The East Helena Site has undergone many changes over the past 20 years due to remediation activities and the 2001 plant shutdown.
Some of these remedial activities included:
Partial remediation of the acid plant and speiss-dross process water facilities in the late 1980s-early 1990s.
Dredging of sediments from Lower Lake in the mid-1990s.
Elimination of the plant process fluids circuit.
Removal of the various soil, sediment and ore stockpiles from the plant site and placement in the CAMU I cell in the early 2000s.
Construction of slurry walls at the Acid Plant Sediment area and Speiss/Dross area.
The plant demolition program with all wastes being placed in a second CAMU II.
The existing site infrastructure, including plant site structures, ground surface conditions and underground utilities, may have implications for surface water/groundwater flow, contaminant transport, and access for sample collection and testing at the site.
Since 2005, the EPA (NRMRL Ada, Oklahoma) has been conducting a pilot study for in-situ groundwater treatment using Permeable Reactive Barrier (PRB) technology. The pilot-scale study uses zero-valent iron in the PRB in treating arsenic-contaminated groundwater.