Abstract
In 2004, the Environmental Protection Agency released a Record of Decision for the remediation of one of the nation's largest Superfund sites - the upper Clark Fork River in western Montana. Fluvially deposited hard rock mine, mill, and smelter wastes from the Butte/Anaconda industrial complex have contaminated the river's floodplain. These acid metalliferous materials vary in depth from a few centimeters to at least one meter. Phytotoxic conditions limit agricultural production, barren river banks are unstable, and the amount of Cu released to the river results in both acute and chronic impacts to aquatic receptors. As stipulated in the Record of Decision, exposed tailings are to be removed, backfilled with appropriate quality cover soil, and revegetated. Streambanks will be stabilized by soft engineering - vegetation fabric, willows, logs, and root wads. Areas of impacted soils and vegetation will be treated in place, using careful addition of lime and other amendments, soil mixing, and revegetation. The Record of Decision also specified all land within the site be classified so impacted areas requiring remediation could be identified. Such a classification system, called the Riparian Evaluation System (RipES) uses key indicators of landscape stability and plant community dysfunction to categorize delineated portions of the site as unique polygons. Each polygon is associated with exact location, surface area, waste volume, and other attributes displayed as geographic information system layers over base area photographs. During the 2006/2007 field seasons, the first 80 km of floodplain were classified into one of four major types: (1) streambank length classified by stability type, (2) exposed tailings, (3) impacted soils and vegetation areas, or (4) slightly impacted soils and vegetation areas. For each of these polygons, a RipES score was derived to determine the most appropriate cleanup remedy specified by the record of decision. In this paper, the RipES system will be described and examples of remedial polygons will exhibited. This pre-remedial design approach is applicable to other large metal-contaminated watershed sites.
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