2017-082 Resolution - Laserfiche WebLink

Home Browse Search

EXHIBIT A (Tc'osultants SCOPE OF ENGINEERING SERVICES CITY OF NORTH OLMSTED, OHIO SOUTH INTERCEPTOR INFILTRATION/INFLOW STUDY Project Understanding The Southern Interceptor has been determined to have capacity issues that the City would like to address. Based on discussions with staff and summaries of known issues provided by them, an investigation of the reasons for sewer capacity issues is to be performed. The reasons for capacity issues are not believed to be related to sewer condition, but more attributed to collector sewer inflow and infiltration (1/1) impacts, sewer configurations with 90 degree bends, or size reduction transitions. In order to investigate these issues, the City has identified a hydraulic model/flow metering program to review the flow characteristics in the interceptor during wet weather events. This strategy should meet the City's goal. Strategic placement of flow meters will provide flow characteristics of the sewer during wet weather events and compare them against characteristics of the hydraulic model. Comparison of the two should provide insights into the reasons the various flow characteristics are occurring in different portions of the interceptor that have been previously identified in the field. The City has suggested that capacity issues may be alleviated through construction of equalization basins at sites currently owned by the City. One site is located on the Northeast corner of Stearns Road and 1-480. The other is south of Lorain Road behind Chestnut Intermediate Elementary School. The shallowest point in the interceptor that is known to experience significant surcharge during rainfall events is considerably further downstream near Columbia Road. It is CT's understanding that the South Interceptor contains several locations with 90 degree manholes and a transition to a smaller diameter sewer at a steeper slope near the WWTP. While the sewers on either side of these items can have capacity, the hydraulics at these locations could create significant head loss conditions at higher flows. While using equalization basins to reduce peak flows can resolve surcharging due to configuration restrictions, the cost benefit over modifying the restrictive area versus construction and maintenance of a basin should be reviewed. The flow metering for head loss related characteristics such as transitions and bends, differs from flow metering for investigating 1/1 flow impacts. The intent of the project is not to perform an SSES analysis but to identify if 1/1 is the reason for lack of sewer capacity. The metering for 1/1 capacity issues can provide additional benefits in identifying future action plan priorities. Prepared by CT Consultants, Inc. I November 9, 2017