Impacts of Urban Stormwater-Associated Polycyclic Aromatic Hydrocarbons on Receiving Sediment
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Stormwater runoff from an urban environment is recognized as a major source of particle-associated polycyclic aromatic hydrocarbons (PAHs) whose endpoint is often the sediment of a receiving water body.

Stormwater assessment has been traditionally centered on loads instead of impacts and that can lead to misevaluating the risk associated with runoff discharges. The objective of this study was to characterize storm runoff solids from a mixed-use urban watershed and determine the physical, chemical and biological effects they incur on receiving sediment.

The experimental approach involved a 2-year sampling plan (2015-2017) in Paleta creek at Naval Base San Diego (NBSD) utilizing a variety of sampling approaches including intensive sampling of individual storms with size-fractionation, water and sediment collection before and after the winter storm season and settling traps collecting depositing sediments throughout the storm season. Pore water sampling and both in-situ and ex-situ bioassays with bent-nose clams (Macoma Nasuta) were employed to determine the response of the receiving benthic ecosystem.

Size fractionated stormwater loads combined with settling trap solids analysis were identified as the most effective tools to assess sources and sediment contamination. Analysis showed that PAHs in stormwater are associated with coarser, organic-carbon rich particles that settle close to the creek discharge point. Parent and alkylated PAH ratios allowed stormwater from this watershed to be distinguished from sediments settling in areas away from the stormwater discharges and confirmed that the physicochemical effects of runoff are localized in the near-field. The bioaccumulation studies indicated that solids-associated PAHs in stormwater runoff have limited bioavailability that is significantly lower than what sediment PAH concentrations would predict. However, bioaccumulation was more closely predicted by pore water concentration measurements indicating that pore water passive sampling can be a relatively inexpensive surrogate for assessing PAH uptake of benthic ecosystems.

Publication Summary

  • Geosyntec Authors: Megan Otto
  • All Authors: Megan Otto
  • Title: The Association for Environmental Health and Sciences (AEHS) Foundations' 30th Annual International Conference on Soil, Water, Energy, and Air
  • Event or Publication: Event
  • Practice Areas: Urban Stormwater Management Planning and Design
  • Citation: Geosyntec practitioners will present at the Association for Environmental Health and Sciences (AEHS) Foundations' 30th Annual International Conference on Soil, Water, Energy, and Air on March 16-19, 2020. The conference will be held at the DoubleTree Mission Valley in San Diego, California.
  • Date: March 16-19, 2020
  • Location: San Diego, California
  • Publication Type: Platform Presentation