1. A Saltwater Upconing Model to Evaluate Wellfield Feasibility Gregory W. Council Christopher J. Richards June 2008 Salt Water Intrusion Meeting (SWIM) Naples, Florida, USA

2. Location & Purpose Franklin Co., FL Tate’s Hell Proposed Wellfield Drawdown? Upconing?

3. Hydro- geology

4. Field Data Slug Tests –Surficial Aquifer Aquifer Performance Tests –Floridan Aquifer –Intermediate Confining Unit Borehole Geophysical Logs

5. APT Calibration

6. Lateral Boundary Conditions Fresh: c = 0 Saline: c = 35 g/L

7. Simulation Method Top Boundary –Recharge: 500 mm/yr (20 in/yr) –ET: 330 mm/yr (13 in/yr) max Pre-pumping equilibrium –Reasonable initial head, concentration –1000 yr simulation (10 d – 10 yr step) –Solute mass stable; head & conc. stable Simulate Pumping –7,600 m 3 /d (2 mgd)

8. Drawdown Floridan Aquifer

9. Upconing Surficial Aquifer

10. Model Sensitivity: Upconing Initial Depth of the Brackish Zone –Lateral Boundary Conditions –Dispersivity Vertical Hydraulic Conductivity Effective Porosity Well Location

11. Conclusions Upconing of 250 mg/L chloride: ~35 m in 50 yr ~85 m equilibrium Need to identify current position of brackish zone Top boundary important for Surficial Aquifer drawdown Well placement Simple, general method for impact assessment