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Sinkhole study to educate builders

- The Washington Times - Sunday, August 5, 2007

BALTIMORE (AP) — A state-funded study of sinkholes in pockmarked Frederick County won its author a national award for shaking up assumptions about why the earth sometimes collapses.

David K. Brezinski of the Maryland Geological Survey, a division of the Department of Natural Resources, said his findings about sinkholes can help engineers and construction crews prevent sinkholes from forming, thereby avoiding loss of work time, property and lives.

His study, completed in 2004, won the John C. Frye Environmental Geology Award last month from the Geological Society of America and the Association of State Geologists.

Mr. Brezinski's work "showed a basis for recognizing the relationships between rock types associated with various geologic formations and the development of what are called cover-collapse sinkholes," said award committee member John H. Talley, director of the Delaware Geological Survey. "These sinkholes pose a serious threat to infrastructure such as homes, roads, railroads, sewer and water systems, drainage ways [and] property."

The danger of sinkholes was underscored by the 1994 death of Robert W. Knight of Taneytown, Md., after his minivan fell into a 45-foot-wide sinkhole on Route 31 in neighboring Carroll County.

Mr. Brezinski, 50, of Ellicott City, Md., spent four years examining the topography of the Frederick Valley, a 154-square-mile oblong area drained by the Monocacy River, which stretches from the state's southern border to Woodsboro, Md., near the Frederick-Carroll county line. The valley includes much of Frederick city and part of Interstate 70 in an area known for troublesome sinkholes.

In the late 1990s, the State Highway Administration, mystified by the frequency of sinkholes along I-70 and near new building construction sites in Frederick County, funded Mr. Brezinski's $400,000 study. The fewer than 100 sinkholes documented at that time didn't follow the pattern of sinkhole formation in other, well-known sinkhole-prone areas in Missouri, Kentucky and western Ohio, Mr. Brezinski said.

In those areas, sinkholes typically occur near rivers or major streams. But in Frederick County, they appear to be related to highways and building construction, Mr. Brezinski said.

His detailed survey of 1,800 sinkholes, surface depressions and natural springs revealed that the pattern of sinkhole formation is different in the Frederick Valley because the bedrock is different. Like sinkhole-prone areas elsewhere, the Frederick Valley is underpinned by limestone that dissolves under groundwater pressure and forms underground voids, a type of bedrock called karst.

Mr. Brezinski, who specializes in studying rock layers, found that the Frederick Valley karst differs significantly from karst in Missouri and Kentucky. In those areas, the rock is all one type, but the Frederick Valley bedrock is composed of many varieties of rock that were tilted and folded during the creation of the Appalachian Mountains some 240 million years ago.

"You can no longer assume when you move from one area to another within the Frederick Valley that the rocks are homogenous. They are not," said Mr. Brezinski, adding that the discovery means any area in the valley could be susceptible to sinkhole formation.

It was no coincidence, then, that the places in which Frederick Valley sinkholes appeared tend to be near highways and construction sites. Those activities expose bedrock or alter the flow of water, causing erosion that can eventually result in voids and collapses.

Mr. Brezinski said his findings could apply in neighboring Pennsylvania and Virginia, and to other parts of Maryland. He is currently doing a similar study of the Hagerstown Valley of Washington County.