2009-05-19_REVISION - M1981021 (32)

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Section 4 Potential for Rock to be Toxic-Forming • Exhibit 4-3 summarizes the results of, the modeling effort for the West Sunday and Topaz Mines on an annual basis. Additional detail, including daily percolation estimates are included in Attachment 6. The estimate was completed for the West Sunday and Topaz Mines and for average annual precipitation and the wettest year on record. Exhibit 4-3. Summary of UNSAT-H modeling results • Model Run Annual Annual Annual Annual Annual Annual Potential Precipitation Actual Runoff (in.) Infiltration Percolation ET (in.) (in.) Evap. (in.) (in.) (in.) West 67.0 12.8 12.7 0.0527 12.7 0.0103 Sunday- Average Precipitation West 67.0 19.9 18.07 0.190 19.7 0.0106 Sunday- Wettest year on Record Topaz- 67.0 12.8 12.7 0.0185 12.7 0.00822 Average Precipitation Topaz- 67.0 19.9 18.1 0.0619 19.8 0.00849 Wettest year on Record Based on the UNSAT-H simulations, the estimated percolation through the rock piles is estimated to range from 0.008 to 0.011 inches per year. The simulations show the importance of evaluating upward movement of water from the rock piles caused by evaporation because the majority of water that infiltrates the surface of the development rock piles evaporates in the semi-arid environment present at the Sunday Mines Group. The UNSAT-H simulations suggest that significant percolation from the base of the development rock piles is unlikely. However, a small amount of percolation is estimated for all simulations. The simulations further suggest that infiltration of precipitation followed by upward evaporative flux of water stored within the development rock areas are dominant mechanisms controlling the volume of percolation through the development rock areas. Minor differences in the physical characteristics of the development rock from West Sunday and Topaz mines as well as the magnitude of annual precipitation are less important controls on the expected volume of percolation. Additional sensitivity analyses were also conducted and indicate that the model is not particularly sensitive to modifications in convergence parameters, node spacing or initial moisture conditions. Detailed sensitivity analysis information is presented in Attachment 6. Summary of Findings: The water balance estimates and the UNSAT-H simulations indicate that . significant percolation from the base of the development rock piles is unlikely. These evaluations further indicate that infiltration of precipitation followed by upward evaporative Cm 4-13 TA64986 3anison Mines%Task Order 3 - DMO Sampling and Maysis PlanlTask 3.12 - Soil, Ore, Rock Data Assessment ReportlSunday Rock Repornfinal reportlReporhFinal Sunday Mines Group Soil Ore Rock Data Assessment Report_951509.doe