic. In both types of valley fill, elevated arsenic concentrations are linked to the underlying bedrock on the basis of spatial relations and geochemical correla-tions. In shallow (<50 ft) till with sand lenses, arsenic was detected in oxic or mixed waters, but concentra-tions were rarely greater than the MCL. In shallow out-wash-plain deposits, arsenic concentrations greater than the MCL were detected in waters that were reduc-ing and young (recharged after 1953). Although arsenic concentrations were signifi-cantly higher in deep wells (>150 ft), all deep wells were from a distinctive aquifer type (confined valley fill). It is not known whether wells at similar depths in other aquifer types would produce waters with simi-larly high arsenic concentrations. Correlations of arsenic with fluoride, strontium, and barium suggest that arsenic might be related to epi-genetic (Mississippi Valley-type) sulfide deposits in Paleozoic bedrock. Arsenic is typically released from sulfides by oxidation, but in the current study, the highest arsenic concentrations in glacial deposits were detected in reducing waters. Therefore, a link between epigenetic sulfides and elevated arsenic concentrations in glacial deposits would probably require a multi-step process.

Illinois, Indiana, Ohio↗
USGS2003

Ground-water resources in the lower Milliken--Sarco--Tulucay Creeks area, southeastern Napa County, California, 2000-2002

Ground water obtained from individual private wells is the sole source of water for about 4,800 residents living in the lower Milliken-Sarco-Tulucay Creeks area of southeastern Napa County. Increases in population and in irrigated vineyards during the past few decades have increased water demand. Estimated ground-water pumpage in 2000 was 5,350 acre-feet per year, an increase of about 80 percent since 1975. Water for agricultural irrigation is the dominant use, accounting for about 45 percent of the total. This increase in ground-water extraction has resulted in the general decline of ground-water levels. The purpose of this report is to present selected hydrologic data collected from 1975 to 2002 and to quantify changes in the ground-water system during the past 25 years. The study area lies in one of several prominent northwest-trending structural valleys in the North Coast Ranges. The area is underlain by alluvial deposits and volcanic rocks that exceed 1,000 feet in thickness in some places. Alluvial deposits and tuff beds in the volcanic sequence are the principal source of water to wells. The ground-water system is recharged by precipitation that infiltrates, in minor amounts, directly on the valley floor but mostly by infiltration in the Howell Mountains. Ground water moves laterally from the Howell Mountains into the study area. Although the area receives abundant winter precipitation in most years, nearly half of the precipitation is lost as surface runoff to the Napa River. Evapotranspiration also is high, accounting for nearly one-half of the total precipitation received. Because of the uncertainties in the estimates of precipitation, runoff, and evapotranspiration, a precise estimate of potential ground-water recharge cannot be made. Large changes in ground-water levels occurred between 1975 and 2001. In much of the western part of the area, water levels increased; but in the central and eastern parts, water levels declined by 25 to 125 feet. Ground-water extraction produced three large pumping depressions in the northern and east-central parts of the area. The general decline in ground-water levels is a result of increases in ground-water pumpage and possibly changes in infiltration capacity caused by changes in land use. Ground-water-level declines during 1960-2002 are evident in the records for 9 of 10 key monitoring wells. In five of these wells, water levels dropped by greater than 20 feet since the 1980s. The largest water-level declines have occurred since the mid 1970s, corresponding with a period of accelerated well construction and ground-water extraction. Analysis of samples from 15 wells indicates that the chemical quality of ground water in the study generally is acceptable. However, arsenic concentrations in samples from five wells exceed the U.S. Environmental Protection Agency primary drinking-water standard of 10 micrograms per liter, and iron concentrations in samples from five wells exceed the U.S. Environmental Protection Agency and the California Department of Health Services secondary drinking-water standard of 300 micrograms per liter. Water from 12 of 15 wells sampled contained concentrations of manganese that exceed the U.S. Environmental Protection Agency and the California Department of Health Services secondary drinking-water standard of 50 micrograms per liter. Two wells produced water that had boron in excess of the California Department of Health Services action level of 1 milligram per liter. Stable isotope, chlorofluorocarbon, and tritium data indicate that ground water in the area is a mixture of waters that recharged the aquifer system at different times. The presence of chlorofluorocarbons and tritium in water from the study area is evidence that modern recharge (post 1950) does take place. Water-temperature logs indicate that ground-water temperatures throughout the study area exceed 30?C at depths in excess of 600 feet. Further, water at

Water-Resources Investigations Report↗
USGS2003

Conjunctive-use optimization model of the Mississippi River Valley alluvial aquifer of northeastern 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 over 100 feet deep 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 14,104 square miles, extending northeast from the Arkansas River into the northeast corner of Arkansas and parts of southeastern Missouri. The flow model showed 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. To develop estimates of withdrawal rates that could be sustained in compliance with the constraints of critical ground-water area designation, conjunctive-use optimization modeling was applied to the flow model of the alluvial aquifer in northeastern Arkansas. Ground-water 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 flow conditions were selected because the maximized withdrawals are intended to represent sustainable yield of the system (a rate that can be maintained indefinitely). Within the optimization model, 11 rivers are specified. Surface-water diversion rates that occurred in 2000 were subtracted from specified overland flow at the appropriate river cells. Included in these diversions were the planned diversions of 63,339,248 ft3/d for the Bayou Meto project area and 55,078,367 ft3/d for the Grand Prairie project area, which factor in an additional 30 and 40 percent transmission loss, respectively. Streamflow constraints were specified at all 1,165 river cells based on average 7-day minimum flows for 10 years. Sustainable yield for all rivers ranged from 0 (Current, Little Red, and Bayou Meto Rivers) to almost 5 billion cubic feet per day for the Arkansas River. Total sustainable yield from all rivers combined was 12.8 billion cubic feet per day, which represents a substantial source for supplementing ground water to meet the total water demand. Sustainable-yield estimates are affected by the allowable upper limit on withdrawals from wells specified in the optimization model. Ground-water withdrawal rates were allowed to vary as much as 200 percent of the withdrawal rate in 1997. As the overall upper limit on withdrawals is increased, the sustainable yield generally increases. Tests with the optimization model show that without limits on pumping, wells adjacent to sources of water would have optimized withdrawal rates that were orders of magnitude larger than rates corresponding to those of 1997. The sustainable yield from ground water for the entire study area while setting the maximum upper limit as the amount withdrawn in 1997 is 360 million cubic feet per day, which is only about 57 percent of the amount withdrawn in 1997 (635.6 million cubic feet per day). Optimal sustainable yields from within the Bayou Meto irrigation project area and within the Grand Prairie irrigation project area are 18.1 and 9.1 million cubic feet per day, respectively, assuming a maximum allowable withdrawal rate equal to 1997 rates. These values of sustainable yield represent 35 and 30 percent respectively of the amount pumped from these project areas in 1997. 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-yield estimates are those obtained using upper limits of withdrawal rates of 100-, 150-, and 200-percent of 1997 withdrawal rates, then the resulting unmet demand for the entire model area is 275.5, 190.9, and 110 million cubic feet per day, respectively. Whereas, if the demand is specified as 100-, 150-, and 200-percent of the 1997 withdrawal rate, and the sustainable-yield estimates remain the same, then the resulting unmet demand for the entire model area is 275.5, 508.8, and 745.8 million cubic feet per day, respectively. These unmet demands for ground water could be obtained from large sustainable surface-water withdrawals.

Arkansas↗
USGS2004

Conjunctive-use optimization model and sustainable-yield estimation for the Sparta aquifer of southeastern Arkansas and north-central Louisiana

Conjunctive-use optimization modeling was done to assist water managers and planners by estimating the maximum amount of ground water that hypothetically could be withdrawn from wells within the Sparta aquifer indefinitely without violating hydraulic-head or stream-discharge constraints. The Sparta aquifer is largely a confined aquifer of regional importance that comprises a sequence of unconsolidated sand units that are contained within the Sparta Sand. In 2000, more than 35.4 million cubic feet per day (Mft3/d) of water were withdrawn from the aquifer by more than 900 wells, primarily for industry, municipal supply, and crop irrigation in Arkansas. Continued, heavy withdrawals from the aquifer have caused several large cones of depression, lowering hydraulic heads below the top of the Sparta Sand in parts of Union and Columbia Counties and several areas in north-central Louisiana. Problems related to overdraft in the Sparta aquifer can result in increased drilling and pumping costs, reduced well yields, and degraded water quality in areas of large drawdown. A finite-difference ground-water flow model was developed for the Sparta aquifer using MODFLOW, primarily in eastern and southeastern Arkansas and north-central Louisiana. Observed aquifer conditions in 1997 supported by numerical simulations of ground-water flow show that continued pumping at withdrawal rates representative of 1990 - 1997 rates cannot be sustained indefinitely without causing hydraulic heads to drop substantially below the top of the Sparta Sand in southern Arkansas and north-central Louisiana. Areas of ground-water levels below the top of the Sparta Sand have been designated as Critical Ground-Water Areas by the State of Arkansas. A steady-state conjunctive-use optimization model was developed to simulate optimized surface-water and ground-water withdrawals while maintaining hydraulic-head and streamflow constraints, thus determining the 'sustainable yield' for the aquifer. Initial attempts to estimate sustainable yield using simulated 1997 hydraulic heads as initial heads in Scenario 1 and 100 percent of the baseline 1990-1997 withdrawal rate as the lower specified limit in Scenario 2 led to infeasible results. Sustainable yield was estimated successfully for scenario 3 with three variations on the upper limit of withdrawal rates. Additionally, ground-water withdrawals in Union County were fixed at 35.6 percent of the baseline 1990-1997 withdrawal rate in Scenario 3. These fixed withdrawals are recognized by the Arkansas Soil and Water Conservation Commission to be sustainable as determined in a previous study. The optimized solutions maintained hydraulic heads at or above the top of the Sparta Sand (except in the outcrop areas where unconfined conditions occur) and streamflow within the outcrop areas was maintained at or above minimum levels. Scenario 3 used limits of 100, 150, and 200 percent of baseline 1990-1997 withdrawal rates for the upper specified limit on 1,119 withdrawal decision variables (managed wells) resulting in estimated sustainable yields ranging from 11.6 to 13.2 Mft3/d in Arkansas and 0.3 to 0.5 Mft3/d in Louisiana. Assuming the total 2 Conjunctive-Use Optimization Model and Sustainable-Yield Estimation for the Sparta Aquifer of Southeastern Arkansas and North-Central Louisiana water demand is equal to the baseline 1990-1997 withdrawal rates, the sustainable yields estimated from the three scenarios only provide 52 to 59 percent of the total ground-water demand for Arkansas; the remainder is defined as unmet demand that could be obtained from large, sustainable surface-water withdrawals.

Water-Resources Investigations Report↗
USGS2003

Recalibration of a ground-water flow model of the Mississippi River Valley alluvial aquifer in southeastern Arkansas, 1918-1998, with simulations of hydraulic heads caused by projected ground-water withdrawals through 2049

To evaluate the effects of projected ground water withdrawals, three scenarios were used to simulate a range of possible withdrawals. Five additional stress periods of 10 years each were added to the model to facilitate predictive scenario generation. The predictive scenarios control pumpage by either continuing 1997 pumpage into the future (scenario 1) or by increasing water-use trends into the future (scenario 2 and 3). The ASWCC Critical Ground Water area designation includes a requirement that a 50-percent saturated formation thickness be maintained. For this reason, the level of 50-percent saturated formation thickness is used as a reference surface in the scenario output presented. Animations of simulated heads changing through time are included on the compact disc in the "Animations" folder. In the animations, the level of 50 percent saturated formation thickness is indicated by a mesh surface and the dry cells appear as voids in the model surface.

Arkansas↗
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↗
USGS2003

Ground-water flow and ground- and surface-water interaction at McBaine Bottoms, Columbia, Missouri-2000-02

McBaine Bottoms southwest of Columbia, Missouri, is the site of 4,269 acres of the Eagle Bluffs Conservation Area operated by the Missouri Department of Conservation, about 130 acres of the city of Columbia wastewater-treat-ment wetlands, and the city of Columbia munici-pal-supply well field. The city of Columbia wastewater-treatment wetlands supply treated effluent to the Eagle Bluffs Conservation Area. The presence of a sustained ground-water high underlying the Eagle Bluffs Conservation Area has indicated that ground-water flow is toward the municipal well field that supplies drinking water to the city of Columbia. The U.S. Geological Survey, in cooperation with the Missouri Department of Conservation and the city of Columbia, measured the ground-water levels in about 88 monitoring wells and the surface-water elevation at 4 sites monthly during a 27-month period to determine the ground-water flow and the ground- and surface-water interaction at McBaine Bottoms. Lateral ground-water flow was dominated by the presence of a ground-water high that was beneath the Eagle Bluffs Conservation Area and the presence of a cone of depression in the northern part of the study area. The ground-water high was present during all months of the study. Ground-water flow was radially away from the apex of the ground-water high; west and south of the high, flow was toward the Missouri River, east of the high, flow was toward Perche Creek, and north of the high, flow was toward the north toward the city of Columbia well field. The cone of depression was centered around the city of Columbia well field. Another permanent feature on the water-level maps was a ground-water high beneath treatment wetland unit 1. Although the ground-water high beneath the Eagle Bluffs Conservation Area was present throughout the study period, the configuration of the high changed depending on hydrologic conditions. Generally in the spring, the height of the ground-water high began to decrease and hydraulic gradients around the high became more shallow than in the winter months. In early summer, the high was the least pronounced. During mid-sum-mer, the high became more pronounced, and it continued to become higher, increasing until it reached its maximum height in late fall or early winter. Fluctuations in the ground-water high were partially produced by the cycle of flooding of the Eagle Bluffs Conservation Area wetland pools in the fall and subsequent drainage so crops could be planted in many of the wetland pools. The cone of depression in the northern part of the study area generally extended from the base of the ground-water high in the northern part of the Eagle Bluffs Conservation Area throughout the rest of the study area. The depth of the cone primarily was affected by the altitude of the Missouri River and the quantity of water being pumped from the alluvial aquifer by the city of Columbia well field. Ground-water flow in the alluvial aquifer in McBaine Bottoms in the late 1960?s before the development of the city of Columbia well field and the Eagle Bluffs Conservation Area was from northwest to southeast approximately parallel to the Missouri River. The ground-water high beneath the Eagle Bluffs Conservation Area and the cone of depression around the city of Columbia well field were not present in water-level maps for 1968 and 1978. The Missouri River can be a source of recharge to the alluvial aquifer. Generally the altitude of the river in the northern part of the study area was higher than the water table in the aquifer. Ground-water flow in this area was from the river into the alluvial aquifer. In the southern part of the study area adjacent to the Eagle Bluffs Conservation Area, the Missouri River was lower than the water table in the alluvial aquifer, indicating that the river was receiving water from the alluvial aquifer beneath the Eagle Bluffs Conservation Area.

Missouri↗
USGS2003

Water quality at fixed sites in the Great Salt Lake basins, Utah, Idaho, and Wyoming, water years 1999-2000

The Great Salt Lake Basins (GRSL) study unit of the National Water-Quality Assessment program encompasses the Bear River, Weber River, and Utah Lake/Jordan River systems, all of which discharge to Great Salt Lake in Utah. Data were collected during each month at 10 sites in the GRSL study unit from October 1998 to September 2000 to define spatial and temporal distribution and variability in concentration of nutrients, major ions, trace elements, suspended sediments, and organic compounds. Water samples collected from rangeland and forest sites in the GRSL study unit generally contained low concentrations of dissolved solids. Median dissolved-solids concentration in water samples was highest at sites with mixed land uses. Dissolved-solids concentration in some parts of the Bear River during low flow exceeded Utah State standards for agricultural use. Total-nitrogen concentration in water samples from GRSL sites ranged from 0.06 to 11 milligrams per liter. Water samples from predominantly forest and rangeland sites generally had a low total-nitrogen concentration. Many samples from sites with a higher percentage of agricultural and urban land cover had higher concentrations of total nitrogen. Fifty percent of the samples collected at GRSL sites had total phosphorus concentrations that exceeded 0.1 milligram per liter, the recommended limit for the prevention of nuisance aquatic-plant growth in streams not discharging directly into lakes or impoundments. Concentration of most trace elements in water samples from the fixed sites generally was low; however, arsenic concentrations, as high as 284 micrograms per liter, sometimes exceeded aquatic-life guidelines. Forty-three pesticides and 35 volatile organic compounds were detected in water samples from three GRSL sites; however, the concentration of most was low, less than 1 microgram per liter. The herbicides atrazine and prometon and the insecticides carbaryl and diazinon were the most frequently detected pesticides. Chloroform and toluene were detected in more than 90 percent of the samples and were the most frequently detected volatile organic compounds. The concentration of carbaryl, diazinon, malathion, and toluene in water samples from GRSL sites sometimes exceeded aquatic-life guidelines.

Idaho,Utah, Wyoming↗
USGS2003

Simulation of hydrodynamics, temperature, and dissolved oxygen in Table Rock Lake, Missouri, 1996–1997

Outflow from Table Rock Lake and other White River reservoirs support a cold-water trout fishery of substantial economic yield in south-central Missouri and north-central Arkansas. The Missouri Department of Conservation has requested an increase in existing minimum flows through the Table Rock Lake Dam from the U.S. Army Corps of Engineers to increase the quality of fishable waters downstream in Lake Taneycomo. Information is needed to assess the effect of increased minimum flows on temperature and dissolved- oxygen concentrations of reservoir water and the outflow. A two-dimensional, laterally averaged, hydrodynamic, temperature, and dissolved-oxygen model, CE-QUAL-W2, was developed and calibrated for Table Rock Lake, located in Missouri, north of the Arkansas-Missouri State line. The model simulates water-surface elevation, heat transport, and dissolved-oxygen dynamics. The model was developed to assess the effects of proposed increases in minimum flow from about 4.4 cubic meters per second (the existing minimum flow) to 11.3 cubic meters per second (the increased minimum flow). Simulations included assessing the effect of (1) increased minimum flows and (2) increased minimum flows with increased water-surface elevations in Table Rock Lake, on outflow temperatures and dissolved-oxygen concentrations. In both minimum flow scenarios, water temperature appeared to stay the same or increase slightly (less than 0.37 °C) and dissolved oxygen appeared to decrease slightly (less than 0.78 mg/L) in the outflow during the thermal stratification season. However, differences between the minimum flow scenarios for water temperature and dissolved- oxygen concentration and the calibrated model were similar to the differences between measured and simulated water-column profile values.

Missouri↗