CSG was selected by the Town of Hillsborough to provide construction management and inspection services for its trunk sewer improvement project. In accordance with a Cease and Desist Order (CDO) issued by the Regional Water Board, the Town installed over two miles of new 26”-28” fusible high density polyethylene (HDPE) gravity sewer main to replace the existing, undersized vitrified clay pipe (VCP) along El Cerrito Avenue and Crystal Springs Road. The large pipe upsize increase required the main installation to be completed with open trench construction.
The project included the installation of over 60 new sewer manholes, 75 service lateral re-connections, system bypassing through portions of the existing pipeline, and four drilled concrete stitch pier walls to stabilize the adjacent San Mateo Creek embankment and support the utility work. The project included multiple agency stakeholders and funding sought through the Clean Water State Revolving Loan Fund Program, which included environmental and cultural resources mitigation measures. The stabilization wall work required a stream bed alteration agreement with the State Department of Fish and Wildlife (CDFW) due to the proximity to San Mateo Creek. Environmental mitigation required coordination with a biological consultant to mitigate construction activity impacts to local fish and wildlife species that are California species of special concern and/or listed as threatened under the Endangered Species Act. Cultural resources mitigation required coordination with an archaeological consultant and a Native American tribal band to minimize impacts to uncovered Native American artifacts and human remains. The mitigation efforts included preliminary data excavations, cataloging the discoveries, monitoring the treatment of the findings, and burial relocation efforts.
Some of the project challenges included traffic control, communications/public relations, and utility coordination. Traffic control required daily monitoring and Town updates as the project streets are important thoroughfares for the Town. Public relations efforts were ongoing for the project duration to ensure coordination with adjacent property owners on landscaping restorations, property access, and sewer service bypass notifications. Coordination with PG&E included joint pole protection and bracing during construction, and monitoring of drilling operations in proximity to overhead lines. Coordination with SFPUC consisted of their consent to the new sewer pipe’s alignment and profile in proximity to the larger diameter transmission lines on El Cerrito Avenue. Additional field coordination was required for the drilling operations to ensure the soil/rock material and minimum drilled depths were in accordance with the site geotechnical recommendations.
