Council reviews Ramble report on stormwater box culvert after basement flooding; staff recommends further investigation estimated at about $100,000

The Oshkosh Common Council on May 27 discussed the final report from Ramble Americas Engineering Solutions regarding stormwater infrastructure near a recently replaced box culvert and ongoing reports of basement flooding. Staff said a series of inspections had cleared some possibilities but that further subsurface investigation — including additional soil borings and permanent monitoring wells with transducers — was likely needed to better understand groundwater behavior near the culvert.

Public Works staff told the council that one of the four inspection methods used on the replaced storm sewer — electromagnetic leak detection — found only minor defects and “nothing was discernible in that connection between outside and inside,” meaning the replaced box culvert did not show an obvious path where groundwater and storm sewer water were mixing. Staff said that conclusion applied to the replaced sections; the previous, older storm sewer no longer exists in the project area.

Staff recommended a next-phase investigation to try to locate any connection between groundwater and the storm system and to better map the historic creek bed beneath the area. The recommended work includes additional soil borings and installation of monitoring wells instrumented with transducers to capture groundwater elevation and storm-sewer elevation over time. Public Works estimated the study at roughly $100,000 and emphasized that the work would produce data to inform solutions rather than being a repair itself.

Council members said they understood the scientific limitations of the study and wrestled with whether more data would move the city toward a solution. Council member Abila asked about the chance that further study would still not pinpoint a cause; staff replied that groundwater can be complex and that additional data might still leave uncertainty, but that “more data is good data.”

Council member Larson asked whether, in some cases, digging a trench to inspect directly would be a faster and cheaper path to a fix. Staff replied that the recommended approach — targeted borings and monitoring wells — is intended to be more precise and less intrusive than large test excavations in an area where it is unclear where to dig.

Council and staff also discussed the claims process: several residents have reported basement flooding and property damage, and council members asked whether further internal discussion or a closed session with claims staff and legal counsel would be appropriate. The city attorney said a closed session could be used to discuss pending claims if council decides that is necessary. The council directed staff to continue internal discussions, consult with claims adjusters and counsel as needed, and return with a recommendation at a future meeting.

Mayor and council members thanked staff for the work done to date and instructed Public Works to follow up with additional analysis and to return with an update at the next regular council meeting. Staff offered to meet individually with residents and to pursue the next-phase investigation pending council direction.