The Amite aquifer and the “2,800-foot” sand of the Baton Rouge area (hereafter referred to as the “2,800-foot” sand) are principal sources of fresh ground water in southeastern Louisiana. Both the Amite aquifer and the “2,800-foot” sand are part of the Jasper equivalent aquifer system. The Amite aquifer is heavily pumped in the Bogalusa area, and the “2,800-foot” sand is one of the most heavily pumped aquifers in East Baton Rouge Parish. The Baton Rouge fault zone, which acts as a barrier to flow, trends approximately west-northwest from a point just south of The Rigolets through southern West Baton Rouge Parish, and is the approximate southern limit of freshwater in the aquifers.

For the purposes of this report, freshwater is defined as water having less than 250 milligrams per liter (mg/L) of chloride, and most of the water withdrawals described in this report were assumed to be fresh. In 2005, about 18 million gallons per day (Mgal/d) was withdrawn from the Amite aquifer, primarily for public-supply use (8.4 Mgal/d) and industrial use (9.6 Mgal/d). During this same period, about 32 Mgal/d was withdrawn from the “2,800-foot” sand, primarily for public-supply use (13 Mgal/d) and industrial use (19 Mgal/d). Public-supply and industrial withdrawals from the Amite aquifer and the “2,800-foot” sand are listed in table 1.

According to data from the Louisiana State Census Data Center, some of the largest population increases in the State during the period 1990 to 2000 occurred in St. Tammany (32.4 percent), Livingston (30.2 percent), and Tangipahoa (17.4 percent) Parishes. These population increases have been accompanied by increased withdrawals of ground water during the same period: 40 percent in St. Tammany Parish, 63 percent in Livingston Parish, and 35 percent in Tangipahoa Parish. An increase in population in these parishes is expected from population displacement due to damages from Hurricanes Katrina and Rita crossing the Louisiana coast in August and September of 2005.

Additional information about ground-water flow and effects of increased withdrawals on water levels in the Amite aquifer and the “2,800-foot” sand is needed to assess ground-water-development potential and to protect this resource. To meet this need, the U.S. Geological Survey, in cooperation with the Louisiana Department of Transportation and Development, began a study in 2005 to determine water levels, flow direction, and water-level trends for the Amite aquifer and “2,800-foot” sand. This report presents data and a map that describe the generalized potentiometric surface of the Amite aquifer and “2,800-foot” sand in southeastern Louisiana. Graphs of water levels in selected wells and a table of withdrawals from the Amite aquifer and “2,800-foot” sand show historical changes in water levels and water use. The generalized potentiometric-surface map illustrates the water levels and ground-water flow directions for June–August 2006. These data are on file at the USGS office in Baton Rouge, Louisiana.