Dale J. Nyman, PG, 3168 Sherry Dr., Baton Rouge, LA, 70816: nyman7883@gmail.com
The Baton Rouge “2000-foot” sand was one of the first aquifers developed in the Baton Rouge Industrial Area and provides insight into the groundwater development of the system. There are 10 aquifers named for their depth in the Baton Rouge Industrial Area. It is currently well understood that these aquifers act as a system therefore hydraulic changes in any one aquifer is transferred to the entire system to some extent.
The first well drilled in the “2000-foot” sand was EB-97, completed October 1916. Well EB-97 had a hydrostatic head 105.0 ft above land surface (142.0 ft, NGVD). This well was plugged and the U.S.G.S. began monthly measurements using nearby well EB-90. The first water level at EB-90 was 12.70 ft above land surface (71.75 ft NGVD) measured February 1943. The industrial area developed rapidly and the deepest water level recorded at EB-90 was 292.54 ft below land surface measured in August 1973. This was a water-level decline of over 305 ft during a 28-year period. Water levels at EB-90 have averaged about 225 ft below land surface from 1990 to the present time.
Questions may arise as to the source of this initially high water level in the “2000-foot” sand. During research for this project each aquifer was projected to its outcrop. The outcrop (recharge area) for the “2000-foot” sand projected into Wilkinson and Amite Counties, Mississippi. The outcrop coincides with the highest topographic elevations in these counties, which is the river basin divide for the Homochitto River. The current potentiometric surface along the basin divide ranges from 120 to 260 ft (NGVD) (Nyman, 2009). While projecting the “2000-foot” sand to its outcrop the aquifer’s changes in permeability were noted, a potentiometric map drawn, and a two-dimensional groundwater flow model (MODFLOW/MODPATH) run to estimate travel time. Numerous clay bodies were found in East and West Feliciana Parish, some of which extend into East Baton Rouge Parish in the “2000-foot” sand. Estimated travel times for ground water flowing from the recharge area to the northern border of East Baton Rouge Parish, a distance of about 40 miles, ranged from 1800 to more than 20,000 years. It also should be noted that it probably took thousands of years for hydrostatic heads to reach an equilibrium throughout the aquifer system and the water levels first observed in industrial area. Similar clay lenses were found in most of the aquifers and these greatly slowed groundwater flow from outcrops to the industrial area. Aquifer permeabilities and potentiometric data were interpreted from well-registration information submitted to DOTD. This presentation is based on work done for the Louisiana Department of Transportation and Development, Water Resources Division, under State Project 750-63-0002, completed in 2009. The project was an update and summary of the hydrogeology of the entire Baton Rouge aquifer system from near the northern boundary of East Baton Rouge Parish northward to each aquifer’s outcrop, often into southern Mississippi.
Key words: aquifer, groundwater, outcrop, travel time
Reference
Nyman, Dale J., 2009, Hydrogeology of the Baton Rouge aquifers in West Feliciana Parish and vicinity: Louisiana Department of Transportation and Development, Public Works and Water Resources Division, 45pp, 5tbls, 80figs.