PFAS MIGRATION INTO AND BENEATH THE ROGUE RIVER IN NORTHERN KENT COUNTY, MICHIGAN

Per- and polyfluoroalkyl substances (PFAS) are an important class of emerging environmental contaminants with multiple health concerns at low concentrations in the part per trillion (ppt) range. In northern Kent County, Michigan, large PFAS plumes are spreading from landfills that contain tannery waste generated in the late 1960s and early 1970s. The largest known PFAS plume starts at the House Street Disposal Site and is interpreted to have migrated approximately 4 km (3 mi) downgradient to the Rogue River. However, monitoring wells located as far as 500 m (1,600 ft) from the opposite side of the river contain detectable levels of PFAS that are not explained by the current interpretation. Questions remain, therefore, about whether all or part of the plume vents into or underruns the river.

We constructed a hydrogeologic cross section along the axis of the main PFAS plume emanating from the House Street Disposal Site to investigate whether PFAS is entering or going beyond the Rogue River. We interpreted available monitoring well data, static water levels, and perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and total PFAS concentrations to evaluate potential flow paths in this area. Our analysis suggests high complexity of preferential groundwater flow paths. Vertical gradients at nested monitoring wells indicate the potential for both upward and downward flow within the same well. Moreover, vertical gradients near the river indicate both upward and downward flow, suggesting that groundwater could be flowing into and beneath the river, explaining the PFAS found in the monitoring wells on the opposite side of the river.