TWM: relay sewer preferred to fix Hunter Street lift station after survey error

Kurt Zurni, project manager for engineering firm TWM, told the Lebanon City Council on Aug. 25 that a post-installation inspection of the new Hunter Street lift station discovered a measurement error: the existing wet well is roughly four feet deeper than shown in the original survey. The discovery followed a severe rainfall event the firm said totaled about seven inches in one evening and led staff to inspect installation issues before the station has been fully commissioned.

Zurni described two feasible remedies. The lower-risk recommendation (Option 1) is to relay about 440 linear feet of gravity sewer — replacing an 8-inch line with a 10-inch line at a slightly flatter slope — and then transfer home laterals as needed. That option requires easements across primarily Kendry property and a small area on McKendree property but keeps the prefabricated wet well in place and avoids major disassembly work. The riskier Option 2 would disconnect mechanical and electrical connections, pull the prefabricated fiberglass station out, bolt on an additional barrel section to deepen it, and reset it in a deeper excavation; that work would be confined but technically complex and carries a higher chance of damage to the prefabricated unit.

Zurni said relay-of-sewer construction would have a larger surface footprint but be more straightforward for contractors, while deepening the wet well would keep construction localized but require confined excavation, temporary disconnection of valves and wiring, and careful lifting so as not to break the fiberglass unit. He told the council that lowering the wet well would reduce pump duty by roughly 10% and slightly increase daily pump run time, but the manufacturer has indicated the pumps would still be within acceptable performance ranges.

TWM and city staff estimated the order-of-magnitude cost for either path at about $100,000. If the council chose to reset and extend the prefabricated well, Zurni said lead time for required materials was roughly three to four weeks. If the council chose to relay the sewer, Zurni said work could proceed on completing current installations and testing with Hair Plumbing (the lift-station contractor) while sewer design and permitting proceed.

Council members and residents pressed about responsibility, basement flooding, and whether the station could accommodate a similar heavy rainfall in the future. Zurni and TWM staff said collection systems and pump stations are not typically designed for extreme, one-in-500-year flood events because the cost would be prohibitive; crews had deployed temporary pumps during the event. Multiple council members asked for more detail and for staff to return with a recommended path and a plan to minimize resident disruptions during construction.

Next steps: TWM said it will prepare sewer-extension plans and details to allow the city to give firm direction to Hair Plumbing; the council directed staff to gather additional information and consider options at upcoming committee meetings before taking a final vote.