SR 06:282 - Laserfiche WebLink

Honorable Mayor and Members of the City Council: BACKGROUND During last year's rain storms, the S-6 sewer line which runs under the Arroyo Mocho channel to the S-6 Sewer lift station suffered damage. The concrete sewer line is Reinforced Concrete Pipe, 24-inches in diameter and caries 2.2 million gallons of raw sewage per day. The line is approximately 18-24 inches below the channel bottom grade and storm flow velocities during a series of heavy storms were high enough to scour the soil support in and around the pipe and concrete encasement. The loss of soil cover further exposed the pipeline to storm flows within the arroyo, which created the potential to wash out the line and dump raw sewage downstream. The pipeline's existing construction is encased in concrete and steel immediately under the low flow channel. However, the extent and condition of the concrete encasement was unknown since it was still underwater and the City had placed sand bags on top of the pipe to keep it in place. In this effort to protect the sewer, an emergency contract was let to McGuire and Hester to secure the pipeline in place. Heavy equipment was mobilized to the site and soil was pushed back into place and sandbags were dropped on and around the pipe to anchor it in place. The pipeline was secured and the sewer line remained in operation. As part of the permanent fix, staff completed design plans for permanent repairs and bid the project. Work included: the removal of sand bags, dewatering the site, exposing the existing pipe and concrete encasement for inspection, relocating a storm outlet from the top of the embankment to the toe of the slope, repairs to the pipe and concrete encasement if necessary, import of soil and recompaction of the soil around the pipe, repair of the channel sideslopes, and stabilization of the channel embankments to handle winter storm flows. Upon removing the sandbags and dewatering the site, it was determined that the existing pipe and encasement was in good condition and that the concrete encasement extended further into the channel embankment than originally thought. Therefore, repairs were limited to importing and recompacting the soil in and around the sewer pipe, the relocation of storm outflow pipe to the toe of the slope, the placement of an erosion control mat, and the revegetation of the embankment slopes. Environmental Permits To allow this work to occur, environmental permits were required from regulatory agencies, which included the Army Corps of Engineers, the Department of Fish and Game and the Regional Water Quality Control Board. To help with this effort, a contract was executed with Mosaic Associates LLC to provide assistance with the required permitting. Included in the permitting effort was the preparation of a biotic assessment, a site assessment for the California Red Legged Frog, and a preconstruction survey for western pond turtles and nesting birds. Additionally, the permitting required the removal of vegetation 130 feet SR 06:282 Page 2 of 4