USGS Science⌕ Search

SEARCH · USGS Science

Results for “Groundwater”

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

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

At least 1,567 records · Page 87Linked to original sources
USGS2009

Apparent Resistivity and Estimated Interaction Potential of Surface Water and Groundwater along Selected Canals and Streams in the Elkhorn-Loup Model Study Area, North-Central Nebraska, 2006-07

In 2005, the State of Nebraska adopted new legislation that in part requires local Natural Resources Districts to include the effect of groundwater use on surface-water systems in their groundwater management plan. In response the U.S. Geological Survey, in cooperation with the Upper Elkhorn, Lower Elkhorn, Upper Loup, Lower Loup, Middle Niobrara, Lower Niobrara, Lewis and Clark, and Lower Platte North Natural Resources Districts, did a study during 2006-07 to investigate the surface-water and groundwater interaction within a 79,800-square-kilometer area in north-central Nebraska. To determine how streambed materials affect surface-water and groundwater interaction, surface geophysical and lithologic data were integrated at four sites to characterize the hydrogeologic conditions within the study area. Frequency-domain electromagnetic and waterborne direct- current resistivity profiles were collected to map the near-surface hydrogeologic conditions along sections of Ainsworth Canal near Ainsworth, Nebraska; Mirdan and Geranium Canals near Ord, Nebraska; North Loup River near Ord, Nebraska; and Middle Loup River near Thedford, Nebraska. Lithologic data were collected from test holes at each site to aid interpretation of the geophysical data. Geostatistical analysis incorporating the spatial variability of resistivity was used to account for the effect of lithologic heterogeneity on effective hydraulic permeability. The geostatistical analysis and lithologic data descriptions were used to make an interpretation of the hydrogeologic system and derive estimates of surface-water/groundwater interaction potential within the canals and streambeds. The estimated interaction potential at the Ainsworth Canal site and the Mirdan and Geranium Canal site is generally low to moderately low. The sediment textures at nearby test holes typically were silt and clay and fine-to-medium sand. The apparent resistivity values for these sites ranged from 2 to 120 ohm-meters. The vertical and horizontal variability of the apparent resistivity data were consistently low. Low resistive variability indicates little lithologic heterogeneity for either canal site. The surface-water/groundwater interaction-potential estimates are in agreement with the narrow frequency distribution of resistivity, low apparent resistivities, low spatial heterogeneity, and test-hole grain-size ranges. The estimated surface-water/groundwater interaction potential at the North Loup and Middle Loup River sites is moderate to moderately high. The sediment textures at nearby test holes were predominantly fine, medium, and coarse sand with some silt and silty to sandy clay. The apparent resistivity values for these sites ranged from 34 to 1,338 ohm-meters. The vertical variability of the resistivity data was moderately high. The horizontal variability at these sites is low to moderately low. The higher resistive variability at these sites indicates generally greater lithologic heterogeneity than at either the Ainsworth Canal site or the Mirdan and Geranium Canal site. The surface-water/groundwater interaction-potential estimates are in agreement with the generally moderate to high apparent resistivity, the greater spatial heterogeneity, and the variable lithologic texture. A higher interaction potential as compared to the canal sites is expected because of the higher subsurface resistivity and greater lithologic heterogeneity.

Scientific Investigations Report↗
USGS2010

Simulation of streamflow, evapotranspiration, and groundwater recharge in the lower San Antonio River Watershed, South-Central Texas, 2000-2007

The U.S. Geological Survey (USGS), in cooperation with the San Antonio River Authority, the Evergreen Underground Water Conservation District, and the Goliad County Groundwater Conservation District, configured, calibrated, and tested a watershed model for a study area consisting of about 2,150 square miles of the lower San Antonio River watershed in Bexar, Guadalupe, Wilson, Karnes, DeWitt, Goliad, Victoria, and Refugio Counties in south-central Texas. The model simulates streamflow, evapotranspiration (ET), and groundwater recharge using rainfall, potential ET, and upstream discharge data obtained from National Weather Service meteorological stations and USGS streamflow-gaging stations. Additional time-series inputs to the model include wastewater treatment-plant discharges, withdrawals for cropland irrigation, and estimated inflows from springs. Model simulations of streamflow, ET, and groundwater recharge were done for 2000-2007. Because of the complexity of the study area, the lower San Antonio River watershed was divided into four subwatersheds; separate HSPF models were developed for each subwatershed. Simulation of the overall study area involved running simulations of the three upstream models, then running the downstream model. The surficial geology was simplified as nine contiguous water-budget zones to meet model computational limitations and also to define zones for which ET, recharge, and other water-budget information would be output by the model. The model was calibrated and tested using streamflow data from 10 streamflow-gaging stations; additionally, simulated ET was compared with measured ET from a meteorological station west of the study area. The model calibration is considered very good; streamflow volumes were calibrated to within 10 percent of measured streamflow volumes. During 2000-2007, the estimated annual mean rainfall for the water-budget zones ranged from 33.7 to 38.5 inches per year; the estimated annual mean rainfall for the entire watershed was 34.3 inches. Using the HSPF model it was estimated that for 2000-2007, less than 10 percent of the annual mean rainfall on the study watershed exited the watershed as streamflow, whereas about 82 percent, or an average of 28.2 inches per year, exited the watershed as ET. Estimated annual mean groundwater recharge for the entire study area was 3.0 inches, or about 9 percent of annual mean rainfall. Estimated annual mean recharge was largest in water-budget zone 3, the zone where the Carrizo Sand outcrops. In water-budget zone 3, the estimated annual mean recharge was 5.1 inches or about 15 percent of annual mean rainfall. Estimated annual mean recharge was smallest in water-budget zone 6, about 1.1 inches or about 3 percent of annual mean rainfall. The Cibolo Creek subwatershed and the subwatershed of the San Antonio River upstream from Cibolo Creek had the largest and smallest basin yields, about 4.8 inches and 1.2 inches, respectively. Estimated annual ET and annual recharge generally increased with increasing annual rainfall. Also, ET was larger in zones 8 and 9, the most downstream zones in the watershed. Model limitations include possible errors related to model conceptualization and parameter variability, lack of data to quantify certain model inputs, and measurement errors. Uncertainty regarding the degree to which available rainfall data represent actual rainfall is potentially the most serious source of measurement error.

Texas↗
USGS2010

Simulation of the shallow groundwater-flow system near the Hayward Airport, Sawyer County, Wisconsin

There are concerns that removal and trimming of vegetation during expansion of the Hayward Airport in Sawyer County, Wisconsin, could appreciably change the character of a nearby cold-water stream and its adjacent environs. In cooperation with the Wisconsin Department of Transportation, a two-dimensional, steady-state groundwater-flow model of the shallow groundwater-flow system near the Hayward Airport was refined from a regional model of the area. The parameter-estimation code PEST was used to obtain a best fit of the model to additional field data collected in February 2007 as part of this study. The additional data were collected during an extended period of low runoff and consisted of water levels and streamflows near the Hayward Airport. Refinements to the regional model included one additional hydraulic-conductivity zone for the airport area, and three additional parameters for streambed resistance in a northern tributary to the Namekagon River and in the main stem of the Namekagon River. In the refined Hayward Airport area model, the calibrated hydraulic conductivity was 11.2 feet per day, which is within the 58.2 to 7.9 feet per day range reported for the regional glacial and sandstone aquifer, and is consistent with a silty soil texture for the area. The calibrated refined model had a best fit of 8.6 days for the streambed resistance of the Namekagon River and between 0.6 and 1.6 days for the northern tributary stream. The previously reported regional groundwater-recharge rate of 10.1 inches per year was adjusted during calibration of the refined model in order to match streamflows measured during the period of extended low runoff; this resulted in an optimal groundwater-recharge rate of 7.1 inches per year during this period. The refined model was then used to simulate the capture zone of the northern tributary to the Namekagon River.

Scientific Investigations Report↗
USGS2010

Occurrence and distribution of dissolved solids, selenium, and uranium in groundwater and surface water in the Arkansas River Basin from the headwaters to Coolidge, Kansas, 1970-2009

In 2007, the U.S. Geological Survey (USGS), in cooperation with City of Aurora, Colorado Springs Utilities, Colorado Water Conservation Board, Lower Arkansas Valley Water Conservancy District, Pueblo Board of Water Works, Southeastern Colorado Water Activity Enterprise, Southeastern Colorado Water Conservancy District, and Upper Arkansas Water Conservancy District began a retrospective evaluation to characterize the occurrence and distribution of dissolved-solids (DS), selenium, and uranium concentrations in groundwater and surface water in the Arkansas River Basin based on available water-quality data collected by several agencies. This report summarizes and characterizes available DS, dissolved-selenium, and dissolved-uranium concentrations in groundwater and surface water for 1970-2009 and describes DS, dissolved-selenium, and dissolved-uranium loads in surface water along the main-stem Arkansas River and selected tributary and diversion sites from the headwaters near Leadville, Colorado, to the USGS 07137500 Arkansas River near Coolidge, Kansas (Ark Coolidge), streamgage, a drainage area of 25,410 square miles. Dissolved-solids concentrations varied spatially in groundwater and surface water in the Arkansas River Basin. Dissolved-solids concentrations in groundwater from Quaternary alluvial, glacial drift, and wind-laid deposits (HSU 1) increased downgradient with median values of about 220 mg/L in the Upper Arkansas subbasin (Arkansas River Basin from the headwaters to Pueblo Reservoir) to about 3,400 mg/L in the Lower Arkansas subbasin (Arkansas River Basin from John Martin Reservoir to Ark Coolidge). Dissolved-solids concentrations in the Arkansas River also increased substantially in the downstream direction between the USGS 07086000 Arkansas River at Granite, Colorado (Ark Granite), and Ark Coolidge streamgages. Based on periodic data collected from 1976-2007, median DS concentrations in the Arkansas River ranged from about 64 mg/L at Ark Granite to about 4,060 mg/L at Ark Coolidge representing over a 6,000 percent increase in median DS concentrations. Temporal variations in specific conductance values (which are directly related to DS concentrations) and seasonal variations in DS concentrations and loads were investigated at selected sites in the Arkansas River from Ark Granite to Ark Coolidge. Analyses indicated that, for the most part, specific conductance values (surrogate for DS concentrations) have remained relatively constant or have decreased in the Arkansas River since about 1970. Dissolved-solids concentrations in the Arkansas River were higher during the nonirrigation season (November-February) than during the irrigation season (March-October). Average annual DS loads, however, were higher during the irrigation season than during the nonirrigation season. Average annual DS loads during the irrigation season were at least two times and as much as 23 times higher than average annual DS loads during the nonirrigation season with the largest differences occurring at sites located downstream from the two main-stem reservoirs at USGS 07099400 Arkansas River above Pueblo, Colorado (Ark Pueblo), (which is below Pueblo Reservoir) and USGS 07130500 Arkansas River below John Martin Reservoir, Colorado (Ark below JMR). View report for unabridged abstract.

Scientific Investigations Report↗
USGS2010

Distribution of Isotopic and Environmental Tracers in Groundwater, Northern Ada County, Southwestern Idaho

Residents of northern Ada County, Idaho, depend on groundwater for domestic and agricultural uses. The population of this area is growing rapidly and groundwater resources must be understood for future water-resource management. The U.S. Geological Survey, in cooperation with the Idaho Department of Water Resources, used a suite of isotopic and environmental tracers to gain a better understanding of groundwater ages, recharge sources, and flowpaths in northern Ada County. Thirteen wells were sampled between September and October 2009 for field parameters, major anions and cations, nutrients, oxygen and hydrogen isotopes, tritium, radiocarbon, chlorofluorocarbons, and dissolved gasses. Well depths ranged from 30 to 580 feet below land surface. Wells were grouped together based on their depth and geographic location into the following four categories: shallow aquifer, intermediate/deep aquifer, Willow Creek aquifer, and Dry Creek aquifer. Major cations and anions indicated calcium-bicarbonate and sodium-bicarbonate water types in the study area. Oxygen and hydrogen isotopes carried an oxygen-18 excess signature, possibly indicating recharge from evaporated sources or water-rock interactions in the subsurface. Chlorofluorocarbons detected modern (post-1940s) recharge in every well sampled; tritium data indicated modern water (post-1951) in seven, predominantly shallow wells. Nutrient concentrations tended to be greater in wells signaling recent recharge based on groundwater age dating, thus confirming the presence of recent recharge in these wells. Corrected radiocarbon results generated estimated residence times from modern to 5,100 years before present. Residence time tended to increase with depth, as confirmed by all three age-tracers. The disagreement among residence times indicates that samples were well-mixed and that the sampled aquifers contain a mixture of young and old recharge. Due to a lack of data, no conclusions about sources of recharge could be drawn from this study.

Scientific Investigations Report↗
USGS2010

Hydrology of Eagle Creek Basin and effects of groundwater pumping on streamflow, 1969-2009

Urban and resort development and drought conditions have placed increasing demands on the surface-water and groundwater resources of the Eagle Creek Basin, in southcentral New Mexico. The Village of Ruidoso, New Mexico, obtains 60-70 percent of its water from the Eagle Creek Basin. The village drilled four production wells on Forest Service land along North Fork Eagle Creek; three of the four wells were put into service in 1988 and remain in use. Local citizens have raised questions as to the effects of North Fork well pumping on flow in Eagle Creek. In response to these concerns, the U.S. Geological Survey, in cooperation with the Village of Ruidoso, conducted a hydrologic investigation from 2007 through 2009 of the potential effect of the North Fork well field on streamflow in North Fork Eagle Creek. Mean annual precipitation for the period of record (1942-2008) at the Ruidoso climate station is 22.21 inches per year with a range from 12.27 inches in 1970 to 34.81 inches in 1965. Base-flow analysis indicates that the 1970-80 mean annual discharge, direct runoff, and base flow were 2,260, 1,440, and 819 acre-ft/yr, respectively, and for 1989-2008 were 1,290, 871, and 417 acre-ft/yr, respectively. These results indicate that mean annual discharge, direct runoff, and base flow were less during the 1989-2008 period than during the 1970-80 period. Mean annual precipitation volume for the study area was estimated to be 12,200 acre-feet. Estimated annual evapotranspiration for the study area ranged from 8,730 to 8,890 acre-feet. Estimated annual basin yield for the study area was 3,390 acre-ft or about 28 percent of precipitation. On the basis of basin-yield computations, annual recharge was estimated to be 1,950 acre-ft, about 16 percent of precipitation. Using a chloride mass-balance method, groundwater recharge over the study area was estimated to average 490 acre-ft, about 4.0 percent of precipitation. Because the North Fork wells began pumping in 1988, 1969-80 represents the pre-groundwater-pumping period, and 1988-2009 represents the groundwater-pumping period. The 5-year moving average for precipitation at the Ruidoso climate station shows years of below-average precipitation during both time periods, but no days of zero flow were recorded for the 11-year period 1970-80 and no-flow days were recorded in 11 of 20 years for the 1988-2009 period. View report for unabridged abstract.

Scientific Investigations Report↗
USGS2011

Simulations of groundwater flow and particle-tracking analysis in the zone of contribution to a public-supply well in San Antonio, Texas

In 2006, a public-supply well in San Antonio, Texas, was selected for intensive study to assess the vulnerability of public-supply wells in the Edwards aquifer to contamination by a variety of compounds. A local-scale, steady-state, three-dimensional numerical groundwater-flow model was developed and used in this study to evaluate the movement of water and solutes from recharge areas to the selected public-supply well. Particle tracking was used to compute flow paths and advective traveltimes throughout the model area and to delineate the areas contributing recharge and zone of contribution for the selected public-supply well. The local-scale model grid has a finer vertical discretization than do previous regional Edwards aquifer models and incorporates refined parameter zones corresponding with multiple (10) hydrogeologic units representing the Edwards aquifer. In the Edwards aquifer, high matrix porosity and permeability likely are overshadowed by high permeability developed in structurally influenced karstic conduit systems that transmit water into, through, and out of the aquifer system. The complexity of the aquifer system in the local-scale study area is further increased by numerous faults with varying vertical displacements. The extensive faulting results in the juxtaposition of hydrogeologic units with differing hydraulic properties and has appreciable effects on groundwater flow in the Edwards aquifer. The local-scale model simulations use the MODFLOW Hydrogeologic-Unit Flow Package and include two hydrogeologic units with high hydraulic conductivities (one or more orders of magnitude higher than for the other simulated hydrogeologic units) that are intended to simulate fast flow paths attributable to karst features. The two “conduit” hydrogeologic units of the Edwards aquifer represent the lower 8 meters of the leached and collapsed members and the Kirschberg evaporite member of the Edwards Group. The MODFLOW Horizontal-Flow Barrier Package was used to simulate faults in the local-scale model. The assumption was made that the degree to which a fault acts as a barrier to groundwater flow is proportional to the fault displacement. The final calibrated hydraulic-conductance values ranged from 0.01 to 0.2 per day for fault displacements ranging from 0 to more than 100 percent of the total aquifer thickness. The calibrated steady-state simulation generally reproduces the spatial distribution of measured water-level altitudes. Simulated water-level altitudes were within 9.0 meters of measured water-level altitudes at 74 of the 84 wells used as targets for the local-scale model for the calibrated steady-state simulation. The overall mean absolute difference between simulated and measured water-level altitudes is 4.2 meters, and the mean algebraic difference is 1.9 meters. The simulated springflow for San Antonio Springs was 7.7 percent greater and for San Pedro Springs was 4.2 percent less than the median measured springflow. Simulated tritium concentrations were within 0.14 tritium units of measured tritium concentrations for 11 of the 13 local-scale study tritium observations from the 10 local-scale study wells used to calibrate the steady-state local-scale model, with a mean absolute difference between simulated and measured tritium concentrations of 0.11 tritium units and a mean algebraic difference of -0.04 tritium units. Simulated tritium concentrations in the selected public-supply well during November 2007 were within 0.09 tritium units of the measured concentrations, with the exception of the shallowest observation from the well. The steady-state simulation water budget indicates that recharge occurring in the local-scale study area accounts for 31.8 percent of the sources of water to the Edwards aquifer in the local-scale model area and that inflow through the model boundaries contributes 68.2 percent. Most of the flow into the local-scale model area through the model boundaries occurs through the western and southern boundaries, 58.2 and 39.6 percent, respectively. The largest discharges from the Edwards aquifer in the local-scale model area are boundary outflow (71.4 percent) and withdrawals by wells (24.9 percent). Most of the flow out of the local-scale model area through the model boundaries occurs through the southern and eastern boundaries, 54.2 and 39.6 percent, respectively. The simulated zones of contribution for the selected public-supply well, Timberhill well nest, and Zarzamora well nest extend to the north, northeast, and northwest from each site in the confined zone of the aquifer into the recharge zone, where all recharge to the aquifer occurs. The area contributing recharge for the selected public-supply well has the greatest extent. The area contributing recharge for the Timberhill well nest encompasses approximately the western one-half of the area contributing recharge for the selected public-supply well, and that for the Zarzamora well nest encompasses approximately the eastern two-thirds of the area contributing recharge for the selected public-supply well. Simulated particle ages ranged from less than 1 day to more than 1,900 years in the 10 local-scale study wells (13 local-scale study tritium observations) used to calibrate the local-scale model. The simulated mean particle ages for the tritium observations representing selected well depths (shallow, intermediate, and deep) ranged from 2.5 to 15 years. The minimum (youngest) mean particle ages for the selected public-supply well and the Timberhill monitoring wells were for the intermediate well depth, while the youngest mean particle age for the Zarzamora monitoring wells was for the intermediate and deep well depth. The maximum (oldest) mean particle ages for the selected public-supply well and the Zarzamora monitoring wells were for the shallow well depth. The mean of simulated particle ages for tritium observations representing well depths open to the simulated conduit hydrogeologic units was 3.8 years, whereas the mean of simulated particle ages for tritium observations representing well depths not open to the simulated conduit hydrogeologic units was 9.6 years. The effect of short-circuit pathways, for example karst conduits, in the flow system on the movement of young water to the selected public-supply well could greatly alter contaminant arrival times compared to what might be expected from advection in a system without short circuiting. In a forecasting exercise, the simulated concentrations showed rapid initial response at the beginning and end of chemical input, followed by more gradual response as older water moved through the system. The nature of karst groundwater flow, where flow predominantly occurs via conduit flow paths, could lead to relatively rapid water quality responses to land-use changes. Results from the forecasting exercise indicate that timescales for change in the quality of water from the selected public-supply well could be on the order of a few years to decades for land-use changes that occur over days to decades, which has implications for source-water protection strategies that rely on land-use change to achieve water-quality objectives.

Texas↗
USGS2011

Groundwater budgets for Detrital, Hualapai, and Sacramento Valleys, Mohave County, Arizona, 2007-08

The United States Geological Survey, in cooperation with the Arizona Department of Water Resources, initiated an investigation of the hydrogeology and water resources of Detrital, Hualapai, and Sacramento Valleys in northwestern Arizona in 2005, and this report is part of that investigation. Water budgets were developed for Detrital, Hualapai, and Sacramento Valleys to provide a generalized understanding of the groundwater systems in this rural area that has shown some evidence of human-induced water-level declines. The valleys are within the Basin and Range physiographic province and consist of thick sequences of permeable alluvial sediment deposited into basins bounded by relatively less permeable igneous and metamorphic rocks. Long-term natural recharge rates (1940-2008) for the alluvial aquifers were estimated to be 1,400 acre-feet per year (acre-ft/yr) for Detrital Valley, 5,700 acre-ft/yr for Hualapai Valley, and 6,000 acre-ft/yr for Sacramento Valley. Natural discharge rates were assumed to be equal to natural recharge rates, on the basis of the assumption that all groundwater withdrawals to date have obtained water from groundwater storage. Groundwater withdrawals (2007-08) for the alluvial aquifers were less than 300 acre-ft/yr for Detrital Valley, about 9,800 acre-ft/yr for Hualapai Valley, and about 4,500 acre-ft/yr for Sacramento Valley. Incidental recharge from leaking water-supply pipes, septic systems, and wastewater-treatment plants accounted for about 35 percent of total recharge (2007-08) across the study area. Natural recharge and discharge values in this study were 24-50 percent higher than values in most previously published studies. Water budgets present a spatially and temporally "lumped" view of water resources and incorporate many sources of uncertainty in this study area where only limited data presently are available. Figures 9, 10, and 11 from this report present water budgets for Detritial, Hualapai, and Sacramento Valleys in Northwestern Arizona. These figures show average values for each water-budget component. Uncertainty is discussed but not shown on these report figures. As an aid to readers, these figures have been implemented as interactive, web-based figures here. Water-budget parameters can be varied within reasonable bounds of uncertainty and the effects those changes have on the water budget will be shown as they are varied. This can aid in understanding sensitivity-which parameters most or least affect the water budgets-and also could provide a generally improved sense of the hydrologic cycle represented in these water budgets.

Scientific Investigations Report↗
USGS2012

Comparison of no-purge and pumped sampling methods for monitoring concentrations of ordnance-related compounds in groundwater, Camp Edwards, Massachusetts Military Reservation, Cape Cod, Massachusetts, 2009-2010

Field tests were conducted near the Impact Area at Camp Edwards on the Massachusetts Military Reservation, Cape Cod, Massachusetts, to determine the utility of no-purge groundwater sampling for monitoring concentrations of ordnance-related explosive compounds and perchlorate in the sand and gravel aquifer. The no-purge methods included (1) a diffusion sampler constructed of rigid porous polyethylene, (2) a diffusion sampler constructed of regenerated-cellulose membrane, and (3) a tubular grab sampler (bailer) constructed of polyethylene film. In samples from 36 monitoring wells, concentrations of perchlorate (ClO 4 - ), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), the major contaminants of concern in the Impact Area, in the no-purge samples were compared to concentrations of these compounds in samples collected by low-flow pumped sampling with dedicated bladder pumps. The monitoring wells are constructed of 2- and 2.5-inch-diameter polyvinyl chloride pipe and have approximately 5- to 10-foot-long slotted screens. The no-purge samplers were left in place for 13-64 days to ensure that ambient groundwater flow had flushed the well screen and concentrations in the screen represented water in the adjacent formation. The sampling methods were compared first in six monitoring wells. Concentrations of ClO 4 - , RDX, and HMX in water samples collected by the three no-purge sampling methods and low-flow pumped sampling were in close agreement for all six monitoring wells. There is no evidence of a systematic bias in the concentration differences among the methods on the basis of type of sampling device, type of contaminant, or order in which the no-purge samplers were tested. A subsequent examination of vertical variations in concentrations of ClO 4 - in the 10-foot-long screens of six wells by using rigid porous polyethylene diffusion samplers indicated that concentrations in a given well varied by less than 15 percent and the small variations were unlikely to affect the utility of the various sampling methods. The grab sampler was selected for additional tests in 29 of the 36 monitoring wells used during the study. Concentrations of ClO 4 - , RDX, HMX, and other minor explosive compounds in water samples collected by using a 1-liter grab sampler and low-flow pumped sampling were in close agreement in field tests in the 29 wells. A statistical analysis based on the sign test indicated that there was no bias in the concentration differences between the methods. There also was no evidence for a systematic bias in concentration differences between the methods related to location of the monitoring wells laterally or vertically in the groundwater-flow system. Field tests in five wells also demonstrated that sample collection by using a 2-liter grab sampler and sequential bailing with the 1-liter grab sampler were options for obtaining sufficient sample volume for replicate and spiked quality assurance and control samples. The evidence from the field tests supports the conclusion that diffusion sampling with the rigid porous polyethylene and regenerated-cellulose membranes and grab sampling with the polyethylene-film samplers provide comparable data on the concentrations of ordnance-related compounds in groundwater at the MMR to that obtained by low-flow pumped sampling. These sampling methods are useful methods for monitoring these compounds at the MMR and in similar hydrogeologic environments.

Massachusetts↗
USGS2012

Estimates of tracer-based piston-flow ages of groundwater from selected sites: National Water-Quality Assessment Program, 2006-2010

Piston-flow age dates were interpreted from measured concentrations of environmental tracers from 812 National Water-Quality Assessment (NAWQA) Program groundwater sites from 27 Study Units across the United States. The tracers of interest include chlorofluorocarbons (CFCs), sulfur hexafluoride (SF 6 ), and tritium/helium-3 ( 3 H/ 3 He). Tracer data compiled for this analysis were collected from 2006 to 2010 from groundwater wells in NAWQA studies, including: * Land-Use Studies (LUS, shallow wells, usually monitoring wells, located in recharge areas under dominant land-use settings), * Major-Aquifer Studies (MAS, wells, usually domestic supply wells, located in principal aquifers and representing the shallow drinking water supply), * Flow System Studies (FSS, networks of clustered wells located along a flowpath extending from a recharge zone to a discharge zone, preferably a shallow stream) associated with Land-Use Studies, and * Reference wells (wells representing groundwater minimally impacted by anthropogenic activities) also associated with Land-Use Studies. Tracer data were evaluated using documented methods and are presented as aqueous concentrations, equivalent atmospheric concentrations (for CFCs and SF 6 ), and tracer-based piston-flow ages. Selected ancillary data, such as redox data, well-construction data, and major dissolved-gas (N 2 , O 2 , Ar, CH 4 , and CO 2 ) data, also are presented. Recharge temperature was inferred using climate data (approximated by mean annual air temperature plus 1°C [MAAT +1°C]) as well as major dissolved-gas data (N 2 -Ar-based) where available. The N 2 -Ar-based temperatures showed significantly more variation than the climate-based data, as well as the effects of denitrification and degassing resulting from reducing conditions. The N 2 -Ar-based temperatures were colder than the climate-based temperatures in networks where recharge was limited to the winter months when evapotranspiration was reduced. The tracer-based piston-flow ages compiled in this report are provided as a consistent means of reporting the tracer data. The tracer-based piston-flow ages may provide an initial interpretation of age in cases in which mixing is minimal and may aid in developing a basic conceptualization of groundwater age in an aquifer. These interpretations are based on the assumption that tracer transport is by advection only and that no mixing occurs. In addition, it is assumed that other uncertainties are minimized, including tracer degradation, sorption, contamination, or fractionation, and that terrigenic (natural) sources of tracers, and spatially variable atmospheric tracer concentrations are constrained.

Scientific Investigations Report↗
USGS2012

Multilevel groundwater monitoring of hydraulic head and temperature in the eastern Snake River Plain aquifer, Idaho National Laboratory, Idaho, 2009–10

During 2009 and 2010, the U.S. Geological Survey’s Idaho National Laboratory Project Office, in cooperation with the U.S. Department of Energy, collected quarterly, depth-discrete measurements of fluid pressure and temperature in nine boreholes located in the eastern Snake River Plain aquifer. Each borehole was instrumented with a multilevel monitoring system consisting of a series of valved measurement ports, packer bladders, casing segments, and couplers. Multilevel monitoring at the Idaho National Laboratory has been ongoing since 2006. This report summarizes data collected from three multilevel monitoring wells installed during 2009 and 2010 and presents updates to six multilevel monitoring wells. Hydraulic heads (heads) and groundwater temperatures were monitored from 9 multilevel monitoring wells, including 120 hydraulically isolated depth intervals from 448.0 to 1,377.6 feet below land surface. Quarterly head and temperature profiles reveal unique patterns for vertical examination of the aquifer’s complex basalt and sediment stratigraphy, proximity to aquifer recharge and discharge, and groundwater flow. These features contribute to some of the localized variability even though the general profile shape remained consistent over the period of record. Major inflections in the head profiles almost always coincided with low-permeability sediment layers and occasionally thick sequences of dense basalt. However, the presence of a sediment layer or dense basalt layer was insufficient for identifying the location of a major head change within a borehole without knowing the true areal extent and relative transmissivity of the lithologic unit. Temperature profiles for boreholes completed within the Big Lost Trough indicate linear conductive trends; whereas, temperature profiles for boreholes completed within the axial volcanic high indicate mostly convective heat transfer resulting from the vertical movement of groundwater. Additionally, temperature profiles provide evidence for stratification and mixing of water types along the southern boundary of the Idaho National Laboratory. Vertical head and temperature change were quantified for each of the nine multilevel monitoring systems. The vertical head gradients were defined for the major inflections in the head profiles and were as high as 2.1 feet per foot. Low vertical head gradients indicated potential vertical connectivity and flow, and large gradient inflections indicated zones of relatively low vertical connectivity. Generally, zones that primarily are composed of fractured basalt displayed relatively small vertical head differences. Large head differences were attributed to poor vertical connectivity between fracture units because of sediment layering and/or dense basalt. Groundwater temperatures in all boreholes ranged from 10.2 to 16.3˚C. Normalized mean hydraulic head values were analyzed for all nine multilevel monitoring wells for the period of record (2007-10). The mean head values suggest a moderately positive correlation among all boreholes, which reflects regional fluctuations in water levels in response to seasonality. However, the temporal trend is slightly different when the location is considered; wells located along the southern boundary, within the axial volcanic high, show a strongly positive correlation.

Idaho↗
USGS2013

Analysis of environmental setting, surface-water and groundwater data, and data gaps for the Citizen Potawatomi Nation Tribal Jurisdictional Area, Oklahoma, through 2011

The Citizen Potawatomi Nation Tribal Jurisdictional Area, consisting of approximately 960 square miles in parts of three counties in central Oklahoma, has an abundance of water resources, being underlain by three principal aquifers (alluvial/terrace, Central Oklahoma, and Vamoosa-Ada), bordered by two major rivers (North Canadian and Canadian), and has several smaller drainages. The Central Oklahoma aquifer (also referred to as the Garber-Wellington aquifer) underlies approximately 3,000 square miles in central Oklahoma in parts of Cleveland, Logan, Lincoln, Oklahoma, and Pottawatomie Counties and much of the tribal jurisdictional area. Water from these aquifers is used for municipal, industrial, commercial, agricultural, and domestic supplies. The approximately 115,000 people living in this area used an estimated 4.41 million gallons of fresh groundwater, 12.12 million gallons of fresh surface water, and 8.15 million gallons of saline groundwater per day in 2005. Approximately 8.48, 2.65, 2.24, 1.55, 0.83, and 0.81 million gallons per day of that water were used for domestic, livestock, commercial, industrial, crop irrigation, and thermoelectric purposes, respectively. Approximately one-third of the water used in 2005 was saline water produced during petroleum production. Future changes in use of freshwater in this area will be affected primarily by changes in population and agricultural practices. Future changes in saline water use will be affected substantially by changes in petroleum production. Parts of the area periodically are subject to flooding and severe droughts that can limit available water resources, particularly during summers, when water use increases and streamflows substantially decrease. Most of the area is characterized by rural types of land cover such as grassland, pasture/hay fields, and deciduous forest, which may limit negative effects on water quality by human activities because of lesser emissions of man-made chemicals on such areas than in more urbanized areas. Much of the water in the area is of good quality, though some parts of this area have water quality impaired by very hard surface water and groundwater; large chloride concentrations in some smaller streams; relatively large concentrations of nutrients and counts of fecal-indicator bacteria in the North Canadian River; and chloride, iron, manganese, and uranium concentrations that exceed primary or secondary drinking-water standards in water samples collected from small numbers of wells. Substantial amounts of hydrologic and water-quality data have been collected in much of this area, but there are gaps in those data caused by relatively few streamflow-gaging stations, uneven distribution of surface-water quality sampling sites, lack of surface-water quality sampling at high-flow and low-flow conditions, and lack of a regularly measured and sampled groundwater network. This report summarizes existing water-use, climatic, geographic, hydrologic, and water-quality data and describes several means of filling gaps in hydrologic data for this area.

Oklahoma↗
USGS2013

Human effects on the hydrologic system of the Verde Valley, central Arizona, 1910–2005 and 2005–2110, using a regional groundwater flow model

Water budgets were developed for the Verde Valley of central Arizona in order to evaluate the degree to which human stresses have affected the hydrologic system and might affect it in the future. The Verde Valley is a portion of central Arizona wherein concerns have been raised about water availability, particularly perennial base flow of the Verde River. The Northern Arizona Regional Groundwater Flow Model (NARGFM) was used to generate the water budgets and was run in several configurations for the 1910–2005 and 2005–2110 time periods. The resultant water budgets were subtracted from one another in order to quantify the relative changes that were attributable solely to human stresses; human stresses included groundwater withdrawals and incidental and artificial recharge but did not include, for example, human effects on the global climate. Three hypothetical and varied conditions of human stresses were developed and applied to the model for the 2005–2110 period. On the basis of this analysis, human stresses during 1910–2005 were found to have already affected the hydrologic system of the Verde Valley, and human stresses will continue to affect the hydrologic system during 2005–2110. Riparian evapotranspiration decreased and underflow into the Verde Valley increased because of human stresses, and net groundwater discharge to the Verde River in the Verde Valley decreased for the 1910–2005 model runs. The model also showed that base flow at the upstream end of the study area, as of 2005, was about 4,900 acre-feet per year less than it would have been in the absence of human stresses. At the downstream end of the Verde Valley, base flow had been reduced by about 10,000 acre-feet per year by the year 2005 because of human stresses. For the 2005–2110 period, the model showed that base flow at the downstream end of the Verde Valley may decrease by an additional 5,400 to 8,600 acre-feet per year because of past, ongoing, and hypothetical future human stresses. The process known as capture (or streamflow depletion caused by the pumping of groundwater) was the reason for these human-stress-induced changes in water-budget components.

Arizona↗
USGS2013

Preliminary groundwater flow model of the basin-fill aquifers in Detrital, Hualapai, and Sacramento Valleys, Mohave County, northwestern Arizona

Preliminary numerical models were developed to simulate groundwater flow in the basin-fill alluvium in Detrital, Hualapai, and Sacramento Valleys in northwestern Arizona. The purpose of this exercise was to gather and evaluate available information and data, to test natural‑recharge concepts, and to indicate directions for improving future regional groundwater models of the study area. Both steady-state and transient models were developed with a single layer incorporating vertically averaged hydraulic properties over the model layer. Boundary conditions for the models were constant-head cells along the northern and western edges of the study area, corresponding to the location of the Colorado River, and no-flow boundaries along the bedrock ridges that bound the rest of the study area, except for specified flow where Truxton Wash enters the southern end of Hualapai Valley. Steady-state conditions were simulated for the pre-1935 period, before the construction of Hoover Dam in the northwestern part of the model area. Two recharge scenarios were investigated using the steady-state model—one in which natural aquifer recharge occurs directly in places where water is available from precipitation, and another in which natural aquifer recharge from precipitation occurs in the basin-fill alluvium that drains areas of available water. A transient model with 31 stress periods was constructed to simulate groundwater flow for the period 1935–2010. The transient model incorporates changing Colorado River, Lake Mead, and Lake Mohave water levels and includes time-varying groundwater withdrawals and aquifer recharge. Both the steady-state and transient models were calibrated to available water-level observations in basin-f ill alluvium, and simulations approximate observed water-level trends throughout most of the study area.

Arizona↗
USGS2013

Potential depletion of surface water in the Colorado River and agricultural drains by groundwater pumping in the Parker-Palo Verde-Cibola area, Arizona and California

Water use along the lower Colorado River is allocated as “consumptive use,” which is defined to be the amount of water diverted from the river minus the amount that returns to the river. Diversions of water from the river include surface water in canals and water removed from the river by pumping wells in the aquifer connected to the river. A complication in accounting for water pumped by wells occurs if the pumping depletes water in drains and reduces measured return flow in those drains. In that case, consumptive use of water pumped by the wells is accounted for in the reduction of measured return flow. A method is needed to understand where groundwater pumping will deplete water in the river and where it will deplete water in drains. To provide a basis for future accounting for pumped groundwater in the Parker-Palo Verde-Cibola area, a superposition model was constructed. The model consists of three layers of finite-difference cells that cover most of the aquifer in the study area. The model was run repeatedly with each run having a pumping well in a different model cell. The source of pumped water that is depletion of the river, expressed as a fraction of the pumping rate, was computed for all active cells in model layer 1, and maps were constructed to understand where groundwater pumping depletes the river and where it depletes drains. The model results indicate that if one or more drains exist between a pumping well location and the river, nearly all of the depletion will be from drains, and little or no depletion will come from the Colorado River. Results also show that if a well pumps on a side of the river with no drains in the immediate area, depletion will come from the Colorado River. Finally, if a well pumps between the river and drains that parallel the river, a fraction of the pumping will come from the river and the rest will come from the drains. Model results presented in this report may be considered in development or refinement of strategies for accounting for groundwater pumping in the river aquifer connected to the Colorado River in the study area.

Arizona;California↗
USGS2014

Documentation of a groundwater flow model (SJRRPGW) for the San Joaquin River Restoration Program study area, California

To better understand the potential effects of restoration flows on existing drainage problems, anticipated as a result of the San Joaquin River Restoration Program (SJRRP), the U.S. Geological Survey (USGS), in cooperation with the U.S. Bureau of Reclamation (Reclamation), developed a groundwater flow model (SJRRPGW) of the SJRRP study area that is within 5 miles of the San Joaquin River and adjacent bypass system from Friant Dam to the Merced River. The primary goal of the SJRRP is to reestablish the natural ecology of the river to a degree that restores salmon and other fish populations. Increased flows in the river, particularly during the spring salmon run, are a key component of the restoration effort. A potential consequence of these increased river flows is the exacerbation of existing irrigation drainage problems along a section of the river between Mendota and the confluence with the Merced River. Historically, this reach typically was underlain by a water table within 10 feet of the land surface, thus requiring careful irrigation management and (or) artificial drainage to maintain crop health. The SJRRPGW is designed to meet the short-term needs of the SJRRP; future versions of the model may incorporate potential enhancements, several of which are identified in this report. The SJRRPGW was constructed using the USGS groundwater flow model MODFLOW and was built on the framework of the USGS Central Valley Hydrologic Model (CVHM) within which the SJRRPGW model domain is embedded. The Farm Process (FMP2) was used to simulate the supply and demand components of irrigated agriculture. The Streamflow-Routing Package (SFR2) was used to simulate the streams and bypasses and their interaction with the aquifer system. The 1,300-square mile study area was subdivided into 0.25-mile by 0.25-mile cells. The sediment texture of the aquifer system, which was used to distribute hydraulic properties by model cell, was refined from that used in the CVHM to better represent the natural heterogeneity of aquifer-system materials within the model domain. In addition, the stream properties were updated from the CVHM to better simulate stream-aquifer interactions, and water-budget subregions were refined to better simulate agricultural water supply and demand. External boundary conditions were derived from the CVHM. The SJRRPGW was calibrated for April 1961 to September 2003 by using groundwater-level observations from 133 wells and streamflow observations from 19 streamgages. The model was calibrated using public-domain parameter estimation software (PEST) in a semi-automated manner. The simulated groundwater-level elevations and trends (including seasonal fluctuations) and surface-water flow magnitudes and trends reasonably matched observed data. The calibrated model is planned to be used to assess the potential effects of restoration flows on agricultural lands and the relative capabilities of proposed SJRRP actions to reduce these effects.

California↗
USGS2014

Stream seepage and groundwater levels, Wood River Valley, south-central Idaho, 2012-13

Stream discharge and water levels in wells were measured at multiple sites in the Wood River Valley, south-central Idaho, in August 2012, October 2012, and March 2013, as a component of data collection for a groundwater-flow model of the Wood River Valley aquifer system. This model is a cooperative and collaborative effort between the U.S. Geological Survey and the Idaho Department of Water Resources. Stream-discharge measurements for determination of seepage were made during several days on three occasions: August 27–28, 2012, October 22–24, 2012, and March 27–28, 2013. Discharge measurements were made at 49 sites in August and October, and 51 sites in March, on the Big Wood River, Silver Creek, their tributaries, and nearby canals. The Big Wood River generally gains flow between the Big Wood River near Ketchum streamgage (13135500) and the Big Wood River at Hailey streamgage (13139510), and loses flow between the Hailey streamgage and the Big Wood River at Stanton Crossing near Bellevue streamgage (13140800). Shorter reaches within these segments may differ in the direction or magnitude of seepage or may be indeterminate because of measurement uncertainty. Additional reaches were measured on Silver Creek, the North Fork Big Wood River, Warm Springs Creek, Trail Creek, and the East Fork Big Wood River. Discharge measurements also were made on the Hiawatha, Cove, District 45, Glendale, and Bypass Canals, and smaller tributaries to the Big Wood River and Silver Creek. Water levels in 93 wells completed in the Wood River Valley aquifer system were measured during October 22–24, 2012; these wells are part of a network established by the U.S. Geological Survey in 2006. Maps of the October 2012 water-table altitude in the unconfined aquifer and the potentiometric-surface altitude of the confined aquifer have similar topology to those on maps of October 2006 conditions. Between October 2006 and October 2012, water-table altitude in the unconfined aquifer rose by as much as 1.86 feet in 6 wells and declined by as much as 14.28 feet in 77 wells; average decline was 2.9 feet. A map of changes in the water‑table altitude of the unconfined aquifer shows that the largest declines were in tributary canyons and in an area roughly between Baseline and Glendale Roads. From October 2006 to October 2012, the potentiometric-surface altitude in 10 wells completed in the confined aquifer declined between 0.12 and 20.50 feet; average decline was 6.8 feet. A map of changes in the potentiometric-surface altitude of the confined aquifer shows that the largest declines were in the southwestern part of the Bellevue fan. Reduced precipitation prior to the October 2012 water-level measurements likely is partially responsible for 2006–12 water-table declines in the unconfined aquifer; the relative contribution of precipitation deficit and groundwater withdrawals to the declines is not known. Although the confined aquifer may not receive direct recharge from precipitation or streams, groundwater withdrawal from the confined aquifer induces flow from the unconfined aquifer. Declines in the confined aquifer are likely due to groundwater withdrawals and declines in the water table of the unconfined aquifer. A statistical analysis of five long-term monitoring wells (three completed in the unconfined aquifer, one in the confined aquifer, and one outside the aquifer system boundary) showed statistically significant declining trends in four wells.

Idaho↗
USGS2014

Water quality of the Ogallala Formation, central High Plains aquifer within the North Plains Groundwater Conservation District, Texas Panhandle, 2012-13

In cooperation with the North Plains Groundwater Conservation District (NPGCD), the U.S. Geological Survey collected and analyzed water-quality samples at 30 groundwater monitor wells in the NPGCD in the Texas Panhandle. All of the wells were completed in the Ogallala Formation of the central High Plains aquifer. Samples from each well were collected during February–March 2012 and in March 2013. Depth to groundwater in feet below land surface was measured at each well before sampling to determine the water-quality sampling depths. Water-quality samples were analyzed for physical properties, major ions, nutrients, and trace metals, and 6 of the 30 samples were analyzed for pesticides. There was a strong relation between specific conductance and dissolved solids as evidenced by a coefficient of determination ( R 2 ) value of 0.98. The dissolved-solids concentration in water from five wells exceeded the secondary drinking-water standard of 500 milligrams per liter set by the U.S. Environmental Protection Agency. Water from 3 of these 5 wells was near the north central part of the NPGCD. Nitrate values exceeded the U.S. Environmental Protection Agency maximum contaminant level of 10 milligrams per liter in 2 of the 30 wells. A sodium-adsorption ratio of 23.4 was measured in the sample collected from well Da-3589 in Dallam County, with the next largest sodium-adsorption ratio measured in the sample collected from well Da-3588 (12.5), also in Dallum County. The sodium-adsorption ratios measured in all other samples were less than 10. The groundwater was generally a mixed cation-bicarbonate plus carbonate type. Twenty-three trace elements were analyzed, and no concentrations exceeded the secondary drinking-water standard or maximum contaminant level set by the U.S. Environmental Protection Agency for water supplies. In 2012, 6 of the 30 wells were sampled for commonly used pesticides. Atrazine and its degradate 2-Chloro-4-isopropylamino-6-amino-s-triazine were detected in two samples. Tebuthiuron was detected in one sample at a detection level below the reporting level but above the long-term method detection level. There were no detections of the glyphosate, aminomethylphosphonic acid (AMPA), or glufosinate.

Texas↗