Valley water officials do not expect a toxic mine spill in Colorado to cause any measurable problems at Lake Mead, but they are stepping up their sampling program just to be sure.
The Southern Nevada Water Authority already collects water samples every two weeks where the Colorado River empties into the eastern end of the lake. Those samples will now be collected twice a week and tested more extensively in response to last week's spill that turned a stretch of Colorado's Animas River mustard yellow.
A crew from the U.S. Environmental Protection Agency accidentally triggered the spill while working at the abandoned Gold King Mine site near Silverton, Colo., roughly 600 miles northeast of Las Vegas. An estimated 3 million gallons of mine pollution laced with heavy metals entered the Animas, a tributary to the Colorado River.
Dave Johnson, the authority's deputy general manager for engineering and operations, said he's "very concerned" about the communities immediately downstream from the spill, but the plume has too far to travel and too much water to mix with to ever contaminate Lake Mead or Lake Powell.
"We don't believe we will even be able to detect a difference," said Johnson, a chemical engineer who has served as treatment manager and water quality director for the authority.
If any unusual levels of heavy metals or other contaminants are detected, the sampling will be stepped up and expanded even further, but Johnson said he would be "very surprised" if that happens. "We completely expect this to be a nonissue for us."
The EPA is now reporting that contamination levels in the Animas have returned to pre-spill levels, and much of the orange-yellow sediment has settled at the bottom of the river channel.
Before it reaches the intake pipes that supply about 90 percent of the Las Vegas Valley's water, the roughly 9 acre-foot plume of pollution will mix with more than 13 million acre-feet of water in Lake Powell and another almost 10 million acre-feet of water in Lake Mead.
"The dilution factor is extremely high," Johnson said.
He added that it could take two weeks for any pollution from the spill to make its way through Lake Powell and another two weeks for it to reach Lake Mead.
Since the spill, the authority has been receiving regular updates from the EPA and running its own analytical models that show very little chance of trouble. The increased sampling should remove all doubt, Johnson said. "We're trusting the data that we have, but we're verifying."
Contact Henry Brean at email@example.com or 702-383-0350. Find him on Twitter: @RefriedBrean.