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3.0 Hydrologic Analysis and Design <br />Hydrologic analysis and design were completed for the proposed RPE East refuse pile to establish <br />design requirements for the underdrain and to develop surface water drainage controls. The facility <br />layout with drainage features are shown on the permit drawings provided in Appendix D. A <br />summary of the results of water balance and surface water models are provided below. <br />3.1 Hydrologic Water Balance Analysis <br />The infiltration rates through the cover, refuse, and drainage blanket layers were modeled using <br />Hydrologic Evaluation of Landfill Performance (HELP), Version 3.07, a computer modeling program <br />designed to perform water balance analyses for design and evaluation of land disposal facilities. The <br />hydrologic inputs to the modeling, modeling parameters, and the modeling results are presented <br />below. HELP model output is provided in Appendix E. <br />3.1.1 Hydrologic Inputs <br />Precipitation and Temperature Data <br />Historical precipitation and temperature data for the mine site were used in the HELP modeling. <br />Daily precipitation and average daily mean temperatures were implemented into the model for each <br />year from 1998 to 2008. <br />Evapotranspiration and Solar Radiation Data <br />Evapotranspiration data was obtained from historical data for Grand Junction, Colorado, that is <br />included in the HELP software. The maximum leaf area index was assumed to be 1.0 for final cover <br />soil areas and 0 for bare refuse areas. The evaporative zone for the final cover and bare refuse layers <br />was assumed to be 12 inches and 6 inches, respectively. <br />The solar radiation data was synthetically generated using coefficients for Grand Junction, Colorado, <br />and station latitude equal to 38.93 degrees. <br />Soils <br />Three soil types were used in the HELP model for the three soil layers: cover soil, refuse, and <br />drainage blanket. The cover soil layer is assumed to be composed of native colluvium soil material <br />that will be stripped from the RPE East refuse pile area prior to filling. The refuse material is <br />assumed to be crushed rock material primarily composed of 8 +- millimeter sandstone, claystone, and <br />mudstone particles with small amounts of fines largely consisting of clay fines with a noticeable <br />amount of carbonaceous material. The drainage blanket is assumed to be from native ripped <br />P:\Mpls \06 CO \26 \06261003 MCC Refuse Pile Site Review & Permit \WorkFiles\Permit Application \Text \2010- 04- 19_RPE East Permit Application.doc 9 <br />