LEHILLIER — South Bend Fire personnel patrolling the flood control system at midnight Tuesday discovered a sink hole forming near the earthen dike along the Blue Earth River.
The sinkhole, which is suspected to have formed from a separated or collapsed storm sewer pipe, is not threatening the integrity of the dike, said Grant Riddick, an Army Corps of Engineers geologist who was surveying the problem along with South Bend Township officials.
The sinkhole, north of Highway 169 and west of the CHS processing plant, is very near where a similar storm pipe collapse took place in 2010. That incident created more concern as it affected a larger area and caused soil under the dike to erode.
Deb Schwichtenberg said the sinkhole slowly grew all day Tuesday to a size of about 20 feet by 30 feet and about 10 feet deep.
"I'm glad it didn't happen last night because I was mowing here," said Schwichtenberg, who lives next door and owns the large expanse of lawn next to the dike. She is also the township's clerk.
Jerry Eken, township supervisor, said their concern is safeguarding their large and expensive pumps that ultimately pump the water from the storm-drain pipes.
"It can be hard on the pumps with mud and gravel in the water."
One of the pumps failed in 2010 because of the same problem, causing a $200,000 rebuilding of the pump. Even though the township maintains the pump station, federal aid is available for repairs because it is part of the federal flood control project.
Before repairs on the sinkhole could start, crews had to determine which of three storm-drain pipes was causing the problem. The Army Corps has a large 54-inch pipe, installed in the late 1970s, that runs along the dike. The Minnesota Department of Transportation installed another along Highway 169 in the 1980s when the highway was rebuilt. And the township has a third storm-drain pipe hooked into the system.
"We need to figure out whose it is so we know who takes the lead on this," Riddick said.
With a 50 percent chance of thunderstorms this weekend, including the possibility for heavy rains, there was added urgency to getting the storm system repaired as quickly as possible.