Mirant temporarily closed its coal-burning Potomac River power plant last month after studies showed that it may have been spewing dangerous pollutants into the air for many years.

This is hardly surprising given that the plant was built in 1949. Despite some modest technological improvements, retrofitting the facility with pollution controls or converting it to burn gas would not be easy or perhaps even possible.

Although the plant burns low-sulfur Appalachian coal, it still emits relatively large amounts of sulfur dioxide, nitrogen dioxide and mercury. Even at low levels, mercury is converted into toxic methyl-mercury in water, where it accumulates in fish, eventually making them unsafe for consumption. Small particles laced with toxic metals also can penetrate the lungs and cause asthma and lung and heart disease.

The latest modeling studies -- one paid for by Alexandria and another by Mirant -- used emissions data from the plant to estimate the likelihood that people living near the facility would be exposed to unsafe levels of chemicals that the Environmental Protection Agency deems hazardous to human health. Both studies suggest that the plant has been unable to meet the standards set forth by the Clean Air Act. Both studies also show that people living near the plant likely are being exposed to dangerous levels of sulfur dioxide, nitrogen dioxide and particulate matter.

The Alexandria study further indicated that a "zone of public health concern" extends as much as a half-mile around the plant, which encompasses homes, businesses, apartments and a bike trail.

Now the D.C. Public Service Commission has reached across the river to fight the plant's temporary closure by filing an appeal with the Federal Energy Regulatory Commission, which can force a plant to operate under certain emergency conditions. The commission was joined by Pepco -- which once owned the plant and now buys the electricity it produces at favorable rates -- and the Blue Plains Sewage Treatment Plant. The Southern Environmental Law Center and Alexandria have asked the federal commission to dismiss the request -- and rightly so.

Mirant's aging coal-fired plant should never be restarted, not just for the sake of Alexandria residents but for the health of all the people who live in the region and deserve to breathe cleaner air.

-- Andrew H. Macdonald

a Democrat, is a member

of the Alexandria City Council.