Availability and Mobility of Legacy and Emerging Organic Contaminants in Stormwater

As point source treatment and management has improved, non-point source stormwater is increasingly a concern for contamination of waterways and sediments. The rapid expansion of urban areas and increased impervious surfaces lead to higher stormwater volumes and contaminant loads. However, treating stormwater presents challenges due to variable contaminant loads, event-driven factors, and cumulative effects over time. Moreover, the sediment impacts of stormwater are a strong function not only of the total contaminant load but how it is distributed onto particles of different sizes and settling rates. This dissertation presents the usefulness of characterizing stormwater loads by different particle sizes on sediment recontamination and resulting biota impacts. The first part of the research focuses on legacy hydrophobic organic contaminants, PAHs, and PCBs in Paleta Creek Watershed, Naval Base San Diego, CA. In this study, extensive stormwater sampling was conducted at different locations of Paleta Creek discharge. The stormwater samples were size fractioned into particle size fractions <0.7μm (filtered/dissolved), 0.7-2.7μm (fine silt), 2.7-20μm (coarse silt), and >63μm (sand). Three temporal samples (early, mid, and late storm) were also sampled. Settling traps were deployed in four locations in the receiving water to collect particles discharged from stormwater. Sediment cores were collected from four areas, and bioaccumulation studies were performed on bent-nosed clam (Macoma Nasuto) along with porewater sampling using PDMS fibers. The results indicate that the majority of PAHs and PCBs loads are carried by the rapidly settling coarser particles during the initial part of the storm events. The sediment and settling traps deployed in the receiving waters confirmed the above observations that sediment close to discharge has a higher concentration than in distant locations. The results from bioaccumulation indicated that the depositing particles are largely unavailable for organism uptake, and hence stormwater impacts on sediment concentration do not directly impact organism bioaccumulation. The second part of the dissertation focuses on the emerging organic contaminants, Per-and poly-fluoroalkyl substances (PFAS), at Reese Technological Center. Lubbock, TX. PFAS contamination has been identified at this site due to the use of firefighting foams. The PFAS contamination was mobilized from the source area, and stormwater is one of the potential contributors. The particle size characterization of PFAS loads indicated that most of the analyzed PFAS loads were associated with the dissolved fraction (<0.7μm). The PFHxS associated with dissolved fraction dominated the surface water, while PFOS, partially associated with stormwater solids, was the dominant compound in sediments. The fate and behavior of the PFAS in the stormwater management system and in a retention pond was evaluated. The mass balance of PFAS compounds associated with dissolved fraction in the retention pond was modeled by changes in volume, while the mass balance for compounds associated with solids fraction was influenced greatly by settling and other partitioning processes such as sediment and suspended algae. Conventional stormwater control systems are currently not designed to treat PFAS removal, and their efficacy is poorly understood. PFAS inputs and discharges were also monitored in other conventional stormwater treatment systems, including bioinfiltration systems, vortex separators, and media filters. Overall, conventional stormwater managements systems, which are primarily designed to remove particulates, perform poorly in the removal of PFAS from stormwater

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