By Tim Hilmo, Project Manager, Atlantic Richfield Company
With minimal headlines, treated water was discharged from the Butte Mine Flooding site to Silver Bow Creek for the first time starting on September 30, 2019. Water from the Berkeley Pit is being treated at the Horseshoe Bend Water Treatment Plant, then the water helps convey Continental Mine mill tailings to the Yankee Doodle Tailings Impoundment. Then water from the Yankee Doodle Tailings Impoundment is sent through miles of “gravity flow” pipelines to the new Polishing Facility located just east of Shields Avenue (adjacent to the Berkeley Pit viewing stand). The Polishing Plant is staffed 24 hours a day to manage the water treatment processes and ensure the water treatment plant is operating as designed. Once water is treated to meet the strict regulatory standards that apply to this plant, the water is discharged into Silver Bow Creek. Water has been treated and discharged on an ongoing basis since September 30, 2019 at rates between 4-6 Million Gallons per Day (~6-9 Cubic Feet Per Second). In total through the end of January 2020, roughly 600 million gallons have been treated to the required standards and released so far. That’s over 900 Olympic sized swimming pools of water!
Atlantic Richfield Company constructed the Polishing Plant, in cooperation with Montana Resources, over the winter of 2018/2019, while Montana Resources constructed pump houses and installed piping to convey these waters around the site. Construction was completed in September 2019 when system performance testing and treatment verification began. Strict standards for metals concentrations, pH, and toxicity were established by the US EPA and Montana DEQ in the Butte Mine Flooding Consent Decree, to assure protection of surface water and aquatic life. These requirements include daily compliance sampling of the treated water. After a two week demonstration period of testing and agency review of the compliance sampling, approval was granted of the treatment process, and the much-awaited release of treated water to Silver Bow Creek began on September 30, 2019. For the first time in over 37 years, the water level in the Berkeley Pit is being controlled!
The treatment system is anticipated to operate for several more years as part of the ongoing Berkeley Pit and Discharge Pilot Project being implemented by Atlantic Richfield Company and Montana Resources under the Butte Mine Flooding Consent Decree. Daily sampling will continue as a very close eye is kept on the quality of the treated water.