Cottage Grove High Zone Water Main

Challenge

In Cottage Grove, Minnesota, the City recognized that continued growth and long-term water reliability depended on a stronger connection between its existing wells and a future treatment facility. A planned Intermediate Zone Water Treatment Plant, centrally positioned within the city limits, represented a critical investment in the city’s long-term water system, but one major gap remained.

Untreated water from Wells 11 in Highlands Park and 12 in Sunnyhill Park had no direct, reliable path to reach the future treatment facility. Without that connection, the plant would not be able to receive the raw water needed to support system expansion, remove PFAS contamination, or meet the community’s future demand. Ensuring dependable water delivery became essential to protecting both growth and long-term service reliability.

Creating that connection introduced several challenges. The required alignment would span nearly the entire northern portion of the city, traveling primarily through public green space while also crossing established residential corridors lined with homes and private property. The City needed to advance critical infrastructure while minimizing disruption to neighborhoods, preserving community assets, and maintaining public trust throughout construction.

Because the water line installation required reconstructing portions of the corridor, the project also triggered additional regulatory requirements. Local and watershed district standards required treatment of the first half inch of stormwater runoff from the reconstructed roadway surface. Traditional stormwater solutions risked extending impacts far beyond the project limits, potentially requiring additional right-of-way acquisition, higher costs, and greater disturbance to surrounding areas.

The City faced a complex balancing act: deliver essential water infrastructure, meet evolving environmental regulations, protect neighborhoods, and ensure responsible use of public funds, all within a single coordinated project.

Solution

The City of Cottage Grove collaborated with SEH to transform a complex utility extension into a coordinated investment in both water reliability and environmental management.

Connecting Wells to the Future

Construction focused on a clear goal: creating a reliable raw water connection between Wells 11 and 12 and the future treatment plant.

The work began at Well 12, where a 12-inch main ran south along a 500-foot stretch and tied into the north end of a 16-inch main installed during a previous project. From there, the system connected to the south end of that same 16-inch main a half mile away, then turned south and continued for 0.75 miles to reach Well 11, where it upsized to a 16-inch main.

Together, these connections form a continuous raw water pipeline across the northern part of the city, linking both wells to the future treatment plant.

By routing much of the line through green space, the team minimized disruptions to traffic and nearby residents while maintaining access and safety throughout construction. What emerged is more than a buried pipe. It is a resilient framework that allows untreated water to be efficiently delivered for treatment and pumped back into the system, strengthening capacity and ensuring dependable service as Cottage Grove continues to grow.

Turning Constraints into Opportunity

Stormwater requirements could have complicated the project and expanded its footprint, but instead, they became an opportunity for innovation. The team identified a city-owned stormwater pond adjacent to the corridor that already received drainage from the project area. Nearby land with no practical alternative use created space for enhancement without encroaching on private property.

Rather than pursuing costly off-site infrastructure, SEH designed a sand bench adjacent to the pond to intercept drainage when water levels rise after storm events. The sand filtration system, installed along a portion of the perimeter of the wet pond, improves water quality by treating runoff before it exits. As runoff enters the pond, the sand bench filters the required water volume and removes pollutants prior to discharge.

The solution delivered several additional benefits beyond improved water quality, including:

• Maximized the existing pond footprint, avoiding significant reconstruction and reducing overall project costs  

• Met regulatory water quality requirements without expanding the site or introducing complex mechanical systems

• Provided a low-maintenance, passive treatment system that performs reliably during fluctuating storm events

• Integrated seamlessly into existing infrastructure through strategic modifications to the pond outlet

This approach met regulatory standards, avoided additional right-of-way acquisition, and delivered long-term water quality benefits in a cost-effective way. By aligning infrastructure improvements with environmental responsibility, the city gained a solution that works quietly in the background, protecting local waterways while supporting essential services.

Building Today with Tomorrow in Mind  

Through careful planning, collaboration, and creative problem solving, Cottage Grove now has the raw water infrastructure needed to serve its future treatment plant and a stormwater solution that adds value beyond the original scope. The result is a forward-looking investment that strengthens the community today and prepares it for tomorrow.