Emergency Sewer Repair - 18” Sewer at Dubail Ave. under Bowman Creek – Selge Construction Co., Inc.

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S:\Public Works\Projects\Projects by Year\2021 Projects\121-060 Dubail Sewer and Structure Emergency Repairs\1 - Admin\1 - BPW Documents\20211123_121-060 Emergency Sewer Repair Dubail and Bowman Creek_Memo to BPW.doc Page 1 INTER-OFFICE MEMORANDUM DEPARTMENT OF PUBLIC WORKS DIVISION OF ENGINEERING TO: Board of Public Works FROM: Sue Ellen Doudrick, PE SUBJECT: 121-060 Emergency Sewer Repair E Dubail and Bowman Creek DATE: November 23, 2021 On Saturday 8/21/2021, Sewer Department received a call from 211 from the SBPD that there was a large sinkhole near 817 E Dubail Street. The issue was in Bowman Creek. Upon inspection the creek was flowing fully into the sinkhole within the creek under the structure. Due to the vicinity of the hole being near the recently lined 72” sewer, the project contractor, Inland Waters Pollution Control (IPR), was immediately contacted to be onsite to inspect the sewer. Wastewater Crew was contacted to remove the EmNet Sensor equipment from the manhole in Dubail directly adjacent to the creek. Upon review of data, an 18” sewer crossed under the creek and tapped the manhole in Dubail east of the creek. On Sunday 8/22/21, IPR mobilized to the site and inspected the sewer on Dubail from Hight Street to the manhole east of Bowman Creek. The sewer was backed up with sand and water and a full video inspection could not be performed. IPR inspected the manhole east of the sinkhole in the creek and inspected the 72” sewer. IPR confirmed that all flow from Bowman Creek was flowing into the manhole thru the 18” sewer. They also inspected the sewer from Dubail to Indiana Avenue. Upon this inspection, they discovered the liner in the sewer upstream of Indiana had failed and was blocking flow. On Monday 8/23/21, the EmNet flow sensor data was retrieved and during previous rain events in August water levels in the manhole surcharged to 17 feet and 21 feet on three occassions. At these surcharged levels the pipe going under the creek would have been completed submerged due to the surcharged manhole. It is likely that the pipe became pressurized due to the full flow condition and water level head conditions. On Monday 8/23/21, two Contractors were contacted to meet onsite: Selge Construction and GE Marshall. Both met immediately and were present at the same time and walked the site with us. The scope of the discussion was to bypass Bowman Creek within the structure and around the sinkhole, mobilize equipment into Bowman Creek and perform a repair of the sewer without impacting the structure. There were many unknowns, but the goal was to stop all flow from Bowman from getting into the combined sewer before the forecasted rains. On 8/23/21, Selge confirmed availability to perform work starting on 8/23 with a manhole entry and mobilization starting 8/24. Selge provided a cost of $100k and indicated there could be a couple problems to repair and suggested the higher cost would be if we had to open cut the road next to the culvert bridge structure. They indicated if no open cutting was required the cost may be around $50k. Selge was selected due to the urgency of the matter and due to rain being