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expected sediment yield from Pond A (2.05 Ac-Ft or 3300 cu-yds) is <br />relatively small with respect to the annual expected refuse • I <br />disposal volume. <br />Pond A will not receive water from the process/slurry systems <br />during normal operation. Water will be diverted to Pond A from the <br />process/slurry circuit only during emergency shutdown or equipment <br />failure. This water will be pumped back to the process/slurry <br />circuit via pipeline and pumps described above (Figure 4.2-3). <br />9.3.9.2 Diversions and Culverts <br />The sizing of Sediment Pond A, as described in Section 9.3.9.1, in <br />order to include the upland runoff has eliminated the need for <br />large unstable, upgradient diversion channels. Roadside and <br />intersection ditches have been installed to collect and route the <br />10-year, 29-hour storm flows from the site and direct them to Pond <br />A. Design details of the diversion ditches are included in <br />Appendir. 9.3-2. <br />• <br />The details include information about the various reaches of the <br />ditches as located on Figure 4.2-3. The data includes peak 10-yr, <br />29-hour discharge rates, maximum ditch gradient in the reach, ditch <br />top width, and peak velocity for the design storm. Two types of <br />ditch cross sections have been used, a triangular section with 2 to <br />1 side slopes and a trapezoidal shape with 3 to 1 side slopes. <br />Both types of ditches have been designed with 1 foot of freeboard <br />above the design water depth. Profiles along the ditches are <br />included in Appendix 9.3-2. These profiles show that ditch slopes <br />vary from less than O.So to a maximum of 15o For limited stretches. <br />Hydraulic calculations indicate that these unlined ditches may be <br />prone to erosion in areas where the slope e}:ceeds So. (The ditch <br />profiles in Appendix 9.3-2 show the 5~ slope line for comparison). <br />However, based upon nearly 5 years of operating experience, none of <br />the ditch sections show degradation even in the steepest areas. <br />NCIG - Coal Ridge #1 4-40 ASC/1145/910509 • <br />