20th Salt Water Intrusion Meeting Utilizing Stable Isotopes (2H & 18O) to Identify Water Types of the Floridan Aquifer System in Southwest Florida 20th Salt Water Intrusion Meeting June 24 , 2008 Authors: Ed Rectenwald, PG MWH Americas Michael Bennett, PG Boyle Engineering

Presentation Overview Background Hydrogeology Geochemistry Inorganics Stable Isotopes Summary Conclusions Overview Background Hydrogeology Geochemistry Summary Conclusions

Why Stable Isotopes? Identify different water bodies in the aquifer system Better understand groundwater circulation patterns Identify possible recharge and discharge areas Overview Background Hydrogeology Geochemistry Summary Conclusions

Investigated Wells Five FAS test wells (TW) owned by the SFWMD GLF-5 LAB-TW IWSD-TW I-75 TW BICY-TW Seven FAS monitor wells owned and operated by various Water Reclamation Facilities (WRF) Zemel Road Landfill Burnt Store WRF North Fort Myers WRF Fort Myers Beach WRF North Collier Regional WRF South Collier Regional WRF Marco Island WRF Overview Background Hydrogeology Geochemistry Summary Conclusions

Quantity of Wells Sampled Per Hydrogeologic Unit Upper Floridan Aquifer – Nine wells Middle Confining Unit – Thirteen wells Lower Floridan Aquifer – Five wells Overview Background Hydrogeology Geochemistry Summary Conclusions

Study Area Overview Background Hydrogeology Geochemistry Summary Conclusions

Southwest Florida Hydrogeology Overview Background Hydrogeology Geochemistry Summary Conclusions

Hydrogeology Generalized Cross-Section Overview Background Hydrogeology Geochemistry Summary Conclusions

Chlorides and TDS in the FAS Aquifer Unit Cl- (mg/L) TDS (mg/L) UFA 625 to 15,244 1,530 to 26,900 MCU 500 to 19,281 1,500 to 35,100 LFA 18,155 to 20,790 35,100 to 37,200 Overview Background Hydrogeology Geochemistry Summary Conclusions

Piper Tri-Linear Diagram Applying Frazee’s Geochemical Pattern Analysis Overview Background Hydrogeology Geochemistry Summary Conclusions

Stable Isotopes in the FAS Aquifer Unit 18O 0/00 2H 0/00 UFA -1.69 to -0.08 -8.79 to -1.53 MCU -1.92 to 0.55 -11.35 to 9.00 LFA 0.12 to 0.73 0.02 to 3.72 Average Rainfall -2.20 -7.60 Seawater 0.35 1.00 Overview Background Hydrogeology Geochemistry Summary Conclusions

Relationship Between 2H and 18O Overview Background Hydrogeology Geochemistry Summary Conclusions Precipitation or meteoric water contains very little dissolved constituents and the oxygen and hydrogen isotope composition of world-wide rainfall fall along a documented line called the Global Meteoric Water Line. Show two different types of water. UFA values are isotopically lighter than ocean water. These values parallel the GMWL, which suggest the source of the water is precipitation from recharge areas in central Florida. The enriched O18 values may indicate that climatic conditions and/or meteoric water that recharged the UFA were slightly different than present day conditions. Evaporation may have been minimal before recharge. MCU plots throughout which may indicate a hydraulic connection between the two other units. The LFA is isotopically heavier and plots close to 0.0 on the graph which suggests that the source is ocean water migrating in from the Gulf of Mexico and/or Straits of Florida. In addition, the δ18O data from MCU and LFA are different from glacial ocean water where the isotopic composition was significantly different than SMOW, δ18O was 1 0/00 heavier than present, suggesting that water may have entered the MCU and LFA after the last glacial period (less than 10,000 years before present).

Spatial Distribution of Isotopes in the UFA -2.08 -10.46 -0.85 -4.54 -1.43 -6.24 -1.60 -7.71 Overview Background Hydrogeology Geochemistry Summary Conclusions -1.46 -8.79 -1.69 -7.77 Legend 18O/2H -1.14 -1.53 -1.19 -5.53 -1.26 -6.60 -0.08 -5.17

Spatial Distribution of Isotopes in the MCU -1.92 -5.36 -0.42 0.97 0.43 2.05 -1.11 -11.35 -1.14 -8.06 Overview Background Hydrogeology Geochemistry Summary Conclusions 0.48 0.18 -1.59 -7.90 0.40 9.00 Legend 18O/2H 0.55 5.33 0.47 0.53 -0.35 0.28

Spatial Distribution of Isotopes in the LFA -0.41 -1.67 Overview Background Hydrogeology Geochemistry Summary Conclusions 0.47 0.02 0.12 3.76 Legend 18O/2H 0.65 1.16 0.73 0.06

Summary Stable Isotopic Analysis UFA MCU LFA Meteoric in origin Different climate and/or meteoric water at time of recharge Evaporation minimal at time of recharge MCU Mixture of meteoric and seawater Concentrations are location dependent Hydraulic connection between UFA and LFA LFA Seawater in origin Recharged after the “Last Glacial Period” (~15,000 years) Overview Background Hydrogeology Geochemistry Summary Conclusions Inorganic analyses tells us salinity increases with depth and identified lateral intrusion of salt water

Conclusions Need to improve our understanding of the FAS Additional geochemical analyses Radiocarbon Noble Gases Modeling the effects of sea level change Potentiometric head data of the FAS Additional inland monitor/test wells Overview Background Hydrogeology Geochemistry Summary Conclusions

Questions?