Sediment

Particles that settle on the beds of waterbodies slowly build up the sediment compartment of the aquatic ecosystem. Sediments can become contaminated either by the settling of contaminated particles or by precipitation of soluble contaminants out of the water column. Benthic organisms can subsequently absorb contaminants from sediment and transfer them to the entire food web. Moreover, sediments in suspension in the water column in significant concentrations may cause physical effects that are hazardous to aquatic life, even if they are not contaminated by pollutants.

The following documents can be used to support sediment quality evaluation and management, as well as dredging project management.

Québec sediment quality criteria

Quebec’s criteria for assessing sediment quality have been developed based on the Canadian Council of Ministers of the Environment (CCME) approach to sediment contamination. To meet Québec’s specific needs in sediment management, three threshold values were added to the two already proposed by the Council. All thresholds were calculated using the same data base, with similar methods.

Open-water disposal of dredged sediments

Along with the criteria, the following publication provides guidance on the assessment of the ecotoxicological risk of freshwater disposal of sediments:
Ecological Risk Assessment of Open-Water Sediment Disposal to Support the Management of Freshwater Dredging Projects

Environmental Monitoring and Surveillance Programs for Dredging and Sediment Management Projects

The Guide for the Development of Environmental Monitoring and Surveillance Programs for Dredging and Sediment Management Projects (PDF, 887 KB) is mainly intended for dredging project managers and environmental evaluation workers. It presents the main steps involved in designing an environmental monitoring and surveillance program and provides guidelines and markers for this type of plan that is adapted to dredging and sediment management projects.

The following publication provides dredging management guidelines for minimizing any negative impact of suspended matter on aquatic life: Recommendations for the Management of Suspended Solids (SS) During Dredging Activities (PDF, 2.6 MB). It is particularly useful when developing dredging monitoring protocols for project managers, main contractors and environmental assessment analysts.

Sediment characterization

The aim of the Guide for physicochemical and toxicological characterization of sediments (PDF, 1.3 MB) is to standardize preparation and analysis methodology for quantifying substances found in sediments, as well as their levels of toxicity. Relying on recognized and validated analytical methods, the Guide details the acceptability of analytical methodology performance threshold and results criteria. The goal here is to minimize any laboratory variance impact, from the time when samples are received to final analytical certification. The Guide is intended as a tool for characterization project managers, environmental consulting firms and sediment analysis laboratories that can be of use in characterizing freshwater and saltwater sediment samples.

The Assessing sediment toxicity in the upper St. Lawrence estuary fact sheet states the recommended toxicity trials to be used for assessing the potential toxicity of sediments in the brackish zone of the river. This zone runs from the eastern tip of île d’Orléans, ending at the mouth of the rivière Saguenay to the north and at the western tip of île Verte to the south. Two species of amphipods (small crustaceans) were selected: Hyallela azteca, recommended for saline levels varying from 0.5 to 15‰, and Eohaustorius estuarius, for a broader range of salinity varying from 0.5 to 30‰.

Other publications about sediments and dredging are available on the St. Lawrence Action Plan Web site.