Board affirms Planning Department categorical exemption for 2142 20th Street project after geotechnical concerns raised

The San Francisco Board of Supervisors voted 11-0 April 15 to affirm the Planning Department's categorical exemption under the California Environmental Quality Act (CEQA) for a proposed six‑unit residential project at 2142 20th Street in Potrero Hill and to table motions that would have required additional CEQA findings or a reversal of that exemption.

The board's decision came after an hourlong public hearing in which the appellants said unusual site conditions — a steep slope, mapped seismic landslide hazard, and underlying serpentine bedrock — create a reasonable possibility of significant environmental impacts that require an initial study under CEQA.

Why it matters: Appellants and an independent geotechnical expert argued that planned excavations of up to about 30 feet and limited shallow borings to 2–5 feet leave key site hazards uncharacterized; the Planning Department and the project sponsor said those issues are addressed through routine building permit processes, local codes and state law.

Appellant Emily Brough, representing the neighboring homeowners association, said the question before the board was not whether the building should be built but “whether the project should receive environmental review under the California Environmental Quality Act.” She and geotechnical engineer Alan Cropp told supervisors that several factors taken together create unusual circumstances: steep grades reported on parts of the parcel of roughly 40 percent, the site's designation on state seismic landslide maps, and exposure of serpentinite bedrock that can release naturally occurring asbestos during deep excavation.

“Serpentinite has the second unfortunate situation that in certain cases it possesses asbestos fibers, which can be hazardous during excavation processes,” said Cropp, a Bay Area geotechnical engineer with more than 50 years of experience. He testified the project lacked certified engineering geology studies, deep borings and a geologist-certified evaluation of deeper materials and stability that would normally inform excavation and shoring design.

Planning Department staff said the project fits within CEQA’s class 1 and class 3 categorical exemptions — demolition of a single‑family residence and construction of up to six units — and concluded that the unusual‑circumstances exception did not apply. Don Lewis, a Planning Department staffer, told the board that steep slopes and serpentine bedrock are common in parts of San Francisco and that local and state building codes, the Slope and Seismic Hazard Protection program, and the Department of Building Inspection (DBI) permit review require geotechnical and geological reporting at the building‑permit stage.

Project counsel Tuya Catalano said the sponsor has engaged with neighbors, modified the project in response to questions and will submit the standard building‑permit materials — including geotechnical and geology reports prepared by licensed professionals — before excavation or demolition. Catalano urged supervisors not to use a CEQA appeal to substitute for the technical peer review that occurs during permitting.

Board action: Supervisor Walton moved to affirm the Planning Department's categorical exemption (item 35), and the board approved that motion 11‑0. Supervisors tabled two related items (motions 36 and 37) that would have conditionally reversed the exemption and directed preparation of findings. The board recorded the final vote on the exemption as 11 ayes; no supervisors voted no on that motion.

What was debated: Appellants said the combination of steeper‑than‑typical slopes, the mapped seismic landslide hazard and uncharacterized serpentinite made a reasonable case that deeper investigation should occur before construction. Planning and the sponsor emphasized that those technical investigations are standard permit conditions — that DBI requires licensed geotechnical engineers and certified engineering geologists, and that site‑specific mitigation (shoring, dust controls for naturally occurring asbestos, peer review) is handled through the building‑permit process.

Next steps and caveats: The Planning Department's exemption stands for now, and the project sponsor may proceed toward building‑permit applications. Any required geotechnical or geological reports, or additional mitigation, would be reviewed and enforced by DBI and other agencies at the permit stage. Appellants retain other administrative remedies if they believe later permit documents are inadequate.

Speakers quoted in this story are identified by name and role as they appeared at the April 15 meeting and are members of the attribution list below. The board's formal motions and vote were recorded on the public hearing docket (items 34–37).