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APPENDIX F - Examples of Mitigation Measures

Table F-1 Examples of Mitigation of Contaminant Migration Routes in the Water Column and in the Terrestrial Environment

Water column
Reduction of the concentrations of resuspended and dissolved solids and contaminants and reduction of their current-driven transport by advection
Dredging/transport
  1. Limiting the work to the suitable tidal or hydrological cycle
  2. Reducing the dredging time and rate
  3. Reducing the cutting depths
  4. Optimizing the disaggregator speed with the power of the pump
  5. Increasing the power of the suction pump
  6. Installing a watertight hood near the disaggregator head
  7. Improving the seals of the mechanical buckets, barges or backflow pipes and the buckets/railway cars or tankers used to transport dredged materials
  8. Installing protective screens/curtains (impermeable membranes, sheet pile bulkheads, bubble curtains) at the job site or near sensitive areas
  9. Prohibiting use of the overflow when filling barges/railway cars
Disposal/containment of materials in open water
  1. Limiting the work to the suitable tidal or hydrological cycle
  2. Reducing the volume of materials for each discharge
  3. Installing submerged diffusers at the end of the pipes
  4. Capping contaminated sediments with clean materials
  5. Depositing sediments in geotextile bags on the barges
  6. Considering the use of barges instead of backflow pipes
Upland disposal/containment
  1. Reducing the hydraulic flows of the deposited materials
  2. Adding flocculants or physical barriers to improve sedimentation
  3. Verifying the operation or installation of a physicochemical effluent treatment system
Terrestrial environment
Reduction of the concentrations of contaminants in gaseous, liquid and solid releases; reduction of the risks of migration of contaminants in the air, soil, groundwater and sewer networks, and reduction of the exposure routes of natural environments and humans
Upland disposal/containment
  1. Maintaining sediments under water or keeping the surface layer wet throughout the containment day
  2. Improving watertightness of dikes
  3. Capping contaminated sediments with clean materials or installing impermeable membranes
  4. Planting vegetation screens or erecting earthen berms surrounding the disposal site
Treatment of contaminated materials
  1. Reducing the treated flows
  2. Verifying the capture of gaseous, liquid and solid releases and rerouting them to treatment facilities
  3. Verifying the operation of the treatment equipment according to the manufacturer’s specifications
  4. Adding complementary treatment systems
  5. Reexamining the choice of technological components of the entire treatment process

Source : tiré de Michaud, J.R. (2000). Programme de surveillance et de suivi environnemental de projets de dragage et de gestion des sédiments. Démarche de conception et de mise en œuvre. Environnement Canada, Direction de la protection de l’environnement, Région du Québec, Section Éco-innovation technologique. Rapport 217 pages.

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