English

Abstract

A passive treatment study involving eight bench-scale biochemical reactors (BCRs) was conducted at the Elizabeth Mine Superfund Site near South Strafford, Vermont from April 2005 through October 2006. The bench BCR cells are vertical flow reactors that were fabricated from 200 liter plastic drums; the cells contained different mixtures of organic media developed with local sources of wood chips, sawdust, crushed limestone, and cow manure. The abandoned Elizabeth Mine consists of underground workings, open cuts, pit lakes, and multiple mine waste piles (tailings, waste rock, and process residues), all of which discharge mining- influenced water (MIW) with elevated concentrations of heavy metals, including Fe, Al, Cu, and Zn, into a tributary of the Connecticut River. A portion of the site is listed on the National Register of Historic Places; the mine supplied the Union with Cu during the Civil War. It closed in the 1950's. In 2005, four of the bench BCR cells accepted mildly acidic MIW from the South Open Cut, whose pit lake chemistry has not discouraged local college students from swimming in it despite a pH of 3. Another four bench BCR cells accepted leachate MIW from an abandoned tailings storage facility, TP-1, whose chemistry is much more aggressive than the South Open Cut water. The eight cells remained on-site throughout the winter, where they were routinely exposed to sub-freezing temperatures. In April 2006, the four South Cut cells were transported to the TP-1 area. The eight bench cells treated comparable MIW chemistries for 26 weeks during 2006. This paper asses the performance of a passive treatment system when the reactors are subjected to sustained sub-freezing temperatures followed by dramatic changes in MIW chemistry. The discussion highlights operational challenges such as vandalism and construction challenges in a remote setting, as well as performance data from 2005 through 2006. The appropriateness of the technology for the passive treatment of MIW at the two sites will be discussed.