The developers of an envisioned "learning community" in Mākaha Valley have published a draft environmental assessment, taking a major regulatory step toward advancing the estimated $149 million project designed for up to 600 homes integrated with educational facilities.

The Department of Hawaiian Home Lands and Kamehameha Schools recently filed the assessment with the state Office of Environmental Quality Control after announcing the project last month.

In the report, the developers said a partial realignment of Mākaha Valley Road and an expanded sewer line largely along Bayview and Pōka'ī Bay streets are anticipated.

Preservation of 'Eku Stream is planned along with likely preservation of a possible pre-contact agricultural terrace. Four other significant historical structures — an irrigation ditch and flume once used by Wai- anae Sugar Co., and foundations of two post-plantation buildings for agricultural use — were documented but not slated for preservation under a plan accepted by the state Historic Preservation Division.

It's possible that the site envisioned for the homes, currently an 18-hole golf course known as Makaha-East or Makaha Valley Country Club, may contain unacceptable levels of residue from pesticides, herbicides and fertilizer, the report said.

DHHL said it will sample soil for harmful chemicals, and take steps if necessary to ensure that soil and groundwater are safe under state Department of Health standards.

The road, sewer and soil issues are major anticipated impacts of the project with which some nearby residents are taking issue. Al Frenzel, a resident of the Mauna 'Olu Estates subdivision bordering part of the golf course, said more improvement needs to be made to the narrow and poorly maintained Mākaha Valley Road that in part is privately owned.

"It's a rural country road," he said. "The road's a disaster."

Frenzel also fears that DHHL may encounter extraordinary costs for remediating soil, especially if the agency includes garden or farm plots within the golf course site.

DHHL and Kamehameha Schools hope to begin construction in 2013 if approvals can be readily obtained. Buildout would take place in phases and last 15 years, though it could take longer depending on economic or other circumstances.

Zoning changes aren't necessary because DHHL, which will own the golf course site slated for homes, isn't subject to City and County zoning rules. The land slated for educational facilities is permitted for such use under present zoning with a conditional use permit.

The learning community is slated for 300 acres donated by local developer Jeff Stone.

Kamehameha Schools would develop and operate a 70-acre educational complex including classrooms, gardens and sports fields. The learning facilities would cater to Wai'anae Coast children, from preschoolers to young adults, and not be an extension of the Kamehameha Schools' network of campuses that are open only to Native Hawaiians.

In the environmental report, Kamehameha Schools anticipates initially developing facilities serving 280 students plus indigenous gardens, an outdoor gathering place, sports fields and recreational paths. A second phase developed from 2026 to 2031 would provide educational facilities for an additional 1,020 students.

DHHL plans to develop 400 to 600 affordable homes on 118 acres. About 80 hillside acres adjacent to the golf course would become a cultural landscape possibly with agricultural terraces, taro and native vegetation.