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Rosemount wastewater plant closes after 35 years of service

While voters were toiling over candidates’ promises of new directions, Election Day 2008 saw the Metropolitan Council’s wastewater operations embark on a new course of a different sort. That’s the day they put a new wastewater pumping station into service and closed the Rosemount Wastewater Treatment Plant after 35 years of service.

Wastewater from homes and businesses in the city of Rosemount now flows to the west along County Road 42 then south along Biscayne Avenue before arriving some 10 miles later at the Council’s Empire Treatment Plant in neighboring Empire Township. The change in course will be a more cost-effective way to collect and treat wastewater in a growing area of Dakota County, tapping into an economy of scale offered by the recently upgraded and expanded Empire Plant.

“The Rosemount Plant was the smallest of the eight plants in our system, treating about 1 million gallons of wastewater per day, but it served us and the Rosemount area well for many years,” said Bill Moore, general manager of Metropolitan Council Environmental Services (MCES). “We had known for some time that this part of our operation could benefit from consolidation, and the pieces came together over the past several years with improvements we were making at the Empire Plant.”

Rosemount Plant served as demonstration project

In 1973, the former Metropolitan Sewer Board opened the small Rosemount Plant as a demonstration project that used chemical additives and physical settling and filtering to clean the wastewater – without traditional biological removal of pollutants. The U.S. Environmental Protection Agency provided a demonstration grant to support the project. As expected, the plant produced a high quality of treated wastewater, but the operational costs ruled out using the technology on a larger scale.

A decade after opening, the Rosemount Plant was retrofitted to employ more traditional treatment processes. Another decade later, growth forecasts for central Dakota County led regional wastewater system planners to take another look at the Rosemount Plant’s future: Should it be further upgraded and expanded, or should the wastewater be sent to one of MCES’s larger treatment plants? The latter option was selected as being more cost-effective in the long run.

That choice, however, presented two additional alternatives: convey the wastewater north to the large Metro Plant in St. Paul, or send it south to the Empire Plant, which already was serving five Dakota County communities.

Council employs a money-saving solution

Drawbacks of the Metro Plant option included difficult terrain for installing a new sewer pipe and the eventual need for a bigger sewer pipe through South St. Paul leading to the plant. The Empire Plant option included an easier pipe construction route, but it also grew in favor when MCES decided to make other modifications to that plant.

The Empire Plant’s treated wastewater (effluent) no longer would be discharged into the environmentally sensitive Vermillion River. Instead, it would be piped 12 miles away to the Mississippi River in Rosemount. This led MCES to combine the Empire Plant improvements with the Rosemount Plant phase-out. The result was a single pipe trench excavated wide enough for one pipe to convey wastewater from the old Rosemount Plant to the Empire Plant and a second pipe to send the effluent in the opposite direction. Piggy-backing the pipes cost approximately 30% less than doing the two projects separately.

Since the daily flow of wastewater was diverted away from the Rosemount Plant on Nov. 4, plant operators spent the remainder of 2008 draining the remaining effluent out of three settling ponds, each covering about 3 acres. The final step in officially closing the plant will be removing the wastewater solids from the bottom of the ponds. MCES is developing a plan to do so, and state regulations call for the removal to be completed by May 2012.