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2-41 2.4 Mining Hydrology The objective of related studies was to provide an evaluation of the hyfrologic impact that the project will have on the mine area, and to serve as a basis for final design of diversion and sedimentation control facilities. 2.4.1 Surface Water Hydrologic Controls The surface runoff area has been subdivided into "disturbed" and "undisturbed" areas. Runoff from most disturbed areas will be conveyed into a sedimentation pond and detained in accordance with applicable criteria before eventual discharge into East Salt Creek. Runoff from three areas addressed in Section 2.4.4.2 will be treated with alternate control measures. Runoff from the undisturbed areas will be diverted around the disturbed area, and conveyed to the receiving ephemeral channel. Figure 2.2-3 depicts the flow of water associated with disturbed and undisturbed areas. • The undisturbed area was divided into sub-basins designated G1 through C-4 and C-6 through C-15. The disturbed area is divided into four sub-basins, designated D-1 through D-5. These sub-basins during mining are shown in Figures 2.2-3 and 4.2- 1 a; their areas and hydrologic parameters are given on Table 4.2-10. The sub-basins vary in size from 3 acres of disturbed area up to 322 acres for the main McClave Creek drainage, see Figure 4.2-1 a. Rainfall values fora 10-year, 24-hour storm were taken from the NOAH atlas; runoff was estimated according the Soil Conservation Service procedures, as given in Procedures for Determining Peak Flows in Colorado. Runoff Calculations for the reclaimed configuration of the mine site are shown on Table 4.2-11. Table 3.1-1 contains the calculations for ditch and rip rap sizing. To provide the necessary detail to evaluate the drainage basin boundaries after mining, the areas are delineated on Figures 4.2-1b and 3.1-1. ~~ LJ M`Clane Volume 1 Rev 09105