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Franklin County investigates Old Highway 100 slide after fresh water found at slope toe
Summary
County staff told commissioners that consultants found fresh water at the toe of a slope on Old Highway 100, prompting geotechnical investigations, temporary traffic controls and contingency planning for a possible closure and excavation.
Franklin County commissioners were briefed at their meeting on an active slope failure at Old Highway 100 after consultants found fresh water emerging at the toe of the slope, county staff said.
County staff said the finding prompted geotechnical consultants to begin further investigation, including coring and subterranean exploration, and prompted the county to install temporary traffic controls and reroute school buses.
The slide was first discussed during the commission meeting when a commissioner asked for an update. Jim, a county staff member, said Cochran (the consultant) “did a visual above the slide and below the slide, and they have discovered fresh water coming out at the toe of the slope.” He added, “We don't know where it's coming from. It's coming out at the toe of the slope right around the just above the creek.”
Jim told commissioners Cochran had not yet begun coring but planned to start on Friday and that geotechnical engineers were performing the investigation: “At this point, they're in at in the investigation mode, they are geo, engineers, and that's what they're telling me.” He said staff observed subsidence beyond surface scuffing and that a void beneath a remaining concrete slab could require a fuller closure if found.
County staff described immediate traffic and safety measures. Temporary one-lane traffic control with a signal is in place; the county is renting the lane-closure equipment. When asked about cost, Jim said the rental runs about “$3,800 a month.” He also said school buses have been notified and “have been rerouted to go down the Saint John's route.”
The county discussed potential impacts and next steps: if excavation is required, the work will need space for barriers and equipment and could require closure of business entrances adjacent to the site for safety. Jim said the project will be monitored daily: “We inspect it every day… We are keeping a very close eye on it.”
Commissioners were also told that MoDOT plans to replace a nearby bridge in the 2027 construction year and that replacement will require a multi-week full closure: “They are going to replace that bridge… It'll probably be 90 to a hundred and 20 day road closure,” Jim said.
County staff said they will forward Cochran's findings and design plans to the commission as they arrive and will continue monitoring and communicating detour and safety measures.
The commission did not take a formal vote related to the slide during the meeting; staff said consultants will complete coring and provide additional recommendations before any closure or construction decisions.
