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The redevelopment of the old Boston State Hospital in Mattapan has added hundreds of modest-priced residences to the city during the past two decades.

But now the state has put the final 10-acre slice of this sprawling 175-acre campus up for grabs. And the Walsh administration has weighed in, singling out one of the bidders for its unusual component: a more environmentally friendly way to heat and cool our homes.

That bidder is Thomas F. Welch & Associates, whose proposal for the 140-unit Orchard Village project at first looks like other residential projects of its size — with one major exception: The entire assemblage of apartments and townhouses would be heated and cooled by geothermal energy, not natural gas. City officials say they’re backing the project because it would further Boston’s “commitment to climate action.” They see its potential to become a model for other micro-district heating systems, a success story that could be replicated elsewhere.

Geothermal systems circulate fluids through pipes drilled down 200 feet or more, using the consistent 50- to 60-degree temperatures from deep underground to provide heating and cooling. The technology isn’t new, but it has primarily been put to use around here by schools and other institutions (such as a Mass Audubon nature center, on a different part of the state hospital campus) or some committed homeowners. Residential developments of this size and scope? Not so much. The upfront costs deter most developers, even with the possibility of state and federal incentives.

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Maybe not for much longer. Utility giants National Grid and Eversource are starting to show a keen interest in geothermal. Eversource has three proposed pilot programs under review at the state Department of Public Utilities. The Mattapan property is in National Grid’s gas service area; National Grid spokeswoman Danielle Williamson said the utility is talking with Welch about its possible involvement, including the ownership and cost issues.

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If Welch wins the bid, Williamson said, National Grid will do more work to determine the best approach to make this “geothermal micro district” a reality.

That victory is not a sure thing. The competition remains strong for this last portion of the state hospital, located behind the UMass Medical MassBiologics lab and between Walk Hill Road and Morton Street. There are four other housing proposals in the running, along with a “green economy” center for small businesses that would feature greenhouses and food manufacturing.

A citizens advisory committee met twice last week to review all six proposals. That committee will work with the state Division of Capital Asset Management and Maintenance to pick a winner. A spokesman for the state agency declined to say whether the geothermal concept gives the Orchard Village proposal a leg up.

Joseph Savage, Welch’s project manager, said his team is working with the Cambridge nonprofit HEET to flesh out the geothermal proposal. The selling point: reducing carbon emissions by up to 60 percent for each household, compared to energy generated by burning natural gas. Savage also pointed to the potential for savings. While this approach adds thousands of dollars to the cost of each new unit at the outset, the energy costs drop significantly in the long run. The geothermal system still needs electricity to run. But the environmental impact of that power, Savage said, will improve over time as the region’s power grid becomes more reliant on renewable energy.

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Controlling heat-related emissions — the stuff that blows out of our chimneys on these cold winter days — will be instrumental in the state’s aggressive ambitions to curb greenhouse gases over the next 30 years. Considerable headway has been made in the power generation sector. The Baker administration is starting to tackle transportation. But widespread solutions to addressing carbon pollution from buildings have proven elusive so far.

Pulling it off requires attractive options to natural gas, the dominant heating source for new construction in Massachusetts.

We could be entering the era of Peak Natural Gas, though. Some communities have imposed moratoriums on new hookups because of pipeline supply constraints. Others are considering them for environmental reasons: Brookline recently became the first in the state to approve a ban on new gas infrastructure, and more than a dozen other communities may follow Brookline’s lead. The 2018 explosions in the Merrimack Valley highlighted one big downside to gas reliance. So did the National Grid labor dispute that year.

Boston officials appear eager to embrace geothermal energy as a viable alternative at the neighborhood level. It will be interesting to see how many other communities are also willing to give it a shot.


Jon Chesto can be reached at jon.chesto@globe.com. Follow him on Twitter @jonchesto.