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City outlines sinkhole and pipe failure on 6th & Walnut; repairs could cost $250k–$300k for immediate fixes
Summary
City project manager Justin Stewart told commissioners a collapsed corrugated metal pipe in the 6th Avenue/Walnut watershed has caused a large sinkhole and extensive internal debris; staff said a near‑term 'bandage' repair is estimated at $250,000–$300,000 and that replacing the historic stone arch would add significant cost and complexity.
City engineering staff briefed the commission on a major stormwater issue in the 6th Avenue and Walnut watershed after a resident report and field inspection uncovered large voids and a nearly blocked pipe.
Justin Stewart, the project manager, described inspections that revealed multiple large voids and substantial debris inside the storm conduit. Photographs spanning 1941 to 2024 showed progressive changes; the present condition includes a large sinkhole at the surface and an internal section where the corrugated metal pipe has lost most of its bottom and the inlet is heavily blocked.
Staff said the immediate repair option — replacing or extending the corrugated metal pipe and stabilizing the opening — was estimated at roughly $250,000–$300,000 to "bandage" the system and protect adjacent houses and the road. Stewart and other staff stressed the complexity: the pipe sits under or very near the roadway, adjacent to house basements and mature trees. Replacing the underlying historic stone arch (to fully restore the structure) would substantially increase the price, potentially adding another ~$200,000 depending on the approach.
Staff noted constraints including limited right‑of‑way, deep excavation needs (pipe/ditch depths around 15–17 feet in places) and potential tree impacts. They emphasized that the city currently finances a small number of stormwater projects annually and faces many backlog needs — one commissioner noted the city has "a list of over 100 projects" while completing only a handful each year. Staff said they would prioritize projects based on immediate safety, property‑damage risk and funding availability and hoped to begin work after structures arrive in mid‑December.
Commissioners asked about responsibility, easements and grant options; staff said many older corrugated installations have reached end of life and that a shift to concrete pipe or aluminized corrugated pipe is common for longer service life. No vote was taken; staff requested direction only on prioritization and will seek design, procurement and available grant funding.
