The Watershed Contaminant Reduction Index measures drainage system releases to the North Saskatchewan River from the city of Edmonton, adjusted for population. The index is calculated annually using measured and estimated amounts of sediments, nutrients (ammonia and phosphorus) and bacteria discharged to the river, referenced to a baseline. Sources of these parameters from the City of Edmonton include the Gold Bar Wastewater Treatment Plant, combined sewer overflow sites and stormwater outfalls. An increase in the index is good and means less contaminants were released into the river. A five-year running average is used to smooth out fluctuations due to weather.
The City of Edmonton is committed to tracking and reducing contaminant discharges into the North Saskatchewan River to reduce the impact these contaminants have on river ecology and downstream communities. Parameters included in the calculation are associated with collection and treatment of wastewater and stormwater and have also been identified as important to the North Saskatchewan River basin by the City’s regulator, Alberta Environment and Parks. The parameters are reported monthly and annually under the City’s approval to operate its sewer systems and are watershed health indicators.
Data sources: Sewer flows and water quality monitored and estimated by the City. Performance data from the Gold Bar wastewater treatment plant forms part of the loading information. Municipal Census and the City of Edmonton Chief Economist estimates (population information). Results from 2010 - 2012 are reported here but the calculation methodology was not comparable to current methodology.
Explanation of Performance
2017 was an average precipitation year, meaning average loads from
the stormwater system, and the 2017 index result was 7.2. Continued
treatment optimization at Gold Bar Wastewater Treatment Plant has
resulted in a decrease of loads discharged into the North Saskatchewan
River. Generally, there were fewer contaminants released into the
North Saskatchewan River in 2017 than originally forecasted. The
city’s current population is also higher than the estimates which were
developed in 2014, driving results upward.