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USGS2001

Methods of analysis by the U. S. Geological Survey National Water Quality Laboratory-Determination of organic plus inorganic mercury in filtered and unfiltered natural water with cold vapor; atomic fluorescence spectrometry

An analytical method using cold vapor-atomic fluorescence spectrometry was developed by the U.S. Geological Survey in 2001 for the determination of organic plus inorganic mercury in filtered and unfiltered natural water. This method was developed to eliminate the use of acid dichromate preservative and to provide capability to measure ambient mercury concentrations in natural water. Dissolved mercury includes all oxidizable mercury species present in natural water that has been filtered through a 0.45- micrometer pore size capsule filter. Wholewater recoverable mercury includes dissolved mercury species and mercury species adsorbed to particulate matter in unfiltered natural water. Mercury species can include elemental mercury, mercury (II), mercury (II) complexes, various alkyl- and phenylmercury compounds, and other forms of mercury. In this method, samples are collected and processed according to standard U.S. Geological Survey protocols. Samples are preserved onsite with 6N hydrochloric acid in a ratio of 1 to 100 in a borosilicateglass bottle with fluoropolymer-lined cap. Mercury species are oxidized to mercury (II) by using bromine monochloride; excess oxidation reagent is neutralized with hydroxylamine hydrochloride. Elemental mercury produced after adding stannous chloride is purged from the solution with ultrapure argon gas into a cell in which the mercury concentration is measured by atomic fluorescence emission at 253.7 nanometers. The analytical response is linear up to 125 nanograms per liter (ng/L) of mercury, and the short-term method detection limit is about 5 ng/L. The analytical variability at 50 ng/L is about 10 percent. This report describes the method and compares the use of hydrochloric acid to acid dichromate as a field preservative. Ambient mercury concentrations in hydrochloric acidpreserved samples stored in borosilicate-glass bottles with fluoropolymer-lined caps are shown to be stable for at least 30 days. Mercury concentrations are stable for at least 5 months after bromine monochloride is added to the sample bottles in the laboratory. The long-term average percent recoveries at 20, 45, and 75 ng/L in reagent water, filtered and unfiltered ground water, and filtered and unfiltered surface water range from 89 to 108, 96 to 103, and 94 to 98 percent, respectively.

Water-Resources Investigations Report↗
USGS2002

An integrated geophysical and hydraulic investigation to characterize a fractured-rock aquifer, Norwalk, Connecticut

The U.S. Geological Survey conducted an integrated geophysical and hydraulic investigation at the Norden Systems, Inc. site in Norwalk, Connecticut, where chlorinated solvents have contaminated a fractured-rock aquifer. Borehole, borehole-to-borehole, surface-geophysical, and hydraulic methods were used to characterize the site bedrock lithology and structure, fractures, and transmissive zone hydraulic properties. The geophysical and hydraulic methods included conventional logs, borehole imagery, borehole radar, flowmeter under ambient and stressed hydraulic conditions, and azimuthal square-array direct-current resistivity soundings. Integrated interpretation of geophysical logs at borehole and borehole-to-borehole scales indicates that the bedrock foliation strikes northwest and dips northeast, and strikes north-northeast to northeast and dips both southeast and northwest. Although steeply dipping fractures that cross-cut foliation are observed, most fractures are parallel or sub-parallel to foliation. Steeply dipping reflectors observed in the radar reflection data from three boreholes near the main building delineate a north-northeast trending feature interpreted as a fracture zone. Results of radar tomography conducted close to a suspected contaminant source area indicate that a zone of low electromagnetic (EM) velocity and high EM attenuation is present above 50 ft in depth - the region containing the highest density of fractures. Flowmeter logging was used to estimate hydraulic properties in the boreholes. Thirty-three transmissive fracture zones were identified in 11 of the boreholes. The vertical separation between transmissive zones typically is 10 to 20 ft. Open-hole and discrete-zone transmissivity was estimated from heat-pulse flowmeter data acquired under ambient and stressed conditions. The open-hole transmissivity ranges from 2 to 86 ft2/d. The estimated transmissivity of individual transmissive zones ranges from 0.4 to 68 ft2/d. Drawdown monitoring in nearby boreholes under pumping conditions identified hydraulic connections along a northeast-southwest trend between boreholes as far as 560 ft apart. The vertical distribution of fractures can be described by power law functions, which suggest that the fracture network contains transmissive zones consisting of closely spaced fractures surrounded by a less fractured and much less permeable rock mass.

Connecticut↗
USGS2001

Geohydrology and limnology of Walden Pond, Concord, Massachusetts

The trophic ecology and ground-water contributing area of Walden Pond, in Concord and Lincoln, Mass., were investigated by the U.S. Geological Survey in cooperation with the Massachusetts Department of Environmental Management from April 1997 to July 2000. Bathymetric investigation indicated that Walden Pond (24.88 hectares), a glacial kettle-hole lake with no surface inlet or outlet, has three deep areas. The maximum depth (30.5 meters) essentially was unchanged from measurements made by Henry David Thoreau in 1846. The groundwater contributing area (621,000 square meters) to Walden Pond was determined from water-table contours in areas of stratified glacial deposits and from land-surface contours in areas of bedrock highs. Walden Pond is a flow-through lake: Walden Pond gains water from the aquifer along its eastern perimeter and loses water to the aquifer along its western perimeter. Walden Pond contributing area also includes Goose Pond and its contributing area. A water budget calculated for Walden Pond, expressed as depth of water over the lake surface, indicated that 45 percent of the inflow to the lake was from precipitation (1.215 meters per year) and 55 percent from ground water (1.47 meters per year). The groundwater inflow estimate was based on the average of two different approaches including an isotope mass-balance approach. Evaporation accounted for 26 percent of the outflow from the lake (0.71 meters per year) whereas lake-water seepage to the groundwater system contributed 74 percent of the outflow (1.97 meters per year). The water-residence time of Walden Pond is approximately 5 years. Potential point sources of nutrients to ground water, the Concord municipal landfill and a trailer park, were determined to be outside the Walden Pond groundwater contributing area. A third source, the septic leach field for the Walden Pond State Reservation facilities, was within the groundwater contributing area. Nutrient budgets for the lake indicated that nitrogen inputs (858 kilograms per year) were dominated (30 percent) by plume water from the septic leach field and, possibly, by swimmers (34 percent). Phosphorus inputs (32 kilograms per year) were dominated by atmospheric dry deposition, background ground water, and estimated swimmer inputs. Swimmer inputs may represent more than 50 percent of the phosphorus load during the summer. The septic-system plume did not contribute phosphorus, but increased the nitrogen to phosphorus ratio for inputs from 41 to 59, on an atom-to-atom basis. The ratio of nitrogen to phosphorus in input loads and within the lake indicated algal growth would be strongly phosphorus limited. Nitrogen supply in excess of plant requirements may mitigate against nitrogen fixing organisms including undesirable blooms of cyanobacteria. Based on areal nutrient loading, Walden Pond is a mesotrophic lake. Hypolimnetic oxygen demand of Walden Pond has increased since a profile was measured in 1939. Currently (1999), the entire hypolimnion of Walden Pond becomes devoid of dissolved oxygen before fall turnover in late November; whereas historical data indicated dissolved oxygen likely remained in the hypolimnion during 1939. The complete depletion of dissolved oxygen likely causes release of phosphorus from the sediments. Walden Pond contains a large population of the deep-growing benthic macro alga Nitella, which has been hypothesized to promote water clarity in other clear-water lakes by sequestering nutrients and keeping large areas of the sediment surface oxygenated. Loss of Nitella populations in other lakes has correlated with a decline in water quality. Although the Nitella standing crop is large in Walden Pond, Nitella still appears to be controlled by nutrient availability. Decreasing phosphorus inputs to Walden Pond, by amounts under anthropogenic control would likely contribute to the stability of the Nitella population in the metalimnion, may reverse oxygen depletion in the hypolimnion, and decreas

Water-Resources Investigations Report↗
USGS2001

Mountain Island Lake, North Carolina: Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics, 1996–97

Mountain Island Lake is an impoundment of the Catawba River in North Carolina and supplies drinking water to more than 600,000 people in Charlotte, Gastonia, Mount Holly, and several other communities. The U.S. Geological Survey, in cooperation with the Charlotte-Mecklenburg Utilities, conducted an investigation of the reservoir to characterize hydrologic and water-quality conditions and to develop and apply a simulation model to predict the response of the reservoir to changes in constituent loadings or the flow regime. During 1996–97, flows into Mountain Island Lake were dominated by releases from Cowans Ford Dam on Lake Norman, with more than 85 percent of the total inflow to the reservoir coming from Lake Norman. Riverbend Steam Station discharges accounted for about 12 percent of the inflows to the reservoir, and inflows from tributary streams contributed less than 1.5 percent of the total inflows. Releases through Mountain Island Dam accounted for about 81 percent of outflows from the reservoir, while Riverbend Steam Station withdrawals, which were equal to discharge from the facility, constituted about 13 percent of the reservoir withdrawals. About 5.5 percent of the withdrawals from the reservoir were for water supply. Strong thermal stratification was seldom observed in Mountain Island Lake during April 1996-September 1997. As a result, dissolved-oxygen concentrations were only infrequently less than 4 milligrams per liter, and seldom less than 5 milligrams per liter throughout the entire reservoir, including the coves. The Riverbend Steam Station thermal discharge had a pronounced effect on surface-water temperatures near the outfall. McDowell Creek, which drains to McDowell Creek cove, receives treated wastewater from a large municipal facility and has exhibited signs of poor water-quality conditions in the past. During April 1996-September 1997, concentrations of nitrate, ammonia, total phosphorus, and chlorophyll a were higher in McDowell Creek cove than elsewhere throughout the reservoir. Nevertheless, the highest chlorophyll a concentration measured during the study was 13 micrograms per liter—well below the North Carolina ambient water-quality standard of 40 micrograms per liter. In the mainstem of the reservoir, near-bottom ammonia concentrations occasionally were greater than near-surface concentrations. However, the relatively large top-to-bottom differences in ammonia and phosphorus that have been observed in other Catawba River reservoirs were not present in Mountain Island Lake. External loadings of suspended solids, nitrogen, phosphorus, and biochemical oxygen demand were determined for May 1996-April 1997. Flows through Cowans Ford Dam contributed more than 80 percent of the biochemical oxygen demand and nitrogen load to the reservoir, with McDowell Creek contributing about 15 percent of the biochemical oxygen demand load. In contrast, McDowell Creek contributed about half of the phosphorus load to the reservoir, while inflows through Cowans Ford Dam contributed about one-fourth of the phosphorus load, and the McDowell Creek wastewater-treatment plant contributed about 15 percent of the total phosphorus load. The remainder of the phosphorus loadings came from Gar Creek and the discharge from the Riverbend ash settling pond. Mountain Island Lake is a relatively small (11.3-square-kilometer surface area) impoundment. An area of 181 square kilometers drains directly to the reservoir, but much of this area is undergoing development. In addition, the reservoir receives treated effluent from a municipal wastewater-treatment facility. The two-dimensional, laterally averaged model CE-QUAL-W2 was applied to Mountain Island Lake. The model was configured to simulate water level, water temperature, and 12 water-quality constituents. The model included the mainstem, four coves, three point-source discharges, and three withdrawals. Simulated water levels generally were within 10 centimeters of measured values, indicating a good calibration of the water balance for the reservoir. The root-mean-square difference between measured and simulated water temperatures was about 1 to 1.5 degrees Celsius, and vertical distributions of water temperature were accurately simulated in both the mainstem and coves. Seasonal and spatial patterns of nitrate, ammonia, orthophosphorus, and chlorophyll a were reasonably reproduced by the water-quality model. Because of the absence of the denitrification process in the model formulation, nitrate concentrations typically were overpredicted. Simulated and measured ammonia concentrations seldom differed by more than 0.01 milligram per liter, and simulations of seasonal fluctuations in chlorophyll a were representative of measured conditions. The root mean square of the difference between measured and simulated dissolved-oxygen concentrations was about 1 milligram per liter. The calibrated water-quality model was applied to evaluate (1) the movement of a conservative, neutrally buoyant material, or tracer, through the reservoir for several sets of conditions; (2) the effects of the Riverbend thermal discharge on water temperature in the reservoir; (3) the effects of changes in water-supply withdrawal rates on water-quality conditions; and (4) changes in reservoir water quality in response to changes in point- and nonpoint-source loadings. In general, dissolved material entering Mountain Island Lake from both Cowans Ford Dam and McDowell Creek during the summer moves along the bottom of the lake toward Mountain Island Dam, with little mixing of dissolved material into the surface layers. Simulations suggest that dissolved material can move upstream in the reservoir when flows from Cowans Ford Dam are near zero. Dissolved material can remain in Mountain Island Lake for a period far in excess of the theoretical retention time of 12 days. Simulations indicated that the Riverbend thermal discharge increases water temperature in the surface layers of the downstream part of the reservoir by as much as 5 degrees Celsius. However, the discharge has little effect on near-bottom water temperature. Based on model simulations, a proposed doubling of the water-supply withdrawals from Mountain Island Lake has no readily apparent effect on water quality in the reservoir. The increased withdrawal rate may have some localized effects on circulation in the reservoir, but a more detailed model of the intake zone would be required to identify those effects. The effects of a 20-percent increase in water-chemistry loadings through Cowans Ford Dam and from McDowell Creek were simulated separately. Increased loadings from Cowans Ford Dam had about the same effect on water-quality conditions near Mountain Island Dam as did increased loadings from McDowell Creek. Maintaining good water quality in Mountain Island Lake depends on maintaining good water quality in Lake Norman as well as in the inflows from the McDowell Creek watershed.

North Carolina↗
USGS2001

An evaluation of borehole flowmeters used to measure horizontal ground-water flow in limestones of Indiana, Kentucky, and Tennessee, 1999

Three borehole flowmeters and hydrophysical logging were used to measure ground-water flow in carbonate bedrock at sites in southeastern Indiana and on the west-central border of Kentucky and Tennessee. The three flowmeters make point measurements of the direction and magnitude of horizontal flow, and hydrophysical logging measures the magnitude of horizontal flowover an interval. The directional flowmeters evaluated include a horizontal heat-pulse flowmeter, an acoustic Doppler velocimeter, and a colloidal borescope flowmeter. Each method was used to measure flow in selected zones where previous geophysical logging had indicated water-producing beds, bedding planes, or other permeable features that made conditions favorable for horizontal-flow measurements. Background geophysical logging indicated that ground-water production from the Indiana test wells was characterized by inflow from a single, 20-foot-thick limestone bed. The Kentucky/Tennessee test wells produced water from one or more bedding planes where geophysical logs indicated the bedding planes had been enlarged by dissolution. Two of the three test wells at the latter site contained measurable vertical flow between two or more bedding planes under ambient hydraulic head conditions. Field measurements and data analyses for each flow-measurement technique were completed by a developer of the technology or by a contractor with extensive experience in the application of that specific technology. Comparison of the horizontal-flow measurements indicated that the three point-measurement techniques rarely measured the same velocities and flow directions at the same measurement stations. Repeat measurements at selected depth stations also failed to consistently reproduce either flow direction, flow magnitude, or both. At a few test stations, two of the techniques provided similar flow magnitude or direction but usually not both. Some of this variability may be attributed to naturally occurring changes in hydraulic conditions during the 1-month study period in August and September 1999. The actual velocities and flow directions are unknown; therefore, it is uncertain which technique provided the most accurate measurements of horizontal flow in the boreholes and which measurements were most representative of flow in the aquifers. The horizontal heat-pulse flowmeter consistently yielded flow magnitudes considerably less than those provided by the acoustic Doppler velocimeter and colloidal borescope. The design of the horizontal heat-pulse flowmeter compensates for the local acceleration of ground-water velocity in the open borehole. The magnitude of the velocities estimated from the hydrophysical logging were comparable to those of the horizontal heat-pulse flowmeter, presumably because the hydrophysical logging also effectively compensates for the effect of the borehole on the flow field and averages velocity over a length of borehole rather than at a point. The acoustic Doppler velocimeter and colloidal borescope have discrete sampling points that allow for measuring preferential flow velocities that can be substantially higher than the average velocity through a length of borehole. The acoustic Doppler velocimeter and colloidal borescope also measure flow at the center of the borehole where the acceleration of the flow field should be greatest. Of the three techniques capable of measuring direction and magnitude of horizontal flow, only the acoustic Doppler velocimeter measured vertical flow. The acoustic Doppler velocimeter consistently measured downward velocity in all test wells. This apparent downward flow was attributed, in part, to particles falling through the water column as a result of mechanical disturbance during logging. Hydrophysical logging yielded estimates of vertical flow in the Kentucky/Tennessee test wells. In two of the test wells, the hydrophysical logging involved deliberate isolation of water-producing bedding planes with a packer to ensure that small horizontal flow could be quantified without the presence of vertical flow. The presence of vertical flow in the Kentucky/Tennessee test wells may preclude the definitive measurement of horizontal flow without the use of effective packer devices. None of the point-measurement techniques used a packer, but each technique used baffle devices to help suppress the vertical flow. The effectiveness of these baffle devices is not known; therefore, the effect of vertical flow on the measurements cannot be quantified. The general lack of agreement among the point-measurement techniques in this study highlights the difficulty of using measurements at a single depth point in a borehole to characterize the average horizontal flow in a heterogeneous aquifer. The effective measurement of horizontal flow may depend on the precise depth at which measurements are made, and the measurements at a given depth may vary over time as hydraulic head conditions change. The various measurements also demonstrate that the magnitude and possibly the direction of horizontal flow are affected by the presence of the open borehole. Although there is a lack of agreement among the measurement techniques, these results could mean that effective characterization of horizontal flow in heterogeneous aquifers might be possible if data from many depth stations and from repeat measurements can be averaged over an extended time period. Complications related to vertical flow in the borehole highlights the importance of using background logging methods like vertical flowmeters or hydrophysical logging to characterize the borehole environment before horizontal-flow measurements are attempted. If vertical flow is present, a packer device may be needed to acquire definitive measurements of horizontal flow. Because hydrophysical logging provides a complete depth profile of the borehole, a strength of this technique is in identifying horizontal- and vertical-flow zones in a well. Hydrophysical logging may be most applicable as a screening method. Horizontal- flow zones identified with the hydrophysical logging then could be evaluated with one of the point-measurement techniques for quantifying preferential flow zones and flow directions. Additional research is needed to determine how measurements of flow in boreholes relate to flow in bedrock aquifers. The flowmeters may need to be evaluated under controlled laboratory conditions to determine which of the methods accurately measure ground-water velocities and flow directions. Additional research also is needed to investigate variations in flow direction with time, daily changes in velocity, velocity corrections for fractured bedrock aquifers and unconsolidated aquifers, and directional differences in individual wells for hydraulically separated flow zones.

Indiana, Kentucky, Tennessee↗
USGS2001

Low-flow characteristics of streams in Ohio through water year 1997

This report presents selected low-flow and flow-duration characteristics for 386 sites throughout Ohio. These sites include 195 long-term continuous- record stations with streamflow data through water year 1997 (October 1 to September 30) and for 191 low-flow partial-record stations with measurements into water year 1999. The characteristics presented for the long-term continuous-record stations are minimum daily streamflow; average daily streamflow; harmonic mean flow; 1-, 7-, 30-, and 90-day minimum average low flow with 2-, 5-, 10-, 20-, and 50-year recurrence intervals; and 98-, 95-, 90-, 85-, 80-, 75-, 70-, 60-, 50-, 40-, 30-, 20-, and 10-percent daily duration flows. The characteristics presented for the low-flow partial-record stations are minimum observed streamflow; estimated 1-, 7-, 30-, and 90-day minimum average low flow with 2-, 10-, and 20-year recurrence intervals; and estimated 98-, 95-, 90-, 85- and 80-percent daily duration flows. The low-flow frequency and duration analyses were done for three seasonal periods (warm weather, May 1 to November 30; winter, December 1 to February 28/29; and autumn, September 1 to November 30), plus the annual period based on the climatic year (April 1 to March 31).

Ohio↗
USGS2001

Hydrologic data and a proposed water-quality monitoring network for the Kobuk River basin, Gates of the Arctic National Park and Preserve, and Kobuk Valley National Park, Alaska

Located in northwestern Alaska, the Kobuk River drains a watershed of approximately 12,300 square miles. Two national parks are located in the basin: the entire Kobuk Valley National Park and and a portion of Gates of the Arctic National Park and Preserve. Reconnaissance-type water-quality data collected on the Kobuk River and some of its tributaries indicate that the water is of a calcium to calcium-magnesium-bicarbonate type. To design a representative water-quality monitoring network, a geographical information system (GIS) of the Kobuk River Basin was created. The GIS was used with a statistical technique, cluster analysis, to stratify the Kobuk River Basin into different regions. Potential water-quality monitoring sites were then selected from these regions.

Alaska↗
USGS2001

Estimated flow-duration curves for selected ungaged sites in Kansas

Flow-duration curves for 1968-98 were estimated for 32 ungaged sites in the Missouri, Smoky Hill-Saline, Solomon, Marais des Cygnes, Walnut, Verdigris, and Neosho River Basins in Kansas. Also included from a previous report are estimated flow-duration curves for 16 ungaged sites in the Cimarron and lower Arkansas River Basins in Kansas. The method of estimation used six unique factors of flow duration: (1) mean streamflow and percentage duration of mean streamflow, (2) ratio of 1-percent-duration streamflow to mean streamflow, (3) ratio of 0.1-percent-duration streamflow to 1-percent-duration streamflow, (4) ratio of 50-percent-duration streamflow to mean streamflow, (5) percentage duration of appreciable streamflow (0.10 cubic foot per second), and (6) average slope of the flow-duration curve. These factors were previously developed from a regionalized study of flow-duration curves using streamflow data for 1921-76 from streamflow-gaging stations with drainage areas of 100 to 3,000 square miles. The method was tested on a currently (2001) measured, continuous-record streamflow-gaging station on Salt Creek near Lyndon, Kansas, with a drainage area of 111 square miles and was found to adequately estimate the computed flow-duration curve for the station. The method also was tested on a currently (2001) measured, continuous-record, streamflow-gaging station on Soldier Creek near Circleville, Kansas, with a drainage area of 49.3 square miles. The results of the test on Soldier Creek near Circleville indicated that the method could adequately estimate flow-duration curves for sites with drainage areas of less than 100 square miles. The low-flow parts of the estimated flow-duration curves were verified or revised using 137 base-flow discharge measurements made during 1999-2000 at the 32 ungaged sites that were correlated with base-flow measurements and flow-duration analyses performed at nearby, long-term, continuous-record, streamflow-gaging stations (index stations). The method did not adequately estimate the flow-duration curves for two sites in the western one-third of the State because of substantial changes in farming practices (terracing and intensive ground-water withdrawal) that were not accounted for in the two previous studies (Furness, 1959; Jordan, 1983). For these two sites, there was enough historic, continuous-streamflow record available to perform record-extension techniques correlated to their respective index stations for the development of the estimated flow-duration curves. The estimated flow-duration curves at the ungaged sites can be used for projecting future flow frequencies for assessment of total maximum daily loads (TMDLs) or other water-quality constituents, water-availability studies, and for basin-characteristic studies.

Water-Resources Investigations Report↗
USGS2001

Regional curve development and selection of a reference reach in the non-urban, lowland sections of the Piedmont physiographic province, Pennsylvania and Maryland

Stream-restoration projects utilizing naturalstream designs frequently are based on the bankfull- channel characteristics of a stream reach that is accommodating streamflow and sediment transport without excessive erosion or deposition. The bankfull channel is identified by the use of field indicators and confirmed with tools such as regional curves. Channel dimensions were surveyed at six streamflow-measurement stations operated by the U.S. Geological Survey in the Gettysburg-Newark Lowlands Section and Piedmont Lowlands Section of the Piedmont Physiographic Province in Pennsylvania and Maryland. Regional curves were developed from regression analyses of the relation between drainage area and cross-sectional area, mean depth, width, and streamflow of the bankfull channel. Regional curves were used to confirm the identification of the bankfull channel at a reference reach. Stream dimensions and characteristics of the reference reach were measured for extrapolation into the design of a steam-restoration project on Bermudian Creek in Adams County, Pa. Dimensions for cross-sectional area, mean depth, width, and computed streamflow of the bankfull channel in all surveyed riffle cross sections in the reference reach were within the 95-percent confidence interval bounding the regression line representing bankfull channel geometry in the Lowland Sections of the Piedmont Physiographic Province. The average bankfull cross-sectional area, bankfull mean depth, and computed bankfull discharge for riffle cross sections in the reference reach ranged from 15.4 to 16.5 percent less than estimates determined from the lowland regional curves. Average bankfull channel width was about 2 percent greater than estimates. Cross-sectional area, mean depth, and computed streamflow corresponding to the bankfull stage at the reference reach were 31.4, 44.4, and 9.6 percent less, respectively, than estimates derived from the regional curves developed by Dunne and Leopold in 1978. Average bankfull channel width at the reference reach was 16.7 percent greater than the Dunne and Leopold estimate. The concepts of regional curves and reference reaches can be valuable tools to support efforts in stream restoration. Practitioners of stream restoration need to recognize them as such and realize their limitations. The small number of stations available for analysis is a major limiting factor in the strength of the results of this investigation. Subjective selection criteria may have unnecessarily eliminated streamflow-measurement stations that could have been included in the regional curves. A bankfull discharge with a recurrence interval within the 1- to 2-year range was used as a criteria for confirmation of the bankfull stage at each streamflow-measurement station. Many researchers accept this range for recurrence interval of the bankfull discharge; however, literature provides contradictory evidence. The use of channel-characteristics data from a reference reach without any monitoring data to document the stability of the reference reach over time is a topic of debate.

Water-Resources Investigations Report↗
USGS2001

Occurrence and distribution of enteric viruses in shallow ground water and factors affecting well vulnerability to microbiological contamination in Worcester and Wicomico counties, Maryland

The U.S. Geological Survey, in cooperation with the Maryland Department of the Environment and the Wisconsin State Laboratory of Hygiene, conducted a study to characterize the occurrence and distribution of viral contamination in small (withdrawing less than 10,000 gallons per day) public water-supply wells screened in the water-table aquifer in the Coastal Plain in Worcester and Wicomico Counties, Maryland.Two hundred seventy-eight well sites were evaluated with regard to simulated ground-water flow paths, land use, natural soils groups, and well characteristics, such as well depth and well age. Flow and transport simulations of the water-table aquifer indicated that wells screened less than about 50 feet below land surface (shallow wells) were most vulnerable to surface contamination, which in some cases could originate from as far as 2,000 feet upgradient of the well. Animal-feeding and agricultural-storage operations were considered among the most likely sources for viral contamination; therefore, sites close to these activities were considered most vulnerable. Soil groups were evaluated with regard to depth to water and moisture-holding capacity. Wells with shallow depths to water or in very sandy soils were considered more vulnerable to contamination than deep wells (greater than 50 feet) and those completed in finer-grained soils. Older wells and wells where coliform bacteria had been detected in the past were classified as highly vulnerable. On the basis of this evaluation, 27 sites considered to be susceptible were sampled.Samples were collected by pumping up to 400 gallons of untreated well water through an electropositive filter. Water concentrates were subjected to cell-culture assay for the detection of culturable viruses and reverse-transcription polymerase chain reaction/gene probe assays to detect nonculturable viruses; grab samples were analyzed for somatic and male-specific coliphages, Bacteroides fragilis, Clostridium perfringens, enterococci, Escherichia coli, total coliforms, total oxidized nitrogen, dissolved organic carbon, organic nitrogen, total phosphate, orthophosphate, acid-neutralizing capacity, pH, specific conductance, temperature, and dissolved oxygen.Eleven percent of the samples analyzed (3 of 27) tested positive for either culturable viruses or the presence of viral ribonucleic acid. Approximately 15 percent of the samples (4 of 27) tested positive for one or more bacterial contaminants.

Water-Resources Investigations Report↗
USGS2001

Ground water near Newton, Jasper County, Iowa

The U.S. Geological Survey, in cooperation with the city of Newton, Iowa, conducted an investigation of the ground-water resources of Jasper County, Iowa, near Newton during 1999-2001. The purpose of the investigation was to provide additional information on the South Skunk River alluvial aquifer from which Newton obtains its present municipal supply and to summarize the available information on other groundwater resources in the county. The South Skunk River alluvial aquifer consists of unconsolidated deposits of sand and gravel of glacial and fluvial origin. These deposits overlie bedrock composed primarily of shale and limestone of Pennsylvanian or Mississippian age. Information on the South Skunk River alluvial aquifer and other Jasper County alluvial aquifers is limited to a few test holes in a few locations. Additional thickness and lithologic information was collected using seismic refraction and test hole drilling to increase the understanding of the South Skunk River alluvial aquifer near Newton. Water-level and water-quality information also was collected. The alluvial deposits along the South Skunk River near Newton range from less than 30 to more than 60 feet thick. Three areas of deposits exceeding 60 feet thick occur near the present city of Newton well field about 5,000 feet west of the present well field, at the present well field, and about 5,000 feet southeast of the present well field. Ground water in the South Skunk River alluvial aquifer near the Newton well field flows toward the municipal well field. Ground-water levels on the well-field side of the South Skunk River were lower than water levels in the river, indicating flow from the river toward the well field. The water quality in the South Skunk River and the alluvial aquifer was similar, except most ground-water samples contained low dissolved oxygen concentrations. The low dissolved-oxygen concentrations in ground water resulted in high concentrations of iron and manganese in some locations and reduced forms of nitrogen.

Iowa↗
USGS2001

Relations for estimating unit-hydrograph parameters in New Mexico

Data collected from 20 U.S. Geological Survey streamflow-gaging stations, most of which were operated in New Mexico between about 1969 and 1977, were used to define hydrograph characteristics for small New Mexico streams. Drainage areas for the gaging stations ranged from 0.23 to 18.2 square miles. Observed values for the hydrograph characteristics were determined for 87 of the most significant rainfall-runoff events at these gaging stations and were used to define regional regression relations with basin characteristics. Regional relations defined lag time (tl), time of concentration (tc), and time to peak (tp) as functions of stream length and basin shape. The regional equation developed for time of concentration for New Mexico agrees well with the Kirpich equation developed for Tennessee. The Kirpich equation is based on stream length and channel slope, whereas the New Mexico equation is based on stream length and basin shape. Both equations, however, underestimate tc when applied to larger basins where tc is greater than about 2 hours. The median ratio between tp and tc for the observed data was 0.66, which equals the value (0.67) recommended by the Natural Resources Conservation Service (formerly the Soil Conservation Service). However, the median ratio between tl and tc was only 0.42, whereas the commonly used ratio is 0.60. A relation also was developed between unit-peak discharge (qu) and time of concentration. The unit-peak discharge relation is similar in slope to the Natural Resources Conservation Service equation, but the equation developed for New Mexico in this study produces estimates of qu that range from two to three times as large as those estimated from the Natural Resources Conservation Service equation. An average value of 833 was determined for the empirical constant Kp. A default value of 484 has been used by the Natural Resources Conservation Service when site-specific data are not available. The use of a lower value of Kp in calculations generally results in a lower peak discharge. A relation between the empirical constant Kp and average channel slope was defined in this study. The predicted Kp values from the equation ranged from 530 to 964 for the 20 flood-hydrograph gaging stations. The standard error of estimate for the equation is 36 percent.

Water-Resources Investigations Report↗
USGS2001

Approach for delineation of contributing areas and zones of transport to selected public-supply wells using a regional ground-water flow model, Palm Beach County, Florida

Rapid urban development and population growth in Palm Beach County, Florida, have been accompanied with the need for additional freshwater withdrawals from the surficial aquifer system. To maintain water quality, County officials protect capture areas and determine zones of transport of municipal supply wells. A multistep process was used to help automate the delineation of wellhead protection areas. A modular ground-water flow model (MODFLOW) Telescopic Mesh Refinement program (MODTMR) was used to construct an embedded flow model and combined with particle tracking to delineate zones of transport to supply wells; model output was coupled with a geographic information system. An embedded flow MODFLOW model was constructed using input and output file data from a preexisting three-dimensional, calibrated model of the surficial aquifer system. Three graphical user interfaces for use with the geographic information software, ArcView, were developed to enhance the telescopic mesh refinement process. These interfaces include AvMODTMR for use with MODTMR; AvHDRD to build MODFLOW river and drain input files from dynamically segmented linear (canals) data sets; and AvWELL Refiner, an interface designed to examine and convert well coverage spatial data layers to a MODFLOW Well package input file. MODPATH (the U.S. Geological Survey particle-tracking postprocessing program) and MODTOOLS (the set of U.S. Geological Survey computer programs to translate MODFLOW and MODPATH output to a geographic information system) were used to map zones of transport. A steady-state, five-layer model of the Boca Raton area was created using the telescopic mesh refinement process and calibrated to average conditions during January 1989 to June 1990. A sensitivity analysis of various model parameters indicates that the model is most sensitive to changes in recharge rates, hydraulic conductivity for layer 1, and leakance for layers 3 and 4 (Biscayne aquifer). Recharge (58 percent); river (canal) leakance (29 percent); and inflow through the northern, western, and southern prescribed flux model boundaries (10 percent) represent the major inflow components. Principal outflow components in the Boca Raton well field area include well discharge (56 percent), river (canal) leakance (27 percent), and water that discharges along the coast (10 percent). A particle-tracking analysis using MODPATH was conducted to better understand well-field ground-water flow patterns and time of travel. MODTOOLS was used to construct zones-of-transport spatial data for municipal supply wells. Porosity estimates were uniformly increased to study the effect of porosity on zones of transport. Where porosity was increased, the size of the zones of transport were shown to decrease.

Water-Resources Investigations Report↗
USGS2001

Ground-water quality in Geauga County, Ohio — Review of previous studies, status in 1999, and comparison of 1986 and 1999 data

Most residents in Geauga County, Ohio, rely on ground water as their primary source of drinking water. With population growing at a steady rate, the possibility that human activity will affect ground-water quality becomes considerable. This report presents the results of a study by the U.S. Geological Survey (USGS), in cooperation with the Geauga County Planning Commission and Board of County Commissioners, to provide a brief synopsis of work previously done within the county, to assess the present (1999) ground-water quality, and to determine any changes in groundwater quality between 1986 and 1999. Previous studies of ground-water quality in the county have consistently reported that manganese and iron concentrations in ground water in Geauga County often exceed the U.S. Environmental Protection Agency (USEPA) Secondary Maximum Contaminant Level (SMCL). Road salt and, less commonly, oil-field brines and volatile organic compounds (VOCs) have been found in ground water at isolated locations. Nitrate has not been detected above the USEPA Maximum Contaminant Level (MCL) of 10 milligrams per liter as N; however, nitrate has been found in some locations at levels that may indicate the effects of fertilizer application or effluent from septic systems. Between June 7 and July 1, 1999, USGS personnel collected a total of 31 water-quality samples from wells completed in glacial deposits, the Pottsville Formation, the Cuyahoga Group, and the Berea Sandstone. All samples were analyzed for VOCs, sulfide, dissolved organic carbon, major ions, trace elements, alkalinity, total coliforms, and Escherichia coli bacteria. Fourteen of the samples also were analyzed for tritium. Water-quality data were used to determine (1) suitability of water for drinking, (2) age of ground water, (3) stratigraphic variation in water quality, (4) controls on water quality, and (5) temporal variation in water quality. Water from 16 of the 31 samples exceeded the Geauga County General Health District’s standard of 0 colonies of total coliform bacteria per 100 milliliters of water. Esthetically based SMCLs were exceeded in the indicated number of wells for pH (8), sulfate (1), dissolved solids (3), iron (19), and manganese (18). Hydrogen sulfide was detected at or above the detection limit of 0.01 milligram per liter in 17 of the 31 water samples. A range of water types was found among and within the four principal stratigraphic units. The waters can be categorized in three groups based on predominant anion type: bicarbonatetype waters, chloride-type waters, and sulfatetype waters. Chloride-to-bromide ratio analyses indicate that water from 8 of the 31 wells is in some way affected by human activity. Five other samples were in a chloride-to-bromide ratio range that could indicate possible effects of human activity. Ground-water-quality data from the current study were compared to data collected in 1986. Statistical analyses of data from the 16 wells that were sampled in both years did not indicate any significant changes that could be attributed to human activity.

Ohio↗
USGS2001

Nutrient and suspended-sediment concentrations and loads and benthic-invertebrate data for tributaries to the St. Croix River, Wisconsin and Minnesota, 1997-99

Nutrient and suspended-sediment data were collected on major tributaries to the St. Croix River during 1997-99 as part of three studies. The first study, done in 1997 as part of the U.S. Geological Survey?s National Water-Quality Assessment Program Upper Mississippi Study Unit, was a widespread synoptic survey of nutrient and suspended-sediment concentrations, loads, and yields during snowmelt. Runoff from snowmelt in agricultural areas and other areas with low permeability soils had significantly greater nutrient concentrations than forested areas, whereas differences in suspended-sediment loading were not detected. In 1998, synoptic samplings of 11 tributaries were done during snowmelt, base-flow, and storm-runoff periods. These studies showed that the Apple, Willow, and Kinnickinnic Rivers were major contributors of suspended sediments and nutrients to the St. Croix River during base flow and storm-runoff events. Nitrate concentrations were high during base flow in the agricultural tributaries?specifically, the Kinnickinnic (4.83 mg/L), Willow (1.53 mg/L), and Apple (0.79 mg/L) Rivers?possibly from ground-water recharge or point-source contributions. Extensive water-quality sampling was done monthly and during high-flow events in water year 1999 (October 1, 1998 to September 30, 1999) in coordination with continuous streamflow monitoring at 12 sites in the St. Croix River Basin. These data were used to compute annual nutrient and suspended-sediment loads and yields at the monitored sites for water year 1999. Relations among environmental characteristics and calculated annual nutrient and suspended-sediment yields were used to estimate loading from unmonitored parts of the basin. The environmental characteristics found to best estimate annual yields were soil characteristics (clay, permeability of soil, and erodibility), basin slope and area, and the percentages of wetland and urban areas in the basins. Variability in 1999 rainfall intensity resulted in annual yields from several northern, forested basins being higher than those from the southern, agricultural basins. The Sunrise River had the highest annual suspended-sediment and nutrient yields in the basin in 1999. Concentrations and instantaneous loading rates varied as much among various flow conditions at individual sites as among sites during the three years of study. Benthic invertebrates were sampled and indices of water quality were calculated at 16 tributaries in fall 1999. Benthic invertebrate indices indicated excellent to good water quality at all tributaries except Valley Creek, Willow River, and Kettle River. No relations were found between benthic invertebrate indices and the calculated and estimated 1999 annual tributary loads and yields.

Minnesota, Wisconsin↗
USGS2001

Evaluation of passive diffusion bag samplers in selected wells at the Naval Surface Warfare Center, Louisville, Kentucky, July 1999 to January 2000

Passive diffusion bag samplers were tested in 11 wells at the Naval Surface Warfare Center, Louisville, Kentucky, by comparing the volatile organic compound concentrations obtained from passive diffusion bag samplers to volatile organic compound concentrations obtained by pumping the wells. The wells were screened in poorly permeable formations, including overburden, shale, and limestone. In five of the tested wells containing detectable volatile organic compound contamination, the data suggest that the diffusion samplers accurately reflected ambient contaminant concentrations (wells 1-NEC-15-P, 1-NEC-MW17-S, 1-NEMW23-S, 1-NW-MW24-S, and 1-NW-MW24-P). Comparison of a third well (1-NEC-MW34-S), in which the passive diffusion bag samplers produced higher concentrations than the pumped sample, is less certain because the passive diffusion bag sampler had passed through a layer of light non-aqueous phase liquid during deployment, suggesting the possibility of carryover contamination. In two wells (1-NE-MW23-P and 1-NEC-MW15-S), it was unclear whether concentrations obtained by using the passive diffusion bag samplers adequately represented in situ concentrations because the comparison of concentrations obtained by using the samplers and the pump was inconsistent between sampling events and/or between volatile organic compounds. In one well (1-NEC-MW34-P), the methodologies matched poorly, with volatile organic compound concentrations obtained by using the passive diffusion bag sampler substantially lower than those obtained by using the pump. Two of the tested wells (1-NW-MW6-I and 1-SE-MW13-I) contained no detectable contaminants in water obtained from either method. Data from wells where multiple passive diffusion bag samplers were deployed showed the lowest volatile organic compound concentrations adjacent to the vuggy limestone and higher volatile organic compound concentrations deeper in the limestone, supporting colloidal-borescope data that indicate the vuggy limestone is not a zone that supplies water to the wells.

Water-Resources Investigations Report↗
USGS2001

Freshwater flow from estuarine creeks into northeastern Florida Bay

Water-level, water-velocity, salinity, and temperature data were collected from selected estuarine creeks to compute freshwater flow into northeastern Florida Bay. Calibrated equations for determining mean velocity from acoustic velocity were obtained by developing velocity relations based on direct acoustic measurements, acoustic line velocity, and water level. Three formulas were necessary to describe flow patterns for all monitoring sites, with R2 (coefficient of determination) values ranging from 0.957 to 0.995. Cross-sectional area calculations were limited to the main channel of the creeks and did not include potential areas of overbank flow. Techniques also were used to estimate discharge at noninstrumented sites by establishing discharge relations to nearby instrumented sites. Results of the relation between flows at instrumented and noninstrumented sites varied with R2 values ranging from 0.865 to 0.99. West Highway Creek was used to estimate noninstrumented sites in Long Sound, and Mud Creek was used to estimate East Creek in Little Madeira Bay. Mean monthly flows were used to describe flow patterns and to calculate net flow along the northeastern coastline. Data used in the study were collected from October 1995 through September 1999, which includes the El Nino event of 1998. During this period, about 80 percent of the freshwater flowing into the bay occurred during the wet season (May-October). The mean freshwater discharge for all five instrumented sites during the wet season from 1996 to 1999 is 106 cubic feet per second. The El Nino event caused a substantial increase (654 percent) in mean flows during the dry season (November-April) at the instrumented sites, ranging from 8.5 cubic feet per second in 1996-97 to 55.6 cubic feet per second in 1997-98. Three main flow signatures were identified when comparing flows at all monitoring stations. The most significant was the magnitude of discharges at Trout Creek, which carries about 50 percent of the total measured freshwater entering northeastern Florida Bay. The mean monthly wet-season (May-October) flow at Trout Creek is about 340 cubic feet per second, compared to 55 cubic feet per second at West Highway Creek, 52 cubic feet per second at Taylor River, 49 cubic feet per second at Mud Creek, and 33 cubic feet per second at McCormick Creek. The other two flow signatures are the decline of freshwater discharge at McCormick Creek at the start of the El Nino event, and the absence of net-negative flows at West Highway Creek. The observed flow distribution within the study area, suggests that the overall flow direction of freshwater in the Everglades wetlands in the lower part of Taylor Slough may have a strong eastward flow component as water approaches the coastline. Data analysis also indicates that Trout Creek could potentially be used as a long-term monitoring station to estimate total freshwater flow into northeastern Florida Bay, provided that the remaining questions regarding flow patterns at McCormick Creek and the creeks in Long Sound are answered and that no major changes in flow characteristics occur in the future.

Water-Resources Investigations Report↗