English

Abstract

In 1929, the Block P Mill and Tailings Site (Block P) near Monarch, MT was the largest lead producer in Montana. When the mill finally closed in 1943 the site left behind a legacy of barren, phytotoxic soil and an ongoing transport of hazardous trace elements into nearby streams. Problems included areas of soil acidity as low as 1.8 pH, and zones with highly elevated concentrations of arsenic, cadmium, copper, lead, zinc and manganese in both soils and tailings materials. As a result, much of Block P, which would have been fully covered with vegetation if undisturbed, was nearly devoid of plant life. In 2001, however, it was decided to clean up and restore Block P to a functional site with natural vegetation. In 2004 and 2005, waste materials were consolidated to a centralized repository. Then, soil amendments (compost, slow-release fertilizer and lime) were added to areas from which tailings were removed, leave-area soils and imported fill materials. In 2005 and 2006, the project site was replanted with native grass and forb seeds, as well as containerized woody plant species that had been propagated from local stock. In July 2008, scientists from ESG monitored the status of revegetation at Block P. Monitoring included assessments of containerized woody plant survival, herbaceous cover, and overall cover on the nine revegetation units at the site. The monitoring results show a continued trend toward successful revegetation. The average containerized woody plant survival, weighted for unit size, was 74 percent, which exceeds the 70 percent project goal. Average herbaceous canopy cover and average total canopy cover of all plants across the entire project site are respectively 46 and 49 percent. The canopy cover of native species far exceeds non-native canopy cover, the cover of weedy exotic species is minimal, and hundreds of woody volunteer plants are appearing. The improvements in vegetation, environmental, and aesthetic values of the Block P Mill and Tailings site are clear and palpable, and demonstrate the efficacy of using appropriate soil amendments and site-adapted native plant species to restore even the most challenging of disturbed sites.