TodayA Hole for a Hole, Searchers track sinkhole
Volunteers find culprit gulping water from historic stream.
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Volunteers look in hole being dug in a search for the sinkhole that is swallowing LeTort Spring Run(Jason Malmont/The Sentinel)
Conservationists are confident they found the source of a sinkhole that had been gulping down water from storied LeTort Spring Run.
They converged on the site Wednesday, just downstream from Union Quarries’ operation off Bonny Brook Road in South Middleton Township, in the hope of locating the sinkhole’s thirsty source.
By midday, a large backhoe had uncovered the culprit about 50 feet from the water’s edge — some porous bedrock.
“You could see the cracks in the bedrock through which the water was flowing,” says Jim Richenderfer, a hydrologist who directed the morning’s search, adding “those are the signs we’re looking for.”
Conservationists representing Cumberland Valley Trout Unlimited and LeTort Regional Authority, using donated equipment and materials, expected to go back to the site this morning to begin constructing a grout plug made of concrete and bentonite, a clay-like substance that expands when wet.
Without the repair, the sinkhole would grow and the legendary stream would continue losing water, says Richenderfer, a geology and hydrology consultant and part-time professor at Dickinson College.
The plug will be placed over the hole at the bottom of the pit, about 12 feet to 14 feet deep. When that sets, the pit will be lined with another type of material that inhibits the flow of water toward the sinkhole. The site will be smoothed out, covered with new top soil and reseeded with native plants and grasses.
“In a couple of years, you won’t know we were in there digging such a big hole,” Richenderfer says.
The backhoe wasn’t the only one doing some heavy lifting at the site.
Some members of CVTU’s “Feet in the Stream” gang — mostly retirees who often work on stream improvement projects — were out Wednesday in their waders.
They used shovels and hoes to backfill a sandbag cofferdam constructed to help keep the LeTort’s waters inside the streambanks.
Chet Hagenbarth, a retired construction engineer, climbed out of the water, put down his hoe and quipped, “I’m busier than when I was working.”
The group previously removed brush and trees from the area and built the cofferdam along the streambank using 491 sandbags.
“A lot of manhours went into this that’s just hard to quantify,” said Herb Weigle, public affairs chairman for LeTort Regional Authority.
A joint press release from the Trout Unlimited chapter and LeTort Regional Authority estimates about 114 manhours went into construction of the cofferdam from January to March.
Sinkholes not unusual
Before the cofferdam was completed in March, water flowing along the east bank appeared to take a right turn into the bank. From there, it flowed through a channel that formed along the top of the ground before dropping back underground.
Richenderfer says the sinkhole is the third major one he’s repaired over the past 25 years.
The previous two occurred near the site of the current one. Other smaller sinkholes were repaired close to some nearby watercress beds.
He jokes that people will think he’s not doing a great job if the stream keeps springing new leaks.
But, they’re not unusual for any stream classified as a limestone spring run, such as the LeTort. The stream emerges from underground sources in South Middleton Township and flows over nine miles, through Carlisle to Conodoguinet Creek in Middlesex Township.
“Anywhere you have limestone, you run the risk of having sinkholes,” Richenderfer says, adding limestone bedrock naturally dissolves over time and acid rain accelerates the process.
An “extreme” example of bedrock dissolving naturally can be seen at Luray Caverns in Virginia and Crystal Caves in Pennsylvania, he says.
The limestone makeup that leaves the stream more vulnerable to pollution and sinkholes also provides an environment that produces nearly 20 times more aquatic life than other streams of its size.
The LeTort traditionally supported a large, healthy population of brown trout that feasted on a rich variety of insects and freshwater shrimp that lived year round in the water, which remains a fairly constant temperature all year.
LeTort trout have reached 30 inches and topped eight pounds.
Legendary fly-tiers like Vince Marinaro and Charlie Fox developed fly patterns while fishing the LeTort, enhancing its reputation as one of the cradles of flyfishing in America.
The following companies contributed to the project by donating the listed equipment or materials: Gleim Environmental Group, excavation and backfill; Valley Quarries Inc. supplied fill for the sandbags and clay for backfilling the cofferdam; American Colloid Co. based in York supplied the bentonite; Genie Trucking of Mt. Holly Springs donated a truck to haul the bentonite from York to the site; Carlisle Syntec donated the geothermal membrane material that will line the pit.
