ASABE Technical Library - Abstract
Member and Access Notice
A RISK ASSESSMENT MODEL FOR ONSITE SYSTEMS APPLIED TO THE CITY OF OTTAWA, CANADA
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 701P0104, . (doi: 10.13031/2013.15759)Authors: C.B. Kinsley, D. Joy, A. Campbell, D. Feniak, D. Branson, T. Albert, J. Sauriol
Keywords: onsite wastewater treatment, risk assessment, modeling
Failing onsite wastewater systems can pose a significant risk to public health and to the
environment. An easy to use risk assessment model using readily available information would
be a useful tool for regulators. Such a model has been developed and successfully applied to 19
villages within the City of Ottawa. The model is being used to identify high risk areas in order to
prioritize re-inspection programs and to develop a management strategy. The model will also be
useful to planners in developing environmentally sustainable growth plans for village areas.
The model is comprised of a series of weighted risk factors applied to lot parcels in a GIS
database. The factors were developed using existing data readily available to the City (soils,
floodplain, parcel and building mapping, census data, aquifer vulnerability study, local hydro
geological knowledge). The factors attempt to account for contaminant loading, contaminant
pathways and operational life of onsite systems.
Data from system inspection reports, replacement permits, local knowledge, groundwater quality
and surface water quality can be used for model validation. Total risk was found to correlate
well with the number of high risk factors per village identified by the local regulatory authority
(Correlation Coefficient = 0.67). An analysis of recent system replacement permits in the study
area indicates that 70% of failed conventional leaching bed systems were greater than 25 years
old while 65% were in impermeable soils, suggesting a good correlation with the risk model
factors for system age and soil type. An analysis of well water data over a 3 year period
indicates a low occurrence of E.coli contamination (2%) and does not show any significant
correlation with risk model factors.