City wastewater plant expansion leads to river erosion project

A backhoe operator excavates into the surface of a bank along the Rum River just below the Princeton Middle School campus on Aug. 16. The plan is to reconstruct three sites along the river where there are curves in order to reduce erosion of the side of the bank and reduce phosphorous going into the river.

A first-time project has started in the city of Princeton, reducing erosion along the banks of the Rum River as part of pollution-control work involving the city’s wastewater plant. It might be difficult to understand the connection between altering a river bank and a municipal wastewater plant, so hold on for the explanation.

First of all, the Minnesota Pollution Control Agency (MPCA) is requiring the reduction of erosion along the banks of the Rum River in Princeton as a condition of the MPCA issuing the final permit for the city’s now nearly-completed wastewater plant expansion.

The erosion-control condition actually came out of a lawsuit by the Minnesota Center for Environmental Advocacy (MCEA) suing the MPCA for issuing the original permit about five years ago to expand the plant that had been completed in 1995.

The MCEA contended that the MPCA had not exhausted the exploration of methods for reducing pollution going into the Rum River in the plant-expansion plan. The courts ruled in favor of the environmental group, so the engineers and the MPCA had to start over again in designing an expansion plan that would satisfy the MCEA.

This would be, after all, a wastewater processing operation with a major difference. The original plant has been discharging its treated wastewater into a lagoon system, which people can see from the south end of the Princeton golf course.

The new plant operation will have the treated wastewater running out of a pipe from the plant right into the Rum River. Pollution control watchdogs are concerned about the amount of phosphorous buildup in waterways that eventually end up in the Mississippi River. The phosphorous buildup causes algae blooms that, if accumulating in large enough quantity, could clog up the Mississippi River’s scenic Lake Pepin, environmentalists warn.

So, as part of getting the new permit to expand the wastewater plant, the city agreed to reduce erosion along the Rum River, as that apparently reduces the amount of phosphorous going into the river. Engineers call this non-point phosphorous reduction, meaning it is being done at points outside the wastewater plant. The whole idea is to keep the amount of phosphorous at a controlled level in the river since the wastewater plant discharge is expected to add a certain amount.

Three sites chosen for river erosion project
The United States Department of Agriculture (USDA) is financing the wastewater plant expansion through a grant and low-interest loan and thus its money is going into the river bank erosion reduction project. This project is occurring in three places. One (the biggest and first segment being tackled) is in a bend in the river below the southeastern corner of the Princeton Middle School.

Erosion is heavier where a river bends because the water moves faster and so these river bends are the candidates for erosion control projects. “We’ve identified sandy soils (as places of river bank erosion) especially where the river tries to turn,” said engineer Ed Youngquist with the city’s consulting engineering firm WSB & Associates. “There is a lot of erosion (in those places) and a shearing of the banks.”

Youngquist noted that this erosion-control project is modeled after the one that the Mille Lacs County Soil and Water Conservation District (SWCD) directed at the Miskowic property in rural Princeton several years ago. Minnesota Native Landscapes, Inc., based in Otsego, is handling the work for the city project.

It will involve making terraces in the river bank slope, placing logs, steel cables and anchors along the bottom of the slope to stabilize the river bank, and the planting of vegetation on the entire slope to root and grow. All of that is designed to reduce water eroding the river bank.

The logs will eventually deteriorate at the bottom but the plan is that the planted vegetation will have rooted deeply long before then and will have taken over the erosion control. An erosion-control blanket will also be placed over the slope to check running water that would drain down from the top, said Youngquist.

The other two river bank erosion-control sites for the project will be along the southeast corner of the golf course, and at a location on the river north of Highway 95 and on the east side of Highway 169.

Youngquist said he is hoping the river bank erosion control project will be completed by this coming mid-October, pending weather conditions.

“If we can eliminate erosion, apparently it will reduce phosphorous and improve water quality,” Youngquist said.

City Administrator Mark Karnowski has always contended that the amount of phosphorous pollution is really greater at non-point sources, such as along the river, especially below cow pastures and crops where runoff may occur, rather than from treated wastewater. This will be a good way to work at keeping the phosphorous down, Karnowski said about the river project.

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