Managers for the company backing the plant -- the publicly traded Mexican firm, Grupo Cementos de Chihuahua -- deny these claims, saying that all smokestack and quarry emissions will be closely monitored and will not violate federal and state laws.
But such assurances have not calmed down many Pueblo residents, who have crammed into public meeting halls in recent months to denounce city leaders for luring the company to the area.
At the most recent meeting on July 19, which lasted roughly eight hours, anywhere from 400 to 600 people filled the Pueblo Convention Center to demand the Colorado Air Quality Control Commission deny the plant's request for a pollution permit.
Residents such as Dorothy Olivier contend the cement plant will add more smog-causing and toxic chemicals to an area that already has two major sources of air pollution: Pueblo's CF&I steel mill and the coal-fired Comanche Power Plant.
"When you look at the numbers for how much Comanche and CF&I put out and how much this plant will produce, the future potential is that we'll once again be what the EPA calls a non-attainment area," Olivier said.
Being declared a non-attainment area can result in a loss of federal highway grants and require cities to take costly steps to clean up air pollution.
Olivier is a member of Citizens for Clean Air and Water in Pueblo and Southern Colorado (CCAPS), which argues that the mine and cement plant is too close to the city, which now has a population of roughly 125,000.
But they also say the plant will have a regional effect, creating haze and exacerbating other air pollution problems along the front range because pollution from the plant will trail north with prevailing winds.
Built on a 5,000-acre tract of land leased from the state, the plant will be allowed to generate roughly 1,000 tons of carbon monoxide, and roughly 1,100 tons of nitrogen oxide each year under the terms of the proposed permit.
The plant will also be allowed to emit 944 tons of sulfur dioxide, almost three times more than CF&I steel is allowed to produce. While sulfur dioxide is a key ingredient of acid rain, nitrogen oxide is a key cause of urban smog.
Critics argue that's far too much pollution for what they say will be a small number of jobs promised by plant officials. While the cement factory is expected to employ roughly 85 people, the CF&I plant employs roughly 600 full-time workers, they note.
But Brian McGill, corporate environmental manager for the company's plant in Tijeras, New Mexico, said there's no way that the proposed plant would affect Pueblo's status of clean-air compliance.
"No, there's not a chance that would happen," McGill said. "Part of the permitting procedure included some pretty sophisticated ambient [air quality] analysis that takes into account the power plant and takes a look at the total impact as well as by the proposed facility.
"Even with all those sources combined, we're well under all the ambient air quality standards; we've been able to show we'd be in compliance," he added.
Emissions will be tracked electronically and hour-by-hour data from smokestack monitors will be given to the state on a quarterly basis, McGill added.
Moreover, the company will only mine 15 acres at a time, then restore the most recently excavated area to its original state as a means of controlling dust, he said. The company will also control dust by watering down some quarry areas and moving rock crushing equipment close to the mining area to cut down truck travel within the site, he said.
Because the limestone to be mined at the site is relatively pure and close to the surface, there's less chance that pollution will be caused during mining and during the intense heating process the limestone undergoes during the cement-making process, he said.
But residents are skeptical because the company is essentially being asked to monitor itself under the state's self-reporting environmental compliance regime. Further, the state Department of Health and Environment is too short-staffed to adequately respond to violations, they contend.
Critics of the plant also want the state to make the company use pollution cleaning devices called "wet scrubbers," which are considered the best available technology and are used in other cement plants and other industries throughout the state. So far, the state and the company have resisted such suggestions.
The proposed quarry and cement kiln is to be located on state trust land at the convergence of the St. Charles and Greenhorn creeks, less than 10 miles south of Pueblo's downtown. The state school system will get royalties from the lime mined at the site.
While proponents of the project describe the plant's proposed location as a barren wasteland that's already been home to some limited open-pit mining, ranchers and farmers nearby say it's also a critical habitat for migratory birds and other small mammals.
As the drama over the plant has unfolded, however, a controversy over clean air and the environment is beginning to take on larger proportions. Residents have asked why elected and non-elected leaders quietly supported the plan before it became public in January.
So far, most of the heat has been directed toward local officials, most of whom wrote letters supporting the plan, and the Pueblo Economic Development Company, or PEDCO, which lured Grupo Cementos de Chihuahua to Pueblo without notifying the public of their plans.
"This is not just about cement, this is about good government," said Alvin Rivera, vice president of CCAP. "More than anything, most of the people who are against this are mad that this was all done in secret, without any public notice."
PEDCO officials did not respond to calls from the Independent seeking comment about the proposed cement plant.