Castilleja School's plan to modernize its campus faced a fresh complication on Monday when the Palo Alto City Council launched its review of the contentious plan by rejecting staff's justification for the school's underground garage, throwing the fate of the proposed parking facility into doubt.

Over a marathon discussion that stretched until well past midnight, the council attempted to navigate a thicket of thorny zoning questions pertaining to Castilleja's proposed underground garage, its planned transportation programs, its tree-removal plan and the adequacy of the environmental analysis for the project. It struggled, however, to reach a decision on a project, and deferred to March 29 key decisions on the school's Environmental Impact Report, its request for a variance and a new "conditional use permit" that would allow it to gradually expand student enrollment.

No topic generated more debate — both among the council and in the greater community — than the underground garage, a facility that would normally not be allowed in single-family zones. But because the zoning code only applies this definition to residential uses, the city's planning staff had determined that the parking facility can be classified as a "basement" — a designation that benefits Castilleja in two ways. Unlike garages, basements are allowed in single-family neighborhoods and their square footage is not counted in calculations of floor area.

On Monday, the council roundly rejected staff's logic and concluded that the garage is, in fact, a garage. Council member Greer Stone spoke for the majority when he likened his view on the garage to Superior Court Justice Potter Stewart's threshold test for obscenity.

"I know it when I see it," Stone said. "We may not have a clear definition for what is considered an underground parking facility in an R-1 neighborhood but I know a parking garage when I see it and it's clearly a parking garage, not a basement."

Vice Mayor Pat Burt concurred and suggested that staff's decision to "rationalize it as a basement" was a "bad path to follow."

"I hope we won't do things that make it look to the public like we're putting our thumb on the scale," Burt said.

But while the council agreed that the facility should be classified as a garage, members could not reach a consensus on what to do about that finding. Because a garage typically counts toward floor area calculations — and Castilleja has vowed not to increase its building area as part of the campus reconstruction — the designation of the parking facility as "garage" would require the school to dramatically scale back its building plans and reduce its academic space to maintain existing square footage.

The council also has the option of approving a zoning text amendment that classifies the facility as a garage and yet precludes it from counting toward square footage. Such an option would effectively reject the staff interpretation while still allowing Castilleja to construct the facility. Ultimately, the council voted 4-3, with council members Alison Cormack, Eric Filseth and Greg Tanaka dissenting, to accept a motion from Burt that officially designates that facility as a garage and directs staff to return with a text amendment.

Mirroring the sentiments of the wider community, which has been deeply polarized on Castilleja's project, several council members favored a more restrictive approach. Mayor Tom DuBois recommended counting the garage toward the school's floor area calculation, a determination that would require a significant redesign. Council member Lydia Kou suggested scrapping the garage from the design altogether and argued that such a facility does not belong in an R-1 zone.

"I really believe that we have to be really careful about developing such intensity and density within the R-1 districts," Kou said.

Aside from its somewhat inconclusive ruling on the garage, the council deferred any further decisions on a project that has been moving through the city's project since 2016 and that continues to generate strong feelings both in favor of Castilleja's plans and against them. In recent months, the council has received hundreds of emails and oral comments in favor and against the school's proposal, which includes the reconstruction of numerous campus buildings, the relocation of a swimming pool from an above-ground location to underground and the construction of a garage.

Nanci Kauffman, head of Castilleja, had maintained at prior hearings, as well as at a virtual town hall last week, that the school included the underground garage in its plans early at the process at the behest of neighbors who requested such a structure. While she said that the vast majority of Castilleja students who come from other cities rely on trains, shuttles and other alternatives to driving, the parking structure is required to accommodate school faculty.

"Most of our teachers cannot live in Palo Alto. They commute and we're required by the code to have sufficient parking for them," Kauffman said. "It'll either be a parking lot above ground or a parking lot below ground."

As part of its plan, the school also hopes to secure the city's permission to gradually increase enrollment from its current level of 426 to 540. Under the conditions of approval that the Planning and Transportation Commission approved in November, the school would only be allowed to increase its enrollment if it succeeds in maintaining traffic levels at 2020 levels.

Another subject that generated significant debate on Monday was trees. At the March 8 council meeting, former city arborist Dave Dockter contended that the environmental analysis for Castilleja has used a flawed interpretation wrongly to justify the removal of two protected oaks. He argued that staff used a code provision that is intended for vacant lots and incorrectly applied it to Castilleja so that it would be allowed to remove the two trees.

Staff's interpretation, Dockter argued, "would allow any development application to remove any protected tree in the buildable area outside the perimeter setbacks, as a simple ministerial process with no other reasoning than the development desires the space where a tree lives."

While planning staff and current city arborist Walter Passmore pushed back against Dockter's interpretation, several council members cited Dockter's testimony and wondered why the city is allowing Castilleja to advance its plan for tree removal. Stone said he is particularly concerned about what he saw as the city's selective application of the tree ordinance to "justify removal of protected trees, when the spirit of the tree ordinance should be to protect trees, and not to remove them."

"It seems like we're bending over backwards to find ways within the code to justify the removal of these protected trees," Stone said.

DuBois also questioned whether the environmental analysis for the project accurately considered tree impacts and suggested that he will pay particular attention to the school's proposed traffic mitigations, a hot topic throughout the lengthy approval process. Echoing comments from other critics of the Castilleja project, DuBois cited its history of exceeding the enrollment cap in its existing permit — a transgression that prompted the city to issue a $265,000 fine in Castilleja in 2013.

"Given the history of the school's violation of the existing CUP both for enrollment and events, I'm just concerned. It's a very complicated (transportation-demand-management plan) and I'm concerned about the city's ability to enforce it," DuBois said.

DuBois suggested that he may have a hard time making the variance findings and aligned himself with those who believe that the school should settle for a smaller enrollment increase and only seek further growth after it proves to the community that it can accommodate more students without adding further impacts to the neighborhood.

Filseth appeared more open to Castilleja's plan, including its garage, which he suggested may be preferable from a design perspective. But like DuBois and Kou, he argued that the school should be required to address all of its traffic, noise and aesthetic impacts.

"In this case, we have a 100-year institution with a rich legacy in a current location, and I don't particularly want to tell Castilleja they need to leave," Filseth said. "But the reality is that Castilleja is running into these constraints that other destination schools in residential neighborhoods hit too. … Mitigating all those impacts is difficult and expensive and it's not really right to ask the neighborhood to shoulder all these costs."

Burt suggested that the school can reduce some of the environmental impacts of the underground garage by reducing the size of the structure. And to reduce the need for driving, Burt suggested raise the school's percentage of students from Palo Alto from its current level of about 25% to about 30% or 40% -- a change that can also be construed as as "public benefit." He and Stone also supported increasing the number of spots offered to individuals from socially and economically disadvantaged communities as part of the growth plan.

DuBois, meanwhile, suggested that Castilleja may simply be asking for too much and that its modernized campus — with an underground garage — may not fit into the residential neighborhood around the school.

"We rarely have projects that generate this amount of public scrutiny and sustained concern over years," DuBois said. "And just the sheer volume of activity around this project should signal to all of us that we may be forcing a very large square peg into a round hole."