In Wallonia, navigable and non-navigable waterways are the site of heavy sedimentation, due to their low relief and a significant input of suspended solids of natural (water erosion of soils, etc.) or anthropogenic (past and present industrial discharges, etc.) origin.
Cleaning is necessary to preserve water quality, prevent flooding and maintain navigability. The volume of sediment accumulated in navigable and non-navigable rivers is estimated at around 5.8 million m³, of which almost 20% should be removed as a matter of priority. As siltation is a continuous phenomenon, annual maintenance dredging operations are also necessary. There is a need to find outlets for the considerable volumes generated by dredging operations. Indeed, landfill is becoming increasingly problematic for reasons of limited budget and space, and compliance with the Waste Framework Directive. However, there are many obstacles to sediment reclamation: legislative, financial, socio-cultural, etc.
Sediment quality correspondent: Florian Lienard – 065 61 08 24
Chemical characterization of sediments
The implementation of sediment quality control in Wallonia stems from the Walloon Government Decree of 11/30/1995 on the management of materials removed from the bed and banks of watercourses and water bodies as a result of dredging or cleaning work (AGW 1995), and, for navigable waterways, from the obligation of the Operational Directorate-General for Mobility and Waterways (DGO2) to carry out regular dredging, dredging and regular maintenance of the navigable waterways, water bodies and structures it manages, and, more generally, Directive 2008/105/EC (“EQS”), which requires member states to carry out long-term trend analyses of concentrations of priority substances that may accumulate in sediments and/or biota.
On behalf of the Directorate General for Agriculture, Natural Resources and the Environment (DGO3), ISSeP is responsible for monitoring sediment quality in non-navigable waterways (network of 90 stations), as well as for analyzing trends in concentrations of priority substances in sediments (network of 54 stations).
In the case of navigable waterways, ISSeP, with the help of BEAGx, takes and performs physico-chemical analysis of sediment samples, either to establish an initial diagnosis before dredging/cleaning or after dredging, or to characterize the sediments present below the dredging level and which are to remain in place. Other samples are taken for particle size analysis. Lastly, ISSeP produces and updates summary maps of seabed quality for DGO2.
Ecotoxicological tests
As part of our mission to monitor sediment quality, the physico-chemical diagnosis of a series of stations is complemented by an ecotoxicological characterization to better assess the bioavailability of pollutants, as well as the toxicity associated with the simultaneous presence of several pollutants (synergistic or antagonistic effects). The proposed approach is based on the Triad, an integrative method defined by Chapman et al. (2000) which combines chemical, toxicity and biological data. This effect-based approach is used in a number of countries (Canada, France, Netherlands), but also routinely in Flanders.
More specifically, in 2012, 11 stations in Walloon rivers were selected from the 18 “priority substances” stations, as well as 5 additional stations within the “Ecotoxicity” network of the surface water quality monitoring program, based on 5 bioassays:
- 3 on interstitial water using specific water column organisms: inhibition of the bioluminescence of Vibrio fischeri (bacterium), inhibition of the growth of the alga Pseudokirchneriella subcapitata and inhibition of the reproduction of the rotifer Brachionus calyciflorus.
- 2 on whole sediment using sediment-specific organisms: mortality and inhibition of development of Chironomus riparius (dipteran larva) and Heterocypris incongruens (ostracod crustacean).
The ecological status (and in particular the biological quality elements of this status) was assessed on the basis of the characterization sheets for surface water bodies in Wallonia (DGO3, 2009).
Revision of legislation
The 1995 AGW and the Walloon Government decree of June 14, 2001 promoting the recovery of certain wastes provide a framework for the management of sediments removed from watercourses. However, these decrees have not led to the emergence of sustainable operational solutions for the recovery/disposal of these materials, with the result that dredging and cleaning work on navigable and non-navigable rivers has been significantly delayed. Furthermore, the classification of sludge (A and B), recommended by the 1995 AGW to define management channels, no longer seems entirely relevant in the light of other regulatory provisions, such as the Decree of December 5, 2008 on soil management. It therefore seems essential to redefine an appropriate legal framework for all these sectors, and to develop the administrative and technical tools required for the sustainable management of these materials.
The main objectives of this study are to :
- take stock of current management, from in situ characterization to sediment reclamation/disposal;
- identify recovery/disposal channels ;
- propose a new legal framework;
- develop new management tools (sediment management map, automatic tracking form, best practice guide for sediment characterization, etc.).
The first year of the project was devoted to compiling a bibliography of studies on Walloon sediments and related materials, and to drawing up a quantitative and qualitative inventory of deposits. At the same time, the various management methods were evaluated, and a legal analysis of existing regulations was undertaken.
The second year of the project was mainly devoted to drafting the new “sediment decree”, thanks to the active participation of the relevant administrations (DGO3, DGO2, DGO1, Société publique de la gestion de l’eau – SPGE) and the law firms Orban de Xivry & Cartuyvels and Bird & Bird, who won the subcontract for the legal study. A study of the expected economic impact of implementing the decree (as the project currently stands) has been carried out, and shows that its application could lead to greater recovery of sediments removed from watercourses, thereby reducing the costs associated with their management.
At present, the main focus is on finalizing the sediment management map. Ultimately, this will be a mapping application for consulting and integrating geo-referenced data on the management of materials removed from watercourses, facilitating implementation of the new regulations concerning them. It will be available in two integrated versions with differentiated access (see Figure below). The first is designed to help the technical officer in his or her task of examining applications, while the second is designed to facilitate administrative procedures for managers by using electronic forms linked to the card. Eventually, it could be linked to electronic application forms for land use or waste certificates (CUD, CUS). These applications will enhance the traceability of operations, by creating automatically updated databases of dredging and cleaning inventories, CUS and CUD, and reclamation areas. These tools will enable sustainable management of watercourses in line with Walloon environmental legislation.
Sampling and analysis
ISSeP takes sediment samples and analyzes them for physico-chemical and granulometric properties. The (non-exhaustive) list of parameters that can be analyzed in sediments is as follows:
- pH, Conductivity.
- Analysis of inorganic element concentrations: Al, As, Ba, Be, Ca, Cd, Co, Cr (total Cr and CrVI), Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sn, Ti, Tl, V, Zn, and anions F-, S=, CN-.
- Analysis of organic compound concentrations: Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs), Hydrocarbon Index (iHC), Volatile Organic Compounds (VOCs).
- Particle size analysis.
Bioassays
Most of the bioassays carried out at ISSeP are 17025 accredited (acute and chronic tests on Vibrio fischeri, Pseudokirchneriella subcapitata, Daphnia magna and Brachionus calyciflorus and Chironomus riparius). All comply with internationally recognized standards. The test on the ostracod Heterocypris incongruens uses a commercial kit, as do the simplified methods for accredited tests.
- Liquid phase testing :
– Inhibition of bioluminescence of Vibrio fischeri bacteria (ISO 11348-3)
– Growth inhibition of freshwater algae (Pseudokirchneriella subcapitata (ISO 8692)).
– Acute toxicity to Daphnia magna Straus (ISO 6341)
– Chronic toxicity by Daphnia magna Straus (ISO/DIS 10706)
– Inhibition of reproduction of the rotifer B. calyciflorus (ISO 20666)
– Determination of the toxicity of freshwater sediments to Chironomus riparius (NF T90-339-1) - Solid-phase testing :
– Acute toxicity – Avoidance test with Eisenia fetida (ISO 17512-1)
– Chronic toxicity – Determination of reproductive effects on Eisenia fetida worms (ISO 11268-2)
– Determination of nitrification potential and inhibition of nitrification (ISO 15685) - Microbiotests (simplified methods)
– PhytotoxkitTM
– Algaltoxkit FTM
– DaphtoxkitTM
– Rotoxkit FTM
– OstracodtoxkitTM
