Isaac Myers inspects a “K-tube” of algae at the Running Tide oyster hatchery on Harpswell Neck. The business grows several species of algae to feed the oysters.

Running Tide Technologies Inc. plans to expand its oyster hatchery at Mitchell Field and grow kelp there for what the startup, which is attracting nationwide press attention and millions of dollars in investment, boasts will become “the most efficient carbon removal system in the world.”

In December 2018, the town leased a run-down garage and a 1.08-acre parcel on Middle Bay to Running Tide, which renovated the building to create the hatchery. The business has grown and is now exercising an option to expand onto a second, larger lot — 3.85 acres of meadow behind the hatchery, where it plans to build a new, state-of-the-art facility.

The Harpswell Board of Selectmen approved an addendum to the lease Thursday, Sept. 30, retroactive to July 1.

Running Tide will pay $28,624.86 in rent for the second half of 2021 and $58,960.68 for 2022. Rent will increase by 3% per year until the lease expires in 2028, at which time the sides could negotiate new terms.

The new building would allow Running Tide to move its kelp-growing operations from Portland to Harpswell, according to a joint statement from the business and the town. Running Tide expects to have 20 full-time employees at the site.

“In its current location, Running Tide hatches millions of oyster and clam seed per year,” the business and the town said in the statement. The document describes Running Tide as “a leading producer of Casco Bay-grown shellfish” that sells oysters and surf clams in the Portland area and grows kelp for carbon removal.

The business “aims to scale its operations to be able to provide consumers with healthy, low-carbon proteins and make a dent in our fight against climate change,” according to the statement.

The new building must comply with town ordinances, including standards specific to the Mitchell Field Marine Business District, and receive approval from the Harpswell Planning Board.

The expansion has been in the works for some time.

“Because of the pandemic, we put off negotiations for about a year or so, and in 2021 we resumed negotiations,” Town Administrator Kristi K. Eiane said. Steve Levesque, executive director of the Midcoast Regional Redevelopment Authority, led negotiations at no cost to the town.

The Midcoast Regional Redevelopment Authority manages the former Brunswick Naval Air Station. George J. Mitchell Field is another former military property. Once a fuel depot for the U.S. Navy, the federal government transferred the 120-acre property to the town in 2001.

Running Tide paid below-market-rate rent under the original lease because “it was kind of a pilot project” and because the business was “taking over a dilapidated building that they were going to rehab,” Levesque said. The new rent represents the market rate.

Levesque called Running Tide’s work “really, really exciting” and “a really good fit for the marine business district in Harpswell.”

Marty Odlin, CEO and founder of Running Tide, spoke briefly at the meeting.

“Right now it’s purely a production facility,” he said of the hatchery. The new building would enable research and development “of different strains of oysters or clams or macroalgae,” such as kelp, and “would allow us to increase the size and scope of our operations.”

Running Tide has yet to design the building, but Odlin said it would stand no more than two stories high and might be a steel-frame structure. The next step is to secure financing.

Of a potential timeline for construction, Odlin said, “It would be optimistic for me to say that it would start in the next year. COVID caused a lot of delays for us in our business plans.”

He wants to schedule construction outside the business’s “shellfish season,” which coincides with the heaviest use of Mitchell Field by the public.

The owner of a house that overlooks the site asked Odlin about how the building would impact his view. Odlin was not sure, but said he would communicate with the neighbor about his concerns.

The neighbor said that if the building blocks his view, he will request “a major tax reduction” from the town. He noted that the business had been responsive to noise concerns in the past. “We’ll be good neighbors,” he said.

Running Tide and its ambitious goals have attracted attention from The New York Times, NPR, CNN, Scientific American and Fast Company, as well as millions of dollars in investment.

Running Tide’s website says it uses “new technologies to optimize shellfish growth,” which allows for “higher output in much smaller spaces.” This, in turn, means “more people can rely on this delicious, low-carbon superfood as a source of protein.”

Of its kelp operation — the subject of much of the media attention — it says, “With the help of photosynthesis, ocean currents and gravity, we can use kelp to store carbon in the deep ocean,” where it will remain “for thousands to millions of years.”

Kelp sequesters 20 times more carbon per acre than a forest, according to The Pew Charitable Trusts, and a tree only stores carbon throughout its relatively short life cycle.

After it grows kelp, Running Tide attaches it to a biodegradable buoy and deploys it in the ocean. As the kelp continues to grow, it sinks to the ocean floor.

The high-pressure, low-oxygen environment at the bottom of the ocean means the kelp will remain intact and in place indefinitely. Odlin believes most of the kelp will eventually turn into oil or sediment.

Running Tide makes money on its kelp operation through the sale of “carbon credits.” Potential customers include corporations with net-zero carbon pledges, eager to offset their emissions through the purchase of such credits. The e-commerce company Shopify is one of its early customers and investors.

A Running Tide executive told Scientific American the business has deployed about 1,600 buoys as part of an experimental phase. It hopes to one day deploy millions.

A grant from the Broad Reach Foundation supports the Harpswell Anchor’s reporting on climate change.