Orange plastic fencing that once surrounded the sinkhole has slipped several feet in less than a year, David K. Brezinski says, peering down the deep narrow hole in a field not far from the rushing traffic on Interstate 70 in Frederick.
The hole's increased size concerns but doesn't surprise the geologist, given the amount of water rushing off a motel parking lot a few steps away. This runoff dissolves the underground limestone - formed in an ancient sea - and enlarges the cluster of sinkholes.
FOR THE RECORD - An article about sinkholes in yesterday's editions of The Sun included an incorrect figure for the total costs of planned road construction projects on Interstates 70 and 270 in Frederick. The total estimated cost will be about $240 million, according to the State Highway Administration. The Sun regrets the error.
What does surprise Brezinski is the number of sinkholes he has found in the Frederick Valley since he began mapping them on foot in July 1999. He has found six times the sinkholes he expected, or "about 1,200 vs. a couple hundred."
And that concerns State Highway Administration road builders, who are in the midst of a $585 million project to add lanes and improve interchanges along I-70, where rush-hour traffic often slows to stop-and-go.
"The presence of sinkholes and the formation of sinkholes - new and old - under our pavement is constantly on our minds. We literally lose sleep over this," says A. David Martin, chief of the agency's engineering geology division.
There are more hazards connected to this project than most road construction because I-70 runs across beds of sinkhole-prone limestone. The concern is for the safety of thousands of commuters - who could be harmed by even a small dip in the road - on that highway and on Interstate 270.
It has happened before. Several years ago, a sinkhole about 60 feet long, 45 feet wide and 18 feet deep opened on Reich's Ford Road near the ramps for eastbound I-70 in Frederick. A motorist crawled out of the hole to safety, and a photograph taken by Martin shows the car on its side just below a natural gas line.
In 1994 in neighboring Carroll County, a 45-foot-wide and 18-foot-deep sinkhole opened in the middle of the night on Route 31 near Westminster, killing a city employee who was working the night shift.
"This is the only death ... directly attributable to a naturally occurring sinkhole," says Barry F. Beck, senior hydrogeologist and chief of operations at Oak Ridge, Tenn., for P.E. LaMoreaux & Associates Inc.
State officials say they want to prevent such tragedies. The Carroll County death led state highway officials to insist that the I-70 contracts include the hiring of an expert in karst terrain.
"On a superhighway, a sink 3 inches deep can cause people to lose control of their cars," causing a chain collision, Martin says. "They're all sinks to me - and we're after them all."
There are some things road builders can do, says Beck, a consultant on the Frederick project since 1999. The state plans to take preventive measures, which include grouting the rock, reinforcing some pavement, and - most important - taming water runoff.
Aiming for precision
So Brezinski, a 45-year-old Maryland geologist, traipses from southwest to northeast along the beds of the Frederick Formation and the younger Grove Formation limestone areas in the Frederick Valley - about six miles wide and 25 miles long.
He has found most of the sinkholes the old-fashioned way - on foot - but maps them with a global positioning system that reads four Department of Defense satellite signals. Later, he'll check his field notes against the satellites' positions and obtain a precise location for each sinkhole.
"All the other sinkhole studies we know of could be off by the length of a football field," he says, referring to maps from the 1970s. "Now we can get to precision within a one-foot scale."
In Frederick, the highway administration has spent about $500,000 grouting cracks in the rock using a thin cement. Some areas will have a reinforced roadbed, which will not prevent a sinkhole but could give provide warning and time to act.
"There are a lot of active sinkholes developing here," Brezinski says, spreading a colorful geological map on the hood of a car.
He has mapped a little more than half the sections of the Frederick Valley and expects to finish by July next year, then publish his report for the state by that December. He is in the field from October through May, when the brush gets too thick for him to work.
Brezinski is a stratigrapher and paleontologist for the Maryland Geological Survey's Environmental Geology and Mineral Resources Program, with 17 years of service. But he calls himself a limestone specialist.
A native of western Pennsylvania, he collected fern fossils as a boy but shifted to limestone because the fossils were better. He has specialized in the origin and formation of limestone since he was an undergraduate at Indiana University of Pennsylvania. He is an adjunct professor at the University of Pittsburgh and a research associate at the Carnegie Museum of Natural History in that city.
"Geology was the first class I took the first morning I was at college," he recalls. "I was a major by the end of the first week."