British Columbia Mine Reclamation Symposium

Treatment of runoff containing suspended solids resulting from mine construction activities using sedimentation ponds Clark, J. P.


Sedimentation control during mine construction is attracting increased interest and regulation. The significance of this for the proponents of new mines and regulators suggests the need for more detailed planning and testing prior to construction for activities that could potentially generate sediment. The topic of designing the appropriate sedimentation pond size to remove nonfilterable residue (TSS) from contaminated runoff is discussed. Designing the appropriate pond size has been based on a "traditional" approach and methodology in BC which has assumed that the surface area of the pond should be large enough to settle out approximately 10 fi and larger particles for the maximum ten-year, 24-hour rainfall event. This approach is not related to the particle size distribution of the soils to be disturbed nor the soil erosion rates, and therefore cannot predict the pond discharge quality. If the "traditional" design methodology results in regulatory compliance, it is merely a fortuitous outcome of the design process, and a reflection of the absence of "abundant fines" in the soils. Modification to this "traditional" approach is suggested so that we predict the optimum surface area of the sedimentation pond, the need to use settling aids and whether the pond discharge will meet statutory requirements. The appropriate time to perform these predictions and testing is recommended; during the review stage (under the Environmental Assessment Act in BC). Although this approach is not novel, it will hopefully enable the more blatantly problematic soils to be identified and receive more focus prior to actual construction (e.g. preparations to select and obtain approval for the use of effective and non-toxic flocculants well ahead of the construction taking place, and placing more emphasis on planning sedimentation control strategies).

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