MARTINEZ -- A resurrected plan to develop the Tassajara Valley with a residential subdivision and mixed uses has opponents nervous about how the county's urban limit line could be violated -- eventually leading to increased urban spawl.

The proposal, dubbed Tassajara Parks, calls for the construction of 152 single-family homes and other mostly park and other recreational uses on 30 acres of the total 771-acre site. There would also be park land, a trail, staging areas and a detention basin. And it would require that the residential neighborhood be built via an adjustment to the urban limit line, as part of a county general plan amendment. In the 616-acre southern portion of the site, a 5-acre lot would be dedicated for use by the San Ramon Valley Fire Protection District for a training facility and another 5-acre lot for unspecified uses for the San Ramon Valley Unified School District. The remaining acres would be for park land, recreation and open space.

But open space and urban limit line preservation advocates such as Donna Gerber, a Contra Costa County supervisor from 1997 to 2003 who worked on the urban limit line, said the proposal is really a "renaming and rebranding" of an old development project that generated plenty of controversy. It was called New Farm, which landowner and former Jordanian transportation minister Samir Kawar tried to build in 2007.

A scoping meeting Monday afternoon by Contra Costa County's Department of Conservation and Development brought out several Tassajara Valley residents as well as an environmental advocate, who had questions they wanted to make sure are addressed by the upcoming environmental impact report, for which the scoping meeting was soliciting comments.

Dorothy Burt, also a Tassajara Valley resident, said the voters had shown time and time again that they were strongly opposed to changes to the urban limit line, and she worried about how water and traffic would be affected in the area.

"Voters all over this area have spoken against moving or expanding the urban limit line. This includes Brentwood, San Ramon and Livermore," she said. "People are against urban sprawl."

Joel Devalcourt of Greenbelt Alliance also said that he wanted to be sure the environmental report addresses the full range of impacts to the area.

"This has never really been done before," he said about the proposed change of the county's urban limit line to support the development. "There are significant concerns about the precedence."

In addition to negatively impacting the environment, the project could mar the water supply, so the current drought conditions should be considered, he said.

For that reason, the environmental impact report needs to really capture "why the voters should lose on the opportunity to weigh in on the urban limit line when it's not that clear whether or not these hundred units are particularly needed," he said.

The deadline for public comments on environmental concerns related to the project, originally set for June 27, is 5 p.m. Friday. Comments should be directed to the Contra Costa Department of Conservation and Development, Community Development Division, Attn: John Oborne, 30 Muir Road, Martinez, CA 94533.

Contact Joyce Tsai at 925-847-2123. Follow her at Twitter.com/joycetsainews.