Tracking PFAS in Miami-Dade, Florida groundwater: trends, hotspots, and regulatory implications from a multi-year monitoring study

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent and mobile contaminants of growing concern in groundwater systems, yet multi-year assessments in large metropolitan areas remain limited. This study investigates PFAS occurrence, spatial distribution, and associated health risks in Miami-Dade County, Florida, using 1600 samples collected from monitoring wells, raw water, and point-of-exit (POE) locations between 2019 and 2023. PFOA and PFOS were detected in over 90% of samples, while 6:2 fluorotelomer sulfonate (6:2 FTS), perfluorohexanoic acid (PFHxA), and perfluoropentanoic acid (PFPeA) exhibited the highest concentrations. Spatial mapping identified contamination hotspots near airports and firefighting training facilities, with elevated 6:2 FTS levels suggesting aqueous film-forming foam (AFFF) as a primary source. PFAS profiles also indicated contributions from wastewater treatment, landfills, and industrial activities. Rainfall events were positively correlated with increased ∑PFAS concentrations, supporting infiltration-driven mobilization. All POE samples exceeded the newly established U.S. National Primary Drinking Water Regulations, frequently due to PFOA and PFOS concentrations, and some samples occasionally surpassed a hazard index of 1. Miami-Dade Water and Sewer Department (MDWASD) has initiated treatment pilot studies to address these exceedances. Cumulative risk assessments revealed elevated exposure levels across all service areas, underscoring the need for improved treatment technologies and regulatory oversight. This study represents a detailed longitudinal PFAS groundwater assessment conducted in a major U.S. urban area. The findings offer critical insights into contamination patterns, exposure risks, and the urgent need for mitigation strategies to protect public health and ensure regulatory compliance.