Berkeley Pit - Important Dates

Important Dates

• 1994 – September, EPA/DEQ issue Record of Decision (ROD) for Butte Mine Flooding Operable Unit.
• 1996 – April, Montana Resources (MR) and ARCO divert Horseshoe Bend (HSB) drainage water away from Berkeley Pit to slow filling rate, per ROD.
• 2000 – July, MR suspends mining operations due to high energy costs; HSB water allowed to flow back into pit, increasing pit filling rate.
• 2002 – March, USEPA and Montana Department of Environmental Quality (MDEQ) enter into a Consent Decree with BP/ARCO and the Montana Resources Group (known as the Settling Defendants) for settlement of past and future costs for this site.
• 2002 – Fall, USEPA and MDEQ issue order for Settling Defendants to begin design of water treatment plant for HSB water. Settling Defendants issue contract and begin construction of treatment plant.
• 2003 – November, MR resumes mining operations.
• 2003 – November 17, HSB water treatment plant comes on line slowing pit filling rate.