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CM0001769 <br />• <br />Page 15 <br />emergency discharge of approximately 331 cubic-feet-per-second (i.e., as identified by Wheeler) <br />from either the Robinson Lake or Seepwater Pond. The design parameters and details for: sizing <br />and concrete reinforcement for the spillway section on the Dam crest; and the design of the <br />cross-section and riprap sizing for the spillway sections along the Dam faces are contained in the <br />`Spillway Design Calculation Brief provided in Appendix E. Table 4 identifies the riprap <br />material quantity required to construct the spillway section down each Dam face as calculated in <br />the `Summary of Construction Materials Calculation Brief' rovided in Appendix E. <br />4.13 Chalk Mountain Discharge <br />The discharge from the existing Chalk Mountain spillway channel would enter upstream of the <br />Dam. To minimize handling of Seepwater Pond water, the Chalk Mountain spillway channel <br />will be redirected with buried HDPE pipe (i.e., as shown on figures 4 and 6) to discharge <br />downstream of the Dam and into Robinson Lake. The HDPE discharge pipe will replace the <br />existing culvert under the Chalk Mountain pump station road to provide one continuous pipe <br />from the Chalk Mountain Reservoir spillway to Robinson Lake. <br />A nominal pipe size of 42 inches was recommended by CMC as having sufficient capacity to <br />pass the maximum discharge from Chalk Mountain, which does not receive run-off directly from <br />the surrounding drainage area. Interceptor channels prevent run-off from entering the reservoir <br />and the inflow is controlled by CMC with a manually operated sluice gate. The discharge pipe <br />thickness of SDR 11 was chosen to withstand damage by construction activities. <br />Based on conversations with site personnel regarding frost protection, the discharge pipe will be <br />buried a minimum of eight feet below the road surface or other areas where the snow is routinely <br />removed from the surface covering the pipe and a minimum of one foot in areas where the snow <br />is not routinely removed. A discharge apron will be placed at the pipe outlet to limit erosion. <br />Table 4 shows the material quantity required to construct the discharge apron as calculated in the <br />`Summary of Construction Material Calculation Brief provided in Appendix E. <br />4.14 Plans and Specifications <br />The construction Plans and Specifications, identified in Appendix F, provide the Dam <br />construction requirements. The Specifications include construction quality assurance/quality <br />c:Wynnbypn \clim \nold=\6104ep2.doe 12/01196 <br />Environmental <br />k <br />4