Évaluation et gestion des risques environnementaux associés aux systèmes de gestion des eaux usées ruraux décentralisés

Rob Jamieson, professeur agrégé, Université Dalhousie , 2008 - 2012
Enjeu

Environ 20 % de la population canadienne dépend d’un système autonome d’assainissement des eaux usées pour la gestion des eaux usées domestiques. Ce pourcentage est encore plus élevé dans certaines provinces : près de la moitié de la population de la Nouvelle-Écosse utilise des installations d’assainissement autonomes. Bien que la majorité des provinces aient des lignes directrices techniques assez détaillées pour la conception et l’installation de systèmes autonomes de gestion et d’évacuation des eaux usées, ces systèmes peuvent tout de même représenter des risques importants pour les eaux de surface et les eaux souterraines. Bon nombre d’installations ne sont pas bien entretenues ou sont mal conçues et construites, ce qui peut entraîner un traitement inadéquat des eaux usées et avoir d’importantes répercussions sur la santé de l’homme et de l’environnement. À l’heure actuelle, la plupart des provinces n’ont pas d’exigences établies en matière d’inspection et d’entretien continus des systèmes autonomes. Il nous faut plus de données sur le rendement à long terme de ces installations si l’on veut être en mesure de prédire les répercussions sur la qualité de l’eau de ces systèmes et planifier des stratégies d’inspection et de remplacement. 

Le projet, sous la direction de Rob Jamieson, vise à évaluer l’efficacité de traitement de divers types de systèmes autonomes et examiner plusieurs modèles de rechange. L’équipe a notamment entrepris de quantifier les charges de contaminants provenant des systèmes autonomes à l’échelle du terrain et du bassin versant et de développer des outils de modélisation du bassin versant permettant d’évaluer les risques que posent ces types de systèmes d’assainissement des eaux usées.

Projet

This project examined onsite wastewater systems; comparing different design alternatives under varied wastewater loading regimes, and studying the lifespan of the systems.  This involved constructing and monitoring field scale onsite wastewater systems.  The team tracked long-term changes in water quality under various controlled loading conditions. Data from these systems was also used to calibrate and validate computer models that simulated water and contaminant movement through the systems.

The research has shown that a variety of onsite wastewater treatment systems used throughout Eastern Canada are capable of providing excellent treatment of wastewater, producing effluent with very low average concentrations of parameters of concern such as total suspended solids or E. coli bacteria.  The team also found that treatment performance of some designs can be extremely variable depending on loading rate, loading method and external hydrologic inputs.  However, one particular design, the lateral flow (sloping) sand filter, provided a very high level of treatment for water quality parameters of interest to regulators.   

Knowledge and modeling approaches were used to develop watershed scale assessment tools.   A watershed simulation framework was developed, which involved the integration of the Soil and Water Assessment Tool (SWAT) with a new model (POWSIM-Phosphorus On-site Wastewater Simulator). This integrated modeling approach was then successfully applied within the Thomas Brook Watershed in Nova Scotia.  The team also developed and tested a GIS (Geographic Information System) -based semi-quantitative risk assessment model for potential onsite system impacts. When the model was applied to Huron-Kinloss Township in Ontario, at-risk areas were successfully identified and validated by local experts.

Produits

End user oriented reports:

  • The effects of dosed versus gravity fed effluent loading on the hydraulic functioning of contour trench disposal fields.  Report prepared for Nova Scotia Environment and Wastewater Nova Scotia.
  • Development of a Hybrid Constructed Wetland. Final report to Canada Mortgage and Housing Corporation.
  • Reed Bed Filter for Septage Treatment. Final report to Ontario Ministry of the Environment.
  • Hybrid Constructed Wetland for Small Community Wastewater Treatment and Reuse FactSheet.
  • Wastewater Treatment and Reuse Case Study - El Attaouia, Morocco.

Tools:

  • Phosphorus On-Site Wastewater Simulator (POWSIM):  This tool was developed to link with the Soil and Water Assessment Tool (SWAT) to provide an integrated physically-based modeling framework for quantifying the impacts of on-site wastewater systems at watershed scales.
  • On-Site Wastewater Risk Assessment Mapping Tool:  This tool was developed as a GIS-based semi-quantitative mapping tool that can be used to assess the relative risk of on-site wastewater impacts at the watershed scale.
  • National Training Program for Community Based Drinking Water Monitors on First Nation Reserves (training manual, Source Water Protection DVD, training DVDs and online exam for Health Canada)
  • Septic System Video for First Nation Communities (developed for Health Canada)

Workshops and meetings:

  • Presentation at Wastewater Nova Scotia 2011 Annual General Meeting and tour of the Nova Scotia On-site Wastewater Research Centre.
  • Presentation to highlight research results - Cornwallis Headwaters Society 2011 Annual General Meeting. 
  • Design seminar on decentralized wastewater management to the largest engineering firm in Morocco and watershed basin association 
  • Seminar on decentralized wastewater systems to planners from First Nation Communities across Quebec
Résultats
  • Changes in practice - based on the strength of the research results that indicated the success of the sloping sand filter design in treating wastewater, Nova Scotia Environment included the technology in a technical guideline outlining acceptable forms of treatment.  Its inclusion in the guideline has provided more options to homeowners when installing new treatment systems. 
  • Informing investment decisions - the quality of the treatment system, as well as the lower cost of installation in some cases, has led to broad uptake of the technology.  In 2010 alone, sloping sand filters were the second most installed systems in Nova Scotia with 340 new installations.
  • Changes in practice related to wastewater treatment systems - the Ontario Ministry of the Environment has started granting Certificates of Approval for full scale application of septage reed bed filter technology. 
  • Capacity-building - this project has led to opportunities in Ontario and Nova Scotia for training at the onsite wastewater research and demonstration facilities developed through the project.
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Équipe de Recherche et Partenaires:

Équipe de Recherche

Rob Jamieson, professeur agrégé, Université Dalhousie
Doug Joy, directeur adjoint (cycles supérieurs), Université de Guelph; directeur général, Ontario Rural Wastewater Centre
Robert Gordon, professeur, Université de Guelph; doyen, Collège de l’agriculture de l’Ontario
Craig Lake, professeur agrégé et chef de département, Génie civil, Université Dalhousie
Chris Kinsley, gestionnaire, Centre Alfred, Université de Guelph
Glenn Stratton, professeur, Nova Scotia Agricultural College

Partenaires

Wastewater Nova Scotia
Cornwallis Headwaters Society
Ministère de l’Environnement de la Nouvelle-Écosse
Ontario Rural Wastewater centre
Ministère de l’Agriculture et des Pêches de la Nouvelle-Écosse
Rideau Valley Conservation Authority
Comté de Tay Valley
Comté de Colchester

RESEARCH SUMMARY
(5-page report)

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