A MULTI-TOOL APPROACH TO EVALUATE GROUNDWATER TRANSPORT PATHWAYS OF PER- AND POLYFLUOROALKYL SUBSTANCES AND NITRATE NEAR A STREAM/WETLAND SYSTEM ON CAPE COD, MASSACHUSETTS

Groundwater is a transport pathway of per- and polyfluoroalkyl substances (PFAS) and nitrate to surface-water. Understanding groundwater transport pathways of PFAS and nitrate to surface-water is often difficult due to complex transport processes and sparse data in the subsurface. This study used a multi-tool approach that combined hydrologic and geochemical data collected from a five square-kilometer site on Cape Cod to better understand groundwater transport pathways. The upper kilometer of the Quashnet River and wetland system on western Cape Cod is a hydrologically complex area receiving surface-water flow from a kettle lake and groundwater discharge from local and regional sources. PFAS and nitrate discharge to the stream and wetlands through focused zones of groundwater seepage. Potential sources of PFAS to the upper Quashnet River and wetlands include aqueous film-forming foam releases on a military airfield and wastewater disposal from septic systems. Wastewater disposal from septic systems is also a major source of nitrate in the watershed. A lack of hydrologic and geochemical data in groundwater limited our understanding of transport pathways of PFAS and nitrate from the sources to the stream and wetlands. This study incorporates data from a synoptic water-level survey, stream-water and lake-water sampling, a lakebed porewater temperature survey, lakebed porewater sampling, and multiport groundwater sampling. The hydrologic and geochemical data collected from the site was used to develop a conceptual model of PFAS and nitrate distributions and groundwater flow paths. The preliminary results indicated vertically and laterally complex distributions of PFAS, nitrate, and stable isotopes of oxygen and hydrogen in water that are affected by an upgradient kettle lake. The findings demonstrated that spatially dense groundwater sampling was key to developing a detailed conceptual model of PFAS and nitrate distributions and groundwater flow paths. The study approach and findings have transferability to other sites in shallow, interconnected groundwater/surface-water flow systems.