TO: Board of Supervisors
FROM: Steven Lederer, Director of Public Works
REPORT BY: Estrella Munoz, Junior Engineer
SUBJECT: Approval of Amendment No. 1 to Agreement with ADKO for the “Diamond Mountain Rd Slide Repair”, RDS 26-39
RECOMMENDATION
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Approve and authorize the Chair to sign Amendment No. 1 to Agreement No. 260303B with ADKO Engineering, Inc. increasing the contract maximum from $19,507 to $427,692 to provide additional engineering services for Diamond Road Slide Repair Project. (Fiscal Impact: $400,000 Expense, additional funds requested for the project costs; General Fund; Reallocation of Budget; Discretionary)
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BACKGROUND
Damage occurred at 1699 Diamond Mtn Rd during the storm events that started in November 2025. The failure at Diamond Mountain Rd consists of an upslope failure on the east side of the roadway that extends approximately 230 linear feet in length. Slide debris filled and blocked the creek channel adjacent to the roadway causing water to be pushed out of the creek channel and across the roadway. Because construction will take place adjacent to or within the channel, environmental regulatory agency permits will be required.
On March 10, 2026, the Board of Supervisors authorized creation of the “Diamond Mountain Rd Slide Repair” project and a budget transfer of $100,000 was allocated for the project using the Roads Operating Fund. Of this amount, $90,000 was allocated for consultant services and $10,000 for staff time. Following the budget transfer and approval of the agreement with ADKO, the County moved forward with a feasibility study that explored three potential repair methods. The feasibility study involved estimation of repair costs and evaluation of potential environmental impacts and mitigation related to each of the following repair methods:
1. 10-foot tall retaining wall adjacent to roadway - Engineer’s Estimate: $866,000
This repair method would protect the edge of the roadway but would not prevent continued debris movement into the creek, resulting in further blockage.
2. 10-foot tall retaining wall adjacent to roadway paired with a culvert to facilitate creek flow - Engineer’s Estimate: $956,000
This repair method will project the edge of roadway and will prevent continued debris movement into the creek by directing the creek through a culvert for the length of the wall.
3. 20-foot tall retaining wall offset from the edge of roadway - Engineer’s Estimate: $1,966,000
This repair method would also protect the edge of roadway, would allow the creek to remain “daylighted”, and protect the creek from debris but is costly to build and difficult to design.
With the feasibility study now complete, County staff is prepared to move forward with Option 2 based on estimated construction cost and input from environmental regulatory agencies. Staff recommends approval and authorization of Amendment No. 1 to Agreement No. 260303B with ADKO Engineering, Inc., to provide design and environmental services to support the project through construction of the chosen repair option. The cost breakdown is $338,000 for consulting and $62,000 for county staff administration time. Once the construction documents are complete, staff will return to the Board to request approval to advertise the project for bids. A future budget amendment will also be required to fund construction upon award of the construction contract.
Included in the Fiscal Year 2026-27 budget is $7 million in Project RDS01 for a list of 2025 November Storm projects with not-to-exceed project amounts approved by the Board. Diamond Mtn. Rd project (26026) was on the list for design only with a not-to-exceed project amount of $500,000. Construction funding was not budgeted as at the time of budget preparation as there was not a design solution chosen or a good estimate of the cost of the project to construct. With respect to this agenda item, a budget amendment and subsequent transfer of funds will be prepared to reallocate $400,000 from RDS01 to Project 26026. These actions will be reviewed and approved by the County Executive Office and the Auditor-Controller Office to ensure compliance with the adopted budget and availability of funds.
Requested Actions:
1. Approve and authorize Amendment No. 1 to Agreement No. 260303B with ADKO Engineering, Inc., for an additional $408,185, and therefore, for a new maximum contract amount of $427,692 to provide additional engineering services for the “Diamond Mountain Rd Slide Repair Project (26026)” RDS 26-39.
FISCAL IMPACT
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Is there a Fiscal Impact? |
Yes |
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Is it currently budgeted? |
Yes |
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Where is it budgeted? |
Roads Fund, Division 20405 |
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Is it Mandatory or Discretionary? |
Discretionary |
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Discretionary Justification: |
The repairs are needed to prevent further damage and ensure safety. |
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Is the general fund affected? |
No |
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Future fiscal impact: |
Funding will be needed for construction as well as possible mitigation planting and monitoring to satisfy the requirements of environmental permits. |
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Consequences if not approved: |
If not approved, the landslide debris will continue to encroach upon and damage the roadway and creek, creating potential safety hazards for residents. |
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Strategic Initiatives: |
Building Healthy, Connected Communities |
ENVIRONMENTAL IMPACT
ENVIRONMENTAL DETERMINATION: The proposed project action is not a project as defined by 14
California Code of Regulations 15378 (State CEQA Guidelines) and therefore CEQA is not applicable.