A federal agency laid out its plans Thursday night to evaluate whether Midlothian's air could be causing health problems because of emissions from three cement plants and a steel mill.

The Agency for Toxic Substances and Disease Registry, an arm of the Centers for Disease Control and Prevention, told about 150 residents that the agency will evaluate years of samples to review whether birth defects, asthma and cancer might be blamed on the industrial sites.

The latest study, to be conducted with doctors, epidemiologists, toxicologists and veterinarians, comes after residents complained that a 2007 draft report from the Texas Department of State Health Services was flawed.

Environmental groups said that review based its findings on insufficient evidence. Last spring, a congressional subcommittee blasted the toxic-substances agency for repeatedly performing shoddy health studies.

"We needed to go back and look again at the evaluation that had been done for Midlothian," Jennifer Lyke, the agency's regional representative, said Thursday. "We needed to take a more comprehensive look at acute health problems."

The new study will evaluate air, soil and water samples.

As part of the new review, the agency is preparing a plan that will allow the community to be updated on the process. The agency is also asking for the public to take an active role in the study.

"We can't operate without public input," Lyke said. "You're the ones that asked these questions. We want to make sure that we're responsive to you."

A timeline for the report's findings is not known, Lyke said.

"We're not talking years," she said. "We are hoping to finish this faster than that."

Another meeting is scheduled Feb. 22.

Also Thursday, an environmentalist group, Downwinders at Risk, that has fought for tougher pollution limits in Midlothian, praised the federal government's settlement with a cement manufacturer that could cut emissions at dozens of plants nationwide.

Although the settlement with Lavarge North America Inc. of Virginia does not involve facilities in Midlothian, environmentalists hope the settlement could lead to better anti-pollution technology at other plants.