By Susan S. Hutson
An inventory of public water-supply systems in Tennessee in 1995 indicated that 530 public water-supply systems supplied water to 4.42 million people, or 84 percent of Tennessee's population. Public-supply water withdrawals totaled 779 million gallons per day, 64 percent (500 million gallons per day) of which was from surface-water sources. All of the surface-water withdrawals for public-water supply took place within the Tennessee (279 million gallons per day) and the Ohio (221 million gallons per day) hydrologic regions. Ground-water withdrawals statewide accounted for 36 percent (279 million gallons per day) of the total public-supply water withdrawal. Ground water is the sole source of public-supply water in the Lower Mississippi hydrologic region of western Tennessee. Public water-supply systems in western Tennessee withdrew 216 million gallons per day, or 77 percent, of the 279 million gallons per day of ground water withdrawn for public supply statewide.
Public water-supply systems withdraw, treat, and distribute water to residential, commercial, and industrial customers and to municipal services such as firefighting. Water lost by leaky pipes from the distribution system (conveyance losses) and system maintenance also are part of the total use by the system. The people of Tennessee depend on public water-supply systems to provide clean water to drink and of sufficient and reliable quantity to ensure both their health and economic well being. Water use and related information about active public water-supply systems in Tennessee change as transfers of system ownership, consolidation and interconnectiveness among systems, and development of alternative sources of supply occur. The need for current and accurate water-use data for public water-supply systems has been underscored by droughts during the 1980's, recent source-water protection initiatives, increasing water requirements for both instream and offstream uses, and concern about available water for development and possible future water shortages.
The U.S. Geological Survey (USGS), as part of its ongoing water-resources programs in Tennessee, compiled data for public water-supply systems. This effort was done in cooperation with the Tennessee Department of Environment and Conservation (TDEC), Division of Water Supply (TDWS) through the Tennessee Water-Use Information Program. This report updates the information on public supply published in the earlier reports, "Drought-related impacts on municipal and major self-supplied industrial withdrawals in Tennessee-Part B" (Alexander and others, 1984) and "Public water-supply systems and water use in Tennessee, 1988" (Hutson and Morris, 1992). In addition to providing data to the State of Tennessee to better manage the State's water resources, this report advances the understanding of the regional and temporal variations in public supply.
This report presents data collected from an inventory of Tennessee public water-supply systems and associated water-use information for 1995. Water withdrawals and wholesale transactions, sources of supply, population served, and design and storage capacities of the public water-supply systems were determined from water-supply records maintained by the Tennessee Division of Water Supply and from records maintained by the USGS containing river basin and aquifer information.
The inventory was limited to water systems that were active on September 30, 1995, and that served at least 15 connections used by permanent residents, or those that regularly served at least 25 permanent residents. The systems inventoried included investor-owned water companies, private water companies, municipal water departments, regional water authorities, institutions, residential developments, mobile home parks, and homeowner associations.
Tennessee is divided into eight physiographic divisions (Miller, 1974) (fig. 1). The diverse topography of these divisions ranges from rolling hills and broad flood plains in the Coastal Plain Physiographic Province in western Tennessee to steep mountains and deep, narrow valleys in the Valley and Ridge Province in eastern Tennessee. The geologic setting of Tennessee includes unconsolidated sediments of the Coastal Plain Province in western Tennessee, limestone and dolomite of the Highland Rim and Central Basin in central Tennessee, and limestone and granite of the folded Appalachian Mountains in eastern Tennessee. Tennessee receives an average of about 50 inches of precipitation per year (U.S. Department of Commerce, 1968). This plentiful rainfall recharges the aquifers and replenishes streamflow, thereby providing water for many uses in the State.
The author thanks the managers of the public water-supply systems for providing the data on which this report is based. The author also thanks Mr. David Draughon, Director of the Division of Water Supply, who initiated the data-collection program and coordinated transmittal of the survey forms from the public water-supply systems to the Tennessee Department of Environment and Conservation (TDEC) central office, and the TDEC Environmental Field Office managers and staff in Chattanooga, Cookeville, Jackson, Johnson City, Knoxville, and Nashville who provided ancillary-system and source-of-supply information.
Local physiographic and geologic variations govern water availability statewide. In the Coastal Plain Province in western Tennessee, ground water is the principal source of public-supply water, whereas, typically, a combination of surface and ground water is used in the rest of the State. An extensive network of reservoirs storing about 8.12 million acre feet (acre-ft) (2,647 billion gallons) of water in the Ohio and Tennessee hydrologic regions (figs. 2 and 3) provides a reliable and abundant source of surface water for water systems in central and eastern Tennessee (U.S. Army Corps of Engineers, 1981). In these two hydrologic regions, however, the many small unregulated tributaries are not reliable sources of public-supply drinking water. These smaller streams are characterized by no flow or low flow during the dry periods of late summer and early fall (table 1).
In contrast to central and eastern Tennessee, few water-storage sites are available in the Lower Mississippi hydrologic region in western Tennessee. Although ground water sustains flow in the main channels during the dry months, the unregulated, sediment-laden streams of this region are not used for any major public-water supply.
Ground water is withdrawn for public supply from eight of the nine principal aquifers in Tennessee (fig. 1). These aquifers are the Alluvial, Tertiary sand, Cretaceous sand, Mississippian carbonate rock, Ordovician carbonate rock, Pennsylvanian sandstone, Cambrian-Ordovician carbonate rock, and crystalline rock aquifers (table 2). Yields to wells of 1,000 gallons per minute (gal/min) are common in the Tertiary sand aquifer in western Tennessee (Hollyday and Bradley, 1985). This aquifer is the most productive aquifer in Tennessee and supplied 76 percent of the ground water pumped in the State in 1995 for all purposes (Hutson, 1998). The Mississippian and Ordovician carbonate rock aquifers in central Tennessee yield limited quantities of water to wells, and are not a principal source of water for public supply. Yields to wells vary widely in the Cambrian-Ordovician carbonate rock and the crystalline rock aquifers of eastern Tennessee. High-yielding springs from carbonate rocks in eastern Tennessee provide water to some public-supply systems. Large yields can be produced from wells completed in the Alluvial aquifer, especially in the western valley of the Tennessee River and the Mississippi alluvial plain of western Tennessee.
In 1995 the Tennessee Division of Water Supply and the U.S. Geological Survey collected data for 530 public water-supply systems. Data for the 530 systems are presented by hydrologic region (Tennessee, Ohio, and Lower Mississippi) (fig. 3) in Supplements A, B, and C at the back of this report. Within each of the hydrologic regions, the individual water-supply systems are arranged by county in numerical order by the Tennessee "Public Water Supply Identification" (PWSID) number. The data consist of water-supply system name, source of water, average daily water withdrawal, average daily wholesale transaction, average daily gross water use, population served, gross per capita water use (gross water use divided by population served), and the storage and design capacities of the water system. Individual water-supply systems are listed alphabetically in the Index with the respective PWSID code and page number of the corresponding supplement.
In 1995, more water-supply systems in Tennessee relied on ground water than on surface water as a source of water supply (fig. 4). Of the 530 water-supply systems, 249 systems (47 percent) reported ground water as at least one source of water supply; 216 systems (41 percent) reported ground water as the sole source of water supply. The other 33 ground-water systems (6 percent) withdrew ground water in conjunction with surface water or purchased water from water-supply systems which reported ground water as one of their sources of water supply.
Surface water was reported as the source of supply for 146 of the water-supply systems (27 percent) and was the sole source of water supply for 114 of the systems. The other 32 water-supply systems (6 percent) withdrew surface water in conjunction with ground water, or purchased water from systems which reported surface water as at least one source of supply. Purchased water provided at least one source of supply for 181 systems (34 percent); 157 of these systems (30 percent) depended solely on purchased water. The other 24 water-supply systems (5 percent) used purchased water in conjunction with surface- or ground-water withdrawals to provide water to their customers. Since 1988, when the last comprehensive inventory of water-supply systems was done (Hutson and Morris, 1992), the number of water-supply systems that rely solely on surface water has increased 15 percent from 99 systems to 114 systems. The number of water-supply systems that rely solely on ground water declined slightly from 218 systems (1988) to 216. The locations of the surface- and ground-water withdrawal sites for public supply are mapped in figure 5.
Public water-supply systems in Tennessee served 84 percent of the population, or 4.42 million people, during 1995. The 530 water-supply systems range in size from small systems serving as few as 25 residential customers to large systems serving hundreds of thousands of residential customers. One-half of the 530 water-supply systems served fewer than 2,246 people each. Eleven public water-supply systems serving 50,000 people or more (2 percent of the systems) provided water to 41 percent of the total population served by public supply.
For this report, public water-supply systems in Tennessee were classified following the U.S. Environmental Protection Agency method based on the population served (American Water Works Association, 1992) (table 3). The classification shows that a few very large systems in the State serve most of the State's population (table 3). The four water systems serving more than 100,000 people provided water to 32 percent of the public water-supply customers. Sixty percent of the water systems (systems serving less than 3,300 people) served less than 9 percent of the population served.
Total water withdrawals for public water supply increased about 53 percent, from 510 million gallons per day (Mgal/d) in 1980 to 779 Mgal/d in 1995. During the same period, surface-water withdrawals for public supply increased 61 percent, from 310 to 500 Mgal/d, and ground-water withdrawals increased 40 percent, from 200 to 279 Mgal/d. Part of the increase is because the population of the State increased by about 15 percent, from 4.59 to 5.26 million people; the population served by public-water systems increased about 19 percent, from 3.72 to 4.42 million people; and the gross per capita use for public-supplied water increased from 137 to 176 gallons per day (gal/d) per person. Factors contributing to the increase in demand related to changes in the local commercial and industrial sectors are not documented in this report.
Surface-water withdrawals accounted for 64 percent (500 Mgal/d) of the water withdrawn by public water-supply systems in Tennessee during 1995. These withdrawals occurred in the Ohio (221 Mgal/d) and the Tennessee (279 Mgal/d) hydrologic regions (table 4). The Lower Mississippi region of western Tennessee does not use any surface water for its drinking water. Davidson County, in the Ohio hydrologic region, had the largest surface-water withdrawals, 107 Mgal/d (Supplement B). Withdrawals in Davidson County (where Nashville is located) accounted for 21 percent of public-supply withdrawals from surface water, statewide. Most public-supply systems that withdraw from surface water are larger than most public-supply systems that withdraw from ground water. Fifty percent of the 146 surface-water systems inventoried withdrew at least 1.36 Mgal/d, but only 9 percent of the 249 ground-water systems inventoried withdrew as much water. Surface-water withdrawal sites and major rivers are presented in figure 5.
Ground-water withdrawals accounted for 36 percent of the 779 Mgal/d (279 Mgal/d) withdrawn by public water-supply systems in Tennessee during 1995. One-half of the ground-water withdrawals for public supply equaled or exceeded 0.159 Mgal/d. The Tertiary and Cretaceous sand aquifers of western Tennessee were the sources for 79 percent of the ground-water public-supply withdrawals (221 Mgal/d). The Tertiary sand aquifer alone accounted for 76 percent (211 Mgal/d) of the total (fig. 6). These two aquifer systems are the source of supply for 21 of the 38 public-supply systems statewide that withdraw at least 1.0 Mgal/d of ground water (table 5). Shelby County (where Memphis is located), in the Lower Mississippi hydrologic region, had the largest ground-water withdrawals (163 Mgal/d) (Supplement C). Withdrawals in Shelby County were from the Tertiary sand aquifer and accounted for 58 percent of the public-supply ground-water withdrawals statewide. One ground-water withdrawal occurred in the South Atlantic-Gulf region, but is included in the Tennessee region (Supplement A) for simplicity.
The Tennessee Division of Water Supply and the U.S. Geological Survey collected data for 530 public water-supply systems to determine water use, supply sources, population served, and design and storage capacities of the systems. During 1995, these systems served 84 percent of the population of the State, or 4.42 million people. The gross per capita use statewide for public-supplied water was 176 gallons per day, about 28 percent higher than in 1980 (137 gallons per day). Total water withdrawals for public supply increased about 53 percent from 510 Mgal/d in 1980 to 779 Mgal/d in 1995. During the same period, the population of the State increased about 15 percent. Surface-water withdrawals accounted for 64 percent (500 Mgal/d) of the total water withdrawn for public supply in the State. Most of these withdrawals occurred in the Tennessee (279 Mgal/d) and the Ohio (221 Mgal/d) hydrologic regions. Ground water supplied 279 Mgal/d or 36 percent of the total water withdrawn by public-supply systems statewide. Of that amount, 79 percent or 221 Mgal/d, was used in western Tennessee.
Alexander, F.M., Keck, L.A., Conn, L.G., and Wentz, S.J., 1984, Drought-related impacts on municipal and major self-supplied industrial water withdrawals in Tennessee-Part B: U.S. Geological Survey Water-Resources Investigations Report 84-4074, 398 p.
American Water Works Association, 1992, Water Industry Data Base: Utility profiles, 116 p.
Fenneman, N.M., 1946, Physical divisions of the United States: U.S. Geological Survey map, scale 1:7,000,000.
Hollyday, E.F., and Bradley, M.W., 1985, Tennessee ground-water resources, in National water summary 1984: Hydrologic events, selected water-quality trends, and ground-water resources: U.S. Geological Survey Water-Supply Paper 2275, 467 p.
Hutson, S.S., 1998, Ground-water use by public-supply systems in Tennessee, 1995: U.S. Geological Survey Open-File Report 98-85, 1 sheet.
Hutson, S.S., and Morris, A.J., 1992, Public water-supply systems and water use in Tennessee, 1988: U.S. Geological Survey Water-Resources Investigations Report 91-4195, 74 p.
Miller, R.A., 1974, The geologic history of Tennessee: Tennessee Division of Geology Bulletin 74, 63 p.
Seaber, P.R., Kapinos, F.P., and Knapp, G.L., 1987, Hydrologic unit maps: U.S. Geological Survey Water-Supply Paper 2294, 63 p.
Solley, W.B., Chase, E.B., and Mann, W.B., IV, 1983, Estimated use of water in the United States in 1980: U.S. Geological Survey Circular 1001, 56 p.
U.S. Army Corps of Engineers, 1981, National inventory of dams: Unpublished data on file in Memphis Subdistrict office, U.S. Geological Survey, updated by the U.S. Geological Survey in 1987.
U.S. Bureau of the Census, 1996, Population estimates for counties, July 1, 1995: paperless product listing, Population paper listing: PPL-39; Atlanta, Statistical Information Staff, Population Division, www.census.gov
U.S. Department of Commerce, 1968, Climatic atlas of the United States: Environmental Science Services Administration, June 1968, 82 p.
Wonnacott, R.J., and Wonnacott, T.H., 1985, Introductory statistics (4th ed.): New York, John Wiley and Sons, 649 p.
Definitions of water-use terms used in this report (modified from Alexander and others, 1984) are listed below:
Design capacity--The amount of water a system is designed to treat daily. Systems which do not treat water either purchase water from another system that has its own treatment plant or withdraw water from a ground-water source which often requires no treatment other than chlorination.
Gross per capita water use--The quantity of water that enters the public-supply distribution system per person per day. The value is calculated by dividing the "gross water use" for a system by the "population served."
Gross water use--The quantity of water that enters the public-supply distribution system. The value is calculated as the sum of water withdrawn by a public water-supply system plus water purchased from other public supplies minus water sold to other public water-supply systems. The water is sold to residential, commercial, and industrial customers or provided free as public-use water, and includes water lost from the distribution system.
Population served--Number of people supplied water by the public water-supply system. In this report, the "population served" value was obtained from records provided by the Tennessee Department of Environment and Conservation, Division of Water Supply. The population served was modified if the population served in a county was greater than the Census population of that county for 1995.
Storage capacity--Capacity for storage of treated or untreated water by the public water-supply system.
Purchased water--Quantity of water purchased or obtained from another public water-supply system.
Wholesale water--Quantity of water sold or provided to another public water-supply system.
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