The Sierra Club plans to sue Ameren Missouri next month over what it contends are thousands of air-pollution violations at three of the utility company’s coal-fired plants, including its Oakville plant.

The environmental organization sent a letter to Ameren last month giving 60 days’ notice that it intends to file a civil lawsuit against Ameren for roughly 10,000 alleged violations of limits on air pollution since 2008.

Sierra Club representatives say that data the organization received from an open-records request to the Missouri Department of Natural Resources, or DNR, shows thousands of self-reported violations of the Clean Air Act in Ameren’s quarterly emissions reports from the Meramec Energy Center in Oakville, the Labadie Energy Center in Franklin County and the Rush Island Energy Center in Jefferson County.

The Sierra Club alleges that Ameren violated limits on opacity, a way to measure how much soot is in emissions by measuring how much light can be seen through air from smokestacks. Missouri plants in the St. Louis area are limited to 20-percent opacity under the Clean Air Act.

“Basically, it means the emissions coming out of these coal plants were at higher levels of soot, smog, toxins and particulate matter than was healthy for the community,” said Sara Edgar, organizer of the Missouri Sierra Club’s Beyond Coal campaign.

Mike Menne, Ameren’s vice-president of environmental services, issued a statement denying the Sierra Club’s allegations, noting that Ameren has “at all times” operated its plants inside of U.S. Environmental Protection Agency, or EPA, regulations and requirements.

“Contrary to the assertions by the Sierra Club, unauthorized opacity exceedances occur infrequently and existing pollution control equipment removes approximately 99 percent of particulates from the flue gas stream. We report all of our emissions as required to EPA, and the agency has not cited our Missouri coal-fired energy centers for opacity or permit violations,” Menne said. “The filing of such litigation is a common tactic used by opponents who are striving to remove coal from energy choices available to customers.”

The Meramec plant, Ameren’s oldest coal plant, is the largest polluter in St. Louis County and has been targeted by the Sierra Club, which alleges that the plant damages the health of nearby residents, increasing levels of asthma and even causing premature deaths.

Ultimately, the Sierra Club wants Ameren to move away from coal as an energy source, Edgar said.

The environmental group has stepped up its efforts since Ameren announced it might open a coal-ash landfill at the Meramec site, on top of its existing coal-ash ponds. Plans are tentative and are several years away from coming to fruition, Ameren representatives have said.

The Meramec plant has a social cost greater than the cost of the electricity it produces, according to a study conducted for the Environmental Integrity Project by Boston University School of Public Health researcher Dr. Jonathan Levy.

Using figures from 2011, Levy calculated that each year, the plant causes 57 to 110 premature deaths and produces $13 million of electricity, but produces societal costs of $493 million.

At her town-hall meetings last year, Rep. Marsha Haefner, R-Oakville, presented statewide health figures favorably comparing the health of Oakville residents to those in the rest of Missouri.

“The Oakville area is really one of the healthiest in the state, is what the data represents,” Meramec Energy Center Director Mark Litzinger said at Haefner’s October town-hall meeting, noting that Ameren has no current plans to retire the Meramec facility and that it is cleaner than it has ever been.

“In spite of what some of you may have seen written on Facebook and in posts on blogs, I want to make it clear I have not taken a position that ignores the health of my family,” Haefner told the crowd. “There are four generations of my family that live within three miles of the Meramec Ameren plant. I take your concerns very seriously, but we need to make decisions based on facts, not opinions and agendas of special-interest groups.”

The state does not monitor the groundwater around the Oakville plant or monitor sulfur-dioxide emissions from the plant, which would provide an official record of the plant’s levels of pollution. The nearest of the state’s sulfur-dioxide monitors to St. Louis County is in Herculaneum in Jefferson County. Ameren was required by state law to monitor the groundwater around its similar coal plants in Illinois, which it sold in December to Dynegy. Four of those five monitored plants were in violation of Illinois EPA standards for groundwater pollution.

Ameren monitors its stacks to know how many tons of pollution the plant emits into the air at any given time. Those readings show that Ameren’s allowed air pollution levels are “quite a bit higher than we will actually emit, and at a level that’s protective of public health,” Menne told the County Council last year.

Sixth District County Councilman Steve Stenger, D-Affton, wrote a letter to the DNR last summer requesting groundwater monitoring. In response, DNR Director Sara Parker Pauley noted that Ameren will be required to install groundwater monitors as part of any future permits at the Oakville site. Ameren has said it will install groundwater monitors once it completes a study on where to locate them.

In the early 1990s, the Mehlville School District built Rogers Elementary near the Meramec plant, which opened in 1953 at the intersection of the Mississippi and Meramec rivers. Former Board of Education member Tom Diehl recounted to the County Council last year how some students at the school have come in from recess with coal-blackened hands from dust released into the air by the plant.

Mehlville Superintendent Eric Knost said the district’s board and administration want to learn more about the effect of the plant on the district’s students at Rogers Elementary, but it is a difficult subject to negotiate since each side is so polarized politically.

“I really do think there are parents and community members that are concerned if there’s contaminants in the air that affect the health of their children and themselves. That needs to be determined. The Sierra Club’s data on the air quality is compelling,” he said. “That’s what somebody needs to focus on, and that’s what Ameren really needs to answer to.

“Someone in authority at Ameren needs to respond and say it matters or it doesn’t, and this is why. Right now, I think everybody interprets everything from each side as opinion.”