OU15, Mill Creek: The remedy, selected in 1987, included permanently relocating all Mill Creek residents, removing demolition debris and contaminated soils for later disposal, regrading and replanting areas disturbed by relocation/demolition activities, monitoring and maintaining the vegetation, and controlling access to the area. Construction of the remedy finished in late 1988. Operation and maintenance activities are ongoing.
OU11, Flue Dust: The remedy, selected in 1991, included stabilization of about 316,500 cubic yards of flue dust, placement of the treated materials in an engineered repository, long-term maintenance and monitoring, and institutional controls. The remedy required that the repository include a liner, leak detection and collection system, groundwater monitoring wells, and a cap. Construction of the remedy finished in September 1996. Operation and maintenance activities are ongoing.
OU7, Old Works/East Anaconda Development Area: The remedy, selected in 1994, included placement of engineered covers over waste, treatment of soils, surface water controls, upgrades or repairs to streambank levees, replacement or repairs to bridges, institutional controls, long-term monitoring and preservation of historic features. OU7 consists of six subareas. Construction is complete at five of the six areas. Construction at the sixth area, the Industrial Area, is nearly complete.
OU16, Community Soils: The remedy for residential soils, selected in 1996 and modified in 2013, included removal of arsenic-contaminated soils and replacement with clean soil. This remedy also called for the cleanup of future residential soils through institutional controls. The remedy for commercial/industrial areas and the active railroad area included placement of engineered covers. Construction of the remedy was finished in 2010. Operation and maintenance activities are ongoing.
The 2013 modification to the Community Soils remedy included cleanup of lead-contaminated residential soil, expanding the institutional controls program and development of an interior dust abatement program. Implementation of this remedy began in 2015 and is ongoing.
OU4, Anaconda Regional Water, Waste and Soil: The remedy, selected in 1998 and modified in 2011, included consolidation of miscellaneous waste materials, placement of engineered covers over waste management areas, treatment of contaminated soils, storm water controls and institutional controls, including the monitoring and regulation of domestic wells in groundwater areas. A Technical Impracticality Waiver for arsenic in groundwater has been applied to large areas of the site. The OU consists of 15 subareas. Remedial action is ongoing at most of the subareas. Over 10,000 acres have been remediated to date. Construction is expected to be completed over the next 10 years.
From the EPA