7/06/2017 Peter Durantine

F&M Researchers Find Ground Water Runs Deeper Than Hydrologists Thought

The Bubble, a spring that provides most of the water for a lake in the central Pennsylvania hamlet of Boiling Springs, is an old mystery to residents who speculate about the spring’s source.

“Everyone who lives near The Bubble has these crazy theories about it – ‘Oh, it comes from New York’s Finger Lakes’ or ‘This water comes all the way from Erie,’” said Tim Bechtel, Franklin & Marshall adjunct assistant professor of geoscience. “Now we know those theories aren’t so crazy. The water really does come from far away.”

  • "The Bubble" has been the source for a nearby recreational lake in Boiling Springs longer than it has been a source of speculation about where its water comes from. Image Credit: Deb Grove
  • Professors Tim Bechtel, left, Robert Walter and Jake Longenecker '17 discuss their findings just before Longenecker dons his wetsuit for a submergence. Image Credit: Deb Grove
  • Even in early July the waters are cold enough that Longenecker must acclimate before diving into the underground cavern to check sensors. Image Credit: Deb Grove
  • Longenecker prepares to go into the Bubble's underground stream to check sensors. Image Credit: Deb Grove
  • Having emerged with the sensors, weighted down by a barbell, Longenecker makes sure the sensors are secure. Image Credit: Deb Grove
  • With young spectators curious about his work watching on, Longenecker prepares to submerge once again to return the sensors to the Bubble's ground water stream. Image Credit: Deb Grove
  • One last dive and then call it a day's work in the Bubble. Image Credit: Deb Grove

What Bechtel, Associate Professor of Geoscience Robert Walter and student-researcher Jake Longenecker ’17 learned after two years of study has recently appeared in “Geophysical Research Letters.” The paper  initially drew strong peer-review skepticism because the spring’s water source is doing something hydrologists did not think geologically possible, but eventually the reviewers were convinced by the data and evidence.

“If you were to ask us before we did this experiment where we would have predicted the recharge area to be, we would not have predicted southeast of The Bubble,” Walter said. “This does not fit the standard ground-water flow models.”

Yet, the water flow comes not just from southeast of The Bubble, but from the other side of mountains along the Maryland border nearly 50 miles away.

“That’s unusual,” Walter said. “If it’s true that this source-region is that far south and east of Boiling Spring, it has to go through 10 different types of rock, and that’s what’s blowing people’s minds.”

To confirm their theory, the researchers this summer will produce a dye-tracing test at the source-region they pinpointed through satellite data obtained from NASA.   

“The dye needs to go from the recharge area to the spring, and we think that could take 18 months, two years, we don’t know,” Bechtel said.

What convinced the researchers about their theory is how they discovered the source. Walter and other students had studied the pond for years, but Longenecker’s diligence and a bit of luck gave them clues. He was in the spring one sunny day checking sensors when the water rose.

“The eureka moment for us was when Jake was actually in the spring on a sunny day and the spring started to get higher,” Bechtel said. “We talked about it and realized that it had to be raining somewhere. We could figure out where the water was coming from by figuring out where in the world it was raining shortly after Jake watched the water level coming up.”

That required contacting NASA about their recently launched constellation of satellites that measures global precipitation at 10 kilometer-by-10 kilometer parcels every half hour. To make the impossibly long calculations, they turned to alumnus Miguel Melchor ’14. He created ECHO, a computer program using an algorithm, developed my Longenecker, Bechtel and Walter, to provide the results.

“We needed to find where it was raining in the region at the same time I was in the pond,” Longenecker said. “ECHO paired satellite data with data we collected from the spring. The satellite data had exactly what we needed, the highest temporal and spatial resolution.”

The researchers took a hydrograph – rate of flow versus time past a specific point – of The Bubble and examined the satellite data’s time and precipitation along the entire East Coast.

“There were only three of these 10-by-10 parcels that matched the temporal correlation of the hydrograph of The Bubble,” Walter said. “They were all contiguous with each other, all about 50 miles south and east of The Bubble, near York, on the other side of South Mountain.”

Said Bechtel: “So it rains down near the Maryland border and on the other side of the mountain, a half hour later, the spring Jake is standing in starts rising.”

Walter believes their findings in the paper will change the way hydrologists look at water flow.

“Most hydrological thinking has been on this very standard, traditional view of how ground water moves, and it does move that way, but what we’re finding out is that there’s this other pathway that may be substantial that people may not have paid attention to,” he said.

Longenecker, a geoscience major who earned praise from Walter and Bechtel for his independent thinking and tireless work on the project, plans to study hydrogeology in graduate school.

“As you know, access to freshwater sources is becoming increasingly problematic around the world,” Longenecker said. “We see the value of this paper as a shift in how people think of water flow, but also to help direct the study of other geophysical, hydrological and geochemical studies, where you really need to know where to look.”

Ground Water Runs Deep: F&M Researchers May Have Discovered the Source of This Pennsylvania Spring
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