Old White Hill Grade Fire Road Landslide Repair

Old White Hill Grade Fire Road Landslide Repair

The purpose of the proposed project is to repair a landslide on Old White Hill Grade Fire Road in the Loma Alta Open Space Preserve that occurred during the winter of 2022- 2023. Old White Hill Grade Fire Road is an earthen road, which is owned by the Marin County Open Space District (MCOSD). The Marin Municipal Water District (MMWD) owns an easement over the Old White Hill Fire Grade Road for a waterline and access. Old White Hill Grade Fire Road also provides emergency access to fire and rescue services. The landslide resulted in damage, and it is now undermined and threatening emergency access and the MMWD’s waterline. Soil boring was completed in April 2023 to assist with the design of the proposed retaining wall. The proposed project would construct a new reinforced concrete retaining wall supported on cast-in-drilled-hole piles to support the outboard side of Old White Hill Grade Fire Road. The retaining wall would be 5.5 feet in height, 92 feet in length, and 2 feet in width. The proposed project would include a new cable rail, approximately 80 square feet Caltrans Class 8 rock slope protection, and minor grading to improve drainage conditions above the proposed new retaining wall and within the 2-foot-wide, 1-foot-deep existing roadside ditch leading to the two existing culverts. The proposed project would be implemented by a contractor. Equipment would include a mid-sized excavator, drill rig, concrete truck, and dump truck. Construction access would be from Sir Francis Drake and Old White Hill Grade Fire Road. Staging for all equipment and construction materials would be limited to the existing road footprint or small portions of the Sir Francis Drake Road right-of-way near the Old White Hill Grade Fire Road entrance. No road closures are expected though traffic control would be in place to ensure safety during project implementation. Implementation of the proposed project would not result in debris therefore no disposal would be required. No vegetation would be removed or affected during project implementation. The project area is not within an area with identified wetlands or special-status plants, wildlife, or habitats and the existing roadside ditch to which the existing culverts discharge is not jurisdictional, therefore no regulatory permit authorizations would be required. Project implementation would begin by mid-August 2026 and would require approximately 35 days to complete. Implementation of the proposed project would be completed by October 15, 2026 so that the repair is in place before the onset of the rainy season

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