Geology, structure, and thickness of hydrogeologic units in part of the Columbia Plateau, Oregon
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Geology topics
Publications and source records attributed to Joseph B. Gonthier.
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The Dallas-Monmouth area is in the west-central Willamette Valley of western Oregon. It comprises a total of about 400 square miles in Polk, Benton, and Marion Counties. Tertiary consolidated rocks underlie the entire area. These rocks include marine sandstone, siltstone, shale, tuff, basalt, and gabbro. In the lowlands, the consolidated rocks are overlain by unconsolidated deposits of clay, silt, sand, and gravel which reach a maximum thickness of about 125 feet locally. The consolidated rocks generally are poor water-bearing formations and yield only small quantities of ground water to wells. From 1956 to 1976, about 6 percent of all wells completed in basalt and 14 percent of those completed in marine sedimentary rocks were reported to be "dry holes." The median yield of wells completed in the consolidated rocks was less than 10 gallons per minute, and the maximum reported yield was 200 gallons per minute. Shallow ground water in the consolidated rocks is generally of good quality, but with increasing depth in these rocks the water contains increasing concentrations of dissolved minerals. It is estimated that about 5 percent of all the wells completed in the consolidated rocks yield poor-quality water. The best water-bearing units are sand-and-gravel beds in the unconsolidated deposits. Near Independence, the sand-and-gravel beds are hydraulically continuous and exceed a saturated thickness of 10 feet over an area covering several tens of square miles chiefly within the Willamette River flood plain. Properly constructed wells in these deposits can generally obtain yields of 100 to 500 gallons per minute, and large quantities of additional ground water can be developed from this source. Outside the above area, sand-and-gravel beds generally are less than 10 feet thick, lenticular in shape, local in extent, and generally yield less than 30 gallons per minute to wells. Sand-and-gravel beds probably are absent in the Baskett Slough drainage basin, in the E. E. Wilson Wildlife Management area, and in the Luckiamute and Little Luckiamute River valleys upstream from the U.S. Highway 99W bridge.
Appraisals of the resources of selected management areas in eastern Oregon are being made by the U.S. Bureau of Land Management. To provide needed hydrologic information the Bureau of Land Management requested the U.S. Geological Survey Water Resources Division to inventory ground-water data for the Drewsey Resource Area. Included in this report are well data, drillers ' lithologic logs, hydrographs, a summary of observation-well data, and chemical analyses of ground water. (Woodard-USGS)
Water resources of the Umatilla Indian Reservation are poorly distributed both geographically and in time. On the reservation, only the Umatilla River and one of its principal tributaries, Meacham Creek, have significant perennial flows. Runoff of the principal streams is largely from snowmelt in the Blue Mountains and is highly variable. The principal aquifers are the Columbia River Basalt Group and the Quaternary alluvium. The basalt underlies the entire reservation to a depth of a few thousand feet, and most wells tap this source. The Quaternary alluvium is present only in the valleys of the principal streams. The alluvium averages about 12 feet (ft) in thickness in the Umatilla River valley, where it has the greatest extent; elsewhere it is generally thinner. Surface-water outflow from the reservation averages about 600 cubic feet per second (ft 3 /s), and the total stream inflow is about 540 ft 3 /s. About 480 ft 3 /s of the outflow is in the Umatilla River, 106 ft 3 /s is in McKay Creek, and 14 ft 3 /s is in other streams. Dependable streamflow, defined here as the 7-day mean low flow that will occur once every 50 years, on the average, is 30 ft 3 /s in Umatilla River above Meacham Creek near Gibbon, 5 ft 3 /s in Meacham Creek below Line Creek at the east boundary, 33 ft 3 /s in Umatilla River at Cayuse, and 14 ft 3 /s in Umatilla River at Pendleton. Monthly mean flows in Umatilla River above Meacham Creek near Gibbon in summer and fall frequently are less than the published recommended minimum flows for spawning and rearing of trout; in the reach of the Umatilla River near Pendleton the summer and fall flows generally are below those recommended minimum flows. Wells in the Columbia River Basalt Group range in depth from a few to 1,910 ft, and their yields range from less than 1 to more than 1,200 gallons per minute (gal/min). Small yields adequate for domestic needs can generally be obtained from the basalt. The depths required for successful wells may be extremely variable. Evaluation of specific-capacity data from wells in the basalt in four geographic areas suggests that the basalt is more permeable beneath the south reservation and the Umatilla River valley, that the permeability decreases on the north reservation, and that it is least in the Blue Mountains. Surface and ground waters generally are of good quality and suitable for most uses. Surface water is soft and generally contains less than 120 milligrams per liter (ug/L) of dissolved solids. Dissolved oxygen in streams is generally at or close to saturation levels at most stream temperatures and discharge rates. Ground water ranges from soft to very hard (28 to 280 mg/L), but it generally ranges between moderately hard to hard (61 to 180 mg/L). Dissolved solids in ground water range from 88 to 561 mg/L, but generally are between 200 and about 250 mg/L. During 1975, an estimated 11 million gallons per day (Mgal/d) of surface and ground water was withdrawn from the reservation for all uses. About 4 Mgal/d was from surface-water sources and 60 percent, or 7 Mgal/d, was from ground-water sources. About 7.2 Mgal/d was used for irrigation, 3.6 Mgal/d for public supply, and the remainder was for domestic and industrial use. About 4 Mgal/d, or 40 percent of the total water withdrawn, was for public supply and for irrigation use outside the reservation boundaries. Local seasonal declines of ground-water levels of 100 ft or more occur in shallow basalt wells in the Umatilla River valley between Mission and the west boundary. The declines are due chiefly to pumping from many small-capacity shallow wells in the basalt for irrigation of lawns and small acreages of pasture or hay. Future potential problems on the reservation include regional decline of ground-water levels in the basalt aquifer and local contamination of surface and ground water from accidental spills of deleterious substances.
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Good-quality water is available from the sand-and-gravel, Niagara, and sandstone aquifers in Waukesha County, Wis. As much as 15 gallons per minute (0.95 litres per second) can be obtained from wells almost everywhere in the county. Several hundred gallons per minute are available from aquifers in the glacial drift that fill bedrock valleys to thicknesses of 300 feet (91 metres) or more. Estimated well yields from much of the surficial outwash in western Waukesha County exceed 500 gallons per minute (31 litres per second). Estimated well yields from most of the Niagara aquifer, a dolomite as much as 325 feet (99 metres) thick in the eastern two-thirds of the county, exceed 50 gallons per minute (3.2 litres per second). The sandstone aquifer underlies the entire county and ranges in thickness from about 400 feet (120 metres) in the northwest corner to about 2,400 feet (730 metres) in the southeast corner. This aquifer yields more than 1,000 gallons per minute (63 litres per second) to wells over most of the county and is the principal source for municipal and subdivision water. Ground water in Waukesha County is of good quality and is suitable for most uses. Most of the water is a calcium magnesium bicarbonate type, is very hard [more than 180 mg/l (milligrams per litre) hardness], and requires softening for some uses. The ground water locally contains iron and manganese concentrations that exceed the limits (0.3 and 0.05 mg/l, respectively) recommended by the U.S. Public Health Service (1962, p. 7). Water high in sulfate and dissolved solids (saline water) is present locally in the Niagara and sandstone aquifers. Water from one well contained excessive nitrate (more than 45 mg/l). With one exception, wells sampled at irregular intervals indicated no significant changes in their chemical characteristics with time. About 24.3 million gallons per day (1.06 cubic metres per second) of ground water was pumped in the county in 1970. Sixty-two percent was withdrawn from the sandstone aquifer. More than one-half of the latter amount was for domestic use, and more than one-third was for industrial and commercial uses.
The lower Pawcatuck River basin in southwestern Rhode Island is an area of about 169 square miles underlain by crystalline bedrock over which lies a relatively thin mantle of glacial till and stratified drift. Stratified drift, consisting dominantly of sand and gravel, occurs in irregularly shaped linear deposits that are generally less than a mile wide and less than 125 feet thick; these deposits are found along the Pawcatuck River, its tributaries, and abandoned preglacial channels. Deposits of stratified sand and gravel constitute the principal aquifer in the lower Pawcatuck basin and the only one capable of sustaining yields of 100 gallons per minute or more to individual wells. Water available for development in this aquifer consists of water in storage--potential ground-water runoff to streams--plus infiltration that can be induced from streams. Minimum annual ground-water runoff from the sand and gravel aquifer is calculated to be at least 1.17 cubic feet per second per square mile, or 0.76 million gallons per day per square mile. Potential recharge by induced infiltration is estimated to range from about 250 to 600 gallons per day per linear foot of streambed for the principal streams. In most areas, induced infiltration from streams constitutes the major source of water potentially available for development by wells. Because subsurface hydraulic connection in the sand and gravel aquifer is poor in several places, the deposits are conveniently divisible into several ground-water reservoirs. The potential yield from five of the most promising ground-water reservoirs is evaluated by means of mathematical models. Results indicate that continuous withdrawals ranging from 1.3 to 10.3 million gallons per day, and totaling 31 million gallons per day, are obtainable from these reservoirs. Larger yields may be recovered by different well placement, spacing, construction and development, pumping practice, and so forth. Withdrawals at the rates indicated will reduce streamflow downstream from pumping centers but generally will not result in streams going dry, provided the water is returned to the basin. Export of water from the basin will require careful consideration of the effects of such withdrawals on low streamflow. Export from the Pawcatuck basin of 27 million gallons per day, estimated to be available from ground-water reservoirs in the upper Pawcatuck basin, in addition to 37.5 million gallons per day available in the lower Pawcatuck basin, will markedly reduce low streamflow. The 90-percent duration flow of the Pawcatuck River at Westerly would be reduced from 75 million gallons per day to perhaps as little as 21 million gallons per day. The chemical quality of water from both the sand and gravel aquifer and associated streams is suitable for most purposes. The water is soft, slightly acidic, and typically has a dissolved-solids content of less than 75 milligrams per liter. Some treatment may be required locally for removal of iron and manganese to meet recommended standards of the U.S. Public Health Service for drinking water.
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