MODIFICATIONS TO THE EAST COAST FLORIDAN AQUIFER GROUNDWATER MODEL: FOCUSING ON THE BOULDER ZONE

Miami-Dade County Water and Sewer Department (WASD) treats about 300 million gallons a day (MGD) of wastewater, of which an average of 195.8 MGD is currently discharged via outfall to the ocean. In 2008, the Ocean Outflow Legislation Compliance Plan for Florida was passed and requires all wastewater discharge via outfalls to cease by 2025. In order to fulfill these goals, WASD is building additional deep injection wells (DIW) on their three main wastewater treatment plants to inject treated water into the Boulder Zone (BZ); the BZ is a confined aquifer filled with salt water, located about 3,000 feet below ground. This means that the rate of injection will increase in the near future, creating a need for new hydrological modeling of the BZ.

This research consists of creating different GIS shapefiles, tables, and other types of information needed to do modifications to the regional East Coast Floridan Model (ECFM). The ECFM was published by South Florida Water Management District in 2014 and covers an extensive area of about 32,600 mi² in South-East Florida. The model has a uniform grid with dimensions of 0.5 by 0.5 miles, 7 layers, 552 rows, 236 columns, and 288 monthly stress periods. The three-dimensional coupled groundwater flow and solute transport model was developed using the U.S. Geological Survey’s SEAWAT model code. Unfortunately, the original model does not fully simulate the BZ, despite its relative importance for ultimate wastewater disposal. Originally, the BZ was established with a constant head and concentration, making this layer effectively inactive.

We modified the model to simulate and track plumes from DIW. This process included modifying the top and bottom of the BZ, adding DIW and injection rates, removing constant head boundaries, and modifying other processes to fully simulate plume migration. ModelMuse and ArcGIS were used to preprocess input data, while the FloPy package for Python and ModelViewer were used as postprocessing tools to read the output binary files from model runs, focusing on head and concentration output files. We successfully ran several simulations injecting freshwater into different layers, confirmed by the increase in heads and visible plumes of fresh water, since the aquifers initially have brackish to saline concentrations.