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This September 2014 photo from Google Earth shows the Berkeley Pit and the surrounding area.

Water level rising more slowly than originally projected

This September 2014 photo from Google Earth shows the Berkeley Pit and the surrounding area.
Click on the image to view a larger version.

Since the Berkeley Pit was designated as a Superfund site in the 1980s, things have gone largely as expected. In one instance the site remedy has proceeded at a faster pace than mandated in the 1994 Record of Decision (or ROD, available in its entirety here).

The ROD called for the water treatment plant for the Pit to be designed 8 years before the water level at any monitoring compliance point reached the Critical Level of 5,410 feet above sea level, and completed 4 years prior. In fact, the Horseshoe Bend Water Treatment Plant was completed in 2003, 20 years before water is expected to reach the Critical Level.

Water level modeling has also been accurate. The Pit water level has risen more slowly than originally predicted due to several factors, most notably the capture and treatment of contaminated surface water flowing in from Horseshoe Bend. This water is treated and reused in Montana Resources mining operations, with no water discharged offsite.

The 1994 ROD included projections that estimated that the water level in the Pit would be at 5,204 feet above sea level in 2000; 5,353 feet in 2010; and 5,417 feet in 2015. With a water level of just 5,326.01 feet recorded on August 5, 2015, the Pit water level is nearly 100 feet below early predictions.

The 1994 model also anticipated a rate of fill of about 5-6 million gallons per day. With surface inflow captured, treated, and reused, the average rate has been much lower, about 2.6 million gallons per day. The model currently used by the Bureau of Mines and Geology uses monitoring data to project the filling rate, and over the past 5 years the model’s projections have varied by only a few months.

Some surprises have occurred over the years. For example, the 1994 ROD projected that the water level in the Anselmo mineshaft would be the highest in the Pit system. That was the case until the past several years, when the water level in the Pilot Butte shaft overtook it. Since then the highest water level is typically recorded at the Pilot Butte mine, which was at 5,351.11 as of August 5, 2015.

At 58.89 feet below the Critical Level, it is likely that the Pilot Butte water will hit the critical point first, triggering full implementation of the Horseshoe Bend Water Treatment Plant. This is currently projected to happen in July 2023, a few months later than projected in the last edition of Pit Watch in 2013.

Due to safety concerns related to landslides (or sloughs) along the Pit rim, the Montana Bureau of Mines and Geology has not taken this research boat out on the Pit lake for water quality sampling since 2012.

Drones in the works for water quality sampling

Montana Resources and Atlantic Richfield are currently funding a Montana Tech graduate student to develop a remote system to sample Pit water quality. The student will review options to collect the required data, including aerial or water-based drones that can be operated from the shore of the Pit.

Due to the size of the Pit and the need to collect samples from locations throughout it, the ability to communicate with the drone at a distance of up to 2 miles is essential. Work began during the summer of 2015 and will continue through the 2015-2016 academic year and summer 2016, with final testing during the June and July, and collection of Pit samples by August 2016.

Electrical engineering assistant professor Bryce Hill is supervising the project. He said the device could potentially be used for applications beyond the Berkeley Pit.

Read more on the project from The Montana Standard.

Due to safety concerns related to landslides (or sloughs) along the Pit rim, the Montana Bureau of Mines and Geology has not taken this research boat out on the Pit lake for water quality sampling since 2012.
Due to safety concerns related to landslides (or sloughs) along the Pit rim, the Montana Bureau of Mines and Geology has not taken this research boat out on the Pit lake for water quality sampling since 2012.
The Berkeley Pit, Continental Fault, and the two wells that showed water level changes after a July 2005 earthquake.

Earthquakes did not affect Pit

The Berkeley Pit, Continental Fault, and the two wells that showed water level changes after a July 2005 earthquake.
The Berkeley Pit, Continental Fault, and the two wells that showed water level changes after a July 2005 earthquake.

A 5.6 magnitude earthquake centered near Dillon on July 25, 2005 did not affect the Berkeley Pit. There was no Pit wall sloughing or change in the water levels in the Berkeley Pit, the underground mine shafts, the alluvial aquifer wells, or the majority of the bedrock monitoring wells.

However, two bedrock monitoring wells (A&B) showed changes. Well A showed an initial water level decline of about one (1) foot after the earthquake, and the level stayed lower for a number of days before rising again. Well B, which is located in an area that wasn’t dewatered as extensively by historic mining activities as other portions of the bedrock aquifer had a 9-foot drop in water levels in the month following the earthquake. Recently, the water elevation in Well B is rising again.

One possible explanation for the lower water level in these wells is that the earthquake opened up existing fractures in the bedrock surrounding the wells. Water then flowed into these fractures until the bedrock adjacent to them became saturated. When that happened, the water levels began to rise again.

Since the July earthquake, there have been two additional quakes in the region, one of which was centered in the Butte Basin. Both of these other quakes were considerably smaller in magnitude, and no effects were noted in the Berkeley Pit or bedrock monitoring wells.

This image from the Montana Bureau of Mines & Geology illustrates the connections between historic underground mining tunnels and the Berkeley Pit. After groundwater pumping ceased in 1982, the tunnels, and eventually the Pit, began to fill with water.

Mine Resumption Affects Treatment Plant Operations

This image from the Montana Bureau of Mines & Geology illustrates the connections between historic underground mining tunnels and the Berkeley Pit. After groundwater pumping ceased in 1982, the tunnels, and eventually the Pit, began to fill with water.
This image from the Montana Bureau of Mines & Geology illustrates the connections between historic underground mining tunnels and the Berkeley Pit. After groundwater pumping ceased in 1982, the tunnels, and eventually the Pit, began to fill with water. Click on the image to view a larger version.

Since the last issue of PITWATCH, Montana Resources has decided to resume operations. With the mine going again and with the water treatment plant coming on line, there have been many questions from the community. Here are some answers to reader questions.

Q: How much total water went into the Berkeley Pit since the suspension of mining at Montana Resources?
A: About 7.5 billion gallons of water or an average of 6 mgd has gone into the Pit since MR suspended operations. An average of 3.4 mgd of this total was from the underground workings and storm water flow. An average of 2.6 mgd of this total was from the Horseshoe Bend discharge.

Q: How much water will go into the Pit once mining operations resume completely and the water treatment facility is operating?
A: The Horseshoe Bend drainage flow will be treated in the new treatment plant, and presently, this water will be entirely consumed in the mining operations. The remaining 3.4 mgd of flow from the underground workings and storm water flow will still flow into the Pit contributing to the rising level there. Eventually, when the water level approaches 5,410′ above sea level (expected about 2018), water will have to be pumped from the Berkeley Pit and treated at the Horseshoe Bend facility. Having the plant in place provides assurance that the capability is there when it becomes necessary to treat Pit water.

Q: Where will the treated water go?
A: Current plans are to treat the entire Horseshoe Bend drainage flow at the treatment plant, and then route all of the treated water to the concentrator for use in mine operations. As a result, and for as long as the treated water is used in the mining circuit, there will be no discharge off-site. In the event the mine was to suspend operations again, Horseshoe Bend drainage water would be treated to discharge standards at the plant. Then it would be transported by a pipeline, being constructed along the historic Silver Bow Creek channel (Metro Storm Drain), to its confluence with Blacktail Creek, just west of the Visitor’s Center on George Street in Butte, Montana.

The Berkeley Pit in 1982. The water seen here is surface runoff flowing into the Leonard mine shaft to the right at the Pit bottom.

Pit Facts

The Berkeley Pit in 1982. The water seen here is surface runoff flowing into the Leonard mine shaft to the right at the Pit bottom.
The Berkeley Pit in 1982. The water seen here is surface runoff flowing into the Leonard mine shaft to the right at the Pit bottom.

PitWatch Issue Volume 4, Number 2

Pit Facts Comparison

Compare Pit elevations to those of…
the Belmont Senior Center at 5,605 feet above sea level;
East Middle School at 5,517 feet;
the Butte Airport at 5,525 feet;
the County Courthouse at 5,755 feet.

Compare the depth of Pit water to the height of…
the Anaconda smelter stack at 585 feet;
Seattle’s Space Needle at 605 feet;
Timber Butte which rises 834 feet above the Municipal Golf Course.

Compare the volume of water in the Pit to…
5 ½ Silver Lakes;
83 Basin Creek Reservoirs;
78,000 Stodden Park pools.

Pit Facts At A Glance

Current Water Level: 5,175 feet above sea level
Average Rate of Rise: About 1 foot per month
Critical Water Level: 5,410 feet above sea level
Rim of Pit at Lowest Point: 5,509 feet above sea level
Number of years before water hits Critical Level: (approximate) 21 years
Depth of Water: 702 feet (plus about 200 feet of sediment at the bottom)
Volume of Water: About 30 billion gallons

Montana Bureau of Mines & Geology

Bureau of Mines Publishes 15-year Report on Mine Flooding



PitWatch Issue Volume 3, Number 2

Montana Bureau of Mines & GeologyThe Montana Bureau of Mines and Geology has issued a 15-year report containing water-level data collected from all of the mine flooding monitoring points from 1982 to 1997. The comprehensive document also includes numerous graphs, maps, and historic photographs, plus explanations of the various areas that comprise the Butte Mine Flooding Superfund Site. To request a copy, call 496-4167. In 1999, the Bureau will release a companion report on water quality in these monitoring wells and shafts. Both reports will be updated annually.

Butte, Montana, mine flooding west camp wells, shafts and area of 1960s flooding. The west camp groundwater system is monitored and maintained separately from the Berkeley Pit and connected east camp mines.

Learning About The Westcamp

Butte, Montana, mine flooding west camp wells, shafts and area of 1960s flooding. The west camp groundwater system is monitored and maintained separately from the Berkeley Pit and connected east camp mines.
Butte, Montana, mine flooding west camp wells, shafts and area of 1960s flooding. The west camp groundwater system is monitored and maintained separately from the Berkeley Pit and connected east camp mines. Click on the image to view a larger version.


PitWatch Issue Volume 3, Number 2

Previous issues of PITWATCH have been devoted almost exclusively to the Berkeley Pit and surrounding “East Camp” underground wells and mine workings. Another area of the underground water system called West Camp also deserves our attention.

The West Camp lies southwest of the Berkeley Pit/East Camp drainage and includes the Travona, Emma, and Ophir mine workings. Like in the East Camp, the groundwater in this area has been closely monitored since 1982 to make sure the water does not rise above a certain level—in this case 5,435 feet. Since November 1989, pumping operations have kept the water below this level.

In the late 1950s, the West Camp mine workings were sealed off from the rest of the shafts and drifts on the Butte Hill by a series of barriers, or bulkheads—some made of wood, some cement. Three main cement bulkheads block the connections between the Emma and Original mines at the 1,600-foot level and the Emma and Colorado mines at the 1,400- and 1,000-foot levels.

Anaconda Company crews installed the bulkheads for two main reasons: 1) they were finished mining in the West Camp and 2) they wanted to increase the efficiency of continued operations in the other mines and the Berkeley Pit. The bulkheads allowed them to eventually reduce both the volume of groundwater pumped and the area underground that required fresh air. However, even after the bulkheads were installed, they continued to pump water out of the Emma shaft until 1965.

Over the years, leakage has occurred through the bulkheads, but according to monitoring data, it appears that the West Camp water system remains mostly independent. The groundwater levels in its shafts are several hundred feet higher than those in the other mine workings, indicating that the bulkheads still separate the two areas.

After studying the West Camp in the late 1980s, the U.S. Environmental Protection Agency (EPA) ruled that the water in the Travona shaft could rise to an elevation of 5,435 feet without threatening human health or the environment. However, if the water were to rise above this level, EPA believes it could eventually flow untreated into Silver Bow Creek, and ARCO would face daily fines starting at $5,000 and increasing to $10,000 after 10 days.

To ensure that the West Camp water stays below 5,435, groundwater is pumped from the Travona shaft into a county sewer line and on to the Metro Sewer plant. ARCO pays Butte-Silver Bow about $30,000 a month to treat this water, depending on the volume received. Treatment mainly involves reducing the water’s arsenic content.

Recently, ARCO installed a larger main pump south of the Travona near Centennial Avenue. It can handle 100 more gallons per minute than the current pump (330 compared to 230), and it should go on line sometime this fall. The Travona pump will then become the back-up, used only when needed.

The old pump is due for some downtime, as it has been working at near full capacity for more than a year to keep up with rising water. For example, in September 1997, the Travona water hit 5,432 feet—just 3 feet below the critical mark. The current level, last measured on September 30, is 5,422 feet.