Contractor outlines $4.7–$5.7 million plan to fix Whitefish Bay sinkhole, seeks GMP by Sept. 16

Tom Zulich, president of Mid City Corporation and a licensed engineer, told the Whitefish Bay Village Board on Aug. 26 that the Big Bay/Buckley Park sinkhole resulted from a collapsed section of a 60‑inch storm outfall and erosion of a manhole sidewall, which allowed soil to wash into the tunnel and form the surface collapse.

Zulich described steps taken to stabilize the site and buy time for a permanent repair: staff and contractors installed a temporary 36‑inch relief sewer to divert flow safely to the lake, poured underwater concrete to plug eroded voids and compacted the shaft to reduce ongoing erosion. He said two geotechnical borings show very poor, sandy soils in the upper 31 feet of the planned repair area, which affects how the permanent shaft will be constructed and which earth‑retention systems are feasible.

Why it matters: the outfall carries stormwater from a large drainage area and sits roughly 72 feet deep at the lake outfall. Zulich said the temporary line gives the village roughly five feet of freeboard before streets or intersections could see water, but the relief system has less capacity than the original and poses winter and storm risks. If the temporary system fails, the bluff and adjacent utilities could be further compromised.

The proposed repair plan calls for excavating a new shaft east of the failed manhole, constructing a permanent manhole and interconnecting it to the existing system, and performing trenchless rehabilitation (lining or slip‑lining) of the outfall to the lake so the entire conveyance meets modern structural and hydraulic standards. Zulich said this approach minimizes disturbance to the bluff and neighborhoods compared with a full open‑cut replacement from the lake and reduces bypass pumping and neighborhood disruption.

Cost and schedule: Zulich said the village has solicited preliminary proposals for earth‑retention systems (ERS) and trenchless rehabilitation and expects to present a guaranteed maximum price (GMP) and contract at the village board meeting on Sept. 16. He provided a preliminary project cost range of $4.7 million to $5.7 million, which includes excavation, structural concrete, trenchless pipe rehabilitation, restoration and contingencies. Zulich warned winter work adds risk and cost and encouraged contracting this fall to limit escalation.

Board follow‑up and safeguards: staff and consultants are evaluating contractors’ ERS approaches with attention to vibration, bluff stability and homeowner foundation risk; the village attorney and staff noted the municipality will investigate any property damage claims connected to construction activity and that typical practice is to inspect and make settlement payments when attributable to village work. Trustees asked about on‑site safety and signage; staff confirmed fencing and warning signs are posted and that village liability immunities and warning signs reduce but do not eliminate risk.

Next steps: Mid City and village staff will complete a scope, finalize RFPs and return to the board on Sept. 16 with a recommended contract and GMP. Zulich said, if awarded quickly, ERS contractors could mobilize in late September with a structural concrete phase in December–January and trenchless lining to follow; full restoration would occur the following spring when asphalt plants reopen.

Notes: Zulich said the temporary relief sewer pumps roughly 300 gallons per minute for four to six hours after storm events to draw levels down; two soil borings have been completed; the village has performed televising of critical sewer reaches and will incorporate a condition‑assessment program for other deep storm structures after the emergency work is complete.