Most towns would rather you didn’t look at their Superfund site. Butte, Montana, charges admission. The local Chamber of Commerce runs a viewing stand on the southwest rim of the Berkeley Pit from May through October, and you can pay to stare down at a flooded copper mine, which is a pretty strange road trip stop if you ask me.<\/p>\n
But if you’d gone this summer, you wouldn’t have spotted the pit’s biggest problem from up there. The pumps were gone.<\/p>\n
Montana Resources pulled them out in January because the slope under the only road down to them had started to move. They didn’t run again until Aug. 31, and the lake rose about 3 feet while they were out.<\/p>\n
So should anyone in Butte be nervous?<\/p>\n
Not yet, as far as I can tell. I went through the monthly water reports that Montana’s state geologists file on this place, and the number I’d keep an eye on comes from a flooded mine up the hill. We’ll get there.<\/p>\n
The Berkeley Pit mined copper from 1955 to 1982. An EPA fact sheet<\/a> puts it at 1,780 feet from the bottom to the highest point on the rim, and about 1.5 miles by 1 mile across. When mining stopped, the pumps in the nearby Kelley Mine shut off “for the first time in over 100 years,” according to PitWatch, the site’s public education project. Groundwater came back, and PitWatch figures about 49 billion gallons have flowed in since.<\/p>\n I’m not going to hand you a water depth, though. EPA’s current site page says the pit’s about 1,600 feet deep with about 900 feet of water in it. The bottom elevation in that fact sheet works out to roughly 1,100 feet of water by my math. The agency’s numbers don’t really agree with each other.<\/p>\n The water itself has picked up sulfuric acid and a long list of dissolved metals, so you can’t just leave it alone. Montana Resources and Atlantic Richfield have been pumping it out and treating it since late 2019 to keep the level from rising. Holding the lake steady takes roughly 3 million gallons a day, KXLF reported in February, and the old setup could manage about 5 million.<\/p>\n Then came December. Montana Resources noticed the slope moving under the ramp to its north wall pump station, and that ramp was the only way in. “If we lose the ramp, we would have lost all the pumps,” Mark Thompson, the company’s VP of environmental affairs, told KXLF. He described it to Montana Right Now as “a relatively small instability, it’s just in a very inconvenient location for access,” which is a pretty calm way to talk about a moving hillside.<\/p>\n Crews hauled the gear out in January and built a new pump station at the pit’s south end, with roughly 3 miles of pipe running to the treatment plant. Honestly, I think that was the only sensible call. A few feet of lake is arguably a much easier problem than a pump house you can’t get to anymore.<\/p>\n You’d figure a lake with no pumps would climb steadily. It didn’t. The December reading was 5,355.77 feet above sea level, and the May reading was 5,355.84 feet. That’s 0.07 feet, or less than an inch, in five months.<\/p>\n Then it took off. The Sept. 1 survey, taken a day after the pumps restarted, came in at 5,358.68 feet. These surveys are done by a firm called Common Sense Engineering and Surveying, which is a pretty great name for anyone working on a Superfund site.<\/p>\n So why the flat stretch? I don’t know, and the reports don’t say. The mine shafts around the pit kept rising the whole time (the Anselmo Mine gained about 2.4 feet between December and May), so the groundwater clearly wasn’t taking a break.<\/p>\n For scale, Mike McGivern of Montana Resources told KTVH the pit was climbing 6 to 7 feet a year before the pumps went in. So 3 feet over a seven-month gap is pretty much what you’d expect, maybe a bit less.<\/p>\n Regulators drew it in a 1994 Superfund decision: 5,410 feet above sea level, known as the Protective Water Level. PitWatch<\/a> says that leaves a 50-foot cushion, since groundwater wouldn’t start moving away from the pit until about 5,460 feet.<\/p>\n Basically, the pit’s supposed to be the drain for the whole hill. As long as it’s the lowest spot around, water runs toward it and stays there, because groundwater can’t flow uphill. Let the level get too high and contaminated water could start heading for Silver Bow Creek instead.<\/p>\n You may be thinking a hole this full could spill over the rim, and the answer is no. PitWatch says it can’t overflow, and that nobody in Butte needs flood insurance because of it. The worry’s all underground. Frankly, a 50-foot buffer on top of the official limit seems pretty conservative to me.<\/p>\n Here’s where it gets more interesting. The 5,410-foot limit covers more than the lake. Under a consent decree, water can’t top it at any of 14 compliance points, which are mostly old mine shafts and bedrock wells around the pit. The Montana Bureau of Mines and Geology tracks them and reports to state regulators and EPA.<\/p>\n Its September report<\/a>, dated Oct. 16, has the lake 51.21 feet under the line and the Pilot Butte Mine 25.83 feet under it. That’s the highest reading in the table, and it’s about half the margin you’d get if you only looked at the lake. I’d argue that’s the number to watch.<\/p>\n Some gap between the lake and Pilot Butte is by design, since the lake’s meant to stay lowest. And Pilot Butte didn’t just wander up to the top of the table. Nearly three years ago, it was already only 28.93 feet under the line.<\/p>\n There’s one oddity, though. Pilot Butte went from 28.64 feet under the line in the June report to 26.37 feet in the July report, a 2.27-foot jump, while the other mine shafts rose less than a foot. The July report doesn’t explain it. It’s barely moved in the two reports since.<\/p>\n How long would it take to actually reach the line? Officials told KXLF in February it’d be about four years with no pumping, and Thompson told Montana Right Now it was more than four and a half at the inflow rates back then. We’re not sure how much the last few months shaved off that. Either way, you’re talking about a matter of years. If you’ve been following Lake Powell<\/a>, you know how much attention a few dozen feet of margin can get. At least here, the pumps are back on.<\/p>\n Thompson told KBZK<\/a> in late September that the companies started pumping “long before we had to” so they’d have room for something like this. That’s a pretty good argument for starting early.<\/p>\n KBZK reported the new station was moving about 6 million gallons a day, compared with the usual 3 million, to bring the lake down another 5 feet. EPA says the Horseshoe Bend treatment plant can handle 7 million gallons a day, so the extra water shouldn’t be a problem there.<\/p>\n Just don’t expect quick results. The lake still rose 0.11 feet between Sept. 1 and Oct. 1 with the pumps back on, and I can’t tell you why it hadn’t turned around yet. One month isn’t much to go on. Old copper mines tend to run on long timelines anyway, as we saw with a 9,889-foot copper and zinc mine in Ontario<\/a>.<\/p>\n The Montana Bureau of Mines and Geology’s next monthly report should tell us whether 6 million gallons a day has started pulling the lake down. Until then, the latest number on the books is the Oct. 1 survey, which had the Berkeley Pit lake at 5,358.79 feet.<\/p>\n","protected":false},"excerpt":{"rendered":" Most towns would rather you didn’t look at their Superfund site. Butte, Montana, charges admission. The local Chamber of Commerce … <\/p>\nThe lake barely moved until June<\/h2>\n
So where’s the line, exactly?<\/h2>\n
The flooded mine is closer than the lake<\/h2>\n
They’re pumping double now<\/h2>\n