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^ caps, covers or diversions to minimize infiltration of rain water or snowmelt, or ^ limited holding times, i.e. limit the time available for precipitation to contact the ore or waste rock. For the Division to allow waste rock to remain unprotected and still assure that impacts to the hydrologic balance have been minimized, the operator should show that pollutants released from either ore or waste rock would be diluted sufficiently prior to entering groundwater at some use point or prior to meeting a classified stream. Because selenium concentrations exceed both ground and surface water standards by the largest percentage factor, selenium is used to derive the dilution values necessary to demonstrate minirnization of impacts to the hydrologic balance (see Table 1). For waste rock, it must be demonstrated that pollutants will be diluted at least 46 times before reaching a stream (see lead, Table 1). I understand that the operator at the JD Mines already has constructed a small nmoffretention features below the waste piles to establish some protection for groundwater. This pond should retain all of the runoff 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 evaporate residues in the pond from becoming blowing dust. Land application of the fluids maybe acceptable provided the permit 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 are to be considered in the dilution calculations. The Division should cazefully 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 of slightly acidified deionized water (initial pH = 4.2 using a mixture of HzSO4 and HNO3 (sulfuric and 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 testis chemically more aggressive than natural conditions might allow, the tests do indicate what parameters aze likely to appear under natural conditions. Operators may wish to focus on these pazameters primarily to minimize 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 Cazl Mount Steve Shuey 3