Underground Map

Geologists cull through 20th century records to create database detailing Massachusetts' subsurface features

By Mark Sullivan
Staff Writer

Using soil data from 60,000 holes drilled in the ground from Cape Cod to the Berkshires, BC Geology and Geophysics Department researchers have created what they call an "X-ray" of Massachusetts.

The team, led by Assoc. Prof. Rudolph Hon (Geology and Geophysics), was commissioned by the Massachusetts Highway Department to chart the subsurface of the entire state by documenting information on soil, bedrock and underground water tables.

The results of the survey - 60,000 pages worth - have been placed in an online database where they can be accessed by contractors building roads, environmentalists tracking ground water, or anyone interested in what lies under the Bay State terra firma.

"Our objective is to have as clear an X-ray as possible of the state of Massachusetts," said Hon.

Under a $450,000 grant from the Massachusetts Highway Department, researchers spent four years copying and scanning archival records of test drillings done across the state.

Assoc. Prof. Rudolph Hon (Geology and Geophysics), seated, is flanked by part-time faculty member Alfredo Urzua and graduate student Jack Huntress. (Photo by Lee Pellegrini)

Since the 1920s, the Highway Department has drilled more than 80,000 holes in the ground across the state to test the makeup of the subsurface. As many as 1,000 test holes, ranging in depth from one to 200 feet, are dug by highway workers each year.

The information is vital to contractors, who need to know what's underground before digging a road or sinking a bridge foundation. But until the BC researchers compiled the database, it had been difficult to access the thousands of pages of test-drilling data filed in the Highway Department archives.

"It sounds very simple, but we are the first to have done it," said part-time faculty member Alfredo Urzua (Geology and Geophysics), who played an active role in the project.

An environmental researcher interested in watersheds in a particular town, for example, can now use the database to search for local test borings of between 20 and 100 feet that have encountered ground water.

"The idea is to have quick access to information that people didn't have," Urzua said.

The project afforded extensive high-tech experience to the 20 or so student assistants - several of whom had no previous scientific experience - who worked on it over four years. Hon recalled an English major who went on to work for a geophysics company after graduating.

"This was something unusual for the Geology and Geophysics Department," Urzua said. "This wasn't collecting rocks, but the application of new technology to an old field. It has broadened students' horizons."

The data recorded on the underground makeup of Massachusetts held few surprises, said research assistant Jack Huntress, a graduate student in Geology and Geophysics. "The Earth is pretty predictable," he said.

The Boston College campus lies on solid rock 600 million years old, said Hon, while downtown Boston sits on Boston blue clay left when Ice Age glaciers receded about 8,000 years ago. Cape Cod lies on glacial deposits of sands, he said, and Cape Ann on granite.

Hon said he was surprised by the extent of peat deposits in eastern Massachusetts. The residue of wetlands and marshes, peat is found in two- to three-foot layers at differing underground depths throughout the area.

The Highway Department has been using the new database since November. Hon said plans are being made to produce maps of the underground composition of different regions.

"Down the road it would be nice to do 3-D imagery of the subsurface, using the data we've compiled," said Hon.

The researchers said they hope to compile an even more complete picture of Massachusetts' subsurface by including information on thousands of test holes drilled by other public agencies, such as the Department of Environmental Protection, the Massachusetts Turnpike Authority and the Massachusetts Water Resources Authority.

"We've done 60,000," said Urzua, "but there are many more holes to go."

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