Michigan’s 138-year-old Capitol is currently undergoing a two-year $70 million upgrade that will include what state officials say will be the largest geothermal system for a state government building in the country.

The heating and cooling system will be coupled with other energy efficiency upgrades that aim to cut the Capitol’s $800,000 annual utility bill in half.

While it will cost nearly $4 million upfront, officials estimate geothermal will save the state $300,000 a year on heating and cooling costs and pay for itself in roughly a decade.

Engineering consultants have demonstrated the property is a prime candidate for geothermal based on conductivity tests.

The planned closed-loop system involves drilling more than 220 bores roughly 500 feet below the surface where state lawmakers currently park on the west side of the building.

Workers broke ground on the infrastructure project two weeks ago.

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