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USGS1976

Hydrologic evaluation of the Upper Duchesne River Valley, Northern Uinta Basin area, Utah

The upper Duchesne River valley was studied during 1971-74 as part of an investigation of the northern Uinta Basin area, Utah and Colorado. The purpose of the study was to determine the relation of ground water to surface water, to estimate the quantity of ground water that moves to the Duchesne River, and to assess the probable effect of increased ground-water withdrawal on streamflow. The primary source of water for the study area is precipitation on the highlands adjacent to and north of the area and on the valley itself. Discharge from the area is mainly by flow in the Duchesne River. Adjacent to and within the valley, ground water and surface water are intimately related, and they can interchange in several ways due to both natural and manmade conditions. Aquifers in the upper Duchesne River valley range from Paleozoic to Quaternary in age. The consolidated aquifers receive recharge from highland precipitation and streamflow, and probably from interformational transfer of water. The consolidated rocks discharge water through springs and by interformational transfer of water to the valley fill of Quaternary age. The valley fill, which is composed mainly of outwash and related glacial debris, constitutes the main ground-water reservoir in the valley. The fill is, in general, highly permeable and transmits water rapidly. It is recharged by a small amount of underflow beneath the Duchesne River and its tributaries, by intermittent precipitation directly on the fill, by interformational movement of ground water from the adjacent consolidated rocks, and by seepage of surface water from streams, canals, and irrigated fields. The ground water in the fill is unconfined. The volume of ground water stored in the fill and theoretically available by gravity drainage is a minimum of 40,000 acre-feet (50 cubic hectometres); this volume fluctuates by a maximum of 10 percent annually. Ground water is discharged from the valley fill by wells and springs, by evapotranspiration, and by seepage into the Duchesne River. The discharge from wells and springs used for domestic, stock, public, and irrigation purposes in 1974 was about 2 cubic feet per second (0.06 cubic metres per second). The discharge by evapotranspiration was about 4 cubic feet per second (0.1 cubic metre per second). Discharge of ground water by seepage to the Duchesne River was about 39 cubic feet per second (1.1 cubic metres per second). Most ground water, except in parts of the Uinta Formation, and all the surface water sampled in the study area, was fresh. Because of the high permeability of the valley fill and because unconsumed ground water discharges to the Duchesne River, it can be concluded that lowering ground-water levels by large withdrawals of ground water in the upper Duchesne River valley ultimately would diminish the baseflow of the Duchesne River by about the amount of ground water with-drawn minus the amount salvaged from evapotranspiration.

Utah↗

USGS1979

Hydrogeologic data from the northern Powder River Basin, southeastern Montana

Hydrologic and geologic data have been collected as part of energy-related projects conducted by the U.S. Geological Survey in the northern Powder River basin of southeastern Montana. Records of 1924 stock, domestic, irrigation, public supply and test wells are tabulated in the report. The data include well location, depth of well, casing diameter, type of lift, type of power, use of water, principal aquifer, altitude of land surface , water level, discharge, field specific conductance, and water temperature. Locations of the inventoried wells are shown on a map at a scale of 1:500,000. Lighologic logs of 373 wells and test holes are also included. The geologic units considered range in age from Late Cretaceous to Holocene. (Kosco-USGS)

Open-File Report↗

USGS1983

Hydrology of the Ogallala aquifer in Ford County, southwestern Kansas

The rapid increase of ground-water withdrawal has caused concern over the future use of the Ogallala aquifer, the principal source of water in Ford County, in southwestern Kansas. Saturated portions of deposits of Tertiary and Quaternary age--excluding the Arkansas River alluvium--form the Ogallala aquifer. Saturated thickness of the Ogallala ranged from 0 to about 350 feet on the downthrown side of the Crooked Creek-Fowler fault and from 0 to about 120 feet on the upthrown side. Ground-water withdrawal was calculated by two methods. The time-discharge method computed withdrawal of about 81,000 acre-feet during 1980 and about 58,000 acre-feet during 1981. The irrigation-requirement method computed withdrawal of about 121,000 acre-feet during 1980 and about 131,000 acre-feet during 1981. Results from the irrigation-requirement method are probably closer to the actual amount of ground-water withdrawal because of problems encountered when applying the time-dischargemethod. Water-level declines between 1939 and 1981 ranged from about 10 to 50 feet. Water withdrawal from the Ogallala aquifer depleted the volume of water in storage by about 688,000 acre-feet (8 percent) during this same period. If withdrawals continue to the point where the water table drops below the top of the bedrock surface on the upthrown side of the Crooked Creek-Fowler fault, base flow in the Arkansas River could cease. (USGS)

Water-Resources Investigations Report↗

USGS2024

Inset groundwater-flow models for the Cache and Grand Prairie Critical Groundwater Areas, northeastern Arkansas

The water resources in the Mississippi alluvial plain, located in parts of Missouri, Kentucky, Tennessee, Mississippi, Louisiana, and Arkansas, supports a multibillion-dollar agricultural industry that relies heavily on pumping of groundwater for irrigation of crops and aquaculture. The primary source of groundwater for agricultural-related pumping is the Mississippi River Valley alluvial aquifer, which has declined in storage for decades; secondary groundwater sources include the middle Claiborne aquifer and Wilcox aquifer system. Two areas in northeastern Arkansas that lie within the Mississippi alluvial plain, part of the Cache and Grand Prairie regions, have been designated as Critical Groundwater Areas owing to decades of groundwater declines that resulted from past and current water use. The multidisciplinary Mississippi Alluvial Plain project, led by the U.S. Geological Survey, and funded by their Water Availability and Use Science Program, included objectives to develop numerical groundwater models in focus regions, including the part of the Cache and Grand Prairie regions of northeastern Arkansas. Two inset models were developed using the child model capabilities of MODFLOW 6, the U.S. Geological Survey’s Modular Hydrologic Model simulation software. Both models, called the Cache model and Grand Prairie model, simulated the groundwater system and surface-water/groundwater interactions for the Mississippi River Valley alluvial aquifer and underlying Tertiary-age aquifers and confining units to the Midway confining unit. Each model was spatially discretized into 500-meter x 500-meter orthogonal cells on a grid with 5-meter constant-thickness vertical layers that represented the Mississippi River Valley alluvial aquifer and increasing thickness layers for the aquifers and confining units below the alluvial aquifer. The Cache and Grand Prairie models were calibrated with the PEST++ iterative ensemble smoother Version 5 and employed high dimensional parameterization schemes of 13,740 and 30,436 parameters, respectively. The Cache mean absolute residual for groundwater-level observations within each model domain for the priority well was 1.58 meters. Grand Prairie mean absolute residuals for the alluvial aquifer and middle Claiborne aquifer groundwater-level observations were 2.71 and 10.78 meters, respectively. The groundwater budgets for the Cache and Grand Prairie models were characterized by substantial outflows to irrigation wells, which constituted about 52 and 54 percent of all outflows, with the primary source of water to those wells being releases from unconfined aquifer storage.

Arkansas↗

USGS2004

Quality and sources of ground water used for public supply in Salt Lake Valley, Salt Lake County, Utah, 2001

Ground water supplies about one-third of the water used by the public in Salt Lake Valley, Utah. The occurrence and distribution of natural and anthropogenic compounds in ground water used for public supply in the valley were evaluated. Water samples were collected from 31 public-supply wells in 2001 and analyzed for major ions, trace elements, radon, nutrients, dissolved organic carbon, methylene blue active substances, pesticides, and volatile organic compounds. The samples also were analyzed for the stable isotopes of water (oxygen-18 and deuterium), tritium, chlorofluorocarbons, and dissolved gases to determine recharge sources and ground-water age. Dissolved-solids concentration ranged from 157 to 1,280 milligrams per liter (mg/L) in water from the 31 public-supply wells. Comparison of dissolved-solids concentration of water sampled from the principal aquifer during 1988-92 and 1998-2002 shows a reduction in the area where water with less than 500 mg/L occurs. Nitrate concentration in water sampled from 12 of the 31 public-supply wells was higher than an estimated background level of 2 mg/L, indicating a possible human influence. At least one pesticide or pesticide degradation product was detected at a concentration much lower than drinking-water standards in water from 13 of the 31 wells sampled. Chloroform was the most frequently detected volatile organic compound (17 of 31 samples). Its widespread occurrence in deeper ground water is likely a result of the recharge of chlorinated public-supply water used to irrigate lawns and gardens in residential areas of Salt Lake Valley. Environmental tracers were used to determine the sources of recharge to the principal aquifer used for public supply in the valley. Oxygen-18 values and recharge temperatures computed from dissolved noble gases in the ground water were used to differentiate between mountain and valley recharge. Maximum recharge temperatures in the eastern part of the valley generally are below the range of valley water-table temperatures indicating that mountain-block recharge must constitute a substantial fraction of recharge to the principal aquifer in this area. Together, the recharge temperature and stable-isotope data define two zones with apparently high proportions of valley recharge on the east side of the valley. The possibility of water samples containing a substantial proportion of water recharged before thermonuclear testing began in the early 1950s (pre-bomb) was evaluated by comparing the initial tritium concentration of each sample (measured tritium plus measured tritiogenic helium-3) to that of local precipitation at the apparent time of recharge. Three interpreted-age categories were determined for water from the sampled wells: (1) dominantly pre-bomb; (2) dominantly modern; and (3) modern or a mixture of pre-bomb and modern. Apparent tritium/helium-3 ages range from 3 years to more than 50 years. Water generally becomes older with distance from the mountain front, with the oldest water present in the discharge area. The presence of anthropogenic compounds at concentrations above reporting levels and elevated nitrate concentrations (affected wells) in the principal aquifer is well correlated with the distribution of interpreted-age categories. All of the wells (10 of 10) with dominantly modern water are affected. Seventy percent (7 of 10) of the wells with dominantly modern or a mixture of modern and pre-bomb waters are affected. Only 1 of the 11 wells with dominantly pre-bomb water is affected. Anthropogenic compounds were not detected in water with an apparent age of more than 50 years, except for water from one well. All of the samples that consisted mostly of modern water contained at least one anthropogenic compound.

Utah↗

USGS1960

Geology, water resources and usable ground-water storage capacity of part of Solano County, California

The area described is confined largely to the valley-floor and foothill lands of Solano County, which lies directly between Sacramento, the State capital, and San Francisco. The area is considered in two subareas: The Putah area, which extends from Putah Creek southward to the Montezuma Hills and from the foothills of the Coast Ranges eastward to the west edge of the Yolo Bypass; and the Suisun-Fairfield area, which is to the southwest in the notch in the Coast Ranges through which the waters of the Great Central Valley of California reach San Francisco Bay. There are no known hydrologic interconnections between the two subareas, through either surface streams or underground aquifers. The climate of the area is characterized by warm, rainless summers and by cool winters in which temperatures seldom drop much below freezing. The rainfall ranges from about 17 inches per year along the east side to perhaps 24 inches in the foothills to the west, and irrigation is necessary for all crops except dry-farmed grains, pastures, and some orchards. PUTAH AREA The Putah area occupies the southwestern corner of the Sacramento Valley, a topographic and structural basin underlain by a thick accumulation of sediments eroded from the surrounding hills and mountains by the Sacramento River and its tributaries. The eastern Coast Ranges and foothills lying west of the Sacramento Valley are a generally northward-trending belt of eastward-dipping sedimentary rocks that range in age from Cretaceous to Pleistocene. Successively younger strata are exposed eastward, and the essentially undeformed deposits of late Pleistocene and Recent age that immediately underlie the valley lap onto the tilted sediments of the foothills. Most of the streams of the Putah area rise east of the high ridge of Cretaceous rocks marking the western boundaries of Solano and Yolo Counties, but Putah Creek, the largest stream in the area, rises far west of that ridge and flows across it in a deep, narrow canyon. Putah Creek and the smaller streams have constructed an alluvial plain, herein designated the Putah plain, which slopes eastward and southeastward from the foothills toward the Sacramento River. A large part of the Putah plain is traversed by a branching set of distributary channel ridges or natural levees formed at times of overflow of Putah Creek. The rocks in the Putah area range in age from Cretaceous to Recent. For the purposes of this investigation they are divided into eight geologic or stratigraphic units, from youngest to oldest: (1) Stream-channel deposits, (2) younger alluvium, (3) older alluvium, (4) Tehama formation and related continental sediments, (5) volcanic sedimentary rocks, (6) basalt, (7) undifferentiated sedimentary rocks of Paleocene(?) and Eocene age, and (8) undifferentiated rocks of Cretaceous age. The stream-channel deposits are predominantly loose sand and gravel along the channel of Putah Creek. In part they are actively moving downstream and shifting. The younger alluvium, of Recent age, consists of flood-plain deposits underlying the Putah plain, Vaca Valley, Pleasants Valley, and the small valleys in the foothills north of Putah Creek and in the English Hills. Exposures of younger alluvium are characterized by soils lacking significant profile development and in many places by channel-ridge topography. The older alluvium occupies the stratigraphic interval between the younger alluvium and the Tehama formation and related continental sediments and is probably of late Pleistocene age. Its contact with the underlying Tehama formation and related continental sediments is unconformable near the foothills, but it may be gradational beneath much of the Putah plain. The base of the older alluvium is not well defined at many places but is inferred to be at the bottom of an irregular and ill-defined zone of coarse deposits, which ranges from about 50 feet to more than 150 feet below the land surface. Exposures of the older

Water Supply Paper↗

USGS2018

Prediction uncertainty and data worth assessment for groundwater transport times in an agricultural catchment

Uncertainties about the age of base-flow discharge can have serious implications for the management of degraded environmental systems where subsurface pathways, and the ongoing release of pollutants that accumulated in the subsurface during past decades, dominate the water quality signal. Numerical groundwater models may be used to estimate groundwater return times and base-flow ages and thus predict the time required for stakeholders to see the results of improved agricultural management practices. However, the uncertainty inherent in the relationship between (i) the observations of atmospherically-derived tracers that are required to calibrate such models and (ii) the predictions of system age that the observations inform have not been investigated. For example, few if any studies have assessed the uncertainty of numerically-simulated system ages or evaluated the uncertainty reductions that may result from the expense of collecting additional subsurface tracer data. In this study we combine numerical flow and transport modeling of atmospherically-derived tracers with prediction uncertainty methods to accomplish four objectives. First, we show the relative importance of head, discharge, and tracer information for characterizing response times in a uniquely data rich catchment that includes 266 age-tracer measurements (SF 6 , CFCs, and 3 H) in addition to long term monitoring of water levels and stream discharge. Second, we calculate uncertainty intervals for model-simulated base-flow ages using both linear and non-linear methods, and find that the prediction sensitivity vector used by linear first-order second-moment methods results in much larger uncertainties than non-linear Monte Carlo methods operating on the same parameter uncertainty. Third, by combining prediction uncertainty analysis with multiple models of the system, we show that data-worth calculations and monitoring network design are sensitive to variations in the amount of water leaving the system via stream discharge and irrigation withdrawals. Finally, we demonstrate a novel model-averaged computation of potential data worth that can account for these uncertainties in model structure.

Maryland↗

USGS2011

Hydrogeologic framework and hydrologic budget components of the Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho

The Columbia Plateau Regional Aquifer System (CPRAS) covers an area of about 44,000 square miles in a structural and topographic basin within the drainage of the Columbia River in Washington, Oregon, and Idaho. The primary aquifers are basalts of the Columbia River Basalt Group (CRBG) and overlying sediment. Eighty percent of the groundwater use in the study area is for irrigation, in support of a $6 billion per year agricultural economy. Water-resources issues in the Columbia Plateau include competing agricultural, domestic, and environmental demands. Groundwater levels were measured in 470 wells in 1984 and 2009; water levels declined in 83 percent of the wells, and declines greater than 25 feet were measured in 29 percent of the wells. Conceptually, the system is a series of productive basalt aquifers consisting of permeable interflow zones separated by less permeable flow interiors; in places, sedimentary aquifers overly the basalts. The aquifer system of the CPRAS includes seven hydrogeologic units-the overburden aquifer, three aquifer units in the permeable basalt rock, two confining units, and a basement confining unit. The overburden aquifer includes alluvial and colluvial valley-fill deposits; the three basalt units are the Saddle Mountains, Wanapum, and Grande Ronde Basalts and their intercalated sediments. The confining units are equivalent to the Saddle Mountains-Wanapum and Wanapum-Grande Ronde interbeds, referred to in this study as the Mabton and Vantage Interbeds, respectively. The basement confining unit, referred to as Older Bedrock, consists of pre-CRBG rocks that generally have much lower permeabilities than the basalts and are considered the base of the regional flow system. Based on specific-capacity data, median horizontal hydraulic conductivity (Kh) values for the overburden, basalt units, and bedrock are 161, 70, and 6 feet per day, respectively. Analysis of oxygen isotopes in water and carbon isotopes in dissolved inorganic carbon from groundwater samples indicates that groundwater in the CPRAS ranges in age from modern (<50 years) to Pleistocene (>10,000 years). The oldest groundwater resides in deep, downgradient locations indicating that groundwater movement and replenishment in parts of this regional aquifer system have operated on long timescales under past natural conditions, which is consistent with the length and depth of long flow paths in the system. The mean annual recharge from infiltration of precipitation for the 23-year period 1985-2007 was estimated to be 4.6 inches per year (14,980 cubic feet per second) using a polynomial regression equation based on annual precipitation and the results of recharge modeling done in the 1980s. A regional-scale hydrologic budget was developed using a monthly SOil WATer (SOWAT) Balance model to estimate irrigation-water demand, groundwater flux (recharge or discharge), direct runoff, and soil moisture within irrigated areas. Mean monthly irrigation throughout the study area peaks in July at 1.6 million acre-feet (MAF), of which 0.45 and 1.15 MAF are from groundwater and surface-water sources, respectively. Annual irrigation water use in the study area averaged 5.3 MAF during the period 1985-2007, with 1.4 MAF (or 26 percent) supplied from groundwater and 3.9 MAF supplied from surface water. Mean annual recharge from irrigation return flow in the study area was 4.2 MAF (1985-2007) with 2.1 MAF (50 percent) occurring within the predominately surface-water irrigated regions of the study area. Annual groundwater-use estimates were made for public supply, self-supplied domestic, industrial, and other uses for the period 1984 through 2009. Public supply groundwater use within the study area increased from 200,600 acre-feet per year (acre-ft/yr) in 1984 to 269,100 acre-ft/yr in 2009. Domestic self-supplied groundwater use increased from 54,580 acre-ft/yr in 1984 to 71,160 acre-ft/yr in 2009. Industrial groundwater use decreased from 53,390 acre-ft/yr in 1984 t

Scientific Investigations Report↗

USGS2008

Base of principal aquifer for the Elkhorn-Loup model area, North-Central Nebraska

In Nebraska, the water managers in the Natural Resources Districts and the Nebraska Department of Natural Resources are concerned with the effect of ground-water withdrawal on the availability of surface water and the long-term effects of ground-water withdrawal on ground- and surface-water resources. In north-central Nebraska, in the Elkhorn and Loup River Basins, ground water is used for irrigation, domestic supply, and public supply; surface water is used in this area for irrigation, recreation, and hydropower production. In recognition of these sometimes competing ground- and surface-water uses in the Elkhorn and Loup River Basins, the U.S. Geological Survey, the Lewis and Clark Natural Resources District, the Lower Elkhorn Natural Resources District, the Lower Loup Natural Resources District, the Lower Niobrara Natural Resources District, the Lower Platte North Natural Resources District, the Middle Niobrara Natural Resources District, the Upper Elkhorn Natural Resources District, and the Upper Loup Natural Resources District agreed to cooperatively study water resources in the Elkhorn and Loup River Basins. The goals of the overall study were to construct and calibrate a regional ground-water flow model of the area and to use that flow model as a tool to assess current and future effects of ground-water irrigation on stream base flow and to help develop long-term water-resource management strategies for this area, hereafter referred to as the Elkhorn-Loup model area. The Elkhorn-Loup model area covers approximately 30,800 square miles, and extends from the Niobrara River in the north to the Platte River in the south. The western boundary of the Elkhorn-Loup model area coincides with the western boundary of the Middle Niobrara, Twin Platte, and Upper Loup Natural Resources Districts; the eastern boundary coincides with the approximate location of the western extent of glacial till in eastern Nebraska. The principal aquifer in most of the Elkhorn-Loup model area is the High Plains aquifer; the principal aquifer in the remaining part of the Elkhorn-Loup model area is an unnamed alluvial aquifer. The upper surface of the geologic units that directly underlie the aquifer is called the 'base of aquifer' in this report. The geologic unit that forms the base of aquifer in the Elkhorn-Loup model area varies by location. The Tertiary-age Brule Formation generally is the base of aquifer in the west; the Cretaceous-age Pierre Shale generally is the base of aquifer in the east. The purpose of this report is to update the altitude and configuration of the base of the principal aquifer in the Elkhorn-Loup model area and a 2-mile buffer area around the Elkhorn-Loup model area, using base-of-aquifer data from test holes, registered water wells, and oil and gas wells within the Elkhorn-Loup model area and a 20-mile buffer area around the Elkhorn-Loup model area that have become available since the publication of earlier maps of the base of aquifer for this area. The base-of-aquifer map is important for the Elkhorn-Loup ground-water flow model because it defines the model's lower boundary. The accuracy of the Elkhorn-Loup ground-water flow model and the accuracy of the model's predictions about the effects of ground-water irrigation on stream base flow are directly related to the accuracy of the model's lower boundary.

Scientific Investigations Map↗

USGS1978

Map showing saturated thickness of unconsolidated aquifer in southwestern Kansas, January 1978

The principal aquifer in the 13-county area of southwestern Kansas occurs in the heterogeneous, unconsolidated alluvial deposits of Tertiary and Quaternary age. The main body of this ground-water reservoir is designated as the unconsolidated aquifer. The map showing the saturated thickness of deposits in the unconsolidated aquifer was prepared by comparing maps showing the altitude and configuration of the underlying bedrock surface and of the potentiometric (water-level) surface in the unconsolidated aquifer in January 1978. About 75 percent of the area (1,460 square miles), as shown within the aquifer boundaries, is underlain by sufficient saturated material to supply ground water for irrigation. Saturated thicknesses range from less than 50 feet to about 630 feet. In the remainder of the area, except for isolated channels, the saturated material generally is thin and yields little or no water to wells.

Kansas↗

USGS2016

Hydrogeological framework, numerical simulation of groundwater flow, and effects of projected water use and drought for the Beaver-North Canadian River alluvial aquifer, northwestern Oklahoma

This report describes a study of the hydrology, hydrogeological framework, numerical groundwater-flow models, and results of simulations of the effects of water use and drought for the Beaver-North Canadian River alluvial aquifer, northwestern Oklahoma. The purpose of the study was to provide analyses, including estimating equal-proportionate-share (EPS) groundwater-pumping rates and the effects of projected water use and droughts, pertinent to water management of the Beaver-North Canadian River alluvial aquifer for the Oklahoma Water Resources Board. The Beaver-North Canadian River alluvial aquifer consists of unconsolidated sand, gravel, silt, and clay in varying proportions that underlies the Beaver and North Canadian River Valleys for approximately 175 miles (mi) from the Oklahoma Panhandle to the western edge of Oklahoma City in central Oklahoma. The aquifer as delineated for this study varies from 4 to 12 mi wide and is as thick as 308 feet (ft) in the northwest where the aquifer includes the Ogallala Formation. There are two distinct but in most areas hydraulically connected alluvial units that compose the Beaver-North Canadian River alluvial aquifer: a Quaternary-age topographically higher terrace deposit and a topographically lower, younger alluvium along the active river channel that includes active and Quaternary-age alluvium. The Beaver River composes the headwaters of the North Canadian River, which begins at the confluence of the Beaver River and Wolf Creek. The aquifer is divided for water management into two geographic areas: Reach I upstream from Canton Dam and Reach II downstream from Canton Dam. Reach I covers an area of approximately 874 square miles (mi 2 ), and Reach II covers an area of approximately 371 mi 2 . The Beaver-North Canadian River alluvial aquifer crosses several climatic zones, from semiarid in the west to continental subhumid in the east. Mean annual precipitation varies from 23.5 inches (in.) in the western part of this aquifer to 35.7 in. in the east. Surface-water demands were met through numerous temporary and permanent surface-water diversions from the Beaver and North Canadian Rivers during the period of study. During the study period, seven diversions removed a mean annual 2,000 acre-feet (acre-ft) of water from Reach I. There were 14 diversions from Reach II with a mean annual permitted volume of approximately 81,000 acre-ft, including diversion into the Lake Hefner Canal for the Oklahoma City public water supply. During the period of this study, 17 temporary surface-water diversion permits were active in Reach I, with total permitted volumes of 2,000 acre-ft, and 41 diversions were active in Reach II, with total permitted volumes of 38,000 acre-ft. The total water use for each temporary permit was assumed to be taken over the 3-month period allotted to temporary withdrawal permits. The groundwater-use analysis full period of record, 1967–2011, was divided into two sub-intervals because of varying water use, 1970–80 and 1981–2011. Groundwater use in Reach I and Reach II was substantially greater from 1970 to 1980 compared to the rest of the period, and the sub-period 1981–2011 was used because this period includes recent population growth and modern irrigation methods. The total mean annual groundwater use in Reach I was 15,309 acre-feet per year (acre-ft/yr) during 1967–2011; 20,724 acre-ft/yr during 1970–80, and 13,739 acre-ft/yr during 1981–2011. Total mean annual groundwater use in Reach II was similar but slightly less than in Reach I, with 14,098 acre-ft/yr during 1967–2011; 19,963 acre-ft/yr during 1970–80; and 12,285 acre-ft/yr during 1981–2011. Irrigation composed 72 percent of groundwater use in Reach I and 48 percent of groundwater use in Reach II during the 1967–2011 period. Public water supply was a much smaller proportion of total groundwater use in Reach I (15 percent) than in Reach II (39 percent). The proportion of groundwater use for power was 10 percent in Reach I and 5.2 percent in Reach II. All other water-use categories in Reach I only composed 2.2 percent of groundwater use in Reach I. In Reach II, industrial, mining, and commercial categories combined accounted for 4.4 percent of groundwater use; recreation, fish, and wildlife groundwater use accounted for 2.3 percent; and nonirrigated agriculture accounted for 1.5 percent of groundwater use. Permian-age bedrock underlies the Beaver-North Canadian River alluvial aquifer. In the east, the Dog Creek Shale, the Duncan Sandstone, and the Blaine and Chickasha Formations, none of which are notable sources of groundwater in the study area, underlie the Beaver-North Canadian River alluvial aquifer. In the northwestern part of Reach I, bedrock is composed of the Rush Springs and Marlow Formations, which are productive aquifers in some areas. The Cloud Chief Formation is not a source of groundwater. One hydrogeological unit was delineated in the Beaver-North Canadian River alluvial aquifer, composed of the terrace deposits and alluvium, with limited flow between this unit and bedrock units. Groundwater in this aquifer generally flows from northwest to southeast and across the aquifer toward the Beaver and North Canadian Rivers. Groundwater recharge from precipitation was estimated for the entire Beaver-North Canadian River alluvial aquifer and then itemized for both reaches by using a soil-water-balance (SWB) model. At two locations in Reach I, a water-table fluctuation method was used to estimate local recharge. Total mean annual groundwater recharge from the soil-water-balance method was estimated to be approximately 136,400 acre-ft in Reach I and 82,400 acre-ft in Reach II; the mean annual recharge for both reaches combined was approximately 218,800 acre-ft. Two sites in Reach I located at observation wells with continuous water-level measurements and nearby streamflow-gaging stations with precipitation gages were used to estimate the percentage of precipitation that becomes groundwater recharge. The Woodward site was located at observation well OW-4 near the Woodward, Okla. (07237500), streamflow-gaging station. Total precipitation and recharge for the Woodward and Seiling sites were calculated for the water year 2013. The Woodward site had a total of 14.18 in. of precipitation and 6.3 in. of recharge was calculated, equaling 44 percent of precipitation. The mean percentage of precipitation that was estimated to become recharge in the SWB model for the period 1980–2011 at that location was 9.2 percent, although adjacent SWB-model cells were as high as 20 percent of precipitation. The Seiling site had a total of 26.84 in. of precipitation during the water year 2013, and a total of 6.9 in. of recharge was estimated, equaling 25.9 percent of precipitation. At the Seiling site, the mean percentage of precipitation that became recharge in the SWB model for the period 1980–2011 was 23.0 percent. The principal inflow to the Beaver-North Canadian River alluvial aquifer was estimated to be surface recharge from precipitation, and plant evapotranspiration was estimated to be the greatest discharge, followed by stream and lake base flow, groundwater pumping, and flow to seeps and springs along the eastern margin of the aquifer. Reach I also included inflow from the High Plains aquifer as lateral inflow of groundwater, though this flow was estimated to be a very minor component of the total water budget. Most of the Beaver and North Canadian Rivers were determined to be gaining streamflow from groundwater, but several reaches in Reach I upstream from Wolf Creek were determined to be losing streamflow through infiltration to the aquifer. Aquifer hydrogeologic characteristics were estimated from borehole lithologic logs, well-construction information, and published aquifer tests and during numerical model calibration. The maximum saturated aquifer thickness in Reach I was estimated to be 308 ft, and the mean thickness was estimated to be 36 ft. The maximum saturated thickness in Reach II was estimated to be 86 ft, and the mean thickness was estimated to be 29 ft. Mean hydraulic conductivity of Reach I was estimated to be 70 feet per day (ft/d) with a range of 7–279 ft/d. Mean hydraulic conductivity in Reach II was estimated to be 92 ft/d with a range of 4–279 ft/d. Both reach models were calibrated manually by using trial-and-error adjustment of recharge, hydraulic conductivity, specific yield, and conductance of boundary conditions. The Reach I model used 28 head observations during the steady-state period of 1980 and 487 head observations during the transient period of 1981–2011. The root-mean-square error of head residuals (observed minus simulated head) was 3.86 ft, and 83 percent of head residuals were between -5 and 5 ft. The Reach II model was calibrated to 75 steady-state head observations and 134 head observations during the transient period. The root-mean-square error of head residuals for that reach was 3.58 ft, and similar to Reach I, 85 percent of residuals were between -5 and 5 ft. Several analyses were performed by using the numeric groundwater-flow models as predictive tools, including estimating the EPS pumping rate for both reaches. The EPS is defined by the Oklahoma Water Resources Board as an annual per-acre groundwater-pumping rate that will reduce saturated thickness in half of the aquifer to 5 ft or less over a period of 20 years; additional estimates were made for periods of 40 and 50 years. Other analyses included using models to estimate the effects of groundwater pumping and a prolonged drought on groundwater in storage and streamflow and lake storage of water. The EPS pumping rate was found to be approximately 0.57 acre-feet per acre per year ([acre-ft/acre]/yr) in Reach I and 0.73 (acre-ft/acre)/yr in Reach II for a 20-year period. For a 40-year period, the annual EPS pumping rate was determined to be 0.54 (acre-ft/acre)/yr in Reach I and 0.61 (acre-ft/acre)/yr in Reach II. For a 50-year period, the EPS pumping rate was determined to be 0.53 (acre-ft/acre)/yr in Reach I and 0.61 (acre-ft/acre)/yr in Reach II. Groundwater pumping at the 2011 rate for 50 years resulted in a 3.6-percent decrease in the amount of water in groundwater storage in Reach I and a decrease of 2.5 percent in the amount of groundwater in storage in Reach II. A cumulative 32-percent increase in pumping greater than the 2011 rate over a period of 50 years caused a decrease in groundwater storage of 4.0 percent in Reach I and 3.3 percent in Reach II. A hypothetical severe drought was simulated by using aquifer recharge flow rates during the drought year of 2011 for a period of 10 years. All other flows including evapotranspiration and groundwater pumping were set at estimated 2011 rates. The hypothetical drought caused a decrease in water in aquifer storage by about 7 percent in Reach I and 7 percent in Reach II. Another analysis of the effects of hypothetical drought estimated the effects of drought on streamflow and lake storage. The hypothetical drought was simulated by decreasing recharge by 75 percent for a selected 10-year period (1994–2004) during the 1980–2011 simulation. In Reach I, the amounts of water stored in Canton Lake and streamflow at the Seiling, Okla., streamflow-gaging station were analyzed. Streamflow at the Seiling station decreased by a mean of 75 percent and was still diminished by 10 percent after 2011. In Reach II, the effect of drought on the streamflow at the Yukon, Okla., streamflow-gaging station was examined. The greatest mean streamflow decrease was approximately 60 percent during the simulated drought, and after 2011, the mean decrease in streamflow was still about 5 percent. Canton Lake storage decreased by as much as 83 percent during the simulated drought and did not recover by 2011.

Oklahoma↗

USGS2023

No evidence for cottonwood forest decline along a flow-augmented western U.S. river

In contrast to many other arid region rivers, streamflow in the South Platte River is heavily augmented by trans-basin water imports and irrigation return flows. Hydrological changes began in the 1880s, resulting in channel narrowing and the development of a continuous Populus-Salix forest by the mid-twentieth century. We assessed the composition, structure and regeneration status of the riparian forest and identified environmental variables affecting annual Populus deltoides tree growth. We sampled forest structure at four sites in 2015, and conducted dendroecological analysis at seven additional sites in 2019. The riparian forest was dominated by P. deltoides , which occurred at all sites, comprising 79% of total tree basal area and 62% of total tree density. Age structure data indicated ongoing though episodic recruitment of P. deltoides , at least over the past ~130 years. We tested 14 linear mixed effects models to describe the effect of climate and streamflow on individual tree growth (modeled as the log of BAI, n = 237 trees). The most parsimonious model selected with AICc explained 28.6% of BAI variability, and included hydrology and climate factors during the growing season (i.e., June–August streamflow, June–July PDSI), some aspects of off-season (i.e., previous November and March) streamflow, along with tree age and study site effects. The riparian forest developed in response to, and has been maintained by, current climate conditions and water management regimes. It may be negatively affected by future climate change and increased urban water demand in the basin.

Colorado↗

USGS1975

Geohydrology and water quality of the Mississippi River alluvial aquifer, northeastern Louisiana

The Mississippi River alluvial aquifer in northeastern Louisiana is in the alluvium of the Mississippi, Arkansas, and Ouachita Rivers and underlies approximately 5,000 square miles (13,000 square kilometers) in the Mississippi River valley. The aquifer, of Pleistocene age, is a southeastward-thickening wedge of sand and gravel that ranges in thickness from about 20 to 135 feet (6 to 41 metres). These sediments are essentially flat lying with an irregular base. Fine sand, silt, and clay of Holocene age overlie and generally confine the aquifer. These fine-grained deposits range in thickness from 0 to 100 feet (0 to 30 metres) but generally do not exceed 40 feet (12 metres). Water levels in the Mississippi River alluvial aquifer generally are less than 30 feet (9 metres) below land surface. Annual water-level fluctuations have a maximum range of about 20 feet (6 metres) near the Mississippi River and a minimum range of only a few feet in interstream areas. Seasonal declines occur locally, especially in Morehouse Parish, because of large withdrawals for irrigation. The Mississippi River alluvial aquifer can yield water in sufficient quantity for most uses throughout the area. Aquifer tests indicate that the transmissivity ranges from 13,000 to 45,000 feet squared per day (1,200 to 4,200 metres squared per day). The hydraulic conductivity ranges from 130 to 530 feet per day (40 to 160 metres per day). Storage coefficients range from 0.001 to 0.05. Large diameter wells yield as much as 7,000 gallons per minute (440 litres per second) near Tallulah in Madison Parish. The quality of ground water in the Mississippi River alluvial aquifer varies areally and with depth, but generally the water is hard to very hard and high in iron concentration, Where fresh, the water typically is a calcium bicarbonate type generally ranging in hardness from 200 to 600 mg/1 (milligrams per litre) and in iron concentration from 0.00 to 30 mg/1. However, in southern Richland Parish and local areas in adjacent parishes, a hardness of less than 100 mg/1 and an iron concentration of less than 0.30 mg/1 are common. Fresh water occurs to or below the base of the alluvial aquifer in most of the area. The chloride concentration typically is less than 50 mg/1. However, chloride concentrations are as high as 4,000 mg/1 in parts of the area. At some localities, salty water (chloride concentrations greater than 250 mg/1) occurs in the aquifer at depths less than 30 feet (9 metres). The largest occurrence of salty water is in Franklin Parish near and parallel to the subsurface contact between clays of the Jackson Group and sands of the Cockfield Formation of the Claiborne Group. Thus, salty water moving from the Cockfield into the alluvium may be the source of some of the high-chloride water. Smaller bodies of salty water occur in the aquifer along the Jackson-Cockfield contact in Madison and Caldwell Parishes. Probably some contamination from pits formerly used for disposal of salty water occurs in northern Franklin and southern Richland Parishes, Other small occurrences of salty water in Concordia, Morehouse, Ouachita, and Tensas Parishes may be related to contamination by salt-water disposal pits and wells, leaky oil-well casings, and oil-well drilling mishaps.

Louisiana↗

USGS2020

Hydrogeologic characterization, groundwater chemistry, and vulnerability assessment, Ute Mountain Ute Reservation, Colorado and Utah

The U.S. Geological Survey, in cooperation with the Ute Mountain Ute Tribe (UMUT), initiated a study in 2016 to increase understanding of the hydrogeology and chemistry of groundwater within select areas of the Ute Mountain Ute Reservation (UMUR) in Colorado and Utah, identify vulnerabilities to the system and other natural resources, and outline information needs to aid in the understanding and protection of groundwater resources. The results presented for this study can be used to support the UMUT’s goal of protecting their vital groundwater resources on the UMUR. Hydrogeologic conditions were characterized for the surficial aquifer contained in Quaternary-age unconsolidated surficial deposits and the Dakota aquifer contained in the Cretaceous-age Dakota Sandstone. In the surficial aquifer, median depth to water ranges from about 5.4 to 17.2 feet below land surface in the Farm and Ranch Enterprise area and 11 to 34 feet below land surface in the Towaoc area, and the water table slopes generally southwest or south. A map of depth to the top of the Dakota Sandstone was constructed from existing well data. Depths range from zero in outcrop areas to more than 3,000 feet below land surface on mesas in the southeastern part of the UMUR. Groundwater-chemistry data were collected by the UMUT from 13 springs and 31 wells from 1996 through 2017. Specific conductance was much lower for samples from springs than from wells; median values were 512 and 6,024 microsiemens per centimeter at 25 degrees Celsius, respectively. Spring samples were well oxygenated. A few well samples were anoxic (dissolved oxygen concentrations less than 0.5 milligrams per liter [mg/L]), indicating reducing conditions in the aquifer. About 75 percent of spring samples had fresh water (total dissolved solids concentrations less than 1,000 mg/L), and about 85 percent of well samples had brackish or highly saline water (total dissolved solids concentrations greater than 1,000 mg/L). Water type for springs on the Ute Mountains was calcium bicarbonate. Lower-altitude springs had a calcium-sulfate water type. Most well samples had sodium as the dominant cation, and sulfate, bicarbonate, and chloride as the dominant anions. Fluoride concentrations in about 45 percent of well samples were greater than an agricultural-use standard of 2 mg/L. Nitrate plus nitrite concentrations in most spring and well samples were less than about 1.6 mg/L per liter. Concentrations in samples from wells in the irrigated agricultural area were elevated; the maximum concentration was 78.5 mg/L. About one-half of the trace-element samples had concentrations that were less than laboratory reporting limits. Only aluminum, arsenic, and selenium in spring samples, and boron and selenium in well samples, were detected at concentrations greater than surface-water standards or water-quality standards for agricultural use of groundwater. Only three organic compounds, the pesticides alachlor and atrazine and the volatile organic compound di(2-ethylhexyl) phthalate, were detected in well samples. The Escherichia coli bacteria was detected in 47 and 23 percent of samples from wells and springs, respectively. The E. coli detections included samples from three culturally significant springs, which did not meet the UMUT cultural-use standard of total absence of E. coli. Tritium and carbon-14 were the primary environmental tracers used for interpreting groundwater ages for Lopez 2 Spring and five wells (AP–1, 5000 Block, Cottonwood Spring, Goodknight, and SE Toe). Water from the AP–1 well contained a mixture of pre- and post-1950s recharge. Tritium and carbon-14 recharge ages for Lopez 2 Spring (post-1950s in age), Goodknight and SE Toe wells (pre-1950s in age), and Cottonwood Spring well (primarily pre-1950s in age) are supported by helium-4 data. The helium-4 data for the 5000 Block well are inconsistent with the tritium and carbon-14 age of pre-1950s recharge because of interference caused by high methane concentrations in the water. Springs and surficial deposits are more vulnerable to contamination from anthropogenic chemicals than deeper bedrock wells. Bedrock aquifers are vulnerable in areas where the geologic formations containing the aquifers are exposed at the land surface. Groundwater in deep bedrock aquifers is likely thousands of years old and is not currently affected by present-day land uses. Both shallow and deep groundwater are vulnerable to naturally occurring salts and minerals, such as of total dissolved solids, major ions, nitrate, and trace elements. Effects of a changing climate on water resources and other ecological characteristics of the UMUR could include changes in evapotranspiration, a decrease in snowpack, decreased aquifer recharge and flow of springs, a decrease in soil moisture, and increased occurrence of wildfires and forest mortality. Of particular interest for the UMUT are possible effects of a changing climate on medicinal and culturally important plants and springs Several information needs were identified during this study that would aid in the understanding and protection of groundwater resources on the UMUR. These include well-completion information for bedrock wells, the collection of environmental tracer data at additional wells, the addition of methane and hydrocarbon analysis to well sampling plans, and the resampling of springs and wells that were last sampled in 2002 or earlier.

Colorado↗

USGS1971

Geology, hydrology, and water quality of the Tracy-Dos Palos area, San Joaquin Valley, California

The Tracy-Dos Palos area includes about 1,800 square miles on the northwest side of the San Joaquin Valley. The Tulare Formation of Pliocene and Pleistocene age, terrace deposits of Pleistocene age, and alluvium and flood-basin deposits of Pleistocene and Holocene age constitute the fresh ground-water reservoir Pre-Tertiary and Tertiary sedimentary and crystalline rocks, undifferentiated, underlie the valley and yield saline water. Hydrologically most important, the Tulare Formation is divided into a lower water-bearing zone confined by the Corcoran Clay Member and an upper zone that is confined, semiconfined, and unconfined in different parts of the area. Alluvium and flood-basin deposits are included in the upper zone. Surficial alluvium and flood-basin deposits contain a shallow water-bearing zone. Lower zone wells were flowing in 1908, but subsequent irrigation development caused head declines and land subsidence. Overdraft in both zones ended in 1951 with import of surface water. Bicarbonate water flows into the area from the Sierra Nevada and Diablo Range. Diablo Range water is higher in sulfate, chloride, and dissolved solids. Upper zone water averages between 400 and 1,200 mg/l (milligrams per liter) dissolved solids and water hardness generally exceeds 180 mg/l as calcium carbonate. Nitrate, fluoride, iron, and boron occur in excessive concentrations in water from some wells. Dissolved constituents in lower zone water generally are sodium chloride and sodium sulfate with higher dissolved solids concentration than water from the upper zone. The foothills of the Diablo Range provide favorable conditions for artificial recharge, but shallow water problems plague about 50 percent of the area and artificial recharge is undesirable at this time.

Open-File Report↗

USGS2012

Distribution and condition of larval and juvenile Lost River and shortnose suckers in the Williamson River Delta restoration project and Upper Klamath Lake, Oregon

Federally endangered Lost River sucker (Deltistes luxatus) and shortnose sucker (Chasmistes brevirostris) were once abundant throughout their range but populations have declined. They were extirpated from several lakes in the 1920s and may no longer reproduce in other lakes. Poor recruitment to the adult spawning populations is one of several reasons cited for the decline and lack of recovery of these species and may be the consequence of high mortality during juvenile life stages. High larval and juvenile sucker mortality may be exacerbated by an insufficient quantity of suitable or high-quality rearing habitat. In addition, larval suckers may be swept downstream from suitable rearing areas in Upper Klamath Lake into Keno Reservoir, where they are assumed lost to Upper Klamath Lake populations. The Nature Conservancy flooded about 3,600 acres (1,456 hectares) to the north of the Williamson River mouth (Tulana) in October 2007, and about 1,400 acres (567 hectares) to the south and east of the Williamson River mouth (Goose Bay Farms) in October 2008, in order to retain larval suckers in Upper Klamath Lake, create nursery habitat, and improve water quality. The U.S. Geological Survey joined a long-term research and monitoring program in collaboration with The Nature Conservancy, the Bureau of Reclamation, and Oregon State University in 2008 to assess the effects of the Williamson River Delta restoration on the early life-history stages of Lost River and shortnose suckers. The primary objectives of the research were to describe habitat colonization and use by larval and juvenile suckers and non-sucker fishes and to evaluate the effects of the restored habitat on the health and condition of juvenile suckers. This report summarizes data collected in 2010 by the U.S. Geological Survey as a part of this monitoring effort and follows two annual reports on data collected in 2008 and 2009. Restoration modifications made to the Williamson River Delta appeared to provide additional suitable rearing habitat for endangered Lost River and shortnose suckers from 2008 to 2010 based on sucker catches. Mean larval sample density was greater for both species in the Williamson River Delta than adjacent lake habitats in all 3 years. In addition to larval suckers, at least three age classes of juvenile suckers were captured in the delta. The shallow Goose Bay Farms and Tulana Emergent were among the most used habitats by age-0 suckers in 2009. Both of these environments became inaccessible due to low water in 2010, however, and were not sampled after July 19, 2010. In contrast, age-1 sucker catches shifted from the shallow water (about 0.5-1.5 m deep) on the eastern side of the Williamson River Delta in May, to deeper water environments (greater than 2 m) by the end of June or early July in all 3 years. Differential distribution among sucker species within the Williamson River Delta and between the delta and adjacent lakes indicated that shortnose suckers likely benefited more from the restored Williamson River Delta than Lost River or Klamath largescale suckers (Catostomus snyderi) . Catch rates in shallow-water habitats within the delta were higher for shortnose and Klamath largescale sucker larvae than for larval Lost River suckers in 2008, 2009, and 2010. Shortnose suckers also comprised the greatest portion of age-0 suckers captured in the Williamson River Delta in all 3 years of the study. The relative abundance of age-1 shortnose suckers was high in our catches compared to age-1 Lost River suckers in 2009 and 2010. The restored delta also created habitat for several piscivorous fishes, but only two appeared to pose a meaningful threat of predation to suckers - fathead minnows (Pimephales promelas) and yellow perch (Perca flavescens) . Fathead minnows that prey on larval but not juvenile suckers dominated catches in all sampling areas. Yellow perch also were abundant throughout the study area, but based on their gape size and co-occurrence with suckers, most were only capable of preying on larvae. Low May lake-surface elevation, below average snow pack, and anticipated irrigation demands indicated late summer water levels in Upper Klamath Lake would be unusually low in 2010. In response to concerns by the Fish and Wildlife Service and The Nature Conservancy that low-water conditions might strand fish on the delta, low water seine surveys were implemented. Eleven fishes, including both endangered suckers, were captured in seine surveys, including both species of suckers, which continued to use shallow water less than 0.4 m deep through September 21. Lake elevation declined to 1,261.54 m (4,138.9 feet) in mid-September 2010, but did not appear to strand fish or cause large-scale fish mortality.

Oregon↗

USGS2004

Chapter 11 The phosphoria formation: A model for forecasting global selenium sources to the environment

Mining of the Permian Phosphoria Formation — a marine, oil-generating, phosphatic shale — provided the selenium (Se) source implicated in the recent deaths of livestock in southeast Idaho. Field studies and the geohydrologic balance of Se in southeast Idaho confirm risk to animals from exposure to Se through leaching of mined waste shale into streams, discharge of regional drainage, and impoundment of drainage in wetland areas. Forage grown to stabilize waste rock contoured into hills or used as cross-valley fill provides an additional mechanism of Se exposure for the environment (Mackowiak et al., Chapter 19). The average Se concentration of the Meade Peak Member of the Phosphoria Formation is an order of magnitude higher than those of other exploited marine shales that have been linked to incidences of Se toxicosis via oil refining and irrigation in the western United States. The Phosphoria Formation accumulated in an environment that preserved organic matter and contributed to the formation of economic-grade phosphate and oil deposits. The addition of this phosphate-mining case study enables a comprehensive approach to the identification of marine sedimentary Se sources and a more complete range of ecotoxic field studies on which to establish the conditions and anthropogenic connections that determine uptake, release, and recycling of Se in food webs. A constructed conceptual model of Se pollution indicates that ancient organic-rich depositional marine basins, unre- stricted by age, are linked to the contemporary global distribution of Se source rocks. A global plot shows (a) the areal association of major basins hosting phosphate deposits and petroleum source rocks and (b) the importance of paleo-latitudinal setting in influencing the composition of the deposits. Given the geographic patterns, Se emerges as a contami- nant within specific regions of the globe that may limit phosphate mining, oil refining, and drainage of agricultural lands because of potential ecological risks to vulnerable food webs. Selenium also may serve as a geochemical exploration tool that signals an ancient productive biological environment.

Handbook of Exploration and Environmental Geochemi↗

USGS2009

Hydrology of Northern Utah Valley, Utah County, Utah, 1975-2005

The ground-water resources of northern Utah Valley, Utah, were assessed during 2003-05 to describe and quantify components of the hydrologic system, determine a hydrologic budget for the basin-fill aquifer, and evaluate changes to the system relative to previous studies. Northern Utah Valley is a horst and graben structure with ground water occurring in both the mountain-block uplands surrounding the valley and in the unconsolidated basin-fill sediments. The principal aquifer in northern Utah Valley occurs in the unconsolidated basin-fill deposits where a deeper unconfined aquifer occurs near the mountain front and laterally grades into multiple confined aquifers near the center of the valley. Sources of water to the basin-fill aquifers occur predominantly as either infiltration of streamflow at or near the interface of the mountain front and valley or as subsurface inflow from the adjacent mountain blocks. Sources of water to the basin-fill aquifers were estimated to average 153,000 (+/- 31,500) acre-feet annually during 1975-2004 with subsurface inflow and infiltration of streamflow being the predominant sources. Discharge from the basin-fill aquifers occurs in the valley lowlands as flow to waterways, drains, ditches, springs, as diffuse seepage, and as discharge from flowing and pumping wells. Ground-water discharge from the basin-fill aquifers during 1975-2004 was estimated to average 166,700 (+/- 25,900) acre-feet/year where discharge to wells for consumptive use and discharge to waterways, drains, ditches, and springs were the principal sources. Measured water levels in wells in northern Utah Valley declined an average of 22 feet from 1981 to 2004. Water-level declines are consistent with a severe regional drought beginning in 1999 and continuing through 2004. Water samples were collected from 36 wells and springs throughout the study area along expected flowpaths. Water samples collected from 34 wells were analyzed for dissolved major ions, nutrients, and stable isotopes of hydrogen and oxygen. Water samples from all 36 wells were analyzed for dissolved-gas concentration including noble gases and tritium/helium-3. Within the basin fill, dissolved-solids concentration generally increases with distance along flowpaths from recharge areas, and shallower flowpaths tend to have higher concentrations than deeper flowpaths. Nitrate concentrations generally are at or below natural background levels. Dissolved-gas recharge temperature data support the conceptual model of the basin-fill aquifers and highlight complexities of recharge patterns in different parts of the valley. Dissolved-gas data indicate that the highest elevation recharge sources for the basin-fill aquifer are subsurface inflow derived from recharge in the adjacent mountain block between the mouths of American Fork and Provo Canyons. Apparent ground-water ages in the basin-fill aquifer, as calculated using tritium/helium-3 data, range from 2 to more than 50 years. The youngest waters in the valley occur near the mountain fronts with apparent ages generally increasing near the valley lowlands and discharge area around Utah Lake. Flowpaths are controlled by aquifer properties and the location of the predominant recharge sources, including subsurface inflow and recharge along the mountain front. Subsurface inflow is distributed over a larger area across the interface of the subsurface mountain block and basin-fill deposits. Subsurface inflow occurs at a depth deeper than that at which mountain-front recharge occurs. Recharge along the mountain front is often localized and focused over areas where streams and creeks enter the valley, and recharge is enhanced by the associated irrigation canals.

Utah↗