The Placer County Board of Supervisors agreed Tuesday to clarify several important issues before deciding whether to move ahead with plans for upgrading an existing North Auburn sewage-treatment plant or to accept the city of Lincoln’s proposal to build a regional system.

Board members said they need more information before deciding which option to pursue, emphasizing they want to make an informed decision that best serves the interests of both the county and the more than 6,000 ratepayers in North Auburn.

“This is an historic decision,” board Chairman Robert M. Weygandt said. “We get to do this once for the next 30 years.”

The issue will return to the board sometime this summer. At Tuesday’s meeting, board members said they expect to make a decision on which option to pursue at that time.

One option is upgrading and expanding the existing wastewater treatment plant that serves North Auburn customers in Sewer Maintenance District 1. Built in 1961, but substantially upgraded several times since then, including the last upgrade in 2001, the plant currently does not meet state sewage discharge standards and is near capacity.

The second option is a regional approach that calls for building a pump station and pipeline to Lincoln’s modern wastewater treatment plant and expanding the Lincoln plant to handle sewage from North Auburn.

For several years, Placer County has been exploring the regional approach with the cities of Lincoln and Auburn under the umbrella of the Placer Nevada Wastewater Authority. At the same time, Placer County has worked on plans for upgrading and expanding the existing plant.

On Feb. 8, the Board of Supervisors received an update from the Facility Services Department on the status of both options. City of Lincoln officials were on hand to present a new proposal for a regional system that would be designed, constructed and operated by the city. At that meeting, board members asked Facility Services to return with an analysis of both options.

During Tuesday’s meeting, Facility Services presented its analysis, Lincoln officials reviewed their proposal and the board took public testimony during a discussion that lasted for several hours. In the end, board members agreed to have county staff continue planning on the plant-upgrade project and to work with Lincoln on a draft agreement for the regional system. The draft agreement will be reviewed by the board when it considers the issue again this summer.

Drafting a proposed agreement will help answer some of the construction, financing, governance and other issues raised by Lincoln’s proposal. The draft agreement, for example, would help clarify the roles each participating agency would play in governing the regional system.

The board also asked county staff Tuesday to seek official word from Auburn on whether it is committed to pursuing the regional option with Placer County and Lincoln. Board members received unofficial testimony Tuesday indicating Auburn wants to participate in a regional effort, but the county has received no official word from elected Auburn officials yet.

Lincoln estimates Placer County’s construction costs for the regional system would be $64.5 million if Auburn participates and $71.5 million if Auburn decides not to participate. The cost of the plant-upgrade project is projected to be $62.2 million.

In its analysis, Facility Services noted that both options offer potential advantages.

Under the plant-upgrade option, for example, monthly sewer fees are projected to be lower for ratepayers initially and ratepayers would maintain more local control of the sewer system that serves them. Planning on the upgrade option is farther along and that option would increase the plant’s capacity to treat 2.7 million gallons of dry weather flow per day at a slightly lower capital cost, while the regional system would be built to handle the current dry weather flow of 1.7 million gallons per day from the North Auburn district.

The regional approach offers the prospect of economies of scale from operating one treatment plant, rather than separate plants in Lincoln, North Auburn and Auburn and of reduced potential for accidental discharges of untreated wastes or harmful chemicals into small streams. Regional approaches are favored by state regulatory agencies and it likely would be less expensive to adapt a regional plant to comply with new regulatory requirements.