Board denies appeals, upholds approval for Cayucos subdivision after geotechnical and stormwater review

The San Luis Obispo County Board of Supervisors on a unanimous 4–0 vote denied two appeals of a Planning Commission approval for an eight‑lot subdivision at the north end of Cayucos, upholding the coastal development permit, vesting tentative tract map and variance with updated indemnification conditions.

Appellants raised technical and safety objections during a lengthy hearing, including claims of hill seepage, slope instability, naturally occurring asbestos in fractured serpentine bedrock, and concerns that deep sewer trenches adjacent to existing homes could destabilize the hillside. Sue Black, a nearby resident, said historic runoff has flooded properties and cautioned the board about repeating past failures.

County planning staff summarized the record and explained that the applicant provided a preliminary geologic hazard study (Cleeth Harris), a full engineering geology investigation and slope stability analysis (GeoSolutions), and hydrology/drainage calculations prepared by a registered civil engineer. County geologists peer‑reviewed the studies; conditions of approval require the contractor to incorporate geotechnical recommendations into construction plans and implement mitigation measures including a naturally occurring asbestos survey prior to grading.

The applicant’s engineers and geologists told the board the design sites lots in flatter portions of the parcel, limit grading in areas with slopes greater than 30 percent to a small segment of access road (covered by a variance), and sized bioretention basins and bioswales conservatively to capture and infiltrate runoff from 2‑year through 100‑year storm events without increasing pre‑development flows. Applicant civil engineer Tim Roberts said the stormwater basins are designed using conservative infiltration rates and include storage and maintenance provisions.

Appellants provided alternate geologic interpretations and real‑world descriptions of localized groundwater and historic movement; the board asked staff and the applicant to confirm the record and peer‑review processes. After deliberations, Supervisor Gibson moved to deny the appeals and require staff’s revised indemnification language; Chairperson Arnold seconded the motion. Roll call was unanimous in favor.

What this means: The Planning Commission approval stands, subject to the conditions adopted by the board (including updated indemnification requirements, site‑specific geotechnical mitigation measures, and required pre‑grading surveys). Any future building permits must comply with the development plan, the county’s coastal zone regulations and the geotechnical conditions attached to the approval.

Next steps: The applicant must submit final construction plans that incorporate the geotechnical and stormwater conditions, obtain required permits and meet monitoring and maintenance requirements for stormwater infrastructure.