Citing independent test results, concerned citizens in Shippingport, Beaver County, say the black soot that belched from a Bruce Mansfield Plant smokestack July 22 could cause serious health effects.

Residents and environmental activists met last night at the Shippingport Community Building to announce their findings and counter FirstEnergy Generation Corp.'s claim the night before that the sooty plume posed no health impact for humans and animals living in the borough and Raccoon Township.

Charles Norris, a Denver hydrologist hired by the residents to analyze the data, said his review found levels of arsenic that exceeded any government standard for the hazardous substance. Tests also indicated the presence of hydrocarbons, including several that are carcinogens.

He also said that FirstEnergy and the state Department of Environmental Protection need to explain in greater detail how the soot was generated and what it contains.

"You need to ask DEP questions that need to be answered," he said to a group of about 50 people. "This increases the level of uncertainty and the level of tension, and I'm sorry about that. You still have a fight ahead of you to find out what occurred on July 22."

Representatives of DEP and FirstEnergy were invited to the meeting, but did not attend, said Lisa Graves Marcucci, a Jefferson Hills environmental activist.

Ms. Marcucci said FirstEnergy is holding meetings in individual municipalities in a "divide and conquer strategy." She recommended that residents demand one meeting where everyone can meet with officials of DEP and the utility company to seek answers.

"Wearing a mask when you mow your lawn is not normal. That's when the red flags went up for me. We are living human beings on the receiving end of deadly pollution," she said.

On Monday night, a team of FirstEnergy officials told Shippingport Borough Council and 30 residents that its test results on soot samples largely matched state Department of Environmental Protection results and show no long-term health impact for humans and animals, as long as certain precautions are followed.

The main precaution is to wash one's hands and wipe off one's face after being outside. One health official also suggested that people wear face masks while cutting grass.

Test results showed arsenic levels below regulatory limits, FirstEnergy officials said.

Early in the evening July 22, a plume of soot spewed from a smokestack and spread as far as five miles south into Raccoon Township.

Soon after the incident, FirstEnergy and DEP said the soot was acidic, and contained silica and some fly ash, a byproduct of the coal-burning process at the 2,410-megawatt power plant that is the largest rated electric generating station in Pennsylvania. The plant employs 500.

FirstEnergy officials said two large, powerful fans that push smoke and other gases into the power plant's smokestack were being washed while still in operation -- a common practice at the plant. But in this case, water laden with soot accidentally was drawn up and out of the smokestack, sending a plume of black soot into the air.

The two-hour incident left people, houses, yards and cars covered with soot. Shippingport police said people outside that Saturday evening looked as though they'd been sprayed with black paint.

The company said it no longer would wash the fans while they're in operation to prevent a recurrence, which FirstEnergy officials described as a unique event.

Donald C. Bluedorn II, an attorney for FirstEnergy, said the company compensated residents for losses of their gardens, orchards, hay fields and crops and bought the full harvest of honey from beekeepers affected by the pollution.

The company also power-washed affected houses, cars and driveways in central Beaver County. It hired mowing companies to cut grass and collect and dispose of soot-laden clippings. It also hired companies to clean swimming pools.