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Chapter IV <br /> 4. Diversions. <br /> The company has designed, constructed, and maintained diversion ditches to control <br /> surface runoff and to minimize water quality degradation. Diversions have been located <br /> to divert water away from disturbed areas or have been constructed in disturbed areas <br /> to convey water to treatment facilities. The diversions have been designed as required <br /> by the CMLRB regulations to minimize erosion and to remove water from contact with <br /> potential acid forming or toxic materials. <br /> Temporary diversions have been located to convey the peak runoff from a rainfall equal <br /> to or greater than the ten year recurrence interval. The diversions have been installed <br /> as approved by the Board on the inside of all cuts and fills in such a manner that the <br /> flow velocities will not induce adverse erosion. The design, where necessary, has <br /> incorporated rip rap, and/or vegetative control measures. Each diversion has been <br /> designed with a minimum free-board of 0.3 feet. In all cases where diversions have <br /> been constructed in disturbed areas they lead to sedimentation ponds for treatment. <br /> 5. Culverts. <br /> A major sediment control measure is the construction and maintenance of road <br /> culverts. The Coal Basin road culverts have been designed for the 10 year/24 hour <br /> runoff. The culverts are constructed with a minimum slope, (to reduce velocities) <br /> covered with at least one foot of compacted cover, and have a minimum diameter of 18 <br /> inches. Where necessary, the company has placed energy dissipators, at the <br /> ientrances of culverts where excessive erosion could occur. In addition, runoff has <br /> been diverted using protected channels or pipes through disturbed areas so as not to <br /> cause additional erosion. <br /> 6. Sedimentation Ponds. <br /> Sedimentation ponds have been installed and maintained to remove sediment from <br /> water collected from the disturbed areas. The impoundments have been located out of <br /> perennial streams, and where surface disturbance can be kept to a minimum. The <br /> types of impoundments, including both embankment and dug out, have been placed <br /> both individually and in series so that the water is held long enough to accomplish the <br /> settling of the total suspended solids. The impoundments have a capacity of less than <br /> 20 acre feet and a vertical height of less than 10 feet below the crest of the emergency <br /> spillway and the toe of the fill. (See Table IV-C-1 on the following page). <br /> The impoundments have been designed and constructed in accordance with 4.05.6(8). <br /> The foundations have been cleared of all organic matter and frozen soil and placed in <br /> separate lifts starting at the base of the foundations. Compaction has been <br /> accomplished using a sheep foot roller and dozer. During construction, proctor <br /> compaction engineering tests are used to ensure that the embankments are structurally <br /> 17 <br /> 1 - <br />