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The Land Desk: The silt remembers

This article was originally published in The Land Desk.

In June 1975, as winter clung stubbornly to the high San Juan Mountains of southwestern Colorado, a heavy rain fell on the still-icy tailings containment ponds at Standard Metal’s Mayflower Mill, just outside of Silverton. The combination of rain and ice caused one of the impoundments’ sand walls to give way, allowing some 75,000 tons of sludge within to break free and flow into the Animas River.

The sludge—a combination of very fine and sandy mill tailings, loaded with acid-forming sulfites and a toxic soup of heavy metals—was carried by the swift current downstream to Durango, where the river ran the color of “aluminum paint,” as a Durango Herald reporter described it at the time.

Of 31 rainbow trout placed in the water in cages, 27 were dead within 24 hours. Cyanide—often used to leach gold from ore—was detected at high levels in Farmington, where the Animas joins the San Juan River, which took on the same eerie hue. From there the material continued westward, ultimately settling into the San Juan River delta where it runs up against the slackwater of Lake Powell.

Over time, the calamity faded from the collective memory. It was dredged back up when the Gold King Mine blew out in 2015, turning the Animas and San Juan Rivers TANG-orange and then electric yellow all the way into Utah. But the immediacy—and color—of the latter event quickly overshadowed the 1975 tailings spill. Lake Powell’s growing depository of silt, however, never forgets, and the memory of the 1975 event lurks some 45 feet deep within the sediment.

In 2018, U.S. Geological Survey scientists set out to unearth the sedimentary memories in Lake Powell, taking core samples from various locations around the reservoir but with a special focus on the San Juan River delta, since that’s where most of the Gold King residue would be. They recently released preliminary, raw data from the coring project, and Zak Podmore of the Salt Lake Tribune summarized their findings. This slide, from the project lead Scott Hynek, encapsulates findings so far:

Yes, the Gold King spill was big and ugly—an estimated 540 tons of metals were carried down the river during the event—and the record of the event shows up as a spike in zinc and lead a few meters under the silty surface. But the events of the 1970s, and the resulting spikes in zinc and lead, were significantly larger, according to the data. In fact, judging from the graphic above, water quality in the seventies was generally nasty, even when tailings piles weren’t bursting or alpine lakes weren’t flushing out mine workings.

Why? Because water pollution laws weren’t yet in place. Yes, Congress passed the Clean Water Act in 1972. But the mining-specific provisions of the Act were not finalized until later, so initially the law had little effect on the operating mines or mills in the San Juan Mountains such as Standard Metals’ Sunnyside Mine or Mayflower Mill.

About 1,600 gallons per minute of acid mine drainage—or nearly one Gold King Mine spill every thirty-six hours—poured out of the Sunnyside’s American Tunnel. It carried with it three hundred pounds of zinc each day, along with an assortment of other metals, all of which flowed directly into Cement Creek without any treatment, then into the Animas, the San Juan, and eventually ending up in Lake Powell’s silt. Meanwhile, dozens of smaller, abandoned mines and tailings and waste rock piles around the area were adding their own toxic soup to the mix.

Eventually the laws kicked in and the state started enforcing them more rigorously, forcing the Sunnyside Mine’s owners to treat their water discharges to a very high standard. And when the Sunnyside mine shut down in 1991, it began a multi-million dollar clean up effort, significantly improving water quality. That, too, is apparent in the sedimentary record, as is the 2005 shutdown of the water treatment plant which, by that time, was cleaning water from the Gold King Mine as well as the American Tunnel.

These findings aren’t exactly revelatory. Yet I find it fascinating, nonetheless. It’s oddly reassuring to know that the silt remembers changes in water quality in much the same way trees remember the variations in climate over their lifetimes. It’s also a bit disturbing to know that as the lake’s level recedes, much of the silt and the stuff it contains—including radioactive waste left over from the Nuclear West—is remobilized, sullying the water in Lake Powell all over again, harming aquatic life, and potentially contaminating drinking water for those downstream.

Equally startling is the sheer volume of silt deposited in Lake Powell each year. In 1986 the Bureau of Reclamation conducted an extensive silt survey of the entire reservoir, finding that 868,231 acre feet—equivalent to one cubic kilometer—of sediment had accumulated in the lake over the previous 23 years. If sediment has continued to pile up at that rate for the ensuing 35 years, now nearly 2.2 million acre feet of silt is sitting in Lake Powell, which is enough sand and mud to fill more than 1 million olympic size swimming pools.

The same 1986 study assured water officials that at that rate it would take 700 years for sediment to completely fill the reservoir to its original capacity of 27 million acre feet. But at the current rate of climate change-induced lake level decline, the reservoir will be more sediment than water within a decade or less. The reservoir will be rendered useless and boaters will have to navigate it with silt-skipper crafts. The vast depository of sediment also poses challenges to proposals to “fill Lake Mead first,” by draining Lake Powell and dismantling Glen Canyon Dam.

Lake Powell in prolonged drought: by the numbers

  • 2.2 million acre feet - Estimated amount of sediment that has been deposited in Lake Powell since Glen Canyon Dam started impounding water (and silt) in 1963. That’s enough to fill 1 million Olympic-size swimming pools.
  • 7.02 million acre feet - Current volume of water stored in Lake Powell.
  • 6.9 million acre feet - Amount of water the reservoir has lost in the last two years.
  • 3,541 feet above sea level - Current surface elevation of Lake Powell.
  • 3,700 feet - Surface elevation when the lake is full.

If current Southwestern snowfall trends continue, then silt volumes may overtake water storage even sooner: With meteorological winter getting underway, the mountain snowpack is worryingly thin, sitting around 30 percent of normal for this date in many places. It seems to get worse the further south one looks.

Three high-elevation sites in the San Juan Mountains show snowpack far below average at Molas Pass and Columbus Basin (in the La Plata range). Red Mountain Pass levels, further north, are healthier, but still below average.
Three high-elevation sites in the San Juan Mountains show snowpack far below average at Molas Pass and Columbus Basin (in the La Plata range). Red Mountain Pass levels, further north, are healthier, but still below average.

Equally alarming are mountain temperatures. October was warm on Red Mountain Pass, which isn’t terribly unusual, but then, after a short cool spell in mid-November, the mercury climbed back up to the high 40s and even low 50s around Thanksgiving, dropping down just to about freezing at night. This melts the little snow that has fallen and hampers ski area snowmaking efforts, further shortening ski season. Meanwhile, the current foot or so of snow is rotting, setting up a classic and unstable San Juan snowpack of new snow atop depth hoar—a potentially deadly combination.

It’s not just the Southwest, either. Denver has already broken a record for the latest first snowfall of the season and is on the way to setting a new one for the longest period between measurable snowfall. As I write this, the National Weather Service was forecasting near-record high temps today for the city.

But, hey, don’t worry! Folks are stepping up cloud seeding efforts. That should save us, right? Probably not. Yet all hope is not lost: It’s far too early in the season to assess the situation. Winter is just getting started and patterns could easily shift in a week, or a month, or even a few months to salvage the snowpack.

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KSUT publishes selected articles from The Land Desk, a newsletter from Jonathan P. Thompson. Articles are archived here.

TheLand Desk explores news from the Four Corners, Colorado Plateau, and Native and Indigenous lands. Jonathan is a longtime Four Corners-based journalist and author of River of Lost Souls, Behind the Slickrock Curtain, and his new book, Sagebrush Empire.

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