Ancient Underground Fractures May Threaten Ground Water Supplies

The reason is that fractures deep underground help contaminated water flow downward and reach water supplies too quickly for it to be purified. In such cases, underground water supplies can become contaminated.

In one recent study, scientists surveyed Ohio soil profiles and found that at least 55 of Ohio's 88 counties have underground fractures that could affect the purity of ground water.

"We once thought that the soils in much of Ohio were so fine-grained and tightly compacted that almost no wastes could seep through," said Ann Christy, an assistant professor of food, agricultural and biological engineering at Ohio State University. "However, now we're finding that is not true."

While comprehensive studies of this type have not been done outside Ohio, the researchers believe that other states which experienced the same type of ancient glaciation may well be affected in the same way.

Much of Ohio was seen as a safe place for landfills because of the presence of glacial tills - the soil, rocks and other material left behind by glaciers that covered much of the state during the last ice age, Christy said. While scientists once thought these glacial tills were nearly impermeable to wastes, the discovery of fractures in these tills is giving researchers second thoughts. Scientists have begun a collective effort to locate and describe underground fractures beneath Ohio counties. The results are reported in a special issue of the Ohio Journal of Science, co-edited by Christy and Julie Weatherington-Rice, a doctoral candidate in the School of Natural Resources at Ohio State.

Fractures are particularly important to the movement of water. They recharge the underground water table, which supplies 800,000 private wells and more than 40 percent of the public water supplies in Ohio. But water that passes through fractures isn't purified in the same way as it would be if it traveled through tightly compacted glacial till, according to Christy.

In one study reported in the special issue, researchers examined soil profile descriptions that have been published in Ohio county soil survey reports since 1900. The researchers were looking in these reports for descriptions that suggest the presence of underground fractures. They found evidence of such fractures in more than half of Ohio counties (55 in total), a figure the researchers believe underestimates the occurrence of fractures.

"We've assumed that the soil will dilute and purify contaminated water," Weatherington-Rice said. "But in reality, water will travel through fractures and cracks in the ground, essentially bypassing the compacted sediment and foregoing any purification.

"Any land areas once covered by glaciers should be screened for fractures," she said, "particularly if those areas are candidates for a landfill site, livestock waste facility or other use that could potentially endanger the water supply."

One way researchers search for the presence of fractures in an area is to dig test pits, Christy said.

"Some investigators have claimed that they have never seen soil fractures in years of experience with excavating tills," Christy said. "But looking at a freshly bulldozed site can be misleading. Earth moving equipment tends to cover fractures that could be found if you follow careful procedures in excavating a pit."

For example, one study reported in the special issue involved a test pit Christy and several colleagues dug in Madison County to search for evidence of fractures. The pit was 33 feet wide by 82 feet long by 12 feet deep. Their analysis suggested that 7 percent of the ground area uncovered by the pit was affected by fractures.

In addition, Christy and her colleagues conducted tests that estimated a molecule of water could move 155 inches (3.9 meters) through a fracture in this test pit during one year, but only 14 inches (0.4 meters) when moving through unfractured soil.

"Our research suggests that substantial amounts of water and contaminants can move through fractures in the glacial till," Christy said, adding that there is evidence of ground water contamination from sources such as leaking landfills; animal manure wastewater lagoons; spills from injection wells (storage facilities for hazardous waste); hazardous waste lagoons; and the land application of wastes.

She and her colleagues are continuing their research, and plan to set up permanent test pits around the state.

Researchers in Ohio first came together in the early 1990s to study fractures amid suspicions that cracks in the ground could be leaking contaminants into the ground water supply.

"Landfills were leaking and we didn't know why," Weatherington-Rice said. Landfills are usually capped and lined in order to contain waste. But caps and liners break down, causing contaminants to leach into the surrounding soil, and many of the older landfills had no liners in the first place.

"We need to think in new ways about how water travels through the ground, and how contaminants travel with it, because soil isn't filtering water nearly as well as we thought," she said.

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Editor's Note: The full text of the journal, along with abstracts of the articles and background information, is available online at http://www.ohiosci.org/Fractures.htm