A controversial plan for converting coal-burning power plants to natural gas produced thousands of pages of testimony Friday from supporters and opponents.

Testimony filed with the Colorado Public Utilities Commission ran the gamut from extolling the plan's environmental benefits to warning of significant economic consequences for businesses and consumers.

Under the plan, Xcel Energy would spend $1.3 billion to phase out coal-fired generators in Denver and Boulder and retool plants to run on cleaner natural gas.

Other power stations near Brush and Hayden would still burn coal but would be upgraded to reduce emissions.

The proposal stems from the Clean Air-Clean Jobs Act passed this year by the Colorado legislature and signed by Gov. Bill Ritter. The act calls for power plants to emit 75 percent less nitrogen-oxide compounds by 2017, as well as reductions in sulfur dioxide, mercury and other emissions.

Xcel has said the plan would add 1 percent annually to customers' electric bills.

But the cost could be far higher, according to testimony submitted by energy economist Roger Bezdek on behalf of the Colorado Mining Association.

Xcel's estimates on customer rate impact are "not reliable," Bezdek said in written testimony.

"Natural-gas prices have been one of the major causes of electricity rate increases over the past decade," he said. "(Xcel's) own strategist forecasts indicate that there will be continued, substantial increases in natural-gas prices — especially compared to the strategist forecast of coal prices."

Adopting the plan could produce Colorado job losses of 30,000 to 120,000, Bezdek said, from coal mining and a ripple effect on other industries. The testimony did not specify how it arrived at that total.

Colorado's natural-gas industry largely supports the plan. Some gas producers testified that the timetable for conversion of coal to natural gas should be accelerated.

The city of Boulder testified in favor of the proposal. Boulder is "particularly encouraged by the emissions reductions estimated by (Xcel), the potential health and environmental benefits, and the comprehensive approach that the company is taking to address multiple reasonably foreseeable environmental regulations."

The city of Denver also testified in favor of the plan.

Xcel Energy said in a statement that it is "gratified with some of the initial support we've seen. We believe our plan is in the best interest of Colorado and our customers."

A public hearing will be held Thursday at the offices of the Public Utilities Commission. The PUC then will hear testimony from intervening parties from Oct. 21 through Nov. 3. A final decision is due by Dec. 15.

Steve Raabe: 303-954-1948 or sraabe [at] denverpost [dot] com

Basics of Xcel Energy's proposal

• Xcel Energy would spend $1.3 billion over 12 years to convert Denver-area power plants from coal to natural gas to meet a state mandate to reduce pollution throughout the Front Range. Additional plants would get upgraded emissions controls.

• Xcel estimates the plan would add an average of 1 percent a year to electric bills. Critics say it could add more.

• Supporters of the proposal include Xcel, environmental groups and natural-gas producers. Opponents include coal-mining interests and independent power generators.

• The Colorado Public Utilities Commission will rule on the plan by Dec. 15.