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H. E. LeGrand

Publications and source records attributed to H. E. LeGrand.

15 recordsLinked to original sources
USGS2006

Environmental framework of ground‐water contamination

Ramifications of contamination are increasingly involved in the majority of ground‐water problems. The volume of usable ground water is shrinking in many places because of dispersion of contaminated water . Consideration of ground‐water contamination as a multitude of independent problems, separately solvable as each problem arises, is outmoded; wise policies, relating water supply to contamination potential, are needed to alleviate and to forestall problems. Methodology of managing contamination problems calls for appropriate classification of the hydrogeologic environment; these classifications include aspects of interdependent factors such as permeability, sorption, hydraulic gradient, position of water table relative to some base, and distance from source of contamination . Effective evaluations relate the dynamics of the hydrogeologic environment to contingencies involving contamination , as man changes his water ‐development and waste‐disposal practices. Ways of contamination and pertinent parts of the physical environment include: waste‐disposal practices (at or near land surface and in deep formations), artificial recharge (at land surface and in aquifers), accidents, and salt‐ water contamination of aquifers (shallow depth from salty surface water and at variable depths from subjacent salty aquifers). Evaluation of waste‐disposal problems calls for appreciation of two opposing tendencies–the tendency of wastes to move with ground water and the tendency to be attenuated near disposal sites by decay or inherent decrease in potency, by chemical and physical sorption, and by dilution through dispersion of ground water . Mixed wastes of differing attenuation habits represent special complex problems.

Groundwater↗
USGS2006

Monitoring of changes in quality of ground water

Ground water of acceptable quality is commonly interspersed with water of inferior quality. Water of inferior quality may be naturally occurring salty water commonly underlying fresh water, or it may be enclaves of contaminated water from wastes that lie in the fresh-water bodies. Disposal of wastes on and in the ground and pumping of water from wells cause a dispersion of contaminated water; migration of contaminated water toward wells may be spontaneously induced by the natural hydraulic gradient, or it may be induced artificially by the cone of depression about one or more wells. Economic methods of determining precisely the boundary zones between contaminated and uncontaminated water are not available. Much reliance is placed on monitoring wells. A prerequisite to monitoring is a synthetic hydrogeologic framework or model in which the behavior of the contaminated water is conceived. Such a conceptual model, using pertinent data that are available, helps to assess the need for monitoring and to guide a monitoring program for optimum results. Unplanned, indiscriminate monitoring of water from wells is expensive, inefficient, and fallible. The need for monitoring will increase in the future; yet, the proper objective is to improve the technology of determining the distribution of contaminated water so that monitoring can be minimized and conducted with optimum results.

Groundwater↗
USGS2006

Water levels in carbonate rock terranes

Many subtle aspects of water levels in carbonate rocks need to be put in perspective even though hydrologists have recognized the fundamental value of characteristics of ground-water levels. The depth to the water table in carbonate rocks is controlled by local factors such as permeability and topography and by the regional factor of climate; both permeability and topography are dynamically developed according to the degree of preferential circulation of subsurface water and of solution of the rock, and the water table responds by lying deep beneath hilly permeable karstlands and shallow beneath flat and poorly permeable carbonate rocks. The uneven distribution of permeability and of topographic conditions is responsible for the intriguing karst phenomena of disappearing and reappearing surface streams. Great infiltration capacities of some karst regions result in large local fluctuations of the water table and in some cases to local reversals in direction of ground-water flow between wet and dry seasons. Water-level behavior in space and time is a primary consideration for interpreting the hydrology of carbonate terranes.

Groundwater↗
USGS1973

Karst hydrology: A review

Karst regions of the world are characterized by limestones and other soluble rocks at or near land surface that have been modified by solutional erosion. Such surface features as sinks, long dry valleys, sparse streams, and bare rock and such subsurface features as caverns, arterial solution openings leading to large springs, and a deep water table are typical of karst terranes. These features result in an uneven distribution of permeability in karst systems and surface and subsurface hydrologic conditions that require special hydrogeologic studies. Local high permeability at shallow depth in mature karst regions leads to an ecology associated with a soilless and water-scarce surface environment. Many practical problems result from this high permeability, including: (1) scarcity and poor predictability of groundwater supplies; (2) scarcity of surface-water supplies; (3) instability of the ground; (4) leakage of surface reservoirs; and (5) an unreliable waste-disposal environment. Interest in karst hydrology has increased greatly in the past decade; this interest has resulted in the international exchange of numerous published reports on local areas and on special topical karst problems. Many of these reports have been used by the authors in preparing this paper, which synthesizes results of many workers and focuses attention on: (1) the development of karst features through hydrologic processes; and (2) hydrologic systems of karst terranes.

Journal of Hydrology↗
USGS1973

Concepts of karst development in relation to interpretation of surface runoff

Some unusual characteristics of streamflow occur in regions underlain by carbonate rocks. The streamflow characteristics are related to processes of karstification, these processes being dependent on circulation of subsurface water and solution of the rock to form characteristic topography and underground cavern systems. Very highly cavernous and permeable unsaturated zones tend to keep the water table depressed below land surface in many karst regions, a condition that leads to a low density of perennial streams. The uneven distribution of permeability beneath surface karst streams causes them to lose or gain water, depending on the position of the water table with reference to stream level. The conventional techniques of interpolation and extrapolation that have been reasonably successful in approximating streamflow of ungaged sites in nonkarstic regions have only limited use in karst regions. An understanding of principles of karstification and an understanding of the hydrogeologic framework of a carbonate terrane provide a useful basis for evaluating the streamflow characteristics.

Journal of Research of the U.S. Geological Survey↗
USGS1971

Tertiary limestone aquifer system in the southeastern states

The hydrogeologic history of the Tertiary limestone system of the Southeastern States is reconstructed, especially as it relates to circulation of ground water and the development of solution cavities. The development of these solution cavities resembles in many respects the development of cavities in carbonates of the Knox Group of Tennessee during Middle Ordovician time, the cavities in the Knox having since been filled with collapse breccia that has been recemented. Some general principles of the circulation of water in limestone terranes and the related development of solution openings are reviewed so that a generic basis for comparison can be made of the modern southeast carbonate setting with the Ordovician carbonate setting in Tennessee.The major requirements for solutional development as cavities--(1) presence of highly soluble material, (2) a fracture system or some other form of incipient permeability, (3) water undersaturated with respect to soluble rocks, such as recharge from precipitation, and (4) hydraulic gradient--are found in the Tertiary limestone terrane of the southeast; much of the limestone has been elevated above sea level as a homoclinal seaward-dipping unit. Such a broad homoclinal setting, which also existed in the Knox at the close of early Ordovician time, facilitates extensive solutional development in the upper part of the zone of saturation. Circulation of water great enough to form a significant cavern network requires concentrated discharge areas, commonly as entrenched permanent streams or near-shore springs and seepage. This condition prevails where the Tertiary limestone is fairly close to land surface.Reconstruction of the geologic and hydrogeologic history of a carbonate region generally reveals the extent of early solution and karst development in relation to current karstification. Caverns, partly filled in some cases with loose or poorly cemented rock fragments that have fallen from cavern roofs, give evidence of karstification that is either current or that probably developed since the last marine inundation of the carbonate terrane. On the other hand, filling of caverns with overlying rock debris and reconstituting the debris into breccia are conditions that require evaluation of paleohydrology.

Alabama, Georgia, Florida, North Carolina, South C↗
USGS1971

Effects of karst features on circulation of water in carbonate rocks in coastal areas

The normal balance between fresh water in coastal aquifers and sea water applies also to carbonate-rock aquifers that have been karstified, but there are local modifications in the balance that need to be considered. Uneven distribution of permeability, expressed by a network of solution channels bounded by relatively impermeabler rock, causes an uneven distribution of head of the environmental water along the seacoast. Where sinkholes and (or) vertical solution shafts below sea level penetrate the aquifer, the fresh ground water may discharge through these karst features if the fresh-water head is greater than that of the salt water. However, under some conditions the salt-water head may exceed that of the fresh water, and the direction of movement is reversed as sea water flows into the aquifer. This sea-water flow into the aquifer occurs (1) where sinkholes, acting as “cased wells,” penetrate less permeable rock before reaching a lateral solution channel and (2) where (or when) the fresh-water head is less than that required to balance the salt water. On Andros Island, Bahamas, the range in tide (as much as 5 feet) from low tide to high tide is sufficient to cause such a reversal locally. During low tide the salt-water head becomes sufficiently low that the ground-water head exceeds that of the sea water, and the ground water flows through the sinkholes to the ocean floor; during high tide sea water flows in the sinkholes. In the Adriatic Sea along the coast of Yugoslavia, apparently the fresh-water head is sufficient to produce perennial springs in some localities, but in other areas, as in the Bay of Kastela near Split, the fresh-water head becomes low enough during some seasons that the flow is reversed and salt water enters the aquifer through the karst features. The development of sinkholes and other karst features near the present coast and extending below sea level occurred generally during a low stand of the Pleistocene sea when the top of the saturated zone stood lower than the bottom of the deepest sinkholes or natural wells. Integrated evaluations of (1) the distribution of permeability in coastal karst regions and (2) the principles relating to the dynamic balance between fresh aquifer water and sea water are leading to better knowledge of methods that may salvage much karst water which is lost to the sea.

Split↗
USGS1969

Hydrology of carbonate rock terranes — A review: With special reference to the United States

Limestone and other carbonate rocks are characterized by many unusual features and extreme conditions, either involving the hydrologic system within them or wrought by hydrologic conditions on them or through them. Perhaps there could be little agreement as to what is typical or average for the many features of carbonate rocks, as indicated by the following conditions: bare rock and thin soils are common, but so are thick soils; very highly permeable limestones are common, but so are poorly permeable ones; and rugged karst topographic features with underlying solution caverns are common, but so are flat, nearly featureless topographic conditions. Some conditions of carbonate terranes are suitable to man's needs and interests, such as the use of some permeable aquifers for water supply and the exploitation of caves for tourist attractions. On the other hand, many problems may exist, including: permeability too low for adequate water supply or so high that the aquifer retains too little water for use during periods of fair weather, soils too thin for growing of crops and for adequate filtration of wastes near the ground surface, instability of the ground for buildings and foundations in sinkhole areas, and unusually rugged topography. Some of the many variable conditions are readily observable, but others can be determined only by careful geologic and hydrologic studies. The need for knowing the specific geologic and hydrologic conditions at various places in limestone terranes, as well as the variations in hydrologic conditions with changing conditions and time, has resulted in many published reports on local areas and on special topical problems of limestone hydrology. Many of these reports have been used to advantage by the present writers in preparing this paper. The concept that secondary permeability is developed by circulation of water through openings with the accompanying enlargement of these openings by solution is now universally accepted in limestone terranes. Emphasis is placed on the hydrogeologic framework, or structural setting, in relation to the ease or difficulty of water to move from a source of recharge, through a part of the limestone, to a discharge area. Parts of the limestone favored by circulating ground water tend to develop solution openings, commonly in the upper part of the zone of saturation; as base level is lowered (sea level or perennial stream level), the related water table lowers in the limestone leaving air-filled caverns above the present zone of saturation in sinkhole areas. Reconstruction of the geologic and hydrologic history of a limestone area aids in determining the extent of development and the positions of fossil and present permeability. References are made to the hydrology of many limestone regions, especially those of the United States.

Journal of Hydrology↗
USGS1969

Relation of sea water to fresh water in carbonate rocks in coastal areas, with special reference to Florida, U.S.A., and Cephalonia (Kephallinia), Greece

The principles controlling the equilibrium between the denser salty water and the lighter fresh water in coastal aquifers apply to carbonate as well as sand systems. However, under certain equilibrium conditions of fresh and salt water in parts of some carbonate aquifers unusual hydrologic phenomena result. Hydrologic conditions at Tarpon Springs, Florida, and Cephalonia, Greece, include deep vertical openings as sinkholes through a relatively impervious part of the aquifer system. In both cases the tops of the sinkholes or natural wells are exposed to sea water. At Tarpon Springs the dynamic equilibrium between salt water and fresh water fluctuates so that the flow of salt water from the spring to a lake 2 miles away is sometimes reversed. At Cephalonia, the head of fresh water does not exceed the head of salty water in the sinkholes; the flow of sea water into the aquifer, aided by a shallow channel from the sea, is continuous, and the water level in the sinkhole is continuously depressed below sea level. Both cases represent a partially confined U-tube system where water at the seaward, sinkhole end is denser than at the other end and where a low fresh-water head is less than the salt-water head.

Cephalonia, Florida↗
USGS1966

Hydrology of limestone terranes in the coastal plain of the Southeastern United States

T he very productive limestone aquifers of Tertiary and Quaternary age in the Coastal Plain of the Southeastern States contain a water-table circulation system where aquifers are at or near the land surface; the Tertiary limestone unit is a homoclinal artesian system confined beneath younger beds in coastal areas. The Tertiary limestone has a total thickness of several thousand feet and ranges in age from Paleocene to Pliocene. The part of the limestone that represents a hydrologic unit, as much as 1000 feet thick, ranges in age from middle Eocene to middle Miocene. That unit is the principal artesian aquifer in Florida and southeastern Georgia. It is also an aquifer, but of lesser importance, in South Carolina, North Carolina, and Alabama. In southeastern Florida the Quaternary limestone forms a shallow, although highly productive, aquifer. In general, the Tertiary formations dip gently toward the coast, except where the regional dip is interrupted by folds such as the Cape Fear arch, the Ocala uplift, and the Chattahoochee anticline, or by faults such as those on the Ocala uplift. A piezometric map showing the head of water in the principal artesian aquifer in Florida and southeastern Georgia reveals chief areas of recharge where limestone crops out in interstream areas and where sinkholes breach overlying beds; it reveals principal discharge areas in certain stream valleys, springs, and offshore. Lateral movement of the water in the limestone is generally controlled by the hydraulic gradient to the nearest discharge area. The movement may be either controlled by or independent of faults and folds; it may be along joints for short distances. Solution by downward movement of water in the zone of aeration to the water table has formed vertical tubular openings or shafts. Lateral movement of the water from areas of recharge to areas of discharge has formed caves and other solution channels, chiefly in the upper part of the zone of saturation. Since they were formed, some caves have been drowned, and others have been exposed in the zone of aeration as the water rose and fell, chiefly in Pleistocene time. The principal aquifer in Florida probably has caves and solution channels comparable in size and extent to those of Mammoth Cave, Kentucky; however, only a small percentage of these are above the water table at the present time. In a large part of the region the most noticeable change in chemical quality of the water in the limestone resulting from circulation of water is the freshening accompanying removal of salty water from the aquifer. Changes in sea level during Pleistocene time have raised and lowered the water table; thus the position of the upper part of the zone of saturation, in which conditions were most favorable for solution and for the formation of cavities, has changed repeatedly. At the lowest stand of the Pleistocene sea, it is conceivable that the water level in part of the limestone in north-central Florida was a few hundred feet lower than at present. The present pattern of solution openings probably was developed in Pleistocene time.

Southeastern United States↗
USGS1966

Development of permeability and storage in the tertiary limestones of the southeastern states, USA

Permeability and storage characteristics in the Tertiary limestone system of southern United States have developed progressively but non-uniformly as circulation of water and solution in the limestone have changed during the geologic and hydrologic history. The limestone formations, predominantly of Eocene age and subordinated of Oligocene and Miocene age, are widespread at and beneath the surface. They commonly dip gently seaward and are covered in coastal areas by Miocene to Recent clays and sands. Sinkholes and other karst features are common, but topographic relief is generally not great. Circulation of water under water-table conditions when the limestone was exposed to meteoric weathering, before middle Miocene time, resulted in development of secondary permeability as solution channels in near-surface parts of the limestone, Marine deposition of middle and late Miocene clays and later emergence converted part of the water-table circulation system to the present great artesian system. Later, Pleistocene changes in sea level caused changed in places where water discharged, which in turn caused changes in rates of circulation and changes in rates and positions of solution of limestone. Both present and past circulation of water have contributed to changes in permeability and storage of this limestone system.

Southeastern United States↗
USGS1962

Perspective on problems of hydrogeology

A trend toward increasing use of test drilling and subsurface exploration is resulting in a decreasing reliance on human experience in coping with problems in hydrogeology . Application of "observation and inference" and discreet abstraction of readily available data will solve more problems than is now realized.

Geological Society of America Bulletin↗
USGS1957

Water resources of the Yadkin-Pee Dee River basin, North Carolina

Sufficient water is available in the basin of the Yadkin and Pee Dee Rivers to meet present requirements and those for many years to come if water use increases at about the present rate. Data presented in this report show that the average annual streamflow from approximately 82 percent of the basin area during the 25-year period, 1929-53, was about 6,200 mgd, representing essentially the total available water supply. Comparison of the available water supply to the estimated withdrawal use (excluding water power) of both surface and ground water of 600 mgd indicates the relative utilization of the water resources of the basin at present. If proper pollution controls are observed and practiced so that water in the various streams may be reused several times, the potential water available is even greater than indicated by the above comparison. Preliminary studies indicate that the quantity of water now being withdrawn from ground-water reservoirs in the basin is only a fraction of the total that may be obtained from this source. Twenty-eight of the 64 municipalities having public water-supply systems use surface water; however, as the largest cities in the area use surface supplies, about 85 percent of the water used for public supplies is from surface sources. Of the 20 complete-record stream-gaging stations now in operation in this area 7 have been in operation for 24 years or longer. Periodic measurements of the rate of flow have been made at 31 additional sites on streams scattered widely over the basin. All available streamflow data including those for 1953 are summarized in either graphic or tabular form, or both. Because of the critically low flows occurring during the drought of 1954, several illustrations include data for 1954 and the early months of 1955 for comparison with the minima of previous years. Adequate water for domestic use is available from wells throughout the basin. The consolidated rocks of the Piedmont furnish water for small industries and for municipalities whose population is less than about 1,500. The yields of wells in rock range from less than 1 gpm to as much as 200 gpm with local, rather than regional, geologic factors controlling the yield. The average municipal well in consolidated rocks yields about 30 gpm. In contrast, the sands of the Coastal Plain, in the eastern part of the basin, furnish as much as 500 gpm to individual wells, and ground-water conditions are generally similar throughout that region. A cumulative deficiency in rainfall from 1953 to 1955, has caused ground-water levels to fall below the seasonal averages, but the decline is thought not to indicate a long-term trend. The most serious problem involving future use of ground water is the lack of knowledge of the characteristics of the ground-water provinces in the basin. Generally the chemical quality of the surface waters in the Yadkin-Pee Dee River basin is good. They are low in mineral matter and soft, although some of the surface water contains excessive quantities of iron. In some local areas the streams have been polluted by municipal and industrial wastes. During periods of high runoff many of the streams transport large quantities of suspended sediment. Tributary streams in the lower eastern part of the basin are highly colored because of drainage from swampy areas. Ground water from the consolidated rocks in the Piedmont region is more variable in quality than water from other areas in the basin. The dissolved solids in water from the consolidated rocks ranged from 26 to 1,480 ppm with a median of 109 ppm. Wells in the Cretaceous clay province normally yield slightly acid waters. The pH ranges from 4.7 to 7.7 with a median of 5.3. Generally ground water in this province is extremely soft and low in dissolved solids. Wells in the Cretaceous sand province yield a sodium bicarbonate type of water ranging in hardness from 2 to 130 ppm.

North Carolina, Virginia↗