In January 2000, Virginia Tech geological sciences professor Thomas Burbey challenged new master's degree candidate Miles Gentry with these questions. There is equipment for determining the source of springs that pump several million gallons per day -- such as Crystal Springs, which is one source of water for the City of Roanoke. But there was no such equipment for low-volume springs -- until Gentry invented it.
The equipment plus a rain gauge has been in the field for 18 months, measuring spring output at sites in Grayson County and Floyd County, Virginia. Gentry will present some of his first findings at the Geological Society of America 114th annual meeting in Denver Oct. 27-30.
"When it rains, if we see a giant increase in flow, it means that the spring's source is connected to the surface, such as through a fracture or fault," says Gentry. At this Floyd County site, the equipment readout shows a shallow then a steep line, indicating two sources of water, he says. Water flows slowly through soil and rocks and quickly through faults.
A second Grayson county site shows no response to rain, which indicates that the spring is not connected directly to surface water. "Chemical analysis also shows it is clear of contaminants that would be washed in from the surface," Gentry says. "It would be an ideal site to drill a well."
Both sites have the same geology -- hard crystalline rocks with fractures.
Gentry's goal is to find out how much water is available for wells, which is becoming a pressing problem in Virginia because of an ongoing drought, and also because rapid growth, particularly as the Washington, D.C.-Northern Virginia growth spreads west, towards the Blue Ridge. "Municipalities need to know whether homes can have wells or if water will have to be provided. Our aim is to develop a method that makes quantifying available water easier," says Gentry.
At the meeting, Gentry will report that the method works for a six-gallon per minute spring. An unanticipated finding is that not all Blue Ridge springs are a result of saturated soil and shallow groundwater systems.
"Blue Ridge geology and hydrogeology is complex and there are multiple ways for water to appear at the surface, which is consistent with previous findings by Virginia Tech Ph.D. graduate Bill Seaton," Gentry reports. Gentry's findings so far have not revealed evidence of water traveling a great distance -- from rain at another site, for instance, or from water being pushed up when forced out of a reservoir by new water. "The small springs have responded to rain within 20 or 30 minutes, or not at all," he says.
Gentry will use his equipment to solidify what is known about aquifers, to determine how much water is available and the properties of the soil and rocks.
His talk, "Analysis of spring discharge for characterization of groundwater flow in the Blue Ridge province, Virginia," will be presented at 2:45 p.m. Sunday, Oct. 27, in room A205 of the Colorado Convention Center. Burbey is co-author.
Gentry, who grew up in Charlottesville, Va., also has his undergraduate degree from Virginia Tech in geological sciences.
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