Slide and Drainage System Repair

Slide and Drainage System Repair

The project is located along Route 92 in San Mateo County between PM 0.91 and PM 2.53. The work will occur in Pilarcitos Creek and on seasonal unnamed drainages that are tributary to Pilarcitos Creek. All work will take place during the summer and fall months when the seasonal drainages are dry. Pilarcitos Creek continues to flow year round although at very low flow levels. Plywood wildlife exculsion barriers will be erected around work areas in Pilarcitos Creek which will isolate the work area from any waters and confine disturbance (see attached plans for specific construction details). At PM 0.91 a soldier pile wall approximately 20 meters long will be constructed and a new drainage system installed by replacing the existing outlets and drainage pipes with new ones in the same location. Due to a landslide and subsequent erosion, cut and fill will be necessary in addition to the soldier pile wall to repair the existing gully. A private dirt access road between the highway embankment and Pilarcitos Creek will be trenched to replace the existing 305 mm plastic pipe with a 600mm CMP. Upon completion of the installation, the road will be restored and stabilized. The new 600mm pipe will outfall onto RSP placed in the bed and bank of Pilarcitos Creek. The RSP will be wrapped in RSP fabric to reduce silt discharge into the Creek. The total amount of RSP to be placed in the Creek at this location is approximately 5 m3. At PM 0.92 a second wall will be constructed adjacent to the eastbound lane of Routh 92. The proposed length of this wall is 38 meters and it will be tied into the soldier pile wall at PM 0.91. At PM 2.5 the existing drainage system will be replaced by installing new inlets and a new 450mm CMP to discharge the water collected from the inlets. The new 450 mm pipe will outfall onto RSP placed in the bed and bank of Pilarcitos Creek. The RSP will be wrapped in RSP fabric to reduce silt discharge into the Creek. The total amount of RSP to be placed in the Creek at this location is approximately 5m3. At PM 2.53 the existing headwall will be replaced with an inlet on the westbound side of Route 92. A second inlet and RSP will be installed on the embankment below the eastbound lanes. A 450mm CMP will collect drainage from the inlets and discharge onto RSP. This pipe will not discharge into Pilarcitos Creek but onto RSP that have been placed on RSP fabric to further reduce soil erosion. To lay the pipe, there may be some cut and fill and it may involve vegetation removal from the slopes above Pilarcitos Creek. Issuance of a Streambed Alteration Agreement Number R3-2002-0115 pursuant to Fish and Game Code Section 1601.

San Mateo