The Seneca Lane Mudslide Sewer Stabilization Project for the County of San Mateo involved the replacement of 174 l.f. of sanitary sewer pipe behind hillside homes on Seneca Lane in San Mateo, impacted by mudslides during the storms in 2017. Stabilization measures to support the sewer replacement consisted of earthwork, excavation and backfill, and a 168 l.f. soldier pile retaining wall with ground anchors.

Additional utility work included reconnecting a sewer lateral and raising a sewer manhole to grade, along with storm drain subdrainage, drainage swales and storm drain outfalls. The finished surface for the slope was engineered backfill or compacted native backfill, while the maintenance access path above the replaced sewer pipe is gravel. Approximately 800 l.f. of an existing 3,600 l.f. access road required improvements to facilitate construction access for materials and equipment to reach the project site. Project construction was completed in 2020.