Failed stormwater pipe creates 10-foot sinkhole near a Johnson County high school

A failed stormwater pipe caused a sinkhole to form on the northeast corner of the Mill Valley High School campus. Now, the Shawnee Public Works Department is approaching the City Council to approve emergency repairs during the summer before school starts.

“There were two things going on: One is we were having separation of pipe segments, dirt getting into it, and rusting of the pipe invert — the bottom of the pipe,” Shawnee Public Works Director Kevin Manning said. “The bottom of the pipe most likely has water in it and experiences rusting and degradation more than other pipes.”

Mill Valley High School, located on Monticello Road, sits in the De Soto School District, but the city of Shawnee is responsible for the stormwater system underneath.

While there isn’t a gaping hole in the ground yet — like other areas of the metro have seen in the past — the surface is starting to sink down on the Northwest corner of the campus. Shawnee Public Works wants to take action in the major corridor before it gets worse.

The repair project, which will go before Shawnee City Council on Monday, is projected to cost $2 million and take four months to complete, according to the staff report. In order to complete the repair work before school starts in mid-August, the city must take action immediately.

Citywide pipe replacements

The piping system underneath the school is made up of corrugated metal pipes — a common technique used in the 1990s and early 2000s that has since faded out of practice and been replaced by the use of sturdier, reinforced concrete pipes to help prevent the system’s erosion, Manning said.

Shawnee has a million linear feet of pipe in the city, which is close to 200 miles. Corrugated metal pipes make up about half of the city’s stormwater system, Manning estimated.

“We are in the process of slowly replacing that,” he said. “It’s a long process, it’s not something we are tackling in a few years. It’s a long term project.”

Manning said that sinkholes do form occasionally in areas still waiting for their stormwater pipes to be replaced but aren’t a major safety concern in the city.

“I would say sinkholes in general, this one is a little larger,” he said of the one at Mill Valley. “We probably have a few every year, but overall for our entire system with a million linear feet of pipe, they are not that common.”

School safety

Since the city is responsible for the stormwater system, the school district doesn’t have to take any action to make the necessary fixes, De Soto Schools Chief of Operations Brian Schwanz said in a statement.

However, the city has kept the district in the loop for its remedies to the situation and the district doesn’t have “any concerns with how the city plans to resolve the issue” he added.

“Based on the location on school district property, there has been no impact on students or the operation of Mill Valley High School,” Shwanz said in an email. “Also, there will be no impact on the remainder of the school year.”

The City Council will vote on Monday and the Public Works Department will take immediate action if the project receives approval.