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that pollutants will be diluted at least 19 times before reaching a stream (see aluminum, Table 1 ). For ore piles, it should be demonstrated that contaminants will be diluted at least 50 times before reaching groundwater (see selenium, Table 1). I understand that the operator at the SM-18 mine. already has constructed a small runoff retention feature below the ore piles to establish some protection for groundwater. This pond should retain all of the nno anticipated from some design storm: I would recommend at least the 100-yeaz storm. If water in this pond is meant to evaporate rather than leach slowly into groundwater, there should be measures in place to prevent evaporite residues in the pond from becoming blowing dust. Land application of the fluids maybe acceptable provided the pemut is revised appropriately. There is precedent in the Division allowing dilution of contaminants with fresh water or groundwater in order to meet groundwater numeric protection levels. If dilution is selected as a means of meeting groundwater numeric protection levels, the operator should construct a model showing what dilution rates can be expected if rain or snow melt drives pollutants from the rock piles into local groundwater. Numeric protection levels may also need to be developed if high ambient levels aze to be considered in the dilution calculations. The division should carefully evaluate the proximity of ore and waste rock piles to surface and groundwater resources. This will require site-specific examinations that consider proximity to streams, proximity to groundwater, size of ore and waste rock facilities, duration of their exposure to weathering, and reclamation and closure techniques. Discussion: The Synthetic Precipitation Leach Procedure (EPA Method SW-846) requires adding 2 liters e€~lightly aeid~ed-deioai2ed ~vater{initiai~H-=-4.2-using amixture-of~z~64 and-I3N03-(sulfinic~trd nitric acid) to 100 g of powdered sample, and agitating the mixture end-over-end at 302 rpm for 18 hours. It is recognized that the SPLP is an aggressive test that tends to overstate the amount of pollutants that may derive from a rock mass under natural conditions, unless their natural state is to be crushed as in the SPLP. Test results for this study are considered maxima that might be expected under worst-case conditions. Although the test is chemically more aggressive than natural conditions might allow, the tests do indicate what pazameters are likely to appear under natural conditions. Operators may wish to focus on these parameters primarily to m;n;mize the release of contaminants from their operations. Overall, I believe the facilities need to examine their ore and waste handling procedures in context of potential exposure to ground and surface water. Cc: Bruce Humphries Carl Mount Wally Erickson Bob Oswald Kate Pickford Allen Sorenson 3