Wed07232014

     Subscribe  |  Contact  |  Advertise  |  RSS Feed Other Publications

Wednesday, 31 August 2011 13:03

Keeping the well full: WCU researchers probe fractured rock aquifers in the mountains

Written by 

A maze of pores and rock fractures in the Appalachian Mountains make it one of the most complex hydrological systems on the planet. More than half the population here relies on groundwater, but the fundamental question of how many wells the landscape can support remains a mystery.

It’s Dave Kinner’s favorite question for new geology students: how porous is the ground underfoot?

“Feel’s solid doesn’t it?” Kinner asked, stomping his foot up and down, making a flat, muffled thud as it hit the earth.

But in fact, 30 to 40 percent of what’s down there is water, seeping, trickling and percolating through the soil and rock layers — and hopefully, if we’re lucky, making its way to the tens of thousands of drinking wells that pepper the mountainsides of Western North Carolina.

“If we are going to be building more houses in this area, is there enough water for everybody?” asked Kinner, assistant geology professor at Western Carolina University. “At what point would they run out of water? That data is not really out there.”

WCU has emerged as ground zero in the field of groundwater research. An outdoor lab on a mostly wooded tract at the edge of campus sports a cluster of well heads poking up here and there, and in one spot, a tangle of wires sticking out of the soil and a rain gauge mounted on a stick.

While unassuming — particularly since most of the apparatus lies underground — the research is plowing new ground in the field of hydrogeology.

“We have some of the most complex rock types anywhere in the world,” said Brett Laverty, a hydrogeologist with the N.C. Division of Water Quality in Asheville. “We know very little about how groundwater moves in this area.”

And, as a result, very little about the carrying capacity for an increasing number of wells being drilled into the mountainsides.

Several summers over the past decade have brought drought conditions to Western North Carolina. Springs that flowed for generations suddenly dried up. Wells that had worked fine before suffered from low flows. New homeowners had to go deeper than ever before to find water.

Kinner hopes the research at WCU will figure out how much rain is actually making it through the top few feet of soil and into the underground aquifer.

Right now, the rate of groundwater “recharge” is a mystery, Kinner said. How quickly groundwater is replenished, compared to how quickly it is being used, is the fundamental question.

“Will it run out before it can recharge?” Kinner said.

The question attracted the interest of the National Science Foundation, which recently made a $200,000 grant to fund the ongoing project at WCU.

Luckily, recharge in the Appalachian mountains is rather quick, compared to underground aquifers in the Southwest that took thousands of years to accumulate but are being used up in a matter of decades.

But even in this temperate rainforest of the Smokies, groundwater isn’t an unlimited resource, and there are lots of variables at play that Kinner and his geology students are probing.

On steep slopes, rain tends to run off instead of soaking in.

Torrential downpours likewise run off instead of soaking in. And if the topsoil is hard and dry, absorption is even more subpar.

Unfortunately, few rains this past summer were the good slow soakers needed for recharge, according to the technical instruments monitored by Kinner and his students.

Rain gauges record both the amount of rain and how fast it comes down. Meanwhile, moisture sensors at various depths and a smattering of nearby test wells record how deep the rain is penetrating and whether it is actually reaching the groundwater table.

Kinner and his students will soon add their very own rain maker to the mix. A rainfall simulator, a homemade contraption sporting a shower head on a giant tripod hooked to a 200-gallon tank, can be maneuvered into place to test absorption on varying slopes and varying types of “rain.”

 

Below the surface

Mountain aquifers are defined by fractures, akin to ant tunnels in the rocks, ranging from visible veins to microscopic cracks.

How many — and how big they are — make or break a well.

“It is all about fractures. The more fractures you have in the bedrock intersecting a well, the more fractures you will find conveying that water,” Laverty said.

But the maze of fractures below the ground are completely random.

“A well driller who pulls up in your yard can’t say ‘I think the northeast corner will have more fractures than the southeast corner,’” Laverty said.

In the old days, a bucket lowered by a rope into a hand-dug well seemed to serve the early settlers fine. But that would hardly suffice today, not only because a shallow well like that is susceptible to contamination, but the water table at such shallow depths doesn’t have the volume or reliability modern households demand.

Wells drilled today are like a giant tube-shaped colander. The water seeps through tiny holes to fill the shaft. If the shaft doesn’t cross paths with the fractures and veins that carry water underground, however, it won’t fill up.

When that happens, drillers may turn to hydrofracking, which forces fractures in the rock to split open larger and pull more water into the well. This doesn’t always bode well for flow of other wells nearby, which can possible lose some of their pressure.

While WCU’s groundwater research will go a long way toward answering fundamental questions about how fractured rock aquifers behave in the mountains, it won’t tell us definitively, in each and every case, how many wells are too many. The geology is so site specific, that no single model that could be applied to all of Western North Carolina.

“The aquifers here are very dissected, and the fractures control everything here,” Laverty said.

But, if baseline data existed, carrying capacity could be calculated for a particular mountainsides.

“If you do have a subdivision in a particular watershed, you can start looking at that question,” Laverty said.

In Jackson County, groundwater recharge took a lead role in the debate over development regulations four years ago. The rules imposed a sliding scale for the size of house lots: the steeper the slope, the larger the lots have to be. The reasoning: on steep slopes, more surface area is needed to achieve adequate groundwater recharge, according to county planners at the time.

Unfortunately, climate change doesn’t bode well for groundwater recharge.

“One of the larger questions in terms of recharge is, as our climate changes, it will become drier overall and the rain we do have will be more intense,” Kinner said.

Laverty also believes the changing weather patterns of global climate change is bad news for groundwater recharge in the mountains.

“In the past we had rainfall that is spread out, good soaking rains, but now we are going to be seeing more heavy rains that come like a monsoon,” Laverty said.

Laverty said there’s a lot riding on groundwater aquifers in the mountains — around 50 percent of the population here has wells.

“If we have summers with prolonged droughts, a lot of communities could be in trouble. If your well runs dry where do you go?” Laverty said.

There are steps developers can take to help homeowners down the road capture rain and channel it into the ground rather than allowing it to run off. Things like rain gardens and bioswails collect rainfall and give it a chance to soak it before running down the mountain, Laverty said.

“If you want your little subdivision to survive and have enough water for everybody, that is something you need to take a look at,” Laverty said.

 

Amassing data, nurturing geologists

Kinner, along with Mark Lord, head of the WCU geology department, recently received a $200,000 grant from the National Science Foundation to support their research.

All together, there are 40 wells of varying depth scattered across three plots on the WCU campus.

The wells were drilled last year courtesy of the state’s Department of Environment and Natural Resources, which is intensely interested in how mountain aquifers work.

The research also aims to understand how shallow groundwater moves laterally through the soil near creeks. Creeks, in essence, are an above ground manifestation of ground water. Creeks are far from static systems, coursing downhill irrespective of the subterranean groundwater around them.

In fact, groundwater not only moves through the soil into creekbed, but in some cases seeps back out of the creeks into the surrounding soil.

This transport of shallow water across soils is being monitored at many of WCU’s test well sites.

There’s another element to the groundwater research that has nothing to do with water, aquifers or hydrology. The geology professors are studying whether undergraduate research approached as a class helps students learn.

WCU has always been big on research. It is actually a requirement of all geology majors.

“The idea is students learn best if they are actually doing things,” Kinner said.

In the past, students undertook an individual research project for a semester, usually in their senior year. This project will engage students from intro to upper level courses, up and down the geology curriculum, allowing the professors to plug different classes in to the long-range research project.

“The grant will allow us to ask the question, ‘How do students at all levels of the geology curriculum benefit from research-based learning?’” Kinner said.

Research fellows will be hired to mentor students engaged in the project. But the applied science will serve a greater good as well.

“We are basically growing more geologists and hydrologists in this area to look at these questions,” Kinner said.

blog comments powered by Disqus
Read 4231 times

Media

blog comments powered by Disqus