Lower Area One — Phase I: Remediation of a metals tailings contaminated site

A case history of the Lower Area One (LAO) CERCLA Site remediation is presented. Past ore processing deposited metals-laden mine waste in the floodplain at the ground water and surface water discharge point for the Silver Bow Creek basin surrounding Butte. In 1992 U.S. Environmental Protection Agency (EPA) and the Atlantic Richfield Company (ARCO) began the reclamation of the site through an Expedited Response Action (ERA) under CERCLA. The work was to be done in a phased manner. The first phase, (Phase I) consists of removing most of the mine waste and is currently being completed. As part of the Phase I activities, Silver Bow Creek is being reconstructed using an elevated gradient. The elevated channel, in conjunction with ground-water hydraulic controls, minimizes the potential for stream flows to collect potentially contaminated ground water. In 1998, the project will enter the Phase II (post-removal) monitoring period during which the effectiveness of the new site hydraulics and post-removal water quality will be evaluated. Phase HI will complete final remediation and land use requirements. The focus of this case history is on Phase I activities.