SANTA CLARA — It’s not your typical site for a new housing development: a former landfill, containing an estimated 5.5 million tons of municipal waste dumped over a quarter century in the heart of this city.

But it’s looking more and more as if the Related Companies’ plan to build a $6.7 billion mixed-use complex with up to 1,680 units of housing across the street from Levi’s Stadium will come to fruition. The project represents the largest housing project ever proposed atop a landfill in the Bay Area, regulators say, and perhaps in the entire state.

Environmental overseers have accepted Related’s massive technical document, which includes elaborate safety systems to block the escape of combustible methane gas and other dangerous vapors, and to prevent groundwater contamination.

“The regulators were pretty skeptical at the start, I have to say,” said Stephen Eimer, an executive vice president with Related and co-managing partner of the 9.2 million-square-foot project, known as City Place. “But we kept at it, working and working, and they came around.”

Set on 240 acres atop what was once the Santa Clara All Purpose Landfill — a golf course and BMX track now occupy the site — the project also would include 5.7 million square feet of offices, 1.1 million square feet of retail space and 700 hotel rooms. The planning document for the development, which calls for a foot-thick concrete barrier covering more than 30 central acres of landfill where the housing would be built, spells out “multiple layers and multiple means of protecting” residents, shoppers and workers “from any kind of problem,” Eimer said.

The housing — probably a combination of condos and apartments — would be built Santana Row-style: above shops, restaurants or parking structures as a way of creating additional distance between residents and any escaped gases in the event of an emergency. But Eimer said safety measures should be nearly bulletproof with extensive sensor and alarm systems, as well as another system to monitor, collect and dispose of gases underground.

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The site will be covered with a foot-thick clay cap topped by the foot-thick concrete slab. Hundreds of piers would be driven up to 150 feet into the ground to anchor the entire inter-connected platform for the project’s center, which the city envisions as its new “uptown” district.

The subject of dozens of meetings over more than three years, Related’s post-closure land use plan has been accepted by the Santa Clara County Department of Environmental Health, California Department of Resources Recycling and Recovery (also known as CalRecycle) and the San Francisco Bay Regional Water Quality Control Board.

City Place was approved by the Santa Clara City Council last summer after the city conducted its own environmental review. According to Related’s projections, the city, schools and other local agencies would receive millions of dollars in revenue, scaling up to about $114 million each year once the project is completed. That could take a while. Construction of City Place’s core elements, including housing, could take 5-7 years, and the whole project could stretch out over two decades.

The project has been stalled by litigation, however. Last year, the city of San Jose sued the city of Santa Clara, charging that the imbalance between the project’s jobs and housing — 23,000 jobs and 1,680 housing units — will increase housing demand in San Jose and tax its overstretched services and infrastructure. The next court date is set for late August, but both sides said they hope for an out-of-court resolution.

Meanwhile, the safety measures proposed for City Place constitute “a solid plan,” said Keith Roberson, senior engineering geologist with the regional water quality control board. “The developer and the city of Santa Clara did go to great lengths to try to address all the issues that we raised.” He added, “We raised a lot of issues.”

Until now, big-box and other retail stores have been built on landfills around the region, and a 170-unit apartment complex was built in Campbell atop a former dump filled with construction and demolition debris — emitting fewer gases than the solid waste at the Santa Clara landfill. But the size and scope of the proposed housing at City Place gave regulators pause.

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Roberson confessed to feeling “angst” at the outset of the process, and he says he still isn’t ready for City Place to become a model for new housing in a built-out region where dozens of closed landfills might attract developers.

“The precedent of this is something that bothers us,” Roberson said. “Every case is going to have to be evaluated on its own merit.”

Even as Related moves toward an 18-month final planning stage prior to groundbreaking, the regional water board remains skeptical: “The concerns that we had about putting housing on a landfill still exist,” Roberson said.

The “big message is that whenever you build on any landfill, there are concerns,” agreed Michael Balliet, director of the Santa Clara County Department of Environmental Health. He added that Related “has cleared major hurdles. They have identified some ways to mitigate the issues.”

However, monitoring will continue throughout the next phase of planning. Balliet said the county has signaled to the developer that “conceptually you’re on the right track. But there’s a lot more to do.”

Ruth Shikada, Santa Clara’s assistant city manager, looked on the sunny side. “The green light to build never really happens until you get the last permit,” she said. “But as long as we stay the course and continue to do the research and prepare the documents … then we’re going to see housing on that site.”

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