Using a Time-of-Travel\nSampling Approach to Quantify\nPer- and Polyfluoroalkyl Substances (PFAS) Stream Loading and Source\nInputs in a Mixed-Source, Urban Catchment

Understanding per- and polyfluoroalkyl substances (PFAS)\nmass distribution\nin surface and groundwater systems can support source prioritization,\nload reduction, and water management. Thirteen sites within an urban\ncatchment were sampled utilizing a time-of-travel sampling approach\nto minimize the influence of subdaily fluctuations in mass from PFAS\npoint sources and to quantify PFAS and ancillary chemical loads from\nvarious PFAS sources. A larger increase in perfluoroalkyl sulfonate\n(PFSA) loads (8 to 11 μg/s, up to 618%) than in perfluoroalkyl\ncarboxylate (PFCA) loads (no change to 3.4 μg/s, up to 122%)\nwas observed at sites below tributaries influenced by military bases\nwith known groundwater discharge. Point discharges from two sewage\ntreatment plants (STPs) resulted in increases in PFCA and PFSA loads\nthat were similar (6 and 10 μg/s respectively) below the first\nSTP and greater for PFCA compared to PFSA loads (23 and 13 μg/s\nrespectively) below the second STP. Overall, percent increases in\ntotal PFAS load ranged from 20 to 277% for military base inputs and\n44 to 77% for STP inputs. A focus catchment that represents only 14%\n(76.9 km<sup>2</sup>) of the drainage area at the most downstream\nsite (544 km<sup>2</sup>) accounted for about 70% of PFSA and 40%\nof PFCA loads observed at the most downstream site. Results show that\nby using a time-of-travel sampling approach in mixed, urban settings\nwith several PFAS sources, it is possible to quantify stream loads\nfrom individual PFAS sources, thereby improving source attribution\nand providing actionable data for water-resource managers.