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• All ponds, sumps, diversion ditches and collection ditches are relatively small in <br />area and shallow in depth. Construction of each is confined to the upper <br />alluvium above the water table. Negligible hydrologic impact is anticipated as a <br />result of drainage structures temporarily containing water. The extent of coal <br />extraction planned below sediment pond drainage ditches, impoundments and <br />diversion ditches is minimal; therefore, negligible subsidence effects are <br />predicted. Each structure is located in competent geologic stratum requiring no <br />geotechnical investigation. <br />All but two sediment ponds are designed to contain the runoff and sediment from <br />a 10 year, 24 hour precipitation event. Sediment Ponds 1 and 2 are being <br />combined to contain a 25 year, 24 hour event in lieu of two spillways or an open <br />channel spillway. Spillways or overflow devices are designed to carry the runoff <br />from a 25 year, 24 hour precipitation event. Collection ditches and diversions <br />associated with the refuse piles are designed for 100 year, 24 hour <br /> <br />CJ <br />13-5i (Rev. 7/01) <br />