Formatted Title:

Evaluation of Performance of Stormwater Control Measures to Limit Sediment Recontamination of PFAS, PAHs, and PCBs

Background/Objectives:

Stormwater runoff is a significant non-point source of sediment recontamination, particularly for PFAS and hydrophobic organic contaminants (HOCs), which pose known environmental and health risks. Historically, stormwater assessment has only focused on total contaminant loads, with little attention paid to the particle-size distribution of contaminants – a critical factor in assessing their fate in receiving water bodies. Coarse particles tend to settle near discharge points, leading to sediment recontamination, while finer particles and dissolved contaminants disperse more widely. This study aims to evaluate the performance of stormwater control measures (SCMs) to reduce particle-size-based pollutant loads and their implications for receiving water systems.

Approach/Activities:

This study evaluated the performance of various existing structural SCMs, including retention ponds, biofilters, hybrid biofilter-media filters, hydrodynamic separators, and zeolite, perlite, granulated activated carbon (ZPG) cartridge filters, in removing sediments and their associated contaminants from stormwater. Automatic samplers collected influent and effluent samples based on rainfall and flow conditions. Contaminant concentrations were measured in filtered water and different particle size fractions (clay, fine silt, coarse silt, and sand). Samples were analyzed for 38 PAHs, 142 PCBs, 30 PFAS, and total organic carbon (TOC). Passive sampling using PDMS fibers was used to determine truly dissolved contaminant concentrations. The study compared influent and effluent concentrations to assess each SCM's ability to remove contaminants based on the particle size with which the contaminants were associated.

Results/Lessons Learned:

Coarse particles (coarse silt and sand), which are more prone to settle near stormwater outfalls, exhibited statistically higher organic carbon contents and thus higher PAH and PCB concentrations. Despite their increased recontamination risk, these particles were effectively removed by most SCMs. In contrast, dissolved contaminants, including the majority of PFAS and low molecular weight PAHs, were generally not effectively removed by most systems, including those incorporating GAC, despite its known remediation capabilities. Dissolved PFAS, such as PFOA, can accumulate over time in the systems, as seen in the retention pond, which had lake concentrations up to five times higher than the inlets, while PFAS associated with solids, such as PFOS, were more readily treated due to particle settling. The performance of the various stormwater management systems was summarized, contextualizing recontamination risks and highlighting the challenge of treating PFAS with conventional stormwater management approaches not designed for their treatment.

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Mathew Demyers