As the Denver Zoo pushes ahead on a $3.3 million City Park plant to convert elephant dung and other waste to power, neighborhood groups and city leaders are demanding details on air quality impact and safety.

Zoo officials — aiming to fire up the plant by the year’s end — insist there will be no problem.

“I am not as comfortable as they are that this technology is proven and belongs in that location,” councilman Paul Kashmann said. “I don’t think anybody would be particularly concerned if this was in an industrial area. … Since it has never been tested and it is a proprietary technology, it makes sense that it be as objectively reviewed as possible.”

Zoo crews have installed hoppers, shredders, pellet-making machines and a “gasifier” — measuring 6 feet in height and 2 feet in diameter — in a long-empty building behind the elephant house and within 150 yards of City Park lakes, paths and the boathouse jazz pavilion. Waste processing would be done in low-oxygen chambers at temperatures up to about 1,470 degrees.

The idea is to cut reliance on coal-fired grid electricity by using waste to light buildings, melt snow on walkways and warm a pool where elephants soak during winter.

A construction permit granted by the Colorado Department of Public Health and Environment sets limits for plant air emissions covering particulates, sulfur dioxide, dioxins, cadmium and carbon monoxide. Zoo officials said they’ll comply, but because the plant isn’t tested, they cannot specify what it will put out.

After the plant is tested, CDPHE would issue an incinerator operating permit with limits for various contaminants.

City Council members in 2014 gave an initial green light. But opponents led by the Sierra Club and Denver’s Inter-Neighborhood Cooperation coalition of 80 registered community groups are concerned about City Park serenity and contend approvals by City Council and CDPHE were based on inadequate scrutiny.

They argue the zoo’s waste-to-power plant — no matter the benefits of less hauling to landfills and reducing use of coal-fired electricity — belongs in an industrial zone, not Denver’s premier park.

“Hopefully, they’ll install it near the guinea pig exhibit,” INC president Larry Ambrose said. “We certainly have a lot of questions that aren’t answered.

“This thing matters because we’re setting up an untested plant, putting an experimental incinerator in the middle of a populated area where there are zoo animals, endangered species, children, parkgoers. How did this happen?”

Zoo officials have been planning it for years, touting the plant as groundbreaking with potential applications at other institutions that generate big waste, such as universities. They’re keeping key components secret, citing patenting trade secret concerns, saying only that the gasifier will help make the zoo the greenest in the world, producing “zero waste.”

The machines would break down dung, wood, plastics and other waste, turning all to tight pellets, then convert these into a “syngas” that could power a generator — producing electricity and heat. The zoo could stop hauling 1.5 million pounds of waste a year to landfills, saving $8,000 on trucking, and cut grid electricity use by 20 percent.

Beyond droppings from elephants and 4,319 other animals, the plant would process food scraps, soiled bedding, trash from 1.9 million annual visitors, and tree and plant cuttings from around the 80-acre zoo.

“We’re committed to a safe and clean system and we’re taking the appropriate time to deliver just that,” zoo vice president George Pond said.

The zoo’s team still is designing the gas-to-electricity part of the plant, which is funded in part by the energy industry. They’ve agreed to manually sort waste — picking out metals, glass and some plastics — to control potentially harmful pollution.

The City Council approved the project in December without a formal technical review. Councilman Paul Lopez met with zoo officials.

Waste from animals and visitors “has to go somewhere,” Lopez said. “It’s very ingenious to be able to convert it into energy. This is safe. And it is not going to stink up anything.”

But the Sierra Club and neighbors are ramping up opposition, wary of increased noise, pollution, odor and other disruption of park serenity.

“The Sierra Club strongly opposes combustion of municipal solid waste. It has proven impossible for industry to develop a combustion process, even with a large biomass proportion, that does not produce unacceptable toxic and hazardous air emissions,” said Joan Seeman, toxic issues chairperson for the club. “The zoo should recycle their paper, cardboard and plastics, as well as compost, instead of destroying these valuable resources.”

TheDenver Zoo already has developed a recycling program.

The INC coalition on Aug. 11 sent Mayor Michael Hancock a letter demanding a City Council-led review using subpoena power and technical experts to determine safety and health risks. Such a review may be unprecedented and the issue is complicated by City Council’s 2010 ceding of zoning power in parks to executive branch officials.

For years, Denver leaders have talked of transforming the city by boosting the natural environment and shifting toward clean energy.

City Park, established in 1886, covers 330 acres east of downtown, traditionally an oasis giving signature views of Denver’s urban skyline against blue sky and snow-capped mountains.

But recent development in City Park of parking and roadways with increasing motorized traffic and frequent staging of noisy fundraisers and other events has fed discontent.

While the zoo’s plant fits Environmental Protection Agency and CDPHE classifications for incinerators, zoo officials contend it is different. Denver hasn’t allowed new incinerators for years. This is a gasifier for converting waste to power, zoo officials emphasized.

“We have no interest in making something bad. … Look, there’s an elephant right there,” Pond said, noting one near the new machinery. “We care about that elephant. And there are zoo guests. We care about them. And here is a park. We don’t want anything bad for any of this. Is this going to ruin our park? We would never allow that.”