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Peabody Sage Creek Mine - Drainage and Sediment Control Plan <br />4.3 Culverts <br />• Culverts were generally designed to safely pass the peak flow from the 10 -year, 24 -hour storm event. <br />Exceptions are Culvert 15A, SC -10, SC -11 and SC -12; when the culverts were evaluated using peak <br />flows from a 25 -year, 234 -hour storm event, with a head elevation of 1.0 feet or less, the culverts had <br />an end area greater than 35 square feet. Rule 4.03.1(4)(e)(i) stipulates that culverts with an end area <br />greater than 35 square feet shall be designed to safely pass the 20 -year, 24 -hour event. SCCC <br />substituted the 25 -year event for the 20 -year event; there is site - specific 25 -year event data and it <br />results in a more conservative design, thereby increasing the safety factor. The culvert sub - routine in <br />SEDCAD4 was used to size the culverts; however, SEDCAD can only size a single diameter pipe at <br />a location - it does not have the ability to design multiples of smaller diameter pipes. Table 2.05.3 - <br />E2-10, Culvert Conversions - Single Culvert to Multiple Culverts, summarizes design multiples. <br />Operational culvert locations are shown on Map 2.05.3 M4; postmine culvert locations are shown on <br />Map 2.05.4 M1. Culvert design demonstrations are found in Appendix 2.05.3- E2.G -2, Operational <br />Ditch and Culvert Designs and Appendix 2.05.3 -E2.11, Postmine Channel and Culvert Designs, <br />respectively. Minimum culvert dimensions for operational culverts are summarized in Table 2.05.3 - <br />E2-11, Operational Culvert Schedule, while postmine culvert dimensions are summarized in Table <br />2.05- E2.12, Postmine Culvert Schedule. <br />TABLE 2.05.3 -E2 -10 <br />Culvert Conversions - Single Culvert to Multiple Culverts <br />Design Size <br />Multiples <br />feet <br />inches <br />cross- <br />sectional <br />area <br />( s q. in. <br />60 -inch <br />48 -inch <br />36 -inch <br />10 <br />120 <br />11309.7 <br />4.0 <br />4 <br />6.3 <br />7 <br />11.1 <br />(11) <br />9 <br />108 <br />9160.9 <br />3.2 <br />4 <br />5.1 <br />5 <br />9.0 <br />9 <br />8 <br />98 <br />7238.2 <br />2.6 <br />(3) <br />4.0 <br />(4) <br />7.1 <br />(7 <br />7 <br />84 <br />5541.8 <br />2.0 <br />(2) <br />3.1 <br />(3) <br />5.4 <br />(6 <br />6 <br />72 <br />4071.5 <br />1.4 <br />2 <br />2.3 <br />(3 ) <br />4.0 <br />4 <br />5 <br />60 <br />2827.4 <br />1.0 <br />(1) <br />1.6 <br />(2 ) <br />2.8 <br />(3) <br />4 <br />48 <br />1809.6 <br />1.0 <br />1 <br />1.8 <br />2 <br />3 <br />36 <br />1017.9 <br />1 <br />1 1.0 <br />1 (1) <br />Note: assume headwater de th is the same for multiples as calculated for design size. <br />5.0 STOCK TANK DESIGNS <br />Twenty -one stock tanks were designed and constructed for the previously reclaimed surface mine <br />area as part of the reclamation activities for the closed Seneca II Mine. The construction occurred in <br />conjunction with the construction of various postmine channels. As part of the Seneca II Mine bond <br />release evaluation activities Seneca Coal Company determined that several of the stock tanks could <br />be reclaimed - 13 stock tanks were subsequently approved as permanent postmine structures by <br />CDRMS. Table 2.05.3- E2 -13, Permanent Postmine Stock Tanks, lists the 13 stock tanks located in <br />• the previously reclaimed surface mine areas. <br />2.05.3 -E2.21 <br />