The Evening Star Mine in Neihart, MT, consists of mine process buildings, mill tailings and waste rock areas, an existing repository, and a discharge at the mine entrance. The entrance discharge water originally flowed downhill to a culvert under a highway and into a creek. The culvert was filled with silt, causing water to flow over the highway at times. Removal activities at the Evening Star Mine site included systematically demolishing two dilapidated historical mine processing buildings, excavating contaminated soils from the demolished building footprints and hillslope, and excavating a catchment basin and drainage channel for routing of the mine entrance discharge water to a gulch adjacent to the site.
Approximately 3,000 cu. yds. of excavated soils were hauled into the existing repository. The EnviroBlend® CS product was selected as the treatment reagent for the lead-contaminated soils by the EPA On-Scene-Coordinator (OSC) after successful treatment was demonstrated in a bench-scale treatability study.
EnviroBlend® CS was applied by spreading supersacks around the repository area and mixing them with the soils via an excavator and bulldozer. A total of 43 cu. yds. of EnviroBlend® CS was mixed with the estimated 3,000 cu. yds. of excavated contaminated soils. Sample results from the contaminated soils in the repository prior to treatment and post-treatment indicate that EnviroBlend® CS showed a decrease in the leaching of lead as determined by the Toxicity Characteristic Leaching Procedure (TCLP). Once the contaminated soils and EnviroBlend® CS were thoroughly mixed and sampled, the repository was graded to ensure there would not be water ponding on the repository, then backfill and restoration activities commenced.