The Manti-La Sal National Forest plans to drain Boulger Reservoir later this summer in anticipation of expanded coal mining under the popular fishing spot high on Utah’s Wasatch Plateau.
The 5-acre reservoir is located in Flat Canyon above Electric Lake where the Skyline Mine has been moving its underground mining operations in recent years, producing more than 3 million tons of coal a year.
Utah’s main coal producer Wolverine Fuels, Skyline’s owner, secured permits to begin mining Flat Canyon coal in 2017 and its operations have been progressing west as it extracts coal through room-and-pillar mining techniques. They are now close enough to Boulger to potentially impact its aging dam.
“It’s being drained as a preventive measure,” said Frank Mueller, a spokesman for the Utah Division of Water Rights. “Once they are done mining, the intent is to refill the reservoir.”
According to a dam-safety database maintained by the Utah State Engineer, Boulger’s dam, built in 1937 by the U.S. Forest Service, is 17 feet high and 274 feet across. Its hazard rating is “low,” unlike many other dams in the area, which are rated as “high,” including Electric Lake’s much larger dam a few miles downstream.
It sits at 8,717 feet above sea level, about 1,000 vertical feet above the coal seam the Skyline Mine is extracting. Nearby is a public campground. Several years ago, Skyline Mine’s previous owner installed a concrete fish ladder to help fish ascend from Electric Lake to the tiny reservoir, which state fisheries managers stock most years with rainbow trout.
A few weeks ago, the Utah Division of Wildlife Resources announced it was lifting the catch limit on Boulger from four to 16 trout since all the reservoir’s water will soon be released downstream to Electric Lake.
The need to drain Boulger illustrates how mining deep underground can affect the surface, especially on the Wasatch Plateau where collapses are common, sometimes with tragic results.
According to Skyline’s permit application for Flat Canyon, there should be no mining-induced surface subsidence in the upper Huntington Creek area, which contains Boulger and Electric Lake. This is because the company will use room-and-pillar techniques in this area rather than longwall methods. This way of mining leaves behind blocks of coal, or pillars, to support the overburden extending 1,000 feet above the mined coal seams.
The collapse of a pillar in the mine, known as a “bounce,” could trigger a dam failure if it happened under Boulger, so officials are emptying the reservoir to be safe.
Wolverine executives did not respond to phone and email messages left Friday.
Documents on file with the Utah Division of Oil, Gas and Mining show Skyline in particular has a complicated relationship with water. At times up to 10,000 gallons per minute has rushed into the mine.
Even though hundreds of vertical feet separate Electric Lake and the mine’s underground workings, water from the lake floods the mine, according to reports and documents found in Skyline’s permit file. Wells must continuously pull water from the mine and return it to Electric Lake.
The amount of water pumped from the mine appears to be increasing the farther west the mine works, according to one 2017 study conducted at the request of the Huntington Cleveland Irrigation Company, the principal water rights holder for Huntington Creek.
Several years ago, Wolverine Fuels, then known as Bowie Resource Partners, secured the 2,700-acre federal lease to the Flat Canyon, a tract holding 42 million tons of recoverable coal, enough to extend the life of the mine by 9 to 12 years.
Skyline opened in 1981 and has produced nearly 100 million tons of coal from its first three mines, which tapped seams in the lower Blackhawk formation. The federal Flat Canyon tract is its fourth mine, called Skyline #4 in various documents. Skyline’s overall 13,800-acre underground footprint covers the area where Carbon, Emery and Sanpete counties converge on the Wasatch Plateau.
The mine workings straddle the hydrological divide separating the Price River and San Rafael River drainages. The new mining area in Flat Canyon drains into the San Rafael to the south, while the mine portal is in Eccles Creek, draining into the Price River to the north.
This topographical quirk has led to serious concerns that mining under Flat Canyon would allow surface and groundwater that belong in the San Rafael basin to flow into the Price basin, depriving irrigators and power plant operators who rely on water from Huntington Creek.
To resolve the issue, Skyline agreed to implement a more robust groundwater monitoring program that would detect problems sooner, according to the irrigation company’s lawyer Craig Smith.
“That a settlement got incorporated into the mining plan,” Smith said. “We’re still concerned about it, but at least now we can have better insight as to what effects this mine is having.”