Board sends Folsom Street development back for more review after pipeline, slope and vibration concerns

San Francisco — The Board of Supervisors on Tuesday asked the Planning Department and project sponsors to do more environmental and engineering work on a proposed small‑lot development on Folsom Street after community members and outside engineers flagged potential risks from construction vibration and the project’s location over a 26‑inch PG&E transmission pipeline.

The action: The board did not certify the earlier mitigated negative declaration for the Folsom project and instructed planning staff to require a more detailed vibration management and site‑specific investigation of the pipeline and subsurface conditions before environmental review is finalized.

Why residents objected: Neighborhood residents and independent engineers told the board the Folsom project — which would build two homes and improve a steep, unimproved section of Folsom Street — could require heavy compaction equipment very near the pipeline and could alter cover depth. They said prior planning analyses relied on data and studies that are not strictly comparable to the local pipeline and soil conditions and did not show visual inspection or potholing of the pipe to verify depth and condition.

What planning staff said: Planning staff said they had consulted PG&E on recommended vibration thresholds and proposed mitigation that includes a vibration monitoring plan, limitations on storage and construction activity within 20 feet of the pipeline, and that any vibration management plan must be approved by planning and PG&E before permits are issued. Planning argued the site is not an “unusual circumstance” under CEQA and that a class of mitigation can be implemented through engineering controls and close agency review.

Independent expert testimony: Engineers and the neighborhood provided assessments that questioned the data used to set vibration thresholds. They said the project’s plans call for an aggregate base that must be compacted in lifts, likely with large rollers; compaction directly over a pipeline with limited cover could present risk. They urged potholing (exposing the pipe) to verify cover depth and condition and recommended a more conservative monitoring threshold and stronger pre‑construction validation by PG&E and the city.

Board decision and next steps: After extended testimony, supervisors voted to return the environmental review to Planning with instructions to require a qualified expert to prepare a revised vibration management plan, include site‑specific potholing/inspection of the pipeline, detail the construction equipment and procedures to be used on the steep grade, and obtain written concurrence from PG&E and public works before permits are issued. Planning will present the revised materials to the board or in committee when available.

Community impact: Residents said their main concern is public safety and preserving emergency‑vehicle access on the narrow, steep streets; supervisors said planning must balance housing goals and neighborhood safety but that the record required additional site‑specific engineering evidence before the city signs off on construction.

Ending: The board’s vote effectively paused final environmental approval; Planning will not issue construction permits until the revised, PG&E‑approved vibration management plan and site verification are complete.