LEVERAGING THE USGS URBAN MIAMI-DADE GROUNDWATER MODEL: FROM PARTICLE TRACKING SIMULATION TO ATTENUATION AND DEGRADATION OF SEPTIC RETURN EFFLUENTS IN SOUTHEASTERN FLORIDA

Miami-Dade County (MDC) is characterized by a low elevation and complex karstic geology making the region vulnerable to sea level and water table rise. The fast-growing population (2.7 million) and over 120,000 septic systems make the study of contaminants from septic effluents in the region imperative, since these pose a threat of polluting the Biscayne Aquifer (the main drinking water source in south Florida) and Biscayne Bay.

This study leveraged the Urban Miami-Dade Groundwater Model, published by the USGS in 2016 (covering an area of 4,772 km²), to simulate regional spatiotemporal distribution of septic effluents in the County using MODPATH. The region receives influxes of over 72,000 m³/d from septic effluents. These results are the first regional particle tracking simulations in southeastern Florida, helping to estimate septic effluent discharge locations, with an overall distribution to canals (70%), well fields (19%), and the bay (7%).

The particle model is being enhanced to simulate dispersion, degradation, attenuation, and transformation of the water constituents from septic returns; this is attained by leveraging existing flow simulations in the Groundwater Solute Transport Simulator for MODFLOW (MT3D-USGS) using FloPy and ModelMuse.