Geology topics

Peter W. Bush

Publications and source records attributed to Peter W. Bush.

10 recordsLinked to original sources

USGS2000

Water quality in south-central Texas, Texas, 1996–98

This report summarizes major findings about water quality in south-central Texas that emerged from an assessment conducted between 1996 and 1998 by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Water quality is discussed in terms of local and regional issues and compared to conditions found in all 36 NAWQA study areas, called Study Units, assessed to date. Findings also are explained in the context of selected national benchmarks, such as those for drinking-water quality and the protection of aquatic organisms. The NAWQA Program was not intended to assess the quality of the Nation’s drinking water, such as by monitoring water from household taps. Rather, the assessments focus on the quality of the resource itself, thereby complementing many ongoing Federal, State, and local drinking-water monitoring programs. The comparisons made in this report to drinking-water standards and guidelines are only in the context of the available untreated resource. Finally, this report includes information about the status of aquatic communities and the condition of instream habitats as elements of a complete water-quality assessment. Many topics covered in this report reflect the concerns of officials of State and Federal agencies, water-resource managers, and members of stakeholder groups who provided advice and input during the assessment. Residents who wish to know more about water quality in the areas where they live will find this report informative as well.

Texas↗

USGS1996

Effects of low-flow diversions from the South Wichita River on downstream salinity of the South Wichita River, Lake Kemp, and the Wichita River, North Texas, October 1982-September 1992

In parts of the upper reaches of the Red River Basin in Texas, streamflow is characterized by levels of salinity that limit its usefulness for most purposes. Large dissolved solids and dissolved chloride concentrations are caused primarily by flow from natural salt springs in tributaries to the Red River. To reduce downstream salinity in the Wichita River, a dam in the South Wichita River downstream of an area of salt springs (designated salinity source area VIII) diverts low flows (which are the most saline) to a manmade brine lake for evaporation. Statistical tests on salinity data for the South Wichita River, Lake Kemp, and the Wichita River for the period October 1982–September 1992 were done to determine the effects on downstream salinity of low-flow diversions from the South Wichita River that began in May 1987. Salinity in the South Wichita River downstream of the low-flow diversion structure was (statistically) significantly less during the 65-month period of record after diversion than during the 55- month period of record before diversion. Wilcoxon rank-sum tests yielded strong evidence that discharge-weighted dissolved solids and dischargeweighted dissolved chloride concentrations, as well as discharge-weighted specific conductance, were significantly less after diversion. Whether salinity in Lake Kemp had a significant downward trend during the period of record August 1989–August 1992 could not be determined conclusively from observed salinity data. Mann-Kendall trend tests yielded weak evidence that volume-weighted dissolved solids and dissolved chloride concentrations in Lake Kemp tended to decrease with time. However, serial correlation in the time series of salinity data could have adversely affected the test results. The significant effects of low-flow diversions on salinity in the South Wichita River are not discernible in the Wichita River downstream from Lake Kemp. Although salinity was significantly less downstream from Lake Kemp after diversion, the decrease probably is mostly a result of dilution of Lake Kemp by large inflows of (assumed) low-salinity water that occurred in the spring of 1989 rather than an effect of diversion.

Texas↗

USGS1994

Dissolved-solids concentrations and hydrochemical facies in water of the Edwards-Trinity aquifer system, west-central Texas

Much of the Edwards-Trinity aquifer system contains freshwater, but sizable parts contain marginally fresh or slightly saline water. The predominant water type in the aquifer system is calcium bicarbonate; however, one of seven other hydrochemical facies characterizes the water in places. The median dissolved-solids concentration of water samples from the Edwards aquifer in the Balcones fault zone is 297 mg/L (milligrams per liter); the interquartile range is 93 mg/L. In the freshwater zone of the Edwards aquifer updip of a freshwater/saline-water transition zone, the water is almost exclusively calcium bicarbonate. The median dissolved-solids concentration of water samples from the Trinity aquifer in the Hill Country is 537 mg/L and the interquartile range is 573 mg/L. Four bicarbonate and sulfate facies, spread vertically throughout the saturated section, characterize most of the Hill Country analyses; calcium bicarbonate predominates. The median concentration of dissolved solids in water samples from the Edwards-Trinity aquifer in the Edwards Plateau is 379 mg/L and the interquartile range is 547 mg/L. Freshwater is nearly everywhere in the southern and northeastern parts of the aquifer, and mostly slightly saline water is in the northwestern part. The distribution of hydrochemical facies shows a similar pattern to dissolved-solids concentration, with bicarbonate water nearly everywhere in the southern and northeastern parts of the aquifer. Sulfate and chloride facies characterize the northwestern part of the Edwards Plateau. The median concentration of dissolved solids among water samples from the Edwards-Trinity aquifer in the Trans-Pecos is 929 mg/L and the interquartile range is 1,626 mg/L. Fresh, calcium bicarbonate water predominates in the southern part, and more saline mixed and sulfate waters are the most common in the northwestern part.

Texas↗

USGS1988

Simulation of saltwater movement in the Floridan aquifer system, Hilton Head Island, South Carolina

Freshwater to supply Hilton Head Island, S.C., is obtained from the upper permeable zone of the Upper Floridan aquifer. Long-term pumping at Savannah, Ga., and the steadily increasing pumping on Hilton Head Island, have lowered Upper Floridan heads near the center of the island from about 10 feet above sea level to about 6 to 7 feet below sea level. The seaward hydraulic gradient that existed before pumping began has been reversed, thus increasing the potential for saltwater intrusion. Simulations of predevelopment, recent, and future ground-water flow in the Floridan aquifer system beneath the north end of Hilton Head Island and Port Royal Sound are presented. A finite-element model for fluid-density-dependent ground-water flow and solute transport was used in cross section. The general configuration of the simulated predevelopment flowfield is typical of a coastal aquifer having a seaward gradient in the freshwater. The freshwater flows toward Port Royal Sound over an intruding wedge of saltwater. The simulated flowfield at the end of 1983 shows that ground water in the Floridan aquifer system beneath most of Hilton Head Island has reversed its predevelopment direction and is moving toward Savannah. The distribution of chloride concentrations, based on simulation at the end of 1983, is about the same as the predevelopment distribution of chloride concentrations obtained from simulation. Results of two 50-year simulations from 1983 to 2034 suggest that there will be no significant threat of saltwater intrusion into the upper permeable zone of the Upper Floridan aquifer if heads on Hilton Head Island remain at current levels for the next 45 to 50 years. However, if head decline continues at the historical rate, any flow that presently occurs from the north end of the island toward Port Royal Sound will cease, allowing lateral intrusion of saltwater to proceed. Even under these conditions, chloride concentrations in the upper permeable zone of the Upper Floridan aquifer beneath Hilton Head Island should remain below 250 milligrams per liter for the next 45 to 50 years. Aquifer properties and selected boundary conditions were tested with several 1,000-year simulations which show that lateral permeability, transverse dispersivity, and landward boundary flow have the most influence on saltwater movement in the Upper Floridan aquifer.

South Carolina↗

USGS1986

Planning report for the Edwards-Trinity Regional Aquifer-System analysis in central Texas, southeast Oklahoma, and southwest Arkansas

The Edwards-Trinity regional aquifer system supplies more than 0.78 million acre-feet per year (700 million gallons per day) of water for central Texas and small adjacent parts of southeast Oklahoma and southwest Arkansas. The system consists of three major aquifers and at least three minor aquifers in predominantly Cretaceous rocks, which together have an areal extent of about 80,000 square miles. The major aquifers are the Edwards-Trinity (Plateau) in west-central Texas, the Edwards (Balcones Fault Zone) in south-central Texas, and the Trinity in north-central Texas, southeast Oklahoma, and southwest Arkansas. Current (1986) and future concerns about the aquifer system involve the ever-increasing demand for water, most of which is associated with rapid population increase. Decreases in or elimination of spring discharges and encroachment of water from downdip salinewater zones into updip freshwater zones are of primary concern in the area underlain by ttie Edwards (Balcones Fault Zone) aquifer. Water-level declines of several hundred feet in the Trinity aquifer are a serious concern in some metropolitan areas. The Edwards-Trinity regional aquifer-system analysis project, begun in October 1985 and scheduled to be completed by October 1991, is one of a series of similar projects being conducted nationwide. The project is intended to define the hydrogeologic framework, and to describe the geochemistry and groundwater flow of the aquifer system in order to provide a better understanding of the system's long-term water-yielding potential. A multidisciplinary approach will be used in which computer-based digital simulation of flow in the system will be the principal method of hydrogeologic investigation.

Arkansas, Oklahoma, Texas↗

USGS1983

Connector well experiment to recharge the Floridan aquifer, east Orange County, Florida

An experimental connector well, screened in the shallow sand aquifer, finished with open hole in the Floridan aquifer and cased through the confining layer between the two aquifers, was drilled in east Orange County, Fla., to obtain information on the nature and function of the shallow aquifer as related to connector well operation. The potentiometric surface of the shallow aquifer is about 45 feet higher than the potentiomettic surface of the Floridan aquifer; hence water flows by gravity from the shallow aquifer to the Floridan aquifer through the well 'connecting' the two aquifers. Continuous flow measurement over 10 months shows the well discharge varies seasonally and averages slightly more than 50 gallons per minute. Observation wells show that, except for seasonal variation, water levels within the area of influence have reached steady state within measurable limits. Vertical anisotropy in the shallow aquifer is apparently caused by the shape and (or) arrangement of the sand grains that comprise the shallow aquifer, rather than because of distinct confining layers of different lithology. Transmissivity of the shallow aquifer at the site is about 600 square feet per clay. Extensive dewatering of wetlands in east Orange County by connector wells alone probably is not feasible. Nevertheless, large amounts of water could be channeled to the Floridan aquifer by connector wells. The results of the connector well experiment imply that water is being captured from evapotranspiration and interception of water that would have discharged to swamps in the vicinity of the connector well. However, the data available from this experiment do not permit a quantitative expression of the net gain in recharge to the Floridan aquifer resulting from operation of the connector well.

Water Supply Paper↗

USGS1982

Predevelopment flow in the Tertiary limestone aquifer, southeastern United States: A regional analysis from digital modeling

The Tertiary limestone aquifer of the southeastern United States is a sequence of carbonate rocks that underlies all of Florida, south Georgia, and adjacent parts of Alabama and South Carolina. It is the principal source of municipal, industrial, and agricultural water supply in south Georgia and most of Florida. The aquifer, known as the Floridan aquifer in Florida and the principal artesian aquifer in Georgia, Alabama, and South Carolina, includes various carbonate units of Paleocene to early Miocene age that are hydraulically connected in varying degrees. Very locally, in the Brunswick, Ga., area, a thin sequence of rocks of Late Cretaceous age is part of the system. In general the aquifer consists of either one vertically continuous permeable zone or two major permeable zones separated by a less permeable unit of highly variable water-transmitting characteristics. Aquifer conditions range from unconfined to confined depending upon whether the clayey Miocene and younger rocks that form the upper confining unit have been removed by erosion. Digital model simulation shows that prior to development, most flow in the aquifer occurred in the unconfined and thinly confined areas of northwest and central Florida and southwest Georgia. Springs in these areas are visible evidence of major flow activity. Spring discharge to streams accounted for about 90 percent of the average predevelopment discharge from the regional aquifer. About 18,100 cubic feet per second left the limestone aquifer as spring flow, and 2,500 cubic feet per second discharged as diffuse upward leakage from the confined areas where the vertical head gradient was upward. Most of the 20,600 cubic feet per second recharge necessary to balance total discharge entered the limestone aquifer in the unconfined and thinly confined areas. Because the areas of greatest recharge before development were near the areas of highest discharge, flow paths were generally short. Much water went into and out of the limestone quickly. A very active shallow flow system at the expense of deep circulation has evolved in unconfined and sligptly confined spring areas. Transmissivities commonly exceed 1,000,000 feet squared per day. In contrast, predevelopment flow in the aquifer in the tightly confined areas of southeast and coastal Georgia, far west Florida, and in south Florida was sluggish. In these areas the aquifer is overlain by several hundred feet of sand and clay, except for the outcrop areas along the updip limit of the aquifer. This thick overburden severely retards discharge from the aquifer, causing lethargic flow. Large-discharge springs are nonexistent. The south Florida and southeast Georgia segments of the flow system, which taken together occupy about 50 percent of the regional system, only accounted for slightly more than 3 percent of the predevelopment regional limestone discharge. Transmissivities are on the average lower (generally less than 250,000 feet squared per day) than those in areas of high-flow activity.

Alabama, Florida, Georgia↗

USGS1982

Summary of hydrologic testing in Tertiary limestone aquifer, Tenneco offshore exploratory well--Atlantic OCS, lease-block 427 (Jacksonville NH 17-5)

A summary of hydrologic testing in an offshore oil-test well (LB427) drilled for Tenneco, Inc., 55 miles east of Fernandina Beach, Florida, is presented. The interval tested (1,050 to 1,070 feet below sea level) is in a calcarenite that is equivalent to the Ocala Limestone (late Eocene) of onshore Florida and South Georgia. At this site the Ocala forms the highly productive Tertiary limestone aquifer system of the southeastern United States. Pressure-head measurements indicate an equivalent freshwater head of 24 to 29 feet above sea level. These pressure-head measurements and an earlier one made in the nearby JOIDES J- I hole are the only hydraulic head determinations to date in the offshore extensions of any of the aquifers underlying the Atlantic coastal plain. A drill-stem test recovered water samples containing about 7,000 milligrams per liter chloride. However, seawater used in the drilling process apparently contaminated the samples and the formation water is considered slightly fresher. The head and salinity data from the Tenneco well suggest that the sampled interval lies in the transition zone between fresh and seawater in the limestone aquifer. These data, when viewed with similar data from JOIDES J-I, show the transition zone to slope very slightly landward. The interface position is probably intermediate between a position compatible with present-day heads and a position compatible with predevelopment heads.

Water Supply Paper↗

USGS1980

Summary of hydrologic testing in Tertiary limestone aquifer, Tenneco offshore exploratory well-Atlantic OCS, lease block 427 (Jacksonville NH-17-5)

A summary of hydrologic testing in an offshore oil-test well drilled for Tenneco, Inc. 55 miles east of Fernandina Beach, Florida, is presented. The interval tested (1,050 to 1,070 feet below sea level) is in a calcarenite that is equivalent to the Ocala Limestone (late Eocene) of onshore Florida and South Georgia. At this site the Ocala forms the highly productive Tertiary limestone aquifer system of the southeastern United States. Pressure-head measurements indicate an equivalent freshwater head of 24 to 29 feet above sea level. These pressure-head measurements and an earlier one made in the nearby JOIDES J-1 hole are the only hydraulic head determinations to date in the offshore extensions of any of the aquifers underlying the Atlantic coastal plain. A drill-stem test recovered water samples containing about 7,000 milligrams per liter chloride. However, seawater used in the drilling process apparently contaminated the samples and the formation water is considered slightly fresher. The head and salinity data from the Tenneco well suggest that the sampled interval lies in the transition zone between fresh and seawater in the limestone aquifer. These data, when viewed with similar data from JOIDES J-1, show the transition zone to slope very slightly landward. Heads at both wells are compatible with the onshore flow system as it existed prior to development.

Florida↗

USGS1973

Salt-water movement in the lower Withlacoochee River-Cross Florida Barge Canal Complex

Construction of the west end of the Cross Florida Barge Canal changed the regimen of the lower Withlacoochee River. The investigation was made to determine how salt water from the Gulf of Mexico moves in the river-canal complex, and how the factors that control salt-water movement--tides and discharge--have changed since canal construction. In the river below the bypass channel, salt water moves inland as a wedge beneath the fresh water with upstream tidal flows and back toward the Gulf with downstream tidal flows. The salt front in the river tends to move farthest upstream near times of relatively high water, or higher high water preceded by relatively high higher low water, especially during of after several days of rising mean tide level.

Florida↗