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At least 307 records · Page 17Linked to original sources
USGS1956

Saline-water resources of Texas

Large quantities of saline water are available in the world, both on the surface and underground; however, these waters have not been studied extensively as sources of potable water. Saline water is defined herein as water containing more than 1,000 parts per million of dissolved solids, or, with certain mineralized irrigation waters whose exact dissolved solids content is not known, water containing more than 60 percent sodium. Saline ground water occurs as connate water or other saline water that entered an aquifer in the geologic past and has not been flushed from the aquifer; as the result of solution of soluble materials in aquifers by percolating ground water; as a result of salt-water encroachment into aquifers which are in hydrologic connection with saline waters; or as the result of concentration by evaporation, especially in the vicinity of playa lakes. Surface water may become saline as a result of seepage of highly mineralized ground water; solution of salts from rocks over which the streams flow; intrusion of sea water in tidal reaches of a stream; and discharge of saline wastes from industrial operations. Most of the aquifers in Texas contain saline water in some parts, and a few are capable of producing large quantities of saline water. Of the early Paleozoic formations, the Hickory sandstone member of the Riley formation of Cambrian age and the Ellenburger group of Ordovician age are potential sources of small to moderate supplies of saline water in parts of central and west-central Texas.

Water Supply Paper↗
USGS1951

Geology and ground-water resources of the northern part of the Ranegras Plain area, Yuma County, Arizona

The Ranegras Plain area is part of the Basin and Range province in west-central Arizona. The report discusses rocks of pre-Cambrian, pre-Cambrian (?), Paleozoic (?), Mesozoic (?), Cretaceous (?), Cretaceous and Tertiary, Tertiary (?), Quaternary (?), and Quaternary age. All the Paleozoic (?) and Cretaceous (?) rocks and parts of the Mesozoic (?),Cretaceous and Tertiary, and Tertiary (?) rocks have been mapped as a unit because they are so intensely faulted that detailed mapping was not practical. Rocks older than Quaternary form the mountain ranges bordering the Ranegras Plain. Quaternary alluvium underlies the broad, gently sloping valley floor to depths of generally a few hundred feet, locally more. Well logs indicate that the underlying Tertiary (?) alluvium exceeds 1,100 feet in thickness. The structure of the area is controlled by faulting typical of the Basin and Range province, but the major faults are covered by alluvium and are inferred from topographic features. Ground water occurs in Quaternary and Tertiary (?) alluvium and the best aquifers are in sand and gravel of the Quaternary alluvium. Ground-water movement is, in general, to the northwest. Recharge to the aquifers is predominantly from stream flow resulting from heavy rains. There is also minor or unevaluated recharge from underflow from Butler Valley to the east, andsince 1948seepage from irrigation. Discharge is by pumping and by natural processes of underflow and evapotranspiration. In addition to small domestic and stock wells, only two irrigation wells, in the vicinity of Utting, are in use. No accurate data on pumpage are available. The safe yield from the ground-water reservoir may be less than 5,000 acre-feet and probably does not exceed 10,000 to 15,000 acre-feet per year. The quality of ground water ranges from permissible to unsuitable for irrigation purposes. The fluoride content is generally too high for the water to be considered satisfactory for use by young children.

Open-File Report↗
USGS2020

Hydrogeology, numerical simulation of groundwater flow, and effects of future water use and drought for reach 1 of the Washita River alluvial aquifer, Roger Mills and Custer Counties, western Oklahoma, 1980–2015

The Washita River alluvial aquifer is a valley-fill and terrace alluvial aquifer along the valley of the Washita River in western Oklahoma that provides a productive source of groundwater for agricultural irrigation and water supply. The Oklahoma Water Resources Board (OWRB) has designated the westernmost section of the aquifer in Roger Mills and Custer Counties, Okla., as reach 1 of the Washita River alluvial aquifer; reach 1 is the focus of this report. The OWRB issued an order on November 13, 1990, that established the maximum annual yield (MAY; 120,320 acre-feet per year [acre-ft/yr]) and equal-proportionate-share (EPS) pumping rate (2.0 acre-feet per acre per year [(acre-ft/acre)/yr]) for reach 1 of the Washita River alluvial aquifer. The MAY and EPS were based on hydrologic investigations that evaluated the effects of potential groundwater withdrawals on groundwater availability in the Washita River alluvial aquifer. Every 20 years, the OWRB is statutorily required to update the hydrologic investigation on which the MAY and EPS were based. Because 30 years have elapsed since the last order was issued, the U.S. Geological Survey, in cooperation with the OWRB, conducted a new hydrologic investigation and evaluated the effects of potential groundwater withdrawals on groundwater flow and availability in the Washita River alluvial aquifer. The Washita River is the primary source of inflow to Foss Reservoir, a Bureau of Reclamation reservoir constructed in 1961 for flood control, water supply, and recreation. Foss Reservoir provides water for Bessie, Clinton, New Cordell, and Hobart, Okla. Nearly 98 percent of the total groundwater use from the Washita River alluvial aquifer during 1967 to 2015 was for irrigation; other uses of groundwater in the study area include public supply, mining, and agriculture. A hydrogeologic framework was developed for the Washita River alluvial aquifer and included the physical characteristics of the aquifer, the geologic setting, the hydraulic properties of hydrogeologic units, the potentiometric surface (water table), and groundwater-flow directions at a scale that captures the regional controls on groundwater flow. The Washita River alluvial aquifer consists of alluvium and terrace deposits that were transported primarily by water and range from clay to gravel in size. The terrace includes windblown deposits of silt size and, in some cases, contains gravel laid down at several levels along former courses of present-day rivers. A conceptual flow model is a simplified description of the aquifer system that includes hydrologic boundaries, major inflow and outflow sources of the groundwater-flow system, and a conceptual water budget with the estimated mean flows between those hydrologic boundaries. During the study period 1980–2015, mean annual groundwater withdrawals, predominantly used for agricultural irrigation, totaled 5,502 acre-ft/yr, or 14 percent of aquifer outflows. When applied across the 132-square-mile aquifer area used for modeling purposes (84,366 acres), mean annual recharge of 3.15 inches per year corresponds to a mean annual recharge volume of 22,169 acre-ft/yr, or 56 percent of aquifer inflows. The annual saturated-zone evapotranspiration outflow was 11,828 acre-ft/yr for the Washita River alluvial aquifer, or about 30 percent of aquifer outflows. For the Washita River alluvial aquifer, lateral flow was 17,157 acre-ft/yr, or 44 percent of the aquifer inflows. The conceptual flow model and hydrogeologic framework were used to conceptualize, design, and build the numerical groundwater-flow model. A numerical groundwater-flow model of the Washita River alluvial aquifer was constructed by using MODFLOW-2005. The Washita River alluvial aquifer groundwater-model grid was spatially discretized into 350-foot (ft) cells and two layers. Layer 1 represented the undifferentiated alluvium and terrace deposits of Quaternary age, and layer 2 represented the bedrock of Permian age, which was given a uniform nominal thickness of 100 ft. The groundwater-simulation period was temporally discretized into 433 monthly transient stress periods, representing January 1980 to December 2015. An initial 365-day steady-state stress period was configured to represent mean annual inflows and outflows from the Washita River alluvial aquifer for the study period. The groundwater-flow model was calibrated manually and by automated adjustment of model inputs by using PEST++. Calibration targets for the Washita River alluvial aquifer model included groundwater-level observations and reservoir-stage observations, as well as base-flow and stream-seepage estimates. Three groundwater-availability scenarios were used in the calibrated groundwater model to (1) estimate the EPS pumping rate that retains the saturated thickness that meets the minimum 20-year life of the aquifer, (2) quantify the effects of projected pumping rates on groundwater storage over a 50-year period, and (3) evaluate how projected pumping rates extended 50 years into the future and sustained hypothetical drought conditions over a 10-year period affect base flow and groundwater in storage. The results of the groundwater-availability scenarios could be used by the OWRB to reevaluate the established MAY of groundwater from the Washita River alluvial aquifer. EPS scenarios for the Washita River alluvial aquifer were run for periods of 20, 40, and 50 years. The 20-, 40-, and 50-year EPS pumping rates under normal recharge conditions were 1.7, 1.6, and 1.6 (acre-ft/acre)/yr, respectively. Given the aquifer area used for modeling purposes (84,366 acres), these rates correspond to annual yields of 142,579, 134,986, and 134,986 acre-ft/yr, respectively. Groundwater storage at the end of the 20-year EPS scenario was about 281,000 acre-feet (acre-ft), or about 306,000 acre-ft (52 percent) less than the starting storage. Considering the land-surface area of the Washita River alluvial aquifer and using a specific yield of 0.12, this decrease in storage was equivalent to a mean groundwater-level decline of about 30 ft. The Washita River downstream from Foss Reservoir and most of the streams in the study area were dry at the end of the 20-year EPS scenario. Foss Reservoir stage was below the dead-pool stage of 1,597 ft after about 7 years of pumping in the 20-year EPS scenario. Four projected 50-year groundwater-use scenarios were used to simulate the effects of selected well withdrawal rates on groundwater storage in the Washita River alluvial aquifer. These four scenarios used (1) no groundwater use, (2) groundwater use at the 2015 pumping rate, (3) mean groundwater use for the simulation period, and (4) increasing groundwater use. Groundwater storage after 50 years with no groundwater use was 545,249 acre-ft, or 693 acre-ft (0.1 percent) greater than the initial groundwater storage; this groundwater storage increase is equivalent to a mean groundwater-level increase of 0.1 ft. Groundwater storage at the end of the 50-year period with 2015 pumping rates was 543,831 acre-ft, or 723 acre-ft (0.1 percent) less than the initial storage; this groundwater storage decrease is equivalent to a mean groundwater-level decrease of 0.1 ft. Groundwater storage after 50 years with the mean pumping rate for the study period was 543,202 acre-ft, or 1,349 acre-ft (0.2 percent) less than the initial groundwater storage; this groundwater storage decrease is equivalent to a mean groundwater-level decrease of 0.1 ft. Groundwater storage at the end of the 50-year period with an increasing demand groundwater-pumping rate, which was 38 percent greater than the 2015 groundwater-pumping rate, was 542,584 acre-ft, or 1,967 acre-ft (0.4 percent) less than the initial storage; this groundwater storage decrease is equivalent to a mean groundwater-level decrease of 0.2 ft. A hypothetical 10-year-drought scenario was used to simulate the effects of a prolonged period of reduced recharge on groundwater storage in the Washita River alluvial aquifer and Foss Reservoir stage and storage. To simulate the hypothetical drought, recharge in the calibrated model was reduced by 50 percent during the simulated drought period (1983–1992). Groundwater storage at the end of the drought period in December 1992 was 562,000 acre-ft, or 36,000 acre-ft (6 percent) less than the groundwater storage of the calibrated groundwater model (598,000 acre-ft). At the end of the hypothetical drought, the largest changes in saturated thickness (as great as 43.5 ft) were in the area upgradient from Foss Reservoir, particularly in the terrace at the model boundary. Substantial decreases in the Foss Reservoir stage began during the fall of 1985 in conjunction with base-flow decreases of up to 100 percent at U.S. Geological Survey streamgage 07324200 Washita River near Hammon, Okla. These lake-stage declines outpaced groundwater-level declines in the surrounding aquifer. The minimum Foss Reservoir storage simulated during the drought period was 77,954 acre-ft, which was a decrease of 46 percent from the nondrought storage.

Oklahoma↗
USGS2020

Predicted pH of groundwater in the Mississippi River Valley alluvial and Claiborne aquifers, south-central United States

Regional aquifers in the Mississippi embayment are the principal sources of water used for public and domestic supply, irrigation, and industrial uses throughout the region. An understanding of how water quality varies spatially, temporally, and with depth are critical aspects to ensuring long-term sustainable use of these resources. A boosted regression tree (BRT) model was used by the U.S. Geological Survey (USGS) to map water quality in the three regional aquifers with the largest groundwater withdrawals in the embayment: the Mississippi River Valley alluvial (MRVA) aquifer, middle Claiborne aquifer (MCAQ), and lower Claiborne aquifer (LCAQ). The BRT model was used to predict pH to 1-kilometer raster grid cells for seven aquifer layers (one MRVA, four MCAQ, two LCAQ) following the hydrogeologic framework of the Mississippi embayment aquifer system regional MODFLOW model. The methods and approach used for pH predictions are the same as those used recently by the USGS to predict specific conductance and chloride in the aquifers. Explanatory variables for the BRT models included variables describing well location and construction, surficial variables such as soil properties and land use, and variables extracted from the groundwater flow model, such as groundwater levels and ages. The primary source of pH data was the USGS National Water Information System database. Additional data from State ambient groundwater monitoring programs and the Safe Drinking Water Information System also were used. For wells sampled multiple times, the most recent sample was used. Because groundwater residence times are long (greater than 100 years) throughout much of the study area, the possible effects of changes in water quality over time were considered small compared to the improvement in overall model accuracy by using available historical data. Values of pH from 3,362 wells for samples collected between 1960 and 2018 were used as training data for the BRT model. An additional 839 samples were used as holdout data to evaluate model performance. The predictive performance of the pH model is lower than for the training dataset, as indicated by an r-squared value of 0.89 for the training data and an r-squared of 0.71 for the holdout data. The root mean squared errors for the training and holdout data are 0.32 and 0.50 standard pH units, respectively. Data generated during this study and the model output are available from the companion data release.

Alabama, Arkansas, Louisiana, Mississippi, Missour↗
USGS2014

Hydrogeologic framework and groundwater/surface-water interactions of the upper Yakima River Basin, Kittitas County, central Washington

The hydrogeology, hydrology, and geochemistry of groundwater and surface water in the upper (western) 860 square miles of the Yakima River Basin in Kittitas County, Washington, were studied to evaluate the groundwater-flow system, occurrence and availability of groundwater, and the extent of groundwater/surface-water interactions. The study area ranged in altitude from 7,960 feet in its headwaters in the Cascade Range to 1,730 feet at the confluence of the Yakima River with Swauk Creek. A west-to-east precipitation gradient exists in the basin with the western, high-altitude headwaters of the basin receiving more than 100 inches of precipitation per year and the eastern, low-altitude part of the basin receiving about 20 inches of precipitation per year. From the early 20th century onward, reservoirs in the upper part of the basin (for example, Keechelus, Kachess, and Cle Elum Lakes) have been managed to store snowmelt for irrigation in the greater Yakima River Basin. Canals transport water from these reservoirs for irrigation in the study area; additional water use is met through groundwater withdrawals from wells and surface-water withdrawals from streams and rivers. Estimated groundwater use for domestic, commercial, and irrigation purposes is reported for the study area. A complex assemblage of sedimentary, metamorphic, and igneous bedrock underlies the study area. In a structural basin in the southeastern part of the study area, the bedrock is overlain by unconsolidated sediments of glacial and alluvial origin. Rocks and sediments were grouped into six hydrogeologic units based on their lithologic and hydraulic characteristics. A map of their extent was developed from previous geologic mapping and lithostratigraphic information from drillers’ logs. Water flows through interstitial space in unconsolidated sediments, but largely flows through fractures and other sources of secondary porosity in bedrock. Generalized groundwater-flow directions within the unconfined part of the aquifers in unconsolidated sediments indicate generalized groundwater movement toward the Yakima River and its tributaries and the outlet of the study area. Groundwater movement through fractures within the bedrock aquifers is complex and varies over spatial scales depending on the architecture of the fracture-flow system and its hydraulic properties. The complexity of the fracturedbedrock groundwater-flow system is supported by a wide range of groundwater ages determined from geochemical analyses of carbon-14, sulfur hexafluoride, and tritium in groundwater. These geochemical data also indicate that the shallow groundwater system is actively flushing with young, isotopically heavy groundwater, but isotopicallylight, Pleistocene-age groundwater with a geochemicallyevolved composition occurs at depth within the fracturedbedrock aquifers of upper Kittitas County. An eastward depletion of stable isotopes in groundwater is consistent with hydrologically separate subbasins. This suggests that groundwater that recharges in one subbasin is not generally available for withdrawal or discharge into surface-water features within other subbasins. Water budget components were calculated for 11 subbasins using a watershed model and varied based on the climate, land uses, and geology of the subbasin. Synoptic streamflow measurements made in August 2011 indicate that groundwater discharges into several tributaries of the Yakima River with several losses of streamflow measured where the streams exit bedrock uplands and flow over unconsolidated sediments. Profiles of stream temperature during late summer suggest cool groundwater inflow over discrete sections of streams. This groundwater/surfacewater connection is further supported by the stable-isotope composition of stream water, which reflects the local stableisotope composition of groundwater measured at some wells and springs. Collectively, these hydrogeologic, hydrologic, and geochemical data support a framework for evaluating the potential effects of future groundwater appropriations on senior surface-water and groundwater rights and streamflows. Although total pumping rates in upper Kittitas County of about 3.5 cubic feet per second are small relative to other components of the water budget, the magnitude, timing, and location of withdrawals may have important effects on the hydrologic system. The heterogeneous and variably fractured bedrock in the study area precluded a detailed evaluation of localized effects of pumping, but several generalizations about the groundwater and surface-water systems can be made. These generalizations include evidence for the continuity between the groundwater and surface-water system apparent from synoptic streamflow measurements, stream-temperature profiles, and stable-isotope data of groundwater and surface waters.

Washington↗
USGS2011

Groundwater quality in the Monterey Bay and Salinas Valley groundwater basins, California

The Monterey-Salinas study unit is nearly 1,000 square miles and consists of the Santa Cruz Purisima Formation Highlands, Felton Area, Scotts Valley, Soquel Valley, West Santa Cruz Terrace, Salinas Valley, Pajaro Valley, and Carmel Valley groundwater basins (California Department of Water Resources, 2003; Kulongski and Belitz, 2011). These basins were grouped into four study areas based primarily on geography. Groundwater basins in the north were grouped into the Santa Cruz study area, and those to the south were grouped into the Monterey Bay, the Salinas Valley, and the Paso Robles study areas (Kulongoski and others, 2007). The study unit has warm, dry summers and cool, moist winters. Average annual rainfall ranges from 31 inches in Santa Cruz in the north to 13 inches in Paso Robles in the south. The study areas are drained by several rivers and their principal tributaries: the Salinas, Pajaro, and Carmel Rivers, and San Lorenzo Creek. The Salinas Valley is a large intermontane valley that extends southeastward from Monterey Bay to Paso Robles. It has been filled, up to a thickness of 2,000 feet, with Tertiary and Quaternary marine and terrestrial sediments that overlie granitic basement. The Miocene-age Monterey Formation and Pliocene- to Pleistocene-age Paso Robles Formation, and Pleistocene to Holocene-age alluvium contain freshwater used for supply. The primary aquifers in the study unit are defined as those parts of the aquifers corresponding to the perforated intervals of wells listed in the California Department of Public Health database. Public-supply wells are typically drilled to depths of 200 to 650 feet, consist of solid casing from the land surface to depths of about 175 to 500 feet, and are perforated below the solid casing. Water quality in the primary aquifers may differ from that in the shallower and deeper parts of the aquifer system. Groundwater movement is generally from the southern part of the Salinas Valley north towards the Monterey Bay. Land use in the study unit is about 44 percent (%) natural (mostly grassland and forests), 43% agricultural, and 13% urban. The primary agricultural uses are row crops, pasture, hay, and vineyards. The largest urban areas are the cities of Santa Cruz, Watsonville, Monterey, Salinas, King City, and Paso Robles. Recharge to the groundwater system is primarily from stream-channel infiltration from the major rivers and their tributaries, and from infiltration of water from precipitation and irrigation. The primary sources of discharge are water pumped for irrigation and municipal supply, evaporation, and discharge to streams.

Fact Sheet↗
USGS1983

Hydrology of area 54, northern Great Plains, and Rocky Mountain coal provinces, Colorado and Wyoming

A nationwide need for information characterizing hydrologic conditions in mined and potential mine areas has become paramount with the enactment of the Surface Mining Control and Reclamation Act of 1977. This report, one in a series covering the coal provinces nationwide, presents information thematically by describing single hydrologic topics through the use of brief texts and accompanying maps, graphs, or other illustrations. The summation of the topical discussions provides a description of the hydrology of the area. Area 54, in north-central Colorado and south-central Wyoming, is 1 of 20 hydrologic reporting areas of the Northern Great Plains and Rocky Mountain coal provinces. Part of the Southern Rocky Mountains and Wyoming Basin physiographic provinces, the 8,380-square-mile area is one of contrasting geology, topography, and climate. This results in contrasting hydrologic characteristics. The major streams, the North Platte, Laramie, and Medicine Bow Rivers, and their principal tributaries, all head in granitic mountains and flow into and through sedimentary basins between the mountain ranges. Relief averages 2,000 to 3,000 feet. Precipitation in the mountains may exceed 40 inches annually, much of it during the winter, which produces deep snowpacks. Snowmelt in spring and summer provides most streamflow. Precipitation in the basins averages 10 to 16 inches annually, insufficient for sustained streamflow; thus, streams originating in the basins are ephemeral. Streamflow quality is best in the mountains where dissolved-solids concentrations generally are least. These concentrations increase as streams flow through sedimentary basins. The increases are mainly natural, but some may be due to irrigation in and adjacent to the flood plains. In the North Platte River, dissolved-solids concentrations are usually less than 300 milligrams per liter; in the Laramie and the Medicine Bow Rivers, the concentrations may average 500 to 850 milligrams per liter. However, water-quality stations on the Laramie and the Medicine Bow Rivers are farther removed from the mountain sources than the stations in the North Platte drainage. Because of the semiarid climate of the basins, soils are not adequately leached. Consequently, flow in ephemeral streams usually has a larger concentration of dissolved solids than that in perennial streams, averaging 1,000 to 1,600 milligrams per liter. Aquifers containing usable ground water are combined into three groups: (1) consolidated and unconsolidated non-coal-bearing Quaternary and Upper Tertiary deposits, (2) Mesozoic and Paleozoic sedimentary rocks, and (3) Lower Tertiary and Upper Cretaceous sedimentary rocks containing coal. These aquifers are used for municipal, domestic, irrigation, and stock supplies. Well yields range from about 5 to 1,000 gallons per minute, and depend on type of aquifer, saturated thickness, and degree of fracturing. The best quality ground water usually comes from the non-coal-bearing Quaternary and Upper Tertiary rocks or the Mesozoic and Paleozoic rocks; often it is dominated by calcium and bicarbonate ions. The coal-bearing formations have a large variability in water chemistry; dominant ions may be bicarbonate or sulfate and sodium, calcium, or magnesium. Dissolved-solids concentrations are generally larger than in the former two groups. The U.S. Geological Survey operates a network of hydrologic stations to observe the streamflow and groundwater conditions. This network currently includes 31 surface-water stations and 35 observation wells; information is available for many other sites observed in the past. Data available include rate of flow, water levels, and water quality; much of the data are available in published reports or from computer storage through the National Water Data Exchange (NAWDEX) or the National Water Data Storage and Retrieval System (WATSTORE). Five formations of Late Cretaceous and early Tertiary age contain coal.

Colorado, Wyoming↗
USGS1984

Hydrology of area 53, northern Great Plains and Rocky Mountain coal provinces, Colorado, Wyoming, and Utah

Hydrologic information and analysis are needed to aid in decisions to lease Federally owned coal and for the preparation of the necessary Environmental Assessments and Impact Study Reports. This need has become even more critical with the enactment of the Surface Mining Control and Reclamation Act of 1977 (Public Law 95-87). This report, one in a series of nationwide coal province reports, presents information thematically by describing single hydrologic topics through the use of brief texts and accompanying maps, graphs, or other illustrations. The report broadly characterizes the hydrology of Area 53 in northwestern Colorado, south-central Wyoming, and northeastern Utah. The report area, located primarily in the Wyoming Basin and Colorado Plateau physiographic provinces, consists of 14,650 square miles of diverse geology, topography, and climate. This diversity results in contrasting hydrologic characteristics. The two major rivers, the Yampa and the White Rivers, originate in humid granitic and basaltic mountains, then flow over sedimentary rocks underlying semiarid basins to their respective confluences with the Green River. Altitudes range from 4,800 to greater than 12,000 feet above sea level. Annual precipitation in the mountains, as much as 60 inches, is generally in the form of snow. Snowmelt produces most streamflow. Precipitation in the lower altitude sedimentary basins, ranging from 8 to 16 inches, is generally insufficient to sustain streamflow; therefore, most streams originating in the basins (where most of the streams in coal-mining areas originate) are ephemeral. Streamflow quality is best in the mountains where dissolved-solids concentrations generally are small. As streams flow across the sedimentary basins, mineral dissolution from the sedimentary rocks and irrigation water with high mineral content increase the dissolved-solids concentrations in a downstream direction. Due to the semiarid climate of the basins, soils are not adequately leached; consequently, flows in the ephemeral streams usually have larger concentrations of dissolved solids than those in perennial streams. Ground-water supplies are restricted by the low yields of wells due to small permeability. Most ground-water use is for domestic and stock-watering purposes; it is limited by the amount and type of dissolved material. The ground-water ionic composition is highly variable. Dissolved-solids concentrations for aquifers sampled in Area 53 range from a minimum of 46 milligrams per liter to a maximum of 109,000 milligrams per liter. Trace element concentrations generally are not a problem. An estimated 82 billion tons of coal exist above a depth of 6,000 feet in the Colorado parts of the area. The coal beds of greatest economic interest occur in the sedimentary deposits of the Upper Cretaceous Iles and Williams Fork Formations of the Mesaverde Group and the Upper Cretaceous Lance Formation and the Fort Union and Wasatch Formations of Tertiary age. The coal characteristically has a low sulfur content. Hydrologic problems related to surface mining are erosion, sedimentation, decline in water levels, disruption of aquifers, and degradation of water quality. Because the semiarid mine areas have very little runoff and the major streams have large buffer and dilution capacities, the effects of mining on surface water are minimal. However, effects on ground water may be much more severe and long lasting.

Colorado, Wyoming and Utah↗
USGS2023

Groundwater quality near the Montebello Oil Field, Los Angeles County, California

Groundwater quality and potential sources and migration pathways of chemical constituents associated with hydrocarbon-bearing formations were assessed by the U.S. Geological Survey for the California State Water Resources Control Board Oil and Gas Regional Monitoring Program (RMP). Groundwater samples were collected as part of the RMP from 21 preexisting wells used for public supply, monitoring, or irrigation in and near the Montebello Oil Field and analyzed for constituents associated with hydrocarbon-bearing formations and constituents used to identify recently recharged groundwater and older groundwater. The newly collected RMP data were supplemented with historical sample data from 849 groundwater wells and analyzed with respect to explanatory factors that have the potential to influence water quality. Potential sources and migration pathways of fluids (water, gas, or oil) from hydrocarbon-bearing formations that could affect groundwater quality in the Montebello Oil Field include large volumes of recycled produced water (water withdrawn from an oil well and brought to the surface that may include oil, water, and gas from the geologic formation and water or gas injected for enhanced recovery) that have been reinjected since the 1960s to enhance oil production, oil and gas wells with well-integrity issues, and oil and gas wells with an uncemented annulus that intersects groundwater resource zones. Trace amounts of dissolved petroleum hydrocarbons, thermogenic gas (propane through pentane range), or both, were detected in seven groundwater samples collected in 2014 and 2018 as part of the RMP. Five of those samples also contained manufactured volatile organic compounds and at least some modern-age groundwater (recharged during or after 1953), indicating that the hydrocarbons could have originated from surficial, or shallow, sources unrelated to oil and gas development. Two samples contained low concentrations of petroleum hydrocarbons (less than 0.1 microgram per liter) and did not contain detections of manufactured volatile organic compounds in pre-modern groundwater. These samples were collected from relatively deep wells (greater than 140 meters below land surface) with perforations completed in marine sediments that may contain water with similar compositions to produced water. The RMP sample results and available historical data in and near the Montebello Oil Field did not provide conclusive evidence that oil and gas development has adversely affected groundwater resources. All samples with detectable petroleum hydrocarbons, thermogenic gases, or both, were collected from sites that also are within 500 meters of anthropogenic hydrocarbon sources not associated with oil and gas development or sources. In addition, naturally occurring sources of hydrocarbons that exist at intervals shallower than, or are in areas outside of, economically productive oil- and gas-producing zones could affect groundwater quality. A definitive analysis of relations of groundwater quality to potential anthropogenic and natural explanatory factors was not possible because of the low density of new and historical sampling data, particularly in parts of the Montebello Oil Field where the largest relative risks to groundwater from hydrocarbon-bearing formations exist. Areas to consider for more detailed monitoring and analysis in the future that may present the largest relative potential risks to groundwater quality include (1) areas downgradient from historical surface ponds and sumps and (2) areas with co-located high net injection (oil reservoir injection exceeds production), old oil and gas wells that may be more likely to develop well-integrity issues than newer wells, and oil and gas wells with uncemented boreholes intersecting groundwater zones. To help fill gaps resulting from sparse groundwater wells, temperature and resistivity borehole log data could be analyzed to locate anomalies that identify potential areas where relatively warm or saline water from deeper hydrocarbon-bearing formations is present in groundwater.

California↗
USGS1972

Quality of the ground water in basalt of the Columbia River group, Washington, Oregon, and Idaho

The ground water within the 50,000-square-mile area of the layered basalt of the Columbia River Group is a generally uniform bicarbonate water having calcium and sodium in nearly equal amounts as the principal cations. water contains a relatively large amount of silica. The 525 chemical analyses indicate that the prevalent ground water is of two related kinds--a calcium and a sodium water. The sodium water is more common beneath the floors of the main synclinal valleys; the calcium water, elsewhere. In addition to the prevalent type, five special types form a small part of the ground water; four of these are natural and one is artificial. The four natural special types are: (1) calcium sodium chloride waters that rise from underlying sedimentary rocks west of the Cascade Range, (2) mineralized water at or near warm or hot springs, (3) water having unusual ion concentrations, especially of chloride, near sedimentary rocks intercalated at the edges of the basalt, and (4) more mineralized water near one locality of excess carbon dioxide. The one artificial kind of special ground water has resulted from unintentional artificial recharge incidental to irrigation in parts of central Washington. The solids dissolved in the ground water have been picked up on the surface, within the overburden, and from minerals and glasses within the basalt. Evidence for the removal of ions from solution is confined to calcium and magnesium, only small amounts of which are present in some of the sodium-rich water. Minor constituents, such as the heavy metals, alkali metals, and alkali earths, occur in the ground water in trace, or small, amounts. The natural radioactivity of the ground waters is very low. Except for a few of the saline calcium sodium chloride waters and a few occurrences of excessive nitrate, the ground water generally meets the common standards of water good for most ordinary uses, but some of it can be improved by treatment. The water is clear and colorless and has a temperature slightly higher than would be indicated by the accepted 'normal' earth gradient. A small amount of iron is present in some of the water and a slight amount of hydrogen sulfide gas is present in water from most wells. Carbon-14 determinations indicate that the water has been underground for periods ranging from modern times to several tens of thousands of years. Generally, an increase in the age of the water corresponds to depth and with location in the central parts of the main structural basins. The evidence of correlations between chemical characteristics and the age of the water is limited to the excessive nitrate which occurs in young, shallow ground water and to the apparent base-exchange removal of calcium and magnesium that has occurred where the ground water is old.

Water Supply Paper↗
USGS2002

A statistical model for estimating stream temperatures in the Salmon and Clearwater River basins, central Idaho

A water-quality standard for temperature is critical for the protection of threatened and endangered salmonids, which need cold, clean water to sustain life. The Idaho Department of Environmental Quality has established temperature standards to protect salmonids, yet little is known about the normal range of temperatures of most Idaho streams. A single temperature standard for all streams does not take into account the natural temperature variation of streams or the existence of naturally warm waters. To address these issues and to help the Idaho Department of Environmental Quality revise the existing State temperature standards for aquatic life, temperature data from more than 200 streams and rivers in the salmon and Clearwater River Basins were collected. From these data, a statistical model was developed for estimating stream temperatures on the basis of subbasin and site characteristics and climatic factors. Stream temperatures were monitored hourly for approximately 58 days during July, August, and September 2000 at relatively undisturbed sites in subbasins in the Salmon and Clearwater River Basins in central Idaho. The monitored subbasins vary widely in size, elevation, drainage area, vegetation cover, and other characteristics. The resulting data were analyzed for statistical correlations with subbasin and site characteristics to establish the most important factors affecting stream temperature. Maximum daily average stream temperatures were strongly correlated with elevation and total upstream drainage area; weaker correlations were noted with stream depth and width and aver-age subbasin slope. Stream temperatures also were correlated with certain types of vegetation cover, but these variables were not significant in the final model. The model takes into account seasonal temperature fluctuations, site elevation, total drainage area, average subbasin slope, and the deviation of daily average air temperature from a 30-year normal daily average air temperature. The goodness-of-fit of the model varies with day of the year. Overall, temperatures can be estimated with 95-percent confidence to within approximately plus or minus 4 degrees Celsius. The model performed well when tested on independent stream-temperature data previously collected by the U.S. Geological Survey and other agencies. Although the model provides insight into the natural temperature potential of a wide variety of streams and rivers in the Salmon and Clearwater River Basins, it has limitations. It is based on data collected in only one summer, during which temperatures were higher and streamflows were lower than normal. The effects of changes in streamflow on the effectiveness of the model are not known. Because the model is based on data from minimally disturbed or undisturbed streams, it should not be applied to streams known to be significantly affected by human activities such as disturbance of the streambed, diversion and return of water by irrigation ditches, and removal of riparian vegetation. Finally, because the model is based on data from streams in the Salmon and Clearwater River Basins and reflects climatological and landscape characteristics of those basins, it should not be applied to streams outside this region.

Idaho↗
USGS1951

Ground-water resources of Baker Valley, Baker County, Oregon

The Baker Valley is the southern part of a small oval-shaped inter-montane structural basin located near tie southeastern edge of the Blue Mountains of northeastern Oregon. The Powder River enters and leaves the valley through narrow rock gorges. The alluviated basin floor at an altitude of about 3,400 feet is bounded by high, Alpine-type mountains on the west and by lover hilly ridges on the north, east, and south. Creeks descend across alluvial fans from the higher western margin of the valley to the Powder River on the valley floor. The valley floor and the contiguous alluvial slopes are formed of unconsolidated deposits of Quaternary age having a thickness of more than 700 feet in the central part of the valley. The surrounding higher lands are formed of consolidated rocks composed of volcanic flows, tuffs, and partly consolidated deposits of Tertiary age, and sedimentary, igneous, and metamorphic roots of late Paleozoic age. The unconsolidated materials underlying the alluvial slopes are mostly fanglomerates - composed of partly consolidated angular rock fragments imbedded in assorted finer materials - and fine-grained sedimentary deposits having much inter-bedded gravel and sand along the valley floor. The unconsolidated deposits contain a body of ground water, the upper surface of which is called the water table. The water table slopes down gradient approximately parallel to tile land surface. Variations in the general inclination of that water table indicate that drainage on different segments of the alluvial slope is influent and effluent to the ground water body. Yields from wells in the fanglomerate along the rest side of the valley are not large, but large yields are obtained from wells on the valley floor just north of Baker. Properly constructed test wells have not been drilled over much of the northern part of the valley floor. The Tertiary rocks of both volcanic and sedimentary origin along the margin of the valley east of Baker contain some ground water under sufficient pressure to cause wells to flow at the surface, but generally those strata are not highly productive. Some water occurring along fault lines in these rocks has all abnormally high temperature. The growing season in this area is short and the use of shallow water for irrigation may aid materially in securing the maximum returns of which the valley is capable.

Oregon↗
USGS1983

Ground-water resources in the Hood Basin, Oregon

The Hood Basin, an area of 1,035 square miles in north-central Oregon, includes the drainage basins of all tributaries of the Columbia River between Eagle Creek and Fifteenmile Creek. The physical characteristics and climate of the basin are diverse. The Wasco subarea, in the eastern half of the basin, has moderate relief, mostly intermittent streams, and semiarid climate. The Hood subarea, in the western half, has rugged topography, numerous perennial streams, and a humid climate. Water-bearing geologic units that underlie the basin include volcanic, volcaniclastic, and sedimentary rocks of Miocene to Holocene age, and unconsolidated surficial deposits of Pleistocene and Holocene age. The most important water-bearing unit, the Columbia River Basalt Group, underlies almost the entire basin. Total thickness probably exceeds 2,000 feet, but by 1980 only the upper 1,000 feet or less had been developed by wells. Wells in this unit generally yield from 15 to 1,000 gallons per minute and a few yield as much as 3,300 gallons per minute. The most productive aquifer in the Columbia River Basalt Group is The Dalles Ground Water Reservoir, a permeable zone of fractured basalt about 25 to 30 square miles in extent that underlies the city of The Dalles. During the late 1950's and mid-1960's, withdrawals of 15,000 acre-feet per year or more caused water levels in the aquifer to decline sharply. Pumpage had diminished to about 5,000 acre-feet per year in 1979 and water levels have stabilized, indicating that ground water recharge and discharge, including the pumping, are in balance. The other principal geologic units in the basin have more limited areal distribution and less saturated thickness than the Columbia River Basalt Group. Generally, these units are capable of yielding from a few to a hundred gallons per minute to wells. Most of the ground water in the basin is chemically suitable for domestic, irrigation, or other uses. Some ground water has objectionable concentrations of iron (0.3 to 6.4 milligrams per liter) and manganese (0.05 to 1.2 milligrams per liter) or is moderately hard to very hard (60 to 260 milligrams per liter as CaCO 3 ). The principal use of ground water in the Hood Basin is for irrigation of crops, with an estimated withdrawal of 7,700 acre-feet in 1979. Additional ground-water withdrawals in 1979 were estimated as: Industrial, 2,600 acre-feet; public supply, 2,100 acre-feet; and domestic and stock supply, 200 acre-feet.

Oregon↗
USGS2005

Changes in ground-water levels in the Carlin Trend area, north-central Nevada, 1989-2003

Ground-water pumpage in support of gold mining activities, including mine dewatering, has resulted in water-level declines and rises in different parts of the Carlin Trend area in north-central Nevada. Total annual pumpage at the Gold Quarry, Carlin, Genesis, and Betze Mines has ranged from about 5,000 acre-feet in 1989 to almost 130,000 acre-feet in 1994 and 1998. Excess water from the mines is stored in the TS Ranch and Maggie Creek Reservoirs. Aquifers in the Carlin Trend area are comprised of carbonate rocks of Cambrian to Permian age and basin-fill deposits and interbedded volcanic rocks of Tertiary and Quaternary age. Since 1992, water levels in carbonate-rock aquifers near the Gold Quarry Mine have declined as much as 680 feet below an elongate area 12 miles long and 6 miles wide northwest and southeast from the mine. Since 1990, water levels have declined by more than 1,600 feet in the deepest part of the cone of depression at the Betze Mine. The area encompassed by the main part of the cone, which is 7 miles long by 4 miles wide, did not change much during 1993-2003, although its depth had doubled. Near both mines, the cones of depression are bounded by faults acting as barriers to ground-water flow. Water levels in the volcanic rocks of northern Boulder Flat began to rise soon after the TS Ranch Reservoir began filling in 1990 because of infiltration. Since 1990, the net water-level rise around the reservoir has been 50 feet or more over an area of about 2 square miles, and 20 feet or more over an area of about 60 square miles. Since 1992, water levels in basin-fill deposits in Boulder Flat have risen 5 feet or more over an estimated area of 20 square miles as a result of (1) use of water from the Betze Mine as a substitute for irrigation pumpage, (2) water from the TS Ranch Reservoir infiltrating volcanic rocks and then flowing southward into adjacent basin-fill deposits, (3) secondary recharge of water from the mine for irrigating about 10,000 acres, and (4) discharge from three new springs in northeastern Boulder Flat. Water-level declines in carbonate rocks near the Gold Quarry Mine have not affected water levels in overlying basin-fill deposits. Declines were no more than a few feet north and west of the mine because older basin-fill deposits at the base of the Carlin Formation consist of fine-grained poorly permeable sediments. Water levels rose 5 feet to more than 20 feet over an area of 6-7 square miles around the Maggie Creek Reservoir in response to infiltration. A few miles farther south, water levels rose as much as 5 feet over an area of 3 square miles as a combined result of the infiltration of irrigation water and flow of Maggie Creek into permeable volcanic rocks in the stream channel. An area of 1,900 acres about 10 miles north of Battle Mountain in the Clovers Area has been pumped for irrigation since the early 1970's. Since 1989, water levels have declined 5-15 feet over an area of 15 square miles.

Scientific Investigations Report↗
USGS1992

Simulation of ground-water flow in the Antlers aquifer in southeastern Oklahoma and northeastern Texas

The Antlers Sandstone of Early Cretaceous age occurs in all or parts of Atoka, Bryan, Carter, Choctaw, Johnston, Love, Marshall, McCurtain, and Pushmataha Counties, a 4,400-square-mile area in southeastern Oklahoma parallel to the Red River. The sandstone comprising the Antlers aquifer is exposed in the northern one-third of the area, and ground water in the outcrop area is unconfined. Younger Cretaceous rocks overlie the Antlers in the southern two thirds of the study area where the aquifer is confined. The Antlers extends in the subsurface south into Texas where it underlies all or parts of Bowie, Cooke, Fannin, Grayson, Lamar, and Red River Counties. An area of approximately 5,400 square miles in Texas is included in the study. The Antlers Sandstone consists of sand, clay, conglomerate, and limestone deposited on an erosional surface of Paleozoic rocks. Saturated thickness in the Antlers ranges from 0 feet at the updip limit to probably more than 2,000 feet, 25 to 30 miles south of the Red River. Simulated recharge to the Antlers based on model calibration ranges from 0.32 to about 0.96 inch per year. Base flow increases where streams cross the Antlers outcrop, indicating that the aquifer supplies much of the base flow. Pumpage rates for 1980 in excess of 35 million gallons per year per grid cell for public supply, irrigation, and industrial uses total 872 million gallons in the Oklahoma part of the Antlers and 5,228 million gallons in the Texas part of the Antlers. Ground-water flow in the Antlers aquifer was simulated using one active layer in a three-dimensional finite-difference mathematical model. Simulated aquifer hydraulic conductivity values range from 0.87 to 3.75 feet per day. A vertical hydraulic conductivity of 1.5x10-4 foot per day was specified for the younger confining unit at the start of the simulation. An average storage coefficient of 0.0005 was specified for the confined part of the aquifer; a specific yield of 0.17 was specified for the unconfined part. Because pumping from the Antlers is minimal, calibration under transient conditions was not possible. Consequently, the head changes resulting from projection simulations in this study are estimates only. Volumetric results of the six projection simulations from the years 1990 to 2040 indicate that the decrease in the volume of ground water in storage due to pumping approximately 9,700,000 acre-feet from 1970 to 2040 is less than 0.1 percent.

Water-Resources Investigations Report↗
USGS1941

Geology and ground-water resources of the Balmorhea area, western Texas

Balmorhea is the center of a thriving farming community, the lands of which are irrigated with water derived chiefly from large springs but partly from the storm flow of Toyah Creek. The storm flow of the creek and a part of the winter flow of the springs is stored in a reservoir near Balmorhea and used later to supplement the flow of the springs. The present investigation was made to determine the geologic and hydrologic relations of the springs, whether additional water can be obtained from wells, and what effect the withdrawal of large amounts of water from wells would have upon the discharge of the springs. Balmorhea is situated near the foot of the Davis and Barrilla Mountains and along the southwestern margin of the Toyah Basin. The mountains and adjacent basin are drained by Toyah and Limpia Creeks. The group of springs around Balmorhea occur in the floor of the valley of Toyah Creek. They have been divided into artesian springs--Phantom Lake, Giffin and San Solomon Springs; and gravity springs--Toyah Creek, Saragosa, East Sandia and West Sandia Springs. The combined discharge of the springs during dry years is about 23,000 gallons a minute, of which amount the artesian springs supply more than 90 percent. The underground reservoir which supplies the artesian springs is the fractured and cavernous Lower Cretaceous limestone. This limestone, about 500 feet thick, is underlain by impermeable rocks, probably of Permian age, and is overlain by impermeable Upper Cretaceous strata that have a maximum thickness of about 500 feet. These are in turn overlain in the mountains by Tertiary lava and on the plains by gravel and other surficial deposits. The Lower Cretaceous limestone is at the surface or covered by a thin layer of gravel in a belt that lies athwart the stream channels and extends from Gomez Peak southeastward along the foothills of the Davis Mountains. In this belt all the streams suffer heavy seepage losses. From this belt the limestone dips gently northeastward to the axis of a northwestward-trending syncline and then rises to the surface in the vicinity of Phantom Lake, where a part of the water is discharged. About 1,000 feet northeast of this lake is a northwestward-trending fault of small displacement, on the northeast side of which the limestone is downthrown, northeastward from this fault the limestone rises gently and appears at the surface about a mile to the northeast, where it is again downfaulted, but the throw is not sufficient to affect the movement of the water. For several miles to the north the water-bearing Lower Cretaceous limestone is covered by 400 to 500 feet of impermeable Upper Cretaceous strata. It is believed that the Lower Cretaceous rocks are again near the surface and covered by only a thin mantle of gravel and other surficial deposits at San Solomon and Giffin Springs and that just northeast of the springs a fault crosses the valley along which the impermeable Upper Cretaceous rocks are faulted into a position opposite the Lower Cretaceous rocks, thus obstructing further northward movement of the water in the Lower Cretaceous limestone and forcing it to issue as large springs. Between this fault and Brogada the Lower Cretaceous rocks are believed to lie at a depth of about 500 feet and are overlain by Upper Cretaceous strata and a blanket of gravel and other surficial deposits, which are the source of the water of Toyah Creek, Sandia, and Saragosa Springs. Northeast of Brogada the Lower Cretaceous lies at a greater depth, and the mantle of gravel is much thicker. Wells put down to the limestone in the vicinity of San Solomon and Giffin Springs would decrease the flow of the springs. The effect of wells in limestone between the fault near these springs and the Brogado Hills on the flow of the springs would depend on the completeness with which the fault cuts off northward movement of ground water in the limestone. If the movement of water across the fault has been prev

Water Supply Paper↗
USGS2026

Evaluation of water quality in the Langford Valley–Irwin Groundwater Subbasin, Fort Irwin National Training Center, California, 1993–2019

The U.S. Army Fort Irwin National Training Center (NTC), 120 miles northeast of Los Angeles in the Mojave Desert of California, obtains its potable water supply from the Bicycle Valley and Langford Valley groundwater basins; Langford Valley groundwater basin is further subdivided into the Langford Well Lake and Irwin groundwater subbasins. The Irwin groundwater subbasin contains younger, unconsolidated deposits that have a saturated thickness of as much as 200 feet (ft) and a lower aquifer within older unconsolidated deposits as thick as 650 ft. Groundwater recharge under predevelopment conditions (before 1941) occurred primarily from infiltration of intermittent streamflow in small washes that cross the Irwin groundwater subbasin. Since that time, groundwater recharge has increased because of growth of the NTC in recent years and as a result of other processes, including (1) infiltration of treated wastewater into the aquifer through ponds near the NTC wastewater treatment facility (WWTF) and (2) infiltration of imported water and treated wastewater used for landscape irrigation at base housing and athletic fields. Water samples were collected from 17 wells and analyzed for field parameters, chemical constituents, and isotope composition in the Irwin groundwater subbasin between 2014 and 2019. These data were supplemented with water-chemistry data collected during 1993–95 and at other times if available. Between 1993–95 and 2015–19, median dissolved solids and nitrate concentrations in water from wells in the Irwin groundwater subbasin increased from 620 to 1,030 milligrams per liter (mg/L) and from 2.8 to 4.5 mg/L as nitrogen, respectively. After 2014, dissolved solids and nitrate concentrations in water from wells near the NTC WWTF decreased as a result of changes in source water quality attributable to reverse osmosis of treated drinking water delivered within the Irwin groundwater subbasin and to increased levels of treatment at the NTC WWTF. Based on delta oxygen-18 and delta deuterium isotope data, increases in dissolved solids concentrations in water from most wells were consistent with evaporation prior to recharge and mobilization of soluble salts from the unsaturated zone. Arsenic and fluoride concentrations in water from wells decreased between 1993–95 and 2015–19 as the basin filled with treated wastewater, but 2015–19 concentrations generally exceeded the California State Water Resources Control Board maximum contaminant levels of 10 micrograms per liter for arsenic and 2 mg/L for fluoride. Most groundwater in the Irwin groundwater subbasin has unadjusted carbon-14 ages ranging from 18,400 to 12,350 years before present. However, water from well 10E3, located along the wash near the subbasin outflow in the southeastern part of the Irwin groundwater subbasin, contained measurable tritium, which is consistent with infiltration of intermittent streamflow and groundwater recharge from the wash after 1952. Chemical and isotopic data indicate that treated wastewater is present in water from most wells in the upper aquifer that underlies the Irwin groundwater subbasin. Wells were not sampled to adequately determine the extent of treated wastewater and changes in water quality within the lower aquifer that underlies the Irwin groundwater subbasin.

California↗
USGS1964

Geology and ground-water resources of Washington, D.C., and vicinity, with a section on chemical quality of the water

The area of this report includes 436 square miles centered about the District of Columbia. The area contains parts of two distinctly different physiographic provinces-the Piedmont and the Coastal Plain. The Fall Line, which separates the Piedmont province on the west from the Coastal Plain Province on the east, bisects the area diagonally from northeast to southwest. Northwest of the Fall Line, deeply weathered igneous and metamorphic rocks are exposed ; to the southeast, these rocks are covered by Coastal Plain sediments; the nonconformity between crystalline rock and sediments dips southeast at an average rate of about 125 feet per mile. The rocks of the Piedmont include: (1) schist, phyllite, and quartzite of the Wissahickon Formation; (2) altered mafic rocks such as greenstone and serpentine; (3) the Laurel Gneiss of Chapman, 1942, and the Sykesville Formation of Jonas, 1928--both probably derived from the Wissahickon ; and (4) later granitic intrusive rocks. Lying upon this basement of hard rocks east of the Fall Line are the generally unconsolidated sediments of the Coastal Plain, which include gravel, sand, and clay, ranging in age from Cretaceous to Recent. These sediments measure only a few inches at their western extremity but thicken to 1,800 feet at the southeast corner of the mapped area. Owing to the great diversity in the geology of the two provinces, the waterbearing characteristics of the rocks also vary greatly. In the Piedmont, ground water occurs under unconfined or water-table conditions in openings and fissures in the hard rocks or in the residual weathered blanket that overlies them. In the Coastal Plain, the shallow wells tap unconfined water, but beneath the upper clay layers the water is contained in the sand and gravel under artesian pressure and must be recovered by deep drilled wells. Wells are of three types--drilled, bored, and dug. Drilled wells furnish a permanent water supply and are the least subject to pollution when properly constructed. Bored or dug wells allow greater storage capacity and are satisfactory for domestic supplies in some locations, but they are polluted easily. If not properly constructed or of sufficient depth, they may fail in dry weather. Ground-water supplies for domestic use, 5 to 10 gpm (gallons per minute), are obtainable in most places. In the Piedmont, recorded yields in drilled wells range from 0.2 to 212 gpm. In the Coastal Plain, wells yield from 1 to 800 gpm. The quality of the ground water in the report area is generally satisfactory for domestic, industrial, and irrigation use. High iron content and corrosiveness are troublesome in places. The water is soft to moderately hard--2 to 175 ppm (parts per million). Water in the Piedmont province is. dominantly the calcium and bicarbonate type; in the Coastal Plain most water is of calcium-magnesium bicarbonate type. In the Piedmont, careful location of wells with respect to the geology (rock type and structure) and to topography usually results in higher yields and may mean the difference between success and failure. In the Coastal Plain, drilled artesian wells are not affected by topography, but the yield obtained depends upon the penetration of a water-bearing sand or gravel bed at sufficient depth. The early settlers obtained water from the springs and streams, and later from dug wells. After Washington was established as the Capital in 1800, water was obtained from public and privately owned wells. Water was piped from some of the springs to government buildings and to private homes and business houses. In 1863 a diversion dam was completed in the Potomac above Great Falls and a conduit was built into the city to furnish a public water supply. This system with modifications has been in use ever since. A new diversion dam and pumping station at Little Falls was put into service in the summer of 1959.

District of Columbia↗