Hearings to consider approval of the proposed Ho‘opili community with 11,750 homes in Ewa are scheduled to begin Oct. 20, and when they get underway three opponents intend to directly contest the project by D.R. Horton’s Schuler Division.

The Sierra Club and state Sen. Clayton Hee have filed petitions to argue against Ho‘opili before the state Land Use Commission.

Hee and the environmental group, if their requests are granted, would join Friends of Makakilo as "intervenors" in the case. Friends of Makakilo, a community group led by Kioni Dudley, challenged Ho‘opili during a round of hearings in 2009 that forced Horton to resubmit its development plan earlier this year before a vote on the merits of the case.

Additional intervenors in the case could make it more difficult for Horton, which believes that modifications it has made to its plan, including the dedication of some land for commercial farming and home gardens, have improved the project’s viability.

Last month the Sierra Club and Hee said they intended to intervene in the case, and since then have formally applied to participate in the hearings with the ability to introduce expert testimony and question Horton witnesses with the assistance of attorneys.

The Sierra Club announced Tuesday that it had formally applied to contest the estimated $4.6 billion project, which would be built on about 1,500 acres that includes some of the best and most actively farmed agriculture land on Oahu.

"The Ho‘opili development would plant 11,750 housing units on the most productive farmland in Hawaii," Randy Ching, a longtime Sierra Club leader, said in a statement. "We should be building in the city, not in the country."

The main concerns of the Sierra Club and other Ho‘opili opponents focus on increased traffic and the loss of farmland that many view as more critical today because of food security issues.

Horton contends that the project is appropriate because it is within the urban growth boundary designated by the city to accommodate population growth and preserve farmland elsewhere on Oahu. This aspect led the Hawaii Farm Bureau Federation to express its support for Ho‘opili.

To mitigate the loss of farmland, Horton revised its original plan by reserving 251 acres within the community for commercial farming, community gardens and home gardens.

Ho‘opili also is designed to accommodate two rail stations on Oahu’s planned commuter rail line. The development will have space for businesses employing an estimated 7,000 people, which Horton said will expand opportunities for residents to work close to where they live and not commute to Honolulu.

Last week the Sierra Club won a partial court decision against Castle & Cooke, the developer of Koa Ridge, a planned community with 5,000 homes between Waipio and Mililani. On July 19 a Circuit Court judge ruled that the state Land Use Commission’s approval of the Koa Ridge project was invalid. The state has challenged the judge’s ruling, and a final decision is pending.