- The Washington Times - Monday, September 13, 2004

FREDERICK, Md. (AP) — A geologist who spent four years traipsing in and around Frederick has mapped out areas most likely to develop sinkholes — depressions in the earth that appear suddenly, often swallowing cars and homes.

Sinkholes occur when groundwater dissolves water-soluble bedrock, usually limestone or dolomite, leaving underground chambers and passageways into which earth can collapse.

A sinkhole in the spring closed a street in a fast-growing residential area south of Frederick. In April, two women were rescued after their car fell into a large sinkhole near Owings Mills Mall in Baltimore County.

The study by geologist David Brezinski of the Department of Natural Resources examines the so-called karst topography, which is more likely to form sinkholes. It showed that certain types of rock are much more prone to sinkholes than others.

Many areas containing sinkhole-prone rock are concentrated around some of the most rapidly developing areas of Frederick County, according to the study.

“Frederick County has had more than its share of sinkhole activity,” Mr. Brezinski said. “That’s mainly because there had been such increased development pressure in the area.”

Mr. Brezinski determined that sinkholes, once considered unpredictable, prevail in certain rock layers, and his study identifies where those are.

Mr. Brezinski examined the terrain in the valley running alongside the Catoctin Mountains, encompassing Point of Rocks, Frederick, Walkersville and Woodsboro. He mapped 1,816 karst-topography features, including depressions, springs and ground collapses, marking them with a hand-held global positioning system.

Human activity, including storm-water management areas, stream rerouting, unlined drainage ditches, quarrying and development can lead to sinkholes, Mr. Brezinski found.

He examined an area between Frederick and Walkersville before and after development.

“It looks like development tripled or quadrupled the number of sinkholes in the area,” he said. “However, you have to recognize that they are concentrated in specific areas” where the rock is prone to the geological phenomena.

Certain rock layers that are more susceptible than others have been pinpointed, Mr. Brezinski said.

“Now, knowing that, developers and planners can determine how they place buildings, highways, structures and the like,” he said.

Frederick city and county planners said they had not seen the study. But city planner Joe Atkins said it might be taken into consideration when city officials develop a new land-management ordinance, which regulates development within the city.

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