Here’s the release from the Bureau of Reclamation (Marlon Duke):
The U.S. Geological Survey reported that an earthquake occurred at 10:22 a.m. MST, on Monday, March 4, 2019, near Reclamation’s Paradox Valley Salinity Control Facility near Bedrock, Colorado. Reclamation maintains a comprehensive network of seismic monitoring instruments in the area, which indicated a preliminary magnitude 4.1 for this earthquake. The quake was felt by employees at the Reclamation facility and residents in surrounding areas.
The Paradox Valley Salinity Control Facility injects highly pressurized, concentrated salt water (brine) into a 16,000-foot-deep well, preventing the brine from entering the Dolores River. The well was not operating at the time of the earthquake due to routine maintenance. Operations will not resume until Reclamation completes a thorough assessment of the situation.
High-pressure brine injection has been known to trigger small earthquakes in the past, and today’s event was within the range of previously induced earthquakes. Reclamation’s seismic network in the area monitors the location, magnitude and frequency around the Paradox Valley Salinity Control Facility. Reclamation will continue using that network to monitor earthquakes in the area.
The Paradox Valley Salinity Control Facility substantially benefits downstream water quality in the Colorado River Basin, and helps the United States meet treaty obligations with Mexico for allowable salinity levels in the river. Historically, the Dolores River picked up an estimated 205,000 tons of salt annually as it passed through the Paradox Valley. Since the mid-1990s much of this salt has been collected by the Paradox Valley Salinity Control Unit in shallow wells along the Dolores River and then injected into deep subsurface geologic formations. The deep well injection program removes about 95,000 tons of salt annually from the Dolores and Colorado rivers.