A Geochemical Tool to Assess the Impact of Seawater Intrusion on Floridian Aquifer Groundwater Supplies

This study used the USGS geochemical model, PHREEQC, to simulate the effect of seawater intrusion into fresh groundwater. The effort assessed the applicability of the model to Floridian aquifer groundwater, all over the South Florida region; it specifically estimated the effect of saline and freshwater mixing on major ion concentrations (i.e., Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^- and SO₄^-2). Model simulations, mixing saline with freshwater water quality compositions, were carried out and then compared with water quality records from over 30 monitoring wells located within the region up to Central Florida. The model simulations and the water quality data from over 30 monitoring wells were analyzed for their matching, regression trends for major ion concentrations as function of salinity. The simulations were found to be good predictors of the water quality data over a wide range of salinity (i.e., up to seawater concentrations). Regression analysis resulted in strong linear trends for all major cations and anions, with very high correlation, except in the case of sulfates, which are overestimated, the latter suggesting possible in-land sources of sulfate other than oceanic. Overall, this study outlines the potential of the modeling approach to serve as a tool to predict major ion concentrations, in support of scenarios that assess the impact of saline intrusion in fresh groundwater supplies, as a result of human actions or sea level rise from climate change.