This report describes the thickness and areal extent of the Sparta aquifer, identifies sands within the fresh-water extent of the aquifer, and presents data and a map that illustrate the generalized potentiometric surface (water levels) during October 1996. The report includes a detailed geophysical log, structure contour maps, hydrogeologic sections, and hydrographs of water levels in selected wells. The potentiometric surface-map can be used for determining direction of ground-water flow, hydraulic gradients, and the effects of withdrawals on the aquifer.

This report describes the thickness and areal extent of the Sparta aquifer, identifies sands within the fresh-water extent of the aquifer, and presents data and a map that illustrate the generalized potentiometric surface (water levels) during October 1996. The report includes a detailed geophysical log, structure contour maps, hydrogeologic sections, and hydrographs of water levels in selected wells. The potentiometric surface-map can be used for determining direction of ground-water flow, hydraulic gradients, and the effects of withdrawals on the aquifer.

This report describes the thickness and areal extent of the Sparta aquifer, identifies sands within the fresh-water extent of the aquifer, and presents data and a map that illustrate the generalized potentiometric surface (water levels) during October 1996. The report includes a detailed geophysical log, structure contour maps, hydrogeologic sections, and hydrographs of water levels in selected wells. The potentiometric surface-map can be used for determining direction of ground-water flow, hydraulic gradients, and the effects of withdrawals on the aquifer.

The Sparta aquifer is a primary source of groundwater in north-central Louisiana. In 2015, more than 60 million gallons per day were withdrawn from the Sparta aquifer, of which over 90 percent was used for public supply and industrial purposes (Collier, 2018). Concentrated withdrawals from the Sparta aquifer have caused regional water-level declines within the Sparta aquifer (McGee and Brantly, 2015). Widespread concern about the potential effects of declining water levels has brought forth many questions regarding the sustainability of the aquifer as well as continued saltwater intrusion.

The Sparta aquifer is the principal source of ground water in north-central Louisiana. In 1985, the aquifer was extensively pumped for public supply (25 Mgal/d) and industrial use (29 Mgal/d and 7 Mgal/d for 1989). More than 100 public supply systems, in 8 parishes, contain water from the Sparta aquifer. Large industrial pumpage from the Sparta aquifer began in 1922 at Bastrop (Sanford, 1973a, p. 60) and in about 1923 at West Monroe. Water levels in wells in the Sparta aquifer have been declining in these arease and in other parts of north-central Louisiana since the early 1920's, when industries began withdrawing large amounts of water. However, in Morehouse Parish the water levels in wells have been recovering since 1982 as a result of a 5 Mgal/d reduction in pumpage at Bastrop (J.K. Lovelace, U.S. Geological Survey, written commun., 1989). Additional knowledge about ground-water flow and the effects of withdrawals on the Sparta aquifer is needed for assessment of ground-water development potential and protection of the resource. Potentiometric contour maps are used to determine direction of ground-water flow, ground-water gradients, and the effects of pumping on an aquifer system. The rate of ground-water movement can be estimated when the hydraulic conductivity of an aquifer is known. This report presents data and maps that illustrate the potentiometric surface and water-level changes for the Sparta aquifer and is the third in a series of map reports that show potentiometric surface and water-level changes of aquifers in Louisiana (Fendick, 1989; Fendick and Nyman, 1987). These maps were prepared in cooperation with the Louisiana Department of Transportation and Development. Reports prepared as part of previous studies of northern Louisiana with emphasis on the Sparta aquifer are included in the Selected References. These maps show the potentiometric surface in the spring of 1989 and water-level changes from 1980 to 1989 for the Sparta aquifer. The regional potentiometric surface of the Sparta aquifer, based on water-level measurements made during May through June 1989, is shown in figure 1. Ground-water flow directions are normal to the contours, from higher to lower head. Water-level changes in wells in the Sparta aquifer from May 1980 to May 1989 are shown in figure 2. Three hydrographs (figs. 3-5) show general water-level trends for periods 1920-89, 1946-89, and 1970-89.

The study of the geohydrology of the Sparta Sand is the initial phase in the investigation of the geohydrology of the Claiborne Group. The thicker sections of the Sparta Sand lie along the axes of the Mississippi embayment and Desha basin. The area of maximum thickness, 1,100-1,200 feet, is in Claiborne and Warren Counties, Miss., and Madison Parish, La. Local thickening or thinning over some structures indicates structural movement during Sparta time. A sand-percentage map prepared from data derived from interpretation of electric logs indicates that the Sparta Sand was deposited as a delta-fluvial plain complex in Arkansas, Louisiana, and Mississippi. This complex shows a text-book example of a well-developed channel pattern. The delta-fluvial plain complex probably resulted from an ancestral Mississippi River system. In most of Texas the sand-percentage map shows a pattern suggestive of offshore or near-shore bar deposition. A map of the maximum sand-unit thickness shows the development during deposition of an interlacing channel pattern in Arkansas, Louisiana, and Mississippi. In the channel areas the maximum thickness of the sand units may be as much as 350 feet; in the inter-channel areas the maximum thickness is generally less than 50 feet. Coefficients of permeability and transmissibility for the Sparta Sand vary widely in localized areas. In the channels and area of Arkansas, Louisiana, and Mississippi, data suggest that the coefficient of permeability increases with an increase in maximum sand-unit thickness. These permeability values which depend on sand unit thicknesses, were used to prepare a map showing the transmissibility of the total sand thickness of the Sparta Sand in Arkansas, Louisiana, Mississippi, and eastern Texas. The data on the map show a close relation between channel development and high transmissibility values. The Sparta Sand is recharged by infiltration of water from precipitation on the outcrop, by leakage from other aquifers, and by seepage from streams. Natural discharge from the Sparta Sand takes place primarily by leakage through the overlying and underlying confining beds. In Texas, west-central Louisiana, and southeastern Mississippi the direction of flow of ground water is down the regional dip toward the gulf coast geosyncline. In most of Arkansas, Louisiana, and Mississippi the regional flow is toward the Mississippi River alluvial valley. In the channel-sand area of Arkansas, Louisiana, and Mississippi the ground-water flow is governed by changes in transmissibility, which in turn reflects the lithology. A study of the ground-water chemistry indicates that the areas of higher transmissibility have lower concentrations of dissolved solids than the areas of low transmissibility. On the basis of anion ratios, the waters of the Sparta Sand are grouped into three chemical provinces: the bicarbonate water province, the chloride water province, and the sulfate water province. The dissolved-solids content of waters from the Sparta Sand is closely related to the lithologic framework of the Sparta Sand area. Differences in water chemistry are attributed to regional differences in the rates of ground-water movement. Interpretation of the data suggests that the channel deposits have undergone a higher degree of flushing by fresh water than the inter-channel deposits.

The study of the geohydrology of the Sparta Sand is the initial phase in the investigation of the geohydrology of the Claiborne Group. The thicker sections of the Sparta Sand lie along the axes of the Mississippi embayment and Desha basin. The area of maximum thickness, 1,100-1,200 feet, is in Claiborne and Warren Counties, Miss., and Madison Parish, La. Local thickening or thinning over some structures indicates structural movement during Sparta time. A sand-percentage map prepared from data derived from interpretation of electric logs indicates that the Sparta Sand was deposited as a delta-fluvial plain complex in Arkansas, Louisiana, and Mississippi. This complex shows a text-book example of a well-developed channel pattern. The delta-fluvial plain complex probably resulted from an ancestral Mississippi River system. In most of Texas the sand-percentage map shows a pattern suggestive of offshore or near-shore bar deposition. A map of the maximum sand-unit thickness shows the development during deposition of an interlacing channel pattern in Arkansas, Louisiana, and Mississippi. In the channel areas the maximum thickness of the sand units may be as much as 350 feet; in the inter-channel areas the maximum thickness is generally less than 50 feet. Coefficients of permeability and transmissibility for the Sparta Sand vary widely in localized areas. In the channels and area of Arkansas, Louisiana, and Mississippi, data suggest that the coefficient of permeability increases with an increase in maximum sand-unit thickness. These permeability values which depend on sand unit thicknesses, were used to prepare a map showing the transmissibility of the total sand thickness of the Sparta Sand in Arkansas, Louisiana, Mississippi, and eastern Texas. The data on the map show a close relation between channel development and high transmissibility values. The Sparta Sand is recharged by infiltration of water from precipitation on the outcrop, by leakage from other aquifers, and by seepage from streams. Natural discharge from the Sparta Sand takes place primarily by leakage through the overlying and underlying confining beds. In Texas, west-central Louisiana, and southeastern Mississippi the direction of flow of ground water is down the regional dip toward the gulf coast geosyncline. In most of Arkansas, Louisiana, and Mississippi the regional flow is toward the Mississippi River alluvial valley. In the channel-sand area of Arkansas, Louisiana, and Mississippi the ground-water flow is governed by changes in transmissibility, which in turn reflects the lithology. A study of the ground-water chemistry indicates that the areas of higher transmissibility have lower concentrations of dissolved solids than the areas of low transmissibility. On the basis of anion ratios, the waters of the Sparta Sand are grouped into three chemical provinces: the bicarbonate water province, the chloride water province, and the sulfate water province. The dissolved-solids content of waters from the Sparta Sand is closely related to the lithologic framework of the Sparta Sand area. Differences in water chemistry are attributed to regional differences in the rates of ground-water movement. Interpretation of the data suggests that the channel deposits have undergone a higher degree of flushing by fresh water than the inter-channel deposits.

The study of the geohydrology of the Sparta Sand is the initial phase in the investigation of the geohydrology of the Claiborne Group. The thicker sections of the Sparta Sand lie along the axes of the Mississippi embayment and Desha basin. The area of maximum thickness, 1,100-1,200 feet, is in Claiborne and Warren Counties, Miss., and Madison Parish, La. Local thickening or thinning over some structures indicates structural movement during Sparta time. A sand-percentage map prepared from data derived from interpretation of electric logs indicates that the Sparta Sand was deposited as a delta-fluvial plain complex in Arkansas, Louisiana, and Mississippi. This complex shows a text-book example of a well-developed channel pattern. The delta-fluvial plain complex probably resulted from an ancestral Mississippi River system. In most of Texas the sand-percentage map shows a pattern suggestive of offshore or near-shore bar deposition. A map of the maximum sand-unit thickness shows the development during deposition of an interlacing channel pattern in Arkansas, Louisiana, and Mississippi. In the channel areas the maximum thickness of the sand units may be as much as 350 feet; in the inter-channel areas the maximum thickness is generally less than 50 feet. Coefficients of permeability and transmissibility for the Sparta Sand vary widely in localized areas. In the channels and area of Arkansas, Louisiana, and Mississippi, data suggest that the coefficient of permeability increases with an increase in maximum sand-unit thickness. These permeability values which depend on sand unit thicknesses, were used to prepare a map showing the transmissibility of the total sand thickness of the Sparta Sand in Arkansas, Louisiana, Mississippi, and eastern Texas. The data on the map show a close relation between channel development and high transmissibility values. The Sparta Sand is recharged by infiltration of water from precipitation on the outcrop, by leakage from other aquifers, and by seepage from streams. Natural discharge from the Sparta Sand takes place primarily by leakage through the overlying and underlying confining beds. In Texas, west-central Louisiana, and southeastern Mississippi the direction of flow of ground water is down the regional dip toward the gulf coast geosyncline. In most of Arkansas, Louisiana, and Mississippi the regional flow is toward the Mississippi River alluvial valley. In the channel-sand area of Arkansas, Louisiana, and Mississippi the ground-water flow is governed by changes in transmissibility, which in turn reflects the lithology. A study of the ground-water chemistry indicates that the areas of higher transmissibility have lower concentrations of dissolved solids than the areas of low transmissibility. On the basis of anion ratios, the waters of the Sparta Sand are grouped into three chemical provinces: the bicarbonate water province, the chloride water province, and the sulfate water province. The dissolved-solids content of waters from the Sparta Sand is closely related to the lithologic framework of the Sparta Sand area. Differences in water chemistry are attributed to regional differences in the rates of ground-water movement. Interpretation of the data suggests that the channel deposits have undergone a higher degree of flushing by fresh water than the inter-channel deposits.

The Sparta aquifer is used in 15 parishes in north-central Louisiana, primarily for public supply and industrial purposes. Of those parishes, eight (Bienville, Claiborne, Jackson, Lincoln, Ouachita, Union, Webster, and Winn) rely on the Sparta aquifer as their principal source of groundwater. In 2010, withdrawals from the Sparta aquifer in Louisiana totaled 63.11 million gallons per day (Mgal/d), a reduction of more than 11 percent from 1995, when the highest rate of withdrawals (71.32 Mgal/d) from the Sparta aquifer were documented. The Sparta aquifer provides water for a variety of purposes which include public supply (34.61 Mgal/d), industrial (25.60 Mgal/d), rural domestic (1.50 Mgal/d), and various agricultural (1.40 Mgal/d). Of the 13 major aquifers or aquifer systems in Louisiana, the Sparta aquifer is currently (2012) the sixth most heavily pumped. The Sparta aquifer is the second most heavily pumped aquifer in Arkansas, which borders Louisiana to the north. In 2005, 170 Mgal/d were withdrawn from the Sparta aquifer in eastern and southern Arkansas; of that total, about 15.55 Mgal/d were withdrawn from the aquifer in Union County, which borders Claiborne and Union Parishes to the north. By 1997, a large cone of depression (a cone-shaped depression in the potentiometric surface caused by and centered on a pumping well or wells) in the Sparta aquifer centered over Union County had merged with the cone of depression at West Monroe. In 2004, the rate of withdrawal from the Sparta aquifer in Union County began to decline and water levels in the aquifer began to rise in nearby areas of Arkansas and Louisiana.

The potentiometric surface of the Sparta Sand in northern Louisiana is shown by contours on four maps. Maps for 1900, 1965 , and spring 1975 are generalized, small-scale maps from previously published reports. The spring 1980 map (1:500,000) is based on measurements in 144 wells and includes the southern tier of counties in southern Arkansas. The map shows regional effects of pumping from the Sparta Sand and effects of local pumping centers at Magnolia and El Dorado, Ark., and at Minden, Ruston, Jonesboro-Hodge, Winnfield, Bastrop, and in the Monroe area of Louisiana. (USGS) First release: April, 2019; revised April 2021 (version 1.1). The previous version can be obtained by contacting the USGS Lower Mississippi-Gulf Water Science Center using the "Point of Contact" link on the landing page on ScienceBase.