Old Mill Pumping Station
The Old Mill Sanitary Pumping Station is being replaced with a larger pumping station to service growth in the community while providing longevity and reliability.
The former Old Mill Sanitary Pumping Station was constructed in 1969, adjacent to the Grand River. With future development potential in mind, the City of Kitchener recognized a need to upgrade the aging infrastructure. The redesign was set in motion with the purpose of bringing the station into compliance with current City standards and as an opportunity to increase emergency storage capacity.
We first completed a Schedule B Class Environmental Assessment (EA) to identify the City’s options and determine the best course of action for sanitary servicing. Throughout the Class EA we considered the various impacts presented with each option. Environmental, cultural heritage, archeological, geotechnical and hydrogeological studies were completed to guide our analysis.
The minimization of disruption to residents and the surrounding natural area was a high priority. Our team engaged the public, First Nations and a wide range of stakeholders for their input. We collaborated with stakeholders through various meetings and open-lines of communications, including a Public Information Centre.
Based on the Class EA, we determined that the preferred solution was to decommission and remove the old station and construct a new sanitary pumping station and forcemain on the opposite side of Old Mill Road. Our team completed the preliminary and detailed design for the new 150 L/s station, which includes:
- An emergency storage tank with tipping bucks for flushing;
- A two-cell divided wet well with a rock trap and grinder;
- A dry well with three pumps and a magnetic flowmeter; and
- A control building housing:
- A pump hoist room with an odour control unit; and
- A generator room, electrical room and washroom.
A larger forcemain is also being constructed for the new station, in addition to a new inlet sanitary sewer and a re-located watermain to accommodate the new station building.
Our group has managed the contract administration for the construction of the new station, as well as the decommissioning of the existing station so that the community can find renewed use for the land. Geotechnical and hydrogeological studies revealed soil and groundwater conditions that would prove to be a challenge for our team. Our design would require careful consideration of the natural setting – the river, a creek, impacted fill, deep excavation, and above all, excavation below the groundwater table in porous granular soil.
The site is located on a glacial outwash area and contained coarse gravel and stone deposit that extended over 30 m down to the fractured shale bedrock, allowing groundwater to flow freely through the porous soils below the site. We recognized that the site was small and the coarse-grained soils allowed a high volume of groundwater flow, which demanded that a soil retention system be utilized throughout construction, as well as shoring methods such as sheet piling or secant walls to allow excavation to a depth in excess of 12.5 metres below ground surface (mbgs).
There was also limited space for stockpiling of excavated materials. This was mitigated through soil retention to reduce the volume of soil that would be sent to a landfill. The high water table necessitated extensive construction dewatering, water quality control and floatation calculations to ensure that the finished station would not float during flood conditions.
Our experience designing this station is a standing reminder of the importance of a well-defined scope in the early phases of a project, as well as thorough pre-design investigations and a willingness to modify construction methods to address real world issues.
Association of Canadian Engineering Companies – Grand River Chapter | 2023 Award of Merit | Diamond Award