Everything Goes Somewhere: Tracking the Movement of Dredged Sediments in Port and Coastal Environments Using Dual Signature Sediment Tracers Kevin Black Partrac Ltd Dredging 2021, San Diego, October, 2012 Title Sediment Sources direct, real world study of contaminant movement Text snapshot only animation Title Particle Tracking: a simple concept Cartoon courtesy of Bairds From: BALSON, P. S. & COLLINS, M. B Coastal and Shelf Sediment Transport. Geological Society ofLondon, Special Publications, 274, 73 We Did A Review Technology analysis Tracer types Tracer sampling Analytical approaches Dual Signature Tracers Coated Natural Particles Coated with fluorescent signature Coating integrated with microscopic magnetic inclusions Silt and sand size tracers available Hydraulic, geometric and geologic properties maintained Fluorescent Tags 4 spectrally distinct colours Unique emission wavelengths Facilitates fluorimetric analytical method Stable and long-lasting Can use non-fluorescent hues Para-magnetic Attributes Para-magnetism particles are not themselves magnetic but respond to an applied external magnetic field Facilitates use of in situ magnets for tracer recovery Facilitates use of magnetic susceptibility sensor Tracer Introduction Directly onto seabed (i.e. prior to dredging) Introduce direct into hopper Release as neat tracer Via overspill Applications in the Dredging Context Resuspension due to dredging process Fate of residuals Fate of offshore disposal material Impact onto sensitive benthic areas Cap sediment stability (contaminated sediments Water injection dredging sediment fate Sampling Design The Critical Component Arrays of in situ magnet moorings instant data, enables adaptive sampling Grid based grab/core sampling In situ fluorimetry Magnetic separation Temporal sampling design IMPORTANT Cap Stability Fate of Residuals Water Injection Dredging DM Fate Text Title CASE STUDY: The Lower Duwamish Length approximately km Width (main channel) approximately m Inflow approximately = < m 3 s -1 (mean approximately 40 m 3 s -1 ) Area of entire cleanup site approximately 1,800,000 m 2 Area of southernmost 1 km of the waterway (including turning basin that acts as sediment trap) approximately 350,000 m 2 Water volume within cleanup site pproximately = 11,000,000 m 3 Title The Study Objectives Overarching Objectives To understand transport pathways of PCB contaminated sediments in the LD Waterway To show how far into or beyond the cleanup site PCB-contaminated particles introduced from upstream areas of the Duwamish/Green river can be transported Text Title Getting the tracer into the water Title Study Design and Sampling Ebb tide injection; day 0, week 1, month 1, month 2 Fixed (and dipped) magnets Bed samples Vessel transects (pump sampling) Day 0 - Sand sand tracer detected in suspension up to m from release point size (200+ m ) some of the very fine sand tracer (particle sizes ~60 to 70 m) were found in suspension at RM 0 Title SAND SILT Day 0 - Silt silt detected in near-field of release mid-stream transects, and along estuary flanks widespread dispersion size analysis indicates all size particles in suspension silt found in suspension ~4.4 miles downstream, as tide turned silt found at mid-depths Suspended silts can be deposited throughout the cleanup site (via downward turbulent mixing), potentially retained by the tidal excursion distances. General Points Sediment tracking is a useful tool to for dredging, seidment impact and environmental/regulatory assessment as long as it is applied properly Provides direct insight into sediment movement (Lagrangian) no other technique can Useful for model validation To be used in conjunction with conventional tools e.g turbidity monitoring, ADCP flow mapping Dual signature tracers offer advantages over mono-signature forbears: Magnetic attribute facilitates in sit interception and laboratory processing search for tracer more earnest better scientifically Silts to cobbles available Lower density materials also available Title General Conclusions