Getting ready to kick the coal habit at IPL's Harding Street Station

• The power station is gearing up for a %2470 million conversion to natural gas.
• Indiana%27s power plants produce more carbon dioxide than plants in all but three other states.

For more than 80 years, it has helped keep the lights on in Indianapolis. It has powered factories, office towers and shopping malls.

It also has spewed millions of pounds of toxic emissions over the city and stirred the wrath of neighbors, environmentalists and health advocates.

But now, the Harding Street Station is about to make a sweeping change.

If all goes according to schedule, the huge power plant on Indianapolis' Southside will burn its last load of coal next spring.

The mountains of coal in the yard will disappear. So will the conveyor belts that haul the coal into the plant, and the machinery that pulverizes it into powder.

"This will all go away," said Mark Holbrook, the plant's leader, pointing to a massive room full of coal-milling equipment during a recent plant tour.

And trains that rumble through the neighborhood, hauling nearly 2 million tons of coal a year into the plant? They're going to disappear, too.

It's the end of an era at one of Indianapolis' largest and most controversial industrial sites.

The power station, owned by Indianapolis Power & Light Co., is gearing up for a massive, $70 million conversion to burn natural gas, considered a cheaper and somewhat cleaner fuel. The natural gas will heat water into steam, which will drive turbine generators and produce electricity.

IPL said the move is the best option for helping it meet clean-air regulations. Coal is widely seen as a dirty fuel that requires expensive technology to reduce harmful emissions.

The conversion will add about $1 a month to an average customer's electric bill, the company said.

The move represents a major victory for anti-coal activists, who call the plant a major polluter and health hazard. And it's a setback for Indiana's coal industry, which prides itself as a supplier of cheap, abundant fuel.

For decades, Indiana outpaced the nation in relying on coal. The state still gets more than 80 percent of its power from coal-fired power plants, about twice the national rate.

But a tidal wave away from coal to other energy forms is sweeping the nation. Coal, which once provided the lion's share of fuel for power plants, has shrunk to about 40 percent. Coal companies are feeling the pinch, laying off workers and watching profits fall. The Dow Jones Coal Index is down 89 percent from its high in 2008.

Indiana is just the latest state to begin seeing sharp changes.

Just last year, Citizens Energy Group's Perry K Steam Plant burned its last trainload of coal, marking the end of a 121-year era Downtown. The plant, which provides steam for heat and hot water to about 200 big customers Downtown, was converted to natural gas.

Indiana's power plants produce more carbon dioxide than plants in all but three other states, and more mercury than all but four other states.

The Obama administration wants to tighten rules on smog-forming pollution. The EPA proposed in November that smog be limited to within a range of 65 to 70 parts per billion. The current standard, set in 2008 under President George W. Bush, is 75 parts per billion.

As many as 25 of Indiana's 92 counties would have trouble meeting the tighter standards if they went into effect immediately. But most areas would have until 2025 to comply.

Gov. Mike Pence has joined 10 other GOP governors in asking the EPA to stick with the current rules, calling the proposed standards "job-crushing."

He is backed by an array of business groups and coal interests.

But on the other side is a formidable alliance of health advocates, anti-coal activists, neighbors, churches and civil rights groups.

The groups, organized by the Sierra Club's Beyond Coal campaign, have held sidewalk rallies, demonstrated at the Statehouse and spread their messages on billboards.

For years, IPL has said that coal-fired plants produce the most affordable, reliable energy.

But it has been working to reduce its dependence on coal. It is closing six coal-fired units at the Martinsville location and replacing them with a 650-megawatt combined-cycle gas turbine.

A large power plant in southwest Indiana, near Evansville, will continue to burn coal.

Two years ago, IPL won state approval to spend more than $500 million on environmental upgrades at its Harding Street and Petersburg plants to allow them to continue burning coal.

At the time, IPL said the upgrades would cut emissions sharply. State regulators also gave the green light for IPL to convert two smaller units at the Harding Street power plant from coal to natural gas.

But the Beyond Coal campaign stepped up its rallies and continued to pressure the utility.

"Let's turn, not burn," they chanted at one rally, urging IPL and the public to support alternative energy such as windmills rather than coal-burning plants.

They called the Harding Street Station the largest industrial polluter in Marion County, using data from the Environmental Protection Agency's Toxic Release Inventory.

Last summer, IPL did an about-face and surprised the city with its announcement that it would stop burning coal at Harding Street in 2016.

IPL officials say what changed was higher-than-expected costs to comply with wastewater treatment.

The company decided it wouldn't make sense to spend millions of dollars for new wastewater treatment technology at Harding Street, which would have just one coal-fired generator left.

So it moved to convert the entire plant to natural gas. State regulators still need to approve that plan.

If they do, the conversion would reduce IPL's dependence on coal, across its Indiana fleet, from 79 percent in 2007 to 44 percent in 2017.

Natural gas will become the largest fuel source for IPL's fleet, representing 45 percent. The smallest chunk, but growing even as coal is shrinking, is wind and solar, representing about 10 percent.

"We have customers and stakeholders who would love us to do all renewables, all the time," said Kelly Huntington, president of IPL. "We also have customers and stakeholders who write to us and say we'd like you to burn as much coal as you can, because I want my bill to be as low as possible."

The Harding Street Station also will take a step back from its leading role as a generator of electricity for IPL's 480,000 customers.

Instead of running around the clock as a "baseload" plant, the Harding Street Station will be used only during peak demand, usually during extreme weather in the summer and winter. IPL officials predict it will run between 10 and 20 percent of capacity.

It's a step back for a plant that began generating electricity in 1931. A walk through the old generating station is a trip through history, with a row of huge old turbines, many of them now retired, with brass plaques from another age.

The control room is more than 40 years old, with gauges and dials that stretch across a huge wall.

"The small screen here is your drum level," said Holbrook, the plant leader. "That's the amount of water you have in your drum. The next screen tells you the megawatts you're generating; right now, it's 435. And that's what your throttle pressure is."

The control room, too, will be upgraded, with many of the switches and panels that deal with coal going away.

Inside and out, the power plant will look different.

But IPL says the plant, in new ways, will continue to do what it has always done: provide the power to light up the city.

Star Washington Bureau reporter Maureen Groppe contributed to this story.

Call Star reporter John Russell at (317) 444-6283. Follow him on Twitter: @johnrussell99.

Harding Street Station at a glance

Address: 3700 S. Harding St., Indianapolis, about 6 miles southwest of Downtown, near the junction of I-465 and Ind. 37.

When went online: 1931.

Generating capacity: 1,004 megawatts of power. That makes it the second-largest of IPL's three generating plants, after the Petersburg Generating Station in southwest Indiana. Eagle Valley Generating Station in Martinsville is the smallest.

Units: Three active and four retired generating units. For decades, all units were coal-fired, but two of the three remaining active units are converting to natural gas, and the third is under review by state regulators to convert to natural gas.

Pollution: The plant has been the largest industrial toxic polluter in Marion County for more than a dozen years. The Environmental Protection Agency's Toxic Release Inventory shows the plant released more than 1.6 million pounds of toxic pollutants into the air, land and water in 2012. IPL says converting all three active units from coal to natural gas will cut mercury by 75 percent, sulphur dioxide by 65 percent, nitrous oxide by 20 percent and particulate matter by 20 percent.

Indianapolis Power & Light at a glance

Headquarters: 1 Monument Circle.

Customers: 480,000 residential, commercial and industrial customers in Central Indiana.

Service territory: 528 square miles.

Parent company: AES, based in Arlington, Va., bought IPL in 2000.