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Main Street overlay contractor encounters soil sloughing; council authorizes up to $115,000 in stormwater reserve
Summary
Engineers reported trench wall sloughing during stormwater detention-system work on Main Street; the city asked council to authorize up to $115,000 in stormwater management reserve from 2024 project savings to cover potential extra costs. Council approved the request unanimously.
City Engineer Rob English updated council on the Main Street Overlay project and requested additional stormwater management reserve funds after unstable sandy soils caused trench wall sloughing during installation of two detention systems.
The lede: The contractor began work in November and after returning from winter suspension encountered sloughing while trenching for underground stormwater detention structures east and west of Seventh Avenue. Soil instability has undermined some adjacent pavement. Staff and the geotechnical consultant recommended excavating a shallow trench adjacent to the undermined pavement, filling with flowable controlled-density fill (CDF), and restoring the pavement subgrade to stabilize the roadway.
Why it matters: The unanticipated excavation and backfill increase costs that were not included in the original award. To avoid tapping roadway grant reserves unnecessarily, staff asked to transfer $115,000 from project savings in the 2024 replacement program to the Main Street stormwater management reserve.
Key details: The original contract award was about $1.4 million with a 10% management reserve. The stormwater schedule’s portion of that reserve (about $52,710) was not sufficient to cover the additional work. Staff therefore requested council authorization to add $115,000 in stormwater funding from project savings identified in the final closeout of the 2024 replacement program. Rob English indicated the contractor will begin the controlled-density fill work the next day and that final costs will be determined as work progresses.
Council action: Council member Olson moved and the council approved the transfer/authorization unanimously. The emergency stabilization and related catch-basin and connection adjustments were described as routine construction contingencies but significant enough to require the additional reserve.
Ending: Staff said some of the TIB (Transportation Improvement Board) grant funds for the roadway portion may be reallocated to stormwater if overlay costs come in under budget; final accounting will follow project closeout.
