The earlier figure was calculated based on retention volumes of the wet well at the McCarthy Boulevard pumping station, she explained. A more refined calculation was then completed using pump rates and the amount the bypass valve was open.
On July 27, Wilson said while most of Regina received roughly 78 millimetres of rain in a 24-hour period, the northwest got pelted with anywhere between 90 and 107 millimetres. She called the rain a one-in-25-year event.
To save infrastructure from getting damaged and to prevent sewer from backing up into homes, a decision was made to bypass most of the usual wastewater treatment process and instead, release screened sewage mixed with rain water directly into the creek.
"A bypass is never a desirable event," she clarified.
Within a few days of the release, Wilson said the creek returned to its pre-bypass condition.
"The diversion did not have a lasting impact on the creek water quality."
Investments and improvements are being made to the McCarthy pumping station to ensure capacity is increased so that the system can handle significant future rainfall events. Of course the new $181-million sewage treatment plant will also help with that.
In the meantime, another big downfall could spell another similar problem.
"Those things all do take time so if we have another large event then that is unfortunately one of the possibilities."