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Numerical modeling of the transport of constituents of concem from the waste rock pile <br />(or temporary ore storage piles) at the SM-18 Mine indicate that the pile poses no <br />significant threat to underlying groundwater resources. The flow and transport <br />model incorporated several conservative assumptions regarding the hydraulic and <br />geochemica] parameters. Most conservative was the assumption that the pore-water <br />in the waste pile contained constituents of concern concentrations that reflected <br />SPLP test conditions. Actual rainwater exhibits a higher pH value (less acidic than <br />SPLP leaching fluid) and would leach constituents of concern at lower concentrations. In <br />addition, for the 1,000 year simulation, concentration of constituents of concern in the <br />waste rock pore water were maintained at initial concentration. In reality, as constituents <br />of concern are leached from the waste rock, concentration would steadily decline in time. <br />The net result is a model that over-predicted the amount and availability of <br />constituents of concern for transport. <br />Even using such conservative assumptions, results of the modeling simulations <br />showed that no contamination reached the underlying groundwater system. <br />[Emphasis added.) <br />The Division commented on the GeoScience October 19, 2005 report in a January 17, <br />2006 letter to Cotter and stated, in part, "The evaluation procedure, which was developed <br />mutually by the operator [i.e., Cotter Corporation and the Division] is similaz to the procedures <br />that the Division has accepted for other sites, including the Occidental Oi] Shell Evaporation <br />Pond.)" <br />In summary, the Division's January 17, 2006 letter review: <br />Identified the rigorous nature of the Synthetic Precipitation Leach Procedure <br />("SPLP") used to test representative samples of ore and waste rock. The Division considered the <br />SPLP test to be conservative for several reasons: <br />(a) The rock samples present an extraordinarily high surface area to the <br />leachant, relative to what would be presented in the field; <br />(b) The tumbling provides maximum exposure to all reactive sites to the <br />leachant; and <br />6 <br />