In-pit disposal program for acid generating waste rock Quesnel, Jamie L.; Stogran, S. Wade
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. Prior to commencing the in-pit disposal program, an Environmental Site Assessment (ESA) of the mine property was conducted. The data collected during the ESA was used to develop a reclamation program that would address the site specific conditions that would maximize the on site resources to minimize the costs of the reclamation program. A testing program was conducted as part of the ESA. The data from the testing program was used to determine the acid generating potential of the waste rock and the surface water quality. Two locations containing waste rock were generating acid during the ESA which had not generated acid at the time of closure, in 1975. One location was an acid generating waste rock dump at a ramp location, hi[in] addition, the access road to the ramp area was constructed of acid generating waste rock. The second location was along the shore of a river, where acid generating waste rock had been used for construction of an access road for a pump house. The water quality of the pit water was within the Class 1 and Class 2 Manitoba Surface Water Quality Objectives and there was no evidence of the pit wall rock degrading the water quality. The quality of the pit water determined that a volume of the pit water could be discharged to the environment prior to placement of the waste rock in the pit. Prior to the field program, the effect of placing the waste rock into the flooded open pit was determined by completing a laboratory column test with the waste rock and the open pit water. The results of the program were used to help predict any changes in water quality that would occur during dewatering of the open pit and waste rock placement. The acid generating waste rock was effectively disposed of in the flooded open pit using a simple underwater disposal method.
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