English

Abstract

Mining wastes comprised of heavy metals and arsenic and deposited along Silver Bow Creek downstream of Butte, Montana have posed a threat to human health and the environment for over 100 years. Under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), the State of Montana has undertaken the remediation of more than three million cubic meters of mine waste deposited along approximately 40 kilometers of Silver Bow Creek and its floodplain. During remediation, mine waste is excavated from the stream and floodplain and the waste is placed in a regional repository or a local repository constructed for the project. The stream and floodplain have been rebuilt to restore their natural functions and maintain streambank stability during vegetation reestablishment. This paper presents results of water quality monitoring on Silver Bow Creek. Surface water and groundwater quality have greatly improved in the remediated reaches compared to pre-remediation conditions although copper and zinc still frequently exceed aquatic life standards. Some water quality problems persist including the elevated nutrient levels originating at the Butte wastewater treatment works and the elevated copper and zinc concentrations in groundwater, which affect aquatic life in surface water systems.