Here in Paonia, Colo., late on January 23rd, I was lying in bed when my house started to tremble. It felt like the whole structure was perched on a pad of Jell-O. There was one short round of shaking, and then another. But before I could become anything more than startled, it stopped.
Local news websites reported that a magnitude 3.9 earthquake had struck the Paradox Valley, about 100 miles to the west near the Utah border. It turned out that the Bureau of Reclamation accidentally caused it by injecting salt brine deep into the earth at its Paradox Valley Salinity Control Facility, which it uses to manage salinity in the Dolores River. This facility is part of a decades-old effort to control salt levels in the Colorado River basin.
Rain and snowmelt seep through the strata of the old bulge, becoming salty enough to be called brine. The brine accumulates in the shallow groundwater that recharges the river, flowing from there into the river itself.
The salt causes all sorts of problems downstream: It poisons agriculture, gums up industrial machinery, and fouls municipal water. In the lower stretches of the Colorado River -- which the Dolores flows into -- salt is a major water quality issue. Irrigation exacerbates the troubles. Diverted water picks up more salt as it flows through unlined canals and over tilled fields, which concentrates as the water evaporates. The water that returns to the river is thus extra salty.
For decades, the Bureau of Reclamation -- pressured by Mexico, farmers in California, and others who divert water from the lower Colorado -- has sought to remove the salt. A regulatory framework for managing salinity in the Colorado River basin was set up in the mid '70s. New standards inspired mega-projects like the Yuma Desalting Plant (see "Draining the budget to desalt the Colorado," HCN 2/21/94), which was completed in 1992 as way of reclaiming water from a large irrigation district in southern Arizona. But the $250 million Yuma plant is so expensive to run that it's sat mostly idle.
BuRec’s approach on the Dolores is a little different. In the late '70s, the agency started studying ways of removing naturally occurring salts from the river. The Paradox Valley Unit that caused the earthquake came on-line in 1996. It removes salt at a cost of $69 per ton, according to Justyn Hock, a BuRec spokeswoman at the agency's Grand Junction office. That's a fraction of the cost of the Yuma plant.
That’s because the Paradox facility removes salt before it ever enters to the river, rather than filtering the water. A series of shallow wells are used to pump the salty groundwater, lowering the groundwater level and keeping brine from rising into the river. The brine is then injected into a 16,000-foot deep well, where it's contained under the bottom of the salt dome. The process removes 110,000 tons of salt from the river annually, about half the amount that the Paradox Valley would send downstream otherwise. That's about 17 percent of the total amount of salt that BuRec removes from the Colorado River system.
The process does have side effects, though, including earthquakes. When the brine is injected at high pressures into the deep well, it works its way into fissures and fractures. If there's existing stress along these small faults, the brine can cause them to slip, says Andy Nicholas, the facility operations specialist at the Paradox facility. Most of the quakes are so small they're never felt; only a couple have been as large as the one in January.
The deep well is actually filling up and nearing the end of its life. BuRec has started scoping studies of other methods, including evaporation ponds. There was a public scoping hearing last fall, and BuRec expects to release its proposal within the coming weeks.
Marshall Swearingen is a High Country News intern.
Images courtesy Flickr user Joel Pomerantz and Bureau of Reclamation.