Nov. 29--A power plant proposed southeast of Boise could produce three times the pollution of nearby Micron Technology Inc. and be one of the largest industrial pollution sources in the Treasure Valley.

The plant could increase industry-generated pollution in the Valley by 10 percent, based on the state's last pollution inventory, which hasn't been updated since 1999.

Mountain View Power Inc. has asked Boise city officials for permission to build a natural gas-fired generating plant on city- owned land just south of the Boise Factory Outlet mall to produce 80 to 250 megawatts of electricity. The company is preparing an application for a state air quality permit that will detail how much pollution the plant and a smaller 25-megawatt plant at the same site would produce and has yet to release that information.

But the company does say that the new plant would be nearly identical in size and emissions to its Bennett Mountain plant north of Mountain Home, which the company built in May.

According to the DEQ, the Bennett Mountain plant is permitted to produce 248 tons of nitrogen oxide, 248 tons of carbon monoxide and 132 tons of particulate matter. These are key pollutants monitored by air quality officials because they contribute to summertime smog and wintertime haze and are unhealthful to humans, especially to people with respiratory illness.

Critics like the Idaho Conservation League say the plant could be more productive and less polluting with better cleanup technology.

A natural gas-fired plant proposed in 2001 near Middleton would have generated almost twice the electricity with significantly less pollution than the plant Mountain View Power wants to build in Boise. The Garnet plant got its state permit but was abandoned for financial reasons by a subsidiary of Idaho Power.

"Do we want a small, dirty plant or a big, clean plant?" asked Justin Hayes, program director for the Idaho Conservation League.

The difference comes down to technology, said Randy Schroeder, a Mountain View Power partner who is also a principal of Greystone Environmental Consultants in Denver.

Schroeder said the reason Bennett's emissions are higher is that better pollution-control technology exists for combined-cycle turbines like Garnet would have used. Garnet would have been a year- round plant consistently supplying energy on a daily basis. The Bennett Mountain and proposed Boise plants are "peaking" plants -- which are used to generate electricity only when needed, such as on hot summer days. Simple-cycle turbines are better suited for such plants, Schroeder said.

Schroeder said his company is looking into using improved technology that would reduce emissions at the Boise plant, and in no case would produce more than Bennett Mountain's 248 tons per year each of nitrogen oxides and carbon monoxide.

The 250 tons is a key threshold. If a plant emits more than 250 tons, it triggers a DEQ permitting program that requires a plant to install "best available control technology." That means the plant would need the best pollution-control equipment or techniques available, said Bill Rogers, regional permit program coordinator with Idaho Department of Environmental Quality.

"Bennett opted out of that program" by staying under the 250-ton emission threshold, Rogers said.

If a plant remains under those thresholds, DEQ is limited in the criteria it can consider when granting a permit, he said.

"As long as they show that they meet all the air quality standards, DEQ has to issue a permit by law," said Rogers.

DEQ cannot consider factors such as location when considering permits, he said. Such siting decisions rest solely with local planners, in this case the Boise Planning and Zoning Commission.

Boise P&Z, however, does not have to approve a power plant just because the land is zoned for industrial uses including power plants, said Hal Simmons, Boise planning director.

The city has some power to look at possible impacts of industrial uses on nearby residential areas and can require mitigation measures -- such as restricting hours of operation or noise controls -- as a condition of approval.

Hayes said the conservation league could consider dropping its opposition if the proposed plant were built to be cleaner and more efficient.

"They're using our air for free," Hayes said. "Do we want them to waste our air or use our air thoughtfully?"