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

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INTER -OFFICE MEMORANDUM DEPARTMENT OF PUBLIC WORKS DIVISION OF ENGINEERING TO: Linda M. Martin, Clerk Board of Public Works FROM: Sue Ellen Doudrick, PE SUBJECT: CSO 018 & Backwater Gate Emergency Repairs Project No. 120-017 DATE: March 30, 2020 Emergency repairs were performed on the backwater Tideflex valve (backwater valve/duckbill) immediately downstream of CSO 018 and on the weir within CSO 018 itself. CSO 018 is located south of Lincoln Way East between the railroad tracks and Bowman Creek. CSO 018 consists of two structures, the CSO itself and the downstream structure. The downstream structure contains a duck bill (60" in diameter). The duckbill is attached to a plate and prevents St. Joseph River water from flowing into the CSO 018 structure. On Monday 1/6/2020, Water Works team discovered the duckbill became dislodged at the top of the plate and river waters flowed into the CSO 018 structure (upstream). This condition damaged the wooden weir wall separating the duckbill structure and 24" throttle line in the CSO 018 structure. There are 4 wooden planks making up the weir. From what we can see, two of the planks have become dislodged from the concrete walls, and another plank is lifting upward. To prevent the planks from further damage, allowing CSO waters to flow directly to the River, and clogging the 24" river crossing, the planks and duck bill are planned to be repaired. These two elements are under 4' of flow conditions and the entry and repair of these were beyond what our in-house teams are trained and equipped to do. On Tuesday 1/7, the project was approved as an emergency repair. The first contractor contacted (Selge Construction) was available to meet onsite immediately on 1/7 to inspect the conditions. Contractor mobilized to site 1/7. Description of work: Due to the forecasted rain for the end of the week, it was critical to first repair the duckbill to reduce river water from further damaging the weir due to increased backwater flow from the increased river water elevations. To get us thru the weekend rains, a fiberglass sheet was installed at the downstream face of the weir to protect the wooden planks from further damage. Sewer Department provided sandbags used to block flow coming from the river. Reducing water levels in the structure to perform work was critical. We wanted to avoid detwatering as this would greatly impact cost on the project. The duckbill repair included installing a cable attached to the top of the downstream structure and connecting the cable to the duckbill to lift it up in place in order to install new bolts to connect the duckbill to the plate. During work, we discovered the duckbill would not close all the way, which would continue to allow water to infiltrate the CSO 018, but the repair helped reduce water coming in. S:APublic 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