SR-1 San Gregorio Embankment and Drainage Facilities Repair DO (EA 1V510)

Caltrans proposes repairing a storm damaged slopes and drainage facilities at multiple locations on State Route (SR-) 1 in San Mateo County from post mile (PM) 15.9 to 17.9. Between April 10 and April 12, 2026, an intense storm system produced heavy rainfall that generated concentrated stormwater runoff, causing erosion of the roadway embankment, damage to drainage facilities, and slope failures. Additional storms between April 20 and April 22 produced further runoff that enlarged the slope failures and continued to undermine the affected embankments. The storm damage has compromised the stability of the roadway embankment and disrupted the drainage system, allowing uncontrolled runoff to continue eroding the slopes. Active erosion remains ongoing and poses an imminent threat to the roadway prism. The proposed project will remove loose and failed slope material along both sides of SR-1 between PM 15.9 and 17.9. Eroded slopes will then be reconstructed with rock slope protection (RSP) and RSP fabric. Damaged asphalt concrete dikes and drainage features will be restored. The existing approximately 30-foot asphalt concrete ditch at PM 17.9 will be cleaned out both upstream and downstream and then reconstructed. The storm-damaged down drain at PM 15.9 will be removed and a new drainage inlet and asphalt dike will be installed to restore positive drainage and safely convey stormwater runoff away from the repaired embankment. Where necessary, subdrains will be installed to stabilize the repaired slopes. Disturbed areas will be hydroseeded after construction to prevent future erosion. Traffic control will be required during construction.