The largest proposed development in Napa County history is officially moving down a long bureaucratic path toward a vote by the Napa County Board of Supervisors.

Developers of the Napa Pipe Project submitted their request for a General Plan amendment this week, seeking a change in the zoning designation of the 150 acre site from industrial to transitional. Such a shift could lead to approval for residences on the site.

Principal developer Keith Rogal has proposed 3,200 townhouse dwellings, 15,000 square feet of restaurant space and 25,000 square feet of commercial space slated to serve the neighborhood. The southern portion of the site would have 50,000 square feet of light industrial, warehouse or research and development space, plus a 150-suite condominium hotel.

Documents filed with county planners Wednesday tout a cache of proposed benefits of the project -- it could shoulder much of the county's burden of state-ordered new housing and aims to provide affordable housing for area workers -- but also revealed a key weakness of the project, mainly that most of it lies within the Napa River flood plain.

Developers plan to raise the site to nine feet above sea level or more.

Now, in various places the site is six to 10 feet above sea level.

Rogal has said the development would ease housing pressure on the county, and would help maintain the agricultural preserve by using a site for homes that is not designated for agricultural use. The county has been moving toward opening up the site for non-industrial purposes through its general plan update process.

If enacted by the Board of Supervisors next year, the change from industrial to transitional zoning would signal at least a symbolic desire to look at different uses for the land.

"My sense of the transitional designation is saying it's time to think about what can these lands do that makes sense for Napa today and tomorrow," Rogal said in a February interview.

In that sense, the documents filed with the county showcase what developers believe will be upsides of the project:

* Housing would reduce the impact of commuting traffic in the county by locating homes within a "jobs core," enabling public-serving employers like hospitals and educational systems to recruit and retain workers.

* It would "recycle" one of the county's largest urban properties "in an environmentally responsible manner," transforming what developers called a highly visible contaminated site.

* The proposal is slated to provide public access to a stretch of the Napa River and provide a link to the proposed Napa River Bay Trail between Napa and American Canyon.

The site plan for the project also includes features not previously presented to the Board of Supervisors, including playgrounds, a "tot lot," a community garden and a park-like knoll where residents could take in surrounding views of the river and hills.

Other previously disclosed bright spots include greenbelts, where railroad tracks run now, a boat launch and a sunken event space that Rogal has shown being used as an outdoor movie theater. There would also be an area where a small museum would be built to illustrate Napa Pipe's ship- and pipe-building heyday.

Hillary Gitelman, county planning director, said with the planning department's workload it will be May at the earliest before an preliminary analysis of the project could be brought before County Supervisors for an up or down vote. The vote would determine if the project meets the criteria to continue through public processes, including public hearings.

Several questions have arisen about the Napa Pipe project in the last few months, such as who will provide utility services for an estimated 4,000 residents and whether such a project should be approved on incorporated county land.

In the documents submitted to the county this week, Napa Pipe developers stated it may be necessary to rely on the city of Napa for water or use on-site wells.

If approved, developers estimate construction of the project would roll out in three to five phases, reaching completion sometime between 2016 and 2018.