When a huge sinkhole opened up on Northwood Drive in Redwood Falls in July, inspection of the sanitary sewer line in that area revealed the concrete pipe initially installed in the 1970s was showing significant deterioration.

A proposal to address that issue was presented to the city council by Jim Doering, city public works project coordinator, during its Oct. 20 meeting.

The plan would be to use a new lining technology utilizing the existing pipeline, rather than replacing the entire system with new lines. 

According to Doering, the city is looking at what is known as cast in place pipe lining, which is a technology the city has not used.

Rather than dig out the old pipe and replace it with new, a lining would be inserted within the existing concrete pipe.

Moving forward with the project, the city council approved a request to have Bolton and Menk, Inc. set up the documents that would result in requests for bids at a cost of $68,500.

Doering said replacing the 15-inch pipe at a length of approximately 4,000 feet would cost in the millions of dollars with all of the addendums being proposed as part of the scope of work.

The estimate for the lining project would be in the $500,000 range.

While the lining would reduce the size of the pipe diameter from 15 to 14 inches, Doering said that difference would not impede the current flow.

The work would also include rehabilitation of the manholes in the area.

Testing data shows that the lining the city is looking to use supports a 50-year life span but is often referred to as a 50- to 100-year product.

In addition to current capacity, the line would also be used to take on the capacity that would come from the new development area the city recently purchased.

In other action, the city council:

• Accepted a grant from the Minnesota Department of Transportation for the purchase of an airport maintenance utility vehicle at a cost of $34,187. The grant will cover 70 percent of the cost.

• Approved a request from Redwood Design & Contracting on behalf of Redwood Industries to vacate two five-foot utility easements in the Zimmer subdivision. The plan is to combine two lots and then construct a two-family duplex on those lots. The utility easement would then be relocated along the new property line.