Generalized contours of the altitude of water levels in wells completed in the Catahoula aquifer in central Louisiana, are illustrated by this map. Most water level measurements used in compiling the map were made in 1980; however, in parts of the State where water levels from 1980 were unavailable and where evidence indicated little change in water level, some measurements from as early as 1961 and as late as 1982 were used. Groundwater levels in and near the outcrop areas fluctuate 2 ft or less yearly and no significant long-term declines have occurred. The slow downward trend in water level altitude since early 1976 may be caused by pumpage from the Catahoula aquifer by a rural water system approximately 3 miles away. Recharge to the Catahoula aquifer occurs by rainfall on the upland outcrop-subcrop areas. Saltwater occurs throughout the Catahoula aquifer downgradient from the outcrop area. The ' approximate limit of freshwater ' line on the map indicates the downgradient limit of water with a concentration of chloride < 250 mg/L; the line was determined using water quality data and analysis of resistivity curves from geophysical well logs. Water from the Catahoula aquifer is used for municipal, industrial, and domestic purposes. Total pumpage from the aquifer in Louisiana was slightly over 1.1 million gallons/day in 1980. Local cones of depression result from pumpage just east of Anacoco in Vernon Parish and northwest of Jonesville in Catahoula Parish. (Lantz-PTT)
