Carroll County officials are worried that an increasing number of sinkholes in residents' yards could mean danger.
The ground is sinking in some spots where developers buried tree limbs, stumps, bricks, stone and other building materials, said James E. Slater, administrator of the Office of Environmental Services.
Burying construction debris is an accepted practice among developers and is not necessarily an environmental hazard, he said. But the sinkholes that sometimes result could cause problems.
County hydrogeologist Tom Devilbiss distributed a newspaper article telling of a 7-year-old New Jersey boy who died in April after slipping into a sinkhole in his yard.
The boy fell into an 8-foot-deep cavern and was trapped under a tree stump that had been buried there.
The accident was "extreme," Mr. Slater said. "But it is something that can happen."
In the past four years, 33 of the 270 sinkholes mapped in Carroll can be attributed to buried debris, Mr. Devilbiss said. Twelve of the 33 sinkholes have been reported since March, he said. The other sinkholes are in areas where there is underground limestone.
The construction-related sinkholes have been as large as 20 feet in diameter and 14 feet deep, he said. They mainly have been in the Westminster area and North and South Carroll.
Water from the surface leaks onto the buried materials, and in three to 10 years the materials begin to rot, Mr. Devilbiss said.
"It's really worrying me," he said.
Yesterday, the commissioners unanimously voted to allow Mr. Slater to study whether the county grading ordinance can be amended to prohibit builders from burying tree stumps, logs and other organic materials on housing lots.
Anne Arundel, Baltimore and Frederick counties prohibit such burying, Mr. Devilbiss said. Howard County allows burial on lots larger than a half-acre.
Developers could rent a machine to grind up wood, stumps and other material and then spread the chips on the lot, Mr. Slater said. Or they could take the material to Northern Landfill where it would be ground up for free, he said.
"Those are both expensive propositions," developer Kip Powell said.
Moving stumps could be expensive because it would require numerous truck trips to the landfill, said Mr. Powell, vice president of Daybreak Estates Corp., which builds homes in Carroll and Baltimore counties.
Renting a grinding machine would be less expensive, but still costly, he said.
On a current project in eastern Baltimore County, his company is burning stumps on site in a specially dug pit using a machine that injects air to speed the burning process, Mr. Powell said.
Mr. Slater said he will discuss the proposed change in the grading ordinance with members of the Carroll County Chapter of the Home Builders Association of Maryland.
"You're going to add to the cost of housing," warned Robert A. "Max" Bair, the commission's executive assistant and acting economic development director.
Surplus building materials that are in good condition would be accepted by the Loading Dock, a nonprofit group that recycles building materials for use by other nonprofit groups and low-income families.
The Loading Dock accepts lumber, roof shingles, cinder blocks, drywall and other materials, and developers can claim the value as a charitable donation.