The Central Treatment Plant (CTP) was inherited by EPA in 1995 through a series of bankruptcies and ownership changes of the Bunker Hill Smelter Complex and the famous Bunker Hill Mine within the epicenter of the Bunker Hill Superfund Site. The CTP, was originally constructed in 1974 by the Bunker Hill Company to treat smelter complex industrial waste waters and acid mine drainage flows from the Bunker Hill Mine. Until 2017, the plant’s original equipment remained and was relied upon, with the exception of the installation of new conveyance lines and a lined storage pond constructed in 1994 and 1999, new lime silos, a new lime feed system and the addition of a control tower along with computer operator workstations in 2005. Meanwhile the nearby Bunker Hill mine remained under private ownership and continued to produce 1400 or greater GPM of acid mine drainage (AMD) that continued to need to be treated. Flows would increase substantially, sometimes double, during spring freshet and the pH would drop to corrosive levels.
Recently EPA has constructed a new treatment system to replace the worn out aeration basin, polymer injection system, lime feed system, new System Control and Data Acquisition system, and multi-media sand filtration. The work included the construction of a groundwater collection system and the entire system was constructed under an Operate/Design/Build/Operate contract administered by the Corps of Engineers. Continued operations were critical to the implementation of this project as the AMD from the Bunker Hill Mine needed to be treated before, during, and after the CTP upgrades were being constructed. The project is now in its final months of shakedown testing prior to operations shifting to the State of Idaho.
This presentation will provide an overview of the new groundwater collection system and CTP and the influent sources along with some of the technical challenges that have been encountered.