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USGS2003

Potential for saltwater intrusion into the lower Tamiami aquifer near Bonita Springs, southwestern Florida

A study was conducted to examine the potential for saltwater intrusion into the lower Tamiami aquifer beneath Bonita Springs in southwestern Florida. Field data were collected, and constant- and variable-density ground-water flow simulations were performed that: (1) spatially quantified modern and seasonal stresses, (2) identified potential mechanisms of saltwater intrusion, and (3) estimated the potential extent of saltwater intrusion for the area of concern. MODFLOW and the inverse modeling routine UCODE were used to spatially quantify modern and seasonal stresses by calibrating a constant-density ground-water flow model to field data collected in 1996. The model was calibrated by assuming hydraulic conductivity parameters were accurate and by estimating unmonitored ground-water pumpage and potential evapotranspiration with UCODE. Uncertainty in these estimated parameters was quantified with 95-percent confidence intervals. These confidence intervals indicate more uncertainty (or less reliability) in the estimates of unmonitored ground-water pumpage than estimates of pan-evaporation multipliers, because of the nature and distribution of observations used during calibration. Comparison of simulated water levels, streamflows, and net recharge with field data suggests the model is a good representation of field conditions. Potential mechanisms of saltwater intrusion into the lower Tamiami aquifer include: (1) lateral inland movement of the freshwater-saltwater interface from the southwestern coast of Florida; (2) upward leakage from deeper saline water-bearing zones through natural upwelling and upconing, both of which could occur as diffuse upward flow through semiconfining layers, conduit flow through karst features, or pipe flow through leaky artesian wells; (3) downward leakage of saltwater from surface-water channels; and (4) movement of unflushed pockets of relict seawater. Of the many potential mechanisms of saltwater intrusion, field data and variable-density ground-water flow simulations suggest that upconing is of utmost concern, and lateral encroachment is of second-most concern. This interpretation is uncertain, however, because the predominance of saltwater intrusion through leaky artesian wells with connection to deeper, more saline, and higher pressure aquifers was difficult to establish. Effective management of ground-water resources in southwestern Florida requires an understanding of the potential extent of saltwater intrusion in the lower Tamiami aquifer near Bonita Springs. Variable-density, ground-water flow simulations suggest that when saltwater is at dynamic equilibrium with 1996 seasonal stresses, the extent of saltwater intrusion is about 100 square kilometers areally and 70,000 hectare-meters volumetrically. The volumetric extent of saltwater intrusion was most sensitive to changes in recharge, ground-water pumpage, sea level, salinity of the Gulf of Mexico, and the potentiometric surface of the sandstone aquifer, respectively.

Florida↗
USGS2003

Public Water-Supply Systems and Associated Water Use in Tennessee, 2000

Public water-supply systems in Tennessee provide water to meet customer needs for domestic, industrial, and commercial users and municipal services. In 2000, more than 500 public water-supply systems distributed about 890 million gallons per day (Mgal/d) of surface water and ground water to a population of about 5 million in Tennessee. Surface-water sources provided 64 percent (about 569 Mgal/d) of the State?s water supplies, primarily in Middle and East Tennessee. Ground water produced from wells and springs in Middle and East Tennessee and from wells in West Tennessee provided 36 percent (about 321 Mgal/d) of the public water supplies. Springs in Middle and East Tennessee provided about 14 percent (about 42 Mgal/d) of ground-water supplies used in the State. Per capita water use for Tennessee in 2000 was about 136 gallons per day. An additional 146 public water-supply systems provided approximately 84 Mgal/d of water supplies that were purchased from other water systems. Water withdrawals by public water-supply systems in Tennessee have increased by over 250 percent; from 250 Mgal/d in 1955 to 890 Mgal/d in 2000. Although Tennessee public water-supply systems withdraw less ground water than surface water, ground-water withdrawal rates reported by these systems continue to increase. In addition, the number of public water-supply systems reporting ground-water withdrawals of 1 Mgal/d or more in West Tennessee is increasing.

Water-Resources Investigations Report↗
USGS2004

Characteristics of and Areas Contributing Recharge to Public-Supply Springs in Massachusetts

The geohydrologic and physical characteristics were determined for 28 public-supply springs, 27 of which are in western Massachusetts. Discharge ranged from zero at various small intermittent springs to more than 240 gallons per minute at Waubeeka Springs in Williamstown, Massachusetts. To determine the annual variability of spring discharge, discharge from 12 springs was measured during different seasonal conditions from June 2001 to November 2002, and the discharge from Red Mill Spring in Clarksburg, Massachusetts was recorded continuously from April 2002 to November 2002. The area contributing recharge to each spring was delineated on the basis of the geohydrologic conditions determined from reconnaissance investigations; these areas ranged from 0.010 to 0.682 square mile. Ground-water recharge, estimated on the basis of average discharge and the areas contributing recharge, ranged from 0.5 to 24.4 inches per year. High ground-water recharge rates for some of the high-discharge springs indicate that the areas contributing recharge for these springs may be too small. Detailed water-table mapping in the vicinity of two low-discharge springs indicates that the area contributing recharge to some of the smaller springs may be smaller than the area indicated by reconnaissance investigation. Monthly flow durations and low flow statistics were determined for the index streamflow-gaging stations for a 25-year period from 1976 to 2000. Annual hydrographs were prepared for each index station from median streamflows at the 50-percent monthly flow duration, normalized by drainage area. A median monthly flow of 1 ft3/s/mi2 was used to split hydrographs into a high-flow period (November?May), and a low-flow period (June?October). The hydrographs were used to classify index stations into groups with similar median monthly flow durations. Index stations were divided into four regional groups, roughly paralleling the coast, to characterize streamflows for November to May; and into two groups, on the basis of base-flow index and percentage of sand and gravel in the contributing area, for June to October.

Water-Resources Investigations Report↗
USGS2004

Estimating hydraulic properties of the Floridan Aquifer System by analysis of earth-tide, ocean-tide, and barometric effects, Collier and Hendry Counties, Florida

Aquifers are subjected to mechanical stresses from natural, non-anthropogenic, processes such as pressure loading or mechanical forcing of the aquifer by ocean tides, earth tides, and pressure fluctuations in the atmosphere. The resulting head fluctuations are evident even in deep confined aquifers. The present study was conducted for the purpose of reviewing the research that has been done on the use of these phenomena for estimating the values of aquifer properties, and determining which of the analytical techniques might be useful for estimating hydraulic properties in the dissolved-carbonate hydrologic environment of southern Florida. Fifteen techniques are discussed in this report, of which four were applied. An analytical solution for head oscillations in a well near enough to the ocean to be influenced by ocean tides was applied to data from monitor zones in a well near Naples, Florida. The solution assumes a completely non-leaky confining unit of infinite extent. Resulting values of transmissivity are in general agreement with the results of aquifer performance tests performed by the South Florida Water Management District. There seems to be an inconsistency between results of the amplitude ratio analysis and independent estimates of loading efficiency. A more general analytical solution that takes leakage through the confining layer into account yielded estimates that were lower than those obtained using the non-leaky method, and closer to the South Florida Water Management District estimates. A numerical model with a cross-sectional grid design was applied to explore additional aspects of the problem. A relation between specific storage and the head oscillation observed in a well provided estimates of specific storage that were considered reasonable. Porosity estimates based on the specific storage estimates were consistent with values obtained from measurements on core samples. Methods are described for determining aquifer diffusivity by comparing the time-varying drawdown in an open well with periodic pressure-head oscillations in the aquifer, but the applicability of such methods might be limited in studies of the Floridan aquifer system.

Florida↗
USGS2004

Documentation of revisions to the regional aquifer system analysis model of the New Jersey coastal plain

The model, which simulates flow in the New Jersey Coastal Plain sediments, developed for the U.S. Geological Survey Regional Aquifer System Analysis (RASA) program was revised. The RASA model was revised with (1) a rediscretization of the model parameters with a finer cell size, (2) a spatially variable recharge rate that is based on rates determined by recent studies and, (3) ground-water withdrawal data from 1981 to 1998. The RASA model framework, which subdivided the Coastal Plain sediments into 10 aquifers and 9 confining units, was preserved in the revised model. A transient model that simulates flow conditions from January 1, 1968 to December 31, 1998, was constructed using 21 stress periods. The model was calibrated by attempting to match the simulated results with (1) estimated base flow for five river basins, (2) measured water levels in long-term hydrographs for 28 selected observation wells, and (3) potentiometric surfaces in the model area for 1978, 1983, 1998, 1993, and 1998 conditions. The estimated and simulated base flow in the five river basins compare well. In general, the simulated water levels matched the interpreted potentiometric surfaces and the measured water levels of the hydrographs within 25 feet.

Water-Resources Investigations Report↗
USGS2003

Spatial distribution and trends in trace elements, polycyclic aromatic hydrocarbons, organochlorine pesticides, and polychlorinated biphenyls in Lake Worth sediment, Fort Worth, Texas

In spring 2000, the Texas Department of Health issued a fish consumption advisory for Lake Worth in Fort Worth, Texas, because of elevated concentrations of polychlorinated biphenyls (PCBs) in fish. In response to the advisory and in cooperation with the U.S. Air Force, the U.S. Geological Survey collected 21 surficial sediment samples and three gravity core sediment samples to assess the spatial distribution and historical trends of selected hydrophobic contaminants, including PCBs, and to determine, to the extent possible, sources of hydrophobic contaminants to Lake Worth. Compared to reference (background) concentrations in the upper lake, elevated PCB concentrations were detected in the surficial sediment samples collected in Woods Inlet, which receives surface runoff from Air Force facilities and urban areas. Gravity cores from Woods Inlet and from the main part of the lake near the dam indicate that the concentrations of PCBs were three to five times higher in the 1960s than in 2000. A regression method was used to normalize sediment concentrations of trace elements for natural variations and to distinguish natural and anthropogenic contributions to sediments. Concentrations of several trace elements—cadmium, chromium, copper, lead, and zinc—were elevated in sediments in Woods Inlet, along the shoreline of Air Force facilities, and in the main lake near the dam. Concentrations of these five trace elements have decreased since 1970. Polycyclic aromatic hydrocarbons also were elevated in the same areas of the lake. Concentrations of total polycyclic aromatic hydrocarbons, normalized with organic carbon, were mostly stable in the upper lake but steadily increased near the dam, except for small decreases since 1980. The Woods Inlet gravity core showed the largest increase of the three core sites beginning about 1940; total polycyclic aromatic hydrocarbon concentrations in post-1940 sediments from the core showed three apparent peaks about 1960, 1984, and 2000. The concentrations of organochlorine pesticides were low relative to consensus-based sediment-quality guidelines and either decreased or remained constant since 1970. The two likely sources of hydrophobic contaminants to the lake are urban areas around the lake and the drainage area of Meandering Road Creek that contributes runoff to Woods Inlet and includes Air Force facilities.

Texas↗
USGS2003

Baseline assessment of fish communities, benthic macroinvertebrate communities, and stream habitat and land use, Big Thicket National Preserve, Texas, 1999-2001

The Big Thicket National Preserve comprises 39,300 hectares in the form of nine preserve units connected by four stream corridor units (with two more corridor units proposed) distributed over the lower Neches and Trinity River Basins of southeastern Texas. Fish and benthic macroinvertebrate data were collected at 15 stream sites (reaches) in the preserve during 1999–2001 for a baseline assessment and a comparison of communities among stream reaches. The fish communities in the preserve were dominated by minnows (family Cyprinidae) and sunfishes (family Centrarchidae). Reaches with smaller channel sizes generally had higher fish species richness than the larger reaches in the Neches River and Pine Island Bayou units of the preserve. Fish communities in geographically adjacent reaches were most similar in overall community structure. The blue sucker, listed by the State as a threatened species, was collected in only one reach—a Neches River reach a few miles downstream from the Steinhagen Lake Dam. Riffle beetles (family Elmidae) and midges (family Chironomidae) dominated the aquatic insect communities at the 14 reaches sampled for aquatic insects in the preserve. The Ephemeroptera, Plecoptera and Trichoptera (EPT) Index, an index sensitive to water-quality degradation, was smallest at the Little Pine Island Bayou near Beaumont reach that is in a State 303(d)-listed stream segment on Little Pine Island Bayou. Trophic structure of the aquatic insect communities is consistent with the river continuum concept with shredder and scraper insect taxa more abundant in reaches with smaller stream channels and filter feeders more abundant in reaches with larger channels. Aquatic insect community metrics were not significantly correlated to any of the stream-habitat or land-use explanatory variables. The percentage of 1990s urban land use in the drainage areas upstream from 12 bioassessment reaches were negatively correlated to the reach structure index, which indicates less stable habitat for aquatic biota.

Texas↗
USGS2004

Effect of water-column pH on sediment-phosphorus release rates in Upper Klamath Lake, Oregon, 2001

Sediment-phosphorus release rates as a function of pH were determined in laboratory experiments for sediment and water samples collected from Shoalwater Bay in Upper Klamath Lake, Oregon, in 2001. Aerial release rates for a stable sediment/water interface that is representative of the sediment surface area to water column volume ratio (1:3) observed in the lake and volumetric release rates for resuspended sediment events were determined at three different pH values (8.1, 9.2, 10.2). Ambient water column pH (8.1) was maintained by sparging study columns with atmospheric air. Elevation of the water column pH to 9.2 was achieved through the removal of dissolved carbon dioxide by sparging with carbon dioxide-reduced air, partially simulating water chemistry changes that occur during algal photosynthesis. Further elevation of the pH to 10.2 was achieved by the addition of sodium hydroxide, which doubled average alkalinities in the study columns from about 1 to 2 milliequivalents per liter. Upper Klamath Lake sediments collected from the lake bottom and then placed in contact with lake water, either at a stable sediment/water interface or by resuspension, exhibited an initial capacity to take up soluble reactive phosphorus (SRP) from the water column rather than release phosphorus to the water column. At a higher pH this initial uptake of phosphorus is slowed, but not stopped. This initial phase was followed by a reversal in which the sediments began to release SRP back into the water column. The release rate of phosphorus 30 to 40 days after suspension of sediments in the columns was 0.5 mg/L/day (micrograms per liter per day) at pH 8, and 0.9 mg/L/day at pH 10, indicating that the higher pH increased the rate of phosphorus release by a factor of about two. The highest determined rate of release was approximately 10% (percent) of the rate required to explain the annual internal loading to Upper Klamath Lake from the sediments as calculated from a lake-wide mass balance and observed in total phosphorus data collected at individual locations.

Water-Resources Investigations Report↗
USGS2003

Geochemistry of the Birch Creek Drainage Basin, Idaho

The U.S. Survey and Idaho State University, in cooperation with the U.S. Department of Energy, are conducting studies to describe the chemical character of ground water that moves as underflow from drainage basins into the eastern Snake River Plain aquifer (ESRPA) system at and near the Idaho National Engineering and Environmental Laboratory (INEEL) and the effects of these recharge waters on the geochemistry of the ESRPA system. Each of these recharge waters has a hydrochemical character related to geochemical processes, especially water-rock interactions, that occur during migration to the ESRPA. Results of these studies will benefit ongoing and planned geochemical modeling of the ESRPA at the INEEL by providing model input on the hydrochemical character of water from each drainage basin. During 2000, water samples were collected from five wells and one surface-water site in the Birch Creek drainage basin and analyzed for selected inorganic constituents, nutrients, dissolved organic carbon, tritium, measurements of gross alpha and beta radioactivity, and stable isotopes. Four duplicate samples also were collected for quality assurance. Results, which include analyses of samples previously collected from four other sites, in the basin, show that most water from the Birch Creek drainage basin has a calcium-magnesium bicarbonate character. The Birch Creek Valley can be divided roughly into three hydrologic areas. In the northern part, ground water is forced to the surface by a basalt barrier and the sampling sites were either surface water or shallow wells. Water chemistry in this area was characterized by simple evaporation models, simple calcite-carbon dioxide models, or complex models involving carbonate and silicate minerals. The central part of the valley is filled by sedimentary material and the sampling sites were wells that are deeper than those in the northern part. Water chemistry in this area was characterized by simple calcite-dolomite-carbon dioxide models. In the southern part, ground water enters the ESRPA. In this area, the sampling sites were wells with depths and water levels much deeper than those in the northern and central parts of the valley. The calcium and carbon water chemistry in this area was characterized by a simple calcite-carbon dioxide model, but complex calcite-silicate models more accurately accounted for mass transfer in these areas. Throughout the geochemical system, calcite precipitated if it was an active phase in the models. Carbon dioxide either precipitated (outgassed) or dissolved depending on the partial pressure of carbon dioxide in water from the modeled sites. Dolomite was an active phase only in models from the central part of the system. Generally the entire geochemical system could be modeled with either evaporative models, carbonate models, or carbonate-silicate models. In both of the latter types of models, a significant amount of calcite precipitated relative to the mass transfer to and from the other active phases. The amount of calcite precipitated in the more complex models was consistent with the amount of calcite precipitated in the simpler models. This consistency suggests that, although the simpler models can predict calcium and carbon concentrations in Birch Creek Valley ground and surface water, silicate-mineral-based models are required to account for the other constituents. The amount of mass transfer to and from the silicate mineral phases was generally small compared with that in the carbonate phases. It appears that the water chemistry of well USGS 126B represents the chemistry of water recharging the ESRPA by means of underflow from the Birch Creek Valley.

Idaho↗
USGS2004

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

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

Water-Resources Investigations Report↗
USGS2004

Assessment of fish assemblages and minimum sampling effort required to determine botic integrity of large rivers in southern Idaho, 2002

A critical issue surrounding biomonitoring in large rivers (fifth- through seventh-order) is the minimum sampling-reach distance required to collect an adequate number of fish to represent the fish assemblage within a reach. Excessive sampling effort (excessive reach length) is costly in terms of work hours, reduces the number of sites that can be visited, can compromise field-crew safety, can be logistically unfeasible, and can cause unnecessary injury to captured fish. On the other hand, inadequate sampling effort can produce considerable variability in multiple samples collected at a site and may underrepresent the species or river condition present. During the summer of 2002, the U.S. Geological Survey, in cooperation with the Idaho Department of Environmental Quality, determined the minimum sampling effort required to characterize fish assemblages at 17 large-river sites in southern Idaho. The study was done as part of the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program. Electrofishing methods and multiple gear types were used to collect sample populations of fish in river reach lengths representing 40 and 100 times the wetted channel width. Minimum sampling effort was assessed by comparing the relation between reach length and the number of species collected, total individuals collected, and final Index of Biotic Integrity (IBI) scores. Thirty-two species of fish in the families Catostomidae, Centrarchidae, Cottidae, Cyprinidae, Ictaluridae, Percidae, and Salmonidae were collected. Of these, 12 alien species were collected, representing about 38 percent of all species collected during the study. Wetted channel width was determined to be sufficient for collecting an adequate number of fish to estimate species richness and evaluate biotic integrity. At most sites, about 250 fish were needed to effectively represent 95 percent of the species present. Fifty-three percent of the sites assessed, using an IBI developed specifically for large Idaho rivers, received scores of less than 50, indicating poor biotic integrity.

Idaho↗
USGS2004

Water-quality characteristics and ground water quantity of the Fraser River watershed, Grand County, Colorado, 1998-2001

The U.S. Geological Survey, in cooperation with the Grand County Board of County Commissioners, conducted a 4-year study to assess ground- and surface-water-quality conditions and ground-water quantity in the 302-square-mile Fraser River watershed in north-central Colorado. The Fraser River flows north about 28 miles from the headwaters near the Continental Divide, through the towns of Winter Park, Fraser, Tabernash, and Granby, and is one of the major tributaries to the Upper Colorado River. Increasing urban development, as well as the seasonal influx of tourists, is placing more demands on the water resources in the Fraser River watershed. A ground-water sampling network of 11 wells was established to represent different aquifer systems (alluvial, Troublesome Formation, Precambrian granite), land uses (urban, nonurban), and areas with or without individual septic disposal system use. The well network was sampled for ground-water quality on a semiannual basis from August 1998 through September 2001. The sampling included field properties and the collection of water samples for analysis of major ions, trace elements, nutrients, dissolved organic carbon, bacteria, methylene blue active substances, and radon-222. One surface-water site, on the Fraser River just downstream from the town of Tabernash, Colorado, was sampled bimonthly from August 1998 through September 2001 to assess the cumulative effects of natural and human processes on water quality in the upper part of the Fraser River watershed. Surface-water-quality sampling included field properties and the collection of water-quality samples for analysis of major ions, trace elements, nutrients, organic carbon, and bacteria. Ground water was a calcium-bicarbonate type water and is suitable as a drinking-water, domestic, municipal, industrial, and irrigation source. In general, no widespread ground-water-quality problems were indicated. All pH values and concentrations of dissolved solids, chloride, fluoride, sulfate, nitrite, and nitrate in the ground-water samples met or were substantially less than U.S. Environmental Protection Agency drinking-water standards and health advisories or State of Colorado water-quality standards. Federal standards for turbidity and concentrations of iron, manganese, methylene blue active substances, and radon-222 were not met in water samples from at least one well. The only ground-water-quality concern assessed by this study is radon-222, which was detected in all radon- analyzed samples from 10 wells at levels exceeding the proposed U.S. Environmental Protection Agency drinking-water standard of 300 picocuries per liter. Concentrations of chloride, magnesium, and sulfate were statistically different (higher) in ground-water samples from wells completed in the alluvial aquifer, urbanized areas, and areas with individual septic disposal system use than those from wells completed in the Troublesome Formation, nonurban areas, and areas without individual septic disposal system use. Dissolved organic carbon concentrations were statistically higher in ground-water samples from wells completed in the alluvial aquifer and areas without individual septic disposal system use than those from wells completed in the Troublesome Formation and areas with individual septic disposal system use. Differences in dissolved organic-carbon concentrations between the latter category and areas without septic systems likely had no environmental significance. Surface water at the site Fraser River below Crooked Creek at Tabernash was a calcium-bicarbonate type water and is suitable as a drinking-water, residential, commercial, and irrigation resource. All pH values and concentrations of dissolved oxygen were within the State of Colorado instream water-quality standards, and all concentrations of chloride, sulfate, iron, manganese, un-ionized ammonia, nitrite, nitrate, and fecal coliform bacteria met State standards. Seasonal changes in the values or conc

Colorado↗
USGS2003

Evaluation of tracer tests completed in 1999 and 2000 on the upper Santa Clara River, Los Angeles and Ventura Counties, California

The interaction of surface water and hyporheic water along the Santa Clara River in Los Angeles and Ventura Counties, California, was evaluated by conducting tracer tests and analyzing water-quality data under different flow conditions in October 1999 and May 2000. Tracer and water-quality samples were collected at multiple river and hyporheic sites as well as at the Los Angeles County Sanitation Districts Saugus and Valencia Water Reclamation Plants. These water reclamation plants provide the main source of base flow in the river. Rhodamine WT dye was injected into the river to determine river traveltimes and to indicate when Lagrangian water-quality sampling could be performed at each site. Sodium bromide was injected into the river at a constant rate at the water reclamation plants to evaluate the surface-water and shallow ground-water interactions in the hyporheic zone. In the upper reach of the study area, which extends 2.9 river miles downstream from the Saugus Water Reclamation Plant, traveltime was 3.2 hours during May 2000. In the lower reach, which extends 14.1 river miles downstream from the Valencia Water Reclamation Plant, traveltime was 9.6 hours during October 1999 and 7.1 hours during May 2000. The sodium bromide tracer was detected at both hyporheic locations sampled during October 1999, and at two of the three hyporheic locations sampled during May 2000. On the basis of Rhodamine dye tests, flow curves were constructed from the discharge measurements in the Valencia reach. Flow-curve results indicate net gains in flow throughout most, but not all, of the upper parts of the reach and net losses in flow at the lower part of the reach. Lagrangian water-quality sampling provides information on the changes in chemistry as the water flows downstream from the water reclamation plants. Along both reaches there is an increase in sulfate (40-60 mg/L in the Saugus reach and 160 mg/L in the Valencia reach) and a decrease in chloride (about 45 mg/L in the Saugus reach and about 10 mg/L in the Valencia reach). The increasing sulfate concentrations are consistent with discharge of higher sulfate ground water into the river. Along both reaches there is a trend of decreasing ammonia and slightly increasing nitrate concentrations. This trend is consistent with nitrification. Samples were also analyzed for numerous compounds associated with wastewater, but analysis focused on four indicators. Concentrations of wastewater indicators in the Santa Clara River were low and decreased downstream from the reclamation plants. There is general consistency between the chemical and tracer data collected from the hyporheic and the river-aquifer flow regime within a reach. The water quality at the hyporheic site in a gaining reach of the river resembled that of the local ground water and no wastewater indicators or injected tracers were observed; whereas, the water quality at the hyporheic sites in a losing reach of the river resembled the water quality of the river at the corresponding river site, and injected tracers were observed.

California↗
USGS2003

Aquifer susceptibility in Virginia, 1998-2000

The U.S. Geological Survey (USGS), in cooperation with the Virginia Department of Health, sampled water from 171 wells and springs across the Commonwealth of Virginia between 1998 and 2000 as part of the Virginia Aquifer Susceptibility study. Most of the sites sampled are public water supplies that are part of the comprehensive Source Water Assessment Program for the Commonwealth. The fundamental premise of the study was that the identification of young waters (less than 50 years) by multiple environmental tracers could be used as a guide for classifying aquifers in terms of susceptibility to contamination from near-surface sources. Environmental tracers, including chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), tritium (3H), and tritium/helium-3 (3H/3He), and carbon isotopes (14C and d13C) were used to determine the age of water discharging from wells and springs. Concentrations of CFCs greater than 5 picograms per kilogram and 3H concentrations greater than 0.6 tritium unit were used as thresholds to indicate that parts of the aquifer sampled have a component of young water and are, therefore, susceptible to near-surface contamination. Concentrations of CFCs exceeded the susceptibility threshold in 22 percent of the wells and in one spring sampled in the Coastal Plain regional aquifer systems. About 74 percent of the samples from wells with the top of the first water zone less than 100 feet below land surface exceeded the threshold values, and water supplies developed in the upper 100 feet of the Coastal Plain are considered to be susceptible to contamination from near-surface sources. The maximum depth to the top of the screened interval for wells that contained CFCs was less than 150 feet. Wells completed in the deep confined aquifers in the Coastal Plain generally contain water older than 1,000 years, as indicated by carbon-14 dating, and are not considered to be susceptible to contamination under natural conditions. All of the water samples from wells and springs in the fractured-rock terrains (the Appalachian Plateaus, Valley and Ridge, Blue Ridge, and Piedmont regional aquifer systems) contained concentrations of CFCs and 3H greater than one or both of the thresholds. Because all of the water samples exceeded at least one of the threshold values, young water is present throughout most of these regional aquifer systems; therefore, water supplies developed in these systems are susceptible to contamination from near-surface sources. No relation between well depth and presence of CFCs is evident from samples in the fractured-rock terrains. More than 95 percent of the samples for which the dating methods were applicable contained waters with apparent ages less than 35 years. About 5 percent of these samples, most of which were from the Blue Ridge and Piedmont regional aquifer systems, contained young waters with apparent ages of less than 5 years. Most of the samples from the Valley and Ridge Carbonate, Blue Ridge, and Piedmont regional aquifer systems had young water fractions of more than 50 percent, whereas samples from the Coastal Plain Shallow and Appalachian Plateaus regional aquifer systems contained less than 40 percent young waters. Concentrations of CFCs in excess of air-water equilibrium, which can indicate that nonatmospheric sources (such as sewage effluent) have introduced CFCs into the ground-water system, were measured in 6 and 48 percent of the water samples from the Coastal Plain and fractured-rock regional aquifer systems, respectively. The nitrate (NO3) concentrations greater than the USGS detection level of 0.05 milligrams per liter generally increase as the apparent age of the young water fraction decreases, with the highest NO3 concentrations for samples in which one or more of the CFCs are above modern atmospheric mixing ratios (commonly referred to as 'contaminated' for ground-water dating purposes).

Virginia↗
USGS2003

Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Angeles County, California

Tertiary-treated municipal wastewater (recycled water) has been used to replenish the Central Basin in Los Angeles County for over 40 years. Therefore, this area provides an excellent location to investigate (1) the fate and transport of wastewater constituents as they travel from the point of recharge to points of withdrawal, and (2) the long-term effects that artificial recharge using recycled water has on the quality of the ground-water basin. The U.S. Geological Survey has been conducting such investigations in this area for about 10 years, beginning in 1992. For this investigation, a variety of inorganic, organic, and isotopic constituents were analyzed in samples from 23 production wells within 500 feet of the San Gabriel and Rio Hondo Coastal Basin Spreading Grounds, and tritium/helium-3, chlorofluorocarbons, dissolved gases, and nitrogen isotopes were analyzed in five multiple-well monitoring sites along a 10-mile flow path extending from just upgradient of the spreading grounds southward through the Central Basin. Spearman rank-order correlation coefficients and level of significance calculated for about 40 water-quality indicators and several physical features show significant correlations between numerous inorganic and organic constituents that indicate the presence of wastewater. On the basis of a simple two-member mixing model, chloride, boron, ultraviolet absorbance at 254 nanometers, and excitation-emission fluorescence yielded the most reasonable estimates of wastewater percentages in the production wells. Tritium/helium-3 age determinations indicated that samples of ground water tested range in age from less than 2 to more than 50 years. Chloride and boron concentrations, along with tritium/helium-3 age determinations, indicate more rapid recharge and (or) displacement of pre-existing ground water at the San Gabriel Coastal Basin Spreading Grounds than at the Rio Hondo Coastal Basin Spreading Grounds. Nitrogen-15 enrichment of the ground-water nitrate and dissolved nitrogen indicates that denitrification, an important process for the removal of nitrate at the shallower depths beneath the spreading grounds, continues to occur at distances of several miles from the spreading grounds and over a period of many years. Analysis of dissolved gases shows that areas that contain recycled water have no detectable methane, whereas methane is present in the native ground water older than 50 years. The absence of methane in the younger ground water suggests that artificial recharge using recycled water has the desirable effect of increasing slightly the redox potential of the ground-water basin. Finally, measured chlorofluorocarbon concentrations and tritium/helium-3 age determinations indicate that chlorofluorocarbon concentrations are markedly elevated above atmosphere-water equilibrium in ground water older than about 20 years but still young enough to contain recycled water.

Water-Resources Investigations Report↗
USGS2004

Water-quality characteristics and trends for selected sites in or near the Earth Resources Observation Systems (EROS) Data Center, South Dakota, 1973-2000

This report presents data on water-quality samples that were collected in and near the Earth Resources Observation Systems (EROS) Data Center from 1973 through 2000. The investigation is a collaborated effort between the U.S. Geological Survey, Water Resources Discipline (WRD), and Geography (formerly National Mapping) Discipline, EROS Data Center. A water-quality monitoring program was initiated in 1973, when the EROS Data Center was constructed, and continues at the present time (2003). Under this program, water-quality samples were collected at various sites on the EROS Data Center's property and in the surrounding area. These sites include 4 wastewater-treatment lagoons, 1 site on EROS Lake located behind the EROS Data Center, 2 stream sites near the EROS Data Center, and 9 ground-water wells surrounding the EROS Data Center. Additionally, 3 sites on EROS Lake, 7 stream sites, and 9 ground-water sites are located within the study area and have been sampled during the period covered in the report. Some of these additional sites were part of the initial water-quality monitoring conducted during and immediately after the construction of the EROS Data Center. For other sites, some special sampling (depth-profile and bottom material) has occurred at times during the sampling history; however, these sites have little water-quality data and were not used for statistical or trend analysis. A trend-analysis program, Estimate TREND (ESTREND), was used to analyze for trends for one surface-water site, the Big Sioux River, which was the only site that had a substantial number of samples collected during an extensive period. The ESTREND trend-analysis program was used to analyze 16 constituents. Specific conductance and dissolved orthophosphate were the only constituents determined to have statistically significant trends. Results showed an increasing trend for specific conductance and a decreasing trend for dissolved orthophosphate. Scatter plots with regression smoothing lines for selected constituents are presented for selected surface-water and ground-water sites. Regression analyses using a Lowess (Locally Weighted Scatterplot Smoothing) smoothing line for Split Rock Creek, EROS Lake, the lagoon sites, and the ground-water sites indicated variable results, with some constituents indicating an increasing or decreasing trend, some having varied results, and others indicating no change during the sampling period.

South Dakota↗
USGS2003

Atlas of interoccurrence intervals for selected thresholds of daily precipitation in Texas

A Poisson process model is used to define the distribution of interoccurrence intervals of daily precipitation in Texas. A precipitation interoccurrence interval is the time period between two successive rainfall events. Rainfall events are defined as daily precipitation equaling or exceeding a specified depth threshold. Ten precipitation thresholds are considered: 0.05, 0.10, 0.25, 0.50, 0.75, 1.0, 1.5, 2.0, 2.5, and 3.0 inches. Site-specific mean interoccurrence interval and ancillary statistics are presented for each threshold and for each of 1,306 National Weather Service daily precipitation gages. Maps depicting the spatial variation across Texas of the mean interoccurrence interval for each threshold are presented. The percent change from the statewide standard deviation of the interoccurrence intervals to the root-mean-square error ranges from a magnitude minimum of (negative) -24 to a magnitude maximum of -60 percent for the 0.05- and 2.0-inch thresholds, respectively. Because of the substantial negative percent change, the maps are considered more reliable estimators of the mean interoccurrence interval for most locations in Texas than the statewide mean values.

Texas↗
USGS2003

Estimation of Monthly Evaporation from Lake Ashtabula in North Dakota, Orwell Lake in Minnesota, and Lake Traverse in Minnesota and South Dakota, 1931-2001

Reservoirs on tributaries of the Red River of the North provide water for Fargo and Grand Forks, N. Dak., and other cities along the river. Adequate estimates of evaporative losses from the reservoirs are needed to determine the total water supply in the Basin. Many equations could be used to estimate lake or reservoir evaporation. However, in addition to measurements of air temperature, the equations require measurements of net radiation, wind speed, and relative humidity. Evaporation and air temperature data from energy budget evaporation sites at Wetland P1 in North Dakota and at Williams Lake in Minnesota are available. Air temperature data collected from climate stations near Lake Ashtabula in North Dakota, from Orwell Lake in Minnesota, and from Lake Traverse in Minnesota and South Dakota also are available. Therefore, the combined data sets were used to estimate monthly evaporation from Lake Ashtabula, Orwell Lake, and Lake Traverse. Averaged monthly mean air temperatures determined for each reservoir study site were used to calculate monthly evaporation data sets for 1931-2001. Results from the procedure that estimates reservoir evaporation indicate that slight downward trends in annual evaporation occurred from 1931-2001. The trends may have been caused by the selected time period of the study, which began with the drought conditions in the mid 1930's and ended with the more wet conditions in the late 1990's. Average annual evaporation values for each reservoir for 1931-2001 correspond well with published average annual lake evaporation values for 1946-55.

Water-Resources Investigations Report↗