Residents of the Altoona, Mapleton and Marlin Drive neighborhood in the Municipality of Mt. Lebanon had experienced flooding during intense rainfall events due to an overloading of both the storm and sanitary sewer systems. The neighborhood is unique in that many of the homes have the municipal-owned sanitary sewer system traveling under private structures. 18 Backwater Valves were discovered to have been installed on private residences after a GIS was used to identify the impacted properties.
A plan was prepared and approved by the Mt. Lebanon Commission to mitigate the flooding/basement backups and to re-route the sewers from under the homes, through a proposed parallel sanitary and storm sewer. The project included the installation of a new 12” sanitary sewer and a 36” storm sewer starting at the intersection of Rae Avenue and Jayson Avenue, continuing down Rae and Mapleton Avenue to Altoona Place. The project continued to the intersection of Altoona and Cochran Road.
The Municipality decided that due to the installation of the two sewers within the Road Right-of-Way Limits, the project would include the complete reconstruction of Altoona Place, Mapleton Avenue and Rae Avenue. Reconstruction included the complete removal and replacement of the concrete curbs, removal of the existing pavement to a depth of seventeen (17”) inches, installation of new stone subbase, and road pavement. Altoona and Rae were replaced with bituminous pavement and Mapleton was replaced with concrete pavement.
During the design phase of the project, four meters were installed throughout the neighborhood. Once data had been collected, a model showed the pre-design and post-design effects on the sanitary sewer.
Once completed, meters were again installed to determine the amount of infiltration removed by the system. The average GWI values was reduced by 40% while the peak storm values were reduced by approximately 25%. The flow reduction was approximately 9.5 million gallons of flow per year removed.