Geology topics
Harry G. Rodis
Publications and source records attributed to Harry G. Rodis.
The shallow aquifer : a prime freshwater resource in eastern Palm Beach County, Florida
The shallow aquifer underlies all of Palm Beach County and is the source of almost all fresh-water supplies in the eastern part of the county. It consists of mixtures of sand, shell sandstone, and limestone. In this area the concentration of dissolved solids in the ground water usually does not exceed 500 milligrams per litre. A section of cavity-riddled limestone and other permeable rocks is located several miles inland and extends north to south almost the entire length of the county. This section yields up to 2,000 gallons per minute (130 litres per second) of water to large wells and offers an excellent potential for the development of future ground-water supplies. Sea-water intrusion into the shallow aquifer is a potential threat to several coastal well fields. The wells nearest the coast are most vulnerable.
Ground-water in the Teresina-Campo Maior area, Piaui, Brazil
The Teresina-Campo Maior area lies in a presently developing farming and grazing region near the margin of drought-prone northeast Brazil where irrigated farming offers the best potential for economic development. The area comprises 9,700 square kilometers largely of catinga-covered tabular uplands which are drained by the perennial Rio Parnatba. The climate is hot and humid most of the year but with distinct wet and dry seasons. Temperature extremes range from 20?C to 39?C and the annum rainfall averages 1,200 millimeters. The area's ground-water reservoir is contained chiefly in sandstone aquifers of six westward-dipping sedimentary rock formations, all part of the Maranhao sedimentary basin. The youngest of these formations, namely the Piaut (Pennsylvarian), Poti (Mississippian), Longa (Upper Devonian), and Cabecas (Middle Devoniar), contain the principal aquifers. Precipitation is the primary source of recharge to these aquifers and is more than sufficient to replenish current withdrawals from wells. Underlying the principal aquifers are the untapped Pimenteiras and Serra Grande Formations (both Lower Devonian) which in areas adjacent to the report area are moderately good to excellent water producers. These aquifers are recharged principally by lateral inflow from the east. Water also occurs in the alluvial deposits (Quaternary) underlying the flood plain of the Rio Parnatba but recurrent and uncontrolled flooding at present (1966) precludes their development. Of little economic importance, because they lie above the zone of saturation, are the thin erosional remnants of the Pastos Bons (Upper Triassic), Matuca, and Pedra de Fogo (both Permian) Formations. There are in the report area about 200 drilled wells most of which are pumped with power-driven engines. The wells range from 40 to 500 meters deep but most do not exceed 150 meters, and practically all are completed open hole. Yields range from 500 liters per day for 6-inch-diameter domestic wells to 240,000 liters per hour for 10-inch high-capacity municipal wells. Although there are many more dug wells than drilled wells, dug wells account for less than 1 percent of the current (1966) draft. The current annual withdrawal from the principal aquifers is approximately 5 million cubic meters of which almost half is used for municipal supply and the rest for rural household and irrigation uses. Additional water for public supply is available from aquifers now being pumped, and larger yields probably could be obtained from rural wells designed to take full advantage of the aquifer. Analyses of 28 samples show that the chemical quality of the water is well below the accepted limits of mineral concentration for most uses. Water from the Longa Formation averages 842 milligrams per liter in total dissolved solids and is more mineralized than that in the Piaul and Port Formations which contain water averaging less than 300 milligrams per liter. The water in the Piaui and Poti aquifers is the most suitable in the area for irrigation and has SAR values of C1-S1 and C2-S1. The quantities of water currently being used for irrigation are relatively small (600,000 cubic meters annually) but will increase substantially when intensive irrigation becomes a reality. Divisio de Hydrogeologia da Superintendancia do Desenvolvimento do Nordeste estimates that about 2,500 million cubic meters of water per year would be needed to irrigate about 250,000 hectares in the Teresina-Campo Maior area (about 25 percent of the total area). This goal, however, is not likely to be realized as the water requirement is five times the estimated natural recharge to the aquifers of the area. Most of the water-bearing formations in the report area have barely been tapped and can be developed a great deal more. In fact, the current annual withdrawal from the principal aquifers is less than 0.0025 percent of a conservative estimate of annual replenishment from rainfall. Additionally, only the
Ground-water resources of the Acu Valley, Rio Grande Norte, Brazil
The Acu Valley is the lower part of the Rio Piranhas valley in the northwestern part of the State of Rio Grande do Norte, Brazil. It begins where the Rio Piranhas leaves the crystalline Precambrian rocks to flow across the outcrop of sedimentary rocks. The area considered in this report extends northward for about 45 kilometers; it is terminated arbitrarily where encroachment by sea water has contaminated the aquifer and imparted a disagreeable saline taste to the water in it. The boundary was not determined in the field, however, for lack of special equipment. Part of the extensive uplands on either side of the valley are included. This makes the total area approximately 2,500 square kilometers. The largest town, Acu, had a population of about 8,000 in 1960. The area is considered to be part of the Drought Polygon of northeast Brazil because the precipitation, although averaging 448 millimeters annually at Acu, varies widely from year to year and often is deficient for many months. The precipitation has been supplemented by use of irrigation wells, but irrigated agriculture is not yet far advanced, and the quantities of water used in irrigation are small. Geologically, the area consists of basement crystalline rocks (Precambrian), a wedge of sedimentary rocks thickening northward (Cretaceous), and alluvial sediments constituting a narrow band in the bottom of the valley (Alluvium and terrace deposits). The crystalline rocks contain water mainly in fractures and, in general, are impermeable. The sedimentary rocks of Cretaceous age comprise two units: a thick but fine-grained sandstone grading upward into siltstone and shale (Acu Sandstone), and limestone and dolomite with an included shale zone (Jandaira Limestone). The sandstone especially and the limestone to a lesser degree are ground-water reservoirs of large capacity. The limestone has been tapped at several places, but the sandstone and its contained water are practically untested and, hence, imperfectly understood. The alluvium of the first terrace is the aquifer supplying most of the ground water being used in the area. Wells in the alluvium yield as much as S0,000 liters per hour. Larger yields probably could be obtained from wells designated to take full advantage of the aquifer. There are in the valley about 300 dug wells which are used for irrigation. Half of these are equipped with pumps and engines. The rest, together with about 500 drive-point wells, are equipped with manual or windmill-driven pumps. In addition to irrigation, the water is used in homes and for cattle. The quantities of water currently used in irrigation are relatively small, both per hectare and in the area as a whole, but .this will probably increase substantially when intensive irrigation becomes a reality. The annual pumpage from the alluvium, nearly constant since 1959, was about 2.5 million cubic meters in 1964, which is only about 90 cubic meters from each hectare-meter of saturated alluvium. This amount would lower the water table about 1 meter in 11 years, if there were no recharge. Actually, no such decline is likely to occur, because the recharge from precipitation alone is estimated to be more than enough to replace the water currently being pumped. Chemical analyses of eight samples show that the ground water in the alluvium is acceptable for most uses. The water in the Acu Sandstone and Jandazra Limestone is more mineralized than that in the alluvium and at some places, at least, is not acceptable for human consumption. The available chemical data on this water, however, are not adequate to judge fully the quality of the water in these formations. It is estimated that about .'22 million cubic meters of water would be needed annually if irrigation were extended to all the bottom land, which totals about 25,000 hectares. This amount is only one-fourth to one-half the estimated recharge from precipitation alone. The present rate of application of water is very low
Ground-water geology of Kordofan Province, Sudan
For much of Kordofan Province, surface-water supplies collected and stored in hafirs, fulas, and tebeldi trees are almost completely appropriated for present needs, and water from wells must serve as the base for future economic and cultural development. This report describes the results of a reconnaissance hydrogeologic investigation of the Province and the nature and distribution of the ground-water resources with respect to their availability for development. Kordofan Province, in central Sudan, lies within the White Nile-Nile River drainage basin. The land surface is largely a plain of low relief; jebels (hills) occur sporadically, and sandy soils are common in most areas except in the south where clayey soils predominate. Seasonal rainfall, ranging from less than 100 millimeters in the north to about 800 millimeters in the south, occurs almost entirely during the summer months, but little runoff ever reaches the Nile or White Nile Rivers. The rocks beneath the surficial depsits (Pleistocene to Recent) in the Province comprise the basement complex (Precambrian), Nawa Series (upper Paleozoic), Nubian Series (Mesozoic), laterite (lower to middle Tertiary), and the Umm Ruwaba Series (Pliocene to Pleistocene). Perennial ground-water supplies in the Province are found chiefly in five hydrologic units, each having distinct geologic or hydrologic characteristics. These units occur in Nubian or Umm Ruwaba strata or both, and the sandstone and conglomerate beds form the :principal aquifers. The water is generally under slight artesian head, and the upper surface of the zone of saturation ranges from about 50 meters to 160 meters below land surface. The surficial deposits and basement rocks are generally poor sources of ground water in most of the Province. Supplies from such sources are commonly temporary and may dissipate entirely during the dry season. Locally, however, perennial supplies are obtained from the surficial deposits and from the basement rocks. Generally, water from Nubian aquifers is satisfactory for most uses and is of better quality than that obtained from Umm Ruwaba aquifers. The relatively high mineralization of water from the Umm Ruwaba, especially in the eastern part of the Province, makes the water unsuitable for many municipal ad industrial uses. The water is generally usable, however, for domestic and livestock purposes. Some 175 drilled wells located at 75 water yards yield an average, of about 1,000 imperial gallons .per hour per well from Nubian or Umm Ruwaba. aquifers. Generally the water yards provide sufficient water for minimum domestic and livestock requirements throughout the year. Commonly, however, the water yards are widely separated and, hence, not always properly spaced for good range management or for serving the needs of the dispersed rural population. In 1962, withdrawals from Nubian and Umm Ruwaba aquifers in the Province were approximately 600 million gallons annually. This rate of draft: could probably be continued almost indefinitely without significant depletion of the water supply. Nubian and Umm Ruwaba aquifers in the southwestern part of Kordofan offer excellent potential for future development. Nubian aquifers in northern Kordofan need extensive exploration by test drilling before their economic potential can be properly evaluated.
Geology and occurrence of ground water in Lyon County, Minnesota
Lyon County is in southwestern Minnesota, mostly within the drainage basin of the Minnesota River. The basement rocks in the area consist largely of Precambrian granite and quartzite. These are overlain locally by flat-lying Upper Cretaceous strata composed of thick sections of soft dark-bluish-gray shale and some thin beds of loosely consolidated sandstone. The Cretaceous strata are more than 500 feet thick near the center of the county but gradually pinch out toward the northeast and southwest against the highs of the Precambrian bedrock surface. Glacial drift overlies the Precambrian and Cretaceous rocks and forms the surface of the area. The drift consists largely of till and ranges in thickness from about 10 feet in the north and northeast to approximately 550 feet in the southwest. The most prominent surflcial glacial deposits are five southeast-trending end moraines, two of which are associated with, and parallel to, relatively extensive belts of outwash. Recent deposits averaging less than 20 feet in thickness overlie the glacial drift in stream valleys. The principal aquifers in Lyon County are glacial-melt-water deposits of sand and gravel, and sandstone of Cretaceous age. The underlying Precambrian rocks and the Recent alluvium are of only local importance as water sources. Melt-water deposits composed of stratified clay and silt as well as sand and gravel occur in channels having surficial expression, in buried channels having no direct surface expression, and as small isolated bodies within the till. Well logs of test holes show that the buried melt-water channels are generally parallel to the surflcial channels. However, melt-water deposits are not necessarily confined to the area beneath the surflcial channel but may extend laterally 1 mile or more beyond its limits. Sand and gravel are commonly interbedded with other melt-water materials. They range in thickness from 10 to 75 feet, are usually less than 1 mile in width, and may be as much as 8 miles in length. Although these aquifers are extensive, they underlie less than 10 percent of the county area. In most places, water from the drift is obtained from small isolated bodies of sand and gravel within the till. Water in the glacial drift is usually very hard (more than 500 parts per million) and low in chlorides (less than 50 parts per million). Drift wells generally yield from 2 to 30 gallons per minute; however, in areas where wells tap melt-water-channel deposits, sustained yields of as much as 500 gallons per minute are obtained. The sandstone beds of Cretaceous age occur between the Precambrian bedrock surface and an altitude of 825 feet as a basal sandstone, between altitudes of 890 and 1.020 feet, and between altitudes of 1,050 and 1,160 feet. Water-well data, supplemented by test drilling, show that each of these stratigraphic intervals is developed only in the county. The sandstone beds are of low permeability and are usually less than 2 feet thick, but they may be more than 20 feet thick in places. Water from these aquifers range in quality from soft (less than 60 parts per million) to very hard (more than 500 parts per million) and may contain excessive amounts of chloride (500 to 2,000 parts per million). Wells tapping rocks of Cretaceous age usually yield 2 to 7 gallons per minute, but in areas where the sandstone beds are thicker or hydrologically interrelated with aquifers of other geologic units, yields of as much as 75 gallons per minute have been obtained. Large quantities of ground water are available from melt-water channels in the county. Moderate quantities, adequate for domestic and small industrial needs, are available from many of the small isolated deposits of sand and gravel in the till. Small quantities of ground water, adequate only for domestic supply, generally can be obtained from Cretaceous sandstone.
Use of water-well data in interpreting occurrence of aquifers in northeastern Lyon County, Minnesota
In northeastern Lyon County the areal distribution of aquifers of Cretaceous age determined from well-bottom altitudes suggests a series of interbedded sandstones striking northwestward and overlapping one another to the northeast. Probably the numerous thin sandstone aquifers in the area were deposited near the flanks of a Precambrian granite “high” area by a transgressing Late Cretaceous sea.
Availability of ground water in Lyon County, Minnesota
Lyon County is in southwestern Minnesota, about 150 miles southwest of Minneapolis and St. Paul The basement rocks in the area consist of granite and quartzite of Precambrian age. These materials are in turn overlain by shale and sandstone of Cretaceous age, glacial drift of Pleistocene age, and alluvium of Recent age. Ground water is available primarily from aquifers in Pleistocene and Cretaceous strata from depths ranging from 15 to 500 feet below the land surface. The county is divided into areas of ground-water availability based on the quality and quantity of ground water available from the different geologic units. The glacial drift which covers all of the area, yields very hard water from sands and gravels occurring in melt-water channel deposits or as small, isolated melt-water bodies. Wells in the drift commonly yield from 2 to 30 gpm (gallons per minute), but sustained yields of as much as 500 gpm are obtained in areas where thick melt-water channel deposits occur. Cretaceous strata underlie about two-thirds of the county and yield water from poorly consolidated sandstone, The water ranges in hardness from soft to very hard and is sometimes high in chloride content. Wells in Cretaceous strata commonly yield from 2 to 7 gpm; however, in areas where the sandstone is in contact with the underlying weathered granite, sustained yields of as much as 75 gpm are obtained. The geographic and stratigraphic distribution of the geologic units suggests that additional water supplies may be available from Pleistocene and Cretaceous strata in areas not yet fully explored.
Aquifers in melt-water channels along the southwest flank of the Des Moines Lobe, Lyon County, Minnesota
During the Gary and Mankato substages of Wisconsin glaciation the Des Moines lobe advanced southeastward through the broad lowland of the Minnesota River valley of southwestern Minnesota, and thence southward to central Iowa. Among the most prominent topographic features in Lyon County, Minn., are five southeastward-trending end moraines, two of which are associated with and parallel to belts of surficial outwash that are approximately half a mile to a mile wide. Test drilling indicated that one of the belts of outwash is underlain by a complex system of buried melt-water channels. The other is the upper part of a series of deposits in an incised channel. The channels are filled with till, glaciolacustrine deposits, and outwash, which includes permeable deposits of water-bearing sand and gravel. Associated with the surficial melt-water channels is a pronounced southeastward-trending linear drainage pattern. By studying the lineation of streams and lakes, analyzing the available water-well data, and drilling test holes, several elongate deposits of buried outwash having little or no topographic expression were located. The long axes of the deposits are generally parallel to the lineation of the drainage and the end moraines. The melt-water channels in Lyon County trend southeastward because the flank of the ice sheet was confined by a landmass that sloped to the northeast. Similar buried channels may be present elsewhere along the southwest flank of the Des Moines lobe. If so, they probably can be located by the methods described.
Occurrence of ground waters of low hardness and of high chloride content in Lyon County, Minnesota
The ground water in Lyon County and elsewhere in southwestern Minnesota is generally hard and low in chloride. It is the purpose of this report to describe briefly the occurrence in Lyon County of waters of low hardness and of high chloride content. The waters are found largely in Cretaceous sandstone. The data were collected in conjunction with a countywide study of the geology and groundwater resources that is being made as part of a statewide investigation in cooperation with the Division of Waters, Minnesota Department of Conservation. The work is under the direct supervision of the junior author, who is district geologist for Minnesota. Hardness and chloride determinations were made with field-testing kits at the time data were obtained on most of the farm wells in the county. Tests were made on wells that were reported to yield relatively soft or "salty" water.