Laserfiche WebLink
C: \Documents an <br />The UNSAT -H model was chosen for this evaluation because it simulates both <br />downward movement of water into the development rock piles during infiltration <br />and upward movement of water from the rock piles caused by evaporation. <br />Consideration of upward unsaturated flow is critical for accurate simulation of <br />percolation through mine rock piles in semiarid and arid environments (Swanson et <br />al. 2000). Application of rigorous unsaturated flow models based on Richard's <br />equation is becoming a widely used approach to simulate unsaturated flow through <br />mine waste piles (e.g. Ford et al, 2000; Swanson et al., 2000, Fala et al., 2005). Benson et <br />al. (2006) provides basic requirements for unsaturated flow models including: <br />• The model must simulate unsaturated flow in a rigorous manner (i.e. must solve <br />Richard's 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 (Benson et al. 2006). <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. A <br />calculation brief, model input files, input data tables, and model output files are <br />included Attachment 0. The calculation brief provides a summary of the modeling <br />approach including description of model nodes and boundary conditions, description <br />of climate data sources, and definition of soil characteristics. <br />Exhibit 13 -3 summarizes the results of the modeling effort for the West Sunday and <br />Topaz Mines on an annual basis. Additional detail, including daily percolation <br />estimates are included in Attachment 0. The estimate was completed for the West <br />Sunday and Topaz Mines and for average annual precipitation and the wettest year <br />on record. <br />Settinaslcwoodward.DMC\Desktop \Environmental Protection Plan Sunday Mines Revised November 2011 revl (21 11 10 11.docx <br />Section 13 <br />Geochemical Data and Analysis <br />13 -8 <br />