PitWatch | Comprehensive Info on the Berkeley Pit Superfund Site in Butte, Montana

Q:	What is the current water level of the Pit?
A:	As of October 27, 2010, the Pit's water level was 5,290.90 feet above sea level. The water level climbed about 7 feet since the October 2009. The October 27, 2010 water level is about 119 feet below the critical water level.

Is the water level in the Pit rising according to predictions?

No, the water level has been rising slower than predicted. For the past several years, the average monthly water level rise has been about 0.65 feet comapred to a rise of 2 feet per month in the mid-1990s.

Previously predicted factors that influence the declining rate of rise include the diversion of the Horseshoe Bend Drainage water (to the north of the Berkeley Pit; this water is captured and treated at the Horseshoe Bend Plant and used in mining operations) and the widening circumference of the Pit.

The most recent evaluation of monitoring data confirms previous predictions that it will be approximately 2022 when water levels will approach the critical level of 5,410 feet above sea level. The current model and prediction assumes the amount of water flowing to the Pit will stay fairly constant - enough water to raise the level in the Pit about six to eight inches per month.

Also, data indicate that the water level at the Anselmo shaft is still the highest among all the monitoring points in the program, which means it will be used as the trigger to operate the treatment plant at full capacity. As shown on the timeline, a design assessment must be completed four years before the water level in any of the designated wells or shafts is expected to reach 5,410 feet, and the treatment plant must be ready to operate two years ahead of time. This timeline is reviewed and evaluated every year and updated as needed.

Q:	How will this slower rate of rise affect the future?
A:	The slower rate of rise has resulted in changes to the anticipated date at which the critical water level will be reached. Due to the slower rate of rise, the critical water level is currently predicted to be reached around 2022.

How is the Horseshoe Bend Water Treatment Plant operating?

In the six months since the last edition of PITWATCH, the amount of water treated at the plant has increased - from about two million gallons per day to an average of about 3.4 million gallons per day. The reasons for the increase - it appears the drought has finally ended and the Yankee Doodle Tailings Ponds (north of the plant) have fully recharged, after being dried out during the mine suspension from 2000-2003, and there's more water runoff coming from the Horseshoe Bend flow.

All treated water is still being used in Montana Resources, Inc. mine operations as makeup water at the concentrator, and the residual sludge from the treatment process is still being piped to the Berkeley Pit at a rate of 250,000 gallons per day. No water is discharged to Silver Bow Creek. In general, operations are going as expected.

Is Montana Resources "mining" the Berkeley Pit water?

Yes. The company is still recovering copper from the water in the Berkeley Pit.

Since February 2004, 13 million gallons of water per day have been pumped out of the Berkeley Pit and up to a precipitation plant. The water is collected at a depth of 150 feet from the far west side of the Pit below the viewing stand, and is pumped up and around the south and east walls of the Pit to the precipitation plant northeast of the Pit.

The precipitation plant uses a centuries-old technology where the acidic (pH of about 2.5) and copper-rich water flows through piles or "cells" of recycled scrap iron. The process is known as "cementation." The iron in the cells and the copper in the water trade places through a replacement reaction. The iron-rich water is returned to the Pit, creating the waterfall seen on the north rim near the Horseshoe Bend Plant. The product, containing about 70% copper, is dried through a filter press and then sent to an off-site smelter.

Q:	What is the waterfall on the northeast wall of the pit?
A:	Historically, the waterfall was created by water flows from Horseshoe Bend north of the Berkeley Pit, but that water is now treated and used in Montana Resources, Inc. mining operations. Since February 2004, water returned to the Pit from the precipitation plant forms the waterfall.

What is going to happen to the old creek bottom that runs from Continental Drive to Montana Street? Is it safe?

Before the Berkeley Pit was developed, that old creek bottom was the main channel of Silver Bow Creek, and recent studies indicate the creek corridor and surrounding land contain mine tailings. Today the drainage is referred to as the Metro Storm Drain. A French Drain collects contaminated groundwater along the channel, preventing it from contaminating Blacktail Creek or downstream reaches of Silver Bow Creek.

Where can I find more information about alternative clean-up methods that were presented for consideration concerning the Pit?

Several technologies were considered before the Agencies (federal EPA and state DEQ) approved the selected method to treat water from the Berkeley Pit. The official Feasibility Study for this Superfund site detailed a number of water treatment technologies for the Pit and provided thorough evaluations of the pros and cons of each cleanup method. Since then, many organizations and companies have conducted a variety of research projects on alternative clean-up methods. Examples of groups that have requested water from the Pit (through the Montana Bureau of Mines and Geology at Montana Tech in Butte) to support their research include:

EPA National Risk Management Research Laboratory (Cincinnati, OH): treatability studies focused on product recovery;
MSE (Butte, MT): treatability studies associated with the Horseshoe Bend treatment plant;
Montana Tech (Butte, MT): various research projects;
Ion Resolution (Virginia City, MT): treatability studies focused on product recovery;
Virotec (Australia): treatability studies using Bauxsol;
ASARCO Technology Research Center (Salt Lake City);
Wilder Construction (Everett, WA); and
Frontier Geosciences (Seattle, WA).

For more information, visit the website of the EPA's Mine Waste Technology Program.

Could the Pit have any bearing on the water quality of wells near the East Ridge?

There is no connection between the Berkeley Pit water and well water near the East Ridge. The water levels in the Berkeley Pit and the flooding underground mines are well below the lowest groundwater levels in the greater Butte Basin. The Berkeley Pit is the "sink" or lowest water-level point in the basin, and all groundwater near the Pit flows towards the sink. Water levels in alluvial aquifers (loose-sediment aquifers within the valley above the bedrock level) are generally several hundred feet or more above the Pit level, while water levels in the bedrock along the East Ridge and foothills south of Butte are a hundred or more feet above the Pit level. Water quality monitoring of bedrock wells surrounding the Pit continues to show that wells outside the area are not being impacted by rising Pit and mine water levels.

What is the Critical Water Level?

The official "Record of Decision" (called a ROD), issued in September 1994 by the U.S. EPA and Montana Department of Environmental Quality (MDEQ), established the critical water level at 5,410 feet above sea level.

According to the agencies, the 5,410 feet level includes a safety buffer of at least 50 feet, and represents the point at which the Pit water could potentially seep into Silver Bow Creek or into the alluvial groundwater aquifer that supplies some local wells.

The ROD stipulates that the parties responsible for treating the Pit water—BP-ARCO and Montana Resources—must begin pumping and treating Pit water before it reaches this critical level. If they do not comply, they will be fined $25,000 per day. The ROD requires certain actions to be completed, such as upgrades to the Horseshoe Bend Water Treatment Plant to allow it to treat higher volumes of contaminated water, as the critical level approaches.

Currently, water levels in the Berkeley and surrounding flooded underground mines are expected to approach the critical level around 2022.

Does this Critical Water Level apply only to the Pit?

No. Pumping and treating of Pit water must begin when the 5,410-foot level is reached at ANY of the water-level monitoring sites on the Hill, in what is called the East Camp. These sites include the Anselmo, Granite Mountain, Kelley, Belmont, and Steward mine shafts, as well as several other monitoring wells established to the south and the east of the Pit.

Presently, the water level at these sites is about 20-40 feet higher than the level in the Pit. So, the 5410-foot level should be reached sooner at these sites than in the Pit, which means water pumping and treating would begin that much sooner.

When will the Critical Water Level be reached?

It is impossible to predict exactly when the water will reach the 5,410-foot mark. Today, we know the water level in the Pit is 284 feet below the 5,410-foot mark, and it is expected to take about 12 years, until the year 2022, for the water to reach that critical level.

But over time things can happen that may affect the prediction. For example, in 1995, more water flowed into the Pit than was expected, presumably due to higher than normal rainfall.

Over the next decades, we have to keep a close watch on the actual data from the monitoring sites. If the measurements prove to be different from the predictions, the timeline to upgrade the Horseshoe Bend Water Treatment Plant before full-scale pumping begins will have to be adjusted accordingly.

How has the Horseshoe Bend pumping project affected the water level in the Pit?

Now that the Horseshoe Bend pumping station is online, the amount of water entering the Pit has been cut in half. The water level rate of rise has slowed considerably.

Before the diversion project, 3 million gallons of water flowed into the Pit from underground aquifers, and another 3 million gallons of surface water flowed in via the Horseshoe Bend waterfall, which was visible from the Pit viewing stand. On April 15, 1996, BP-ARCO and Montana Resources started diverting this surface water into Montana Resources' tailings ponds.

This action is the first of many that were ordered by the EPA and the MDEQ as part of the ROD concerning the Pit Superfund project.

Q:	Why wait until the water reaches the 5,410-foot level before starting pumping and water treatment?
A:	Many factors, both economic and scientific, affected this decision. Berkeley Pit water poses no human health risk prior to reaching the critical level.

How much water evaporates off the surface of the Pit?

According to Montana Resources, about twice as much water evaporates off the surface of the Pit each year than enters the Pit through rain and snow. About 12 inches of precipitation fall into the Pit each year, and about 23.65 inches evaporate, for an annual net loss from evaporation of roughly 11.65 inches. This water balance translates into an annual average of about 20,000 gallons per day of evaporating water.

Could the Pit ever overflow?

This is one of the most common questions we receive, as people imagine the water rising up and flowing out onto Continental Drive. While no one can say that this could never happen, we can with confidence report that as long as the water levels in the Pit and the associated underground workings stay below the Critical Water Level of 5,410 feet, there is no significant danger of the Pit overflowing.

The more realistic concern is that, if the water levels were left unchecked, contaminated water might flow into the alluvial aquifer, eventually showing up in nearby wells and in Silver Bow Creek. Keeping the water levels below the critical point will prevent this from happening. For an explanation of the underground water flows in the Pit area, refer to the News & Notes section or the Watching the Pit Water section.

Q:	Has the Critical Water Level been changed?
A:	No. The Critical Water Level is still 5,410 feet above sea level. The regulatory officials remain convinced that the situation is safe and under control as long as the water stays below 5,410 feet. Pumping and treatment of the water must be well underway when the water approaches this elevation in the Pit or in any of the bedrock monitoring wells and mine shafts.

What is the water monitoring program?

23 wells and 14 mine shafts supply information about the deep bedrock aquifer. 36 wells provide similar data about the alluvial aquifer, which is much closer to the surface. Each month, scientists manually check and record the water levels in these wells. Twice a year, they collect samples to analyze the water's chemistry. All of this information helps scientists understand where the water is coming from and how it is moving underground.

Have the monitoring efforts revealed any surprises?

Yes. One involves changes in bedrock Well H. The water level of this well is usually about 10 feet above the level of the Berkeley Pit, just like other bedrock wells nearby. But one July, Well H's level started falling, and by September it had dropped about 3 ½ feet. Meanwhile, the Pit kept rising. From December through February, the water levels of the Pit and Well H were just inches apart. Well H is now gaining on the Pit again.

What is the significance of the surprise reading in Well H? It appears to be an isolated incident caused by underground subsidence (shifting of dirt) adjacent to the well. Well H is southeast of the Pit in the middle of the old Pittsmont Mine workings, where the ground is known to be unstable. The water levels in all of the surrounding bedrock wells remain high, indicating that flow is still toward the Pit. It is important to look at the monitoring well system as a whole, rather than focus solely on the performance of a single well.

And Well H is not the only surprise to date. In 1989, the water level in the Kelley shaft dropped two feet in one month, but it, too, recovered. Well DDH-5 also occasionally fluctuates. The monitoring program was set up specifically to detect changes like these. When something unusual turns up, monitoring is heightened at that spot, and scientists determine what action, if any, needs to be taken. At Well H, water levels have been checked weekly since October. On February 18, a special camera was lowered 927 feet into the well to look for abnormalities, and none were found.

Future years will bring many more monitoring well changes, especially in the area between the Berkeley and Continental Pits.

Have there been any major rock slides along the Pit walls?

Yes. Wet weather may have also played a role in the 1998 Pit wall sluff that sent about 3 million tons of rock and dirt into the water. Rising groundwater saturated and gradually weakened that section of the southeast wall, eventually causing it to break away.

Montana Resources, Inc. (MR) is taking steps to stabilize the piles of waste rock that form sections of the Pit walls. Two options are available: The first is to remove material from the tops of the dumps (the crests) to relieve pressure, and the second is to add material to the bottoms of the dumps (the toes) to bolster their foundations.

MR is employing both strategies to minimize future problems. Using a bulldozer, crews shaved the crest of what is called the "Bird Watch Dump" along the Pit's south wall. And to shore up the underwater toe of another dump in the Pit's southeast corner, crews pushed in material from the Bird Watch Dump, plus additional waste rock and dirt from the active Continental Pit.

How would an earthquake affect the Pit and surrounding area?

This question was asked because a series of faults (including the Continental Fault), which are cracks in the earth's crust, run just east of the Pit. The answer would depend, of course, on the magnitude and duration of the quake. A major earthquake most likely would cause material from the Pit's walls to cave in, boosting the water level. And, unfortunately, "earthquake-proofing" the Pit is not possible.

However, Montana Resources, Inc. (MR) is taking steps to ensure the stability of the Yankee Doodle Tailings Dam north of the Berkeley, the east end of which sits directly above the Continental Fault. In 1993, MR hired a San Francisco-based engineering firm to evaluate the dam's seismic stability. The investigators declared the dam "safe" and stated it could likely withstand an earthquake of Richter magnitude 6.5.

The consultants' report also provided specific recommendations for maintaining this level of safety as the dam expands. MR officials said that they have been following the recommendations.

Where is the water in the Berkeley Pit coming from?

The water is naturally occurring groundwater. It started flowing back into the area in 1982 when the central pump station in the Kelley Mine was turned off. For nearly a century before 1982, groundwater under the Butte Hill had been constantly pumped to the surface to allow for underground and open pit mining.

This pumping created a vast cone-shaped area underground that was kept unnaturally dry. The bottom of the Berkeley Pit lies near the bottom of this dry area. When the pumping stopped, the Pit started working like a big sink, drawing water toward it from all directions.

Why is the water polluted?

The water in the Berkeley Pit is a good example of acid mine drainage, which is mainly caused by the high sulfur content in the rock in the Butte Hill. The sulfur reacts with air and water to become sulfuric acid. As this acidic water (pH around 2.5) flows through the underground mine workings and rock fractures, it eats away at the metals in the rocks and dissolves them into the water, leading to high concentrations of potentially toxic material.

When will the water be pumped and treated?

Some pumping and treating is underway. In April 1996, water flow into the Pit was reduced by about half when a contaminated surface flow called Horseshoe Bend was diverted. Horseshoe Bend water is treated with lime and pumped up to Montana Resources, Inc.'s (MR) Yankee Doodle Tailings Pond north of the Pit. From there, some of the water is piped down to MR's concentrator for reuse.

As for the water in the Pit, pumping and treating must start before the Pit water level - OR the water level in surrounding mine shafts and monitoring wells - approaches 5,410 feet above sea level. If present trends continue, the water will approach that elevation around 2022.

What would happen if the water were to rise above 5,410 feet?

Above 5,410 above sea level, the water would not flood Butte by coming up over the rim of the Pit onto Continental Drive. The rim's elevation, at its lowest point, is about 5,510 feet, some 100 feet higher. But above 5,410, scientists believe at about the 5,460-foot level, the water could begin to flow away from the Pit into the cracks and crevices of the groundwater system below the surface, potentially harming the water quality of local wells and Silver Bow Creek.

Who is responsible for treating the water?

The Atlantic Richfield Co., a subsidiary of British Petroleum (ARCO or BP-ARCO) which bought out the Anaconda Co. in 1977, and Montana Resources (MR), the company now mining in the Continental Pit adjacent to the east of the Berkeley, are responsible, along with four other entities affiliated with MR: Asarco, Inc.; AR Montana Corp.; MR Inc., and Dennis Washington. If they fail to pump and treat the water to keep levels below 5,410 feet, the U.S. government (EPA) can take over the project and charge these companies up to three times the project cost.

What is the water quality of the Continental Pit compared to the Berkeley Pit?

Current sampling indicates that the water quality is significantly different in the two pits. The pH of the water in the Continental Pit is about 6.5-7.0, which is much more neutral than the water in the Berkeley Pit, which has a pH of about 2.5. Also, the levels of arsenic, copper and cadmium are many times less in the Continental Pit water.

In the future, as part of the reclamation effort, the Continental Pit water will likely require some management to sustain water levels and treatment to remove metals. However, that treatment should be less costly and less complicated compared to the Berkeley Pit.

Is water from the Berkeley Pit expected to flow to the Continental Pit?

Presently there is no evidence that water is moving from the Berkeley Pit to the Continental Pit or that there is any underground connection between the two pits. Right now, the mining level in the Continental Pit is below the water level in the Berkeley Pit. In the future, by the end of the mine life, the bottom of the Continental Pit may be as much as 400 feet below the water level in the Berkeley. But even then, there is no expectation that Berkeley water will enter the Continental Pit.

Why is the water in the Pit allowed to rise higher and higher? Why wait to pump and treat contaminated water?

PITWATCH readers have asked these questions repeatedly. It's hard for residents to understand why something isn't being done right away to deal with the toxic water in the Pit. For the parties responsible for the problem and for any adverse impacts from the water, the reasons for waiting are a combination of science, time and money.

In general, the Berkeley Pit is considered a big holding tank with a well-defined capacity. Based on years of scientific study, the EPA and MDEQ have determined that the water in the Pit does not and will not pose a threat to human health or the environment as long as the level stays below the 5,410 feet above sea level. This conclusion is part of the Record of Decision that dictates Berkeley Pit management. As owners responsible for water treatment, Montana Resources and ARCO are trying to use the Pit "storage space" in the most effective way.

Any delay reduces costs to operate and maintain a treatment facility. Annual costs are expected to exceed $3 million, so for as long as possible, it is considerably cheaper to manage the Pit as storage space. Also, some scientists believe that letting the water rise to maximum safe levels will eventually lower the water's acid and metals content by reducing the amount of sulfur-bearing rock that is exposed to air. That may improve water quality and make it cheaper to treat the water when the time comes.

In addition, the delay allows time for new treatment technologies to be perfected. With the benefit of time, the hope is that innovative, cost-effective technologies will emerge to recover valuable metals in the water, or at the very least, reduce the amount of toxic sludge produced.

For now, the emphasis is to monitor the water carefully. As storage space in the Pit begins to run out, safeguards are in place to make sure the Horseshoe Bend Water Treatment Plant will be ready to treat the needed capacity of contaminated Berkeley Pit water. The timeline for Berkeley Pit Management is reviewed and evaluated by the Agencies every year and updated as needed.

Q:	Who would be responsible for water treatment if the mine closes permanently?
A:	Under a clear EPA order, both Montana Resources and BP-ARCO are responsible for treating Berkeley Pit water. Under the Superfund law, if one company is unable to pay its share, the other company must pay all the costs of cleanup. The company paying the full cleanup costs would likely take some legal actions to recover a fair share of those costs from the other company.