Environmental issues have put plans for a new $130 million Mill Valley Middle School on hold, according to consultants for the school district.

The delay is for more studies at the campus at the 425 Sycamore Ave., which used to be a burn dump. The district’s plan is to demolish the school and rebuild it at the same site.

Sandrine Hitchcock, a program manager for the construction consulting firm AECOM, discussed the project during a public forum on Thursday. Hitchcock said the last step of the California Environmental Quality Act process is expected in July.

“We don’t know how soon after that we could begin construction — it could be five months, it could be six months or more,” Hitchcock said.

The original deadline for the CEQA final determination was January 2025, the district said in a presentation at the forum. Grassetti Environmental Consulting, a firm in Berkeley, is working on the environmental impact report, the district said. The draft EIR, which had been scheduled to be finished this month, is now set to be released in February.

Laura Knauss, a project architect, confirmed that she is suspending work on the school design in the event the environmental reports indicate that changes need to be made. A demographic report could also mean the size of the new school would be reduced.

“We don’t want to overbuild,” Knauss said of the preliminary demographic data, which indicate that the school capacity could be lowered from 1,200 students to 950 students. “We’re waiting on the demographic projections.”

Knauss said that even if the CEQA process is over by July, it will still take her firm several months to restart work and complete the design.

“And we would still need to send it to DSA,” Knauss said, referring to the California Division of the State Architect, which governs approvals for school designs.

School parent Susan Dawson, one of several dozen people to attend the forum in person or online, said she was glad the design plans were put on hold. Dawson said the break will preserve funds from the $197 million bond measure that voters approved for school upgrades.

“It seems there’s been a lot of inefficient sequencing,” Dawson said. “Things have been occurring out of order.”

In recent weeks, more than 200 parents have signed an online petition calling for the district to rethink both the middle school site and the site of temporary classrooms during construction. The petition calls the project site “dangerous” because of its position on the former dump.

In previous testing, the petition states, “soil samples show hazardous levels of lead — over 81 times the limit for the State of California — and one area of explosive methane gas, all of which is presently capped by just 2-3 feet of clay soil that would be disrupted during construction.”

As for the temporary classrooms, which would be next to the construction zone for two years, the petition expresses even more outrage.

“The proposed interim site will be directly across from the Sewerage Agency of Southern Marin,” the petition states. “The site smells of sewage due to hydrogen sulfide. Daily exposure to these fumes can impact student health, and will certainly impact student and teacher morale.”

Construction noise and dust are also a concern.

A new parents’ website, MVMSModernizationMess.com, says the district should take over its Terra Marin preschool site at 70 Lomita Ave. and use it for the temporary classrooms. The district has been trying to evict Terra Marin over a lease dispute.

“The district is asking us to trust their consultants,” said Dawson, whose fifth-grade child will be in middle school next year. “In my mind, it’s more a trust and verify situation. My child’s health is on the line.”

Parent Tracy Urquhart agreed.

“I was disappointed about the meeting outcome last night,” Urquhart said. “There were some questions in the queue that I wanted to hear answered, and the community deserved the extra 15 or so minutes it would have taken to get those answers.”

According to Ryan Bast, a geologist with the Ninyo and Moore consulting firm, the delay in the CEQA determination stems from “confusion” over which agency or agencies are handling the regulatory oversight.