Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Ground Water Modeling Investigation Report”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
USGS2007

Ground-Water Nutrient Flux to Coastal Waters and Numerical Simulation of Wastewater Injection at Kihei, Maui, Hawaii

Water sampling and numerical modeling were used to estimate ground-water nutrient fluxes in the Kihei area of Maui, where growth of macroalgae (seaweed) on coral reefs raises ecologic concerns and accumulation on beaches has caused odor and removal problems. Fluxes and model results are highly approximate, first-order estimates because very few wells were sampled and there are few field data to constrain model calibration. Ground-water recharge was estimated to be 22.6 Mgal/d (million gallons per day) within a 73-square-mile area having a coastline length of 8 miles or 13 km (kilometers). Nearly all of the recharge discharges at the coast because ground-water withdrawals are small. Another 3.0 Mgal/d of tertiary-treated wastewater effluent is injected into the regional aquifer at a County treatment plant midway along the coast and about a mile from shore. The injection plume is 0.93 miles wide (1.5 km) at the shore, as estimated from a three-dimensional numerical ground-water model. Wastewater injected beneath the brackish ground-water lens rises buoyantly and spreads out at the top of the lens, diverting and mixing with ambient ground water. Ground water discharging from the core of the injection plume is less than 5 years old and is about 60 percent effluent at the shore, according to the model. Dissolved nitrogen and phosphorus concentrations in treated effluent were 7.33 and 1.72 milligrams per liter, roughly 6 and 26 times background concentrations at an upgradient well. Background nitrogen and phosphorus fluxes carried by ground water are 7.7 and 0.44 kg/d-km (kilograms per day per kilometer of coast). Injected wastewater fluxes distributed across the plume width are 55 and 13 kg/d-km nitrogen and phosphorus, roughly 7 and 30 times background flux. However, not all of the injected load reaches coastal waters because nutrients are naturally attenuated in the oxygen-depleted effluent plume. Water from a downgradient well reflects this attenuation and provides a more conservative estimate of injection flux approaching the shore: 27 and 1.5 kg/d-km nitrogen and phosphorus, roughly one-half and one-ninth the injection-source estimates, and 3.5 and 3.4 times background flux. Effluent has 8 O and 2 H stable-isotope signatures that are distinct from local ground water, as well as 15 N and 11 B signatures diagnostic of domestic waste and laundry detergents, respectively. Pharmaceuticals and organic wastewater compounds also were present in effluent and the downgradient well. These isotopes and chemicals served as wastewater tracers in Kihei ground water and may be useful tracers in nearshore marine waters and aquifers elsewhere in Hawaii.

Scientific Investigations Report↗
USGS2009

Hydrogeology and Ground-Water Flow in the Opequon Creek Watershed area, Virginia and West Virginia

Due to increasing population and economic development in the northern Shenandoah Valley of Virginia and West Virginia, water availability has become a primary concern for water-resource managers in the region. To address these issues, the U.S. Geological Survey (USGS), in cooperation with the West Virginia Department of Health and Human Services and the West Virginia Department of Environmental Protection, developed a numerical steady-state simulation of ground-water flow for the 1,013-square-kilometer Opequon Creek watershed area. The model was based on data aggregated for several recently completed and ongoing USGS hydrogeologic investigations conducted in Jefferson, Berkeley, and Morgan Counties in West Virginia and Clarke, Frederick, and Warren Counties in Virginia. A previous detailed hydrogeologic assessment of the watershed area of Hopewell Run (tributary to the Opequon Creek), which includes the USGS Leetown Science Center in Jefferson County, West Virginia, provided key understanding of ground-water flow processes in the aquifer. The ground-water flow model developed for the Opequon Creek watershed area is a steady-state, three-layer representation of ground-water flow in the region. The primary objective of the simulation was to develop water budgets for average and drought hydrologic conditions. The simulation results can provide water managers with preliminary estimates on which water-resource decisions may be based. Results of the ground-water flow simulation of the Opequon Creek watershed area indicate that hydrogeologic concepts developed for the Hopewell Run watershed area can be extrapolated to the larger watershed model. Sensitivity analyses conducted as part of the current modeling effort and geographic information system analyses of spring location and yield reveal that thrust and cross-strike faults and low-permeability bedding, which provide structural and lithologic controls, respectively, on ground-water flow, must be incorporated into the model to develop a realistic simulation of ground-water flow in the larger Opequon Creek watershed area. In the model, recharge for average hydrologic conditions was 689 m3/d/km2 (cubic meters per day per square kilometer) over the entire Opequon Creek watershed area. Mean and median measured base flows at the streamflow-gaging station on the Opequon Creek near Martinsburg, West Virginia, were 604,384 and 349,907 m3/d (cubic meters per day), respectively. The simulated base flow of 432,834 m3/d fell between the mean and median measured stream base flows for the station. Simulated base-flow yields for subwatersheds during average conditions ranged from 0 to 2,643 m3/d/km2, and the median for the entire Opequon Creek watershed area was 557 m3/d/km2. A drought was simulated by reducing model recharge by 40 percent, a rate that approximates the recharge during the prolonged 16-month drought that affected the region from November 1998 to February 2000. Mean and median measured streamflows for the Opequon Creek watershed area at the Martinsburg, West Virginia, streamflow-gaging station during the 1999 drought were 341,098 and 216,551 m3/d, respectively. The simulated drought base flow at the station of 252,356 m3/d is within the range of flows measured during the 1999 drought. Recharge was 413 m3/d/km2 over the entire watershed during the simulated drought, and was 388 m3/d/km2 at the gaging station. Simulated base-flow yields for drought conditions ranged from 0 to 1,865 m3/d/km2 and averaged 327 m3/d/km2 over the entire Opequon Creek watershed. Water budgets developed from the simulation results indicate a substantial component of direct ground-water discharge to the Potomac River. This phenomenon had long been suspected but had not been quantified. During average conditions, approximately 564,176 m3/d of base flow discharges to the Potomac River. An additional 124,379 m3/d of ground water is also estimated to discharge directly to the Potomac River and rep

Scientific Investigations Report↗
USGS1974

Mathematical model of San Juan Valley ground-water basin, San Benito County, California

A mathematical model study of the San Juan Valley ground-water basin in San Benito County, Calif., has quantitatively described the ground-water hydrology of the basin under past, present, and future conditions of development. An analysis of conditions in the basin prior to large-scale ground-water development indicates that net recharge equaled 9.23 cubic feet per second and occurred as subsurface flow to the eastern part of the basin and infiltration of rain, direct runoff, and minor streamflows. Net predevelopment discharge equaled 9.23 cubic feet per second and occurred as aquifer discharge to the San Benito River. The 9.23 cubic feet per second of predevelopment recharge is considered to be perennial recharge to the basin. Large-scale ground-water development occurred in the area during the period 1945-68 and caused water levels to decline throughout most of the basin. Progressive depletion of aquifer storage during this period changed the San Benito River from a gaining (perennial) stream to a losing stream along most of its reach in the basin area. Net discharge from the basin during the period 1945-68 averaged 18.10 cubic feet per second. Of this amount 17.82 cubic feet per second occurred as pumpage from wells, and 0.28 cubic foot per second occurred as basin discharge to the San Benito River. Net recharge to the basin during the same period averaged 13.57 cubic feet per second. Of this amount 4.34 cubic feet per second occurred as infiltration from the San Benito River and 9.23 cubic feet per second occurred as perennial recharge. Use of the calibrated mathematical model to simulate quantities of imported water entering the basin from the San Benito River indicates that water levels in San Juan Valley will stabilize or recover when additional recharge equals or exceeds 3,000 acre-feet per year.

California↗
USGS1979

Ground water in Dale Valley, New York

Dale Valley is a broad valley segment, enlarged by glacial erosion, at the headwaters of Little Tonawanda Creek near Warsaw , New York. A thin, shallow alluvial aquifer immediately underlies the valley floor but is little used. A deeper gravel aquifer, buried beneath many feet of lake deposits, is tapped by several industrial wells. A finite-difference digital model treated the deep aquifer as two-dimensional with recharge and discharge through a confining layer. It was calibrated by simulating (1) natural conditions, (2) an 18-day aquifer test, and (3) 91 days of well-field operation. Streamflow records and model simulations suggest that in moderately wet years such as 1974, a demand of 750 gallons per minute could be met by withdrawal from the creek and from the aquifer without excessive drawdown at production wells or existing domestic wells. With reasonable but unverified model adjustments to simulate an unusually dry year, the model predicts that a demand of 600 gallons per minute could be met from the same sources. Water high in chloride has migrated from bedrock into parts of the deep aquifer. Industrial pumpage, faults in the bedrock, and the natural flow system may be responsible. (Woodard-USGS)

Water-Resources Investigations Report↗
USGS1990

Geohydrology and simulation of ground-water flow in the carbonate rocks of the Valley Creek basin, eastern Chester County, Pennsylvania

Sixty-eight percent of the 22.6-square-mile Valley Creek basin is underlain by Cambrian and Ordovician limestone and dolomite. Ground water flows through a network of interconnected secondary openings; primary porosity is virtually nonexistent. Some of these openings have been enlarged by solution. Secondary porosity and permeability exhibit great spatial variability, and the yield and specific capacity of wells are highly variable. The number of water-bearing zones decreases with depth. Fifty percent of water-bearing zones are encountered within 100 feet of the land surface, and 81 percent are within 200 feet. Most ground-water flow in the Valley Creek basin is local and discharges to nearby streams. Ground-water discharge comprised an average of 76 percent of the flow of Valley Creek during 1983--87, including both natural ground- water discharge and quarry pumpage discharged to Valley Creek. Discharge from the Cedar Hollow quarry comprised 21 to 26 percent of the base flow of Valley Creek; the average was 23 percent. The average natural base flow of Valley Creek would be 8 percent lower if the quarry were not operating. Regional ground-water flow is to the northeast to the Schuylkill River. On the western side of the Valley Creek basin, the ground-water divide is 1/2 mile west of the surface-water divide. An estimated 0.75 million gallons per day of ground water flows from the adjacent West Valley Creek basn eastward into the Valley Creek basin. A ground-water divide is not present on the eastern side of the basin; the water table slopes gently eastward toward the Schuylkill River. On the northeaster side, an estimated 1.76 million gallons per day of ground water flows northeastward out of the basin to the Schuylkill River beneath the surface-water divide. On the southeaster side, an estimated 0.85 million gallons per day of ground water flows beneath the surface-water divide into the basin. Annual water budgets and an average water budget were calculated for 1983-87 for the 20.8-square-mile area bove the streamflow-gaging station. Annual precipitation for 1983-87 ranged from 40.61 to 56.55 inches and averaged 47.25 inches; annual streamflow ranged from 15.55 to 28.57 inches and averaged 22.31 inches; annual evapotranspiration ranged from 18.21 to 24.83 inches and averaged 22.90 inches; and annual recharge ranged from 15.89 to 26.84 inches and averaged 21.04 inches. The Valley Creek basin was modeled as a two-dimensional water-table aquifer. Recharge to, ground-water flow through, and discharge from the rocks of Chester valley were simulated. In order to include the natural hydrologic boundaries of the ground-water-flwo system, the 66.4-square-mile area between the Brandywine Creek and the Schuylkill River was modeled. The model was calibrated under stead-state conditions using avareage recharge and evapotranspiration rates. Aquifer hydraulic conductivity was estimated from specific-capacity and quifer-test data. The average (1983-87) annual water budget for hte Valley Creek basin was simualted. The effect of increased ground-water development on base flow and underflow was simulated by locating a hypothetical well field produceing 4 million gallons per day in different parts of the basin. Pumpage from a well field near surface-water divides would induce as much as an additional 1.41 inches per year of underflow from an adjacent surface-water basin. Pumpage from a well field near the center of the basin would affect base flow more than underflow. Increased seepage of ground water into quarries as a result of their expansion was simulated as increased withdrawal by pumping. A 100-percent increase in the pumping rate of the Cedar Hollow quarry, from 3.93 to 7.86 million gallons per day, owuld reduce the natural base flow of Valley Creek by 18 percent. However, the quarry pumpage would be discharged to Valley Creek, thereby increasing the base flow at the gaging station by

Pennsylvania↗
USGS1995

Hydrogeology, ground-water quality, and source of ground water causing water-quality changes in the Davis well field at Memphis, Tennessee

An investigation was conducted by the U.S. Geological Survey from 1992 to 1994 to collect and interpret hydrogeologic and water-quality data to determine the source of ground water causing water-quality changes in water from wells screened in the Memphis aquifer in the Davis well field at Memphis, Tennessee. Water-quality changes in aquifers used for water supply are of concern because these changes can indicate a potential for contamination of the aquifers by downward leakage from near-surface sources. The water-quality changes at the Davis well field were detected by Memphis Light, Gas and Water Division, which has periodically sampled and analyzed water from many of the 14 production wells since the well field began operation in 1971. Memphis Light, Gas and Water Division analyzed the water samples primarily for hardness, alkalinity, chloride, ulfate, and iron. Results of the e analy es and results of more recent (1992) analyse of water samples by the U.S. Geological Survey indicate that the quality of water from eight of the production wells has changed since the well field began operation. For example, from 1972 to 1991, hardness of water from one well has increased from 90 to 292 milligrams per liter (224 percent). The confining unit, which separates the fluvial deposits aquifer from the Memphis aquifer in the area of the well field, is relatively thick and contains many clay layers. However, a test hole drilled for one of five shallow wells installed in the alluvial aquifer in the Mississippi Alluvial Plain just west of the well field indicated that the confining unit separating the alluvial aquifer from the Memphis aquifer locally is absent. Differences in hydrauLic head between the alluvial and fluvial deposits aquifers and the Memphis aquifer favor downward leakage of ground water. Thus, the absence of the confining unit beneath the Mississippi Alluvial Plain just west of the well field provides a direct pathway for water in the alluvial aquifer to enter the Memphis aquifer. Comparison of selected water-quality properties and major inorganic and trace element constituent concentrations in samples from the alluvial, fluvial deposits, and Memphis aquifers indicates that the source of ground water causing waterquality changes at the Davis well field is the alluvial aquifer west of the well field . The presence of tritium and chlorofluorocarbons in water from wells screened in the Memphis aquifer in the western part of the well field indicates that relatively young (post-1940) water from the alluvial aquifer has entered the Memphis aquifer. NETPATH geochemical model code was used to mix waters from the alluvial aquifer with water from the Memphis aquifer using chloride as a conservative tracer. The resulting models indicated that a mixture containing 3 percent alluvial aquifer water mixed with 97 percent unaffected Memphis aquifer water would produce the chloride concentration measured in water from the Memphis aquifer well most affected by water-quality changes. NETPATH also was used to calculate mixing percentages of alluvial and Memphis aquifer Abstract waters based on changes in the concentrations of selected dissolved major inorganic and trace element constituents that define the dominant reactions that occur during mixing. These models indicated that a mixture containing 18 percent alluvial aquifer water and 82 percent unaffected Memphis aquifer water would produce the major constituent and trace element concentrations measured in water from the Memphis aquifer well most affected by water-quality changes. However, these model simulations predicted higher dissolved methane concentrations than were measured in water samples from the Memphis aquifer wells.

Tennessee↗
USGS2007

Simulation of Regional Ground-Water Flow in the Suwannee River Basin, Northern Florida and Southern Georgia

The Suwannee River Basin covers a total of nearly 9,950 square miles in north-central Florida and southern Georgia. In Florida, the Suwannee River Basin accounts for 4,250 square miles of north-central Florida. Evaluating the impacts of increased development in the Suwannee River Basin requires a quantitative understanding of the boundary conditions, hydrogeologic framework and hydraulic properties of the Floridan aquifer system, and the dynamics of water exchanges between the Suwannee River and its tributaries and the Floridan aquifer system. Major rivers within the Suwannee River Basin are the Suwannee, Santa Fe, Alapaha, and Withlacoochee. Four rivers west of the Suwannee River are the Aucilla, the Econfina, the Fenholloway, and the Steinhatchee; all drain to the Gulf of Mexico. Perhaps the most notable aspect of the surface-water hydrology of the study area is that large areas east of the Suwannee River are devoid of channelized, surface drainage; consequently, most of the drainage occurs through the subsurface. The ground-water flow system underlying the study area plays a critical role in the overall hydrology of this region of Florida because of the dominance of subsurface drain-age, and because ground-water flow sustains the flow of the rivers and springs. Three principal hydrogeologic units are present in the study area: the surficial aquifer system, the intermediate aquifer system, and the Floridan aquifer system. The surficial aquifer system principally consists of unconsoli-dated to poorly indurated siliciclastic deposits. The intermediate aquifer system, which contains the intermediate confining unit, lies below the surficial aquifer system (where present), and generally consists of fine-grained, uncon-solidated deposits of quartz sand, silt, and clay with interbedded limestone of Miocene age. Regionally, the intermediate aquifer system and intermediate con-fining unit act as a confining unit that restricts the exchange of water between the over-lying surficial and underlying Upper Floridan aquifers. The Upper Floridan aquifer is present throughout the study area and is extremely permeable and typically capable of transmitting large volumes of water. This high permeability largely is due to the widening of fractures and formation of conduits within the aquifer through dissolu-tion of the limestone by infiltrating water. This process has also produced numerous karst features such as springs, sinking streams, and sinkholes. A model of the Upper Floridan aquifer was created to better understand the ground-water system and to provide resource managers a tool to evaluate ground-water and surface-water interactions in the Suwannee River Basin. The model was developed to simulate a single Upper Floridan aquifer layer. Recharge datasets were developed to represent a net flux of water to the top of the aquifer or the water table during a period when the system was assumed to be under steady-state conditions (September 1990). A potentiometric-surface map representing water levels during September 1990 was prepared for the Suwannee River Water Management District (SRWMD), and the heads from those wells were used for calibration of the model. Additionally, flows at gaging sites for the Suwannee, Alapaha, Withlacoochee, Santa Fe, Fenholloway, Aucilla, Ecofina, and Steinhatchee Rivers were used during the calibration process to compare to model computed flows. Flows at seven first-magnitude springs selected by the SRWMD also were used to calibrate the model. Calibration criterion for matching potentiometric heads was to attain an absolute residual mean error of 5 percent or less of the head gradient of the system which would be about 5 feet. An absolute residual mean error of 4.79 feet was attained for final calibration. Calibration criterion for matching streamflow was based on the quality of measurements made in the field. All measurements used were rated ?good,? so the desire was for simulated values to be wi

Florida, Georgia↗
USGS1993

Potential for ground-water contamination from movement of wastewater through the unsaturated zone, upper Mojave River Basin, California

Septic-tank wastewater disposed in 30-foot-deep seepage pits (dry wells) at 46,000 residences is estimated to equal 18 percent of the natural recharge to the sole-source aquifer in the rapidly developing upper Mojave River Basin (Victor Valley) in the high desert northeast of Los Angeles. Vertical rates of movement of the wastewater wetting front through the unsaturated zone at three newly occupied residences ranged from 0.07 to 1.0 foot per day. These rates translate to traveltimes of several months to several years for the wastewater wetting front to reach the water table and imply that wastewater from many disposal systems already has reached the water table, which averages about 150 feet below land surface in the Victor Valley. As wastewater percolates from seepage pits into the adjacent unsaturated zone, the nitrogen present in reduced form is rapidly converted to nitrate. Analyses on soil-core extracts and soil moisturefrom suction lysimeters installed beneath the seepage pits at eight residences showed that nitrate concentrations and nitrate/ chloride ratios generally become lower with increasing depth. The intervals of greatest decline seemed to coincide with finer soil texture or were near the water table. Nitrate-reducing bacteria were tested for and found to be present in soil cores from two residences. Sparse nitrogen-15 data from suction lysimeters at one of these residences, where thenitrate concentration decreased by about one-half at a depth of 200 feet, indicate that the nitrate decline was accompanied by nitrogen-15 enrichment in the residual nitrate with an isotope-separation factor of about -10 permil. Despite the potential input of abundant nitrogen with the domestic wastewater recharge, nitrate concentrations in the area's ground water are generally low. The absence of high nitrate concentrations in the ground water is consistent with the existence of denitrification, a microbial nitrogen-removal mechanism, as wastewater moves through the thick unsaturated zone and mixes with the ground water. The observed low nitrate concentrations also could be explained by a dilution by vertical mixing in the saturated zone and retention of the wastewater in the unsaturated zone. Results of a single-cell mixing model that allows nitrate from wastewater to be mixedinstantaneously with the underlying ground water suggest that measurable increases in nitrate concentration should be expected within 5 to 10 years after wastewater reaches the water table if the mixing depth is less than 100 feet. Although high fecal-coliform densities were measured in wastewater from septic tanks and seepage pits, removal of these enteric bacteria in the unsaturated zone is very effective, as was indicated by their absence in soil only a few feet from the seepage pits. In testing for organic priority pollutants in wastewater, 17 of 85 compounds were detected. Most compounds detected were present in low concentrations, except at one residence where the concentration of three compounds exceeded 100 micrograms per liter. These high concentrations may be a consequence of disposal practices unique to this residence. Extractable organic priority pollutants were not found in any soil cores taken adjacent to seepage pits and, therefore, are not of concern.

Water-Resources Investigations Report↗
USGS2000

Simulation of ground-water flow in an unconfined sand and gravel aquifer at Marathon, Cortland County, New York

The Village of Marathon, in Cortland County, N.Y., has three municipal wells that tap a relatively thin (25 to 40 feet thick) and narrow (less than 0.25 mile wide) unconfined sand and gravel aquifer in the Tioughnioga River valley. Only one of the wells is in use because water from one well has been contaminated by petroleum chemicals from a leaking storage tank, and water from the other well contains high concentrations of manganese. The operating well pumps about 0.1 million gallons per day and supplies about 1,000 people. A three-dimensional, finite-difference ground-water-flow model was used to (1) compute hydraulic heads in the aquifer under steady-state conditions, (2) develop a water budget, and (3) delineate the areas contributing recharge to two simulated wells that represent two of the municipal wells: one 57 feet east of the Tioughnioga River, the other 4,000 feet to the south and 75 feet from a man-made pond. The water budget for simulated long-term average, steady-state conditions with two simulated pumping wells indicates that the principal sources of recharge to the unconfined aquifer are unchanneled runoff and ground-water inflow from the uplands (41 percent of total recharge), precipitation that falls directly on the aquifer (34 percent), and stream leakage (23 percent). Only 2 percent of the recharge to the aquifer is from ground-water underflow into the northern end of the modeled area. Most of the simulated groundwater discharge from the modeled area (78 percent of total discharge) is to the Tioughnioga River; the rest discharges to the two simulated wells (19 percent) and as underflow at the southern end of the modeled area (3 percent). Results of a particle-tracking analysis indicate that the aquifer contributing area of the northern (simulated) well is 0.10 mile wide and 0.15 mile long and encompasses 0.015 square miles; the contributing area of the southern (simulated) well is 0.20 mile wide and 0.11 mile long and encompasses 0.022 square miles. The average traveltime of ground water from the valley wall to either simulated well is about 1.5 years, calculated on the basis of an assumed aquifer porosity of 0.3. The flowpath analysis indicates that both contributing areas contain surface-water sources of recharge; the Tioughnioga River and Hunts Creek contribute water to the northern well, and a pond and a small tributary contribute water to the southern well. Ground-water temperature in an observation well between the Tioughnioga River and the municipal well fluctuated several degrees Fahrenheit in response to pumping of the municipal well. This temperature fluctuation, in conjunction with the pumping well causing a ground-water gradient from the Tioughnioga River to the pumping well (ground-water levels in the pumping well were generally greater than 3 ft lower than that of the Tioughnioga River), indicate that there is a hydraulic connection between the river and aquifer at this site.

Water-Resources Investigations Report↗
USGS1994

Hydrology of Cache Valley, Cache County, Utah, and adjacent part of Idaho, with emphasis on simulation of ground-water flow

A hydrologic investigation of Cache Valley was done to better understand the ground-water system in unconsolidated basin-fill deposits and the interaction between ground water and surface water. Ground-water recharge occurs by infiltration of precipitation and unconsumed irrigation water, seepage from canals and streams, and subsurface inflow from adjacent consolidated rock and adjacent unconsolidated basin-fill deposit ground-water systems. Ground-water discharge occurs as seepage to streams and reservoirs, spring discharge, evapotranspiration, and withdrawal from wells. Water levels declined during 1984-90. Less-than-average precipitation during 1987-90 and increased pumping from irrigation and public-supply wells contributed to the declines. A ground-water-flow model was used to simulate flow in the unconsolidated basin-fill deposits. Data primarily from 1969 were used to calibrate the model to steady-state conditions. Transient-state calibration was done by simulating ground-water conditions on a yearly basis for 1982-90. A hypothetical simulation in which the dry conditions of 1990 were continued for 5 years projected an average lO-foot water-level decline between Richmond and Hyrum. When increased pumpage was simulated by adding three well fields, each pumping 10 cubic feet per second, in the Logan, Smithfield, and College Ward areas, water-level declines greater than 10 feet were projected in most of the southeastern part of the valley and discharge from springs and seepage to streams and reservoirs decreased.

Idaho, Utah↗
USGS2011

Assessment of channel changes, model of historical floods, and effects of backwater on flood stage, and flood mitigation alternatives for the Wichita River at Wichita Falls, Texas

In cooperation with the City of Wichita Falls, the U.S. Geological Survey assessed channel changes on the Wichita River at Wichita Falls, Texas, and modeled historical floods to investigate possible causes and potential mitigation alternatives to higher flood stages in recent (2007 and 2008) floods. Extreme flooding occurred on the Wichita River on June 30, 2007, inundating 167 homes in Wichita Falls. Although a record flood stage was reached in June 2007, the peak discharge was much less than some historical floods at Wichita Falls. Streamflow and stage data from two gages on the Wichita River and one on Holliday Creek were used to assess the interaction of the two streams. Changes in the Wichita River channel were evaluated using historical aerial and ground photography, comparison of recent and historical cross sections, and comparison of channel roughness coefficients with those from earlier studies. The floods of 2007 and 2008 were modeled using a one-dimensional step-backwater model. Calibrated channel roughness was larger for the 2007 flood compared to the 2008 flood, and the 2007 flood peaked about 4 feet higher than the 2008 flood. Calibration of the 1941 flood yielded a channel roughness coefficient (Manning's n ) of 0.030, which represents a fairly clean natural channel. The step-backwater model was also used to evaluate the following potential mitigation alternatives: (1) increasing the capacity of the bypass channel near River Road in Wichita Falls, Texas; (2) removal of obstructions near the Scott Avenue and Martin Luther King Junior Boulevard bridges in Wichita Falls, Texas; (3) widening of aggraded channel banks in the reach between Martin Luther King Junior Boulevard and River Road; and (4) reducing channel bank and overbank roughness. Reductions in water-surface elevations ranged from 0.1 foot to as much as 3.0 feet for the different mitigation alternatives. The effects of implementing a combination of different flood-mitigation alternatives were not investigated.

Texas↗
USGS1980

Development of a digital model of ground-water flow in deeply weathered crystalline rock, Chester County, Pennsylvania

The model developed in this study simulates .recharge to, flow through, and discharge from the water-table aquifer in the upper Pickering Creek basin, a 5.98-square-mile basin representative of most of Chester County, Pennsylvania. The two-dimensional finite-difference model of Trescott, Pinder, and Larson was used with slight modification. The way ground-water evapotranspiration varies with depth was modified, and a minimum transmissivity was used to prevent the model from "going dry" during water-table simulations. Tests of the model showed good correlation with field data, but also showed that certain additional types of information would be useful to make the model more reliable. Particularly helpful would be more water-level and evapotranspiration data, synoptic base-flow measurements in the subbasins, and better information on the variation of permeability and specific yield with depth. Predictive simulations made by the model show the effects of imposing various changes on the hydrologic system. Residential development was simulated in 1 square mile of the basin by combinations of the following conditions: 1-acre, 1/2-acre, and 1/4-acre lot size; wastewater disposal by septic systems or by public sewers; domestic wells or public-supply wells for water supply; and 0, 1, and 5 percent reduction in recharge in the developed area. Where water is supplied locally by wells, decreased lot size and reduced recharge result in increased drawdowns and reduced base flow. When wastewater is exported by sewers, these effects are magnified. The simulations by the model show the relative severity of the effects of various development schemes.

Pennslyvania↗
USGS1992

Documentation of a digital spatial data base for hydrologic investigations, Broward County, Florida

Geographic information systems have become an important tool in planning for the protection and development of natural resources, including ground water and surface water. A digital spatial data base consisting of 18 data layers that can be accessed by a geographic information system was developed for Broward County, Florida. Five computer programs, including one that can be used to create documentation files for each data layer and four that can be used to create data layers from data files not already in geographic information system format, were also developed. Four types of data layers have been developed. Data layers for manmade features include major roads, municipal boundaries, the public land-survey section grid, land use, and underground storage tank facilities. The data layer for topographic features consists of surveyed point land-surface elevations. Data layers for hydrologic features include surface-water and rainfall data-collection stations, surface-water bodies, water-control district boundaries, and water-management basins. Data layers for hydrogeologic features include soil associations, transmissivity polygons, hydrogeologic unit depths, and a finite-difference model grid for south-central Broward County. Each data layer is documented as to the extent of the features, number of features, scale, data sources, and a description of the attribute tables where applicable.

Florida↗
USGS1998

Hydrology and geochemistry of a slag-affected aquifer and chemical characteristics of slag-affected ground water, northwestern Indiana and northeastern Illinois

Slag is a by-product of steel manufacturing and a ubiquitous fill material in northwestern Indiana. Ground water associated with slag deposits generally is characterized by high pH and elevated concentrations of many inorganic water-quality constituents. The U.S. Geological Survey, in cooperation with the Indiana Department of Environmental Management, conducted a study in northwestern Indiana from June 1995 to September 1996 to improve understanding of the effects of slag deposits on the water quality of a glacial-outwash aquifer. The Bairstow Landfill, a slag-fill deposit overlying the Calumet aquifer near Hammond, Indiana, was studied to represent conditions in slag-deposit settings that are common in northwestern Indiana. Ground water from 10 observation wells, located in four nests at the site, and surface water from the adjacent Lake George were analyzed for values of field-measured parameters and concentrations of major ions, nutrients, trace elements, and bulk properties. Solid-phase samples of slag and aquifer sediment collected during drilling were examined with X-ray diffraction and geochemical digestion and analysis. Concentrations of calcium, potassium, sodium, and sulfate were highest in wells screened partly or fully in slag. Potassium concentrations in ground water ranged from 2.9 to 120 milligrams per liter (mg/L), were highest in water from slag deposits, and decreased with depth. The highest concentrations for aluminum, barium, molybdenum, nickel, and selenium were in water from the slag. Silica concentrations were highest in wells screened directly beneath the slag-aquifer interface, and magnesium concentrations were highest in intermediate and deep aquifer wells. Silica concentrations in shallow and intermediate aquifer wells ranged from 27 to 41 mg/L and were about 10 times greater than those in water from slag deposits. The highest concentrations for chromium, lead, and zinc were in ground water from immediately below the slag-aquifer interface. The solid-phase analyses indicated that calcite, dolomite, and quartz generally were present throughout the slag-aquifer system; barian celestite, cristobalite, manganese-bearing calcite, and minrecordite were present in fewer samples. Trace elements that are liberated from the slag may be incorporated as impurities during precipitation of major minerals, sorbed onto clays and other grainsize fractions not analyzed as part of this study, or present in low-abundance minerals that were not detected by the X-ray analysis. Mass-balance and speciation programs were used to identify geochemical processes that may be occurring as water infiltrates through the slag, flows into the aquifer, and discharges into Lake George. The geochemical models indicate that precipitation of calcite may be occurring where slag-affected water enters the aquifer. Models also indicate that dolomite precipitation and clay-mineral dissolution may be occurring at the slag-aquifer interface; however, dolomite precipitation is generally believed to require geologically long time periods. Silica may be dissolving where slag-affected ground water enters the aquifer and may be precipitating where slag-affected ground water discharges to the lakebed of Lake George. In addition to the site-specific study, a statistical analysis of regional water quality was done to compare ground water in wells affected and unaffected by slag. When com-pared to wells in background locations in the Calumet aquifer, wells screened in slag across northwestern Indiana and northeastern Illinois generally had relatively higher pH and specific-conductance values and relatively higher concentrations of alkalinity, dissolved solids, suspended solids, total organic carbon, calcium, potassium, sodium, chloride, aluminum, barium, and possibly magnesium, sulfate, chromium, cobalt, copper, cyanide, manganese, mercury, nickel, and vanadium. When compared to wells in slag and wells in background locations, ground water from immediately beneath or immediately downgradient from slag had relatively high concentrations of arsenic and silica. Water-quality characteristics in ground water at the Bairstow Landfill were similar to water-quality characteristics in slag-contact and slag-affected wells throughout northwestern Indiana.

Illinois, Indiana↗
USGS2005

Hydrogeology and simulation of source areas of water to production wells in a colluvium-mantled carbonate-bedrock aquifer near Shippensburg, Cumberland and Franklin Counties, Pennsylvania

This report presents the results of a study by the U.S. Geological Survey in cooperation with the Shippensburg Borough Authority to evaluate the source areas of water to production wells in a colluvium-mantled carbonate-bedrock aquifer in Cumberland and Franklin Counties, Pa. The areal extent of the zone of contribution was simulated for three production wells near Shippensburg, Pa. by use of a ground-water-flow model. A 111-square-mile area was selected as the model area and includes areas of the South Mountain Section and the Great Valley Section of the Valley and Ridge Physiographic Province. Within the model area, the geologic units in the South Mountain area are predominantly metamorphic rocks and the geologic units in the Great Valley are predominantly carbonate rocks. Hydrologic and geologic information were compiled to establish a conceptual model of ground-water flow. Characteristics of aquifer materials were determined, and streamflow and water levels were measured. Streamflow measurements in November 2003 showed all streams lost water as they flowed from South Mountain over the colluvium-mantled carbonate aquifer into the Great Valley. Some streams lost more than 1 cubic foot per second to the aquifer in this area. The Shippensburg Borough Authority owns three production wells in the model area. Two wells, Cu 969 and Fr 823, are currently (2004) used as production wells and produce 500,000 and 800,000 gallons per day, respectively. Well Cu 970 is intended to be brought on line as a production well in the future. Water levels were measured in 43 wells to use for model calibration. Water-level fluctuations and geophysical logs indicated confined conditions in well Cu 970. Ground-water flow was simulated with a model that consisted of two vertical layers, with five zones in each layer. The units were hydrostratigraphic units that initially were based on geologic formations, but boundaries were adjusted during model calibration. Model calibration resulted in a root mean square error of 9.8 feet. A parameter-estimation package was used during model calibration to estimate three parameters. The parameter estimation resulted in a value of 233 feet per day for horizontal hydraulic conductivity of the highly fractured carbonate rocks and sandy colluvium in layer 1; 3.97 feet per day for horizontal hydraulic conductivity of the ridge-forming unit in layer 1; and a value of 1.73 for horizontal anisotropy in both layers. The calibrated model was used to delineate the areal extent of the zone of contribution for wells Cu 969 and Fr 823. Although well Cu 970 is not currently (2004) being used, the areal extent of its zone of contribution also was simulated without additional model calibration. The shape of the areal extent of the zone of contribution was similar for each well and included an area that extended from the well southwest along the Tomstown Formation, and then extended southeast into the metamorphic rocks of South Mountain. The contributing areas from the watersheds of losing streams were also delineated because losing stream reaches bisect the areal extent of the zones of contribution. Spatial uncertainty of the areal extent of the zone of contribution was illustrated using a Monte-Carlo analysis. The model was run 1,000 times using randomly generated parameter sets that were normally distributed within the confidence interval around the optimal values for the three estimated parameters. The model converged and had a reasonable water budget for 980 of the model runs. For each of those 980 model runs, the recharge area was determined, and the results for all runs were compiled and contoured. The results of the Monte-Carlo analysis were compared to the results of the deterministic model, illustrating that the deterministic model has the greatest certainty in the area closest to each well in the Tomstown Formation. The areas farther from the well, upgradient, and in the metamorphic rocks have a higher degree

Pennsylvania↗
USGS1981

Simulated interactions between the proposed Narrows Reservoir and the water-table aquifer along the South Platte River, Morgan County, Colorado

A computer model, including a ground-water-flow component and a mass balance reservoir-operations component, was developed to simulate the proposed Narrows Reservoir and the adjacent alluvial aquifer of the South Platte River, Morgan County, Colo. This model, using a weekly time step, simulated the transient interactions of these two systems for an initial-fill condition and general-operational condition. A sensitivity analysis was made to test the effects of possible errors in the description of aquifer characteristics on the model results. The initial-fill simulation indicated that to fill the reservoir when hydraulic connection between the surface-water system and the aquifer is simulated would take 2 additional years than if no connection was assumed. Simulated ground-water return flow to the river downstream of the proposed dam was about 85 percent of the estimated maximum values, computed under steady-state conditions in an earlier study. The general operation simulation indicated that during the period of lowest reservoir contents the aquifer provided about 80,000 acre-feet of recoverable storage to the reservoir 's capacity. Average return flow was only about 70 percent of the estimated maximum values computed in the earlier, steady-state analysis. Monthly ground-water outflow from the reservoir to the aquifer ranged from 55,200 to -10,400 acre-feet. Parameters tested for sensitivity, in order of decreasing sensitivity, were: Hydraulic conductivity, specific yield, hydraulic connection between reservoir and aquifer, local recharge, boundary conditions, and dam permeability. The probable error in the parameters tested would not seem to warrant significant new data collection. (USGS)

Colorado↗
USGS2006

Simulation of ground-water flow and areas contributing recharge to extraction wells at the Drake Chemical Superfund Site, City of Lock Haven and Castanea Township, Clinton County, Pennsylvania

Extensive remediation of the Drake Chemical Superfund Site has been ongoing since 1983. Contaminated soils were excavated and incinerated on site between 1996 and 1999. After 1999, remedial efforts focused on contaminated ground water. A ground-water remediation system was started in November 2000. The source area of the contaminated ground water was assumed to be the zone 1 area on the Drake Chemical site. The remedial system was designed to capture ground water migrating from zone 1. Also, the remediation system was designed to pump and treat the water in an anoxic environment and re-infiltrate the treated water underground through an infiltration gallery that is hydrologically downgradient of the extraction wells. A numerical ground-water flow model of the surrounding region was constructed to simulate the areas contributing recharge to remedial extraction wells installed on the Drake Chemical site. The three-dimensional numerical flow model was calibrated using the parameter-estimation process in MODFLOW-2000. The model included three layers that represented three poorly sorted alluvial sediment units that were characterized from geologic well and boring logs. Steady-state ground-water flow was simulated to estimate the areas contributing recharge to three extraction wells for three different pumping scenarios--all wells pumping at 2 gallons per minute, at approximately 5 gallons per minute, and at 8 gallons per minute. Simulation results showed the contributing areas to the three extraction wells encompassed 92 percent of zone 1 at a pumping rate of approximately 5 gallons per minute. The contributing areas did not include a very small area in the southwestern part of zone 1 when the three extraction wells were pumped at approximately 5 gallons per minute. Pumping from a fourth extraction well in that area was discontinued early in the operation of the remediation system because the ground water in that area met performance standards. The areas contributing recharge to the three extraction wells did encompass zone 1 at a pumping rate of 8 gallons per minute. At pumping rates of 2 gallons per minute, the contributing areas for the three extraction wells did not encompass zone 1.

Pennsylvania↗
USGS2010

Initial Results from a Study of Climatic Changes and the Effect on Wild Sheep Habitat in Selected Study Areas of Alaska

Climate change theorists have projected striking changes in local weather on earth due to increases in temperature. These predicted changes may cause melting glaciers and ice caps, rising sea levels, increasing desertification and other environmental changes which seem likely to affect presumed indicator species as harbingers of more significant changes. Wild sheep, even though they are one of the more successful mammalian taxa since Pleistocene times, exhibit a suite of adaptations to glacier driven environments which may be presumed to render them sensitive to environmental changes. The authors began investigation with these assumptions by comparing changes, as determined by satellite imagery, in glacier extent in our study areas in Denali National Park, Alaska, during the last 30 years. Our findings showed the extent of glacial retreat in Alaska during this time period was approximately 40-50 percent as measured by ablation zone and retreat of terminal moraines. During the first half of this 30-year period, Dall sheep (Ovis dalli dalli) populations were stable at historically recorded highs. In the early to mid-1990s, Dall sheep populations in Alaska declined from an historical estimated high of 75,000 sheep to the presently estimated 40-50,000. The declines seemed to be weather related, on the basis of the presumption that lamb survival rates are primarily weather-mediated in Alaska. Changes in local weather appear, at this point, to be correlated with oscillation in the Pacific Current in the Northern Pacific ocean. Of course, changes in local weather affect forage abundance and quality seasonally. In investigating a possible linkage of weather to seasonal forage abundance and quality, we also investigated changes in snow and ice extent and distribution, as well as increased water runoff associated with permafrost and depleted glaciers. Databases were assembled from a wide variety of remotely sensed satellite data, ground-based observations, and historical data bases relating to Dall sheep habitats in selected study areas. Alaska's sheep habitats are typified by long, narrow bands of mountainous uplifts generally arrayed west-to-east, and perpendicular to prevailing south-to-north weather-front movements. Classic Dall sheep habitat occurs on snow-shadowed slopes within these narrow mountainous habitats. On the basis of these data, we offer an explanatory hypothesis relating Dall sheep welfare to weather and climate-influenced nutrition and a monitoring scheme, which should produce data sufficient to test the robustness of this hypothesis. If correlated with population changes, the methods used in our comparative observations may provide long-term monitoring tools for wildlife managers and be applicable in other widely-dispersed wild sheep habitats. If no significant correlations emerge from our modeling exercises, the notion that wild sheep are a sufficiently sensitive species to be seen as an indicator species will have to be reexamined.

Open-File Report↗