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Assessing Sediment Recontamination and Bioaccumulation by Stormwater Heavy Metals
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Background/Objectives

Contaminated sediments serve as the source and/or sink of metal contaminants and pose some of the most difficult and cost-effective remediation challenges. Continued metal inputs from stormwater discharges can cause recontamination of remediated sediment sites, potentially limiting or reversing recovery of the sites. Heavy metals in stormwater can affect receiving sediments by suspended solid deposition and bioaccumulation in living organisms entering the food chain. The study objective is to present approaches for assessing sediment recontamination and bioaccumulation from metals in stormwater. The selected field site was Paleta Creek, downstream of Naval Base San Diego and an urban mixed-use watershed in San Diego, CA.

Approach/Activities

Simultaneous stormwater and receiving water and sediment monitoring were undertaken during 2015-2017. The stormwater samples were fractionated by size to relate discharges to sediment recontamination and analyzed for a variety of contaminants. Here we will focus on the metals Cd, Cu, Ni, Zn, Pb, Hg, and the metalloid As and evaluate stormwater discharges and receiving water impacts. Sediment traps with hyper-saline brine were deployed to help relate discharges with those impacts. Ex situ bioaccumulation exposures using the clam Macoma Nasuta as well as inorganic passive sampling using DGTs were applied to extend bulk sediment impacts to assess availability and biological impacts.

Results/Lessons Learned

Size-segregated contaminant loads of intensively monitored stormevents with settling traps in the receiving waters were best able to link discharges to sediment recontamination. Sediment cores that are influenced by a variety of long term processes do not necessarily indicate the effects of recent storm events. Cd in the downstream Creek location was associated with larger particles (>63 μm) mostly associated with highway/residential sources, that settled directly to the near shore sediment. By contrast, Cu settled throughout the receiving waters due to both to association with smaller particles and evidence of additional sources or sediment resuspension and settling from elsewhere. Other metals showed similar behavior to varying degrees. Lessons learned are used to develop a semi-quantitative framework for identifying sediment recontamination potential due to stormwater (Phase II of the project - that will not be discussed here).
Despite increases in bulk sediment concentration of some metals as a result of stormwater recontamination during wet seasons, bioassays showed reduced metal bioaccumulation after stormwater impacts. This was apparently the result of the deposition of stormwater contaminants in large particles and low bioavailable forms. Porewater measurements by DGTs showed similar trends and correlated much better with observed bioaccumulation than bulk sediment concentrations. Bulk sediment recontamination due to stormwater should not be assumed to lead directly to greater biota impacts such as bioaccumulation without bioavailability assessment.

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Publication Summary

  • Geosyntec Authors: Ilektra Drygiannaki (Geosyntec Consultants, Chicago, IL, USA), Brandon Steets, Megan Otto and Jared Ervin (Geosyntec Consultants, Santa Barbara, CA, USA)
  • All Authors: Ilektra Drygiannaki (Geosyntec Consultants, Chicago, IL, USA), Danny Reible Balaji Rao, John A. Dawson, Magdalena Rakowska and Michelle Bejar (Texas Tech University, Lubbock, TX, USA), Nicholas T. Hayman, Gunther Rosen, Marienne A. Colvin and Bart Chadwick (Naval Information Warfare Center Pacific, San Diego, CA, USA), Robert Pitt (University of Alabama, Tuscaloosa, AL, USA ret.), Brandon Steets, Megan Otto and Jared Ervin (Geosyntec Consultants, Santa Barbara, CA, USA)
  • Title: 2023 Battelle Sediments Conference
  • Event or Publication: Event
  • Practice Areas: Sediment assessment and remediation, Contaminated site assessment and clean up
  • Citation: Battelle's International Conference on the Remediation and Management of Contaminated Sediments at the JW Marriott in Austin, Texas, on January 9 through 12, 2023
  • Date: January 9 through 12, 2023
  • Location: JW Marriott in Austin, Texas
  • Publication Type: Platform Presentation