April 1998

Active Mining in Butte and the Berkeley Pit
PitWatch Issue Volume 3, Number 1

We can explain some, but not all, aspects of the relationship between the Berkeley Pit and Montana Resources (MR), the corporation actively mining here in Butte. As you may recall, last year MR and ARCO hammered out an agreement on Berkeley Pit clean-up responsibilities, but the details were not made public. Here's what we do know:

The Present

Horseshoe Bend. For the past two years, MR and ARCO have been diverting and treating the stream of water that once flowed directly into the Berkeley Pit from the northeast. The Horseshoe Bend diversion project has reduced by about half the amount of water entering the Pit. MR reuses this water in its concentrating operations. MR and ARCO share the project's annual operating cost of about $2 million. Around $1.6 million of that goes toward buying and transporting lime, which is used to treat the water.

Continental Pit Dewatering. From March through October, MR pumps groundwater out of the south end of the Continental Pit to keep the area dry for future mining. Starting this summer, the company may begin pumping additional water out of the north end of the pit, with all water routed to the MR concentrator. This pumping diverts water that could otherwise flow into the Berkeley Pit from the east.

The Future

Monitoring Program Expansion. Over time, the monitoring well system will be expanded south and east to cover the entire Berkeley Pit/Continental Pit Complex, rather than just the area around the Berkeley Pit. This expansion will be necessary because groundwater pumping at the Continental Pit will eventually take place at an elevation lower than the water level of the Berkeley Pit. Pumping now occurs about 90 feet above the Berkeley Pit water level, but over the next 20 years, MR plans to expand the Continental Pit eastward and southward and mine it down to 4,986 feet—166 feet below the current Berkeley Pit water level (all USGS elevations).

When this new low spot is created, some water that would otherwise flow west toward the Berkeley may instead start flowing east toward the Continental. Water levels in the monitoring wells between the two pits (such as Well H) will be affected by this change, although exactly how they will react is unknown. Most importantly, however, all water will still be confined to the mining area with flow going toward the two pits.

Central Zone Mining. MR may also expand active mining westward into the Central Zone area between the two pits. Five bedrock monitoring wells (H, C, D1, D2, and DDH-2) lie within this zone and would be mined out. The Continental Fault, which runs along the Continental Pit's current west border, would also be mined out, eliminating what is now a partial groundwater barrier between the two pits. MR officials said the Central Zone is rich in copper, but they also admitted that a great deal of research must be done to determine the feasibility of mining there.

High Water History
PitWatch Issue Volume 3, Number 2

When the Anaconda Company stopped pumping groundwater out of the West Camp in 1965, the water level in the Travona quickly climbed to over 5,500 feet. Water started seeping into basements in the area bounded by Iron Street in the north, Front Street in the south, Montana Street in the west, and Maryland Street in the east. Surface water seeps were also observed north of Centennial Avenue between Montana Street and Missoula Gulch. In response, what became known as "Relief Well No. 21" was installed close to the spot where today’s new main pump is located. Keeping the Travona water more than 70 feet lower than it was back in 1965 should ensure that this case of ‘high water history’ won’t repeat itself.

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.

Bureau of Mines Publishes 15-year Report on Mine Flooding
PitWatch Issue Volume 3, Number 2

The 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.