named Rio Tinto to this day.
A “normal” and healthy stream will have a pH of 6.5 to 7.5. Drop below that (or go above it), and the creatures that live in or rely on the stream begin to struggle. Mayflies, stoneflies, and caddisflies can’t survive below pH 6; rainbow trout perish at pH 5.5. Hardier fish species can hang on in water with a pH as low as 4.5, but their health will be impacted, their eggs won’t hatch, and their food sources will be diminished. When a stream’s pH drops below 4, all deals are off for aquatic life. Water draining from the Gold King Mine prior to the blowout had a pH ranging from 2 to 3. Since the Silverton Caldera’s geology offers up no natural buffers such as limestone, Cement Creek retains its high acidity (pH 3.5, similar to Mountain Dew) all the way to its juncture with the Animas River. Cement Creek (and, presumably, Mountain Dew) is uninhabitable, extremophiles notwithstanding.
After the waters of Cement Creek, Mineral Creek, and the Animas River come together, and as the now combined streams leave the Silverton Caldera, the pH rises quickly thanks to dilution and natural geologic buffering. Even the Gold King slug’s acidity diminished as it moved downstream, measuring in at a healthy pH 6.8 as it slithered through Durango. Acid, however, is not the only, or even most harmful, element of acid mine drainage. The metals contained in that water can be far more deleterious in the long run. And those metals remain in the river, either in solution or as tiny, suspended particles, for miles and miles downstream, even as the acidity dissipates.
Zinc, copper, and cadmium, in both dissolved and solid states, are particularly toxic to trout and other fish and the bugs on which they depend. In very high concentrations, these dissolved metals can bring death in a fell swoop; a single high runoff event at California’s Richmond Mine killed forty-seven thousand fish. At lower concentrations, it’s a slow ecocide. The metals accumulate in the food chain, hindering fish growth, stifling reproduction, and wiping out more sensitive species altogether. Some metals are more persistent than others, and aren’t broken down by natural processes. So they bioaccumulate, building up in a fish’s organs over time without killing it, making the fish toxic to whatever eats it, including humans. Mercury is especially pernicious in this regard, because it tends to build up in the fish’s muscles, the part most commonly eaten, and mercury is also biomagnified as it moves up the food chain. That’s why tuna, near the top of the chain, is likely to have higher mercury concentrations than sardines. Changes in water chemistry and temperature can make metals more or less bioavailable and toxic. Zinc and cadmium have a synergistic relationship, meaning in combination they are more pernicious than alone. Relatively benign iron becomes toxic at lower concentrations when the pH drops below 5, and warmer water temperatures generally increase metals’ toxicities, yet another reason to fear climate change.
Metals in solid form are not as easily ingested or absorbed, so pose less threat to bugs or fish as toxins. Yet they can snuff out a stream’s oxygen and light, they can build up on and kill plants, and accumulate on or abrade a fish’s gills. Iron is not especially toxic, but it is abundant in acid mine drainage and as it precipitates out of solution it settles onto the stream bed and hardens into ferricrete, thus damaging bug habitat and cementing over gravel in which fish spawn. Cement Creek probably got its name from the ubiquitous coating of ferricrete throughout its length.
Acid mine drainage spews into western watersheds daily from thousands of abandoned hardrock, coal, and uranium mines. It amounts to a round-the-clock defilement of aquatic ecosystems. Yet except on rare occasions—such as when three million gallons of it got backed up in the Gold King Mine, then came blasting out over just a few hours—acid mine drainage is invisible, and goes mostly unnoticed. When mines are active in a region, however, a far more apparent form of pollution, mill tailings, or slimes, can cause even more damage—call it acid mine drainage, supersized.
“THE ANIMAS RIVER WAS ONCE A BEAUTIFUL, CLEAR AND SPARKLING FLOW of wholesome water, and the home of the finest specimens of mountain trout in the state,” wrote Durango Democrat editor David F. Day in the spring of 1900. “The flow of the Animas River is rapidly being destroyed as a beverage and agency for irrigation by the absolute and unlawful recklessness of Silverton mill men and steps should be taken at once to force the mill operators to either impound their tailings or cease to run.”
With this blistering editorial targeting the Silverton-area mines and mills, Day had yanked the communities along the Animas River into a statewide row over the dumping of mill tailings into Colorado streams. By that time, Front Range farmers had been battling upstream mines and mills for decades, trying to get state lawmakers to clamp down on mine-related pollution. Mostly it was for naught. But with the irascible Day in the fray, the anti-pollution crowd had gained a potent weapon.
IF THE RAILROAD WAS THE CATALYST FOR INDUSTRIALIZATION of the region’s landscape, then large-scale milling had an even more profound effect on the mines around Silverton and, consequently, on the water that spills out of the mountains here. When Olaf Nelson and Jonathan Peterson were hit by their first landslide in 1879, San Juan mines were mostly small-scale operations. Nelson and his colleague followed the vein using hand tools and dynamite, then sorted through the ore by hand, picking only the chunks with the highest concentrations of metals, which they took by wagon or burro to the nearest smelter, where the metals would be cooked out of the rock.
While the miners could scale up their side of the operation by adding more laborers or using more efficient means of transporting ore, they were still limited by the smelting process. Smelting only works on high-grade ores, those containing relatively high concentrations of valuable metals. That meant that the miners had to leave the low-grade ore in the mountain or toss it aside in waste dumps. For the first decade or so, that wasn’t a problem; there was an ample supply of high-grade ore. But there was a lot more low-grade ore to be had, if only it could be smelted. This is where milling—an intermediate step between mining and smelting—comes in.
Milling ore is simple in concept: You grind up the rocks and separate the valuable stuff out from the “chaff.” But in the late 1800s, engineers still struggled to make it work on a large scale in the San Juans. Mills were constructed at various mines in the Silverton Caldera throughout the 1880s, but none really achieved the desired economies-of-scale until Edward and Lena Stoiber built their revolutionary mill.
Stoiber and his brother Gustav, German engineers, came to Silverton in the early 1880s to get a foothold in the nascent mining boom. They acquired a group of claims on the shores of Silver Lake, a classic, high alpine gem northeast of Silverton in a hanging basin ringed on three sides by steep, rocky peaks. In 1888, Edward was married to Lena Allen, a young divorceé whom he met in either Silverton or Denver. Soon after, Lena bought into the Silver Lake Mine, becoming an equal partner in the venture with her husband.
The veins were not especially rich at the Silver Lake, but Stoiber figured he could make a profit there anyway, with proper engineering. In 1890 he had a mill constructed on the shores of the lake, designed specifically to go after low-grade ore, along with a hydropower plant far below on the Animas River to supply the juice to run the thing. While it wasn’t the most efficient operation, it worked well enough to turn a profit from rock that had once been considered worthless, and soon other mines were following the Stoibers’ lead.
The mills that emerged during this era were enormous, dangerous, noisy structures, usually built up a slope so that gravity could help move the ore through the byzantine process. At the Silver Lake mill, the high-grade ore was sorted out by hand to go directly to the smelter. The rest of the rock went through two crushers before it was further pulverized by fifty stamps, each of which weighed hundreds of pounds, crashing down at high repetitions. The crushed ore was ground down even further by four sets of cylindrical rolls. The resulting fine-grained
