Water Quality Changes along the South Platte River in the Denver Metro Area: PFAS, Organic, and Select Inorganic Constituents

Abstract The South Platte River is a major Colorado waterway and effluent-dominated river receiving inputs from wastewater treatment plants and tributaries. Among the contaminants of concern, poly- and perfluoroalkyl substances (PFAS) have gained increasing attention due to their persistence and widespread occurrence in impacted rivers. This study investigates the occurrence, composition, and spatial variability of PFAS and select constituents in the South Platte River. Samples were collected (two campaigns) from multiple locations along the river (upstream, downstream, side streams, and major wastewater discharge points) and analyzed for both regulated and unregulated PFAS, major ions, nitrogen species, total organic carbon, and sucralose. Results indicate that effluents from wastewater treatment facilities are important contributors to nutrient loading and the primary source of sucralose in the river. However, total detected PFAS concentrations in several natural tributaries exceeded those in all effluents, highlighting the substantial role of tributary inputs in watershed PFAS loading and variability. Moreover, river foam samples contained PFAS concentrations of ∼25,000 ng/L, substantially higher than surrounding waters, highlighting the potential for foam-mediated contaminant transport. Results indicate that while sucralose effectively traces municipal wastewater inputs, its lack of correlation with total detected PFAS concentrations limits its use as a standalone tool for PFAS source attribution in complex watersheds.