Sparta Groundwater Study –Approach Scenarios

Meyer, Meyer, LeCroix, and Hixson selected several scenarios of Sparta use, using the ground-flow model described in the section above (5.f.3.a.).  For all scenarios, they assumed that Sparta pumpage would be reduced by 8 mgd by El Dorado industries converting from Sparta to surface water.   For all scenarios except the ‘No Change in Use’ scenario they projected demographic changes in the base case Scenario 2.

For the No Change in Use scenario, the model calculates for well water levels, by the Year 2025:  (Ref. 2, p.6-2)

• in the Ouachita Parish area:  recovery of approximately five feet, largely because of decreased pumping in Morehouse Parish, Louisiana and Union County, Arkansas;

• at the western edge of Ouachita Parish: additional drawdown;

• in Lincoln and Winn Parishes: additional drawdown greater than 25 feet, (simulation was influenced by pumpage increases, between 1980 to 1999, in Winn Parish (from 1.67 to 3.74 mgd) and Lincoln Parish (from 4.24 to 8.94 mgd).

Meyer, Meyer, LeCroix, and Hixson reported in the Sparta Groundwater Study (2) results of the application of their model to Ouachita Parish, which is at particular risk of salt water intrusion because of heavy pumping in the area and close proximity to the freshwater/saltwater interface.  The optimized solutions maintained hydraulic heads at or above the top of the Sparta Sand by the end of the simulation period (2025). 

The researchers reported the following results by Scenarios 1 through 6:  (2, pages 6-1 to 6-10)

• Scenario 1.  No Change resulted in an increase in westward hydraulic gradient and associated potential movement westward of the saltwater front.  The sustainable yield for Ouachita Parish was 78 percent of the current pumpage rate.

• Scenario 2.  Projected Demographic Changes from 2000 through 2025 (5.5% Higher Usage Rates) resulted in a ten foot decline of water levels in areas of Ouachita Parish, water level declines across the area of the cone of depression, and water level declines in Lincoln and Winn Parishes. The sustainable yield for Ouachita Parish was 71 percent of the pumpage rate.

• Scenario 2 was the base case for Scenarios that follow (Scenarios 3 through 6).

• Scenario 3.  Artificial Recharge (14 injection wells near Lake D’Arbonne and along the Ouachita River), replaced less than two percent of amount pumped over twenty years) resulted in a four percent decrease in the west-ward hydraulic gradient.  The sustainable yield for Ouachita Parish was 71 percent of the pumpage rate.

• Scenario 4.  Decreased Groundwater Use by Selected Larger Users, Supplemented with Nearby Surface Water (supply from D’Arbonne 4.6 mgd, Bisteneau 2 mgd, Ouachita 7.5 mgd decreased Sparta use from 70 mgd to 42.86 mgd) resulted in reduced hydraulic gradient with accompanying widespread recovery of Sparta water levels, a rebound in the cone of depression in Ouachita Parish, and reduced potential for saltwater migration. The sustainable yield for Ouachita Parish was 100 percent of the pumpage rate.

• Scenario 5.  Water Use Reductions, through Conservation or Recycling (Sparta use decreased by four percent from 2005 forward) resulted in little change over the ‘Steady State’ scenario. The sustainable yield for Ouachita Parish was 74 percent of the pumpage rate. The researchers concluded that ‘Small scale water conservation efforts will not provide significant reduction in water level declines.’

• Scenario 6.  Potential High Use Estimate (groundwater withdrawal increased by 7 percent each 5 years, from 72.8 to 95.4 mgd over 25 years) resulted in a steep increase in hydraulic gradient leading to deeper, wider cones of depression, especially in Ouachita and Winn Parishes, and increased potential for salt-water migration westward. The sustainable yield for Ouachita Parish was 57 percent of the pumpage rate.

Sparta Groundwater Study –Recommended Approaches to Reduce Sparta Pumpage

Meyer, Meyer, LeCroix, and Hixson reported that the Sparta aquifer can be significantly restored within 25 years with an 18 million gallon per day (mgd) reduction of its current 70 mgd withdrawal rate, and another 12 mgd would provide for population and industrial growth. (2)  The recommendation they put forth in greatest detail was to build new surface water treatment plants and pipe the water to current aquifer users.  They calculated that, if this is the sole approach used, capital costs in 2001 dollars would be approximately $190 million, operating costs would add to those costs, and financing costs would add more. They suggested that revenue to pay capital and financing costs might be generated by a 1/4 cent sales tax in an eleven parish taxing district, surface water contract sales at $1 per thousand gallons, and groundwater extraction fees at 23 cents per thousand gallons.