At a meeting this week of the Donner Summit Public Utility District, critics of a proposed Royal Gorge housing project turned their attention to where the wastewater from the development would be treated.

The utility district has planned to expand its sewage treatment plant to serve existing lots in the area, but not enough for the 950 units planned for Royal Gorge.

As the Royal Gorge project advances through the planning process, the district must answer the question of whether to further expand the treatment plant to accommodate Royal Gorge expansion. A negative answer would force Royal Gorge developers to build their own costly plant.

Royal Gorge consultants from Carollo Engineers studied the two options and other disposal methods for treated sewage, said Carollo's Andre Gharagozian at Tuesday night's utility district board meeting.

The district discharges treated wastewater into the Yuba River in winter and sprays it on vegetation during the summer. The consultants considered effects of continuing those methods and of creating a subsurface dispersal system that would leach treated sewage into the ground. By expanding the existing plant, "there would be less environmental impact, less disturbed area, and it would give the district the option of improving the quality of the discharge," said Gharagozian, suggesting a modular expansion design.

The planned expansion would coincide with the Royal Gorge construction - around 2010, officials said.

Expanding the existing plant would be less expensive than Royal Gorge building a new plant "in the order of tens of millions of dollars," said Project Manager Mike Livak. "Whether it's $40 million or $60 million, depending on the alternative."