Simulated Ground-Water Withdrawals by Cabot WaterWorks from the Mississippi River Valley Alluvial Aquifer, Lonoke County, Arkansas

Cabot WaterWorks, located in Lonoke County, Arkansas, plans to increase ground-water withdrawals from the Mississippi River Valley alluvial aquifer from a 2004 rate of approximately 2.24 million gallons per day to between 4.8 and 8 million gallons per day by the end of 2049. The effects of increased pumping from several wells were simulated using a digital model of ground-water flow. The proposed additional withdrawals by Cabot WaterWorks were specified in three 1-square-mile model cells with increased pumping beginning in 2007. Increased pumping was specified at various combined rates for a period of 44 years. In addition, augmented pumping from wells owned by Grand Prairie Water Users Association, located about 2 miles from the nearest Cabot WaterWorks wells, was added to the model beginning in 2007 and continuing through to the end of 2049 in 10 of the 16 scenarios analyzed. Eight of the scenarios included reductions in pumping rates in model cells corresponding to either the Grand Prairie Water Users Association wells or to wells contained within the Grand Prairie Area Demonstration Project.

Drawdown at the end of 44 years of pumping at 4.8 million gallons per day from the Cabot WaterWorks wells ranged from 15 to 25 feet in the three model cells; pumping at 8 million gallons per day resulted in water-level drawdown ranging from about 15 to 40 feet. Water levels in those cells showed no indication of leveling out at the end of the simulation period, indicating non-steady-state conditions after 44 years of pumping. From one to four new dry cells occurred in each of the scenarios by the end of 2049 when compared to a baseline scenario in which pumping was maintained at 2004 rates, even in scenarios with reduced pumping in the Grand Prairie Area Demonstration Project; however, reduced pumping produced cells that were no longer dry when compared to the baseline scenario at the end of 2049. Saturated thickness at the end of 2049 in the three Cabot WaterWorks wells ranged from about 52 to 68.5 feet for pumping rates of 4.8 million gallons per day, and from about 38 to 64 feet for pumping rates of 8 million gallons per day, the latter causing water level to fall below half the aquifer thickness in the most heavily pumped of the three cells.