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meeting a classified stream. Because selenium concentrations exceed both ground and surface water <br />standazds by the lazgest percentage factor, selenium is used to derive the dilution values necessary to <br />demonstrate minimization of impacts to the hydrologic balance. For waste rock, it must be demonstrated <br />that pollutants will be diluted at least 19 times before reaching a stream (see Aluminum). For ore piles, it <br />must be demonstrated that pollutants will be diluted at least 50 times before reaching groundwater. <br />I understand that the operator already has constructed a small runoff retention feature below the ore piles <br />to establish some protection for groundwater. This pond should retain all of the runoff anticipated from <br />some design storm: I would recommend at least the 100-year storm. If water in this pond is meant to <br />evaporate rather than leach slowly into groundwater, it will be necessary to have measures in place to <br />contend with the insoluble residues in the pond after mining to preclude it from becoming blowing dust. <br />Land application maybe acceptable. <br />There is precedent in the Division to allow dilution of pollutants in order to meet groundwater numeric <br />protection levels. If dilution is selected as a means of meeting groundwater those levels, the operator will <br />need to construct a model showing what dilution rates can be expected if rain or snow melt drives <br />pollutants from the rock piles into local groundwater. <br />It is recognized that the SPLP is very aggressive test that generally overstates the amount of pollutants <br />that may derive from a rock mass under natural conditions. The values provided from the tests are <br />considered maxima that might be expected under worst-case conditions. Nonetheless, the tests are <br />indicative of leachates that will appeaz under natural conditions, and operators should take precautions to <br />minimize the release of pollutants from them. <br />~~ I will be available to the operator or their consultants to discuss what information we might need to cover <br />these requirements. <br />Cc: Cazl Mount <br />Russ Means <br />