Carlton Pump Station Replacement

Challenge

 For decades, Resource Renewal, a brand of the Western Lake Superior Sanitary District (WLSSD), relied on its Carlton, Minnesota, wastewater pump station to keep the southwest portion of the collection system running smoothly. After years of infrastructure wear, they needed to replace the station to enhance reliability, protect a remote five-mile force main, and support future community growth. However, bedrock, a reservoir, and a nearby trout stream created significant site limitations. The new facility had to fit within this tight footprint while still allowing the existing services to remain operational during construction.

Solution

WLSSD partnered with SEH to deliver a modern, resilient wastewater pump station tailored to the community’s operational priorities.

Resilient Pumping and Growth

Hydraulic modeling and pump selection were completed to support both current flows of 2 MGD (million gallons per day) and future capacity of 4 MGD, helping the system plan for wet weather conditions while being prepared for community growth. The split wet well design includes four submersible pumps, allowing operators to keep one side of the station running while performing maintenance on the other. This helps minimize downtime and improve redundancy. A pump-around connection and an emergency diesel generator also help maintain uninterrupted service during both planned maintenance and unexpected events.

Oversized wet wells and influent sewers provide additional storage during extreme wet weather, reducing the risk of sanitary sewer overflows. Flushing valves, instrumentation, and integrated flow monitoring systems improve routine operations and give staff real-time insight into system performance.

Innovative Surge Protection for Critical Infrastructure

Protecting the remote force main was a top priority for the district. The team worked closely with the client to evaluate several options, including full force main replacement and air release valve installation. After careful consideration, the surge tank emerged as the most practical and cost-effective solution.

The final design gives the district greater flexibility and confidence in day-to-day operations. The pump station can operate in both surge and non-surge modes, allowing staff to respond to changing system conditions while maintaining reliable service for the community.

Programming was also incorporated to allow the pump station to operate while the surge tank is out of service by maintaining surge protection through a Programmable Logic Controller (PLC). The control strategy limits the number of pumps that can operate simultaneously, preventing surge conditions while sustaining required flow through the station. This tailored approach provides an added layer of system resilience, preserving downstream infrastructure from damaging pressure fluctuations, safeguarding nearby trout streams, and reducing the risk of costly emergency repairs even with the surge tank offline.

Environmental Stewardship and Long-Term Value

Construction required demolition of the existing station while maintaining service through wet tapping and line stopping, and required careful coordination with permitting authorities. During construction, the team identified and remediated a previously unknown fuel oil tank and contaminated soils, removing environmental risks and reducing future liability.

As part of the project, the old generator was repurposed for use at the City of Carlton Fire Department, extending its benefit to the broader community. 

By prioritizing surge protection, operational flexibility, and operator-friendly design, this system created a solution that supports the district’s long-term needs. The new Carlton Wastewater Pump Station gives staff greater confidence in daily operations while strengthening the reliability of a system the community depends on.  

Awards

• Honor Award | American Council of Engineering Companies of Minnesota (ACEC-MN)