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At least 289 records · Page 16Linked to original sources
USGS1994

Nonlinear-regression flow model of the Gulf Coast aquifer systems in the south-central United States

A multiple-regression methodology was used to help answer questions concerning model reliability, and to calibrate a time-dependent variable-density ground-water flow model of the gulf coast aquifer systems in the south-central United States. More than 40 regression models with 2 to 31 regressions parameters are used and detailed results are presented for 12 of the models. More than 3,000 values for grid-element volume-averaged head and hydraulic conductivity are used for the regression model observations. Calculated prediction interval half widths, though perhaps inaccurate due to a lack of normality of the residuals, are the smallest for models with only four regression parameters. In addition, the root-mean weighted residual decreases very little with an increase in the number of regression parameters. The various models showed considerable overlap between the prediction inter- vals for shallow head and hydraulic conductivity. Approximate 95-percent prediction interval half widths for volume-averaged freshwater head exceed 108 feet; for volume-averaged base 10 logarithm hydraulic conductivity, they exceed 0.89. All of the models are unreliable for the prediction of head and ground-water flow in the deeper parts of the aquifer systems, including the amount of flow coming from the underlying geopressured zone. Truncating the domain of solution of one model to exclude that part of the system having a ground-water density greater than 1.005 grams per cubic centimeter or to exclude that part of the systems below a depth of 3,000 feet, and setting the density to that of freshwater does not appreciably change the results for head and ground-water flow, except for locations close to the truncation surface.

Water-Resources Investigations Report↗
USGS1990

Preconditioned Conjugate-Gradient 2 (PCG2), a computer program for solving ground-water flow equations

This report documents PCG2: a numerical code to be used with the U.S. Geological Survey modular three-dimensional, finite-difference, ground-water flow model. PCG2 uses the preconditioned conjugate-gradient method to solve the equations produced by the model for hydraulic head. Linear or nonlinear flow conditions may be simulated. PCG2 includes two reconditioning options: modified incomplete Cholesky preconditioning, which is efficient on scalar computers; and polynomial preconditioning, which requires less computer storage and, with modifications that depend on the computer used, is most efficient on vector computers. Convergence of the solver is determined using both head-change and residual criteria. Nonlinear problems are solved using Picard iterations. This documentation provides a description of the preconditioned conjugate gradient method and the two preconditioners, detailed instructions for linking PCG2 to the modular model, sample data inputs, a brief description of PCG2, and a FORTRAN listing.

Water-Resources Investigations Report↗
USGS1998

Assessment of ground-water vulnerability to atrazine leaching in Kent County, Michigan; review, comparison of results of other studies and verification

Model assumptions and parameters used in an earlier study of the vulnerability of ground water in Kent County, Michigan, to atrazine contamination were reviewed and compared with other studies. The review indicated that model assumptions are consistent with those used in other models and that the parameters assigned in the Kent County model are within the broad range commonly found in the literature. Model assumptions most likely to limit the accuracy of the previous study include those of uniform transport and steady-state flow. Simulation results are more sensitive to parameter estimates for atrazine half life, organic-carbon content, and organic-carbon partition coefficient than to other model parameters. Potential atrazine detection probabilities and concentrations of atrazine reported in the previous Kent County Study were compared with data from other studies. Detection probabilities of 14 measurements of atrazine concentrations in ground water from shallow wells in the southern Lower Peninsula of Michigan were compared with detection probabilities based on potential atrazine concentrations computed for Kent County. Results indicate that the distribution of detection probabilities based on measured concentrations is similar to that based on adjusted potential concentrations. Potential concentrations were adjusted for effects of differences between sampling and modeling depths and for differences between the uniform application rate used for potential concentrations and the percentage of Kent County that is likely to be treated with atrazine. Potential concentrations of atrazine in the Kent County Study were within the wide range of concentrations measured in other states. A stratified random sampling strategy was developed to verify expected atrazine concentrations in ground water within Kent County. The strategy helps identify strata, determine the optimum allocation of ground-water samples within defined strata, and project the sampling error. Implementation of the strategy was illustrated by use of potential atrazine concentrations computed in the previous Kent County Study. Once detailed information on historical application rates of atrazine is developed, expected atrazine concentrations can be computed by use of the vulnerability model and used to implement the sampling strategy. Sampling results may be used to verify the effectiveness of the vulnerability model and local estimates of historical atrazine application rates by use of analysis of variance.

Michigan↗
USGS2004

Conceptual model and numerical simulation of the ground-water-flow system in the unconsolidated deposits of the Colville River Watershed, Stevens County, Washington

Increased use of ground- and surface-water supplies in watersheds of Washington State in recent years has created concern that insufficient instream flows remain for fish and other uses. Issuance of new ground-water rights in the Colville River Watershed was halted by the Washington Department of Ecology due to possible hydraulic continuity of the ground and surface waters. A ground-water-flow model was developed to aid in the understanding of the ground-water system and the regional effects of ground-water development alternatives on the water resources of the Colville River Watershed. The Colville River Watershed is underlain by unconsolidated deposits of glacial and non-glacial origin. The surficial geologic units and the deposits at depth were differentiated into aquifers and confining units on the basis of areal extent and general water-bearing characteristics. Five principal hydrogeologic units are recognized in the study area and form the basis of the ground-water-flow model. A steady-state ground-water-flow model of the Colville River Watershed was developed to simulate September 2001 conditions. The simulation period represented a period of below-average precipitation. The model was calibrated using nonlinear regression to minimize the weighted differences or residuals between simulated and measured hydraulic head and stream discharge. Simulated inflow to the model area was 53,000 acre-feet per year (acre-ft/yr) from precipitation and secondary recharge, and 36,000 acre-ft/yr from stream and lake leakage. Simulated outflow from the model was primarily through discharge to streams and lakes (71,000 acre-ft/yr), ground-water outflow (9,000 acre-ft/yr), and ground-water withdrawals (9,000 acre-ft/yr). Because the period of simulation, September 2001, was extremely dry, all components of the ground-water budget are presumably less than average flow conditions. The calibrated model was used to simulate the possible effects of increased ground-water pumping. Although the steady-state model cannot be used to predict how long it would take for effects to occur, it does simulate the ultimate response to such changes relative to September 2001 (relatively dry) conditions. Steady-state simulations indicated that increased pumping would result in decreased discharge to streams and lakes and decreased ground-water outflow. The location of the simulated increased ground-water pumping determined the primary source of the water withdrawn. Simulated pumping wells in the northern end of the main Colville River valley diverted a large percentage of the pumpage from ground-water outflow. Simulated pumping wells in the southern end of the main Colville River valley diverted a large percentage of the pumpage from flow to rivers and streams. The calibrated steady-state model also was used to simulate predevelopment conditions, during which no ground-water pumping, secondary recharge, or irrigation application occurred. Cumulative streamflow in the Colville River Watershed increased by 1.1 cubic feet per second, or about 36 percent of net ground-water pumping in 2001. The model is intended to simulate the regional ground-water-flow system of the Colville River Watershed and can be used as a tool for water-resource managers to assess the ultimate regional effects of changes in stresses. The regional scale of the model, coupled with relatively sparse data, must be considered when applying the model in areas of poorly understood hydrology, or examining hydrologic conditions at a larger scale than what is appropriate.

Scientific Investigations Report↗
USGS2001

Hydraulic-property estimates for use with a transient ground-water flow model of the Death Valley regional ground-water flow system, Nevada and California

The Death Valley regional ground-water flow system encompasses an area of about 43,500 square kilometers in southeastern California and southern Nevada, between latitudes 35? and 38?15' north and longitudes 115? and 117?45' west. The study area is underlain by Quaternary to Tertiary basin-fill sediments and mafic-lava flows; Tertiary volcanic, volcaniclastic, and sedimentary rocks; Tertiary to Jurassic granitic rocks; Triassic to Middle Proterozoic carbonate and clastic sedimentary rocks; and Early Proterozoic igneous and metamorphic rocks. The rock assemblage in the Death Valley region is extensively faulted as a result of several episodes of tectonic activity. This study is comprised of published and unpublished estimates of transmissivity, hydraulic conductivity, storage coefficient, and anisotropy ratios for hydrogeologic units within the Death Valley region study area. Hydrogeologic units previously proposed for the Death Valley regional transient ground-water flow model were recognized for the purpose of studying the distribution of hydraulic properties. Analyses of regression and covariance were used to assess if a relation existed between hydraulic conductivity and depth for most hydrogeologic units. Those analyses showed a weak, quantitatively indeterminate, relation between hydraulic conductivity and depth.

California, Nevada↗
USGS2007

Application of FTLOADDS to Simulate Flow, Salinity, and Surface-Water Stage in the Southern Everglades, Florida

The Comprehensive Everglades Restoration Plan requires numerical modeling to achieve a sufficient understanding of coastal freshwater flows, nutrient sources, and the evaluation of management alternatives to restore the ecosystem of southern Florida. Numerical models include a regional water-management model to represent restoration changes to the hydrology of southern Florida and a hydrodynamic model to represent the southern and western offshore waters. The coastal interface between these two systems, however, has complex surface-water/ground-water and freshwater/saltwater interactions and requires a specialized modeling effort. The Flow and Transport in a Linked Overland/Aquifer Density Dependent System (FTLOADDS) code was developed to represent connected surface- and ground-water systems with variable-density flow. The first use of FTLOADDS is the Southern Inland and Coastal Systems (SICS) application to the southeastern part of the Everglades/Florida Bay coastal region. The need to (1) expand the domain of the numerical modeling into most of Everglades National Park and the western coastal area, and (2) better represent the effect of water-delivery control structures, led to the application of the FTLOADDS code to the Tides and Inflows in the Mangroves of the Everglades (TIME) domain. This application allows the model to address a broader range of hydrologic issues and incorporate new code modifications. The surface-water hydrology is of primary interest to water managers, and is the main focus of this study. The coupling to ground water, however, was necessary to accurately represent leakage exchange between the surface water and ground water, which transfers substantial volumes of water and salt. Initial calibration and analysis of the TIME application produced simulated results that compare well statistically with field-measured values. A comparison of TIME simulation results to previous SICS results shows improved capabilities, particularly in the representation of coastal flows. This improvement most likely is due to a more stable numerical representation of the coastal creek outlets. Sensitivity analyses were performed by varying frictional resistance, leakage, barriers to flow, and topography. Changing frictional resistance values in inland areas was shown to improve water-level representation locally, but to have a negligible effect on area-wide values. These changes have only local effects and are not physically based (as are the unchanged values), and thus have limited validity. Sensitivity tests indicate that the overall accuracy of the simulation is diminished if leakage between surface water and ground water is not simulated. The inclusion of a major road as a complete barrier to surface-water flow influenced the local distribution and timing of flow; however, the changes in total flow and individual creekflows were negligible. The model land-surface altitude was lowered by 0.1 meter to determine the sensitivity to topographic variation. This topographic sensitivity test produced mixed results in matching field data. Overall, the representation of stage did not improve definitively. A final calibration utilized the results of the sensitivity analysis to refine the TIME application. To accomplish this calibration, the friction coefficient was reduced at the northern boundary inflow and increased in the southwestern corner of the model, the evapotranspiration function was varied, additional data were used for the ground-water head boundary along the southeast, and the frictional resistance of the primary coastal creek outlet was increased. The calibration improved the match between measured and simulated total flows to Florida Bay and coastal salinities. Agreement also was improved at most of the water-level sites throughout the model domain.

Scientific Investigations Report↗
USGS1987

The principle of superposition and its application in ground-water hydraulics

The principle of superposition, a powerful mathematical technique for analyzing certain types of complex problems in many areas of science and technology, has important applications in ground-water hydraulics and modeling of ground-water systems. The principle of superposition states that problem solutions can be added together to obtain composite solutions. This principle applies to linear systems governed by linear differential equations. This report introduces the principle of superposition as it applies to ground-water hydrology and provides background information, discussion, illustrative problems with solutions, and problems to be solved by the reader.

Techniques of Water-Resources Investigations↗
USGS2006

Preliminary Assessment of Landslides Along the Florida River Downstream from Lemon Reservoir, La Plata County, Colorado

Nearly two-dozen shallow landslides were active during spring 2005 on a hillside located along the east side of the Florida River about one kilometer downstream from Lemon Reservoir in La Plata County, southwestern Colorado. Landslides on the hillside directly threaten human safety, residential structures, a county roadway, utilities, and the Florida River, and indirectly threaten downstream areas and Lemon Dam. Most of the area where the landslides occurred was burned during the 2002 Missionary Ridge wildfire. We performed geologic mapping, subsurface exploration and sampling, radiocarbon dating, and shallow ground-water and ground-displacement monitoring to assess landslide activity. Active landslides during spring 2005 were as large as 35,000 m3 and confined to colluvium. Debris flows were mobilized from most of the landslides, were as large as 1,500 m3, and traveled as far as 250 m. Landslide activity was triggered by elevated ground-water pressures within the colluvium caused by infiltration of snowmelt. Landslide activity ceased as ground-water pressures dropped during the summer. Shallow landslides on the hillside appear to be much more likely following the Missionary Ridge fire because of the loss of tree root strength and evapotranspiration. We used monitoring data and observations to develop preliminary, approximate rainfall/snowmelt thresholds above which shallow landslide activity can be expected. Landslides triggered during spring 2005 occurred within a 1.97 x 107 m3 older landslide that extends, on average, about 40 m into bedrock. The south end of this older landslide appears to have experienced deep secondary landsliding. Radiocarbon dating of sediments at the head of the older landslide suggests that the landslide was active about 1,424-1,696 years ago. A relatively widespread wildfire may have preceded the older landslide, and the landslide may have occurred during a wetter time. The wetter climate and effects of the wildfire would likely have resulted in increased ground-water pressures, which may have triggered the older landslide. This landslide appears to have crossed the valley floor and been subsequently eroded from this area. We found no evidence that landslide debris across the valley floor formed an impoundment of the Florida River, although it is very likely. Erosion of buttressing landslide debris from the valley floor and the lower strength of the landslide basal shear zone relative to pre-slide strength created less stable conditions than were present prior to occurrence of the landslide. However, deep ground-water conditions largely control the stability of the slope and are unknown here; hence, the potential for future deep landsliding is unknown. Additional investigation could be undertaken to further characterize landslide hazards in the area. This investigation could include episodic surveying of monuments we installed across the older landslide, obtaining detailed topographic data and aerial photography, mapping landslide debris and lacustrine deposits related to the potential former landslide dam, mapping secondary landslides, obtaining additional ages of landslide activity, constructing deep boreholes and ground-water monitoring wells, laboratory testing of soil and rock strength and hydraulic properties, and ground-water and slope-stability modeling.

Open-File Report↗
USGS2003

Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado

Tracer-injection studies were done in Belcher Gulch in the upper Animas River watershed, southwestern Colorado, to determine whether the alpine stream infiltrates into underground mine workings of the North Star Mine and other nearby mines in the area. The tracer-injection studies were designed to determine if and where along Belcher Gulch the stream infiltrates into the mine. Four separate tracer-injec-tion tests were done using lithium bromide (LiBr), optical brightener dye, and sodium chloride (NaCl) as tracer solu-tions. Two of the tracers (LiBr and dye) were injected con-tinuously for 24 hours, one of the NaCl tracers was injected continuously for 12 hours, and one of the NaCl tracers was injected over a period of 1 hour. Concentration increases of tracer constituents were detected in water discharging from the North Star Mine, substantiating a surface-water and ground-water connection between Belcher Gulch and the North Star Mine. Different timing and magnitude of tracer breakthroughs indicated multiple flow paths with different residence times from the stream to the mine. The Pittsburgh and Sultan Mines were thought to physically connect to the North Star Mine, but tracer breakthroughs were inconclusive in water from these mines. From the tracer-injection tests and synoptic measure-ments of streamflow discharge, a conceptual model was devel-oped for surface-water and ground-water interactions between Belcher Gulch and the North Star Mine. This information, combined with previous surface geophysical surveys indicat-ing the presence of subsurface voids, may assist with decision-making process for preventing infiltration and for the remedia-tion of mine drainage from these mines.

Water-Resources Investigations Report↗
USGS1999

Ground water and surface water in the Haiku area, East Maui, Hawaii

The Haiku study area lies on the gently sloping eastern flank of the East Maui Volcano (Haleakala) between the drainage basins of Maliko Gulch to the west and Kakipi Gulch to the east. The study area lies on the northwest rift zone of East Maui Volcano, a geologic feature 3 to 5 miles wide marked by surface expressions such as cinder, spatter, and pumice cones. The study area contains two geologic units, the main shield-building stage Honomanu Basalt and the Kula Volcanics. The hydraulic conductivity of the Honomanu Basalt was estimated to be between 1,000 and 3,600 feet per day on the basis of aquifer tests and 3,300 feet per day on the basis of the regional recharge rate and observed ground-water heads. The hydraulic conductivity of the Kula Volcanics is expected to be several orders of magnitude lower. An estimated 191 million gallons per day of rainfall and 22 million gallons per day of fog drip reach the study area and about 98 million gallons per day enters the ground-water system as recharge. Nearly all of the ground water currently withdrawn in the study area is from well 5520-01 in Maliko Gulch, where historic withdrawal rates have averaged about 2.8 million gallons per day. An additional 18 million gallons per day of ground-water withdrawal is proposed. Flow in Waiohiwi Gulch, a tributary to Maliko Gulch, is perennial between about 2,000 ft and 4,000 ft altitude. At lower altitudes in Maliko Gulch, flow is perennial at only a few spots downstream of springs and near the coast. The Kuiaha and Kaupakulua Gulch systems are usually dry from sea level to an altitude of 350 feet and gain water from about 350 feet to about 900 feet altitude. The two main branches of the Kaupakulua Gulch system alternately gain and lose water as high as 2,400 feet altitude. Kakipi Gulch has perennial flow over much of its length but is often dry near the coast below 400 feet altitude. Fresh ground water occurs in two main forms: (1) as perched high-level water held up by relatively low-permeability geologic layers, and (2) as a freshwater lens floating on denser, underlying saltwater. The rocks beneath the contact between the Kula Volcanics and the underlying Honomanu Basalt and above the freshwater lens appear to be unsaturated on the basis of several observations: (1) streams are dry or losing water where they are incised into the Honomanu Basalt, (2) the hydraulic conductivity of the Honomanu Basalt is too high to support a thick ground-water lens given the estimated recharge to the study area, and (3) wells that penetrate through the contact have encountered conditions of cascading water from above the contact and dry lava tubes in the Honomanu Basalt. More than 90 percent of the recharge to the study area is estimated to flow downward through the perched high-level water body to reach the freshwater lens. A cross-sectional, steady-state, variably saturated ground-water flow model using the computer code VS2DT was constructed to evaluate whether a two-layer, variably saturated ground-water flow system could exist given the hydrologic and geologic conditions of the Haiku study area. Using 25 inches per year of recharge and hydraulic characteristics representative of the Kula Volcanics and the Honomanu Basalt, the model demonstrates that a 13-foot thick geologic layer with a saturated vertical hydraulic conductivity less than 6.6Y10-2 feet per day can impede vertical ground-water flow enough to produce two separate saturated zones with an unsaturated zone between them. Subsequent lower vertical hydraulic conductivity values for the impeding layer allow even less water to reach the lower layer.

Hawaii↗
USGS1999

Simulation of ground-water system response to proposed withdrawals from 1993 to 2043 in the northern part of Juab Valley, Juab County, Utah

Information on the ground-water system in the northern part of Juab Valley, Utah, is needed by water managers to plan the optimal use of surface water that will be imported by the Central Utah Project and ground water pumped locally. The response of the ground-water system to an increase in withdrawal with no new sources of recharge was simulated to provide a baseline for comparing possible water-management plans and to determine their potential effects on wetlands in the area. To assess the effects of additional withdrawal on the system, a 50-year-long stress period was added to the end of the existing three-dimensional, finite-difference, ground-water flow model. This stress period simulates recharge and discharge stresses determined for 1987-92. Another model was constructed by simulating 30 additional wells pumping a total of 4,000 acre-feet per year in the 50-year-long stress period. The 30 additional wells were simulated in a north-south trending line along the eastern part of the valley and as pumping from the bottom model layer. The difference between model-computed water-level changes after 10, 30, and 50 years with and without the additional pumped wells was calculated for the uppermost model layer. Water-level declines of more than 6 feet were computed for layer 1 in the area east of Mona Reservoir, and natural sources of ground-water discharge in the northern part of the valley decreased in response to 30 years of additional pumping. Discharge from springs and seeps computed in 2022 of the revised model simulating additional pumping decreased by about 7 percent and computed discharge by evapotranspiration decreased by about 23 percent relative to the same time in the revised model simulating no additional pumping.

Utah↗
USGS1995

Computation of bedrock-aquifer recharge in northern Westchester County, New York, and chemical quality of water from selected bedrock wells

An empirical technique was used to calculate the recharge to bedrock aquifers in northern Westchester County. This method requires delineation of ground-water divides within the aquifer area and values for (1) the extent of till and exposed bedrock within the aquifer area, and (2) mean annual runoff. This report contains maps and data needed for calculation of recharge in any given area within the 165square-mile study area. Recharge was computed by this technique for a 93-square-mile part of the study area and used a ground-water-flow model to evaluate the reliability of the method. A two-layer, steady-state model of the selected area was calibrated. The area consists predominantly of bedrock overlain by small localized deposits of till and stratified drill Ground-water-level and streamflow data collected in mid-November 1987 were used for model calibration. The data set approximates average annual conditions. The model was calibrated from (1) estimates of recharge as computed through the empirical technique, and (2) a range of values for hydrologic properties derived from aquifer tests and published literature. Recharge values used for model simulation appear to be reasonable for average steady-state conditions. Water-quality data were collected from 53 selected bedrock wells throughout northern Westchester County to define the background ground-water quality. The constituents and properties for which samples were analyzed included major cations and anions, temperature, pH, specific conductance, and hardness. Results indicate little difference in water quality among the bedrock aquifers within the study area. Ground water is mainly the calcium-bicarbonate type and is moderately hard. Average concentrations of sodium, sulfate, chloride, nitrate, iron, and manganese were within acceptable limits established by the U.S. Environmental Protection Agency for domestic water supply.

Water-Resources Investigations Report↗
USGS1983

Assessment of the interconnection between Tampa Bay and the Floridan aquifer, Florida

Factors that control interflow between Tampa Bay and the Floridan aquifer are assessed, both qualitatively and quantitatively, with emphasis on the impact of harbor improvement. Hydrogeologic units underlying the 350-square-mile bay include the surficial-sand aquifer, upper sand and clay confining bed, and limestone of the Floridan aquifer. The surficial aquifer and upper confining bed have been eroded away in several areas along the northern coast of the bay to directly expose the Floridan aquifer to saltwater. There also, the top of the aquifer is, has been, or will be exposed to saltwater in numerous channels dredged in the bay. Saltwater-freshwater relations indicate that the degree of bay-aquifer interconnection decreases from north to south. Saltwater intrusion is occurring along the coast of Tampa Bay, as indicated by reduction or reversal of potentiometric-surface gradients and increasing chloride concentrations in coastal monitoring wells. A computer model of ground-water flow developed for a 97-square-mile area was interrogated under five options of channelization and pumping. Model results indicate that the total impact of channelization upon bay-aquifer interconnection are expected to be small and may be imperceptible when considered over the long term with other unknown changes in climate and development. (USGS)

Florida↗
USGS1988

Selected reports that include computer programs produced by the US Geological Survey for simulation of ground-water flow and quality

A summary list of reports that document numerical models that simulate ground-water flow and quality is presented. The list documents the reference by giving a description of each model program, its numerical features, a qualitative expression of the number of past applications and where to obtain a copy. All reports included in the list have been published or developed by the U.S. Geological Survey and most contain listings of the computer programs. (Author 's abstract)

Water-Resources Investigations Report↗
USGS1983

Long-range plans for hydrologic investigations in New Mexico

Objectives of the hydrologic-data-collection projects presented in this report include continuing to identify future data needs; conducting an analysis of the water-quality, ground-water, and surface-water observation networks; and entering all available current and historical hydrologic data into the U.S. Geological Survey Water Data Storage and Retrieval System (WATSTORE). Objectives of areal-appraisal studies include evaluating the water resources in the Gallup-Grants-Zuni-Acoma Sag area and on the eastern flank of the Sandi and Manzano Mountains in Bernalillo County. Potential projects for basin assessments include quantifying the ground-water/surface-water relationships on rivers with flows governed by compacts and an investigation of the water resources of the Estancia Basin. Projects that will assist in the evaluation of energy-related activities include describing the effects of resaturation of coal mines and of milling operations on the quality and quantity of ground and surface water. Activities that need to be undertaken to assist in addressing waste-disposal problems include the evaluation of the hydrologic factors influencing the feasibility of cleanup at the Albuquerque South Valley ' superfund ' site and the establishment of a monitoring network at the Waste Isolation Pilot Plant project near Carlsbad. Scientific methods that need to be developed include (1) the testing of analytical techniques for estimating site-specific conditions with the results of digital hydrologic models, and (2) the determination of the influence of recharge from ephemeral streams on alluvial aquifers. (USGS)

Open-File Report↗
USGS2002

Water budget for and nitrogen loads to Northeast Creek, Bar Harbor, Maine

The potential for nutrient enrichment to coastal estuaries on Mt. Desert Island, Maine, may affect the health of these important ecosystems at Acadia National Park. Inputs of water and nitrogen entering one of these coastal estuaries, Northeast Creek, and adjacent wetlands on Mt. Desert Island were quantified in a recent study conducted by the U.S. Geological Survey, in cooperation with the National Park Service. Streamflow and concentra-tions of nitrogen species in the four perennial streams entering the wetland/estuary system were measured monthly for 18 months to estimate loads and develop a water budget. Old Mill Brook was instrumented with a continuous-recording stream-flow gage; the MOVE.1 record-extension technique was used with this and several other nearby continuous gages to estimate daily surface-water inflow to the wetland. Inflow from ungaged basins was estimated from the unit-area yield calculated from data obtained from the gaged basins. Precipitation data collected at the National Atmospheric Deposition Program (NADP) site at Acadia National Park Headquarters and the Acadia National Park weather station were used to calculate atmospheric inputs. Evapotranspiration from the wetland was calculated using Fennessey and Vogel?s regionalized multivariate regression model of Penman-Montieth evapotranspiration. Geologic data collected in the field and taken from published geologic maps indicate that ground water probably does not contribute significantly to the water budget of this wetland system. Surface-water outflow from the wetland was not calculated because of the tidal nature of the outlet of the wetland and the difficulties associated with measuring flow in a tidal stream.

Maine↗
USGS1995

Hydrogeology and water quality of the Mississippi River alluvium near Muscatine, Iowa, June 1992 through June 1994

A study of the Mississippi River alluvium near Muscatine, Iowa, was conducted to evaluate ground-water flow and water quality using data collected from June 1992 through June 1994. The study area included approximately 80 square miles in parts of Muscatine and Louisa Counties in Iowa and Rock Island and Mercer Counties in Illinois. A steady-state, ground-water flow model was constructed using February 1993 hydrologic conditions. Model results indicate that drawdown in the lower alluvium caused by the pumping centers in Iowa extends beneath the Muscatine Slough in the northwest part of the study area and beneath the Mississippi River in the central and northern parts of the area. The primary sources of ground water in the alluvium are recharge from precipitation, leakage from the Mississippi River, and infiltration of upland runoff. The bedrock is not a major contributor of ground water to the alluvium. The areal distribution of selected water-quality properties and constituents in ground water results from several factors. Localized large chloride and nitrite-plus-nitrate nitrogen concentrations could be indicative of contamination from human activity. Specific conductance and calcium, magnesium, and sulfate concentrations are larger in ground water near the boundary between the river valley and upland area and could result from infiltration of upland runoff or lithologic differences in the alluvium. Large iron or manganese concentrations occur in the ground water near the Mississippi River and Muscatine Slough that result from microbial processes and the presence of dissolved organic carbon. Temporal variations of concentrations for selected water-quality constituents in groundwater samples attest to the dynamic nature of the ground-water system as it responds to natural and human-induced changes in water quality. Leakage from the Mississippi River affects ground-water quality in the alluvium adjacent to the river. Temporal variations in water quality of the Mississippi River can be caused by seasonally, amount of discharge, or upstream human activities. The quality of ground water induced from discrete zones of the alluvium by the pumping centers in Iowa has implications for the entire ground-water resource. The ground-water flow model calculated that 10 percent of the water that enters the zone of active pumping on the Iowa side of the Mississippi River originates from the zone west and north of Muscatine Slough, and that 5.2 percent originates from the zone on the Illinois side of the Mississippi River east of the center of the river channel.

Illinois, Iowa↗
USGS2003

Phosphorus in a ground-water contaminant plume discharging to Ashumet Pond, Cape Cod, Massachusetts, 1999

The discharge of a plume of sewagecontaminated ground water emanating from the Massachusetts Military Reservation to Ashumet Pond on Cape Cod, Massachusetts, has caused concern about excessive loading of nutrients, particularly phosphorus, to the pond. The U.S. Air Force is considering remedial actions to mitigate potentially adverse effects on the ecological characteristics of the pond from continued phosphorus loading. Concentrations as great as 3 milligrams per liter of dissolved phosphorus (as P) are in ground water near the pond's shoreline; concentrations greater than 5 milligrams per liter of phosphorus are in ground water farther upgradient. Temporary drive-point wells were used to collect water samples from 2 feet below the pond bottom to delineate concentration distributions in the pore waters of the pond-bottom sediments. Measurements in the field of specific conductance and colorimetrically determined orthophosphate concentrations provided real-time data to guide the sampling. The contaminant plume discharges to the Fishermans Cove area of Ashumet Pond as evidenced by elevated levels of specific conductance and boron, which are chemically conservative indicators of the sewage-contaminated ground water. Concentrations of nonconservative species, such as dissolved phosphorus, manganese, nitrate, and ammonium, also were elevated above background levels in ground water discharging to the pond, but in spatially complex distributions that reflect their distributions in ground water upgradient of the pond. Phosphorus concentrations exceeded background levels (greater than 0.10 milligram per liter) in the pond-bottom pore water along 875 feet of shoreline. Greatest concentrations (greater than 2 milligrams per liter) occurred within 30 feet of the shore in an area about 225 feet long. Calculations of phosphorus flux in the aquifer upgradient of Ashumet Pond, as determined from water-flux estimates from a steady-state ground-water-flow model and phosphorus concentrations (in 1999) from multilevel samplers about 75 feet upgradient of the pond, indicate that dissolved phosphorus moves towards the pond and discharges to it with the inflowing ground water at a rate as high as about 316 kilograms per year.

Massachusetts↗