Montana Resources’ proposed Berkeley Pit treatment plan
In March, Montana Resources announced they would begin to pump and treat water from the Berkeley Pit as soon as by the end of this year. This came as a welcome surprise to many, as MR is not legally required to begin the process until the pit reaches the critical water level, which is not estimated to occur until 2023. MR is responsible for the treatment, along with BP-ARCO, under the Mine Flooding operable unit Consent Decree, under Superfund. MR has been making a strong effort to explain their plan to the community with media coverage and presentations to various groups.
In early April Mark Thompson, MR’s Vice president of Environmental Affairs, gave a presentation to the Citizens’ Technical Environmental Committee and the public, outlining the process and answering questions. Here’s Mark:
MT “What I’m here to talk about tonight is a proposal, a proposed project we have, in concept right now, we’re working on the detailed work plan. The agencies are interested in the concept, you know obviously they need to see the detailed work plans before we get final approval of anything. And what it is, is pumping of Berkeley Pit water, treated in the water treatment plant, and then discharging from the mine site. And why we’re doing this now, as many of you probably know the critical water level isn’t for a few years out, but why do we do it now? Well there’s a lot of questions out there, a lot of questions in the community, a lot of questions for the regulators, a lot of questions in our minds, too, that can really only be answered by doing it.”
The critical water level is an elevation set by the 1994 Record of Decision, or ROD, for the Butte Mine Flooding Operable Unit. Superfund sites, like the Butte area, are divided into operable units, and the Mine flooding OU includes all of the underground works, as well as the Berkely Pit. Here’s an excerpt from the ROD: “Water levels in the Berkeley Pit and East Camp system shall not be allowed to rise above the established critical water level. These levels and requirements are established to prevent existing hydraulic gradients from changing and thus to prevent releases of contaminated water from the Pit System into the alluvial aquifer or Silver Bow Creek drainage.” End quote. Decades of pumping left a cone of depression in the groundwater system, with the pit near the center. This keeps metals contaminated waters confined and out of Silverbow Creek, separated by a groundwater divide. The critical water level, set at 5,410-ft, is at least 50 ft lower than the level at the alluvial groundwater divide south of the Pit. The 50 foot buffer was established to provide an adequate safety factor while also allowing the underground works to flood to the maximum extent, reducing acid production. But MR recognized the need for a proven treatment plan before the critical water level is reached.
MT 4:48 we want to be sure we can hold the Berkeley Pit water level steady. You think that’s going to happen, but until you do, you don’t know.
Mark went on to give a breakdown of the plan. It starts with the existing pumps at the pit that served to pump water to recover copper until that operation was ceased in 2012.
MT “So we’re going to resurrect this pumping system, and pump it up to the precip plant, again, and remove the copper. Then the water’s going to flow down to the Horseshoe bend Treatment plant in this area. So that’s Berkeley water is now coming into the Horseshoe Bend Treatment plant, that water comes into the return line, just like the Horseshoe bend [water] does now, it’s in the return line, comes down to the mill, comes out of the mill with the tailings, and while it’s there we’re going to add a lot of excess lime, to those tailings.”
Lime addition is the primary method for precipitating metals out of the water, both in the Horseshoe bend treatment facility and in the Yankee Doodle tailings impoundment. Lime is a powdered mineral that when added to these waters will neutralize the acidity and raise the pH. Metals in the water become insoluble and settle out.
MT “So it comes out of the concentrator, out of the mill, up to the tailings impoundment, and is discharged into the tailings impoundment, pretty much just like how we do now. So that is basically swapping the Berkely pit water for the Horseshoe Bend water.”
Horseshoe bend water is surface water in the mining complex that is acidic and contaminated with metals, like the Pit water, and also requires treatment.
MT “So we’re going to bring 3 million gallons a day of Berkeley Pit water and do the same thing we’ve been doing with Horseshoe Bend water. Now what we’re going to do with Horseshoe Bend water is we’re going to capture it up here by the precip plant, and we’re going to build a pumping system and a pipeline to take it up to the tailings impoundment. If you recall, I said these tailings we’re pumping up here have a whole bunch of excess lime in them, we’re going to mix these two together in a mix box type scenario, just like we did in 1996 to 2000. That’s where the lime meets the acid rock drainage and goes out in the tailings impoundment and settles with the tailings. We’ve just put 8 million gallons of water per day into the tailings impoundment where we have only traditionally put 5 million gallons, so now we have a plus 3 million gallons per day in our water balance. So out of the return water coming down here we’re going to pump an additional 7 mgd of return water, above what we do right now, we’re going to split that 7 mgd out of the return line into what we are calling a polishing facility. So that’s going to take that tailings water, it’s going to polish it to discharge water quality standards. From there we’re going to bring it back around over here by the mill, where there is an existing pipeline from the mill yard, all the way down to Blacktail Creek, and we’ll discharge here at the confluence of Blacktail Creek and Silverbow creek.”
In short, MR is proposing a process that will treat both the surface water and enough Pit water to maintain the level, while satisfying the needs of the active mining operation and discharging 3 million gallons a day of clean water. Mark acknowledged there are uncertainties and having time to refine the process just makes sense.
MT “This takes time, you’re not going to come up to 2023 and start saying “Hmm, what about this?”, that’s not a good way to do it, because if something goes wrong you have no time to adjust.”
And questions remain about the quality of the discharge water. In the past, critics of the plan have suggested scaling might occur. Gypsum can form when the lime interacts with the sulfuric acid in these waters, and can scale the creek where it is discharged.
MT “How does this react with the stream, we’ve done a lot of tests, we’ve done a lot of calculations, is it going to scale the creek? All the calculations and all the testing we do say it won’t, but until you actually do it, you don’t know.”
So this plan takes a proactive approach with shaking down the treatment methods, and will look to prove the effectiveness over time.
MT “It’s gonna take more than discharging for a month. To find this out, You’ve got to discharge through all the seasons, if you can go for three or four years, we get a sense of how the seasonal fluctuations can affect this discharge. But until you do it, until you actually discharge, you don’t necessarily recognize all the problems you can encounter.”
A question on many people’s mind is “will this discharge water be available for restoring flow in the uppermost section of Silverbow Creek?” Local group, the Restore Our Creek Coalition, has made a free flowing stream through this corridor their central demand, but the source for the water has remained undetermined. Here’s John Ray
JR “Could that water then, once the pilot is over, be discharged somewhere else so as to provide water for a restored creek?”
MT “Okay, so I’m going to give you a disclaimer right up front: Montana Resources’ liability, I should say responsibility, ends right at the fence, right there. So we are a party on Mine Flooding, we are not a party on Priority Soils [OU]. I am certainly not a technical expert on Priority Soils, so Im going to tell you what I’ve heard. I don’t know how accurate it is. I’ve heard that discharging to Texas ave., which if it were not for downstream remedy outside of our control, that’s where we would discharge, apparently the remedy downstream of that discharge point at Texas ave is not compatible for this discharge, at this time.”
So, MR is not in a position to say this could be the water source for a restored upper Silverbow creek, but they are not eliminating the possibility, either.
In the end, everyone seems to agree this is a positive development. Some even praised MR and Arco for their civic mindedness. Mark responded:
MT “As much as I’d like to take credit that we’re doing all this just for Butte, it really isn’t, this is just the smart thing to do.”
And it is the smart thing to do. Exploring and demonstrating these solutions to their water treatment challenges with plenty of time for refinement makes sense for MR, as a responsible business and as a good neighbor.
I’m Dave Hutchins reporting for KBMF.
Montana Resources’ proposed Berkeley Pit treatment plan