A model railroad group is suing to remain at its longtime Napa Valley Expo home and is basing its legal argument on state environmental law.

The Napa Valley Model Railroad Historical Society filed the lawsuit Friday in Alameda County Superior Court. It is challenging a decision by the Napa Valley Expo Board of Directors in July 2017 to allow the railroad group’s lease to expire on Dec. 31, 2017.

Model railroad enthusiasts want a court order that forces the Expo Board to rescind the lease expiration. They want the 4,600-square-foot, scale-model train exhibit to remain at the Expo at 575 Third St. in Napa, where the group occupies two Quonset huts with arcing, galvanized steel roofs.

“The model railroad is a recreational, cultural, educational and historic resource enjoyed by thousands of visitors each year, with its lease automatically renewing for many decades,” the lawsuit said.

Expo CEO Joseph Anderson on Tuesday said the organization has no comment on the lawsuit. The lawsuit wouldn’t have come as a surprise, given the Expo Board of Directors on Dec. 12 discussed the possibility in a closed session.

This dispute began in earnest after the Expo in February 2017 released a draft master plan to renovate the state-owned, 34-acre fairgrounds. The plan’s many proposals include demolishing the model railroad buildings to make room for parking spaces.

The thrust of the railroad group’s legal argument is that the Expo is violating the California Environmental Quality Act, or CEQA.

CEQA requires environmental review be done before the Expo can approve or implement the draft master plan in any way, the lawsuit said. That means preparing and certifying an environmental impact report. Yet, it claimed, the Expo has taken such steps as approving the railroad group’s lease expiration and planting five acres of sod.

In a press release, the railroad group said CEQA protects not only natural environments, but also important educational, cultural, recreational and historical resources such as the model railroad. It accused the Expo of beginning to implement its draft master plan in piecemeal fashion.

The Napa Valley Model Railroad Historical Society is suing the 25th Agricultural District Fair Board to remain at the Napa Valley Expo. The board made a decision in July to end the group's lease on Dec. 31, 2017. J.L. Sousa, Register

“We know there is a way for the model railroad to continue to serve as a cultural and recreational asset to Napa County families while developing a viable, new master plan,” Railroad Historical Society President Daniel Jonas said in the press release.

The Expo’s draft master plan acknowledged that an environmental impact report is needed before approving a final plan. Such a report would look at cumulative environmental impacts, discuss alternatives, identify ways to lessen or avoid impacts and propose mitigation measures for significant impacts, it said.

But the Expo Board’s recent actions suggest that organization thinks it can allow the railroad group’s lease to expire without doing an environmental impact report.

Expo Board President John Dunbar in August wrote that the railroad group pays below-market rent and that issues exist regarding the model railroad structure’s fire safety, building code compliance and accessibility for the disabled. The Expo master plan focuses on developing multi-use facilities, he wrote.

The draft master plan vision, if enacted as proposed, would roll out in stages over 10 to 15 years. It is designed to further the Expo’s adopted vision of a fairgrounds that is the county’s premier agricultural, recreational and community gathering place.

Such events as the BottleRock music festival and the annual Napa Town & Country Fair use the fairgrounds. Other uses include a bingo hall and a recreational vehicle park.

According to the lawsuit, the Napa Valley Model Railroad Historical Society began in 1955 with a layout in the Southern Pacific West Napa depot. Subsequent homes included a basement at the Veterans Home of California at Yountville.

The Napa Valley Model Railroad Historical Society is suing the 25th Agricultural District Fair Board to remain at the Napa Valley Expo. The board made a decision in July to end the group's lease on Dec. 31, 2017. J.L. Sousa, Register

The group in 1970 moved to the Expo and into two donated, World War II-era Quonset huts from the Basalt ship-building facility along the Napa River. It built a two-story center building to connect the two Quonset huts.

Filing the suit in Alameda County Superior Court is proper because the respondents are a state agency and its directors are represented by the state Attorney General who maintains offices in that county, the lawsuit said.

The Expo Board represents the state's 25th District Agricultural Association. Listed in the lawsuit as defendants are the Expo Board and the California Department of Food and Agriculture Division of Fairs and Expositions.