The Chicot aquifer system is a vital water resource for Southwestern Louisiana, providing nearly half of the fresh groundwater the region consumes (Sargent, 2011). The aquifer’s surficial confining unit (scu) consists of a wedge-shaped thickening sequence of south to southeastern dipping, interbedded clays and courser material (primarily sand and gravel). In collaboration with the Louisiana Department of Transportation and Development (LDOTD), Sargent and others (2004) extracted data from driller’s logs, geophysical logs, and well construction information for 2094 wells overlying the Chicot aquifer to enhance the delineation of the thickness and occurrence of the aquifer’s surficial confining unit. These data were applied here to create tabular data and a shapefile of discrete points that contain thickness data of the confining unit and tops and bottoms of sand and clay layers within the confining unit. A better understanding of the thickness and extent of the Chicot aquifer’s surficial confining unit will provide a framework for future aquifer characterization and will enhance the understanding of groundwater accessibility and availability for the southeast region. 1. Sargent, B.P., Frederick, C.P., Roberts, F.C., 2004, Thickness data for the Chicot aquifer system surficial confining unit: Louisiana Department of Transportation and Development Water Resources Basic Records Report no. 22, 91 p. 2. Sargent, B.P., 2011, Water use in Louisiana, 2010: Louisiana Department of Transportation and Development Water Resources Special Report no. 17, 135 p.

The Chicot aquifer system underlies an area of approximately 9,500 mi2 in southwestern Louisiana and is located within the Gulf Coastal Plain physiographic province. The region includes all or parts of 15 parishes -- Vernon, Rapides, Evangeline, Allen, Beauregard, Calcasieu, Jefferson Davis, Acadia, St. Landry, Lafayette, St. Martin, Cameron, Iberia, Vermilion, and St. Mary. The Chicot aquifer system is a major source of groundwater for southwestern Louisiana, accounts for approximately 48 percent of all groundwater use in the State, and provides freshwater for public supply, industry, agriculture, and aquaculture (Collier and Sargent, 2018). Withdrawals of groundwater have created water-level gradients favorable for saltwater encroachment, and future water-availability and production in the region could be impacted by poor water quality. This product is part of a larger study of the Chicot aquifer system in southwestern Louisiana that will benefit local, State, other Federal cooperators, and stakeholders. The extent given here represents the geographic extent of the Chicot aquifer system in southwestern Louisiana and was created using elevation information from U.S. Geological Survey digital elevation models, surface geology maps, and previously published extents (Lovelace and others, 2004; Casarez, 2020).

The Chicot aquifer system underlies an area of approximately 9,500 mi2 in southwestern Louisiana and is located within the Gulf Coastal Plain physiographic province. The region includes all or parts of 15 parishes -- Vernon, Rapides, Evangeline, Allen, Beauregard, Calcasieu, Jefferson Davis, Acadia, St. Landry, Lafayette, St. Martin, Cameron, Iberia, Vermilion, and St. Mary. The Chicot aquifer system is a major source of groundwater for southwestern Louisiana, accounts for approximately 48 percent of all groundwater use in the State, and provides freshwater for public supply, industry, agriculture, and aquaculture (Collier and Sargent, 2018). Withdrawals of groundwater have created water-level gradients favorable for saltwater encroachment, and future water-availability and production in the region could be impacted by poor water quality. This product is part of a larger study of the Chicot aquifer system in southwestern Louisiana that will benefit local, State, other Federal cooperators, and stakeholders. The extent given here represents the geographic extent of the Chicot aquifer system in southwestern Louisiana and was created using elevation information from U.S. Geological Survey digital elevation models, surface geology maps, and previously published extents (Lovelace and others, 2004; Casarez, 2020).

A hydrogeologic framework was constructed for the Coastal Lowlands aquifer system in southwestern Louisiana. Data from previous hydrogeologic and geologic studies were synthesized and expanded using 2,242 geophysical logs to map four hydrogeologic units: the Chicot aquifer system, Evangeline aquifer, Jasper aquifer system, and Catahoula aquifer. Raster surfaces were created for the base and thickness of each unit to provide a generalized framework to support regional groundwater studies.A table listing the well information and point data used to generate the raster surfaces is included in this data release.

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 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 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.

Digital hydrogeologic surface of the Lower Claiborne aquifer in Alabama, Arkansas, Louisiana, and Mississippi. The hydrogeologic unit dataset contains 414 rows and 394 columns representing 1-mile grid spacing. In general, limitations of data interpolation included areas of sparse geophysical log control points, log datums not clearly defined for some logs, unknown exact extent of each hydrogeologic unit in subcrop, interpolation limitations, and values averaged over 1-mile grid spacing.

Digital hydrogeologic surface of the Lower Claiborne aquifer in Alabama, Arkansas, Louisiana, and Mississippi. The hydrogeologic unit dataset contains 414 rows and 394 columns representing 1-mile grid spacing. In general, limitations of data interpolation included areas of sparse geophysical log control points, log datums not clearly defined for some logs, unknown exact extent of each hydrogeologic unit in subcrop, interpolation limitations, and values averaged over 1-mile grid spacing.