Dale J. Nyman P.G.
The “2,800-foot” sand is the deepest of the ten depth-named aquifers underlying East Baton Rouge Parish. The aquifer was traced to its recharge area in northernmost Wilkinson County, Mississippi and the wells monitoring water levels were identified (Nyman, 2009). Because the “2,800-foot” sand is the deepest, and one of the least pumped, it is often assumed that it is undisturbed and pristine. But hydrologists familiar with the Baton Rouge aquifer system know that there is constant groundwater interchange (leakage) between all of the units because of head differences.
One of the first wells drilled into the “2,800-foot” sand was EB-468 completed in 1948. This well had an initial head of 71.60 feet above land surface (144.60 ft, NGVD). A nearby well EB-581 has been monitored since 1956 and has had over 100 ft of water-level decline between 1956 and 1980. Water levels in this well have apparently stabilized at about +10.0 ft (NGVD) during the period 2005 to 2014. Well EF-185, near Jackson in west-central East Feliciana Parish, has had over 80 feet of water-level decline from about 1960 to 2005 and water levels have stabilized at about +20 ft (NGVD) during the period 2005 to 2014. During 2014 total average pumpage from the “2,800-ft” sand was about 20.3, 1.0, and 1.7 Mgal/d in East Baton Rouge, West Feliciana, and East Feliciana Parishes, respectively (Capital Area Groundwater Commission data).
The northernmost monitor well found to be in the “2,800 foot” sand was T0103 near Centreville in southeastern Wilkinson County, Mississippi (Nyman, 2009). This well is about 10 miles south of the recharge area of the aquifer. The well has a depth of 1685 ft and the water level was monitored from about 1954 to 1996 by the U.S. Geological Survey. The hydrograph for this period of record shows about 30 ft of water-level decline from 1954 to 1988. The measurements from 1988 to 1996 indicated that the water level had stabilized at about +77 ft (NGVD). Total pumpage in Wilkinson County was less than 2.0 Mgal/d during and before 2005 (Nyman, 2009).