Sewershed Approach to Optimize Sewer System Operation

The City of Columbus, OH, Division of Sewerage and Drainage (DOSD) intends to construct a sanitary trunk sewer in the vicinity of the Jackson Pike WWTP to replace an existing segment of the Scioto Main Sanitary Trunk Sewer. The new Scioto Main Trunk Sewer Replacement (SMTR) will eliminate all overflow structures at the Renick Run area as part of the West Columbus Local Protection Project (WCLPP) administered by the U.S. Army Corps of Engineers. Due to the complex hydraulics in the vicinity of the Jackson Pike WWTP a detailed dynamic model was developed to assess the sewer system performance under different operating conditions. The model used the sewershed approach to maximize system storage without affecting the current services and to satisfy the regulatory conditions to operate the sewer system. The developed model investigated sewer system performance using 6-month, 1-, 2-, 5-, 25- and 100-yr storm events to optimize the operation of the collection system. Initial model results indicated potential overflow at the Rhodes Park overflow using the 5-yr storm and above. After a series of model runs to optimize system operation and boundary conditions potential overflow at Rhodes Park is anticipated for storms above the 25-yr storm. The sewershed approach was used to satisfy the following objectives: 1) Provide primary and secondary treatment for combined and separate tributary flow due to dry weather flow and wet weather flow up to the 6-month storm, 2) Provide primary and secondary treatment at Jackson Pike WWTP for separate flow up to the 25-yr storm, 3) Provide primary treatment at Whittier Street Storm Tanks for combined flow due to the 1-yr storm frequency and above, 4) Maximize bypass flow from Jackson Pike WWTP to Southerly WWTP through the flow control structure to avoid backup in the Scioto Main Replacement Sewer, 5) Maximize in-line storage in the 156-inch Interconnector Sanitary Trunk Sewer, 6) Maximize pumping rates at the Interconnector Pump Station to its limit, 7) Regulate tributary flow from Scioto Main Trunk Sewer using the Hydrovex regulator to 60 MGD, and 8) Provide in-line storage upstream the Hydrovex regulator to a maximum elevation of 720.00 feet to avoid overflow at Rhodes Park overflow. The sewershed approach and the developed model allowed the determination of the optimum operating conditions by maximizing in-line storage while meeting all required constraints (e.g., overflow, pumping capacity, control flow devices, sewer capacity).