For many years open pits have been used for the disposal of waste rock. Mine waste disposal has become an environmental issue that is watched closely by government agencies and the public due to the legacies of past mine waste disposal methods.
An in-pit disposal program for acid generating waste rock was conducted by Lakefield Research Limited at an abandoned mine site which operated as an open pit and underground mine. The mine was closed in 1975 and the mine property was included in a provincial park.
The results of the laboratory column test and the anal)1ical results conducted on samples collected during
the field program showed that the column test was a good indicator of what occurred in the field. The column test and field results showed an iron concentration increase of 2 fold. The pH of the water in the column test remained constant and this was also observed in the field. The conductivity of the column test water decreased. This decrease was also reflected in the field results.
Some discrepancies were also noted between the field and laboratory results. The column test showed that
the nickel concentrations would increase, however the field results showed that the nickel concentration
remained stable. The analytical results of the column test results also showed that the Total Suspended
Solids (TSS) concentration levels would increase, but the field results showed that the TSS were not
detectable both before and after placement of the acid generating waste rock into the open pit. This may
have been due to the increased settling time available in the field. It was anticipated at the beginning of the
program that the increased dilution and settling time in the field would result in better water quality than in
the laboratory. Therefore the laboratory was used to determine the worst case scenario which was not
observed during the field program.