Case study
Berkeley Pit

Achieving major mine water treatment in Montana

Project details
Project name:
Berkeley Pit
Client name:
Atlantic Richfield Company
Bob Kimball
Principal Engineer - Environmental
Randy Huffsmith
Vice President, US Mining Sector Lead
Todd Gift
Energy Market Sector Lead
Key stats
Amount of water in pit:
Approx. 50 billion gallons
Possible treatment per day:
10 million gallons
Wood experience:
40 years in mine water treatment

In early May 2020, with much of the world still in the throes of the COVID-19 pandemic, Wood accomplished a crucial milestone at our Berkeley Pit project in Butte, Montana.

We demonstrated that it is possible to treat 10 million gallons per day (MGD) of water circulating at the Butte mine flooding site, to the standards required for discharge of that treated water into Silver Bow Creek, one of the many headwater streams that drains into the Clark Fork of the Columbia River. It was a milestone in a pilot project conducted under the oversight of the US Environmental Protection Agency (EPA) and the Montana Department of Environmental Quality (MDEQ).

The pilot project objective is to test methods to actively manage and treat water that has been flowing into the pit since 1982, when Atlantic Richfield Company closed the pit and stopped dewatering the mine. At one mile long and half-a-mile wide, the Berkeley Pit currently holds about 50 billion gallons of water, much of it acidic with concentrations of heavy metals, including copper, iron, arsenic, cadmium, and zinc. Water levels in the pit are approximately 150 feet below the natural level of the groundwater table, and groundwater currently flows towards and into the pit.

We contracted with Atlantic Richfield to design and construct a mine water treatment and polishing plant that could achieve the stringent criteria mandated by the EPA and MDEQ for discharging treated water into the local waterway.

Experts in industrial water

With 40+ years of expertise in mine water treatment, Wood has built more of these plants than any other company in the world. In this case, Atlantic Richfield needed a flexible and cost-effective solution, capable of treating both metals and dissolved salts to comply with the standards for discharge.

Our design includes multi-media filtration, followed by reverse osmosis treatment, as needed, to meet the effluent discharge criteria. The plant was built with the flexibility to operate in various configurations and the amount of water treated with reverse osmosis can be adjusted as water quality conditions change.  Treated water and stream flow rates are monitored, and effluent discharge is managed to meet effluent compliance discharge standards for metals, toxicity and other parameters.

Facilitating quicker client action

We fast-tracked our work on the project to enable initial operation within 15 months from contract agreement to initial off-site discharge. That timeframe included design, construction, commissioning, and startup. It also included an EPA-mandated two-week demonstration period, where we discharged back into the Butte mine flooding site– to demonstrate not only that the plant operated as intended, but also that we were meeting discharge compliance standards.

Wood’s ability to perform more than 90% of the work from design through operations was key, enabling our client to begin controlling water levels in the pit ahead of schedule.

The project began to release approximately 3 MGD of treated water into Silver Bow Creek on 30 September 2019. Because approximately 3 MGD of water typically flow into the pit, the treatment system could be used as part of a larger project to slow or stop water levels in the Berkeley Pit from rising. The discharge rate rose to an average of about 4-6 MGD until May 2020, when a demonstration test showed that it is possible to treat up to 10 MGD.

panorama of construction on mine site at sunset

Teamwork & commitment

Wood’s engineers and constructors collaborated as one team to overcome numerous challenges during execution of the project, including pouring concrete and erecting the polishing plant in sub-zero temperatures to meet our client’s aggressive schedule.

We still have a large team assigned to the project and will continue actively managing onsite operations through late 2023, to ensure its continued success. Even today, we perform plant operations on a 24/7/365 basis, and by the end of January 2021, had achieved 100,000 hours worked without a recordable safety incident.

We also continuously monitor the effluent for various water quality parameters and collect 24-hour composite samples for laboratory analyses to confirm compliance with the Butte Mine Flooding Operable Unit’s Consent Decree Discharge Standards.

As we worked through start-up operations in 2019 and 2020, the daily volume of treated mine water discharged into Silver Bow Creek ranged from 0 to 10 MGD, with average flows typically in the 3.6 to 8.1 MGD range. In 2021, Wood is continuing to improve pilot plant operations, and to increase the average volume of water treated for release to the creek. By the end of February 2021, we had released a grand total of 2.8 billion gallons of treated mine water into the creek, without exceeding discharge standards.