WEEKEND QUAKES IN PARADOX VALLEY CAUSED BY MAN, OFFICIALS SAY
Earth movements that tickled Paradox Valley over the weekend are believed to have been the result of a desalinization project along the Dolores River.
Officials with the U.S. Bureau of Reclamation said the movements are to be expected when brine that is taken from the river is blasted through a well into a deep layer of rock.
The activity on Saturday and Sunday struck an odd note, officials said, because the bureau’s Paradox Valley Unit has been shut down, as it is twice a year.
Paradox Valley is so named because it runs east-west against the southerly run of the Dolores River. The valley was formed by the collapse of a salt dome.
The tiny temblors of 2.7 and 2.8, respectively, on the Richter scale “fell within our normal area of seismic activity” near the well, so officials believe they were part of the project, said Brad Dodd, chief of the facility maintenance group of the bureau’s western Colorado office in Durango.
Although the earth movements were small, the pump project illustrates the ability of man to “lubricate faults,” said Dave Wolny, an adjunct professor of seismology at Mesa State College, who noticed the motion on seismographs he monitors.
The notion of providing lubrication to the earth’s faults — the slickening of the surfaces of broken rock, thus allowing freer movement — is “more detrimental” to understanding what is happening nearly four miles below the surface, said Dodd, a geologist.
More likely, the events are the result of an operation that is similar to techniques that have become more familiar to Western Slope residents during the energy boom.
At a pumping station in Dry Creek Basin, the briny slurry is pumped nearly 16,000 feet into a limestone layer known as the Leadville Formation, which was formed during the Mississippian Period, which began about 359 million years ago and ended about 318 million years ago.
The slurry is injected at about 12,000 pounds per square inch into the porous rock, expanding existing gaps and fissures, which then fill with brine.
“We’re hydrofracking” the formation deep below, Dodd said.
The pumping station is atop the deepest injection well in the world.
The Bureau of Reclamation pulls salt from the Dolores River so it can prevent the salt from reaching faucets, drinking glasses and irrigation ditches in Utah, Nevada, Arizona, California and Mexico.
Nine collection wells aside the Dolores River collect 70 to 80 percent of the salty water that would otherwise flow downstream. That’s 115,000 dry tons of salt that gets no farther into the Colorado River system. Removing it saves the cost of about $150 a ton to remove it downstream, Dodd said.
Instead, the salty water is pumped 21 miles to Dry Creek Basin for its deep-earth injection.
Officials suspected early on that injecting salt into the rock below could cause tremors, and the bureau uses them to gauge how far the salt plume has expanded. It’s some four to six kilometers from the well, Dodd said.
Most of the tremors measure 1 to 1.5 on the Richter Scale, Dodd said.
The most powerful quake recorded in Colorado was south of Montrose in October 1960 and measured 5.5 on the Richter scale, Wolny said.
The motion associated with the events over the weekend was slight to observers on the surface.
Dodd likened it to being awakened by “a heavy truck going down the road.”
An earthquake measuring 3 on the Richter scale would likely be of little concern, but a 4 could cause the project to be halted so officials could study it, Dodd said.
An earthquake measuring 4.3 in May 2000 did cause the bureau to stop pumping for a time.
“Personally, I don’t think a 3.0 would have me too concerned,” Wolny said. “If they were to start going over 4.0, I would become a little concerned. The problem is that they are impossible to predict.”