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Calculation Brief <br />Estimation of Percolation Through Development Rock Areas Using UNSAT-h <br />• <br />Consideration of upward unsaturated flow is critical for accurate simulation of <br />percolation through mine rock piles in semiarid and and environments (Swanson et <br />al. 2000). Numerous workers are applying rigorous unsaturated flow models based on <br />Richard's equation for simulation of unsaturated flow through mine waste piles (e.g. <br />Ford et al, 2000; Swanson et al., 2000, Fala et al., 2005). Benson et al. (2006) provides <br />basic requirements for unsaturated flow models including: <br />¦ the model must simulate unsaturated flow in a rigorous manner (i.e. must solve <br />Richards equation); <br />¦ The model must include a surface boundary simulating soil-atmosphere <br />interactions (precipitation, infiltration, evaporation, runoff); and <br />¦ The model must integrate climatic data into the solution. <br />UNSAT-H meets these requirements. Although the EPA Hydrological Evaluation of <br />Landfill Performance model (HELP) has been used in the past for these types of <br />estimates, HELP does not meet the criterion of rigorously simulating upward <br />movement of water through the vadose zone through application of Richard's <br />equation. The UNSAT-H model is a fortran-based finite difference 1-dimensional <br />model that simulates liquid water flow using Richard's equation and water vapor <br />• diffusion using Fick's law. UNSAT-H also is capable of simulating heat flow and <br />plant transpiration, although these options were not applied in this estimation. <br />Additional details of the calculation methods and procedure applied by UNSAT-H <br />are presented in Fayer (2000) and are not discussed further in this document. This <br />discussion provides a summary of the modeling approach including description of <br />model nodes and boundary conditions, description of climate data sources, and <br />definition of soil characteristics. Detailed model input files, input data tables, and <br />model output files are presented as attachments to this document. <br />The UNSAT-H model incorporated the following: <br />The model used a 3 meter thick development rock profile, and included 111 nodes. <br />The nodes are spaced very close in the upper portion of the soil profile and are <br />more widely spaced in the deeper portion of the profile. The node spacing is <br />included in the input file and additional information is included in the input list <br />file. Input files and input list files are included in Attachment 1, which is included <br />in this document as a compact disk. <br />The model simulated percolation from the development rock piles at the West <br />Sunday and the Topaz Mines. <br />¦ Hydrologic properties of development rock are based on site-specific trench <br />• sampling and laboratory analyses completed by Advanced Terra Testing in <br />C? <br />7:\64986-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.12 - Soil, Ore, Rock Data Assessment Report\Unsat_h modelsAnal modelsTinal Report\calc bdef.doc