Phase 2 Storm Damage Repair of Los Vaqueros Road and Culvert 24 within the Los Vaqueros Watershed - FEMA 4683

Phase 2 Storm Damage Repair of Los Vaqueros Road and Culvert 24 within the Los Vaqueros Watershed - FEMA 4683

CCWD proposes to perform permanent repairs of Los Vaqueros Road, the roadway embankment, and Culvert 24, which were damaged by the storm events of January 2023. This project is Phase 2 of the Emergency Storm Damage Repair Project of Los Vaqueros and Culvert 24. CCWD completed temporary emergency winterization measures (Phase 1) in November 2023 ahead of the 2023-2024 winter season to prevent further damage. Culvert 24 is 72 inches in diameter and crosses underneath Los Vaqueros Road conveying flows from Kellogg Creek, which runs along Los Vaqueros Road and crosses the road at several points through culverts. At the project site, the storm events caused significant bank erosion and soil displacement upstream and downstream of the culvert and roadway. The compromised upstream inlet (Culvert 24) and continuing storm events caused flooding and overtopping of the roadway on the inlet side towards a low point along the roadway downstream of the outlet side of the culvert (see Photo 1). This caused slope failure along the northbound (NB) lane, undermining the existing pavement and leading to the closure of the NB lane. Within the NB lane there is major road cracking from the edge of pavement towards the centerline of the road (see Photo 2). Phase 1 included cleaning the culvert of debris, stabilizing the eroded embankment around the culvert inlet and along the NB lane with Visqueen and rock slope protection (rip rap), and placing water-filled traffic barriers along the edge of travel way for safety purposes. Currently, Culvert 24 still remains undersized and damaged, and the roadway embankment along NB Los Vaqueros Road remains eroded and has the potential to further undermine the existing pavement during future storm events. CCWD completed Phase 1, the temporary emergency winterization repairs of Los Vaqueros Road and Culvert 24, in November 2023. See Photos 3 and 4 for photos of the temporary winterization repairs at the culvert inlet and NB lane, respectively. Phase 2 is described below and the footprint is shown in Figure 2. Culvert Replacement: CCWD proposes to remove and replace the existing 72-inch corrugated metal pipe (CMP) culvert with a larger 84-inch culvert. The new culvert will be approximately 100 feet long. Rip rap and geotextile fabric that was laid on the culvert inlet side as part of the temporary winterization effort will be removed. The roadway above the culvert will be removed and repaved after the culvert installation. On the inlet side of the new culvert, CCWD will install an angled debris trash rack to help prevent future clogging of the culvert and allow for easier cleaning and maintenance of the culvert inlet. The debris rack will be poured in place and founded on a cast-in-place footing. An example of the angled debris rack is shown in Photo 5. Approximately 2,280 square feet of rip rap (340 tons) will be installed at the replacement culvert’s inlet and outlet. A portion of the rip rap needed for the culvert inlet and outlet may be reused from the emergency winterization effort. Retaining Wall: CCWD plans to restore the shoulder of the NB lane of Los Vaqueros Road and stabilize the roadway by constructing a soldier pile retaining wall with pre-cast concrete lagging along the length of the eroded embankment. Visqueen that was laid along the NB lane embankment as part of the temporary winterization effort will be removed. The NB lane pavement along the damaged embankment area will also be removed and will be repaved after construction of the wall. The wall will be placed approximately 6 feet away from the edge of pavement and will be approximately 200 feet in length. The maximum estimated depth of disturbance will be 28 feet when drilling for the wall’s soldier piles. After holes are pre-drilled into the soil, steel I-beam piles will be inserted and concrete casings will be poured. Next, pre-cast concrete lagging will be placed between the I-beams. The concrete lagging will be placed about 4 feet below grade with 7 feet exposed height, for a total lagging height of 11 feet. The area between the wall and edge of pavement will be backfilled with engineered fill and a Midwest guardrail system will be constructed along the NB lane. A concrete v-ditch along part of the retaining wall will also be constructed. The concrete v-ditch will be approximately 2 feet wide from edge of pavement and will be 105 feet in length. Rip rap that was applied along the NB lane embankment during the emergency winterization project may remain but may be moved to allow for construction of the soldier pile wall. The rip rap may remain to protect the base of the retaining wall. Approximately 500 square feet of additional rip rap (75 tons) will cover the entire length of the retaining wall. See Photo 6 for an example of a similar retaining wall implemented elsewhere at the Watershed. Equipment storage and staging will occur at the shoulder of southbound Los Vaqueros Road and at the County Line Staging Area, a gravel lot near the kiosk at the southern entrance of the Watershed along Los Vaqueros Road. These staging areas are identified in Figures 2 and 3. Wildlife exclusionary fencing will be installed around the staging areas to the extent feasible. The types of equipment that are expected to be present on site consist of the following: • One (1) excavator with a bucket capacity of one cubic yard • One (1) backhoe with a bucket capacity of one cubic yard • One (1) water truck • Five (5) utility trucks • One (1) dump truck • One (1) boom truck • One (1) flatbed truck • One (1) drill rig Phase 2 is estimated to begin in summer 2025 and end in fall 2025, with construction estimated to be about eight weeks. No night work will occur. CCWD will first perform the culvert replacement then proceed to construct the soldier pile wall along the NB lane. The culvert replacement will require a temporary full closure of the roadway that is anticipated to last approximately 5 days. During construction of the retaining wall, the road will be reopened to one-way traffic controlled by flaggers. After the project has been completed, Los Vaqueros Road will be reopened to two-way traffic with no safety restrictions.

Unincorporated

Contra Costa

Unincorporated

Contra Costa