The decommissioning of the b-zone with ecological engineering : 1994 final report

Abstract

Within the decommissioning scenarios for the B-Zone waste rock pile, a passive treatment approach for seepages which might emerge from the recontoured and revegetated pile is being considered. The muskeg areas to be used are within the waste management area, located between the waste rock pile and the pit or lvison Bay. Design criteria for a scale-up of the process to relegate As and Ni to sediments in these areas are based on 3 years of laboratory and field work. In collaboration with CANMET biotechnology, the forms of As and Ni which would be retained in the wetland sediments were determined and found to be environmentally stable under prevailing condition. Both elements are primarily complexed as organic particulates which are formed in association with the decomposition of added organic materials. In this form, the As and Ni settle to the sediment where they are transformed into insoluble metal precipitates as favourable Eh and pH conditions are encountered in the deeper portions of the sediment. Estimates of removal rates based on the experiments are 0.046 to 0.25 g.m-*.day-’ for As and 0.05 to 0.36 gm*.day” for Ni. Loading from the waste rock pile seepages are estimated as 153-398 kg.yr-’ for As and Xl-1,397 kg.yr-’ for Ni for 1992 to 1994 based on 7 % of precipitation reporting as run-off. An open water muskeg in the vicinity has an area of 2.4 ha and therefore theoretically sufficient to accommodate the annual loadings from the pile. Design criteria for scaleup are presented.