On LoudounExtra.com: Loudoun Revisits Rules As Sinkholes Multiply

Sinkholes have been on the rise in Loudoun County, prompting county officials to call for new regulations to protect residents who live in sinkhole-prone areas and to prevent the county's water supply from becoming contaminated.

Since 2000, dozens of sinkholes have opened up in a 28.5-square-mile area stretching from Leesburg to Point of Rocks near the Maryland border. Although many of the sinkholes were less than a foot wide, at least two that formed in an area slated for a housing development were 30 feet wide and 30 feet deep, a county official said. Another in 2005 created a chasm in the middle of Route 15.

No one has been hurt, but one homeowner in Leesburg nearly pushed his lawn mower into a 10-foot-deep pit, said Alex Blackburn, the county's natural resources team leader. At another home, a sinkhole swallowed a large tree growing about 10 feet from the back door.

"They had a fence, and it was just dangling over the air," he said.

The problem, county officials said, is rapid development of land that rests on soft, porous limestone, often referred to as karst. Another danger of building in such areas is groundwater pollution, which occurs when pesticides and other contaminants rush into the water supply.

In 2003, the Board of Supervisors adopted regulations that limited development in limestone areas as part of a broad plan to slow growth in Loudoun, one of the nation's fastest-growing counties. But a year later, the Virginia Supreme Court threw out the plan on a technicality.

The supervisors who took over the board that year generally supported the growth and rejected limits on development in limestone areas. Last year, in the waning weeks of the pro-growth supervisors' term, the members reversed course and said they would support some regulations governing construction in the limestone area.

The current board, which supports a slower rate of growth, is scheduled to consider new regulations today for the county's limestone area. Under the proposed rules, builders would have to take steps to minimize the risk of sinkholes, and homeowners would have to be educated about the danger of groundwater contamination.

"It is one of our most sensitive geographic areas. We have historically seen an increase in sinkholes as development has gone on in the corridor," said Supervisor Sarah R. "Sally" Kurtz (D-Catoctin), whose district includes most of the limestone area. "It's a matter of preventing property loss -- as in, your whole . . . house goes down a sinkhole."

Heavy rains in recent months have caused sinkholes to open up across the region. In May, five homes in Prince George's were deemed temporarily unsafe for habitation because of a 200-yard-long gash in the rear yards. One sinkhole snarled traffic on New York Avenue in the District, and another this spring blocked traffic for hours on Interstate 70 near Frederick.

Limestone is widespread along Virginia's western border, which is home to underwater springs and caves, including Luray Caverns.