The Martha’s Vineyard Commission closed a public hearing Thursday on the first phase of a master plan for Island Grown Initiative after discussing nitrogen mitigation and a plan to protect features of the land significant to Native American culture.

IGI is located at the former Thimble Farm, covering 40 acres in the Iron Hill area off the Edgartown-Vineyard Haven Road. The nonprofit educational farm spans four towns and lies in the Lagoon Pond watershed.

South Mountain Co. of West Tisbury is the architect and builder for the project.

The MVC is reviewing the project as a development of regional impact (DRI). A public hearing opened last month on the plan to add a 3,200-square-foot education and innovation center and two buildings to house farm employees. The new center will include office space for staff. A nitrogen-removing septic system is planned to accommodate the expansion. Additional mitigation measures were introduced Thursday which will involve upgrading two septic systems off the farm but in the Lagoon Pond watershed. The systems have not been identified yet, IGI spokesman and South Mountain founder John Abrams said.

The farm has been identified as a sensitive archeological site, and discussion Thursday also centered around a report from the Public Archeology Laboratory. After excavation at the location of the two proposed housing buildings, PAL identified five Native American cultural features to be avoided and recommended IGI develop a protection plan, according to a staff presentation.

Mr. Abrams told commissioners that the farm should be able to avoid four of the features without altering its construction plan.

“The archeological part is really quite simple,” Mr. Abrams said. “We can satisfy all of PAL’s recommendations 100 per cent.”

The PAL report will not be made public out of concern for protecting sensitive archeological resources. Responding to questions from commissioners later in the hearing, IGI executive director Rebecca Haag described the farm’s strong commitment to respecting the land.

“IGI has been committed to doing historical review of that farm even before we developed this building project,” she said. “Two members of the [Wampanoag] tribe are on our board. We want to treat this land and this issue with great respect.”

Nitrogen loading from the expansion — determined by wastewater and storm runoff — has been calculated at roughly seven kilograms per year above the maximum load. The installation of two upgraded systems elsewhere in the Lagoon Pond watershed are intended to offset the overage.

Mr. Abrams and engineer Chris Alley said further that discussion is under way with The Resource Inc., a Cape-based group which funds home improvement projects for low and moderate-income Island residents. TRI is interested in expanding its work to fund septic upgrades around the Island, Mr. Abrams and Mr. Alley said.

“One advantage of TRI is that they’re regional, they work on the entire Island. So if the best and quickest chance to do mitigation is in the Lagoon Pond watershed but happens to be in Oak Bluffs, then there’s no issue,” Mr. Alley said.

Commissioner Doug Sederholm lauded the idea of a possible Islandwide fund for nitrogen mitigation.

“It looks like something that future applications could be able to use and get the most bang for their buck in terms of mitigating excess nitrogen in watersheds,” Mr. Sederholm said.

The hearing was closed, with the written record left open for two more weeks. After that a post-hearing review and decision by commissioners will be scheduled.