Using a Time-of-Travel Sampling Approach to Quantify Per- and Polyfluoroalkyl Substances (PFAS) Stream Loading and Source Inputs in a Mixed-Source, Urban Catchment

Understanding per- and polyfluoroalkyl substances (PFAS)
mass distribution
in surface and groundwater systems can support source prioritization,
load reduction, and water management. Thirteen sites within an urban
catchment were sampled utilizing a time-of-travel sampling approach
to minimize the influence of subdaily fluctuations in mass from PFAS
point sources and to quantify PFAS and ancillary chemical loads from
various PFAS sources. A larger increase in perfluoroalkyl sulfonate
(PFSA) loads (8 to 11 μg/s, up to 618%) than in perfluoroalkyl
carboxylate (PFCA) loads (no change to 3.4 μg/s, up to 122%)
was observed at sites below tributaries influenced by military bases
with known groundwater discharge. Point discharges from two sewage
treatment plants (STPs) resulted in increases in PFCA and PFSA loads
that were similar (6 and 10 μg/s respectively) below the first
STP and greater for PFCA compared to PFSA loads (23 and 13 μg/s
respectively) below the second STP. Overall, percent increases in
total PFAS load ranged from 20 to 277% for military base inputs and
44 to 77% for STP inputs. A focus catchment that represents only 14%
(76.9 km2) of the drainage area at the most downstream
site (544 km2) accounted for about 70% of PFSA and 40%
of PFCA loads observed at the most downstream site. Results show that
by using a time-of-travel sampling approach in mixed, urban settings
with several PFAS sources, it is possible to quantify stream loads
from individual PFAS sources, thereby improving source attribution
and providing actionable data for water-resource managers.