Assessing sediment recontamination from metals in stormwater

Area of Science:

• Environmental Science
• Water Quality
• Geochemistry

Background:

• Sediment remediation effectiveness is challenged by stormwater recontamination.
• Understanding metal sources and transport in urban watersheds is crucial.

Purpose of the Study:

• To evaluate methods for assessing metal recontamination of sediments by stormwater.
• To identify dominant sources and particle-size fractions of metals in stormwater impacting sediments.

Main Methods:

• Conducted simultaneous stormwater and sediment sampling in Paleta Creek, San Diego.
• Measured size-segregated stormwater contaminant loads and receiving water/sediment concentrations.
• Utilized settling traps to quantify deposition rates and compare with stormwater loads.

Main Results:

• Residential and highway sources dominated stormwater loads of Cadmium (Cd), Copper (Cu), Lead (Pb), and Zinc (Zn).
• Arsenic (As), Nickel (Ni), and Mercury (Hg) were more influenced by downstream watershed areas.
• Cd associated with large particles settled nearshore; Cu associated with fine particles showed less nearshore deposition.
• Sediment traps indicated sources beyond stormwater, including resuspension, for Cu and Hg.

Conclusions:

• Size-segregated stormwater contaminant analysis combined with deposition measurements can distinguish stormwater recontamination from other sources.
• Particle size distribution is a critical factor in metal transport and sediment recontamination.
• Effective sediment remediation strategies must account for diverse metal sources and transport pathways.