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Application Paper

A GIS-Based Model to Assess the Risk of On-Site Wastewater Systems Impacting Groundwater and Surface Water Resources

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Pages 229-246 | Published online: 23 Jan 2013
 

Abstract

On-site systems are successfully used across Ontario and Canada in rural areas to treat and disperse wastewater in areas without access to centralized sewer facilities. Ontario has detailed technical guidelines for the design and installation of on-site systems to help safeguard against contamination to public health and the environment. However, since on-site systems are managed by private users, there are significant risks to either surface and groundwater resources when the systems malfunction or are improperly operated and maintained. This research assesses and models these risks on a regional basis utilizing a GIS-based assessment tool. The developed risk assessment model uses nine pertinent parameters to account for contaminant loading and pathways, and system characteristics. Risk parameters included soil type, slope, lot size, surface water proximity, floodplain, groundwater intrinsic susceptibility, recharge areas and water supply proximity. When applied to Huron-Kinloss Township in Ontario, at-risk areas were successfully determined by the model and then confirmed and validated by local experts. Soil type, groundwater intrinsic susceptibility and system age were the greatest contributors to the overall risk for this area. The GIS-based model is useful for decision-makers in identifying at-risk areas for targeted management strategies such as prioritized re-inspection programs.

Les fosses septiques sont utilises avec succs partout en Ontario et au Canada dans les zones rurales afin de traiter et de disperser les eaux uses dans les rgions qui ne disposent pas d'un accs des installations ou des canalisations dgout centralises. L'Ontario a adopt des directives techniques dtailles pour la conception et la mise en place d'installations septiques afin de contrer la contamination de l'environnement et de protger ainsi la sant publique. Cependant, tant donn que les installations septiques sont gres par des utilisateurs privs, des risques considrables psent sur les ressources en eau de surface ou souterraine lorsque les installations fonctionnent mal ou ne sont pas exploites et entretenues de faon approprie. La prsente recherche vise valuer et modliser ces risques une chelle rgionale l'aide d'un outil dvaluation SIG. Le modle dvaluation du risque qui a t labor fait appel neuf paramtres pertinents pour reprsenter la charge de contaminants et leur cheminement, ainsi que les caractristiques du systme. Les paramtres de risque englobaient le type de sol, la pente, les dimensions du terrain, la proximit des eaux de surface, le primtre d'inondation, la susceptibilit intrinsque des eaux souterraines, les zones d'alimentation et la proximit des rserves ou des sources d'eau. Lorsque le modle a t appliqu au canton de Huron-Kinloss en Ontario, il a permis de dterminer avec succs les zones risque, et celles-ci ont ensuite t confirmes et valides par des experts locaux. Le type de sol, la susceptibilit intrinsque des eaux souterraines et lge de l'installation ont t les facteurs ayant contribu le plus au risque global pour cette rgion. Le modle SIG est utile aux dcideurs en ce qu'il leur permet de cerner les zones risque en vue de l'adoption de stratgies de gestion cibles comme les programmes de rinspection des fosses septiques dans les zones prioritaires.

Acknowledgements

This research was financially supported by the Canadian Water Network. Supporting partners included BM Ross and Associates, Huron County Healentry Unit and Rideau Valley Conservation Authority.

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