Yocha Dehe Wintun Nation received a final letter Friday from Yolo County to address traffic concerns in the Tribal Environmental Impact Report for its proposed casino expansion.

The letter acts as a precursor of sorts for what county officials will argue necessitates the offsetting of environment effects as part of an intergovernmental agreement.

The tribe's most recent expansion plans include a 52,440-square-foot event and conference center, more gambling and dining space and 129,840 square feet of additional facilities and warehouse space.

The Yolo County Board of Supervisors sent the original draft of the letter to the tribe on Aug. 3 to address issues like air and water quality, but was granted an extension to complete further review of traffic issues.

Sacramento-based Analytical Environmental Services prepared the environmental report, which estimates the increase in traffic expected from patrons of the 2,300-seat event center. The county has a $30,000 contract with Fehr & Peers Transportation Consultants, but thus far has spent around $17,000 for its services.

Calculating the event center's trip generation, AES assumed a 47 percent internal trip capture, meaning the amount of event patrons already in the casino. The number is based on events at the Casino's Club 88, which the county believes leads to an understated estimate for the much larger event center, according to County-Tribe Coordinator Christopher Lee.

Furthermore, the county  contends the tribe should also consider the amount of traffic generated after events in order to comprehensively resolve the effects of the new event center.

With as many as 24 events in one year, the county wants the tribe to provide permanent physical improvements rather than traffic management techniques.

Of course the tribe can't be held accountable for all traffic in the Capay Valley, but the county is asking it to take responsibility for a larger portion of the road construction bill.

When analyzing the tribe's fair share percentage on a number of roads, the TEIR does not take into account major events during what is anticipated to be 16 sold-out days a year, according to the letter.

There are also issues pending from the tribe and county's 2004 agreement when the casino first expanded.

The tribe agreed to solve traffic problems at the intersection of Highway 16 and County Road 89 by installing traffic signals and creating a left-turn lane to enable protected left-turn signal phasing.

The tribe and the county later agreed to postpone construction at the intersection because the site is part of Caltrans' 12-mile Highway 16 Safety Improvement Project. Caltrans will realign the road and any improvements to the area will have to be done over after the SIP is completed.

But the county is tired of waiting on Caltrans and is now stipulating that the casino move forward with the construction if Caltrans SIP has not commenced by 2013.

"It's an issue of much consternation on both sides," Lee said. "We want the mitigation done when this event center project is built. The state has a timeline for completing the project, but it's been a while."

As it stand now, Caltrans plans to begin construction in the spring of 2013 with completion at the end of 2014. If the project is postponed and the tribe agrees to the county's request, it will have to pay for the same project to be done twice.

AES Project Director Pete Bontadelli wouldn't comment on the county's request other than to say, "We are waiting for permission from the owner of the road. We cannot work on project until Caltrans gives us permission."

Bontadelli and his team are now working to respond to the letter from the county as well as letters from the city of Woodland, the Yolo County Transportation District, three state agencies and about a dozen private citizens.

Once AES has responded to all comments and released a final environmental impact report, the county and the tribe have 55 days to negotiate mitigation for an intergovernmental agreement.