Emergency CSO Repair - CSO 018 and Backwater Gate Emergency Repair - Selge Construction, Inc.

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The interim repair was completed on Thursday 1/9. Water Works team and Selge were on standby if the wall or duckbill were to fail. On Saturday 1/11, river levels backed up into CSO 018 and the wall overtopped, but the duckbill and weir were not further damaged. Water Works and Engineering met to discuss the options to repair the duckbill and weir. Due to the severe lead time on manufacturing of the duckbill and preparing a design for the duckbill, the team decided it would be best to have this design and repair performed separately from this emergency repair. Three concepts were proposed for the weir wall: 1) if elevation of the weir wall can remain permanent and there is no need to modify the wooden planks, then a reinforced concrete weir wall would be lasting solution (best option) 2) replace the weir wall fully with new wooden boards and fill voids with oakum (better option) 3) repair the damaged boards and fill holes with oakum (risky option). It was discussed that oakum is not permanent and would need maintenance overtime so this was not our best option for solving the problem. Also identifying all voids in the wall under flow conditions would be difficult. Further, the Water Works team had no records for needing to modify (remove/add stop logs) to change the water surface elevation allowed to exit or enter CSO 018; therefore, a permanent structure would be the best option if the Contractor could build it. On Wednesday 1/22, Water Works and Engineering met with Selge on site to go over option for the weir wall repair and determined that concrete wall would be the best solution to prevent water from infiltrating thru the wall and could be done under wet conditions. Construction of the weir wall was completed on 1/23 with reinforced concrete wall. Pictures of the project: 1. Sandbag of blocked 60 outlet pipe; duckbill hoisted by new permanent cable to hold it in place 2. Inside duckbill after interim repair S:\\Public Works\\Projects\\Projects by Year\\2020 Projects\\120-017 CSO 018 & Backwater Gate Emergency Repairs\\1 - Admin\\1 - BPW Documents\\Memo to BPW - CSO 018 Backwater Gate Emergecy Repair.doc