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Research about Memphis, Tennessee

Source-linked reports with geographic coverage including Memphis, Tennessee.

At least 19 recordsLinked to original sources
USGS2025

The acoustic-Doppler current profiler (ADCP): A comprehensive tool for river-reach hydromorphodynamics

This paper introduces the use of acoustic Doppler current profiler (ADCP) measurements as input for the Acoustic Mapping Velocimetry (AMV) method, a technique for characterizing the dynamics of riverine bedforms. The performance of this new approach, ADCP-AMV, is compared with input from a multibeam echosounder through a field study conducted on the Mississippi River (USA). A virtual ADCP tool has been created to support the ADCP-AMV measurements with optimal data density predictions. To the authors’ knowledge, this is the first time ADCP measurements have been used in conjunction with the AMV dune-tracking method. Subsequently, the paper discusses the coupling of ADCP-AMV measurements with ancillary data extracted from the ADCP. These ancillary data are processed using previously developed protocols to characterize hydrodynamics and the suspended sediment distribution in the water column. This paper emphasizes the capability of ADCPs to characterize open-channel river hydromorphodynamic parameters with high spatiotemporal resolution. Recommendations to accurately and efficiently acquire these multi-variable measurements and derived datasets are discussed.

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USGS2018

Altitude of the potentiometric surface, 2000–15, and historical water-level changes in the Memphis aquifer in the Memphis area, Tennessee

The Memphis and Fort Pillow aquifers are the principal sources of water for municipal, industrial, and commercial uses in the Memphis area. About 207 million gallons per day of groundwater were withdrawn in Shelby County, Tennessee, from both aquifers in 2010 for these uses, with most of the water coming from the Memphis aquifer. The U.S. Geological Survey, in cooperation with the City of Memphis, Memphis Light, Gas and Water Division, collects groundwater-level data in the Memphis area and periodically prepares potentiometric-surface maps for the Memphis aquifer to assess conditions in this regionally important water supply aquifer. This report presents the altitudes of the potentiometric surface of water in wells screened in the Memphis aquifer based on water-level measurements made in the fall of 2000, 2005, 2010, and 2015 and describes historical water-level changes in the Memphis aquifer at key observation wells in the Memphis area. The Memphis area is about 1,500 square miles and includes all of Shelby County and parts of Tipton and Fayette Counties in Tennessee, parts of DeSoto and Marshall Counties in Mississippi, and part of Crittenden County in Arkansas.

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USGS2018

Preliminary evaluation of the hydrogeology and groundwater quality of the Mississippi River Valley alluvial aquifer and Memphis aquifer at the Tennessee Valley Authority Allen Power Plants, Memphis, Shelby County, Tennessee

The hydrogeology, groundwater quality, and potential for hydraulic connection between the Mississippi River Valley alluvial aquifer and the Memphis aquifer in the area of the Tennessee Valley Authority (TVA) Allen Combined Cycle and Allen Fossil Plants in southwestern Memphis, Tennessee, were evaluated from September through December 2017. The study was designed as a preliminary assessment of the potential for leakage of groundwater from the Mississippi River Valley alluvial aquifer through the underlying upper Claiborne confining unit into the underlying Memphis aquifer at the plants. A short-term aquifer test of four of the five Memphis aquifer production wells installed at the Allen Combined Cycle Plant induced drawdown in water levels in the Mississippi River Valley alluvial aquifer, locally. The largest drawdown occurred in the eastern and southeastern parts of the TVA plants area, and generally was coincident with locations where stratigraphic data show increased thickness of and depth to the base of the alluvium and decreased thickness and inferred offset in the base of the confining unit relative to nearby locations. In contrast, stratigraphic data for most other locations at the site indicate shallower depths to the base of the alluvium and more consistent thickness of and depth to the base of the confining unit, which corresponds with areas where less drawdown was observed during the test. Water-quality results for samples from the production wells and from monitoring wells screened in the Mississippi River Valley alluvial aquifer indicate that groundwater with higher dissolved-solids concentrations and tritium from this shallow aquifer has mixed with water in the upper part of the Memphis aquifer at one of the production wells. Results of the study collectively confirm that the Mississippi River Valley alluvial and Memphis aquifers are hydraulically connected near the TVA plants area.

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USGS2012

Real-time seismic monitoring of instrumented hospital buildings

In collaboration with the Department of Veterans Affairs (VA), the U.S. Geological Survey's National Strong Motion Project has recently installed sophisticated seismic monitoring systems to monitor the structural health of two hospital buildings at the Memphis VA Medical Center in Tennessee. The monitoring systems in the Bed Tower and Spinal Cord Injury buildings combine sensing technologies with an on-site computer to capture and analyze seismic performance of buildings in near-real time.

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USGS2003

Lithology and shear-wave velocity in Memphis, Tennessee

We have derived a new three-dimensional model of the lithologic structure beneath the city of Memphis , Tennessee , and examined its correlation with measured shear - wave velocity profiles. The correlation is sufficiently high that the better-constrained lithologic model may be used as a proxy for shear - wave velocities, which are required to calculate site-amplification for new seismic hazard maps for Memphis . The lithologic model and its uncertainties are derived from over 1200 newly compiled well and boring logs, some sampling to 500 m depth, and a moving-least-squares algorithm. Seventy-six new shear - wave velocity profiles have been measured and used for this study, most sampling to 30 m depth or less. All log and velocity observations are publicly available via new web sites.

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USGS2001

Hydrogeology and ground-water flow in the Memphis and Fort Pillow aquifers in the Memphis area, Tennessee

On the basis of known hydrogeology of the Memphis and Fort Pillow aquifers in the Memphis area, a three-layer, finite-difference numerical model was constructed and calibrated as the primary tool to refine understanding of flow in the aquifers. The model was calibrated and tested for accuracy in simulating measured heads for nine periods of transient flow from 1886-1985. Testing and sensitivity analyses indicated that the model accurately simulated observed heads areally as well as through time. The study indicates that the flow system is currently dominated by the distribution of pumping in relation to the distribution of areally variable confining units. Current withdrawal of about 200 million gallons per day has altered the prepumping flow paths, and effectively captured most of the water flowing through the aquifers. Ground-water flow is controlled by the altitude and location of sources of recharge and discharge, and by the hydraulic characteristics of the hydrogeologic units. Leakage between the Fort Pillow aquifer and Memphis aquifer, and between the Memphis aquifer and the water-table aquifers (alluvium and fluvial deposits) is a major component of the hydrologic budget. The study indicates that more than 50 percent of the water withdrawn from the Memphis aquifer in 1980 is derived from vertical leakage across confining units, and the leakage from the shallow aquifer (potential source of contamination) is not uniformly distributed. Simulated leakage was concentrated along the upper reaches of the Wolf and Loosahatchie Rivers, along the upper reaches of Nonconnah Creek, and the surficial aquifer of the Mississippi River alluvial plain. These simulations are supported by the geologic and geophysical evidence suggesting relatively thin or sandy confining units in these general locations. Because water from surficial aquifers is inferior in quality and more susceptible to contamination than water in the deeper aquifers, high rates of leakage to the Memphis aquifer may be cause for concern. A significant component of flow (12 percent) discharging from the Fort Pillow aquifer was calculated as upward leakage to the Memphis aquifer. This upward leakage was generally limited to areas near major pumping centers in the Memphis aquifer, where heads in the Memphis aquifer have been drawn significantly below heads in the Fort Pillow aquifer. Although the Fort Pillow aquifer is not capable of producing as much water as the Memphis aquifer for similar conditions, it is nonetheless a valuable resource throughout the area.

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USGS1997

Hydrogeologic framework and simulation of ground-water flow and travel time in the shallow aquifer system in the area of Naval Support Activity Memphis, Millington, Tennessee

Naval Support Activity (NSA) Memphis is a Department of the Navy facility located at the City of Millington, Tennessee, about 5 miles north of Memphis. Contaminants have been detected in surface-water, sediment, and ground-water samples collected at the facility. As part of the Installation Restoration Program, the Navy is considering remedial-action options to prevent or lessen the effect of ground-water contamination at the facility and to control the movement and discharge of contaminants. A numerical model of the ground-water-flow system in the area of NSA Memphis was constructed and calibrated so that quantifiable estimates could be made of ground-water-flow rates, direction, and time-of-travel. The sediments beneath NSA Memphis, to a depth of about 200 feet, form a shallow aquifer system. From youngest to oldest, the stratigraphic units that form the shallow aquifer system are alluvium, loess, fluvial deposits, and the Cockfield and Cook Mountain Formations. The shallow aquifer system is organized into five hydrogeologic units: (1) a confining unit composed of the relatively low permeability sediments of the upper alluvium and the loess; (2) the A1 aquifer comprising sand and gravel of the lower alluvium and the fluvial deposits, and sand lenses in the upper part of the preserved section of the Cockfield Formation; (3) a confining unit composed of clay and silt within the upper part of the Cockfield Formation; (4) the Cockfield aquifer comprising sand lenses within the lower part of the preserved section of the Cockfield Formation; and (5) a confining unit formed by low permeability sediments of the Cook Mountain Formation that composes the upper confining unit for the Memphis aquifer. Thicknesses of individual units vary considerably across the facility. Structural and depositional features that affect the occurrence of ground water in the shallow aquifer system include faulting, an erosional scarp, and 'windows' in the confining units. Underlying the shallow aquifer system is the Memphis aquifer, the primary source of water for NSA Memphis and the City of Memphis, Tennessee. Analyses of sediment cores, aquifer and well specific-capacity tests, and numerical modeling were used to estimate the hydraulic characteristics of units of the shallow aquifer system. The vertical hydraulic conductivity of core samples of the alluvium-loess confining unit ranged from about 8.5 x 10-5 to 1.6 x 10-2 feet per day, and the total porosity of the samples ranged from about 35 to 48 percent. The results of the aquifer test were used to estimate a horizontal hydraulic conductivity of about 5 feet per day for the alluvial-fluvial deposits aquifer. The total porosity of core samples of the alluvial-fluvial deposits aquifer ranged from about 22 to 39 percent. The vertical hydraulic conductivity of core samples of the Cockfield confining unit ranged from about 4.5 x 10-5 to 2.5 x 10-3 feet per day, and the total porosity ranged from about 41 to 55 percent. Well specific-capacity tests indicate that the horizontal hydraulic conductivity of sand units that compose the Cockfield aquifer range from about 0.5 to 3 feet per day. The vertical hydraulic conductivity of core samples of the Cook Mountain confining unit ranged from about 5.0 x 10-6 to 9.9 x 10-4 feet per day. Total porosity of core samples of the Cook Mountain confining unit ranged from about 30 to 42 percent. Ground-water flow and time-of-travel in the shallow aquifer system were simulated using the MODFLOW finite-difference model and the -particle-tracking program MODPATH. A three-layer, steady-state model of the shallow aquifer system was constructed and calibrated to the potentiometric surface of the A1 aquifer. Results of numerical modeling support the proposed conceptual hydrogeologic model of the shallow aquifer system. Ground-water time-of-travel in the A1 aquifer was simulated using an assumed effective porosity of 25 percent. Typical ground-water-flow velocities were on the order of 15 to 25 feet per year in the layer representing the Al aquifer in the model. The average residence time of particles seeded in this layer was about 800 years. Ground-water travel times were simulated at three sites within the Al aquifer: (1) the former N-6 hangar location, (2) the "grassy" area near Solid Waste Management Unit 7, and (3) at Solid Waste Management Unit 2. Results indicate close agreement between the particle-tracking simulations and the measured extent of contaminant plumes at the former N-6 hangar area and the grassy area near Solid Waste Management Unit 7. Based on the results of particle-tracking analyses of ground-water flow and the estimated locations of contaminant plumes at these two sites, the potential for contaminants to reach the Memphis aquifer in the next 100 years is negligible. However, particle-tracking analysis of ground-water flow at Solid Waste Management Unit 2 suggests that the time-of-travel of contaminants to Big Creek Drainage Canal could be less than 30 years.

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USGS1995

Hydrogeology, ground-water quality, and source of ground water causing water-quality changes in the Davis well field at Memphis, Tennessee

An investigation was conducted by the U.S. Geological Survey from 1992 to 1994 to collect and interpret hydrogeologic and water-quality data to determine the source of ground water causing water-quality changes in water from wells screened in the Memphis aquifer in the Davis well field at Memphis, Tennessee. Water-quality changes in aquifers used for water supply are of concern because these changes can indicate a potential for contamination of the aquifers by downward leakage from near-surface sources. The water-quality changes at the Davis well field were detected by Memphis Light, Gas and Water Division, which has periodically sampled and analyzed water from many of the 14 production wells since the well field began operation in 1971. Memphis Light, Gas and Water Division analyzed the water samples primarily for hardness, alkalinity, chloride, ulfate, and iron. Results of the e analy es and results of more recent (1992) analyse of water samples by the U.S. Geological Survey indicate that the quality of water from eight of the production wells has changed since the well field began operation. For example, from 1972 to 1991, hardness of water from one well has increased from 90 to 292 milligrams per liter (224 percent). The confining unit, which separates the fluvial deposits aquifer from the Memphis aquifer in the area of the well field, is relatively thick and contains many clay layers. However, a test hole drilled for one of five shallow wells installed in the alluvial aquifer in the Mississippi Alluvial Plain just west of the well field indicated that the confining unit separating the alluvial aquifer from the Memphis aquifer locally is absent. Differences in hydrauLic head between the alluvial and fluvial deposits aquifers and the Memphis aquifer favor downward leakage of ground water. Thus, the absence of the confining unit beneath the Mississippi Alluvial Plain just west of the well field provides a direct pathway for water in the alluvial aquifer to enter the Memphis aquifer. Comparison of selected water-quality properties and major inorganic and trace element constituent concentrations in samples from the alluvial, fluvial deposits, and Memphis aquifers indicates that the source of ground water causing waterquality changes at the Davis well field is the alluvial aquifer west of the well field . The presence of tritium and chlorofluorocarbons in water from wells screened in the Memphis aquifer in the western part of the well field indicates that relatively young (post-1940) water from the alluvial aquifer has entered the Memphis aquifer. NETPATH geochemical model code was used to mix waters from the alluvial aquifer with water from the Memphis aquifer using chloride as a conservative tracer. The resulting models indicated that a mixture containing 3 percent alluvial aquifer water mixed with 97 percent unaffected Memphis aquifer water would produce the chloride concentration measured in water from the Memphis aquifer well most affected by water-quality changes. NETPATH also was used to calculate mixing percentages of alluvial and Memphis aquifer Abstract waters based on changes in the concentrations of selected dissolved major inorganic and trace element constituents that define the dominant reactions that occur during mixing. These models indicated that a mixture containing 18 percent alluvial aquifer water and 82 percent unaffected Memphis aquifer water would produce the major constituent and trace element concentrations measured in water from the Memphis aquifer well most affected by water-quality changes. However, these model simulations predicted higher dissolved methane concentrations than were measured in water samples from the Memphis aquifer wells.

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USGS1992

Hydrogeology, water quality, and potential for transport of organochlorine pesticides in ground water at the North Hollywood Dump, Memphis, Tennessee

Geologic, hydrologic, and water-quality data indicate that ground-water contamination is confined to shallow horizons within the unconfined aquifer underlying the North Hollywood Dump in Memphis, Tennessee. The dump is a closed municipal-industrial landfill that has been ranked as Tennessee's potentially most dangerous hazardous-waste site. Toxic constituents of concern at the dump include residues from the manufacture of organochlorine pesticides. The dump overlies an unconfined aquifer of unconsolidated sands, silts, and clays. During average hydrologic conditions, ground waterflows beneath the dump at a mean velocity of approximately 3 feet per day and discharges to the Wolf River. Leachate from the dump mixes with underlying ground water, resulting in increased concentrations of dissolved solids and organic carbon downgradient from the dump. The mobility of chlordane, a representative organochlorine pesticide, is limited by its low solubility and its strong affinity for sand, silt, and clays of the aquifer. Degradation of chlordane may occur slowly, if at all, in the aquifer. Based on estimates of mean ground-water velocity and retardation of the pesticide due to sorption, mean travel times for chlordane migrating from the dump to the ground-water discharge zone are of the order of 50 to 500 years. Simulations of chlordane concentration resulting from the discharge of contaminated ground water and complete mixing in the Wolf River are sensitive to assumptions about chlordane persistence in the unconfined aquifer. If the half life of chlordane in the aquifer is assumed to be 30 years or less, the simulated concentration of chlordane in the Wolf River under average flow conditions is less than the most stringent water-quality criterion.

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USGS1992

Hydrogeology, ground-water quality, and potential for water-supply contamination near the Shelby County landfill in Memphis, Tennessee

An investigation was conducted from 1989 to 1991 to collect and interpret hydrogeologic and ground-water-quality data specific to the Shelby County landfill in east Memphis, Tennessee. Eighteen wells were installed in the alluvial and Memphis aquifers at the landfill. Hydrogeologic data collected showed that the confining unit separating the alluvial aquifer from the Memphis aquifer was thin or absent just north of the landfill and elsewhere consists predominantly of fine sand and silt with lenses of clay. A water-table map of the landfill vicinity confirms the existence of a depression in the water table north and northeast of the landfill and indicates that ground water flows northeast from the Wolf River passing beneath the landfill toward the depression in the water table. A map of the potentiometric surface of the Memphis aquifer shows that water levels were anomalously high just north of the landfill, indicating downward leakage of water from the alluvial aquifer to the Memphis aquifer. An analysis of water-quality data for major and trace inorganic constituents and nutrients confirms that leachate from the landfill has migrated northeastward in the alluvial aquifer toward the depression in the water table and that contaminants in the alluvial aquifer have migrated downward into the Memphis aquifer. The leachate plume can be characterized by concentrations of certain major and trace inorganic constituents that are 2 to 20 times higher than samples from upgradient and background alluvial aquifer wells. The major and trace constituents that best characterize the leachate plume are total organic carbon, chloride, dissolved solids, iron, ammonia nitrogen, calcium, sodium, iodide, barium, strontium, boron, and cadmium. Several of these constituents (specifically dissolved solids, calcium, sodium, and possibly ammonia nitrogen, chloride, barium, and strontium) were detected in elevated concentrations in samples from certain Memphis aquifer wells. Elevated concentrations were detected in samples from the Memphis aquifer beneath the leachate plume where the confining unit is thin or absent. The distribution of halogenated alkanes (specifically dichlorodifluoromethane and trichlorofluoromethane) and halogenated alkenes (specifically 1,2-trans-dichloroethene and vinyl chloride) in samples from wells screened in both the alluvial and Memphis aquifers is similar to the distribution of major and trace inorganic constituents that characterize the leachate plume. The ground-water supply most susceptible to contamination from the Shelby County landfill is the Sheahan well field of the Memphis Light, Gas and Water Division. This well field is about 5 miles downgradient from the landfill in the direction of ground-water flow. Based on an estimated velocity of 0.5 to 1.5 feet per day, ground water would require about 50 to 150 years to travel from the Shelby County landfill to the Sheahan wellfield. Given the time and distance of transport, any contaminants in the ground water would not likely persistto reach this well field because of the effects of various physical, chemical, and biological processes, including dilution and adsorption.

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USGS1991

Ground-water hydrology and the effects of vertical leakage and leachate migration on ground-water quality near the Shelby County landfill, Memphis, Tennessee

An investigation of potential leakage of leachate from the Shelby County landfill near Memphis, West Tennessee, was conducted during 1986-87. The migration of leachate from the landfill to the shallow alluvial aquifer system and the potential leakage to the deeper confined Memphis aquifer of Tertiary age were investigated. A network of observation wells was drilled to determine water levels and aquifer properties in the shallow and deep aquifers as well as in the confining layer. Water samples were collected to define potential leachate occurrence. A depression in the water table within the shallow alluvial aquifer was defined from the water-level data. Drawdowns within the cone of depression are as much as 14 feet lower than the adjoining Wolf River. Recharge from the river and leachate from the landfill moves toward the depression. The presence of leachate within the shallow aquifer was confirmed from determinations of dissolved solids and dissolved chloride concentrations and comparisons with areas away from the aflected zone. Leakage from the water-table aquifer to the Memphis aquifer was confirmed from chemical analyses and hydraulic-head data. Dissolved-solids concentrations in water samples from the upper Memphis aquifer near the landfill are higher than in samples from the Memphis aquifer in unaffected areas. Tritium activities in water samples from the upper Memphis aquifer were as high as 34 pico-Curies per liter indicating recent recharge to the Memphis aquifer. The presence of synthetic organic compounds and elevated concentrations of dissolved solids, chloride, and trace metals indicate the leachate has aflected water quality in the alluvial aquifer. Vertical migration of ground water could transmit leachate down to the Memphis aquifer. Although water-quality data indicate that water is leaking from the alluvial aquifer to the Memphis aquifer, most of the data do not indicate the occurrence of leachate in the Memphis aquifer. Chemical data from one well in the Memphis aquifer near the landfill indicates a slightly elevated dissolved-chloride concentration, but the data are limited.

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USGS1990

Hydrogeology and preliminary assessment of the potential for contamination of the Memphis aquifer in the Memphis area, Tennessee

Detailed maps of the thickness of the Jackson-upper Claiborne confining unit and the altitude of the water table in the alluvium and fluvial deposits provide much new information concerning areas where downward leakage is or may be occurring from the water-table aquifers to the Memphis aquifer in the Memphis area. A detailed map of the altitude of the potentiometric surface of the Memphis aquifer and the locations of 44 sites where contaminants have been detected in the water-table aquifers indicate that many of these sites are located in areas where the direction of ground-water flow in the Memphis aquifer is toward municipal well fields. Consequently, if contaminants enter the Memphis aquifer, a hydraulic potential exists for their transport to those wellfields. Recently (1986-88), volatile organic compounds were detected in water from five municipal wells screened in the Memphis aquifer - three in the Allen well field of the Memphis Light, Gas and Water Division at Memphis and two in the west well field at Collierville. Concentrations of seven volatile organic compounds totaled about 11 micrograms per liter in a sample from one well in the Allen wellfield at Memphis, and the concentration of one compound was 25 micrograms per liter in a sample from one well at Collierville. These are the first reported occurrences of synthetic organic compounds in the Memphis aquifer and prove that the principal aquifer in the Memphis area is vulnerable to contamination.

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USGS1988

Concentrations of selected trace inorganic constituents and synthetic organic compounds in the water-table aquifers in the Memphis area, Tennessee

Water quality samples for analysis of selected trace inorganic constituents and synthetic organic compounds were collected from 29 private or observation wells in alluvium and fluvial deposits of Quaternary and Tertiary Age. The alluvium and fluvial deposits are the water table aquifers in the Memphis area. In addition, nine wells were installed in Memphis Light, Gas and Water Division well fields so that samples could be collected and analyzed to characterize the quality of water in the fluvial deposits at these well fields. Samples from seven of these wells (two were dry) were analyzed for major constituents and properties of water as well as for selected trace inorganic constituents and synthetic organic compounds. Analyses of the water from most of the 36 wells sampled indicated ranges in concentration values for the trace inorganic constituents that agreed with those previously known, although some new maximum values were established. The analysis of water from four wells indicated that the water is or may be contaminated. Concentrations of barium (1,400 micrograms/L -- μg/L), strontium (1,100 μg/L)), and arsenic (15 μg/L), along with specific conductance (1,420 microsiemens/centimeter--us/cm) were in water from one well in the alluvium. Low concentrations (0.02 to 0.04 μg/L) of the pesticides aldrin, DDT, endosulfan, and perthane were present in water from two wells in the fluvial deposits. Water from one of these wells also contained 1,1,1 trichloroethane (4.4 μg/L). Analysis of water from another well in the fluvial deposits indicated values for specific conductance (1,100 μS/cm), alkalinity (508 milligrams per liter -- mg/L -- as CaCO 3 ), hardness (550 mg/L as CaCO 3 ), chloride (65 mg/L), and barium (240 μg/L) that are high for water from the fluvial deposits.

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USGS1988

Construction, geologic, and ground-water data for observation wells near the Shelby County landfill, Memphis, Tennessee

Forty-one observation wells and two stratigraphic test holes were drilled near the Shelby County landfill in east Memphis. These wells were installed as part of an investigation on possible vertical leakage of groundwater from the alluvial aquifer into the Memphis Sand aquifer. The alluvial aquifer consists of about 45 to 55 ft of alluvial silt, sand, and gravel. This is separated from the underlying Memphis Sand aquifer by about 30 to 60 ft of silt, silty sand, and clay in the confining layer. Thirty wells completed in the alluvium were generally less than 50 ft deep. The depth to the water table ranged from about 15 to more than 45 ft below land surface. Four observation wells were completed in the upper part of the Memphis Sand aquifer. Water levels in the Memphis Sand aquifer were generally 35 to 40 ft below land surface.

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USGS1987

Quality of water from freshwater aquifers and principal well fields in the Memphis Area, Tennessee

Water from the freshwater aquifers in the Memphis area is suitable for most uses. Freshwater aquifers are the alluvium and fluvial (terrace) deposits of Quaternary age, the Memphis Sand and Fort Pillow Sand of Tertiary age, and the Ripley Formation and McNairy Sand of Cretaceous age. About 180 million gallons/day (mgd) of freshwater are withdrawn from the Memphis Sand, primarily for municipal and industrial use; the Memphis Sand is the principal aquifer supplying the City of Memphis. The alluvium provides water for irrigation and some industrial uses, and the fluvial deposits provide water for domestic use in rural areas. The Fort Pillow Sand supplies water for some municipal and industrial uses. The Ripley-McNairy aquifer is not used as a source of water. Water from the alluvium, fluvial deposits, and Memphis Sand is a calcium bicarbonate type, and water from the Fort Pillow Sand and Ripley-McNairy aquifer is a sodium bicarbonate type. Dissolved solids concentrations are low in the Memphis Sand, with a median value of 83 mg/L, and are high in the Ripley-McNairy aquifer with a value of about 1,000 mg/L. Water is very soft in the Fort Pillow Sand with a median hardness value of 9 mg/L as CaCO3 and is very hard in the alluvium with a median value of 285 mg/L. Iron concentrations are low in the fluvial deposits with a median value of 50 micrograms/L and are high in the alluvium with a median value of 5,200 micrograms/L. Temperature of the water generally increases with depth, ranging from 16.0 C in the alluvium and fluvial deposits to about 32.0 C in the Ripley-McNairy aquifer. Water from the Memphis Sand at Memphis Light, Gas and Water Division well fields has very low mineralization. Median values are 79 mg/L dissolved solids concentrations, 56 mg/L alkalinity as CaCO3, 46 mg/L hardness as CaCO3, 4 mg/L chloride, 3.5 mg/L sulfate, and 600 micrograms/L iron.

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USGS1986

Potential for leakage among principal aquifers in the Memphis area, Tennessee

The principal aquifers in the Memphis area consist primarily of sand or sand and gravel, and the confining beds consist of clay, silt, sand, and lignite. The Jackson Formation and upper part of the Claiborne Group serve as the confining bed separating the water table aquifers from the Memphis Sand; the Flour Island Formation separates the Memphis Sand from the Fort Pillow Sand. Differences in total hydraulic head among the principal aquifers in the Memphis urban area result in vertical hydraulic gradients which create a potential for inter-aquifer exchange of water. Throughout this area, the gradient is downward from the water table aquifers to the Memphis Sand. In the central part of the Memphis urban area, the vertical hydraulic gradient is upward from the Fort Pillow Sand to the Memphis Sand, and in the eastern and western parts, it is downward from the Memphis Sand to the Fort Pillow Sand. The vertical distribution of carbon-14 data for water from the fluvial deposits, Memphis Sand, and Fort Pillow Sand shows an increase in the relative age of the water with depth. The areal distribution of carbon-14 data for water from the upper part of the Memphis Sand indicates that relatively recent water has been brought into the major cone of depression in the potentiometric surface of the Memphis Sand, either by horizontal movement or from downward vertical leakage. The normal, near-surface geothermal gradient in the Memphis area was determined to be 0.6 C/100 ft. Deviations from the normal geothermal gradient, in areas affected by intense pumping from the Memphis Sand, indicate that downward vertical leakage occurs from the water table aquifers through the Jackson-upper Claiborne confining bed to the Memphis Sand. The velocity of downward vertical leakage of water from the Memphis Sand through the Flour Island confining bed to the Fort Pillow Sand was determined to be 0.0066 ft/day by analysis of borehole temperature data from an observation well in the northeastern part of the Memphis area. From this velocity and the head difference between the Memphis Sand and the Fort Pillow Sand at this locality, the hydraulic conductivity of the Flour Island confining bed was determined to be 0.00114 ft/day. (Lantz-PTT)

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USGS1984

Flood frequency and storm runoff of urban areas of Memphis and Shelby County, Tennessee

Techniques are presented for estimating the magnitude and frequency of peak discharges and storm runoff on stream in urban areas of Memphis, Tennessee. Comprehensive analyses were made in which physical characteristics of streams are related to snythetic flood characteristics at gaging stations. Equations derived from analyses provide estimates of peak discharges with recurrence intervals of 2 to 100 years on streams that have drainage areas less than 20 square miles. The regression analyses indicated that size of drainage area and condition of channel (paved or unpaved) are the most significant basin characteristics affecting the magnitude and frequency of floods in urban streams. Data from 27 gaging stations with 8 years of record were used in the analyses. Flood frequency at each gaging station was computed from calibrated parameters in a rainfall-runoff model. Techniques are also presented for estimating discharge hydrographs for individual floods by using the unit hydrograph, lag time, and rainfall excess. (USGS)

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