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~„i ., , <br />• conservatism in design, Peabody utilizes AMC II, a condition that may be atypical for the <br />mine site. This procedure adds conservativeness to Peabody`s runoff calculations. <br />Table 1 and Figure 1 contains the SCS curve numbers that were obtained for the Seneca II-W <br />Mine area based on the above conditions. <br />SCS curve numbers were estimated for each subwatershed based on the cover type, percent <br />vegetation cover, hydrologic conditions, and hydrologic soil type. Several sources were <br />used to obtain this data: <br />1. Cover Type - Aerial photographs of the mine site were used to identify the existing <br />cover type. Maps delineating the proposed mining plan were used to identify areas <br />that will be disturbed by mining. Three general categories of cover type were used: <br />undisturbed, disturbed, and reclaimed. Further subclassifications were made in each <br />category as shown in Table 1. <br />The cover type (and the tributary drainage area) for same structures will vary <br />throughout the life of the structure as mining and subsequent reclamation occurs. <br />For these cases, the anticipated worst condition is assumed for the hydrologic <br />• analysis. <br />2. Percent Vegetation Cover - The percent of ground surface covered by vegetation in <br />undisturbed areas was estimated from field inspections and aerial photographs. <br />3. Hydrologic Condition - The hydrologic condition was directly related to the percent <br />vegetation cover as shown in Table 1 and Figure 1, <br />4. Hydrologic Soil Type - Soil survey maps, as contained in Tab 9 of this application, <br />provides the basis of determining the hydrologic soil type. <br />The curve number for structure was determined as a weighted average based on the various <br />soil types in the watershed area. <br />Sedimentology <br />The SEDIMOT II or SEDCAD computer program will be utilized to calculate the Sedimentology <br />of each watershed using the modified or revised universal soil loss equation (MUSLE), <br />(RUSLE), Using a density of 80 pounds/cubic foot, a quantity of sediment can be <br />calculated that will be deposited in a structure as the result of a given design storm, <br />• The following paragraphs describe the sources of data used as input for the MUSLE and <br />RUSLE calculations. <br />13-1-5 <br />